Estimation of the pK a of the amine groups of benzhydrylamine resin and its lysyl derivative by measurement of swelling

Summary For better evaluation of the potential of benzhydrylamine resin (BHAR), used as a solid support for peptide synthesis, as a novel anion-exchange resin, the pK _a of its amine group was estimated by microscopic measurement of the sizes of the dry and swollen beads. Using the volume of the bead occupied by the solvent (as a percentage) as the swelling parameter, a plot of the degree of swelling of BHAR loaded with 2.4 mmol g^–1 amine groups against the pH of the medium produced a decreasing sigmoidal-type curve with increasing pH. By considering the point of inflection of the curve, a pK _a value of approximately 7.5 was estimated for the amine group of the BHAR. The same approach was also applied to the lysyl derivative of the BHAR (Lys-BHAR) and pK _a values around 6.5 and 10.0 were obtained for the and amine groups, respectively.     

核磁共振和液相色谱-质谱平行动态谱学方法对连翘活性提取物的同步结构分析

以连翘植物的活性提取物为研究对象,基于不完全分离分析策略,以制备型HPLC技术为分离手段,获取含量呈连续动态变化的系列混合物,运用NMR/LC-MS 平行动态谱学方法对提取物中苯乙醇苷类成分进行了同步结构分析研究.采用本方法可获取系列提取物样品中同一成分内在相关且互补的谱学信息,包括保留时间、质荷比(m/z)和化学位移...     

Use of a Graphical Method to Predict the Retention Times of Selected Flavonoids in HPLC from Thin-Layer Chromatographic Data

Similarities and differences between the retention characteristics of octadecylsilica wettable with water used in TLC and RP-18 used in HPLC have been elucidated by use of the linear relationships between log k and R_M. The stationary phases compared were investigated with the same mobile phases—binary mixtures of methanol and water, acetonitrile and water, and tetrahydrofuran and water. For these adsorbents of the same type but differing in specific surface area the correlation line was shifted by log (_systemI/_systemII). High values of the correlation coefficients obtained over the whole range of mobile phase organic modifier concentration examined indicated that the TLC systems could be used to predict HPLC conditions for flavonoid separation.     

The Use of Cyclodextrin-Based LC Stationary Phases for the Separation of Chiral Dihydrobenzofuran Derivatives

The enantiomeric separation of 12 chiral dihydrobenzofurans is reported on derivatized -cyclodextrin stationary phases using high performance liquid chromatography. The hydroxypropyl -cyclodextrin chiral stationary phase (CSP) with acetonitrile/water mobile phases was the most effective combination as it baseline separated 9 of the 12 compounds. The acetyl -cyclodextrin and 2,3-dimethyl -cyclodextrin CSPs were also effective in the reverse phase mode. The native -cyclodextrin was far less effective than the non-aromatic derivatized CSPs. The aromatic functionalized CSPs showed no selectivity in the normal phase mode. Structural characteristics, such as substituent polarity and ring location, were important in the observed enantioselectivity.