Phenomena Affecting the Equilibrium of Al(III) and Zn(II) Extraction with Winsor II Microemulsions

The extraction of Al(III) and Zn(II) from an aqueous solution with two water-in-oil microemulsions, one containing di(2-ethylhexyl)phosphoric acid (DEHPA), was investigated to aid the understanding of the role of the extractant and the metal specific characteristics in the mechanism of microemulsion extraction. The extraction of Al with the DEHPA microemulsion increased by a factor of about 10 with respect to that in the conventional DEHPA system, whereas the extraction of Zn was lower than that in the single DEHPA system. Extraction with the DEHPA-free microemulsion was very low, showing that metal ion solubilization was not important in the mechanism of microemulsion extraction. It is proposed that the effect of the mixed microemulsion on the metal distribution coefficient is the result of the balance between a decrease in the complexation reaction yield due to the interaction between butanol and DEHPA, and the adsorption of the metal complex at the macro- and microinterfaces. The former leads to a decrease in Zn(II) extraction and the latter to Al(III) extraction synergism. Copyright 2000 Academic Press.     

Tumor-specific and photodependent cytotoxicity of hypericin in the human LNCaP prostate tumor model

Hypericin (HYP) has been reported to have photodependent cytotoxic activity in a variety of cancer cell lines. However, this activity has yet to be rigorously tested in vivo in tumor models. In this study LNCaP, PC-3 and DU-145 cells were used to test the cytotoxic effects of HYP in vitro, precursory to an in vivo study designed to investigate the effects of HYP in an established murine model for prostate cancer. Specifically, the model used employs immunocompromised nude mice bearing the LNCaP solid tumor xenograft. In vitro cytotoxicity experiments indicated that the dose causing 50% lethality for HYP in LNCaP, PC-3 and DU-145 cells were 2.07, 2.15 and 2.23 microM, respectively, following irradiation with red light (590 nm) for 30 min at a fluence rate of 0.1 J/cm2/s. Cells treated with HYP in the absence of photoirradiation showed no signs of cytotoxicity. A tissue distribution study was also carried out using the LNCaP solid tumor model to determine whether or not HYP is distributed to the target tissue. HYP was broadly distributed in tissues studied, including LNCaP tumor xenograft tissue. Furthermore, tumor tissue eliminated HYP at a slower rate than any of the other tissues examined. Interestingly, HYP levels were maintained in serum 24 h after oral administration (5 mg/kg dose). A pilot study designed to examine the efficacy of HYP treatment in nude mice bearing LNCaP tumors conducted over 28 days suggested that HYP, in combination with photoirradiation, inhibits both tumor growth and the elevation of prostate-specific antigen levels. Although the results reported for the current studies are preliminary they do provide evidence for an application of HYP PDT to prostate cancer which warrants further investigation.     

Using shared sell-through data to forecast wholesaler demand in multi-echelon supply chains

Operational forecasting in supply chain management supports a variety of short-term planning decisions, such as production scheduling and inventory management. In this respect, improving short-term forecast accuracy is a way to build a more agile supply chain for manufacturing companies. Demand forecasting often relies on well-established univariate forecasting methods to extrapolate historical demand. Collaboration across the supply chain, including information sharing, is suggested in the literature to improve upon the forecast accuracy of such traditional methods. In this paper, we review empirical studies considering the use of downstream information in demand forecasting and investigate different modeling approaches and forecasting methods to incorporate such data. Where empirical findings on information sharing mainly focus on point-of-sale data in two-level supply chains, this research empirically investigates the added value of using sell-through data originating from intermediaries, next to historical demand figures, in a multi-echelon supply chain. In a case study concerning a US drug manufacturer, we evaluate different methods to incorporate this data and consider both time series methods and machine learning techniques to produce multi-step ahead weekly forecasts. The results show that the manufacturer can effectively improve its short-term forecast accuracy by integrating sell-through data into the forecasting process and provide useful insights as to the different modeling approaches used. The conclusion holds for all forecast horizons considered, though it is most pronounced for one-step ahead forecasts. Therefore, our research provides a clear incentive for manufacturers to assess the forecast accuracy that can be achieved by using sell-through data.     

机械泵驱动两相回路的实时动态模型分析

在航空航天领域,为了加速系统设计及测试进度,通常需要进行半实物实时仿真,即控制器用实物,受控对象采用数学模型。本文开发出了基于Matlab/Simulink的两相传热模块,并用其搭建了某机械泵驱动两相回路的实时动态模型。通过与实验的对比,验证了模型的可靠性,表明该模型满足实时要求,可以在下一步用于半实物仿真。     

Vibrational study in the low frequency region (700—100 cm−1) of phosphine monosubstituted group VI B metal carbonyls

IR, FIR and Raman data in the low-frequency region (700-100 cm^?1) are presented for a number of Cr, Mo and W carbonyls of the type R₃PM(CO)₅, with the ligands (CH₃)₃P, (C₂H₅)₃P, (C₆H₅)₃P and (X—C₆H₄)₃P (X = F, Cl, CH₃), and for three further chromium carbonyls LCr(CO)₅, with the ligands PCl₃, C₆H₅PCl₂ and (C₆H₅)₂PCl. The observed δ(MCO) modes are assigned together with all ν(MC) and ν(MP) fundamentals. The behavior of these modes is discussed in relation to the different ligands and in comparison with known ν(CO) data. The dependence of ν(MP) on σ and π properties of the ligands is investigated.     

The <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> Rv2540c DNA sequence encodes a bifunctional chorismate synthase

Background

The emergence of multi- and extensively-drug resistant Mycobacterium tuberculosis strains has created an urgent need for new agents to treat tuberculosis (TB). The enzymes of shikimate pathway are attractive targets to the development of antitubercular agents because it is essential for M. tuberculosis and is absent from humans. Chorismate synthase (CS) is the seventh enzyme of this route and catalyzes the NADH- and FMN-dependent synthesis of chorismate, a precursor of aromatic amino acids, naphthoquinones, menaquinones, and mycobactins. Although the M. tuberculosis Rv2540c (aroF) sequence has been annotated to encode a chorismate synthase, there has been no report on its correct assignment and functional characterization of its protein product.

Results

In the present work, we describe DNA amplification of aroF-encoded CS from M. tuberculosis (Mt CS), molecular cloning, protein expression, and purification to homogeneity. N-terminal amino acid sequencing, mass spectrometry and gel filtration chromatography were employed to determine identity, subunit molecular weight and oligomeric state in solution of homogeneous recombinant Mt CS. The bifunctionality of Mt CS was determined by measurements of both chorismate synthase and NADH:FMN oxidoreductase activities. The flavin reductase activity was characterized, showing the existence of a complex between FMN_ox and Mt CS. FMN_ox and NADH equilibrium binding was measured. Primary deuterium, solvent and multiple kinetic isotope effects are described and suggest distinct steps for hydride and proton transfers, with the former being more rate-limiting.

Conclusion

This is the first report showing that a bacterial CS is bifunctional. Primary deuterium kinetic isotope effects show that C₄-proS hydrogen is being transferred during the reduction of FMN_ox by NADH and that hydride transfer contributes significantly to the rate-limiting step of FMN reduction reaction. Solvent kinetic isotope effects and proton inventory results indicate that proton transfer from solvent partially limits the rate of FMN reduction and that a single proton transfer gives rise to the observed solvent isotope effect. Multiple isotope effects suggest a stepwise mechanism for the reduction of FMN_ox. The results on enzyme kinetics described here provide evidence for the mode of action of Mt CS and should thus pave the way for the rational design of antitubercular agents.

     

Algebraic study of chiral anomalies?

The algebraic structure of chiral anomalies ismade globally valid on non-trivial bundles by the introduction of a fixed background connection. Some of the techniques used in the study of the anomaly are improved or generalized, including a systematic way of generating towers of ??descent equations??.     

The stability constants of some bivalent metal complexes of α-hydroxyisobutyrate and lactate

The stability constants of the lactate and α-hydroxyisobutyrate complexes of Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and UO₂²⁺ were determined by potentiometric titration. The average ligand number exceeds 2, indicating the formation of ML⁺, ML₂ and ML₃^- complexes. The existence of ML₃^- complexes was confirmed by electrophoretic experiments; no polynuclear complexes were formed. α-Hydroxyisobutyrate forms stronger complexes than lactate.     

Study of 19F chemical shifts in p-fluoro- and m-fluoro-phenylphosphine,arsine and stibine substituted metal carbonyls

The ¹⁹F chemical shift parameters provide evidence that the degree of d_π—d_π inter action between a trivalent phosphorus, arsenic or antimony ligand and a metal carbonyl moiety is non-zero.