Separation behaviors of xylenol isomers by gas chromatography with helps of hydrogen bonding

Summary Xylenol isomers can be resolved on most polyols (sugars or sugar alcohols) and polyethers (polyethylene glycol or polypropylene glycol) with hydrogen-bonding interaction. They are separated on vinical polyols which have more hydroxy hydrogen than tetrol, and even on vicinal triol when its hydroxy hydrogen is acidic (stronger proton donor). The stronger is the hydrogen bonding interaction between xylenols and the liquid phase, the better is the separation of 2,4- and 2,5-xylenol, and the poorer the separation of 2,4-and 2,3-xylenol.     

Aspects of stereocontrol in the L-Selectride reduction of 4-acyl-1,3-dioxolane derivatives

The application of L-Selectride, either alone or in combination with ZnCl₂, to aryl ketones 1, 8 and 11 resulted in highly anti-stereoselective reduction. In contrast, lactols 22 and 23 gave a moderate syn-preference using L-Selectride alone and a high syn-preference in the presence of ZnCl₂. Uniquely, high anti- stereoselectivity was observed in the reduction of o-anisyl lactol 37 with L-Selectride alone, which was switched to a high syn-preference when ZnCl₂ was present.     

Stereoselective synthesis of highly functionalized thiopeptide thiazole fragments from uronic acid/cysteine condensation products: access to the core dipeptide of the thiazomycins and nocathiacins

We present the stereoselective synthesis of various highly functionalized thiazole dipeptides that are found in thiopeptide antibiotics like thiazomycins and nocathiacins. The condensation of an uronic acid with l-cysteine methyl ester delivers along two different protocols the stereopure thiazolidine lactones or lactams on the multigram scale, respectively. Oxidation of the thiazolidine moiety to the thiazole and tailoring of the sugar chains yield the thiazole dipeptide as present in the core motif of the thiopeptide antibiotics, as well as its epimer and a homolog. The modular assembly of the potent natural products and their analogs relies on the synthetic accessibility of adequately protected building blocks of tailored absolute stereochemistry.     

The compatibility of (natural) polyols with heavy metal- and zinc-free poly(vinyl chloride): Their effect on rheology and implications for plate-out

This paper describes the rheological effects observed after addition of (natural) polyols to several different types of heavy metal-free PVC formulations. It is found that addition of natural polyols, such as sorbitol, leads to changes in the rheology of the system comparable to the addition of external lubricants. Hence as suggested previously, addition of (natural) polyols may lead to the occurrence of undesirable plate-out phenomena. The magnitude of the effect on the rheology depends on the number of hydroxyl groups in the polyol and its propensity to undergo intramolecular cyclodehydration reactions. It is established that the undesirable rheological effects, which coincide with plate-out phenomena, can be suppressed by the addition of various types of inorganic as well as organic substances, most of which are known PVC additives. This will allow for the use of (natural) polyols as efficient and benign co-stabilisers in next generation stabiliser systems.     

Indirect UV detection of non-ionic substances in liquid chromatography by addition of a UV-absorbing uncharged compound to the mobile phase

Summary Chromatographic systems have been developed, which allow the detection and quantitation of non-ionic substances with low or no UV-absorptive properties. The detector response is obtained by using mobile phases containing an uncharged component with high UV-absorbance. Polar or non-polar bonded stationary phases have been selected, depending on the hydrophobic character of the analytes. The response pattern is compared to that observed in ion-pair reversed-phase systems with a UV-absorbing ion in the eluent. The influence on retention and detection sensitivity of the nature and concentration of the UV-absorbing compound and of the organic modifier added to the mobile phase has been studied. Principles for the optimisation of the response by changing the mobile phase composition are given. The wide application scope of the indirect UV-detection technique in non-ionic systems is demonstrated by examples of separations of various kinds of compounds, such as organic solvents, carbohydrates and polyols. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

利用多元醇共浸渍促进Ni/MCM-41催化剂的萘加氢活性

研究了利用乙二醇、甘油、木糖醇、山梨醇、葡萄糖多元醇共浸渍方法促进Ni负载在MCM-41载体上的萘加氢活性．和传统的浸渍方法比较,只要在硝酸盐的水溶液中添加适合量的多元醇即可以提高金属活性中心和载体表面的相互作用,导致5 nm以下超细NiO粒子的形成,以及高分散的催化活性中心和异常高的催化活性;零价Ni的纳米粒子从36.1 nm减少到5 nm以下,同时萘的加氢活性取决于零价Ni纳米粒子的大小．利用多元醇共浸渍制备的负载型催化剂表现出优异的催化活性,即使在55 oC的低温环境中亦表现出100%的萘转化率．     

利用多元醇共浸渍促进Ni／MCM-41催化剂的萘加氧活性

研究了利用乙二醇、甘油、木糖醇、山梨醇、葡萄糖多元醇共浸渍方法促进Ni负载在MCM-41载体上的萘加氢活性．和传统的浸渍方法比较,只要在硝酸盐的水溶液中添加适合量的多元醇即可以提高金属活性中心和载体表面的相互作用,导致5nm以下超细NiO粒子的形成,以及高分散的催化活性中心和异常高的催化活性;零价Ni的纳米粒子从36．1nm减少到5nm以下,同时荼的加氢活性取决于零价Ni纳米粒子的大小．利用多元醇共浸渍制备的负载型催化剂表现出优异的催化活性,即使在55℃的低温环境中亦表现出100％的荼转化率．     

多元醇及其二元混合物固-固相变的IR研究

固固相变储能物质多元醇类以其有适宜的转变温度、较高的转变焓、具有经济和技术潜力而受到人们的重视,已在热力学和动力学等方面对其进行广泛和深入的研究[1-3],并通过红外光谱法研究了几种纯多元醇固固转变的机理[1].本文对几种多元醇及其二元混合物进行变温红外光谱的测定,进一步探讨了变化的规律.1　实　验11　药品:新戊二醇(ＮＰＧ)为保证试剂(日本东京化成株式工业会社),三羟甲基乙烷(ＰＧ)超纯(日本东京化成株式工业会社),季戊四醇(ＰＥ)化学纯(北京化学试剂公司).12　仪器美国ＰＥ公司Ｍ1730型富里叶变换红外光谱仪;日本Ｅ012Ａ号Ｈ…     

Gas-liquid chromatography of isopropylidene monosaccharides and their trimethylsilyl derivatives

Summary This paper describes the gas chromatographic separation of the mixture of isopropylidene monosaccharides, and their trimethylsilyl derivatives. Based on the total analysis time and resolution the best stationary phase was SF-96 using Chromosorb G as the solid support and temperature programming.