Preparation, Structure and Properties of Acid Aqueous Solution Plasticized Thermoplastic Chitosan.

This work provides a simple method for the preparation of thermoplastic chitosan using the most common dilute inorganic and organic acids in aqueous solutions, namely hydrochloric acid (HCl) and acetic acid (HAc). The melting plasticization behavior of chitosan under different concentrations and types of acid solution was investigated. By means of infrared spectra (IR), scanning electron microscope (SEM), X-ray diffraction (XRD), and other characterization methods, as well as a mechanical property test, it was found that as the acid solution concentration increased, the protonation effect was stronger and the plasticization performance showed a better trend. The structure and performance of the modified chitosan were optimal when the concentration of HCl was around 8 wt %. In addition, it was found that HCl had a better effect on the plasticization of chitosan than HAc, which was because the protonation ability of HCl was stronger than that of HAc. Unlike the casting method, the structure and properties of chitosan sheets prepared by thermoplastic processing were directly affected by protonation, however not by the interaction of anionic-cationic electrostatic attractions between the -NH3+ groups of chitosan chains and the carboxyl groups of acetic acids or the chloridoid groups of hydrochloric acid.

Magnetic impurity in topological nodal loop semimetals.

We investigate the Kondo effect of a spin-1/2 magnetic impurity in a topological nodal loop semimetal, in which band touchings form a nodal loop. The Fermi surface of a nodal loop semimetal is a torus or a drum-like structure, which is determined by chemical potential. When the chemical potential µ lies at the nodal loop ([Formula: see text]), the magnetic impurity and the conduction electrons form bound states only if their coupling exceeds a critical value. As the chemical potential is tuned away from the nodal loop, the Fermi surface becomes a torus or drum-like structure and the impurity and the host material always favor a bound state due to the finite density of state. Due to the anisotropic dispersion relationship in the energy band, the spatial spin-spin correlations [Formula: see text]([Formula: see text]) are of power-law decay with the decay rates proportional to [Formula: see text] and [Formula: see text] in different directions, respectively. The product [Formula: see text] and [Formula: see text] oscillates in coordinate space and the period is enhanced gradually as the Fermi surface evolves from a torus surface into a drum-like structure.

Development of an N-hydroxysuccinimidyl fluorescein-O-acetate-labeled probe for competitive capillary electrophoretic immunoassay of bovine serum albumin.

A highly fluorescent reagent, N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA) has been labeled on bovine serum albumin (BSA) to construct a new immunofluorescent probe, SIFA-BSA, for the competitive immunoassay of BSA with capillary electrophoresis. Labeling conditions of SIFA with BSA such as the reaction molar ratio and reaction time, as well as separation conditions for free and antibody-bound SIFA-BSA including the pH and concentration of buffer were systematically investigated. Under the optimized conditions, SIFA-labeled BSA and free BSA competitively reacted with a limited amount of anti-BSA antibody. Free and antibody-bound SIFA-BSA could be well separated within 5min using 100mM boric acid buffer (pH 9.3) for background electrolyte, 28kV for the separation voltage, and 25 degrees C for the column temperature. With the proposed method, a much lower detection limit (S/N=3) of 0.1microg/mL was obtained compared with the competitive capillary electrophoresis immunoassay of BSA with fluorescein isothiocyanate (FITC) labeled BSA probe, in which the detection limit (S/N=3) is 0.0031mg/mL.

Trace determination of short-chain aliphatic amines in biological samples by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection.

In this study, a new capillary electrophoresis (CE) method is described originally for the sensitive and selective determination of short-chain aliphatic amines in biological samples. These amines were converted into their N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA) derivatives and measured by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection. The derivatization conditions and separation parameters for the aliphatic amines were optimized in detail. The SIFA-labeled amines were fully separated within 8.5 min using 25 mM pH 9.6 boric acid electrolyte containing 60mM sodium dodecyl sulfate (SDS). The parameters of validation such as linearity of response, precision and detection limits were determined. The detection limits were obtained in the range from 0.02 to 0.1 nM, which was the lowest value reported by CE methods. The developed method was successfully employed to monitor aliphatic amines in serum and cells samples. After comparison of other CE methods using different fluorescent probes, the present method represents a powerful tool for the trace determination of aliphatic amines in complex biological samples.

Determination of amino acid neurotransmitters in human cerebrospinal fluid and saliva by capillary electrophoresis with laser-induced fluorescence detection.

A CE-LIF detection method has been developed to identify and quantitate six amino acid neurotransmitters including glutamic acid, aspartic acid, gamma-aminobutyric acid, glycine, taurine, and glutamine. N-hydroxysuccinimidyl fluorescein-O-acetate, a fluorescein-based dye, was employed for the derivatization of these neurotransmitters prior to CE-LIF analysis. Different parameters which influenced separation and derivatization were optimized in detail. Under optimum conditions, linearity was achieved within concentration ranges of up to three orders of magnitudes for those analytes with correlation coefficients from 0.9989 to 0.9998. The LODs ranged from 0.06 nM to 0.1 nM, and are thus superior or equivalent to those previously reported in the literature using CE-LIF detection. The proposed method has been successfully applied to the determination of amino acid neurotransmitters in biological samples such as human cerebrospinal fluid and saliva with satisfactory recoveries.

Sensitive determination of biogenic amines by capillary electrophoresis with a new fluorogenic reagent 3-(4-fluorobenzoyl)-2-quinolinecarboxaldehyde.

An effective approach was proposed to the derivatization of seven biogenic amines using 3-(4-fluorobenzoyl)-2-quinolinecarboxaldehyde (FBQCA) as a fluorogenic reagent. The sensitive determinations of these derivatives were achieved by micellar electrokinetic capillary chromatography (MEKC) with laser-induced fluorescence (LIF) detection. The derivatization and electrophoretic conditions have been optimized. A running buffer was composed of mixtures of 25 mM pH 9.5 boric acid, 25 mM SDS, and 27% ACN. At 25 degrees C and 22.5 kV, the baseline separation of the derivatives was accomplished in 13 min. The detection limit (S/N=3) was found as low as 0.4 nM. The proposed method was validated by the linearity of two orders magnitude and correlation coefficient in the range 0.9969-0.9998. Also, the procedure was successfully applied to the determination of biogenic amines in soy sauce, fish and wine samples.

Rapid and sensitive determination of phosphoamino acids in phosvitin by N-hydroxysuccinimidyl fluorescein-O-acetate derivatization and capillary zone electrophoresis with laser-induced fluorescence detection.

A method was developed for the determination of phosphoamino acids by capillary zone electrophoresis-laser-induced fluorescence detection (argon ion laser, excitation at 488 nm and emission at 520 nm) using derivatization with N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA). Different variables affecting the derivatization (SIFA concentration, derivatization pH, reaction temperature and reaction time) and the separation (type, pH and concentration of buffer, applied voltage and injection mode) were investigated in detail. The optimized separation conditions were 40 mM boric acid buffer (pH 9.2) for background electrolyte, 25 kV for the separation voltage, 25 degrees C for the capillary temperature and 5 s at 0.5 psi for the sample injection. Under the optimal conditions, the SIFA-labeled phosphoamino acids were fully separated within 7 min. The detection limits ranged from 0.1 to 0.3 nM, which are the lowest values reported for capillary electrophoresis (CE) methods. The proposed methodology allowed the rapid, sensitive and selective determination of phosphoamino acids in hen egg yolk phosvitin by the standard addition method. The recovery of these compounds in real sample was 94.0-103.5%. The developed method surpasses previously published CE methods in terms of detection limit, separation time, stability and simplicity of the electrophoretic procedure.

6-Oxy-(acetyl ethylenediamine) fluorescein, a novel fluorescent derivatization reagent for carboxylic acids and its application in HPLC.

A novel fluorescent derivatization reagent for carboxylic acids, 6-oxy-(acetyl ethylenediamine) fluorescein (AEF), was well designed, synthesized, and applied to HPLC. The derivatization reaction with 12 fatty acids, including n-valeric acid (C5), n-hexanoic acid (C6), n-heptanoic acid (C7), n-octanoic acid (C8), n-nonanoic acid (C9), n-decanoic acid (C10), lauric acid (C12), myristic acid (C14), palmitic acid (C16), stearic acid (C18), oleic acid (C18:1), and linoleic acid (C18:2), was completed at 55 degrees C within 40 min. The derivatives of fatty acids were separated on a C18 RP column and detected by fluorescence detection. The LODs attained were 0.4-1.2 nM (S/N of 3). It has been demonstrated that AEF is a prominent derivatization reagent for carboxylic acids which is suitable for HPLC.

Quantification of biogenic amines in human plasma based on the derivatization with N-hydroxy-succinimidyl fluorescein-O-acetate by high-performance liquid chromatography.

An HPLC method for the determination of biogenic amines based on the precolumn derivatization with N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA) has been developed. The derivatization was performed at 45 degrees C for 30 min in borate buffer (pH 8.0). The derivatives were separated on a ZORBAX Eclipse XDB-C8 column (150 mm x 4.6 mm id; 5 mum) and monitored by fluorescence detection (excitation, 469 nm; emission, 512 nm). The LODs (S/N = 3) for spermine, spermidine, putrescine, cadaverine, and phenethylamine were 0.4, 0.2, 0.3, 0.5, and 0.4 nM, respectively. The developed method has been successfully applied to the determination of biogenic amines in human plasma of three healthy volunteers and four cancer patients. Average recoveries for plasma samples ranged from 94 to 106% and coefficients of variation ranged from 1.8 to 4.6%. Deproteinization of plasma was accomplished with ACN to precipitate interfering substances and the centrifuged supernatant was used directly for analysis.

Design and synthesis of a novel fluorescent reagent, 6-oxy-(ethylpiperazine)-9-(2'-methoxycarbonyl) fluorescein, for carboxylic acids and its application in food samples using high-performance liquid chromatography.

A novel derivatization reagent for carboxylic acids, 6-oxy-(ethylpiperazine)-9-(2'-methoxycarbonyl)fluorescein (EPMF) has been well designed and synthesized. It was used to label 13 fatty acids, n-butyric acid (C4), n-valeric acid (C5), n-hexanoic acid (C6), n-heptanoic acid (C7), n-octanoic acid (C8), n-nonanoic acid (C9), n-decanoic acid (C10), lauric acid (C12), myristic acid (C14), palmitic acid (C16), stearic acid (C18), oleic acid (C18:1) and linoleic acid (C18:2), successfully. The derivatization reaction with fatty acids was completed at 50 degrees C, 50 min. The derivatives of fatty acids were separated on a C18 reversed-phase column with gradient elution and fluorescence detection at lambda(ex)/lambda(em)=469/518 nm. The detection limits obtained were 0.4-2 nmol L(-1) (signal-to-noise ratio of 3). The proposed method has been applied to the quantification of fatty acids in edible oil with recoveries over 93%. It has been demonstrated that EPMF is a prominent derivatization reagent for fatty acids and is suitable for HPLC.

Liquid chromatographic analysis of phosphoamino acids at femtomole level using chemical derivatization with N-hydroxysuccinimidyl fluorescein-O-acetate.

Phosphorylation of amino acid residues in proteins plays a major role in biological systems. In this paper, a reversed-phase high performance liquid chromatographic (HPLC) method based on chemical derivatization has been described for the separation and quantification of phosphoamino acids at femtomole level, using fluorimetric detection (FLD). The protocol involved pre-column derivatization of phosphoamino acids with N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA) and subsequent separation on ZORBAX Eclipse XDB-C8 column. Several experimental factors that influenced derivatization and separation were carefully investigated. The derivatization was performed at 40 degrees C for 40 min in borate buffer (pH 8.5). Under the optimum conditions, phosphoserine (P-Ser), phosphothreonine (P-Thr) and phosphotyrosine (P-Tyr) were satisfactorily separated in 8 min. The detection limits (signal-to-noise ratio=3) for the phosphoamino acids could reach 10-20 fmol, which was the lowest value reported for HPLC methods and comparable to those obtained by capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection methods. The proposed method has been validated and used to characterize the phosphoamino acids in the hydrolyzed phosphorylated protein samples. The results clearly demonstrated the potential of this technique to study phosphoamino acids as well as provided a new analytical methodology that should be applicable to the study of phosphorylation of protein in biological system.

6-oxy-(acetyl piperazine) fluorescein as a new fluorescent labeling reagent for free fatty acids in serum using high-performance liquid chromatography.

A new fluorescein-based fluorescent derivatizating reagent, 6-oxy-(acetyl piperazine) fluorescein (APF), has been designed, synthesized and developed for carboxylic acid labeling. It was used as a pre-column derivatizing reagent for the determination of seven free fatty acids (lauric acid, myristic acid, arachidonic acid, linoleic acid, palmitic acid, oleic acid, and stearic acid) with high-performance liquid chromatography (HPLC). The derivatization reaction of APF with seven fatty acids was completed at 60 degrees C for 1 h using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as the condensing reagent. On a C18 column, the derivatives of APF with seven free fatty acids could be separated completely in 22 min using a mobile phase of methanol-water (88:12, v/v) containing 7 mmol L(-1) pH 6.5 Na2HPO4-H3Cit3 buffer with fluorescence detection at lambdaex/lambdaem=467/512 nm. The detection limits could reach 0.1-6.4 nmol L(-1) (signal-to-noise=3). This reagent was applied to the determination of the free fatty acids in human serum samples with satisfying recovery efficiencies varying from 93 to 105%.