Low frequency vibrational modes

Since the stochastic Langevin force mimics collisions among solvent molecules and the biomolecule (the solute), the characteristic vibrational frequencies of a molecule in vacuum are dampened. In particular, the low-frequency vibrational modes are overdamped, and various correlation functions are smoothed (see Case [35] for a review and further references). The magnitude of such disturbances with respect to Newtonian behavior depends on 7, as can be seen from Fig. 8 showing computed spectral densities of the protein BPTI for three 7 values. Overall, this effect can certainly alter the dynamics of a system, and it remains to study these consequences in connection with biomolecular dynamics. 

Microwave studies also provide Important Information regarding molecular force fields, particularly with reference to low frequency vibrational modes in cyclic structures (74PMH(6)53). 

Fig. 13. The low-frequency vibrational mode spectrum for 5CB in several phases. The calculated mode frequencies are shown as tick marks along the bottom...

Fig. 15. The low-frequency vibrational mode spectrum for 8CB in its smectic phase. The broad and weak spectral feature at about 8 cm has been attributed to intermolecular forces extending across smectic layers...

Go, N. Noguti, T. Nishikawa, T., Dynamics of a small globular protein in terms of low-frequency vibrational-modes, Proc. Natl Acad Sci. USA - Biol. Sci. 1983, 80, 3696-3700... 

Why the break at 30 °C Kohen and Klinman " suggest that the fluctuational excursions to locate a mnneling sub-state depend on low-frequency vibrational modes of the enzyme, which are freely operational in the high-temperature regime. At lower temperatures, the enzyme structure may become rigid and incapable of such motions and a slower reaction, perhaps involving some tunneling near the transition state of the semiclassical reaction, sets in. 

The direct evidence on which our view of cation solvation in polymer electrolytes is based comes mainly from spectroscopic techniques. IR and Raman studies have been carried out on a variety of systems (see Chapter 5, Torell and Schantz, 1989 and Freeh, Manning, Teeters and Black, 1988). Low frequency vibrational modes, around 860-870 cm associated with the cation-ether oxygen interactions in PEG based systems have been observed they are absent in PEO itself... 

For low-frequency vibrational modes, or at high T, the summation in Eq. 8.70 may be slow to converge. The list of terms on the right-hand side of Eq. 8.70 can be recognized as the series expansion of ( -e Xi), where x-t = hVj/ksT. Thus the vibrational partition function has the simple form... 

Aside from the possession of a permanent dipole moment and sufficient volatility, a molecule must be reasonably small for its microwave spectrum to be profitably studied. Large molecules have many low-frequency vibrational modes these modes will be appreciably populated at room temperature, giving many strong pure-rotation transitions between levels with nonzero vibrational quantum numbers. The microwave spectrum of a large molecule will thus have so many lines that assignment of the lines will be virtually impossible. 

The DFT calculated temperature profiles are somewhat different for Cu-(tj1-02 i) and Co(i71-02 I). The maximum is predicted to occur at a lower temperature for the copper complex, which also exhibits the larger 180 EIE. An explanation for this behavior again can be found within the DFT calculations and the analysis of vibrational frequencies. Comparing the gas-phase structures and vibrational frequencies below 100 cm-1 indicates an isotope shift that is more than two times greater for Co(p1-02)Sal (7.7 cm ) than for Cu(rj1-02)TMG3Tren (3.0-3.4 cm-1). Therefore, the more temperature-dependent 180 EIE is associated with the greater isotope sensitivity of the low-frequency vibrational modes. This observation underscores the... 

We have presented experimental and theoretical results for vibrational relaxation of a solute, W(CO)6, in several different polyatomic supercritical solvents (ethane, carbon dioxide, and fluoroform), in argon, and in the collisionless gas phase. The gas phase dynamics reveal an intramolecular vibrational relaxation/redistribution lifetime of 1.28 0.1 ns, as well as the presence of faster (140 ps) and slower (>100 ns) components. The slower component is attributed to a heating-induced spectral shift of the CO stretch. The fast component results from the time evolution of the superposition state created by thermally populated low-frequency vibrational modes. The slow and fast components are strictly gas phase phenomena, and both disappear upon addition of sufficiently high pressures of argon. The vibrational... 

From accurate measurements of the Stark effect, when electrostatic fields are applied, information about the electron distribution is also obtained. Further information is obtained from nuclear quadrupole coupling effects and Zeeman effects <1974PMH(6)53>. Microwave studies also provide important information regarding molecular force fields, particularly with reference to low-frequency vibrational modes in cyclic structures <1974PMH(6)53>. 

Rischel, C., Spiedel, D., Ridge, J. P., Jones, M. R., Breton, J., Lambry, J. C., Martin, J. L., and Vos, M. H., 1998, Low-frequency vibrational modes in proteins large frequency-shifts induced by point-mutations in ftie protein-cofactor matrix of bacterial reaction centers. Proc. Natl. Acad. Sci. USA, 95 12306nl2311. 

Recently Tanimura and Mukamel have proposed a fifth order nonlinear spectroscopy that is capable of distinguishing homogeneous and inhomogeneous contributions to low frequency vibrational modes. 1 As shown in Fig. 1, a medium interacts with two pairs of short pulses with the same wavelength at... 

One can see that G-band is characterized with the highest intensity in the spectra (Fig. 7.6a). It should be noted as well that the SWCNT 2vd band is noticeably higher in intensity in comparison with the main D band, which can be seen from the lower curve 1. Broadband noise is typically not strong in Raman spectra of SWCNT but became more noticeable for the bulk systems (graphite and polymer-SWCNT composite, curves 2 and 3 in the Fig. 7.6a). SWCNT possess also a low-frequency vibration mode at Vrbm 160 cm corresponding to radial oscillations of carbon atoms in plane of the cross section, which exhibits a strong variation with nanotube diameter [7]. The SWCNT vibration spectra show a sum harmonic signal Vg+Vrbm with a spectral shape, which will be discussed below. 

Relaxation rate, which looks into the low-frequency vibrational modes of protein molecules, is considered to play a significant role in biological process. A fractal-related parameter, called the fracton dimension, d-p, has been used to describe the relaxation rate at low temperature.f ... 

Ov93 G. Overney, W. Zhong and D. Tomanek, Structural Rigidity and Low Frequency Vibrational Modes of Long Carbon TUbuIes, Z. Phya. D27, To93 93-96 (1993). 

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