Rapid determination of underivatized pyroglutamic acid, glutamic acid, glutamine and other relevant amino acids in fermentation media by LC-MS-MS

Determination of amino acids in a complex matrix without derivatization is advantageous, however, difficulties are found in both the detection and the separation of those compounds. In this study, a rapid and reliable LC-MS-MS method for the quantitation of underivatized amino acids in exocellular media was established. Injections were made directly after centrifugation of the samples, without further preparation. The separation of seven underivatized amino acids was achieved on a reversed-phase C18 column with pentadecafluorooctanoic acid as a volatile ion-pair reagent, and the specific detection of most amino acids was achieved by MS-MS of the specific transitions [M + H]+-->[M + H - 46]+. The calibration curves of all analytes were linear over the range of 1.0-1000 microg ml(-1) and the detection limits ranged from 0.1 to 5 ng ml(-1), with an injection volume of 20 microl. The inter-day and intra-day precisions ranged from 2.6 to 5.7% and 4.8 to 8.2%, respectively; the mean recoveries of the seven analytes were 81-104%, 91-107% and 93-101% respectively at the spiked level of 10, 40 and 200 microg ml(-1). A large number of fermentation samples were analysed using this method. The technique is simple, rapid, selective and sensitive, and shows potential for the high-throughput quantitation of amino acids from other biological matrices.     

A quick method for the simultaneous determination of ascorbic acid and sorbic acid in fruit juices by capillary zone electrophoresis

A method of quickly determining ascorbic acid and sorbic acid by capillary zone electrophoresis with ultraviolet detection was developed. The choice of background electrolyte, wavelength, injection time and applied voltage were discussed. Ascorbic acid and sorbic acid were well separated in 80 mmol L⁻¹ boric acid-5 mmol L⁻¹borax (pH = 8.0) in 5 min at the detecting wavelength of 270 nm. Under the optimum condition, the method has linear ranges of 2.54-352.00 mg L⁻¹ for ascorbic acid and 1.08-336.39 mg L⁻¹ for sorbic acid with the detection limit of 1.70 mg L⁻¹ for ascorbic acid and 0.54 mg L⁻¹ for sorbic acid, respectively. Other organic acids in fruit juices have no effect on the detection. This method is very feasible and simple and can be used to detect ascorbic acid and sorbic acid in fruit juices.     

Synthesis of fluorinated imines and carbodiimides from azides via aza-Wittig reaction

The Staudinger reaction of fluoroalkylazides were studied. A series of N-fluoroalkylimines were synthesized via aza-Wittig reaction of N-fluoroalkyliminophosphoranes. The N,N′-difluoroalkylated carbodiimide was also synthesized via the reaction of N-fluoroalkyliminophosphoranes with carbon dioxide or carbon disulfide.     

Sc(OTf)3-catalyzed efficient synthesis of beta,beta-bis(indolyl) ketones by the double indolylation of acetic acid 2-methylene-3-oxobutyl ester

In the presence of 5 mol% Sc(OTf)3, double indolylation of acetic acid 2-methylene-3-oxo-butyl ester with differently substituted indoles readily afforded beta,beta-bis(indolyl) ketones. The reaction may proceed via a Sc(OTf)3-catalyzed SN2'-type substitution and subsequent conjugate addition.     

聚合物在碳纤维表面的电沉积

用电沉积方法将苯乙烯-马来酸酐、乙酸乙烯酯-马来酸酐、甲基丙烯酸甲酯-马来酸酐共聚物沉积于碳纤维表面。通过实验初步证实了此过程的负离子-自由基机理,以及沉积层在纤维表面的物理粘附。由于电沉积的聚合物中间层改善了碳纤维增强塑料中纤维-基体树脂间的界面粘接作用,使原来的剪切破坏基本上发生于界面的情况转变成发生于基体本身为主。并将单向碳纤维增强环氧树脂复合材料的层间剪切强度,由原来的600kg/cm~2左右提高到1000kg/cm~2以上,经沸水浸泡100小时后的强度损失也减少了。