A MODIFIED PORE FILLING ISOTHERM WITH APPLICATION TO DETERMINATION OF PORE-SIZE DISTRIBUTIONS

A modification of the Dubinin theory of volume filling is proposed here by combining it with a Langmuirian model at low pressures. The hybrid model satisfies the requirement of a Henry's law asymptote as well as predicts a limiting micropore size for this kind of filling. For the mesopores the classical Kelvin theory is extended here by correcting for finite molecular size, and the modified model results are found to match recent molecular simulation predictions for the condensation pressure in small as well as large pores. These two developments presented here also interpret the lower closure point of adsorption-desorption hysteresis as corresponding to the critical pressure for condensate-vapor equilibrium at the limiting micropore size, below which filling by the modified theory proposed here occurs. A large amount of hysteresis closure data is examined here and generally found to be well correlated by this interpretation. Techniques for utilizing these developments in the evaluation of pore size distributions are also proposed, and applied to the interpretation of carbon dioxide and nitrogen adsorption data for various activated carbons. It is found that convergence of the pore size distribution is generally achieved, without resort to regularization, by representing it as the product of a suitable standard distribution and a polynomial. This procedure is also seen to predict bimodal forms and, even for this situation, yields more reliable results than the standard bimodal distributions by virtue of its convergence behavior

INTERPRETATION OF ADSORPTION-ISOTHERMS AT ABOVE-CRITICAL TEMPERATURES USING A MODIFIED MICROPORE FILLING MODEL

A new micropore filling model, which has a Henry's law region and predicts an upper limit to micropore size, is applied here to adsorption at supercritical temperatures. Data obtained here on the adsorption of methane and carbon dioxide on activated carbons are interpreted in terms of this model, while utilizing independently obtained pore size distributions. The results show that the contributions of micropore filling and mesopore surface adsorption can vary considerably with temperature as well as adsorbate, because of the dependency of the upper limit of micropore size in which filling occurs on these variables. In light of these findings it appears that concepts such as micropore volume and mesopore surface area are not reliable characteristics of the pore structure as they vary with process conditions

Purification, crystallization and partial characterization of the antitumour and insecticidal protein subunit from the σ-endotoxin of Bacillus thuringiensis var. thuringiensisstar, open

The antitumour protein from the α-endotoxin of Bacillus thuringiensis var. thuringiensis has been purified, crystallized and partially characterized. The same protein also shows the insecticidal activity. According to amino acid analysis it is an acidic protein with a molecular weight of approx. 13 000

Spore and crystal formation in Bacillus thuringiensis var thuringiensis during growth in cystine and cysteine.

The effect of the addition of different concentratons of cystine and cysteine on sporulation and parasporal crystal formation in Bacillus thuringiensis var. thuringiensis was studied. The effect was well pronounced when the systine/cysteine additions were made after the stationary phase. Heat stable spores and crystals were formed when the culture was provided with a low concentration of cystine/cysteine (0.05 per cent w/v). At a moderate concentration of cystine or cysteine (0.15%), only heat labile spores were formed without the production of the crystal. When the cystine/cysteine concentration was high (0.25%), spore and crystal formation were completely inhibited. Partial reversal of inhibition of sporulation was brought about by sodium sulphate or zinc sulphate and lead, copper, cadmium or cobalt acetate at 0.2 mM or at 0.2% of sodium or potassium pyruvate, citrate, isaconitate, oxalosuccinate, ∝ -keto-glutarate, succinate, fumarate, malate, or oxalacetate. Glutamate (0.2%) overcame the inhibitory effect of cystine/cysteine completely. The structural changes observed using phase contrast microscopy were dependent upon the concentration of cystine/cysteine

Effect of L-cystine on macromolecular changes during spore and parasporal crystal formation inBacillus thuringiensis var.thuringiensis

High concentration of L-cystine (0.25%) when present in a glucose-mineral salt medium inhibited sporulation-specific events like protease production, calcium uptake and dipicolinic acid synthesis inBacillus thuringiensis var.thuringiensis. In addition, the enzymes of the Krebs cycle from aconitase onwards were completely inhibited by a high concentration of cystine. At a low concentration of cystine (0.05%), none of the above mentioned macromolecular changes were affected. Lipid synthesis monitored by [1,214 C]-acetate incorporation into lipid as well as into whole cells was completely inhibited

Purification, crystallization and partial characterization of the antitumour and insecticidal protein subunit from the delta-endotoxin of Bacillus thuringiensis var. thuringiensis

The antitumour protein from the α-endotoxin of Bacillus thuringiensis var. thuringiensis has been purified, crystallized and partially characterized. The same protein also shows the insecticidal activity. According to amino acid analysis it is an acidic protein with a molecular weight of approx. 13 000