Name: hkust-1 as a heterogeneous catalyst for the synthesis of vanillin
Uploaded: 2016-07-23T14:00:00
Description: Watch this Scientific Journal Video about HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin at JoVE.com

The authors thank Dr. A. Tejeda-Cruz (X-ray; IIM-UNAM). R.Y. thanks CINVESTAV, Mexico for technical support. M.S.S acknowledges the financial support by Spanish Government, MINECO (MAT2012-31127). I.A.I thanks CONACyT (212318) and PAPIIT UNAM (IN100415), Mexico for financial support. E.G-Z. thanks CONACyT (156801 and 236879), Mexico for financial support. Thanks to U. Winnberg (ITAM and ITESM) for scientific discussions.

CAUTION: The chemicals used in this catalytic procedure are relatively low in toxicity and non-carcinogenic. Please use all appropriate safety precautions when performing this experimental procedure such as safety glasses, gloves, lab coat, full length pants and closed-toe shoes. One part of the following procedures involves standard air-free handling techniques.
1. Activation of the Catalyst (HKUST-1)
<ol>
	<li>Crystallinity Characterization of the Catalyst 
	Note: HKUST-1 is a commercially available porou...

<ol>
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J., Narbad, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vanilin.">Vanilin.</a> Phytochemistry. 63 (5), 505-515 (2003).</li><li>Serra, S., Fuganti, C., Brenna, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biocatalytic+preparation+of+natural+flavours+and+fragrances.">Biocatalytic preparation of natural flavours and fragrances.</a> Trends Biotechnol. 23 (4), 193-198 (2005).</li><li>Longo, M. A., Sanrom&#225;n, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+of+Food+Aroma+Compounds:+Microbial+and+Enzymatic+Methodologies.">Production of Food Aroma Compounds: Microbial and Enzymatic Methodologies.</a> Food Technol. 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The fundamental step for the catalytic conversion of trans-ferulic acid to vanillin was the activation of the catalyst (HKUST-1). If the catalyst is not activated in situ (under vacuum and at 100 &#176;C), only partial conversion of trans-ferulic acid to vanillin was observed44. In other words, the accessibility to open metal sites is crucial for the catalytic cycle44, and this can be achieved by the elimination of coordinated water to the Cu(II) metal sites within the por...

The use of porous coordination polymers (PCPs) as heterogeneous catalysts1-4 is a relatively new research field. Due to very interesting properties that PCPs show, e.g., porous regularity, high surface area and metal access, they can offer new alternatives for heterogeneous catalysts5-6. The generation of catalytically active PCPs has been the main focus of many research groups7-10. A porous coordination polymer is constituted by metal ions and organic linkers and thus, the catalytic activity of these materials is provided by any of these parts. Some PCPs contain unsaturated (active) metals that can catalyze a chemical reaction11. However, the generation of unsaturated metal sites (open metal sites) within coordination polymers is not a trivial task and it represents a synthetic challenge that can be summarized in: (i) the generation of vacant coordination by removal of labile ligands7-11; (ii) the generation of bimetallic PCPs by incorporating organometallic ligands (previously synthesized)8,12-13; (iii) the post-synthetic variation of the metal ions9,14-15 or to the organic ligands10, 16-17 within the pores of the PCPs. Since the methodology (i) is the simplest thus, it is the most frequently used. Typically, the generation of open metal sites has been used for enhancing the affinity of PCPs towards H218-19, as well as for designing active heterogeneous catalysts20-27. In order to achieve good catalyst properties, PCPs need to show, additionally to the accessibility of open metal sites, retention of the crystallinity after the catalytic experiment, relatively high thermal stability and chemical stability to the reaction conditions.
HKUST-1 (Cu3(BTC)2(H2O)3, BTC = 1,3,5-benzene-tricarboxylate)7 is a well-investigated porous coordination polymer constructed with Cu(II) cations, that are coordinated to the carboxylate ligands and water. Interestingly, these water molecules can be eliminated (by heating) and this provides a square planar coordination around the copper ions which exhibit hard Lewis acid properties11. Bordiga and co-workers28 showed that the elimination of these H2O molecules did not affect the crystallinity (retention of the regularity) and the oxidation state of the metal ions (Cu(II)) was not affected. The use of HKUST-1 as a catalyst has been extensively investigated29-33 and in particular (very relevant for the present work) the oxidation with hydrogen peroxide of aromatic molecules34.
Vanilla is one of the most widely used flavoring agents in the cosmetic, pharmaceutical and food industries. It is extracted from the cured beans of the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon. The Mayan and Aztec civilizations (pre-Columbian people) first realized the enormous potential of vanilla as a flavoring agent since it improved the chocolate flavor35-37. Vanilla was first isolated in 185838 and it was not until 187439 that the chemical structure of vanillin was finally determined. The natural extraction of vanillin (from the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon) represents only 1% of the worldwide production and since this process is expensive and very long40, the rest of vanillin is synthesized40. Many biotechnological approaches can be used for the synthesis of vanillin from lignin, phenolic stilbenes, isoeugenol, eugenol, guaicol, etc. However, these approaches have the disadvantage of harming the environment since these processes use strong oxidizing agents and toxic solvents41-43. Herein, we report a synthetic strategy for the production of vanillin by the oxidation of trans-ferulic acid using HKUST-1 as a catalyst.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>HKUST-1</td>
			<td>Sigma-Aldrich</td>
			<td>MFCD10567003</td>
			<td></td>
		</tr>
		<tr>
			<td>Ferulic Acid (trans-4-Hydroxy-3-methoxycinnamic acid)</td>
			<td>Sigma-Aldrich</td>
			<td>537-98-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>64-17-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrogen peroxide solution</td>
			<td>Sigma-Aldrich</td>
			<td>&#160;7722-84-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetonitrile</td>
			<td>Sigma-Aldrich</td>
			<td>75-05-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl acetate</td>
			<td>Sigma-Aldrich</td>
			<td>141-78-6</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>12125-02-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium sulfate anhydrous</td>
			<td>Sigma-Aldrich</td>
			<td>7757-82-6</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl acetate</td>
			<td>Sigma-Aldrich</td>
			<td>141-78-6</td>
			<td></td>
		</tr>
		<tr>
			<td>n-Hexane</td>
			<td>Sigma-Aldrich</td>
			<td>110-54-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Silica Gel</td>
			<td>Sigma-Aldrich</td>
			<td>112926-00-8</td>
			<td>&#160;Size 70/230</td>
		</tr>
		<tr>
			<td>250 mL two-neck round-bottom flask</td>
			<td>Sigma-Aldrich</td>
			<td>Z516872-1EA</td>
			<td>250 mL capacity</td>
		</tr>
		<tr>
			<td>Magnetic stirring bar</td>
			<td>Bel-Art products</td>
			<td>371100002</td>
			<td>Teflon, octagon</td>
		</tr>
		<tr>
			<td>Condenser</td>
			<td>Cole-Parmer</td>
			<td>JZ-34706-00</td>
			<td>200 mm Jacket length</td>
		</tr>
		<tr>
			<td>Vacuum pump (Approx. 10X-2 bar)</td>
			<td>Cole-Parmer</td>
			<td>JZ-78162-00</td>
			<td>Vacuum/Pressure Diaphragm Pump</td>
		</tr>
		<tr>
			<td>Stopcock</td>
			<td>Cole-Parmer</td>
			<td>EW-30600-00</td>
			<td>with a male luer slip</td>
		</tr>
		<tr>
			<td>Hose</td>
			<td>Cole-Parmer</td>
			<td>JZ-06602-04</td>
			<td>16.0 mm ID and 23.2 mm ED</td>
		</tr>
		<tr>
			<td>Rubber septums</td>
			<td>Cole-Parmer</td>
			<td>JZ-08918-34</td>
			<td>Silicone with PTFE coating</td>
		</tr>
		<tr>
			<td>Hot plate</td>
			<td>Cole-Parmer</td>
			<td>JZ-04660-15</td>
			<td>10.2 cm x 10.2 cm, 5 to 540 &#176;C</td>
		</tr>
		<tr>
			<td>Sand bath&#160;</td>
			<td>Cole-Parmer</td>
			<td>GH-01184-00</td>
			<td>Fluidized Sand Bath SBS-4, 50 to 600 &#176;C</td>
		</tr>
		<tr>
			<td>N2 gas</td>
			<td>INFRA</td>
			<td>Cod. 103</td>
			<td>Cylinder 9m &#179;</td>
		</tr>
		<tr>
			<td>Ballons (filled with N2 gas)</td>
			<td>Sigma-Aldrich</td>
			<td>Z154989-100EA</td>
			<td>Thick-wall, natural latex rubber</td>
		</tr>
		<tr>
			<td>Syringes with removable needles</td>
			<td>Sigma-Aldrich</td>
			<td>Z116912-100EA</td>
			<td>10 mL capacity</td>
		</tr>
		<tr>
			<td>Filter paper</td>
			<td>Cole-Parmer</td>
			<td>JZ-81050-24</td>
			<td>Grade No. 235 qualitative filter paper (90 mm diameter disc)</td>
		</tr>
		<tr>
			<td>Buchner funnel</td>
			<td>Cole-Parmer</td>
			<td>JZ-17815-04</td>
			<td>320 mL capacity which accept standard paper filter sizes&#160;</td>
		</tr>
		<tr>
			<td>Buchner flask</td>
			<td>Cole-Parmer</td>
			<td>JZ-34557-02</td>
			<td>250 mL capacity</td>
		</tr>
		<tr>
			<td>Rotary Evaporator</td>
			<td>Cole-Parmer</td>
			<td>JZ-28710-02</td>
			<td></td>
		</tr>
		<tr>
			<td>Beakers</td>
			<td>Cole-Parmer</td>
			<td>JZ-34502-(02,04,05)</td>
			<td>Pyrex Brand 1000 Griffin; 20, 50 and 100 mL</td>
		</tr>
		<tr>
			<td>Separation funnel&#160;</td>
			<td>Cole-Parmer</td>
			<td>JZ-34505-44</td>
			<td>Capacity for 125 mL with steam lenght of 60 mm</td>
		</tr>
		<tr>
			<td>Glass column for chromatography</td>
			<td>Cole-Parmer</td>
			<td>JZ-34695-42</td>
			<td>Column with fritted disk, 10.5 mm ID x 250 mm L</td>
		</tr>
		<tr>
			<td>PXRD diffractometer</td>
			<td>Bruker</td>
			<td></td>
			<td>AXS D8 Advance XRD</td>
		</tr>
		<tr>
			<td>FTIR spectrophotometer</td>
			<td>Thermo scientific</td>
			<td>FT-IR (JZ-83008-02); ATR (JZ-83008-26)</td>
			<td>Nicolet iS5 FT-IR Spectrometer, with KBr Windows and iD5 Diamond ATR</td>
		</tr>
	</tbody>
</table>

hkust-1 as a heterogeneous catalyst for the synthesis of vanillin

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately 200 different odorant compounds in addition to vanillin. The natural extraction of vanillin (from the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon) represents only 1% of the worldwide production and since this process is expensive and very long, the rest of the production of vanillin is synthesized. Many biotechnological approaches can be used for the synthesis of vanillin from lignin, phenolic stilbenes, isoeugenol, eugenol, guaicol, etc., with the disadvantage of harming the environment since these processes use strong oxidizing agents and toxic solvents. Thus, eco-friendly alternatives on the production of vanillin are very desirable and thus, under current investigation. Porous coordination polymers (PCPs) are a new class of highly crystalline materials that recently have been used for catalysis. HKUST-1 (Cu3(BTC)2(H2O)3, BTC = 1,3,5-benzene-tricarboxylate) is a very well known PCP which has been extensively studied as a heterogeneous catalyst. Here, we report a synthetic strategy for the production of vanillin by the oxidation of trans-ferulic acid using HKUST-1 as a catalyst.

Three representative samples of HKUST-1 were analyzed by infrared spectroscopy: non-activated, activated at 100 &#176;C for 1 hr in an oven (exposed to air), and activated under vacuum (10-2 bar) at 100 &#176;C for 1 hr. Thus, Fourier transform infrared (FTIR) spectra were recorded using a spectrometer with a single reflection diamond ATR accessory (Figure 1). For all spectra, 64 scans in the 4,000 to 400 cm-1 range were recorded with a spectral reso...

Watch this Scientific Journal Video about HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin at JoVE.com

HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin

The conversion of trans-ferulic acid to vanillin was achieved by heterogeneous catalysis. HKUST-1 was employed in this synthesis and the essential step in the catalytic process was the generation of unsaturated metal sites. Thus, when the catalyst was activated under vacuum, full vanillin conversion (yield of 95%) was obtained.

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately ...

The overall goal of this methodology is the conversion of trans ferulic acid to vanillin by heterogeneous catalysis using the porous coordination polymer HKUST-1. The essential step in the catalytic process is the generation of unsaturated metal sites in HKUST-1. These methods can help us answer key questions in the heterogeneous catalysis field, such as in the production of vanillin, which is one of the most widely employed flavoring agents in the world.The main advantage of this technique is that we provide an experimental protocol to catalytically convert ferulic acid to vanillin under mild oxidation conditions. The implications of this technique extend toward the use of porous coordination polymers as catalysts. Generally, individuals new to this method will struggle, because activation of the HKUST-1 material is fundamental.Demonstrating the procedure will be Rebeca Yepez, a graduate student from my laboratory. To characterize the crystallinity of the catalyst, collect the powder x-ray diffraction pattern of a 0.1 gram sample of HKUST-1, as described in the text protocol. Record a powder x-ray diffraction pattern from five degrees to 60 degrees in 0.02 degree steps, and one second counting time.Then, perform dissolvation of HKUST-1 by first weighing 0.05 grams of the catalyst. Next, prepare the activation system by clamping a 250 milliliter two neck round bottom flask to a stand and inserting a magnetic stirring bar into the round bottom flask. Attach a condenser to the round bottom flask.Use some vacuum grease or Teflon tape between the joints of the flask and condenser to generate a perfect seal. Connect the condenser from the top to a vacuum pump. Make sure that the vacuum generated by the pump is approximately 0.1 bar.Place the catalyst inside the 250 milliliter two neck round bottom flask. Insert a rubber septum in the second neck of the round bottom flask, and make sure that it seals properly. Carefully place the activation system into a sand bath.Start the vacuum pump and carefully turn the stopcock until it is fully opened. With a hot plate, heat the activation system up to 100 degrees Celsius for one hour. Stir at the lowest speed, the hot plate to homogeneously distribute the catalyst at the bottom of the round bottom flask.When the catalyst is activated, a color change must be clearly observed. This is an indication of the removal of coordinated water molecules, and therefore the generation of coordinately unsaturated copper to metal sites within the catalyst. A color change from turquoise to dark blue upon activation is observed.Turn off the heat after one hour of heating and let the activation system cool to room temperature. Once the activation system is cooled down to room temperature, turn the stopcock off, and turn the pump off. Connect a balloon filled with nitrogen though the septum to the two neck round bottom flask, and wait a few seconds to reach the equilibrium pressure.After the activation of the catalyst, leave it under an inert atmosphere, since the access to the uncoordinated metal sites is the key to obtaining an active catalyst. Remove the balloon filled with nitrogen when the equilibrium pressure has been achieved. De-gas approximately 70 milliliters of ethanol by bubbling nitrogen for five minutes.To prepare the catalytic reaction, add 10 milliliters of de-gassed ethanol to the two neck round bottom flask and gently stir the suspension on a hot plate. Then, add five milliliters of hydrogen peroxide followed by 25 milliliters of acetonitrile to the suspension. Weigh 0.5 grams of ferulic acid and dissolve it in 20 milliliters of de-gassed ethanol in a beaker.Add the dissolved ferulic acid to the suspension, then wash the beaker with 20 milliliters of de-gassed ethanol and add it to the suspension. For oxidation of trans ferulic acid to vanillin, first unplug the hose that connects the condenser to the vacuum pump. Turn on the tap water, or preferably, the water pump that goes though the condenser.Heat the suspension up to 100 degrees Celsius and reflux for one hour. After turning off the heat and stirring, carefully lift the two neck round bottom flask attached to the condenser and let it cool to room temperature. Next, filter off the reaction mixture using a Buchner funnel and flask.Recover the catalyst and wash it with 200 milliliters of ethyl acetate. Concentrate the combined organic phases under vacuum with a rotary evaporator and re-dissolve it with 100 milliliters of ethyl acetate. Wash the organic phases in a separation funnel with a 30 milliliter saturated solution of ammonium chloride.Then, recover the organic phases and mix them with 30 grams of anhydrous sodium sulfate. After letting the suspension stand for 15 minutes, filter the suspension off, and recover the filtrate. Then, concentrate the filtrate to approximately 20 milliliters under vacuum with a rotary evaporator.Purify the residue by flash column chromatography. The stationary phase is silica gel, and the mobile phase is a solvent mixture of ethyl acetate and hexane. Pack the glass column for chromatography with a silica gel.Then, saturate the column with the ethyl acetate hexane solvent mixture. Carefully pour the concentrated filtrate on top of the glass column. Slowly add the solvent mixture to the glass column and collect all of the fractions until 1, 200 milliliters are collected.Concentrate the 1, 200 milliliters of the organic fractions with a rotary evaporator until dry. Recover the final solid powder that is the purified vanillin. Shown here are fourier transform infrared spectra of the HKUST-1 catalyst at 25 degrees Celsius.The spectrum of the non-activated catalyst is shown in green. The spectrum of the activated catalyst in a conventional oven is shown in purple, and the spectrum of the activated catalyst under vacuum is shown in orange. Shown here is a proton NMR spectra of vanillin after column chromatography purification on silica gel when the catalyst was activated under vacuum and 100 degrees Celsius for one hour.Once mastered, this technique can be done in four hours, if it is performed properly. Though this method can provide insight into the mechanism for the oxidation of trans ferulic acid, it can also be applied to other systems, such as oxidation of other alpha beta unsaturated carboxylic acid. While attempting this procedure, it's important to remember to emphasize on the correct purification of vanillin by column chromatography.Following this procedure, other methods like the oxidation of other alpha beta unsaturated carboxylic acid can be performed in order to answer additional questions, like oxidation mechanisms. After its development, this technique paved way for researchers in the field of porous coordination polymers to explore these materials as heterogeneous catalyst to synthesize molecules of high chemical relevance. After watching this video, you should have a good understanding of how to carry out the oxidation of ferulic acid to vanillin.Don't forget that working with a high volatility solvents under reflexive conditions can be extremely hazardous, and precautions such as wearing a lab coat, safety glasses, and working in a fume hood, should always be taken while performing this procedure.

hkust-1-as-a-heterogeneous-catalyst-for-the-synthesis-of-vanillin

Research

JoVE Journal

Chemistry

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

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

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

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

Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand.

This protocol describes the use of amide coupling reactions of isonicotinic acid and diaminoalkanes to form bridging ligands suitable for use in the synthesis of multinuclear platinum complexes, which combine aspects of the anticancer drugs BBR3464 and picoplatin.

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. ...

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 ...

Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins with the synthesis of a hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) homopolymer using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under mild visible light irradiation (&#955; = 460 nm, 0.7 mW/cm2), this macro-chain transfer agent (macro-CTA) in the presence of a ruthenium based photoredox catalyst, Ru(bpy)3Cl2 can be chain extended with a second monomer to form a well-defined block copolymer in a process known as Photoinduced Electron Transfer RAFT (PET-RAFT). When PET-RAFT is used to chain extend POEGMA with benzyl methacrylate (BzMA) in ethanol (EtOH), polymeric nanoparticles with different morphologies are formed in situ according to a polymerization-induced self-assembly (PISA) mechanism. Self-assembly into nanoparticles presenting POEGMA chains at the corona and poly(benzyl methacrylate) (PBzMA) chains in the core occurs in situ due to the growing insolubility of the PBzMA block in ethanol. Interestingly, the formation of highly pure worm-like micelles can be readily monitored by observing the onset of a highly viscous gel in situ due to nanoparticle entanglements occurring during the polymerization. This process thereby allows for a more reproducible synthesis of worm-like micelles simply by monitoring the solution viscosity during the course of the polymerization. In addition, the light stimulus can be intermittently applied in an ON/OFF manner demonstrating temporal control over the nanoparticle morphology.

This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins ...

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

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

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

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

NMR Spectroscopy as a Robust Tool for the Rapid Evaluation of the Lipid Profile of Fish Oil Supplements

The western diet is poor in n-3 fatty acids, therefore the consumption of fish oil supplements is recommended to increase the intake of these essential nutrients. The objective of this work is to demonstrate the qualitative and quantitative analysis of encapsulated fish oil supplements using high-resolution 1H and 13C NMR spectroscopy utilizing two different NMR instruments; a 500 MHz and an 850 MHz instrument. Both proton (1H) and carbon (13C) NMR spectra can be used for the quantitative determination of the major constituents of fish oil supplements. Quantification of the lipids in fish oil supplements is achieved through integration of the appropriate NMR signals in the relevant 1D spectra. Results obtained by 1H and 13C NMR are in good agreement with each other, despite the difference in resolution and sensitivity between the two nuclei and the two instruments. 1H NMR offers a more rapid analysis compared to 13C NMR, as the spectrum can be recorded in less than 1 min, in contrast to 13C NMR analysis, which lasts from 10 min to one hour. The 13C NMR spectrum, however, is much more informative. It can provide quantitative data for a greater number of individual fatty acids and can be used for determining the positional distribution of fatty acids on the glycerol backbone. Both nuclei can provide quantitative information in just one experiment without the need of purification or separation steps. The strength of the magnetic field mostly affects the 1H NMR spectra due to its lower resolution with respect to 13C NMR, however, even lower cost NMR instruments can be efficiently applied as a standard method by the food industry and quality control laboratories.

Here, high-resolution 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy was used as a rapid and reliable tool for quantitative and qualitative analysis of encapsulated fish oil supplements.

The western diet is poor in n-3 fatty acids, therefore the consumption of fish oil supplements is recommended to increase the intake of these essential ...

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.

Electrochemical impedance spectroscopy (EIS) of species that undergo reversible oxidation or reduction in solution was used for determination of rate constants of oxidation or reduction.

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). ...

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

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

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

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

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

Heterogeneous Removal of Water-Soluble Ruthenium Olefin Metathesis Catalyst from Aqueous Media Via Host-Guest Interaction

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst removal via host-guest interactions. The new NHC ligand possesses an adamantyl (guest) tethered linear ethylene glycol units for hydrophobic inclusion into the cavity of a &#946;-cyclodextrin (&#946;-CD) host compound. The new NHC ligand was applied to a Ru-based olefin metathesis catalyst. The Ru catalyst demonstrated excellent activity in representative ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions in aqueous media as well as organic solvent, CH2Cl2. After the reaction was complete, the lingering Ru residue was removed from the aqueous solution with the efficiency of more than 99% (53 ppm of Ru residue) by simple filtration utilizing a host-guest interaction between insoluble silica-grafted &#946;-CD (host) and the adamantyl moiety (guest) on the catalyst. The new Ru catalyst also demonstrated high removal efficiency via extraction when the reaction is run in organic solvent by partitioning the crude reaction mixture between layers of diethyl ether and water. In this way, the catalyst stays in aqueous layer only. In organic layer, the residual Ru amount was only 0.14 ppm in the RCM reactions of diallyl compounds.

A removable water-soluble N-heterocyclic carbene (NHC) ligand in aqueous media via host-guest interaction has been developed. We demonstrated representative olefin metathesis reactions in water as well as in dichloromethane. Via either host-guest interaction or extraction, the residual ruthenium (Ru) catalyst was as low as 0.14 ppm after the reaction.

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst ...