Crystallization models for

A 1969 paper presented a mathematical crystallization model for the continuous crystallization of zeolite A [174]. The successful implementation of continuous synthesis of zeoHtes must accommodate the relatively slow crystallization rates with the reactor design to allow sufficient residence time at the necessary digestion temperature. A recent patent publication describes continuous zeolite synthesis using microwave heating, which couples the often significant advantages of faster zeolite crystallization under microwave radiation with a continuous synthesis, dewatering and work-up process [175],... 

Lofgren G. (1996) A dynamic crystallization model for chondrules melts. In Chondrules and the Protoplanetary Disk (eds. R. H. Hewins, R. H. Jones, and E. R. D. Scott). Cambridge University Press, Cambridge, pp. 187-196. 

Kramers, J. D. 1988. An open-system fractional crystallization model for very early continental crust formation. Precambrian Research, 38, 281-295. 

Penzien K. and Schmidt G.M. (1969) Reactions in chiral crystals an absolute asymmetric synthesis, Angew. Chem. Int. Ed. Engl. 8, 608-609. Saeva F.D., Sharpe P.E. and Olin G.R. (1975) Asymmetric synthesis in a cholesteric liquid crystal solvent, J. Amer. Chem. Soc. 97, 204-205. Thiemann W. and Teutsch H. (1990) Possible amplification of enantiomeric excess through structural properties of liquid crystals-model for origin of optical activity in the biosphere. Origin ofLife Evolution of Biosphere 20, 121-126 1986,16,420. 

Vanderkooi, G., and Green, D. E., 1970, Biological membrane structure. I. the protein crystal model for membranes, Proc. Natl. Acad. Sci. USA 66 615. 

It has not proved possible to develop general analytical hard-core models for liquid crystals, just as for nonnal liquids. Instead, computer simulations have played an important role in extending our understanding of the phase behaviour of hard particles. Frenkel and Mulder found that a system of hard ellipsoids can fonn a nematic phase for ratios L/D >2.5 (rods) or L/D <0.4 (discs) [73] however, such a system cannot fonn a smectic phase, as can be shown by a scaling... 

McMillan W L 1971 Simple molecular model for the smectic A phase of liquid crystals Phys.Rev A 4 1238-46... 

Polarons of Molecular Crystal Model 451 for complex z with a nonvanishing imaginary part Eq.(25) is written as... 

A5 The Gay-Beme model for liquid crystal systems and some typical arrangements. 

The chemistry of interest is often not merely the inhnite crystal, but rather how some other species will interact with that crystal. As such, it is necessary to model a system that is an inhnite crystal except for a particular site where something is diherent. The same techniques for doing this can be used, regardless of whether it refers to a defect within the crystal or something binding to the surface. The most common technique is a Mott-Littleton defect calculation. This technique embeds a defect in an inhnite crystal, which can be considered a local perturbation to the band structure. 

Optical parametric oscillators (OPOs) represent another tunable soHd-state source, based on nonlinear optical effects. These have been under development for many years and as of this writing (ca 1994) are beginning to become commercially available. These lasers may be tuned by temperature or by rotating a crystal. Models available cover a broad wavelength range in the visible and infrared portions of the spectmm. One commercial device may be tuned from 410 to 2000 nm. 

Similar models for the crystal stmcture of Fortisan Cellulose II came from two separate studies despite quite different measured values of the diffraction intensities (66,70). Both studies concluded that the two chains in the unit cell were packed antiparallel. Hydrogen bonding between chains at the corners and the centers of the unit cells, not found in Cellulose I, was proposed to account for the increased stabiUty of Cellulose II. The same model, with... 

Hydrated bilayers containing one or more lipid components are commonly employed as models for biological membranes. These model systems exhibit a multiplicity of structural phases that are not observed in biological membranes. In the state that is analogous to fluid biological membranes, the liquid crystal or La bilayer phase present above the main bilayer phase transition temperature, Ta, the lipid hydrocarbon chains are conforma-tionally disordered and fluid ( melted ), and the lipids diffuse in the plane of the bilayer. At temperatures well below Ta, hydrated bilayers exist in the gel, or Lp, state in which the mostly all-trans chains are collectively tilted and pack in a regular two-dimensional... 

Figure 3 Comparison of the densities (in g/cm ) of model compounds for membrane lipids computed from constant-pressure MD simulations with the coiTespondmg experimental values. The model compounds include solid octane and tricosane, liquid butane, octane, tetradecane, and eico-sane, and the glycerylphosphorylcholme, cyclopentylphosphorylcholme monohydrate, dilauroly-glycerol, anhydrous cholesterol, cholesterol monohydrate, and cholesterol acetate crystals. (Models from Refs. 18, 42, and 43).

Stein, P.E., et al. Crystal stmcture of ovalbumin as a model for the reactive centre of serpins. Nature 347 99-102, 1990. 

Early diffraction photographs of such DNA fibers taken by Rosalind Franklin and Maurice Wilkins in London and interpreted by James Watson and Francis Crick in Cambridge revealed two types of DNA structures A-DNA and B-DNA. The B-DNA form is obtained when DNA is fully hydrated as it is in vivo. A-DNA is obtained under dehydrated nonphysiological conditions. Improvements in the methods for the chemical synthesis of DNA have recently made it possible to study crystals of short DNA molecules of any selected sequence. These studies have essentially confirmed the refined fiber diffraction models for A- and B-DNA and in addition have given details of small structural variations for different DNA sequences. Furthermore, a new structural form of DNA, called Z-DNA, has been discovered. 

Wolberger, C., et al. Crystal structure of a Mat o2 home-odomain operator complex suggests a general model for homeodomain-DNA interactions. Cell 67 517-528, 1991. 

---