Crystallization research

The catalysts with the simplest compositions are pure metals, and the metals that have the simplest and most uniform surface stmctures are single crystals. Researchers have done many experiments with metal single crystals in ultrahigh vacuum chambers so that unimpeded beams of particles and radiation can be used to probe them. These surface science experiments have led to fundamental understanding of the stmctures of simple adsorbed species, such as CO, H, and small hydrocarbons, and the mechanisms of their reactions (42) they indicate that catalytic activity is often sensitive to small changes in surface stmcture. For example, paraffin hydrogenolysis reactions take place rapidly on steps and kinks of platinum surfaces but only very slowly on flat planes however, hydrogenation of olefins takes place at approximately the same rate on each kind of surface site. 

UCL Crystallization Research Group Publications Composition, density and viscosity of saturated solutions", Go to the following web site for information http //WWW. ucl. ac. uk/ ucec02j/Xm pubs. htm. 

Jones, A.G. and Teodossiev, N.M., 1988. Microcomputer programming of dosage rate during batch precipitation. Crystal Research and Technology, 23, 957-966. 

Jones, A.G., Akers, S.R.G. and Budz, J., 1986. Microcomputer programming of temperature in a batch cooling crystallizer. Crystal Research and Technology, 21, 1383-1390. 

Another direction in liquid crystal research is the fabrication of new molecules that mimic natural materials. The molecule shown here forms two different liquid crystals because of the cylindrical properties of the color-shaded portions of the molecule. These two trios are tethered together by long hydrocarbon chains. In addition to forming liquid crystals, this molecule self-assembles into organized larger units, as do proteins and DNA. The techniques used to synthesize this particular molecule can be adapted to incorporate... 

In summary, it appears that gold(I) will continue to be a very rich source of inspiration and experimentation, not only in liquid crystal research but in research using gold liquid crystals at the interface of gold chemistry and the material... 

Also there seems to be a certain time delay between photoreaction and complete recovery of the nematic phase. This problem is relevant to molecular mobility in liquid crystals as a function of temperature, rubbing condition, external electric field and most importantly, the type of liquid crystal. Research is now being undertaken on direct determination of molecular mobility by fluorescence technique. 

Collings, P. J. and Patel, J. S., Handbook of Liquid Crystal Research, Oxford University Press, New York, 1997. 

Ciystallization from solution is an important separation and purification process in a wide variety of industries. These range from basic materials such as sucrose, sodium chloride and fertilizer chemicals to pharmaceuticals, catalysts and specialty chemicals. The major purpose of crystallization processes is the production of a pure product. In practice however, a number of additional product specifications are often made. They may include such properties as the ciystd size distribution (or average size), bulk density, filterability, slurry viscosity, and dry solids flow properties. These properties depend on the crystal size distribution and crystal shape. The goal of crystallization research therefore, is to develop theories and techniques to allow control of purity, size distribution and shape of crystals. 

Method of lines. This method, which was introduced in the crystallization research by Tsuruoka and Randolph (JJ, transforms the population balance into a set of ordinary differential equations by discretization of the size axis in a fixed number of grid points. The differential 3 G L,t)n(L,t) /3L is then approximated by a finite difference scheme. As has been shown (X) a fourth-order accurate scheme using an equidistant grid (i- l.z) results in ... 

Allied with the diffraction methods, such as low-energy electron diffraction (LEED) and photoelectron diffraction (PED), which can also be applied in single-crystal research, these advances have led to much better interpretations of the vibrational spectra of chemisorbed hydrocarbons in terms of the structures of the surface species. The new results have in turn led to the possibility of reassessing more reliably earlier interpretations of the infrared or Raman spectra of adsorbed hydrocarbons on the finely divided metal samples (usually oxide supported) that are more closely related to working solid catalysts. Such spectra are more complicated because of the occurrence of a variety of different adsorption sites on the metal particles, with the consequence that the observed pattern of absorption bands frequently arises from overlapping spectra from several different surface species. 

Pure, precisely ordered protein crystals of sufficient size and uniformity for X-ray analysis are in demand by the pharmaceutical industry as tools for research. Structural information gained from protein crystals can provide a belter understanding of the role of a given protein in the budy s immune system. Protein crystal research could ultimately aid in the development of more effective drugs and life-saving treatments for many diseases. 

F. Cser, K. Nitrai, G. Hardy Advances in Liquid Crystal Research and Applications, ed. L. Bata Pergamon Press, Oxford, p. 845 (1980)... 

As is known, the question of how to predict the type of mesophase on the basis of the molecular structure of liquid crystals alone is not yet solved in spite of its vital importance for low-molecular crystals. Researchers rely only on some empirical... 

Shibaev, V. P. in Advances in liquid crystal, research and applications (Ed. L. Bata) Oxford Pergamon Press — Budapest Akademiai Kiado, v. 2, 869 (1980)... 

Kazuaki Tarumi, one of the liquid crystal research/physics team at Merck, is particularly aware of Ignorance , without which he might have taken seriously the many arguments against his research project and never achieved the goal. 

Since the concept of topochemically controlled reactions was established, various approaches to asymmetric synthesis using a solid-state reaction have been attempted, most actively by the research group at the Weismann Institute. Their studies have been concerned with the bimolecular reactions of chiral crystals in the solid state. In these studies, successful absolute asymmetric synthesis has been performed by using topochemically controlled four-centered photocyclodimerizations of a series of unsymmetrically substituted diolefin crystals. Research on reactivity in the crystalline state has been extended in recent years to a variety of new systems, and many absolute asymmetric syntheses have been provided. Successful examples of absolute asymmetric synthesis using chiral crystals are listed in Tables 2 to 4, which are divided into three categories intermolecular photoreaction in the solid state (Table 2), intramolecular photoreaction in the solid state (Table 3, A-D), and asymmetric induction in the solid-gas and homogeneous reactions (Table 4). 

Microcrystallites represent highly interesting objects for research in the field of heterogenous catalysis. Big clusters can serve as model compounds for metal crystallites. Questions arising in crystal research may be answered by studying the growth and prop-... 

A.G. Petrov, M.D. Mitov and A.I. Derzhanski, in Advances in Liquid Crystal Research... 

H.-J. Deutscher, M. Korber and H. Schubert, Advances in Liquid Crystal Research and Application , Ed. L. Bata, Pergamon Press, Oxford, 1980, p. 1075. 

As was pointed out in the introduction, optical detection of the Zeeman transitions of the triplet state preceded the optical detection in zf. Since these former experiments resemble those in ionic crystals, researchers in this field called this technique MODR (microwave-optical double resonance). The assignment of the zf transitions as well as the relative order of the zf levels could be concluded also from the MODR techniques as in the PMDR technique. The first reported MODR experiment was made by Sharnoff (15), in which the Am = 2 transition of the C10D8 tr Plet state in a biphenyl host, using amplitude modulation of the microwave power. A few months later Kwiram reported the optical detection of the Am = + 1 for phenanthrene in biphenyl (16). The experiments were... 

YICHENG WU AND CHUANGTIAN CHEN Beijing Center for Crystal Research and Development, Chinese Academy ofScience, Beijing... 

---