Molecular polarizability of organic compounds and their complexes: LVI. Molar volume and structure in a solution of the compounds with several axes of intramolecular rotation

Molar volumes in solutions of compounds like orthoformic esters, trialkyl phosphates, trialkylphosphites, substituted aziridines, cyclopropanes, cyclohexanes, boroxines, N-aryl-4-pyridones, decalines, and cyclooctane were determined and discussed. Conformations of alkyl substituents in the esters were found to be similar to the conformations of the corresponding alkanes. Molar volumes of aziridines and cyclopropanes were found to be additive with respect to the molar volumes of bond and group increments. The nature of solvation of the molecules of these compounds was found to be similar to that in the model systems which served for the calculations of the increments. Molar volumes of cyclohexane, decaline, and cyclooctane also were found to be additive with respect to the contributions of the molar volumes of increments of the corresponding bonds and groups. The solvation and the steric structure of substituted boroxines were found to be similar to those of the structurally analogous substituted benzenes. Conformations of N-aryl-4-pyridone and its substituted derivatives in solutions were found to be similar to the conformations of biphenyl and its derivatives. A possibility of simplification of the methods for determining the dipole moments and Kerr constants of compounds from their additive molar volumes was demonstrated.     

Access to polyfunctionalized diquinanes, hydrindanes, and decalines via TiCl4 promoted Michael-aldol and Baylis-Hillman reactions

The addition of 0.5 equiv of TiCl(4) to (cyclo)alkanones tethered to α,β-unsaturated ketones afforded polyfunctionalized diquinanes, hydrindanes, and decalines. These products, resulting from a Michael-aldol or a Baylis-Hillman reaction, can be obtained with high or total diastereoselectivity in moderate to high yields. These scaffolds represent interesting building blocks for the synthesis of complex natural products.     

Palladium complexes of bis(acyclic diaminocarbene) ligands with chiral N-substituents and 8-membered chelate rings

Reaction of cis-dichloridobis(p-trifluoromethylphenylisocyanide)palladium(II) with N,N′-bis[(R)-1-phenylethyl]-1,3-diaminopropane afforded an enantiomerically pure, C₁-symmetric bis(acyclic diaminocarbene)PdCl₂ complex in 41% yield. The X-ray crystal structure of the complex revealed that three of the four carbene nitrogens are twisted out of conjugation with the carbene units, apparently as a result of steric interactions between one phenyl group and the propylene backbone of the chelate. A similar reaction with N,N′-bis[(R)-1-(1-naphthyl)ethyl]-1,3-diaminopropane did not lead to an isolable bis(carbene) complex, instead forming significant amounts of bis(ammonium) salt as a decomposition product. However, reaction of the same palladium isocyanide precursor with a mixture of all diastereomers of N,N′-bis[1-(1-naphthyl)ethyl]-1,3-diaminopropane provided an achiral, C_s-symmetric palladium bis(acyclic diaminocarbene) complex derived exclusively from the (R,S) diamine in 20% yield. An X-ray structure showed that the (R,S) stereochemistry allows the bulky naphthyl groups to adopt an orientation that avoids steric interactions with the backbone that likely lead to the instability of the homochiral analogue. The two palladium carbene complexes catalyzed the aza-Claisen rearrangement of an allylic imidate to an allylic amide in 24–34% yield, with an enantiomeric excess of 8% ee for the [(R)-1-phenylethyl]-substituted complex.     

Peculiarities of the Interaction of Short Oligonucleotides with Supported Lipid Films and Langmuir Monolayers

Summary.  The method of electrostriction was applied to supported bilayer lipid membranes (sBLM) and Langmuir monolayers with the aim to study the peculiarities of the interaction of short oligonucleotides with lipid films and of the duplex formation between complementary oligonucleotides. The bilayer lipid membranes (sBLM) were formed on an agar support, whereas Langmuir monolayers were generated on the air-water interface. As an oligonucleotide, the 15-mer 5^′-cholesterolphosphoryl-dT15 (CHpdT15) was synthesized. We could show that the interaction of CHpdT15 with sBLM resulted in a considerable increase of the elasticity modulus perpendicular to the membrane plane (E _⊥) and an increase of the surface potential. Interaction of complementary oligodeoxyadenylate (dA15) with sBLM modified by CHpdT15 resulted in a slight increase of the surface potential whereas E _⊥ slightly decreased. CHpdT15 forms monomolecular layers on the air/water interface. Interaction of dA15 with such monolayers resulted in an increase of the surface pressure, probably due to an increase of the surface charge of the monolayer; similar effects were observed for lipid monolayers modified by CHpdT15. Prospects of using such interactions for detecting DNA hybridization are discussed. Received June 23, 2000. Accepted (revised) September 19, 2000     

Molecular engineering of liquid crystal polymers by living polymerization. II. Living cationic polymerization of 11-[(4-cyano-4′-biphenyl) oxy] undecanyl vinyl ether and the mesomorphic behavior of the resulting polymers

The synthesis and living cationic polymerization of 11-[(4-cyano-4′-biphenyl)oxy]-undecanyl vinyl ether ( 6 – 11 ) are described. The mesomorphic phase behavior of poly( 6 – 11 ) with different degrees of polymerization was compared to that of 6 – 11 and of 11-[(4-cyano-4′-biphenyl) oxy] undecanyl ethyl ether ( 8 – 11 ) which is the model compound of the monomeric structural unit of poly( 6 – 11 ). 6 – 11 displays a monotropic S_A and a monotropic nematic mesophase while 8 – 11 an enantiotropic S_A mesophase. Poly( 6 – 11 ) with low degrees of polymerization exhibits an enantiotropic S_A mesophase. Poly( 6 – 8 ) with high degrees of polymerization displays an enantiotropic S_X (i. e., an unidentified smectic phase) and an enantiotropic S_C mesophase. These results demonstrate that the transformation of the nematic mesophase of the monomer into a smectic mesophase after polymerization, occurs at the level of monomeric structural unit.     

Analysis of the melt viscosity and glass transition of polystyrene

The melt viscosity, the glass transition, and the effect of pressure on these are analyzed for polystyrene on the basis of the Tammann-Hesse viscosity equation: log η = log A + B/(T ? T₀). Evidence that the glass transition is an isoviscosity state (log η_g ? 13) for lower molecular weight fractions (M < M_c) is reviewed. For a polystyrene fraction of intermediate molecular weight (M ? 19,000; t_g = 89°C.), it is shown that B is independent of the p–v–T state of the polymer liquid and that dT₀/dP = dT_g/dP. This is consistent with the postulate that B is determined by the internal barriers to rotation in the isolated polymer chain. Relationships are derived for flow “activation energies” at constant pressure and at constant volume, and for the “activation volume.” Values for polystyrene along the zero-pressure isobar and along the constant viscosity, glasstransition line are reported. For the latter, ΔV_g* is constant and corresponds to about 10 styrene units. The “free volume” viscosity equation: log η = log A + b/2.3?, is reexamined. For polystyrene and polyisobutylene, ?_g/b = 0.03, but ?_g and b themselves differ appreciably in these polymers. The parameter b is the product of an equilibrium term Δα and the kinetic term B, and none of these is a “universal” constant for different polymers. The physical significance of the free volume parameter ?, particularly with regard to the “excess” liquid volume, remains undefined. Two new relationships for dT_g/dP, one an exact derivation and the other an empirical correlation, are presented.     

New derivation and a k-particle generalization of SCF-type theories

A hierarchy of necessary conditions that an exact density matrix of a pure state or an ensemble has to satisfy is derived, namely the hermiticity of certain operators F^(k). For k = 1 this reduces to the well-known Hartree-Fock condition. It is then shown that the kth set of conditions is equivalent to stationarity of the energy with respect to unitary k-particle transformations. k-Particle generalizations of Hartree-Fock theory are then discussed both in the spirit of k-particle pseudoeigenvalue equations and in the framework of a Newton–Raphson-type constructive scheme.     

Peculiarities of the Interaction of Short Oligonucleotides with Supported Lipid Films and Langmuir Monolayers

 The method of electrostriction was applied to supported bilayer lipid membranes (sBLM) and Langmuir monolayers with the aim to study the peculiarities of the interaction of short oligonucleotides with lipid films and of the duplex formation between complementary oligonucleotides. The bilayer lipid membranes (sBLM) were formed on an agar support, whereas Langmuir monolayers were generated on the air-water interface. As an oligonucleotide, the 15-mer 5^′-cholesterolphosphoryl-dT15 (CHpdT15) was synthesized. We could show that the interaction of CHpdT15 with sBLM resulted in a considerable increase of the elasticity modulus perpendicular to the membrane plane (E _⊥) and an increase of the surface potential. Interaction of complementary oligodeoxyadenylate (dA15) with sBLM modified by CHpdT15 resulted in a slight increase of the surface potential whereas E _⊥ slightly decreased. CHpdT15 forms monomolecular layers on the air/water interface. Interaction of dA15 with such monolayers resulted in an increase of the surface pressure, probably due to an increase of the surface charge of the monolayer; similar effects were observed for lipid monolayers modified by CHpdT15. Prospects of using such interactions for detecting DNA hybridization are discussed.     

Semiempirical study of electronic and bonding properties of cobalt silicide clusters

The electronic structure of cobalt silicide clusters Co₇Si₇ and Si₇Co₇ was studied in comparison to that of Co₁₉ and Si₁₇ clusters under the scope of the MINDO/SR method. Clusters Co₇Si₇ and Si₇Co₇ represent the environment of a cobalt atom and that of a silicon atom in the cobalt monosilicide bulk, respectively. It is found that the Co? Si bond is essentially sp in character with an indirect participation (by electrostatic interaction) of the cobalt d orbitals. Our calculations show a charge transfer from silicon to the d orbitals of cobalt via sp–sp interaction with an internal sp–d hybridization. The theoretical density of states for cobalt silicide clusters are reported and compared with experimental results of surface spectroscopies. © 1992 by John Wiley & Sons, Inc.     

Random copolycondensation of isophthalic acid/terephthalic acid with bisphenols by tosyl chloride/dimethylformamide/pyridine in terms of the monomer reactivity ratios of bisphenols

The random copolycondensation of isophthalic acid/terephthalic acid with various combinations of bisphenols (M₁ and M₂) with a tosyl chloride/dimethylformamide/pyridine condensing agent was carried out to investigate the effects of the monomer reactivity ratios, r₁′ and r₂′, on the reaction, like r₁ and r₂ in radical copolymerization. The ratios were calculated from the probabilities of finding an M₂ unit next to an M₁ unit and of finding an M₁ unit next to an M₂ unit, which were determined by an NMR analysis of the resultant copolymers. They were discussed with respect to the inherent viscosities (molecular weights) of the resultant copolymers. There was a fairly good relationship between r₁′ and r₂′ and the inherent viscosity values of the copolymers, indicating that copolycondensation could be facilitated by a combination of bisphenols; the lowering of r₁′ and r₂′ was indicative of random distributions in the copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3908–3915, 2003     

Dynamics of a polymer attached to a surface: Bead and spring model

The Smoluchowski formalism is used to solve the problem of a bead of frictional resistance β attached to a surface with a spring of force constant _k over which a linear shear field of strenght α flows. The power dissipation is given by βα²kT/_k. k and T have their usual meanings. The result is generalized to an n-bead polymer. It is found that the power dissipation of a Rouse model polymer attached to a surface at one end is twice that of an identical polymer flowing freely in solution. If the force constant _k arises from an entropy force, then, because of the effect of the surface on the number of polymer configurations, there is an additional factor of two. The same relationship is expected to also hold for the frequency-dependent power dissipation. It is argued that a net circulation exists in the beads above the surface and that the magnitude of the circulation is roughly comparable to that which exists in a polymer freely rotating in solution under a shear field of the same magnitude.     

α-单取代环十二酮肟及缩氨基硫脲的合成及晶体结构

单晶X射线衍射分析表明, α-单取代环十二酮与氨衍生物羟胺和氨基硫脲发生缩合反应得到两种母体构象均为[3333], 而取代基为边外向或角反向的α-单取代环十二酮肟或缩氨基硫脲. 利用底物的“角位羰基参与反应”原理, “记忆效应”及进攻试剂与底物是否形成氢键解释了这一实验结果. 通常情况下, 试剂从空间障碍小的一面进攻羰基而生成α-角反取代环十二酮肟或缩氨基硫脲. 当试剂与底物的取代基之间能够形成分子间氢键时, 则生成α-边外取代环十二酮肟或缩氨基硫脲.     

A family of two-stage two-step methods for the numerical integration of the Schr?dinger equation and related IVPs with oscillating solution

We develop a family of six methods for the numerical integration of the Schr?dinger equation and related initial value problems with oscillating solution. Three of the methods are constructed so that they are P-stable, using the methodology of Wang (Comp Phys Comm 171(3):162–174, 2005). Also two of these three methods are trigonometrically fitted with trigonometric orders one and two. The other three methods are constructed so that they are trigonometrically fitted with orders one, two and three. We show that there is an equivalence between the three pairs of methods, as if the property of P-stability can be substituted by an extra trigonometric order, that is the P-stable method is equivalent to the method with trigonometric order one, the P-stable method with trigonometric order one is equivalent to the method with order two, and the P-stable method with order two is equivalent to the method with order three. There is a condition that we choose the same frequency for the P-stability test problem y′′ = −θ ² y and the functions that the method has to integrate exactly, in order to be trigonometrically fitted: {cos(ω x), sin(ω x), x cos(ω x), x sin(ω x), x ² cos(ω x), x ² sin(ω x)}. A stability analysis and a local truncation error analysis are performed on the methods and also the v–s diagrams are produced, where v = ω h and s = θ h. Finally the methods are applied to IVPs with oscillating solutions, such as the one-dimensional time independent Schr?dinger equation and the nonlinear problem.     

甲基纤维素(MC)疏水作用的电化学研究

应用电化学循环伏安法, 以电活性小分子亚甲基蓝(MB)为探针, 研究了不同温度下修饰在玻碳电极表面的甲基纤维素(MC)凝胶的疏水性. 研究发现, 在45～70 ℃温度范围内, MB在MC凝胶修饰电极上的式电位E⁰⁽较相应的裸电极均正移, 氧化峰电流i_pa和还原峰电流i_pc分别较相应裸电极增大, 且随温度升高而增大. 这些结果表明MC分子之间发生了疏水相互作用, 且随温度的升高, 疏水作用增强. 此外, 在上述温度下, MC凝胶修饰电极上峰电流的比值i_pc/i_pa均小于1, 为0.70, 且没有观察到MB单独的吸附峰, 因此MB分子在凝胶修饰电极上发生了弱吸附. 本文研究显示电化学方法是研究该类多糖凝胶机理的一个补充手段.     

The thermal properties of poly(pivalolactone)

Quantitative thermal analysis was carried out for poly-(pivalolactone) (PPVL), including heat capacity determinations from 140 to 550 K. The experimental C_p below the glass transition temperature was fitted to an approximate vibrational spectrum and the ATHAS computation scheme was used to compute the “vibration only” heat capacities from 0.1 to 1000 K. The liquid C_p was derived from an empirical addition scheme and found to agree with the experimental C_p with an RMS of ±2.8% from 240 K to 550 K. A glass transition, T_g, could be detected at 260 K, and the change in heat capacity for 100% amorphous PPVL was calculated to be 38.8 J/(K mol). Above T_g, semicrystalline samples seem to show a rigid amorphous fraction that does not contribute to the increase in heat capacity at T_g. Using the ATHAS recommended heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) were derived. The residual entropy at 0 K for the amorphous PPVL was calculated to be 5.2 J/(K mol) per mobile bead, and was comparable to that obtained for a series of linear, aliphatic polyesters analyzed earlier.     

Improving the Cβ Stereoselectivity of l-Threonine Aldolase for the Synthesis of l-threo-4-Methylsulfonylphenylserine by Modulating the Substrate-Binding Pocket To Control the Orientation of the Substrate Entrance

l -Threonine aldolase from Actinocorallia herbida (AhLTA) is an ideal catalyst for producing l -threo-4-methylsulfonylphenylserine [(2S,3R)- 1 b ], a key chiral precursor for florfenicol and thiamphenicol. The moderate C_β stereoselectivity is the main obstacle to the industrial application of AhLTA. To address this issue, a combinatorial active-site saturation test (CAST) together with sequence conservatism analysis was applied to engineer the AhLTA toward improved C_β stereoselectivity. The optical mutant Y314R could asymmetrically synthesize l -threo-4-methylsulfonylphenylserine with 81 % diastereomeric excess (de), which is 23 % higher than wild-type AhLTA. Molecular dynamic (MD) simulations revealed that the mechanism for the improvement in C_β stereoselectivity of Y314R is due to the acylamino group of residues Arg314 controlling the orientation of substrate 4-methylsulfonyl benzaldehyde ( 1 a ) in the active pocket by directed interaction with the methylsulfonyl group; this leads to asymmetric synthesis of l -threo-4-methylsulfonylphenylserine. The success in this study demonstrates that direct control of substrates in an active pocket is an attract strategy to address the C_β stereoselectivity problem of LTA and contribute to the industrial application of LTA.     

Atomic level picture of stress relaxation in polymer melts

We have been developing a physical picture on the atomic level of stress relaxation in polymer melts by means of computer simulation of the process in model systems. In this article we treat a melt of freely jointed chains, each with N = 200 bonds and with excluded-volume interactions between all nonbonded atoms, that has been subjected to an initial constant-volume uniaxial extension. We consider both the stress relaxation history σ(t) based on atomic interactions, and the stress history σ_e(t; N_R) based on subdividing the chain into segments with N_R bonds each, with each segment regarded as an entropic spring. It is found that at early times σ(t) > σ_e(t; N_R) for all N_R, and that, for the remainder of the simulation, there is no value of N_R for which σ(t) = σ_e(t; N_R) for an extended period; by the end of the simulation σ(t) has fallen just below the value σ_e(t; 50). The decay of segment orientation, 〈P₂(t; N_R)〉, and of bond orientation 〈P₂(t; 1)〉, is computed during the simulation. It is found that the decay of the atom-based stress σ(t) is closely related to that of 〈P₂(t; 1)〉. This result may be understood through the concept of steric shielding. The change in local structure of the polymer melt during relaxation is also studied. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 143–154, 1998     

Crystallographic studies of cinnamamide derivatives as a means of searching for anticonvulsant activity

A cinnamamide (3‐phenylprop‐2‐enamide) core is present in many pharmacologically active compounds. We report three new crystal structures of N‐substituted cinnamamide derivatives which were screened for anticonvulsant activity, namely (R ,S )‐(2E )‐N‐(2‐hydroxypropyl)‐3‐phenylprop‐2‐enamide, C₁₂H₁₅NO₂, ( 1 ), (R ,S )‐(2E )‐N‐(1‐hydroxybutan‐2‐yl)‐3‐phenylprop‐2‐enamide, C₁₃H₁₇NO₂, ( 2 ), and (2E )‐1‐(4‐hydroxypiperidin‐1‐yl)‐3‐phenylprop‐2‐en‐1‐one, C₁₄H₁₇NO₂, ( 3 ). Compounds ( 1 ) and ( 2 ) crystallize in the Pbca space group with one molecule in the asymmetric unit, whereas compound ( 3 ) crystallizes in the P 2₁/c space group with two molecules in the asymmetric unit. All the crystal structures are stabilized by intermolecular O—H…O hydrogen bonds and additionally by N—H…O hydrogen bonds in the structures of ( 1 ) and ( 2 ). The investigated compounds possess fragments that are considered as beneficial for anticonvulsant activity. The conformations of these compounds were analyzed in comparison with the characteristic features of the proposed pharmacophore model of anticonvulsants active in the maximal electroshock test, i.e. a phenyl ring or other hydrophobic unit, an electron‐donor atom and a hydrogen‐bond acceptor/donor domain. In the reported series, two calculated distances fitted the reference model, while the third did not. Structure–activity analysis suggests that anticonvulsant properties may be related to the N‐atom substituent. It is beneficial to combine an electron‐donor atom (e.g. an O atom) with an H atom in the substituent to ensure appropriate interactions with the molecular target. We analyzed the intermolecular interactions in order to find an appropriate spatial arrangement of the important features responsible for anticonvulsant activity.     

Effect of the initiator content and temperature on the curing of an unsaturated polyester resin

The influence of temperature and the initiator concentration on the curing of an unsaturated polyester resin was studied by means of differential scanning calorimetry (DSC) and Fourier‐transform infrared spectroscopy (FTIR). It was established that there is an isoconversional relationship of the type lnt = a − bln[I]₀ between the curing time, t, and the initial initiator concentration, [I]₀, at a given temperature. This relationship indicates that the degree of conversion curves vs. the logarithm of the curing time at different [I]₀ may be superposed by displacement relative to a reference curve. It was confirmed that the reaction mechanism varies throughout the whole curing process, although it does not vary with the temperature and the [I]₀ at each degree of conversion. It was established that there is a universal isoconversional relationship of the type lnt = d − bln[I]₀ + E/RT that expresses the dependency of the curing time on the temperature, T, and the [I]₀. The parameters a, b, and d depend on the reaction mechanism, and can be calculated on the basis of isothermal experiments at different temperatures and with different [I]₀. The adjustment lnt = d − bln[I]₀ + E/RT shows that there is an equivalence between the effect on the curing kinetics of the temperature and the initiator concentration. The same curing process can be achieved by using different combinations of curing temperatures and the [I]₀. In the two adjustments established, it is not necessary to know the reaction mechanism, and the only assumption made is that for a given conversion the reaction mechanism is invariant with respect to the [I]₀ and the temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 751–768, 1999     

Total Synthesis,Stereochemical Assignment,and Field‐Testing of the Sex Pheromone of the Strepsipteran Xenos peckii

The sex pheromone of the endoparasitoid insect Xenos peckii (Strepsiptera: Xenidae) was recently identified as (7E,11E)‐3,5,9,11‐tetramethyl‐7,11‐tridecadienal. Herein we report the asymmetric synthesis of three candidate stereostructures for this pheromone using a synthetic strategy that relies on an sp³–sp² Suzuki–Miyaura coupling to construct the correctly configured C7‐alkene function. Comparison of ¹H NMR spectra derived from the candidate stereostructures to that of the natural sex pheromone indicated a relative configuration of (3R*,5S*,9R*). Chiral gas chromatographic (GC) analyses of these compounds supported an assignment of (3R,5S,9R) for the natural product. Furthermore, in a 16‐replicate field experiment, traps baited with the synthetic (3R,5S,9R)‐enantiomer alone or in combination with the (3S,5R,9S)‐enantiomer captured 23 and 18 X. peckii males, respectively (mean±SE: 1.4±0.33 and 1.1±0.39), whereas traps baited with the synthetic (3S,5R,9S)‐enantiomer or a solvent control yielded no captures of males. These strong field trapping data, in combination with spectroscopic and chiral GC data, unambiguously demonstrate that (3R,5S,9R,7E,11E)‐3,5,9,11‐tetramethyl‐7,11‐tridecadienal is the X. peckii sex pheromone.