Analysis of plasma catecholamines by high-performance liquid chromatography with fluorescence detection: simple sample preparation for pre-column fluorescence derivatization

Analysis of plasma catecholamines (norepinephrine, epinephrine and dopamine) by high-performance liquid chromatography using 1,2-diphenylethylenediamine as a fluorescent reagent is described. We have developed an automatic catecholamine analyser, based on pre-column fluorescence derivatization and column switching. The analysis time for one assay was 15 min. The correlation coefficients of the linear regression equations were greater than 0.9996 in the range 10-10,000 pg/ml. The detection limit, at a signal-to-noise ratio of 3, was 2 pg/ml for dopamine. A new method of sample preparation for the pre-column fluorescence derivatization of plasma catecholamines was used. In order to protect the catecholamines from decomposition, an ion-pair complex between boric acid and the diol group in the catecholamine was formed at a weakly alkaline pH. The stabilities of plasma catecholamines were evaluated at several temperatures. After complex formation, the catecholamines were very stable at 17 degrees C for 8 h, and the coefficients of variation for norepinephrine, epinephrine and dopamine were 1.2, 4.2 and 9.3%, respectively.     

Action Spectra for Photoinhibition of Sexual Development in Phycomyces blakesleeanus

The sexual development of the fungus Phycomyces is inhibited by light. The action spectra for this photoinhibitory effect were determined for 48 h continuous exposure between 350 and 700 nm wavelengths during the mating process. Effective wavelengths were shorter than 490 nm, but the most effective wavelengths depended on the stage of sexual development. In early stages of progametangium formation, the major peaks appeared near 360 nm with small shoulders at 410 nm, but in later stages, after gametangium formation, only single peaks were detected in the UVA range (350–390 nm). Low-fluence irradiation in the later stage, however, revealed inhibitory effectiveness at 370–410 nm, implying the existence of a dual photoresponse and multiple regulatiory systems in the mating process of Phycomyces.     

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. III. Simultaneous formation of hydrofluoric acid

Simultaneous formation of hydrofluoric acid (HF) in the radiation-induced polymerization of tetrafluoroethylene (TFE) was investigated. HF concentration in PTFE latex was determined mainly by conductometric titration with 0.01 and 0.001N NaOH. The amount of HF formed is almost independent of agitation speed and the amount of n-hexadecane added and is maximal at ca. 70°C corresponding to the rate of polymerization. The rate of HF formation increases with the initial pressure of TFE monomer and dose rate and decreases with polymerization or TFE consumption. This fact suggests that HF is formed mainly by TFE reactions and not by the degradation of PTFE. The mechanism of HF formation in this reaction system in the absence of oxygen is shown in the following two schemes: scheme I is the reaction of TFE with primary radicals (OH·, H·, e) from the radiolysis of water; scheme II is the reaction of water with the species from the radiolysis of TFE. On the assumption that HF is formed only according to scheme I, the G value of HF formation G(HF)_calc can be calculated as 11.25. All observed G values G(HF)_obs are larger than G(HF)_calc. When the polymerization is carried out at 20 kg/cm² under various dose rates, G(HF)_obs increases with the dose rate. When the polymerization is carried out at 3.0 × 10⁴ rad/hr under various pressures, G(HF)_obs decreases with the decrease in pressure from 20 to 2 kg/cm² and is fairly close to G(HG)_calc at 2 kg/cm². This indicates that HF formation is due mainly to scheme II at high pressure (in the presence of enough TFE) and to scheme I as the pressure is lowered.     

Infrared emissions, visible up-conversion, thermoluminescence and defect centres in Er3Al5O12 phosphor obtained by solution combustion reaction

The Er₃Al₅O₁₂ phosphor powders were prepared using the solution combustion method. Formation and homogeneity of the Er₃Al₅O₁₂ phosphor powders have been verified by X-ray diffraction and energy-dispersive X-ray analysis respectively. The frequency up-conversion from Er₃Al₅O₁₂ phosphor powder corresponding to the ²H_9/2 → ⁴I_15/2, ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, ⁴F_9/2 → ⁴I_15/2 and the infrared emission (IR) due to the ⁴I_13/2 → ⁴I_15/2 transitions lying at ∼410, ∼524, ∼556, 645–680 nm and at ∼1.53 μm respectively upon excitation with a Ti-Sapphire pulsed/CW laser have been reported. The mechanism responsible for the frequency up-conversion and IR emission is discussed in detail. Defect centres induced by radiation were studied using the techniques of thermoluminescence and electron spin resonance. A single glow peak at 430°C is observed and the thermoluminescence results show the presence of a defect center which decays at high temperature. Electron spin resonance studies indicate a center characterized by a g-factor equal to 2.0056 and it is observed that this center is not related to the thermoluminescence peak. A negligibly small concentration of cation and anion vacancies appears to be present in the phosphor in accordance with the earlier theoretical predictions.     

Abnormal Li diffusion in β-LiGa by the formation of defect complex

The diffusion coefficients of Li in the NaTl-type Li intermetallic compound of β-LiGa have been measured by using a short-lived radioactive diffusion tracer. As the tracer, the α-emitting radioisotope of ⁸Li delivered as the energetic and pulsed beam from Tokai Radioactive Ion Accelerator Complex (TRIAC) was implanted into the β-LiGa compounds with the composition in the range of about 43 to 54 at.% Li. By analyzing the time-dependent yields of the α-particles measured according to the repetition cycle of the beam, the tracer diffusion coefficients were extracted over the wide range of Li composition. Abnormal composition-dependence of Li diffusion coefficients in β-LiGa was observed; the stoichiometric β-LiGa showed the highest diffusivity of Li. By referring to the composition-dependent diffusivity of Li in the iso-structural β-LiAl and β-LiIn, we could identify the abnormal diffusion of Li in very Li-poor composition of β-LiGa. The anomaly has been discussed qualitatively in terms of the formation of defect complex and the interaction between the constitutional defects.     

Preparation of Ring and Chain Condensed Oligophosphates

Preparations of small-ring and short-chain condensed phosphates were made by dry and wet processes, respectively. The crystallization of tetra- hexa-, and octaphosphates from the phosphate solution was not easy, and metal salts of these oligophosphates were amorphous and unstable at normal temperature. Guanidine tetraphosphate and ammonium hexaphosphate were crystalline and stable at normal temperature.     

Synthesis,Redox Properties,and Electronic Spectra of Sterically Crowded Triarylphosphines Conjugated with Electron Acceptors

Abstract

Synthesis, redox properties, and electronic spectra of the sterically crowded triarylphosphines conjugated with π-electron systems, especially electron acceptors such as carbonyl group, are briefly reviewed. The sterically crowded triarylphosphines conjugated with various π-electron systems were synthesized from the common synthetic intermediate, (bromoaryl)phosphine, by conventional manner. The sterically crowded triarylphosphines conjugated with the electron acceptors exhibit visible absorption and fluorescence with large Stokes shift. Large solvent effect, redshift in polar solvent, and good correlation with the difference of the oxidation potential of the phosphine moiety and the reduction potential of the acceptor moiety suggest polar excited state resulting from HOMO-LUMO transition.     

Decreased l-tryptophan concentration in distinctive brain regions of mice treated repeatedly with phencyclidine

It has been reported that repeated phencyclidine (PCP) treatment induces schizophrenia-like behavior in mice. l-Tryptophan (Trp) concentrations in brain tissues of control (n?=?8) and PCP-treated mice (10 mg/kg/day, s.c., 14 days, n?=?10) were determined using high-performance liquid chromatography (HPLC) with fluorescence detection. The HPLC method involved pre-column fluorescence derivatization with (R)-(?)-4-(N,N-dimethylaminosulfonyl)-7-(3-isothiocyanatopyrrolidin-1-yl)-2,1,3-benzoxadiazole (DBD-PyNCS). Eight different parts of the brain, namely, the frontal cortex, nucleus accumbens, striatum, hippocampus, amygdala, thalamus, hypothalamus, and cerebellum, of both groups were investigated. A significant decrease in the l-Trp concentration in the nucleus accumbens (p?=?0.024) and hippocampus (p?=?0.027) was observed in PCP-treated mice, suggesting that alteration of the l-Trp metabolism might occur in these brain parts.     

Rotamer decomposition and protein dynamics: Efficiently analyzing dihedral populations from molecular dynamics

Molecular mechanics methods have matured into powerful methods to understand the dynamics and flexibility of macromolecules and especially proteins. As multinanosecond to microsecond length molecular dynamics (MD) simulations become commonplace, advanced analysis tools are required to generate scientifically useful information from large amounts of data. Some of the key degrees of freedom to understand protein flexibility and dynamics are the amino acid residue side chain dihedral angles. In this work, we present an easily automated way to summarize and understand the relevant dihedral populations. A tremendous reduction in complexity is achieved by describing dihedral timeseries in terms of histograms decomposed into Gaussians. Using the familiar and widely studied protein lysozyme, it is demonstrated that our approach captures essential properties of protein structure and dynamics. A simple classification scheme is proposed that indicates the rotational state population for each dihedral angle of interest and allows a decision if a given side chain or peptide backbone fragment remains rigid during the course of an MD simulation, adopts a converged distribution between conformational substates or has not reached convergence yet. © 2012 Wiley Periodicals, Inc.