Molecular dimensions, direct

Kobayashi used molecular dimensions directly (101-4). For paraffins he defined an unstability factor which was a measure of approach to a sphere. A fair correlation was obtained between his factor and blending octane number. The calculated factors indicated the observed rise in knock rating with centralization of the double bond in a straight-chain olefin. Gaylor (69) applied Kobayashi s method to aromatics and compared calculations with both clear and blending octane numbers. It is difficult to select molecular dimensions of a flexible molecule representative of its configuration during reaction. 

The chemical effects of ultrasound do not arise from a direct interaction with molecular species. Ultrasound spans the frequencies of roughly 15 kH2 to 1 GH2. With sound velocities in Hquids typically about 1500 m/s, acoustic wavelengths range from roughly 10 to lO " cm. These are not molecular dimensions. Consequently, no direct coupling of the acoustic field with chemical species on a molecular level can account for sonochemistry or sonoluminescence. 

The development of a host of scanning probe devices such as the atomic force microscope (AFM) [13-17] and the surface forces apparatus (SFA) [18-22], on the other hand, enables experimentalists to study almost routinely the behavior of soft condensed matter confined by such substrates to spaces of molecular dimensions. However, under conditions of severe confinement a direct study of the relation between material properties and the microscopic structure of confined phases still remains an experimental challenge. 

Ad(ii) On catalysts with pores and cavities of molecular dimensions, exemplified by mordenite and ZSM-5, shape selectivity provides constraints of the transition state on the S 2 path in either preventing axial attack as that of methyl oxonium by isobutanol in mordenite that has to "turn the comer" when switching the direction of fli t through the main channel to the perpendicular attack of methyl oxonium in the side-pocket, or singling out a selective approach from several possible ones as in the chiral inversion in ethanol/2-pentanol coupling in HZSM-5 (14). Both of these types of spatial constraints result in superior selectivities to similar reactions in solutions. 

Hb and GOx, respectively. The variation in nanopartide size showed a direct correlation with the respective molecular dimensions of the different proteins, suggesting that each nanoparticle comprised a single biomolecule enveloped by a continuous condensed sheet of organoclay oligomers, one unit cell layer in thickness. 

An E-map is computed for the best set and the peaks picked. We then use our knowledge of molecular dimensions and conformations to extract a trial structure. This is the first point at which chemical knowledge is used actively i.e. the direct methods procedure is model free until this point. The structure is completed and refined in the usual way. 

Size. Most commonly-used drugs have molecular weights of less than 1000 daltons and their molecular dimensions are small compared with those of the complex lipids and, especially, the proteins of the cell wall. So their size provides little hindrance to crossing cell walls. Molecules as big as moderately-sized proteins (30,000 daltons and above) have much more difficulty in getting across and normally have to be administered directly into the blood stream (e.g., gene transfer, immunoglobulins). 

If orientation is assumed to occur only in one dimension (an oversimplification), birefringence and several related phenomena (infrared dichroism, etc.) measure the quantity , which is the average angle 8 between the molecular chain direction and that of the orienting force, such as the fiber stretch axis. It is convenient to introduce an orientation function [12]... 

Krigbaum, W. R., Godwin, R. W. Direct measurement of molecular dimensions in bulk polymers. J. Cbem. Phys. 43,4523-4524 (1965). 

PORE. I A minute cavity in epidermal tissue as in skin, leaves, or leather, having a capillary channel to the surface that permits transport of water vapor from within outward but not the reverse. 2. A void of interstice between particles of a solid such as sand minerals or powdered metals, that permits passage of liquids or gases through the material in either direction. I11 some structures, such as gaseous diffusion barriers and molecular sieves, the pores ate of molecular dimensions, i.e 4-10 A units. Such microporous structures are useful for filtration and molecular separation purposes in various industrial operations. 3. A cell in a spongy structure made by gas formation (foamed plastic) that absorbs water on immersion but releases it when stressed. 

The term three-dimensional , as used in this context, loosely refers to substantial molecular dimension in the direction of each of the x, y, and z coordinates that define the geometry of a particular macroassembly. 

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