Rational design of an inhibitor of dethiobiotin synthetase; interaction of 6-hydroxypyrimindin-4(3H)-one with the adenine base binding site

Modelling of the H-bonding interactions involved in the binding of the adenine base component of ATP to E. coli dethiobiotin synthetase (DTBS) suggested that 6-hydroxypyrimidin-4(3H)-one (6-HP4) should selectively bind to this site in the enzyme. Kinetic studies show that 6-HP4 is a competitive inhibitor of DTBS and x-ray crystallography shows that 6-HP4 binds specifically in the purine base binding site of the enzyme.     

A ruthenium-bound diquaternary viologen analogue: The[1,1′-(1,3-propanediyl)-bis(4,4′-bipyridinium]-pentaammineruthenium(II) cation

Transition Metal Chemistry -     

The concept of energy and its early historical development

The concept of energy, the premier concept of physics and indeed of all science, is here investigated from the standpoint of its early historical origin and the philosophical implications thereof. The fundamental assumption is made that the root of the concept is the notion of invariance or constancy in the midst of change. Salient points in the development of this idea are presented from ancient times up to the publication of Lagrange'sMécanique Analytique (1788).     

Interaction of nonionic dextrans with silver bromide hydrosols

Summary The effects of nonionic dextrans of different molecular weights on the stability of silver bromide solsin statu nascendi in aqueous solutions and watermethanol mixtures have been studied. Regardless of the molecular weight of the polymer no flocculation of the sol is observed. In the presence of indifferent electrolytes sols are destabilized over a given concentration range of the polymer, which depends little on the molecular weight of the latter. The concentration of the electrolytes required to cause destabilization in the presence of dextrans depends on the counterion charge (theSchulze-Hardy rule) but in each case the critical coagulation concentration is lower for the same sol than in the absence of the polymers. At still higher dextran concentrations the sols are protected toward electrolytes. In the presence of methanol more polymer and less electrolyte is needed to destabilize the sol. An explanation of these effects is offered.

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Zusammenfassung Die Effekte der nichtionogenen Dextran-Polymeren von verschiedenen Molekulargewichten auf die Stabilität von Silberbromid Solenin statu nascendi in wässerigen Lösungen und in Wasser-Methylalkohol Gemischen wurden untersucht. Die Makromoleküle allein konnten die Sole nicht koagulieren. Die Sole wurden jedoch destabilisiert in Anwesenheit von bestimmten Mengen von Polymeren wenn Neutralelektrolyte zugesetzt wurden: Die kritischen Koagulationskonzentration der Gegenionen hängt von deren Ladung ab (Schulze-Hardy Regel); jedoch in allen Fällen ist die für die Koagulation notwendige Salzmenge beträchtlich niedriger als in der Abwesenheit von Dextran in denselben Solen. Bei höheren Polymerkonzentrationen werden die Silberhalogenidsole gegen Elektrolytkoagulation geschützt. In Wassser-Alkohol Lösungen ist mehr Polymer und weniger Elektrolyt zur Koagulation der Sole notwendig. Eine Erklärung dieser Beobachtungen wurde angeboten.

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With 14 figures and 2 tables

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1) Supported by the NSF grant GP 42331X.

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2) A part of a Ph.D. thesis byDavid Lindsay.     

Acceleration waves and second sound in a perfect fluid

The evolutionary behaviour of acceleration waves of arbitrary shape in a perfect fluid is investigated. The theory employed allows two coupled mechanical and temperature acceleration waves to propagate with finite wavespeeds. New results are described for waves entering isothermal regions but where the exterior flow velocity is non-zero.