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Biomedical subjects

A Brown

Publications and source records attributed to A Brown.

At least 685 records · Page 38Linked to original sources
PubMed1971

On the concept of orbital steering in catalytic reactions.

Angular displacement from linear overlap of but a few degrees in the transition state of the enzyme-substrate complex has been postulated to be of great kinetic significance ("orbital steering"). The concept of orbital steering is shown to have evolved from the orientation parameters of an equation previously proposed to evaluate the kinetic importance of propinquity. This equation is shown to be naive. Arguments provided against the concept of orbital steering include: (a) force constants predicted from orbital steering are about 100 times those experimentally determined from displacement of nuclei in a direction normal to the axis of a covalent bond (for example, at room temperature vibrational bending amplitudes of +5 degrees or more are common); (b) because of the lessened directionality of orbitals containing nonbonded electron pairs, the force constants in transition states should be even smaller than in the case of a covalent bond; and (c) molecular orbital calculations predict shallow total energy minima for orbital alignment. The experimental rate data offered as a basis for the concept of orbital steering are shown to find rationalization in the previously observed dependence of DeltaSdouble dagger on kinetic order and the energy requirements for the freezing-out of single bonds in the transition state leading to the formation of medium-size ring compounds from extended ground states. It is concluded that if orbital steering does exist, experimental and theoretical evidence to support this concept have yet to be presented.

Journal Article↗
PubMed1970

Bile pigment formation in plants.

The unicellular alga Cyanidium caldarium evolves carbon monoxide during the syntheis of the bile pigment, phycocyanobilin. Carbon monoxide and phycocyanobilin were produced in stoichiometric amounts at comparable rates. Therefore, the mechanism of bile pigment formation in this plant parallels that in mammals.

Bile Pigments↗
PubMed1969

In Canada: a trial of chemoprophylaxis in inactive tuberculosis.

One thousand five hundred and thirty-six patients with inactive tuberculosis were given a course of preventive treatment consisting of either INH alone or INH and PAS while 840 similar patients served as a control group. Discontinuation of the treatment was frequent and was usually caused by development of complaints which the patients ascribed to the drugs they were taking.The annual reactivation rate among controls was 4.9 per 1000. During the period of taking drugs the treated group suffered a reactivation rate of 0.7 per 1000 and those who had taken the medication for at least six months suffered a subsequent annual reactivation rate of 1.3 per 1000. The rate for those who discontinued treatment in the first six months was 5.1 per 1000. There were no reactivations in patients who took INH and PAS for over six months. Bacilli from two of the patients with reactivations who were treated for a prolonged period with INH alone showed resistance to this drug.Chemoprophylaxis of inactive cases is a potent weapon in tuberculosis control; however, it requires thorough motivation and supervision.

Aminosalicylic Acids↗