Membrane crystallisation

Key words membrane contactors, hydrophobic membranes, interfaces, self-assembly, colloidal crystals, phase separation, water desalination, membrane crystallisation, membrane distillation. 

Approaches to achieve supersaturation in membrane crystallisation processes... 

However, the effective surface area of mass transfer in the membrane crystalliser is very large, and changes in the solvent evaporation rate can be controlled by modifying the difference of temperature between the crystallising solution and stripping solution, and by altering the concentration of the stripping solutions. 

Furthermore, membrane crystallisation also presents a viable and practical route to present molecules of pharmaceutical interest, such as proteins, in the form of perfect crystals. This is an important target for research, as the identification of protein-activity relationships can accelerate the design of new generation drugs, as well as assist in the development of advanced diagnostic tools and effective therapies for the treatment of human diseases. 

H. Michel (Ed.), Crystallisation of Membrane Proteins, CRC Press, Boca Raton, 1991. ISBN 0849348161. 

The formation of host-guest inclusion compounds in crystals (or in highly ordered membranes or other biological structures) is a phenomenon more organised than simple co-crystallisation of a pair of substances. The special characteristic of inclusion crystallisation is a constant identity of one member in a series of pairs, this member thereby being identified as host, and a constancy of structure type (but not necessarily dimensions) for the host. The higher molecular organisation involved in inclusion... 

X-ray diffraction studies on gramicidin commenced as early as 1949 218-219> and this early work pointed to a helical structure 220). Recent work by Koeppe et al. 221) on gramicidin A crystallised from methanol (/%) and ethanol (.P212121) has shown that the helical channel has a diameter of about 5 A and a length of about 32 A in both cases. The inclusion complexes of gramicidin A with CsSCN and KSCN (P212121) have channels that are wider (6-8 A) and shorter (26 A) than the uncomplexed dimer 221 222). Furthermore there are two cation binding sites per channel situated either 2.5 A from either end of the channel or 2.5 A on each side of its centre 222) Unfortunately these data do not permit a choice to be made from the helical models (i)—(iv) and it is not certain if the helical canals studied are the same as those involved in membrane ion transport. 

To date, very limited information on the atomic structure is available, since crystallisation of hydrophobic membrane proteins remains a challenging problem. 

One of the distinctive features of basophils is that they possess plasma membrane IgE receptors (FceR), which bind the fragment crystallisable (Fc) region of IgE with high affinity. This is in contrast to the FceR on lymphocytes and macrophages, which binds IgE with only low affinity. 

Dichloroselenoacetone, (CHg.CO.CH SeCla.1—Two molecular proportions of pure acetone in a large volume of absolute ether are treated with selenium tetrachloride (1 mol.) in small quantities. The resulting product crystallises in white needles, M.pt. 82° C., which emit a vapour tending to attack the mucous membrane. The compound decomposes on keeping and also on boiling with water, selenium separating. 

Phosphonitrilechloride trimer with an impurity of tetramer is a ciystal-line product (the melting point is. 108-114 °C) with a light odour. It has a slight irritating effect on mucuous membranes. Trimer and tetramer can be separated by fractional vacuum distillation, fractional crystallisation or vacuum sublimation. 

Hunte, C., and Michel, H. (2002). Crystallisation of membrane proteins mediated by antibody fragments. Curr. Opin. Struct. Biol. 12, 503-508. 

Hunte C, Michel H. Crystallisation of membrane proteins mediated... 

Under physiological conditions the fat is normally liquid, but even in mammals the fat can crystallise, for example in the subcutaneous adipose layer. It is therefore most important that the crystal grows in a specially adapted form in parallel with the membremes, so as not to cause mechanical damage. The triglycerides that constitute fat crystallise in three polymorphic forms, and the form obtained first, when the liquid solidifies, can adapt to the curvature of the membrane [67]. It is the so-called a-form, with partly disordered hydrocarbon chains. This disordered nature of the chains results in plastic properties of the crystals and a tendency to grow in thin films perpendicular to the chain direction. 

Proteins embedded in the lipid bilayer of membranes play an important role in membrane functions, involving transport across the bilayer, electron flow and energy conversion, cell recognition, receptor functions, etc. There is not much information available on structural features of these proteins due to difficulties in crystallisation, necessary for complete structure determination. 

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