Function Of Mol Research Articles

A Computational and Experimental View of Hydrogen Bonding in Glycerol Water Clusters.

Polyol-water clusters provide a template to probe ionization and solvation processes of paramount interest in atmospheric and interstellar chemistry. We generate glycerol water clusters in a continuous supersonic jet expansion and interrogate the neutral species with synchrotron-based tunable vacuum ultraviolet photoionization mass spectrometry. A series of glycerol fragments (m/z 44, 61, 62, and 74) clustered with water are observed. A judicious combination of backing pressure, nozzle temperature, and water vapor pressure allows for tuning the mol % of glycerol. The recorded appearance energies of the water cluster series m/z 62 and 74 are similar to that observed in pure glycerol, while the m/z 61 series shows a dependence on cluster composition. Furthermore, this series also tracks the water concentration of the beam. Theoretical calculations on neutral and ionized clusters visualize the hydrogen bond network in these water clusters and provide an assessment of the number of glycerol-glycerol, glycerol-water, and water-water hydrogen bonds in the cluster, as well as their interaction energies. This method of bond counting and interaction energy assessment explains the changes in the mass spectrum as a function of mol % and offers a glimpse of the disruption of the hydrogen bond network in glycerol-water clusters. The calculations also reveal interesting barrierless chemical processes in photoionized glycerol water clusters that are either activated or do not occur without the presence of water. Examples include spontaneous intramolecular proton transfer within glycerol to form a distonic ion, nonactivated breaking of a C-C bond, and spontaneous proton transfer from glycerol to water. These results appear relevant to radiation-induced chemical processing of alcohol-water ices in the interstellar medium.

Structural and spectroscopic studies on lead germanate glasses doped with V2O5

Vanadium doped lead germanate glasses were synthesized by melt quenching technique. The samples were characterised by XRD and DSC patterns. Optical absorption and ESR studies of the samples indicated that a considerable proportion of vanadyl ions exist in V4+ and V5+states due to substitution of germanate ions with vanadium. The IR spectra of samples have proved the existence of various conventional germanium and vanadium structural units. The variations observed as a function of mol% of dopant in all these studies were analysed keeping in view of different oxidation states and environment of vanadium ions in the glass network.

The role of subphase chemistry in controlling monolayer behaviour

Intermolecular interactions lie at the root of many fundamental processes in nature. For example, they define membrane formation and crystallisation processes. Here, using Langmuir monolayers, we have investigated the role of intermolecular interactions in defining non-equilibrium monolayer structure and response, specific to a nucleating subphase chemistry. In particular, the interactions in mixed alcohol/carboxylic acid systems have been explored on four different subphases: ultrapure water, calcium chloride, sodium bicarbonate and a calcium carbonate crystallising subphase. Area per molecule, surface pressure and surface potential were analysed as a function of mol% ratio of acid to alcohol on each of the subphases. Comparison of the data across the subphases showed that three main interactions dictate the behaviour of the monolayer: (1) formation of a hydrogen-bonding network (predominantly dominating intramonolayer structure), (2) electrostatic interactions between the charged monolayer and strongly binding counterions and (3) the formation of a hydrogen-bonded soap network induced by the presence of bicarbonate coions. The latter provides a potential mechanism for defining directionality of interfacial interactions, and therefore face-selective nucleation.

Initial responses of carbonate-rich shelf sediments to rising atmospheric pCO 2 and “ocean acidification”: Role of high Mg-calcites

Carbonate-rich sediments at shoal to shelf depths (<200 m) represent a major CaCO 3 reservoir that can rapidly react to the decreasing saturation state of seawater with respect to carbonate minerals, produced by the increasing partial pressure of atmospheric carbon dioxide ( pCO 2) and “acidification” of ocean waters. Aragonite is usually the most abundant carbonate mineral in these sediments. However, the second most abundant (typically ∼24 wt%) carbonate mineral is high Mg-calcite (Mg-calcite) whose solubility can exceed that of aragonite making it the “first responder” to the decreasing saturation state of seawater. For the naturally occurring biogenic Mg-calcites, dissolution experiments have been used to predict their “stoichiometric solubilities” as a function of mol% MgCO 3. The only valid relationship that one can provisionally use for the metastable stabilities for Mg-calcite based on composition is that for the synthetically produced phases where metastable equilibrium has been achieved from both under- and over-saturation. Biogenic Mg-calcites exhibit a large offset in solubility from that of abiotic Mg-calcite and can also exhibit a wide range of solubilities for biogenic Mg-calcites of similar Mg content. This indicates that factors other than the Mg content can influence the solubility of these mineral phases. Thus, it is necessary to turn to observations of natural sediments where changes in the saturation state of surrounding waters occur in order to determine their likely responses to the changing saturation state in upper oceanic waters brought on by increasing pCO 2. In the present study, we investigate the responses of Mg-calcites to rising pCO 2 and “ocean acidification” by means of a simple numerical model based on the experimental range of biogenic Mg-calcite solubilities as a function of Mg content in order to bracket the behavior of the most abundant Mg-calcite phases in the natural environment. In addition, observational data from Bermuda and the Great Bahama Bank are also presented in order to project future responses of these minerals. The numerical simulations suggest that Mg-calcite minerals will respond to rising pCO 2 by sequential dissolution according to mineral stability, progressively leading to removal of the more soluble phases until the least soluble phases remain. These results are confirmed by laboratory experiments and observations from Bermuda. As a consequence of continuous increases in atmospheric CO 2 from burning of fossil fuels, the average composition of contemporary carbonate sediments could change, i.e., the average Mg content in the sediments may slowly decrease. Furthermore, evidence from the Great Bahama Bank indicates that the amount of abiotic carbonate production is likely to decline as pCO 2 continues to rise.

Polyhydroxyalkanoate copolymers from forest biomass

The potential for the use of woody biomass in poly-beta-hydroxyalkanoate (PHA) biosynthesis is reviewed. Based on previously cited work indicating incorporation of xylose or levulinic acid (LA) into PHAs by several bacterial strains, we have initiated a study for exploring bioconversion of forest resources to technically relevant copolymers. Initially, PHA was synthesized in shake-flask cultures of Burkholderia cepacia grown on 2.2% (w/v) xylose, periodically amended with varying concentrations of levulinic acid [0.07-0.67% (w/v)]. Yields of poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) [P(3HB-co-3HV)] from 1.3 to 4.2 g/l were obtained and could be modulated to contain from 1.0 to 61 mol% 3-hydroxyvalerate (3HV), as determined by 1H and 13C NMR analyses. No evidence for either the 3HB or 4HV monomers was found. Characterization of these P(3HB-co-3HV) samples, which ranged in molecular mass (viscometric, Mv) from 511-919 kDa, by differential scanning calorimetry and thermogravimetric analyses (TGA) provided data which were in agreement for previously reported P(3HB-co-3HV) copolymers. For these samples, it was noted that melting temperature (Tm) and glass transition temperature (Tg) decreased as a function of 3HVcontent, with Tm demonstrating a pseudoeutectic profile as a function of mol% 3HV content. In order to extend these findings to the use of hemicellulosic process streams as an inexpensive carbon source, a detoxification procedure involving sequential overliming and activated charcoal treatments was developed. Two such detoxified process hydrolysates (NREL CF: aspen and CESF: maple) were each fermented with appropriate LA supplementation. For the NREL CF hydrolysate-based cultures amended with 0.25-0.5% LA, P(3HB-co-3HV) yields, PHA contents (PHA as percent of dry biomass), and mol% 3HV compositions of 2.0 g/l, 40% (w/w), and 16-52 mol% were obtained, respectively. Similarly, the CESF hydrolysate-based shake-flask cultures yielded 1.6 g/l PHA, 39% (w/w) PHA contents, and 4-67 mol% 3HV compositions. These data are comparable to copolymer yields and cellular contents reported for hexose plus levulinic acid-based shake-flask cultures, as reported using Alcaligenes eutrophus and Pseudomonas putida. However, our findings presage a conceivable alternative, forestry-based biorefinery approach for the production of value-added biodegradable PHA polymers. Specifically, this review describes the current and potential utilization of lignocellulosic process streams as platform precursors to PHA polymers including hemicellulosic hydrolysates, residual cellulose-derived levulinic acid, tall oil fatty acids (Kraft pulping residual), and lignin-derived aromatics.

N-WASP as a PIP 2 Density Sensor

Neuronal Wiskott-Aldrich syndrome protein (N-WASP) is a stimulator of actin nucleation through the actin-related protein complex, ARP2/3. N-WASP is activated in a cooperative manner by binding of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P 2 ] to the polybasic B motif and binding of the guanosine triphosphatase (GTPase) Cdc42 to the GTPase binding domain (GBD). Papayannopoulos et al. explored the mechanism by which PI(4,5)P 2 regulates N-WASP activity. Using in vitro assays with N-WASP peptide fragments, they demonstrated that the B motif bound with highest affinity to PI(4,5)P 2 compared with other phosphoinositide lipids and that the 10-lysine motif was the minimum sequence that bound PI(4,5)P 2 . In vesicle sedimentation assays, PI(4,5)P 2 concentration can be increased by either increasing the number of PI(4,5)P 2 -containing vesicles in the preparation or by increasing the concentration of PI(4,5)P 2 within a given vesicle [the mole percent (mol%) of PI(4,5)P 2 ]. The curve representing binding of the B-GBD fragment of N-WASP to vesicles with increasing mol% of PI(4,5)P 2 showed a sigmoidal shape, indicating cooperative binding. Furthermore, binding of B-GBD to PI(4,5)P 2 -containing vesicles that also included cholesterol to induce the formation of membrane microdomains was higher affinity (with cooperative binding) than binding in the absence of cholesterol. Using two N-WASP constructs (one only lacking the EVH1 domain and one consisting of the B, GBD, and VCA domains--called mN-WASP), the authors demonstrated a sigmoidal, highly cooperative curve (Hill coefficient of ~18) for stimulation of ARP2/3-mediated actin polymerization as a function of mol% PI(4,5)P 2 . The sensitivity of N-WASP to PI(4,5)P 2 -containing vesicles was increased by the presence of prenylated Cdc42 in the vesicles. Increasing or decreasing the number of lysines in the B motif in the context of mN-WASP changed the sensitivity to PI(4,5)P 2 density, with an increase from the native 9 lysines to 14 lysines yielding a Hill coefficient for actin nucleation of ~50. Similar dependency on the number of lysines was observed for the ability of mN-WASP to stimulate endosomal vesicle motility in Xenopus egg extracts. The 14-lysine version of mN-WASP also stimulated a phenomenon called vesicle rocketing in transfected cells, even in the absence of conditions that increased basal PI(4,5)P 2 concentrations. Thus, using multiple in vitro and in vivo tests, the B motif of N-WASP appears to confer switchlike activity to N-WASP, allowing N-WASP to be poised to respond to changes in the density of PI(4,5)P 2 , which may allow cells to link changes in the actin cytoskeleton to signals that alter membrane microdomains and prevent activation of N-WASP in response to "noise" during the quiescent state. V. Papayannopoulos, C. Co, K. E. Prehoda, S. Snapper, J. Taunton, W. A. Lim, A polybasic motif allows N-WASP to act as a sensor of PIP 2 density. Mol. Cell 17 , 181-191 (2005). [PubMed]

Production and Characterization of Poly-β-hydroxyalkanoate Copolymers from Burkholderia cepacia Utilizing Xylose and Levulinic Acid

Poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) (P(3HB-co-3HV)) copolymers were prepared via shake-flask fermentations of Burkholderia cepacia (formerly Pseudomonas cepacia) containing 2.2% (w/v) xylose and concentrations of levulinic acid ranging from 0.07% to 0.67% (w/v). Periodic harvest of shake-flask cultures from 48 to 92 h post-inoculation yielded 4.4-5.3 g/L of dry cell biomass, containing 42-56% (w/w) P(3HB-co-3HV), with optimal product yield occurring between 66 and 74 h. Growth and PHA accumulation enhancement were observed with concentrations of levulinic acid from 0.07 to 0.52% (w/v), producing dry cell biomass and P(3HB-co-3HV) yields of 9.5 and 4.2 g/L, respectively, at the 0.52% (w/v) concentration of levulinic acid. Representative samples were subjected to compositional analysis by 300 MHz 1H and 150 MHz 13C NMR, indicating that these random copolymers contained between 0.8 and 61 mol % 3-hydroxyvalerate (3HV). Solvent-cast film samples were characterized by differential scanning calorimetry, which demonstrated melting temperatures (Tm) to decrease in a pseudoeutectic fashion from 174.3 degrees C (0.8 mol % 3HV) to a minimum of 154.2 degrees C (25 mol % 3HV) and the glass transition temperatures (Tg) to decrease linearly from 2.1 to -11.9 degrees C as a function of increasing mol % 3HV. Thermogravimetric analysis of the copolymer series showed the temperature for onset of thermal decomposition (T(decomp)) to vary as a function of mol % 3HV from 273.4 to 225.5 degrees C. Intrinsic viscosities (eta) varied from 3.2 to 5.4 dL/g, as determined by dilute solution viscometry. Viscosity average molecular weights (Mv) of the copolymers were determined to range from 469 to 919 kDa, indicating that these P(3HB-co-3HV) copolymers are of sufficient molecular mass for commercial application.

Study of the Comparative Solvation Behaviour of Na+ and Cu+ Cations in Acetonitrile + N,N-Dimethylformamide Mixtures at 298.15 K

Viscosity and molar conductance of Bu4NBPh4, Bu4NClO4, [Cu(CH3CN)4]ClO4, NaClO4 and NaBPh4 have been measured in the concentration ranges 0.02 - 0.5 mol dm−3 and 0.0005 - 0.0065 mol dm−3 at 298.15 K in AN + DMF mixtures containing 0, 10, 20, 40, 60, 75, 80, 90, and 100 mol % DMF. The viscosity data have been analyzed by the extended form of the Jones-Dole equation in the form: (η/η0) = 1+AC1/2+BC+DC2 to evaluate B and D parameters and the conductance data by the Shedlovsky equation to evaluate Λo and KA values of the salts. Ionic viscosity B-coefficients (B±) and ionic molar conductances (λ◦ i) have been calculated by using Bu4NBPh4 as a reference electrolyte. Solvated radii (ri) for Na+, Cu+ and ClO4 − have been estimated by using Gill’s modification of Stokes’ law. The variation of B± and ri as a function of mol % DMF shows that both Na+ and Cu+ are highly solvated in AN + DMF mixtures over the entire composition region. The solvation passes through a maximum between 40 to 80 mol % DMF. Both Na+ and Cu+ are more strongly solvated between 40 to 80 mol % DMF. Cu+ is relatively more strongly solvated than Na+ in AN + DMF mixtures. ClO4 − shows poor solvation in AN + DMF mixtures.

Biodistribution of pH-responsive liposomes for MRI and a novel approach to improve the pH-responsiveness

The potential of pH-sensitive paramagnetic liposomes as a probe for monitoring acidic pH in tumours with magnetic resonance imaging has recently been demonstrated. If the blood retention time is prolonged, such liposomes can accumulate in tumour interstitium due to increased vascular permeability and interstitial retention. In the present study, biodistribution studies in healthy rats showed rapid clearance of the pH-sensitive system dipalmitoylphosphatidylethanolamine (DPPE)/dipalmitoylglycerosuccinate (DPSG) liposomal GdDTPA-BMA from the blood circulation with most of the Gd dose in the liver at 15 min post intravenous injection. Incorporation of 1.5 mol% polyethylene glycol (PEG) grafted DPPE (DPPE-PEG) in the above-mentioned formulation resulted in a significantly prolonged blood circulation time. However, the relaxometric pH-response of the DPPE/DPSG/DPPE-PEG system decreased as a function of mol% DPPE-PEG. Therefore, a compromise would be necessary between long blood residence time and a suitable pH-sensitivity of the liposomes. A possible approach to compensate for the reduced pH-sensitivity was investigated. Gadofosveset, a low-molecular weight Gd-chelate with high affinity for albumin, was encapsulated within DPPE/DPSG liposomes. This promising system showed in blood a markedly higher relaxometric response than the corresponding system with GdDTPA-BMA, due to release of gadofosveset at low pH and subsequent binding to albumin.

Structural Relationships among Bismuth-Rich Phases in the Bi2O3–Nb2O5, Bi2O3–Ta2O5, Bi2O3–MoO3, and Bi2O3–WO3 Systems

The crystal structures of bismuth-rich phases in the Bi2O3–M2O5 (M=Nb, Ta) and Bi2O3–M2O6 (M=W, Mo) systems are investigated, and the most probable model for the crystal structure of each phase is used to propose a crystal–chemical scheme unifying key features of these structures in terms of their relationships to a fluorite-type δ-Bi2O3-related parent structure. This scheme is based on the incorporation of pyrochlore-type structural motifs (e.g., strings of M atoms along 〈1 1 0〉F directions) into the underlying fluorite-type metal atom array. The relative orientations of these M atom strings and their interactions are driven by the competing requirements of overall charge-balance (a function of mol% M2O5 or M2O6) and local coordination environment (a function of the element M) within the flexible fluorite-type oxygen atom array. These interactions interrelate the oxygen atom array, the metal atom array, and the composition. As the composition moves further from pure Bi2O3, they force the abandonment of pyrochlore-type structural motifs, and hence any meaningful relationship to a fluorite-type δ-Bi2O3-related parent structure is lost. The descriptive and predictive utilities of this crystal–chemical scheme are discussed.

Contributions to Maxima in Protein Kinase C Activation

In many lipid systems, the activity of protein kinase C (PKC) exhibits a peak followed by a decline as the mol % of one component is increased. In these systems, an increase in one lipid component is always at the expense of another or accompanied by a change in total lipid concentration. Here we report that in saturated phosphatidylserine (PS)/phosphatidylcholine (PC)/diacylglycerol (DAG) mixtures, increasing PS or DAG at the expense of PC revealed an optimal mol % PS, dependent on mol % DAG, with higher mol % PS diminishing activity. The decrease at high mol % PS is probably not attributable simply to more gel-phase lipid due to the higher melting temperature of saturated PS versus PC because a similar peak in activity occurred in unsaturated lipid systems. Increasing the total lipid concentration at suboptimal mol % PS provided the same activity as higher mol % PS at lower total lipid concentration. However, at optimal mol % PS, activity increased and then decreased as a function of total lipid concentration. PKC autophosphorylation also exhibited an optimum as a function of mol % PS, and increasing the PKC concentration increased the mol % PS at which activity decreased, both for autophosphorylation and for heterologous phosphorylation. Formation of two-dimensional crystals of PKC on lipid monolayers also exhibited a peak as a function of mol % PS, and the unit cell size of the crystals formed shifts from 50 x 50 A at low mol % PS to 75 x 75 A at higher PS. Collectively, these data suggest the existence of optimal lipid compositions for PKC activation, with increased quantity of these domains serving to dilute out enzyme-substrate aggregates and/or enzyme-enzyme aggregates on the lipid surface.

Thermal analysis of chiral drug mixtures: the DSC behavior of mixtures of ephedrine HCl and pseudoephedrine HCl enantiomers

A method for peak shape analysis and deconvolution of overlapping endotherms in differential scanning calorimetry (DSC) data has been previously reported. In this study the method is applied to binary mixtures of, (i) (1S,2S)-(+)- and (1R,2R)-(−)-ψ-ephedrine HCl, and (ii) (1S,2S)-(+)-ψ-ephedrine HCl and its diastereomer, (1S,2R)-(+)-ephedrine HCl. Phase diagrams based on enthalpies of fusion at the melting point ( ΔH m f ) as a function of mol% composition are linear. However, the phase diagrams based on melting temperature as a function of mol% composition are non-linear and show deviations from the theoretical Prigogine-Defay and Schröder-van Laar equations. Estimates of eutectic compositions are more definitive from the diagrams based on ΔH m f values. The phase diagram for the ψ-ephedrine HCl enantiomers demonstrates racemic compound formation with eutectic points for the compound and the pure enantiomers at 28.1 ± 2.5 mol% and 71.9 ± 2.5 mol%. The ΔH m f phase diagram for mixtures of (1S,2R)-(+)-ephedrine HCl and (1S,2S)-(+)-ψ-ephedrine HCl suggested the formation of a weak complex with a composition close to 60 mol% of the (1S,2S)-(+)-isomer.

Association phenomena between copolymers of p‐styrenesulfonate(Cs+)/3‐methacryloxypropyltrimethoxysilane and hydroxypropylcellulose in aqueous solution and solvent‐cast films

AbstractAssociation between copolymers of p‐styrenesulfonate (Cs+)/3‐methacryloxypropyltrimethoxysilane [copolySS(Cs+)/MAPTMS], and hydroxypropylcellulose (HPC) are shown to exist in dilute aqueous solution. Gels form at concentrations as low as 0.05 g/dL. The tendency to form gels is a function of mol % MAPTMS in the copolymer and molecular weight of HPC. Gels can be dispersed by the addition of dimethylformamide (DMF), a known disruptor of hydrogen bonding. Homopolymers of SS(Cs+) and MAPTMS were also prepared. PolyMAPTMS shows anamolous behavior with regards to association with HPC in that gels form to a lesser degree than the trend exhibited by the copolymers. This is rationalized on the basis of the lack of chain expansion due to the absence of salt groups and their intrapolymer repulsions. In addition to the hydrodynamic data, the phase relationship of blends of HPC with either copolySS(Cs+)/MAPTMS, polySS(Cs+), or polyMAPTMS cast from aqueous solution strongly suggests specific interactions between polymers.

Photoredox chemistry of nitrobenzyl alcohols in aqueous solution. Acid and base catalysis of reaction

The photochemistry of several m- and p-nitrobenzyl alcohols (1–5) has been studied in aqueous solution. These compounds react via an intramolecular photoredox pathway to give reduced and oxidized moieties of the substituent groups. The reaction is an example of a new type of photoreaction of nitro-substituted aromatic derivatives that is not observed in organic solvents, the presence of water being essential. This effect is exemplified by measuring the quantum efficiency as a function of mol% water in aqueous acetonitrile, methanol, and formamide: the reaction efficiency decreases rapidly as water is depleted in the mixture. Catalytic effects due to the hydronium and hydroxide ions were studied: the para derivatives exhibited hydroxide ion catalysis; the meta derivatives exhibited hydronium ion catalysis. Quantum yields, solvent isotope effects, and α-deuterium isotope effects are reported for the parent derivatives.