Heterogeneous interaction between zwitterions of some l-α-amino acids and ethanol molecule in water at 298.15 K

Dissolution enthalpies of l-α-aminobutyric acid, l-α-isoleucine, l-α-serine, l-α-threonine and l-α-cysteine in water and aqueous ethanol solutions have been measured by calorimetry at a temperature of 298.15 K. The obtained results were used to calculate the enthalpic heterogeneous pair interaction coefficients between zwitterions of amino acids and a molecule of ethanol in water. These values were interpreted in the terms of the hydrophobic or hydrophilic effects of the side chains of amino acids on their interactions with a polar molecule of ethanol in water.     

Simultaneous analysis of citrulline and arginine in serum and tissue

We developed a method for simultaneously determining l-citrulline and l-arginine levels in serum and tissue samples using RP-HPLC with ultraviolet (UV) detection. The serum was deproteinized by trichloroacetic acid and heat; the tissue was homogenized by trichloroacetic acid and deproteinized as the same as serum. Phenyl-isothiocyanate (PITC) solution was used as derivatization reagent and a gradient elution was carried out. The linearity for l-arginine and l-citrulline ranged from 0 to at least 1000 μmol/L. R² values were above 0.9999 for both. LODs for l-arginine and l-citrulline were 0.0462 μmol/L and 0.0195 μmol/L, respectively, while LOQs were 0.530 μmol/L and 0.417 μmol/L, respectively. Intra- and inter-day CVs were less than 3.5% and 7.5% in serum, respectively. The average recovery was from 85.5% to 116.5% in serum. Intra-assay CVs were 3.8% and 10.3%, and inter-assay CVs were 13.7% and 10.7% for l-arginine and l-citrulline respectively in tissue. The average recovery was from 92.8% to 113.5% in tissue. This is a reliable and convenient analytical method which is suitable for most clinical laboratories.     

Simultaneous reactive extraction separation of amino acids from water with D2EHPA in hollow fiber contactors

Reactive extraction separation of binary amino acids from water using a microporous hollow fiber has been studied, in which the acidic extractant di(2-ethylhexyl)phosphoric acid (D2EHPA) was selected as an active carrier dissolved in kerosene. l-Phenylalanine (Phe) was extracted from an aqueous solution through the shell side of module to the organic phase through the lumen of fiber in the extraction module, in which l-Phe was then back-extracted to stripping phase in stripping module. Experiments were conducted as a function of the initial feed concentration of equimolar Phe and l-aspartic acid (l-Asp) (5 mol/m³), feed pH (3–5), the carrier concentration (0.1–0.5 mol/dm³), and stripping acidity (0.1–2 mol/dm³). The effect of process variables on the separation factor of Phe/Asp and the possible transport resistances including aqueous-layer diffusion, membrane diffusion, organic-layer, and interfacial chemical reaction were quantitatively studied and discussed. The high separation factor (β) of Phe/Asp was obtained to be 18.5 at feed pH 5 and 2 mol/dm³ of strip solution (HCl). The extraction and stripping processes appear to rely on pH dependence of the distribution coefficient of amino acids in reactive extraction system. The separation factor (β) was enhanced in hollow fiber membrane (HFM) process compared with conventional solvent process, which was a result of the counter transport of hydrogen ions.     

A new and short synthesis of naturally occurring 1-deoxy-l-gulonojirimycin from tri-O-benzyl-d-glucal

A new and short synthesis of naturally occurring 1-deoxy-l-gulonojirimycin from tri-O-benzyl-d-glucal, via a regioselective intramolecular cyclization of an amino triol intermediate, is described. Its absolute configuration was deduced from the single crystal X-ray analysis of compound 11.     

New low-molecular weight gelators based on l-valine and l-isoleucine with various terminal groups

New low-molecular weight gelators based on l-valine and l-isoleucine, which have various terminal groups such as ester, carboxyl, and carboxylate, function as a good organogelator that form an organogel in many organic solvents. In addition, the sodium salt compounds form not only organogels but also a hydrogel in the presence of a cationic surfactant.     

Host-guest interaction of L-tyrosine with beta-cyclodextrin

The inclusion complexes of beta-cyclodextrin (beta-CD) with l-tyrosine (l-TYN) were investigated by using spectrophotometers. The absorption and fluorescence enhancement occurs with beta-CD and l-TYN forms 1:1 inclusion complex. The unusual blue shift of hydroxyl ion in the beta-CD medium confirms OH groups present in the interior part of the beta-CD cavity and -COOH group present in the upper part of the beta-CD cavity. A mechanism is proposed to explain inclusion process. The inclusion interaction was examined and the thermodynamic parameters of inclusion process DeltaG, DeltaH and DeltaS were determined. The results indicated that the inclusion process was an exergonic and spontaneous process. Stable solid inclusion complexes were established and characterized by FT-IR, scanning electron microscope (SEM) methods.     

DNA binding and oxidative cleavage activity of ternary (l-proline)copper(II) complexes of heterocyclic bases

Ternary copper(II) complexes [Cu(l-pro)(B)(H₂O)](NO₃) (1, 2) where l-pro = l-proline, B is a N,N-donor heterocyclic base, viz. 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), are synthesized, characterized, and their DNA binding and cleavage activity studied. The bpy complex (1) is structurally characterized by single-crystal X-ray crystallography. The complexes show the presence of a distorted square-pyramidal (4 + 1) CuN₃O₂ coordination geometry. Complex [Cu(l-pro)(bpy)(H₂O)](NO₃) (1) crystallizes in the triclinic space group P1 with unit cell parameters: a = 7.082(3) Å, b = 10.483(5) Å, c = 11.581(5) Å, α = 89.700(7)°, β = 83.488(8)°, γ = 84.109(8)° and V = 849.7(7) Å³. The one-electron paramagnetic complexes display a d–d band near 600 nm in water and show a cyclic voltammetric response due to Cu(II)/Cu(I) couple near 0.1 V (versus SCE) in Tris–HCl buffer–0.1 M KCl. Binding interactions of the complexes with calf thymus (CT) DNA have been investigated by emission, absorption, viscosity and DNA thermal denaturation studies. The phen complex displays significant binding propensity to the CT DNA giving an order: 2 (phen)  1 (bpy). The bpy complex does not show any apparent binding to the DNA and hence poor cleavage efficiency. Complex 2 shows efficient oxidative cleavage of SC-DNA in the presence of 3-mercaptopropionic acid (MPA) involving hydroxyl radical species as evidenced from the control data showing inhibition of DNA cleavage in the presence of DMSO and catalase.     

Racemization behavior of l,l-lactide during heating

To control the depolymerization process of poly(l-lactic acid) into l,l-lactide for feedstock recycling, the racemization of l,l-lactide as a post-depolymerization reaction was investigated. In the absence of a catalyst, the conversion to meso-lactide increased with increase in the heating temperature and time at a higher rate than the conversion into oligomers. The resulting high composition of meso-lactide suggests that the direct racemization of l,l-lactide had occurred in addition to the known racemization mechanism that occurs on the oligomer chains. In the presence of MgO, the oligomerization rapidly proceeded to reach an equilibrium state between monomers and oligomers. The equilibrium among l,l-, meso-, and d,d-lactides was found to be a convergent composition ratio l,l-:meso-:d,d-lactides = 1:1.22:0.99 (wt/wt/wt) after 120 min at 300 °C. This composition ratio also indicates that in addition to the known racemization reaction on the oligomer chains, direct racemization among the lactides is also a frequent occurrence.     

Improving mechanical and biological properties of macroporous HA scaffolds through composite coatings

Interconnected porous hydroxyapatite (HA) scaffolds are widely used for bone repair and replacement, owing to their ability to support the adhesion, transfer, proliferation and differentiation of cells. In the present study, the polymer impregnation approach was adopted to produce porous HA scaffolds with three-dimensional (3D) porous structures. These scaffolds have an advantage of highly interconnected porosity (≈85%) but a drawback of poor mechanical strength. Therefore, the as-prepared HA scaffolds were lined with composite polymer coatings in order to improve the mechanical properties and retain its good bioactivity and biocompatibility at the same time. The composite coatings were based on poly(d,l-lactide) (PDLLA) polymer solutions, and contained single component or combination of HA, calcium sulfate (CS) and chondroitin sulfate (ChS) powders. The effects of composite coatings on scaffold porosity, microstructure, mechanical property, in vitro mineralizing behavior, and cell attachment of the resultant scaffolds were investigated. The results showed that the scaffolds with composite coatings resulted in significant improvement in both mechanical and biological properties while retaining the 3D interconnected porous structure. The in vitro mineralizing behaviors were mainly related to the compositions of CS and ChS powders in the composite coatings. Excellent cell attachments were observed on the pure HA scaffold as well as the three types of composite scaffolds. These composite scaffolds with improved mechanical properties and bioactivities are promising bone substitutes in tissue engineering fields.     

Separation and determination of l-tyrosine and its metabolites by capillary zone electrophoresis with a wall-jet amperometric detection

A method of capillary electrophoresis with wall-jet amperometric detection (AD) has been developed for separation and determination of l-tyrosine (Tyr) and its metabolites, such as Tyramine (TA), p-hydroxyphenylpyruvic (pHPP), homogentisic acid (HGA) and some dipeptides containing Tyr, such as Tyr-Gly-Gly (YGG), Tyr-Arg (YR) and Tyr-d-Arg (Y-d-R). A carbon disk electrode was used as the working electrode and the optimal detection potential was 1.00 V (versus Ag/AgCl). At 18 kV of applied voltage, the seven compounds were completely separated within 20 min in 110 × 10⁻³ mol/L Na₂HPO₄–NaH₂PO₄ buffer (pH 7.10) containing 3 × 10⁻³ mol/L β-cyclodextrin (β-CD). Good linear relationship was obtained for all analytes and the detection limits of seven analytes were in the range of 0.95–4.25 ng/mL. The proposed method has been applied to examine the metabolic process of l-tyrosine in rabbit's urine.     

An efficient synthesis of l-allono-1,4-lactone from 2,3:5,6-di-O-isopropylidene-d-mannono-1,4-lactone

We reported herein an efficient synthesis of l-allono-1,4-lactone from 2,3:5,6-di-O-isopropylidene-d-mannono-1,4-lactone in five steps. The key feature of this method involved a one-pot, ‘double inversion’ procedure at the stereocenters of C-4 and C-5 of d-mannono-1,4-lactone to afford the target molecule.     

One-pot inversion of d-mannono-1,4-lactone for the practical synthesis of l-ribose

l-Ribose was synthesized in a concise manner from d-mannono-1,4-lactone using one-pot inversion conditions. Treatment of d-mannono-1,4-lactone with piperidine, followed by mesylation-induced S_N2-type O-alkylation, afforded the desired one-pot inversion in an optimum yield, and the following straightforward transformations provided l-ribose in good yields.     

Determination of L- and D-enantiomers of methotrexate using amperometric biosensors

In order to determine the enantiopurity of methotrexate (Mtx), seven biosensors were proposed for the assay of l-Mtx and three biosensors for the assay of d-Mtx. The biosensors were designed using physical and chemical immobilization of glutamate oxidase and/or l-amino acid oxidase (l-AAOD) and/or horseradish peroxidase (HRP) for the assay of l-methotherexate, and d-amino acid oxidase (d-AAOD) and HRP for the assay of d-Mtx. Electrode characteristics were obtained and compared for the different carbon paste based biosensors. The linear concentration ranges for the proposed biosensors were in the ranges of fmol l⁻¹ to pmol l⁻¹, magnitude order with limits of detection in the fmol l⁻¹ to nmol l⁻¹ concentration range. All biosensors were successful for the determination of the enantiopurity of Mtx as raw material, and in its pharmaceutical formulations (tablets and injections).     

A highly efficient synthesis of unnatural l-sugars from d-ribose

A preparative and short synthesis of l-ribose and l-apiose was accomplished starting from d-ribose via stereoselective cis-dihydroxylation and C2-hydroxymethylation, respectively. These l-sugars can serve as versatile intermediates for the synthesis of l-nucleosides.     

Concise and practical synthesis of (2S,3R,4R,5R) and (2S,3R,4R,5S)-1,6-dideoxy-1,6-iminosugars

The syntheses of (2S,3R,4R,5R) and (2S,3R,4R,5S)-1,6-dideoxy-1,6 iminosugars 1a and 1b, respectively, from d-glucose are described. The key transformations in this reaction sequence include regio-selective epoxide ring opening with N-benzylamine followed by intramolecular reductive amination of amino-aldehyde.     

Degradation behaviors of polyester monolayers at the air/water interface: Alkaline and enzymatic degradations

The degradation kinetics of Langmuir monolayer films of a series of biodegradable polyesters has been studied to investigate the effect of degradation medium, alkalinity and enzymes. The degradation behavior of polyester monolayers strongly depended on both degradation medium and surface pressure. As the surface pressure was increased, the degradation rates of poly(l-lactide) (PLLA) and poly[(R)-3-hydroxybutyrate] (P(3HB)) increased in both degradation media. When monolayers were exposed to an alkaline subphase, the degradation of PLLA monolayers occurred at relatively low surface pressures; the PLLA monolayers were hydrolyzed at pH 10.5 regardless of surface pressure, while the alkaline degradation of P(3HB) monolayer occurred over a constant surface pressure of 7 mN/m at pH 11.8. These results have been explained by the difference in hydrophilic/hydrophobic balance of the polymers; PLLA is more hydrophilic than P(3HB). In contrast, the enzymatic degradations of both polymer monolayers occurred at higher constant surface pressures than those of the alkaline treatment; 7 mN/m for PLLA and 10 mN/m for P(3HB). This behavior was attributed to the enzymes being much larger than the alkaline ions: the enzymes need a larger contact area with the submerged monolayers to be activated.     

Synthesis of novel N-methylated thiazole-based cyclic octa- and dodecapeptides

Novel N-methylated valine-thiazole cyclic octa- and dodecapeptides are produced by cyclooligomerisation of a N-methylated-l-valine thiazole amino acid HCl in the presence of pentafluorophenyl diphenylphosphinate (FDPP).     

Direct electrochemistry behavior of cytochrome c/L-cysteine modified electrode and its electrocatalytic oxidation to nitric oxide

Cytochrome c (Cyt c) was successfully immobilized on L-cysteine modified gold electrode by multicyclic voltammetry method. The electrochemical behavior of Cyt c on the L-cysteine modified electrode was explored. In 0.10 M, pH 7.0 phosphate buffer solution (PBS), Cyt c showed a quasi-reversible electrochemical redox behavior with E(pc)=0.180 V, E(pa)=0.208 V (versus Ag/AgCl). The Cyt c/L-cysteine modified electrode gave an excellent electrocatalytic activity towards the oxidation of nitric oxide, and the catalysis currents were proportional to the nitric oxide concentration in the range of 7.0 x 10(-7) to 1.0 x 10(-5) M, the linear regression equation is I (microA)=-0.124-0.003 C(NO) (microM), with a correlation coefficient 0.996, The detection limit was 3.0 x 10(-7) M (times the ratio of signal to noise, S/N=3).