Moisture-sensitive proteins

Despite recent advances in understanding the influence of moisture on the physical state of the solid, it is perhaps the effect of sorbed moisture on the chemical stability of moisture-sensitive drugs that is most important, particularly because many new bioactive agents are expensive moisture-sensitive proteins. 

We have seen a quantum leap in progress in the coordination chemistry of copper-dioxygen interactions, resulting in a complete change in thinking about Cu202 structure and related protein chemistry. The problems of copper ion lability, peroxide disproportionation and air/moisture sensitivity have been overcome, and it has been proved that low-molecular-weight Cu 02 or Cu (0)2 complexes can be prepared, and that several different structural types exist. It is apparent that u-r 2 r 2-peroxo coordination is present in oxy-Hc and oxy-Tyr. 

It is most desirable that a given amino acid should form a single-derivative peak after treatment with a single derivatization agent. Unfortunately, that is not the case for many important determinations. Thus, for example, permethylation [481] and the formation of W-dimethylaminomethylene alkyl esters [482] appeared limited to only some amino acids. Persilylation of all amino acid functional groups with potent silyl donors [483] comes perhaps closest to definition of a universal reaction , but even here some problems are encountered (a) derivatization can be time-consuming (b) multiple derivatives are occasionally formed even under precautions (c) Si-N bonds are moisture-sensitive and (d) truly quantitative derivatization is difficult to achieve for all protein amino acids. 

DPNR is a highly purified form of NR with very low nitrogen and ash contents and low water absorption. The preparation of this rubber from DPNR latex is described in Section 4.5.4. DPNR is well suited for electrical and engineering applications and is used in fabricating seismic isolators for buildings in earthquake-prone areas, for example. DPNR exhibits low creep, which is essential for such applications. Removal of proteins from NR reduces its moisture sensitivity, thereby improving its engineering properties. 

Wheat gluten is another protein from plants, which was intensively studied for its material applications. Wheat processing requires the presence of plasticizers such as glycerol or water to disrupt disulfide bonds. To control the formation of a crosslinked network, cysteine, formaldehyde or glutaraldehyde can be added. This contributes also to an improvement in moisture sensitivity and in elongation at break. On the other hand, the wheat gluten fibres have better properties compared to other protein-based bio products for biomedical applications. 

For hydrophilic compounds such as polysaccharides (thermoplastic starch) and proteins, multilayer structures provide certain advantages compared with polymer blends. For instance, moisture sensitivity of these hydrophilic polymers is not completely protected in blends because the phase distribution is close to the surface. However, starch or another hydrophilic film can be held between hydrophobic biodegradable components by using multilayers, thus avoiding the plasticization of the hydrophilic materials. 

Tape stripping can be further used to investigate intercorneocyte cohesion within the SC by quantifying the amount of SC removed.11 When using standardized tape stripping conditions, the more SC removed, the smaller the SC cohesion. For instance, tape stripping in combination with a protein assay to accurately quantify SC removal proved to be a sensitive method in detecting keratolytic efficacy of salicylic acid preparations within hours of application.27 This method may also be useful to measure the influence of moisturizers or other skin care preparations on SC cohesion. 

The compensation phenomena considered above are not only characterise of enzyme reactions. The compensation relationships in protein denaturation are noted for enormous ranges of Ea values (from 0 to 120 kcal/mole) and AS of (from 10 to 400 eu) (Likhtenshtein and Troshkina, 1968). These quantities have been found to be highly sensitive to to external condidion (pH, additive, moisture content, etc.) and rotational diffusion of spin labels introduced into various portions of globular proteins. They have also been observed, though to a less extend, in various processes in the condenced phase (chemical reactions, diffusion, evaporation, electrical, conduction, electron transfer, etc. The main property of all these systems, which differ from simple gas reactions, is the cooperative behavior of particle assemblies surrounding the reaction centers. 

They are polymerized by ring opening with separation of C02, yielding poly(amino acids) which are a useful protein model. More than 100 of these anhydrides, their polymers and copolymers are known [58]. AH these compounds are very sensitive to moisture and to the effects of chemical agents. 

The physical/chemical states and the thermal transitions of food materials determine the process conditions, functionality, stability and overall quality, including the texture, of the final food products. Carbohydrates and proteins— two major biopolymers in various food products—can exist in an amorphous metastable state that is sensitive to moisture and temperature changes (Cocero and Kokini 1991 Madeka and Kokini 1994, 1996). The physical states of components in a biopolymer mixture determine the transport properties, such as viscosity, density, mass and thermal dif-fusivity, together with reactivity of the material. 

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