Spatial restriction

Valentin G, Haas P, Gilmour D (2007) The chemokine SDFla coordinates tissue migration through the spatially restricted activation of Cxcr7 and Cxcr4b. Curr Biol 17 1026-1031 Wallace VC, Blackboard J, Segerdahl AR, Hasnie F, Pheby T, McMahon SB, Rice AS (2007) Characterization of rodent models of HlV-gpl20 and anti-retroviral-associated neuropathic pain. Brain 130(Pt 10) 2688-2702... 

The situation becomes quite different in heterogeneous systems, such as a fluid filling a porous medium. Restrictions by pore walls and the pore space microstructure become relevant if the root mean squared displacement approaches the pore dimension. The fact that spatial restrictions affect the echo attenuation curves permits one to derive structural information about the pore space [18]. This was demonstrated in the form of diffraction-like patterns in samples with micrometer pores [19]. Moreover, subdiffusive mean squared displacement laws [20], (r2) oc tY with y < 1, can be expected in random percolation clusters in the so-called scaling window,... 

Lu, S Bogorad, L. D Murtha, M. T., and Ruddle, F. (1992). Expression of a murine homeobox gene, Dbx, displays extreme spatial restriction in embryonic forebrain and spinal cord. Proc. Natl. Acad. Sci. USA 89 8053-8057. 

Robinson, G. W Wray, S. and Mahon, K. A. (1991). Spatially restricted expression of a member of a new family of murine Distal-less homeobox genes in the developing forebrain. New Biologist 5 1183-1194. 

We wondered why NSCs proliferated exclusively on surfaces with EGF-His ligands anchored by coordination. We focused on two aspects in particular the conformational integrity of coordinated EGF-His and the stability of coordinate bonds at the interface. Conformational information was acquired with multiple internal reflection-infrared absorption spectroscopy (MIR-IRAS) [97]. The stability of coordinate bonds was assessed by culturing NSCs on a surface with a small region of EGF-His ligands anchored by coordination. This spatially restricted EGF-His anchoring enabled an intuitive exploration of EGF-His release under cell culture conditions. 

To diffuse rapidly in the plane of the membrane (lateral diffusion), a molecule must simply move around in the lipid environment (including the polar head groups). It need not change how it interacts with phospholipids or with water since it is constantly exposed to pretty much the same environment. Lateral diffusion can be slowed (or prevented) by interactions between membrane proteins and the cellular cytoskeleton. This spatially restricts a plasma membrane protein to a localized environment. 

STOCs arise from the concerted activation of up to 100 Ca2+-activated K+ channels (KCa) in the sarcolemma as a consequence of Ca2+ release from the SR. This release may take the form either of non-propagating focal events such as sparks or puffs , or of more regenerative Ca2+ waves. Since a temporal correlation between them exists, STOCs have been attributed to focal nonpropagating Ca2+ release events. However, this view requires that each STOC is a spatially restricted membrane current that occurs at selected areas of membrane closely apposed to the SR. While essential to the prevalent hypothesis for STOCs,... 

In this study, features of the control of both Kca and STOCs have been examined. The results suggest that STOCs may be spatially restricted membrane currents and that KCa channels are sensitive to both depolarization and local subsarcolemma Ca2+ increases but not to alterations in bulk average [Ca2+]c. 

Up to this point only overall motion of the molecule has been considered, but often there is internal motion, in addition to overall molecular tumbling, which needs to be considered to obtain a correct expression for the spectral density function. Here we apply the model-free approach to treat internal motion where the unique information is specified by a generalized order parameter S, which is a measure of the spatial restriction of internal motion, and the effective correlation time re, which is a measure of the rate of internal motion [7, 8], The model-free approach only holds if internal motion is an order of magnitude (<0.3 ns) faster than overall reorientation and can therefore be separated from overall molecular tumbling. The spectral density has the following simple expression in the model-free formalism ... 

Protein substrates are degraded in the cell at specific times in response to physiological stimuli. In addition, degradation of substrates is probably spatially restricted within a cell. Based on accumulated evidence, it appears that the vulnerability or resistance to ubiquitin—proteasome-mediated degradation is regulated usually by a posttranslational modification. The protein substrates are modified in two main ways (1) by phosphorylation or (2) by allosteric modifications. 

In addition to imposing spatial restrictions on the distributions of adjacent water molecules, the various groups in the solute sugar molecule also impose orientational structuring upon these solvent molecules. Figure 10 displays the distributions of orientations for water molecules aroimd the methylene carbon C6. 

In mixed Tishchenko reactions using benzaldehyde combined with fural or 2,3-dimethyoxybenzaldehyde in a 1 1 ratio (Scheme 12.24/b), the Sm-supported material 17 gave a better selectivity in cross products P (53-67%) than the molecular Sm[N(SiMe3)2]3 (36-51%). Again, the changed selectivity was attributed to phenomena like spatial restriction and diffusion controlled surface confine-... 

The vdW force is always attractive between any two materials in a vacuum. This is because there is no interaction between a dielectric material and a vacuum. However, in the Casimir effect, the spatial restriction of vacuum quantum fluctuations when two metal plates are placed in close proximity, creates an attractive pressure on them, in addition to the vdw force. 

This description is elaborated below with an idealized model shown in Figure 17. Imagine a molecule tightly enclosed within a cube (model 10). Under such conditions, its translational mobility is restricted in all three dimensions. The extent of restrictions experienced by the molecule will decrease as the walls of the enclosure are removed one at a time, eventually reaching a situation where there is no restriction to motion in any direction (i.e., the gas phase model 1). However, other cases can be conceived for a reaction cavity which do not enforce spatial restrictions upon the shape changes suffered by a guest molecule as it proceeds to products. These correspond to various situations in isotropic solutions with low viscosities. We term all models in Figure 17 except the first as reaction cavities even... 

This last problem is perhaps not strictly within the realm of photochemistry. It is however so important potentially that it cannot be overlooked on grounds of arbitrary separations between different branches of scientific research (perhaps the expression of interdisciplinary approach would best describe it). A few pages will therefore be devoted to the science and technology of artificially organized molecular systems such as monomolecular and multimolecular layers, micelles and spatially restricted environments like zeolites and since we reach here another of the frontiers of photochemistry, section 8.4 in the final chapter is devoted to these systems. 

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