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Cephalosporin C was extracted from diluted or whole broth by PEG/salt aqueous two-phase systems. Parameters such as PEG molecular weight, salt type, pH, and salt concentration were investigated for finding a suitable extraction system. In PEG 600/ammonium sulfate or phosphate systems, K(c) (partition coefficienct of cephalosporin C) was observed to be larger than 1, with K(d) (partition coefficient of desacetyl cephalosporin C) being smaller than 1. The particular values of these coefficients would imply that the difficult separation of cephalosporin C and desacetyl cephalosporin C could possibly be achieved via the aqueous two-phase extraction. The addition of surfactants, water-miscible solvents, and neutral salts for enhancement of the separation efficiency was also investigated. The addition of surfactants to the system did not affect the separation efficiency substantially. K(c) would increase whereas K(d) decreased as a result of the addition of acetone, MeOH, EtOH, IPA, and n-BuOH. Meanwhile both K(c) and K(d) would decrease whenever neutral salts, NaCl, KCl, Kl, or KSCN, were added. The partitioning behavior of cephalosporin C and desacetyl cephalosporin C in filtered, whole, and different batches of broth was notably quite similar to that of diluted broth. The recovery yield of cephalosporin C in whole broth extraction was observed to be a function of centrifugal force used in phase separation. (c) 1994 John Wiley & Sons, Inc.

To investigate a potential candidate material for making artificial red blood cells to supplement blood transfusion, the X-ray structure of porcine haemoglobin at 1.8 A resolution was determined as part of research towards synthesizing human blood. Porcine haemoglobin was crystallized by the vapor-diffusion method, producing crystals of dimensions 0.3-0.5 mm after successive seeding. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 68.10, b = 72.27, c = 114.85 A. The initial phase was determined by the molecular-replacement method, using human oxyhaemoglobin as a model. The final R factor was 21.1% for 36 820 reflections after validation of 574 water molecules. The r.m.s. deviations of bond lengths, angles, torsion angles and improper angles from their ideal values are 0.017 A, 3.0, 20.6 and 1.8 degrees, respectively. The average B factor is 33.63 A(2) for the haemoglobin molecule and 50.53 A(2) for the water molecules. The structure could be superimposed on a 2.8 A resolution structure with an r.m.s. difference of 0.59 A in main-chain atomic positions and 1. 27 A in side-chain atomic positions. Porcine and human haemoglobins are compared. A tentative model for artificial blood is proposed based on the complementarity relationship of the surface charges between haemoglobin and the surrounding cell membrane.

A model based on a feedforward back-propagation neural network was employed to predict the phase equilibrium diagram of the aqueous two-phase systems. The PEG/potassium phosphate/water system (pH 7) was selected as the model system to demonstrate the point of interest. A variety of molecular weights (MW) of PEG systems including PEG 600, 1500, 3400, 8000, and 20 000 were considered for training the patterns in order to estimate the systems with PEG MW of 400 and 1000. After the optimal architecture of the network was investigated and finally determined, the extrapolated and interpolated simulations by this model exhibited an excellent agreement with experimental data. The characteristics of the phase diagram such as the binodal curve and tie lines were illustrated in precision in all trials. The model can associate the dependence of PEG MW with the subtle shift of the corresponding phase diagrams over the test MW range. All the equilibrium data of the PEG/potassium phosphate systems with continuously variable PEG MW ranging from 20 000 to 400 could be predicted by the model. The results indicated the applicability of the neural network model as a design-oriented technique for optimization of extraction condition. The neural network model should be a potent means to deal with more complex models such as PEG/dextran systems and partition of proteins in aqueous two-phase systems.