Molybdate sulfonic acid: preparation, characterization, and application as an effective and reusable catalyst for octahydroxanthene-1,8-dione synthesis

Molybdate sulfonic acid (MSA) as a highly efficient catalyst was synthesized and employed for the synthesis of octahydroxanthene-1,8-dione derivatives. MSA efficiently catalyzed condensation of a wide range of aryl aldehydes and cyclohexane-1,3-diones to obtain octahydroxanthene-1,8-diones. It was characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), and FT-IR spectroscopy. This catalyst can be recovered and reused several times in other reactions maintaining its high activity. This novel and green method is very cheap and has many advantages such as excellent yields, the use of recoverable and eco-friendly catalysts, and a simple work-up procedure.     

Preparation of High‐Performance Water‐Soluble Quantum Dots for Biorecognition through Fluorescence Resonance Energy Transfer

An improved method for the synthesis of high‐performance and water‐soluble quantum dots (QDs) involving the encapsulation of mercaptosuccinic acid coated QDs (MSA‐QDs) with poly(diallyldimethylammonium chloride) (PDDA) followed by their direct photoactivation with fluorescent radiation near 295 K to yield PDDA‐coated QDs (PDDA‐QDs) has been demonstrated. The quantum yield (QY) of the PDDA‐QDs was significantly improved from 0.6 (QY of MSA‐QDs) to 48 %. By using this synthetic strategy, highly photoluminescent PDDA‐QDs of varied size were readily prepared. The surface properties of PDDA‐QDs and MSA‐QDs were extensively characterized. The highly luminescent and positively charged PDDA‐QDs serve as a useful and convenient tool for protein adsorption. With a Δ⁵‐3‐ketosteroid isomerase adsorbed PDDA‐QD complex, the biorecognition of steroids was demonstrated through the application of fluorescent resonance energy transfer.     

Application of an automated synthesis suite to parallel solution-phase peptide synthesis

An in-house developed automated synthesis suite was used to prepare a library of 72 tetrapeptide derivatives, the starting materials for pharmaceutically attractive pentapeptides, employing a convergent strategy. An initial set of 18 dipeptides were synthesized on a large-scale (100-1000 g) using automated synthesis workstations, and then 72 tetrapeptides were synthesized on a medium scale (5-10 g) using an automated system. Each di- or tetrapeptide was prepared in a single operating cycle using a modified methanesulfonic acid method, then a sub-library of 56 pentapeptides were synthesized in parallel, on a small-scale (100 mg-1 g) using a robotic workstation.     

Ion-exclusion/adsorption chromatography of dimethylsulfoxide and its derivatives for the evaluation to quality-test of TiO(2)-photocatalyst in water

Ion-exclusion/adsorption chromatography of dimethylsulfoxide (DMSO) and its derivatives, i.e., methanesulfinic acid (MSI), methanesulfonic acid (MSA) and sulfuric acid (SA), was developed in order to clear the decomposition mechanism of DMSO on quality-test of TiO₂-photocatalyst in water. The separation was achieved by the adsorption effect for DMSO and ion-exclusion effect for MSI, MSA and SA under optimum conditions, using a weakly acidic cation-exchange resin column with 20 mM succinic acid as the eluent. In this system, DMSO and MSI with UV at 195 nm and MSA and SA with conductivity detection were consecutively determined by single injection and single separation column. This method was used to monitor the artificial decomposition of DMSO induced by a photocatalyst. The concentration of DMSO by active oxygens (e.g., OH radical) generated from surface of photocatalyst was found to be decreased through the stoichiometric reaction in the order of MSI, MSA and SA.     

颜色可调的高荧光CdTe量子点的水相合成

以亚碲酸钠为碲源,硼氢化钠为还原剂,一步合成了巯基丁二酸(MSA)稳定的CdTe量子点.研究了反应液pH值、镉与碲的摩尔比及镉与巯基丁二酸的摩尔比等实验条件对CdTe量子点体系荧光量子产率的影响,并用荧光光谱、X射线粉末衍射及透射电子显微镜等对其进行了表征.结果表明,CdTe量子点具有闪锌矿结构,形貌呈球状;在pH=1...     

A microfluidic SELEX prototype

Aptamers are nucleic acid binding species capable of recognizing a wide variety of targets ranging from small organic molecules to supramolecular structures, including organisms. They are isolated from combinatorial libraries of synthetic nucleic acid by an iterative process referred to as SELEX (Systematic Evolution of Ligands by Exponential Enrichment). Here we describe an automated microfluidic, microline-based assembly that uses LabView-controlled actuatable valves and a PCR machine, and which is capable of the selection and synthesis of an anti-lysozyme aptamer as verified by sequence analysis. The microfluidic prototype described is 1) a simple apparatus that is relatively inexpensive to assemble, making automated aptamer selection accessible to many investigators, and 2) useful for the continued “morphing” of macro→meso→microfabricated structures until a convergence to a few functional systems evolves and emerges, partly or completely achieving simpler, smaller and more rapid SELEX applications.     

Acidity function of methanesulfonic acid solutions in ethyl acetate

The acidity function of solutions of methanesulfonic acid (MSA) in ethyl acetate (EA) was measured by the indicator method at 25 °C in the 0.4—100% concentration range. Molecular complexes formed by MSA and EA show a higher ionizing activity than H₅O₂ ⁺ ions. The relative ionizing activity of the MSA·EA complexes and ion pairs formed by MSA and DMF was determined.     

Adsorption of carboxylate-modified gold nanoparticles on an octadecylamine monolayer at the air/liquid interface

Gold nanoparticles (Au NPs) were prepared and surface-modified by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups (MSA-Au). Octadecylamine (ODA) was used as a template monolayer to adsorb the Au NPs dispersed in the subphase. The effect of MSA concentration on the incorporation of Au NPs on the ODA monolayer and the relevant behavior of the mixed monolayer were studied using the pressure-area (pi-A) isotherm and transmission electron microscopy (TEM) observations. The experimental results showed that the adsorbed density of Au NPs is low without the surface modification by MSA. When MSA was added into the Au NP-containing subphase, the incorporation amount of Au NPs increased with increasing MSA concentration up to approximately 1 x 10-5 M for the particle density of 1.3 x 1011 particles/mL. With a further increase in the MSA concentration, the adsorbed particle density decreases due to competitive adsorption between the free MSA molecules and the MSA-Au NPs. It is inferred that free MSA molecules adsorb more easily than the MSA-Au NPs on the ODA monolayer. Therefore, an excess amount of MSA present in the subphase is detrimental to the incorporation of gold particles. The study on the monolayer behavior also shows that the pi-A isotherm of the ODA monolayer shifts right when small amounts of Au NPs or free MSA molecules are incorporated. However, when larger amounts of particles are adsorbed at the air/liquid interface, a left shift of the pi-A isotherm appears, probably due to the adsorption of ODA molecules onto the particle surface and the transferring of the particles from beneath the ODA monolayer to the air/water interface. According to the present method, it is possible to prepare uniform particulate films of controlled densities by controlling the particle concentration in the subphase, the MSA concentration, and the surface pressure of a mixed monolayer.     

Polyacrylamide-methanesulfonic acid gel polymer electrolytes for tin-air battery

The present work describes the synthesis and characterization of gel polymer electrolytes containing methanesulfonic acid (MSA) with Polyacrylamide (PAAm). The PAAm–MSA gel electrolytes were prepared with different concentrations of MSA. Addition of 0.5 M of MSA into the electrolyte increased the ionic conductivity of PAAm from 1.35 × 10^?3 to 1.56 × 10^?2 S cm^?1. The maximum ionic conductivity of 7.0 × 10^?1 S cm^?1 was obtained with 3 M MSA at room temperature. The chemical interaction between PAAm and MSA was studied by Fourier transformed infra-red. The performance as a polymer electrolyte was evaluated from the cell discharge and open circuit potential measurements of a tin-air cell. The tin-air cell supported relatively high current, up to 12 mA cm^?2 with a maximum power density of 5 mW cm^?2. The open-circuit potential of the cell was 1.27 V for 24 h.     

Efficiency of pretreatment of aqueous samples using a macroporous strong anion-exchange resin on the determination of nerve gas hydrolysis products by gas chromatography-mass spectrometry after tert.-butyldimethylsilylation

A pretreatment procedure, using a macroporous strong anion-exchange resin (MSA) has been established for the determination of nerve gas hydrolysis products by gas chromatography-mass spectrometry (GC-MS) after tert.-butyldimethylsilyl (TBDMS) derivatization. Aqueous solutions of methylphosphonic acid (MPA) and three alkyl methylphosphonic acids (AMPAs) (ethyl, isopropyl and pinacolyl methylphosphonic acid), were retained on the MSA column, and then quantitatively eluted with 0.1 M hydrochloric acid. The neutralized column eluate was dried, and MPA and AMPAs were derivatized with N-methyl-N-(tert.-butyldimethylsilyl)-trifluoroacetamide and analyzed by GC-MS. The column eluate was also analyzed in order to determine the exact hydrolysis product levels by capillary electrophoresis using borate and benzoate buffer (pH 6). The MSA pretreatment was examined for the clean-up of aqueous extracts of three types of soils and an aqueous solution containing 10% sucrose, which is regarded as model for a typical soft drink, after spiking with MPA and AMPAs. MPA and AMPAs were quantitatively recovered in the MSA eluate fraction from those samples, except for MPA from volcanic acid and alluvial soils. The yields of TBDMS derivatives were remarkably improved, compared with for which no pretreatment was used and also for those in which a strong cation-exchange resin was used. The achieved detection limits of MPA and AMPAs ranged from 0.12 to 0.18 microg/g of soil (S/N=3). The established MSA method was applied to the pretreatment of spiked sea water, two types of beverages, Pepsi Cola and canned coffee. Although the yields of TBDMS derivatives of MPA and AMPAs in sea water (in a range between 44 and 96%) and AMPAs in Pepsi Cola (in a range between 58 and 92%) were rather high, those for MPA in the Pepsi Cola (27%) and those for MPA and AMPAs in the canned coffee (in a range between 5 and 17%) were low.     

Ag(9) quantum cluster through a solid-state route

A silver cluster having the composition Ag(9)(H(2)MSA)(7) (H(2)MSA = mercaptosuccinic acid) was synthesized in macroscopic quantities using a solid-state route. The clusters were purified by PAGE and characterized by UV-vis, FTIR, luminescence, and NMR spectroscopy, TEM, XPS, XRD, TG, SEM/EDAX, elemental analysis, and ESI MS. The solid-state route provides nearly pure Ag(9) clusters, and nanoparticle contamination was insignificant for routine studies. Formation of various clusters was observed by modifying the conditions. The effect of ligands on the synthesis was checked. The cluster decomposed slowly in water, and the decomposition followed first-order kinetics. However, it could be stabilized in solvent mixtures and in the solid state. Such materials may be important in cluster research because of their characteristic absorption profiles, which are similar to those of Au(25) and Au(38). The cluster showed luminescence with a quantum yield of 8 × 10(-3) at 5 °C.     

Kinetic Study of the Bromine-Catalyzed Isomerization of Methyl- and Chloro-Maleic Acids in Aqueous Ce(IV)-Br -H2SO4 Medium

Methylmaleic (citraconic, CTA) acid and methylfumaric (measaconic, MSA) acid in aqueous sulfuric acid solution undergo bromine-catalyzed reversible cis-trans isomerization in the presence of ceric and bromide ions. The positional isomerization of CTA or MSA to itaconic acid (ITA) is not observed. The method of high performance liquid chromatography (HPLC) was applied to study the kinetics of this catalyzed isomerization. The major catalytic species is best expressed as the Br^?₂ · radical anion. Under suitable catalytic conditions, there is a tendency for the [MSA]/[CTA] ratio to reach an equilibrium value of 4.10 at 25° for the CTA+Br^?₂ · ? MSA+Br^?₂ · reaction. Chloromaleic (CMA) and chlorofumaric (CFA) acids undergo similar isomerization with an equilibrium [CFA]/[CMA] ratio of 10.3 at 25°. The isomerization of maleic acid (MA) to fumaric acid (FA) is essentially irreversible with 50 as the lower limit of the equilibrium [FA]/[MA] ratio. The substituent has an important effect on the reversibility of this catalyzed isomerization of butenedicarboxylic acids. The thermodynamic parameters ΔH° and ΔS° at 25° for the CTA+Br^?₂ · ? MSA+Br^?₂ · reaction were found to be ?5.1±0.7 kj/mol and ?6.0±3.3 J/mol K, respectively. The present method gives a plausible way to measure the differences in enthalpy and entropy between the trans- and cis-isomers of butenedicarboxylic acids (CRCO₂H=CR'CO₂H) in aqueous solution.     

Synthesis of cleavable peptides with authentic C-termini: an application for fully automated SPOT synthesis

A simple method for the synthesis of carboxyl-free peptides on cellulose membranes was improved and adapted for fully automated SPOT synthesis. Using 1,1′-carbonyl-di-imidazole (CDI) or 1,1′-carbonyl-di-(1,2,4-triazole) (CDT) as an activator within a defined period of time, we were able to reduce the formation of di- or oligomerization of the C-terminal amino acid. The soluble peptides are obtained in a purity range of 60-95% and could be used directly for different biological assays (e.g., CD8 T-cell epitope) that require authentic C-termini.     

聚苯撑苯并二噻唑的甲基磺酸溶液的相转变过程及其动力学研究

用退偏振光强度法及偏光显微镜研究了溶致性液晶高分子聚苯撑苯并二噻唑的甲基磺酸溶液(PBT/MSA)由液晶相至各向同性相(N→I转变),及由各向同性相至液晶相(I→N转变)的相变过程.液晶相的形成(I→N)服从Av-rami方程,Avrami指数为1左右,表明该体系的液晶相是以一维棒状方式形成的.相转变温度与浓度有关,提高温度可加速在应力下液晶相长程有序结构的形成.     

聚苯撑苯并二噻唑的甲基磺酸溶液的相转变过程及其动力学研究

 用退偏振光强度法及偏光显微镜研究了溶致性液晶高分子聚苯撑苯并二噻唑的甲基磺酸溶液(PBT/MSA)由液晶相至各向同性相(N→I转变),及由各向同性相至液晶相(I→N转变)的相变过程.液晶相的形成(I→N)服从Av-rami方程,Avrami指数为1左右,表明该体系的液晶相是以一维棒状方式形成的.相转变温度与浓度有关,提高温度可加速在应力下液晶相长程有序结构的形成.     

Hydrolytic cleavage of pyroglutamyl-peptide bond. V. selective removal of pyroglutamic acid from biologically active pyroglutamylpeptides in high concentrations of aqueous methanesulfonic acid

Application of aqueous methanesulfonic acid (MSA) for selective chemical removal of pyroglutamic acid (pGlu) residue from five biologically active pyroglutamyl-peptides (pGlu-X-peptides, X=amino acid residue at position 2) was examined. Gonadotropin releasing hormone (Gn-RH), dog neuromedin U-8 (d-NMU-8), physalaemin (PH), a bradykinin potentiating peptide (BPP-5a) and neurotensin (NT) as pGlu-X-peptides were incubated in either 70% or 90% aqueous MSA at 25 degrees C. HPLC analysis of the incubation solutions showed that the main decomposition product was H-X-peptide derived from each pGlu-X-peptide by the removal of pGlu. The results revealed that the pGlu-X peptide bond had higher susceptibility than various internal amide bonds in the five peptides examined, including the Trp-Ser bond in Gn-RH, the C-terminal Asn-NH(2) in d-NMU-8, and the Asp-Pro bond in PH, whose acid susceptibility is well known. Thus, mild hydrolysis with high concentrations of aqueous MSA may be applicable to chemically selective removal of pGlu from pGlu-X-peptides for structural examinations.     

Sensitive and selective determination of Cu2+ by electrochemiluminescence of CdTe quantum dots

For the first time, we report a sensitive and selective method to detect Cu²⁺ based on the electrochemiluminescence quenching of CdTe quantum dots (QDs) in aqueous solution. The mercaptosuccinic acid (MSA) protected CdTe QDs were prepared and characterized with UV, fluorescence and ECL. The anodic ECL quenching mechanism was attributed to the fact that MSA capping was removed from the surface of the CdTe QDs and preferentially bound with Cu²⁺. The displacement of MSA capping layer created imperfections on the CdTe QDs surface, and eventually led to the ECL quenching. The quenching effect of Cu²⁺ on the anodic ECL of CdTe QDs was found to be selective and concentration dependent, so we applied it to develop a method for the sensitive and selective detection of Cu²⁺. With the proposed method, the concentration of Cu²⁺ could be detected in the range of sub-nanomolar to micromolar levels.     

Acid-base interactions in the methanesulfonic acid-propylene carbonate system

The methanesulfonic acid (MSA)—propylene carbonate (PC) system with component concentrations of 0–100% was studied at 30°C using the Multiple Attenuated Total Reflection (MATR) IR spectroscopy. The formation of a strong 1∶1 molecular complex of MSA with PC was established. In the presence of an excess of the acid, a second MSA molecule adds to this complex to give the molecular complex (2MSA)·PC. When excess propylene carbonate is used, the MSA·PC complex is solvated by a propylene carbonate molecule. No protonation of the base or formation of complexes with a strong symmetrical H bond was observed. Continuous absorption was not detected in IR spectra of the solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 313–318 February, 1999.     

Construction of an ion-exchange amino acid analyser kit for use with high-performance liquid chromatography apparatus

A conventional ion-exchange amino acid analyser kit has been simply and economically constructed for use with existing high-performance liquid chromatography (HPLC) apparatus. Sequential elution conditions are fully programmable by virtue of a 32K BBC microcomputer interfaced with an elution buffer selection valve and a thermostatically controlled column. Post-column derivatization with o-phthaladehyde-2-mercaptoethanol reagent enables fluorimetric detection at the picomole level. The system enables sensitive amino acid analysis of complex mixtures to be carried out by clinical and research laboratories who already possess HPLC apparatus but whose sample turnover does not merit purchase of a dedicated fully automated analyser.     

Ionizing properties of complexes with strong symmetrical hydrogen bonds in acid solutions in aprotic solvents

The acidity functions H₀ of solutions of trifluoroacetic acid (TFA) in DMF and methanesulfonic acid (MSA) in 2-pyrrolidone over an acid (HA) concentration range of 0–100% and of H₂SO₄ solutions in 2-pyrrolidone (66.7–100 mol % HA) at 25°C were determined using the indicator method. Data were obtained on the relative ionizing powers of the quasi-ion pairs S· · · H· · ·A (S is a solvent molecule) formed by DMF with acids (HCl, MSA, and TFA) and by MSA with DMF and 2-pyrrolidone. The effects of the acid anion (with MSA and H₂SO₄ solutions in 2-pyrrolidone acting as examples) and the counterion SH⁺ (with MSA solutions in DMF and 2-pyrrolidone acting as examples) on the ionizing power of (Ä · · ·H· · ·A)^– ions with strong symmetrical H-bonds were studied. It was found that, under comparable conditions, the replacement of a 2-pyrrolidone molecule by a DMF molecule in the SH⁺ cation insignificantly decreased the acidity of solution, whereas the (Ä· · ·H· · ·A)^– ions in H₂SO₄ solutions exhibited a much higher ionizing power than that of structurally similar anions in MSA solutions.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 44–49.Original Russian Text Copyright © 2005 by Kislina, Sysoeva, Librovich.