Strain Substrate

Wlrile quaternary layers and stmctures can be exactly lattice matched to tire InP substrate, strain is often used to alter tire gap or carrier transport properties. In Ga In s or Ga In Asj grown on InP, strain can be introduced by moving away from tire lattice-matched composition. In sufficiently tliin layers, strain is accommodated elastically, witliout any change in the in-plane lattice constant. In tliis material, strain can be eitlier compressive, witli tire lattice constant of tire layer trying to be larger tlian tliat of tire substrate, or tensile. 

The formation of nanostructures such as nanodot arrays has drawn a great attention due to the feasible applications in a variety of functional structures and nanodevices containing optoelectronic device, information storage, and sensing media [1-3]. The various methods such as self-assembled nanodots from solution onto substrate, strain-induced growth, and template-based methods have been proposed for the fabrication of nanodot arrays on a large area, [4-6]. However, most of these works can be applied to the small scale systems due to the limited material systems. 

Gsell M, Jakob P, Menzel D. 1998. Effect of substrate strain on adsorption. Science 280 717. 

Promoters and genes(s) proteins Function (substrate) Strain, plasmid Reference... 

At different times of anaerobic adaptation cells were pelleted and Ars-activity was measured spectrophotometrically in the supernatant as a change in absorbance at 650 nm using X-SO4 as substrate. Strain MR16 carrying the chimeric hydA ars construct pMR16 and the recipient strain of C. reinhardtii were tested. 

Instead of assuming a solid enzyme, in which active center the substrate molecule is bent (the concept of substrate strain), the idea was developed (Koshland 1958,1966) that enzymes can embrace the substrate molecule flexibly in the active center and effect reaction by the formation of specific interactions, the so-called induced jit . This picture is especially appropriate with allosterically activated enzymes or in situations in which part of the enzyme molecule has to turn or move over longer distances to effect catalysis (hinge movement), as for instance with most NAD(P)(H)-dependent enzymes (Stillman, 1999). 

There are several processes that account for the enhancement of reaction rates by enzymes. The major mechanisms are proximity-entropy effects, substrate strain, covalent catalysis, and acid-base catalysis. 

Ranaghan KE, L Ridder, B Szefczyk, WA Sokalski, JC Hermann, AJ Mulholland (2004) Transition state stabilization and substrate strain in enzyme catalysis ab initio QM/MM modelling of the chorismate mutase reaction. Organic Biomolecular Chemistry 2 (7) 968-980... 

The so-called torsion model by Kakitani and Kakitani [203] was developed to explain the high quantum yield of photoisomerization in rhodopsins as compared to isomerization yields observed in model protonated Schiff bases. The main feature of this model is the twist around double bonds in retinal when it is bound to opsin, which would make this substrate strained to be near the transition state for isomerization (Fig. 17). The most important twist as estimated by this model would be around the 11,12 double bond, although other double bonds would simultaneously be twisted to some extent ([204] and refs, therein). The protein was considered to be responsible for inducing the selective twist. This model predicted a... 

Faupel et al. have analyzed the adhesion of metal films deposited on polymer substrates strained in an optical microscope. The deadhesion energy was deduced from the difference in the stress versus strain curves between the film/substrate system and the substrate only. 

Yin J, Andryski SE, Beuscher AE, Stevens RC, Schultz PG. Structural evidence for substrate strain in antibody catalysis. 

The calculated barrier to reaction in chorismate mutase was 17.8 kcal/mol, compared to 42 kcal/mol in the gas phase. Factors other than substrate distortion also play an important part in reducing the barrier to reaction in the enzyme important interactions were identified by a simple decomposition analysis (as described in sections 6.1 and 6.2 above). It was found that Glu78 and Arg90 specifically stabilize the transition state, relative to the bound substrate [8]. Overall, therefore, catalysis in chorismate mutase can be rationalized in terms of a combination of substrate strain and transition state stabilization. While it is possible to analyse all these catalytic effects as arising from maximal binding in the enzyme being achieved at the transition state, it appears useful to separate the different types of contribution. The possible role of substrate destabilization/distortion or strain in lowering the barrier to reaction in enzyme reactions, as put forward by Haldane [219], and invoked in... 

When a dimensional change in a polymer coating does not match that of its constraint (such as the substrate to which it adheres), the resulting strain generates stress in both the polymer and the substrate. Strain arises in polymers by thermal expansion and contraction ( ), from solvent and by-product evaporation (2), from moisture absorption (2), from cure (2), and from physical aging (12). ... 

A mechanistic model has been proposed for PPIase catalysis in which a twisted peptide bond, a structure involving substrate strain, is stabilized by noncovalent interaction with the enzyme [156], However, catalytic antibodies generated to transition state analogs containing twisted carbonyl moieties do not show a PPIase-like catalytic efficiency [157,158], Consequently, small detergent micelles and phosphatidylcholine membranes are able to catalyze CTI of typical PPIase substrates in a manner reminiscent of that observed for catalytic antibodies [159]. Apparently, sequestration of hydrophobic substrates within the enzyme may account for both a small portion of the catalytic power of FKBP and the acceleration of CTI by catalytic antibodies. Despite overall amino acid sequence dissimilarity the structural features making up the active sites of prototypic enzymes such as Cypl8 and ParlO proved to be similar (Fig. 10.6). 

By inserting the calculated substrate strain, es, into formulas (1) and (2), one finds a decrease of the stress in the scale with distance from the periphery of the indent according to the decrease of es. For the example of the piling-up of the surface, a circumferential tensile stress arises, and for the example of the sinking-in a radial tensile stress. Correspondingly, in the former case radial cracks are expected, and in the latter case circumferential cracks. The tensile stresses calculated at positions, which correspond to the observed tip of radial cracks and of the outermost circumferential-tike... 

Enzyme-Substrate Reactions at Equilibrium. Substrate Strain Studies of Chymotrypsin-N-Acetyltyrosine Semicarbazide Complexes. 

Fig. 6.33. Schematic diagram of a thin elastic film bonded to a thin viscous layer which, in turn, is bonded to a thick substrate. Strain in the layer is relaxed by flow in the viscous layer which progresses in a diffusive manner from the edges of the film inward toward its center.

Frame with thumbscrews supports substrate Strain increases with each turn of the screw Quasi-static stretch applied Eccentric disks rotated axially by a motor Translates rotary motion into oscillatory linear motion Dynamic stretch applied... 

STM images indicate that ceria also grows on Rh(lll) forming ordered CeOsClll) islands with their (111) faces parallel and orien-tationally aligned to the main azimuthal directions of the substrate. Strain caused by the mismatch between the lattices of the oxide and metal facilitated the formation of O vacancies in ceria.A similar... 

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