Geometric modification research

Research of Soviet scientists is surveyed. Contributions to various aspects of the colloid chemistry of silica are examined preparation and stabilization of silica hydrosols preparation of silica gels structural characterization of silicas surface chemistry elucidation adsorption and ion-exchange property examination and geometric and chemical modification of silicas, silica coatings, and so forth. 

A group of papers dealing with the intramolecular photodimerization reaction of a,a>-bis(9-anthryl)alkanes (185 n = 2—10) fails to produce agreement about the detailed mechanism of the reaction. Measurements of quantum yields for fluorescence, photoreaction, and intramolecular deactivation as a function of temperature are said to provide no support for a biradical intermediate, but rather to support a concerted mechanism. In reply, the proposers of the biradical mechanism reinterpret these data and find them consistent with their mechanism. A third research group reports results in fluid solution at room tempera-ture " their concern is more with the question of excimer involvement in the mechanism, and they report that in many of the systems unidentified photoproducts are formed via excimers that do not lead to the normal 9,9 -linked photodimer. The internal photodimer from (185 n = 3) has been studied in a matrix at 10 and photodissociation is shown to lead to two different modifications of (185 n = 3) with different reactivities. A geometrical constraint on the intramolecular photoreactions of 9,9 -linked bisanthracenes is demonstrated by the failure of the di-substituted ethylenes (186) to give internal dimers. 

In the USSR, parallel development of theory, interpretation and equipment of induction logging, based on Doll s concepts of the geometric factor and focusing probe, was started at almost the same time. Also, during this research, new modifications of induction logging were introduced and some of them became conventional and are now used over the world. 

A number of researchers have explored synthetic strategies for the construction of porphyrinic solids that contain molecule-sized cavities or channels. Porphyrin macrocycles can be envisioned as flat, rigid, geometrically square building blocks approximately I nm wide. Out-of-plane twisting by the 5,10,15,20-substituted phenyl rings (as necessitated by steric constraints) provides a route to constmct structures extending beyond the porphyrin macrocycle plane. Chemical modification of the perimeter is facile in many cases. Additionally the thermal stability makes them an attractive precursor for potential use at elevated temperatures. Furthermore, metalloporphyrins have demonstrated catalytic ability in a wide variety of reactions ... 

The researcher should not be overly concerned with the minutiae of the model parameters. Considering the variances between people, an overview covering most of the noted effects should be the goal. The purpose of the models is to examine system behavior when changes are made, such as the effects of geometric and material modifications. Although the actual behavior may not be exact, the variances due to changes in the model may well mimic those of the device or human system. 

Selective permeability allows chemical reactions to be performed exclusively in the capsule interior. The in-situ modification of polyelectrolyte capsules by conducting syntheses inside inorganic nanoparticles creates a new class of multifunctional capsules that combines the properties of inorganic nanomaterials. These multifunctional, composite capsules may find applications for the protection, delivery, and storage of biochemical compounds that are unstable in solution or under UV/visible irradiation, where the use of capsules composed solely of polymeric components cannot be envisaged. Clearly, much further research is required in this area, most notably in understanding the mechanism of the chemical reactions that occur in the confined microsized geometric and diffusional limitations of polyelectrolyte multilayers. 

---