Determination of kinetic constants of the cationic copolymerization of isobutylene with isoprene

A theoretical kinetic model has been developed for cationic isobutylene–isoprene copolymerization in methyl chloride with an AlCl₃ catalyst. Kinetic constants of this process have been derived from experimental data available on copolymerization kinetics (isobutylene conversion curve) and on molecular weight characteristics of the isobutylene–isoprene copolymer (butyl rubber). The adequacy of the theoretical kinetic model of the isobutylene–isoprene copolymerization process has been demonstrated by comparing the calculated molecular weight characteristics and degree of unsaturation of butyl rubber to the corresponding independent experimental data.     

C-C bond unsaturation degree in monosubstituted ferrocenes for molecular electronics investigated by a combined near-edge x-ray absorption fine structure, x-ray photoemission spectroscopy, and density functional theory approach

We present the results of an experimental and theoretical investigation of monosubstituted ethyl-, vinyl-, and ethynyl-ferrocene (EtFC, VFC, and EFC) free molecules, obtained by means of synchrotron-radiation based C 1s photoabsorption (NEXAFS) and photoemission (C 1s XPS) spectroscopies, and density functional theory (DFT) calculations. Such a combined study is aimed at elucidating the role played by the C-C bond unsaturation degree of the substituent on the electronic structure of the ferrocene derivatives. Such substituents are required for molecular chemical anchoring onto relevant surfaces when ferrocenes are used for molecular electronics hybrid devices. The high resolution C 1s NEXAFS spectra exhibit distinctive features that depend on the degree of unsaturation of the hydrocarbon substituent. The theoretical approach to consider the NEXAFS spectrum made of three parts allowed to disentangle the specific contribution of the substituent group to the experimental spectrum as a function of its unsaturation degree. C 1s IEs were derived from the experimental data analysis based on the DFT calculated IE values for the different carbon atoms of the substituent and cyclopentadienyl (Cp) rings. Distinctive trends of chemical shifts were observed for the substituent carbon atoms and the substituted atom of the Cp ring along the series of ferrocenes. The calculated IE pattern was rationalized in terms of initial and final state effects influencing the IE value, with special regard to the different mechanism of electron conjugation between the Cp ring and the substituent, namely the σ/π hyperconjugation in EtFC and the π-conjugation in VFC and EFC.     

Satellite bands in the X-Ray Photoelectron spectrum of formaldehyde

The energies and intensities of satellite bands in the X-ray photoelectron spectrum of formaldehyde have been calculated using molecular wave functions obtained from a combination of multi-configuration self-consistent field theory and configuration-mixing formalism. The intensities of monopole allowed shake-up processes have been obtained from the sudden approximation formula whose derivation by an alternative route is detailed. It is found that the satellite spectra of carbon and oxygen hole states are predicted to differ substantially; giving insight into the atomic orbital character of the molecular orbitals concerned. The significance of the appearance of satellite bands on a quantitative analytical use of X-ray photoelectron spectroscopy is pointed out. The possibilities and condition for the appearance of monopole forbidden valence shell shape-up processes is discussed.     

Rapid characterization of edible oils by direct matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis using triacylglycerols

Direct matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis of solutions of edible fats/oils yielded spectra useful for their rapid differentiation and classification. Results also reflected the individual fatty acid components and their degree of unsaturation. After dissolution in hexane, MALDI-MS analysis revealed spectra showing characteristic triacylglycerols (TAGs), the main fat/oil components, as sodium adduct ions. The Euclidean distances calculated using the mass and intensity values for 20 TAGs were used to evaluate and compare spectra. With cluster analysis, animal fats grouped together differently than vegetable oils and the individual oils grouped together by type. The ion abundances for the individual TAGs and their presumed compositions were used to approximate the overall fatty acid composition of canola, soybean, corn, olive and peanut oil, as well as lard. Using this approach the calculated fatty acid compositions and degree of unsaturation generally fell within about 4% of literature values. When the degree of saturation was compared with values calculated from the package labeling the differences were about 7%.     

Polyunsaturation in lipid membranes: dynamic properties and lateral pressure profiles

We elucidate the influence of unsaturation on single-component membrane properties, focusing on their dynamical aspects and lateral pressure profiles across the membrane. To this end, we employ atomistic molecular dynamics simulations to study five different membrane systems with varying degrees of unsaturation, starting from saturated membranes and systematically increasing the level of unsaturation, ending up with a bilayer of phospholipids containing the docosahexaenoic acid. For an increasing level of unsaturation, we find considerable effects on dynamical properties, such as accelerated dynamics of the phosphocholine head groups and glycerol backbones and speeded up rotational dynamics of the lipid molecules. The lateral pressure profile is found to be altered by the degree of unsaturation. For an increasing number of double bonds, the peak in the middle of the bilayer decreases. This is compensated for by changes in the membrane-water interface region in terms of increasing peak heights of the lateral pressure profile. Implications of the findings are briefly discussed.     

An empirical relation between oscillator strengths calculated from the dipole length and dipole velocity formalisms in the optical absorption of conjugated molecules

It is found that a ratio between the oscillator strengths of the optical absorption calculated from the dipole length formalism and those calculated from the dipole velocity formalism is almost constant for many conjugated molecules if the calculation is made using the theoretically obtained transition energy. The value of the ratio becomes very sensitive to the molecular geometry if the calculation is made using the experimentally obtained transition energy. The origin of the constancy of the ratio is discussed.     

Three-dimensional spatial characteristics of primary and secondary basis set superposition error

Both the SCF and MP2 basis set superposition error (BSSE) calculated around a molecule of HF are strongly distance-dependent but nearly isotropic, with the highest degree of unsaturation centered along the HF bond. The secondary BSSE ( in the dipole moment), on the other hand, is highly anisotropic with larger effects identified near the F atom. Calculations on H₃N-HF indicate that some cancellation may occur between the secondary BSSEs of the two subunits but that nonetheless, correction of this error is important in forming a proper picture of electronic rearrangements in molecular complexes.     

分子结的非弹性隧道谱和电子-振动的耦合

研究了分子结的非弹性隧道谱, 给出了基于微扰理论近似的非平衡格林函数. 深入研究了非弹性隧道谱和电子-振动耦合常数的相互关系. 同时, 还计算了OPV和OPE分子结的IETS, 计算结果与有关的实验结果具有很好的可比性.     

Silver-phase high-performance liquid chromatography–electrospray mass spectrometry of triacylglycerols

Silver-phase chromatography hyphenated with on-line electrospray mass spectrometry can be applied to characterize triacylglycerols present in vegetable oils with respect to their degree of unsaturation, the position of the most unsaturated fatty acid and the carbon number (CN). The CN information obtained with silver-phase HPLC–ESP–mass spectrometry is complementary to the unsaturation information obtained by silver-phase HPLC-flame ionization detection. Both information is essential to monitor or study modified vegetable oils on the presence of non-natural triacylglycerols. The quantitative results obtained with the method are in agreement with the results obtained in the silver-phase HPLC-flame ionization detection and with theoretical values calculated from the fatty acid distribution of the oil. Silver-phase HPLC–ESP-mass spectrometry gives direct information on fatty acid position and triacylglycerol CN, for each of the triacylglycerols in the sample. This in contrast with non-aqueous reversed-phase HPLC hyphenated with on-line atmospheric pressure chemical ionization-mass spectrometry, which requires a more extensive data processing. The results obtained with silver-phase HPLC–ESP-mass spectrometry can be presented in a three-dimensional overview (relative amount, CN, fatty acid position) serving as a fingerprint for the oil.     

Theory of light scattering from vesicles

The scattering and depolarization of light from spherical membrane systems, vesicles, is calculated in a new succinct formalism appropriate to spherical systems and the rotations of anisotropic elements composing them. The results of Tinker (1972) and Mishima (1980, 1981) are readily derived within this formalism and there is a considerable saving in numerical computation. The problem of fluctuations in the molecular packing of the component phospholipid molecules is also addressed.     

Novel corresponding-states principle approach for the equation of state of isotopologues: H2(18)O as an example

The corresponding-states principle (CSP) has been considered for the development of the equations of state (EOS) of minor isotopologues that are usually unknown. We demonstrate that, for isotopologues of a given molecular fluid, a general extended multi-parameter corresponding-states EOS can be reduced to the three-parameter EOS, utilizing the critical parameters (temperature and density) and Pitzer's acentric factor as correlation parameters. Appropriate general CSP mathematical formalism and equations for constructing the EOS of minor isotopologues are described in detail. The formalism and equations were applied to isotopologues of water and demonstrated that the isotopic effect on the critical parameters and the acentric factor of H(2)(18)O can be successfully calculated from the EOS of H2O and experimental data on the isotope effects (liquid-vapor isotope fractionation factor and molar volume isotope effect). We have also shown that the experimental data on the vapor pressure isotope effect (VPIE) for 18O-substituted water are inconsistent within the framework of thermodynamics with the liquid-vapor oxygen isotope fractionation factor. The novel approach of CSP to isotopologues developed in this study creates a new opportunity for constructing the EOS of minor isotopologues for many other molecular fluids.     

Gas chromatographic separation of triglycerides according to their degree of unsaturation on glass capillary columns

Triglycerides are separated according to their molecular weight and their degree of unsaturation on glass capillary columns by use of the on-column injection technique. The columns employed are silylated SE-30 columns of 4.5, 8, and 10m length with a film thickness of ca. 0.15 μm. The paper gives several examples of chromatograms of natural and hydrogenated triglycerides as well as of mixtures of pure, known triglycerides before and after interesterification.     

An analysis of the solution of groups method for component activity coefficients

The solution of groups method is analyzed via a statistical mechanical formalism in order to uncover its inherent physical assumptions. Viewing the molecules in solution as a physical ‘cluster’ of groups, or interaction sites, provides a framework through which the implicit assumptions may be cast in standard molecular terminology. We find that, in addition to the assumed site-site form of the molecular pair potential, asymmetric distribution of sites within each molecule and use of an ‘effective’ angle average of the pair correlation function are also necessary in order to arrive at the commonly used solution of groups formula. Alternatively, the latter approximations can be interpreted as the site analogue of the n-fluid theory for simple mixtures. Attempts to improve upon the present empirical models may be made by relaxing some of the more restrictive assumptions.     

Synthesis and characterization of biodegradable poly(butylene succinate-co-butylene fumarate)s

A series of aliphatic biodegradable polyesters modified with fumaric residues was synthesized by transesterification in the melt of dimethyl succinate, dimethyl fumarate and 1,4-butanediol. The amount of unsaturation, originating from the fumaric acid residues in the polyesters chains was varied from 5 to 20 mol%. The molecular structure and composition of the polyesters were determined by ¹H NMR spectroscopy. The effects of the content of fumaric residues on the thermal and thermo-oxidative properties of the synthesized polyesters were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. The degree of crystallinity was determined by DSC and wide angle X-ray scattering. The degrees of crystallinity of the unsaturated copolyesters were reduced, while the melting temperatures were higher in comparison to poly(butylene succinate). Biodegradation of the synthesized copolyesters was estimated in enzymatic degradation tests using a buffer solution with Rhizopus arrhizus lipase at 37 °C. Although the degree of crystallinity of the copolyesters decreases slightly with increasing unsaturation, the biodegradation is not enhanced suggesting that not only the chemical structure and molecular stiffness but also the morphology of the spherulites has an influence on the biodegradation properties. The highest biodegradability was observed for the copolyesters containing 5 and 10 mol% of fumarate units.     

A numerical measure of the degree of oxidation (DOX) of an organic molecule,with special attention to heteroatoms and heterocyclic compounds

The degree of oxidation (DOX) of an organic compound C_nH_mE_p, where E is any one or more of eleven elements more electronegative than hydrogen, is defined with respect to an alkane C_nH_2n+2 (DOX = 0) as a reference, One can calculate DOX either from the molecular or the structural formula of the compound by the relationship DOX = DU + p, where DU is the degree of unsaturation (i.e. index of hydrogen deficiency) in the molecule. The concept is developed for E is oxygen, and is extended to other chalcogens, as well as to halogens, nitrogen, phosphorus, and arsenic. Particular examples of heterocyclic compounds are considered. It is noted that addition of a simple hydride of E to an organic compound or elimination of the hydride from C_nH_mE_p leaves DOX unchanged.     

硝基烃光异构化反应的密度泛函理论计算

采用DFT(B3LYP)计算方法, 在6-31G*水平上获得了反式-β-硝基苯乙烯、硝基乙烯和硝基甲烷基态异构化反应时的过渡态分子结构, 并计算了异构化能垒及激发态电子跃迁能. 结果显示, 反式-β-硝基苯乙烯和硝基苯与硝基甲烷相比具有较短的过渡态C—N键长, 较低的异构化能垒, 并且随着不饱和度的增加, 硝基苯和反式-β-硝基苯乙烯电子垂直跃迁能与基态异构化反应过渡态之间能量的差值ΔE迅速减小. 从能量的角度分析, 取代基的不饱和度越大, 越有利于激发态势能面与异构化反应势能面发生锥型或漏斗交叉, 因而越有利于光化学反应沿光异构化通道进行. 激发态分子的初始电子运动的定域或离域特征的差别可能是导致硝基苯等硝基芳烃与硝基甲烷等硝基烷烃光解通道不同的一个重要原因.     

Impact of the computational method on the geometric and electronic properties of oligo(phenylene vinylene) radical cations

We report on a quantum-chemical study of the electronic and optical properties of unsubstituted oligo(phenylene vinylene) (OPV) radical cations. Our goal is to distinguish the impact of the choice of molecular geometry from the impact of the choice of quantum-chemical method, on the calculated optical transition energies. The geometry modifications upon ionization of the OPV chains are found to depend critically on the theoretical formalism: Hartree-Fock (HF) geometry optimizations lead to self-localization of the charged defects while pure density functional theory (DFT) results in a complete delocalization of the geometric modifications over the whole conjugated backbone. The electronic structure and vertical transition energy associated with the lowest excited state of the radical cations have been calculated at the post-Hartree-Fock level within a configuration interaction (HF-CI) scheme and using the time-dependent DFT (TD-DFT) formalism for different radical cation geometries. Interestingly, the changes in the calculated optical properties obtained when using different geometric structures are less important within a given method than the differences between methods for a given structure. The optical excitation is localized with HF-CI and delocalized with TD-DFT, almost irrespective of the molecular geometry; as a result, HF-CI excitation energies tend to saturate as the chain length increases, in contrast to the results from TD-DFT.     

Evaluation of a quantitative structure-property relationship (QSPR) for predicting mid-visible refractive index of secondary organic aerosol (SOA)

In this work we describe and evaluate a simple scheme by which the refractive index (λ = 589 nm) of non-absorbing components common to secondary organic aerosols (SOA) may be predicted from molecular formula and density (g cm(-3)). The QSPR approach described is based on three parameters linked to refractive index-molecular polarizability, the ratio of mass density to molecular weight, and degree of unsaturation. After computing these quantities for a training set of 111 compounds common to atmospheric aerosols, multi-linear regression analysis was conducted to establish a quantitative relationship between the parameters and accepted value of refractive index. The resulting quantitative relationship can often estimate refractive index to ±0.01 when averaged across a variety of compound classes. A notable exception is for alcohols for which the model consistently underestimates refractive index. Homogenous internal mixtures can conceivably be addressed through use of either the volume or mole fraction mixing rules commonly used in the aerosol community. Predicted refractive indices reconstructed from chemical composition data presented in the literature generally agree with previous reports of SOA refractive index. Additionally, the predicted refractive indices lie near measured values we report for λ = 532 nm for SOA generated from vapors of α-pinene (R.I. 1.49-1.51) and toluene (R.I. 1.49-1.50). We envision the QSPR method may find use in reconstructing optical scattering of organic aerosols if mass composition data is known. Alternatively, the method described could be incorporated into in models of organic aerosol formation/phase partitioning to better constrain organic aerosol optical properties.