The impact of higher polarization basis sets on molecular ab initio results.: III. The ground state of Cl2 in comparison with other diatomics

The ground state potential curve of Cl₂ has been computed near R_c by means of the SCF, MC SCF, CI(SD), and the recently proposed CPF methods. The convergence of the total energy, of D_c and R_c is studied with the aid of computations for various basis sets which include up to three d, two f and one g set. Higher polarization functions have a larger effect than for F₂ for all methods, the g set still affects D_c by 0.15 eV and R_c by 0.02 a₀ on the CPF level. The most elaborate calculation, on the CPF [7,4,3,2,1] level, yields D_c and R_c with an accuracy of 0.08 eV and 0.02 a₀. The same accuracy is obtained for the MC-178 CAS SCF treatment employing a 2d1f polarization basis set. The present results allow us to order the polarization functions according to their relative importance as: d⁽¹⁾ > f⁽¹⁾ > d⁽²⁾ > f⁽²⁾ = d⁽³⁾ > g⁽¹⁾ for the SCF and d⁽¹⁾ > f⁽¹⁾ > d⁽²⁾ > g⁽¹⁾ > f⁽²⁾ = d⁽³⁾ for methods including external correlation. CI(SD) or CPF. A comparison of the results for N₂, F₂, P₂, and Cl₂ shows the higher polarization functions d⁽³⁾, f⁽²⁾, g⁽¹⁾ to contribute 0.1 (F₂) to 0.3 eV (F₂, Cl₂) to D_c and affect R_c by 0.005 a₀ (N₂) to 0.01 7 a₀ (P₂).We have focused our attention mainly on the impact of the atomic basis set incompleteness on the accuracy of results obtained from various methods of computation. Cl₂ turns out to be more demanding than the first-row counterpart F₂ on all levels of theory, which is mainly due to the slower angular convergence rate for E, D_c and R_c (for Cl₂), tables 2 and 3. The more pronounced influence of higher polarization functions is already noticed on the SCF and MC SCF level: f⁽¹⁾ increases D_c by 0.18 eV and reduces R_c by 0.052 a₀ on the MC-178 level for Cl₂, table 6, typical corresponding results for F₂ are only 0.04 eV and 0.013 a₀ [1]. CAS SCF calculations furthermore appear to require larger active spaces for Cl₂, as discussed in section 3.3.On the CI(SD) or CPF level — which aim to account for the entire external correlation — one even finds a pronounced influence of the first g set which contributes ≈ 0.15 eV to D_c and reduces R_c by ≈ 0.02 a₀ (on the CPF level, table 3), the corresponding effects for F₂ were only ≈ 0.04 eV and 0.01 a₀ [1]. The 2d1f polarization basis, which will remain the “standard” large basis for treatments of tri- and tetraatomic molecules, appears to underestimate D_c by still 0.5 eV and to overestimate R_c by ≈ 0.02 a₀ for P₂ and Cl₂, table 7, and probably all molecules in-between. This conclusion emerges from the cumulative effect of adding d⁽³⁾, f⁽²⁾ and g⁽¹⁾ which amounts already to 0.3 eV and 0.015 a₀, table 7.     

Influence of multidentate N-donor ligands on highly electrophilic zinc initiator for the ring-opening polymerization of epoxides

A set of multidentate ligands have been synthesized and used to stabilize the putative highly electrophilic zinc species initiating ring-opening polymerization (ROP) of cyclohexene oxide (CHO) and propylene oxide (PO). Reaction of the bidentate C₂-chiral bis(oxazoline) ligand (^R2,R3BOX: R₂ = (4S)-tBu, R₃ = H (a); R₂ = (4S)-Ph, R₃ = H (b); R₂ = (4R)-Ph, R₃ = (5S)-Ph (c)) with Zn(R₁)₂ (R₁ = Et (1), Me (2)) led to the heteroleptic three-coordinate complexes (^R2,R3BOX)ZnR₁, 1a-c and 2a, which were isolated in 92-96% yield. Next, two pyridinyl-functionalized N-heterocyclic carbene (NHC) ligands have been designed and synthesized: the 1,3-bis(2-pyridylmethyl)imidazolinium salt (d) and the protected NHC adduct 2-(2,3,4,5,6-pentafluorophenyl)-1,3-bis(2-pyridylmethyl)imidazolidine (e). The reaction of ligands d and e with ZnEt₂ led directly to the formation of (NHC)ZnEt(Cl) 3d complex with ethane elimination and the adduct (NHC-C₆F₅(H))ZnEt₂4e, respectively, in high yield. In situ combinations of selected complexes 1a-c, 3d and 4e with B(C₆F₅)₃ (1 or 2 equivalents) give active systems for ROP, with high productivity (3.3-5.9 10⁶ g_polym. mol_Zn⁻¹ h⁻¹) and high molecular weight (M_n up to 132 10³ g mol⁻¹) for CHO polymerization. Although the in situ B(C₆F₅)₃-activated zinc species were not isolated, the sterically demanding BOX ligands (1c > 1b > 1a) and functionalized NHC ligands seem to enhance the stability of highly electrophilic zinc complexes over ligand redistribution, allowing a better control of the cationic ROP as reflected particularly for 3d and 4e complexes by their respective efficiency (42-88%).     

Effect of Gel Structure on the In Vitro Gastrointestinal Digestion Behaviour of Whey Protein Emulsion Gels and the Bioaccessibility of Capsaicinoids

This study investigated the effect of gel structure on the digestion of heat-set whey protein emulsion gels containing capsaicinoids (CAP), including the bioaccessibility of CAP. Upon heat treatment at 90 °C, whey protein emulsion gels containing CAP (10 wt% whey protein isolate, 20 wt% soybean oil, 0.02 wt% CAP) with different structures and gel mechanical strengths were formed by varying ionic strength. The hard gel (i.e., oil droplet size d_4,3 ~ 0.5 μm, 200 mM NaCl), with compact particulate gel structure, led to slower disintegration of the gel particles and slower hydrolysis of the whey proteins during gastric digestion compared with the soft gel (i.e., d_4,3 ~ 0.5 μm, 10 mM NaCl). The oil droplets started to coalesce after 60 min of gastric digestion in the soft gel, whereas minor oil droplet coalescence was observed for the hard gel at the end of the gastric digestion. In general, during intestinal digestion, the gastric digesta from the hard gel was disintegrated more slowly than that from the soft gel. A power-law fit between the bioaccessibility of CAP (Y) and the extent of lipid digestion (X) was established: Y = 49.2 × (X − 305.3)^0.104, with R² = 0.84. A greater extent of lipid digestion would lead to greater release of CAP from the food matrix; also, more lipolytic products would be produced and would participate in micelle formation, which would help to solubilize the released CAP and therefore result in their higher bioaccessibility.     

Times of metastable droplet relaxation to equilibrium states

Times of metastable droplet relaxation to their equilibrium state are calculated at saturated vapor pressures, depending on the droplet size. It is shown that for small droplets with radius R = 6 molecular diameters (or ~2 nm) the relaxation times are ~1 ns (which is comparable to the characteristic flight times of rarefied gas molecules). For large droplets with radius R ~ 800 molecular diameters, the relaxation times are as long as 10 μs. At a fixed droplet radius (6 ≤ R ≤ 800), the range of variation in relaxation time from the melting point to the critical temperature does not exceed one order of magnitude: the lower the temperature, the slower the relaxation process.     

Theoretical study on the insertion reactions of the germylenoid H2GeClMgCl with RH (R = F, OH, NH2)

The insertion reactions of the germylenoid H₂GeClMgCl with RH (R = F, OH, NH₂) have been studied by using the DFT B3LYP and QCISD methods. The geometries of the stationary points on the potential energy surfaces of the reactions were optimized at the B3LYP/6-311+G(d, p) level of theory. The calculated results indicate that all the mechanisms of the three insertion reactions are identical to each other. The QCISD/6-311++G(d, p)//B3LYP/6-311+G(d, p) calculated potential energy barriers for the three insertion reactions of R = F, OH, and NH₂ are 164.62, 193.30, and 200.73 kJ mol^?1, and the reaction energies for the three reactions are ?57.46, ?35.65, and ?22.22 kJ mol^?1, respectively. Under the same situation, the insertion reactions should occur easily in the following order H-F > H-OH > H-NH₂. In THF solvent the insertion reactions get more difficult than in gas phase.     

A theoretical approach to dehydrodimerization reactions

In this work, the sequence of two elementary processes called dehydrodimerization, namely (i) RH+M^.→R^.+HM and (ii) 2R^.→RR are considered. These reactions are particularly helpful for cleaning a medium from free radicals (radioprotection of the medium). In the first step the trapping of radical M^. generates a hydrogenated product MH and another radical R^. which disappears in the second step. Both abstraction and recombination reactions obey an Evans—Polanyi type of relation: the activation energies linearly depend on the dissociation energies of the bond (s) involved in the corresponding process. In this paper, a theoretical approach to the classification of RH compounds according to their capability to behave as good radical scavengers is proposed. It is shown that good candidates should have a small BDE (RH) and correspond to RR dimers having either very small or rather large BDE(RR).     

Synthesis of porous vinylnaphthalene/divinylnaphthalene copolymers and their sorptive properties towards phenol and its derivatives

Four porous vinylnaphthalene/divinylnaphthalene (VN/DVN) polymers having three different nominal crosslinking degrees (60, 80 and 100 wt.%) have been synthesized using the suspension polymerization method in the presence of toluene and decane.The use of various crosslinking levels and inert diluents was aimed at changing the extent of polymeric network-diluent interactions. The resultant polymers have specific surface area in the range 450-700 m²/g depending on the DVN content. Two sets of pores were detected in all resins: one with the diameter of ≈2 nm and the second one in the range of 30-40 nm. Their sorptive properties have been studied using dilute (0.5 mmol/l) solutions of phenol and its derivatives (o-chlorophenol, 2-methylphenol, o-nitrophenol, m-nitrophenol and p-nitrophenol). It has been found that sorption, at low equilibrium concentration, follows the order: o-nitrophenol > o-chlorophenol > m-nitrophenol > o-methylphenol > p-nitrophenol > phenol. Full characteristics of the porous structure of resultant polymers was obtained by nitrogen adsorption at 77 K and their surface properties analyzed using Inverse Gas Chromatography.     

Fluorescence polarization anisotropy and kinetics of malachite green measured as a function of solvent viscosity

The fluorescence kinetics and polarization anisotropy of the triphenylmethane dye malachite green were measured as a function of solvent viscosity. The relationshp between the relaxation kinetics and the solvent viscosity was investigated in order to obtain information on the effect of enviromnental changes on the orientational order of dye molecules in solution. It was found that the fluorescence lifetimes follow an η^{$\text{2}\text{3}$} dependence for 1 < η < 60 P, η^{$\text{1}\text{2}$} dependence for 60 P < η < 1000 P and approach a constant for η > 1000 P. The dependence of the fluorescence decay rates on the solvent viscosity was fit to k = 5 × 10¹⁰η^{?$\text{2}\text{3}$} + 5 × 10⁸ s^?1. The fluorescence polarization anisotropy term, R(0), was also measured as a function of solvent viscosity. A marked decrease in R(0) was observed at a viscosity of 1000 P. For η < 1000 P, R(0) was found to be close to the expected value for a random distribution of molecules, 0.4; and for η > 3000 P, R(0) was measured to be ≈0.11. This small value of R(0) may indicate a nonrand The observed change of the polarization anisotropy with increasing viscosity indicates that the dye molecules become ordered at higher viscosities. This may arise through the formation of a long range order due to lack of rotational deexcitation of the malachite green dye molecules at high viscosities.     

Intra- and inter-chain fluctuations in entangled polymer melts in bulk and confined to pore channels

It is known that topological restraints by “chain entanglements” severely affect chain dynamics in polymer melts. In this field-cycling NMR relaxometry and fringe-field NMR diffusometry study, melts of linear polymers in bulk and confined to pores in a solid matrix are compared. The diameter of the pore channels was 10 nm. It is shown that the dynamics of chains in bulk dramatically deviate from those observed under pore constraints. In the latter case, one of the most indicative signatures of the reptation model is verified 28 years after its prediction by de Gennes: The frequency and molecular mass dependencies of the spin-lattice relaxation time obey the power law T_! ∝ M⁰ v^3/4 on a time scale shorter than the longest Rouse relaxation time τ_R. The mean squared segment displacement in the pores was also found to be compatible to the reptation law < r²>∝ M^−1/2t^1/2 predicted for τ_R < t < τ_d, where τ_d is the so-called disengagement time. Contrary to these findings, bulk melts of entangled polymers show frequency and molecular mass dependencies significantly different from what one expects on the basis of the reptation model. The data can however be described with the aid of the renormalized Rouse theory.     

Chemoenzymatic preparation of (2S,3S)- and (2R,3R)-2,3-butanediols and their esters from mixtures of d,l- and meso-diols

An efficient method of preparing the pure enantiomers of 2,3-butanediol from commercially available mixtures of the d,l- and meso-isomers was developed. It furnished (2S,3S)-2,3-butanediol with >99% e.e. and a >99.5/0.5 diastereomeric ratio and (2R,3R)-2,3-butanediol in 95% e.e. and >95/<5 diastereomeric ratio.     

Synthesis of the antiepileptic (R)-Stiripentol by a combination of lipase catalyzed resolution and alkene metathesis

The enantiopure (ee >99%) antiepileptic (R)-(+)-Stiripentol has been stereoselectively synthesized via cross metathesis of 5-vinylbenzo[d][1,3]dioxole 1 and (R)-(+)-4,4-dimethylpent-1-en-3-ol (R)-(+)-2. A novel one-pot two-step pathway for the synthesis of 5-vinylbenzo[d][1,3]dioxole 1 starting from 3,4-dihydroxycinnamic acid has been introduced. A lipase catalyzed kinetic resolution access to enantiopure (R)-(+)-4,4-dimethylpent-1-en-3-ol (R)-(+)-2 (ee >99%) has also been developed.     

Fractal structure and microporosity of nascent particles and sintered powders based on poly(tetrafluoroethylene)

Fractal characteristics of the surface of various powders based on the suspension poly(tetrafluoroethylene) F-4 are studied by the method of low-temperature adsorption of argon. Analysis of the degree of crystallinity, density of the solid phase, and free-volume characteristics (positron-annihilation lifetime spectroscopy) makes it possible to conclude that the granules contain nanopores. Owing to the separation of the contributions from nanoporous and fractal components of the specific surface of the particles, fractal dimension d = 2.60 is estimated in the scaling relationship σ ～ R ^{d ? 3}, where σ is the specific surface and R is the radius of the particle. For this set of powders, the linear dependence of specific air permeability q of the pressed pellets with a porosity of 70 vol % on the dimensions of granules is obtained. This case corresponds to fractal dimensions of the surface of d = 2.5 in the other scaling expression, q ～ R ^{6 ? 2d} . Similar fractal parameters estimated by the adsorption and aerodynamic methods confirm that the hydrodynamic resistance of a porous layer increases owing to an irregular surface of the powder granules. The correlation between the parameters of the heterophase dispersion polymerization and the specific features of the morphology and characteristics of the polymerizate is found for three types of PTFE.     

Steric mode of enzymic hydroxylation at primary carbon atoms: Hydroxylation of (1R)- and (1S)-[1-3H, 2H, 1H][1-14C]-octanes by Pseudomonas Oleovorans

(1R)- and (1S) [1-³H, ²H, ¹H]-octanes and mixed with [1-¹⁴C]-octane, were synthesized. The mixed samples were incubated with homogenats of P. oleovorans strain TF4-1L and the biosynthesized mixtures of octanols isolated. It was shown that mainly the achiral termini [-C¹H₃] were hydroxylated and that chiral methyls were oxygenated to the extent of 20–30%. In all instances the products derived from hydroxylation at the chiral methyls [-C-³H, ²H, ¹H] were mixtures of (1R)- and (1S)-octanols, the major component of which was the alcohol obtained by displacement of ¹H. The results indicate that hydroxylation proceeded with a normal isotope effect k_h>k_d>k_t. The amount of (1R)-octanol in the mixtures of octanols derived from (1R)- and (1S)-octane was determined. It was found that the C-1 hydroxylation of octane proceeded with retention, i.e. the incoming hydroxyl assumed the orientation of the displaced hydrogen (or isotopic hydrogen) atom.     

A multitracer Study on the Adsorption of 36 Elements on a Silica: Effects of pH and Fulvic Acid

The distribution coefficients,K _d of 36 elements from Na to Bi on a silica were determined at pH 4, 7, 9 and in the absence and presence of fulvic acid (FA) using a multitracer technique. The multitracer solution was prepared by irradiation of Th(NO₃)₄ with ⁴⁰Ar ion beam. The effects of pH and fulvic acid on the K _d values of 36 elements were studied. It was found that the sequences of the K _d values of alkali elements (Cs>Rb>K>Na) and of alkaline earth elements(Ba>Ca>Mg) in the absence of FA can be qualitatively explained in terms of chemical bond formation and hydration. Various effects of pH and the negative or positive effect of FA on the adsorption of 36 elements were observed and are probably related to the species of 36 elements in the aqueous solutions containing CO₃ ^2–, OH^–, Cl^– and FA. For most of the elements studied here the K _d values are increased with increasing pH and are decreased with adding FA.     

Growth and motion of heterogeneous water droplets in laminar diffusion chambers: 2. High nanoparticle concentrations

The heterogeneous condensation of water vapor on nanoparticles and the growth of formed droplets are numerically studied under conditions of laminar diffusion chamber (LDC) of a new type with a hot porous wall. The main attention is focused on the growth of heterogeneous droplets in the gas flow at high number densities of nanoparticles exceeding 10⁸ droplet/m³. Under these conditions, there is an interrelation between the growth of droplets and processes of heat and mass transfer in LDC due to vapor depletion and the release of latent heat of phase transition on growing droplets. The efficiency of the coverage of nanoparticles with water film is studied under LDC nonuniform conditions. It is shown that, at initial number densities of nanoparticles (N _d > 10¹¹ droplet/m³), heterogeneous droplets do not grow to optically detected sizes.     

Suitable dose of 60Co γ-ray for mutation in Roegneria seeds

Seeds from six accessions of three species of Roegneria were radiated with ⁶⁰Co γ-ray at different doses (50, 100, 150, 200, 250, 300 and 400 Gy). Following these treatments, germination energy, germination rate, seedling height, plant height, plant survival, and seed set were observed. Plant survival was highly correlated with seedling height (R ² > 0.91, P < 0.01) and seed set (R ² > 0.82, P < 0.01). The semi-lethal dose of each accession, calculated using a ‘Multi-target single-hit’ model, ranged from 60 to 173 Gy. The most suitable absorbed doses for each accession were deduced from these data. The suitable doses for Roegneria kamoji, Roegneria ciliaris and Roegneria japonensis were 65–100 Gy, 63–150 Gy and 80–170 Gy, respectively. According to the range of suitable doses, R. kamoji (Pr87-88-353) was the most sensitive to radiation, and R. japonensis (88-89-267) was the most resistant to radiation. Suitable doses of R. ciliaris were close to that of R. kamoji (ZY1007). This research provides preliminary guidelines for radiation induced mutagenesis in Roegneria.     

Size exclusion chromatography on porous fractals

Summary Some porous packings used in chromatography have been claimed to be fractals with a scale of sizes a<l<L, where a is a molecular size and L is the size of the largest pores. For a fractal porous packing, the excluded volume for molecules in solution in the vicinity of the packing surface is directly related to D_f, the fractal dimension of the pore surface (2<D_f<3). Since retention in size exclusion chromatography is itself directly related to this excluded volume, the fractal nature of the packing provides a model of retention in this technique. According to this model there is a linear relationship between log R_s and log(1-K_d), where R_s is the hydrodynamic radius of the solute macromolecules and K_d the distribution coefficient. The fractal dimension is derived from the slope of this plot. Size exclusion chromatographic retention data have been analyzed according to the model. It is found that some HPLC packings are fractals with fractal dimensions ranging from about 2.15 to 2.6, depending on the material. Such a large range of D_f values indicates large variations in the selectivities and domains of applications of the different packings. For some classical gel filtration chromatographic gels, the fractal retention model does not seem to apply.Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria.     

Water-soluble chiral monosulfonamide-cyclohexane-1,2-diamine-RhCp complex and its application in the asymmetric transfer hydrogenation (ATH) of ketones

Monosulfonamide ligands with heteroatom/heterocyclic systems were derived from trans-(1R,2R)-cyclohexane-1,2-diamine and complexed with [Ru(benzene)Cl₂]₂, [Cp^∗RhCl₂]₂ in situ and used in the ATH of aromatic ketones with aqueous sodium formate as the hydrogen source. The chiral secondary alcohols were obtained with >93% enantioselectivity and >89% yield. Reduction in water was faster than in isopropanol/KOH. Addition of surfactants showed little or no effects.     

A novel sorptive extraction method based on polydimethylsiloxane frit for determination of lung cancer biomarkers in human serum

In this study, a porous polypropylene frit was coated with polydimethylsiloxane (PDMS) as extraction medium, based on the home-made PDMS-frit, a rapid, simple and sensitive sorptive extraction method was established for analysis of potential biomarkers of lung cancer (hexanal and heptanal) in human serum samples. In the method, derivatization and extraction occurred simultaneously on the PDMS-frit, then the loaded frit was ultrasonically desorbed in acetonitrile. Polymerization, derivatization–extraction and desorption conditions were optimized. Under the optimal conditions, satisfactory results were gained, a wide linear application range was obtained in the range of 0.002–5.0 μmol L⁻¹ (R > 0.997) for two aldehydes, the detection limits (S N⁻¹ = 3) were 0.5 nmol L⁻¹ for hexanal and 0.4 nmol L⁻¹ for heptanal. The relative standard deviations (RSDs, n = 5) of the method were below 7.9% and the recoveries were above 72.7% for the spiked serum. All these results hint that the proposed method is potential for disease markers analysis in complex biological samples.     

Studies on the Imide-Amide Rearrangement of Cyclic Phosphorimidates

Abstract

The imide-amide rearrangement of cyclic phosphorirnidates 1 leads to the formation of phosphoramidates 3, either thermally (> 180°C) or by the action of a Lewis acid (BF₃ OEt₂, 60°C)¹. In an attempt to develop a synthetic pathway to β aminoalcohols based on this rearrangement, we have thoroughly studied the influence of the structure of the reactants on the Lewis acid catalysed rearrangement. This study brought some insight into the mechanism of this particular reaction, namely the identification of a new polymeric structure 2. not yet described, which is converted into 3 by thermolysis². The formation of 2 at rt was followed by ³ P NMR. In the case of R′? Ph, the reactivity observed for R₂N was: i-Pr₂N > Pyrrolidine > n-Bu²N For R²=i-Pr₂, the observed R′ group effect was: Bn > 4-NO₂Bn > Ph. No reaction was observed for R′ ? Ts, n-Oct. In the case of the groups R′ ? Bn and R₂=i Pr₂ the Lewis acid effect was also studied: BF₃OEt₂, BF₃MeOr-Bu, Sc(OTf)₃ or CITi(Oi-Pr)₃ or Me₂SnCl₂.