We gratefully acknowledge the financial support from National Natural Science Foundation of China (21703104), Jiangsu Science and Technology Plan (SBK2017041514) Nanjing Tech University (39837131), and SICAM Fellowship from Jiangsu National Synergetic Innovation Center for Advanced Materials.

Caution: Please check the material safety data sheets (MSDS) of the chemicals for detailed handling and storage instruction. Please be careful while handling the nanomaterials, as there may be unidentified risk. Please perform the experiments in a fume hood and wear appropriate personal protective equipment.
1. Synthesis of Seed Nanoparticles
Note: To avoid failure caused by the premature nucleation during the nanoparticle synthesis, wash the glassware and stir bar used in the synthesis with aqua regia and rinse thoroughly with water.
<ol>
	<li>Synthesis of 3-5 nm Au nanoparticles
	<ol>
		<li>Prepare a hydrogen tetrachloroaurate (III) (HAuCl4) solution by dissolving 10 mg of HAuCl4&#8729;3H2O in 1 mL of deionization&#160;water (DI water) in a 4 mL vial. Pipette 0.197 mL of the HAuCl4 solution into a 50 mL round-bottom flask.</li>
		<li>Add 19.7 mL of DI water to the flask to dilute the HAuCl4 solution.</li>
		<li>Dissolve 10 mg of sodium citrate in 1 mL of DI water in another 4 mL vial to prepare a 1% sodium citrate stock solution. Add 0.147 mL of the 1% sodium citrate solution to the diluted HAuCl4 solution prepared in step 1.1.2.</li>
		<li>Prepare a 0.1 M sodium borohydride (NaBH4) solution by dissolving 2.3 mg of NaBH4 in 0.6 mL of DI water.</li>
		<li>Quickly inject 0.6 mL of 0.1 M NaBH4 solution into the mixture from step 1.1.3 under vigorous stirring. Check for an immediate color change of the solution from pale yellow to bright orange.</li>
		<li>Stir the mixture for another 10 min. Wait for a gradual color change of the solution to reddish orange.</li>
		<li>Confirm the size of the obtained Au nanoparticles with UV-Vis spectroscopy and scanning electron microscopy (SEM).</li>
	</ol>
	</li>
	<li>Synthesis of 15 and 40 nm Au nanoparticles
	<ol>
		<li>Add 100 mL of DI water in a 250 mL round-bottom flask. Weigh 10 mg of HAuCl4&#8729;3H2O solid and dissolve it in the round-bottom flask.</li>
		<li>Add a magnetic stir bar into the flask and equip the flask with a condenser. Stir and heat the solution prepared in 1.2.1 to 100 &#176;C in an oil bath. Reflux the solution for 10 min.</li>
		<li>Weigh 40 mg of sodium citrate and dissolve it in 4 mL of DI water to prepare a 1% sodium citrate stock solution.</li>
		<li>To synthesize 15 nm Au nanoparticles, add 3 mL of the 1% sodium citrate solution from step 1.2.3 to the boiled mixture with a syringe. 
		Note: The color of the solution turns gray in 1 min, and then gradually to red.
		<ol>
			<li>To synthesize 40 nm Au nanoparticles, inject 1.5 mL of the 1% sodium citrate solution to the boiling solution from step 1.2.2 with a syringe. Keep the solution boiling until it changes to red in about 10 min. 
			Note: The color of the solution changes from transparent to dark gray, then to black, and finally to purple in about 1 min.</li>
		</ol>
		</li>
		<li>Continue to reflux the reaction solution for 30 min. Cool down the solution to room temperature at ambient conditions.</li>
		<li>Characterize the size and uniformity of the resulting Au nanoparticles with UV-Vis spectroscopy and SEM.</li>
	</ol>
	</li>
</ol>
2. Synthesis of Au Nanowires (Length = ~500 nm ) on Silicon (Si) Wafers and Various Substrates
<ol>
	<li>Prepare the substrate for seed adsorption.
	<ol>
		<li>Cut the Si wafer into 5 mm &#180; 5 mm pieces. Clean the Si wafer pieces with DI water and ethanol sequentially in an ultrasonic bath, each for 15 min.</li>
		<li>Treat the Si wafer with 29.6 W of O2 plasma (operated at 220 V) for 20 min. 
		Note: The surface of the wafer becomes hydrophilic.</li>
		<li>Prepare a 5 mM 3-aminopropyltriethoxysilane (APTES) solution by dissolving 11.1 mg of APTES to a mixture of DI water (5 mL) and ethanol (5 mL) in a 20 mL vial.</li>
		<li>Soak a piece of Si wafer in the APTES solution prepared in step 2.1.3 in a 20 mL vial for 30 min.</li>
		<li>Take out the Si wafer and wash it thoroughly with ethanol and DI water.</li>
	</ol>
	</li>
	<li>Adsorb seed nanoparticles onto the substrate.
	<ol>
		<li>Soak the Si wafer in the 3-5 nm Au seeds solution prepared in step 1.1 for 2 h.
		<ol>
			<li>To grow Au nanowires from 15 nm Au seeds, soak the Si wafer in the 15 nm Au nanoparticle solution for 2 h.</li>
			<li>To grow Au nanowires from 40 nm Au seeds, soak the Si wafer in the 40 nm Au nanoparticle solution for 2 h.</li>
		</ol>
		</li>
		<li>Take out the Si wafer and wash it with 50 mL of DI water to remove unabsorbed Au nanoparticles.</li>
	</ol>
	</li>
	<li>Grow the substrate-bound Au nanowires.
	<ol>
		<li>Prepare a 1.65 mM 4-mercaptobenzoic acid (4-MBA) solution by dissolving 2.5 mg of 4-MBA in 10 mL of ethanol.</li>
		<li>Prepare a 5.10 mM HAuCl4 solution by dissolving 20.1 mg of HAuCl4&#8729;3H2O in a mixture of 5 mL of ethanol and 5 mL of DI water.</li>
		<li>Prepare a 12.3 mM L-ascorbic acid solution by dissolving 21.7 mg of L-ascorbic acid in 10 mL of DI water.</li>
		<li>Mix 0.5 mL of 5.10 mM HAuCl4 solution with 0.5 mL of 1.65 mM 4-MBA solution in a 10 mL vial.</li>
		<li>Soak the seed-adsorbed Si wafer from step 2.2.2 in the mixed solution prepared in step 2.3.4.</li>
		<li>Add 0.5 mL of 12.3 mM L-ascorbic acid solution into the wafer-soaked mixed solution. Shake the vial gently to evenly mix the solution.</li>
		<li>Leave the wafer and the solution undisturbed for 15 min. Check the bubble formation during the growth process, and the color change of the surface of the Si wafer from shiny gray to reddish brown.</li>
		<li>Take out the Si wafer and rinse it with ethanol and DI water. Dry the Si wafer at ambient conditions and wait for the surface of the wafer to turn to gold.</li>
		<li>Characterize the morphology of the Au nanowires with the SEM.</li>
	</ol>
	</li>
	<li>For growth of Au nanowires on a glass slide, Al2O3, SrTiO3, LaAlO3, indium tin oxide (ITO) and F-doped tin oxide (FTO) substrates, follow the same procedures, including the cleaning processes.</li>
</ol>
3. Synthesis of Au Nanowires with Different Ligands
<ol>
	<li>Synthesis of Au nanowire forests with various thiolated ligands: 2-naphthalenethiol (2-NpSH), 4-mercaptophenylacetic acid (4-MPAA) and 3-mercaptobenzoic acid (3-MBA).
	<ol>
		<li>Treat the Si wafer following the same procedures in steps 2.1-2.2.</li>
		<li>Prepare a 1.65 mM 2-NpSH solution by dissolving 2.6 mg of 2-NpSH in 10 mL of ethanol.
		<ol>
			<li>Prepare a 1.65 mM 4-MPAA solution by dissolving 2.8 mg of 4-MPAA in 10 mL of ethanol.</li>
			<li>Prepare a 1.65 mM 3-MBA solution by dissolving 2.5 mg of 3-MBA in 10 mL of ethanol.</li>
		</ol>
		</li>
		<li>Prepare the 5.10 mM HAuCl4 solution and 12.3 mM L-ascorbic acid solution following the same procedure in steps 2.3.1-2.3.3.</li>
		<li>In a 10 mL vial, mix 0.5 mL of the HAuCl4 solution with 0.5 mL of 2-NpSH solution, and shake the mixture to get a homogeneous solution.
		<ol>
			<li>In a 10 mL vial, mix 0.5 mL of the HAuCl4 solution with 0.5 mL of 4-MPAA solution, and shake the mixture to get a homogeneous solution.</li>
			<li>In a 10 mL vial, mix 0.5 mL of the HAuCl4 solution with 0.5 mL of 3-MBA solution, and shake the mixture to get a homogeneous solution.</li>
		</ol>
		</li>
		<li>Add 0.5 mL of 12.3 mM L-ascorbic acid solution to the wafer-soaked mixed solution. Shake the vial gently to get an evenly mixed solution.</li>
		<li>Leave the wafer and the solution undisturbed for 15 min. Observe the surface of the Si wafer turning slowly from shiny gray to reddish brown.</li>
		<li>Take out the Si wafer and rinse it with ethanol and DI water, and dry the Si wafer at ambient conditions until the surface of the wafer turns to gold.</li>
		<li>Confirm the Au nanowires forest structure with SEM.</li>
	</ol>
	</li>
	<li>Synthesis of tapered Au nanowires with mixed ligands.
	<ol>
		<li>Synthesis of thickened Au nanowires with mixed ligands of 4-MBA and 3-mercaptopropanoic acid (3-MPA) (c4-MBA/c3-MPA = 3:1).
		<ol>
			<li>Treat the Si wafer following the same procedures in steps 2.1-2.2, except dilute the seed solution 100 times.</li>
			<li>Prepare a 3 mM 4-MBA solution by dissolving 4.6 mg of 4-MBA in 10 mL of ethanol.</li>
			<li>Prepare a 3 mM 3-MPA solution by dissolving 3.2 mg of 3-MPA in 10 mL of ethanol.</li>
			<li>Mix 0.75 mL of 3 mM 4-MBA solution with 0.25 mL of 3 mM 3-MPA solution (in a 10 mL vial. Shake gently to get a homogeneous solution.</li>
			<li>Prepare the 5.10 mM HAuCl4 solution and 12.3 mM L-ascorbic acid solution following the same procedure in steps 2.3.2-2.3.3.</li>
			<li>Add 0.5 mL of 5.10 mM HAuCl4 solution to the mixed solution in step 3.2.1.4 and shake gently to homogenize the solution.</li>
			<li>Soak the Si wafer from step 3.2.1.1 in the mixed solution in a 10 mL vial. Add 0.5 mL of 12.3 mM L-ascorbic acid solution to the mixed solution.</li>
			<li>After 10 min, take the Si wafer out and rinse with ethanol and DI water.</li>
			<li>Dry the wafer at ambient conditions and confirm the structure by SEM.</li>
		</ol>
		</li>
		<li>Synthesize tapered Au nanowires with mixed ligand of 4-MBA and 3-MPA (c4-MBA/c3-MPA = 6:4). Follow the same procedures in step 3.2.1 with 0.6 mL of 3 mM 4-MBA solution and 0.4 mL of 3 mM 3-MPA solution instead.</li>
		<li>Synthesize tapered Au nanowires with mixed ligands of 4-MBA and 3-MPA (c4-MBA/c3-MPA = 1:1). Follow the same procedures in step 3.2.1 with 0.5 mL of 3 mM 4-MBA solution and 0.5 mL of 3 mM 3-MPA solution instead.</li>
	</ol>
	</li>
</ol>
4. Synthesis of Au Nanowire-Based Complex Nanostructures
<ol>
	<li>Synthesis of segmental Au nanowires with thick-thin-thick-thin segments.
	<ol>
		<li>Treat the Si wafer following the same procedures in steps 2.1-2.2.</li>
		<li>Prepare a 1.65 mM 4-MBA solution by dissolving 2.5 mg of 4-MBA in 10 mL of ethanol.</li>
		<li>Prepare a 0.0830 mM 4-MBA solution by diluting the 1.65 mM 4-MBA solution 20 times.</li>
		<li>Prepare the HAuCl4 and L-ascorbic acid solution following the same procedures in steps 2.3.2-2.3.3.</li>
		<li>Prepare 1.5 mL of growth solution A by mixing 0.5 mL of 1.65 mM 4-MBA solution, 0.5 mL of 5.10 mM HAuCl4 solution, and 0.5 mL of 12.3 mM L-ascorbic acid solution (the final concentration: c4-MBA = 0.550 mM, cHAuCl4 = 1.70 mM, cL-ascorbic acid = 4.10 mM).</li>
		<li>Prepare 1.5 mL of growth solution B by mixing 0.5 mL of 0.0830 mM 4-MBA solution, 0.5 mL of 5.10 mM HAuCl4 solution, 0.5 mL of 12.3 mM L-ascorbic acid solution&#160;(the final concentration: c4-MBA = 0.0280 mM, cHAuCl4 = 1.70 mM, cL-ascorbic acid = 4.10 mM).</li>
		<li>Immerse the Si wafer in a 10 mL vial containing growth solution B for about 1 min.</li>
		<li>Rapidly transfer the Si wafer without drying to another 10 mL vial containing growth solution A and leave it to grow for 2 min.</li>
		<li>Repeat steps 4.1.7-4.1.8 one more time.</li>
		<li>Take the Si wafer out and rinse with 50 mL of ethanol and 50 mL of DI water.</li>
		<li>Confirm the structure of the resulting segmented Au nanowires by SEM.</li>
	</ol>
	</li>
	<li>Synthesis of the nanoflowers
	<ol>
		<li>Treat the Si wafer following the same procedures in steps 2.1-2.2, except with a 5 min O2 plasma treatment.</li>
		<li>Soak the Si wafer in a 10 mL vial containing a 10000x diluted 3-5 nm Au seeds solution for 15 min.</li>
		<li>Wash the Si wafer from step 4.2.2 thoroughly with DI water to remove unabsorbed Au nanoparticles.</li>
		<li>Prepare a growth solution containing 0.550 mM 4-MBA, 1.70 mM HAuCl4, and 4.10 mM L-ascorbic-acid, following the same procedures in step 4.1.5.</li>
		<li>Soak the wafer in a 10 mL vial containing the growth solution for 30 s.</li>
		<li>Remove the wafer from the growth solution and leave a thin layer of the solution (~ 13- 15 &#956;L) on the wafer.</li>
		<li>Quickly blow-dry the wafer at room temperature.</li>
		<li>Confirm the nanoflower structure by SEM.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The mechanism of this active surface growth governed nanowire synthesis has been discussed comprehensively in previous work19. In addition, the effects of seed sizes and types as well as the effect of ligand types and sizes have also been investigated20,21. Generally. the nanowire growth is very different from previous reported routes. No template is required, and the asymmetric growth is induced by the differences between the ligand-cappe...

Typical of one dimensional nanomaterials, nanowires possess both the bulk-related properties and the unique properties originated from the quantum effects of the nanoscale structure. As a bridge between the nanoscale and the bulk scale materials, they have been widely applied in various fields of catalysis, sensing, and nanoelectronic devices, etc.1,2,3.
However, the synthesis of nanowires has long been a great challenge, as it usually requires breaking the intrinsic symmetry in the crystals. Traditionally, a template is employed to regulate the deposition of materials. For instance, template-electrodeposition has been used for the formation of various types of nanowires like Ag nanowires and CdS nanowires4,5,6,7,8,9,10. Another common approach is vapor-liquid-solid (VLS) growth, which employs a molten catalyst to induce the anisotropic growth on the substrate at an elevated temperature11. Common strategies for the synthesis of metal nanowires are the polyol methods for Ag nanowires and the oleylamine-assisted ultrathin Au nanowires12,13,14,15. Both approaches are material-specific, and the nanowire parameters are not readily tuned during the synthesis. In addition, metal nanowires can also be formed by the pressure-driven method, where the assembled metal nanoparticles are mechanically compressed and fused into nanowires16,17,18.
Recently, we reported a distinctive method to synthesis Au nanowires19. With the assist of a thiolated small molecule ligand, the nanowires could grow and form a vertically aligned array on the bulk Si wafer substrate at ambient conditions. It was found that the ligands play an important role in the symmetry-breaking growth. It binds to the surface of the substrate-adsorbed Au seeds strongly, forcing the Au to deposit selectively at the ligand-deficient interface between seeds and substrate. The interface between the newly deposited Au and the substrate remains ligand deficient, therefore, the active surface exists throughout the whole growth. By tuning the ligand concentration, the seed type and concentration as well as several other parameters, a series of Au nanowire-based nanostructures could be synthesized.
In this work, we will provide a detailed protocol for this convenient Au nanowires synthesis. The derived synthesis is also presented, including the synthesis of Au nanowires with hydrophobic surface property, Au nanowires on other substrates, tapered Au nanowires by mixing two ligands and the nanowire-based Au nanostructures formed by tuning the growth conditions.

<table border="0" cellpadding="0" cellspacing="0" width="846">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:256px;">Trisodium citrate dihydrate</td>
			<td style="width:209px;">Alfa Aesar</td>
			<td style="width:179px;">LoT: 5008F14U</td>
			<td style="width:203px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium borohydride</td>
			<td style="width:209px;">Fluka</td>
			<td style="width:179px;">LoT: STBG0330V</td>
			<td>NaBH4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hydrogen tetrachloroaurate(III) trihydrate</td>
			<td style="width:209px;">Alfa Aesar</td>
			<td style="width:179px;">LoT: T19C006</td>
			<td style="width:203px;">HAuCl4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">3-aminopropyltriethoxysilane</td>
			<td style="width:209px;">J&#38;K Scientific</td>
			<td style="width:179px;">LoT: LT20Q102</td>
			<td style="width:203px;">APTES</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">L-ascorbic acid&#160;</td>
			<td>Sigma-Aldrich</td>
			<td style="width:179px;">LoT: SLBL9227V</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">4-mercaptobenzoic acid</td>
			<td>Sigma-Aldrich</td>
			<td style="width:179px;">LoT: MKBV5048V</td>
			<td style="width:203px;">4-MBA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">2-Naphthalenethiol</td>
			<td>Sigma-Aldrich</td>
			<td style="width:179px;">LoT: BCBP4238V</td>
			<td>2-NpSH</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">4-Mercaptophenylacetic acid</td>
			<td style="width:209px;">Alfa Aesar</td>
			<td style="width:179px;">LoT: 10199160</td>
			<td>4-MPAA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">3-mercaptobenzoic acid</td>
			<td style="width:209px;">Aladdin</td>
			<td style="width:179px;">LoT: G1213027</td>
			<td>3-MBA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">3-Mercaptopropionic acid</td>
			<td style="width:209px;">Aladdin</td>
			<td style="width:179px;">LoT: E1618095</td>
			<td>3-MPA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">absolute ethanol</td>
			<td style="width:209px;">Sinopharm chemical Reagent</td>
			<td style="width:179px;">20170802</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:256px;">Silicon wafer</td>
			<td style="width:209px;">Zhe Jiang lijing</td>
			<td style="width:179px;">P</td>
			<td>Si</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Scanning Electron Microscope</td>
			<td style="width:209px;">Quanta FEG 250</td>
			<td style="width:179px;"></td>
			<td>SEM</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Centrifuge&#160;</td>
			<td style="width:209px;">Eppendorf</td>
			<td style="width:179px;">5424</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ultrasonic cleaner&#160;</td>
			<td style="width:209px;">Kun Shan hechuang</td>
			<td style="width:179px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:256px;">Ultra-pure water system</td>
			<td style="width:209px;">NanJing qianyan</td>
			<td style="width:179px;">UP6682-10-11</td>
			<td>for deionized water</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:256px;">Plasma cleaner</td>
			<td style="width:209px;">Harrick Plasma</td>
			<td style="width:179px;">PDC-002</td>
			<td>for oxygen plasma</td>
		</tr>
	</tbody>
</table>

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.

The Au nanoparticle seeds, substrate-bound Au nanowires and Au nanowire-based derivative nanostructures are characterized with SEM. Figure 1 shows the representative SEM images of the 3-5 nm Au nanoparticles, 15 nm Au Nanoparticles and 40 nm Au nanoparticles adsorbed on the Si wafer, confirming their sizes, adsorption and distribution. The Au nanowires grown from the respective seeds on the Si wafer substrate are also presented. The representative SEM images ...

Watch this Scientific Journal Video about Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism at JoVE.com

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

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 ...

synthesis-substrate-bound-au-nanowires-via-an-active-surface-growth

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JoVE Journal

Chemistry

7.7K Views.  Nanjing Tech University. 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.

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

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides (CHIPS)

The direct functionalization of C-H bonds is an important and long standing goal in organic chemistry. Such transformations can be very powerful in order to streamline synthesis by saving steps, time and material compared to conventional methods that require the introduction and removal of activating or directing groups. Therefore, the functionalization of C-H bonds is also attractive for green chemistry. Under oxidative conditions, two C-H bonds or one C-H and one heteroatom-H bond can be transformed to C-C and C-heteroatom bonds, respectively. Often these oxidative coupling reactions require synthetic oxidants, expensive catalysts or high temperatures. Here, we describe a two-step procedure to functionalize indole derivatives, more specifically tetrahydrocarbazoles, by C-H amination using only elemental oxygen as oxidant. The reaction uses the principle of C-H functionalization via Intermediate PeroxideS (CHIPS). In the first step, a hydroperoxide is generated oxidatively using visible light, a photosensitizer and elemental oxygen. In the second step, the N-nucleophile, an aniline, is introduced by Br&#248;nsted-acid catalyzed activation of the hydroperoxide leaving group. The products of the first and second step often precipitate and can be conveniently filtered off. The synthesis of a biologically active compound is shown.

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides CHIPS

A two-step procedure for the synthesis of pharmaceutically active indole-derivatives by C-H functionalization with anilines is described, using photo- and Br&#248;nsted acid catalysis.

The direct functionalization of C-H bonds is an important and long standing goal in organic chemistry. Such transformations can be very powerful in order ...

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

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 ...

Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2&#215;1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

This work details the procedures for the growth and characterization of crystalline SrTiO3 directly on germanium substrates by atomic layer deposition. The procedure illustrates the ability of an all-chemical growth method to integrate oxides monolithically onto semiconductors for metal-oxide semiconductor devices.

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and ...

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 &#176;C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 &#176;C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

&#160; The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen ...

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of NixNb1-xO nanoparticles with different atomic compositions (x = 0.03, 0.08, 0.15, and 0.20) have been prepared by chemical precipitation. These NixNb1-xO catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The study revealed the sponge-like and fold-like appearance of Ni0.97Nb0.03O and Ni0.92Nb0.08O on the NiO surface, and the larger surface area of these NixNb1-xO catalysts, compared with the bulk NiO. Maximum surface area of 173 m2/g can be obtained for Ni0.92Nb0.08O catalysts. In addition, the catalytic hydroconversion of lignin-derived compounds using the synthesized Ni0.92Nb0.08O catalysts have been investigated.

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

A protocol for the synthesis of sponge-like and fold-like Ni1-xNbxO nanoparticles by chemical precipitation is presented.

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

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 ...

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) with a 4.6 nm pore size, and ordered silica porous matrix, SBA-15, with a 5.3 nm pore size. This work describes the surface properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the differently ordered porous materials with similar pore sizes. For this purpose, OMC and SBA-15 with highly ordered nanoporous structures are synthesized via impregnation of the silica matrix by applying a carbon precursor and by the sol-gel method, respectively. The porous structure of investigated systems is characterized by an N2 adsorption-desorption analysis at 77 K. To determine the electrochemical character of the surface of synthesized materials, potentiometric titration measurements are conducted; the obtained results for OMC shows a significant pHpzc shift toward the higher values of pH, relative to SBA-15. This suggests that investigated OMC has surface properties related to oxygen-based functional groups. To describe the surface properties of the materials, the contact angles of liquids penetrating the studied porous beds are also determined. The capillary rise method has confirmed the increased wettability of the silica walls relative to the carbon walls and an influence of the pore roughness on the fluid/wall interactions, which is much more pronounced for silica than for carbon mesopores. We have also studied the melting behavior of D2O confined in OMC and SBA-15 by applying the dielectric method. The results show that the depression of the melting temperature of D2O in the pores of OMC is about 15 K higher relative to the depression of the melting temperature in SBA-15 pores with a comparable 5 nm size. This is caused by the influence of adsorbate/adsorbent interactions of the studied matrices.

Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the materials.

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) ...

Synthesis of Esters Via a Greener Steglich Esterification in Acetonitrile

The Steglich esterification is a widely-used reaction for the synthesis of esters from carboxylic acids and alcohols. While efficient and mild, the reaction is commonly performed using chlorinated or amide solvent systems, which are hazardous to human health and the environment. Our methodology utilizes acetonitrile as a greener and less hazardous solvent system. This protocol exhibits rates and yields that are comparable to traditional solvent systems and employs an extraction and wash sequence that eliminates the need for the purification of the ester product via column chromatography. This general method can be used to couple a variety of carboxylic acids with 1&#176; and 2&#176; aliphatic alcohols, benzylic and allylic alcohols, and phenols to obtain pure esters in high yields. The goal of the protocol detailed here is to provide a greener alternative to a common esterification reaction, which could serve useful for ester synthesis in both academic and industrial applications.

A modified Steglich esterification reaction was used to synthesize a small library of ester derivatives with primary and secondary alcohols. The methodology uses a non-halogenated and greener solvent, acetonitrile, and enables product isolation in high yields without the need for chromatographic purification.

The Steglich esterification is a widely-used reaction for the synthesis of esters from carboxylic acids and alcohols. While efficient and mild, the ...