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The concept of variable stoichiometry cocrystallization is explored in halogen-bonded systems. Three novel cocrystals of 1,4-diiodotetrafluorobenzene and 3-nitropyridine with molar ratios of 1:1, 2:1, and 1:2, respectively, are prepared by slow evaporation methods. Single-crystal X-ray diffraction analysis reveals key differences between each of the nominally similar cocrystals. For instance, the 1:1 cocrystal crystallizes in the [P2.sub.1]/n space group and features a single chemically and crystallographically unique halogen bond between iodine and the pyridyl nitrogen. The 2:1 cocrystal crystallizes in the P1 space group and features a halogen bond between iodine and one of the nitro oxygens in addition to an iodine--nitrogen halogen bond. The 1:2 cocrystal crystallizes with a large unit cell (V = 9896 [A.sup.3]) in the Cc space group and features 10 crystallographically distinct iodine-nitrogen halogen bonds. Powder X-ray diffraction experiments carried out on the 1:1 and 2:1 cocrystals confirm that gentle grinding does not alter the crystal forms. [.sup.1]H [right arrow] [.sup.13]C and [.sup.19]F [right arrow] [.sup.13]C cross-polarization magic angle spinning (CP/MAS) NMR experiments performed on powdered samples of the 1:1 and 2:1 cocrystals are used as spectral editing tools to select for either the halogen bond acceptor or donor, respectively. Carbon-13 chemical shifts in the cocrystals are shown to change only very subtly relative to pure solid 1,4-diiodotetrafluorobenzene, but the shift of the carbon directly bonded to iodine nevertheless increases, consistent with halogen bond formation (e.g., a shift of +1.6 ppm for the 2:1 cocrystal). This work contributes new examples to the field of variable stoichiometry cocrystal engineering with halogen bonds. Key words: solid-state NMR, X-ray diffraction, halogen bond, cocrystal, polymorphism, stoichiometry, stoichiomorphism. Nous avons etudie le concept de cocristallisation a stoechiometrie variable dans des systemes a liaison halogene. Nous avons prepare par evaporation lente trois nouveaux cocristaux de 1,4-diiodotetrafluorobenzene et de 3-nitropyridine avec des rapports molaires de 1:1, de 2:1 et de 1:2, respectivement. L'analyse par diffraction des rayons X sur monocristal revele des differences importantes entre les cocristaux theoriquement similaires. Par exemple, le cocrystal 1:1 cristallise selon le groupe d'espace [P2.sub.1]/n et presente une seule liaison halogene, sur les plans chimique et cristallographique, entre l'iode et l'azote du groupe pyridyle. Le cocrystal 2:1 cristallise selon le groupe d'espace P1 et presente une liaison halogene entre l'iode et l'un des oxygenes du groupe nitro, en plus de la liaison halogene iode-azote. Le cocristal 1:2 cristallise en formant une grande cellule unitaire (V = 9896 [A.sup.3]) selon le groupe d'espace Cc et presente 10 liaisons halogene iode-azote distinctes sur le plan cristallographique. Des experiences de diffraction des rayons X sur poudre realisees sur les cocristaux 1:1 et 2:1 confirment qu'un broyage leger ne modifie pas les formes cristallines. Nous avons utilise des experiences de RMN [.sup.1]H [right arrow] [.sup.13]C et [.sup.19]F [right arrow] [.sup.13]C a polarisation croisee en rotation a l'angle magique (CP/MAS, cross-polarization/magic angle spinning), realisees sur des echantillons de cocristaux 1:1 et 2:1 sous forme de poudre, comme outils d'edition spectrale pour selectionner l'accepteur ou le donneur de liaison halogene, respectivement. Les deplacements chimiques du carbone-13 dans les cocris-taux ne changent que de facon tres subtile par rapport au 1,4-diiodotetrafluorobenzene solide pur, mais le deplacement du carbone directement lie a l'iode augmente neanmoins, ce qui concorde avec la formation de liaisons halogene (p. ex., un deplacement de +1,6 ppm dans le cas du cocrystal 2:1). Ces travaux apportent de nouveaux exemples au domaine de l'ingenierie des cocristaux a stoechiometrie variable comportant des liaisons halogene. [Traduit par la Redaction] Mots-cles : RMN a l'etat solide, diffraction des rayons X, liaison halogene, cocristal, polymorphisme, stoechiometrie, stoechiomorphisme., Introduction Molecular and ionic solids can adopt a range of forms depending on how they are prepared. (1,2) Such forms include pure crystalline or amorphous phases, hydrates, or solvates. In [...]

The epithelial [Na.sup.+] channel (ENaC) is a mulfimeric membrane protein consisting of three subunits, [alpha], [beta], and [gamma]. The total number of subunits per functional channel complex has been described variously to follow either a tetrameric arrangement of 2[alpha]:1 [beta]:1[gamma] or a higher-ordered stoichiometry of 3[alpha]:3[beta]:3[gamma]. Therefore, while it is clear that all three ENaC subunits are required for full channel activity, the number of the subunits required remains controversial. We used a new approach, based on single-channel measurements in Xenopus oocytes to address this issue. Individual mutations that alter single-channel conductance were made in pore-lining residues of ENaC [alpha], [beta], or [gamma] subunits. Recordings from patches in oocytes expressing a single species, wild type or mutant, of [alpha], [beta], and [gamma] showed a well-defined current transition amplitude with a single Gaussian distribution. When cRNAs for all three wild-type subunits were mixed with an equimolar amount of a mutant a-subunit (either $589D or S592T), amplitudes corresponding to pure wild-type or mutant conductances could be observed in the same patch, along with a third intermediate amplitude most likely arising from channels with at least one wild-type and at least 1 mutant [alpha]-subunit. However, intermediate or hybrid conductances were not observed with coexpression of wild-type and mutant [beta]G529A or [gamma]G534E subunits. Our results support a tetrameric arrangement of ENaC subunits where 2[alpha], 1[beta], and 1[gamma] come together around central pore.

A novel ratio method is developed and automated for finding the bromine-chlorine-sulfur stoichiometry in the molecular formula of an unknown. This method is also useful in spectrometric analysis or beginning organic chemistry.

The Utah Surrogate Mechanism was employed to model a stoichiometric premixed cyclohexane flame. The results were found to be satisfactory when compared with the experimental data of oxygen, major products and important intermediates, including major soot precursors of [C.sub.2]-[C.sub.5] unsaturated species.

First-principles calculations are used with ultrasoft pseudopotential formalism and the generalized gradient approximation for the exchange-correlation functional to study the stability of [Mo.sub.n][S.sub.m] (n = 1-6 and m ranging from n to 3n) clusters and obtain the optimal stoichiometry for each n corresponding to the magic cluster. The variance in energy due to a change in the sulfur composition has indicated that sulfurization of the magic clusters is more favorable than desulfurization.

The synthesis and characterization of the homoleptic octahydrotriborate complex Cr[([B.sub.3][H.sub.8]).sub.2] and its Lewis base adducts are described. Along with several Lewis base adducts of Cr[([B.sub.3][H.sub.8]).sub.2], a purple volatile liquid believed to be Cr(III) hydride of stoichiometry CrH[([B.sub.3][H.sub.8]).sub.2] was also synthesized and these compounds were the first in which there is more than one octahydrotriborate group per transition metal center.

The study focuses on transition temperature variations as a function of Ba/Ti ratio and in undoped BaTiO(sub)3 powders with particle size to understand stoichiometric effects on transition behavior when materials are processed under equilibrium conditions, before introducing additional degrees of freedom such a dopants, size effect or applied stress. It is found that all the different defects contribute to the changes of transition temperature and enthalpy of transition.

Taxol (paclitaxel, PTX) is an important anticancer drug that owes it unique activity to its ability to bind to tubulin in a stoichiometric ratio and promote its assembly into microtubules. Experimental results from [sup.2.H]{[sup.19.F}] rotational-echo double resonance nuclear magnetic resonance (REDOR NMR) are presented that provide direct confirmation that paclitaxel adopts a T-shaped conformation when it is bound to tubulin.

We have extended the method of single-molecule fluorescence, two-color coincidence detection (TCCD) to detect coincident events due to a low fraction of a complex against a background of chance coincident events, due to monomers. We developed two complementary methods to determine the number of chance coincident events using the experimental data and without the need for additional experiments. We show that the subtraction of the chance coincidence level is essential for accurate quantification of the relative number of complexes and their stoichiometry. By performing experiments on model samples made from fluorophore-labeled duplex DNA and free dye, a linear dependence on the fraction of duplex DNA was found, independent of the level or ratio of free dye, with quantification down to a level of 0.5% and 500 fM duplex DNA. The method was then used to measure the equilibrium dissociation constant and offrate of a 9-mer duplex DNA, demonstrating the application of this method to systems with nanomolar dissociation constants. These improvements to the method of TCCD analysis significantly extend the application of TCCD to weakly bound complexes and large multicomponent biomolecular systems.

Reactions involving feldspars are of great importance in the environment, influencing geochemical cycles in many ways. Dissolution of feldspars has been widely studied in the laboratory, with attempts being made to reproduce and understand the processes of 'weathering' as seen in the environment. It has long been recognised that weathering of feldspars involves the attachment and detachment of atoms at the surface of the mineral. A wide range of factors influences the reactions involved, from the composition of the feldspar to the nature of the solution, but it is generally accepted that weathering leads to the presence of a leached layer, with a composition different from both the bulk mineral and the fluid. The aim of this paper is to review recent work carried out on feldspars, focusing particularly on developing an understanding of the leached layer using both spectroscopic methods (including Secondary Ion Mass Spectroscopy and X-ray Photoelectron Spectroscopy), and microscopic imaging techniques (including Atomic Force Microscopy and Scanning Electron Microscopy) to follow changes at the mineral/solution interface. Contrasting models of surface evolution are discussed. Keywords: feldspar; weathering; leached layer; stoichiometry; dissolution--reprecipitation

This paper reports on a study of the influence of In and Sn substitution for Ga in [Ni.sup.2]MnGa on the magnetism and magnetostriction in arc-melted-and-cast and directionally solidified alloys. Magnetostriction measurements were carried out from room temperature down to-125 [degrees] C for these alloys. Magnetic property measurements for the stoichiometric as arc-melted-and-cast rods of [Ni.sup.2]MnGa, [Ni.sup.2]MnSn, and [Ni.sup.2]MnIn show room temperature Ms values of 58.8, 44.3, and 39.1 emu/g, respectively. Each of the stoichiometric alloys reveals similar magnetostrictive behavior with respect to temperature. For near-stoichiometric compositions, the behavior of magnetostriction in Ni-Mn-In and Ni-Mn-Sn is comparable to that in Ni-Mn-Ga in the directionally solidified samples. Index Terms--FSMA, Heusler alloy, magnetostriction, [Ni.sup.2]MnGa, [Ni.sup.2]MnIn, [Ni.sup.2]MnSn.

Electron paramagnetic resonance study of the surface basicity of calcium oxide was carried out. CaO forms ozonide ions upon [O.sub2.] adsorption and N[O.sub.3][.sup.2-] anions under low pressures of NO indicating presence of defects like positive holes dispersed in the bulk and originated by the unavoidable presence of [Na.sup.} ions in the composition of the solid.

The simple salt approximation for the lattice energy of double salts is used to provide an estimate of their molar solubilities. These calculations are compared with solubilities obtained from literature thermodynamic data and are within an order of magnitude for about 75% of the 81 minerals and other double salts examined. The solubilities of about two-thirds of the double salts are similar to the solubilities of the less soluble simple salt 'constituents,' and the solubilities of the other one-third lie between the solubilities of the 'constituents.' In general, the solubilities of a series of salts with different stoichiometries containing the same ions are dependent on both the stoichiometry of the salt and the proportion of the less soluble constituent. This generalization is rationalized with the simple salt approximation and is used to explain the observed stoichiometries of a variety of minerals. Keywords: Thermodynamics, solubility, stoichiometry, lattice energy

Key aspects of the growth process of epitaxial SrTi[O.sub.3] with crystalline interface on silicon are outlined. An important step in this process is the solid epitaxy in ultrahigh vacuum of amorphous SrTi[O.sub.3] on top of a few monolayer thick , low-temperature grown, epitaxial (Ba, Sr)O/Si(100) template.

At a stoichiometrical relation of silicon and oxygen during the growth of a rapid thermal silicon-oxide layer (RTO) the electrical parameters of the corresponding metal-insulator-semiconductor capacitor show significant behavior. Combining the Henry-Dalton law and the Boyle-Mariotte law with the Deal-Grove model allows an estimation of the fundamental (T, t, C) process, parameters, temperature, time and concentration of the reactive gas [3] for a stoichiometrical processing of ultra thin Si[O.sub.2] films. Electrical measurements show the (T, t, C)-dependency of I-V, time dependent dielectric breakdown (TDDB) and C-V measurements especially of direct tunneling currents jDT, relative difference of tunneling currents [[DELTA].sub.RDT] [3], charge-to-breakdown [Q.sub.BD] and interface state density [D.sub.it]. Index Terms--Rapid thermal oxidation (RTO), (T, t, C) parameters, stoichiometry, metal-insulator-semiconductor capacitor, MIS capacitor, I-V measurements, time dependent dielectric breakdown measurements, TDDB measurements, C-V measurements, direct tunnelling currents, relative difference of tunnelling currents, charge-to-breakdown, interface state density.

Selective enrichments yielded bacterial cultures able to utilize the osmolyte N-methyltaurine as sole source of carbon and energy or as sole source of fixed nitrogen for aerobic growth. Strain MT1, which degraded N-methyltaurine as a sole source of carbon concomitantly with growth, was identified as a strain of Alcaligenes faecalis. Stoichiometric amounts of methylamine, whose identity was confirmed by matrix-assisted, laser-desorption ionization time-of-flight mass spectrometry, and of sulfate were released during growth. Inducible N-methyltaurine dehydrogenase, sulfoacetaldehyde acetyltransferase (Xsc) and a sulfite dehydrogenase could be detected. Taurine dehydrogenase was also present and it was hypothesized that taurine dehydrogenase has a substrate range that includes N-methyltaurine. Partial sequences of a tauY-like gene (encoding the putative large component of taurine dehydrogenase) and an xsc gene were obtained by PCR with degenerate primers. Strain N-MT utilized N-methyltaurine as a sole source of fixed nitrogen for growth and could also utilize the compound as sole source of carbon. This bacterium was identified as a strain of Paracoccus versutus. This organism also expressed inducible (N-methyl)taurine dehydrogenase, Xsc and a sulfite dehydrogenase. The presence of a gene cluster with high identity to a larger cluster from Paracoccus pantotrophus NKNCYSA, which is now known to dissimilate N-methyltaurine via Xsc, allowed most of the overall pathway, including transport and excretion, to be defined. N-Methyltaurine is thus another compound whose catabolism is channelled directly through sulfoacetaldehyde.

Protein phosphorylation stoichiometry was assessed by two analytical strategies. Both are based on element mass spectrometry (ICPMS, inductively coupled plasma mass spectrometry) and simultaneous monitoring of [sup.31]P and [sup.34]S. One strategy employs a combination of 1D gel electrophoresis, in-gel digestion, and final [micro]LC-ICPMS analysis [micro]LC = capillary liquid chromatography). The other strategy uses the combination of 1D gel electrophoresis, protein blotting, and imLA-ICPMS (imLA = imaging laser ablation). The two methods were evaluated with standard phosphoproteins and were applied to the analysis of the cytoplasmatic proteome of bacterial cells (Corynebacterium glutamicum) and eukaryotic cells (Mus musculus). The eukaryotic proteome was found to exhibit a significantly higher phosphorylation degree (~0.8 mol of P/mol of protein) compared to the bacterial proteome (~0.01 mol of P/mol of protein). Both analytical strategies revealed consistent quantitative results, with the [micro]LC-ICPMS approach providing the higher sensitivity. In summary, two ICPMS-based methods for quantitative estimation of the phosphorylation degree of a cellular proteome are presented which access the native proteome state and do not require any type of label introduction or derivatization.

Experimental results for the investigation of chromatographic columns containing two mobile phases are presented. The eluent was composed of mixtures of methanol and carbon dioxide. The column was an uncoated fused-silica-lined stainless steel capillary column. At certain experimental conditions, the eluent divided into two phases, both of which moved through the column. The predominant component of the liquid phase was methanol whereas the gas phase was composed of at least 93 mol % C[O.sub.2]. The columns were studied over a range of feed compositions (45-95 mol % C[O.sub.2]), pressures (61-101 bar), and temperatures (30-100 [degrees]C). The compositions and densities of each phase were calculated from the Peng-Robinson equation of state. The residence times of the two mobile phases were determined by tracer pulse chromatography. The partition coefficients of a probe solute, benzene, were measured along with the retention times of neon and the total volume of the chromatographic column as a function of temperature, pressure, and stoichiometric feed composition. The calculated column volumes, that is the volume of the liquid and gas, were constant over the full range of feed composition. The partition coefficient of benzene was constant at fixed pressure and temperature, varied logarithmically with density at fixed temperature and feed composition, and displayed a maximum at intermediate temperatures at fixed pressure and feed composition. The measured retention times of neon were consistently equivalent to the calculated residence times of the gas phase, indicating that neon did not dissolve in the liquid phase and could thus serve as an accurate dead time marker. The implementation of chromatography with two mobile phases produces a chromatographic 'window'. There is a lower limit for the retention volume of all solutes, viz., the residence time of the gas phase, exactly the same as normal chromatography. However, elimination of the stationary phase produces an upper limit to the retention volumes of solutes. This upper limit is the residence time of the liquid phase, so there is a retention window such that [t.sup.G] [less than or equal to] [t.sub.i] [less than or equal to] [t.sup.L] for all solutes.

In a previous paper (Andre et al., in press), a novel chromatographic column was developed in our laboratory for studying the binding of pesticides with humic acid (HA), the main organic component in soil. It was demonstrated that this column supported a low fraction of organic modifier in the aqueous mobile phase (

Ero1p is a key enzyme in the disulfide bond formation pathway in eukaryotic cells in both aerobic and anaerobic environments. It was previously demonstrated that Ero1p can transfer electrons from thiol substrates to molecular oxygen. However, the fate of electrons under anaerobic conditions and the final fate of electrons under aerobic conditions remained obscure. To address these fundamental issues in the Ero1p mechanism, we studied the transfer of electrons from recombinant yeast Ero1p to various electron acceptors. Under aerobic conditions, reduction of molecular oxygen by Ero1p yielded stoichiometric hydrogen peroxide. Remarkably, we found that reduced Ero1p can transfer electrons to a variety of small and macromolecular electron acceptors in addition to molecular oxygen. In particular, Ero1p can catalyze reduction of exogenous FAD in solution. Free FAD is not required for the catalysis of dithiol oxidation by Ero1p, but it is sufficient to drive disulfide bond formation under anaerobic conditions. These findings provide insight into mechanisms for regenerating oxidized Ero1p and maintaining disulfide bond formation under anaerobic conditions in the endoplasmic reticulum. electron transfer | Ero1 | flavoenzyme | hydrogen peroxide

The capability of terrestrial ecosystems to sequester carbon (C) plays a critical role in regulating future climatic change yet depends on nitrogen (N) availability. To predict long-term ecosystem C storage, it is essential to examine whether soil N becomes progressively limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. A critical parameter to indicate the long-term progressive N limitation (PNL) is net change in ecosystem N content in association with C accumulation in plant and soil pools under elevated C[O.sub.2]. We compiled data from 104 published papers that study C and N dynamics at ambient and elevated C[O.sub.2]. The compiled database contains C contents, N contents, and C:N ratio in various plant and soil pools, and root:shoot ratio. Averaged C and N pool sizes in plant and soil all significantly increase at elevated in comparison to those at ambient C[O.sub.2], ranging from a 5% increase in shoot N content to a 32% increase in root C content. The C and N contents in litter pools are consistently higher in elevated than ambient C[O.sub.2] among all the surveyed studies whereas C and N contents in the other pools increase in some studies and decrease in other studies. The high variability in C[O.sub.2]induced changes in C and N pool sizes results from diverse responses of various C and N processes to elevated C[O.sub.2]. Averaged C:N ratios are higher by 3% in litter and soil pools and 11% in root and shoot pools at elevated relative to ambient C[O.sub.2]. Elevated C[O.sub.2] slightly increases root:shoot ratio. The net N accumulation in plant and soil pools at least helps prevent complete down-regulation of, and likely supports, long-term C[O.sub.2] stimulation of C sequestration. The concomitant C and N accumulations in response to rising atmospheric C[O.sub.2] may reflect intrinsic nature of ecosystem development as revealed before by studies of succession over hundreds to millions of years. Key words: carbon sequestration; ecosystem development; global change; meta-analysis; nitrogen; stoichiometry.

Measuring the statistical distribution of deuterium incorporated into enzymatically derived peptide fragments provides a valuable dimension to hydrogen/deuterium exchange mass spectrometry data. In this paper, we will discuss our improvement to the linear least-squares method for determining this distribution, through the addition of 'zeroes' to the end of the deuterated isotopic envelope, to partially compensate for data truncation due to finite instrumental signal-to-noise ratios. The value of the distribution is demonstrated in a simple experimental example, where the linearity between average deuteration and percent [D.sub.2]O used to label test peptides hides a more complex relationship between the site-labeling probability. and the total number of sites. This method offers the opportunity to resolve cases where a single peptide experiences distinct, independent biochemical states with each bearing a unique average deuteration; this can occur when a protein is modified to substoichiometric levels. From the experimentally determined distribution of a heterogeneously deuterated peptide, it was possible to extract the average deuteration of each component of the mixture.

While the silicon microoptical bench with purely passive locational features was an attempt at breadboard-like integration for photonic applications, it failed to provide the high-precision alignment required for efficient light coupling between devices and/or fibers. To optimize the final alignment without the introduction of on-board active actuators or external high-precision manipulators, we have developed and demonstrated a low-cost, micromachined optical bench with quasipassive locational features capable of submicron alignment optimization. The concept capitalizes on inherent residual tensile stresses produced during the stoichiometric [Si.sub.3][N.sub.4] thin-film deposition process. By selectively trimming stress element on either side of a suspended platform, the equilibrium position can be biased to one side or another, enabling high-resolution relative motion between the suspended platform and the base. We have demonstrated, as a first attempt, high-efficiency fiber-to-fiber alignment using this concept. Index Terms--Fiber coupling, laser trimming, microoptical bench, nanoscale motion, residual stress, stoichiometric silicon nitride film.

The compensation process in semi-insulating CdTe-based compounds is known to be related to the interaction among shallow and deep levels induced by impurities, grown-in lattice defects and by their complexes. We have carried out Photo-Induced Current Transient Spectroscopy (PICTS) and Photo-Deep Levels Transients Spectroscopy (P-DLTS) analyzes together with DLTS analyzes to investigate the role that acceptors and donors play in the compensation mechanism. To this purpose we have compared semi-insulating materials with different stoichiometry and different resistivity, i.e., with different free carrier concentration. We have examined also semiconducting material in order to compare extrinsically compensated and self-compensated CdTe-compounds. Our attention has been focused on the deep levels close to midgap in order to deepen our understanding of their behavior as a function of the position of the Fermi level since they are critical for the compensation process. We have achieved experimental evidence that in [Cd.sub.(1-x)][Zn.sub.x]Te the level H at [E.sub.V] + 0.75 eV has a donor-like character. The possible extension of the donor-like character of this defect to CdTe:Cl should be positively considered albeit it can not be assessed by the present investigation. Index Terms--Charge transport properties, deep traps, detectors.

The activating NKG2D receptor plays a critical role in innate and adaptive immune responses by natural killer cells and subpopulations of T cells. The human receptor assembles with the DAP10 signaling dimer, and it is thought that one NKG2D homodimer pairs with a single DAP10 dimer by formation of two salt bridges between charged transmembrane (TM) residues. However, direct stoichiometry measurements demonstrated that one NKG2D homodimer assembles with four DAP10 chains. Selective mutation of one of the basic TM residues of NKG2D resulted in loss of two DAP10 chains, indicating that each TM arginine serves as an interaction site for a DAP10 dimer. Assembly of the hexameric structure was cooperative because this mutation also significantly reduced NKG2D dimerization. A monomeric NKG2D TM peptide was sufficient for assembly with a DAP10 dimer, indicating that the interaction between these proteins occurs in the membrane environment. Formation of a three-helix interface among the TM domains involved ionizable residues from all three chains, the TM arginine of NKG2D and both TM aspartic acids of the DAP10 dimer. The organization of the TM domains thus shows similarities to the T cell antigen receptor-CD3 complex, in particular to the six-chain assembly intermediate between T cell antigen receptor and the CD3[delta][epsilon] and CD3[gamma][epsilon] dimers. Binding of a single ligand can thus result in phosphorylation of four DAP10 chains, which may be relevant for the sensitivity of NKG2D receptor signaling, in particular in situations of low ligand density. natural killer cells | stoichiometry | membrane biochemistry

The Nowotny chimney ladders are a family of intermetallics in which helical transition metal chimneys encapsulate main group helics. Behind these seductive structures are simple regularities, an electron counting rule and a connection between stoichiometry and satellite diffraction peaks.

Equations were determined for the calculation of the second stoichiometric (molality scale) dissociation constant, [K.sub.m2], of glycine, in aqueous NaCl and KCl solutions at 298.15 K, from the thermodynamic dissociation constant, [K.sub.a2], of this acid and the ionic strength, [I.sub.m], of the solution. The ionic strength of the solutions considered in this study is determined mostly by the salt alone, and the equations for [K.sub.m2] were based on the single-ion activity coefficient equations of the Huckel type. New data measured by potentiometric titrations in a glass electrode cell were used in the estimation of the parameters for the Huckel equations of glycine species. By means of the calculation method suggested in this study, [K.sub.m2] can be obtained almost within experimental error up to an [I.sub.m] of about 1.0 mol [kg.sup.-1] for glycine in NaC1 and KCI solutions. The [K.sub.m2] values obtained by these methods were also compared with the values suggested in the literature for this quantity. Key words: ionic strength dependence, stoichiometric dissociation constant, Debye-Huckel equation, potentiometry, glycine.

Research has been conducted on P-glycoprotein which mediates drug transport. The number of nucleotides bound to this P-glycoprotein during different stages of catalytic cycles and nucleotide binding affinity have been measured via the use of fluorescence techniques, and the results are reported.

The study reports are on the influence of target charging on ion beam sputtering of Al(sub 2)O(sub 3) and LiNbO(sub 3) films on Si and Al(sub 2)O(sub 3)/Si substrates. It is found that undesirable ionic emission could be minimized by eliminating target charging, controlled via electron to ion neutralization ratio of the incident beam.

The adsorption of H2 molecules on the (100) MoS2 surfaces, considering various edge sulfur stoichiometries is investigated theoretically, by quantum density functional theory (DFT) calculations. A thermodynamic diagram is constructed by using the adsorption energies, which gives the stoichiometry of the edges and the nature of the adsorbed hydrogen atoms as a function of the total pressure.

The complementary fragment of the heptameric protective moiety of anthrax toxin, PA(sub)63 binds three ligand molecules at saturation as determined by measuring isotope ratios in complexes and determining molecular masses of unlabled complexes.

Research has been conducted on the conditions developed during the Baylis-Hillman reaction. The use of the stoichiometric base catalyst and the aqueous medium in investigating the problems associated with the Baylis-Hillman reaction such as low reaction yields and long reaction time is described.

Byline: Istvan Szalkai (1) Keywords: stoichiometry; linear; valuation operator; additive quantities Abstract: We investigate physical and chemical quantitative characteristics of species, reactions and mechanisms which are linear (additive and homogeneous) in general, using linear algebraic methods. We call such characteristics here as 'valuation operators'. After revealing the properties of these operators we reach to some practical consequences at the end of our paper which could be used either for calculating or forecasting the behaviour and the magnitude of these characteristics. Though these results might have already been used by experts for a long time, the present paper could serve as a firm theoretical background for their computation methods. Author Affiliation: (1) Department of Mathematics, University of Veszprem, P.O.B. 158, Veszprem, H8201, Hungary Article History: Registration Date: 08/10/2004

Regions of three types of net stoi-chiometry in the parametric space of the applied electric field and propagation velocity are determined experimentally. The complexation reaction involving starch, Iodine and Iodide reduced the relative mobility of Iodine, which could result in smaller changes in the propagation velocities in the elctromigration of nonbound Iodide.

The structural and electronic properties of bismuth oxide clusters of stoichiometry Bi3Oy+ (y = 3, 4, 5, 6) and Bi4Oy+ (y = 6, 7, 8) as well as their interaction with ethene have been examined using an accurate ab initio density functional approach. In conclusion, it is found that an oxirane molecule can be released from the peroxide form, allowing the formation of reactive chain units, which might be an interesting species for researching the role of bismuth oxide clusters in catalytic processes.

Research has been conducted on the cellular location of the Menkes protein. Expression and purification of the N-terminal domain and the second metal-binding module of the Menkes protein in Escherichia coli are analyzed.

The role of lauric acid (LAH) in the transport of copper(II) through a permeation liquid membrane (PLM) comprising 1,10-didecyldiaza-18-crown-6 (22DD) and lauric acid (ratio 1:1) in 1:1 v/v toluene/phenylhexane has been investigated by determining the stoichiometry of metal extraction and of the metal complex formed in the organic phase by performing (super 1)H NMR and liquid/liquid and liquid/membrane extraction measurements. In the absence of copper(II), the (super 1)H NMR data suggest that there is a strong interaction between the proton of IAH and the nitrogen of the 22DD macrocycle but no interaction between the aliphatic long chains of LAH and 22DD. Thus, in the organic solution, the two compounds are associated as (22DD-H)(super +)-LA(super -), the laurate being away from (22DD-H)(super +). The signal intensity of the acidic proton was found to decrease when the metal Pb(II) was incorporated by the carrier after its extraction from the aqueous phase. Additionally, liquid/liquid as well as liquid/ membrane extraction results reveal that Cu(II) extraction proceeds via the loss of two protons from the organic phase. The Cu(II) is found to be located in the 22DD cavity and the stoichiometry of the complex in the organic phase is (22DD-Cu)(super 2+)-2LA(super -). Metal extraction is governed by 22DD and laurate acts only as counteranion. An unexpected feature was observed in the liquid/liquid extraction which was that, at low 22DD and LAH concentrations, the slope for log(K(sub p)) = f(pH) was 2 whereas it was much lower at high carrier concentration. This unexpected result seems to stem from impurities present in 22DD: only 0.1 mol % of impurity can indeed influence the exchange ratio of Cu(II) and H(super +). This type of anomaly, however, is not found in the normal procedure of liquid/ membrane extraction possibly due to the lower carrier/ metal molar ratio which is used in the classical PLM conditions.

The structures of the Ln0.50Ca0.50MnO3 manganites (Ln = Pr, Nd, Sm, Eu and Gd) are studied using electron diffraction and lattice imaging. Results show that the tendency to form an incommensurate structure at temperatures below 92 Kelvin increases with increasing lanthanide size. A transition towards a commensurate state is also observed for the smaller cations Nd, Sm, Eu and Gd with further cooling.

The stoichiometry and specificity of in vitro phosphopantetheinylation and aminoacylation of the SrfB1 module were studied by examining the N-terminal hexahistidine fusions of the entire module and other truncated constructs. The capacity of the altered enzymes to experience both inter and intra-molecular covalent aminoacylation was also evaluated. The results indicated three domains for condensation, aminoacylation and thioesterification for the valine-activating module of surfactin synthetase.

The point defect levels in single CuInSe2 crystals grown with a deviation from valence stoichiometry were studied using extrinsic photoresponse and photoluminescence methods. Comparison of the optical activation energy and thermal activation from other reported studies reveal point defects of identical nature are exhibited in the CuInSe2 ternary material grown by various methods. The electric parameters are also found to correspond with the defect chemistry of the crystals obtained, with the specific conductivity increasing with the valence stoichiometry.

Raman difference spectroscopy studies were used on C24S mutant variant of the acyl enzyme, 5-methylthiophene acryoyl hepatitis A virus 3C (HAV 3C) to investigate its active site properties. Results have shown the presence of two alpha, beta-unsaturated thiolesters s-cis and s-trans isomers between the c1-c2 bond with s-cis being the more polarized and dominant on the active site. Furthermore, there is no association between changes in pH and changes in the protonation state of any structural amino acid residue.