This work was supported by the New Professor Research Foundation Program, funded by Gyeongsang National University (Grant Number 2015-04-020).

1. Preparation of Plant Phenol-derived Polymeric Dyes
<ol>
	<li>Dissolve catechol (0.1 g) and (+)-catechin hydrate (0.1 g) in 32 ml of 100 mM sodium acetate buffer (pH 5.0) and 8 ml of absolute ethanol.</li>
	<li>Add 10 mg of T. versicolor laccase to the catechol- and catechin-containing buffer. Mix vigorously and pour the solution into a square Petri dish. Incubate the dish at room temperature in a shaking incubator (25 rpm) for 24 hr. Dramatic color change of the solution from transparent to dark black can be observed with the naked eye after laccase-induced coupling reactions.</li>
	<li>Centrifuge the solution for 10 min at 20,000 x g in order to spin down insoluble polymeric particles. Use the deep black supernatant for further desalting.</li>
	<li>Desalt the reaction solution with a 5 kDa ultrafiltration disc. After concentrating the reaction volume to 20 ml through ultrafiltration, exchange the reaction buffer by adding 300 ml of distilled water. Finally, using filtration, concentrate the volume of the solution to 25 ml.</li>
</ol>
2. Dyeing Solutions for Gray Keratin Hair
<ol>
	<li>Prepare the following six polymeric solutions: polymeric dyes, polymeric dyes/FeSO4, polymeric dyes/FeSO4 in pH 3 water, polymeric dyes/FeSO4 in pH 11 water, polymeric dyes/FeSO4 with acetic acid, and polymeric dyes/FeSO4 with ammonia.
	<ol>
		<li>For the polymeric dye, mix 5 ml of distilled water with 1 ml of the desalted polymeric dyes (1.4).</li>
		<li>For the mordant solutions, add 0.33 g of FeSO4 to the mixture from step 2.1.1. Vigorously vortex to dissolve the FeSO4 completely.</li>
		<li>For the pH 3 or 11 water solution, adjust the pH of 5 ml distilled water using 1 N HCl or 1 N NaOH. Then add 1 ml of the desalted polymeric dyes (1.4) and 0.33 g of FeSO4.</li>
		<li>For acetic acid- or ammonia-treated solution, mix 1.0 ml of glacial acetic acid or 1.0 ml of ammonia water with 5 ml of distilled water. Then add 1 ml of the desalted polymeric dyes (1.4) and 0.33 g of FeSO4.</li>
	</ol>
	</li>
	<li>For the plant monomers, mix catechol (0.1 g) and (+)-catechin hydrate (0.1 g) in 6 ml of distilled water, with or without 0.33 g of FeSO4, to soak the hair in.</li>
	<li>As soon as the dyeing solutions from step 2.1 and 2.2 are prepared, completely soak 5-cm long gray human hair tresses (0.2 g) in the solutions. Incubate the hair tresses at 32 &#176;C in a shaking incubator (160 rpm) for 2.5 hr.</li>
	<li>Afterwards, take out the hair tresses and rinse them with running water. Use an electronic hair drier to remove the moisture. Color change caused by the polymeric dyes can be visualized with the naked eye.
	<ol>
		<li>To obtain the color parameters (i.e., L*, a*, and b*), employ a conventional colorimeter according to the manufacturer&#39;s protocol. Crumple the hair tresses into a ball, thus allowing them to be measured with the lens of a colorimeter. Repeat this process on a different region of the hair with the colorimeter lens.</li>
		<li>Measure the color parameters of each dyed tress seven times. Calculate averages and standard deviations of the parameters. Calculate &#916;E using the formula: [(100 - L*)2 + (a*)2 + (b*)2]1/2.</li>
	</ol>
	</li>
</ol>
3. Color Durability Tests
<ol>
	<li>Dissolve 200 mg of sodium dodecyl sulfate (SDS) in 40 ml of distilled water. Soak the dyed hair completely in the SDS-containing water for 5 min at room temperature. Take out the hair tresses and then rinse them with enough running water to remove the detergents. Use an electronic hair drier to remove the moisture.</li>
	<li>To obtain the color parameters (i.e., L*, a*, and b*), employ a conventional colorimeter according to the manufacturer&#39;s protocol. Repeat the soaking described in step 3.1 once more with the same dyed hair and then measure the parameters again.</li>
	<li>Dissolve 800 mg of SDS in 40 ml of distilled water. As described in step 3.1, repeat the soaking twice more with the same dyed hair. Overall, treat each dyed hair tress with the SDS solution a total of four times.</li>
</ol>

<ol>
	<li>Jeon, J. R., Chang, Y. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laccase-mediated+oxidation+of+small+organics:+bifunctional+roles+for+versatile+applications.">Laccase-mediated oxidation of small organics: bifunctional roles for versatile applications.</a> Trends Biotechnol. 31, 335-341 (2013).</li><li>Kudanga, T., Nyanhongo, G. S., Guebitz, G. M., Burton, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Potential+applications+of+laccase-mediated+coupling+and+grafting+reactions:+a+review.">Potential applications of laccase-mediated coupling and grafting reactions: a review.</a> Enzyme Microb Technol. 48, 195-208 (2011).</li><li>Jeon, J. R., Le, T. T., Chang, Y. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dihydroxynaphthalene-based+mimicry+of+fungal+melanogenesis+for+multifunctional+coatings.">Dihydroxynaphthalene-based mimicry of fungal melanogenesis for multifunctional coatings.</a> Microb. Biotechnol. 9, 305-315 (2016).</li><li>Jeon, J. R., Baldrian, P., Murugesan, K., Chang, Y. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laccase-catalyzed+oxidations+of+naturally+occurring+phenols:+From+in+vivo+biosynthetic+pathways+to+green+synthetic+application.">Laccase-catalyzed oxidations of naturally occurring phenols: From in vivo biosynthetic pathways to green synthetic application.</a> Microb. Biotechnol. 5, 318-332 (2012).</li><li>Chung, K. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mutagenicity+and+toxicity+studies+of+p-phenylenediamine+and+its+derivatives.">Mutagenicity and toxicity studies of p-phenylenediamine and its derivatives.</a> Toxicol. Lett. 81, 23-32 (1995).</li><li>Bai, Y. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=p-aminophenol+and+p-phenylenediamine+induce+injury+and+apoptosis+of+human+HK-2+proximal+tubular+epithelial+cells.">p-aminophenol and p-phenylenediamine induce injury and apoptosis of human HK-2 proximal tubular epithelial cells.</a> J. Nephrol. 25, 481-489 (2012).</li><li>Jeon, J. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laccase-catalyzed+polymeric+dye+synthesis+from+plant-derived+phenols+for+potential+application+in+hair+dyeing:+Enzymatic+colorations+driven+by+homo-+or+hetero-polymer+synthesis.">Laccase-catalyzed polymeric dye synthesis from plant-derived phenols for potential application in hair dyeing: Enzymatic colorations driven by homo- or hetero-polymer synthesis.</a> Microb. Biotechnol. 3, 324-335 (2010).</li><li>Franca, S. A., Dario, M. F., Esteves, V. B., Baby, A. R., Velasco, M. V. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Types+of+hair+dye+and+their+mechanisms+of+action.">Types of hair dye and their mechanisms of action.</a> Cosmetics. 2, 110-126 (2015).</li><li>Ball, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deposition+mechanism+and+properties+of+thin+polydopamine+films+for+high+added+value+applications+in+surface+science+at+the+nanoscale.">Deposition mechanism and properties of thin polydopamine films for high added value applications in surface science at the nanoscale.</a> BioNanoSci. 2, 16-34 (2012).</li><li>Barrett, D. G., Sileika, T. S., Messersmith, P. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+diversity+in+phenolic+and+polyphenolic+precursors+of+tannin-inspired+nanocoatings.">Molecular diversity in phenolic and polyphenolic precursors of tannin-inspired nanocoatings.</a> Chem. Commun. 50, 7265-7268 (2014).</li><li>Sileika, T. S., Barrett, D. G., Zhang, R., Lau, K. H. A., Messersmith, P. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Colorless+multifunctional+coatings+inspired+by+polyphenols+found+in+tea,+chocolate,+and+wine.">Colorless multifunctional coatings inspired by polyphenols found in tea, chocolate, and wine.</a> Agnew. Chem. 52, 10766-10770 (2013).</li><li>Boonsong, P., Laohakunjit, N., Kerdchoechuen, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Natural+pigments+from+six+species+of+Thai+plants+extracted+by+water+for+hair+dyeing+product+application.">Natural pigments from six species of Thai plants extracted by water for hair dyeing product application.</a> J. Clean. Prod. 37, 93-106 (2012).</li><li>Bechtold, T., Turcanu, A., Ganglberger, E., Geissler, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Natural+dyes+in+modern+textile+dyehouses+-+how+to+combine+experiences+of+two+centuries+to+meet+the+demands+of+the+future.">Natural dyes in modern textile dyehouses - how to combine experiences of two centuries to meet the demands of the future.</a> J. Clean. Prod. 5, 499-509 (2003).</li><li>Zheng, H., Gao, C., Peng, B., Shu, M., Che, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=pH-responsive+drug+delivery+system+based+on+coordination+bonding+in+a+mesostructured+surfactant/silica+hybrid.">pH-responsive drug delivery system based on coordination bonding in a mesostructured surfactant/silica hybrid.</a> J. Phys. Chem. C. 115, 7230-7237 (2011).</li><li>Robbins, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Chemical and physical behavior of human hair. , 105-176 (2011).</li></ol>

The authors declare that they have no competing financial interests.

Interestingly, our method reduced the time it took to dye keratin hair with oxidant-induced polymerizations of natural phenolics. It also induced diverse colors in the hair through simple manipulations of the polymeric dyes, such as changing the pH and applying mordant.
In situ incubation of keratin hair with laccase-catalyzed oxidation of plant phenols requires overly long incubation times to attain effective dyeing7. Such slow dyeing kinetics may be due to the poor bindin...

Laccases are oxidases that are active towards phenolic and polyphenolic compounds. They have been identified in various living organisms, including plants, fungi, insects, and bacteria. Their enzymatic actions contribute to several morphogenetic phenomena1. The enzymes catalyze single-electron oxidation of the substrates, resulting in the formation of radicals that are further coupled to small organics and to solid surfaces. Such coupling processes lead to syntheses of oligomers and polymers and to surface functionalizations2, 3. When laccase substrates are from natural sources, such as plant phenolics, the enzymatic reactions are of great interest with respect to green chemistry. Here, both reactants and catalysts are from natural sources. In addition, the resulting products are similar to the natural products, since the overall reactions mimic the in vivo syntheses of natural phenolic polymers-including plant lignin, poly(flavonoid), and humus-wherein small plant phenolic compounds are highly cross-linked by oxidase-induced radical coupling4.
Products derived from laccase-catalyzed coupling reactions of plant-derived phenols can be used to dye gray hair through in situ incubation and can be developed as alternatives to commercially available dyes1. Such alternatives are important, since commercial hair-dyeing agents are based on p-phenylenediamine (PPD), PPD-related diamine compounds, and hydrogen peroxide, which have been shown to be toxic, carcinogenic, and allergenic to humans5, 6. In the laccase-catalyzed coupling reactions, the laccases and plant phenols functionally replace hydrogen peroxide and p-phenylenediamine, respectively7. However, the dyeing speed of the laccase-based systems is much slower than that of the commercial one. In general, the PPD-based dyeing agents require less than one hour to achieve effective color change in keratin hair, while the laccase-based reactions require an overnight incubation7. The slow dyeing kinetics could be explained by two possible phenomena. First, the use of a low-pH buffer (e.g., pH 5) to maximize laccase activity has been observed to decrease the degree of swelling in the keratin matrices, thus inhibiting deep penetration of dyes into the matrices. Indeed, agents allowing the dyeing reactions to proceed in high-pH conditions have been shown to be integral to commercial hair-dyeing products8. Second, the number of possible chromophore molecules exhibiting strong adsorption to keratinous surfaces during the polymerization reaction has been shown to be proportional to the incubation time (i.e., the extent of polymerization). For example, the transformation of dopamine to polydopamine was shown to induce a strong adhesion to many surfaces that was concomitant with the formation of a black color9.
In the current work, pre-synthesized polymeric products obtained from T. versicolor laccase-catalyzed oxidation of catechin and catechol were used to treat keratin hair for dyeing. We hypothesized that the adsorption ability of the polymers would be much stronger than that of the monomeric plant phenols and that they would initially form low-molecular-weight oligomers. Results demonstrated that, when using the pre-synthesized polymers, the enzymatic oxidation power was no longer necessary. This indicates that the pH can be controlled and that metal ions can be used in hair-dyeing treatments, regardless of enzyme activity. This protocol provides a simple and fast method to dye keratin hair in various shades of color while using eco-friendly and renewable plant-derived phenolics (Figure 1).

<table border="0" cellpadding="0" cellspacing="0" width="802">
	<tbody>
		<tr height="32">
			<td height="32" style="height:32px;width:208px;">Sodium dodecyl Sulfate</td>
			<td style="width:205px;">Promega</td>
			<td style="width:208px;">H5114</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:208px;">Laccase from Trametes versicolor</td>
			<td style="width:205px;">Sigma</td>
			<td style="width:208px;">38429-1G</td>
			<td style="width:181px;">Enzyme activity is denoted as 0.53 U/mg</td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:208px;">(+)-catechin hydrate</td>
			<td style="width:205px;">Sigma</td>
			<td style="width:208px;">C1251-5G</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:208px;">1,2-dihydroxybenzene (catechol)</td>
			<td style="width:205px;">Sigma</td>
			<td style="width:208px;">135011-5G</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:208px;">Ammonia water&#160;</td>
			<td style="width:205px;">Duksan</td>
			<td style="width:208px;">701</td>
			<td style="width:181px;">Ammonia contents is denoted as 25 ~ 30%</td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:208px;">Acetic acid, glacial</td>
			<td style="width:205px;">Duksan</td>
			<td style="width:208px;">448</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:208px;">Iron (II) sulfate heptahydrate</td>
			<td style="width:205px;">JUNSEI</td>
			<td style="width:208px;">83380-1250</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Ultracell 5kDa</td>
			<td style="width:205px;">Amicon</td>
			<td style="width:208px;">PLCC06210</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Stirred ultrafiltration cells</td>
			<td style="width:205px;">Millipore</td>
			<td style="width:208px;">Model 8200</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Human gray hair</td>
			<td style="width:205px;">PheonixKorea</td>
			<td style="width:208px;">Not available</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Colorimeter</td>
			<td style="width:205px;">SPEC</td>
			<td style="width:208px;">JCS-10</td>
			<td style="width:181px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Square dish</td>
			<td style="width:205px;">SPL</td>
			<td style="width:208px;">10125</td>
			<td style="width:181px;">125 * 125 * 20 (mm)</td>
		</tr>
	</tbody>
</table>

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.

First, the dyeing ability of polymeric dyes was compared to that of plant-derived monomers (i.e., catechin and catechol). The polymeric dyes induced a significant change in the color of gray keratin hair (Figure 2A and Figure 3), while the innate gray color of the hair remained very stable with plant monomers (data not shown). The effects of mordanting agents on the dyeing abilities of polymeric products were then evaluated. As s...

Watch this Scientific Journal Video about Synthesis of Plant Phenol-derived Polymeric Dyes for Direct or Mordant-based Hair Dyeing at JoVE.com

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

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 ...

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9.2K Views.  Gyeongsang National University. 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.

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

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to the preparation of new organic dyes. Although numerous strategies have been reported to access naphthalene scaffolds, many procedures still present limitations in terms of incorporating functionality, which in turn narrows the range of available substrates. The development of versatile methods for direct access to substituted naphthalenes is therefore highly desirable.
The Diels-Alder (DA) cycloaddition reaction is a powerful and attractive method for the formation of saturated and unsaturated ring systems from readily available starting materials. A new microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives described herein generates a variety of functionalized cyclopenta[b]naphthalenes that could not be prepared using existing synthetic methods. When compared to conventional heating, microwave irradiation accelerates reaction rates, enhances yields, and limits the formation of undesired byproducts.
The utility of this protocol is further demonstrated by the conversion of a DA cycloadduct into a novel solvatochromic fluorescent dye via a Buchwald-Hartwig palladium-catalyzed cross-coupling reaction. Fluorescence spectroscopy, as an informative and sensitive analytical technique, plays a key role in research fields including environmental science, medicine, pharmacology, and cellular biology. Access to a variety of new organic fluorophores provided by the microwave-assisted dehydrogenative DA reaction allows for further advancement in these fields.

Microwave-assisted intramolecular dehydrogenative Diels-Alder (DA) reactions provide concise access to functionalized cyclopenta[b]naphthalene building blocks. The utility of this methodology is demonstrated by one-step conversion of the dehydrogenative DA cycloadducts into novel solvatochromic fluorescent dyes via Buchwald-Hartwig palladium-catalyzed cross-coupling reactions.

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to ...

Synthesis of Indoxyl-glycosides for Detection of Glycosidase Activities

Indoxyl glycosides proved to be valuable and versatile tools for monitoring glycosidase activities. Indoxyls are released by enzymatic hydrolysis and are rapidly oxidized, for example by atmospheric oxygen, to indigo type dyes. This reaction enables fast and easy screening in vivo without isolation or purification of enzymes, as well as rapid tests on agar plates or in solution (e.g., blue-white screening, micro-wells) and is used in biochemistry, histochemistry, bacteriology and molecular biology. Unfortunately the synthesis of such substrates proved to be difficult, due to various side reactions and the low reactivity of the indoxyl hydroxyl function. Especially for glucose type structures low yields were observed. Our novel approach employs indoxylic acid ester as key intermediates. Indoxylic acid esters with varied substitution patterns were prepared on scalable pathways. Phase transfer glycosylations with those acceptors and peracetylated glycosyl halides can be performed under common conditions in high yields. Ester cleavage and subsequent mild silver mediated glycosylation yields the peracetylated indoxyl glycosides in high yields. Finally deprotection is performed according to Zempl&#233;n.

Indoxyl glycosides are well-established and widely used tools for enzyme screening and enzyme activity monitoring. Especially for glucose type structures previous syntheses proved to be challenging and low yielding. Our novel approach employs indoxylic acid esters as precious intermediates to yield a considerable number of indoxyl glycosides in good yields.

Indoxyl glycosides proved to be valuable and versatile tools for monitoring glycosidase activities. Indoxyls are released by enzymatic hydrolysis and are ...

A Direct, Early Stage Guanidinylation Protocol for the Synthesis of Complex Aminoguanidine-containing Natural Products

The guanidine functional group, displayed most prominently in the amino acid arginine, one of the fundamental building blocks of life, is an important structural element found in many complex natural products and pharmaceuticals. Owing to the continual discovery of new guanidine-containing natural products and designed small molecules, rapid and efficient guanidinylation methods are of keen interest to synthetic and medicinal organic chemists. Because the nucleophilicity and basicity of guanidines can affect subsequent chemical transformations, traditional, indirect guanidinylation is typically pursued. Indirect methods commonly employ multiple protection steps involving a latent amine precursor, such as an azide, phthalimide, or carbamate. By circumventing these circuitous methods and employing a direct guanidinylation reaction early in the synthetic sequence, it was possible to forge the linear terminal guanidine containing backbone of clavatadine A to realize a short and streamlined synthesis of this potent factor XIa inhibitor. In practice, guanidine hydrochloride is elaborated with a carefully constructed protecting array that is optimized to survive the synthetic steps to come. In the preparation of clavatadine A, direct guanidinylation of a commercially available diamine eliminated two unnecessary steps from its synthesis. Coupled with the wide variety of known guanidine protecting groups, direct guanidinylation evinces a succinct and efficient practicality inherent to methods that find a home in a synthetic chemist&#39;s toolbox.

Here, we present a protocol for direct, early stage guanidinylation that enables rapid total synthesis of aminoguanidine-containing small organic molecules. An advanced synthetic intermediate used in the synthesis of a blood coagulation factor XIa inhibitor was prepared using this protocol.

The guanidine functional group, displayed most prominently in the amino acid arginine, one of the fundamental building blocks of life, is an important ...

Hydroquinone Based Synthesis of Gold Nanorods

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the synthetic methods for the preparation of gold nanorods are still not fully optimized. In this paper we describe a new, highly efficient, two-step protocol based on the use of hydroquinone as a mild reducing agent. Our approach allows the preparation of nanorods with a good control of size and aspect ratio (AR) simply by varying the amount of hexadecyl trimethylammonium bromide (CTAB) and silver ions (Ag+) present in the "growth solution". By using this method, it is possible to markedly reduce the amount of CTAB, an expensive and cytotoxic reagent, necessary to obtain the elongated shape. Gold nanorods with an aspect ratio of about 3 can be obtained in the presence of just 50 mM of CTAB (versus 100 mM used in the standard protocol based on the use of ascorbic acid), while shorter gold nanorods are obtained using a concentration as low as 10 mM.

This paper describes a protocol for the synthesis of gold nanorods, based on the use of hydroquinone as reducing agent, plus the different mechanisms for controlling their size and aspect ratio.

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the ...

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

A protocol for the synthesis and characterization of diffusive motion of cyclic polymers at the single molecule level is presented.

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single ...

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.

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.

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 ...

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb explosion imaging setup in which a hitherto-impractical camera angle is realized. In our imaging technique, diatomic molecules are irradiated with a circularly polarized strong laser pulse. The ejected atomic ions are accelerated perpendicularly to the laser propagation. The ions lying in the laser polarization plane are selected through the use of a mechanical slit and imaged with a high-throughput, 2-dimensional detector installed parallel to the polarization plane. Because a circularly polarized (isotropic) Coulomb exploding pulse is used, the observed angular distribution of the ejected ions directly corresponds to the squared rotational wave function at the time of the pulse irradiation. To create a real-time movie of molecular rotation, the present imaging technique is combined with a femtosecond pump-probe optical setup in which the pump pulses create unidirectionally rotating molecular ensembles. Due to the high image throughput of our detection system, the pump-probe experimental condition can be easily optimized by monitoring a real-time snapshot. As a result, the quality of the observed movie is sufficiently high for visualizing the detailed wave nature of motion. We also note that the present technique can be implemented in existing standard ion imaging setups, offering a new camera angle or viewpoint for the molecular systems without the need for extensive modification.

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

Microfluidic-based Synthesis of Covalent Organic Frameworks (COFs): A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Covalent Organic Frameworks (COFs) are a class of porous covalent materials which are frequently synthesized as unprocessable crystalline powders. The first COF was reported in 2005 with much effort centered on the establishment of new synthetic routes for its preparation. To date, most available synthetic methods for COF synthesis are based on bulk mixing under solvothermal conditions. Therefore, there is increasing interest in developing systematic protocols for COF synthesis that provide for fine control over reaction conditions and improve COF processability on surfaces, which is essential for their use in practical applications. Herein, we present a novel microfluidic-based method for COF synthesis where the reaction between two constituent building blocks, 1,3,5-benzenetricarbaldehyde (BTCA) and 1,3,5-tris(4-aminophenyl)benzene (TAPB), takes place under controlled diffusion conditions and at room temperature. Using such an approach yields sponge-like, crystalline fibers of a COF material, hereafter called MF-COF. The mechanical properties of MF-COF and the dynamic nature of the approach allow the continuous production of MF-COF fibers and their direct printing onto surfaces. The general method opens new potential applications requiring advanced printing of 2D or 3D COF structures on flexible or rigid surfaces.

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

We present a novel microfluidic-based method for synthesis of covalent organic frameworks (COFs). We demonstrate how this approach can be used to produce continuous COF fibers, and also 2D or 3D COF structures on surfaces.

Covalent Organic Frameworks (COFs) are a class of porous covalent materials which are frequently synthesized as unprocessable crystalline powders. The ...

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 &#176;C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications.
In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

Here, we present a protocol for the synthesis of porous barium titanate (BaTiO3) thin film by a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles are used as an organic template.

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its ...

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.