Vapor-Phase Detection of Trinitrotoluene by AIEE-Active Hetero-oligophenylene-Based Carbazole Derivatives

New AIEE-active hetero-oligophenylene carbazole derivatives 3 and 4 have been synthesized and serve as fluorescent probes for the selective detection of 2,4,6-trinitrotoluene (TNT) in the vapor phase, the solid phase, and aqueous media. In addition, paper strips prepared by dip-coating a solution of aggregates of derivatives 3 and 4 can provide a simple, portable, sensitive, selective, low-cost method for the detection of TNT on the picogram level.     

Effect of HPC and Water Concentration on the Evolution of Size,Aggregation and Crystallization of Sol-gel Nano Zirconia

Nano-sized zirconia (ZrO₂) powder is synthesized using sol-gel technique involving hydrolysis and condensation of zirconium(IV) n-propoxide in an alcohol solution, utilizing hydroxypropyl cellulose (HPC) polymer as a steric stabilizer. It is demonstrated that ZrO₂ nanoparticle size can be reduced using high R-value (defined as the ratio of molar concentrations of water and alkoxide). It is also shown that ZrO₂ nanoparticle size can be reduced further by synthesizing these particles in the presence of HPC polymer. The agglomeration tendency of ZrO₂ nanoparticles is demonstrated to decrease due to the steric hindrance created by the adsorbed polymer. The nanocrystallite size and their 'hard-aggregates' formation tendency are observed to affect the high temperature metastable tetragonal phase stabilization at room temperature within ZrO₂ particles.     

Infrared spectroscopic study of a phenyl benzoate side group—methacrylate main chain polymeric liquid crystal

The temperature dependence of the infrared dichroism of a side chain polymeric liquid crystal was investigated for two homogeneously oriented samples, one aligned with a PVA coating and the other aligned by a magnetic field. From the apparent order parameters, it was found that the rotation of the mesogenic side group was restricted. Not only the rigid part of the side group, but also the alkyl chains were found to be partly ordered. Realignment of the side groups was observed in the case of the magnetically aligned sample at the smectic-nematic transition temperature. Unlike the other absorption bands, the C=O bond vibration band shifted to higher wavenumbers with increasing temperature. This behaviour was explained by the influence of the neighbouring mesogenic groups on the conjugation existing between the π-electron cloud of the benzene rings and the π-electrons of the C=O bond.     

Power absorption coefficient constants for water, acetonitrile, and methylene chloride at far infrared wavelengths

The problem of multiple internal reflections within the windows of an optical cell is analysed using Abele's matrix method. The Beer-Lambert power law is modified by the standing waves formed in between the cell and the detector. Power absorption coefficient of a material is calculated by a fit to the modified version of the equation. Precise values for water, acetonitrile and methylene chloride are calculated at far infrared wavelengths using a molecular laser source.     

Brownian motion in a periodic potential: Application to dielectric relaxation

The relaxational dynamics of a planar rotator in anM-fold cosine potential subject to a random torque is investigated in detail. For the case of a periodic potential with large barrier height, the numerical results of the relaxation dynamics are in complete agreement with an approximate analytical solution. The latter, is derived on assuming a harmonic potential at the bottom of the potential minima and a large time-scale separation between the short-time libration inside each potential minima and a long-time hopping phenomenon over the potential barriers. ForM2, the hopping phenomenon is found to be the dominant feature of the orientational autocorrelation function. The average hopping time is explained satisfactorily in terms of the Kramers activation rate theory. In particular a complete agreement is found between the numerical results of the escape rate and those obtained from the modified Kramers' predictions valid for low friction coefficient. The cosine model is applied to the study of dielectric spectroscopy. The particle mobility and the complex permitivity, of a dielectric material are calculated by numerical solutions for rotational velocity and orientational auto-correlation functions, respectively. The main features of the experimental observables are determined analytically and compared to the corresponding numerical results. The applicability of the plane rotator model to dielectric spectroscopy is also discussed.From Jan. 1^st 1985: Institut für Theoretische Physik, RWTH, Aachen, FRG     

Synthesis and characterization of the SO(2)N(3)(-), (SO(2))(2)N(3)(-), and SO(3)N(3)(-) anions

SO(2) solutions of azide anions are bright yellow, and their Raman spectra indicate the presence of covalently bound azide. Removal of the solvent at -64 degrees C from CsN(3) or N(CH(3))(4)N(3) solutions produces yellow (SO(2))(2)N(3)(-) salts. Above -64 degrees C, these salts lose 1 mol of SO(2), resulting in white SO(2)N(3)(-) salts that are marginally stable at room temperature and thermally decompose to the corresponding azides and SO(2). These anions were characterized by vibrational and (14)N NMR spectroscopy and theoretical calculations. Slow loss of the solvent by diffusion through the walls of a sealed Teflon tube containing a sample of CsSO(2)N(3) in SO(2) resulted in white and yellowish single crystals that were identified by X-ray diffraction as CsSO(2)N(3).CsSO(3)N(3) with a = 9.542(2) A, b = 6.2189(14) A, c = 10.342(2) A, and beta = 114.958(4) degrees in the monoclinic space group P2(1)/m, Z = 2, and Cs(2)S(2)O(5).Cs(2)S(2)O(7).SO(2), respectively. Pure CsSO(3)N(3) was also prepared and characterized by vibrational spectroscopy. The S-N bond in SO(2)N(3)(-) is much weaker than that in SO(3)N(3)(-), resulting in decreased thermal stability, an increase in the S-N bond distance by 0.23 A, and an increased tendency to undergo rotational disorder. This marked difference is due to SO(3) being a much stronger Lewis acid (pF(-) value of 7.83) than SO(2) (pF(-) value of 3.99), thus forming a stronger S-N bond with the Lewis base N(3)(-). The geometry of the free gaseous SO(2)N(3)(-) anion was calculated at the RHF, MP2, B3LYP, and CCSD(T) levels. The results show that only the correlated methods correctly reproduce the experimentally observed orientation of the SO(2) group.     

Johari-Goldstein relaxation and crystallization of sorbitol to ordered and disordered phases

The equilibrium permittivity epsilon(s) and the dielectric relaxation spectra of supercooled liquid D-sorbitol were measured during its crystallization to orientationally disordered or ordered phases depending on the sample preparation procedure at several fixed temperatures up to a period of 6 days. The epsilon(s) measurements showed that when the sample was contaminated by a minute amount of crystals, it crystallized to an ordered phase. When the liquid was not contaminated, the sample crystallized to an orientationally disordered phase. When supercooled D-sorbitol was kept close to its T(g), its dielectric spectra did not change over a period of 138.5 h. It was found that the Johari-Goldstein (JG) relaxation rate of the orientationally disordered crystalline phase is higher in comparison with that of the supercooled liquid, the spectrum broader, and the relaxation strength lower. Its glasslike transition temperature is higher than T(g) of the liquid. The results on crystallization showed that the structural changes occurring at a temperature where the alpha relaxation emerges from the JG relaxation affects the crystallization kinetics of the liquid.     

The structure-based design of novel AMPA bioisosteres

The reaction of 4-acetyl-5-methyl-3-isoxazolyl carboxylate with a variety of hydrazines and semicarbazides yielded molecules which are viable antagonist candidates for the AMPA receptor. Molecular modeling studies used in conjunction with the x-ray crystal structures of these derivatives show a close correlation between the hydrogen bonding characteristics of AMPA with that of the hydrazone and semicarbazone isoxazole derivatives. Uncyclized hydrazones and semicarbazones (1–5) were formed by using corresponding hydrazines and semicarbazides containing strong electron withdrawing groups to prevent cyclization with the ethyl ester. The crystals of 1 are orthorhombic with a = 14.2997(3), b = 15.4112(4),c = 16.0153(4) Å, Z = 8, and space group Pbca; 2 monoclinic with a = 19.738(2), b = 10.4155(7), c = 15.583(1) Å, = 92.348(2)°, Z = 8, and space group C2/c; 3 triclinic with a = 8.3365(5), b = 8.4930(5), c = 12.2379(7) Å, = 92.568(2), = 102.229(2), = 104.449(1)°, Z = 2, and space group P .     

High-pressure freezing, crystal structure studies and SiCF3 bond polarizability of trimethyl(trifluoromethyl)silane

Trimethyl(trifluoromethyl)silane, (CH₃)₃SiCF₃, has been in situ pressure frozen in a diamond anvil cell and its structure determined at 0.90(5) GPa/296 K by single-crystal X-ray diffraction. The crystal is monoclinic, space group P2₁/m, with the molecules lying on crystallographic mirror planes. The CH₃ and CF₃ groups assume the fully staggered conformation. The 14-fold coordination scheme of the molecules is similar to those in (CH₃)₃SiCl polymorphs, but different from that in crystalline tetramethylsilane, (CH₃)₄Si (TMS). The longest SiC bond length of 1.943(12) Å observed in the crystal structure has been documented. The shortest intermolecular contacts in the structure of pressure-frozen CF₃Si(CH₃)₃ are observed between the hydrogen atoms, and those involving fluorine atoms are longer than sums of van der Waals’ radii. These structural features explain the facile cleavage of SiCF₃ bond for CF₃ group transfer in organic reactions.