Enantioresolution of Some β-Blockers and a β2-Agonist Using Ligand Exchange TLC

JPC – Journal of Planar Chromatography – Modern TLC - Cu(II) complexes of l-threonine, l-serine, and l-tartaric acid were prepared and used as ligand exchange reagents for enantiomeric...     

Sorption properties of perbenzoylated β-cyclodextrin deposited onto a carbon support

Thermodynamic parameters are determined for the adsorption of vapors of hydrocarbons and polar compounds of different structure on carbon adsorbent modified by a monomolecular layer of heptakis(2,3,6-tri-O-benzoyl)-β-cyclodextrin. The effect of the structure and polarity of organic compounds on adsorption onto an adsorbent support with a chiral macrocyclic modifier are considered.     

Vibrational and thermodynamic properties of β-HMX: a first-principles investigation

Thermodynamic properties of β-HMX crystal are investigated using the quasi-harmonic approximation and density functional theory within the local density approximation (LDA), generalized gradient approximation (GGA), and GGA + empirical van der Waals (vdW) correction. It is found that GGA well describes the thermal expansion coefficient and heat capacity but fails to produce correct bulk modulus and equilibrium volume. The vdW correction improves the bulk modulus and volume, but worsens the thermal expansion coefficient and heat capacity. In contrast, LDA describes all thermodynamic properties with reasonable accuracy, and overall is a good exchange-correlation functional for β-HMX molecular crystal. The results also demonstrate significant contributions of phonons to the equation of state. The static calculation of equilibrium volume for β-HMX differs from the room-temperature value incorporating lattice vibrations by over 5%. Therefore, for molecular crystals, it is essential to include phonon contributions when calculated equation of state is compared with experimental data at ambient condition.     

Purification and Characterization of a Glycoside Hydrolase Family 43 β-xylosidase from Geobacillus thermoleovorans IT-08

The gene encoding a glycoside hydrolase family 43 β-xylosidase (GbtXyl43A) from the thermophilic bacterium Geobacillus thermoleovorans strain IT-08 was synthesized and cloned with a C-terminal His-tag into a pET29b expression vector. The recombinant gene product termed GbtXyl43A was expressed in Escherichia coli and purified to apparent homogeneity. Michaelis–Menten kinetic parameters were obtained for the artificial substrates p-nitrophenyl-β-d-xylopyranose (4NPX) and p-nitrophenyl-α-l-arabinofuranose (4NPA), and it was found that the ratio k _cat/K _m 4NPA/k _cat/K _m 4NPX was ～7, indicting greater catalytic efficiency for 4NP hydrolysis from the arabinofuranose aglycon moiety. Substrate inhibition was observed for the substrates 4-methylumbelliferyl xylopyranoside (muX) and the arabinofuranoside cogener (muA), and the ratio k _cat/K _m muA/k _cat/K _m muX was ～5. The enzyme was competitively inhibited by monosaccharides, with an arabinose K _i of 6.8?±?0.62 mM and xylose K _i of 76?±?8.5 mM. The pH maxima was 5.0, and the enzyme was not thermally stable above 54 °C, with a t _1/2 of 35 min at 57.5 °C. GbtXyl43A showed a broad substrate specificity for hydrolysis of xylooligosaccharides up to the highest degree of polymerization tested (xylopentaose), and also released xylose from birch and beechwood arabinoxylan.     

Oxidation properties of β-substituted pyrroles

Pyrroles represent building blocks of conjugated poly(heterocycles) which, as organic conductors, are potential materials for organic electronics. Oxidation of β-substituted pyrroles constitutes an important first step in the process of electropolymerization. Ionization energy and the electron spin density distribution are two the most important properties regarding monomers. These properties are studied as a function of electron-withdrawing and electron-donating substituents of pyrrole ring. Evolution of molecular structure, nature of bonding, and electronic density are studied as an effect of ionization process.     

Dynamic relaying properties of a β-turn peptide in long-range electron transfer

The relay stations play a significant role in long-range charge hopping transfer in proteins. Although studies have clarified that many more protein structural motifs can function as relays in charge hopping transfers by acting as intermediate charge carriers, the relaying properties are still poorly understood. In this work, taking a β-turn oligopeptide as an example, we report a dynamic character of a relay with tunable relaying properties using the density functional theory calculations. Our main finding is that a β-turn peptide can serve as an effective electron relay in facilitating long-range electron migration and its relay properties is vibration-tunable. The vibration-induced structural transient distortions remarkably affect the lowest occupied molecular orbital (LUMO) energy, vertical electron affinity and electron-binding mode of the β-turn oligopeptide and the singly occupied molecular orbital (SOMO) energy of the corresponding electron adduct and thus the relaying properties. Different vibration modes lead to different structural distortions and thus have different effects on the relaying properties and ability of the β-turn peptide. For the relaying properties, there approximately is a linear negative correlation of electron affinity with the LUMO energy of the β-turn or the SOMO energy of its electron adduct. Besides, such relaying properties also vary in the vibration evolution process, and the electron-binding modes may be tunable. As an important addition to the known static charge relaying properties occurring in various protein structural motifs, this work reports the dynamic electron-relaying characteristics of a β-turn oligopeptide with variable relaying properties governed by molecular vibrations which can be applied to different proteins in mediating long-range charge transfers. Clearly, this work reveals molecular vibration effects on the electron relaying properties of protein structural motifs and provides new insights into the dynamics of long-range charge transfers in proteins. © 2018 Wiley Periodicals, Inc.     

Mycelia-associated β-xylosidase in pellets ofAspergillus sps.

A screening of 10 strains ofAspergillus for pellet formation and mycelia-associated β-xylosidase activity was performed in media containing glucose and glucose supplemented with methyl β-d-xylopyranoside. The aim was to produce an immobilized enzyme preparation. Three strains with high mycelia-associated β-xylosidase activity were investigated for enzyme leakage and enzyme stability:A. terreus QM 1991,A. phoenicis ATCC 13157, andA. phoenicis QM 329. The pellets ofA. phoenicis QM 329 had the highest β-xylosidase activity (280 IU/g dry wt mycelia) after 333 h of incubation. From measurements of both cell-bound enzyme activity and the activity in solution, it could be concluded that forAspergillus phoenicis QM 329 and ATCC 13157 the decrease in β-xylosidase activity bound to the pellets was owing to enzyme leakage. ForAspergillus terreus QM 1991, the decrease of pellet-bound β-xylosidase activity was the result of both leakage and enzyme deactivation at 50°C. β-Xylosidase in pellets ofA. phoenicis QM329 hydrolyzes xylobiose andp-nitrophenyl β-d-xylopyranoside with the same rate of conversion.

     

Synthesis and properties of group 9 metal complexes bearing a β-ketophosphenato ligand

A novel β-ketophosphenato ligand bearing a bulky substituent, Tbt(2,4,6-tris[bis(trimethylsilyl)methyl]phenyl), on the phosphorus atom was newly designed and synthesized as a heavier congener of a β-ketoiminato ligand. Rhodium and iridium complexes bearing this new β-ketophosphenato ligand have been synthesized and fully characterized by spectroscopic and elemental analyses together with X-ray crystallographic analyses. The results of NMR spectroscopic studies and the X-ray structural analyses suggested that the β-ketophosphenato ligand has unique electronic features due to the low-coordinated phosphorus atom. Comparison of properties between rhodium β-ketophosphenates 2a,b and rhodium β-ketoiminate 7 revealed the character of the β-ketophosphenato ligand, where the trans influence of the phosphorus atom should be stronger than the nitrogen atom of the β-ketoiminato ligand.     

Synthesis and fluorescence properties of novel pyrazine-boron complexes bearing a β-iminoketone ligand

A novel fluorescence dye based on pyrazine-boron complexes bearing a β-iminoketone ligand has been synthesized by using a simple two-step reaction. Synthesized complexes exhibited fluorescence in solution (F(max): 472-604 nm) and in the solid state (F(max): 496-624 nm). These complexes showed a larger Stokes shift (3690-4900 cm(-1)) than well-known boron dipyrromethene dyes (400-600 cm(-1), in most cases).     

Conformational and Electronic Interaction Studies of Some β-Ketosulfoxides

ABSTRACT.

The analysis of the carbonyl I.R. band and the U.V. phoelectron spectroscopic data along with the ab-initio calculations and X-ray diffraction of α-(methylsulfinyl)- and α-(phenylsulfinyl)-acetophenones indicated the predominance of the cis rotamers over the qauche ones.     

Screening of variables in β-xylosidase recovery using cetyl trimethyl ammonium bromide reversed micelles

β-Xylosidase recovery by micelles using cetyl trimethyl ammonium bromide (CTAB) cationic surfactant was verified under different experimental conditions. A 2⁵⁻¹ fractional factorial design with center points was employed to verify the influence of the following factors on enzyme extraction: pH (x ₁), CTAB concentration (x ₂), electrical conductivity (x ₃), hexanol concentration (x ₄), and butanol concentration (x ₅). Statistical analysis of the results shows that of the fivevariables studied only hexanol and electrical conductivity did not have significant effects on the recovery of β-xylosidase. The other factors had significant effects in increasing order: (x ₁)>(x ₂)>(x ₅). The model predicts a recovery value of about 45%, which is similar to that obtained experimentally (43.5%).     

Synthesis and photoluminescent properties of benzodioxan β-aminoketones

A series of benzodioxan β-aminoketones with various substituents in their carbonyl and amino groups are prepared and their photoluminescence spectra are studied. Comparison of the luminescence spectra of β-amino-7-propionyl-1,4-bexodioxane and o-aminophenylethyl ketone demonstrates that the presence of an ethylendioxy fragment in the aromatic region of β-aminoketones increases the intensity of their luminescence in the blue region of the spectra. The photoluminescence intensity of the synthesized benzodioxane β-aminoketones depends on the nature of the substituent when carbonyl carbon is present and decreases in the sequence C₂H₅ > C₃H₇ > CH(CH₃)₂ > C₆H₅. Introduction of a substituent in the amino group of benzodioxane β-aminoketones reduces the intensity of luminescence.     

synthesis and properties of β-brominated metal complexes of meso-triphenylcorrole

Spectral properties and chemical stability of Mn(III), Mn(IV), Fe(III), Fe(IV), and Cu(III) complexes of β-octabromotriphenylcorrole [(β-Br)₈(ms-Ph)₃Cor], synthesized from β-unsubstituted compounds by their reaction with molecular bromine, were studied. Cyclic voltammetry, electron microscopy, and X-ray spectral microanalysis were used to obtain electrochemical characteristics of metal corroles M(β-Br)₈(ms-Ph)₃Cor and gain insight into the surface texture of active catalysts on the basis of metal corroles. The electron-acceptor β-bromine substitution in the MCor macrocycle shifts the equilibrium in electron-donor solvents to lower oxidation states of the metals and also stabilizes manganese and destabilizes copper complexes in the protondonor medium HOAc-H₂SO₄. The electrocatalytic activity of the complexes in the reduction of molecular oxygen depends on the nature of the ligand and increases in the order Mn ≤ Cu ? Fe in the case of β-octabrominated macrocycles. The character of distribution of active centers on the surface of the catalysts was established for the first time.     

Effect of β-cyclodextrin complexation on physicochemical properties of zaleplon

The physicochemical properties and dissolution profile of zaleplon (ZPN) β-cyclodextrin (βCD) inclusion complex were investigated. The phase solubility profile of ZPN with β-cyclodextrin was classified as A_L-type. Stability constant with 1:1 molar ratio was calculated from the phase solubility diagram and the aqueous solubility of ZPN was found to be enhanced by 714% (p < 0.001) for β-cyclodextrin. Binary systems of ZPN with βCD were prepared by kneading method. The solid-state properties of complex were characterized by differential scanning calorimetry, Fourier transformation-infrared spectroscopy and powder X-ray diffractometry. It could be concluded that ZPN could form inclusion complex with β-cyclodextrin. The dissolution profile of inclusion complex was determined and compared with those of ZPN alone and its physical mixture. The dissolution rate of ZPN was significantly increased by complexation with βCD, as compared with pure drug and physical mixture.     

Synthesis of a New C-15 Phosphorus Ylide Used for the Preparation of Some β-End-Group Retinoid Derivatives

A synthesis of a new C-15 phosphorus ylide from a C-14 enaminone is reported. This reagent, which undergoes selective 1,2- or 1,4-additions with saturated and unsaturated aldehydes, may find some synthetic use for the preparation of β-end-group retinoid derivatives.     

The physical properties and unusual pyrolysis behaviour of a supramolecular complex of β-cyclodextrin and potassium ferrioxalate

The thermal pyrolysis behaviour of a complex of β-cyclodextrin (CD) and potassium ferrioxalate (PF) was analyzed using gas chromatography coupled to time-of-flight mass spectrometry. Two rare inorganic ions: CO(2)(2+) and O(4)(+), neither of which was found in the cases of free β-CD and PF, were synchronously observed during the decomposition of the complex. Our observations led to proposed formation mechanisms of the ions, in which the structural transformation of a metastable intermediate ion (C(2)H(4)O(3)(+)) was employed to qualitatively explain our data. Besides this, the formation, structure and magnetic properties of the complex were evaluated carefully. First, XPS analysis indicates a decrease of electron densities of Fe(III) ions in the presence of β-CD. We think that this is due to an effect of the noncovalent complexation between PF and β-CD. This gives an indication on the effect of second sphere coordination of β-CD on the electronic structure of the Fe(III) in the first coordination sphere. Second, structural changes in stacking modes and morphologies provide further support for the noncovalent complexation. For example, the surface feature of the complex gives us an impression that both β-CD and PF are evenly dispersed with each other. Also, the complex presents a uniform sponge-like porous nanostructure with diameters of less than 50 nm. This seems to be an important reason for those changes that occurred in the thermal analysis. Finally, the result of magnetic experiments implies that the coordination compound PF upon complexation with β-CD will experience a gradual decrease in magnetization with the increase of magnetic fields. These observations have significant implications for a better understanding of the importance of the construction and deconstruction of a second sphere coordination in modifying the physical properties of an σ-coordination compound.     

Stereoselective synthesis of a β-D-phosphatidylgalactose

The stereoselective synthesis of a -D-phosphatidylgalactose has been achieved by the interaction of a benzyl phosphatidate with D-galactose tert-butyl orthoacetate or trichloroacetimidate.M. V. Lomonosov Institute of Fine Chemical Technology, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 16–19, January–February, 1991.     

A comparative study of the structure and properties of β-galactosidases

A comparative study of β-galactosidase amino acid sequences of E. coli and another four out of 11 microorganisms selected at the first stage was performed. It was shown that the functional amino acid residues in the catalytic domain and the ligand environment of the magnesium cation for all five sequences are identical. The mechanism of the catalytic action of E. coli and K. lactis β-galactosidases was investigated by the method of nucleophilic competition. It was shown that the mechanism of the effects of nucleophilic agents is kinetically identical both enzymes: the presence of methanol or butanediols affects the stage of degalactosylation; the presence of magnesium cations promotes the activity of both β-galactosidases; and the mechanisms of the thermal inactivation of E. coli and K. lactis β-galactosidases are different.     

Interfacial and emulsifying properties of designed β-strand peptides

The structural and surfactant properties of a series of amphipathic β-strand peptides have been studied as a function of pH. Each nine-residue peptide has a framework of hydrophobic proline and phenylalanine amino acid residues, alternating with acidic or basic amino acids to give a sequence closely related to known β-sheet formers. Surface activity, interfacial mechanical properties, electronic circular dichroism (ECD), droplet sizing and zeta potential measurements were used to gain an overview of the peptide behavior as the molecular charge varied from ±4 to 0 with pH. ECD data suggest that the peptides form polyproline-type helices in bulk aqueous solution when highly charged, but may fold to β-hairpins rather than β-sheets when uncharged. In the uncharged state, the peptides adsorb readily at a macroscopic fluid interface to form mechanically strong interfacial films, but tend to give large droplet sizes on emulsification, apparently due to flocculation at a low droplet zeta potential. In contrast, highly charged peptide states gave a low interfacial coverage, but retained good emulsifying activity as judged by droplet size. Best emulsification was generally seen for intermediate charged states of the peptides, possibly representing a compromise between droplet zeta potential and interfacial binding affinity. The emulsifying properties of β-strand peptides have not been previously reported. Understanding the interfacial properties of such peptides is important to their potential development as biosurfactants.