Biotransformations in Supercritical Fluids

Fontes, Nuno; Almeida, M. Conceição; Barreiros, Susana

doi:10.1385/1-59259-112-4:565

Cited by 6 publications

(6 citation statements)

References 9 publications

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“…Variable-volume stainless steel cells (reaction mixture volume of ∼14 cm 3 ) equipped with a sapphire window and with loading and sampling valves were used. Details of the high-pressure apparatus and experimental technique have been given elsewhere (22). The reaction studied was the esterification of geraniol with acetic acid.…”

Section: Methodsmentioning

confidence: 99%

Water Activity Effects on Geranyl Acetate Synthesis Catalyzed by Novozym in Supercritical Ethane and in Supercritical Carbon Dioxide

Peres

Silva

Barreiros

2003

J. Agric. Food Chem.

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The esterification reaction of geraniol with acetic acid catalyzed by Novozym was studied in supercritical ethane (sc-ethane) and in supercritical carbon dioxide (sc-CO(2)). Water activity (a(W)) had a very strong effect on enzyme activity, with reaction rates increasing up to a(W) = 0.25 and then decreasing for higher a(W). Salt hydrate pairs could not prevent changes in a(W) during the course of reaction but were able to control a(W) to some extent and had a beneficial effect on both initial rates of esterification and conversion in sc-ethane. The enzyme was more active in sc-ethane than in sc-CO(2), confirming the deleterious effect of the latter already observed with some enzymes. Temperatures between 40 and 60 degrees C did not have a strong effect on initial rates of esterification, although reaction progress declined considerably in that temperature range. For the mixture of 50 mM acetic acid plus 200 mM geraniol, 100% conversion was achieved at a reaction time of 10 h at 40 degrees C, 100 bar, an a(W) of incubation of 0.25, and a Novozym concentration of 0.55 mg cm(-)(3) in sc-ethane. Conversion was below 50% in sc-CO(2) at otherwise identical conditions. With an equimolar mixture of the two substrates (100 mM), 98% conversion was reached at 10 h of reaction in sc-ethane (73% conversion in sc-CO(2)).

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Section: Methodsmentioning

confidence: 99%

Water Activity Effects on Geranyl Acetate Synthesis Catalyzed by Novozym in Supercritical Ethane and in Supercritical Carbon Dioxide

Peres

Silva

Barreiros

2003

J. Agric. Food Chem.

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“…After introduction of CO 2 , the system was allowed to equilibrate for at least 1 h, after which the reaction was initiated by the addition of Ac‐Phe‐OEt dissolved in PrOH. Reactions were carried out in our standard cells for enzymatic reaction (11) and were followed by HPLC (RP‐18 HiChrom column, mobile phase 50% water, 50% acetonitrile at pH 3 by addition of orthophosphoric acid, UV detection at 220 nm). The reaction rate data (calculated from the production of Ac‐Phe‐OPr) are the average of at least two measurements, except for experiments with zeolite NaA.…”

Section: Methodsmentioning

confidence: 99%

Enhancement of Enzyme Activity in Supercritical Carbon Dioxide via Changes in Acid‐Base Conditions

Harper

Barreiros

2002

Biotechnology Progress

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Enzyme performance is often impaired in supercritical carbon dioxide. We were able to enhance enzyme activity in this medium via changes in acid-base conditions by using ion-exchange materials (solid H(+)/Na(+) buffer pairs and a zeolite), which were selected on the basis of the response of an organosoluble acid-base indicator. The concentration of ion-exchange materials had an important effect on the catalytic activity of subtilisin Carlsberg cross-linked enzyme crystals (CLECs), and this was related to the protonation and hydration states of the enzyme. The buffer Na(2)CO(3)/NaHCO(3) gave the highest enhancement in enzyme activity (by a factor of 54), probably as a result of its high basicity and capacity to counteract the deleterious effect of carbonic acid to a greater extent than the other materials tested.

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“…For reactions in sc-fluids, we used variable-volume stainless steel cells (reaction mixture volume of about 12 cm 3 ) equipped with a sapphire window and with loading and sampling valves. Details of the high-pressure apparatus and experimental technique have been given elsewhere [42]. Reactions in organic solvents were performed in screw-capped polypropylene vials (3.5 cm 3 reaction volume).…”

Section: Enzyme Assaysmentioning

confidence: 99%

Cutinase activity in supercritical and organic media: water activity, solvation and acid–base effects

García

Vidinha

Arvana

et al. 2005

The Journal of Supercritical Fluids

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We performed a comparative study on the activity of Fusarium solani pisi cutinase immobilized on zeolites NaA and NaY, in n-hexane, acetonitrile, supercritical ethane (sc-ethane) and sc-CO 2 , at two different water activity (a W) values set by salt hydrate pairs in situ and at acid-base conditions fixed with solid-state buffers of aqueous pK a between 4.3 and 10.6. The reaction studied was the transesterification of vinyl butyrate by (R,S)-2-phenyl-1-propanol. The transesterification activity of cutinase was highest and similar in sc-ethane and in n-hexane, about one order of magnitude lower in acetonitrile and even lower in sc-CO 2. Activity coefficients (γ) generated for the two substrates indicated that they were better solvated in acetonitrile and thus less available for binding at the active site than in the other three solvents. γ data also suggested higher reaction rates in sc-ethane than in n-hexane, as observed, and provided evidence for a direct negative effect of sc-CO 2 on enzyme activity. Manipulation of the acid-base conditions of the media did not afford any improvement of the initial rates of transesterification relative to the blanks (no added acid-base buffer, only salt hydrate pair), except in the case of cutinase immobilized on zeolite NaA in sc-ethane at a W = 0.7. The poor performance of the blank in this case and the great improvement observed in the presence of a basic buffer suggest a deleterious acidic effect in the medium which, an experiment without additives confirmed, was not due to the known acidic character of the salt hydrate pair used to set a W = 0.7. In acetonitrile, increasing a W was accompanied by a decrease in initial rates of transesterification, unlike in the other solvents. There was considerable hydrolysis in acetonitrile, where initial rates of hydrolysis increased about 20-fold from a W = 0.2 to 0.7. Hydrolysis was less pronounced in sc-ethane and in n-hexane, and only at a W = 0.7, and in sc-CO 2 butyric acid was detected only at very long reaction times, in agreement with a generally low catalytic activity. Cutinase enantio-selectivity towards the alcohol substrate was low and unaffected by any manipulation of medium conditions.

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Biotransformations in Supercritical Fluids

Cited by 6 publications

References 9 publications

Water Activity Effects on Geranyl Acetate Synthesis Catalyzed by Novozym in Supercritical Ethane and in Supercritical Carbon Dioxide

Water Activity Effects on Geranyl Acetate Synthesis Catalyzed by Novozym in Supercritical Ethane and in Supercritical Carbon Dioxide

Enhancement of Enzyme Activity in Supercritical Carbon Dioxide via Changes in Acid‐Base Conditions

Cutinase activity in supercritical and organic media: water activity, solvation and acid–base effects

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