Chemical Coupling Reaction Research Articles

Expanding the application potential of DNA aptamers by their functionalization

Side-by-side development of two competing technologies for obtaining affinity antibody-based and aptamer-based molecules opens new horizons for the creation of diagnostic and therapeutic agents of extremely high efficiency. Benefits of aptamers, such as relatively small size and selection simplicity, have been jeopardized for a long time by their intrinsic downsides, i.e., obscure process of obtaining aptamers against certain targets because of a low diversity of functional groups (purine and pyrimidine bases) in DNA and RNA aptamers. Another side effect of the aptamer technique inherent to the traditional SELEX method is unspecific enrichment with aptamers with high affinity to off-target reaction components. Today, due to current progress in the development of new technology methods and chemical coupling reactions, the modern aptamer technology helps to avoid its disadvantages and become capable of being the source of new diagnostic and therapeutic tools, which are properly unique in their efficiency. The review focuses on modern methods of increasing efficiency of the aptamer selection and on synthetic nucleotide modifications, which make it possible to prepare high-affinity aptamers against traditionally ‘hard’ targets.

A novel hyperbranched polyphosphoramidate-poly(trimethylene carbonate) amphiphilic copolymer: synthesis, characterization and influence of its architecture on self-assembly

The main feature that determines the self-assembly property and the structure of linear-hyperbranched copolymer consists of the architecture of the copolymer and exterior factors such as the solvent, initial copolymer concentration, crosslinking, and molecular recognition. To gain an understanding of the feature, hyperbranched polyphosphoramidate-poly(trimethylene carbonate) (HPPAE-PTMC n ) copolymer with different topological structures was synthesized through chemical coupling reaction. HPPAE-PTMC n copolymer can form core–shell micelles. Via core-crosslinking, the stability of HPPAE-PTMC n micelles was enhanced and their comprehensive self-assembly behavior including its size, stability and morphology was further investigated by Transmission Electron Microscopy (TEM), dynamic light scattering and fluorescence analysis. Diameter of the core-crosslinked micelles increased with arm grafting ratio but decreased with arm length, which was contrary to their non-crosslinked analogues. Interestingly, a morphological transformation was observed after β-CD was introduced to the copolymer solution as a result of host–guest inclusion complexation. TEM results revealed that HPPAE-PTMC n aggregates evolved from rods to a coexistence of rods and spherical micelles as the initial concentration increased and further to vesicles after increasing the molar ratio of β-CD/PTMC segments.

Hydrogen-Bond Acid Group Functionalized Mesoporous-Silica MCM-41 as Sensing Material to Detect Trace Level Organophosphorus Vapor

The hydrogen-bond acid compound 2,2-bis (4-hydroxyphenyl)-hexafluoropropane (BHPHFP) has been used as the sensing group progressively grafted on the mesoporous-silica MCM-41 carrier featured higher BET surface area via chemical coupling reaction by trimethoxysilanebutyraldehyde. Furthermore, it is successfully characterized by transmission electron microscopy (TEM), high resolution scanning electron microscopy (HR-SEM), flourier transform infrared (FT-IR) and N2 sorption isotherms. Then taking the quartz crystal microbalance sensor (QCM) as platform to form the organophosphorus vapor detection sensor, the sensing date of QCM sensor obtains the high sensitivity, repeatability and selectivity properties to detect the ppb-level concentration of organophosphorus vapor, which strongly testify the new material is a suitable sensing material for detecting organophosphorus trace-level vapor.

High-performance field-effect transistor-type glucose biosensor based on nanohybrids of carboxylated polypyrrole nanotube wrapped graphene sheet transducer

We report a rapid-response and high-sensitivity field-effect transistor (FET)-based sensor with specificity towards glucose, based on reduced graphene oxide (rGO)-carboxylated polypyrrole (C-PPy) nanotube (NT) hybrids as the conductive channel. The rGO, C-PPy NTs, and rGO/C-PPy NT hybrids were characterized using Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results indicate that a well-organized structure was successfully prepared, based on specific interactions between the C-PPy NTs and the graphene sheets. Reliable electrical contacts were developed between the rGO/C-PPy NTs and the patterned-microelectrodes, which remained stable when exposed to the liquid-phase electrolyte. Liquid-ion-gated FETs composed of these rGO/C-PPy NT hybrids exhibited hole-transport behavior with higher conductivity than those of graphene sheets or C-PPy NTs because the C-PPy NTs formed a bridge between the graphene layers, resulting in effective electron transport. Glucose oxidase (GOx) was used as the capture probe, and was tightly combined with C-PPy NTs via a chemical coupling reaction, and glucose detection was performed via GOx, which catalyzes the oxidation of glucose in the rGO/C-PPy NTs hybrid FET biosensor. The FET biosensor provided a rapid response (< 1s) with high sensitivity toward glucose with a limit of detection of 1nM. This result is ca. 2–3 orders more sensitive than previous reported glucose sensor. The FET-type biosensor was highly reproducible and stable in air over a period of one month. Furthermore, the liquid-gated FET-type biosensor displayed specificity toward glucose in a mixed solution containing compounds found in biological fluids.

ChemInform Abstract: Synthetic Strategies for Free &amp; Stable N‐Heterocyclic Carbenes and Their Precursors

Recently, chemical cross coupling reactions have emerged as a powerful tool in the hands of synthetic organic chemist to synthesize complicated organic scaffolds like drugs, natural products, optical devices and industrially impor- tant materials. Stable N-Heterocyclic Carbene (NHC) acts as an important catalyst system in various cross coupling reac- tions. This review describes various strategies used for the synthesis of free and stable NHCs. Historical developments made in the propagation of the idea of free and stable carbene have also keenly been illustrated in the introduction of this

Gold-ISH: A nano-size gold particle-based phylogenetic identification compatible with NanoSIMS

The linkage of microbial phylogenetic and metabolic analyses by combining ion imaging analysis with nano-scale secondary ion mass spectrometry (NanoSIMS) has become a powerful means of exploring the metabolic functions of environmental microorganisms. Phylogenetic identification using NanoSIMS typically involves probing by horseradish peroxidase-mediated deposition of halogenated fluorescent tyramides, which permits highly sensitive detection of specific microbial cells. However, the methods require permeabilization of target microbial cells and inactivation of endogenous peroxidase activity, and the use of halogens as the target atom is limited because of heavy background signals due to the presence of halogenated minerals in soil and sediment samples. Here, we present “Gold-ISH,” a non-halogen phylogenetic probing method in which oligonucleotide probes are directly labeled with Undecagold, an ultra-small gold nanoparticle. Undecagold-labeled probes were generated using a thiol-maleimide chemical coupling reaction and they were purified by polyacrylamide gel electrophoresis. The method was optimized with a mixture of axenic 13C-labeled Escherichia coli and Methanococcus maripaludis cells and applied to investigate sulfate-reducing bacteria in an anaerobic sludge sample. Clear gold-derived target signals were detected in microbial cells using NanoSIMS ion imaging. It was concluded that Gold-ISH can be a useful approach for metabolic studies of naturally occurring microbial ecosystems using NanoSIMS.

Amino-group Hybrid Magadiite Support: Preparation, Characterization, and Application for Hydrogen Generation

A simple method of preparing durable magadiite-supported catalyst for hydrogen generation was developed in this article. This magadiite-supported catalyst was the structure of ruthenium nanoparticles immobilized on the surface of amino-group hybrid magadiite. The amino-group hybrid magadiite support (NH2-magadiite) was successfully prepared by oxidation and chemical coupling reaction, and then was used as the template to trap Ru nanoparticles (Ru/NH2-magadite). Many techniques were used to characterize the structure of amino-group hybrid magadiite and the morphology of the supported Ru nanoclusters, including UV-Vis, FT-IR, XRD, SEM, TEM and EDX. The hydrolysis of alkaline sodium borohydride (NaBH4) solution was used as probe to evaluate the catalytic activity of the supported Ru catalysts by NH2-magadiite and Na-magadiite supports, respectively. The results show that amino group was successfully grafted on the external surface of magadiite, and Ru nanoparticles could be trapped evenly onto the external of magadiite by the NH2-magadiite support template. Ru/NH2-magadite catalyst shows higher catalytic activity than that of Na-magadiite supported Ru catalyst (Ru/Na-magadiite). Highly dispersed Ru nanoparticles on the external surface of NH2-magadiite support played an important role in improving catalytic activity of NaBH4 hydrolysis.

Gallic Acid Tailoring Surface Functionalities of Plasma-Polymerized Allylamine-Coated 316L SS to Selectively Direct Vascular Endothelial and Smooth Muscle Cell Fate for Enhanced Endothelialization

The creation of a platform for enhanced vascular endothelia cell (VEC) growth while suppressing vascular smooth muscle cell (VSMC) proliferation offers possibility for advanced coatings of vascular stents. Gallic acid (GA), a chemically unique phenolic acid with important biological functions, presents benefits to the cardiovascular disease therapy because of its superior antioxidant effect and a selectivity to support the growth of ECs more than SMCs. In this study, GA was explored to tailor such a multifunctional stent surface combined with plasma polymerization technique. On the basis of the chemical coupling reaction, GA was bound to an amine-group-rich plasma-polymerized allylamine (PPAam) coating. The GA-functionalized PPAam (GA-PPAam) surface created a favorable microenvironment to obtain high ECs and SMCs selectivity. The GA-PPAam coating showed remarkable enhancement in the adhesion, viability, proliferation, migration, and release of nitric oxide (NO) of human umbilical vein endothelial cells (HUVECs). The GA-PPAam coating also resulted in remarkable inhibition effect on human umbilical artery smooth muscle cell (HUASMC) adhesion and proliferation. These striking findings may provide a guide for designing the new generation of multifunctional vascular devices.

Evidence of chemical compatibilization reaction between poly(ether ether ketone) and irradiation-modified poly(tetrafluoroethylene)

Poly(tetrafluoroethylene) (PTFE) micropowder is used as a lubricant in thermoplastic high-performance polymers, for example, in poly(ether ether ketone) (PEEK) to improve their tribological properties regarding friction and wear significantly. The achievable effect for improving such properties by using PTFE is not only determined by the added amount of PTFE micropowder in the PEEK-PTFE compound but rather by the possibility to couple and compatibilize the PTFE with the matrix material chemically that has a direct influence on the distribution of the PTFE particles in the polymer matrix and causes improved tribological and mechanical properties. The proof of a chemical reaction between PTFE and PEEK is difficult because the high-molecular weight PEEK is insoluble in all common solvents. The evidence of chemical coupling reaction between PEEK and irradiation-modified PTFE is shown by model studies using reactive OH-terminated PEEK oligomers. The use of diphenyl sulfone as a high-boiling reaction medium was necessary for the precondition to melt both reactants. In this way, qualitative differences have been achieved and confirmed using Fourier transform infrared spectroscopy. Thus, a safer and indirect detection of the chemical coupling (cc) between PEEK and PTFE (PEEK–PTFE–cc) was achieved.

A Simple Chemical Synthesis of Sugar Nucleoside Diphosphates in Water

Chemoenzymatic oligosaccharide synthesis is attractive since it eliminates the tedious multistep protection-deprotection requirements of pure chemical synthesis. Chemoenzymatic synthesis using glycosyltransferases, however, requires not only the correct enzyme to control both regio- and stereospecificity, but also the glycosyl donor to provide the sugar that is added. This unit describes a simple synthesis of sugar-nucleoside diphosphates (sugar-NDPs), the type of glycosyl donor (e.g., UDP-Glc, UDP-Gal, ADP-Glc) required by most glycosyltransferases, by using a chemical coupling reaction in water. The preparation of sugar-NDPs by this method therefore does not require any skills in synthetic organic chemistry.

Synthetic Strategies for Free &amp; Stable N-Heterocyclic Carbenes and Their Precursors

Recently, chemical cross coupling reactions have emerged as a powerful tool in the hands of synthetic organic chemist to synthesize complicated organic scaffolds like drugs, natural products, optical devices and industrially important materials. Stable N-Heterocyclic Carbene (NHC) acts as an important catalyst system in various cross coupling reactions. This review describes various strategies used for the synthesis of free and stable NHCs. Historical developments made in the propagation of the idea of free and stable carbene have also keenly been illustrated in the introduction of this review. Keywords: Cyclopropylidene derivatives, Diphenylimidazolium perchlorate, Imidazolium ion, N-Heterocyclic Carbene, Tschugajeff’s carbene complex.

Preparation of thermostable PBO/graphene nanocomposites with high dielectric constant

In this study, poly(p-phenylene benzobisoxazole) (PBO)/graphene composites were prepared using PBO and poly(4,6-dihydroxymetaphenylenediamine terephthalamide) (PHA)-modified graphene oxide (GO–PHA). PHA is the precursor of PBO. GO–PHA was obtained via chemical coupling reaction of amino-terminated PHA and acyl-chloride-functionalized GO. Partially reduced graphene nanosheets and benzoxazole rings were formed after heating. GO–PHA could be stably dispersed in methane sulfonic acid (MSA), which facilitated its uniform distribution in the PBO matrix. The PBO/graphene nanocomposites were obtained by the dissolution of GO–PHA and PBO in MSA. The thermogravimetric analysis results showed that the PBO/graphene composites had good thermal stability below 400 ° C. The dielectric constant of the composites increased as the amount of GO–PHA increased, and the percolation threshold was fc = 0.037. The nanocomposite had a dielectric constant of 15.8, which was approximately five times larger than that of pure PBO polymer.

Thermo-Sensitive Nanogated System Based on Polymer-Modified Mesoporous Silica Hybrid Nanoparticles

Mesoporous silica nanoparticles (MSNs) have been employed as a versatile solid support for constructing a variety of hybrid materials for controlled drug delivery. Controlled release systems that integrate external stimuli with nanocarriers have attracted much attention for sensors and drug delivery applications. Mesoporous silica nanoparticles grafted with thermo-sensitive polymers on the surface were fabricated via “grafting to” approach through chemical coupling reaction. The encapsulation and release of drug based on the thermo-sensitive nanogated system were investigated. The thermo-sensitive nanogated system can be expected as one of the promising candidates for drug delivery and controlled release.

Chemical modification of poly(tetrafluoroethylene) micropowder — basis for special lubricant additives

ABSTRACTThis contribution presents results of the chemical coupling reaction between the poly(tetrafluoroethylene) (PTFE) micropowder and oils. For the preparation of such dispersions, the reaction between the perfluoroalkyl(peroxy) radicals, which are generated by irradiation of PTFE in presence of oxygen, and the olefinic unsaturated groups of the oils was used.The modified and charged PTFE micropowder particles prevent the agglomeration by repulsion and therefore also the sedimentation. Processes of structural formation in the dispersions were studied by rheological characterisation and observed into dependence of the PTFE concentration and the chosen kind of PTFE. The tribological characterisation should explore the influence of the chemical coupling reaction between PTFE and oil in the dispersions. In addition, the tribological effect of the dispersions as an additive in a synthetic lubricant was investigated.The results obtained were discussed from rheological and tribological point of view taking into account the effect of the chemical coupling in dependence of the oils used and the chosen PTFE type. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Some thoughts about controllable assembly (I) &amp;mdash; From catalysis to cassemblysis

Molecular assembly processes are in general much more complex than chemical synthesis. Their goal is the same, that to create a variety of new matter and new functional materials. In accordance with their similarities, the concept of catalysis, which is widely used in chemical synthesis, could be extended to assembly. Herein we suggest that the term “cassemblysis” be used when referring to increased rates and control during assembly. The role played by a cassemblyst in molecular assembly is similar to that played by a catalyst in a synthesis with high efficiency and selectivity. Furthermore, it may be helpful to classify some terms which are used often but without clarity in the literature, such as self-assembly and assisted self-assembly. Molecular assembly can be divided into two major types, self-assembly and assisted assembly. Most assembly processes belong to assisted assembly, which can be further divided into three categories: cassemblysis, co-assembly and field-assisted assembly. Of these three, cassemblysis is the most efficient way to create new materials (e.g., soft matter) above the molecular level. After cassemblysis, some assembly systems undergo a chemical coupling reaction which significantly enhances stability and prevents them from de-assembling. This increased stability is essential for practical applications. We call this cassembly-reaction process “catassemblysis”. We present some typical examples involving small molecules and large biological molecules to show that cassemblysis and catassemblysis are very common, especially in biological systems. We believe that photo-electro-cassemblysis is possible and that the concept of cassembly could be extended to controllable nanoparticle (or other nanostructure) assembly. Finally we discuss the primary mechanism of cassemblysis and catassemblysis. With emphasis on the experimental and theoretical methodologies of cassemblysis, controllable assembly could play a greater role in creating new matter and new functional materials.

Additives for lubricants containing poly(tetrafluoroethylene). Part 2: Tribological characterization

This article describes the tribological characterization of dispersions consisting of irradiated poly(tetrafluoroethylene) (PTFE) micropowder (Zonyl® MP1100) and an ester oil (Synative ES TMP 05). A series of PTFE/oil dispersions were prepared with different amounts of PTFE micropowder (10–25 wt%) to study the influence of the PTFE in these dispersions on their tribological properties. The PTFE/oil dispersion with 10 wt% PTFE micropowder was additionally synthesized in the presence of two additives which are derived from phosphoric acid to study the influence on the tribological properties. In addition, a physical mixture of the ester oil and the PTFE micropowder was prepared to illustrate the impact of the chemical coupling reaction with regard to the tribological properties. A higher concentration of PTFE micropowder more clearly reduces the coefficient of friction in the ester oil. Low coefficient of friction and transition values from static to dynamic friction were observed. The resistance to wear was increased with the amount of PTFE micropowder in the dispersions and clearly reflects the difference between chemical coupling and physical mixture of the components.

Oxidation of methyl linoleate in the presence of lignin

The overall aim of this study is to develop new wood modifications using vegetable oils to obtain improved durability of wood materials in an environmentally friendly way. Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopies were used to study oxidation and possible chemical coupling reactions between polyunsaturated fatty acids and model lignin compounds in order to better understand the interactions between oxidatively drying systems such as vegetable oils or alkyds with the lignin part in wood. This was done by studying mixtures of different model lignin compounds and methyl linoleate. The oxidation process was analyzed at 70 °C both in methyl linoleate alone and in combination with 20 wt% of lignin model compounds. The effects of those compounds on the oil polymerization processes were monitored by NMR (both 13C and 1H experiments) and the domain specific reactivity and patterning were then combined with FT-IR data. No covalent bonds having formed between the oil and the model compounds were detected by combination of several 13C/ 1H 2D NMR methods. From the spectra, the oxidation degrees of model compounds were calculated, and for some lignin model compounds alcohols were oxidized to carbonyls during the process. Those results were in excellent agreement with FT-IR data and oxidation mechanisms were proposed. The combination of both analytical techniques was necessary to have a better understanding of these systems: NMR demonstrated the absence of chemical bond and quantified oxidation degree of model lignin molecules while FT-IR focused on oil oxidation.

Synthesis and characterization of the fullerene–terthiophene dyads

AbstractTwo derivatives of propylenedioxy‐substituted terthiophene–fullerene dyads were prepared as the precursors for polythiophene with fullerene side chains. By the chemical coupling reaction of the dyad, the soluble polythiophene 8 was obtained, Gel‐permeation chromatography analysis showed that the average molecular weight was approximately 10,847 g/mol, and the polydispersity was 1.3 in THF against polystyrene standards. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:72–78, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20659

Relative positioning of diazepam in the benzodiazepine‐binding‐pocket of GABAA receptors

GABA(A) receptors are the major inhibitory neurotransmitter receptors in the brain. Some of them are targets of benzodiazepines that are widely used in clinical practice for their sedative/hypnotic, anxiolytic, muscle relaxant and anticonvulsant effects. In order to rationally separate these different drug actions, we need to understand the interaction of such compounds with the benzodiazepine-binding pocket. With this aim, we mutated residues located in the benzodiazepine-binding site individually to cysteine. These mutated receptors were combined with benzodiazepine site ligands carrying a cysteine reactive group in a defined position. Proximal apposition of reaction partners will lead to a covalent reaction. We describe here such proximity-accelerated chemical coupling reactions of alpha(1)S205C and alpha(1)T206C with a diazepam derivative modified at the C-3 position with a reactive isothiocyanate group (-NCS). We also provide new data that identify alpha(1)H101C and alpha(1)N102C as exclusive sites of the reaction of a diazepam derivative where the -Cl atom is replaced by a -NCS group. Based on these observations we propose a relative positioning of diazepam within the benzodiazepine-binding site of alpha(1)beta(2)gamma(2) receptors.

The Design And Use of Covalently Bound Agonists To Probe Kappa‐Opioid Receptors

Salvinorin A, the most potent naturally occuring hallucinogen, has gained great attention since the Kappa‐Opioid Receptor (KOR) was identified as its principal molecular target (Roth et al, PNAS 2002). Previously, extensive efforts were made to understand how salvinorin A binds to and activates KOR. Our goal here was to design a series of ligands capable of covalently binding to KOR to further explore the ligand‐receptor interactions at atomic level. From substituted cysteine accessibility methods (SCAM) we knew that C315(7.38) is water accessible and highly reactive to methanethiosulfonate (MTS) reagents, therefore C315(7.38) could provide an anchoring point for proximity‐accelerated chemical coupling reaction. We designed a series of covalent binding ligands of variable size and electrophilic properties. Thus far, two compounds–RB‐48 and RB‐64–were the most promising candidates after extensive molecular pharmacology examinations. They showed high affinity, high efficacy and irreversible binding properties. We are currently using these ligands along with mass spectrometry to identify the anchoring residue(s). This study will facilitate our goals to elucidate the structure and function of KOR, a family A GPCR, which is involved in analgesia, pain, mood and reward. To our knowledge, this is the first design and application of site‐directed chemical coupling ligands to probe KOR.