BaF（Cl,Br）：Sm^2＋的光谱烧孔与光激励发光过程

Ｘ射线辐照前后，在ＢａＦ（Ｃｌ，Ｂｒ）：Ｓｍ＾２＋中以５６０ｎｍ的Ｎｄ：ＹＡＧ脉冲光在液氮温度下进行了双光子烧孔实验和光激励发光实验，结果表明，Ｓｍ＾２＋掺杂的碱土金属氟卤化物光谱烧孔过程中伴随着光激励发光过程，这一过程直接影响光谱烧孔过程的进行。     

Competition between pi and non-pi cation-binding sites in aromatic amino acids: a theoretical study of alkali metal cation (Li+, Na+, K+)-phenylalanine complexes

To understand the cation-pi interaction in aromatic amino acids and peptides, the binding of M(+) (where M(+) = Li(+), Na(+), and K(+)) to phenylalanine (Phe) is studied at the best level of density functional theory reported so far. The different modes of M(+) binding show the same order of binding affinity (Li(+)>Na(+)>K(+)), in the approximate ratio of 2.2:1.5:1.0. The most stable binding mode is one in which the M(+) is stabilized by a tridentate interaction between the cation and the carbonyl oxygen (O[double bond]C), amino nitrogen (--NH(2)), and aromatic pi ring; the absolute Li(+), Na(+), and K(+) affinities are estimated theoretically to be 275, 201, and 141 kJ mol(-1), respectively. Factors affecting the relative stabilities of various M(+)-Phe binding modes and conformers have been identified, with ion-dipole interaction playing an important role. We found that the trend of pi and non-pi cation bonding distances (Na(+)-pi>Na(+)-N>Na(+)-O and K(+)-pi>K(+)-N>K(+)-O) in our theoretical Na(+)/K(+)-Phe structures are in agreement with the reported X-ray crystal structures of model synthetic receptors (sodium and potassium bound lariat ether complexes), even though the average alkali metal cation-pi distance found in the crystal structures is longer. This difference between the solid and the gas-phase structures can be reconciled by taking the higher coordination number of the cations in the lariat ether complexes into account.     

Development and validation of analytical methodology using capillary electrophoresis for separation and determination of anions in rainwater

A new capillary electrophoresis (CE) procedure was developed for simultaneous determination of both organic and inorganic anions in rain water using a background electrolyte (BGE) containing 5 mM molybdate, 0.15 mM CTAH, 0.01% PVA and 5 mM Tris buffer to adjust pH at 7.9. Under optimised conditions, good repeatability (RSD for sulphate in migration time=0.36% and peak area=4.2%), low detection limit (2 ppb for chloride) and satisfactory working range (50 ppb-20 ppm for hydrodynamic injection, 10 ppb-3 ppm for electrokinetic injection for chloride) were obtained. The reliability of the CE procedure developed was established by satisfactory recovery tests and good agreement of results obtained by both the CE and ion chromatography (IC) methods. The procedure developed had been successfully applied for field monitoring of rainwater showing good repeatability and capability of detecting trace anions at ppb levels beyond the IC working range. Thus, the new CE procedure developed provides a quick, sensitive, economic and reliable method to meet the need for the simultaneous determination of both organic and inorganic anions in the acid rain monitoring programme.     

Isolation and Determination of Volatile Organic Compounds from Water by Dynamic Purge-and-Trap Technique Coupled with Capillary Gas Chromatography

The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water.     

Nitro-oxidized carboxycellulose nanofibers from moringa plant: effective bioadsorbent for mercury removal

Cellulose - Mercury contamination in drinking water is a worldwide problem due to its severely harming effects on the human body. A nanostructured natural bioadsorbent, carboxycellulose nanofiber...     

Orientational ordering of 4-substituted phenylcyclohexanes studied by carbon-13 two-dimensional N.M.R.

Abstract

An N.M.R. method combining the techniques of separated local field spectroscopy (SLF) and variable angle spinning (VAS) is valuable in the investigtion of nematic liquid crystals. Rapid sample spinning causes the nematic director to align along the spinning axis, resulting in narrow peaks in the C-13 N.M.R. spectrum. SLF is a two-dimensional N.M.R. method which produces a first order splitting pattern for each carbon signal from which C–H dipolar coupling constants can be determined. The order parameters for all segments of the liquid crystal molecule can then be calculated. Results for three 4′-cyanophenylcyclohexanes are considered here. These compounds are trans-substituted at the 4 position of cyclohexane ring with n-pentane (PCH5), 1-pentene (3d ₁CP) and 3-pentene (1d ₃CP), respectively.     

New laterally aromatic branched liquid crystal materials with large nematic ranges

Abstract

Three new homologous series of mesogens containing three rings in the main structure and a lateral aromatic branch have been synthesized. When the lateral aromatic branch is attached to the middle ring, monotropic phases are observed, and there is a strong tendency to form the smectic C phase. When the lateral aromatic branch is attached to an outer ring, the compounds possess purely enantiotropic nematic phases. The terminal alkoxy chain in the outer ring which has a lateral aromatic substituent can be replaced by a rigid group without disturbing the large nematic range. Selective introduction of a particular substitutent may be useful for the construction of devices possessing desirable characteristics such as non-linear optical properties.