Homogeneous Agents Research Articles

Electrochemical transformations of 2 [formula omitted]hydroxychalcones into flavanoids

2′-Hydroxychalcones are cyclized to flavanones, and flavone, or flavonol, by electrochemically generated tris-(4-bromophenyl)amine cation radical as homogeneous electron-transfer agent.

Stationary Equilibrium In A Market For Durable Assets

This paper presents a dynamic model of consumer trading on the primary, secondary, and scrap markets for a stochastically deteriorating durable good in a stationary economy with perfect information and no transaction costs. We explicitly model the trading process by tracking each durable from its birth in the primary market, through its sequence of owners in the secondary market, until its death in the scrap market. We prove that a stationary equilibrium exists, characterize the distribution of consumer holdings of durables, and show that equilibrium asset prices are shadow prices to a particular regenerative optimal stopping problem. We show that each heterogeneous agent equilibrium is observationally equivalent to a homogeneous agent equilibrium. We derive a differential equation for equilibrium rental rates, and a functional equation which links rental rates to asset prices. These equations show precisely how the structure of durable prices and rental rates embody the functional form and population distribution of preferences, and the technological characteristics of durable goods.

Stationary Equilibrium in a Market for Durable Assets

This paper presents a dynamic model of consumer trading on the primary, secondary, and scrap markets for a stochastically deteriorating durable good in a stationary economy with perfect information and no transaction costs. We explicitly model the trading process by tracking each durable from its "birth" in the primary market, through its sequence of owners in the secondary market, until its "death" in the scrap market. We prove that a stationary equilibrium exists, characterize the distribution of consumer holdings of durables, and show that equilibrium asset prices are shadow prices to a particular regenerative optimal stopping problem. We show that each heterogeneous agent equilibrium is observationally equivalent to a homogeneous agent equilibrium. We derive a differential equation for equilibrium rental rates, and a functional equation which links rental rates to asset prices. These equations show precisely how the structure of durable prices and rental rates embody the functional form and population distribution of preferences, and the technological characteristics of durable goods.

Competition between strains of scrapie depends on the blocking agent being infectious.

Compton White mice (Sincs7) were injected twice intraperitoneally, first with the 22A strain of scrapie agent (in brain homogenates) and then, after 105 days, with the 22C strain. Incubation periods were calculated from the time of the first injection. The experiment was designed so that, with no interaction between strains, the second strain (22C) should have produced cases about 300-350 days after the first injection, depending on the dose of 22C. This was well before the limit of 470 days set by the mean incubation period minus 3 SD of 22A alone: a limit which was used to distinguish 22C from 22A clinical cases. In fact, 22A blocked 22C as shown by (i) the lengthening of 22C incubation periods, (ii) the reduced proportion of cases due to 22C, and (iii) the reduced effective titer of 22C. The blocking efficiency of 22A was not greatly reduced by physicochemical treatments that had little or no effect on its infectivity by the intraperitoneal route. However, treatment of 22A homogenates with 6 M urea virtually eliminated infectivity and also abolished blocking ability. It is concluded that competition depends on the infectivity of the scrapie strain used for blocking.

Oxidative Deblocking of the 4‐Methoxybenzyl Thioether Protecting Group: Application to the Directed Synthesis of Poly‐cystinyl Peptides

AbstractThe 4‐methoxybenzyl thioether protecting group is deblocked efficiently by oxidation with the homogeneous electron transfer agent tris(4‐bromophenyl)ammoniumyl (2.⊕) leading to the disulfide in high yields. S‐(4‐methoxybenzyl)cysteine derivatives like 9 in this way can be transformed into the corresponding cystine derivatives like 10 in 90% yield. Many N and carboxy protecting groups like the Boc and Z group and tert‐butyl or benzyl ester functions are stable under the cleavage conditions. On the other hand the 4‐methoxybenzyl thioether protecting group is totally unaffected by the conditions for oxidative deblocking of the S‐trityl functions by either iodine or rhodanolysis. This opens up new opportunities for the directed synthesis of cystinyl peptides with more than one intra‐ or interchain disulfide bridge. Application of the new method to the synthesis of a cystine peptide with one intrachain SS‐bridge and a double‐chain biscystinyl peptide is reported.

Mild and Effective Removal of Dithioketal Protecting Groups by Triarylamine Cation Radicals as Homogeneous Electron Transfer Agents

Abstract1,3‐Dithianes 2 can effectively be converted in to the parent carbonyl compounds 7 by a very mild oxidative procedure using tri‐p‐tolylammoniumyl (1a+.) or tris(4‐bromophenyl)ammoniumyl (1b+.) as homogeneous electron transfer agents. The yields are equally good for the cleavage by stoichiometric amounts of the triarylammoniumyl hexachloroantimonates as well as for the indirect electrochemical procedure using catalytic amounts of the triarylamine together with electrochemical generation and regeneration of the cation radicals. In the case of 1,3‐dithiolanes 3 the application of stoichiometric amounts of tris(4‐bromophenyl)ammoniumyl hexachloroantimonate is very effective while during the indirect electrochemical procedure the deposition of polymeric sulfur compounds onto the electrode surface has to be prevented by the use of a flow‐through cell. In all cases the conditions for the cleavage are so mild that hydroxy functions and double bonds are tolerated without problems.

Biosynthesis and physiological role of homarine in marine shrimp.

Glycine, which contributes 2 carbon atoms and the nitrogen for the biosynthesis of homarine by homogenates of shrimp muscle, reacts metabolically with succinyl coenzyme A to form N-succinylglycine. The latter product is effectively converted by such homogenates to homarine, and it is concluded that N-succinylglycine is on the main pathway of this biosynthetic series of reactions and provides all of the required atoms in homarine, except for the N-methyl carbon. A possible pathway for the complete biosynthesis of homarine is described. Evidence is presented that homarine acts as a transmethylating agent in shrimp muscle homogenates and is capable of transferring its N-methyl group to form mono-, di-, and trimethylamines, trimethylamine oxide, choline, and betaine. In this process, homarine loses its methyl groups to form picolinic acid, and, conversely, picolinic acid can be methylated to yield homarine. It is speculated that homarine is not only a "methyl" donor but may serve as a reservoir of methyl groups in crustacea.

An effective and mild electrocatalytic procedure for the removal of 1,3-dithiane protecting groups

The 1,3-dithiane protecting group can effectively be removed by indirect electrochemical oxidation under extremely mild conditions, if catalytic amounts of tris(p-tolyl)amine are used as homogeneous electron transfer agents.

Sedimentation properties of the scrapie agent.

The sedimentation behavior of the scrapie agent in homogenates of spleen from infected mice has been determined. Approximately 90% of the scrapie agent was sedimented at an omega2t value of 3 X 10(10) rad2/sec in a fixed-angle rotor. Sedimentation of the agent was not substantially affected by sonication or by treatment with the detergent sodium deoxycholate. The sedimentation profiles of the scrapie agent were similar to those observed for free polyribosomes, but differed from those exhibited by five other subcellular markers. Comparative studies showed that the sedimentation profiles of subcellular markers in spleen suspensions from mice infected with scrapie did not differ from uninoculated controls. These studies suggest that the scrapie agent is a discrete infectious particle which should be separable from cellular membranes.

Modification and extension of a model for predicting the erosion of ductile materials

A statistically derived model for predicting the erosion of ductile target materials was modified and its range was extended to incorporate maximum particle velocities of approximately 3000 m/sec. The usefulness of the modified model in predicting the erosion of ductile targets by both homogeneous and heterogeneous erosive agents was assessed. It was found that soft erosive particles can produce higher erosion rates than hard particles for the same target material. It was concluded that the geometry of the particle acceleration tube employed in the erosion test facility had a significant effect on the magnitude of observed erosion rates.

Crown Gall on Castor Bean Leaves

Secondary tumours were formed on the cotyledonary leaf petiole, the hypocotyl, and first true leaf of castor bean seedlings after inoculating the blades of the cotyledonary leaves with Agrobacterium tumefaciens. Depending on the strain of bacteria employed, 0 to 80 per cent of the plants developed secondary tumours. The ability of different strains to initiate secondary tumours was not obviously correlated with their relative effectiveness in initiating primary tumours. Though all produced primary tumours, five out of ten auxotrophic strains failed to yield secondary tumours, whereas only one out of 14 prototrophic strains failed to do so. Both the number of plants developing secondary tumours and the frequency with which these tumours occurred on different parts of the plant were positively correlated with the concentration of the primary inoculum. Tumours also developed on the cotyledonary leaf petiole and on the hypocotyl after vacuum infiltration of A. tumefaciens into the blade of cotyledonary leaves. In most instances (9 out of 11 plants) no tumours were formed on the blade of the infiltrated leaf. Thus, tumour formation equivalent to secondary tumours can occur in the absence of a primary tumour or an overt primary wound. Excision of inoculated leaves showed that the stimulus for secondary tumour formation moves from the blade to the hypocotyl within 24 h. Attempts to demonstrate the presence of a sub-cellular tumour-initiating agent in homogenates of inoculated leaves were unsuccessful. A. tumefaciens, however, was found in the petiole of the cotyledonary leaf and in the hypocotyl within 24 h of inoculation. The migrating agent responsible for secondary tumour formation in castor beans is concluded to be intact bacteria.

Properties of the Agent of Rous No. 1 Sarcoma

Publisher Summary Viruses that have been obtained in states of significant purity have revealed characteristic forms in electron micrographs, present in repeated examinations, in amounts greatly predominant over other particles; single boundaries in the ultracentrifuge compatible with the variation in size found in electron micrographs; single boundaries in the Tiselius electrophoresis apparatus; and the uniformity of chemical constitution. Judged by these criteria, the Rous agent preparations hitherto described are not composed of pure or homogeneous agents. This chapter discusses isolation and properties of Rous No. 1, elucidating the aspects of isolation, the size of an agent, the lipid content of an agent, and the stability of an agent. The stability of the agent is determined by studying the pH, oxidation, chemical inactivation, enzymic inactivation, irradiation, and freezing and freeze-drying properties of Rous No. 1 agent. Preoccupation with the chemical and physical properties of isolated viruses has been the inevitable result of a situation in which the extracellular infective phase of a virus was the only experimentally accessible one. The interest of the virus-induced tumors for the study of malignant growth does not lie in the naive assumption that all tumors are results of virus infections but lies in the conviction that the knowledge of the mode of intervention of a tumor virus in the normal organization of the infected cell helps elucidate the nature of the change from the normal to the malignant cell.