Polyfunctional low-capacity cation-exchange packing material for the separation of underivatized amino acids

Mixed-acidic cation-exchange material for the separation of underivatized amino acids

Mixed-acidic cation-exchange (MCX) columns with both strongly (SCX) and weakly (WCX) acidic functional groups were developed for the separation of standard amino acids. The resins were prepared by carboxylation of highly crosslinked monodisperse poly(styrene-divinylbenzene) copolymer particles with performic acid and subsequent sulfonation with sulfuric acid. The degree of functionalization was varied independently for each processing step and controlled by measuring pH dependent retention of the obtained resins. A series of mixed-acidic resins with different SCX/WCX-ratios was chromatographically characterized by variation of formic acid and acetonitrile concentration in the aqueous eluent. The overall cation-exchange capacity was varied from 33 to 68 µmol/mL. The comparison with two commercial columns (Metrohm Metrosep C6, WCX and Hamilton PRP X-200, SCX) revealed the additive character of the different functional group properties within MCX columns and a unique selectivity which can be adjusted by both eluent composition and SCX/WCX-ratio of the resin. The retention window between neutral and basic amino acids was altered by varying the amount of sulfonic acid groups attached to the polymer. Orthogonality plots demonstrated constant selectivity for neutral amino acids. Correlating the retention data with log P data demonstrated the influence of non-ionic hydrophobic and π-π-interactions for the separation of amino acids on PS/DVB-based cation-exchangers. An isocratic IC-ESI-MS method was developed to separate and quantitate 20 underivatized standard amino acids within 30 min. Limits of detection were between 4 and 64 nmol L^-1 and a high linearity of calibration curves was obtained for all analytes. The method was validated by comparing a certified reference standard with external calibration data.

Optimization of l-arginine purification from Corynebacterium crenatum fermentation broth

l-Arginine has many special physiological and biochemical functions, with wide applications in the food and pharmaceutical industry. Few studies on the purification of l-arginine from fermentation broth have been conducted; however, none of them were systematic enough for industrial scale-up. Therefore, it is necessary to develop a highly efficient and systematic process for the purification of l-arginine from fermentation broth. In this study, we screened out a cation exchange resin, D155, having high exchange capacity, high selectivity, and easy elution capacity, and analyzed its adsorption isotherm, thermodynamics, and kinetics using different models. Further, the process parameters of fixed-bed ion exchange adsorption and elution were optimized, and the penetration curve during the operation was modeled. Based on the fixed-bed ion-exchange parameters, a 30-column continuous ion-exchange system was designed, and the flow velocity in each zone was optimized. Finally, to obtain a high purity of l-arginine, the purification tests were conducted using anion exchange resin 711, and an l-arginine yield of 99.1% and purity of 98.5% was obtained. This effective and economical method also provides a promising strategy for separation of other amino acids from the fermentation broth, which is of great significance to the l-arginine fermentation industry.

Current knowledge of intestinal absorption of bioactive peptides

Peptides have been demonstrated as potentially beneficial compounds against several life-style related diseases such as hypertension, hypercholesterolemia, and atherosclerosis, among others. However, limited research has been carried out on peptide absorption, resulting in a lack of understanding and control of this process. Therefore, this review discusses the recent insights gathered on in vitro and in vivo absorption of peptides across intestinal membranes, into blood circulation. Briefly, some di-/tripeptides permeate through intestinal membranes in their intact forms via peptide transporter systems, while others are vulnerable to protease degradation. Oligopeptides (>tetrapeptides) show a lower transport ability than di-/tripeptides, possibly due to the presence of paracellular tight junctions. The hydrophobicity of peptides (log P) does not seem to influence absorption, while peptide length and degradation of peptides (and peptide sequences) by intestinal proteases may be determinant factors of the absorption process.