Showing papers in "Accounts of Chemical Research in 1975"

Disodium tetracarbonylferrate, a transition metal analog of a Grignard reagent

Abstract: This account describes how antibodies specific for nicotine and its metabolites and for various prostaglandins and their metabolites have been used to develop sensitive RIA's for these compounds. Thus far, antibodies have been prepared and RIA's developed for at least 100 other compounds of pharmacological importance. It has been calculated that an individual animal has the potential to produce antibodies that can recognize 10$sup 7$ and perhaps up to 10$sup 8$ diverse immunodominant moieties. Nature, therefore, has provided the pharmacologist and synthetic chemist with an analytical system of extraordinary specificity that can be adapted to the quantitative determination of a wide variety of pharmacologically active molecules. It is clear that RIA will be an important analytical tool in research as well as in the clinical laboratory. (auth)

Classification of photochemical reactions

Abstract: Classification has been the dream of chemists for centuries. We now propose a classification of photochemical reactions built on a single unifying concept, Three striking features of photochemistry are the extreme variety of reactions which are known, the apparent haphazardness which governs the nature of the reactive state, and the lack of predictability of the consequences of slight modifications in reactant structural changes and/or experimental conditions. For instance, the photochemical cis-trans isomerization of dienes seems totally unrelated to the photodimerization of these same dienes to divinylcyclobutanes. Similarly there seems to be little -relationship between the addition of an electron-rich olefin to a ketone and the photoreduction of pyridine. One may therefore ask: is each photochemical reaction unique? A second question is: why does one reaction occur in the singlet state, another in the triplet state, and yet another in a different triplet state? Thus ketones generally photoabstract hydrogen atoms in n , r* states, not T,T* states, and again more efficiently in the triplet state than in the singlet state. A third typical question is: what effect does a

Block copolymers, polymer-polymer interfaces, and the theory of inhomogeneous polymers

Abstract: Most of the polymeric materials one encounters so widely are heterogeneous. For instance, commercial plastics may be blends of immiscible polymers; they may contain antioxidants or other modifiers which are not totally soluble; andfrequently they have added inorganic fillers. Other examples of inhomogeneity in polymer systems are composites, partially crystalline materials, surface layers, ionomers, and block and graft copolymers. In some cases the heterogeneity is the essence of the material's virtue (e.g., its mechanical properties). In other cases heterogeneity is an affliction. But, whether one's goal is to maximize or minimize the effect of nonuniformity, it is well to understand the factors which determine the features of inhomogeneous polymers. This we will attempt to do in a qualitative way by describing, from a simple molecular point of view, the entropy and energy terms which control the systems' physical features. Rather than dealing in generalities, however, let us focus on two partic...

Studies of chemical and physical processes with picosecond lasers

Abstract: One of the basic questions in chemistry today is concerned with the degradation of energy in a molecular system. The time dependent redistribution of energy between the various degrees of freedom'within a molecule on excitation to some excited state and the interactions and energy exchange of the excited molecule with surrounding molecules and external fields is of fundamental importance to a description of molecular phenomena. It is the completion between the various dissipative pathways which determines whether light is emitted or nonradiative physical and chemical processes dominate in the degradation of energy by the molecules of interest Studies of these processes in the picosecond time domain brings new insight of these decay mechanisms since the competitive channeling of energy is often determined on this time scale.