Nonaqueous environments

The maximum plasticisation of the matrix will occur under these conditions which will lead to a high potential to creep under off-axis loads. The residual stress state will also be significantly modified, as discussed in this chapter. 

Schulte [46,47] has demonstrated how different organic solvents, such as hydraulic fluid encountered in the aerospace stmctures, lead to a reduction in the secant modulus of 45° glass fibre laminate under flexural fatigue and the number of cycles to failure. The matrix in this case was a polyether imide (PEI) which is plasticised by ingress of the fluid. A reduction in the matrix modulus means that the shear strength of the matrix will also be reduced with the consequence that the failure mechanism in flexure will change from matrix-fracture to delamination. 

Matrix swelling also contributes to the loss of durability in the 0° composite where plasticisation causes buckling in the compressive face of the coupon [46,47]. This occurs because in compression, the plasticised matrix is unable to support the reinforcement. 

The reader should be reminded that PEI is an amorphous polymer and is much more susceptible to solvents than partially crystalhne polymers such as PEEK, which are used for structural composites. 

Weatherhead [48] and Jones [7] provide a survey of the durability of resins to a range of environments. 

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Hydrophobic substances are soluble in nonpolar solvents, whereas their solubiUty in water is very limited. Many of these substances are also soluble in fats and Hpids and are also called hpophile compounds. Such substances have a tendency to avoid contact with water and to associate with a nonpolar, nonaqueous environment, such as a surface, eg, an organic particle, a particle containing organic material, or the lipid-containing biomass of an organism. 

As described above, the application of classical liquid- liquid extractions often results in extreme flow ratios. To avoid this, a completely symmetrical system has been developed at Akzo Nobel in the early 1990s [64, 65]. In this system, a supported liquid-membrane separates two miscible chiral liquids containing opposite chiral selectors (Fig. 5-13). When the two liquids flow countercurrently, any desired degree of separation can be achieved. As a result of the system being symmetrical, the racemic mixture to be separated must be added in the middle. Due to the fact that enantioselectivity usually is more pronounced in a nonaqueous environment, organic liquids are used as the chiral liquids and the membrane liquid is aqueous. In this case the chiral selector molecules are lipophilic in order to avoid transport across the liquid membrane. 

Because water is a common solvent we might think of it merely as a passive medium in which chemical reactions take place. However, water is a reactive compound, and an alien raised in a nonaqueous environment might consider it aggressively corrosive and be surprised at our survival. For instance, water is an oxidizing agent ... 

Formation of the activated species, whether with a carboxylate or a hydroxyl, must take place in nonaqueous environments due to the rapid breakdown of CDI by hydrolysis. Even in solvents containing small amounts of water, CDI quickly hydrolyzes to CO2 and imidazole. It is best to use solvents with less than 0.1 percent water to prevent extensive CDI breakdown. 

Another advantage of using inorganic silica particles over polymer particles is that they don t shrink or swell when exposed to aqueous or nonaqueous environments. In the case of... 

The tendency of apolar side chains of amino acids (or lipids) to reside in the interior nonaqueous environment of a protein (or membrane/micelle/vesicle). This process is accompanied by the release of water molecules from these apolar side-chain moieties. The effect is thermodynamically driven by the increased disorder (ie., AS > 0) of the system, thereby overcoming the unfavorable enthalpy change (ie., AH < 0) for water release from the apolar groups. 

Lyophilized enzymes have a pH memory, meaning that the activity of the enzyme in organic solvent parallels its pH-activity profile of the aqueous solution from which it was lyophilized [36, 79-81]. However, very often acidic or basic mixtures within a nonaqueous reaction mixture such as reactant, products, or impurities, can disrupt this delicate protonation state, leading to changes in catalytic activity. To counteract this potential problem, solid-state buffers have been developed to protect the enzyme s protonation state in the nonaqueous environment [53, 82]. These solid-state buffers contain pairs of crystalline solids that can be intercon-... 

Khmelnitsky et al. were the first to observe the activating effects salt showed on enzymes in the nonaqueous environment [88]. As shown in Figure 3.7, the transesterification activity of the serine protease subtilisin Carlsberg in anhydrous solvents is strongly dependent on the KC1 content in a lyophilized enzyme preparation and increases sharply as the salt content is increased. This increase in activity was determined to be a result primarily of an increase in kcat and not a decrease in Km, as shown in (Table 3.4). 

Driving-force studies, using mixed-ligand coordination to alter formal potentials, show only normal-region behavior (Fig. 11), not the inverted Marcus curve seen for electrostatically bound compounds. Similar behavior has been reported for phosphonate-bound dyes on 2 in water [67]. Other studies on 2 in nonaqueous environments have yielded Marcus inverted rate behavior or else no sensitivity to driving force, suggesting that water may induce mechanistically distinct behavior [14,37,68]. 

Transfer of a hydrophobic molecule (e.g., a hydro-phobic amino acid and side chain) from an aqueous to a nonaqueous environment is entropically favorable. Explain. 

Consider the entropic effect of decreasing water organization by moving the hydrophobic residue side chains from an aqueous to a nonaqueous environment. 

The hydrophobic amino acid side chains on the exterior of the integral membrane protein interact with the hydrophobic lipid of the membrane exterior and are stable in the nonaqueous environment. These residues pack in the interior, hydrophobic environment of globular proteins. 

Enzymes need some water to remain catalytically active, but this amount of water is small. Randolph et al. (1988) investigated the use of cholesterol oxidase from Cleocysticum chrysocreas by placing the immobilized enzyme in a packed bed and exposing it to bone-dry carbon dioxide. While the enzyme quickly lost activity, it was rapidly restored with only 1% v/v water in the system. Water acts not only to help the enzyme retain its native conformation, but also it can act as a solubility modifier. Organic solvents and other nonaqueous environments can remove the enzyme s essential water (Zaks and Klibanov 1988). 

In hemoglobin, O2 binding to Fe2+ does not oxidize it to Fe3+, as it is protected by protein units around the heme group. A nonaqueous environment is required for reversible O2 binding. 

What kinds of polymeric structures (or monomer collections) might support catalysis and genetics in nonaqueous environments, particularly in solvents found on solar system bodies other than Earth ... 

Can a system capable of Darwinian evolution be demonstrated in the laboratory using nonstandard monomers and/or biopolymers in nonaqueous environments ... 

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