Effect of Alkynyl Group on Reactivity in Photoaffinity Labeling with 2-Thienyl-Substituted α-Ketoamide

Minimalist photo-reactive probes, which consist of a photo-reactive group and a tag for detection of target proteins, are useful tools in chemical biology. Although several diazirine-based and aryl azide-based minimalist probes are available, no keto-based minimalist probe has yet been reported. Here we describe minimalist probes based on a 2-thienyl-substituted α-ketoamide bearing an alkyne group on the thiophene ring. The 3-alkyne probe showed the highest photo-affinity labeling efficiency.     

Effect of Temperature on The Solubility of α-Amino Acids and α,ω-Amino Acids in Water

The aqueous solubilities of glycine, dl-α-alanine (2-aminopropanoic acid), dl-α-aminobutyric acid (2-aminobutanoic acid), dl-α-norvaline (2-aminopentanoic acid), dl-α-norleucine (2-aminohexanoic acid), β-alanine (3-aminopropanoic acid), γ-aminobutyric acid (4-aminobutanoic acid), 5-aminovaleric acid (5-aminopentanoic acid), and 6-aminocaproic acid (6-aminohexanoic acid) were determined from 293.15 to 323.15 K at intervals of 5.00 K using the gravimetric method. The temperature dependence of the solubility of α-amino acids and α,ω-amino acids in water is well described by the van’t Hoff equation. Linear van’t Hoff plots were used to determine the differential enthalpy of solution. The results obtained are compared with reported values in literature and are discussed in terms of the position of the ionic groups in the hydrocarbon chain.     

Effect of magnesium cations on the activity and stability of β-galactosidases

It was shown that the presence of magnesium cations in the reaction mixture increases, approximately twofold, the activity of bacterial Escherichia coli and yeast Kluyveromyces lactis β-galactosidases but does not affect the activity of bovine liver and fungous Penicillium canescens β-galactosidases. The catalytic constants for E. coli and yeast K. lactis β-galactosidases in the presence of 0.01 M and in the absence of Mg²⁺ cations were determined (490 and 220 s^?1 and 59.8 and 37.4 s^?1, respectively). It was shown that the Michaelis constants for these two enzymes are higher in the presence of Mg²⁺ cations, that the thermal stability of E. coli and K. Lactis β-galactosidases is higher in the presence of 0.01 M Mg²⁺, and that the effective rate constants of thermal inactivation of the enzymes are two-to eightfold lower, depending on conditions, in the presence of Mg²⁺ cations. The maximum stabilizing effect of magnesium cations was observed at weak alkaline pH values (7.5–8.5).     

Study on the complexation of isoquercitrin with β-cyclodextrin and its derivatives by spectroscopy

The inclusion complexes of isoquercitrin (IQ) with cyclodextrins (CDs) including β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and dimethyl-β-cyclodextrin (DM-β-CD) have been investigated using the methods of steady-state fluorescence, UV-vis absorption and induced circular dichroism. The stoichiometric ratio of the three complexes was found to be 1:1 and the stability constants (K) were estimated from spectrofluorometric titrations, as well as the thermodynamic parameters. Maximum inclusion ability was measured in the case of DM-β-CD due to the increased hydrophobicity of the host cavity, followed by HP-β-CD and β-CD. The effect of pH on the complexation process was also quantitatively assessed. IQ exists in different molecular forms depending on pH and β-CDs were most suitable for inclusion of the neutral form of IQ. The phase-solubility diagrams obtained with β-CD, HP-β-CD and DM-β-CD were all classical A_L type. And DM-β-CD provided the best solubility enhancement, 12.3-fold increase compared to 2.8- and 7.5-fold increase for β-CD and HP-β-CD. The apparent stability constants obtained from the solubility data at 25 °C were comparable with those obtained from the fluorescence assays. Moreover, ¹H NMR was carried out, which revealed that the IQ favorably inserted into the inner cavity from the chromone part instead of the phenyl part, which was in agreement with molecular modeling studies.     

The Effect of Dansyl-Modified β-Cyclodextrin on the Chaperone Activity of Heat Shock Proteins

The effect of dansyl modified -cyclodextrin (1)on the chaperone activity of heat shock proteins such as HSP70 and HSP90 hasbeen studied. The fluorescence intensity of 1 was decreased when HSP70 and HSP90 were added to the host solution. This phenomenon suggested that host–guest complexation was occuring. The binding constants of 1 were obtained using a 1:1 complex formation type equation by employing the guest-induced fluorescence variations. Host 1 exhibited a higher binding ability forHSP70 than for HSP90. The effects of 1 on the chaperone activity and degradation of HSP70 and HSP90 were studied by measuring the absorption of aggregation of citrate synthase (C.S.) and sodium dodecyl sulfate (SDS)polyacrylamide gel electrophoresis of trypsin degradation, respectively. Host1 can contribute to regulate C.S. aggregation andpromote trypsin degradation of HSP70 and HSP90.     

Reactivity of the anti-Criegee intermediate of β-pinene with prevalent atmospheric species

Structural Chemistry - The reaction of the anti-Criegee intermediate (anti-CI) of β-pinene with prevalent atmospheric species has been investigated using quantum-chemical calculations. The...     

Effect of substituents on the solubility and the distribution of alkyl-substituted β-diketone iron chelates

The solubilities and the distributions of nine alkyl-substituted β-diketone iron chelates were measured in a number of common organic solvents, in order to establish the effect of substituents. In synthesis of iron chelates, acetylacetone, di-isobutyrylmethane and di-pivaloylmethane chelates were available with red-orange solid, while other chelates were red-orange oil. Using the solubilities and the respective molar volumes of these solid chelates, the solubility parameter values (δ_M) were calculated. The constancy of the calculated values was taken as evidence of the adequacy of the regular solution concept for explaining the observed solubility trends in the solvents studied. The molar volumes of iron chelates were nearly 1.5 times those of corresponding copper chelates and the solubility parameter values of the former were about the same as those of the latter. In the extraction of iron chelates, the extracted species were identified to be FeA₃ (A: β-diketone anion). The extraction constants (K_ex) of iron chelates does not depend on the nature of organic solvents. The distribution coefficients (P_Fe) of iron chelates increase regularly with the increase in the number of additional carbon atoms of the alkyl chain in the chelate molecule. The relationship between the solubilities or the distribution ratios of iron chelates and those of corresponding copper chelates were discussed.     

The Effect of a Covalent and a Noncovalent Small-Molecule Inhibitor on the Structure of Abg β-Glucosidase in the Gas-Phase

The effects of binding two small-molecule inhibitors to Agrobacterium sp. strain ATCC 21400 (Abg) β-glucosidase on the conformations and stability of gas-phase ions of Abg have been investigated. Biotin-iminosugar conjugate (BIC) binds noncovalently to Abg while 2,4-dinitro-2-deoxy-2-fluoro-β-d-glucopyranoside (2FG-DNP) binds covalently with loss of DNP. In solution, Abg is a dimer. Mass spectra show predominantly dimer ions, provided care is taken to avoid dissociation of dimers in solution and dimer ions in the ion sampling interface. When excess inhibitor, either covalent or noncovalent, is added to solutions of Abg, mass spectra show peaks almost entirely from 2:2 inhibitor-enzyme dimer complexes. Tandem mass spectrometry experiments show similar dissociation channels for the apo-enzyme and 2FG-enzyme dimers. The +21 dimer produces +10 and +11 monomers. The internal energy required to dissociate the +21 2FG-enzyme to its monomers (767?±?30 eV) is about 36 eV higher than that for the apo-enzyme dimer (731?±?6 eV), reflecting the stabilization of the free enzyme dimer by the 2FG inhibitor. The primary dissociation channels for the noncovalent BIC-enzyme dimer are loss of neutral and charged BIC. The internal energy required to induce loss of BIC is 482?±?8 eV, considerably less than that required to dissociate the dimers. For a given charge state, ions of the covalent and noncovalent complexes have about 15 % and 25 % lower cross sections, respectively, compared with the apo-enzyme. Thus, binding the inhibitors causes the gas-phase protein to adopt more compact conformations. Noncovalent binding surprisingly produces the greatest change in protein ion conformation, despite the weaker inhibitor binding.

The Regulation Effect of Phosphoryl Group on Amino Acid Side Chain

The amino acids' side chains act as the relay device to modulate the chemical reactivity of the N-phosphoryl amino acids. The N-dialkyl phosphoryl cysteine is stable, but the N-dialkyl phosphoryl serine or threoine was converted into many kinds of products at 40℃. The N-dialkyl phosphoryl gltamic acid is a stable compound, while the N-dislkyl phosphoryl aspartic acid was transferred into the peptides, esters and the phosphoryl ester-exchanged products under mild conditions. The N-dialkyl phosphoryl histidine has the similar reactivity through the co-participation of the side chain, carboxyl and phosphoryl groups. A hexacoordinate phosphorus was proposed to account for this differentiation and promotion effect.     

Effect of preparation method on complexation of Cefdinir with β-cyclodextrin

The inclusion behaviour of β-cyclodextrin (βCD) was studied toward Cefdinir (CEF) in order to enhance the solubility and dissolution rate, following cyclodextrin complexation. Drug cyclodextrin solid systems were prepared by conventional methods of kneading (KN), co-evaporation (CE), spray drying (SD) and with a novel approach of microwave irradiation (MWI). The formation of inclusion complexes with βCD in the solid state, were confirmed by Differential scanning calorimetry (DSC), Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) studies, and comparative studies on the in vitro dissolution of CEF were carried out. Characterization of binary system by DSC, FTIR and SEM indicated that SD and MWI method resulted in formation of true complexes. Binary systems showed significant increase in dissolution rate as compared to plain drug. Amongst the binary systems MWI products were prepared in least time with better yield and highest dissolution rate.     

Comparative Study on the Effect of NaBr on the Interaction Between Alkyltrimethylammonium Bromide and β-Cyclodextrin

The effect of NaBr on the interaction between alkyltrimethylammonium bromide (CnTAB (n = 14 for TTAB and 16 for CTAB)) and ß-CD was studied by surface tension method. The first decrease in the γ_cmc of TTAB/ß-CD in the presence of NaBr mainly due to the elongated effective chain length of the hydrophobic part of the TTAB/ß-CD complexes; while the increase in the γ_cmc of both of the TTAB/ß-CD and CTAB/ß-CD in the presence of NaBr could be attributed to the close pack of CnTAB at the air/water interface.     

Effect of the Charge and the Nature of Both Cations and Anions on the Solubility of Zwitterionic Amino Acids,Measurements and Modeling

The effect of the charge and the nature of both the cations and the anions of some electrolytic salts: sodium fluoride (NaF), potassium fluoride (KF), sodium bromide (NaBr), potassium bromide (KBr), sodium iodide (NaI), potassium iodide (KI), sodium sulfate (Na₂SO₄), potassium sulfate (K₂SO₄), calcium chloride (CaCl₂), and barium chloride (BaCl₂), on the solubility of zwitterionic amino acids (glycine, DL-alanine, DL-valine, and DL-serine) in aqueous solutions at 298.15 K are studied and discussed. A salting-in effect is observed for all amino acids under investigation with all electrolytes used in the present study, except for DL-alanine and DL-valine in aqueous solutions containing sodium fluoride where a salting-out effect was observed. The orders of the effect of the nature and the charge of both the anions and the cations are: F^- < Cl^- < Br^- < I^- < NO₃^- < SO₄^2-\mathrm{F}^{-}<{}\mathrm{Cl}^{-}<{}\mathrm{Br}^{-}<{}\mathrm{I}^{-}<\mathrm{NO}_{3}^{-}<{}\mathrm{SO}_{4}^{2-} with both sodium and potassium cations; Na⁺<K⁺<Ca²⁺<Ba²⁺ with chloride anion.     

The Influence of β-Ammonium Substitution on the Reaction Kinetics of Aminooxy Condensations with Aldehydes and Ketones

The click-chemistry capture of volatile aldehydes and ketones by ammonium aminooxy compounds has proven to be an efficient means of analyzing the carbonyl subset in complex mixtures, such as exhaled breath or environmental air. In this work, we examine the carbonyl condensation reaction kinetics of three aminooxy compounds with varying β-ammonium ion substitution using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). We determined the activation energies for the reactions of the aminooxy compounds ATM, ADMH and AMAH with a panel of ketones and aldehydes that included acrolein and crotonaldehyde. The measurements indicate that the activation energies for the oximation reactions are quite low, less than 75 kJ mol⁻¹. ADMH is observed to react the fastest with the carbonyls studied. We postulate this result may be attributed to the ADMH ammonium proton effecting a Brønsted-Lowry acid-catalyzed elimination of water during the rate-determining step of oxime ether formation. A theoretical study of oxime ether formation is presented to explain the enhanced reactivity of ADMH relative to the tetraalkylammonium analog ATM.     

Study on the Supramolecular Interaction of β-Cyclodextrin with Gemfibrozil by Spectrofluorimetry and Its Analytical Application

The supramolecular interaction of gemfibrozil with β-cyclodextrin （β-CD） was studied by spectrofluorimetry. The mechanism of the inclusion was discussed by spectrofluoremetry, infrared spectrum and ^1H NMR spectrum. The results showed that a 1 ： 1 （β-CD ： gemfibrozil） complex was formed with an apparent association constant of 3.844 × 10^3 L·mol^-1. Based on the enhancement of the fluorescent intensity of gemfibrozil, a spectrofluorimetric method for the determination of gemfibrozil in bulk aqueous solution in the presence of β-CD was developed. The linear range was 3.30 ng·mL^- 1 -6.00 ug·mL^-1 with the detection limit of 0.980 ng·mL^-1. There was no interference from the excipients normally used in tablet composition and the serum main compositions. The proposed method was then successfully applied to the determination of gemfibrozil in capsules and serum.     

Effect of the Composition of the Aqueous Organic Solvent on the Kinetics of N-Acylation of α-Amino Acids with 4-Nitrophenyl 4-Nitrobenzoate

Equations relating the N-acylation rate constants of glycine, L--alanine, DL-threonine, and L-proline with 4-nitrophenyl 4-nitrobenzoate in water-acetonitrile, water-2-propanol, and water-2-methyl-2-propanol solvents to the composition of the medium were obtained, and reaction rate constants in water were calculated.     

Effect of Temperature on the Solubility of Short-Chain Carboxylic Acids in Water

The aqueous solubilities of pentanoic and hexanoic acids were measured between 298.15 and 333.15 K at intervals of 5.00 K. Nonlinear dependences were found for the variation of solubility with temperature. The temperature dependences of the solubility of the acids in water are described by nonlinear van’t Hoff plots. Experimental data were fitted by the method of least-squares to a second-order polynomial equation, which was then used to determine the differential solution enthalpies at selected temperatures. The values for the apparent Gibbs energy and the apparent entropy of solution are calculated.     

Effect of the Allyl Group in Reactions of Allyl Alcohol and Its Derivatives with ε-Caprolactam

Unlike saturated alcohols, allyl alcohol reacts with -caprolactam under considerably milder conditions. Allyl esters react with -caprolactam to give the corresponding allyl -acylaminocaproates. The yield of the latter decreases in going from formyl to acetyl and propionyl derivatives. The observed effect of the allyl group is explained in terms of possible allylic rearrangement in the transition state.     

Effect of urea on the β-hairpin conformational ensemble and protein denaturation mechanism

Despite the daily use of urea to influence protein folding and stability, the molecular mechanism with which urea acts is still not well understood. Here the use of combined parallel tempering and metadynamics simulation allows us to study the free-energy landscape associated with the folding/unfolding of β-hairpin GB1 equilibrium in 8 M urea and pure water. The nature of the unfolded state in both solutions has been analyzed: in urea solution the addition of denaturants acts to expand the denatured state, while in pure water solution the unfolded state is noticeably more compact. For what concerns the mechanism by which urea acts as a denaturant, a preferential direct interaction between urea molecules and protein backbone has been found. However, the bias toward urea solvation is largest at intermediate values of the gyration radius.     

Green Procedure for the Synthesis of β-Nitro Sulfides by Michael Addition of Thiols to Nitroolefins

Michael addition of thiols to nitroolefins was carried out in water at room temperature without any catalyst, and β-nitro sulfides were obtained in excellent yields. This is the first example of Michael addition of thiols to nitroolefins in water without use of any catalyst. It provides a highly efficient, general, and practical green route to synthesis of β-nitro sulfides. Twenty-four new β-nitro sulfides were synthesized using this technique.