Glycol modified titanosiloxane as molecular precursor for homogenous titania–silica material: synthesis and characterization

Ti(OPrⁱ)₄ reacts with HOSi(O^tBu)₃ in anhydrous benzene in 1:1 and 1:2 molar ratios to afford alkoxy titanosiloxane precursors, [Ti(OPrⁱ)₃{OSi(O^tBu)₃}] (A) and [Ti(OPrⁱ)₂{OSi(O^tBu)₃}₂] (B), respectively. Further reactions of (A) or (B) with glycols in 1:1 molar ratio afforded six complexes of the types [Ti(OPrⁱ)(O–G–O){OSi(O^tBu)₃}] (1A–3A) and [Ti(O–G–O){OSi(O^tBu)₃}₂] (1B–3B), respectively [where G = (CH₂)₂ (1A, 1B); (CH₂)₃ (2A, 2B) and {CH₂CH₂CH(CH₃)} (3A, 3B)]. Both (A) and (B) are liquids while all the other products are viscous liquids which get solidified on ageing. Cryoscopic molecular weight measurements of the fresh products indicate their monomeric nature. FAB mass studies of (A) and (B) also indicate monomeric nature. However, FAB mass spectra of the two representative solids (1A) and (2B) suggest dimeric behavior of the glycolato derivatives. (A) distills at 85 °C/5 mm while other products get decomposed even under reduced pressure. TG analyses of (A), (B), (1A), and (1B) suggest formation of titania–silica materials at 200 °C for (A) and (B) and 350 °C for (1A) and (1B). The products have been characterized by elemental analyses, FTIR and ¹H, ¹³C & ²⁹Si-NMR techniques. All these products are soluble in common organic solvents indicating a homogenous distribution of the components on the molecular scale. The Si/Ti ratio of the oxide may be controlled easily by the composition of the starting precursors. Hydrolysis of the glycol modified derivative, (1A) by the Sol–Gel technique affords the desired homogenous titania–silica material, TiO₂·SiO₂ in nano-size while, the precursor (A) yields a non-stiochiometric silica doped titania material. However, pyrolysis of (A) yields nano-sized crystallites of TiO₂·SiO₂. All these materials were characterized by FTIR, powder XRD patterns, SEM images, and EDX analyses.     

Non-conventional multi-arm ester liquid crystal derived from cholic acid: synthesis,thermal and optical behaviour

ABSTRACT

With cholic acid as the core, five multi-arm ester liquid crystals were synthesised with different terminal substituents. B₁–B₅ were mesogenic arms which were linked to multifunctional chiral core cholic acid. The effect of electron-withdrawing and electron-donating groups on the mesogenic behaviour of the compounds was discussed. All products were structurally well characterised by elemental analysis, ¹HNMR, and FT-IR. The phase behaviours were investigated by means of polarised optical microscopy and differential scanning calorimetry. B₂, B₄, B₅ and C₂, C₄, C₅ and D₂, D₄, D₅ exhibited typical nematic texture and belonged to thermotropic enantiotropic nematic liquid crystals. B₃, C₃ and D₃ also displayed typical nematic texture of thermotropic monotropic nematic liquid crystal. B₁, C₁ and D₁ did not have mesogenic performance. Wider mesogenic range for 81.6°C of C₅ whose terminal substituent is nitro on heating cycle while 121.1°C on cooling cycle. The results indicated that terminal substituents have a pretty important effect on the mesogenic phase and range of multi-arm liquid crystal compounds. The mesomorphic behaviour of compounds with polar groups terminally substituted performance much better than those without polar groups. In this ester multi-arm liquid crystal system, electron-withdrawing groups terminally substituted behave better than those electron-donating groups substituted.     

The bacitracin biosynthesis operon of Bacillus licheniformis ATCC 10716: molecular characterization of three multi-modular peptide synthetases

Background: The branched cyclic dodecylpeptide antibiotic bacitracin, produced by special strains of Bacillus, is synthesized nonribosomally by a large multienzyme complex composed of the three bacitracin synthetases BA1, BA2 and BA3. These enzymes activate and incorporate the constituent amino acids of bacitracin by a thiotemplate mechanism in a pathway driven by a protein template. The biochemical features of these enzymes have been studied intensively but little is known about the molecular organization of their genes.Results: The entire bacitracin synthetase operon containing the genes bacA-bacC was cloned and sequenced, identifying a modular structure typical of peptide synthetases. The bacA gene product (BA1, 598 kDa) contains five modules, with an internal epimerization domain attached to the fourth; bacB encodes BA2 (297 kDa), and has two modules and a carboxy-terminal epimerization domain; bacC encodes BA3, five modules (723 kDa) with additional internal epimerization domains attached to the second and fourth. A carboxy-terminal putative thioesterase domain was also detected in BA3. A putative cyclization domain was found in BA1 that may be involved in thiazoline ring formation. The adenylation/thioester-binding domains of the first two BA1 modules were overproduced and the detected amino-acid specificity coincides with the first two amino acids in bacitracin. Disruption of chromosomal bacB resulted in a bacitracin-deficient mutant.Conclusions: The genes encoding the bacitracin synthetases BA1, BA2 and BA3 are organized in an operon, the structure of which reflects the modular architecture expected of peptide synthetases. In addition, a putative thiazoline ring formation domain was identified in the BA1 gene.     

Normal Phase High Performance Liquid Chromatography of Some Prostaglandin B1 Derivatives

Abstract

15-Keto-13, 14-trans-prostaglandin B₁ methyl ester, 13,14-trans-prostaglandin B₁ methyl ester, 13,14-cis-prostaglandin B₁ methyl ester, 13,14-dihydro-prostaglandin B₁ methyl ester and 13,14-dehydro-prostaglandin B₁ are organic intermediates used in the synthesis of prostaglandin B_x, a polymeric derivative of 15-keto-prostaglandin B₁ methyl ester. PGB_x has been shown to protect laboratory animals against cardiogenic shock, cerebral ischemia and hypoxia. A normal phase, high performance liquid chromatographic analysis is presented which permits the identification and quantitation of these PGB₁ intermediates.     

Zur Darstellung unsymmetrisch substituierter Bis(organylamino) silane

The title compoundsR ₂Si(NHR ¹) (NHR ²) (B) were prepared according to Equ. (2) and (3) and via formerly unknown diphenyl-chloro-organylaminosilanes (A) as intermediates. The complex course of formation ofB in competition withR ₂Si (NHR ¹)₂ (C) andR ₂Si(NHR ²)₂ (D) (Scheme 1, Equ. (4)–(7), Table 2) was investigated in detail. Results of thermal rearrangement ofB are given in Table 5. Five novelA and six novelB compounds are confirmed by properties, elemental and structural data (Tables 1, 3 and 4).

Mit Auszügen aus der DissertationS. Klemke, Techn. Univ. Braunschweig 1978.     

Supramolecular system composed of B12 model complex and organic photosensitizer: impact of the corrin framework of B12 on the visible-light-driven dechlorination without the use of noble metals

The visible-light-driven dechlorination system without the use of a noble metal has been developed. We screened the combination of cobalt catalysts having square-planar monoanionic ligands (hydrophobic B₁₂ model complex 1/imine-oxime type complex 2) and typical red dyes (Rose Bengal 3/Rhodamine B 4/Nile Red 5) for the construction of a dehalogenation system via a noble-metal-free and visible-light-driven process. The combination of the hydrophobic B₁₂ model complex 1 and Rose Bengal 3 exhibited the highest catalytic activity to 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) to form the monodechlorinated compound, 1,1-bis(4-chlorophenyl)-2,2-dichloroethane, as the major product. The prolonged photocatalysis of DDT by the B₁₂–Rose Bengal system afforded the tri-dechlorinated compound, trans-4,4′-dichlorostilbene, as the major product. Furthermore, we investigated the mechanism of the dehalogenation cycle using various methods such as UV–vis spectroscopy and laser flash photolysis. Finally, we clarified the advantage of using the hydrophobic B₁₂ model complex 1 as an electron acceptor as well as a cobalt catalyst in the organic dye-involved photocatalysis.     

Influence of Molar Mass Distribution on the Compatibility of Polymers

Abstract

Phase equilibria were calculated by means of a new method (direct minimization of the Gibbs energy of mixing) for polymer blends consisting of monodisperse polymer A and polydisperse polymer B. The results obtained for a Schulz-Flory distribution of B (molecular nonuniformity U = (M _w/M _n) ?1 = 1 and 100 components of model B) agree quantitatively with that of computations on the basis of continuous thermodynamics. The influence of U _B on the miscibility of A and B in 1:1 mixtures was studied for constant M _w of B, quantifying the incompatibility of the polymers by the length of the tie lines. The outcome of these calculations demonstrates that the typical effect of an augmentation of U _B (keeping M _w and the overall composition constant) consists in an enlargement of the mutual solubility of A and B. However, for an almost compatible pair of polymers (i.e., interaction parameters g are only slightly larger than the critical values for U _B = 0), this statement remains true only in the case of sufficiently small U _B. In order to gain some understanding of these findings, calculations were also performed for ternary systems (A and two species B). They demonstrate that it is the distance of the overall composition in the Gibbs phase triangle to the critical line (connecting the critical points for different U _B) which governs the changes in compatibility. Normally the critical point comes closer to the overall composition as U _B is raised, except for low g values where the critical point — after an initial approach — drifts apart as U _B becomes larger.     

Semi-Preparative High Performance Liquid Chromatographic Separation of Carbon-14 Labeled Avermectin B1a from a Mixture of Avermectins

Abstract

A semi-preparative high performance liquid chromatographic method has been developed to separate carbon-14 labeled avermectin B_1a from a fermentation mixture of carbon-14 labeled avermectins, i. e., avermectins A₁a, A₁b, A₂a, A₂b, B₁a, B₁b, B₂a, and B₂b. Two HPLC systems were employed for the separation: I. A Whatman M20, Partisil 10, normal phase column and a solvent system of 10% ethanol in isooctane (v/v), and II. A Whatman M20, Partisil 10, ODS-3, reverse phase column and a solvent system of acetonitrile/methanol/water (56:18:26, v/v/v); the flow rate was 18 ml/ min. Avermectin separations were monitored using ultraviolet detection (254 nm). Further analyses of avermectin B₁a were done using analytical HPLC and TLC/radioassay to check compound purity and identity.     

Viscosity of nematic mixtures: A free-volume approach

Abstract

The five Leslie viscosities for a mixture of two nematic materials are computed as functions of the temperature, composition and order parameter. It is shown that, for a nematic mixture of A and B, the equations describing the composition and temperature behaviour of the Leslie viscosities have the same form as those for the pure components, provided that composition-averaged values of the parameters are used. For the case where the free volume is additive, the relaxation times for the mixtures can be directly expressed as functions of the parameters for the pure components. These results are compared with the experimental data on λ₁ for MBBA/EBBA mixtures, and fairly good agreement is found.     

Angucycline antibiotics and its derivatives from marine-derived actinomycete Streptomyces sp. A6H

Vineomycin A₁ (1) and B₂ (2) were isolated from the culture broth of marine actinomycete Streptomyces sp. A6H. Five hydrolysis products were obtained by rational hydrolysis and methanolysis of the fermentation extract. Their structures were characterised as aquayamycin (3), vineomycinone B₂ (4), 9-C-_D-olivosyltetrangulol (5), 7-O-methylgaltamycinone (6) and vineomycinone B₂ methyl ester (7). In addition to these compounds, two ester derivatives, vineolactone A (8) and vineomycinone B₂ benzyl ester (9) of compound 4 were generated semisynthetically. Compound 6 is a new analogue of galtamycinone, while compounds 8 and 9 are new members of vineomycins. Cytotoxic activities and antimicrobial activities were determined for all compounds. The results indicate that only compound 1 showed significant activities with IC₅₀ value of 0.34 μM against H1975 and MIC value of 4 μg/mL against Staphylococcus aureus.     

半夹芯16电子碳硼烷化合物Cp*CoS2C2B10H10与含磷化合物的反应性

半夹芯16电子碳硼烷化合物Cp~*CoS_2C_2B_(10)H_(10)分别与二苯基甲基膦、苯基二甲基膦和三甲基膦反应得到碳硼烷衍生物(Cp~*CoS_2C_2B_(10)H_(10))(PPh_2Me)(1)、(Cp~*CoS_2C_2B_(10)H_(10))(PPhMe_2)(2)和(Cp~*CoS_2C_2B_(10)H_(10))(PMe_3)(3)。分别用红外、核磁、元素分析、质谱和单晶X射线衍射等表征方法对1、2和3进行了结构表征。紫外可见吸收光谱结果显示化合物1、2和3在乙腈溶剂中均有2个吸收峰,第一个吸收峰分别位于321、316和321 nm;第二个吸收峰分别位于425、399和407 nm。荧光光谱结果显示化合物1、2和3在乙腈中的最大发射波长位于406 nm左右。     

能量最低构型Ca2B4团簇的储氢性能

基于密度泛函理论,研究了Ca₂B₄团簇的几何结构、电子特征和储氢性能。前2个与第4个能量最低构型Ca₂B₄ 01、Ca₂B₄02和Ca₂B₄ 04有很高的热力学稳定性,分别最多可以吸附12、12和10个氢分子,达到16.3%、16.3%和14.0%的储氢量,超过了美国能源部提出的目标(5.5%）。Ca₂B₄ 01(H₂)₁₂、Ca₂B₄ 02(H₂)₁₂和Ca₂B₄ 04(H₂)₁₀的平均每个氢分子吸附能量分别为0.58~4.21 eV、0.54~3.69 eV和0.10~0.12 eV。玻恩-奥本海默分子动力学模拟表明,Ca₂B₄ 01和Ca₂B₄ 02可作为潜在吸附氢气的候选目标,而Ca₂B₄ 04不行。吉布斯自由能校正的氢吸附能结果表明,在101 325 Pa下,Ca₂B₄ 01和Ca₂B₄ 02吸附12个氢气分子有较大的可调节的温度范围。     

Synthesis,structure and methyl methacrylate polymerization of cobalt(II), zinc(II) and cadmium(II) complexes with N,N′,N-bidentate versus N,N′,N-tridentate N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines

Mononuclear Co(II), Zn(II) and Cd(II) complexes derived from bidentate or tridentate N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines (L_n = L_A, L_B), where L_A is N,N-bis((1H-pyrazol-1-yl)methyl)-3-methoxypropan-1-amine and L_B is 3-methoxy-N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)propan-1-amine, have been synthesized and characterized. The geometry at Co(II) and Cd(II) for [L_ACoCl₂], [L_BCoCl₂] and [L_BCdBr₂] with N,N′,N-tridentate ligands (L_n = L_A, L_B) can be described as a distorted trigonal bipyramid achieved by coordinative interaction of N_pyrazole, two halides and the nitrogen of amine moiety. However, the molecular structure of four-coordinate [L_AZnCl₂] can be best described as tetrahedral, resulting in an eight-membered chelate ring. [L_ACoCl₂] polymerized methyl methacrylate in the presence of modified methylaluminoxane at 60 °C and resulted in poly(methylmethacrylate) (PMMA) with higher molecular weight and narrower polydispersity index compared to the other synthesized complexes. However, all the synthesized complexes yielded syndiospecific PMMA, characterized using ¹H NMR spectroscopy, with ca. 0.70.     

The binary system composed of a bent-core compound forming a B7 phase and a nematogenic calamitic compound

The isobaric phase diagram for a binary system of liquid crystals is presented. One mixing component is a bent-core mesogen forming a B₇ phase and the other one is a nematogenic calamitic compound. The occurring mesophases have been identified by their optical textures as well as by X-ray investigations. The B₇ phase exists down to about 60 mol% of the bent-core compound A / 40 mol% of the calamitic compound B. Two additional mesophases are induced in the mixed phase region. At medium concentrations (around 50 mol%) an oblique columnar phase appears which shows a similar X-ray pattern to the B₇ phase but an utterly different nucleation on cooling the isotropic liquid and a completely dissimilar texture. At concentrations below 35 mol% A, a further phase is induced which possesses an irregularly modulated layer structure. This phase can be regarded as an intermediate state between the regularly modulated Col_r (B₁) phase and the intercalated B₆ phase. It transforms on cooling into the phase with a regularly modulated structure.     

The Use of HPLC/Thermospray Ms for the Confirmation of Aflatoxins in Peanuts

Abstract

An HPLC/Thermospray MS method is described for the determination of aflatoxins B₁, B₂, G₁ and G₂ in peanut extracts. Samples are extracted and prepared for analysis using an SPE method. The final determination utilizes reversed phase HPLC with a thermospray MS detector. The use of the MS allowed for unequivocal identification of aflatoxins in the extracts.     

Coordination interactions in the crystalline lattice of alkaline ions with the polyoxometalate [V12B18O60H6]10− ligand

In the present work, the synthesis and structural characterization of two new polyoxovanadoborate (BVO) frameworks, based on the [V₁₂B₁₈O₆₀H₆]^10? polyanion, are reported, K(H₃O)(enH₂)₄[V₁₂B₁₈O₆₀H₆]·9.60H₂O (1) and Li₈(NH₄)₂[V₁₂B₁₈O₆₀H₆]·8.02H₂O (2). Both compounds are obtained in a mixed valence ratio of 10V^IV/2V^V. Framework 1 is characterized by potassium ions coordinated by the BVO cluster and ethylenediammonium and hydronium ions as charge-compensating agents. In framework 2, the BVO clusters are coordinating lithium ions and the charge is compensated by ammonium ions. Using the SHAPE 2.1 program, it was possible to calculate the best geometry for the existing lithium and potassium ions. For 2, the lithium ions are five-coordinate, best described by a square pyramid (SPY-5), while the coordination sphere around the potassium ions in 1 are six-coordinate. For 1, the coordination sphere of the existing potassium ions in the framework can be described as trigonal prism (TPR-6). Calculations were also done for a previously reported cluster [Na₁₀[(H₂O)V₁₂B₁₈O₆₀H₆]·18H₂O] (3), in which the sodium ions are six-coordinate but in two different geometries, these being octahedral and TPR-6. The influence of the interactions of the alkali ions with the [V₁₂B₁₈O₆₀H₆]^10? polyanion, on the vanadate and borate absorption bands observed in the infrared spectra, is discussed.     

Simultaneous Quantification of Neomycin and Bacitracin by LC-ELSD

The first simultaneous quantification of neomycin and bacitracin using liquid chromatography evaporative light scattering detection as an alternative to MS detection and pre-/post-column derivatisation, respectively, was the aim of this study. The developed method was validated for two strength of neomycin and one strength of bacitracin in sterile pharmaceutical formulation and is a fast and efficient tool for content uniformity tests in quality control. With this method the separation of neomycin from sulfate and the base line separation of the four major components of bacitracin (bacitracin A, B1, B2 and B3) was achieved. These four components are responsible for 96% of the microbiological activity. A Phenomenex Synergi POLAR analytical column (250 mm × 4.6 mm, 4 μm I.D.) in combination with 0.5% perfluoropropionic acid and acetonitrile in gradient mode, the peaks of interest could be separated with high efficiency within 14 min. The calibration was performed using a second order regression with an R ² = 0.9999 for neomycin (B and C) sulfate and R ² = 0.9996 for bacitracin A, B1, B2 and B3. The results of the accuracy evaluation were 99.2 and 99.7%, respectively, for neomycin and 100.8% for bacitracin. Injection precision results are 0.4–1.5 RSD% recorded for six injections. The established method has a high potential for routine high-throughput analyses in the pharmaceutical industry.

     

AFB1–AP Conjugate for Enzyme Immunoassay of Aflatoxin B1 in Corn Samples

Abstract

This article describes the conjugation between aflatoxin B₁ (AFB₁), one of the major mycotoxins, and alkaline phosphatase (AP), one of the most used enzymes for immunoassays. In addition, an application of the ELISA method for aflatoxin B₁ determination in corn is presented. Three AFB₁–AP conjugates in different toxin–enzyme ratios were prepared and tested. The ELISA results, developed with the most effective conjugate obtained, showed a satisfactory working range between 2.4 and 4000 ng of toxin/g of corn. The detection limit was 2 ng/g in corn samples, and recoveries ranged from 105 to 120%.     

Photochemical arene exchange in the ferracarborane complex [1-(η-C6H6)-12-ButNH-1,2,4,12-FeC3B8H10]+

The benzene complex [1-(η-C₆H₆)-12-Bu^tNH-1,2,4,12-FeC₃B₈H₁₀]⁺ (3a) was synthesized by the photochemical reaction of [(η⁵-C₆H₇)Fe(η-C₆H₆)]⁺ (1) with the anion [7-Bu^tNH-7,8,9-C₃B₈H₁₀]⁻ followed by the treatment of ferracarborane 1-(η⁵-C₆H₇)-12-Bu^tNH-1,2,4,12-FeC₃B₈H₁₀ (2) with hydrochloric acid. The benzene ligand in cation 3a is replaced by alkyl-substituted benzenes under visible light irradiation in CH₂Cl₂ to form [1-(η-C₆R₆)-12-Bu^tNH-1,2,4,12-FeC₃B₈H₁₀]⁺ (3b–e; C₆R₆ is toluene (b), mesitylene (c), hexamethylbenzene (d), or anisole (e)). The structure of [3c]PF₆ was established by X-ray diffraction.     

Synthesis of μ-diborolyl triple-decker complexes [CpCo(1,3-C<Subscript>3</Subscript>B<Subscript>2</Subscript>Me<Subscript>5</Subscript>)Ru(arene)]<Superscript>+</Superscript>

Cationic triple-decker complexes [CpCo(1,3-C₃B₂Me₅)Ru(arene)]PF₆ (arene is benzene (2a), p-cymene (2b)) with a bridging diborolyl ligand were synthesized by the reaction of the sand-wich anion [CpCo(1,3-C₃B₂Me₅)]⁻ (1) with [(arene)RuCl₂]₂. The structure of [2b]PF₆ was confirmed by X-ray diffraction analysis.