SOLUTION PROPERTIES OF PACHYMAN FROM PORIA COCOS MYCELIA IN DIMETHYL SULFOXIDE

A linear β-(1→3)-d-glucan PCM3 (pachyman), a major polysaccharide in Poria cocos mycelia, formed aggregates in aqueous solution or dimethyl sulfoxide (DMSO) with absorbed moisture, thereby considerably complicating its fractionation and study of solution properties. In this work, the pachyman PCM3 having narrow polydispersity (M _w/M _n = 1.9) was carefully fractionated by a preparative size exclusion chromatography (SEC) using dehydrated DMSO as the mobile phase. The weight-average molecular mass M _w and intrinsic viscosity [η] of the fractions were measured by static and dynamic laser light scattering, SEC combined with light scattering, and viscometry in DMSO at 25°C, thus eliminating the aggregation. The Mark-Houwink equation for the pachyman in DMSO is established to be: [η] = 6.79 × 10^?4 M _w ^0.95 (mL/g) in the M _w range from 1.2 to 3.5 × 10⁵. The characteristic ratio C _∞ of the PCM3 in DMSO at 25°C, from light scattering by using Flory theory, was obtained to be 10.1, thus indicating that it behaves as a relatively expanded, flexible coil. In addition, the M _w of the pachyman from Poria cocos mycelia was 1.68 × 10⁵, obviously larger than that from the sclerotium (8.9 × 10⁴).     

Branching in anionic polyacrylonitriles

The morphological and hydrodynamic properties of three series of anionic polyacrylonitrile fractions (10⁵<M _w< 5 × 10⁶) have been studied in dilute dimethylformamide (DMF) solution. All the observed values of the molecular parameters (M _w, S ² _w A₂, [η], S) are consistent with a trifunctional randomly branched structure characterized by a decrease of branching density with molecular weight. The sample obtained in a strongly dipolar solvent (DMF, ?70°C, diphenylmethylsodium) shows a unimodal molecular weight distribution and higher branching densities (2.5 × 10^?2 to 10^?1); on the other hand, the sample obtained in a nonpolar solvent (toluene, ?70°C, n-butyllithium) shows a binodal molecular weight distribution and smaller branching densities (10^?4 to 1.4 × 10^?3). These characteristic branched structures may be explained by transfer to polymer as the main branching process, taking into account the polarity of the medium and its thermodynamic quality for the polymer.     

Straight‐Chain Segment Length Distribution in Oriented Polyethylene as Revealed by LAM-Raman Spectroscopy

With the help of low-frequency Raman spectroscopy, the peculiarity of structural organization of oriented PE produced by multistage zone drawing of melt-crystallized films was studied. The draw ratios varied from DR=6 to 21 for PEI with M_η=8·10⁴ and from 3.5 to 5.7 for PEII with M_η≈10⁶.

The half widths (Δν) of all observed LAM bands were larger than 10–20 cm^?1. This means that the bands comprise a continuum of the overlapped elementary bands with Δν≈3 cm^?1 because of the wide straight–chain segments (SCS) length distribution. The length (L) of straight segments calculated from LAM-spectra, following a routine procedure, lies in the range from 7–8 to 60 nm.

Weight fractions G_MW of the SCS, as functions of their length, have a bell-like shape. Comparison of the SCS lengths with the value of the long periods (D) inferred from SAXS data for the same samples indicates that the lengths do not exceed 2D. The structural interpretation of the data obtained is given on the basis of microfibrillar models of oriented polymers. The peculiarity of the microfibrillar structure in PEI and PEII samples such as crystallite sizes and shapes and concentrations of inter- and intrafibrillar tie molecules, manifest themselves as the shape of G_MW (L) functions obtained for PE samples of various M_w and DR.     

Room‐temperature scavengers for macromolecular crystallography: increased lifetimes and modified dose dependence of the intensity decay

The advent of highly intense wiggler and undulator beamlines has reintroduced the problem of X‐ray radiation damage in protein crystals even at cryogenic temperatures (100 K). Although cryocrystallography can be utilized for the majority of protein crystals, certain macromolecular crystals (e.g. of viruses) suffer large increases in mosaicity upon flash cooling and data are still collected at room temperature (293 K). An alternative mechanism to cryocooling for prolonging crystal lifetime is the use of radioprotectants. These compounds are able to scavenge the free radical species formed upon X‐ray irradiation which are thought to be responsible for part of the observed damage. Three putative radioprotectants, ascorbate, 1,4‐benzoquinone and 2,2,6,6‐tetramethyl‐4‐piperidone (TEMP), were tested for their ability to prolong lysozyme crystal lifetimes at 293 K. Plots of relative summed intensity against dose were used as a metric to assess radioprotectant ability: ascorbate and 1,4‐benzoquinone appear to be effective, whereas studies on TEMP were inconclusive. Ascorbate, which scavenges OH radicals (k_OH = 8 × 10⁹ M^?1 s^?1) and electrons with a lower rate constant (k_e‐(aq) = 3.0 × 10⁸ M^?1 s^?1), doubled the crystal dose tolerance, whereas 1,4‐benzoquinone, which also scavenges both OH radicals (k_OH = 1.2 × 10⁹ M^?1 s^?1) and electrons (k_e‐(aq) = 1.2 × 10¹⁰ M^?1 s^?1), offered a ninefold increase in dose tolerance at the dose rates used. Pivotally, these preliminary results on a limited number of samples show that the two scavengers also induced a striking change in the dose dependence of the intensity decay from a first‐order to a zeroth‐order process.     

Heavy particles and the ϱ parameter in the standard model

A new formalism is presented for the calculation of the contribution δ? to ? = M_w²/M_z²cos²θ_w from heavy particles transforming according to arbitrary representations of SU(2) × U(1). A conjecture for the necessary and sufficient conditions that δ??0 for all values of masses and mixing angles within a particular multiplet is formulated. A number of examples are given (all consistent with the conjecture) and the significance of improved knowledge of ? vis à vis the possible existence of undiscovered heavy particles discussed.     

Synthesis and Evaluation of a Schiff-Based Fluorescent Chemosensors for the Selective and Sensitive Detection of Cu<Superscript>2+</Superscript> in Aqueous Media with Fluorescence Off-On Responses

Copper being an essential nutrient; also pose a risk for human health in excessive amount. A simple and convenient method for the detection of trace amount of copper was employed using an optical probe R1 based on Schiff base. The probe was synthesized by Schiff base condensation of benzyl amine and 2-hydroxy-1-napthaldehyde and characterized by single X-ray diffraction, ¹H NMR and FTIR. By screening its fluorescence response in a mixture of DMSO and H₂O (20:80, v/v) R1 displayed a pronounced enhancement in fluorescence only upon treatment with copper. Other examined metal ions such as alkali, alkaline and transition had no influence. Within a wide pH range 5–12 R1 could selectively detect copper by interrupting ICT mechanism that results in CHEF. From Job’s plot analysis a 2:1 binding stoichiometry was revealed. The fluorescence response was linear in the range 1–10?×?10^?9 M with detection limit 30?×?10^?9 M. Association constant was determined as 1?×?10¹¹ M^?2 by Benesi-Hilderbrand plot. As a fast responsive probe it possesses good reproducibility and was employed for detection of copper in different water samples.     

Gas‐phase oxidation of CH2 = C(CH3)CH2Cl initiated by OH radicals and Cl atoms: kinetics and fate of the alcoxy radical formed

Relative kinetics of the reactions of OH radicals and Cl atoms with 3‐chloro‐2‐methyl‐1‐propene has been studied for the first time at 298 K and 1 atm by GC‐FID. Rate coefficients are found to be (in cm³ molecule^?1 s^?1): k₁ (OH + CH₂ = C(CH₃)CH₂Cl) = (3.23 ± 0.35) × 10^?11, k₂ (Cl + CH₂ = C(CH₃)CH₂Cl) = (2.10 ± 0.78) × 10^?10 with uncertainties representing ± 2σ. Product identification under atmospheric conditions was performed by solid phase microextraction/GC‐MS for OH reaction. Chloropropanone was identified as the main degradation product in accordance with the decomposition of the 1,2‐hydroxy alcoxy radical formed. Additionally, reactivity trends and atmospheric implications are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Nucleophilic reactivity of thiolate, hydroxide and phenolate ions towards a model O-arylated diazeniumdiolate prodrug in aqueous and cationic surfactant media

The kinetics of aromatic nucleophilic substitution of the nitric oxide‐generating diazeniumdiolate ion, DEA/NO, by thiols (L ‐glutathione, L ‐cysteine, DL ‐homocysteine, 1‐propanethiol, 2‐mercaptoethanol, and sodium thioglycolate) from the prodrug, DNP‐DEA/NO, has been examined in aqueous solution and in solutions of cationic DOTAP vesicles. Second‐order rate constants in buffered aqueous solutions (k_RS‐ = 3.48–30.9 M^?1 s^?1; 30 °C) gave a linear Brønsted plot (β_nuc = 0.414 ± 0.068) consistent with the rate‐limiting S_NAr nucleophilic attack by thiolate ions. Cationic DOTAP vesicles catalyze the thiolysis reactions with rate enhancements between 11 and 486‐fold in Tris‐HCl buffered solutions at pH 7.4. The maximum rate increase was obtained with thioglycolate ion. Thiolysis data are compared to data for nucleophilic displacement by phenolate (k_PhO‐ = 0.114 M^?1 s^?1) and hydroxide (k_OH‐ = 1.82 × 10^?2 M^?1 s^?1, 37 °C) ions. The base hydrolysis reaction is accelerated by CTAB micelles and DODAC vesicles, with the vesicles being ca 3‐fold more effective as catalysts. Analysis of the data using pseudo‐phase ion‐exchange (PIE) formalism implies that the rate enhancement of the thiolysis and base hydrolysis reactions is primarily due to reactant concentration in the surfactant pseudo‐phase. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectrophotometric Determination of the Stability Constants of Co(II) and DPKBH (DI-2-Pyridyl Ketone Benzoylhydrazone)

Abstract

In order to have more information about the thermodynamic properties of the complexes formed by Cobalt(II) and DPKBH (di-2-pyridyl ketone benzoylhydrazone) and for the development of speciation methods for cobalt, the respective stepwise formation constants were determined in ethanolic solution 50% (V/V), at pH 5.3 and 25.0°C. The spectrophotometric method of corresponding solutions was used and the following overall formation constants were obtained: β₁ = 5.305 × 10⁶ M^?1 and β₂ = 8.476 × 10¹⁰ M^?2. The molar absorptivities of the 1:1 (ε₁) and 1:2 (ε₂) complexes (Co(II):DPKBH) were determined to be 4.475 × 10 and 2.994 × 10 (M^?1cm^?1), respectively. The calculated distribution diagram shows the percentage of the species at equilibrium as a function of the free DPKBH concentration.     

ESR and optical study of Cu2+-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II)

ESR studies were conducted on Cu²⁺-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II). Two Cu²⁺ lattice sites, Cu²⁺(I) and Cu²⁺(II), were identified. These sites exhibit two sets of four hyperfine lines in all directions. The g factor and hyperfine splitting were calculated from ESR absorption spectra: g_x ?=?2.0201?±?0.002, g_y ?=?2.0900?±?0.002, g_z ?=?2.1634?±?0.002, A_x ?=?(30?±?2)?×?10^?4?cm^?1, A_y ?=?(40?±?2)?×?10^?4?cm^?1 and A_z ?=?(154?±?2)?×?10^?4?cm^?1. It was found that Cu²⁺ enters the lattice substitutionally. The ground-state wavefunction of the Cu²⁺ ion in this lattice was determined from the spin Hamiltonian constants obtained from the ESR studies. With the help of an optical absorption study, the nature of the bonding in the complex is also discussed.     

Structure-dependent magnetic susceptibility of sharp poly(ethylene oxide) fractions

Nine sharp fractions of poly(ethylene oxide) (PEO) glycol with number-average molar masses (M _n) in the range from 0.6 × 10³ to 20 × 10³ (PEO-0.6 to PEO-20) were characterized by magnetic susceptibility χ measured in the temperature interval 293 K to 378 K. In contrast to the liquidlike PEO-0.6 with temperature-invariant χ, the values of χ for each of the remaining solid samples, after the initial increase, exhibited two plateaus separated by a relatively narrow temperature interval of their second increase. The jumps of χ at lower and higher temperatures were attributed to a solid-state transition of unspecific nature and to the melting of the crystal fraction, respectively.

The temperature-invariant values of χ_n in the melt state above T _m pass through a minimum for the sample PEO-2.0 and then increase again with (M_n) to a limiting value χ_∞ = ?0.622 × 10^?6. It is concluded that a considerable contribution of the molar-mass-dependent “paramagnetism” χ_P = χ ^? χ_d (where χ_d is the diamagnetic contribution estimated by Kirkwood's equation) to the total magnetic susceptibility of PEO fractions reflects distortions of the spherical symmetry of the electron shells around chain atoms resulting from the discontinuous change of both inter- and intrachain interactions as the (M_n) increases through and above the critical crossover molar mass (M_cr ) = 2 × 10³.     

Dimer radical cation of 4‐thiouracil: a pulse radiolysis and theoretical study

Pulse radiolysis with optical absorption detection has been used to study the reactions of hydroxyl radical (OH^?) with 4‐thiouracil (4TU) in aqueous medium. The transient absorption spectrum for the reaction of OH^? with 4TU is characterized by λ_max 460 nm at pH 7. A second‐order rate constant k_(4TU+OH) of 1.7 × 10¹⁰ M^?1 s^?1 is determined via competition kinetics method. The transient is envisaged as a dimer radical cation [4TU]₂^?+, formed via the reaction of an initially formed radical cation [4TU]^?+ with another 4TU. The formation constant of [4TU]₂^?+ is 1.8 × 10⁴ M^?1. The reactions of dibromine radical ion (Br₂^??) at pH 7, dichlorine radical ion (Cl₂^??) at pH 1, and azide radical (N₃^?) at pH 7 with 4TU have also produced transient with λ_max 460 nm. Density functional theory (DFT) studies at BHandHLYP/6–311 + G(d,p) level in aqueous phase showed that [4TU]₂^?+ is characterized by a two‐centerthree electron (2c‐3e) [?S∴S?] bond. The interaction energy of [?S∴S?] bond in [4TU]₂^?+ is ?13.01 kcal mol^?1. The predicted λ_max 457 nm by using the time‐dependent DFT method for [4TU]₂^?+ is in agreement with experimental λ_max. Theoretical calculations also predicted that compared with [4TU]₂^?+, 4‐thiouridine dimer is more stable, whereas 4‐thiothymine dimer is less stable. Copyright © 2013 John Wiley & Sons, Ltd.     

Reactivity of the insecticide chlorpyrifos‐methyl toward hydroxyl and perhydroxyl ion. Effect of cyclodextrins

The reactivity of Chlorpyrifos‐Methyl ( 1 ) toward hydroxyl ion and the α‐nucleophile, perhydroxyl ion was investigated in aqueous basic media. The hydrolysis of 1 was studied at 25 °C in water containing 10% ACN or 7% 1,4‐dioxane at NaOH concentrations between 0.01 and 0.6 M ; the second‐order rate constant is 1.88 × 10^?2 M ^?1 s^?1 in 10% ACN and 1.70 × 10^?2 M ^?1 s^?1 in 7% 1,4‐dioxane. The reaction with H₂O₂ was studied in a pH range from 9.14 to 12.40 in 7% 1,4‐dioxane/H₂O; the second‐order rate constant for the reaction of HOO^? ion is 7.9 M ^?1 s^?1 whereas neutral H₂O₂ does not compete as nucleophile. In all cases quantitative formation of 3,5,6‐trichloro‐2‐pyridinol ( 3 ) was observed indicating an S_N2(P) pathway. The hydrolysis reaction is inhibited by α‐, β‐, and γ‐cyclodextrin showing saturation kinetics; the greater inhibition is produced by γ‐cyclodextrin. The reaction with hydrogen peroxide is weakly inhibited by α‐ and β‐cyclodextrin (β‐CD), whereas γ‐cyclodextrin produces a greater inhibition and saturation kinetics. The kinetic data obtained in the presence of β‐ or γ‐cyclodextrin for the reaction with hydroxyl or perhydroxyl ion indicate that the main reaction pathway for the cyclodextrin‐mediated reaction is the reaction of HO^? or HOO^? ion with the substrate complexed with the anion of the cyclodextrin. The inhibition is attributed to the inclusion of the substrate with the reaction center far from the ionized secondary OH groups of the cyclodextrin and protected from external attack of the nucleophile. Sucrose also inhibits the hydrolysis reaction but the effect is independent of its concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

Selective Fluorescence Sensing of Deoxycytidine 5��-Monophosphate (dCMP) Employing a Bis(diphenylphosphate)diimine Ligand

A new bis(diphenylphosphate)diimine ligand (BP1) was prepared and evaluated for its ability for selective detection of deoxycytidine 5??-monophosphate (dCMP). BP1 exhibited off-type fluorescence in the presence of dCMP. The fluorescence of BP1 was significantly quenched upon the addition of 2.5?×?10^?4 M dCMP and the detection limit was 1.25?×?10^?5 M in MeCN-H₂O (1:1, v/v). The binding ratio between BP1 and dCMP was determined to be 1:1 with the binding constant of 3.98?±?0.60?×?10^?3 M^?1.     

Shear‐Enhanced Nucleation of Isotactic Polypropylene in Limited Space

The nucleation rate was measured by directly counting the number of nuclei, which were developed while an isotactic polypropylene melt was flowing under shear in a thin film. The nucleation rate was enhanced with an increased rate of shear, e.g., by a factor of 10 larger at the rate of shear of 14 s^?1 compared with the quiescent state, at 134°C. The ratio of the shear‐enhanced nucleation rate to the nucleation rate in the quiescent state was larger at a higher temperature of crystallization, i.e., about 10 times at 134°C to 590 times at 140°C. The increase of the nucleation rate under shear flow was explained by a reduction of the lateral and end (fold) surface free energies; the product σ _s ² σ _e decreased to 3.2×10^?7 for the sheared melt, from 6.0×10^?7 (J m^?2)³ for the isotropic state. The free energy reduction was caused by transition of the nucleus formation mode from three‐dimensional folded chain nuclei to two‐dimensional bundle nuclei, in which chains lie down on the glass substrate, aligning parallel to the flow direction.     

Effects of linking chain length and magnetic field on the kinetics of photoprocesses in covalently bonded porphyrin—viologen dyads

The formation and decay kinetics of chain linked triplet radical pairs derived from photo-induced electron transfer reactions in a series of 21 zinc porphyrin-flexible spacer-viologen (ZnP-Sp _n -Vi²⁺) dyads containing 2–138 atoms (n) in the spacer, have been examined by nanosecond laser flash photolysis techniques in an external magnetic field. In non-viscous polar solvents (acetone and CHCl₃ plus CH₃OH = 1:1 v/v), the effect of the spacer length on the rate constant of forward electron transfer can be described by the equation: k _et = k ⁰ _et(n + 6)^?1.5, with k ⁰ _et = 3 × 10¹⁰ s^?1 and 1.2 × 10¹⁰ s^?1 for electron transfer from the singlet and triplet states of ZnP, respectively. In zero magnetic field, the value of the triplet radical pair recombination rate constant, k _r(0) = 0.7 × 10⁶-8 × 10⁶ s^?1, is significantly smaller than k _et. The dependence of k _r(0) on n has an extremum with the maximum near n = 20. In a strong magnetic field (B = 0.21 T), significant retardation of triplet radical pair recombination is observed. In strong magnetic fields the effect of the chain length on triplet radical pair recombination rates is rather small and k _r(B) may vary in the range 0.3 × 10⁶-1 × 10⁷ s^?1. The phenomena observed are discussed in terms of the interplay of molecular and spin dynamics in the limits of slow and fast encounters, taking into account the exchange-interaction.     

A Fe<Superscript>3+</Superscript>/Hg<Superscript>2+</Superscript>-Selective Anthracene-Based Fluorescent PET Sensor with Tridentate Ionophore of Amide/β-Amino Alcohol

A new anthracene-based fluorescent PET sensor 1 with a tridentate ionophore of amide/β-amino alcohol displays very good selectivity and sensitivity for Fe³⁺ (K _a = 1.6 × 10³ M⁻¹) and Hg²⁺ (K _a = 2.1 × 10³ M⁻¹) in CH₃CN–H₂O (3:7, v/v) with detection limit of 1 μM. More fluorescence enhancement was observed when 1 selectively detected Fe³⁺ or Hg²⁺ in CH₃CN and its detection limit was up to 0.03 μM.     

Facile Synthesis of Gd(OH)3‐Doped Fe3O4 Nanoparticles for Dual‐Mode T1‐ and T2‐Weighted Magnetic Resonance Imaging Applications

The facile hydrothermal synthesis of polyethyleneimine (PEI)‐coated iron oxide (Fe₃O₄) nanoparticles (NPs) doped with Gd(OH)₃ (Fe₃O₄‐Gd(OH)₃‐PEI NPs) for dual mode T₁‐ and T₂‐weighted magnetic resonance (MR) imaging applications is reported. In this approach, Fe₃O₄‐Gd(OH)₃‐PEI NPs are synthesized via a hydrothermal method in the presence of branched PEI and Gd(III) ions. The PEI coating onto the particle surfaces enables further modification of poly(ethylene glycol) (PEG) in order to render the particles with good water dispersibility and improved biocompatibility. The formed Fe₃O₄‐Gd(OH)₃‐PEI‐PEG NPs have a Gd/Fe molar ratio of 0.25:1 and a mean particle size of 14.4 nm and display a relatively high r₂ (151.37 × 10^?3m ^?1 s^?1) and r₁ (5.63 × 10^?3m ^?1 s^?1) relaxivity, affording their uses as a unique contrast agent for T₁‐ and T₂‐weighted MR imaging of rat livers after mesenteric vein injection of the particles and the mouse liver after intravenous injection of the particles, respectively. The developed Fe₃O₄‐Gd(OH)₃‐PEI‐PEG NPs may hold great promise to be used as a contrast agent for dual mode T₁‐ and T₂‐weighted self‐confirmation MR imaging of different biological systems.     

Gas‐phase reactions of Cl atoms with hydrochloroethers: relative rate constants and their correlation with substituents' electronegativities

Rate constants for the reactions of Cl atoms with CH₃OCHCl₂ and CH₃OCH₂CH₂Cl were determined at (296 ± 2) K and atmospheric pressure using synthetic air as bath gas. Decay rates of these organic compounds were measured relative to the following reference compounds: CH₂ClCH₂Cl and n‐C₅H₁₂. Using rate constants of 1.33 × 10^?12 and 2.52 × 10^?10 cm³ molecule^?1 sec^?1 for the reaction of Cl atoms with CH₂ClCH₂Cl and n‐C₅H₁₂, respectively, the following rate coefficients were derived: k(Cl + CH₃OCHCl₂) = (1.05 ± 0.11) × 10^?12 and k(Cl + CH₃OCH₂CH₂Cl) = (1.14 ± 0.10) × 10^?10, in units of cm³ molecule^?1 s^?1. The rate constants obtained were compared with previous literature data and a correlation was found between the rate coefficients of some CH₃OCHR¹R² + Cl reactions and ΔElectronegativity of ? CHR¹R². Copyright © 2008 John Wiley & Sons, Ltd.     

EPR and Optical Absorption Study of VO2+-Doped Lithium Hydroxylammonium Sulphate

ABSTRACT

Single-crystal and powder EPR studies of VO²⁺-doped lithium hydroxylammonium sulphate (LiNH₃OHSO₄) were carried out at room temperature. The results indicate the presence of two magnetically inequivalent VO²⁺ sites. The VO²⁺ ion takes up a substitutional position in the host lattice. The angular variation of EPR spectra in three mutually perpendicular planes were used to determine the spin Hamiltonian parameters, and the values obtained were the following: For Site 1, g_x = 2.0249 ± 0.0002, g_y = 1.9698 ± 0.0002, g_z = 1.9552 ± 0.0002, A_x = (51 ± 2) × 10^?4 cm^?1, A_y = (93 ± 2) × 10^?4 cm^?1, and A_z = (165 ± 2) × 10^?4 cm^?1; and for Site 2, g_x = 2.0267 ± 0.0002, g_y = 1.9743 ± 0.0002, g_z = 1.9213 ± 0.0002, A_x = (40 ± 2) × 10^?4 cm^?1, A_y = (80 ± 2) × 10^?4 cm^?1, and A_z = (155 ± 2) × 10^?4 cm^?1. The optical absorption spectrum recorded at room temperature shows four bands. From the optical and EPR data, various molecular coefficients are evaluated, and the nature of bonding in the crystal is discussed.