Solid-liquid equilibrium of substrates and products of the enzymatic synthesis of ampicillin (original) (raw)
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Effect of different variables in the solubility of ampicillin and corresponding solid phase
Fluid Phase Equilibria, 2018
Ampicillin belongs to the class of beta-lactam antibiotics, which corresponds the most prescribed antibiotics in medicine. This justifies the importance of elucidating the effect of several variables for the synthesis process (pH, temperature, co-solvent) on the behavior of the compounds involved in the enzymatic reaction. This paper aims to present new ampicillin solubility data in aqueous medium and the characterization of the solid phase of the antibiotic. In the phase equilibrium experiments it was considered the effect of pH (3 up to 7.5), temperature (283.15 K up to 298.15 K) and the ethanol concentration in the aqueous solution (varying between 0 and 70 wt% ethanol). The solubility curves deviate from U-shape solubility curves with respect to pH in the range of 0 to 70 wt%. This is due to ampicillin anhydrous becomes trihydrated molecule in the solid phase at alkaline pH region, changing the antibiotic properties significantly. This change in crystalline structure was confirmed by characterization of antibiotic solid phase carried out from thermogravimetric (TGA), Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analyses. Dissociation constants have also been measured at the studied values of temperature and ethanol composition, using potentiometric titration. Finally, a thermodynamic model considering the ideal solution was applied to describe mathematically the solubility curves measured close to experimental uncertainties.
Molecular Physics, 2001
The aggregation of ampicillin in water has been examined by conductivity measurements over the temperature range 288.15±313.15 K and light scattering. These measurements indicate the formation of two critical concentrations over the range 0±0.35 mol kg ¡ 1 . Aggregation number and e ective aggregate charge were calculated from the static light scattering data according to the Anacker and Westwell treatment. Thermodynamic parameters of aggregate formation were obtained from a form of the mass action model applicable to systems of low aggregation number. This method was applied at both critical concentrations. A valence of one was used for the monomers present in the ®rst equilibrium. The second equilibrium was between aggregates of two di erent sizes, in this case, the valence of the aggregates being the e ective charge calculated from the Anacker and Westwell treatment. Experimental results show that free energies of micellization for ampicillin are higher for the ®rst critical concentration and in the same range, but lower than for other penicillins. The enthalpies of micellization become negative when the temperature is increased, but the variation is three times greater for the ®rst critical concentration than for the second.
Journal of Molecular Catalysis B: Enzymatic, 2000
Penicillin acylase-catalyzed ampicillin synthesis via acyl group transfer in aqueous solution is highly dependent on the Ž . initial substrate concentration. The solubility of one substrate, 6-aminopenicillanic acid 6-APA , can be advantageously enhanced by the presence of acyl donor, the second substrate. Furthermore, a comparison of enzymatic synthesis in homogeneous solution with synthesis in a heterogeneous system having partially undissolved reactants, reveals major advantages for the latter approach. In this ''aqueous solution-precipitate'' system, accumulation of both products, ampicillin Ž . and D-y -phenylglycine, proceeds through the formation of their supersaturated solutions. Subsequent precipitation of the product ampicillin positively influences the efficiency of the biocatalytic process. As a result, ampicillin synthesis proceeds Ž . in 93% conversion on 6-APA and in 60% conversion on D-y -phenylglycine methyl ester. q
Effect of pH in the synthesis of ampicillin by penicillin acylase
Enzyme and microbial …, 1996
Recombinant Escherichia coli cells with high penicillin acylase (PA) activity were immobilized by gel entrapment with agar. This biocatalyst was used to study the effect of pH on the synthesis of ampicillin from phenylglycine methylester (PGME) and 6-aminopenicillanic acid ...
Biotechnology and Bioengineering, 2001
The synthesis of ampicillin catalyzed by Escherichia coli penicillin acylase was optimized in an aqueous system with partially dissolved antibiotic nucleus 6-aminopenicillanic acid (6-APA). The yields of both 6-APA and acyl donor could be improved by repetitively adding substrates to the reaction, allowing the concentration of 6-APA to remain saturated throughout. In this reaction concept, with four subsequent additions of substrates, 97% conversion of 6-APA and 72% of D-(−)phenylglycine methyl ester (D-PGM) to ampicillin was achieved. The synthetic potential of this concept was estimated using a mathematical model which showed that by increasing the amount of added substrates a nearly quantitative conversion of 6-APA and 85% conversion of acyl donor into ampicillin could be achieved.
Journal of Molecular Liquids, 2012
The interactions of some simple amino acids (AA) like alanine, valine and leucine with drug ampicillin (AMP) as a function of temperature have been investigated by combination of volumetric and acoustic methods. Densities and speeds of sound of alanine, valine and leucine in aqueous solutions of ampicillin have been measured at T = (305.15, 310.15 and 315.15) K and atmospheric pressure. The apparent molar volume (V ϕ), the partial molar volume (V ϕ 0), limiting apparent molar expansibility (ϕ E 0) and standard partial molar volumes of transfer (ΔV ϕ) for amino acids from water to aqueous ampicillin solutions have been calculated from density data. Partial molar adiabatic compressibility (K ϕ,s) and partial molar adiabatic compressibility of transfer (ΔK ϕ,S 0) have been calculated from speed of sound data. The pair and triplet interaction coefficients have been calculated from both the properties. The results have been explained on the basis of competing patterns of interactions of co-solvent and the solute.
Journal of Molecular Catalysis B-enzymatic, 2001
Penicillin acylase (PA) is used in the industrial production of 6-amino penicillanic acid (6-APA). However, by proper control of reaction medium, the enzyme can be used in the reverse synthesis of β-lactam antibiotics from the corresponding β-lactam nuclei and suitable acyl donors. Under thermodynamically controlled strategy, the use of organic cosolvents can favor synthesis over hydrolysis by lowering water activity and favoring the non-ionic reactive species. Under kinetically controlled strategy using activated acyl donors, organic solvents can favor synthesis by depressing hydrolytic reactions. Results are presented on the synthesis of ampicillin from phenylglycine methyl ester and 6-APA with immobilized Escherichia coli PA in the presence of organic cosolvents. Several solvents were tested in terms of enzyme stability and solubility of substrates. Ethylene glycol, glycerol, 1–2 propanediol and 1–3 butanediol were selected accordingly and ampicillin synthesis was performed in al...
Biotechnology and Bioengineering, 2002
The penicillin acylase-catalyzed synthesis of ampicillin by acyl transfer from D-(±)-phenylglycine amide (D-PGA) to 6-aminopenicillanic acid (6-APA) becomes more effective when a judiciously chosen pH gradient is applied in the course of the process. This reaction concept is based on two experimental observations: 1) The ratio of the initial synthesis and hydrolysis rates (V S /V H ) is pH-dependent and exhibits a maximum at pH 6.5±7.0 for a saturated solution of 6-APA; 2) at a ®xed 6-APA concentration below saturation, V S /V H increases with decreasing pH. Optimum synthetic ef®ciency could, therefore, be achieved by starting with a concentrated 6-APA solution at pH 7 and gradually decreasing the pH to 6.3 in the course of 6-APA consumption. A conversion of 96% of 6-APA and 71% of D-PGA into ampicillin was accomplished in an optimized procedure, which signi®cantly exceeds the ef®ciency of enzymatic synthesis performed at a constant pH of either 7.0 or 6.3. ã 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 589±593, 2002.
Journal of Molecular Liquids, 2014
The viscosities, of L-alanyl-L-alanine (Ala-Ala), L-alanyl-L-valine (Ala-Val), L-alanyl-L-leucine (Ala-Leu) with drug ampicillin (AMP) have been measured as a function of temperature at T = (305.15, 310.15 and 315.15) K. The change in viscosity of dipeptides with increase in AMP concentration and temperature is attributed to dipeptide-AMP interactions. The viscosity B-coefficients and viscosity interaction parameters obtained from Jones-Dole equation and transition state theory respectively have been discussed to interpret interactions between ions of dipeptides and ampicillin.