| 1. |
- Virto, Carmen, et al.
(författare)
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Candida antarctica lipase B-catalysed synthesis of dihydroxyacetone fatty acid esters
- 2000
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 18:1, s. 13-29
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Tidskriftsartikel (refereegranskat)abstract
- The enzymatic syntheses of 1-lauroyl-dihydroxyacetone and 1,3-dilauroyl-dihydroxyacetone were investigated. Lipase B from Candida antarctica (SP435) was used to catalyse the acylation of dihydroxyacetone (DHA) with lauric acid in organic solvent media at controlled water activity. High conversions of dihydroxyacetone (> 90%) are achieved when the water activity is 0.11 or below in solvents of various hydrophobicities, such as diethyl ether, methyl-tert-butyl ether (MTBE) and diphenyl ether. The main product in the esterification of DHA with lauric acid is 1-lauroyl-DHA, while the amount of 1,3-dilauroyl-DHA that is produced can be increased by changing the reaction conditions. Thus, decreasing the water activity from 0.75 to 0.06 resulted in an increase in the total yield of 1,3-dilauroyl-DHA from 3% to 20%. Solvents which have high log P values favoured the acylation of 1-lauroyl-DHA and thereby the formation of 1,3-dilauroyl-DHA. Thus, when diphenyl ether was used in this reaction, the yield of 1,3-dilauroyl-DHA was 45%. Complete acylation to 1,3-dilauroyl-DHA was achieved when a fatty acid vinyl ester was used as acyl donor in a closed reactor.
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| 2. |
- Virto, Carmen
(författare)
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LIPASES AND PHOSPHOLIPASES IN PHOSPHOLIPID SYNTHESIS
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The synthesis of phospholipids with defined fatty acid and polar head composition catalysed by lipases and phospholipases was investigated. Lipases from Rhizopus arrhizus and Candida antarctica were used for the direct acylation of DL-a-glycerophosphate and L-a-glycerophosphatidylcholine, with different fatty acids. Esterification reactions can be carried out in systems with low water activity, in which the equilibrium is favoured towards synthesis, and hydrolysis is minimised. For optimisation of the processes, it is important to consider various reaction parameters, principally the water content of the media. In the acylation of glycerophosphate and glycerophosphorylcholine, fatty acid vinyl esters gave better yields (>95%) than free fatty acid, in the formation of lysophosphatidic acid and phosphatidic acid or lysophosphatidylcholine and phosphatidylcholine. Solvent free systems were chosen for both reactions, but in some cases conversions could be easily improved by the addition of a small amount of solvent, such as t-butanol. The choline polar head group of lysophosphatidylcholine was exchanged with glycerol in a reaction catalysed by a phospholipase D from Savoy cabbage, in an aqueous micellar system. Characterisation of this reaction and of the hydrolysis showed that both reactions are similar in their Ca2+ ion dependence, kinetic parameters and pH optima. Contrary to the action of the enzyme towards phosphatidylcholine, phospholipase D does not need detergents or solvents to display optimum activity, with lysophosphatidylcholine as substrate. A combination of two phospholipases was used for the formation of lysophosphatidic acid and the analogue, 1-acyl-dihydroxyacetonephosphate, in diethyl ether-aqueous two-phase systems. Microbial phospholipase D from Streptomyces sp. was used in the transesterification of egg phosphatidylcholine with 1-lauroyl-glycerol or 1-lauroyl-dihydroxyacetone, to form two complex phospholipids, 1-lauroyl-phosphatidylglycerol and 1-lauroyl-phosphatidyldihydroxyacetone, respectively. The Km values for the alcohol acceptors were very low, 23±7 and 104±5 mM for 1-lauroyl-glycerol and 1-lauroyl-dihydroxyacetone, respectively. Phospholipase C from Bacillus cereus selectively hydrolysed the obtained products, giving the desired 1-acyl-glycerophosphate and 1-acyl-dihydroxyacetonephosphate in stoichiometric amounts. The facile recovery of the products from the ether phases in both PL D and PL C catalysed reactions, makes this a very attractive system. Finally, the direct esterification of dihydroxyacetone and lauric acid in solvent systems at controlled water activity is described. High yields (>90%) were easily achieved at low water activities of 0.06-0.11. The main product of this reaction was 1-lauroyl-dihydroxyacetone under most of the conditions tested, but the formation of the 1,3-dilauroyl-dihydroxyacetonephosphate could easily be increased by selection of a more hydrophobic solvent, or with the use of vinyl laurate as acyl donor. Using the latter approach, sole formation of 1,3-dilauroyl-dihydroxyacetone was achieved if the reactions were carried out in hermetically closed reactors.
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| 3. |
- Virto, Carmen, et al.
(författare)
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Lysophosphatidylcholine synthesis with Candida antarctica lipase B (Novozym 435)
- 2000
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 26:8, s. 630-635
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Tidskriftsartikel (refereegranskat)abstract
- Immobilized lipase from Candida antarctica lipase B (Novozym 435) was effective in the synthesis of lysophosphatidylcholine (LPC). The transesterification of L-α-glycerophosphorylcholine (GPC) and vinyl laurate was carried out in a solvent free system or in the presence of 50% (v/v) t- butanol. High conversions (>95%) were easily achieved. The lipase was selective for the sn-1 position of the glycerol backbone, and almost no phosphatidylcholine was produced in the first 24 hours of the reaction. However, and probably due to acyl migration, the formation of phosphatidylcholine (PC) increased slowly if the reactions were incubated over a long period of time. The synthetic reaction was only possible with a high excess of vinyl laurate over glycerophosphorylcholine (>10 times). High purity products could be produced by a decrease of the reaction temperature to induce precipitation of the product. The temperature needed depended on the fatty acid chain length. Thus, only lysophosphatidylcholine was produced with palmitic acid vinyl ester at 45°C, whereas for the vinyl esters of lauric acid, capric acid, and caprylic acid, a lower reaction temperature (25°C) was necessary to obtain solely the lysophospholipid products. (C) 2000 Elsevier Science Inc.
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| 4. |
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| 5. |
- Pidek, Irena Agnieszka, et al.
(författare)
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Taxon-specific pollen deposition dynamics in a temperate forest zone, SE Poland: the impact of physiological rhythmicity and weather controls
- 2015
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Ingår i: Aerobiologia. - : Springer Science and Business Media LLC. - 0393-5965 .- 1573-3025. ; 31:2, s. 219-238
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Tidskriftsartikel (refereegranskat)abstract
- High and low pollen deposition years in the period 1998-2010 were recorded for ten forest-forming trees in Roztocze (SE Poland) using Tauber-style traps. The coincidence of very high/low pollen deposition years recorded in Tauber traps and aerobiological data obtained by volumetric samplers shows that these phenomena occur simultaneously in different places across vast areas of a tree's distribution range. The natural physiological rhythms displayed in abundance of flowering were considered on the basis of the observed data and published sources. The results obtained from applying Spearman's correlation to pollen accumulation rates from Roztocze and the meteorological parameters confirmed several statistically significant correlations between temperature and summer precipitation prior to pollen emission and a negative correlation with the winter temperature before pollen emission. Air temperature, precipitation, growing season duration (its start and end), winter length and the number of winter days with a daily mean temperature below 0 A degrees C were all considered. The best correlation coefficient results were obtained for the trees most abundant in the vegetation, namely Abies alba, Fagus sylvatica and Pinus sylvestris. Earlier findings on the controlling role of temperature and precipitation during the summer prior to pollen emission were confirmed, and a long period of winter dormancy was stressed as a factor favouring high pollen production. The examples from Roztocze reflected situations when a strong weather signal overrode the natural flowering rhythm. This was observable in the case of P. sylvestris, where pollen production reflected the air temperature of the previous summer or in the case of a mast year, which occurred across the whole distribution range of F. sylvatica in 2006.
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| 6. |
- Pidek, Irena Agnieszka, et al.
(författare)
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Two pollen-based methods of Eemian climate reconstruction employed in the study of the Żabieniec-Jagodne palaeolakes in central Poland
- 2022
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Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182. ; 632, s. 21-35
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to estimate the range of climate variability in Central Poland during the Eemian Interglacial (MIS 5e). High resolution pollen records are available for all seven RPAZs typical of this interglacial in Central Europe. These pollen records were used to estimate total annual precipitation and mean annual temperature, as well as the mean temperatures of the warmest and the coldest months based on the plant indicator method and the modern analogue technique. The reconstructions indicate that the combination of these two methods provides a much clearer insight into the climate changes of the Eemian optimum. The results confirmed no drastic drop in temperature in the Middle Eemian, with high total precipitation in the hazel phase, and that this was followed by a decrease in temperature in the Late Eemian (fir-spruce and pine phases). A drop in precipitation occurred during the youngest part of the Carpinus phase, while coincided with a marked lowering of the water level in lakes and their transformation into peatbogs. The last part of the Eemian is characterized by decreasing temperature, particularly during the coldest month, rising water levels due to a combination of lower evaporation and higher air humidity, and a transition to glacial conditions. Principal Component Analysis found all investigated sites to follow the same pattern of changes. Mean winter temperature, annual temperature and precipitation were found to have a strong positive correlation with the occurrence of thermophilus temperate broadleaved trees (hazel, linden, and ash) typical for the mid-Eemian optimum. These three factors also have a negative correlation with the presence of cold tolerant boreal trees (birch and pine) and open land taxa characteristic of the beginning and end of the interglacial. Mean July temperature was found to be positively correlated with the occurrence of temperate broadleaved trees (oak, ash and elm) typical for early stages of the Eemian and negatively with that of coniferous trees (fir and spruce) characteristic for later stages of the interglacial.
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| 7. |
- Pidgeon, CR, et al.
(författare)
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Pump-probe measurement of lifetime engineering in SiGe quantum wells below the optical phonon energy
- 2005
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Ingår i: Semiconductor Science and Technology. - 0268-1242 .- 1361-6641. ; 20:10, s. L50-L52
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Tidskriftsartikel (refereegranskat)abstract
- We have directly determined with pump/probe spectroscopy the light hole (LH1) excited state lifetime for the lowest heavy hole to light hole intrawell subband transition (HH1-LH1) for three prototype samples of Si/SiGe strain-symmetrized multi-quantum well structures, designed to have the final LH1 state increasingly unconfined. The transition energy is below the optical phonon energy. We find that a decay time of 20 ps for sample 1 with a well width of 5.0 nm lengthens to 40 ps for sample 3 with a well width of 3.0 nm, in good agreement with the design. In addition, we have measured the lifetime for holes excited out of the well, from which we determine the lifetime for diagonal transitions (back into the well) to be of approx. several hundred picoseconds.
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| 8. |
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| 9. |
- Pidgeon, R. T., et al.
(författare)
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Annealing history of zircons from Apollo 14083 and 14303 impact breccias
- 2018
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Ingår i: Meteoritics and Planetary Science. - : John Wiley & Sons, Ltd (10.1111). - 1086-9379 .- 1945-5100. ; 53:12, s. 2632-2643
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Breccia boulders scattered around the 25 Ma Cone Crater near the Apollo 14 landing site provide a potential source of material ejected from the underlying Fra Mauro formation, which is interpreted to form from the ejecta blanket of the ~3.9 Ga Imbrium impact. However, questions remain as to whether all or some of the rocks collected are from the Fra Mauro Formation. In this contribution, we present new Raman measurements on zircons from impact breccias 14083 and 14303 that indicate a zircon radiation damage age of the breccias of 3900 ± 120 (2σ) Ma. These ages are compatible with a history of thermal shock during their emplacement as part of the Imbrium impact ejecta blanket. In contrast, previously published Raman analyses of zircons from a sample of breccia 14311 have a younger radiation damage age of 3410 ± 80 (2σ) Ma, confirming that this breccia had a different thermal history and was possibly unrelated to the Fra Mauro Formation. The radiation damage ages of breccias 14083 and 14303, in combination with previously published apatite U-Pb ages, place constraints on the thermal conditions within the Imbrium ejecta blanket.
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| 10. |
- Virtasalo, J.J., et al.
(författare)
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Pyritic event beds and sulfidized Fe (oxyhydr)oxide aggregates in metalliferous black mudstones of the Paleoproterozoic Talvivaara formation, Finland
- 2015
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 432, s. 449-460
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Tidskriftsartikel (refereegranskat)abstract
- The Paleoproterozoic, 2.0–1.9 Ga Talvivaara formation of Finland was deposited during the Shunga Event, a worldwide episode of enhanced accumulation of organic-rich sediments in the aftermath of the Lomagundi–Jatuli carbon isotope excursion. Sulfidic carbonaceous mudstones in the Talvivaara formation contain one of the largest known shale-hosted nickel deposits. In order to gain new insight into this Shungian sedimentary environment, sedimentological, petrographical and in situ S and Fe isotopic microanalyses were carried out on samples representing depositional and early-diagenetic conditions. The event-bedded lithology with tidal signatures in the organic-rich mudstones strongly indicates deposition from predominantly river-delivered mud on a highly-productive coastal area, below storm-wave base. The riverine supply of phosphorus, sulfate and iron supported high primary productivity and resulted in strong lateral and vertical chemical gradients in the nearshore waters with a shallow oxic surface layer underlain by euxinic water. The stratigraphic upper part of the Talvivaara formation contains banded intervals of thin alternating pyrite beds and carbonaceous mudstone beds. The pyrite beds were deposited by seaward excursions of the concentrated, acidic Fe-rich river plume subsequent to droughts or dry seasons, which led to intense pyrite precipitation upon mixing with euxinic waters. δS34 and δFe56 values of the bedded pyrite (median δS34=−10.3‰ and δFe56=−0.79‰) are consistent with the reaction of dissolved Fe(II) with H2S from bacterial sulfate reduction. Organic-rich clayey Fe-monosulfide-bearing granules were transported from the muddy estuary, and enclosed in Fe (oxyhydr)oxide aggregates that were forming by wave and current reworking in nearshore accumulations of river-delivered iron. The isotopic composition of these presently pyrrhotitic inclusions (median δS34=−3.3‰ and δFe56=−1.6‰) indicates microbial iron reduction. The Fe (oxyhydr)oxide aggregates were transported in muddy debris flows to the distal euxinic seafloor. Their Fe (oxyhydr)oxide matrix was replaced by pyrite (median δS34=+5.8‰ and δFe56=+0.81‰) at shallow sediment depths with 34S and 56Fe-enriched porewater. Wavy-crinkly laminae of possible microbial origin developed on the euxinic seafloor during low sedimentation. These results indicate episodic deposition at seasonal to multiannual time scales. δS34 and δFe56 values in the studied Fe-sulfides provide evidence of microbial isotope fractionation processes and syndepositional and early-diagenetic origin, finding no support for the previously proposed local hydrothermal activity in the Talvivaara mudstones.
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| 11. |
- Virto, Carmen, et al.
(författare)
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Catalytic activity of noncovalent complexes of horse liver alcohol dehydrogenase, NAD+ and polymers, dissolved or suspended in organic solvents
- 1995
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Ingår i: Biotechnology Letters. - 0141-5492. ; 17:8, s. 877-882
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Tidskriftsartikel (refereegranskat)abstract
- Noncovalent complexes were formed by lyophilization of aqueous solutions containing horse liver alcohol dehydrogenase, NAD+ and a polymer [ethyl cellulose or poly(vinyl butyral)]. The complexes expressed higher specific catalytic activity in organic solvents as compared to a corresponding amount of enzyme deposited on to Celite or lyophilized enzyme powder. The noncovalent complexes were soluble in toluene. In butyl acetate and methyl t-butyl ether, suspensions of fine particles were formed.
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| 12. |
- Virto, Carmen, et al.
(författare)
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Enzymatic synthesis of lysophosphatidic acid and phosphatidic acid
- 1999
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 24:10, s. 651-658
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Tidskriftsartikel (refereegranskat)abstract
- Immobilised 1,3-specific lipase from Rhizopus arrhizus was used as catalyst for the esterification of dl-glycero-3-phosphate and fatty acid or fatty acid vinyl ester in a solvent-free system. With lauric acid vinyl ester as acyl donor, a(w)<0.53 favored the synthesis of lysophosphatidic acid (1-acyl-rac-glycero-3-phosphate, LPA1) and the spontaneous acyl migration of the fatty acid on the molecule. Subsequent acylation by the enzyme resulted in high phosphatidic acid (1,2-diacyl-rac-glycero-3-phosphate, PA) formation and high total conversions (>95%). With oleic acid, maximum conversions of 55% were obtained at low water activities. Temperatures below melting point of the product favored precipitation and resulted in high final conversion and high product ratio [LPA/(PA+LPA)]. Thus, LPA was the only product with lauric acid vinyl ester as acyl donor at 25°C. Increased substrate ratio (dl-glycero-3-phosphate/fatty acid) from 0.05 to 1 resulted in a higher ratio of LPA to PA formed, but a lower total conversion of dl-glycero-3-phosphate. Increased amounts of enzyme preparation did not result in higher esterification rates, probably due to high mass-transfer limitations. Copyright (C) 1999 Elsevier Science Inc. All rights reserved.
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