Mixtures Of Thiols Research Articles

Efficiency of Volatile Corrosion Inhibitors in the Presence of n-Heptane: An Experimental and Molecular Simulation Study

Volatile corrosion inhibitors (VCIs), specifically formulations based on thiols and amines, can be used to mitigate top-of-the-line corrosion (TLC) that arises during the transportation of wet gas through transmission pipelines. Nevertheless, the VCI inhibition efficiency (IE) can be compromised by the presence of condensable hydrocarbon phases. In this research, the IE of two thiol compounds (decanethiol and hexanethiol) and three combinations of VCIs for TLC scenarios, both in the presence and absence of n-heptane, representing a condensing hydrocarbon phase were studied. The results proved the IE of thiols in a water-only condensing environment, with effectiveness increasing with the alkyl tail length. Conversely, in a water/n-heptane co-condensing environment, a reversed trend was observed, where hexanethiol exhibited higher corrosion IE compared to decanethiol. Molecular simulation results indicated a synergistic adsorption behavior when the alkane was of a similar length as the alkyl tails of the inhibitors, leading to the incorporation of alkane molecules with the inhibitor molecules. A mixture of thiols (decanethiol and hexanethiol) and two mixtures of thiol and amines (decanethiol and diethylamine/t-butylamine) were also considered in both water-only and water/n-heptane co-condensing environments. In the presence of n-heptane, only the thiol mixture, featuring molecules with different tail lengths, demonstrated high IE. This behavior was attributed to the superior IE provided by thiol-based molecules with a shorter alkyl tail (hexanethiol) in the presence of n-heptane. Additionally, the results revealed that the mixtures of decanethiol and amines did not enhance corrosion inhibition in the presence of n-heptane within the system.

Versatile synthesis of siloxane‐based graft copolymers with tunable grafting density

AbstractA versatile synthetic platform is reported that affords high molecular weight graft copolymers containing polydimethylsiloxane (PDMS) backbones and vinyl‐based polymer side chains with excellent control over molecular weight and grafting density. The synthetic approach leverages thiol‐ene click chemistry to attach an atom‐transfer radical polymerization (ATRP) initiator to a variety of commercially available poly(dimethylsiloxane‐co‐methylvinylsiloxane) backbones (PDMS‐co‐PVMS), followed by controlled radical polymerization with a wide scope of vinyl monomers. Selective degradation of the siloxane backbone with tetrabutylammonium fluoride confirmed the controlled nature of side‐chain growth via ATRP, yielding targeted side‐chain lengths for copolymers containing up to 50% grafting density and overall molecular weights in excess of 1 MDa. In addition, by using a mixture of thiols, grafting density and functionality can be further controlled by tuning initiator loading along the backbone. For example, solid‐state fluorescence of the graft copolymers was achieved by incorporating a thiol‐containing fluorophore along the siloxane backbone during the thiol‐ene click reaction. This simple synthetic platform provides facile control over the properties of a wide variety of grafted copolymers containing flexible PDMS backbones and vinyl polymer side chains.

One-pot ternary sequential reactions for photopatterned gradient multimaterials

One-pot ternary sequential reactions for photopatterned gradient multimaterials

PEG-Based Photo-Cross-Linked Networks with Adjustable Topologies and Mechanical Properties.

We report the synthesis of networks having adjustable topologies and mechanical properties. Our approach consists of photopolymerizing poly(ethylene glycol) diacrylates (PEG-DA) in the presence of mixtures of mono- and multifunctional thiols. We show that the introduction of monothiols as non-cross-linking transfer agents provides a simple way to tune the topology of the networks and produce soft extensible networks. In a systematic study with model short PEG-DA (Mn = 700 g·mol-1), we explored how the gel point and network properties, such as the swelling ratio, the soluble fraction, the viscoelastic moduli, and the ultimate stress and strain, can be adjusted by varying the ratio of thiol to acrylate functions and the average functionality of the thiol mixture. We applied this strategy to longer chains of PEG-DA (Mn = 2300 and 3200 g·mol-1) and varied the viscoelastic and tensile responses of these networks to optimize their adhesive performance. This simple and robust approach further enriches the toolbox of thiol-acrylate polymerization and expands the application scope of PEG-based hydrogels.

A nanozyme-based colorimetric sensor array as electronic tongue for thiols discrimination and disease identification

Thiol analysis is of vital significance due to the essential roles in disease diagnosis, while the highly similar structures of thiols are a major challenge in practical determination. Herein, a nanozyme-based colorimetric sensor array has been proposed as electronic tongue for excellent discrimination and sensitive quantitation of thiols. The sensing units are fabricated by integrating the terephthalic acid modified graphene quantum dots (TPA@GQDs) with three transition metal ions (Fe2+, Cu2+ and Zn2+) via coordination, respectively, which not only provide sufficient substrate binding sites but also form the metal ion-regulated catalytic active centers. In this way, disparate promotion degrees on the peroxidase-like catalytic activity have been achieved in different metal ion-TPA@GQD ensembles. Based on the strong binding affinity between metal ions and thiols, the catalytic active centers are removed from TPA@GQDs, which inhibits the catalytic activity of sensing unit to diverse degrees. Accordingly, using 3, 3′, 5, 5′-tetramethylbenzidine (TMB) as chromogenic substrate in the presence of hydrogen peroxide (H2O2), each sensing unit can generate differential colorimetric signals (fingerprints) for six thiol analytes, which can be accurately discriminated through linear discriminant analysis (LDA) with a detection limit of 50 nM. In addition, the discrimination of the same thiol with different concentrations and thiol mixtures have also been achieved. Furthermore, inspired by the distinct levels of thiols in practical samples, the proposed sensor array enables the identification of thiol-associated diseases by means of machine learning algorithm, which makes a positive contribution to medical diagnosis.

A review on chemistry, therapeutic applications, extraction & purification of bromelain

This review focused on the usage of bromelain in numerous applications, as well as the most recent literature on the chemistry, extraction, and purification of bromelain from pineapple (Ananas comosus). Bromelain is a crude, aqueous extract obtained from the stems and fruits of pineapple, leading edible member of the family Bromeliaceae. Bromelain contains a mixture of different thiol endopeptidases as well as phosphatases, glucosidases, peroxidases, cellulases, & glycoproteins. It exerts its enzymatic activity over a PH range 4.5 – 9.5. The isolation & purification of bromelain has been done by various methods includes aqueous two-phase extraction, reverse micellar extraction, ultrafiltration & precipitation & chromatographic techniques. Bromelain, a cysteine protease, has found commercial use in a variety of industries including food, beverage, tenderization, cosmetic, pharmaceutical, and textile. Bromelain act as an immunomodulatory, anti-inflammatory agent, anti-oedematous, anti-thrombotic & anti-metastatic. Although the precise mechanism of action of bromelain has not been established, bromelain has received widespread acceptance as a phytotherapeutic agent due to its long history of safety and absence of adverse effects

Substituted Thiols in Dynamic Thiol–Thioester Reactions

The thiol–thioester reaction has emerged as a promising method for developing covalent adaptable networks (CANs) due to its ability to exchange rapidly under low temperature conditions in a number of solvents, orthogonality among other functional groups, and tunability. Here, the effects of thiol substitution (i.e., primary vs secondary) were assessed with respect to their reactivity in two dynamic thioester reactions: the thiol–thioester exchange and the reversible thiol–anhydride addition. Model NMR experiments were conducted using small-molecule compounds to observe how polymers of similar components would behave in thiol–thioester exchange. It was determined that the Keq was near unity for mixtures of primary thiols and secondary thioesters, and vice versa, in both a polar solvent, DMSO-d6, and at most slightly favors primary thioesters in a relatively nonpolar solvent, CDCl3. Dielectric spectroscopy and stress relaxation experiments were used to determine the relaxation times and activation energies of the two thioester-containing networks: Thiol-ene networks, which undergo thioester exchange, displayed activation energies of 73 and 71 kJ/mol from dielectric measurements and 36 and 53 kJ/mol from stress relaxation for the primary and secondary thiols, respectively. Thiol–anhydride-ene networks, which undergo both thioester exchange and reversible thiol–anhydride addition, displayed activation energies of 94 and 114 kJ/mol from dielectric and 111 and 139 kJ/mol from stress relaxation for primary and secondary thiols, respectively. In both types of networks, the secondary thioester-based networks demonstrated slower dynamics as compared to the same primary network by at least one order of magnitude. In the anhydride network, the secondary thiol also biased the dynamics toward reversible addition.

Electrochemical properties of tethered lipid bilayers on thin film silver substrates

In this work, the assembly of functional tethered bilayer membranes (tBLMs) on silver surface was demonstrated for the first time. To avoid degradation of thin silver films the non-corrosive mixture of thiols composed of WC14 molecular anchor and 3-mercapto-1-propanol (3M1P) serving as a backfiller was used to self-assemble monolayers which allowed fusion of multilamellar vesicles and tBLM formation. tBLMs on silver films exhibited high stability and low residual defect densities as measured by the electrochemical impedance spectroscopy (EIS). Silver supported tBLMs demonstrated all features typical for interactions of pore-forming proteins and bilayer membranes. Specifically, the EIS spectral response was typical for the formation of water filled defects when tBLMs were exposed to the solution of vaginolysin (VLY), the cholesterol dependent cytolysin. Increase of defect density was observed only in case tBLMs contained significant amount, e.g., 50 %, of cholesterol, thus confirming functional reconstitution of vaginolysin into tBLMs. This observation is consistent with the biological nature of interaction between the bilayer and the cholesterol dependent cytolysins. The reconstitution of VLY was confirmed by the direct imaging of the protein entities in tBLMs by the atomic force microscopy (AFM). Notably, the quantitative estimate of the functional protein-pores in tBLMs measured by EIS, was found to be close to the number of VLY entities in tBLMs measured by the AFM. Our work demonstrates that silver can serve as less expensive alternative to gold in designing tBLM based devices, for example phospholipid biosensors, as well as the experimental platform for studying membrane protein interactions by electrochemical, and microscopy techniques.

Highly sensitive electrochemical detection of circulating EpCAM-positive tumor cells using a dual signal amplification strategy

Circulating tumor cells (CTCs) play an important role in diagnosing cancer and metastasis; thus, appropriate sensors are required for analyzing CTCs in patient samples. Here, we developed a simple electrochemical aptasensor for highly sensitive and selective detection of CTCs based on rolling circle amplification (RCA) coupled with the catalytic ability of the hemin/G-quadruplex complex. In detail, we first modified the surface of a screen-printed carbon electrode using a biocompatible mixture of thiol functionalized mesoporous silica nanoparticles and ionic liquid. Next, gold nanostar structures were prepared by electrodeposition to increase the electrode surface area and electrochemical signal, followed by EpCAM aptamer immobilization. When EpCAM-positive cancer cells are present in the sample, they bind to the EpCAM aptamer on the modified electrode, and a number of cholesterol-labeled DNA probes that act as initiators for RCA are inserted into the cell membrane. Consequently, RCA is initiated to generate multiple tandem repeats of the G-quadruplex DNA structure, which is complexed with hemin to catalyze the H2O2-mediated oxidation of 3,3’,5,5’-tetramethyl benzidine and produces strong electrochemical signals. Using this strategy, we could sensitively determine target cancer cells down to a single cell with high selectivity even in human serum. The proposed strategy with the dual signal amplification can thus be a promising platform for simple and ultrasensitive detection of CTCs, and be used for the detection of other cancer cells and biomarkers in different clinical and biological samples.

Formation of hydroxyl radical in aqueous solutions containing selenite and glutathione

The present study examined generation of hydroxyl radical (HO) in aqueous aerobic solutions (pH 7.1) containing selenite (SeO32−) and glutathione (GSH) using terephthalic acid (TA) scavenging HO to give highly fluorescent 2-hydroxyterephthalic acid (TA-OH). The highest reaction rate and yield of TA-OH were observed in a micromolar concentration range of selenite at [GSH] = 0.5 mM. Accumulation of TA-OH was substantially lower in the case of other selenium species (viz. selenomethionine, selenocystine and selenate) and their mixtures with GSH. Addition of superoxide dismutase notably increased the rate of TA-OH formation, whereas catalase inhibited the reaction. Mixture of other thiols (i.e., cysteine or cysteamine) with SeO32− hydroxylates TA as well, although the rate of the reaction is lower than in the case of GSH. The mechanism consists of the rapid reduction of SeO32− by GSH to Se(0), reversible formation of glutathione perselenide (GS-Se−) and its further reaction with hydrogen peroxide to give HO.

Facile Synthesis of Novel Thermo‐Responsive Polyvalerolactones with Tunable LCSTs

AbstractThermoresponsive polymers have emerged as promising candidates for biomedical applications. Seven novel oligoethylene glycol (OEG) functionalized polyvalerolactones P1–P7 are synthesized from poly(α‐allyl‐δ‐valerolactone) via thiol‐ene addition post‐polymerization modification. All seven polymers exhibit thermoresponsive behavior with lower critical solution temperatures (LCSTs) ranging from 13.8 to 92.2 °C. Polymers P5–P7 are synthesized via thiol‐ene addition reaction using two thiol mixtures at three different ratios. LCSTs of P5–P7 fall in between those of P1 and P2, and exhibit a linear relationship, indicating a tunable thermoresponsive system. This newly developed system offers great control for a desired thermoresponsive biocompatible, biodegradable polymeric system with desired LCSTs.

DNA aptamer-based non-faradaic impedance biosensor for detecting E. coli

Developing a real-time, portable, and inexpensive sensor for pathogenic bacteria is crucial since the conventional detection approaches such as enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) assays are high cost, time-consuming, and require an expert operator. Here we present a portable, inexpensive, and convenient impedance-based biosensor using Interdigitated Electrode (IDE) arrays to detect Escherichia coli (E. coli) as a model to demonstrate the feasibility of an impedance-based biosensor. We manipulated the affinity of the IDE array towards E. coli (E. coli BL21 series) by functionalizing the IDEs’ surface with an E. coli outer membrane protein (OMP) Ag1 Aptamer. To determine the dominant factors affecting the sensitivity and the performance of the biosensor in detecting E. coli, we investigated the roles of the substrate material used in the fabrication of the IDE, the concentration of the aptamer, and the composition of the carboxy aliphatic thiol mixture used in the pre-treatment of the IDE surface. In the sensing experiments we used an E. coli concentration range of 25–1000 cfu mL−1 and confirmed the binding of the OMP Ag1 Aptamer to the outer membrane protein of the E. coli by Field Emission Scanning Electron Microscopy (FESEM), Optical Microscopy, and Atomic Force Microscopy (AFM). By tuning the surface chemistry, the IDEs’ substrate material, and the concentration of the OMP Ag1 Aptamer, our sensor could detect E. coli with the analytical sensitivity of approximately 1.8 Ohm/cfu and limit of detection of 9 cfu mL−1. We found that the molecular composition of the self-assembled monolayer (SAM) formed on the top of the IDEs before the attachment of the OMP Ag1 Aptamer significantly impacted the sensitivity of the sensor. Notably, with straightforward changes to the molecular recognition elements, this platform device can be used to detect a wide range of other microorganisms and chemicals relevant for environmental monitoring and public health.

Tailorable, 3D structured and micro-patternable ionogels for flexible and stretchable electrochemical devices

A new family of ionogels for electrochemical devices was developed from a mixture of multifunctional thiols, diacrylate and triethylamine in the presence of ionic liquid using Michael addition chemistry.

Dual-responsive pegylated polypeptoids with tunable cloud point temperatures.

A series of pegylated polypeptoids have been readily synthesized by a strategy combining ring-opening polymerization (ROP) and thiol-yne photoaddition. The polypeptoids simultaneously incorporated branched oligo(ethylene glycol) (OEG) units and thioether bonds in the side-chains. All the polypeptoids are readily soluble in aqueous solution and show reversible thermo-responsive properties. The cloud points (CPs) were demonstrated to be readily tunable in the range of ~25°C-60°C by varying the chemical composition, OEG chain length and the degree of polymerization. Attractively, the chemical compositions of the side chains are readily tunable via adjusting the molar ratios of a mixture of thiol terminated OEG molecules, which avoid synthesizing new monomers or copolymerization of different monomers. Further, the oxidation/reduction of thioether groups shows significant influence on the CPs, providing a second stimulus to tune the phase transition behaviors. Considering the biocompatibility and degradability, the dual-responsive polypeptoids are potential candidates for various biomedical or biotechnological applications.

Mixing End Groups in Thiol-Ene/Yne Reactions as a Simple Approach toward Multienzyme-Responsive Polymeric Amphiphiles

Taking advantage of the high fidelity of thiol-ene and thiol-yne chemistries, we used mixtures of thiols to prepare degradable PEG-dendron amphiphiles functionalized with two different types of enzymatically cleavable end groups. By tuning the feed ratios of the two thiols, we achieved mixtures of hybrids with statistically different ratios of end groups. Studies of the disassembly of statistically mixed hybrids showed that these amphiphiles have higher degrees of response when incubated with each of the activating enzymes, whereas a greater degree of selectivity was observed for a control mixture of two distinct amphiphiles, which required the presence of both types of enzyme to undergo complete disassembly. The potential to introduce different end groups by using a mixture of thiols in an efficient single thiol-ene or thiol-yne step opens the way for simple modification of various ene- or yne-containing polymers and tailoring of their structural and functional properties.

Reductive Cleavage of Organic Peroxides by Iron Salts and Thiols.

Despite the low bond strength of the oxygen–oxygen bond, organic peroxides are often surprisingly resistant to cleavage by nucleophiles and reductants. As a result, achieving decomposition under mild conditions can be challenging. Herein, we explore the reactivity of a selection of peroxides toward thiolates, phenyl selenide, Fe(II) salts, and iron thiolates. Peroxides activated by conjugation, strain, or stereoelectronics are rapidly cleaved at room temperature by thiolate anions, phenylselenide, or Fe(II) salts. Under the same conditions, unhindered dialkyl peroxides are only marginally reactive; hindered peroxides, including triacetone triperoxide and diacetone diperoxide (DADP), are inert. In contrast, all but the most hindered of peroxides are rapidly (<1 min at concentrations down to ∼40 mM) cleaved by mixtures of thiols and iron salts. Our observations suggest the possible intermediacy of strongly reducing complexes that are readily regenerated in the presence of stoichiometric thiolate or hydride. In the case of DADP, an easily prepared explosive of significant societal concern, catalytic amounts of iron and thiol are capable of promoting rapid and complete disproportionation. The availability of inexpensive and readily available catalysts for the mild reductive degradation of all but the most hindered of peroxides could have significant applications for controlled remediation of explosives or unwanted radical initiators.

PH-Responsive Superwetting Fabric for On-demand Oil-Water Separation

Utilizing the redox property of polyaniline (PANI), Ag nanoparticles were uniformly grafted on PANI-coated fabric. After modification with a thiol mixture of HS(CH2)9CH3 and HS(CH2)10COOH, the prepared fabric exhibited pH-responsive reversible switching between superhydrophobicity and superhydrophilicity. Such smart fabric can be applied for on-demand corrosive water-oil separation with high flux and efficiency.

A Versatile AuNP Synthetic Platform for Decoupled Control of Size and Surface Composition.

While a plethora of protocols exist for the synthesis of sub-10-nm gold nanoparticles (AuNPs), independent control over the size and surface composition remains restricted. This poses a particular challenge for systematic studies of AuNP structure-function relationships and the optimization of crucial design parameters. To this end, we report on a modular two-step approach based on the synthesis of AuNPs in oleylamine (OAm) followed by subsequent functionalization with thiol ligands and mixtures thereof. The synthesis of OAm-capped AuNPs enables fine-tuning of the core size in the range of 2-7 nm by varying the reaction temperature. The subsequent thiol-for-OAm ligand exchange allows a reliable generation of thiol-capped AuNPs with target surface functionality. The compatibility of this approach with a vast library of thiol ligands provides detailed control of the mixed ligand composition and solubility in a wide range of solvents ranging from water to hexane. This decoupled control over the AuNP core and ligand shell provides a powerful toolbox for the methodical screening of optimal design parameters and facile preparation of AuNPs with target properties.

Tailored coating of gold nanostars: rational approach to prototype of theranostic device based on SERS and photothermal effects at ultralow irradiance

The last decade has come across an increasing demand for theranostic biocompatible nanodevices possessing the double ability of diagnosis and therapy. In this work, we report the design, synthesis and step-by-step characterization of rationally coated gold nanostars (GNSs) for the SERS imaging and photothermal therapy of HeLa cancer cells. The nanodevices were realized by synthesizing GNSs with a seed growth approach, coating them with a controlled mixture of thiols composed of a Raman reporter and a polyethylene glycol with a terminal amino group, and then reacting these amino groups with folic acid (FA), in order to impart selectivity towards cancer cells which overexpress folate receptors on their membranes. After a complete characterization, we demonstrate that these FA-functionalized GNSs (FA-GNSs) are able to bind selectively to the membranes of HeLa cells, acting as SERS tags and allowing SERS imaging. Moreover, we demonstrate that once bound to HeLa cell membranes, FA-GNSs exhibit photothermal effect which can be exploited to kill the same cells in vitro using laser irradiation in the NIR at a very low and safe irradiance. We thus demonstrate that the FA-GNSs designed following the described approach are an efficient prototype of theranostic nanodevices.

Electrochemical genoassays on gold-coated magnetic nanoparticles to quantify genetically modified organisms (GMOs) in food and feed as GMO percentage

The integration of nanomaterials in the field of (bio)sensors has allowed developing strategies with improved analytical performance. In this work, ultrasmall core-shell Fe3O4@Au magnetic nanoparticles (MNPs) were used as the platform for the immobilization of event-specific Roundup Ready (RR) soybean and taxon-specific DNA sequences. Firstly, monodisperse Fe3O4 MNPs were synthesized by thermal decomposition and subsequently coated with a gold shell through reduction of Au(III) precursor on the surface of the MNPs in the presence of an organic capping agent. This nanosupport exhibited high colloidal stability, average particle size of 10.2 ± 1.3 nm, and spherical shape. The covalent immobilization of ssDNA probe onto the Au shell of the Fe3O4@Au MNPs was achieved through a self-assembled monolayer (SAM) created from mixtures of alkane thiols (6-mercapto-1-hexanol and mercaptohexanoic acid). The influence of the thiols ratio on the electrochemical performance of the resulting electrochemical genoassays was studied, and remarkably, the best analytical performance was achieved for a pure mercaptohexanoic acid SAM. Two quantification assays were designed; one targeting an RR sequence and a second targeting a reference soybean gene, both with a sandwich format for hybridization, signaling probes labelled with fluorescein isothiocyanate (FITC), enzymatic amplification and chronoamperometric detection at screen-printed carbon electrodes (SPCE). The magnetogenoassays exhibited linear ranges from 0.1 to 10.0 nM and from 0.1 to 5.0 nM with similar detection limits of 0.02 nM and 0.05 nM for the event-specific (RR) and the taxon-specific (lectin) targets, respectively. The usefulness of the approach was demonstrated by its application to detect genetically modified organisms (GMOs) in feed and food.