Recovery of antibiotics by aqueous two-phase partition —Partitioning behavior of pure acetylspiramycin solution in polyethylene glycol/potassium phosphate aqueous two-phase systems

Summary The effects of average molecular weight of PEG, concentrations of PEG and KH₂PO₄ and pH on the partition equilibrium of acetylspiramycin in PEG/KH₂PO₄ aqueous two-phase systems were studied in detail. The partition coefficients of acetylspiramycin in PEG/ KH₂PO₄ systems were measured at room temperature 25 °C. It was found that acetylspiramycin partitioned unevenly in the aqueous two-phase systems composed of PEG and KH₂PO₄ and could be purified by this technique. A suitable phase-forming system (pH=6.7, 12w/w% PEG2000, 11w/w% KH₂PO₄) was found out after partition coefficient (Kp=42) , extraction ratio (=96%) and recovery ratio(R=98.8%) were investigated comprehensively in this paper.Hua qiang is one of the cooperators of the experimetal.     

Partitioning and separation of α-lactalbumin and β-lactoglobulin in polyethylene glycol/ammonium sulphate aqueous two-phase systems

The partition behaviour of -lactalbumin (la) and -lactoglobulin (lg) on PEG/(NH₄)₂SO₄ system was studied. For purified proteins, a partition coefficient of 12.8 for la and 0.34 for lg, with mass recovery yields of 96.7% for la in the upper phase and 83.8% for lg in the lower phase was obtained, in 18% (w/w) PEG 900/14% (w/w) (NH₄)₂SO₄ system, at pH 7. PEG/(NH₄)₂SO₄ system was an economical alternative for the recovery and separation of the two proteins in cheese whey, allowing a 50% reduction in costs. An efficient and inexpensive separation of both proteins in cheese whey could be achieved, by using 16% (w/w) PEG 900/15% (w/w) (NH₄)₂SO₄, at pH 7.5.     

Molecular dynamics study on thermal dehydration process of epsomite (MgSO4·7H2O)

Water vapour sorption in salt hydrates is one of the most promising means of compact, low loss and long-term solar heat storage in the built environment. Among all, epsomite (MgSO₄·7H₂O) excels for its high-energy storage density and vast availability. However, in practical applications, the slow kinetics and evident structural changes during hydration and dehydration significantly jeopardise the heat storage/recovery rate. A molecular dynamics (MD) study is carried out to investigate the thermal properties and structural changes in the thermal dehydration process of the epsomite. The MD simulation is carried out at 450 K and a vapour pressure of 20 mbar, in accordance with experimental heat storage conditions. The study identifies the dehydration as multiple stages from the initial quick water loss and collapse of the crystal framework to the adsorption of water molecules, which inhibits complete dehydration. Further, the anisotropic diffusion behaviour supports the important role of the porous matrix structure in the heat and mass transfer process. The enthalpy changes, partial densities, mass diffusion coefficients of water and radial distribution functions are calculated and compared with corresponding experimental data to support the conclusions.     

Influence of partition parameters on a recombinant antigen of Schistosoma mansoni expressed on E. coli using poly(ethylene glycol)–hydroxypropyl starch aqueous two-phase system

This work describes the partition of a Schistosoma mansoni tegumental antigen produced by a recombinant Escherichia coli strain using an aqueous two-phase system (ATPS) composed of polyethylene glycol (PEG) and purified hydroxypropyl-starch (Reppal PES 100). The effects of the polymer molecular weight, tie line length and pH on antigen partitioning were investigated. The detection of the antigen in both phases was determined by ELISA. The system composed of PEG 8000 (5.1% w/w) and Reppal PES 100 (13.0% w/w) led to a yield of 92% and a purification factor of 12 concerning the antigen in the PEG-rich phase. It was observed that antigen partition in ATPSs was strongly affected by the pH and tie line length. In addition, it was possible in a single step, to remove the cell debris, which precipitated at the interface of the system.     

The electronic structure of the C2H4O···2HF tri-molecular heterocyclic hydrogen-bonded complex: a theoretical study

The geometries of three isomers of the C₂H₄O···2HF tri-molecular heterocyclic hydrogen-bonded complex were examined through B3LYP/aug-cc-pVDZ calculations. Analysis of structural parameters, determination of CHELPG (charge electrostatic potential grid) intermolecular charge transfer, interpretation of infrared stretching modes, and Bader’s atoms in molecules (AIM) theory calculations was carried out in order to characterize the hydrogen bonds in each isomer of the C₂H₄O···2HF complex. The most stable structure was determined through the identification of hydrogen bonds between C₂H₄O and HF, (O···H), as well as in the hydrofluoric acid dimer, (HF^D–R···HF^D). However, the existence of a tertiary interaction (F^λ···H^α) between the fluoride of the second hydrofluoric acid and the axial hydrogen atoms of C₂H₄O was decisive in the identification of the preferred configuration of the C₂H₄O···2HF system. Figure Geometries of three isomers of the C₂H₄O···2HF tri-molecular heterocyclic hydrogen-bonded complex     

Resonance Raman studies of the peroxotitanate(IV) complexes K2(Ti(O2)(SO4)2)·5H2O and K2(Ti(O2)(C2O4)2)·3H2O

The resonance Raman spectra of K₂(Ti(O₂)(SO₄)₂)·5H₂O and K₂(Ti(O₂)(C₂O₄)₂)·3H₂O are recorded. The results are consistent with the triangular structure of the peroxotitanium unit, Ti(O₂), with C_2ν symmetry. The ν(OO), ν_s(TiO) and ν_as(TiO) are observed around 890, 610 and 535 cm⁻¹, respectively. The resonance effects are shown to be associated with the 425 nm absorption band. This band is assigned to the O₂²⁻ → Ti(IV) charge-transfer transition. The calculated force constant values for the O₂²⁻ and TiO bonds are 320 and 275 N m⁻¹, respectively.     

The structure and properties of tetrakis(tironato)cerate(IV), Na12[Ce(C6H2O2(SO3)2)4]·9H2O·6C3H7NO

The title complex, prepared in 1 M NaOH, was crystallized from hot N,N-dimethylformamide/ ethanol solutions to give Na₁₂[Ce(C₆H₂O₂(SO₃)₂)₄]· 9H₂O·6DMF. The purple—brown crystals were examined by X-ray diffraction while inside quartz capillaries filled with DMF, (λ_max 425 nm, ϵ 3664; λ_sh 520 nm, ϵ 2240) and belong to space group Pbca, Z=8 with a=21.846(4), b=17.348(2), c=43.103- (6) Å, V=16.335(7) ų, D_c=1.693 gcm^t−3, D_o=1.725 g cm^t−3. Diffractometer data were collected using Mo Kα radiation to 2θ=43^o. For 7331 independent data with F_o²>3σ(F_o²) full matrix least squares refinement converged to unweighted and weighted R factors of 0.072 and 0.110, respectively, with a mixture of anisotropic and isotropic thermal parameters. The disordered DMF atom parameters were not refined. The structure consists of discrete monomeric Ce(C₆H₂S₂O₈)₄¹²⁻ units with 12 Na⁺ counter cations and 10 H₂O molecules (two with half occupancy), and 6 DMF molecules of solvation filling up spaces between cations and anions. Cerium(IV) is in a general position with a coordination polyhedron close to the trigonal-faced dodecahedron, D_2d, with the angles between the two BAAB trapezoids of 2.3^o and 3.7^o. The average CeO(A) distance, 2.363(9) Å is longer than the average CeO(B) distance, 2.326(15)Å, with the reverse being true for one of the four tironato ligands. The average ring OCeO angle is 67.9(1)^o. The cerium (IV) complex is found by cyclic voltammetry to undergo a quasi-reversible one-electron reduction (in strongly basic solution with excess tiron) with Ef=−497 mV vs. SCE, hence the ratio of the formation constants for tetrakis(tironato)cerate(IV) to that for tetrakis(tironato)cerate(III), K_IV/K_III, is 10³³. Characterization of other tiron salts is reported.     

Weak coherent radiation of OH and ortho- H2O space masers as a carrier in biocommunication: the ortho/para-conversion of H2O spin isomers?

A conception of biocommunication based on the principle of radiophysics stating that the carrier modulation takes place at the resonance frequency in the transmission-receiver system has been substantiated and proved. The coherent radiation of space OH-masers (1.6-1.7 GHz) and ortho-H2O-maser (22.3 GHz) is proposed as a source of the carrier frequency. The narrow lines of rotational transition of H2O and OH molecules in liquid water were proposed to be considered as an analog of selective resonances of transmitter and receiver in radiocommunication. The possibility of the ortho-para conversion of H2O spin isomers, induced by weak electromagnetic fields, is discussed.     

Platinum(II) complexes of methyl-substituted xanthines: crystal structures of K[Pt(theobromine)Cl3]·H2O,trans-[ Pt(isocaffeine)2Cl2]·H2O and K(isocaffeinium)[PtCl4]·H2O

The preparations of Pt(theophylline)₂Cl₂, K[Pt- (theophylline)Cl₃], K[Pt(theobromine)Cl₃]·H₂O (1), trans-[Pt(isocaffeine)₂Cl₂]·H₂O (2), and K(isocaffeinium)[PtCl₄]·H₂O (3) are reported.Crystals of 1 are monoclinic P2₁/n with a=7.641- (2), b=11.873(3), c=15.868(4) Å, β=90.80(2)°, Z=4. The structure was refined on 1443 reflections to R=0.028. In the planar [Pt(theobromine)Cl₃]⁻ anion Pt-N(9)=2.016(6) Å, Pt-Cl=2.299(2), 2.289(2), and 2.303(2) Å. The imidazole ring is rotated away from the coordination plane by 79.8°. Symmetry related theobromine units pack parallel to each other with a mean inter-ring separation of 3.27 Å.Crystals of 2 are monoclinic P2₁/a with a=7.345- (2), b=20.021(5), c=8.031(2) Å, β=104.18(2)°, Z=2. The structure was refined on 1132 reflections to R=0.029. The Pt-N(7) distance is 2.003(3) Å and Pt-Cl=2.298(1) Å. The imidazole ring is rotated away from the PtCl₂N₂ plane by 76.8°. In this compound, the isocaffeine units do not stack, but form a staggered arrangement within the unit cell.Crystals of 3 are monoclinic P₁/c with a= 7.382- (1), b=14.014(4), c=15.757(4) », β=92.30(2)°, Z=4. The structure was refined on 2057 reflections to R=0.032. The isocaffeine is protonated at N(7). The Pt-Cl distances in the PtCl₄²⁻ anion range between 2.29–2.31 Å. The protonated isocaffeine cations and the PtCl₄²⁻ anions form a very nearly parallel infinitely stacked arrangement with minimum interlayer atomic separations of 3.37 and 3.44 Å.     

Analysis of [2H7]methionine, [2H4]methionine,methionine, [2H4]homocysteine and homocysteine in plasma by gas chromatography–mass spectrometry to follow the fate of administered [2H7]methionine

Homocysteine plays a key role in several pathophysiological conditions. To assess the methionine–homocysteine kinetics by stable isotope methodology, we developed a simultaneous quantification method of [²H₇]methionine, [²H₄]methionine, methionine, [²H₄]homocysteine and homocysteine in rat plasma by gas chromatography–mass spectrometry (GC–MS). [¹³C]Methionine and [¹³C]homocysteine were used as analytical internal standards to account for losses associated with the extraction, derivatization and chromatography. For labeled and non-labeled homocysteine measurements, disulfide bonds between homocysteine and other thiols or proteins were reduced by dithiothreitol. The reduced homocysteine and methionine species were purified by cation-exchange chromatography and derivatized with isobutyl chlorocarbonate in water–ethanol–pyridine. Quantification was carried out by selected ion monitoring of the molecular-related ions of N(O,S)-isobutyloxycarbonyl ethyl ester derivatives on the chemical ionization mode. The intra- and inter-day precision of the assay was less than 6% for all labeled and non-labeled methionine and homocysteine species. The method is sensitive enough to determine pharmacokinetics of labeled methionine and homocysteine.     

Uric acid salts of magnesium: crystal and molecular structures and thermal analysis of two phases of Mg(C5H3N4O3)2 · 8H2O

Two structurally different phases of a uric acid salt of magnesium, Mg(hydrogenurate)₂ · 8H₂O, have been prepared by crystallization from solution at pH = 7.5–8.0 and were investigated by x-ray crystallography, thermal analysis, and ir spectroscopy. Both phases are monoclinic, space group P2₁/c with a = 9.573(2), b = 14.627(3), c = 7.170(1) Å, β = 101.91(1)° (phase I) and a = 10.397(2), b = 14.306(3), c = 6.732(1) Å, β = 104.64(2)° (phase II). The crystal structures of both phases (R = 0.053 and 0.051, respectively) contain isolated octahedral [Mg(H₂O)₆]²⁺ cations, hydrogenurate monoanions, and two molecules of water of crystallization per formula unit. The structural formula representing these facts is [Mg(H₂O)₆] (hydrogenura-te)₂·2H₂O. The tautomeric form of the hydrogenurate molecule corresponds to the tri-keto form of uric acid deprotonated at N(3). Differences in bond length between uric acid and the hydrogenurate molecule may be described in terms of three additional resonance structures distributing the formal negative charge at N(3) within the pyrimidine (but not the imidazole) ring. Deprotonation at N(3) significantly decreases the internal C-N-C angle at N(3). Alternating pairs of medium-strong intermolecular N-HO hydrogen bonds lead to infinite chains of hydrogenurate molecules extending along the b axis of the unit cells in both phases. The main difference between the two phases lies in their stacking pattern of the hydrogenurate molecules. Infrared data confirm the hydrogen bonding characteristics resulting from the crystal structure analysis. Thermogravimetric measurements and differential scanning calorimetry data show that the dehydration of both phases occurs in two distinct steps with Mg(hydrogenurate)₂.6H₂O as an intermediate phase. The first dehydration step (−2H₂O) is a topotactic reaction with three-dimensional preservation of the main structure elements of the octahydrate in the structure of the hexahydrate.     

The relative effectiveness of .OH,H2O2,O2−, and reducing free radicals in causing damage to biomembranes: A study of radiation damage to erythrocyte ghosts using selective free radical scavengers

The relative effectiveness of oxidizing (^.OH, H₂O₂), ambivalent (O₂^?) and reducing free radicals (e^? and CO₂^?) in causing damage to membranes and membrane-bound glyceraldehyde-3-phosphate dehydrogenase of resealed erythrocyte ghosts has been determined. The rates of damage to membranebound glyceraldehyde-3-phosphate dehydrogenase ($\text{R}$(enz)) were measured and the rates of damage to membranes ($\text{R}$(mb)) were assessed by measuring changes in permeability of the resealed ghosts to the relatively low molecular weight substrates of glyceraldehyde-3-phosphate dehydrogenase. Each radical was selectively isolated from the mixture produced during gamma-irradiation, using appropriate mixtures of scavengers such as catalase, superoxide dismutase and formate. ^.OH, O₂^? and H₂ O₂ were approximately equally effective in inactivating membrane-bound glyceraldehyde-3-phosphate dehydrogenase, while e^? and CO₂^? were the least effective. $\text{R}$(enz) values of O₂^? and H₂O₂ were 10-times and of ^.OH 15-times that of e^?. $\text{R}$(mb) values were quite similar for e^? and H₂O₂ (about twice that of O₂^?), while that of ^.OH was 3-times that of O₂^?. Hence, with respect to $\text{R}$(mb): ${}^{\mathrm{.}}\text{OH}\text{>}\text{e}{}^{\mathrm{?}}\text{=}\text{H}{}_2\text{O}{}_2\text{>}\text{O}{}_2{}^{\mathrm{?}}$ , and with respect to $\text{R}$(enz): ${}^{\mathrm{.}}\text{OH}\text{>}\text{O}{}_2{}^{\mathrm{?}}\text{=}\text{H}{}_2\text{O}{}_2\text{>}\text{e}{}^{\mathrm{?}}$. The difference between the effectiveness of the most damaging and the least damaging free radicals was more than 10-fold greater in damage to the enzyme than to the membranes. Comparison between H₂O₂ added as a chemical reagent and H₂O₂ formed by irradiation showed that membranes and membrane-bound glyceraldehyde-3-phosphate dehydrogenase were relatively inert to reagent H₂O₂ but markedly susceptible to the latter.     

SnCl4 · 5H2O-catalyzed synthesis of β-amino carbonyl compounds via a direct Mannich-type reaction

An efficient three-component, one-pot synthesis of β-amino carbonyl compounds from aromatic ketones, aromatic aldehydes, and aromatic amines using tin tetrachloride at room temperature in ethanol is described. The advantages of the new method are good yields (62-96%), simple workup, and inexpensive catalyst.     

2′,4′-BNA/LNA aptamers: CE-SELEX using a DNA-based library of full-length 2′-O,4′-C-methylene-bridged/linked bicyclic ribonucleotides

DNA-based aptamers that contain 2′-O,4′-C-methylene-bridged/linked bicyclic ribonucleotides (B/L nucleotides) over the entire length were successfully obtained using a capillary electrophoresis systematic evolution of ligands by exponential enrichment (CE-SELEX) method. A modified DNA library was prepared with an enzyme mix of KOD Dash and KOD mutant DNA polymerases. Forty 2′-O,4′-C-methylene bridged/locked nucleic acid (2′,4′-BNA/LNA) aptamers were isolated from an enriched pool and classified into six groups according to their sequence. 2′,4′-BNA/LNA aptamers of groups V and VI bound human thrombin with K_d values in the range of several 10 nanomolar levels.     

15α-Hydroxylation of a steroid (13-ethyl-gon-4-en-3,17-dione) by Penicillium raistrickii in an ionic liquid/aqueous biphasic system

Biphasic processes are used in whole-cell biotransformation to overcome the low water solubility of substrates and products as well as their inhibitory effects on the biocatalyst. Commercially available [NTf₂]- and [PF₆]-based ionic liquids (ILs) were used in a biphasic system for the 15α-hydroxylation of 13-ethyl-gon-4-en-3,17-dione by Penicillium raistrickii. With the substrate at 5 g l^?1 and a volume ratio of IL to buffer, buffer pH and cell density at, 1:9, 6.5, 16.8 g_DW l^?1, respectively, the 15α-hydroxylation of 13-ethyl-gon-4-en-3,17-dione was achieved with a yield of 70 % after 72 h using [BMIm][NTf₂] in a 50 ml biphasic system. This is compared to a 30 % yield in a monophasic aqueous system. This suggests the potential industrial application of ILs-based biphasic systems for steroid biotransformation.     

4′-C-Aminomethyl-2′-deoxy-2′-fluoroarabinonucleoside increases the nuclease resistance of DNA without inhibiting the ability of a DNA/RNA duplex to activate RNase H

An antisense oligonucleotide is expected as an innovative drug for cancer and hereditary diseases. In this paper, we designed and synthesized DNAs containing a novel nucleoside analog, 1-(4-C-aminomethyl-2-deoxy-2-fluoro-β-d-arabinofuranosyl)thymine, and evaluated their properties. It was revealed that the analog slightly decreases the thermal stability of the DNA/RNA duplex but significantly increases the stability of DNA in a buffer containing bovine serum. Furthermore, it turned out that the DNA/RNA duplex containing the analog is a good substrate for Escherichia coli RNase H. Thus, DNAs containing the nucleoside analog would be good candidates for the development of therapeutic antisense oligonucleotides.