Name: the synthesis of [sn10(si(sime3)3)4]2- using a metastable sn(i) halide solution synthesized via a co-condensation technique
Uploaded: 2016-11-28T13:00:00
Description: Watch this Scientific Journal Video about The Synthesis of [Sn10SiSiMe334]2- Using a Metastable SnI Halide Solution Synthesized via a Co-condensation Technique at JoVE.com

We are grateful to the Deutsche Forschungsgemeinschaft (DFG) for financial support, and we thank Dr. Daniel Werner for helpful discussions.

CAUTION! Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in these syntheses are acutely toxic, pyrophoric, and carcinogenic. Nanomaterials may have additional hazards compared to their bulk counterpart. Please use all appropriate safety practices when performing a reaction, including the use of engineering controls (fume hood and glovebox) and personal protective equipment (safety glasses, gloves, lab coat, full length pants, and closed-toe shoes)....

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Ed. 41, 3532-3554 (2002).</li><li>Ecker, A., Weckert, E., Schn&#246;ckel, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+structural+characterization+of+an+Al77+cluster.">Synthesis and structural characterization of an Al77 cluster.</a> Nature. 387, 379-381 (1997).</li><li>Schnepf, A., Schn&#246;ckel, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+structure+of+a+Ga84R204-+cluster-a+link+between+metalloid+clusters+and+fullerenes?.">Synthesis and structure of a Ga84R204- cluster-a link between metalloid clusters and fullerenes?.</a> Angew. Chem. Int. 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By applying the preparative co-condensation technique (Figure 1)25, novel materials based on molecules like SnBr are obtained. Due to the high flexibility in temperature, pressure, metal, and reactive gas, a large variety of metastable solutions of high reactive species can be synthesized. For example, subhalides of silicon and germanium are already obtained in this way. However, finding the right conditions to obtain a metastable solution for further synthesis is not trivial, and the solution...

Due to recent progress in the field of nanotechnology, the nanoscale size range between molecules and&#160;the solid state became more and more important and is the focus of various research efforts1. Research with nanoscaled compounds is especially of interest for metals or semimetals, as drastic changes take place during the transformation from small molecular species (e.g., oxides, halides: non-conducting; e.g., AlCl3, AuCl3, GeO2, etc.) to metalloid clusters2 of the general formulae MnRm (n&#62;m; M = metal such as Al, Au, Sn, etc.; R = ligand such as S-C6H4-COOH, N(SiMe3)2, etc.), to the final bulk elemental phase (metal: conducting; semimetal: semiconducting; e.g., elemental Al, Au, or Ge)3.
The synthesis of a definite molecular nanoscaled compound is challenging due to its metastable character. Many synthetic procedures give metal nanoparticles with a certain size distribution4, meaning a mixture of metalloid cluster compounds of different sizes. Consequently, to establish a basis for a structure-property relationship of nanoscaled materials, synthetic procedures must be developed to access definite nanoscaled molecular compounds. These definite molecular compounds (metalloid clusters in the case of metals5,6,7,8) will shed light on the complexity and the fundamental principles of deceptively simple chemistry, such as the dissolution and the formation of metals9.
One synthetic route to access metalloid clusters of various metals starts from the reduction of stable precursors that are reduced to form a metalloid cluster, mostly in low yield (e.g., metalloid group 14 clusters like Sn15(DippNSiMe3)6 (Dipp = 2,6-iPr2-C6H3)10, Pb10(Hyp)6 (Hyp = Si(SiMe3)3)11, or Ge5(CH(SiMe3)2)412). Additionally, an increasing number of metalloid clusters of coinage metals are synthesized via the reduction of precursors in the presence of a trapping ligand like [Ag44(p-MBA)30]4- (p-MBA = p-mercaptobenzoic acid)13 and Au102(p-MBA)4414. Beside the synthetic route of applying the reductive dehalogenation, Schn&#246;ckel et al. introduced a synthetic route to metalloid group 13 clusters by applying the disproportionation reaction of highly reactive metastable monohalides of the corresponding element (e.g., 3AlCl &#8594; 2Al + AlCl3).
The synthesis of the needed monohalides is thereby performed via a preparative co-condensation technique, where at high temperatures, gas-phase molecules of AlX and GaX (X = Cl, Br, I) are synthesized and afterwards trapped in a matrix of frozen solvents (Figure 1)15. This technique thus gives access to novel reagents, opening the way to novel areas of chemistry (e.g., starting from the metastable monohalides, metalloid clusters with diameters in the nanometer range like [Al77(N(SiMe3)2)20]2- or [Ga84(N(SiMe3)2)20]4- could be obtained)16,17.
The synthetic route via the disproportionation reaction is thus the most productive, leading to clusters with diameters in the nanometer range. However, this synthetic route is only possible if a metastable subhalide is at hand that disproportionates at low temperatures (normally far below 0 &#176;C). Again, in the case of group 14, monohalides are needed, as the subvalent dihalides MX2 (M = Ge, Sn, Pb) are too stable and disproportionate at temperatures well above 100 &#176;C. The synthesis of metastable group 14 monohalide solutions is possible via the preparative co-condensation technique. However, group 14 monohalides are obtained at much higher temperatures with respect to the group 13 monohalides, which are readily available as gas phase species at 1,000 &#176;C. Hence, SnBr is obtained in maximum yield at 1,250 &#176;C18, whereas GeBr19, as well as SiCl220, are obtained at even higher temperatures, up to 1,600 &#176;C. The monohalides are &#34;trapped&#34; via a preparative co-condensation technique (Figure 1), leading to metastable monohalide solutions. Starting from these metastable solutions, we were recently able to synthesize a variety of novel metalloid group 14 cluster compounds of germanium and tin, namely [Li(thf)2]3[Ge14(Hyp)5] (Hyp = Si(SiMe)3)21, Sn10(Hyp)622, and {[Li([12]crown-4)2]}2 [Sn10(Hyp)4]23. Here, we present the synthesis of a metastable Sn(I)Cl solution within a homemade co-condensation apparatus and describe its reactivity with LiHyp to give the metalloid cluster [Sn10(Hyp)4]2- 1 in high yield.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Tin 99.999%</td>
			<td>ABCR</td>
			<td>AB122397</td>
			<td></td>
		</tr>
		<tr>
			<td>HydrogenchlorideN28&#160; 99.8%</td>
			<td>Air Liquide</td>
			<td>P0820S10R0A001</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>Toluene anhydrous 99.8%</td>
			<td>Sigma Aldrich</td>
			<td>244511</td>
			<td></td>
		</tr>
		<tr>
			<td>Tri-n-butylphosphine &#62;93.5%</td>
			<td>Sigma Aldrich</td>
			<td>90827</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>TMEDA, &#62;99.5%</td>
			<td>Sigma Aldrich</td>
			<td>411019</td>
			<td></td>
		</tr>
		<tr>
			<td>12-crown-4</td>
			<td>Sigma Aldrich</td>
			<td>194905</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>THF anhydrous, &#62;99.9%</td>
			<td>Sigma Aldrich</td>
			<td>401757</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium, 99.95%</td>
			<td>Sigma Aldrich</td>
			<td>262715</td>
			<td></td>
		</tr>
		<tr>
			<td>Benzophenone, &#62;99%</td>
			<td>Sigma Aldrich</td>
			<td>427551</td>
			<td></td>
		</tr>
		<tr>
			<td>Differential pressure manometer&#160;</td>
			<td>MKS</td>
			<td>MKS Baratron 223B</td>
			<td></td>
		</tr>
		<tr>
			<td>Mass flow controller&#160;</td>
			<td>Bronckhorst&#160;</td>
			<td>Low &#916;p flow mass flow controller</td>
			<td></td>
		</tr>
		<tr>
			<td>High frequency generator</td>
			<td>Trumpf H&#252;ttinger</td>
			<td>TruHeat MF 5020</td>
			<td></td>
		</tr>
		<tr>
			<td>NMR spectrometer</td>
			<td>Bruker</td>
			<td>Bruker DRX-250</td>
			<td></td>
		</tr>
		<tr>
			<td>Glovebox</td>
			<td>GS Systemtechnik</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Argon 5.0</td>
			<td>Westfalen</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nitrogen 4.8</td>
			<td>Westfalen</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Graphite</td>
			<td>SGL</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Quartz glass tube</td>
			<td>Gebr. Rettberg GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Steel transferring cannula</td>
			<td>Rohre Ketterer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Balance</td>
			<td>Kern</td>
			<td>Kern PFB200-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Oil diffusion pump</td>
			<td>Balzers</td>
			<td>Balzers Diff900</td>
			<td></td>
		</tr>
		<tr>
			<td>Rotary vane pump</td>
			<td>Balzers</td>
			<td>Balzers QK100L4D</td>
			<td></td>
		</tr>
		<tr>
			<td>Pyrometer</td>
			<td>Sensotherm</td>
			<td>6285</td>
			<td></td>
		</tr>
		<tr>
			<td>Schlenk tubes with glassy stopcocks</td>
			<td>Gebr. Rettberg GmbH</td>
			<td>J.-Young-type valve with glassy stopcock</td>
			<td></td>
		</tr>
	</tbody>
</table>

the synthesis of [sn10(si(sime3)3)4]2- using a metastable sn(i) halide solution synthesized via a co-condensation technique

The number of well-characterized metalloid tin clusters, synthesized by applying the disproportionation of a metastable Sn(I) halide in the presence of a sterically demanding ligand, has increased in recent years. The metastable Sn(I) halide is synthesized at&#160;&#34;outer space conditions&#34; via the preparative co-condensation technique. Thereby, the subhalide is synthesized in an oven at high temperatures, around 1,300 &#176;C, and at reduced pressure by the reaction of elemental tin with hydrogen halide gas (e.g., HCl). The subhalide (e.g., SnCl) is trapped within a matrix of an inert solvent, like toluene at -196 &#176;C. Heating the solid matrix to -78 &#176;C gives a metastable solution of the subhalide. The metastable subhalide solution is highly reactive but can be stored at -78 &#176;C for several weeks. On heating the solution to room temperature, a disproportionation reaction occurs, leading to elemental tin and the corresponding dihalide. By applying bulky ligands like Si(SiMe3)3, the intermediate metalloid cluster compounds can be trapped before complete disproportionation to elemental tin. Hence, the reaction of a metastable Sn(I)Cl solution with Li-Si(SiMe3)3 gives [Sn10(Si(SiMe3)3)4]2- 1 as black crystals in high yield. 1 is formed via a complex reaction sequence including salt metathesis, disproportionation, and degradation of larger clusters. Further, 1 can be analyzed by various methods like NMR or single crystal X-ray structure analysis.

The principle of the matrix isolation technique in conjugation with the preparative co-condensation technique is shown (Figure 1), as well as the setup of the co-condensation apparatus (Figure 2) and the graphite reactor (Figure 3). Figures 4 and 5 show photos of the assembly of the co-condensation apparatus. In Figure 6, the gas supply components with the mass flow controller are shown. ...

Watch this Scientific Journal Video about The Synthesis of [Sn10SiSiMe334]2- Using a Metastable SnI Halide Solution Synthesized via a Co-condensation Technique at JoVE.com

The Synthesis of [Sn10SiSiMe334]2- Using a Metastable SnI Halide Solution Synthesized via a Co-condensation Technique

The disproportionation reaction of a metastable Sn(I) chloride solution, obtained via the preparative co-condensation technique, is used for the synthesis of a metalloid tin cluster compound.

The Synthesis of [Sn10(Si(SiMe3)3)4]2- Using a Metastable Sn(I) Halide Solution Synthesized via a Co-condensation Technique

The number of well-characterized metalloid tin clusters, synthesized by applying the disproportionation of a metastable Sn(I) halide in the presence of a ...

The overall goal of the preparative co-condensation technique is to access novel reagents based on molecules that are unattainable from classical synthetic procedures, which opens the door to new fields in chemistry. The main advantage of this method is that highly reactive reagents are obtained and subsequent reactions can be done at low temperature, which is important for the synthesis of metastable metalloid clusters. This method can help to answer key questions in the field of nanotechnology, as structure-property relations might be established from structurally well-characterized metalloid cluster compounds.Though the metastable tin-halide solution gives access to nanoscale cluster, it might also be used for coordination or adducts chemistry or for the synthesis of novel materials. Visual demonstration of this method is critical as the construction steps are difficult to learn due to the high complexity of the co-condensation apparatus. First, fill five reaction chambers with six grams of elemental tin.Stack the reaction chambers over a terminal ring, each of them twisted by 30 degrees, and fix the stack with a 0.7 millimeter graphite rod. Insert the stack into a hollow graphite tube, so that the holes of the terminal ring fit with the holes in the graphite tube. Fix the setup with a second 0.7 millimeter graphite rod.Then, weigh the whole setup with a scale and note the value to determine the amount of tin consumed during the reaction. Next, place the graphite reactor inside the copper induction coil of a co-condensation apparatus, and pass the cord's tube through the central hole of the top copper sheet, placed above the induction coil. Fix the cord's tube to a hydrogen chloride supply pipe with a gasket and a screw nut.Check the position of the reactor inside the coil, to ensure that the reactor protrudes from the coil by five, plus or minus 0.5, millimeters. Connect the cooling shield to the water pins of the connector with screw nuts. After fixing the cooling shield at the other side with a screw, test the water tightness of the cooling cycle by opening the tap water for 30 seconds.Following this, fix the fiber optics of a pyrometer to the holder at the copper shield with a screw. Fix the solvent vapor diffuser with a screw nut, and ensure that it is centered under the cavity of the copper shield. Re-check that the graphite reactor is still in the center of the induction coil and that there is no contact of the coil to the top copper sheet.Connect a steel tube with a valve to the vapor diffuser. Now, mount the Schlenk vessel for solvent evaporation onto the valve. Attach a previously prepared solvent mixture flask to the Schlenk vessel.Then, add a hemispherical heating mantle to the evaporating Schlenk vessel. Connect a long steel cannula to the apparatus with a screw nut, and close the outer tail with a small round-bottom flask. After placing a 10 centimeter magnetic stir bar inside a stainless steel vessel, place a gasket into the cavity of the plane flange, and connect the vessel to the co-condensation apparatus.Next, connect the hydrogen chloride-containing glass vessel to a small steel tube, and then to a four point adapter. Close the rear exit of the four point adapter with a blind flange. Then, connect a differential pressure manometer to the front exit, and set up a valve at the top exit.Now, connect a fine needle valve to the valve at the top exit of the four point adapter. Then, use a long steel tube to connect the gas supply part to the co-condensation apparatus. After complete assembly, evacuate the co-condensation apparatus overnight to a final pressure of around 10 to the minus five millibar.The next day, fill the cooling trap of an oil diffusion pump with four liters of liquid nitrogen. Switch on the cooling water cycle of a high frequency generator, and open the tap water. After turning on the generator, slowly bake out the graphite reactor by increasing the output power in incremental steps of 0.1 to 0.5 kilowatts until the reaction temperature is around 1300 degrees Celsius.Following bake-out, adjust the value of the generator to 1.0 kilowatt to cool down the reactor. After filling a steel dewar with 30 liters of liquid nitrogen, lift it with a lifting platform so that the reaction vessel is placed within the dewar. Then, add more liquid nitrogen to the dewar to reach the final level of liquid nitrogen.Switch on the hemispherical heating mantle on the lowest level to maintain evaporation. At this point, evaporate the solvent drop-wise. Fix the drop rate so that all solvent is used during the reaction.Close the fine needle and the gas valve, then open the hydrogen chloride-containing glass vessel. If the displayed voltage at the differential pressure manometer is not higher than 1600 millivolts, apply low pressure at the second connection of the manometer by connecting an evacuated vessel to the outer connection of the manometer. Record the displayed starting value.Next, heat the graphite reactor to 1300 degrees Celsius by adjusting the value of the generator to 3.6 kilowatts. After opening the gas valve, slowly open the fine needle valve to let in the hydrogen chloride gas at a constant rate of eight millivolts per minute. Check the rate at least every 10 minutes, and record the measured values.Add two liters of liquid nitrogen to the dewar, approximately every 10 minutes, so that the level of liquid nitrogen is always at the upper third of the stainless steel vessel. After the value of the differential manometer is decreased by 1600 millivolts, close the gas valve. Then introduce the remaining hydrogen chloride gas that is within the gas supply part by slowly opening the fine needle valve, and shut down the high frequency generator.Disconnect the oil diffusion pump by closing the main valve, and flush the apparatus with dry nitrogen to a pressure around one atmosphere. Replace the liquid nitrogen-filled steel dewar with an insulated bucket placed on a magnetic stirrer. Then, add about five kilograms of fine powdered dry ice to the bucket, and turn on the magnetic stirrer.After allowing the solution to stir for at least 45 minutes, replace the round-bottom flash at the press cannula with a double-valve Schlenk tube while still cooling with dry ice under constant flow of nitrogen. Fix the height of the press cannula so that it touches the bottom of the stainless steel vessel. Now, push out the tin chloride solution with slight over-pressure by opening the valves at the double-valve Schlenk tube.To determine the solution quality, perform a halide titration by dissolving two milliliters of the solution in 50 milliliters of dilute nitric acid. Then, add one milliliter of 30 percent hydrogen peroxide to the mixture. After stirring for 10 minutes, perform a potentiometric titration of silver nitrate against the calomel electrode.Following this, weigh the graphite tube to determine the amount of consumed tin, which should be between 4 and 4.8 grams. Using a steel or Teflon cannula, add 20 milliliters of the 0.2 molar tin chloride solution to a cooled Schlenk vessel, containing two grams of the ligon source. Turn on the magnetic stirrer, allowing the reaction to stir, and slowly warm to room temperature within three hours.Once the reaction is complete, stop the magnetic stirrer and allow all insoluble precipitate inside the Schlenk tube to settle. Then, filter the dark brown solution into another Schlenk vessel. Finally, add 0.2 milliliters of TMEDA to the mixture, allow it to stand overnight to form black crystals.After isolation, identify the crystals via proton NMR. The principle of the matrixed isolation technique, in conjugation with preparative co-condensation technique, is shown here. A schematic of the co-condensation apparatus setup is displayed here.Here, the synthetic root to the metalloid cluster compound one is shown, applying the disproportionation reaction of the metastable sub-valent tin chloride. The proton, carbon, and silicon NMR spectra of the metalloid tin 10-cluster crystals are shown here. The molecular structure of compound one, as determined by x-ray crystallographic analysis, is displayed here.Once mastered, the co-condensation can be performed within two days, if it is performed properly. The synthesis of the metalloid tin 10-cluster requires another week for the crystallization of the product. While attempting this procedure, it's important to remember that the settings during the co-condensation reaction must at constant to obtain a suitable metastable solution that can be used for the synthesis of metalloid clusters.Following this procedure, subsequent reactions with the metalloid tin 10-cluster can be performed in order to answer additional questions like chemical reactivity of metalloid tin clusters. After its development, this technique paved the way for researches in the field of nanotechnology to explore properties on defined nano-scaled metalloid cluster compounds. After watching this video, you should have a good understanding of how preparative co-condensation is performed, leading to novel reagents, based on molecules that are unattainable via classical synthetic procedures, which opens the door to new fields in chemistry.Don't forget that working with a co-condensation apparatus and the highly reactive metastable sub-halide solution can be extremely hazardous, and personal protective equipment such as safety glasses, gloves, and lab hood should be worn while performing the reactions.

the-synthesis-sn10sisime3342-using-metastable-sni-halide-solution

Research

JoVE Journal

Chemistry

Preparation and Use of Samarium Diiodide (SmI2) in Organic Synthesis: The Mechanistic Role of HMPA and Ni(II) Salts in the Samarium Barbier Reaction

Although initially considered an esoteric reagent, SmI2 has become a common tool for synthetic organic chemists. SmI2 is generated through the addition of molecular iodine to samarium metal in THF.1,2-3 It is a mild and selective single electron reductant and its versatility is a result of its ability to initiate a wide range of reductions including C-C bond-forming and cascade or sequential reactions. SmI2 can reduce a variety of functional groups including sulfoxides and sulfones, phosphine oxides, epoxides, alkyl and aryl halides, carbonyls, and conjugated double bonds.2-12 One of the fascinating features of SmI-2-mediated reactions is the ability to manipulate the outcome of reactions through the selective use of cosolvents or additives. In most instances, additives are essential in controlling the rate of reduction and the chemo- or stereoselectivity of reactions.13-14 Additives commonly utilized to fine tune the reactivity of SmI2 can be classified into three major groups: (1) Lewis bases (HMPA, other electron-donor ligands, chelating ethers, etc.), (2) proton sources (alcohols, water etc.), and (3) inorganic additives (Ni(acac)2, FeCl3, etc).3
Understanding the mechanism of SmI2 reactions and the role of the additives enables utilization of the full potential of the reagent in organic synthesis. The Sm-Barbier reaction is chosen to illustrate the synthetic importance and mechanistic role of two common additives: HMPA and Ni(II) in this reaction. The Sm-Barbier reaction is similar to the traditional Grignard reaction with the only difference being that the alkyl halide, carbonyl, and Sm reductant are mixed simultaneously in one pot.1,15 Examples of Sm-mediated Barbier reactions with a range of coupling partners have been reported,1,3,7,10,12 and have been utilized in key steps of the synthesis of large natural products.16,17 Previous studies on the effect of additives on SmI2 reactions have shown that HMPA enhances the reduction potential of SmI2 by coordinating to the samarium metal center, producing a more powerful,13-14,18 sterically encumbered reductant19-21 and in some cases playing an integral role in post electron-transfer steps facilitating subsequent bond-forming events.22 In the Sm-Barbier reaction, HMPA has been shown to additionally activate the alkyl halide by forming a complex in a pre-equilibrium step.23
Ni(II) salts are a catalytic additive used frequently in Sm-mediated transformations.24-27 Though critical for success, the mechanistic role of Ni(II) was not known in these reactions. Recently it has been shown that SmI2 reduces Ni(II) to Ni(0), and the reaction is then carried out through organometallic Ni(0) chemistry.28
These mechanistic studies highlight that although the same Barbier product is obtained, the use of different additives in the SmI2 reaction drastically alters the mechanistic pathway of the reaction. The protocol for running these SmI2-initiated reactions is described.

Preparation and Use of Samarium Diiodide SmI2 in Organic Synthesis: The Mechanistic Role of HMPA and NiII Salts in the Samarium Barbier Reaction

A straightforward procedure for the preparation of samarium diiodide (SmI2) in THF is described. The role of two main additives namely hexamethylphosphoramide (HMPA) and Ni(acac)2 in Sm mediated reactions is demonstrated in the Sm-Barbier reaction.

Although initially considered an esoteric reagent, SmI2 has become a common tool for synthetic organic chemists. SmI2 is generated through the addition of ...

Synthesis and Purification of Iodoaziridines Involving Quantitative Selection of the Optimal Stationary Phase for Chromatography

The highly diastereoselective preparation of cis-N-Ts-iodoaziridines through reaction of diiodomethyllithium with N-Ts aldimines is described. Diiodomethyllithium is prepared by the deprotonation of diiodomethane with LiHMDS, in a THF/diethyl ether mixture, at -78 &#176;C in the dark. These conditions are essential for the stability of the LiCHI2 reagent generated. The subsequent dropwise addition of N-Ts aldimines to the preformed diiodomethyllithium solution affords an amino-diiodide intermediate, which is not isolated. Rapid warming of the reaction mixture to 0 &#176;C promotes cyclization to afford iodoaziridines with exclusive cis-diastereoselectivity. The addition and cyclization stages of the reaction are mediated in one reaction flask by careful temperature control.
Due to the sensitivity of the iodoaziridines to purification, assessment of suitable methods of purification is required. A protocol to assess the stability of sensitive compounds to stationary phases for column chromatography is described. This method is suitable to apply to new iodoaziridines, or other potentially sensitive novel compounds. Consequently this method may find application in range of synthetic projects. The procedure involves firstly the assessment of the reaction yield, prior to purification, by 1H NMR spectroscopy with comparison to an internal standard. Portions of impure product mixture are then exposed to slurries of various stationary phases appropriate for chromatography, in a solvent system suitable as the eluent in flash chromatography. After stirring for 30 min to mimic chromatography, followed by filtering, the samples are analyzed by 1H NMR spectroscopy. Calculated yields for each stationary phase are then compared to that initially obtained from the crude reaction mixture. The results obtained provide a quantitative assessment of the stability of the compound to the different stationary phases; hence the optimal can be selected. The choice of basic alumina, modified to activity IV, as a suitable stationary phase has allowed isolation of certain iodoaziridines in excellent yield and purity.

A protocol for the diastereoselective one-pot preparation of cis-N-Ts-iodoaziridines is described. The generation of diiodomethyllithium, addition to N-Ts aldimines and cyclization of the amino gem-diiodide intermediate to iodoaziridines is demonstrated. Also included is a protocol to rapidly and quantitatively assess the most appropriate stationary phase for purification by chromatography.

The highly diastereoselective preparation of cis-N-Ts-iodoaziridines through reaction of diiodomethyllithium with N-Ts aldimines is described. ...

Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2&#183;H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.

A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and ...

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the development of antibody drug conjugates (ADCs) and nanomedicine, fluorescent microscopy and systems chemistry. For many of these applications, specificity of the bioconjugation method used is of prime concern. The Michael addition of maleimides with cysteine(s) on the target proteins is highly selective and proceeds rapidly under mild conditions, making it one of the most popular methods for protein bioconjugation.
We demonstrate here the modification of the only surface-accessible cysteine residue on yeast cytochrome c with a ruthenium(II) bisterpyridine maleimide. The protein bioconjugation is verified by gel electrophoresis and purified by aqueous-based fast protein liquid chromatography in 27% yield of isolated protein material. Structural characterization with MALDI-TOF MS and UV-Vis is then used to verify that the bioconjugation is successful. The protocol shown here is easily applicable to other cysteine - maleimide coupling of proteins to other proteins, dyes, drugs or polymers.

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

This protocol details the important steps required for the bioconjugation of a cysteine containing protein to a maleimide, including reagent purification, reaction conditions, bioconjugate purification and bioconjugate characterization.

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the ...

Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH3NH3I) and methylammonium bromide (CH3NH3Br) from methylamine and the corresponding halide acid (HI or HBr). Then, we describe the fabrication of pinhole-free, continuous methylammonium-lead halide perovskite (CH3NH3PbX3 with X = I, Br, Cl and their mixture) films with the LP-VASP. This process is based on two steps: i) spin-coating of a homogenous layer of lead halide precursor onto a substrate, and ii) conversion of this layer to CH3NH3PbI3-xBrx by exposing the substrate to vapors of a mixture of CH3NH3I and CH3NH3Br at reduced pressure and 120 &#176;C. Through slow diffusion of the methylammonium halide vapor into the lead halide precursor, we achieve slow and controlled growth of a continuous, pinhole-free perovskite film. The LP-VASP allows synthetic access to the full halide composition space in CH3NH3PbI3-xBrx with 0&#160;&#8804; x&#160;&#8804; 3. Depending on the composition of the vapor phase, the bandgap can be tuned between 1.6 eV&#160;&#8804; Eg&#160;&#8804; 2.3 eV. In addition, by varying the composition of the halide precursor and of the vapor phase, we can also obtain CH3NH3PbI3-xClx. Films obtained from the LP-VASP are reproducible, phase pure as confirmed by X-ray diffraction measurements, and show high photoluminescence quantum yield. The process does not require the use of a glovebox.

Here, we present a protocol for the synthesis of CH3NH3I and CH3NH3Br precursors and the subsequent formation of pinhole-free, continuous CH3NH3PbI3-xBrx thin films for the application in high efficiency solar cells and other optoelectronic devices.

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, ...

Protocol for the Solid-phase Synthesis of Oligomers of RNA Containing a 2'-O-thiophenylmethyl Modification and Characterization via Circular Dichroism

Solid-phase synthesis has been used to obtain canonical and modified polymers of nucleic acids, specifically of DNA or RNA, which has made it a popular methodology for applications in various fields and for different research purposes. The procedure described herein focuses on the synthesis, purification, and characterization of dodecamers of RNA 5&#39;-[CUA CGG AAU CAU]-3&#39; containing zero, one, or two modifications located at the C2&#39;-O-position. The probes are based on 2-thiophenylmethyl groups, incorporated into RNA nucleotides via standard organic synthesis and introduced into the corresponding oligonucleotides via their respective phosphoramidites. This report makes use of phosphoramidite chemistry via the four canonical nucleobases (Uridine (U), Cytosine (C), Guanosine (G), Adenosine (A)), as well as 2-thiophenylmethyl functionalized nucleotides modified at the 2&#39;-O-position; however, the methodology is amenable for a large variety of modifications that have been developed over the years. The oligonucleotides were synthesized on a controlled-pore glass (CPG) support followed by cleavage from the resin and deprotection under standard conditions, i.e., a mixture of ammonia and methylamine (AMA) followed by hydrogen fluoride/triethylamine/N-methylpyrrolidinone. The corresponding oligonucleotides were purified via polyacrylamide electrophoresis (20% denaturing) followed by elution, desalting, and isolation via reversed-phase chromatography (Sep-pak, C18-column). Quantification and structural parameters were assessed via ultraviolet-visible (UV-vis) and circular dichroism (CD) photometric analysis, respectively. This report aims to serve as a resource and guide for beginner and expert researchers interested in embarking in this field. It is expected to serve as a work-in-progress as new technologies and methodologies are developed. The description of the methodologies and techniques within this document correspond to a DNA/RNA synthesizer (refurbished and purchased in 2013) that uses phosphoramidite chemistry.

Protocol for the Solid-phase Synthesis of Oligomers of RNA Containing a 2&#039;-O-thiophenylmethyl Modification and Characterization via Circular Dichroism

This article provides a detailed procedure on the solid-phase synthesis, purification, and characterization of dodecamers of RNA modified at the C2&#39;-O-position. UV-vis and circular dichroism photometric analyses are used to quantify and characterize structural aspects, i.e., single-strands or double-strands.

Solid-phase synthesis has been used to obtain canonical and modified polymers of nucleic acids, specifically of DNA or RNA, which has made it a popular ...

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another &#34;bad&#34; ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized.

We report a solution-based method to synthesize substrate-bound Au nanowires. By tuning the molecular ligands used during the synthesis, the Au nanowires can be grown from various substrates with different surface properties. Au nanowire-based nanostructures can also be synthesized by adjusting the reaction parameters.

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

Regioselective O-Glycosylation of Nucleosides via the Temporary 2',3'-Diol Protection by a Boronic Ester for the Synthesis of Disaccharide Nucleosides

Disaccharide nucleosides, which consist of disaccharide and nucleobase moieties, have been known as a valuable group of natural products having multifarious bioactivities. Although chemical O-glycosylation is a commonly beneficial strategy to synthesize disaccharide nucleosides, the preparation of substrates such as glycosyl donors and acceptors requires&#160;tedious protecting&#160;group manipulations and a purification at each synthetic step. Meanwhile, several research groups have reported that boronic and borinic esters serve as a protecting or activating group of carbohydrate derivatives to achieve the regio- and/or stereoselective acylation, alkylation, silylation, and glycosylation. In this article, we demonstrate the procedure for the regioselective O-glycosylation of unprotected ribonucleosides utilizing boronic acid. The esterification of 2&#39;,3&#39;-diol of ribonucleosides with boronic acid makes the temporary protection of diol, and, following O-glycosylation with a glycosyl donor in the presence of p-toluenesulfenyl chloride and silver triflate, permits the regioselective reaction of the 5&#39;-hydroxyl group to afford the disaccharide nucleosides. This method could be applied to various nucleosides, such as guanosine, adenosine, cytidine, uridine, 5-metyluridine, and 5-fluorouridine. This article and the accompanying video represent&#160;useful (visual) information for the O-glycosylation of unprotected nucleosides and their analogs for the synthesis of not only disaccharide nucleosides, but also a variety of biologically relevant derivatives.

Regioselective O-Glycosylation of Nucleosides via the Temporary 2&#039;,3&#039;-Diol Protection by a Boronic Ester for the Synthesis of Disaccharide Nucleosides

Here, we present protocols for the synthesis of disaccharide nucleosides by the regioselective O-glycosylation of ribonucleosides via a temporary protection of their 2&#39;,3&#39;-diol moieties utilizing a cyclic boronic ester. This method applies to several unprotected nucleosides such as adenosine, guanosine, cytidine, uridine, 5-methyluridine, and 5-fluorouridine to give corresponding disaccharide nucleosides.