A Single Column Packing for The Gas-Liquid Chromatographic Separation of Various Biologically Important Compounds

The use of a single, commercially available column packing, Tabsorb_R, is described for the g. l. c. separation of a large number of different compounds. The resolution of the homologous members of the following series of compounds was achieved: (1) saturated fatty acids (C₁-C₁₈), (2) normal aliphatic saturated dlcarboxylic acids (C₂-C₁₄), (3) normal aliphatic saturated alcohols (C₁-C₂₄), (4) normal aliphatic saturated amines (C₁C₁₂), (5) the common amino acids except arginlne, histidlne and cysteine, (6) aliphatic hydrocarbons (C₁₀-C₂₀) and (7) monosaccharides. It should be noted that twenty-two monosaccharides including three hexosamines and two anhydrohexoses, could be resolved as aldltol acetates In a single run. In addition, galacturonic, glucuronic and lduronlc acids could be separated from one another as their 1, 4-lactones. The resolution achieved in these series of compounds was found to be consistent and highly reproducible. It is of further interest that certain Isomers of the higher fatty acids and hydrocarbons with one double bond could also be separated from the normal and saturated compounds, respectively. The applicability of “Tabsorb” for the g. l. c. separation, although noted above to be considerably broad, is by far not yet exhausted. These procedures which form the basis for the quantitative determinations of the various compounds studied as demonstrated by analysis of glycopeptldes for neutral hexoses and proteins for the amino acids, can readily be adapted to preparative methods. From the biochemical point of view “Tab-sorb” is an extremely versatile column packing in that it can be used for the identification of many of the common building blocks of natural products.     

Solvent Effects on Equilibrium Position and Initial Rate of Lipase-catalyzed Esterification Reactions in Organic Solvents: Experimental Results and Prediction Capabilities

The solvent effect on the equilibrium position and the initial rate of esterification of 1-hexanol with acetic acid catalyzed by a lipase has been experimentally investigated. A variety of non-polar and polar solvents have been considered and the results obtained indicate that the solvent effect on the equilibrium conversion is very important compared to that for transesterification reactions. A theoretically sound methodology using the group-contribution UNIFAC model for the prediction of solvent effects on the equilibrium position of enzymatic reactions is presented and it is applied to the reaction of 1-hexanol with acetic acid as well as to a similar reaction from the literature. The results obtained are better than those from empirical methods proposed in the literature such as correlations with the octanol-water partition coefficient of the solvent, as well as the solubility of water in the solvent. Moreover, the proposed methodology can be used for the determination of the equilibrium constant of the reaction. For the prediction of the solvent effect on the initial rate of enzymatic reactions it is found that it is more accurately determined using the product of the activities of the reactants, which can be predicted by the UNIFAC model, than the octanol-water partition coefficient of the solvent or the solubility of water in the solvent.     

Internal Mass Transfer Limitation During Enzymatic Esterification in Supercritical Carbon Dioxide and Hexane

A kinetic study of ethyl myristate formation by esterification of myristic acid with ethanol catalysed by a lipase from Mucor miehei immobilized on Duolite A 568, has been carried out.

The reaction was done in a two liquid phase system in which the non-aqueous solvent was supercritical carbon dioxide (P= 12.5 MPa, T = 323 K) or n-hexane (P = 0.1 MPa, T = 323K). In heteregenous catalysis, it is important to study the internal mass transfer limitation. For this, the support was sieved into different size series (from 300 to 600 mm) and the reaction was carried out for each size series. The samples were analyzed by gas chromatography and the esterification was shown to follow Ping Pong Bi Bi kinetics with competitive substrate inhibition. The Thiele modulus values show that there is, in the hexane case, a diffusional control while in SCCO₂ media, we obtained an intermediate rate between reactional and diffusional rates.     

Immobilization in quartz fiber felt reinforced silica aerogel improves the activity of Candida rugosa lipase in organic solvents

Candida rugosa lipase is a very useful catalyst, but its rapid inactivation by simple alcohols is a drawback. The present study was focussed on the encapsulation of this enzyme in silica aerogels reinforced with quartz fiber felt. The activity of the immobilized lipase in an organic solvent could be significantly improved over that of the free enzyme and of previous immobilization techniques, by evaporating the alcohol formed during a pre-hydrolysis of the silica precursor, before adding the aqueous enzyme solution. The alcohol evaporation technique was previously used by other authors to immobilized enzymes, but applied to xerogels dried by evaporation, while in the present case the wet gels obtained were dried by the CO₂ supercritical method to obtain aerogels. Besides, such silica aerogels were also reinforced by impregnating a commercial ceramic quartz fiber felt of St. Gobain with the silica sol containing the enzyme, before gelation. The ceramic composites heterogeneous biocatalysts obtained could be used for a large number of times without any apparent deterioration.     

Esterification of chlorophyllide b in higher plants

Chlorophyllide b and four chemically different chlorophyll b specieis, chlorophyllide b esterified with geranylgeraniol, dihydrogeranylgeraniol, tetrahydrogeranylgeraniol and phytol have been detected in addition to the same derivatives of chlorophyll a in the greening cotyledons of cucumber. These esters could be separated and determined by high-performance liquid chromatography. The results suggest that chlorophyll b phytol is formed from the esterification of chlorophyllide b and geranylgeraniol followed by three hydrogenations of the alcohol moiety, as in the case of chlorophyll a and protochlorophyll phytol formation     

Methyl esters production,in aqueous medium,by an enzymatic extract fromCandida deformans (Zach) Langeron and Guerra.

Summary Oleic acid methyl esters production was studied in aqueous medium (a_w>0.9) in the presence of an enzymatic extract fromCandida deformans and methanol. The yields of the reaction were 82% and 58% when the subtrates were oleic acid and triolein respectively.