The Effect of Trifluoromethyl and Difluoromethoxy Groups on Mesomorphic Properties

Abstract

This paper describes the effect of terminal substituent on the mesomorphic properties in 3-and 4-(4-alkoxyphenoxycarbonyl)phenyl 3- and 4-R-benzoate and 4-(4-alkoxybenzoyloxy)phenyl 2-, 3-, and 4-R-benzoates (R = CF₃, OCF₃, OCF₂H). The meta-trifluoromethoxy and para-difluoromethoxy compounds tend to show a smectic C phase, as well as smectic A and nematic ones, and introduction of a chiral carbon in the alkoxyl group induces the chiral smectic C one.     

Pharmaceutical Salts of Fluoroquinolone Antibacterial Drugs with Acesulfame Sweetener

Novel organic salts of norfloxacin and ciprofloxacin with artificial sweeteners such as saccharin and acesulfame were prepared. The two salts 1 and 2 were characterized by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). Finally, the crystal structures were solved by single crystal X-ray diffraction data and the structures were analyzed in terms of supramolecular synthons. In norfloxacin acesulfamate 1, two norfloxacin cations and two acesulfame anions form an eight membered cyclic tetramer supramolecular synthon. The salt, ciprofloxacin acesulfamate 2, has a similar structure as salt 1. This study contributes the importance of crystal engineering and supramolecular chemistry to the pharmaceutical applications in terms of interactions and structural correlations in the design of new solid phases.

Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.     

Formation and Structure of Cluster-Included Carbon Nanocapsules Prepared by Polymer Pyrolysis

Abstract

Formation of carbon nanocapsules with various clusters (SiC, Au, Fe. Co. Ge. and GeO₂) by polymer pyrolysis was investigated, and nanocapsules with SiC and Au nanoparticles were produced by thermal decomposition of polyvinyl alcohol at ?500°C in Ar gas atmosphere. The formation mechanism of nanocapsules and a structural model for the nanocapsule/SiC interface were proposed. In addition, carbon clusters were formed at the surface of carbon nanocapsules, and carbon onions were produced by electron irradiation of amorphous carbon produced from polyvinyl alcohol. The present work indicates that the pyrolysis of polymer materials with clusters is a useful fabrication method for the mass-production of carbon nanocapsules and onions at low temperatures compared to the ordinaly are discharge method.     

3-(benzo[d]thiazol-2-YL)phenol and 4-(benzo[d]thiazol-2-YL)phenol: Crystal Structure Determination,DFT Calculations and Visualizing Intermolecular Interactions Using Hirshfeld Surface Analysis

This article describes the synthesis and X-ray crystal structure analysis of 3-(benzo[d]thiazol-2-yl) phenol (I) and 4-(benzo[d]thiazol-2-yl)phenol (II), crystallized in centrosymmetric triclinic and orthorhombic space groups respectively. The packing in the unit cell of these two positional isomers are different resulting difference in various types of intermolecular interactions (C-H…S, O-H…O_w and O-H…N) connect the molecules into 2D frameworks. Due to presence of lattice water in compound (I), H-bonding interactions are strong and melting point of (I) is comparatively higher than (II). The DFT optimized molecular geometries in (I) and (II) agree closely with those obtained from crystallographic studies.     

Self-Assembled Superstructure of Xanthene Derivatives

Various multi carbon homologations of 9-phenyl-9H-xanthen-9-ol (1) were obtained through a C-C bond formation by reacting it with various enolisable ketones in the presence of 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT). All the ten derivatives along with the starting xanthen-9-ol have been characterized by single crystal X-ray diffraction. They all form self-assembled superstructure in the solid state. The self-assembling patterns in these supramolecular architectures were explained based on steric and electronic nature of the pendant arm. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Spectral and barrier properties of heterocomposites based on poly (para-phenylene) disposed between the silicon films

ABSTRACT

Within the framework of the methods of the electron density functional and the ab initio pseudopotential, we have obtained the spatial distributions of the valence electrons density, the electron energy spectra and the Coulomb potential for heterocomposites based on poly (para-phenylene) and carbon nanotube disposed between the silicon films.

?It was revealed that the maximal value of the potential barrier was noticed in a composite material from polyparaphenylene filaments placed between silicon films and completed with carbon nanotubes perpendicularly to the surface of the silicon films and along them.     

DISTORTIONS INDUCED BY A MAGNETIC FIELD IN PLANAR ALIGNED SAMPLES OF SMECTIC-C LIQUID CRYSTALS

Abstract

This article presents some preliminary theoretical results for the onset of the Helfrich-Hurault transition in smectic-C liquid crystals induced by a magnetic field applied parallel to the smectic layers. An energy in terms of the smectic layer displacement u is minimized via averaging to enable the calculation of a critical field strength H _c for the onset of layer distortions.     

Synthesis,Spectroscopy, In Vitro Biological Activity and X-ray Structure of (4-Methylpiperidine-dithiocarbamato-<Emphasis Type="Italic">S</Emphasis>,<Emphasis Type="Italic">S</Emphasis>′)triphenyltin(IV)

Abstract (4-Methylpiperidine-dithiocarbamato-S,S′)triphenyltin(IV) derivative of 4-methyl-1-piperidine carbodithioic acid (4-MePCDTA) have been synthesized and characterized by elemental, IR, multinuclear NMR (¹H and ¹³C) and mass spectrometric studies. The crystal structure of the complex has been determined by X-ray single crystal analysis, which shows unsymmetrical nature of the ligand towards coordination to tin. It crystallizes in monoclinic P21/c space group with the crystal cell parameters: a = 10.1863(10) ?, b = 21.200(2) ?, c = 11.7332(11) ?, β = 111.2020(10)°, Z = 4 and V = 2,362.2(4) ?³. The tin atom is coordinated to the two sulfur atoms of the dithiocarbamate ligand and three carbon atoms of the phenyl groups are in distorted trigonal bipyramid geometry. This complex was tested for its antimicrobial activity against six different plant and human pathogens. The screening results show that the complex exhibit higher antibacterial and antifungal activity than the free ligand. Index abstract Synthesis, Spectroscopy, in vitro Biological Activity and X-Ray Structure of (4-Methylpiperidine-dithiocarbamato-S,S′)triphenyltin(IV) Saira Shahzadi, Saqib Ali and Mohammmed Fettouhi 4-Methyl-1-piperidine carbodithioic acid behaves as anisobidentate ligand and chelates the tin atom by means of sulfur atoms giving cis-trigonal bipyramid geometry around the tin atom. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Enol tautomer of the acetate ester of 3-methoxy-4-hydroxyphenylpyruvic acid: Crystallographic and NMR spectroscopic evidence

The para acetate ester azlactone of vanillin 2 was synthesized from vanillin 1 and hydrolyzed with sodium hydroxide. The yielded product 3 was investigated with X-ray Crystallographic and nuclear magnetic resonance techniques. Compound 3 crystallized in the orthorhombic Pbca space group (Z = 8) and with cell dimensions a = 14.732(2), b = 12.756(3), c = 12.747(6)Å revealing the enolate tautomer and not the keto form of 3-methoxy-4-hydroxyphenylpyruvic acid as the acetate ester. The structure exhibited the pyruvic acid side chain in the trans extended conformation. A single proton on the benzylic carbon atom further suggested the existence of the enolate tautomer form of 3 in solution. The chemical shift values and peak integration in the NMR spectra add additional support to this finding.     

Conformational polymorphism in thiophenyl substituted quinones and the disappearing NMR spectrum

The stepwise addition of thiophenol to benzoquinone gives thiophenylbenzoquinone (1b), 2,5-and 2,6-di-(thiophenyl)benzoquinone (2,3),2,3,6-tri(thiophenyl)benzoquinone (4) and 2,3,5,6-tetra(thiophenyl)benzoquinone. (5). Compounds1–4 can be crystallized, and the¹³C NMR spectra are readily interpreted. Compound5 could not be crystallized easily, and the NMR showed more than twice as many lines as the number of carbon atoms. Slow evaporation in an NMR tube produced three distinct crystals. X-ray analysis of two crystals (5a and5c) showed the compounds to be conformational polymorphs. Direct synthesis of5 from tetrachlorobenzoquinone and thiophenol yielded only conformer5a, and the¹³C NMR spectrum showed only the 6 lines expected for four equivalent phenyl substituents on benzoquinone. Subjecting5a to a variety of solvents, reagents and temperatures did not regenerate the original¹³C NMR spectrum. The crystal structures, conformations, and polymorphs are discussed.     

Electron Spin Resonance of K-Doped Single-Wall Carbon Nanohorns and Single-Wall Carbon Nanotubes

Abstract

K-doping into the aggregate of single-wall carbon nanohorns (SWNHs) and into the bundle of single-wall carbon nanotubes (SWNTs) are introduced in this study. Electron spin resonance (ESR) of the pristine SWNHs and SWNTs show that the pristine SWNHs are ESR active and the linewidth (ΔH) is susceptive to the partial pressure of O₂, while the pristine SWNTs are ESR silent. ΔH of K-doped SWNHs becomes wider by a factor of ?2 than that of the pristine one. For K-doped SWNTs, the Dysonian type ESR comes to be observed. Details of the ESR features are discussed.     

Effects of Lattice Vacancy in Carbon Nanotubes Conductance Quantization

Abstract

Conductance of carbon nanotubes (CN's) with a lattice vacancy or strong and short-range impurity potential is studied within a tight-binding model. The conductance is quantized into zero, one, or two times the conductance quantum e ²/π? depending on the type of the vacancy if its size is much smaller than the circumference of CN.     

Carbon-limited Dissolution of Oxygen in Niobium

This article deals with results of the invsetigations connected with limitation of oxygen dissolution in niobium by means of creating of the carbide protective coating on the niobium surface or forming of the solid solution of carbon in niobium. It is shown that the carbide coating increases essentially the life time of the niobium parts for vacuum equipment and is consumed as a result of interaction with oxygen. The carbon dissolution in niobium does not hinder redox reaction at the Nb(C)/Nb₂O₅ boundary and causes the conductivity increase of the dielectric film Nb₂O₅.     

Synthetic nanodiamonds (SNDs) containing bimetallic Ni(Co)–Fe composites: preparation,characterization and catalytic performance in the reaction of CO2 methanation

Abstract

In this article, we present the preparation, characterization, and catalytic performance of bimetallic Co₉₃Fe₀₇ and Ni₈₀Fe₂₀ active mass loaded on synthetic nanodiamonds (SNDs) in the carbon dioxide (CO₂) methanation. The pristine SNDs possessing a developed specific surface are thermally stable and inert to the reaction mixture of CO₂ and dihydrogen. However, it is shown that 100% conversion of CO₂ into methane can be reached at the lower temperature than that for a massive Co₉₃Fe₀₇ or Ni₈₀Fe₂₀ catalyst when 20?wt.% of the catalyst mass was loaded on the surface of SNDs. The catalytic activity of the prepared bimetallic/SNDs composites is estimated as the minimum temperature at the maximum conversion of CO₂ at atmospheric pressure: it is 325 and 290?°C for Co₉₃Fe₀₇/SNDs and Ni₈₀Fe₂₀/SNDs, respectively. Thermal desorption studies showed that the methanation over Co-Fe/SNDs and Ni-Fe/SNDs catalysts run through the stage of CO₂ dissociation into carbon and oxygen atoms and their subsequent interaction with hydrogen to form methane and water molecules. Scanning electron microscopy studies have shown that the presence of transition metal-rich sites on the surface of the carrier contributes to the improvement of efficiency of the Ni₈₀Fe₂₀ catalyst action.     

On the Stability of Travelling Waves Arising in Nematic Liquid Crystals

Abstract

The stability of travelling waves which occur when a nematic liquid crystal is subjected to crossed electric and magnetic fields has been studied previously where conditions on a control parameter q for stability to occur have been given. This article is concerned with the behaviour of the stable perturbations as time increases. For each of the three travelling wave solutions we can determine the long-term monotonic or oscillatory behaviour of the perturbations using knowledge of the spectrum of the operator governing the perturbation equation.     

Conformations of 2-C:1-N-carbonyl-2-deoxy-d-glycopyranosylamines

Geometry and molecular conformation of theN-toluenesulfonyl1 andN-acetyl-2 derivatives of peracetylated 2-C:1-N-carbonyl-2-deoxy--d-glucopyranosylamine were investigated with the use of X-ray diffraction methods. Compound1 (C₂₀H₂₃NSO₁₀) crystallizes in the monoclinic P2₁ space group, withZ=2 anda=8.238(1),b=7.988(1),c=16.928(2)Å, =99.12(1)°. Compound2 (C₁₅H₁₉NO₉) crystallizes in orthorhombic P2₁2₁2₁ space group withZ=4 anda=8.385(1),b=8.550(1),c=24.000(2) Å. Analysis of differences in bond lengths and angles between compounds1 and2 and other compounds of this class showed that the electronwithdawing effect by the residue located at the nitrogen atom can be manifested by lengthening of the -lactam C-N bonds, with simultaneous shortening of the distance between two carbon atoms at the ring fusion. Semi-empirical calculations suggested that the title compounds displayed two positively charged centers, susceptible for attack of nucleophiles, one at the carbonyl group of -lactam and the second at the anomeric carbon atom. Atomic charges, however, calculated for compounds1 and2 did not explain their different reaction directions during alcoholysis.Part 3. For part 1 and 2, see Refs. 5 and 6.     

From natural photosynthesis to molecular photovoltaics

ABSTRACT

In many technological applications the mankind mimics the nature. One of the excellent examples is photosynthesis. The knowledge of the natural photosynthesis mechanisms is extremely useful in understanding of molecular processes occurring in photovoltaics.

In this review article the photophysical fundamental aspects of photosynthetic units are presented. The similarity and dissimilarity between photosynthesis processes and photovoltaic ones is also shown. This paper is based first of all on the results of the investigations of corroles and corrole-fullerene dyads. The results of spectroscopic examinations supported by chemical calculations are presented.     

Chirality-Dependent Resistivity in Carbon Nanotubes

Abstract

The phonon-mediated resistivity is calculated for metallic carbon nanotubes based on a continuum model for electrons and phonons. In armchair nanotubes, only twisting modes contribute to the resistivity, while both stretching and breathing modes are important in zigzag nanotubes. The resistivity shows chirality dependence at low temperatures where breathing modes are not populated but becomes independent of the chirality at high temperatures.     

Potassium Doped Single Wall Carbon Nanotubes: Resistance under Pressure

Abstract

We report in situ measurements of four-probe de resistance (R) of K-doped purified single wall carbon nanotube (SWNT) “buckypaper” as a function of quasi-hydrostatic pressure. Doped samples show completely different behavior compared to that of pristine nanotubes in the pressure range up to 90 kbar. The characteristic increase in the resistance of pristine buckypaper above 10 kbar, associated with the formation of kinks or/and twists of tubes, is not observed in K-doped samples. This may originate from 1) a substantial change in electronic band structure of donor intercalated nanotubes, 2) completely different transport properties of defect structures, or 3) higher stiffness of doped SWNT's which prevents formation of kinks and twists in this pressure range. On deintercalation, the pristine behavior of R(P) is restored, establishing the reversibility of potassium vapor-transport doping.     

Synthesis,Structure and Electrochemical Property of a New Copper(II) Complex Based on Benzene-1,2,4,5-tetracarboxylate and 2,5-Bis(3-pyridyl)-1,3,4-oxadiazole Ligands

Abstract  

A new three-dimensional (3-D) supramolecular complex, [Cu₂(btec)(bpo)₂(H₂O)₂]·8H₂O (1), has been synthesized by hydrothermal reaction with the mixed ligands benzene-1,2,4,5-tetracarboxylate (btec) and bent dipyridyl based ligand 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (bpo), and structurally characterized by elemental analysis, IR, TG, powder-XRD and single-crystal X-ray diffraction analysis. The results reveal that each Cu(II) ion is bridged by two different ligands (btec and bpo) to form a 2-D polymer layer in complex 1. The adjacent layers are further linked by 1-D H-bonded water chains simultaneously containing (H₂O)₆ rings and (H₂O)₈ rings to form a 3-D supramolecular framework. Moreover, the electrochemical behavior of complex 1 bulk-modified carbon paste electrode (1-CPE) has been reported.