EAAC1 is expressed in rat and human prostate epithelial cells; functions as a high-affinity L-aspartate transporter; and is regulated by prolactin and testosterone

Background  

Prostate epithelial cells accumulate a high level of aspartate that is utilized as a substrate for their unique function of production and secretion of enormously high levels of citrate. In most mammalian cells aspartate is synthesized; and, therefore is a non-essential amino acid. In contrast, in citrate-producing prostate cells, aspartate is an essential amino acid that must be derived from circulation. The prostate intracellular/extracellular conditions present a 40:1 concentration gradient. Therefore, these cells must possess a plasma membrane-associated aspartate uptake transport process to achieve their functional activity. In earlier kinetic studies we identified the existence of a unique Na+-dependent high-affinity L-aspartate transport process in rat prostate secretory epithelial cells. The present report is concerned with the identification of this putative L-aspartate transporter in rat and human prostate cells.     

Site-specific polymer attachment to a CCL-5 (RANTES) analogue by oxime exchange

A synthetic strategy that allows for the site-specific attachment of polymers such as poly(ethylene glycol) (PEG) to protein pharmaceuticals is described. PEG was attached to a 67-amino acid fully synthetic CCL-5 (RANTES) analogue at its GAG binding site both to reduce aggregation and to increase the circulating lifetime. Effective protection of an Aoaa chemoselective linker during peptide assembly, total chemical protein synthesis, and protein folding was achieved with an isopropylidene group. Mild deprotection of the resulting folded synthetic protein and subsequent polymer attachment occur without interference with the native folded structure and activity.     

Crystal structure of (3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocen-2-yl) carboxylic acid and its bis-[W(CO)5] complex·0.5C5H12: Conformation of 1,1′-diphosphaferrocenes

The structures of (3,3,4,4-tetramethyl-1,1-diphosphaferrocen-2-yl)carboxylic acid (1) and its bis-[W(CO)₅] pentane solvate complex (2) have been determined by X-ray analysis. The compound 1 crystallizes in the monoclinic P2₁ /n space group with Z = 4; a = 7.8404(9), b = 14.9441(16), c = 11.7730(14) Å, = 92.773(10)°, V = 1377.8(3) ų, and D_calc = 1.553 g cm^–3. The compound 2 crystallizes in the triclinic space group with two complex molecules and one pentane molecule in the unit cell. Cell parameters: a = 10.7070(2), b = 12.577(2), c = 13.239(3) Å, = 84.00(2), = 77.58(1), = 66.06(1)°, V = 1591.0(5) ų, and D_calc = 2.100 g cm^–3 .The fully eclipsed conformation of the phospholyl rings with P···P secondary bonding of 3.353(1) Å is observed in 1 and a partially eclipsed conformation is found in 2. The 10 possible conformations of 1,1-diphosphaferrocenes were described as the function of conformational parameter and observed geometry of the phospholyl rings.⁷ We suppose that the earlier conclusions concerning the destabilizing nature of 1,1-diphosphaferrocene conformations with < 100° cannot be considered as general. The mode of W – P coordination, the structural changes of 1 by W(CO)₅ coordination, the structural effect of phospholyl rings substitution by the –COOH group, and hydrogen bonds are analyzed.     

Three-step synthesis of chiral and sterically hindered amino alcohols based on cyclic enol phosphates

The new synthesis of chiral and sterically hindered 1,2-amino alcohols derivatives of 2-methyl-indane and 1,2,3,4-tethrahydrophenanthrene based on cyclic enol phosphates were investigated. The desired products were obtained using three step procedure: oxidation of accessible enol phosphates, transformation α-hydroxy ketones into corresponding oximes and finally reduction of the last one to 1,2-amino alcohols. The optimal conditions of all stages to obtain products with high enantioselectivity or diastereomeric ratio were found and elaborated. The structures and absolute configurations of (3R)-2,3-dihydro-3-hydroxy-1H-phenanthren-4-one and corresponding oxime were confirmed by X-ray analysis.     

Development of a new method for the separation of vanadium species and chloride interference removal using modified silica capillaries-DIN-ICP-MS

A new on-line method for the separation of vanadium (IV) and vanadium (V) as well as for the removal of ClO⁺ mass spectral interference on vanadium determination by quadrupole-ICP-MS has been developed. The sample introduction system consists of a modified fused silica capillary coupled to a direct injection nebuliser (DIN), between the solvent delivery system and the ICP. Fused silica capillaries were treated with different anion and cation exchanger reagents and were tested for the retention of Cl⁻ and the separation of vanadium ions at μg l⁻¹ levels. A suitable strong anion exchanger functional group (3-aminopropyltrimethoxy silane) was selected. Chlorine anions were retained in this anionic capillary and the separation between V(IV) and V(V) was possible in the pH range 2–4. The selections of instrumental ICP-MS conditions for the minimisation of the ClO+ interference were carefully considered. Factors affecting the chromatographic separation such as sample pH, sample flow rate, effect of methanol in the mobile phase and length of the capillary for the separation were optimised. The proposed methodology provides a simple and rapid method for vanadium speciation. A relative detection limit of 12 l⁻¹ (i.e. absolute detection limits of 120 pg) for V(IV) based on peak height measurements was obtained. The relative standard deviation for V(IV) was 2.4% for a 10 μl injection (n=6).     

A programme to improve the quality of butyltin determinations in environmental matrices

One of the major prerequisites for the certification of various analytes in different Certified Reference Materials (CRMs) is that the analytical methods used are of verified performance and, hence, that no systematic errors have been left undetected. In the case of difficult measurements, research and feasibility studies are often necessary to ensure that the methods are operating under good quality control. The EC Standards Measurements and Testing Programme (SMT, formerly BCR) usually follows a step-by-step approach which consists in series of interlaboratory studies to assess and improve the quality of measurements prior to certification by comparing different analytical techniques. A programme following such stepwise approach has started in 1987 with the aim of improving the quality of butyltin determinations in environmental matrices. The project involved ca. 20 laboratories from different Member States of the European Union. The first interlaboratory study dealt with simple solutions containing mixtures of organotin compounds and a second exercise focused on the analysis of a tributyltin-spiked sediment. These exercises were continued by two certifications on butyltins in sediment, the first of which could not be successfully concluded owing to the high spread of results observed between the results of different techniques. The second certification allowed a CRM certified for its contents of di- and tributyltin (CRM 462) to be produced. This programme on Sn speciation is now focusing on the certification of butyltin and phenyltin compounds in candidate CRMs of mussel and sediment. This paper gives an account of the step-by-step approach followed and presents the results of the two certification exercises carried out so far. The preparation of the mussel candidate CRM is also described.     

Flow-injection and liquid chromatographic determination of aluminum based on its fluorimetric reaction with 8-hydroxyquinoline-5-sulphonic acid in a micellar medium

Aluminum reacts with 8-hydroxyquinoline-5-sulphonic acids (HQS) in cationic micelles of cetyltrimethylammonium bromide (CTAB) to form a strongly fluorescent compound. In the micellar media the formation of the Al—HQS complex is very fast, allowing a useful continuousdetermination of aluminum in flow systems. At pH 6.3, for 2 × 10^-4 M HQS and 2 × 10^-3 M CTAB the detection limit for a luminum by flow injection is 0.1 ng ml^-1. The calibration is linear up to 100 ng ml^-1 and the peak-height precision is 2% at the 10 ng ml^-1 level. Interfences are greatly decreased compared with the batch method. The reaction has also been applied to the post-column detection by ion chromatography of aluminium in fresh and high-salinity wates and for speciation of aluminium in blodd serum after separation of serum proteins by ion-exchange liquid chromatography.     

Modelling the adsorption of Cd(II), Cu(II), Ni(II), Pb(II), and Zn(II) onto Fithian illite

Illite samples from Fithian, IL were purified and saturated with Na(+) ions. The acid-base surface chemistry of the Na-saturated illite was studied by potentiometric titration experiments with 0.1, 0.01, and 0.001 M NaNO(3) solutions as the background electrolyte. Results showed that the titration curves obtained at different ionic strengths did not intersect in the studied pH range. The adsorption of Cd(II), Cu(II), Ni(II), Pb(II), and Zn(II) onto illite was investigated as a function of pH and ionic strength by batch adsorption experiments. Two distinct mechanisms of metal adsorption were found from the experimental results: nonspecific ion-exchange reactions at lower pH values on the basal surfaces and 'frayed edges' and specific adsorption at higher pH values on the mineral edges. Ionic strength had a greater effect on the ion-exchange reactions. The binding constants for the five heavy metals onto illite were determined using the least-square fitting computer program FITEQL. Linear free energy relationships were found between the surface binding constants and the first hydrolysis constants of the metals.     

Synthesis, characterization, and biomimetic chemistry of cis-oxosulfidomolybdenum(VI) complexes stabilized by an intramolecular Mo(O)=S...S interaction

The reactions of jade-green Tp*MoIVO(S2PR2) [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; R = Et, Pri, Ph] with propylene sulfide produce ochre-red Tp*MoVIOS{SP(S)R2}. The complexes have been characterized by microanalysis, mass spectrometry, cyclic voltammetry, spectroscopy (IR, NMR, UV-vis, and X-ray absorption), and X-ray crystallography. The distorted-octahedral isopropyl and phenyl derivatives feature a tridentate fac-Tp* ligand, a terminal oxo ligand, and a unique five-membered Mo(=S){SP(=S)R2 ring moiety formed by a weak, intramolecular, bonding interaction between the Mo=S1 and (uncoordinated) S3=P moieties. The Mo=S1 [2.227(2) A (R = Pri) and 2.200(2) A (R = Ph)] and S1...S3 distances [2.396(3) A (R = Pri) and 2.383(2) A (R = Ph)] are indicative of a pi-bonded Mo=S1 unit and a weak (bond order ca. 1/3) S1...S3 interaction; the solid-state structures are maintained in solution according to S K-edge X-ray absorption data. The complexes react with excess cyanide to form thiocyanate and Tp*MoO(S2PR2), under anaerobic conditions, or Tp*MoO2(S2PR2), under aerobic conditions; the latter models the production of thiocyanate and desulfo molybdenum hydroxylases upon cyanolysis of molybdenum hydroxylases. The complexes react with triphenylphosphine to give Tp*MoO(S2PR2) and SPPh3, with cobaltocene or hydrosulfide ion to produce [Tp*MoVOS(S2PR2)]-, and with ferrocenium salts to yield [Tp*MoVO(S3PR2)]+; in the last two reactions, Mo(V) is produced by direct or induced internal redox reactions, respectively. The presence of the Mo(O)=S...S interaction does not radically lengthen the Mo=S bond in the complexes or preclude them from reactions typical of unperturbed oxosulfidomolybdenum(VI) complexes.     

An evaluation of reversed-phase and ion-exchange chromatography for use with inductively coupled plasma—mass spectrometry for the determination of organotin compounds

An evaluation of reversed-phase high-performance liquid chromatography (HPLC) employing mobile phases compatible with direct coupling to inductively coupled plasma-mass spectrometry (ICP-MS) is described for the selective and sensitive detection of organotin species. The findings of this study are compared with established methods, employing ion-exchange chromatography. In order to achieve optimum performance, both the HPLC and ICP-MS were optimized for speciation work. The results from studies using various mobile phases for the separation of a range of tin compounds (inorganic tin, tributyltin, dibutyltin and monobutyltin) are discussed both in terms of resolution and compatibility with ICP-MS instrumentation. Tropolone, a commonly used complexing agent for organotin species, is also discussed with reference to the chromatographic separation of tin species. Finally, the role of isotope dilution analysis in conjunction with HPLC-ICP-MS for organotin speciation is described with respect to the European Community Standards, Measurements and Testing (BCR) certified material programme.