Water activity dependence of lipase catalysis in organic media explains successful transesterification reactions

The water activity dependence of lipase kinetics in organic media was evaluated using lipases from Rhizopus oryzae and Candida rugosa immobilised on polypropene EP-100. The conversion studied was the transesterification of ethyl decanoate to hexyl decanoate with hydrolysis to decanoic acid as competing reaction. The reactions were carried out at controlled water activity in diisopropyl ether. Substrate inhibition was observed at hexanol concentrations of 100 mM or higher. The Rhizopus lipase expressed the highest activity and the best selectivity for transesterification at the lowest water activity (a_w=0.06). The Candida lipase expressed the highest transesterification/hydrolysis ratio at a_w=0.11 and the highest total activity at a_w=0.53. Several glycosidases previously tested under conditions similar to those used here expressed both maximal total activity and the best selectivity at water activities close to 1.0. The water activity dependence of the lipases is thus fundamentally different from that of glycosidases and it is a major part of the reason why lipases are more suited for transferase-type reactions than the glycosidases.     

Controlling the hydration of covalently immobilised penicillin G amidase in low-water medium: properties and use of Celite R-640

The study describes how Celite R-640 adsorbs liquid water in toluene and vapour water from a gas phase. In toluene, Celite R-640 is able to maintain the water activity (a_w) constant within broad ranges of water concentrations. The a_w values are strongly related to the original hydration of the Celite batches, but prolonged drying confers comparable and reproducible properties to the different batches. The use of Celite R-640 in controlling the hydration and activity of covalently immobilised PGA in toluene is reported.     

Compared esterification kinetics of the lipase from Burkholderia cepacia either free or encapsulated in a silica aerogel

This paper presents an experimental comparison of the kinetics of esterification catalyzed with the lipase from Burkholderia cepacia, either free, or encapsulated in a silica aerogel dried by the supercritical CO₂ method. The operational characteristics, in terms of pre-equilibration at given water thermodynamic activity a_w, mass of enzyme in the gel, size of aerogel particles, are presented. The kinetic model known as BiBi Ping Pong with inhibition by both substrates has been found to fit relatively well with the experimental results, except when both substrate concentrations were high with the encapsulated enzyme. All kinetics constants were found to be increased by aerogel encapsulation. In particular V_max was increased by a factor of the order of 10 per mg of enzyme.     

Solid substrate cultivation of Gibberella fujikuroi on an inert support

Growth of Gibberella fujikuroi on Amberlite, an inert support, and gibberellic acid (GA₃) production was studied in glass columns under different conditions of temperature and water activity (a_w). Maximum biomass concentration and GA₃ production were respectively 40 (mg/g inert support) and 0.73 (mg/g inert support). While high specific growth rates were obtained, low initial nitrogen resulted in low biomass concentrations. Maximum GA₃ (31°C, a_w=0.985) was not produced by the maximum concentration of biomass (25°C, a_w=0.992). Peaks in the rate curves of either outlet gas, CO₂ or O₂, occurred on exhaustion of urea indicating, for future works, just when to feed the culture additional nitrogen.     

Water activity as a key parameter of synthesis reactions: The example of lipase in biphasic (liquid/solid) media

Ester synthesis catalyzed by Candida cylindracea lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) was investigated in solid/liquid biphasic media containing the enzyme preparation and reactants without addition of organic solvents not participating in the reaction. Although the effects of water on enzyme kinetics have been abundantly studied in nearly anhydrous media, reactions in which water is produced have not been investigated. The effect of water produced by the reaction itself on the enzymatic activity was studied. The dispersion of water in a shaken, nearly anhydrous medium was shown to be responsible for the lack of activity of the enzyme. In contrast, when slowly shaken, the enzyme was fully activated by the water furnished as a product of the reaction. However, when experiments were performed in a two-phase aqueous/organic system with previously solubilized enzyme in water, the enzyme activity was increased by shaking and was of the same order of magnitude as in nearly anhydrous media. Under low water activity conditions, a powerful agitation can lead to slower reaction rate, because water, a product of esterification, is not retained in the microenvironment of the enzyme to activate it. The activation effect of water produced by the reaction was clearly shown using enzyme preparations shaken in an anhydrous medium and previously equilibrated at low water activities (a_w = 0.13 and 0.69). This activation did not occur for an enzyme preparation equilibrated at high a_w (0.89) or for a preparation gently shaken in a water-saturated medium. The lag time preceding activation of the enzyme increased with the extent of enzyme dehydration. The mass of the enzyme preparation was shown to be a parameter affecting the capacity of the lipase to produce enough water in its immediate environment. The lack of activity observed for a small quantity of enzyme was eliminated by addition of heat-denaturated lipase.     

Catalysis by amine oxidases in nonaqueous media

The synthetic potential of amine oxidases was examined in different reaction systems, ranging from aqueous solutions to organic solvents with low water content. Substantial conversion was achieved in biphasic systems, which eliminated the product inhibition observed in the aqueous system. The conversion was particularly high in the more hydrophobic solvents. The use of low water systems was studied using amine oxidase immobilized on celite and pre-equilibrated in a salt hydrate environment to reach a constant water activity. Addition of water in the solvent was shown to be unnecessary, with significant conversion being attained through the water supplied by pre-equilibration of the immobilized enzyme at a_w=0.55. The use of organic solvent-containing reaction systems thus presents a convenient method for oxidising poorly water-soluble amines using amine oxidases.     

昆诺阿藜链格孢叶斑病病原及其生物学特性

为明确昆诺阿藜链格孢叶斑病病原,在山西省昆诺阿藜种植区采集典型症状的标本分离病原菌,选择代表性菌株LGB-b和LGB-h对其形态学、分子生物学、致病性及生物学特性进行了研究。综合形态学和多基因系统发育(Alt a 1、endoPG 和OPA10-2)分析,确定昆诺阿藜链格孢叶斑病病原为Alternaria alternata。致病性测定发现接种6 d后病斑呈灰绿至黄绿色,表面具有灰棕至灰褐色霉层,周围具黄绿色晕圈,与田间症状基本一致。菌株LGB-b和LGB-h均可侵染昆诺阿藜、藜和台湾藜。菌株LGB-b菌丝生长的最适培养基为V8 蔬菜汁琼脂培养基(V8)、温度为25-30 ℃、水活度≥0.98、pH为6-7;分生孢子萌发的最适水活度≥0.98、pH为6-7。菌株LGB-h菌丝生长的最适培养基为马铃薯胡萝卜琼脂培养基(PCA)、温度为20-25 ℃、水活度≥0.98、pH为6-7;分生孢子萌发的最适水活度≥0.98、pH为7-8。     

Characterisation of optimum cultural environmental conditions for the production of high numbers of Metarhizium anisopliae blastospores with enhanced ecological fitness

The aim of this study was the production of high numbers of M. anisopliae blastospores with enhanced germination efficiency under conditions of water-stress (ecological fitness). Different nitrogen sources and concentrations were screened for their ability to induce blastospore production while keeping pH and water activity (a_w) at fixed levels (6.8, and 0.98 a_w, respectively). After optimum nitrogen status was determined (cornsteep solid (CS) + yeast extract (YE); or cottonseed flour (CF) + YE), the effect of interaction of nitrogen source, pH (3.5, 5, 6.8, 8, 9 and 10) and solutes for a_w adjustment (KCl, NaCl, PEG 200) on blastospore production, endogenous polyol content (glycerol, erythritol, arabitol and mannitol) and total protein, were determined. For both ionic (NaCl, KCl) and non-ionic solutes (PEG 200), optimum blastospore production (between 4×10⁷ and 2×10⁸ blastospores ml^-1) and growth occurred in the pH range 6.8-8, with the CF + YE nitrogen profile giving higher yields than CS + YE. Optimum conditions for high erythritol and total protein endogenous concentrations (40.37-73.44 and 14.33-18.90 mg g^-1 fresh weight, respectively) occurred between pH 6.8 and 8 by ionic a_w modification (KCl, NaCl) and with the CF + YE nitrogen profile. Germination of blastospores produced under these cultural conditions was between 62 and 89% under conditions of water-stress (0.96 a_w). On the other hand, blastospores with lower amounts of erythritol and total protein content had decreased germination (8-67%). These results could have significant implications for developing a liquid fermentation medium for the production of high numbers of fungal propagules with enhanced efficacy under non-optimum environmental conditions.     

Chemical Modification Causes Similar Change in Dependence on Water Activity of Chymotrypsin Hydration and Catalysis in Hexane

Amino groups in alpha-chymotrypsin were reacted with pyromellitic anhydride, introducing 17 to 32 additional carboxyl groups. This modification causes a major change in the water adsorption isotherm of the lyophilized protein powder. Little water is bound by the modified enzyme at water activity (a_w) below 0.35, but it shows increased water binding at a_w over 0.5. This correlates with a similar change in the a_w dependence of the catalytic activity of the enzyme powder suspended in hexane, with a much steeper increase in activity of the modified chymotrypsin.     

Response surface modelling of the production of ω-3 polyunsaturated fatty acids-enriched fats by a commercial immobilized lipase

The aim of this study was to model the production of fats, enriched with ω-3 polyunsaturated fatty acids (ω-3 PUFA) for nutraceutical purposes, via the response surface methodology. These fats were obtained by transesterification of palm oil stearin (POS) with a concentrate (EPAX 2050TG) of triglycerides enriched with ω-3 PUFA and soybean oil, catalysed by a commercial immobilized Candida antarctica lipase (“Novozym 435”).

The initial water activity (a_w) of the biocatalyst, POS and EPAX 2050TG concentrations, time and temperature showed a significant effect on the transesterification reaction, as well as on the competing reactions of hydrolysis and lipid oxidation.

Depending on the factors included, the transesterification reaction was described either by first- or second-order models.

The production of free fatty acids, which is ascribed both to the hydrolytic reaction and the mechanism of lipase-catalysed transesterification, showed a second-order dependence on the initial a_w of the biocatalyst.     

Comparative behaviour of proteinases from the latex of Carica papaya and Funastrum clausum as catalysts for the synthesis of Z-Ala-Phe-OMe

The proteolytic extract obtained from the latex of Funastrum clausum (Jacq.) Schlechter (Asclepiadaceae), a South American climbing plant, was assayed as a novel catalyst for peptide synthesis and compared with commercial papain under the same conditions. After immobilization on polyamide, the synthesis of the bitter peptide precursor Z-Ala-Phe-OMe was performed and different conditions were tried. Acetonitrile and ethyl acetate with low water content were tested as organic solvents. Equilibrium- and kinetically-controlled synthesis were tried by using either Z-Ala-OH or Z-Ala-OMe as acyl donors, respectively. The best conditions for the synthesis of the desired product varied according to the catalyst used. For papain, thermodynamic control in acetonitrile (a_w  0.12) in the presence of triethylamine (TEA) or boric acid–borate buffer (40 mM), and equilibrium- and kinetic-controlled synthesis in ethyl acetate (a_w  0.75) proved to be the best conditions. The thermodynamic control in either acetonitrile with a_w  0.12 (40 mM TEA or Na₂CO₃) or ethyl acetate (a_w  0.75) were the best conditions found for funastrain. In all cases, the formation of oligopeptides up to three Phe was observed. The proteolytic extract of F. clausum latex showed more selectivity than papain towards the conversion to Z-Ala-Phe-OMe leading to less proportion of oligopeptides.     

Study of the effects of temperature, pH, NaCl, and aw on the proteolytic and lipolytic activities of cheese-related lactic acid bacteria by quadratic response surface methodology

The individual and interactive effects of temperature, pH, NaCl, and a_w on the proteolytic and lipolytic activities of Lactobacillus delbrueckii subsp. bulgaricus B397, Lactococcus lactis subsp. lactis T12, and Lb. plantarum 2739 were studied by quadratic response surface methodology. The effects on enzyme activities depended on the interactions among the independent variables, type of activity, substrate and, especially, species. The proteinase activity of strains B397 and T12 was affected differently by pH as individual or interactive terms depending on the type of substrate _sl- or β-casein. The increase of NaCl concentration (2.5–7.5%) under cheese-like conditions had a negative effect on the proteinase activity of strain T12. The effect of NaCl was related to the corresponding decrease in a_w. Aminopeptidases N and A, iminopeptidase and endopeptidase of Lc. lactis subsp. lactis T12 were strongly inhibited by pH 5–6 and NaCl concentration higher than 3.75%. The negative effects of these independent variables was in several cases enhanced by their interaction and/or by the interaction with the lowest temperatures. In contrast, the same peptidases of Lb. plantarum 2739 retained a high activity under the very hostile environmental conditions. Iminopeptidase and especially endopeptidase activities of strain 2739 were stimulated slightly by NaCl at concentrations up to 5%. Lipase/esterase activity of Lb. delbrueckii subsp. bulgaricus B397 was markedly inhibited under cheese-like conditions.     

Enhancing carrot somatic embryos survival during slow dehydration, by encapsulation and control of dehydration

In order to obtain dry artificial seeds, carrot somatic embryos were encapsulated and dehydrated. Encapsulation in some hydrogels delayed the dehydration and preserved the water content of carrot somatic embryos. In particular, a matrix made of alginate with gellan gum was found to be the most efficient in maintaining a high water activity (a_w) around somatic embryos. By delaying dehydration, and also rehydration, encapsulation seemed to protect somatic embryos against desiccation and imbibition damages, giving better germination and emergence of cotyledons. Matrices made of alginate mixed with kaolin or gellan gum were particularly adapted to protect the embryos during the dehydration. Apart from the matrix composition, the control of dehydration speed enhanced the survival and regeneration of encapsulated-dehydrated somatic embryos. Using a slow dehydration protocol (95-15% RH—relative humidity into the chamber—in 11.5 days), it was possible to exert different dehydration speeds. Slowing the dehydration between 70 and 45% RH stabilized the water activity (a_w) of the encapsulation matrix, and enhanced the survival and regeneration frequencies of encapsulated-dehydrated embryos. In the absence of any maturing pretreatment, alginate-gellan gum encapsulated carrot somatic embryos, dehydrated to 15% RH, and rehydrated in moistured air (90% RH), germinated up to 72.9%. Therefore, encapsulation in alginate-gellan gum, combined with a slow dehydration, leads to enhance the somatic embryos' desiccation tolerance.     

Wax esters synthesis from heavy fraction of sheep milk fat and cetyl alcohol by immobilised lipases

Wax esters were obtained from lipase-catalysed alcoholysis of triglycerides with cetyl alcohol, using n-hexane as solvent. The heavy triglyceride fraction (HTF), obtained by fractionation of sheep milk fat, was used as raw material. In the natural fat mixture GC analysis showed that palmitic, myristic, stearic and oleic acids are the most abundant fatty acids which are useful to produce wax esters. Reactions were tested for different amounts of Lipozyme RMIM catalyst, and the optimum concentration of 10 mg catalyst/ml solution has been determined. The formation of the four main products, i.e. cetyl myristate, cetyl palmitate, cetyl oleate and cetyl stearate, was determined by HPLC/ELSD quantitative analysis. The optimum water activity in the reaction medium a_w=0.35 in the case of Lipozyme RMIM, and a_w=0.53 for Novozym 435 was found. Lipozyme RMIM (immobilised sn-1,3-specific lipase from Rhizomucor miehei) was more active than Novozym 435 (immobilised nonspecific lipase-B from Candida antarctica) towards wax esters production. The acyl migration of 2-monoglycerides was suggested as a crucial step to explain the higher yields produced by the 1,3-specific lipase.     

Control of enzyme ionization state in supercritical ethane by sodium/proton solid-state acid–base buffers

We have previously demonstrated that a solid-state buffer could be successfully used to control the ionization state of subtilisin Carlsberg cross-linked microcrystals (CLECs) suspended in supercritical ethane (sc-ethane) in the presence of acid–base active species such as salt hydrates and zeolite molecular sieves. Here we studied the effect of six zwitterionic proton/sodium (pH–pNa) solid-state acid–base buffers on the catalytic activity of subtilisin CLECs in sc-ethane at high and low water activity (a_W). CLECs were strongly activated by increasing a_W. At high a_W, and despite the high hydrolysis rates, transesterification activities were still about one order of magnitude higher than those observed at lower a_W. This is in contradiction with what was previously reported in the absence of acid–base control and supports the hypothesis that the poor catalytic performance of subtilisin CLECs at high a_W observed in those studies was due to the inhibitory effect of the hydrolytic by-product, rather than to the competition of water with propanol for the acyl-enzyme intermediate. Although the catalytic activity of subtilisin showed a general positive correlation with the aqueous pK_a of the acid–base buffers tested here, our results also show that as expected, the acid–base behavior of the buffers in nonaqueous media is more complex than what can be predicted from aqueous-based parameters alone. This work further confirms the usefulness of solid-state acid–base buffers in supercritical biocatalysis but highlights the need for further research on the topic.     

Reactions Catalyzed by Peg-Modified α-Chymotrypsin in Organic Solvents. Influence of Water Content and Degree of Modification

-Chymotrypsin was modified with cyanuric chloride activated monomethoxypolyethylene glycol (MPEG) with molecular weights 1900 and 5000. Using the higher molecular weight MPEG a product that was soluble in benzene at moderate levels of modification was obtained, whereas with MPEG 1900 almost all the enzyme's amino groups had to be modified for dissolving the conjugate. The catalytic activity decreased with increasing degree of substitution. Apparent V_max was considerably higher for the less modified enzyme preparation than for the more modified one, while K_m,app stayed almost constant. The modified enzyme was used for peptide synthesis. The reaction was dependent on the content of dissolved water. Both V_max,app and K_m,app increased with increasing water content. It was possible to achieve a process with complete conversion of substrate to dipeptide.     

Azide inhibition of mitochondrial electron transport I. The aerobic steady state of succinate oxidation

The azide inhibition of the succinate oxidase activity of rat-liver mitochondria is specific for active (State 3) respiration with no observable inhibition of resting (State 4) respiration. In the range of azide concentrations which inhibit State 3 to rates less than those of State 4, a negative control of respiration by ADP and inorganic phosphate is observed. The inhibition is specific for a site between cytochromes a and a₃, causing a crossover between these two cytochromes with cytochrome a becoming reduced and cytochrome a₃ remaining highly oxidized. Trapped steady-state difference spectra at liquid nitrogen temperatures show that the reduced cytochrome a in the azide-inhibited system has an band at 596 mμ, 6 m μ displaced from its usual position at 602 mμ.

The azide inhibition is released by uncouplers of oxidative phosphorylation such that the uncoupled respiration requires up to ten times as much azide as does coupled (State 3) respiration for comparable inhibition. The release of inhibition by uncouplers occurs with no change in the steady-state concentration of reduced cytochrome a₅₉₆ and the increased respiration is attributed to an increased rate of oxidation of the cytochrome a₅₉₆. This cytochrome is postulated to be either an intermediate in electron transport and energy conservation reactions or an azide compound of such an intermediate.     

Activation by reduction of the resting form of cytochrome c oxidase: Tests of different models and evidence for the involvement of CuB

(1) The reaction of the resting form of oxidised cytochrome c oxidase from ox heart with dithionite has been studied in the presence and absence of cyanide. In both cases, cytochrome a reduction in 0.1 M phosphate (pH 7) occurs at a rate of 8.2 · 10⁴ M⁻¹ · s⁻¹. In the absence of cyanide, ferrocytochrome a₃ appears at a rate (k_obs) of 0.016 s⁻¹. Ferricytochrome a₃ maintains its 418 nm Soret maximum until reduced. The rate of a₃ reduction is independent of dithionite concentration over a range 0.9 mM–131 mM. In the presence or cyanide, visible and EPR spectral changes indicate the formation of a ferric a₃/cyanide complex occurs at the same rate as a₃ reduction in the absence of cyanide. A g = 3.6 signal appears at the same time as the decay of a g = 6 signal. No EPR signals which could be attributed to copper in any significant amounts could be detected after dithionite addition, either in the presence or absence of cyanide. (2) Addition of dithionite to cytochrome oxidase at various times following induction of turnover with ascorbate/TMPD, results in a biphasic reduction of cytochrome a₃ with an increasing proportion of the fast phase of reduction occurring after longer turnover times. At the same time, the predominant steady state species of ferri-cytochrome a₃ shifts from high to low spin and the steady-state level of reduction of cytochrome a drops indicating a shift in population of the enzyme molecules to a species with fast turnover. In the final activated form, oxygen is not required for fast internal electron transfer to cytochrome a₃. In addition, oxygen does not induce further electron uptake in samples of resting cytochrome oxidase reduced under anaerobic conditions in the presence of cyanide. Both findings are contrary to predictions of certain O-loop types of mechanism for proton translocation. (3) A measurement of electron entry into the resting form of cytochrome oxidase in the presence of cyanide, using TMPD or cytochrome c under anaerobic conditions, shows that three electrons per oxidase enter below a redox potential of around +200 mV. An initial fast entry of two electrons is followed by a slow (k_obs ≈ 0.02 s) entry of a third electron. Above +200 mV, the number of electrons taken up in the initial fast phase drops as a redox center (presumably Cu_A) titrates with an apparent mid-point potential of +240 mV. The slow phase of reduction remains at the more positive redox values. (4) The results are interpreted in terms of an initial fast reduction of cytochrome a (and Cu_A at redox values more negative than +240 mV) followed by a slow reduction of Cu_B. Cu_B reduction is proposed to spin-uncouple cytochrome a₃ to form a cyanide sensitive center, and trigger a conformational change to an activated form of the enzyme with faster intramolecular electron transfer.     

Calcium-induced formation of chlorophyll b and light-harvesting chlorophyll a/b-protein complex in cucumber cotyledons in the dark

Dark-grown cucumber seedlings were exposed to intermittent light (2 min light and 98 min dark) and then cotyledons were incubated with 50 mM CaCl₂ in the dark. Chlorophyll (Chl) a was selectively accumulated under intermittent light and Chl b was accumulated during the subsequent dark incubation with CaCl₂. The change in chlorophyll-protein complexes during Chl b accumulation induced by CaCl₂ in the dark was investigated by SDS-polyacrylamide gel electrophoresis. Chlorophyll-protein complex I and free chlorophyll were major chlorophyll-containing bands of the cotyledons intermittently illuminated 10 times. When these cotyledons were incubated with CaCl₂ in the dark, the light-harvesting Chl a/b-protein complex was formed. When the number of intermittent illumination periods was extended to 55, small amounts of Chl b and light-harvesting Chl a/b-protein complex were recognized at the end of intermittent light treatment, and these two pigments were further increased during the subsequent incubation of the cotyledons with CaCl₂ in the dark compared to water controls.     

Structures and magnetism of rubidium and cesium salts of dimeric oxovanadium(IV) tartrate(4−) complexes

Complexes of type A₄[VO(tart)]₂·nH₂O, where A = Rb or Cs and tart =d,l-tartrate(4−) (n = 2) or d,d-tartrate(4−) (n = 2 for Rb and n = 3 for Cs), were prepared from an aqueous mixture of V₂O₅, AOH and H₄tart. These complexes were studied by single-crystal X-ray diffraction methods: Rb₄[VO(d,l-tart)]₂·2H₂O, space group P1 with a = 8.156(1),b = 8.246(1),c = 8.719(1)Å, = 66.09(1)°, β = 65.07(1)°, γ = 82.40(1)°,Z = 2, 1917 observed reflections, and final R_w = 0.035; Cs₄[VO(d,l-tart)]₂·2H₂O, space group P₂₁/c with a = 9.350(1),b = 13.728(2),c = 8.479(1)Å, β = 106.77(1)°,Z = 4, 2235 observed reflections, and final R_w = 0.054; Rb₄[VO(d,d-tart)]₂·2H₂O, space group P₄₁₂₂ with a = 8.072(1),c = 32.006(3)Å,Z = 8, 1014 observed reflections and final R_w = 0.038; Cs₄[VO(d,d-tart)]₂·3H₂O, space group P₁₂₂ with a = 8.184(1),c = 33.680(5)Å,Z = 8, 1310 observed reflections, and final R_w = 0.063. Bulk magnetic susceptibility data (1.5–300 K) for these compounds and A₄[VOl,l-tart)]₂·nH₂O (A = Rb, Cs) were obtained on polycrystalline samples. These data were analyzed in terms of a Van Vleck exchange coupled S = 1/2 model which was modified to include an interdimer exchange parameters Θ. Analysis of the low-temperature (1.5–20 K) susceptibility data gave 2J = +1.30 cm⁻¹ and Θ = −1.86 K for Rb₄[VO(d,l-tart)]₂·2H₂O, 2J = +1.16 cm⁻¹ and Θ = −1.69 K for Cs₄[VO(d,l-tart)]₂·2H₂O, 2J = +1.90 cm⁻¹ and Θ = −0.82 K for Rb₄[VO(d,d-tart)]₂·2H₂O, 2J = +2.04 cm⁻¹ and Θ = −0.80 K for Rb₄[VO(l,l-tart)]₂·2H₂O, 2J = +1.52 cm⁻¹ and Θ = −0.25 K for Cs₄[VO(d,d-tart)]₂·3H₂O, and 2J = +1.64 cm⁻¹ and Θ = −0.31 K for Cs₄[VO(l,l-tart)]₂·3H₂O. These results suggest the magnitudes of intradimer (ferromagnetic and interdimer (antiferromagnetic) exchange interactions are similar in these complexes, as observed for the analogous Na salts.