Study on the Enhancement of Proton Affinity by N-Diisopropyloxy Phosphorylation of Amino Acid in Mass Spectrometry

With introduction of a diisopropyloxy phosphoryl group into the N terminal of amino acids,it was found that proton affinity(PA) of amino acid was enhanced in mass spectrometry.Density functional theory calculations showed that the energy for protonation of DIPP-amino acid is lower than that of amino acid,which means PA of DIPP-AA ishigher than that of corresponding amino acid.These results.Coincident with our empirical results.offer a useful interpretation of experimental observations.     

A Green Synthesis of Diisopropyl Phosphoryl Amino Acid

In this paper,we report that diisopropyl phosphoryl amino acid be prepared with reasonable yields under solvent-free condition by adding amino acid to the mixture of diisopropyl phosphite and N-chlorodiisopropylamine.     

Inhibition of TX‐100 on the Rate of Hexacyanoferrate(III) Oxidation of Reducing Sugars: A Kinetic Study

An inhibition effect of nonionic micelles (polyoxyethylene (10) octyl phenol, commonly known as TX‐100) on the rate of oxidation of the reducing sugars, fructose, glucose, and maltose by alkaline hexacyanoferrate(III) has been observed. The kinetic data support a 1:1 association/binding between substrate and micelles. The binding constant and free energy transfer from water to micelle have been determined.     

Micellar Catalysis on Pentavalent Vanadium Ion Oxidation of D-Sorbitol in Aqueous Acid Media: A Kinetic Study

Vanadium(V) oxidation of D-sorbitol shows a first-order dependency on the concentrations of D-sorbitol, vanadium(V), H⁺ and HSO₄⁻. These observations remain unaltered in the presence of externally added surfactants. The effects of the cationic surfactant (i.e., CPC), anionic surfactant (i.e., SDS) and neutral surfactant (i.e., TX-100) have been studied. CPC inhibits the reactions whereas SDS and TX-100 accelerate the reaction to different extents. SDS and TX-100 can be used as catalysts in the production of D-glucose from D-sorbitol.     

Synthesis of β–Amino Acid Derivatives

In recent years, β-amino acids and their derivatives have attracted considerable attention due to their occurrence in biologically active natural products, such as dolastatins, cyclohexylnorstatine and Taxol. β–Amino acids also find application in the synthesis of β–lactams, piperidines, indolizidines. Moreover, the peptides consisting of β–amino acids, the so-called β–peptides, have been extensively studied recently. Consequently, considerable efforts have been directed to the synthe…     

First Example of Intramolecular C-H Insertion Reaction in an Amino Acid Derived α-Diazoketone

Rh-Catalyzed intramolecular C-H insertion reaction of L-leucine derived α-diazoketone is described.     

A Novel Oscillating Chemical Reaction Using Ninhydrin as Single Organic Substrate

Nonlinear chemistry has been a focus in recent years1. Many chemical oscillating reactions have been found and studied intensively, such as Belousov-Zhabotinskii (BZ) reaction2, Briggs-Rauscher reaction3, peroxidase-oxidase4, Bray-Liebhafsky reaction5 and…     

A New Hybrid Model of Amino Acid Substitution for Protein Functional Classification

In recent years, methods of protein sequences analysis have been gradually evolved into two directions: One is based on the models of probability and statistics1-4; the other is based on the digital signal processing technologies 5-8. The latter mainly converts the protein character sequences into digital signals and uses some signal processing methods to analyze them, i.e., fast Fourier transform (FFT). However, it is still unsolved how to characterize the protein sequences accurately with …     

Studies on the Total Synthesis of Crotocembreneic Acid and Neocrotocembreneic Acid:A Perchloric Acid-induced Lactonization Reaction of Epoxy Ester

Cembranoids, a large family of diterpenoid natural products characterized by the presence of fourteen-membered ring, have been isolated from various marine sources as well as some terrestrial organisms since the 1960's1. Crotocembraneic acid 1 and neocrotocembraneic acid 2 have been isolated from the stem bark of Croton oblongifolius Roxb. (Euphorbiaceae)2. In our studies on the total synthesis of 1 and 2, we find a novel perchloric acid-induced lactonization reaction of epoxy ester 9 (Scheme…     

Ab initio Mechanism Study on the Reaction of Chlorine Atom with Formic Acid

The potential energy surface(PES) for the reaction of Cl atom with HCOOH is predicted using ab initio molecular orbital calculation methods at UQCIDS(T,full)6-311 G(3df,2p)//UMP2(full)/6-311 G(d,P) level of theory with zero-point vibrational energy (ZPVE) correction.The calculated results show that the reaction mechanism of Cl atom with formic acid is a C-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom with a 3.73kJ/mol reaction barrier height,leading to the formation of cis-HOCO radical which will reacts with Cl atom or other molecules in such a reaction system.Because the reaction barrier height of O-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom which leads to the formation of HCO2 radical is 67.95kJ/mol,it is a secondary reaction channel in experiment,This is in good agreement with the prediction based on the previous experiments.     

Ab initio Calculation and Kinetic Study for the Abstraction Reaction of H with Sihcl3

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Catalytic Hydrolysis of Lipophilic Amino Acid Esters by Metallomicelles as Carboxypeptidase A Models

Metallondcellesasthemodelofhydrolyticmetalloenzymes.havebegunrecently'.Exam-plesarethemetal-ioncomplexesoflipophilicinddazoles2andpyridines'co-ndcelledwithsurfactantS.Hereinwereportthecomplexesofanovelmacrocyclicl2-membereddioxotetradrineligandbearingbis-hydroxygroupsasfunctionalpendantSwhichcanmindcthecatalyticfunctionofcarboxypeptidaseAinndcellarmedia.2,6-Dioxo-l,4,7,lo-tetraazacyclo1(O.2Og,1.onuno1)'anddodecylglycidylether(O.54g,2.2nunol)'wererefluxedinEtOH(3OoInL)for24h.Thesolventwase…     

A Study of Bioactivity of Corn Peptides with Low Molecular Weight Ⅱ： Effect on Plasma Free Amino Acid Concentrations in Rats

The effects of the ingestion of corn peptides with a low molecular weight(LMCP) prepared from zein on some plasma free amino acid concentrations in rats that had taken ethanol were investigated. LMCP(1.0g/kg body weight) in 15~ ethanol(10 mL/kg body weight) was given to Wister rats by intragastrical administration. The amino acid analysis showed that the concentrations of aianine, leucine, and proline in the plasma reached their maximum levels at 30 min for the LMCP-intake group. They are 582.39, 99.60 and 272.51 μg/L, respectively. But in the control group, the plasma free amino acid levels were not changed obviously.Therefore, LMCP could cause an increase in concentration of some free amino acids such as alanine, leucine and proline etc. in plasma of the rats that have taken ethanol.     

DFT Study on Intermolecular Cleavage Reaction of N-（2-Hydroxyphenyl）-phthalamic Acid

The reaction mechanisms of intermolecular cleavage reaction of N-（2-hydroxyphenyl）-phthalamic acid were studied via the density functional theory（DFT）. All geometries of the reactant, transition states, and products were optimized at the B3LYP/6-31G（d, p） level. Vibration analysis was carried out to confirm its identity as transitions＇ structure, and the intrinsic reaction coordinate method（IRC） was used to search the minimum energy path. Two possible reaction channels are reported in this article. The calculated results indicate that O-cyclization reaction channel has the lower activation barrier, and therefore, it occurs more easier than the other.     

A New Route to the Synthesis of Ninhydrin

邻苯二甲酸二丁酯同乙酰乙酸乙酯的钠盐反应得到１，３－二酮氢化茚，再经二氧化硒氧化合成出较高收率的茚三酮。     

Oxidation of Some α-Amino Acids by Pyridinium Bromochromate in an Aquo-Acetic Acid Medium—A Kinetic and Mechanistic Study

Oxidation of -amino acids by pyridinium bromochromate (PBC) was studied in acetic acid–water mixture containing perchloric acid. The reaction rate is first order in [PBC] and inverse first order in [H⁺] and has aldehyde as a product. The results are contrary to that of Karim and Mahanti, who observed first order with [H⁺] and cyanide as the product in the oxidation of amino acids by quinolinium dichromate. Michaelis–Menten type kinetics has been observed with respect to -amino acids. The rate of reaction increases with a decrease in the polarity of solvent indicating an ion–dipole interaction in the slow step. The reactions exhibit no primary kinetic isotope effect. The activation parameters have been evaluated. The reaction mechanism involving the formation of chromate-ester between unprotonated PBC and unprotonated amino acid followed by C–C bond fission in the slow step has been suggested. The value of the Michaelis constant (substrate–oxidant complex formation constant) increases as the number of carbon atoms increases in the amino acid.     

Lewis Acid Assisted Brønsted Acid Catalysed Decarbonylation of Isocyanates: A Combined DFT and Experimental Study

An efficient and mild reaction protocol for the decarbonylation of isocyanates has been developed using catalytic amounts of Lewis acidic boranes. The electronic nature (electron withdrawing, electron neutral, and electron donating) and the position of the substituents (ortho/meta/para) bound to isocyanate controls the chain length and composition of the products formed in the reaction. Detailed DFT studies were undertaken to account for the formation of the mono/di-carboxamidation products and benzoxazolone compounds.     

Synthesis of Ribavirin Analogues Containing Amino‐Acid Residues

Abstract

A convenient procedure for coupling 1,2,3,5‐tetra‐O‐acetyl‐β‐D‐ribofuranose and 4‐nitroimidazole was developed to obtain β‐anomer as the major product. A novel category of nucleoside analogues with the introduction of natural L‐amino acids to the base moiety were designed and synthesized to develop selective and effective antiviral agents.