Localization, intramolecular

One of the major problems of the theory of intramolecular local mobility or kinetic flexibility lies in the establishment of the principal mechanism of mobility for the macromolecules of a given chemical structure and constitution and of local conformational microstructure. The question arises, which of the elementary acts leads to the ability of individual parts of the macromolecule for changing their shape during definite time intervals characteristic of a certain class of motions 38-148)... 

Intramolecular localization of rabbit allotypic determinants. See text and Fig. 2 for more detailed description. 

Both absorption and emissirm processes may be intramolecular, localized in a single molecule. On the other hand, they can also involve whole crystals that may act as absorbers and emitters. Such energy transfers can manifest themselves in different ways that include sensitized fluorescence or phosphorescence, concentration depolarization of fluorescence, photo-conduction, and formation of triplet acceptor molecules. 

One of the most important intramolecular local reactivity descriptors is the Fukui function which is defined... 

Minimal END has also been applied to a model system for intramolecular electron transfer. The small triatomic system LiHLi is bent C2v structure. But the linear structure presents an unrestricted Haiti ee-Fock (TJHF) broken symmetry solution with the two charge localized stmctures... 

The systematic study of piezochromism is a relatively new field. It is clear that, even within the restricted definition used here, many more systems win be found which exhibit piezochromic behavior. It is quite possible to find a variety of potential appUcations of this phenomenon. Many of them center around the estimation of the pressure or stress in some kind of restricted or localized geometry, eg, under a localized impact or shock in a crystal or polymer film, in such a film under tension or compression, or at the interface between bearings. More generally it conveys some basic information about inter- and intramolecular interactions that is useful in understanding processes at atmospheric pressure as well as under compression. 

Once the model of a ligand-receptor complex is built, its stability should be evaluated. Simple molecular mechanics optimization of the putative ligand-receptor complex leads only to the identification of the closest local minimum. However, molecular mechanics optimization of molecules lacks two crucial properties of real molecular systems temperature and, consequently, motion. Molecular dynamics studies the time-dependent evolution of coordinates of complex multimolecular systems as a function of inter- and intramolecular interactions (see Chapter 3). Because simulations are usually performed at nonnal temperature (—300 K), relatively low energy barriers, on the order of kT (0.6 kcal), can... 

While being very similar in the general description, the RLT and electron-transfer processes differ in the vibration types they involve. In the first case, those are the high-frequency intramolecular modes, while in the second case the major role is played by the continuous spectrum of polarization phonons in condensed 3D media [Dogonadze and Kuznetsov 1975]. The localization effects mentioned in the previous section, connected with the low-frequency part of the phonon spectrum, still do not show up in electron-transfer reactions because of the asymmetry of the potential. 

The proximity effect. This is the simple idea that in an intramolecular reaction the substrate function may be exposed to a larger local concentration of the reagent than in an intermolecular reaction, because the two functions are covalently constrained to occupy adjacent space. This effect has been called the approximation or propinquity effect. The proximity effect certainly seems physically reasonable and is likely to make some contribution to intramolecular reactivity, but it cannot be a major contributor when EM is large, because EM is itself a measure of a presumed local concentration, and the observed large EM values are physically impossible concentrations. The magnitude of rate enhancement achievable by prox-... 

Next come the dihedral angles (or torsions), and the contribution that each makes to the total intramolecular potential energy depends on the local symmetry. We distinguish between torsion where full internal rotation is chemically possible, and torsion where we would not normally expect full rotation. Full rotation about the C-C bond in ethane is normal behaviour at room temperature (although 1 have yet to tell you why), and the two CH3 groups would clearly need a threefold potential, such as... 

Ideal localized adsorption, 5, 10 Infrared method, 373, 374 Initiators of polymerization, 148 Intramolecular London energies, 74, 78 Iodine molecule intramolecular London energy, 78... 

The investigation of structural dynamics of CP is particularly topical in connection with the establishment of correlation between local intramolecular mobility and the reactivity of chain fragments. It has been established that groups located in the most mobile parts of the polymer chain exhibit the greatest reactivity [48], The chemical heterogeneity in relationship to local mobility is particularly... 

The hydroxypropyl derivative of guar GaM (HPG) was prepared with propylene oxide in the presence of an alkaline catalyst. HPG was subsequently etherified as such with docosylglycidyl ether in isopropanol and presence of an alkaline catalyst [432]. The peculiar features of the long-chain hydrophobic derivatives were ascribed to a balance between inter- and intramolecular interactions, which is mainly governed by the local stress field. 

Some information concerning the intramolecular relaxation of the hyperbranched polymers can be obtained from an analysis of the viscoelastic characteristics within the range between the segmental and the terminal relaxation times. In contrast to the behavior of melts with linear chains, in the case of hyperbranched polymers, the range between the distinguished local and terminal relaxations can be characterized by the values of G and G" changing nearly in parallel and by the viscosity variation having a frequency with a considerably different exponent 0. This can be considered as an indication of the extremely broad spectrum of internal relaxations in these macromolecules. To illustrate this effect, the frequency dependences of the complex viscosities for both linear... 

In summary, all the experiments expressly selected to check the theoretical description provided fairly clear evidence in favour of both the basic electronic model proposed for the BMPC photoisomerization (involving a TICT-like state) and the essential characteristics of the intramolecular S and S, potential surfaces as derived from CS INDO Cl calculations. Now, combining the results of the present investigation with those of previous studies [24,25] we are in a position to fix the following points about the mechanism and dynamics of BMPC excited-state relaxation l)photoexcitation (So-Si)of the stable (trans) form results in the formation of the 3-4 cis planar isomer, as well as recovery of the trans one, through a perpendicular CT-like S] minimum of intramolecular origin, 2) a small intramolecular barrier (1.-1.2 kcal mol ) is interposed between the secondary trans and the absolute perp minima, 3) the thermal back 3-4 cis trans isomerization requires travelling over a substantial intramolecular barrier (=18 kcal moM) at the perp conformation, 4) solvent polarity effects come into play primarily around the perp conformation, due to localization of the... 

Various other interactions have been considered as the driving force for spin-state transitions such as the Jahn-Teller coupling between the d electrons and a local distortion [73], the coupling between the metal ion and an intramolecular distortion [74, 75, 76] or the coupling between the d electrons and the lattice strain [77, 78]. At present, based on the available experimental evidence, the contribution of these interactions cannot be definitely assessed. Moreover, all these models are mathematically rather ambitious and do not show the intuitively simple structure inherent in the effect of a variation of molecular volume considered here. Their discussion has to be deferred to a more specialized study. 

The local conformational preferences of a PE chain are described by more complicated torsion potential energy functions than those in a random walk. The simulation must not only establish the coordinates on the 2nnd lattice of every second carbon atom in the initial configurations of the PE chains, but must also describe the intramolecular short range interactions of these carbon atoms, as well as the contributions to the short-range interactions from that... 

Avoidance of the intramolecular collapses in PE can be achieved by selection of a relationship between the 2nnd lattice and its underlying diamond lattice at the outset of the simulation, and then prohibition of occupation by three beads of that half of the equilateral triangles with area L2/2 that form the local collapse. Implementation of this restriction did not decrease the acceptance rate significantly (the decrease is less than 1%) in our simulations of amorphous PE at bulk density. The acceptance rate is scarcely affected because the moves that would have created the intramolecular collapse were already of low probability, due to their weighting by oj, which is much less than one. There was, however, a reduction in the mean square displacement of the center of mass per MC step, as discussed in Sect. 4.3.1.3. 

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