Citrate System Research Articles

Partial purification of penicillin acylase from Escherichia coli in poly(ethylene glycol)–sodium citrate aqueous two-phase systems

Studies on the partition and purification of penicillin acylase from Escherichia coli osmotic shock extract were performed in poly(ethylene glycol)–sodium citrate systems. Partition coefficient behavior of the enzyme and total protein are similar to those described in other reports, increasing with pH and tie line length and decreasing with PEG molecular weight. However, some selectivity could be attained with PEG 1000 systems and long tie line at pH 6.9. Under these conditions 2.6-fold purification with 83% yield were achieved. Influence of pH on partition shows that is the composition of the system and not the net charge of the enzyme that determines the behaviour in these conditions. Addition of NaCl to PEG 3350 systems significantly increases the partition of the enzyme. Although protein partition also increased, purification conditions were possible with 1.5 M NaCl where 5.7-fold purification and 85% yield was obtained. This was possible due to the higher hydrophobicity of the enzyme compared to that of most contaminants proteins.

Interaction of Alkaline Earth Metal Ions with Carboxylic Acids in Aqueous Solutions studied by 13C NMR Spectroscopy

Abstract 13C NMR spectroscopic measurements of aqueous solutions containing alkaline earth metal chloride and a carboxylic acid have been carried out to acquire some insight into the coordination manners of various carboxylic acids to alkaline earth metal ions. The dependence of the 13C NMR signal positions of the carboxylate carbons on the magnesium ion concentration in a magnesium carboxylate system is a good index to understand the coordination manner of the carboxylate ion. The upfield shift of the carboxylate carbon signal with increasing magnesium ion concentration indicates that the carboxylate ion acts as a bidentate ligand to form a ring structure. Only in the citrate systems, the existence of a relatively stable complex is evidenced in which the citrate ion is expected to act as a tridentate ligand.

Interactions between citrate and montmorillonite-Al hydroxide polymer systems

Interactions between citrate and montmorillonite-Al hydroxide polymer systems

Oxovanadium(IV) complexes of citric and tartaric acids in aqueous solution

The complex-formation processes taking place in the systems containing VO(IV) and d-, l-, dl- or meso-tartaric acid or citric acid in aqueous solution were re-examined by combined use of pH potentiometry and spectroscopic (EPR and electronic absorption) methods. The results allowed a full characterization of the dinuclear species existing in the VO(IV)— d-, l- and dl-tartrate systems and indicated a different complexation behaviour in the corresponding meso-tartrate system. As its conformation is unfavourable for dimer formation, the meso ligand yields predominantly cyclic trinuclear species, one of them exhibiting distinctive EPR features. In the VO(IV)-citrate system, dinuclear species with structures different from those of the VO(IV) tartrates are suggested.

Electrochemical behavior of NbV–EDTA and NbV–citrate systems in aqueous solutions

AbstractThe electrochemical reduction of NbV using oxalatoniobic acid and ammonium oxooxalatoniobate salts was studied in aqueous solutions of citric acid and sodium ethylenediaminetetraacetate (EDTA), in a wide range of supporting electrolyte concentrations and pH. In EDTA two reduction processes were observed: NbV to NbIV, E = −1.000 V vs. Ag/AgCl at pH 4.50 and NbIV to NbIIIE = −1.400 V vs. Ag/AgCl (pH 4.50). In citric acid there was only one reduction process: (NbV to NbIV), E = −1.260 V vs. Ag/AgCl at pH 4.50. In both electrolytes a linear relationship was found between the diffusion current and the niobium concentration in the 1.0 × 10−5 to 5.0 × 10−3 M range. Using cyclic voltammetry, it waa observed that the charge transfer process in the NbV to NbIV process is reversible in EDTA and reversible–quasireversible in citric acid.

The Response of the Strongly Coupled AB System of Citrate to Typical 1H MRS Localization Sequences

The response of the strongly coupled AB system of citrate to the STEAM and PRESS spatial localization sequences is developed analytically and then verified experimentally at 2.35 T. At this field strength, the response predicted by the complete Strong-coupling calculation is shown to differ greatly from that of the simpler weak-coupling approximation. It is shown that the strong-coupling effects induce a significant field-strength dependence in the time-dependent modulations of the response to either sequence. These effects are illustrated for the STEAM and PRESS responses at field strengths of 1.5, 2.35, and 4.7 T. Independent of the chosen sequence, the increase in the signal-to-noise ( S/ N) of the frequency response with increasing field strength is shown to be significantly less for the citrate system than for uncoupled spins. The factors which weaken the S/ N dependence of the citrate AB signal with increasing field strength are quantified and discussed.

Aluminum(III)-Isocitrate Solution Chemistry. A Potentiometric Study

The equilibrium reactions of isocitrate with protons and Al3+ have been studied by potentiometric titration in aqueous 0.10 M KCl at 25°C. The protonation constants, corrected for K+-isocitrate complexing , were logβ0,1,1 = 5.838, logβ0,2,1 = 10.126 and logβ0,3,1 = 13.219. The stabilities and stoichiometries of the complexes, AlpHqLr, were defined by the constants logβ1,1,1 = 9.55(05), logβ1,0,1 = 6.90(02), logβ1,-1,1 = 3.06(04) and logβ2,-3,2 = 4.08(04) or logβ3,-4,3 = 10.36(06). Compared with the Al3+-citrate system, complexes are of lower thermodynamic stability, but equilibrate more rapidly.

Calorimetric investigation of complex formation in the aqueous Fe (III)–citrate system

We have made calorimetric measurements of thermal effects associated with adding NaOH(aq) or HCl(aq) to aqueous solutions (pH = 1.623) of ferric chloride + sodium citrate. Combination of these measured heats with concentrations of various species calculated from stoichiometric compositions and previously known K and ΔH values leads to ΔH values for four aqueous Fe(III)–citrate complexes. Further combination of ΔG0 values from equilibrium constants with our ΔH values leads to ΔS0 values, which are discussed in relation to conventional ideas about relationships between entropy and solute–water interactions.

Alkali Metal Salts of Hydroxy Acids as Catalysts in Durable Press Finishing with Butanetetracarboxylic Acid

Alkali metal salts of hydroxy acids have been investigated as catalysts for esterification cross-linking of cotton with 1,2,3,4-butanetetracarboxylic add to produce cotton fabrics with smooth drying properties. Of the sodium salts of several acids studied, the sodium citrates produce fabrics with the best appearance properties. The sodium citrates serve both as donors of citric acid for cross-linking and of sodium ions for catalysis of the esterification of cotton cellulose by the two polycarboxylic acids. Although the use of citric acid as an extender for the more expensive butanetracarboxylic acid has been reported in non-formaldehyde finishing of cotton fabrics for smooth drying properties the catalyst used was sodium hypophosphite. Comparisons are made between fabrics finished with the phosphorus-containing system and the butanetetracarboxylic acid/sodium citrate systems. Textile properties, fabric whiteness, effect of pad bath pH, and extent of esterification are discussed.

Lactose hydrolysis by β-galactosidase in aqueous two-phase systems

Lactose hydrolysis was studied in aqueous two-phase systems with β-galactosidases from bacteria ( Escherichia coli), yeast ( Saccharomyces fragilis), and fungi ( Aspergillus oryzae). Salts such as potasium phosphate, ammonium sulfate, and sodium citrate used at concentrations forming phase systems could severely inhibit β-galactosidase activity from yeast and inhibit E. coli enzyme activity to a lesser extent, but had no effect on fungal β-galactosidase activity. Polymers such as polyethylene glycol (PEG) and a modified starch (Reppal PES) could increase the enzyme activity toward hydrolyzing o- nitrophenyl-β- d-galactopyranoside . E. coli β-galactosidase showed a partition coefficient of 127 in a PEG/Reppal PES system to provide an efficient system for carrying out extractive hydrolysis of lactose. A. oryzae β-galactosidase showed a partition coefficient of 0.0042 in a PEG/sodium citrate system. Continuous hydrolysis of lactose in this system with a mixer-settler enzyme reactor could be operated for a period of 84 h with only 10% loss of enzyme activity. Slower reaction rates in two-phase systems than in buffer systems may arise from preferential distributions of both enzyme and inhibitory products into the same phase.

Solubilization of gellan gels by chelation of cations

Chelation solubilization of gellan under mild conditions has been accomplished for the first time by exposure to either 10 mM sodium citrate buffer (pH 6.0) or to 1 mM sodium hexametaphosphate (pH 6.6). The citrate system was preferred for most applications since its is a ubiquitous cellular component, its solutions are autoclavable, and because viable plant tissues, fungi, and bacteria could be recovered from culture. Such recovery is not possible from more commonly used media such as agar.

Influence of oral contraceptives on coagulation tests in native blood and plasma

Routine coagulation laboratory tests, clotting times in native (not anticoagulated) whole blood, platelet-rich and platelet-poor plasma, and recalcification times in citrated whole blood, platelet-rich and platelet-poor plasma were performed in 14 healthy premenopausal women. Blood was taken before and after one or two cycles of low-dose oral contraceptives. After oral contraceptives a reduction in clotting time in native platelet-rich plasma and activated partial thromboplastin time were observed. Recalcification times in whole blood and platelet-rich plasma were shorter than clotting times in their native counterparts. The observed changes are compatible with a procoagulant effect seen soon after the start of oral contraceptive use. The absence of these changes in the recalcification times in citrate systems suggests a masking effect of citrate. The reduction in clotting times in native platelet-rich but not in platelet-poor plasma indicates that the hypercoagulability in oral contraceptives users is mainly related to platelets. (Am J Obstet Gynecol 1990;163:417-20.)

Kinetic Determination of Tantalum in the Presence of Niobium

The rates of the ligand substitution reactions of niobium and tantalum complexes involving oxalate, tartrate, citrate or nitrilotriacetate as an auxiliary complexing agent with 4-(2-pyridylazo) resorcinol have been studied spectrophotometrically in acidic media. In the citrate system at pH 5, the maximum difference in rate of substitution between the niobium and the tantalum complexes was achieved. Under the chosen conditions, where the total concentrations of citrate and 4-(2-pyridylazo)resorcinol are 2×10−2 and 1×10−4 mol dm−3 respectively, the absorbance change during the reaction progress can be kinetically separated for each metal ion and less reactive tantalum in the range 10−6–10−5 mol dm−3 can be determined by a logarithmic extrapolation method. In the determination of 5×10−6 mol dm−3 of tantalum, the presence of 5-fold amounts (by molarity) of niobium can be tolerated. The effects of 52 diverse ions were examined.

Ophthalmic solution buffer systems. II. Effects of buffer type and concentration on the ocular absorption of pilocarpine and a method of ocular bioavailability prediction from physicochemical data

The objective of the study has been to quantitatively determine the effects of the concentrations and types of buffer used in ophthalmic drug solutions or formulations on the corneal absorption efficiency or ocular bioavailability of a representative amine drug, pilocarpine. The ophthalmic solutions containing pilocarpine (as nitrate or hydrochloride salts) are buffered in the pH range of 4.5–5.0 for reasons of optimum chemical stability. But such a pH range causes only a smaller fraction of total pilocarpine (pK a of protonated base 6.85 at 25° C) to be available as preferentially absorbed unionized species. Since tear fluid has a very low buffer capacity, ophthalmic solutions containing buffers of high buffer capacities within the pH range of 4.75–7.40 would tend to resist the pH alteration of the instilled fluid by tear fluid to a greater degree and consequently would lower the extent of drug absorption. Miosis-time profiles were obtained following the instillation of 25.0 μl of isotonic 1.0% (w/v) pilocarpine nitrate solutions which were buffered at a pH of 4.75 with the same initial 0.075 M concentration of citrate, phosphate or acetate buffers. Relative pharmacological response, as measured by the areas under the miosis-time profiles (AUC) and the maximum observed pupillary diameter changes (ΔPD max), decreased in the order of: no buffer > acetate > phosphate > citrate. These isotonic buffer solutions containing 1% (w/v) pilocarpine nitrate were titrated in vitro with a standard base and the volume of 1.0 N sodium hydroxide needed to titrate the drug solutions from a pH of 4.75 to 7.40 showed excellent inverse linear relationships with the ocular bioavailability parameters. The correlations developed appear to have the capability of predicting relative ocular bioavailabilities of pilocarpine solutions as a function of buffer concentration for citrate, phosphate and acetate buffer systems.

Formation and stability of zinc(II) and cadmium(II) citrate complexes in aqueous solution at various temperatures

The citrate complexes of Zn 2+ and Cd 2+ have been investigated by pH titration at I = 0.1 M (KNO 3) and 10, 25, 35 and 45°. The species found were [Zn(cit)] −, [Zn(cit)H], [Zn(cit) 2] 4− and [Zn 2(cit) 2H − 2] 4−, [Cd(cit)] −, [Cd(cit)H], [Cd(cit) 2] 4− and [Cd(cit)H −1] 2−. From the dependence of the formation constants on temperature, Δ H° and Δ S° values were calculated. Speciation in the Zn 2+]- and Cd 2+-citrate systems is discussed with particular attention to formation of polynuclear species. Some comparisons with literature data are made.

Einfluß des Komplexbildungsgrades auf die Migrationsgeschwindigkeit von Eisen(II, III)‐Verbindungen

AbstractThis paper describes relations between the degree of complexation calculated with a mathematical model (FISCHER and REISSIG, 1984) and the ion‐exchange and migration behaviour of iron(II, III)‐compounds in a simulated aquifer. In general, the bonding of the complexes to the soil matrix becomes stronger with increasing positive charge. Negatively charged or neutral complex compounds do not show any, or show only slight interactions with the soil matrix. By complexation it is possible to achieve great differences in the migration behaviour of a particular metal. In the course of migration in the deposit there was found a separation of the complex mixture in accordance with charge. The break‐through curves are characterized by a stepped shape, for this case. If weak acids or weak bases act as complex‐forming ligands, the pH‐dependent dissociation of the complexing species has to be taken into account in the complex calculation; this is represented by the example of the iron(III)‐citrate system in this paper. Moreover, experimental results concerning the migration behaviour of iron(II, III)‐fulvic acid complexes are given

Complexation between molybdenum(VI) and citrate: a potentiometric and calorimetric investigation

The molybdenum(VI)-citrate system has been investigated in the pH c range 7.5–2.0 by potentiometric and enthalpimetric titrations at 25°C in 1 M NaCl. The potentiometric data were treated with the computer program MINIQUAD taking into account side reactions of molybdate and citrate with hydrogen ions. A reaction model comprising the complexes (1,1,1) 4−,(1,1,2) 3−,(1,1,3) 2−,(2,1,4) 3− and (2,1,5) 2− gave a satisfactory description of the data; the numbers refer to the values of p, q and r in the general formula (MoO 2− 4) p (Cit 3−) q (H +) r . The enthalpy and entropy changes for the formation of these complexes were calculated from the enthalpimetric data using the values of the now known formation constants. Equilibrium constants as well as enthalpy and entropy changes for the successive protonations of citrate have also been determined.

Zirconium isotope separation by means of cation-exchange chromatography

The separation of zirconium isotopes has been studied by means of cation-exchange chromatography using zirconium-triammonium citrate and zirconium-diammonium citrate systems. Small but appreciable isotope fractionations were observed in both systems. In the former system, the lighest isotope 90Zr was enriched at the rear part of the zirconium band, while in the latter case 90Zr was depleted at the rear part. The elemental separation coefficients, ε, were around 1 · 10 -6 for the zirconium-triammonium citrate systems and around −0,5 · 10 −6 for the zirconium-diammonium citrate systems. The isotope effect is discussed in terms of the hydrolysis of the zirconium species.

Ionic strength dependence of formation constants. Part 4. Potentiometric study of the system Cu2+-Ni2+-citrate

The ternary Cu2+-Ni2+-citrate (cit3−) system was investigated potentiometrically in aqueous solution, at different temperatures, 10≤t≤45°C, and ionic strengths, 0.03≤I≤0.8 mol dm−3, using potassium nitrate or tetraethylammonium bromide as background salt. Since the citrate anion forms weak complexes with potassium, the stability constants here reported differ according to whether the potassium association is considered or not. In the presence of both Cu2+ and Ni2+, the mixed metal species, [CuNi(cit)2H−2]4− is formed with citrate in solution, in addition to the various binary complexes. We have obtained the dependence for all the formation constants on ionic strength and temperature. The previous suggestions concerning a general equation for describing the dependence, log β=f(I), are confirmed; from the study of log β=f(T) we have obtained the values of thermodynamic parameters. The dependence of ΔH on ionic strength is discussed.

Determination of the charge of complex species that are reduced at the dme and of the coefficient of transfer, α, in the Cu(II)aq. M citrate (M: Li +, Na + and K +) system

The minimum presented by the polarograms of the reduction of Cu(II) in Li +, Na + and K + citrate is analysed in order to determine the charge of the reacting species and the coefficient of transfer, α, of the process. The results obtained allow the participation of the complex anions (Cu 2Cit 2) 2− and (CuCit 2) 4− in dilute and concentrated citrate solutions to be established, respectively, as well as a cation—reacting anion interaction, increasing in the order K + > Na + > Li +. The value of the coefficient of transference α = 0.40 is in agreement with that found by other techniques.