Effect of pH on the Binding of Sodium,Lysine, and Arginine Counterions to <Emphasis Type="SmallCaps">l</Emphasis>-Undecyl Leucinate Micelles

Micelle formation by the amino acid-based surfactant undecylenyl l-leucine was investigated as a function of solution pH with NMR, dynamic light scattering, and fluorescence spectroscopy. NMR and dynamic light scattering showed that 50 mM undecylenyl l-leucine and 50 mM NaHCO₃ solutions contained micelles approximately 20 Å in diameter and that micelle radius and the mole fraction of surfactant molecules associated with micelles changed very little with solution pH. The binding of the amino acids arginine and lysine to the anionic micelles was also investigated from pH 7.0 to 11.5. Below pH 9.0, the mole fraction of arginine cations bound to the micelles was approximately 0.4. Above pH 9.0, the arginine counterions became zwitterionic, and the mole fraction of bound arginine molecules decreased steadily to less than 0.1 at pH 11. When arginine dissociated from the micelles, their radii decreased from 14 to 10 Å. Similar behavior was observed with lysine; however, when lysine dissociated from the micelle surface, little change in micelle radius was observed. Two-dimensional NMR experiments suggested that below pH 9.0, l-arginine bound perpendicular to the micelle surface primarily though its side chain amine while l-lysine bound parallel to the surface through both of its amine functional groups. Finally, the rate at which the amide protons on the surfactant headgoup exchanged with solvent was investigated with NMR spectroscopy. The exchange reaction was faster in solutions containing only surfactant monomers and slower when the surfactants were in micellar form and the headgoup amide protons were less exposed to solvent.     

Effect of Amino Acids and Glycyl Dipeptides on Micellization of Antibacterial Drug Domiphen Bromide

The effects of amino acids (glycine, l-alanine, l-valine, l-leucine) and glycyl dipeptides (glycylglycine, glycyl-l-valine, glycyl-l-leucine) on the micellization behaviour of antibacterial drug domiphen bromide in aqueous solution as a function of temperature were studied by both conductivity and fluorescence spectroscopy. Critical micellar concentration, degree of counterion dissociation (α), limiting molar conductivity (Λ ₀), and a series of thermodynamic parameters of micellization of domiphen bromide have been calculated from the specific conductivity data. The I ₁/I ₃ ratios associated with pyrene fluorescence vibronic bands were used to interpret the variation of micropolarity caused by the interactions between domiphen bromide and amino acids/glycyl dipeptides. The mean aggregation number of domiphen bromide was determined by a fluorescence quenching method. Effects of temperature, concentration, and alkyl chain length of the amino acids/glycyl dipeptides on the above properties were examined. Amino acids and glycyl dipeptides effectively enhance the surface activity of domiphen bromide solution. The intensity of amino acid/dipeptide-domiphen bromide interaction increased with the hydrophobicity of the amino acid/glycyl dipeptide.     

Ring-opening polymerization of <Emphasis Type="SmallCaps">l</Emphasis>-lactide catalyzed by a novel molybdenum-based catalytic system

As a transparent material that can be completely biodegradable, poly(l-lactide) (PL-LA) has recently received considerable attention. In this study, it our first efforts to fabricate l-lactide (L-LA) by a novel molybdenum-based catalytic system consisting of molybdenum pentachloride (MoCl₅) as the main catalyst and m-cresol substituted alkyl aluminum Al(OPhCH₃)(i-Bu)₂ as the co-catalyst. The effects of different types of phosphorus ligands, Al:Mo molar ratios, catalyst contents,catalyst components (separate catalysis of m-cresol aluminum and cocatalysis of Al/Mo system) and polymerization temperature were investigated. The T_g and T_m of the resulting poly(l-lactide) (PL-LA) were characterized by differential scanning calorimetry (DSC), and the molecular weight and molecular weight distribution were determined by gel permeation chromatography (GPC). The GPC results showed that the molecular weight of the PL-LA was higher than that 10⁴ g/mol and the molecular weight distribution was narrow. The structures of PL-LA was detected by ¹H NMR spectroscopy (¹H NMR) and X-ray diffraction (XRD) validation, which demonstrated that a moalr ratio of Mo/Al/l-lactide?=?1:30:1000 showed the higher conversion rate and molecular weight. In comparison to the separate catalysis of m-cresol aluminum, the molecular weight of PL-LA prepared by the cocatalysis of Al/Mo system was slightly improved, and the molecular chains were relatively regular and the crystallinity was higher.     

One-Pot Preparation of <Emphasis Type="SmallCaps">d</Emphasis>-Amino Acids Through Biocatalytic Deracemization Using Alanine Dehydrogenase and ω-Transaminase

d-Amino acids are pharmaceutically important building blocks, leading to a great deal of research efforts to develop cost-effective synthetic methods. Preparation of d-amino acids by deracemization has been conceptually attractive owing to facile synthesis of racemic amino acids by Strecker synthesis. Here, we demonstrated biocatalytic deracemization of aliphatic amino acids into d-enantiomers by running cascade reactions; (1) stereoinversion of l-amino acid to a d-form by amino acid dehydrogenase and ω-transaminase and (2) regeneration of NAD⁺ by NADH oxidase. Under the cascade reaction conditions containing 100 mM isopropylamine and 1 mM NAD⁺, complete deracemization of 100 mM dl-alanine was achieved after 24 h with 95% reaction yield of d-alanine (>?99% ee^D, 52% isolation yield).

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Driving Transamination Irreversible by Decomposing Byproduct α-Ketoglutarate into Ethylene Using Ethylene-Forming Enzyme

The transformations of transaminases have been extensively studied as an approach to the production of chiral amino moieties. However, the low equilibrium conversion of the reaction is a critical disadvantage to transaminase application, and a strategy for shifting the reaction equilibrium is essential. Herein, we have developed a novel method to effectively prevent the reversibility of transamination by fully decomposing byproduct α-ketoglutarate into ethylene and carbon dioxide in situ using ethylene-forming enzyme (EFE). Two transaminases and one EFE were expressed in E. coli and purified to be used in the cascade reaction. After optimal reaction conditions were determined based on the enzymatic properties, a cascade reaction coupling transaminase with EFE was conducted and showed high efficiency in the synthesis of l-phosphinothricin. Finally, using this approach with only an equivalent amount of amino donor l-glutamate increased the conversions of various keto acids from <?60% to >?99%. This strategy shows great potential for transamination using glutamate as the amino donor.

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Transcriptome and Gene Ontology (GO) Enrichment Analysis Reveals Genes Involved in Biotin Metabolism That Affect l-Lysine Production in Corynebacterium glutamicum

Corynebacterium glutamicum is widely used for amino acid production. In the present study, 543 genes showed a significant change in their mRNA expression levels in l-lysine-producing C. glutamicum ATCC21300 than that in the wild-type C. glutamicum ATCC13032. Among these 543 differentially expressed genes (DEGs), 28 genes were up- or downregulated. In addition, 454 DEGs were functionally enriched and categorized based on BLAST sequence homologies and gene ontology (GO) annotations using the Blast2GO software. Interestingly, NCgl0071 (bioB, encoding biotin synthase) was expressed at levels ~20-fold higher in the l-lysine-producing ATCC21300 strain than that in the wild-type ATCC13032 strain. Five other genes involved in biotin metabolism or transport—NCgl2515 (bioA, encoding adenosylmethionine-8-amino-7-oxononanoate aminotransferase), NCgl2516 (bioD, encoding dithiobiotin synthetase), NCgl1883, NCgl1884, and NCgl1885—were also expressed at significantly higher levels in the l-lysine-producing ATCC21300 strain than that in the wild-type ATCC13032 strain, which we determined using both next-generation RNA sequencing and quantitative real-time PCR analysis. When we disrupted the bioB gene in C. glutamicum ATCC21300, l-lysine production decreased by approximately 76%, and the three genes involved in biotin transport (NCgl1883, NCgl1884, and NCgl1885) were significantly downregulated. These results will be helpful to improve our understanding of C. glutamicum for industrial amino acid production.     

Synthesis and Properties of Alkyl <Emphasis Type="Italic">β</Emphasis>-<Emphasis Type="SmallCaps">d</Emphasis>-Galactopyranoside

A series of alkyl β-d-galactopyranosides were prepared by the trichloroacetimidate method with d-galactose and alcohols with different chain lengths as raw materials. Their solubility, surface tension, emulsification, foaming, wettability, thermotropic liquid crystalline properties, and thermal stability were investigated. Alkyl β-d-galactopyranosides are soluble in water and ethanol, and the solubility decreases with increasing alkyl chain length. Decyl β-d-galactopyranoside was insoluble in water, but soluble in ethanol. Dissolution of alkyl β-d-galactopyranoside in water is an endothermic process with dissolution enthalpies greater than zero. Nonyl β-d-galactopyranoside had an excellent emulsifying property, better foaming ability and the best foam stability. The CMC values of alkyl β-d-galactopyranosides decrease with increasing of alkyl chain length. Alkyl β-d-galactopyranosides are thermally stable up to 270 °C. Alkyl β-d-galactopyranosides show the distinctive optical texture of a thermotropic liquid crystal smectic A type phase. Decyl β-d-galactopyranoside showed the strongest wettability.     

Profiling influences of gene overexpression on heterologous resveratrol production in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Metabolic engineering of heterologous resveratrol production in Saccharomyces cerevisiae faces challenges as the precursor l-tyrosine is stringently regulated by a complex biosynthetic system. We overexpressed the main gene targets in the upstream pathways to investigate their influences on the downstream resveratrol production. Single-gene overexpression and DNA assembly-directed multigene overexpression affect the production of resveratrol as well as its precursor p-coumaric acid. Finally, the collaboration of selected gene targets leads to an optimal resveratrol production of 66.14±3.74 mg·L^–1, 2.27 times higher than the initial production in YPD medium (4% glucose). The newly discovered gene targets TRP1 expressing phosphoribosylanthranilate isomerase, ARO3 expressing 3-deoxy-d-arabino-heptulosonate-7-phosphate synthase, and 4CL expressing 4-coumaryl-CoA ligase show notable positive impacts on resveratrol production in S. cerevisiae.

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Preparation and properties of alumina foams via thermally induced foaming of molten <Emphasis Type="SmallCaps">d</Emphasis>-glucose monohydrate

Alumina foams with porosity of 92.6–94.4 % were obtained by thermally induced foaming of powder dispersions in molten d-glucose monohydrate. Effects of alumina to d-glucose monohydrate weight ratio on the preparation and properties of the alumina foams were investigated. The bubbles generated in molten d-glucose monohydrate were stabilized by alumina particles adsorbed at the gas–liquid interface and the increase in viscosity of the dispersions. The foam rise decreased with the increase in alumina to d-glucose monohydrate weight ratio up to 1.2 and then slightly increased. The alumina foams showed cellular microstructure and the cells had a near spherical morphology. Increasing alumina to d-glucose monohydrate weight ratio widened the cell and window size distribution. The density and compressive strength of the alumina foam showed a maximum at alumina to d-glucose monohydrate weight ratio of 1.2. The corresponding maximum density and compressive strength were 0.293 g/cc and 1.14 MPa, respectively.     

Immobilized iron Schiff base histidine complexes on Al-MCM-41 and zeolite Y as catalyst for oxidation of cycloalkanes

Iron complexes of N-salicylidene-l-histidine with or without bipyridine ligand immobilized on Al-MCM-41 and zeolite Y designated as Fe(sal-l-his)(bipy)complex/Al-MCM-41 or Fe(sal-l-his)complex/Al-MCM-41 and Fe(sal-l-his)(bpy)complex/Y or Fe(sal-l-his)complex/Y respectively, were prepared and characterized by X-ray powder diffraction (XRD), FT-IR, N₂ adsorption/desorption and chemical analysis techniques. Fe(sal-l-his)/Al-MCM-41 and Fe(sal-l-his)(bipy)complex/Al-MCM-41 were found to successfully catalyze the oxidation of cyclohexane, methyl cyclohexane, cyclooctane and adamantane with H₂O₂. The oxidation results and promising catalytic behavior of Fe(sal-l-his)(bipy)complex/Al-MCM-41 for oxidation of cyclooctane with 90 % conversion and excellent selectivity toward the formation of cyclooctanone will be discussed in this presentation.     

<Emphasis Type="SmallCaps">d</Emphasis>-Pinitol in Fabaceae: an Oviposition Stimulant for the Common Grass Yellow Butterfly, <Emphasis Type="Italic">Eurema mandarina</Emphasis>

The common grass yellow butterfly, Eurema mandarina (formerly Eurema hecabe mandarina) (Lepidoptera, Pieridae), recently has been separated taxonomically from a subtropical population of Eurema hecabe in Japan. This species is widely distributed in the temperate region of Japan, and feeds mainly on various ligneous plants within the Fabaceae. We attempted to identify an oviposition stimulant for E. mandarina from its primary hosts, Albizia julibrissin and Lespedeza cuneata. In both hosts, crude extract and an aqueous fraction elicited oviposition responses from gravid females. A polar subfraction of the aqueous fraction also stimulated high oviposition-stimulatory activity, comparable to the original aqueous fraction, suggesting that E. mandarina females use water-soluble compounds for host recognition. Subsequent activity-directed fractionation by ion exchange chromatography indicated that one of the key substances was contained in the neutral/amphoteric fraction. Chemical analyses revealed that the active fractions of both hosts contained d-(+)-pinitol as the major component. We examined female responses to authentic d-pinitol and found that it induced oviposition responses at concentrations greater than 0.1 %. Since this cyclitol is omnipresent in Fabaceae, we conclude that d-pinitol plays a role in mediating oviposition of E. mandarina on fabaceous plants.     

Production of polycaprolactone–polyethylene glycol–sodium alginate biocomposites for spray drying encapsulation of <Emphasis Type="SmallCaps">l</Emphasis>-ascorbic acid

l-Ascorbic acid was encapsulated in biopolymers to enhance (1) its encapsulation efficiency and (2) drug release ratio using different pH media. To achieve this goal, we used polycaprolactone (PCL), polyethylene glycol (PEG), and sodium alginate (SA) to prepare drug delivery system and spray dryer as our tool to obtain microspheres. In this manner, the importance of the study was to produce a stable and effective drug encapsulation system by PCL–PEG–SA polymer mixture by spray dryer. First we evaluated the effects of drying conditions and composition on the microencapsulation formulation and in the next stage the most uniformly distributed particles were selected and l-ascorbic acid was loaded. After that, drug encapsulation and drug release studies were performed. Drug release experiments were conducted at different pH solutions (pH 2.5, 7.4, and 9.6). Finally, drug release kinetics was determined by widely used equations to describe the degradation kinetics; zero-order, first-order, Higuchi, Hixson–Crowell, and Korsmeyer–Peppas. Furthermore, l-ascorbic acid release mechanism from microspheres was also determined. The release profiles of three microspheres obeyed the earlier developed kinetic models for performing possible release mechanisms. The Korsmeyer–Peppas model best described each release scenario.     

Synthesis of lactate (LA)-based poly(ester-urethane) using hydroxyl-terminated LA-based oligomers from a microbial secretion system

D-Lactate (LA)-based oligomers (D-LAOs), consisting of D-LA and D-3-hydroxybutyrate (D-3HB), are biobased compounds which are produced and spontaneously secreted by recombinant Escherichia coli. By supplementing the bacterial cultivation with diethylene glycol (DEG), the oligomers featuring hydroxyl groups at both ends of their structures, the D-LAOs-DEG, can be efficiently biosynthesized. In the present work, we attempted to verify the feasibility of D-LAOs-DEG as building blocks to be assembled into LA-based poly(ester-urethane) via polyaddition reaction with diisocyanate. The polymeric products were demonstrated by SEC and the urethane bound formation in the polymer was determined by FT-IR analysis, indicating that the polymerization was successfully performed. These results suggested that the one-step biosynthesized D-LAOs-DEG are potential substrates for the synthesis of LA-based poly(ester-urethane) and can be further applied to the synthesis of other LA copolymers.     

Asymmetric Dimethylarginine in Chronic Obstructive Pulmonary Disease (ADMA in COPD)

l-Arginine metabolism including the nitric oxide (NO) synthase and arginase pathways is important in the maintenance of airways function. We have previously reported that accumulation of asymmetric dimethylarginine (ADMA) in airways, resulting in changes in l-arginine metabolism, contributes to airways obstruction in asthma and cystic fibrosis. Herein, we assessed l-arginine metabolism in airways of patients with chronic obstructive pulmonary disease (COPD). Lung function testing, measurement of fractional exhaled NO (FeNO) and sputum NO metabolites, as well as quantification of l-arginine metabolites (l-arginine, l-ornithine, l-citrulline, ADMA and symmetric dimethylarginine) using liquid chromatography-mass spectrometry (LC-MS) were performed. Concentrations of l-ornithine, the product of arginase activity, correlated directly with l-arginine and ADMA sputum concentrations. FeNO correlated directly with pre- and post-bronchodilator forced expiratory volume in one second (FEV₁). Sputum arginase activity correlated inversely with total NO metabolite (NO_x) and nitrite concentrations in sputum, and with pre- and post-bronchodilator FEV₁. These findings suggest that ADMA in COPD airways results in a functionally relevant shift of l-arginine breakdown by the NO synthases towards the arginase pathway, which contributes to airway obstruction in these patients.     

Large-Scale Domain Motions and Pyridoxal-5′-Phosphate Assisted Radical Catalysis in Coenzyme B12-Dependent Aminomutases

Lysine 5,6-aminomutase (5,6-LAM) and ornithine 4,5-aminomutase (4,5-OAM) are two of the rare enzymes that use assistance of two vitamins as cofactors. These enzymes employ radical generating capability of coenzyme B₁₂ (5′-deoxyadenosylcobalamin, dAdoCbl) and ability of pyridoxal-5′-phosphate (PLP, vitamin B₆) to stabilize high-energy intermediates for performing challenging 1,2-amino rearrangements between adjacent carbons. A large-scale domain movement is required for interconversion between the catalytically inactive open form and the catalytically active closed form. In spite of all the similarities, these enzymes differ in substrate specificities. 4,5-OAM is highly specific for d-ornithine as a substrate while 5,6-LAM can accept d-lysine and l-β-lysine. This review focuses on recent computational, spectroscopic and structural studies of these enzymes and their implications on the related enzymes. Additionally, we also discuss the potential biosynthetic application of 5,6-LAM.     

Effect of l-Histidine Substitution on Sol–Gel of Transition Metal Coordinated Poly Ethyleneimine: Synthesis and Biochemical Characterization

The study was aimed to investigate the effect of chemical modification of branched poly ethyleneimine (PEI) on chelation of transition metal ions (Me²⁺) including Zn²⁺, Cu²⁺ or Ni²⁺ and sol–gel conversion thereof. To modulate chelation property of PEI, imidazole moieties were introduced into the polymer backbone by carbodiimide chemistry at different molar ratios of fmoc-protected l-histidine. The synthesis was characterized by ¹H-NMR spectroscopy and size exclusion chromatography. Potentiometric titration of PEI/Me²⁺ aqueous dispersions showed formation of stable complexes at pH above 5 depending on the degree of l-histidine substitution. FT-IR spectroscopy showed the imidazole ring of l-histidine was involved in the coordination interactions between PEI and Me²⁺. Addition of Zn²⁺ to PEI solution induced sol–gel conversion at a critical molar ratio decreasing by a higher degree of l-histidine modification. The gelation process led to formation of stable globular nanostructures as confirmed by atomic force microscopy with projected mean diameters less than 200 nm. Cellular experiment showed that l-histidine substitution enhanced cyto-compatibility of PEI, moreover cytotoxicity decreased significantly upon coordination of Zn²⁺ with the polymers. Conclusively, the coordination complexes of Zn²⁺ and l-histidine substituted PEI could serve as a nano system for biomedical applications.     

Tryptophanase-Catalyzed l-Tryptophan Synthesis from d-Serine in the Presence of Diammonium Hydrogen Phosphate

Tryptophanase, an enzyme with extreme absolute stereospecificity for optically active stereoisomers, catalyzes the synthesis of l-tryptophan from l-serine and indole through a β-substitution mechanism of the ping-pong type, and has no activity on d-serine. We previously reported that tryptophanase changed its stereospecificity to degrade d-tryptophan in highly concentrated diammonium hydrogen phosphate, (NH₄)₂HPO₄ solution. The present study provided the same stereospecific change seen in the d-tryptophan degradation reaction also occurs in tryptophan synthesis from d-serine. Tryptophanase became active to d-serine to synthesize l-tryptophan in the presence of diammonium hydrogen phosphate. This reaction has never been reported before. d-serine seems to undergo β-replacement via an enzyme-bonded α-aminoacylate intermediate to yield l-tryptophan.     

Development and Assessment of Electrospun Poly(ε-caprolactone)–Poly(vinylalcohol) Blend Nanofibers for Pest Control in Stored Products

l-Carvone is a constituent of essential oil consisting of monoterpene ketone that possesses various medicinal properties. In this context, the present study focuses on the fabrication and assessment of electrospun poly(ε-caprolactone)–poly(vinylalcohol blend nanofibers imbibed with l-Carvone (5%, w/v) that served as a suitable polymeric carrier to preserve the antimicrobial and antioxidant activities of l-Carvone for a longer period of time. The fumigant potential of l-Carvone and C-PP fibers were assessed toward saw-toothed beetle, a major pest found in stored products. The prepared fragrant C-PP fibers displayed a promising potential formulation for the control of stored product pest such as saw-toothed beetle.     

Critical Surface Tension of Acrylamide-Grafted Polypropylene Copolymer by the Contact Angle Method

The contact angles θ of polar liquids on PP-g-AM copolymer (AM content 0.19, 0.26, and 0.37 wt%) were measured. The critical surface tension γ_C of PP-g-AM films were evaluated by the Zisman plot (cos θ versus-γl), the Young-Dupre-Good-Girifalco plot (1 + cos θ) versus 1/γ^0.5 l, and the log(1 + cos θ) versus log-γl plot. The-γl values estimated by the plot log(1 + cos θ) versus log-γl were smaller than those obtained by the other plots.