Large scale molecular dynamics simulations of a 4-n-pentyl-4′-cyanobiphenyl (5CB) liquid crystalline model in the bulk and as a droplet

Molecular dynamics simulations for 4-n-pentyl-4′-cyanobiphenyl (5CB) with as many as 944 molecules are reported. The order-N fast multipole method (FMM) is used to treat the long-range interactions. For a droplet of 944 molecules, the simulation shows a correlation between the droplet shape and the nematic order and a strong surface effect; little nematic order is found in a 118 molecule droplet. Simulations of the bulk system result in similar order parameters for both the 118 and 944 molecular ensembles. Although the nematic–isotropic transition was not observed at temperatures as high as 400 K using the CHARMM force field, a modification of the force field using ab initio determined partial atomic charges lowers the order parameters.     

Electron beam irradiation-induced transformations in the electrical properties of 4’-octyl-4-cyanobiphenyl (8CB)

Changes in the dielectric and thermodynamical properties of electron beam-irradiated 4′-octyl-4-cyanobiphenyl (8CB) were studied. Irradiation-induced changes in the phase transition temperature, dielectric anisotropy, relaxation frequency and activation energy of an observed non-collective relaxation mode corresponding to molecular rotation about the short axis were determined in both nematic and smectic A_d phases. In the nematic phase, dielectric anisotropy increased for a small dose but decreased for a relatively high dose, whereas the relaxation frequency increased due to the irradiation. The pure and irradiated samples were characterised by UV–visible spectroscopy, Fourier transform infrared spectroscopy, gas chromatography, gas chromatography coupled with mass spectroscopy and pulse radiolysis. The observed changes in the dielectric parameters are related to the detachment of the CN group from some of the 8CB molecules due to the electron beam irradiation.     

Molecular dynamics simulations on the adsorption of 4-n-octyl-4′-cyanobiphenyl (8CB) at the air/water interface

The influence of surface coverage to the structural properties of 4-n-octyl-4´-cyanobiphenyl (8CB) monolayer at the air/water interface was studied by full atomistic molecular dynamics simulations. These properties include density profiles, interface thickness, monolayer width, orientational order parameters, and atom-pair radial distribution functions. The calculated tilt angles of the cyanobiphenyl and alkyl parts are in fairly good agreement with the experiments. The simulation results exhibit the general trends in the previous experimental and simulation data.     

Investigation of liquid crystalline property of a new calamitic liquid crystalline system methyl 4-(4ʹ-(4ʹʹ-(decyloxy)benzyloxy) benzylideneamino)benzoate

A new polar calamitic liquid crystal, methyl 4-(4?-(4?-(decyloxy)benzyloxy) benzylideneamino)benzoate (M3BA) containing ether and Schiff base groups as linker with terminal polar ester group, has been synthesised and mesomorphic properties are studied by differential scanning calorimetry, polarising optical microscopy, density functional theory, temperature-dependent X-ray diffraction and temperature-dependent micro- Raman study. The smectic A (SmA) mesophase with focal conic texture has been observed with wide mesomorphic range. Layer thickness in SmA phase is greater than the optimised length of the molecule, indicating partially bilayer SmA phase. Analysis of Raman marker bands of C–H in-plane bending of phenyl rings, C=C stretching of rings, C=N stretching and C=O stretching shows structural changes at molecular level at Cr → SmA phase transition and provides proper intermolecular interactions responsible for dimeric unit in partially bilayer SmA phase.     

Crystal Structure of 5ʹ-Oxospiro-(fluorene-9,4ʹ-imidazolidine)-2ʹ-thione and Biological Activity of Its Derivatives

Russian Journal of General Chemistry - The presented study is devoted to the structural and biological properties of four derivatives of fluorenylspirohydantoin based on experimental data. The...     

Phase transition and elastic constants of 4-n-octyl-4′-cyanobiphenyl (8CB) obtained using the light-scattering anisotropy of turbidity

Abstract

A light-scattering technique was used to study the anisotropy of turbidity and the three elastic constants K ₁, K ₂ and K ₃ of 8CB as a function of temperature and sample thickness. The turbidity was measured in the nematic and schematic A phases at sample thicknesses l of 0.02, 0.04, 0.1 and 0.2 cm. The effect of the smectic-like (cybotactic nematic) order was observed near the smectic A-nematic phase transition. Owing to the surface-enhanced cybotactic order, evaluation of the elastic constants and order parameter was possible only from the turbidity data at l = 0.2 cm. From the divergence of both K ₂ and K ₃ near T_{S A N} we estimated an average critical exponent value v of 0.65, suggesting that S_A-N in 8CB is a second-order phase transition. The magnetic-field quenching of director fluctuations showed observed effects on the order of magnitude of the temperature dependence of the turbidities, elastic constants and order parameter.     

Synthesis of (4R,5S)-(−)- and (4S,5S)-(+)-L-Factors and Muricatacin from D-Glucose

Abstract

In connection with our projects on the synthesis of biologically active 5-hydroxyalkan-4-olides which have a chiral 2.3-diol unit,¹ we have carried out the synthesis of (4R,5S)-(?)- and (4R,5S)-(+)-L-factors (1).² the proposed autoregulators from Streptomyees griseus, and muricatacin (2),³ a biologically active constituent from the seeds of Annona muricata L. via 2.3-dihydroxy aldehydes derived from D-glucose. Hex-3-enofuranose4 was prepared by the elimination of thetriflate derived from D-glucose.     

Thermal properties and structure of (As2S3)100−x(Sb4S4)x glassy system

Thermal properties and structure of bulk glasses of (As₂S₃)_1?x(Sb₄S₄)_x system (x varies from 0 to 60 mol%) were studied by differential scanning calorimetry and Raman spectroscopy. It was found that with increasing Sb content the glasses can be sorted out to the three groups. The structure of glasses with x ≤ 10 is build-up mainly from AsS_3/2 pyramidal units and the well-known crystallization resistance of As₂S₃ can explain the reluctance of these undercooled liquids against crystallization. In glasses with a higher content of antimony, i.e., 10 < x ≤ 30 mol%, the vibration characteristics of As₄S₄ clusters appear. Undercooled melts of these glasses crystallize forming both β-As₄S₄ and high-temperature phases of Sb₂S₃. Structure of glasses with the highest antimony content (x > 30 mol%) is based on SbS_3/2 structural units significantly lowering stability of their undercooled melts from which only Sb₂S₃ crystallizes.     

Interference from 2,3,5,6-3′,4′-Hexachlorobiphenyl (CB 163) in the Determination of 2,3,4-2′,4′,5′-Hexachlorobiphenyl (CB 138) in Environmental and Technical Samples

Abstract

In Intern. J. Enuiron. Anal. Chem. 66 (1989), 155-161, Roos et al.¹ reported on problems encountered in the determination of 2,3,4-2′,4′,5′-hexachlorobiphenyl (CB 138) in environmental samples. These authors indicated that an interference was present for the capillary column gas chromatographic (HRGC) determination of CB 138. This interference was tentatively identified (without standard) as 2,3,5,6-3′,4′-hexachlorobiphenyl (CB 163). We have synthesized CB 163 and can confirm that it co-elutes with CB-138 on the widely used HRGC phase for polychlorinated biphenyl (PCB) analysis, 5%, phenyl, 95% methylpolysiloxane (CP-SIL8-CB) even on a 50m column. However, we managed to separate CB 163 from CB 138 on the very polar phase, bis-cyanopropylphenyl polysiloxane (SP-2330), using a 30 m column. We have quantified CB 163 and CB 138 in various environmental and technical samples and have found CB 163 to CB 138 ratios from I: 10 up to 3: 10.     

Synthesis of (−)-(1′S,4aS,8aR)- and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1′-phenylethyl)-octahydroquinolin-7-ones

A synthesis of the enamine (−)-(1′S)-5-ethyl-1-(1′-phenylethyl)-1,2,3,4-tetrahydropyridine 4 and its application in a synthesis of (−)-(1′S,4aS,8aR)- and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1′-phenylethyl)-octahydroquinolin-7-ones 5 and 6 is described. In addition, an X-ray study of 6 is reported. Finally, the preparation of (+)-(4aS,8aR)-4a-ethyl-octahydroquinolin-7-one 7 is described.     

Study of η5-(1-chloro-4-methylcyclohexadienyl) and η5-(1-methyl-4-chlorocyclohexadienyl)tricarbonylmanganese complexes in solution and in the solid state

The spectroscopic studies of neutral η⁵-(1-chloro-4-methylcyclohexadienyl) and η⁵-(1-methyl-4-chlorocyclohexadienyl) tricarbonylmanganese complexes have been realized in solution by ¹H NMR spectroscopy as well as in the solid state. The structures showed a dihedral angle of the sp³ carbon of 33.2° and 36.6° with respect to the cyclohexadienyl ring. To cite this article: F. Rose-Munch et al., C. R. Chimie 6 (2003).     

Quantum dynamics of Renner-Teller and isotopic effects in NH(a1Δ) + D(2S) reactions

A quantum dynamics study for the NH(a(1)Δ) + D((2)S) reactions using coupled channel time dependent real wavepacket formalism is presented. Moreover, the Renner-Teller (RT) interactions between two electronic states of NHD (X[combining tilde](2)A' and ?(2)A') have been taken into account by means of semiempirical RT matrix elements. The introduction of RT effects opens the possibility of studying not only the adiabatic reactions [depletion (d) to N((2)D) + HD(X(1)Σ(+)) and exchange (e) to ND(a(1)Δ) + H((2)S)] but also nonadiabatic ones [quenching (q) to NH(X(3)Σ(-)) + D((2)S) and exchange-quenching (eq) to ND(X(3)Σ(-)) + H((2)S)]. Reaction probabilities, cross sections, isotopic effects, and rate constants are presented for all the before mentioned reactions. RT results are compared with Born-Oppenheimer, quasiclassical, and experimental data. Contrasting with previous NH + H results, we point out interesting RT and isotopic effects, which depend on the D and H masses and on the tunneling of the H atom. In fact, RT effects, near-threshold cross sections, and rate constants are smaller in NH + D than in NH + H, as expected from the masses of the attacking atoms. Our rate constants and quenching branching ratio agree well with previous quasiclassical and experimental data, validating the semiempirical RT coupling we employ. Some small differences between calculated and measured rate constants might be due to the theoretical approximations and to the large experimental error bars.     

The synthesis and crystal structure of a copper-sulfur cluster [Cu4(S5)2(C5H5N)4]·S8

The cluster [Cu₄(S₅)₂(C₅H₅N)₄]·S₈ with cage structure has been obtained by reaction of copper powder with sulfur and K₂S _x in pyridine, and its structure was determined by X-ray crystallography. The crystal data for the title compound: triclinic, P (No. 2),Z = 2,a = 11.818(4) Å,b = 13.155(3) Å,c = 14.177(4) Å, = 93.79(2)°, = 96.68(2)°, = 115.76(2)°,V = 1954.52(1) ų. The structure was refined toR = 0.038R _w = 0.053) for 6444 data withI > 3.0(I).Dedicated to Professor Jiaxi Lu on the occasion of his 80th birthday.     

Unexpected retro-Michael reaction of (−)-(1′S,4aS,8aR)- and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1-phenylethyl)octahydroquinolin-7-ones

An unexpected retro-Michael reaction of (−)-(1′S,4aS,8aR)-and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1′-phenylethyl)octahydroquinolin-7-ones 1 and 2 is described. In addition, a diastereospecific intramolecular Michael reaction of 3·HCl and 4·HCl is reported.     

Synthesis and Structural Determination of (2R,4S,SS)-( )-Threo-5-(2,2-dichloroacetamido)-4-(4-nitrophenyl)-2-aryl-1,3-dioxanes

Acetalscanbesynthesizedinanumberofways.Themainproblemintheacetalformationinacidicmediumistoshifttheequilibriumtotherightbyremovalofthewaterformedduringthereactionl.Wesynthesized(2R,4S,SS)-( )-threo-5-(2,2-dich(4-nitrophenyl)-2-aryl-1,3-dioxanesbyacet...     

Studies on Acylthiosemicarbazides and Related Heterocycles(ⅪⅤ)——Synthesis and Bactericidal Activity of 1-(5-(3-Pyridyl)-2H-Tetrazol-2-ylacetyl) -4-Arylthiosemicarbazides and 3- (5- (3-Pyridyl)-2H-Tetrazol-2-ylmethyl)-4-Aryl-1,2 ,4-Triazole-5-Thiones

Introduction In the preceding paper it was described that various 1-acyl-4-substituted thiosemicarbazides and their derivatives exhibited a broad spectrum of antibacterial activities. Kothari pointed out that some heterocycles linked with tetrazole and 1,2,4-triazole can be used as antiinflammatory agent. We have also demonstrated that both 3-(5-a- naphthyl)-2H-tetrazol-2-ylmethyl)-4-aryl-1,2,4-triazole-5-thiones and 3-(3-pyridyl)-     

(+)-(1S,2S,5R)-8-联苯薄荷醇的合成

以(R)-( )-pu legone为起始原料,经1,4-加成,还原两步反应合成了手性辅助试剂( )-(1S,2S,5R)-8-联苯薄荷醇及其差向异构体(-)-(1R,2S,5R)-8-联苯薄荷醇,总产率95%。其结构经1H NMR,13C NMR,IR,MS和X-射线衍射仪表征。