Mixtures Of Thiols Research Articles

Facile synthesis of nearly monodispersed copper sulfide nanocrystals

We synthesized monodispersed copper sulfide (Cu x S) NCs at nearly ambient temperature. Alkan thiol and amphiphilic amine mixture (ligand mixture) enable us to use relatively low toxic, stable and low cost materials as metal and sulfur source. Furthermore, oleylamine (OA) and dodecanethiol (DT) play important roles to control Cu/S composition on NCs. This compositional change of Cu x S NCs was attributed to the introducing of S–S bonding (S n 2−) into NCs.

Solvent Effects in the Adsorption of Alkyl Thiols on Gold Structures: A Molecular Simulation Study

We carried out Monte Carlo simulations of gold nanocrystals (NCs) and (111) slabs covered with alkyl thiols, with and without explicit solvent (n-hexane), at T = 300 K. Adsorption isotherms for propane- and octanethiol showed a phase behavior measured previously in experiments. Comparison of the adsorption isotherm of octanethiol in hexane on a (111) slab with experimental data suggests that, in this system, no thiolate bond was formed. The geometry of a gold surface strongly influences the formation and structure of the capping monolayer. On a (111) surface, attractive interactions between carbon chains are more pronounced than on a NC. This leads to a stronger penetration of the capping layer by the solvent. Adsorption selectivity for binary alkyl thiol mixtures is stronger in vacuum than in solution. The convex shape of the NCs also reduces the adsorption selectivity of binary thiol mixtures. This result shows that the solvent cannot be ignored in simulations.

Isolation of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine from culture broths by covalent chromatography.

An efficient procedure for the isolation of reduced delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) from culture supernatants of beta-lactam antibiotic-producing microorganisms is described. The method utilises covalent chromatography to isolate thiols from culture broths that have been deproteinised and undergone borohydride reduction. 2-Pyridyl disulphide activated thiopropyl Sepharose was employed batchwise to isolate the thiols present in such broths from cultures of the known ACV excreter Cephalosporium acremonium N2 and the penicillin producer Penicillium chrysogenum P2. ACV was separated from these mixtures of thiols by gel permeation chromatography. Reversed-phase HPLC analysis showed the ACV to be of a high purity unless isolated from a highly complex culture medium.

Effects of Modulus and Surface Chemistry of Thiol-Ene Photopolymers in Nanoimprinting

Thiol-ene photopolymers were studied as patternable resins for nanocontact molding imprint lithography. Photopolymerizable thiol and ene monomer mixtures were used, and after molding, patterned thiol-ene polymer features the size and shape of the original molds were replicated. Adhesion and release were examined and controlled by manipulating the surface chemistry of the substrate and mold. A direct correlation between cured thiol-ene polymer modulus and pattern fidelity was observed.

Phase separation in mixed self-assembled monolayers and its effect on biomimetic membranes

Self-assembled monolayers (SAMs) comprised of a mixture of thiol–lipid and spacer–thiol have been used to tether bilayer lipid membranes. However, the properties of these mixed SAMs and their effect on the tethered bilayer lipid membranes (tBLMs) are not fully understood. In this paper, these SAMs have been characterised by electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and cyclic voltammetry. A complex pattern of mixing and phase separation is observed that is dependent on the type of spacer–thiol used. The influence of phase separation, lipid composition and surface flatness on the formation of the tBLMs have also been studied. Large differences between EggPC and lipid extracts of Escherichi coli were detected, while the surface flatness of the gold has a relatively minor influence. tBLM formation is also relatively insensitive to the type of spacer–thiol used, while the quality of the bilayer is strongly influenced by the relative amount of thiol–lipid on the surface. Impedance spectroscopy of the tBLMs shows varying degrees of frequency dispersion and these results are discussed with respect to the quality of the tBLM.

Synthesis and Surface Assembly of Ruthenium Bipyridine Complexes

Disulfide-functionalized bipyridine and the corresponding thiol derivative were prepared starting from xanthogenate-functionalized bipyridine. The reduction of the xanthogenate by hydrazine led to the formation of a mixture of thiol and disulfide-functionalized bipyridines that could be separated by size exclusion chromatography. The chelating properties of the bipyridine units were used to prepare fluorescent heteroleptic ruthenium complexes, whereas the thiol or disulfide group on the other end of the molecule was used to anchor the individual ligands as well as the formed complexes to solid substrates. Scanning tunnelling microscopy was used to visualize the assembly of these species on a flat gold(111) substrate.

Immobilization of Protein A on SAMs for the elaboration of immunosensors

Binary mixtures of 11-mercaptoundecanoic acid (MUA) and other thiols of various lengths and terminal functions were chemisorbed on gold-coated surfaces via S–Au bonds to form mixed self-assembled monolayers (SAMs). Several values of the mole fraction of MUA in the thiol mixtures were tested and the structure and composition of the resulted thin films were characterized by X-ray photoelectron spectroscopy (XPS) and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The results made it clear that co-adsorption of MUA with thiols of similar chain length led to well-ordered monolayers whereas the co-adsorption of MUA with shorter thiols yielded less crystalline-like thin films, but with more reactive carboxylic acid terminal groups. This criterion appeared decisive for efficient covalent binding of Staphylococcus aureus Protein A (PrA), a protein that displays high affinity for the constant fragment (Fc) of antibodies of the IgG type from various mammal species. The ability of immobilized Protein A to recognize and bind a model IgG appeared to be optimal for the mixed SAM of MUA and the short-chain, ω-hydroxythiol 6-mercaptohexanol in the proportion 1–3.

Electrospray Ionization and Triple Quadrupole Tandem Mass Spectrometry Study of Some Biologically Relevant Homo- and Heterodimeric Cadmium Thiolate Conjugates

A series of 19 compounds of general formula R1S-Cd-SR2, R1, and R2, being some biologically relevant thiol amino acids and peptides, were prepared by direct reaction of cadmium(II) ions and thiols in water at millimolar concentration. The obtained products were characterized by electrospray ionization and triple quadrupole tandem mass spectrometry. The source spectra of stoichiometric 1:2 Cd-thiol systems containing either an individual thiol or equimolar mixtures of two different thiols featured several Cd-containing signals, although at much lesser intensity than in the previously reported experiments with mercury(II) (J. Am. Soc. Mass Spectrom. 2004, 15, 288-300). Also, the relative intensity of the homo- and heterodimeric thiolates were significantly different from the theoretically expected 1:2:1 ratio, thus pointing at some degree of discrimination between the different thiols. In particular, homo-cysteine showed much less reactivity than cysteine, and penicillamine and cysteine methyl ester much less than the free amino acid. The fragment spectra show structure-specific ions for the different ligands bound to the metal ion and allow a stand-alone determination of the connectivity also of isomeric pairs. The fragmentation pathways are similar to those observed for the corresponding mercury(II) analogues, with the addition of further intense and specific fragments, one formally carrying a Cd-bound OH ligand and one connected as a five-membered oxazolone carrying a cadmium-bis-thiolate side chain, both formed with a high intensity. Energy-resolved fragmentation data show that metal-free ions can be generated from cysteine but not from glutathione conjugates and point to the possibility of unveiling differences in the biochemical behavior of the conjugates of different heavy metals through the detailed study of their mass spectrometric fragmentation.

Fluorescent Labeling of RAFT-Generated Poly(N-isopropylacrylamide) via a Facile Maleimide−Thiol Coupling Reaction

We report a facile labeling technique in which the telechelic thiocarbonylthio functionality of well-defined poly(N-isopropylacrylamide) (PNIPAM) prepared by room temperature RAFT polymerization is first converted to the thiol and subsequently reacted with a maleimido-functional fluorescent dye, N-(1-pyrene)maleimide (PM). Nearly monodisperse PNIPAM (M(n) = 39 500 g/mol, M(w)/M(n) = 1.07) was synthesized using a trithiocarbonate-based CTA, 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid (DMP), and a conventional azo-initiator, namely, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), as the primary source of radicals. The key to successful conjugation of PM to PNIPAM is the implementation of a two-step reduction process involving (1) the cleavage of the trithiocarbonate with a strong reducing agent, in this case, NaBH4, to form a mixture of polymeric thiols and disulfides and (2) the conjugation of PM to the pure polymeric thiol in the presence of tris(2-carboxyethyl)phosphine.HCl (TCEP). We show that TCEP efficiently eliminates the formation of polymeric disulfides and thus allows for the desired addition of the free polymeric thiol across the maleimide double bond. This concept is demonstrated using SEC-MALLS and UV-vis spectroscopy measurements.

Sum Frequency Generation Microscopy of Microcontact-Printed Mixed Self-Assembled Monolayers

Sum frequency generation imaging microscopy (SFGIM) is used to image the chemically distinct regions of a microcontact-printed monolayer surface. The contrast in the images is based on the vibrational spectrum of each component in the monolayer. Mixtures of C16 thiols on gold with CH3 and phenyl termination are imaged with a resolution of approximately 10 microm. Microcontact printing produces films that are different compared to the immersion procedure of forming self-assembled monolayers. The SFGIM technique is able to obtain a vibrational spectrum at each point on the surface and demonstrate that the stamped area has significant mixing with the molecules deposited from the backfilling solution.

Electrochemical impedance spectroscopy study of mixed thiol monolayers on gold

We demonstrate how electrochemical impedance spectroscopy (EIS) measurement of the capacitance can be used to calculate the composition of mixed self assembled monolayers (SAMs) consisting of binary mixtures of octanethiol (OTT) with hexadecanethiol (HDT) and dodecanethiol (DDT) with 11-mercaptoundecanoic acid (MUA) on gold. We monitor as a function of immersion time changes in composition of the mixed SAM and examine the displacement of one thiol in a SAM with another thiol from solution. Under the experimental conditions the composition of the mixed SAM formed by co-adsorption from a mixture of thiols in solution is determined by thermodynamic, not kinetic, factors given sufficiently long immersion times (up to 10 days). Fully formed SAM consisting of a single component behave differently in that some pure SAM (e.g., DDT) are completely displaced when exposed to a competing thiol in solution, whereas others (e.g., MUA) can only be partially displaced, presumably because of strong interlayer cohesion between the carboxylate end groups.

Interactions between Volatile and Nonvolatile Coffee Components. 2. Mechanistic Study Focused on Volatile Thiols

This study is the second of two publications that investigate the interactions between volatile and nonvolatile components in coffee brew. The purpose here was to shed some light into the chemical mechanisms responsible for the decrease of volatile thiols when in contact with coffee nonvolatiles. A mixture of volatile thiols covering a large range of physicochemical properties was monitored over time in the presence of a coffee brew model. The binding potential was estimated by SPME-GC-MS. Additives inhibiting specific reaction pathways were preincubated with the coffee brew 1 h prior to addition of the volatile compounds. Degradation kinetics of the volatile thiols were characterized by their rate constants k(obs). The effect of individual additives was shown by calculating k(rel), the relative rate constant as compared to the reference without additive. The conclusion was that thiols, mainly responsible for the "roasty" and "burnt" notes, disappear via two main chemical mechanisms. The results suggest that nucleophilic addition is the major pathway for thiol degradation. Addition occurs on oxidized species generated in the matrix in the presence of air. This mechanism prevails for aliphatic thiols (e.g., ethanethiol, methanethiol). Benzylic thiols (such as 2-furfurylthiol) can react in parallel via another pathway that is slowed in the absence of oxygen and in the presence of a radical scavenger. This points to a radical mechanism, but further work is needed to support this hypothesis. A direct correlation between thiol hydrophobicity and the magnitude of the interactions was shown as well. Therefore, weak physical interactions or hydrophobic assistance accelerating chemical reactions cannot be excluded at this point of the study.

Thiol–enes: Chemistry of the past with promise for the future

AbstractThe photopolymerization of mixtures of multifunctional thiols and enes is an efficient method for the rapid production of films and thermoset plastics with unprecedented physical and mechanical properties. One of the major obstacles in traditional free‐radical photopolymerization is essentially eliminated in thiol–ene polymerizations because the polymerization occurs in air almost as rapidly as in an inert atmosphere. Virtually any type of ene will participate in a free‐radical polymerization process with a multifunctional thiol. Hence, it is possible to tailor materials with virtually any combination of properties required for a particular application. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5301–5338, 2004

Catalytic Desulfurization of Dibenzothiophene and 4,6-Dimethyldibenzothiophene with Nickel Compounds

Catalytic amounts of the compounds [(dippe)NiH]2 (1), [(dcpe)NiH]2 (2), and [Ni(PEt3)4] (3) (1−0.1 mol %) with alkyl Grignard reagents promoted the desulfurization of dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene, to produce the corresponding biphenyls (90−100%) in toluene or mixtures of biphenyls and thiols favored in THF. Also, the thianickelacycle [(dippe)Ni(η2-C,S-C12H8)] (4) was used as a catalyst precursor to test its participation as an active intermediary in the catalytic cycle.

Characterization of a self-assembled monolayer of thiol on a gold surface and the fabrication of a biosensor chip based on surface plasmon resonance for detecting anti-GAD antibody

A biosensor chip utilizing surface plasmon resonance (SPR) was fabricated for detecting anti-glutamic acid decarboxylase (GAD) antibody, which is an indicator of the presence of type I diabetes mellitus. The sensor surfaces were constructed from various thiol mixtures of different molar ratios of 3-mercaptopropionic acid (3-MPA) to 11-mercaptoundecanoic acid (11-MUA). To determine the surface characteristics of the different alkanethiol monolayers, several quantitative and kinetic measurements were carried out. The extent of immobilization of streptavidin (SA) and biotin-GAD (the anti-GAD receptor) and the immune response of anti-GAD antibody against GAD were measured using the SPR biosensor. The terminal functional group of a thiol has different effects on the adsorption and covalent binding of protein depending on the steric hindrance. The protein chip described herein permits simple, rapid detection of anti-GAD antibody.

Thiol−Ene Photopolymerization Kinetics of Vinyl Acrylate/Multifunctional Thiol Mixtures

The photopolymerization of multifunctional thiol (trimethylolpropane tris(3-mercaptopropionate))/vinyl acrylate mixtures as a function of thiol content in the presence and absence of photoinitiators has been investigated using real-time FTIR, thin-film calorimetry, and 2D-COSY NMR. The addition of a multifunctional thiol to vinyl acrylate significantly enhances the conversion of the vinyl double bonds of vinyl acrylate due to the preferential addition of the thiyl radical to the vinyl group. Two separate free-radical polymerization processes, acrylate homopolymerization and thiol/vinyl ester copolymerization, occur simultaneously in thiol/vinyl acrylate mixtures. Thin-film calorimetry and 2D-COSY NMR results are consistent with real-time FTIR results, giving strong evidence for two simultaneous free-radical processes.

Facile Double Nucleophilic Addition of Thiols and Tetraallyltin to Latent 2‐Alkynals Using in situ Hydrolysis of the Imino Functionality Promoted by Tin(IV) Chloride Pentahydrate.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Mixed Monolayer-Protected Gold Clusters from Thiol Mixtures: Variation in the Tail Group, Chain Length, and Solvent

We present a systematic study on the synthesis of mixed monolayer-protected clusters (MMPCs) from mixtures of alkanethiols. Our results show that solvation-driven thermodynamic preferential adsorption of precursor ligands governs monolayer composition of MMPCs. In the mixed system HO(CH2)nSH/ CH3(CH2)mSH (n = m or n ≠ m) in toluene, adsorption of the polar component is largely favored because of the poorer solvation of polar tail groups in toluene compared to tetrahydrofuran (THF). When MMPCs are generated from the mixed system HO(CH2)nSH/CH3(CH2)mSH (n = m) in THF, the tail group effect is much less. The MMPC synthesis in THF solutions containing HO(CH2)nSH/CH3(CH2)mSH (n ≠ m) shows large thermodynamic control, which promotes a preferential adsorption of the thiols with a longer alkyl chain onto the surface of clusters. Transmission electron microscopy (TEM) and UV−vis spectroscopy data suggest that the average core dimension of MPCs generated from alkanethiols in THF is slightly smaller than that of MPC...

Human Serum Albumin on Fluorinated Surfaces

The aim of this work is to investigate the stabilization of the conformation of adsorbed human serum albumin (HSA) on surfaces containing CF3 and/or OH groups. These groups are structural characteristics (mimics) of trifluoroethanol, which is known to stabilize the secondary structure of several proteins. We focused on three different types of organic surfaces: (i) self-assembled monolayers (SAMs) prepared from mixtures of thiols with CF3 and OH end groups, (ii) polymer surfaces of a poly(vinyl methyl ketone) (PVMKCF3/OH), which was modified with OH and CF3 groups, and (iii) surfaces of polymer fluorosurfactant complexes containing CF3 groups. It was revealed that the secondary structure of HSA in contact with the SAMs depends on the thiol composition. SAMs of mixed monolayers displayed the highest HSA recognition measured by antibody binding. CD measurements showed that PVMKCF3/OH surfaces retain the secondary structures of adsorbed HSA. Examples of polymer fluorosurfactant complexes are given that retain the secondary structure of adsorbed HSA and a complex that increase the content of α-helices. A combination of CF3 and OH groups is proposed as a new approach to prepare biocompatible surfaces.

Dynamic covalent chemistry on self-templating peptides: formation of a disulfide-linked beta-hairpin mimic.

Dynamic covalent chemistry on self-templating peptides: formation of a disulfide-linked beta-hairpin mimic.