Magnetic Resonance Spectra and Statistical Geometry

Methods of statistical geometry are introduced which allow one to estimate, on the basis of computable criteria, the conditions under which maximally informative data may be collected. We note the important role of constraints which introduce curvature into parameter space and discuss the appropriate mathematical tools for treating curvature effects. Channel capacity, a term from communication theory, is suggested as a useful figure of merit for estimating the information content of spectra in the presence of noise. The tools introduced here are applied to the case of a model nitroxide system as a concrete example, but we stress that the methods described here are of general utility.     

Cucurbitane Glycosides from Siraitia grosvenorii

Systematic phytochemical studies of the extract of Luo Han Go (Siraitia grosvenorii) furnished six known cucurbitane glycosides, namely, mogrosides IVa, mogrosides V and VI, isomogroside V, 11-oxomogroside V, and siamenoside I. The structures of all the isolated compounds were characterized on the basis of extensive spectral and chemical studies. Though the partial NMR spectral data has been reported for some of the isolated compounds previously, the complete ¹H and ¹³C NMR spectral assignments of all the isolated compounds are reported herewith for the first time based on COSY, HSQC, HMBC, and NOESY spectroscopic data.     

On intrinsic properties of steady gas flows

Summary Considering the geometric theory of triply orthogonal spatial curves, the basic equations governing a steady gas flow are transformed into the intrinsic form and the results obtained are:(1) The pressure is uniform along the binormal to the stream line and the radius of curvature varies as the square of the velocity along it, for the baratropic fluids.(2) Acceleration is irrotational field when the fluid is compressible but baratropic or incompressible, in which case the relations existing between the flow quantities, curvature and torsions of the curves under consideration are obtained.(3) Considering incompressible flows, it is observed that either velocity in magnitude is uniform or the vorticity lies in the normal plane, in which case the stream lines are orthogonal to the vortex lines.Stream lines are observed to be either right circular helices or circles or straight lines.If the stream lines are not straight then the torsions of the binormal congruences and stream lines are equal.(4) The compatibility conditions of Berker¹) are transformed into intrinsic form, involving the curvatures and torsions of the above curves.     

Probing the interaction of the potassium channel modulating KCNE1 in lipid bilayers via solid‐state NMR spectroscopy

KCNE1 is known to modulate the voltage‐gated potassium channel α subunit KCNQ1 to generate slowly activating potassium currents. This potassium channel is essential for the cardiac action potential that mediates a heartbeat as well as the potassium ion homeostasis in the inner ear. Therefore, it is important to know the structure and dynamics of KCNE1 to better understand its modulatory role. Previously, the Sanders group solved the three‐dimensional structure of KCNE1 in LMPG micelles, which yielded a better understanding of this KCNQ1/KCNE1 channel activity. However, research in the Lorigan group showed different structural properties of KCNE1 when incorporated into POPC/POPG lipid bilayers as opposed to LMPG micelles. It is hence necessary to study the structure of KCNE1 in a more native‐like environment such as multi‐lamellar vesicles. In this study, the dynamics of lipid bilayers upon incorporation of the membrane protein KCNE1 were investigated using ³¹P solid‐state nuclear magnetic resonance (NMR) spectroscopy. Specifically, the protein/lipid interaction was studied at varying molar ratios of protein to lipid content. The static ³¹P NMR and T₁ relaxation time were investigated. The ³¹P NMR powder spectra indicated significant perturbations of KCNE1 on the phospholipid headgroups of multi‐lamellar vesicles as shown from the changes in the ³¹P spectral line shape and the chemical shift anisotropy line width. ³¹P T₁ relaxation times were shown to be reversely proportional to the molar ratios of KCNE1 incorporated. The ³¹P NMR data clearly indicate that KCNE1 interacts with the membrane. Copyright © 2017 John Wiley & Sons, Ltd.     

Syntheses of 2,4,6-tris(di-tetrahydrofurfuroxy)phosphinyl-s-triazine and its derivatives as fire-retardants for cellulose

The synthesis of 2,4,6-tris(di-tetrahydrofurfuroxy)phosphinyl-s-triazine (2) was achieved by the reaction of cyanuric chloride with tris(tetrahydrofurfuryl)-phosphite (1) or with sodium bis(tetrahydrofurfuryl)phosphite (5). 2 on treatment with anhydrous ammonia yielded ammonium salt of 2,4-diamino-6-tetrahydro-furfuroxy-phosphinyl-s-striazine (3), which on methylolation yielded (4). The reaction of 2 and 4 with cellulose powder under different experimental conditions was carried out and they were found to exhibit promising fire-retardant properties.     

Crystal structures of the benzene and ethanol solvates of neotame

The benzene and ethanol solvates of neotame crystallized from solutions of neotame anhydrate in benzene and ethanol, respectively. The crystal structures of the two solvates were determined by single-crystal X-ray diffraction using synchrotron radiation. The benzene solvate crystallizes in the monoclinic space group, P2₁, Z = 2, with one neotame molecule and one benzene molecule per asymmetric unit. The cell constants are a = 13.060 (6) Å, b = 5.582 (2) Å, c = 17.954 (9) Å, and = 102.079 (15)°. The ethanol solvate crystallizes in the orthorhombic space group, P2₁2₁2₁ with Z = 8 (Z = 2). The cell constants are a = 10.047 (4) Å, b = 17.001 (4) Å, and c = 28.948 (7) Å. Intermolecular hydrogen bonding among neotame molecules is evident in the two crystals. The benzene solvate has a nonpolar region containing the benzene molecules, with the benzene rings and alkyl chains of the neotame molecules.     

Multi-functional coordination crosslinks in poly(vinylamine) complexes with cobalt chloride

Poly(vinylamme) complexes with cobalt chloride hexahydrate exhibit the largest glass transition temperature enhancements that have been measured in this laboratory. T_g increases from 56°C in the undiluted polymer to 193°C when the molar concentration of cobalt is only 3%, based on the moles of polymeric repeat units. This translates to a 45°C enhancement in T_g per mol% cobalt. Higher glass transition temperatures have been measured for other polymeric complexes with d-block salts, but this study reports the largest ΔT_g=T_g(complex)-T_g(undiluted polymer) when transition-metal catalyzed chemical crosslinking reactions do not occur. A plausible explanation for this effect is based on the fact that cobalt chloride hexahydrate maintains pseudo-octahedral symmetry in the undiluted crystalline state and in an amorphous glassy complex with the polymer. The lone pair on nitrogen in the amino sidegroup is a strong base and, most likely, displaces all four waters of hydration that coordinate directly to the metal center. In fact, estimates of the ligand field splitting and the ligand field stabilization energy for octahedral cobalt complexes that contain methyl amine (CH₃NH₂) model ligands suggest that five or six amino sidegroups from several different chains might coordinate to each metal center, drastically reducing the mobility of the polymer. Both chloride anions remain near each divalent Co²⁺ center, but either one or two Cl⁻ might not reside in the first-shell coordination sphere of the transition metal. This bonding picture suggests that octahedral cobalt acts as a multi-functional bridge between five or six amino sidegroups. Empirical ligand field stabilization calculations support the concept that octahedral Co²⁺ is a multi-functional coordination crosslinking agent, and the inorganic literature provides experimental verification that similar small-molecule complexes (i.e., [Co(NH₃)₆]²⁺) exist. It is proposed that the onset of T_g occurs when sufficient thermal energy is supplied to remove either x or (x-1) amino sidegroup ligands from the coordination sphere of cobalt, where x is either 5 or 6. This is an endothermic process based on bond energies, as well as calculations which focus on the relative energies of the metal d-electrons.     

Changes in 13C/12C of oil palm leaves to understand carbon use during their passage from heterotrophy to autotrophy

The carbon isotope composition of leaf bulk organic matter was determined on the tropical tree Elaeis guineensis Jacq. (oil palm) in North Sumatra (Indonesia) to get a better understanding of the changes in carbon metabolism during the passage from heterotrophy to autotrophy of the leaves. Leaf soluble sugar (sucrose, glucose and fructose) contents, stomatal conductance and dark respiration, as well as leaf chlorophyll and nitrogen contents, were also investigated. Different growing stages were sampled from leaf rank ?6 to rank 57. The mean values for the δ¹³C of bulk organic matter were ?29.01 ± 0.9‰ for the leaflets during the autotrophic stage, ?27.87 ± 1.08‰ for the petioles and ?28.17 ± 1.09‰ for the rachises, which are in the range of expected values for a C₃ plant. The differences in δ¹³C among leaf ranks clearly revealed the changes in the origin of the carbon source used for leaf growth. Leaves were ¹³C‐enriched at ranks below zero (around ?27‰). During this period, the ‘spear’ leaves were completely heterotrophic and reserves from storage organs were mobilised for the growth of these young emerging leaves. ¹³C‐depletion was then observed when the leaf was expanding at rank 1, and there was a continuous decrease during the progressive passage from heterotrophy until reaching full autotrophy. Thereafter, the δ¹³C remained more or less constant at around ?29.5‰. Changes in sugar content and in δ¹³C related to leaf ranks showed an interesting similarity of the passage from heterotrophy to autotrophy of oil palm leaves to the budburst of some temperate trees or seed germination reported in the literature. Copyright © 2009 John Wiley & Sons, Ltd.     

Fixed-bed study for adsorptive removal of furfural by activated carbon

In our previous study [A.K. Sahu, V.C. Srivastava, I.D. Mall, D.H. Latye, Sep. Sci. Technol. 43 (5) (2008) 1239], commercial grade activated carbon (ACC) was used for adsorptive removal of furfural from aqueous solution using batch studies. In the present study, continuous fixed-bed adsorption was carried out in ACC packed bed for the removal of furfural from aqueous solution. The effects of important factors namely bed height (Z = 15–60 cm), influent concentration of furfural (C_o = 50–200 mg/l), the flow rate (Q = 0.02–0.04 l/min) and column diameter (D = 2–4 cm) were studied. Capacity of the bed to adsorb furfural was found to increase with an increase in the value of Z, C_o and D; and with decrease in the value of Q. Adams–Bohart, Bed-Depth Service-Time, Thomas, Yoon–Nelson, Clark and Wolborska models were applied to the experimental data for the prediction of the breakthrough point, and to determine the characteristic parameters of the column. Error analysis showed that the Yoon–Nelson model best described the experimental breakthrough curve, while Wolborska model showed good prediction of breakthrough curve for the relative concentration region up to 0.5.     

First principles study and database analyses of structural preferences for sodium ion (Na+) solvation and coordination

Extensive computations were performed on aqueous clusters of monovalent sodium cation [Na⁺(H₂O) _n ; (n = 1–20)] using MP2/cc-pVTZ and density functional theory. The structure, energy, and coordination number (CN) preference of a large number of competing conformations of different complexes have been explored. For complexes up to n = 12, the CN 4 is most preferred while 5, 6 CNs are favored in case of larger complexes containing up to 20 water molecules. These results are in very good agreement with experimental observations. The strength of hydrogen bonding among the waters coordinated to the Na⁺ ion is found to play a major role in the stability of the complexes. The varying preferences for CN of Na⁺ ion were explored by screening two important databases: Protein Databank and Cambridge Structural Database. A linear correlation is observed between the M (Metal)–O distance and the charge on metal ion in complex with the increase in CN of metal ion.