Oxidative Stability of Polyunsaturated Fatty Acids in an Aqueous Solution

The relative oxidative stability of six kinds of typical polyunsaturated fatty acids (PUFAs) was investigated in an aqueous solution (pH=7.4 at 37°C) with Fe²⁺-ascorbic acid as a catalyst. The highest stability was shown by docosahexaenoic acid (22: 6n-3, DHA), followed by eicosapentaenoic (20: 5n-3), arachidonic (20: 4n-6), α-linolenic (18: 3n-3), γ-linolenic (18: 3n-6), and linoleic (18: 2n-6, LA) acids, indicating that the stability increased with increasing degree of unsaturation. The significant difference found between α-linolenic and γ-linolenic acids also suggests the higher oxidative stability of n-3 PUFAs than of n-6 PUFAs in an aqueous solution. Moreover, when a mixture of DHA and LA was oxidized in an aqueous solution, the stability increased with increasing molar ratio of DHA to LA in the mixture. This characteristic oxidative stability of PUFAs in the aqueous phase is quite different from that in the neat phase, and can be explained by correlating with the conformation of PUFAs in the aqueous medium.     

Ionization and phase behavior of fatty acids in water: application of the Gibbs phase rule

The phase behavior of several medium-chain (10- and 12-carbon) and long-chain (18-carbon) fatty acids in water was examined as a function of the ionization state of the carboxyl group. Equilibrium titration curves were generated above and below fatty acid and acid-soap chain melting temperatures and critical micelle concentrations, and the phases formed were characterized by X-ray diffraction, 13C NMR spectroscopy, and phase-contrast and polarized light microscopy. The resulting titration curves were divided into five regions: (i) at pH values less than 7, a two-phase region containing oil or fatty acid crystals and an aqueous phase; (ii) at pH approximately 7, a three-phase region containing oil, lamellar, and aqueous (or fatty acid crystals, 1:1 acid-soap crystals, and aqueous) phases; (iii) between pH 7 and 9, a two-phase region containing a lamellar fatty acid/soap (or crystalline 1:1 acid-soap) phase in an aqueous phase; (iv) at pH approximately 9, a three-phase region containing lamellar fatty acid-soap (or crystalline 1:1 acid-soap), micellar, and aqueous phases; and (v) at pH values greater than 9, a two-phase region containing micellar and aqueous phases. Interpretation of the results using the Gibbs phase rule indicated that, for oleic acid/potassium oleate, the composition of the lamellar fatty acid/soap phase varied from approximately 1:1 to 1:3 un-ionized to ionized fatty acid species. In addition, constant pH regions observed in titration curves were a result of thermodynamic invariance (zero degrees of freedom) rather than buffering capacity. The results provide insights into the physical states of fatty acids in biological systems.(ABSTRACT TRUNCATED AT 250 WORDS)     

Polyethylene glycol-modified hemin having peroxidase activity in organic solvents

Hemin, having two carboxyl groups, was coupled with monomethoxypolyethylene glycol, PEG, through the ester bond formed with carbodiimide. The PEG-modified hemin was readily soluble not only in neutral aqueous solution but also in organic solvents. Its absorption spectrum in 1,1,1-trichloroethane showed a sharp Soret band at 398 nm. The modified hemin catalyzed the peroxidase-reaction in organic solvent and in aqueous solution using hydrogen peroxide or peroxidized linolenic acid as hydrogen acceptor and o-phenylene diamine as hydrogen donor. The activity of PEG-hemin in 1,1,1-trichloroethane was greater than that in an aqueous solution; k1 values in 1,1,1-trichloroethane were 2.3 X 10(3) M-1 sec-1 with hydrogen peroxide and 7.0 X 10(2) M-1 sec-1 with peroxidized linolenic acid, and the value in an aqueous solution was 3.0 X 10 M-1 sec-1 with hydrogen peroxide.     

Effect of the cation and the anion of an electrolyte on the solubility of DL-aminobutyric acid in aqueous solutions: measurement and modelling

The solubilities at 298.2 K of dl-aminobutyric acid in aqueous solutions of NaCl, KCl, NaNO(3) and KNO(3) were measured. The solubility of DL-aminobutyric acid was found to be influenced by the concentration and by the nature of both the cation and the anion of the electrolyte. Comparison of the results obtained in this study and those for other amino acids reported in the literature, indicates that the structure of the hydrocarbon backbone of an amino acid plays an important role in the interactions of an amino acid with an electrolyte. A thermodynamic model has been used to correlate the solubilities of DL-aminobutyric acid in aqueous electrolyte solutions. The activity coefficients of the amino acid in the electrolyte solutions, were represented by a model proposed by Khoshkbarchi and Vera [M.K. Khoshkbarchi, J.H. Vera, AIChE J. 42 (1996) 2354; M.K. Khoshkbarchi, J.H. Vera, Ind. Eng. Chem. Res. 35 (1996) 4755]. This model, which considers a combination of both long- and short-range interactions, contains only two adjustable parameters. All other parameters are available in the literature. The model can accurately correlate the solubility of dl-aminobutyric acid in aqueous solutions of electrolytes.     

Alkylation by propylene oxide of deoxyribonucleic acid, adenine, guanosine and deoxyguanylic acid

1. Propylene oxide reacts with DNA in aqueous buffer solution at about neutral pH to yield two principal products, identified as 7-(2-hydroxypropyl)guanine and 3-(2-hydroxypropyl)adenine, which hydrolyse out of the alkylated DNA at neutral pH values at 37 degrees C. 2. These products were obtained in quantity by reactions between propylene oxide and guanosine or adenine respectively. 3. The reactions between propylene oxide and adenine in acetic acid were parallel to those between dimethyl sulphate and adenine in neutral aqueous solution; the alkylated positions in adenine in order of decreasing reactivity were N-3, N-1 and N-9. A method for separating these alkyladenines is described. 4. Deoxyguanylic acid sodium salt was alkylated at N-7 by propylene oxide in neutral aqueous solution. 5. The nature of the side chain in the principal alkylation products was established by mass spectrometry, and the nature of the products is consistent with their formation by the bimolecular reaction mechanism.     

生姜水浸液对生姜幼苗根际土壤酶活性、微生物群落结构及土壤养分的影响

本文以生姜为材料,研究生姜不同部位（根茎、茎和叶）、不同浓度（10、20、40和80 g L-1）的水浸液对生姜幼苗根际土的微生物数量、土壤酶活性及土壤养分含量的影响,并通过HPLC定量分析了生姜各部位水浸液中所含酚酸类（香草酸、丁香酸、对羟基苯甲酸、香豆酸和阿魏酸）、香豆素类（伞花内脂和7-甲氧基香豆素）化合物的含量。结果表明：三种生姜水浸液对所测六种土壤酶活性均产生了不同程度的影响,其中影响最大的是酸性磷酸酶和蔗糖酶,在10 g L-1 时就达到了显著性差异水平,并且所有酶均有随着水浸液浓度的增加而呈增大的趋势;相同部位的水浸液随着浓度的增加,细菌和真菌的数量呈增加趋势,而放线菌的数量呈减少趋势;三种生姜水浸液均随着浓度的增加降低了土壤中有机质的含量,加剧了土壤中硝态氮含量的积累,根茎水浸液对土壤有效磷、速效钾和铵态氮均显示出低浓度提高其含量而高浓度降低其含量的趋势,而茎和叶水浸液则随着浓度的增加均降低了其含量。生姜水浸液中主要化感成分包括：根茎水浸液主要是丁香酸和伞花内脂;茎水浸液主要是阿魏酸,且其含量最高为73.4 ug/g;叶水浸液除了阿魏酸,其他六种物质均被检测出,但含量较高的主要有丁香酸、伞花内脂和香豆酸。     

GABA interaction with lipids in organic medium

The interaction of 3H-GABA (gamma-aminobutyric acid and 14C-glutamate with lipids in an aqueous organic partition system was studied. With this partition system 3H-GABA and 14C-glutamate were able to interact with sphingomyelin, sulfatide, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine and phosphatidic acid but not with cholesterol or ceramide. In an homogeneous aqueous medium we could not demonstrate any interaction between 3H-GABA and lipids. The apparent dissociation constants (Kd) for 3H-GABA-lipids or 14C-glutamate-lipids interactions in organic medium were in the millimolar range and maximal charge (Bmax) between 3 and 7 moles of GABA or glutamate by mole of lipid. Amino acids such as glutamic acid, beta-alanine and glycine displaced 3H-GABA with the same potency as GABA itself; thus these results show that the interaction lacks pharmacological specificity. To detect this interaction lipid concentrations higher than 2 microM were required and in the partition system 3H-GABA and lipid phosphorus were both concentrated at the interface. Therefore lipids tested with a biphasic partition system do not fulfill the classical criteria for a neurotransmitter receptor at least not for GABA and glutamate.     

Thermodynamics of the conversion of aqueous L-aspartic acid to fumaric acid and ammonia

The thermodynamics of the conversion of aqueous L-aspartic acid to fumaric acid and ammonia have been investigated using both heat conduction microcalorimetry and high-pressure liquid chromatography. The reaction was carried out in aqueous phosphate buffer over the pH range 7.25-7.43, the temperature range 13-43 degrees C, and at ionic strengths varying from 0.066 to 0.366 mol kg(-1). The following values have been found for the conversion of aqueous L-aspartateH- to fumarate2- and NH4+ at 25 degrees C and at zero ionic strength: K = (1.48 +/- 0.10) x 10(-3), DeltaG degrees = 16.15 +/- 0.16 kJ mol(-1), DeltaH degrees = 24.5 +/- 1.0 kJ mol(-1), and DeltaC(p) degrees = -147 +/- 100 J mol(-1) K(-1). Calculations have also been performed which give values of the apparent equilibrium constant for the conversion of L-aspartic acid to fumaric acid and ammonia as a function of temperature, pH and ionic strength.     

The spectral and paramagnetic properties of oxyhemoglobin solutions UV-irradiated in the presence of ascorbic acid]

Absorption spectra and ESR of aqueous and aqueous/glyceric solutions of oxyhemoglobin exposed to UV radiation (250-400 nm) at 293 and 77 K in the presence of ascorbic acid have been analyzed. Vitamin C (5 x 10(-5) M) has been shown to exert a photoprotective effect with regard to oxyhemoglobin (2 x 10(-6) M) UV-irradiated with a dose of 0.86 x 10(5) J/m2 at 293 K. The photoprotective effect of ascorbic acid is also displayed after UV irradiation of frozen (77 K) aqueous/glyceric oxyhemoglobin solutions (2.53 x 10(-5) M). It is concluded that ascorbic acid can be a scavenger with respect to active UV-induced particles in protein systems, including O2-. and OH. Proposed is a mode of processes leading to UV inactivation of hemoprotein molecules.     

Coordination chemistry of vitamin C. Part II. Interaction of L-ascorbic acid with Zn(II), Cd(II), Hg(II), and Mn(II) ions in the solid state and in aqueous solution

The reaction of L-ascorbic acid with the zinc group and manganese ions has been investigated in aqueous solution at pH 6-7. The solid salts of the type M (L-ascorbate)2.2H2O, where M = Zn(II), Cd(II) and Mn(II) were isolated and characterized by 13C NMR and Fourier Transform infrared (FT-IR) spectroscopy. Spectroscopic evidence showed that in aqueous solution, the bindings of the Zn(II) and Mn(II) ions are through the ascorbate anion O-3 and O(2)-H groups (chelation), while the Cd(II) ion binding is via the O-3 atom only. In the solid state, the binding of these metal ions would be through two acid anions via O-3, O-2 of the first and O-1, O-3 of the second anion as well as to two H2O molecules, resulting in a six-coordinated metal ion. The Hg(II) ion interaction leads to the oxidation of the ascorbic acid in aqueous solution.     

Acid stability of anti-Helicobacter pyroli IgY in aqueous polyol solution

IgY was separated from a hen's egg yolk that was immunized with Helicobacter pyroli. The anti-H. pyroli IgY activity at acidic pH and the suppressive effect of polyol on acid-induced inactivation of IgY were investigated. Sorbitol and xylitol were used as polyols. IgY was quite stable at pH 5-7. Irreversible inactivation of IgY was observed at pH below 4, and proceeded rapidly at pH below 3. The acid stability of IgY was enhanced in the presence of 30% sorbitol or above. In a 50% aqueous sorbitol solution, an acid-induced inactivation was almost completely suppressed at pH 3. However, the improvement of IgY activity was not observed in the aqueous xylitol solution. IgY showed almost the same activity as native IgY when sucrose was substituted for sorbitol. On the other hand, the xylitol replacement with sucrose did not enhance the acid stability of IgY. The acid-induced inactivation of IgY was related to tryptophyl fluorescence. Fluorescence emission spectra suggested that structural changes near the tryptophan residues may occur under acidic conditions. An increase in sorbitol concentration induced a blue shift. The fluorescence emission of IgY in a 50% sorbitol solution had a peak at 330 nm, which was the same emission peak that was exhibited by native IgY. Sorbitol could, therefore, be used as a good stabilizer of IgY under acidic conditions.     

Studies in Plant Growth Hormones: V. CHROMATOGRAPHY OF HORMONES IN EXCISED AND INTACT ROOTS OF TOMATO SEEDLINGS

1. An examination has been made of the hormones present in extractsof excised roots and intact seedling roots of tomato. Acid andneutral ether-soluble fractions and the ether-insoluble aqueousfraction were chromatographed, and the chromatograms assayedusing oat coleoptile sections. 2. The pattern of hormone activity in excised roots differedlittle from that in seedling roots. 3. On chromatograms of the aqueous fraction developed in isopropanol/ammonia, growth promotion occurred at the position of 3-indolylaceticacid (IAA, Rf 0·5) and sometimes at the position of 3-indolylacetonitrile(IAN, Rf 0·8). When the IAA zone was eluted off the paperand rechromatographed, it formed the IAN zone and another zoneof promotion at Rf 0·1–0·2. 4. When the aqueous fraction was developed in n-butanol/ammonia,promotion occurred at the position of IAA (Rf 0·15),at Rf 0·5, and at the position of IAN (Rf 0-85). Thesezones have been called X, Y, and Z respectively. They were alsoformed when the IAA zone in wopropanol/ammonia was rechromatographedin ammoniacal n-butanol. It is shown that X and Y are interconvertible,and that each can form Z on rechromatography; also, there issome evidence that Z can form X and Y. When Z was separatedinto ether-soluble (acid and neutral) and ether-insoluble fractionswith sodium bicarbonate solution and chromatographed in iiopropanol/ammonia,growth resulted at the position of Z in the neutral and aqueousfractions, but in the acid fraction it occurred at Rf 0·24–O·35.Comparison with other chromatograms indicates that this lastzone does not occur in the aqueous fraction but has been formedas a result of extraction with sodium bicarbonate solution. 5. The zones found in the aqueous fraction also occurred insmall quantities in acid and neutral ethereal fractions in anumber of experiments. 6. The ethereal fractions gave no chromogenic reactions withferric chloride/ perchloric acid, nitrous/nitric acid, or p-dimethylaminobenzaldehyde(MeAB). In the aqueous fraction only MeAB gave a reaction (yellow)which showed any consistent correlation with biological activity.A yellow colour with this reagent is not a characteristic chromogenicreaction of indole compounds. It is suggested that a non-indolehormone system may be operating in tomato roots.     

Effect of lactic and citric acid on the stability of B-aflatoxins in extrusion-cooked sorghum

Aims:  To evaluate the effect of the extrusion-cooking process with the addition of different acids concentration on the stability of B-aflatoxins in sorghum.
Methods and Results:  Experimental units (EU) of sorghum flour contaminated with B-aflatoxins (140 ppb) were extrusion cooked with aqueous lactic or citric acid at six different concentrations. The effects of the two extrusion variables (moisture content and acid concentration) were analysed as a completely randomized factorial 3 × 6 design. Under some conditions, the aflatoxin reduction is more effective when using aqueous citric acid (up to 92%), than when using aqueous lactic acid (up to 67%).
Conclusions:  With citric acid, some extrusion treatments produced higher aflatoxin degradation rates, than those produced with lactic acid.
Significance and Impact of the Study:  Aflatoxin contamination is a great risk both for human as well as for animal health in underdeveloped countries; consequently, practical and economical detoxification procedures are needed that eliminate or at least minimize the aflatoxin risk, through lowering aflatoxin concentrations in grains. Under these considerations, extrusion process can be used for reduction in the aflatoxin content in contaminated grains.     

Viscosity B-coefficients and activation parameters for viscous flow of a solution of heptanedioic acid in aqueous sucrose solution

Viscosity and density data for the system of heptanedioic acid dissolved in aqueous sucrose solution at temperature range from 288.15 to 313.15 K have been measured. The viscosity B-coefficients for heptanedioic acid in aqueous sucrose solution has been calculated. The effect of temperature and sucrose concentration on the B-coefficients is discussed. On the basis of the Feakins equation, the activation parameters (Deltamu3++, DeltaH3++, DeltaS3++, DeltaG12(0)++, DeltaH12(0)++ and DeltaS12(0)++) for viscous flow of the solution have been evaluated, together with the Gibbs energy of transfer for the solute from the ground state solvent to the hypothetical viscous transition state solvent (DeltaG3++(1-1')). The effect of sucrose concentration and temperature on the activation parameters has been discussed.     

A Protargol Method for Staining Nerve Fibers in Frozen or Celloidin Sections

Extensive experimentation with protargol staining of neurons in celloidin and frozen sections of organs has resulted in the following technic: Fix tissue in 10% aqueous formalin. Cut celloidin sections IS to 25 μ, frozen sections 25 to 40 μ. Place sections for 24 hours in 50% alcohol to which 1% by volume of NH₄OH has been added. Transfer the sections directly into a 1% aqueous solution of protargol, containing 0.2 to 0.3 g. of electrolytic copper foil which has been coated with a 0.5% solution of celloidin, and allow to stand for 6 to 8 hours at 37° C. Caution: In this and the succeeding step the sections must not be allowed to come in contact with the copper. From aqueous protargol, place the sections for 24 to 48 hours at 37° C. directly into a pyridinated solution of alcoholic protargol (1.0% aqueous solution protargol, 50 ml.; 95% alcohol, 50 ml.; pyridine, 0.5 to 2.0 ml.), containing 0.2 to 0.3 g. of coated copper. Rinse briefly in 50% alcohol and reduce 10 min. in an alkaline hydroquinone reducer (H₃BO₃, 1.4 g.; Na₂SO₃, anhydrous, 2.0 g.; hydroquinone, 0.3 g.; distilled water, 85 cc; acetone, 15 ml.). Wash thoroly in water and tone for 10 min. in 0.2% aqueous gold chloride, acidified with acetic acid. Wash in distilled water and reduce for 1 to 3 min. in 2% aqueous oxalic acid. Quickly rinse in distilled water and treat the sections 3 to 5 min. with 5% aqueous Na₂S₂O₃+5H₂O. Wash in water and stain overnight in Einarson's gallocyanin. Wash thoroly in water and place in 5% aqueous phosphotungstic acid for 30 min. From phosphotungstic acid transfer directly to a dilution (stock solution, 20 ml.; distilled water, 30 ml.) of the following stock staining solution: anilin blue, 0.01 g.; fast green FCF, 0.5 g.; orange G, 2.0 g.; distilled water, 92.0 ml.; glacial acetic acid, 8 ml.) and stain for 1 hour. Differentiate with 70% and 95% alcohol; pass the sections thru butyl alcohol and cedar oil; mount.     

铁观音茶水提物对小鼠高尿酸血症的缓解作用

近年来,高尿酸血症（hyperuricemia,HUA）在人群中频发,危害性强,并发症多。为了探究日常饮品--半发酵茶铁观音茶水对于缓解HUA是否具有辅助作用,以小鼠为实验对象,采用氧嗪酸钾和次黄嘌呤联合法构建小鼠高尿酸血症模型,21只模型鼠随机分为模型组、铁观音茶水提物组、阳性药物组,7只非模型鼠作为对照。做不同处理2周后,取小鼠血清及肾、肝、小肠。观察各器官病理变化,从细胞层面鉴定铁观音茶水提物对高尿酸血症小鼠各脏器的影响;测定与HUA相关度较高的生化指标：血清尿酸（uric acid,UA）浓度、肝黄嘌呤氧化酶（xanthine oxidase,XOD）活力,以明确造模是否成功以及判断铁观音茶水提物对HUA是否具有缓解作用;利用qRT-PCR检测尿酸合成和排泄相关基因的mRNA表达水平,并利用Western blot检测肝XOD蛋白的表达水平,以从分子层面明确铁观音茶水提物对HUA的影响。病理切片显示,相比于阳性药物组,铁观音茶水提物组小鼠的肾和肝损害程度较轻;生化指标测定结果显示,铁观音茶水提物可降低血清尿酸水平,并且抑制XOD活性;从分子层面可以看出,铁观音茶水提物显著升高了尿酸重吸收转运体尿酸转运蛋白1(uric acid transporter 1,URAT1)和有机阴离子转运蛋白3(organic anion transporter 3,OAT3)的mRNA表达水平（P<0.05）,显著降低了葡萄糖转运子9（glucose transporter 9,GLUT9）和有机阴离子转运蛋白1(organic anion transporter 1,OAT1)的表达水平（P<0.05）。虽然qRT-PCR和Western blot提示,XOD的mRNA和蛋白质的表达水平升高,但尿酸生成量却下降,推测可能是铁观音茶水提物中的某种成分使得无催化活性的XOD蛋白表达增加进而对XOD基因的转录表达造成一种正反馈。研究提示,铁观音茶水提物对小鼠高尿酸血症具有缓解作用,其缓解高尿酸血症的作用与抑制XOD活性、干预尿酸生成过程和刺激或抑制相关阴离子转运体mRNA的表达相关。     

Chemoenzymatic syntheses of amylose-grafted chitin and chitosan

Amylose-grafted chitin and chitosan were synthesized by chemoenzymatic methods according to the following reaction manners. First, maltoheptaose was introduced to chitosan by a reductive amination using sodium cyanotrihydroborate in a mixed solvent of 1.0 mol/L aqueous acetic acid and methanol at room temperature to produce a maltoheptaose-grafted chitosan (1). The functionality of maltoheptaose to chitosan in 1 depended on reaction time. The phosphorylase-catalyzed enzymatic polymerization of R-D-glucose 1-phosphate was then performed from 1 to obtain amylose-grafted chitosan (2). Maltoheptaose-grafted chitin (3) was synthesized by N-acetylation of 1 using acetic anhydride in a mixed solvent of aqueous acetic acid and methanol. Then, synthesis of amylose-grafted chitin (4) was performed by the phosphorylase-catalyzed enzymatic polymerization under conditions the same as those for 2. The average DPs of amylose graft chains in 2 and 4 depended on the feed ratios of R-D-glucose 1-phosphate to maltoheptaose primers in 1 and 3.     

The kinetic behaviour of a two-enzyme system in biphasic media: coupling hydrolysis and lipoxygenation

Analysis of the kinetic behaviour of a two-enzyme-system carrying out two consecutive reactions was investigated in macroheterogeneous biphasic media (octane/buffer pH 9.6, v/v=1:1). The lipase-catalysed hydrolysis of trilinolein and the subsequent lipoxygenation of the liberated linoleic acid, were coupled in a modified Lewis cell with a well-defined liquid/liquid interfacial area. Trilinolein was dissolved in the organic phase and hydrolysed in the presence of Mucor javanicus lipase at the organic/aqueous interface. Linoleic acid, liberated after hydrolysis was transferred to the aqueous phase and reacted with lipoxygenase. This reaction consumed linoleic acid and produced hydroperoxides, which favoured the transfer of residual linoleic acid, since they possess surface active properties. Catalysis and transfer influenced each other reciprocally. At low substrate concentrations, cooperativity phenomena were observed in the experimental and also the modelled two-enzyme systems. When the initial substrate concentration was high, the kinetic behaviour of the two-enzyme system in a compartmentalised medium, seemed to be independent of the substrate concentration, unlike that observed in homogeneous monophasic enzymology. The numerical integration program used to model the two-enzyme system was based on results obtained in separate studies of the following three phenomena: (1) trilinolein hydrolysis in biphasic medium, (2) linoleic acid transfer across a liquid/liquid interface and (3) lipoxygenation in an aqueous media. Results obtained by modelling were similar to the results observed experimentally.     

Partition and substrate concentration effect in the enzymatic synthesis of cephalexin in aqueous two-phase systems

The kinetically controlled synthesis of cephalexin in aqueous two-phase systems was studied, using immobilized penicillin acylase, 7-amino 3-desacetoxycephalosporanic acid as nucleophile and phenylglycine methyl ester as acyl donor. The organic phases used were 80% (v/v) polyethyleneglycol 400 and 600 and the aqueous phase was 2.5 M (NH₄)₂SO₄. 7-amino 3-desacetoxycephalosporanic acid and cephalexin partition coefficients were determined at pH 7.4 and 7.8, at 14 °C and 20 °C. Highest partition coefficient for cephalexin was obtained for polyethyleneglycol 400–(NH₄)₂SO₄ at pH 7.4 and 20 °C, while the lowest partition coefficient for 7-amino desacetoxycephalosporanic acid was obtained in the same system at pH 7.8 and 14 °C. No significant effect of pH was observed on conversion yield and productivity of cephalexin synthesis; however, higher values were obtained with polyethyleneglycol 400 as organic phase. Higher conversion yields with both biphasic systems were obtained at the lowest temperature, where product hydrolysis was lower; volumetric productivity was higher for the fully aqueous medium (control), being higher at 20 °C. All parameters of synthesis were improved at higher substrates concentrations, obtaining conversion yields of 78.2% and 65.4%, with 60 mM 7-amino desacetoxycephalosporanic acid for the polyethyleneglycol 400–(NH₄)₂SO₄ system and the control, respectively.     

Time dependent inhibition of xanthine oxidase in irradiated solutions of folic acid, aminopterin and methotrexate

The xanthine oxidase catalyzed oxidation of hypoxanthine was followed by monitoring the formation of uric acid at 290 nm. Inhibition of xanthine oxidase occurs in aqueous solutions of folic acid methotrexate and aminopterin. These compounds are known to dissociate upon exposure to ultraviolet light resulting in the formation of their respective 6-formylpteridine derivatives. The relative rates of dissociation were monitored spectrophotometrically by determining the absorbance of their 2,4-dinitrophenylhydrazine derivatives at 500 nm. When aqueous solutions of folic acid, aminopterin and methotrexate were exposed to uv light, a direct correlation was observed between the concentrations of the 6-formylpteridine derivatives existing in solution and the ability of these solutions to inhibit xanthine oxidase. The relative potency of the respective photolysis products were estimated.