Name: combining solid-state and solution-based techniques: synthesis and reactivity of chalcogenidoplumbates(ii or iv)
Uploaded: 2016-12-29T15:00:00
Description: Watch this Scientific Journal Video about Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of ChalcogenidoplumbatesII or IV at JoVE.com

This work was supported by the Deutsche Forschungsgemeinschaft (DFG) within the framework of SPP 1708. GT thanks the Leopoldina Nationale Akademie der Wissenschaften for a postdoctoral scholarship.

Caution: Always be cautious when working with chemicals. Apply common safety precautions, including the appropriate utilization of gloves, goggles, and a lab coat at all times. In particular, be aware that all discussed compounds containing heavy elements, as well as their elemental sources, are of high toxicity. 1,2-diaminoethane is a corrosive liquid. Alkaline metals and ternary solid-state products may react pyrophorically with air and moisture.
Note: All manipulations are performed in an a...

<ol>
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The combination of classical high-temperature, solid-state reactions with solution-based methods allows for the generation and isolation of novel compounds that cannot be synthesized by only one of these pathways. Even though, in most cases, a clear identification and full characterization of the intermediate species is difficult or essentially impossible, the general idea is straightforward and can be applied to a variety of elemental combinations. Furthermore, the actual synthetic conditions for the generation of one s...

Metal chalcogenides, such as SnSe or CuInSe, are versatile materials with a wide range of applications, for instance, as semiconductor, thermoelectric, or nonlinear optic materials1-6. Similar elemental compositions are found within chalcogenidometalates, where the metal is in a formally positive oxidation state and coordinated by negative (poly-)chalcogenide ligands to yield an overall anionic species. Different from the abovementioned materials, such metalates are additionally comprised of counter-ions, which are well separated from the anionic substructure. Typical cations are (solvated) alkali or alkaline earth metals, ammonium, or phosphonium ions. Most often, such salts with chalcogenidometalate anions have physical properties that are similar to their parental binary or ternary compounds, such as similar band gaps or photo- and semiconductivity properties. However, due to the broad range of possible anionic architectures within each elemental combination, ranging from isolated molecular species through strands and sheets of interconnected anions to extended three-dimensional frameworks, an even finer tuning of various properties can be achieved, ultimately aiming at the designed synthesis of compounds with the desired properties. Within the concept of dimensional reduction, it has been shown that a relative increase of counter ions per formula unit, which accompanies a reduction from 3D via 2D and 1D to 0D anionic architectures (0D representing molecular species), decreases the observed band gap7. Moreover, by the utilization of different (or mixtures of) chalcogenide ligands, it is even possible to achieve an ultra-fine adjustment of the band gap8,9.
Apart from these practical applications and visionary relevancies, chalcogenidometalates are still investigated for fundamental understanding, such as for the generation of novel anionic structure types or the discovery and interpretation of an unusual bonding, as well as for their unprecedented properties. Whereas the lighter congeners (i.e., oxidometalates, commonly referred to as oxometalates) have been extensively studied, in particular for potential catalytic applications, the heavier chalcogenidometalates are far less explored.
Our own interest has been focused on the synthesis, properties, and further reactivity of chalcogenidotetrelates (i.e., the heavier homologs of silicates)10,11. There is a broad variety of such compounds, ranging from water-stable and soluble binary anions, such as the [SnTe4]4- anion12; to organic, functionalized, and multinary cluster compounds, such as {[Ir3(cod)3(&#181;3-S)2](&#181;3-S)SnCl}2 (cod = cycloocta-1,5-diene)13. Our most recent studies deal with chalcogenidoplumbates, with lead as the central metal atom(s). In line with the inert-pair concept for heavy atoms, addressing the stabilization of the 6s orbital due to relativistic effects, lead is usually observed in the formal +II oxidation state. Exceptions like PbO2 are strong oxidizing agents, and the heavier lead(IV) chalcogenides, &#34;PbCh2,&#34; have not been discovered to date14. The same holds for the chalcogenidoplumbate(IV) anions, of which only [PbO4]4- has been reported15 until recently (see below).
Apart from a diverse group of structurally investigated oxidoplumbates(II,IV), there have been only few examples of chalcogenidoplumbates(II), namely [PbTe3]4-, with a trigonal pyramidal anion16; and [Pb2Ch3]2-, where Ch = Se or Te, with a trigonal bipyramidal anion17. These are synthesized by a route that has also been applied for the generation of Zintl ions18. Upon preparation of multinary intermetallic phases by fusion of the elements at high temperatures, subsequent extraction by solvents in the presence of a sequestering agent affords the desired products in (single-)crystalline form. In the case of the [Pb2Ch3]2- anions, for instance, a phase of the nominal composition &#34;KPbCh&#34; has been extracted with 1,2-diaminoethane (en) in the presence of 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane ([2.2.2]crypt). The cryptand is necessary both for crystallization upon increase of the effective cation radius in the {K[2.2.2]crypt}+ complex counter ion, to better match the anionic size, and for a shielding of the positive charge that suppresses an electron back-donation from the anion in solution. Such salts with encapsulated cations usually reveal high tendencies for crystallization and thus, fairly good yields when compared to the corresponding salts without sequestration agents. However, a rather cumbersome synthesis or the high prices of cryptands prevent the excessive scaling of such approaches.
In contrast, K4[PbTe3]&#183;2en is synthesized via in situ reduction in solution, as has already been used as early as 1891 for the generation of the famous Pb94- anion19,20. For the latter, elemental alkaline metals were added to suspensions of lead in liquid ammonia at low temperatures, whereas for the telluridoplumbate, an alloy of the nominal composition &#34;PbTe2&#34; was reduced at room temperature, again by the addition of elemental potassium.
Our first approach towards such metalate species to be presented herein is a combination of both pathways. Here, solid-state synthesis is followed by either reduction in solution in the presence of inexpensive sequestering agents, such as 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6), or via reduction with alkaline metals that are chelated by the solvent itself, without the need for additional sequestering agents, similar to the synthesis of [Na4(en)7][Sn9]21. Our second approach also starts with high-temperature synthesis, but it is followed by solvothermal extraction of the resulting phases (i.e., extraction at elevated temperatures and pressures)22. In the following, we will present both synthetic approaches and some of our recent results upon application of these reaction pathways.

<table border="0" cellpadding="0" cellspacing="0" width="655">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Ethan-1,2-diamine</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td style="width:136px;">E26266-2.5L</td>
			<td style="width:191px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Calcium hydride</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>213268-100G</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Tetrahydrofuran</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>401757-1L</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Sodium</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>71172-1KG</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Potassium</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>244864-50G</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Tris-triphenylphosphine rhodium chloride</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>199982-5G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Lead</td>
			<td style="width:81px;">Acros</td>
			<td align="right">222625000</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Selenium</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>209643-50G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">18-crown-6</td>
			<td style="width:81px;">Acros</td>
			<td align="right">181561000</td>
			<td></td>
		</tr>
	</tbody>
</table>

combining solid-state and solution-based techniques: synthesis and reactivity of chalcogenidoplumbates(ii or iv)

The phases of &#34;PbCh2&#34; (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica glass ampules). Reduction of such phases by elemental alkaline metals in amines affords crystalline chalcogenidoplumbate(II) salts comprised of [PbTe3]2- or [Pb2Ch3]2- anions, depending upon which sequestering agent for the cations is present: crown ethers, like 18-crown-6, or cryptands, like [2.2.2]crypt. Reactions of solutions of such anions with transition-metal compounds yield (poly-)chalcogenide anions or transition-metal chalcogenide clusters, including one with a &#181;-PbSe ligand (i.e., the heaviest-known CO homolog).
In contrast, the solid-state synthesis of a phase of the nominal composition &#34;K2PbSe2&#34; by successive reactions of the elements and by the subsequent solvothermal treatment in amines yields the first non-oxide/halide inorganic lead(IV) compound: a salt of the ortho-selenidoplumbate(IV) anion [PbSe4]4-. This was unexpected due to the redox potentials of Pb(IV) and Se(-II). Such methods can further be applied to other elemental combinations, leading to the formation of solutions with binary [HgTe2]2- or [BiSe3]3- anions, or to large-scale syntheses of K2Hg2Se3 or K3BiSe3 via the solid-state route.
All compounds are characterized by single-crystal X-ray diffraction and elemental analysis; solutions of plumbate salts can be investigated by 205Pb and 77Se or 127Te NMR techniques. Quantum chemical calculations using density functional theory methods enable energy comparisons. They further allow for insights into the electronic configuration and thus, the bonding situation. Molecular Rh-containing Chevrel-type compounds were found to exhibit delocalized mixed valence, whereas similar telluridopalladate anions are electron-precise; the cluster with the &#181;-PbSe ligand is energetically favored over a hypothetical CO analog, in line with the unsuccessful attempt at its synthesis. The stability of formal Pb(IV) within the [PbSe4]4- anion is mainly due to a suitable stabilization within the crystal lattice.

The existence of an ortho-selenidoplumbate anion [PbSe4]4-23 (see Figure 1, top right) has been confirmed by single crystal diffraction experiments, elemental analysis, and quantum chemical calculations. The crystal structure refinement confirms the almost-perfect tetrahedral coordination geometry, as would be expected for a lead(IV) ion, whereas DFT calculations rationalize the energetically stabilized a1...

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Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of ChalcogenidoplumbatesII or IV

The synthesis of chalcogenidoplumbates(II,IV) via the in situ reduction of nominal "PbCh2" (Ch = Chalcogen) and via a solid-state reaction and subsequent solvothermal reactions is presented. Additionally, reactivities of plumbate(II) solutions are portrayed, which yield the heaviest-known CO homolog known to date: the &#181;-PbSe ligand.

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of Chalcogenidoplumbates(II or IV)

The phases of &#34;PbCh2&#34; (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica ...

The overall goal of this combinational approach of solid-state and solution-based chemistry is to synthesize novel materials with intrinsic semi-conducting properties. This method can help answer key questions in the inorganic and materials chemistry field, such as how to synthesize compounds not accessible via traditional synthetic methods or access compounds with uncommon oxidation states, coordination modes, or ligands. The main advantage of this technique is that it is high-yielding and provides access to reactive, pure metallate and iron solutions to be used as precursors or for further reactivity studies.Though this method can provide insight into the chemistry of metalloid compounds of the heaviest metal atoms, it can also be applied to other metallates. Generally, individuals new to this method will struggle because all manipulations have to be performed under strict exclusion of air, moisture and, in some cases, light. To prepare the dry solvents for synthesis, first add one liter of freshly-purchased one-two diaminoethane to 25 grams of calcium hydride.Heat the mixture under reflux until hydrogen is no longer generated, than distill the mixture under ambient pressure. Add one liter of tetrahydrofuran, THF, to 10 grams of sodium-potassium alloy. Heat the mixture under reflux for at least twelve hours, then distill the mixture at ambient pressure.Make a saturated solution of Wilkinson's catalyst by adding 20 milliliters of THF to 300 milligrams of the catalyst. After stirring overnight at room temperature, filter the mixture with an inert gas filter frit of low porosity. Place 3.81 grams of elemental selenium in a silica ampule and add five grams of elemental lead.Heat the solids with an oxygen-methane burner until optical homogeneity of the melt is achieved, which is approximately ten minutes. Knock the ampule gently with a cork ring throughout the synthesis to detach sublimed selenium from the ampule wall, which will then drop back into the reaction mixture. After allowing the reaction mixture to cool to room temperature, break the ampule with a pestle and a mortar.Manually remove all remaining splinters of the ampule, then pestle the crude lead selenide thoroughly. Next, place 0.95 grams of elemental potassium and five grams of elemental lead in a thick-walled silica ampule. Slowly heat the solids with an oxygen-methane burner until optical homogeneity of the melt is achieved, which is approximately 20 minutes.Carefully add 1.9 grams of elemental selenium pellets to the molten alloy. Upon complete addition, increase the temperature until the reaction mixture emits bright yellow-white radiation, and hold the temperature for 10 minutes. Decrease the reaction temperature slightly if the radiation color turns to pure, bright white.After allowing the reaction mixture to cool to room temperature, break the ampule with a pestle and a mortar. Manually remove all remaining splinters of the ampule and the regulus of elemental lead, then pestle the crude potassium lead selenide thoroughly. Place one gram of lead selenide, 1.55 grams of 18 crown 6 and a large stir bar in a round-bottom nitrogen flask.Transfer the flask onto a stir-plate and add 125 milliliters of one two diaminoethane. Stir vigorously at room temperature, and then add 0.23 grams of elemental potassium. The freshly-cut potassium is very sticky.Here it was covered in the lead selenide powder prior to its addition. Zero moisture must absolutely not enter the flask during the addition of the diverse chemicals. We apply counter-flow technique with the inert gas blowing out of the flasks such that air cannot go in.After stirring overnight at room temperature, fill the solution with an inert gas filter frit of low porosity. Now, place 0.5 grams of potassium lead selenide and two milliliters of one two diaminoethane in a five milliliter glass vial. Place the glass vial in a 15 milliliter PTFE vial and place the PTFE vial in a standard stainless steel autoclave, Close the autoclave tightly, and heat in a oven at 150 degrees Celsius for five days.After five days, turn off the oven and allow it to slowly cool to room temperature for one day, then transfer the reaction mixture into paratone oil and manually select crystals of the product under a standard-light microscope at 15 to 40 fold magnification. Place ten milliliters of the crown ether solution in a 50 milliliter flask. Add ten milliliters of the saturated Wilkinson's catalyst solution and stir overnight.Once the reaction is complete, filter the solution with an inert gas filter frit of low porosity and remove the solvent under dynamic vacuum slowly over 24 hours. After transferring the crude reaction product into paratone oil, manually select crystals of the Chevrel type cluster under a standard-light microscope at 15 to 40 fold magnification. Following this, place ten milliliters of the crown ether solution in a Schlenk tube and carefully layer it with ten milliliters of the saturated Wilkinson's catalyst solution.Cover the Schlenk tube with aluminum foil and leave it undisturbed for four weeks. After four weeks, transfer the resulting solid into paratone oil and select single crystals under a light microscope. The existence of an ortho-selenidoplumbate anion was confirmed by single crystal diffraction experiments, elemental analysis, and quantum chemical calculations.The crystal structure refinement confirms the almost-perfect tetrahedral coordination geometry, whereas DFT calculations rationalize the energetically stabilized A-one representation contributing to the overall stability of the anion. Other metallate materials can be obtained by this protocol, such as potassium two mercury two selenium three, which is a semi-and photo-conductor material with a polyanionic substructure. As it exhibits a too-large band gap, the band gap can be decreased by synthesizing the heavier tellurium homologue, which increases the photo-conductivity.High-yield impurity metallate anions can be utilized for further reactivity studies yielding molecular Chevrel-type compounds. The phosphine-saturated species include mixed-valence rhodium ions, and as the charge is highly de-localized, the structure determined by single crystal diffraction does not allow for formal oxidation state assignment. The telluridopalladate cluster is electron-precise, and palladium ions adopt a distorted square planar geometry.Similar synthetic procedures afford compounds with trirhodium disalinide units, adopting a trigonal, biparametal shape with selenium at the apical positions and rhodium in the basal plane. These units represent the core of different anionic cluster complexes. They can be isolated by the addition of counter-ion sequestering agents.Once mastered, this technique can be done in a day to obtain high-purity metallates in high yield. While attempting this procedure, it's important to remember that the compounds are highly sensitive to air and moisture, and in the case of heavy-element metallates, like telluridoplumbates, also to light. Following this procedure, other metallate materials that contain, for instance, light or early transition metal atoms, should accessible, too.This extends the library of known compounds and enables fine-tuning of desired properties. After watching this video, you should have a good understanding of how to synthesize novel metallate materials with a combination of solid-state and solution-based techniques. Don't forget that working with heavy elements and their compounds can be extremely hazardous, and precautions, such as wearing appropriate lab attire and having sand readily available for fire-extinguishing purpose, should always be taken while performing this procedure.

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Research

JoVE Journal

Chemistry

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the hydroxylmethylene phosphine precursor with ammonia in methanol under a nitrogen atmosphere. The N-triphosPh ligand precipitates from the solution after approximately 1 hr of reflux and can be isolated analytically pure via simple cannula filtration procedure under nitrogen. Reaction of the N-triphosPh ligand with [Ru3(CO)12] under reflux affords a deep red solution that show evolution of CO gas on ligand complexation. Orange crystals of the complex [Ru(CO)2{N(CH2PPh2)3}-&#954;3P] (2) were isolated on cooling to RT. The 31P{1H} NMR spectrum showed a characteristic single peak at lower frequency compared to the free ligand. Reaction of a toluene solution of complex 2 with oxygen resulted in the instantaneous precipitation of the carbonate complex [Ru(CO3)(CO){N(CH2PPh2)3}-&#954;3P] (3) as an air stable orange solid. Subsequent hydrogenation of 3 under 15 bar of hydrogen in a high-pressure reactor gave the dihydride complex [RuH2(CO){N(CH2PPh2)3}-&#954;3P] (4), which was fully characterized by X-ray crystallography and NMR spectroscopy. Complexes 3 and 4 are potentially useful catalyst precursors for a range of hydrogenation reactions, including biomass-derived products such as levulinic acid (LA). Complex 4 was found to cleanly react with LA in the presence of the proton source additive NH4PF6 to give [Ru(CO){N(CH2PPh2)3}-&#954;3P{CH3CO(CH2)2CO2H}-&#954;2O](PF6) (6).

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Ruthenium phosphine complexes are widely used for homogeneous catalytic reactions such as hydrogenations. The synthesis of a series of novel tridentate ruthenium complexes bearing the N-triphos ligand N(CH2PPh2)3 is reported. Additionally, the stoichiometric reaction of a dihydride Ru&#8211;N-triphos complex with levulinic acid is described.

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the ...

Synthesis and Characterization of Supramolecular Colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

X-ray Powder Diffraction in Conservation Science: Towards Routine Crystal Structure Determination of Corrosion Products on Heritage Art Objects

The crystal structure determination and refinement process of corrosion products on historic art objects using laboratory high-resolution X-ray powder diffraction (XRPD) is presented in detail via two case studies.
The first material under investigation was sodium copper formate hydroxide oxide hydrate, Cu4Na4O(HCOO)8(OH)2&#8729;4H2O (sample 1) which forms on soda glass/copper alloy composite historic objects (e.g., enamels) in museum collections, exposed to formaldehyde and formic acid emitted from wooden storage cabinets, adhesives, etc. This degradation phenomenon has recently been characterized as &#34;glass induced metal corrosion&#34;.
For the second case study, thecotrichite, Ca3(CH3COO)3Cl(NO3)2&#8729;6H2O (sample 2), was chosen, which is an efflorescent salt forming needlelike crystallites on tiles and limestone objects which are stored in wooden cabinets and display cases. In this case, the wood acts as source for acetic acid which reacts with soluble chloride and nitrate salts from the artifact or its environment.
The knowledge of the geometrical structure helps conservation science to better understand production and decay reactions and to allow for full quantitative analysis in the frequent case of mixtures.

Modern high resolution X-ray powder diffraction (XRPD) in the laboratory is used as an efficient tool to determine crystal structures of long-known corrosion products on historic objects.

The crystal structure determination and refinement process of corrosion products on historic art objects using laboratory high-resolution X-ray powder ...

Synthesis of Plant Phenol-derived Polymeric Dyes for Direct or Mordant-based Hair Dyeing

Effective hair dyeing through in situ incubation of keratin hair with the products of fungal laccase-catalyzed polymerization of plant phenols has been previously demonstrated. However, the dyeing process takes a long time to complete compared to commercial hair-dyeing products. To overcome this bottleneck, pre-synthesized polymeric products of the oxidative reaction of Trametes versicolor laccase on catechin and catechol, either with or without mordant agents (e.g., FeSO4), were here employed to achieve permanent keratin hair dyeing in various colors and shades. The laccase action in acidic sodium acetate buffer led to a deep black coloration after coupling reactions between the plant phenols. The colored dye products were then desalted and concentrated with ultrafiltration. The dyes, with or without mordant agents, caused a significant increase in &#916;E values (i.e., color difference value) in gray human hair within 2.5 hours. In addition, different keratin colors and shades were induced depending upon the mordanting and pH changes. The dyed hair also exhibited a strong resistance to detergent treatments, indicating that our methods can give rise to permanent hair dyeing.&#160;Overall, our work has provided novel insight into developing eco-friendly hair-dyeing methods as alternatives to commercial toxic diamine-based dyes.

Here, we present a protocol to use pre-synthesized polymeric products derived from fungal laccase-catalyzed polymerization of plant phenols, either with or without mordant agents (e.g., FeSO4), to induce detergent-resistant keratin hair dyeing within 2.5 hours.

Effective hair dyeing through in situ incubation of keratin hair with the products of fungal laccase-catalyzed polymerization of plant phenols has been ...

Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a technique used to measure the size distribution of polymer solutions or colloidal particles. Although this technique is widely used for the assessment of polymer solutions, it is difficult to measure the particle size in concentrated solutions due to the multiple scattering effect or strong light absorption. Therefore, the concentrated solutions should be diluted before measurement. Implementation of the confocal optical component in a dynamic light scattering microscope1 helps to overcome this barrier. Using such a microscopic system, both transparent and turbid systems can be analyzed under the same experimental setup without a dilution. As a representative example, a size distribution measurement of a temperature-responsive polymer solution was performed. The sizes of the polymer chains in an aqueous solution were several tens of nanometers at a temperature below the lower critical solution temperature (LCST). In contrast, the sizes increased to more than 1.0 &#181;m when above the LCST. This result is consistent with the observation that the solution turned turbid above the LCST.

A protocol for the direct measurement of particle size distribution in concentrated solutions using dynamic light scattering microscopy is presented.

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a ...

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)

We present herein the optimized synthesis of a triphosphenium bromide salt. Apart from being a versatile metathesis reagent, this unusually stable low-valent-phosphorus-containing compound acts as a useful P+ transfer agent. Unlike traditional methods employed to access low-coordinate phosphorus species which usually require pyrophoric phosphorus-containing precursors (white phosphorus, Tris(trimethylsilyl)phosphine, etc.), or harsh reducing agents (alkali metals, potassium graphite, etc.), the current approach does not involve pyrophoric or explosive reagents and can be done on large scales (&#62;20 g) in excellent yields by undergraduates with basic air-free synthetic training. The bromide counter ion is readily exchanged with other anions such as tetraphenyl borate (described herein) using typical salt metathesis reagents to obtain materials with desired properties and reactivities. The versatility of this P+ transfer approach is exemplified by the reactions of these triphosphenium precursors with an N-heterocyclic carbene and an anionic bisphosphine, each of which readily displace the neutral bisphosphine to give an NHC-stabilized phosphorus(I) cation and a phosphorus(I) containing zwitterion, respectively.

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of PhosphorusI

The synthesis of a triphosphenium bromide salt is described and its use as a P+ transfer agent is outlined by reactions with an N-heterocyclic carbene and an anionic bisphosphine, yielding an NHC-stabilized P(I) cation and a P(I) containing zwitterion, respectively.

We present herein the optimized synthesis of a triphosphenium bromide salt. Apart from being a versatile metathesis reagent, this unusually stable ...

Synthesis and Mass Spectrometry Analysis of Oligo-peptoids

Peptoids are sequence-controlled peptide-mimicking oligomers consisting of N-alkylated glycine units. Among many potential applications, peptoids have been thought of as a type of molecular information storage. Mass spectrometry analysis has been considered the method of choice for sequencing peptoids. Peptoids can be synthesized via solid phase chemistry using a repeating two-step reaction cycle. Here we present a method to manually synthesize oligo-peptoids and to analyze the sequence of the peptoids using tandem mass spectrometry (MS/MS) techniques. The sample peptoid is a nonamer consisting of alternating N-(2-methyloxyethyl)glycine (Nme) and N-(2-phenylethyl)glycine (Npe), as well as an N-(2-aminoethyl)glycine (Nae) at the N-terminus. The sequence formula of the peptoid is Ac-Nae-(Npe-Nme)4-NH2, where Ac is the acetyl group. The synthesis takes place in a commercially available solid-phase reaction vessel. The rink amide resin is used as the solid support to yield the peptoid with an amide group at the C-terminus. The resulting peptoid product is subjected to sequence analysis using a triple-quadrupole mass spectrometer coupled to an electrospray ionization source. The MS/MS measurement produces a spectrum of fragment ions resulting from the dissociation of charged peptoid. The fragment ions are sorted out based on the values of their mass-to-charge ratio (m/z). The m/z values of the fragment ions are compared against the nominal masses of theoretically predicted fragment ions, according to the scheme of peptoid fragmentation. The analysis generates a fragmentation pattern of the charged peptoid. The fragmentation pattern is correlated to the monomer sequence of the neutral peptoid. In this regard, MS analysis reads out the sequence information of the peptoids.

A protocol is described for the manual synthesis of oligo-peptoids followed by sequence analysis by mass spectrometry.

Peptoids are sequence-controlled peptide-mimicking oligomers consisting of N-alkylated glycine units. Among many potential applications, peptoids have ...

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 ...

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material&#8217;s rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such ...