Substantially enhancing enzymatic regioselective acylation of 1-β-d-arabinofuranosylcytosine with vinyl caprylate by using a co-solvent mixture of hexane and pyridine

Novozym 435-catalyzed regioselective acylation of 1-β-d-arabinofuranosylcytosine (ara-C) with vinyl caprylate for the preparation of its 5′-O-acyl derivative has been performed in six co-solvent mixtures and three pure polar solvents for the first time. Novozym 435 displayed low activity towards 1-β-d-arabinofuranosylcytosine in pure polar solvents, although those solvents can dissolve the nucleosides well. When a hexane–pyridine co-solvent system was adopted, both the initial rate and the substrate conversion were enhanced markedly. The most suitable co-solvent, initial water activity, reaction temperature and the molar ratio of vinyl caprylate to ara-C were hexane/pyridine (28/72, v/v), 0.03, 40 °C and 15, respectively. Under these conditions, the initial rate, the substrate conversion and the regioselectivity were as high as 99.0 mmol h⁻¹, 98% and >99%, respectively. The product of the Novozym 435-catalyzed reaction was characterized by ¹³C NMR and confirmed to be 5′-O-octanoyl 1-β-d-arabinofuranosylcytosine.     

Novel stereo controlled glycosylation of 1,2,3,4,6-penta-o-acetyl-β-d-glucopyranoside using MgO–ZrO2 as an environmentally benign catalyst

Glycosylation reactions are most commonly encountered in nature. Synthetically, glycosylations are carried out with Lewis acid catalysts or mineral acids. However an environmental threat associated with catalysts has encouraged process modification by alternative development of solid catalysts based glycosylation reactions, which are commercially viable as well. In this contribution comparative study of glycosidic bond formation of 1,2,3,4,6-penta-o-acetyl-β-d-glucopyranoside with various alcohols over variety of reaction promoters/catalyst like p-toluene sulphonic acid, HCl, H₂SO₄ and MgO–ZrO₂ were taken up to evaluate the performance of this potential promoter/catalysts systems. The best catalyst for the selective synthesis of alkyl-β-d-glucopyranosides was MgO–ZrO₂ which remains active upto three runs. This replacement of homogeneous acid catalysts by heterogeneous base catalyst shows alkyl-β-d-glucopyranoside as major product at comparatively low temperature range. The effects of variety of parameters were studied in a batch reactor. The mechanism of the reaction over basic mixed metal oxide at 363 K is put forth.     

Separation of phenylalanine racemates using d-phenylalanine imprinted microbeads as HPLC stationary phase

A successful enantioseparation of d,l-phenylalanine (Phe) was achieved for the first time by using d-Phe imprinted P(MAA-co-EGDMA) microbeads as HPLC stationary phase. The d-Phe imprinted microbeads were prepared by a novel modified suspension polymerization method without derivatization of the water-soluble template molecule. This preparation method was employed in order to capture template molecules in organic phase droplets during polymerization. The prepared d-Phe imprinted P(MAA-co-EGDMA) microbeads were packed into an empty stainless steel column, which was used for the separation of the Phe enantiomers. The selection of a suitable mobile phase, mobile phase composition, pH and flow rate were investigated for determining the best resolution of the Phe enantiomers. Baseline separation was achieved using an organic–aqueous buffer (EtOH–acetate buffer) solution as a mobile phase. Separation factors of more than 2.56, with a resolution of 1.38, were obtained with a mobile phase containing 9–18% (v/v) EtOH in a 0.030 M acetate buffer solution. d-Phe imprinted microbeads were superior to the majority of the reported molecularly imprinted polymers with respect to chiral separation abilities. The column backpressure was less than 300 psi.     

Studies on the oxidation reaction of l-cysteine in a confined matrix of layered double hydroxides

The amino acid l-cysteine (l-Cys) was intercalated into a MgAl layered double hydroxide (LDH), and its oxidation reaction by hexacyanoferrate (III) (Fe(CN)₆³⁻) in the confined region between sheets of LDH has been studied in detail. Based on the measurement results of XRD, Raman and FT-IR, it was found that the interlayer l-Cys was oxidized to cystine by Fe(CN)₆³⁻. Furthermore, the kinetics of this reaction was investigated in batch mode. The influences of initial Fe(CN)₆³⁻concentration, l-Cys-LDH quantity and reaction temperature on the interlayer oxidation reaction have been studied, respectively. The reaction follows a diffusion-controlled mechanism represented by Crank-Ginstling and Brounshtein kinetic model with the apparent activation energy of 29.93 kJ/mol. Therefore, this layered material may have prospective application as a novel “molecular reactor” for confined chemical reactions.     

Effect of d-isomer concentration on the coloration properties of poly(lactic acid)

Poly(lactic acid) (PLA) fibre is derived from annually renewable crops, it is 100% compostable and its life cycle potentially reduces the earth's carbon dioxide level. In this work PLA fabrics containing variable concentrations of the d- and l-isomers have been studied to ascertain their dyeability, the characteristics of those dyed polymers, and their subsequent performance and properties. Comparison of poly(lactic acid) fabrics with varying d-isomer content revealed differences in melting temperature; by virtue of a higher d-isomer concentration, ‘high d-’ fibres have greater fibre entropy which causes a decrease in melting temperature. As a result of greater fibre entropy, high d- fibres have more amorphous and less crystalline regions in the polymer, with respect to low d- fibres, hence, high d- fabrics display greater dye exhaustion and colour strength in comparison with their low d- counterpart in all dyes and all concentrations. In application of a dye mixture for a black shade, high d- fibres are able to be dyed to an excellent black shade, whereas low d- fibres appear very brown, due to lower exhaustion of the blue component of the mix. In terms of wash fastness, there is very little difference between high d- fibres and low d- fibres; this is because the glass transition temperature for both fibres is very similar.     

Tailor-made gold brush nanoelectrode ensembles modified with l-cysteine for the detection of daunorubicine

A new functionalized l-cysteine surface modified 3D gold brush nanoelectrode assembly BNEE (l-cys/BNEEs) was prepared. The BNEEs consisted of gold nanowires 100 nm in diameter and up to 400 nm in length fabricated by template synthesis in track etched polycarbonate membranes. The nanowires were exposed by controlled chemical etching of the membrane and were then modified by coating l-cys on the surface of the exposed gold nanowires. The morphology of the BNEEs was imaged by scanning electron microscopy and the real active area of BNEEs was determined by electrochemical impedance spectroscopy. The redox of daunorubicine (DNR) at the l-cys/BNEEs exhibited absorption-controlled characteristics and higher current activity than that at l-cys surface modified 2D disk NEEs (l-cys/DNEEs). The square wave voltammetry technique was employed to detect DNR. The detection limit was 1.0 × 10⁻⁸ M (s/n = 3). The linear detection concentration range of DNR was from 2.5 × 10⁻⁸ to 4.0 × 10⁻⁷ M.     

Synthesis and characterization of calcium–alumino-silicate hydrates from oil shale ash – Towards industrial applications

The influence of the alkaline medium on the hydrothermal activation of the oil shale fly ash with NaOH and KOH was studied using SEM/EDX, XRD, ²⁹Si and ²⁷Al high-resolution MAS-NMR spectra. In the presence of NaOH the silicon in the original fly ash was completely converted into calcium–aluminum–silicate–hydrates, mainly into 1.1 nm tobermorite structure during 24-h treatment at 160 °C. At similar reaction conditions, the activation with KOH resulted only to the formation of amorphous calcium–silica-hydrate gel on the surface of ash particles at temperature. The results obtained in this study indicate that the oil shale fly ash can be used for production of Al-substituted tobermorites when strongly alkaline media (NaOH) is applied. The synthesized product was used in a catalytic d-lactose isomerization reaction.     

Chiral recognition of alanine across modified carbon electrodes with 3,4-dihydroxyphenylalanine

3,4-Dihydroxyphenylalanine (DOPA) was covalently grafted onto a glassy carbon electrode (GCE) by the formation of an amine cation radical in the electro-oxidation of the amino-containing compound. Cyclic voltammetric experiments proved that the DOPA was formed on the GCE as a monolayer. Its electron transfer over the GCE surface at different pH values was studied by cyclic voltammetry. Changes in solution pH resulted in the variation of the charge state of the terminal group and the surface pK_a was estimated on the basis of these results. Because of electrostatic interactions between the negatively charged groups on the electrode surface and the alanine (Ala) in solution, the modified electrode was used as an enantioselective sensor. The peak current for d(+) or l(−)DOPA over the modified electrode decreased as a result of the chiral recognition across the blocking interaction with the respective enantiomer of l(−) or d(+)Ala. The recognition was verified with the protection of l(−)DOPA with a Fmoc group.     

New Glycosylated Dihydrochalcones Obtained by Biotransformation of 2′-Hydroxy-2-methylchalcone in Cultures of Entomopathogenic Filamentous Fungi

Flavonoids, including chalcones, are more stable and bioavailable in the form of glycosylated and methylated derivatives. The combined chemical and biotechnological methods can be applied to obtain such compounds. In the present study, 2′-hydroxy-2-methylchalcone was synthesized and biotransformed in the cultures of entomopathogenic filamentous fungi Beauveria bassiana KCH J1.5, Isaria fumosorosea KCH J2 and Isaria farinosa KCH J2.6, which have been known for their extensive enzymatic system and ability to perform glycosylation of flavonoids. As a result, five new glycosylated dihydrochalcones were obtained. Biotransformation of 2′-hydroxy-2-methylchalcone by B. bassiana KCH J1.5 resulted in four glycosylated dihydrochalcones: 2′-hydroxy-2-methyldihydrochalcone 3′-O-β-d-(4″-O-methyl)-glucopyranoside, 2′,3-dihydroxy-2-methyldihydrochalcone 3′-O-β-d-(4″-O-methyl)-glucopyranoside, 2′-hydroxy-2-hydroxymethyldihydrochalcone 3′-O-β-d-(4″-O-methyl)-glucopyranoside, and 2′,4-dihydroxy-2-methyldihydrochalcone 3′-O-β-d-(4″-O-methyl)-glucopyranoside. In the culture of I. fumosorosea KCH J2 only one product was formed—3-hydroxy-2-methyldihydrochalcone 2′-O-β-d-(4″-O-methyl)-glucopyranoside. Biotransformation performed by I. farinosa KCH J2.6 resulted in the formation of two products: 2′-hydroxy-2-methyldihydrochalcone 3′-O-β-d-(4″-O-methyl)-glucopyranoside and 2′,3-dihydroxy-2-methyldihydrochalcone 3′-O-β-d-(4″-O-methyl)-glucopyranoside. The structures of all obtained products were established based on the NMR spectroscopy. All products mentioned above may be used in further studies as potentially bioactive compounds with improved stability and bioavailability. These compounds can be considered as flavor enhancers and potential sweeteners.     

Synthesis of -leucine nanoparticles via physical vapor deposition at varying saturation conditions

Preparation of L-leucine nanoparticles by a process based on physical vapor deposition has been presented. In an aerosol flow reactor method, aqueous L-leucine droplets were first dried followed by the sublimation of L-leucine to produce vapor that upon vapor deposition resulted in L-leucine nanoparticles with size ranging from 40 to 200 nm. Onset temperature for the sublimation of L-leucine at concentrations from 0.02 to increased from 135 to , respectively. The formation of nanoparticles was initiated in three different ways: (i) via droplet drying, (ii) via heterogeneous nucleation of L-leucine vapor on solid L-leucine particles, and (iii) via homogeneous nucleation of L-leucine vapor to form new-born nanoparticles. Consequently, the saturation conditions of L-leucine vapor in the reactor determined the resulting particle size, size distribution and number concentration, those depending very much on nucleation mode. In general, the both nucleation modes produced narrow size distributions, that is, geometric standard deviation (GSD) was <1.8 although the number concentration increased with the increased amount of L-leucine vapor. Upon desublimation and vapor deposition, L-leucine formed leafy crystals whose size was the largest when produced from the heated section at the vicinity of the onset temperature and the smallest far above the onset temperature. All the particles prepared in the conditions (i)–(iii) were crystalline. However, X-ray diffraction analysis showed preferential direction for crystal growth according to the way of particle formation.     

Structure and Antitumor and Immunomodulatory Activities of a Water-Soluble Polysaccharide from Dimocarpus longan Pulp

A new water-soluble polysaccharide (longan polysaccharide 1 (LP1)) was extracted and successfully purified from Dimocarpus longan pulp via diethylaminoethyl (DEAE)-cellulose anion-exchange and Sephacryl S-300 HR gel chromatography. The chemical structure was determined using Infrared (IR), gas chromatography (GC) and nuclear magnetic resonance (NMR) analysis. The results indicated that the molecular weight of the sample was 1.1 × 10⁵ Da. Monosaccharide composition analysis revealed that LP1 was composed of Glc, GalA, Ara and Gal in a molar ratio of 5.39:1.04:0.74:0.21. Structural analysis indicated that LP1 consisted of a backbone of →4)-α-d-Glcp-(1→4)-α-d-GalpA-(1→4)-α-d-Glcp-(1→4)-β-d-Glcp-(1→ units with poly saccharide side chains composed of →2)-β-d-Fruf-(1→2)-l-sorbose-(1→ attached to the O-6 position of the α-d-Glcp residues. In vitro experiments indicated that LP1 had significantly high antitumor activity against SKOV3 and HO8910 tumor cells, with inhibition percentages of 40% and 50%, respectively. In addition, LP1 significantly stimulated the production of the cytokine interferon-γ (IFN-γ), increased the activity of murine macrophages and enhanced B- and T-lymphocyte proliferation. The results of this study demonstrate that LP1 has potential applications as a natural antitumor agent with immunomodulatory activity.     

Synthesis of hectorite–TiO2 and kaolinite–TiO2 nanocomposites with photocatalytic activity for the degradation of model air pollutants

We studied the synthesis and photocatalytic activity of small-sized TiO₂ supported on hectorite and kaolinite. Deposition of TiO₂ on the clay mineral surface was conducted by using a sol–gel method with titanium isopropoxide as precursor. Anatase TiO₂ particles formation was achieved by hydrothermal treatment at 180 °C. Material characterization was conducted using XRD, SEM, XPS, ICP-OES, BET and porosimetry analysis. fficiency in synthesizing clay–TiO₂ composites depended strongly on the clay mineral structure. Incorporation of anatase in hectorite, an expandable clay mineral, was found to be very significant (> 36 wt.% Ti) and to be followed by important structural changes at the clay mineral surface. Instead, no major structural modifications of the clay were observed for kaolinite–TiO₂, as compared with the untreated material. Photocatalytic performance of clay–TiO₂ composites was evaluated with ATR-FTIR following the oxidation of adsorbed toluene and d-limonene, two model air pollutants. In either case, the photocatalytic removal efficiency of these hydrophobic substrates by the synthesized clay–TiO₂ composites was comparable to that observed using pure commercial TiO₂ (Degussa P25).     

Fungal Biotransformation of 2′-Methylflavanone and 2′-Methylflavone as a Method to Obtain Glycosylated Derivatives

Methylated flavonoids are promising pharmaceutical agents due to their improved metabolic stability and increased activity compared to unmethylated forms. The biotransformation in cultures of entomopathogenic filamentous fungi is a valuable method to obtain glycosylated flavones and flavanones with increased aqueous solubility and bioavailability. In the present study, we combined chemical synthesis and biotransformation to obtain methylated and glycosylated flavonoid derivatives. In the first step, we synthesized 2′-methylflavanone and 2′-methylflavone. Afterwards, both compounds were biotransformed in the cultures of two strains of entomopathogenic filamentous fungi Beauveria bassiana KCH J1.5 and Isaria fumosorosea KCH J2. We determined the structures of biotransformation products based on NMR spectroscopy. Biotransformations of 2′-methyflavanone in the culture of B. bassiana KCH J1.5 resulted in three glycosylated flavanones: 2′-methylflavanone 6-O-β-d-(4″-O-methyl)-glucopyranoside, 3′-hydroxy-2′-methylflavanone 6-O-β-d-(4″-O-methyl)-glucopyranoside, and 2-(2′-methylphenyl)-chromane 4-O-β-d-(4″-O-methyl)-glucopyranoside, whereas in the culture of I. fumosorosea KCH J2, two other products were obtained: 2′-methylflavanone 3′-O-β-d-(4″-O-methyl)-glucopyranoside and 2-methylbenzoic acid 4-O-β-d-(4′-O-methyl)-glucopyranoside. 2′-Methylflavone was effectively biotransformed only by I. fumosorosea KCH J2 into three derivatives: 2′-methylflavone 3′-O-β-d-(4″-O-methyl)-glucopyranoside, 2′-methylflavone 4′-O-β-d-(4″-O-methyl)-glucopyranoside, and 2′-methylflavone 5′-O-β-d-(4″-O-methyl)-glucopyranoside. All obtained glycosylated flavonoids have not been described in the literature until now and need further research on their biological activity and pharmacological efficacy as potential drugs.     

Trehalose Analogues: Latest Insights in Properties and Biocatalytic Production

Trehalose (α-d-glucopyranosyl α-d-glucopyranoside) is a non-reducing sugar with unique stabilizing properties due to its symmetrical, low energy structure consisting of two 1,1-anomerically bound glucose moieties. Many applications of this beneficial sugar have been reported in the novel food (nutricals), medical, pharmaceutical and cosmetic industries. Trehalose analogues, like lactotrehalose (α-d-glucopyranosyl α-d-galactopyranoside) or galactotrehalose (α-d-galactopyranosyl α-d-galactopyranoside), offer similar benefits as trehalose, but show additional features such as prebiotic or low-calorie sweetener due to their resistance against hydrolysis during digestion. Unfortunately, large-scale chemical production processes for trehalose analogues are not readily available at the moment due to the lack of efficient synthesis methods. Most of the procedures reported in literature suffer from low yields, elevated costs and are far from environmentally friendly. “Greener” alternatives found in the biocatalysis field, including galactosidases, trehalose phosphorylases and TreT-type trehalose synthases are suggested as primary candidates for trehalose analogue production instead. Significant progress has been made in the last decade to turn these into highly efficient biocatalysts and to broaden the variety of useful donor and acceptor sugars. In this review, we aim to provide an overview of the latest insights and future perspectives in trehalose analogue chemistry, applications and production pathways with emphasis on biocatalysis.     

Mathematical modelling of the solubility of supercritical CO2 in poly(l-lactide) and poly(d,l-lactide-co-glycolide)

Two mathematical models, Sanchez–Lacombe equation of state and the Perturbed-Chain Statistical Associating Fluid Theory were applied for modelling the phase equilibrium for the poly(l-lactide)–CO₂ and poly(d,l-lactide-co-glycolide)–CO₂ systems. Aspen Polymer Plus software was used. The results were compared with previously obtained experimental values for solubility. The solubility of scCO₂ in the two biodegradable polymers was calculated for three different temperatures (308, 313 and 323 K) in the pressure range (10–30 MPa). The characteristic parameters for the components and the binary interaction parameters for the models were optimized in order to obtain the best fit between the estimated and the experimental gas solubility data. The results suggest that both SL EOS and PC-SAFT are reliable models in describing the phase equilibrium of the PLLA–CO₂ and PLGA–CO₂ systems at the proposed working conditions.     

Investigation of chemical transformations of thiophenylglycoside of muramyl dipeptide on the fumed silica surface using TPD-MS,FTIR spectroscopy and ES IT MS

In this study, chemical transformations of benzyl ester of О-(phenyl-2-acetamido-2,3-dideoxy-1-thio-β-d-glucopyranoside-3-yl)-d-lactoyl-l-alanyl-d-isoglutamine (SPhMDPOBn) on the fumed silica surface were examined, and the surface complex structure was characterized by temperature-programmed desorption mass spectrometry (TPD-MS), infrared spectroscopy (FTIR) and electrospray ion trap mass spectrometry (ES IT MS). Stages of pyrolysis of SPhMDPOBn in pristine state and on the silica surface have been determined. Probably, hydrogen-bonded complex forms between silanol surface groups and the C = O group of the acetamide moiety NH-(CH₃)-C = O…H-O-Si≡. The thermal transformations of such hydrogen-bonded complex result in pyrolysis of SPhMDPOBn immobilized on the silica surface under TPD-MS conditions. The shifts ∆ν of amide I band (measured from 1,626 to 1,639 cm^−l for SPhMDPOBn in pristine state) of 33 and 35 cm^−l which occurred when SPhMDPOBn was immobilized on the silica surface may be caused by a weakening of the intramolecular hydrogen bonding of the SPhMDPOBn because the interaction with the silica surface as hydrogen bond with silanol groups is weaker than that in associates.     

Synthesis of tadpole-shaped copolyesters based on living macrocyclic poly(-caprolactone)

Synthesis of an asymmetric tadpole-shaped aliphatic copolyester consisting of a poly(-caprolactone) ring and two poly(l-lactide) tails was reported for the first time. First, a high molecular weight cyclic PCL macroinitiator (M_n = 31,000) was prepared by intramolecular photocross-linking of “living” chains. Polymerization of l-lactide was resumed by the tin dialkoxide containing macrocycles, thus making the targeted tadpole-shaped copolyester available. A preliminary investigation of the crystallization of these copolyesters was carried out by differential scanning calorimetry and polarized optical microscopy.     

Structural Determination and Genetic Identification of the O-Antigen from an Escherichia coli Strain,LL004, Representing a Novel Serogroup

The O-antigen is the outermost component of the lipopolysaccharide layer in Gram-negative bacteria, and the variation of O-antigen structure provides the basis for bacterial serological diversity. Here, we determined the O-antigen structure of an Escherichia coli strain, LL004, which is totally different from all of the E. coli serogroups. The tetrasaccharide repeating unit was determined as →4)-β-d-Galp-(1→3)-β-d-GlcpNAc6OAc(~70%)-(1→3)-β-d-GalpA-(1→3)-β-d-GalpNAc-(1→ with monosaccharide analysis and NMR spectra. We also characterized the O-antigen gene cluster of LL004, and sequence analysis showed that it correlated well with the O-antigen structure. Deletion and complementation testing further confirmed its role in O-antigen biosynthesis, and indicated that the O-antigen of LL004 is assembled via the Wzx/Wzy dependent pathway. Our findings, in combination, suggest that LL004 should represent a novel serogroup of E. coli.     

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.     

Design,Synthesis and Bioactivity of N-Glycosyl-N′-(5-substituted phenyl-2-furoyl) Hydrazide Derivatives

Condensation products of 5-substituted phenyl-2-furoyl hydrazide with different monosaccharides d-glucose, d-galactose,d-mannose, d-fucose and d-arabinose were prepared. The anomerization and cyclic-acyclic isomers were investigated by ¹H NMR spectroscopy. The results showed that, except for the d-glucose derivatives, which were in the presence of β-anomeric forms, all derivatives were in an acyclic Schiff base form. Their antifungal and antitumor activities were studied. The bioassay results indicated that some title compounds showed superior effects over the commercial positive controls.