人参二醇类皂苷的生物转化动态及人参稀有皂苷C-K或F2的制备

为了低成本有效制备人参稀有皂苷C-K或F₂, 将A. niger g.848菌酶用于转化含有人参皂苷(质量分数)分别为49.6% Rb₁, 25.9% Rd, 19.3% Rc和5.23% Rb₂的西洋参二醇混合皂苷. 霉菌发酵时, 采用人参二醇皂苷诱导物比人参提取液诱导物的产酶总活力提高10%~15%. 所产的2种诱导酶均能水解人参二醇皂苷的3-O-和20-O-多种糖基, 均为人参皂苷酶Ⅰ型; 但是人参二醇皂苷诱导物所产酶几乎全部转化人参二醇皂苷为C-K, 而人参提取液诱导物所产酶则残留中间产物. 使用黑曲霉人参二醇皂苷诱导所产酶, 在转化西洋参二醇皂苷的动态研究中发现, 酶反应1.5~2.5 h, 主要为产物F₂; 酶反应12 h后, 主要产物为C-K皂苷. 基于此, 40 g人参二醇类皂苷在45 ℃粗酶反应24 h, 经处理得到含C-K质量分数为87%的23 g酶反应产物, C-K转化率达85%(摩尔分数). 用40 g西洋参二醇皂苷在45 ℃粗酶反应2.5 h, 经处理得到含有质量分数为58%的F₂和27%的C-K的26 g酶反应产物, F₂转化率为50.4%, C-K转化率为29.5%. 通过人参二醇皂苷诱导的黑曲霉粗酶转化人参二醇类皂苷动态研究, 建立了C-K转化率为85%, F₂转化率为50%的制备方法, 为大批量制备提供了基础依据.     

An inequality for self-inversive polynomials

A sharp L^p, p ? 1, inequality for the class of self-inversive polynomials is obtained.     

Solvent effects on proton chemical shifts in thiophenes

The effects of various polar and non-polar solvents on the proton chemical shifts in thiophene and its derivatives have been investigated. Results have been interpreted in terms of possible solute-solute, solute-solvent and solvent-solvent interactions in these systems.     

Inosine — Adenosine base pairing in d-GGTACIAGTACC: Duplex and hairpin with a two-base loop

An oligonucleotide dodecamer d-GGTACIAGTACC containing two inosine-adenosine mismatched base-pairs has been studied by¹H and³¹P NMR spectroscopy. Unique assignments of¹H and³¹P spins have been achieved by using a recently proposed two-dimensionalheteronuclearlong rangecorrelation (2D-HELCO) technique. The 2D nuclear Overhauser enhancement spectroscopy (NOESY) spectrum recorded in a mixed solvent of 90% H₂O+10%²H₂O has been used to assign all the exchangeable imino and amino proton resonances. NMR results indicate that at concentrations above 5 mM, the molecule adopts a duplex structure where the inosine imino protons are hydrogen bonded. Cross-strand NOEs between the imino proton of I6 and H2 proton of A7 and that between H2 of I6 and H2 of A7 provide evidence for inosine-adenosine base-pairing, with both bases I6 and A7 inanti conformation. The observed NOE connectivitiesd1,d2 andd3 from almost the middle of the molecule to the two ends are consistent with a right handed B-DNA conformation. However, the molecule adopts a more extended conformation in the mismatch region to accomodate the bulky purine-purine (IA) base pairs. NMR experiments at lower concentrations indicate the coexistence of a monomeric hairpin with a two base loop, consisting of I6 and A7 units, in equilibrium with the duplex. 2D-ROESY experiment at such a concentration shows that the conformation of the stem of the hairpin does not deviate much from the corresponding region of the duplex and four nucleotides C5, I6, A7 and G8 undergo significant structural changes during the formation of hairpin loop.     

High resolution NMR spectra of some tri-substituted benzenes

This paper presents the analysis of the proton magnetic resonance spectra of 2:4 dinitro phenol, 1-chloro 2:4 dinitro benzene, 1-nitro, 2-methyl, 3-chloro benzene (2-chloro, 6-nitro toluene) and 5-sulpho, 3-nitro benzoic acid based on the exact solution obtained by Jha for the splitting of NMR lines of a three nuclei system of the ABC type.     

Estimation of aromaticity by NMR dilution shifts

A correlation between the dilution shifts of aromatic protons in non-polar, isotropic solvents and the aromaticity of the ring has been established. The aromaticities of thiophene, furan and pyridine have been estimated and the values thus obtained are compared with those obtained from other methods. The merits and the limitations of the method have been pointed out.     

NMR spectra of five spin systems

The NMR spectrum of five non-equivalent nuclei each with spin 1/2 inm-fluoronitrobenzene has been discussed and the values of the various parameters obtained have been interpreted in terms of the molecular structure of this compound.     

Self-association in aromatic thiols

Hydrogen bonding inortho andmeta toluene thiols has been studied from the dilution shifts of the SH and the aromatic protons in these compounds in non-polar, isotropic solvents. It has been shown that the thiols are present essentially as dimers and monomers. The values of the monomer-dimer equilibrium constants have been estimated, for both the thiols.