We thank B. Konkena und W. Schuhmann for valuable scientific discussions. Financial support by the Fonds of the Chemical Industry (Liebig grant to U.-P.A.) and the Deutsche Forschungsgemeinschaft (Emmy Noether grant to U.-P.A., AP242/2-1).

1. High-temperature Synthesis of Fe 4.5 Ni 4.5 S 8
NOTE: The herein described procedure for the synthesis of Fe4.5Ni4.5S8 is adopted from the literature.8,10 The strict application of the reported heating ramps is of high importance to prevent formation of phase impurities and defects of the silica ampule.
<ol>
	<li>Mix iron (1.66 g, 29.8 mmol), nickel (1.75 g, 29.8 mmol) and sulfur (1.70 g, 53.1 mmol) thoroughly in a mortar and transfer the mixture to a silica ampule (10 mm diameter).</li>
	<li>Evacuate the ampule overnight at 10-2 mbar.</li>
	<li>Seal the ampule and place it in a tubular furnace.</li>
	<li>Increase the temperature from room temperature (RT) to 700 &#176;C at 5 &#176;C/min followed by an isothermal step for 3 h.</li>
	<li>Increase the temperature to 1100 &#176;C within 30 min and keep it isotherm for 10 h.</li>
	<li>Slowly cool the sample to RT by switching off the furnace. Crack the ampule to collect the solid product. Make sure to separate the Fe4.5Ni4.5S8 completely from silica glass fragments.</li>
</ol>
2. Physical Characterization
<ol>
	<li>Mount a 10 mm x 5 mm x 3 mm piece of Fe4.5Ni4.5S8 rock on the sample holder and place in the vacuum chamber of the SEM instrument. Record the SEM images at 650X and 6,500X magnification at 20 kV. Simultaneously, use the same sample for EDX analysis at 4.4 kV.</li>
	<li>For the collection of PXRD data, apply finely ground powder of Fe4.5Ni4.5S8 and mount it on an amorphous silicon wafer using silicon grease. Mount the wafer on the sample holder and collect the data in a continuous scan mode from 10-50&#176; at a scan rate of 0.03&#176; per 5 s using Cu-K&#945; radiation (&#955; = 1.5418 &#197;).</li>
	<li>For M&#246;ssbauer analysis finely ground powder is used and placed in a polyoxymethylene (POM) cup. Record zero-field M&#246;ssbauer spectra at 25 &#176;C using a 57Co radiation source in a Rh-matrix.</li>
	<li>For DSC analysis, finely ground powder is placed in a tared &#945;-Al2O3 crucible. Perform DSC measurements in the range from RT to 1,000 &#176;C recording the heating and cooling curve at a rate of 10 &#176;C/min. Perform the experiment under a flow of high purity nitrogen.</li>
</ol>
3. Preparation of &#39;Rock&#39; Electrodes
<ol>
	<li>Solder a copper wire to a wire ferrule.</li>
	<li>Cut the Fe4.5Ni4.5S8 bulk material into smaller pieces (approx. 5 mm x 5 mm x 5 mm).</li>
	<li>Place the small piece of Fe4.5Ni4.5S8 in the ferrule in a way that approx. 2 mm of material sticks out of the ferrule.</li>
	<li>Mantle the ferrule and copper wire with 100 mm of Teflon tubing.</li>
	<li>Seal the tip of the electrode with two-component epoxide glue and dry the electrode overnight under ambient conditions.</li>
	<li>Grind off the tip until the shiny surface (metallic finish) of the Fe4.5Ni4.5S8 is exposed. Further polish with fine grade sand paper (20, 14, 3 and 1 &#181;m grit) to obtain a smooth surface.</li>
	<li>Clean the surface with deionized water and let it dry on air.</li>
</ol>
4. Preparation of &#39;Pellet&#39; Electrodes
NOTE: Custom-built Teflon casings with a brass rod were used as contact for &#39;pellet&#39; electrodes (3 mm diameter).
<ol>
	<li>Grind 50 mg of material to obtain a fine powder of the Fe4.5Ni4.5S8 material.</li>
	<li>Fill the finely ground powder into a compressing tool (3 mm in diameter) and press the material with a maximum weight force of 800 kg/cm2.</li>
	<li>Remove the pellet from the mold using a distance holder.</li>
	<li>Apply a two-component silver-epoxide glue on the brass rod in the cavity of the Teflon casing. Avoid any pollution of the tip of the Teflon-casing.</li>
	<li>Place the pellet in the Teflon casing. The flat side of the pellet must stick out ~1 mm.</li>
	<li>Remove any pollution on the Teflon casing with a paper tissue.</li>
	<li>Verify the contact between the brass wire and the Fe4.5Ni4.5S8 pellet with a voltmeter to assure proper conductivity.</li>
	<li>After 12 h of curing the two-component glue at 60 &#176;C, cool down the electrode to ambient temperature.</li>
	<li>Polish the electrode with sand paper (20, 14, 3 and 1 &#181;m grit) to obtain a shiny flush flat surface within the Teflon case.</li>
	<li>Clean the surface with deionized water and let it dry under ambient conditions.</li>
</ol>
5. Electrochemical Testing of Electrodes
NOTE: The experiments were accomplished with a standard three-electrode setup using the Fe4.5Ni4.5S8 electrode as working electrode, Ag/AgCl (sat. KCl or 3 M KCl solution) electrode as reference electrode and Pt wire or Pt-grid as counter electrode. A gas-tight cell equipped with a stirring bar was filled with the electrolyte consisting of 0.5 M H2SO4 for all electrochemical experiments. The electrolyte was not exchanged during the electrochemical testing of an electrode. All potentials are referenced to ERHE (RHE = reversible hydrogen electrode) according to ERHE = EAg/AgCl + X + 0.059 pH with X = 0.197 V (saturated KCl) or X = 0.210 V (3 M KCl), unless noted otherwise.
<ol>
	<li>Preliminary steps
	<ol>
		<li>Connect all three electrodes with the wires of the potentiostat.</li>
		<li>Add 25 mL of electrolyte (0.5 M H2SO4) into the electrochemical cell and adjust the electrodes to ensure that the electrodes are fully immersed into solution. Subsequently, switch on the potentiostat.</li>
		<li>Switch on the magnetic stirring.</li>
	</ol>
	</li>
	<li>Electrochemical cleaning of the electrode surface
	<ol>
		<li>Perform a cyclic voltammetry (CV) experiment to obtain fast overview on the electrochemical processes that can be observed.</li>
		<li>Set the potential range from 0.2 to -0.2 V with a scan rate of 100 mV/s (non-catalytic potential area). Further, set the number of cycles to 20.</li>
		<li>Start the cycling process and wait until the last cycle is finished. If at least the last 3 to 4 obtained cycles coincide, the electrochemical electrode cleaning is completed. In case of divergence add more cycles until stable curves are obtained.</li>
	</ol>
	</li>
	<li>Measurement of the catalytic performance &#8211; linear sweep voltammetry
	<ol>
		<li>Before starting the experiment determine the iR compensation value for the electrochemical setup.</li>
		<li>Select the program for linear sweep voltammetry (LSV) experiments and set the potential range from 0.2 to -0.6 V and the scan rate to 5 mV/s, including the iR drop into the experiment. Start the experiment.</li>
		<li>Repeat the linear sweep experiments to ensure reproducibility. In case of non-reproducible results start over from step 5.2.</li>
	</ol>
	</li>
	<li>Stability measurement &#38; quantification
	<ol>
		<li>Perform a controlled potential coulometry experiment (CPC).</li>
		<li>Set the potential to -0.6 V with an experiment time of at least 20 h (72,000 s).</li>
		<li>Simultaneously collect gas samples with a gas tight syringe from the headspace of the sealed cell through a septum for every hour for at least 4 h of the experiment. Inject the samples into a GC instrument for quantification and determine the amount of hydrogen produced using a calibration curve recorded on this instrument.</li>
	</ol>
	</li>
	<li>Estimation of the electrochemical surface area (ESCA) 
	NOTE: Do not stir the electrolyte solution during this experiment.
	<ol>
		<li>Determine the iR compensation to measure the resistance of the solution.</li>
		<li>Select a potential range between 0.1 and 0 V in the cyclic voltammetry experiment and set the scan rate to 10 mV s-1. Use the iR drop correction. Set the number of cycles for the experiment to 5.</li>
		<li>Repeat steps 5.4.1) to 5.4.2) for scan rates of 20, 30, 40, 50 and 60 mV s-1.</li>
		<li>From the obtained CV curves pick the fifth cycle for further interpretation.</li>
		<li>Determine the charging current density differences (&#916;j = ja jc) and plot these values as a function of the scan rate. The linear slope is equivalent to twice of the double-layer capacitance Cdl, which is proportional to the electrochemical surface area (ECSA).</li>
	</ol>
	</li>
	<li>Electrochemical impedance spectroscopy (EIS)
	<ol>
		<li>Record electrochemical impedance spectra in the frequency range from 50 kHz to 1 Hz at the corresponding open-circuit potential and an overpotential of 0.3 V.</li>
		<li>Plot the Nyquist plot from the received data to determine the charge transfer resistance.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>May, M. M., Lewerenz, H. -. J., Lackner, D., Dimroth, F., Hannappel, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+direct+solar-to-hydrogen+conversion+by+in+situ+interface+transformation+of+a+tandem+structure.">Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure.</a> Nat Comm. 6, 8286 (2015).</li><li>Sheng, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlating+hydrogen+oxidation+and+evolution+activity+on+platinum+at+different+pH+with+measured+hydrogen+binding+energy.">Correlating hydrogen oxidation and evolution activity on platinum at different pH with measured hydrogen binding energy.</a> Nat Comm. 6, 5848 (2015).</li><li>Li, X., Hao, X., Abudula, A., Guan, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+catalysts+for+electrochemical+water+splitting:+Current+state+and+prospects.">Nanostructured catalysts for electrochemical water splitting: Current state and prospects.</a> J. Mater. Chem. A. 4 (31), 11973-12000 (2016).</li><li>Merki, D., Hu, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+developments+of+molybdenum+and+tungsten+sulfides+as+hydrogen+evolution+catalysts.">Recent developments of molybdenum and tungsten sulfides as hydrogen evolution catalysts.</a> Energy Environ. Sci. 4 (10), 3878 (2011).</li><li>Kibsgaard, J., Chen, Z., Reinecke, B. N., Jaramillo, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+the+surface+structure+of+MoS2+to+preferentially+expose+active+edge+sites+for+electrocatalysis.">Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis.</a> Nat Mater. 11 (11), 963-969 (2012).</li><li>Kong, D., Cha, J. J., Wang, H., Lee, H. R., Cui, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=First-row+transition+metal+dichalcogenide+catalysts+for+hydrogen+evolution+reaction.">First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction.</a> Energy Environ. Sci. 6 (12), 3553 (2013).</li><li>Voiry, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+catalytic+activity+in+strained+chemically+exfoliated+WS(2)+nanosheets+for+hydrogen+evolution.">Enhanced catalytic activity in strained chemically exfoliated WS(2) nanosheets for hydrogen evolution.</a> Nat Mater. 12 (9), 850-855 (2013).</li><li>Konkena, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pentlandite+rocks+as+sustainable+and+stable+efficient+electrocatalysts+for+hydrogen+generation.">Pentlandite rocks as sustainable and stable efficient electrocatalysts for hydrogen generation.</a> Nat Comm. 7, 12269 (2016).</li><li>Jeon, H. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+Chemical+Solution+Deposition+of+Co&#8323;O&#8324;+Thin+Film+Electrocatalyst+for+Oxygen+Evolution+Reaction.">Simple Chemical Solution Deposition of Co&#8323;O&#8324; Thin Film Electrocatalyst for Oxygen Evolution Reaction.</a> ACS Appl Mater Interfaces. 7 (44), 24550-24555 (2015).</li><li>Xia, F., Pring, A., Brugger, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+mechanism+and+kinetics+of+pentlandite+oxidation+in+extractive+pyrometallurgy+of+nickel.">Understanding the mechanism and kinetics of pentlandite oxidation in extractive pyrometallurgy of nickel.</a> Mine Eng. 27-28, 11-19 (2012).</li><li>Drebushchak, V. A., Kravchenko, T. A., Pavlyuchenko, V. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+pure+pentlandite+in+bulk.">Synthesis of pure pentlandite in bulk.</a> J Crystal Growth. 193 (4), 728-731 (1998).</li><li>Knop, O., Huang, C. -. H., Reid, K., Carlow, J. S., Woodhams, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chalkogenides+of+the+transition+elements.+X.+X-ray,+neutron,+M&#246;ssbauer,+and+magnetic+studies+of+pentlandite+and+the+&#960;+phases+&#960;(Fe,+Co,+Ni,+S),+Co8MS8,+and+Fe4Ni4MS8+(M+=+Ru,+Rh,+Pd).">Chalkogenides of the transition elements. X. X-ray, neutron, M&#246;ssbauer, and magnetic studies of pentlandite and the &#960; phases &#960;(Fe, Co, Ni, S), Co8MS8, and Fe4Ni4MS8 (M = Ru, Rh, Pd).</a> J Solid State Chem. 16 (1-2), 97-116 (1976).</li><li>Kullerud, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+stability+of+pentlandite.">Thermal stability of pentlandite.</a> The Canadian Mineralogist. 7 (3), 353-366 (1963).</li><li>Siracusano, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+electrochemical+study+of+a+PEM+stack+for+water+electrolysis.">An electrochemical study of a PEM stack for water electrolysis.</a> Int J Hydrogen Energy. 37 (2), 1939-1946 (2012).</li></ol>

The authors have nothing to disclose.

The synthesis of Fe4.5Ni4.5S8 was performed in a vacuum-sealed ampule to prevent oxidation of the material during synthesis. During the synthesis, temperature control is the key to obtain a pure product. The first, very slow heating step thereby prevents superheating of the sulfur, which might cause cracking of the ampule due to high sulfur pressure. Even more crucial is the prevention of phase impurities like mono-sulfide solid solutions (mss) by slow heating of the sample. The subsequent annealing step at 700 &#176;C ensures equilibration of the system. Following, annealing at 1100 &#176;C finally leads to the formation of a pure pentlandite phase, which is a high temperature phase of iron nickel sulfides.13
When preparing &#39;rock&#39; electrodes, it is important that the piece of &#39;rock&#39; sticks out of the ferrule approx. 2 mm to be able to cut enough material to obtain a smooth electrode surface (A = 0.135cm2) without exposing the ferrule. Epoxy glue is used to fixate the &#39;rock&#39; in the ferrule as well as fixating the Teflon tubing, which prevents contact between the electrolyte and any parts of the electrode apart from the active material. Otherwise side reactions can take place and reproducibility is hampered. The application of the epoxy glue should be done in a way that no bubbles are enclosed in the glue. These bubbles might cause unwanted exposure of the ferrule or material. The epoxy glue should dry at least overnight to be fully processible. In case of &#39;pellet&#39; electrodes, the Teflon casing serves a similar role as mentioned before for the &#39;rock&#39; electrodes. The used catalyst should be a well ductile material with good conductivity. Otherwise the material is not qualified to be pressed and instead conductive binder material has to be added to provide stability and conductivity. The gap dimensions between the case and the pellet must be negligibly small. It is thus better to prepare a pellet that is slightly bigger than the Teflon casing. The removal of excess silver epoxide glue is also important, to avoid the reaction of silver during electrochemical measurements. After curing the glued electrode at 60 &#176;C, it is advisable to let the electrode cool down to room temperature before further preparation or the compressed material might crumble. To obtain a well-defined geometrical surface area (A = 0.071 cm2) without any cracks and indentations, the pellet has to stick out at least 1 mm. It has to be polished down until it is flush with the case. Since the pellet can be very brittle it might be helpful to use Teflon housings with a wall strength of at least 2 mm, so it provides sufficient support, while grinding and polishing. To provide a consistent quality and uniformity of the surface, it is reasonable to start with the coarsest and end up with the finest abrasive.
In general, for bulk electrodes as described herein it has to be noted that a conductive catalyst material is mandatory to ensure a fast electron transfer and prevent resistivity limitations. An approach to implement non-conductive catalyst materials into this electrode type could be accomplished by immobilizing the catalyst on a conductive substrate (e.g. carbon black, graphite) and preparing electrodes starting from this composite powder. This method, however, would exclude the possibility to prepare &#39;rock&#39; electrodes. A further step to obtain high quality and especially more industrial relevant electrodes using a similar approach to the &#39;pellet&#39; electrode is pressing the material directly on a current collector (e.g. Ni-mesh) and will be explored by us in future work.
Polishing the electrodes prior to testing the electrocatalytic properties is crucial to obtain reproducible results. The electrochemical cleaning of the electrode equilibrates the electrode and removes any adsorbed impurities from the electrode surface. Multiple LSV&#180;s are recorded to ensure reproducibility of the data. In contrast to commonly reported stability tests, which are generally accomplished in a galvanostatic manner at relatively low current densities (mostly 10 mA/cm2), we opted to perform a potentiostatic stability test at high over potential, which leads to high current densities (&#62;500 mA/cm2). The advantage of such a stress test is to push the material to its electrochemical and mechanical limits as well as providing a more realistic electrode test. For quantification the gas tightness of the electrochemical cell and syringe is crucial to obtain consistent results. Furthermore, a good calibration of the GC is mandatory. Stirring during this experiment provides a thorough mixing of the electrolyte and promotes desorption of hydrogen bubbles from the electrode surface. However, stirring must be turned off during ECSA experiments, since the correct build-up of the electrochemical double layer is required. From the ESCA, conclusions on the dependency of a materials activity and its active site count, which is proportional to the ESCA, can be obtained. Hence, ECSA analysis is a facile tool that enables a comparison of the performance of different catalysts.
In summary, we synthesized Fe4.5Ni4.5S8, a highly conductive transition metal sulfide, and prepared two types of bulk electrodes using this material. The electrodes were tested towards hydrogen evolution reaction using standard electrochemical methods such as LSV, CPC and ECSA determination. The hydrogen evolution rate was determined using a GC and is among the highest observed for non-noble metal catalysts at low overpotential. The performance of both types of electrodes is similar with the &#39;pellet&#39; electrode being slightly ahead in performance and especially electrode activation. This, however, might stem from an overestimated surface area in &#39;rock&#39; electrodes. Notably, the &#39;pellet&#39; electrodes have the advantage that the surface area can be more easily and more exactly determined and reproduced. This feature renders &#39;pellet&#39; electrodes more valuable for comparable studies, while &#39;rock&#39; electrodes are easier and cheaper to prepare. Future work will focus on the design of an up-scale version of &#39;pellet&#39; electrodes.

The storage of fluctuating renewable energy sources such as solar and wind energy is of significant social interest due to the gradual fade of fossil fuels and subsequent need of alternative energy sources. In this respect, hydrogen is a promising sustainable candidate for a molecular energy storage solution because of a clean combustion process.1 Additionally hydrogen could be used as fuel or as starting material for more complex fuels, e.g. methanol. The preferred way for a facile synthesis of hydrogen using carbon neutral resources is the electrochemical reduction of water using sustainable energies.
Currently, platinum and its alloys are known to be the most effective electrocatalysts for the hydrogen evolution reaction (HER) showing low over-potential, a fast reaction rate and operation at high current densities.2 However, due to its high price and low natural abundance, alternative non-noble metal catalysts are required. Among the vast amount of alternative non-precious transition metal catalysts,3 especially transition metal dichalcogenides (MX2; M = Metal; X = S, Se) have been shown to possess high HER activity.4,5,6,7 In this respect, we recently presented Fe4.5Ni4.5S8 as a highly durable and active &#39;rock&#39; HER electrocatalyst. This naturally abundant material is stable under acidic conditions and shows a high intrinsic conductivity with a well-defined catalytic active surface.8
While numerous materials with high HER activities have been reported, the electrode preparation is often accompanied with multiple problems, e.g. reproducibility and satisfactory stabilities (&#62;24 h). Additionally, since the intrinsic conductivity of transition metal based catalysts in bulk is usually high, electrode preparation requires nano-structured catalysts to allow for an efficient electron transfer. These catalysts are then converted into a catalyst ink containing binders such as Nafion and the catalyst. Afterwards, the ink is drop-coated on an inert electrode surface (e.g. glassy carbon). Whereas being reasonably stable at low current densities an increased contact resistance and mediocre adhesion of the catalyst on the electrode support is commonly observed at high current densities.9 Hence, the need for more sufficient preparation methods and electrode materials is evident.
This protocol presents a novel preparation procedure for highly durable and cost efficient electrodes using bulk materials. The prerequisite for such an electrode is a low intrinsic materials resistance. Fe4.5Ni4.5S8 fulfills this criterion and can be obtained from the elements via a simple high-temperature synthesis in sealed silica ampules. The obtained material is characterized with respect to its structure, morphology and composition using powder Xray diffractometry (PXRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive Xray spectroscopy (EDX). The synthesized material is processed to afford two types of bulk electrodes, namely &#39;rock&#39; and &#39;pellet&#39; electrodes. The performance of both electrode types is then investigated using standard electrochemical tests and H2 quantification performed via gas chromatography (GC). A comparison of the performance of both types of electrodes in comparison to commonly used drop-coating experiments is presented.

<table border="0" cellpadding="0" cellspacing="0" width="1228">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Iron, powder</td>
			<td style="width:309px;">Sigma-Aldrich, http://www.sigmaaldrich.com</td>
			<td style="width:115px;">12310-500G-R</td>
			<td style="width:495px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:311px;">Nickel, powder</td>
			<td style="width:309px;">Sigma-Aldrich, http://www.sigmaaldrich.com</td>
			<td>203904-25G</td>
			<td style="width:495px;">H: 351-372-317-412; 
			P: 281-273-308-313-302+352</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Sulfur, powder</td>
			<td style="width:309px;">Sigma-Aldrich, http://www.sigmaaldrich.com</td>
			<td style="width:115px;">13803-1KG-R</td>
			<td>H: 315</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Silver Epoxy Glue EC 151 L</td>
			<td style="width:309px;">Polytec PT, http://www.polytec-pt.de/de/</td>
			<td style="width:115px;">161010-1</td>
			<td>-</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:311px;">Two Component Epoxy Glue Uhu Plus Endfest</td>
			<td>Uhu, http://www.uhu.com</td>
			<td style="width:115px;">-</td>
			<td style="width:495px;">&#160;H: 315-319-317-411; 
			&#160;P: 101-102-261-272-280-302+352-333+313-362-363-305+351+338-337+313</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:311px;">Sulfuric Acid &#62;95%</td>
			<td style="width:309px;">VWR, https://ru.vwr.com</td>
			<td style="width:115px;">231-639-5</td>
			<td style="width:495px;">H: 290-314; 
			S: (1/2)-26-30-45</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">PTFE Tube</td>
			<td style="width:309px;">-</td>
			<td style="width:115px;">-</td>
			<td>Prepare 8 cm long peaces</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Iron Sleeves</td>
			<td style="width:309px;">-</td>
			<td style="width:115px;">-</td>
			<td>Connect to the copper wire</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Copper Wire</td>
			<td style="width:309px;">-</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Lapping Film 3&#181;m, 215.9 x 279 mm</td>
			<td style="width:309px;">3M, http://3mpro.3mdeutschland.de</td>
			<td style="width:115px;">60-0700-0232-8</td>
			<td>Polish with a small amount of water</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Lapping Film 1&#181;m, 215.9 x 279 mm</td>
			<td style="width:309px;">3M, http://3mpro.3mdeutschland.de</td>
			<td style="width:115px;">60-0700-0266-6</td>
			<td>Polish with a small amount of water</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Sand Paper 20 &#181;m, SiC</td>
			<td style="width:309px;">-</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Sand Paper 14 &#181;m, SiC</td>
			<td style="width:309px;">-</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Dremel Model 225</td>
			<td>Dremel, https://www.dremeleurope.com</td>
			<td style="width:115px;">2615022565</td>
			<td>Use grinding pulley wheel for cutting&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Hand Made Pellet Press</td>
			<td style="width:309px;">Hand Made</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Stirring Plate</td>
			<td style="width:309px;">-</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:311px;">GAMRY Reference 600</td>
			<td style="width:309px;">GAMRY Instruments, https://www.gamry.com</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Gero Furnace 30-3000&#176;C</td>
			<td>http://www.carbolite-gero.de</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Quartz glass ampule</td>
			<td style="width:309px;">Hand Made</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Vacuum pump</td>
			<td style="width:309px;">-</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Hydraulic press</td>
			<td style="width:309px;">-</td>
			<td style="width:115px;">-</td>
			<td>-</td>
		</tr>
	</tbody>
</table>

simple methods for the preparation of non-noble metal bulk-electrodes for electrocatalytic applications

The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and composition of the material was characterized via powder X-ray diffraction (PXRD), M&#246;ssbauer spectroscopy (MB), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and energy dispersive X-ray spectroscopy (EDX). Two preparation methods of pentlandite bulk electrodes are presented. In the first approach a piece of synthetic pentlandite rock is directly contacted via a wire ferrule. The second approach utilizes pentlandite pellets, pressed from finely ground powder, which is immobilized in a Teflon casing. Both electrodes, whilst being prepared by an additive-free method, reveal high durability during electrocatalytic conversions in comparison to common drop-coating methods. We herein showcase the striking performance of such electrodes to accomplish the hydrogen evolution reaction (HER) and present a standardized method to evaluate the electrocatalytic performance by electrochemical and gas chromatographic methods. Furthermore, we report stability tests via potentiostatic methods at an overpotential of 0.6 V to explore the material limitations of the electrodes during electrolysis under industrial relevant conditions.

The successful synthesis of Fe4.5Ni4.5S8 possessing the Pentlandite structure is confirmed by powder X-ray diffraction experiments due to the prominent (111), (311), (222), (331) and (511) reflections being present (Figure 1a). A proper temperature control during the reaction, however, is the key to obtain phase pure materials. Notably, mono-sulfide solid solutions (mss), a common impurity of pentlandite materials11, have been observed, when the mixture was heated to 700 &#176;C at a higher heating rate (e.g. 20 &#176;C/min). An exemplary XRD pattern of such a sample is also depicted (Figure 1a, red). On the contrary, if an appropriate heating rate of 5 &#176;C/min is applied, the appearance of mss can be significantly reduced if not even eliminated (Figure 1a, black). M&#246;ssbauer spectroscopy (Figure 1b) confirms the pentlandite structure of the Fe4.5Ni4.5S8 sample. The material reveals two distinct different iron sites with isomeric shifts of 0.13 (&#177;0.02) and 0.50 (&#177;0.02) mm/s as well as quadrupole couplings of 0.12 (&#177;0.02) and 0.13 (&#177;0.02), respectively (Figure 1b). This observation is in good agreement with literature reports and structural findings showing two different iron sites.12 Additionally, differential scanning calorimetry (DSC) (Figure 1c) revealed two main phase transitions at 612 &#176;C and 861 &#176;C, proving the absence of undesirable phases according to literature reports.13
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56087/56087fig1.jpg" /> 
Figure 1: XRD and M&#246;ssbauer Spectroscopy. (a) XRD patterns of samples prepared with heating rates of 5 &#176;C/min (black) and 20 &#176;C/min (red). For reference, a pattern of Pentlandite simulated from single crystal diffraction data is shown (blue). Reflections corresponding to mss are marked with #. (b) M&#246;ssbauer spectrum and (c) DSC curve of Fe4.5Ni4.5S8. Parts of the figure were reproduced from a previous publication in Nat Comm.8 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56087/56087fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
SEM images of polished Fe4.5Ni4.5S8 rock and pellet electrodes are depicted in Figure 2a. We employed EDX analysis to determine the elemental composition of the material on the surface. The EDX spectrum is shown in Figure 2b. The carbon peak in the spectrum yields from the use of carbon pads to mount the sample on the holder. From the EDX quantification &#8211; shown in Figure 2c &#8211; the ratio between iron and nickel was determined to be 1.06: 1.00. Assuming that the sum of iron and nickel is 9, the actual sum formula is Fe4.64Ni4.36S8.11. The deviation from the ideal formula Fe4.5Ni4.5S8 is within the margin of error. This result is consistent with the observation of a pure Pentlandite phase in the XRD pattern of the sample.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56087/56087fig2.jpg" /> 
Figure 2: SEM and EDX analysis. SEM micrograph of (a) &#39;rock&#39; and (b) &#39;pellet&#39; electrodes. Scale bars = 1 &#181;m. (c) EDX spectrum and (d) composition analysis of the &#39;rock&#39; electrode. Parts of the figure were reproduced from a previous publication in Nat Comm.8 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56087/56087fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
For electrochemical performance testing towards HER, first the electrodes have been prepared using a cut piece of rock and a pellet pressed from finely ground powder, respectively. The key steps of the &#39;rock&#39; and &#39;pellet&#39; electrode preparation are shown in Figures 3a and 3b, respectively. The standard testing procedure involves first, polishing and electrochemical washing of the electrodes. Then, linear sweep voltammograms (LSV) are recorded, followed by stability testing, coupled with product quantification. Finally, the electrochemical surface area (ESCA) is estimated. In Figure 3c, the LSV&#180;s of both types&#39; electrodes are shown. From the LSV the over potential for the HER is estimated to be -280 mV and -285 mV vs. RHE at a current density of 10 mA/cm2 for &#39;rock&#39; and &#39;pellet&#39; electrode, respectively. An exfoliated drop coated electrode did not show any improved electrocatalytic performance. Therefore, the influence of the preparation method on the performance is minor. Neglecting the drop-coating procedure, a similar behavior can be observed for the long-term stability of the electrodes (Figure 3d), whereas the &#39;pellet&#39; shows a faster activation behavior as we have reported before for &#39;rock&#39; Fe4.5Ni4.5S8 electrodes.8 Both electrodes show comparable current densities after the activation is finished. However, if a drop-coated electrode is exposed to comparable electrochemical conditions, the high amount of hydrogen produced, leads to detachment of the catalyst from the electrode support and thus to inactivation of the system. Figure 3d (inset) shows the amount of hydrogen produced depending on the time of electrolysis using a &#39;rock&#39; electrode. Comparable hydrogen amounts can be observed for &#39;pellet&#39; electrodes. From the slope of a linear fit of the GC quantification, a hydrogen production rate of 2.14 mmol H2 h-1 cm-2 is determined, which is &#8211; to our best knowledge &#8211; only beaten by platinum (11 mmol H2 h-1 cm-2) at comparable applied potentials.14 For determination of the ECSA, the charging current density difference was plotted as a function of the scan rate. The resulting graph is shown in Figure 3e. From the slope, only marginal differences in ECSA and hence the number of active sites, which are well in the margin of error of such measurements, can be observed. Therefore, both preparation types offer electrodes of similar performance. In Figure 3f an exemplary Nyquist plot from the EIS data of a &#39;rock&#39; electrode is shown. Likewise, the &#39;pellet&#39; electrodes reveal the same behavior. This plot reveals a very low charge-transfer resistance (Rct = 57.2 &#8486;) of the Fe4.5Ni4.5S8 bulk electrode, which is consistent with the high intrinsic conductivity of the material.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56087/56087fig3.jpg" /> 
Figure 3: Electrode preparation and electrochemical analysis. Preparation steps of &#39;rock&#39; (a) and &#39;pellet&#39; (b) type Fe4.5Ni4.5S8 electrodes. Linear sweep voltammograms (c) at 5 mV s-1 of a &#39;rock&#39; (black), a &#39;pellet&#39; (red) and a drop coated (blue) electrode. (d) over 18 h at 0.6 V of &#39;rock&#39; (black) and &#39;pellet&#39; electrodes (red). Inset shows the hydrogen production over the first 4 h of electrolysis using a &#39;rock&#39; electrode. The blue line indicates the linear fit of the data. (e) Charging current density differences as a function of the scan rate for &#39;rock&#39; (black) and &#39;pellet&#39; electrodes (red). The linear slope represents the electrochemical surface area (ECSA). f) Nyquist plot and the equivalent circuit at HER overpotential (&#951; = 300 mV) of a &#39;rock&#39; electrode. Parts of the figure were reproduced from a previous publication in Nat Comm.8 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56087/56087fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications at JoVE.com

Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications

A facile preparation method of electrodes using the bulk material Fe4.5Ni4.5S8 is presented. This method provides an alternative technique to conventional electrode fabrication and describes prerequisites for unconventional electrode materials including a straightforward electrocatalytic testing method.

The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and ...

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11.3K Views.  Ruhr-University Bochum. A facile preparation method of electrodes using the bulk material Fe4.5Ni4.5S8 is presented. This method provides an alternative technique to conventional electrode fabrication and describes prerequisites for unconventional electrode materials including a straightforward electrocatalytic testing method.

Video: Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox reactions. The Cu (I) complex of the peptide model of a Cu (I) binding metallochaperone protein, which includes the sequence MTCSGCSRPG (underlined is conserved), was determined in solution under inert conditions by NMR spectroscopy.
NMR is a widely accepted technique for the determination of solution structures of proteins and peptides. Due to difficulty in crystallization to provide single crystals suitable for X-ray crystallography, the NMR technique is extremely valuable, especially as it provides information on the solution state rather than the solid state. Herein we describe all steps that are required for full three-dimensional structure determinations by NMR. The protocol includes sample preparation in an NMR tube, 1D and 2D data collection and processing, peak assignment and integration, molecular mechanics calculations, and structure analysis. Importantly, the analysis was first conducted without any preset metal-ligand bonds, to assure a reliable structure determination in an unbiased manner.

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

The NMR-solution structure of a metallochaperone model peptide with Cu (I) was determined, and a detailed protocol from sample preparation and 1D and 2D data collection to a three-dimensional structure is described.

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox ...

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

Preparation of Highly Porous Coordination Polymer Coatings on Macroporous Polymer Monoliths for Enhanced Enrichment of Phosphopeptides

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous polymer monoliths. The developed approach is based on the preparation of a macroporous polymer containing carboxylic acid functional groups and the subsequent step-by-step solution-based controlled growth of a layer of a porous coordination polymer on the surface of the pores of the polymer monolith. The prepared metal-organic polymer hybrid has a high specific micropore surface area. The amount of iron(III) sites is enhanced through metal-organic coordination on the surface of the pores of the functional polymer support. The increase of metal sites is related to the number of iterations of the coating process.
The developed preparation scheme is easily adapted to a capillary column format. The functional porous polymer is prepared as a self-contained single-block porous monolith within the capillary, yielding a flow-through separation device with excellent flow permeability and modest back-pressure. The metal-organic polymer hybrid column showed excellent performance for the enrichment of phosphopeptides from digested proteins and their subsequent detection using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The presented experimental protocol is highly versatile, and can be easily implemented to different organic polymer supports and coatings with a plethora of porous coordination polymers and metal-organic frameworks for multiple purification and/or separation applications.

A procedure for the preparation of porous hybrid separation media composed of a macroporous polymer monolith internally coated by a high surface area microporous coordination polymer is presented.

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous ...

Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, quantum dots should be highly fluorescent and small/monodisperse in size. While commonly used cadmium-based quantum dots possess these qualities, they are potentially toxic due to the possible release of Cd2+ ions through nanoparticle degradation. Indium-based quantum dots, specifically InP/ZnS, have recently been explored as a viable alternative to cadmium-based quantum dots due to their relatively similar fluorescence characteristics and size. The synthesis presented here uses standard hot-injection techniques for effective nanoparticle growth; however, nanoparticle properties such as size, emission wavelength, and emission intensity can drastically change due to small changes in the reaction conditions. Therefore, reaction conditions such temperature, reaction duration, and precursor concentration should be maintained precisely to yield reproducible products. Because quantum dots are not inherently soluble in aqueous solutions, they must also undergo surface modification to impart solubility in water. In this protocol, an amphiphilic polymer is used to interact with both hydrophobic ligands on the quantum dot surface and bulk solvent water molecules. Here, a detailed protocol is provided for the synthesis of highly fluorescent InP/ZnS quantum dots that are suitable for use in biomedical applications.

In this protocol, the synthesis of Cd-free InP/ZnS quantum dots (QDs) is detailed. InP-based QDs are gaining popularity due to the toxicity of Cd2+ ions that may be released through nanoparticle degradation. After synthesis, QDs are solubilized in water using an amphiphilic polymer for use in biomedical applications.

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

A Simple and Efficient Protocol for the Catalytic Insertion Polymerization of Functional Norbornenes

Norbornene can be polymerized by a variety of mechanisms, including insertion polymerization whereby the double bond is polymerized and the bicyclic nature of the monomer is conserved. The resulting polymer, polynorbornene, has a very high glass transition temperature, Tg, and interesting optical and electrical properties. However, the polymerization of functional norbornenes by this mechanism is complicated by the fact that the endo substituted norbornene monomer has, in general, a very low reactivity. Furthermore, the separation of the endo substituted monomer from the exo monomer is a tedious task. Here, we present a simple protocol for the polymerization of substituted norbornenes (endo:exo ca. 80:20) bearing either a carboxylic acid or a pendant double bond. The process does not require that both isomers be separated, and proceeds with low catalyst loadings (0.01 to 0.02 mol%). The polymer bearing pendant double bonds can be further transformed in high yield, to afford a polymer bearing pendant epoxy groups. These simple procedures can be applied to prepare polynorbornenes with a variety of functional groups, such as esters, alcohols, imides, double bonds, carboxylic acids, bromo-alkyls, aldehydes and anhydrides.

We describe the catalytic insertion polymerization of 5-norbornene-2-carboxylic acid and 5-vinyl-2-norbornene to form functional polymers with a very high glass transition temperature.

Norbornene can be polymerized by a variety of mechanisms, including insertion polymerization whereby the double bond is polymerized and the bicyclic ...

Synthesis of Core-shell Lanthanide-doped Upconversion Nanocrystals for Cellular Applications

Lanthanide-doped upconversion nanocrystals (UCNs) have attracted much attention in recent years based on their promising and controllable optical properties, which allow for the absorption of near-infrared (NIR) light and can subsequently convert it into multiplexed emissions that span over a broad range of regions from the UV to the visible to the NIR. This article presents detailed experimental procedures for high-temperature co-precipitation synthesis of core-shell UCNs that incorporate different lanthanide ions into nanocrystals for efficiently converting deep-tissue penetrable NIR excitation (808 nm) into a strong blue emission at 480 nm. By controlling the surface modification with biocompatible polymer (polyacrylic acid, PAA), the as-prepared UCNs acquires great solubility in buffer solutions. The hydrophilic nanocrystals are further functionalized with specific ligands (dibenzyl cyclooctyne, DBCO) for localization on the cell membrane. Upon NIR light (808 nm) irradiation, the upconverted blue emission can effectively activate the light-gated channel protein on the cell membrane and specifically regulate the cation (e.g., Ca2+) influx in the cytoplasm. This protocol provides a feasible methodology for the synthesis of core-shell lanthanide-doped UCNs and subsequent biocompatible surface modification for further cellular applications.

A protocol is presented for the synthesis of core-shell lanthanide-doped upconversion nanocrystals (UCNs) and their cellular applications for channel protein regulation upon near-infrared (NIR) light illumination.

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Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

Here, we present a one-pot, transition-metal-free synthesis of thiols and thioesters from aromatic halides and sodium thiomethoxide, followed by the preparation of single crystals of a metal-dithiolene network using thiol species generated in situ from the more stable and tractable thioester.

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Ion Mobility-Mass Spectrometry Techniques for Determining the Structure and Mechanisms of Metal Ion Recognition and Redox Activity of Metal Binding Oligopeptides

Electrospray ionization (ESI) can transfer an aqueous-phase peptide or peptide complex to the gas-phase while conserving its mass, overall charge, metal-binding interactions, and conformational shape. Coupling ESI with ion mobility-mass spectrometry (IM-MS) provides an instrumental technique that allows for simultaneous measurement of a peptide&#8217;s mass-to-charge (m/z) and collision cross section (CCS) that relate to its stoichiometry, protonation state, and conformational shape. The overall charge of a peptide complex is controlled by the protonation of 1) the peptide&#8217;s acidic and basic sites and 2) the oxidation state of the metal ion(s). Therefore, the overall charge state of a complex is a function of the pH of the solution that affects the peptides metal ion binding affinity. For ESI-IM-MS analyses, peptide and metal ions solutions are prepared from aqueous-only solutions, with the pH adjusted with dilute aqueous acetic acid or ammonium hydroxide. This allows for pH dependence and metal ion selectivity to be determined for a specific peptide. Furthermore, the m/z and CCS of a peptide complex can be used with B3LYP/LanL2DZ molecular modeling to discern binding sites of the metal ion coordination and tertiary structure of the complex. The results show how ESI-IM-MS can characterize the selective chelating performance of a set of alternative methanobactin peptides and compare them to the copper-binding peptide methanobactin.

Ion mobility-mass spectrometry and molecular modeling techniques can characterize the selective metal chelating performance of designed metal-binding peptides and the copper-binding peptide methanobactin. Developing new classes of metal chelating peptides will help lead to therapeutics for diseases associated with metal ion misbalance.