Showing papers on "Intramolecular force published in 1973"
TL;DR: It was found that interactions between amino acids of opposite charge and between large hydrophobic amino acids in the overlapping region between two chains are maximal when the chains are staggered by 0D, 1D, 2D, 3D and 4D, where D = 234 ± 1 residues.
399 citations
TL;DR: In this paper, the authors considered the vibrational relaxation of a guest molecule in a host matrix and derived explicit solutions for the Wigner-Weisskopf approximation for both single phonon and multiphonon processes, which was applied for the study of the time evolution of the distribution, the cooling and heating processes of the oscillator by a thermal field and for the coupling between vibrati...
Abstract: In this paper we consider some features of vibrational relaxation of a guest molecule in a host matrix. The model system involves a harmonic molecule interacting with a harmonic medium. The molecule-medium coupling was handled by the rotating wave approximation considering linear terms in the intramolecular displacements and high terms in the medium displacements. Three specific models for the molecule-medium coupling were considered, which involve single phonon decay, vibron-phonon decay and multiphonon decay. Within the framework of the random phase approximation the Heisenberg equations of motion for the system could be expressed in terms of a unified scheme which is valid for both single phonon and multiphonon processes. Explicit solutions were derived utilizing the Wigner-Weisskopf approximation. This generalized formalism was applied for the study of the time evolution of the distribution, the cooling and the heating processes of the oscillator by a thermal field and for the coupling between vibrati...
168 citations
146 citations
TL;DR: In this article, the authors consider the problem of interpreting quenching kinetics in small molecules (e.g., CN, CH 2, NO 2 and SO 2 ) and argue the importance of analyzing these data in terms of collisional transitions between perturbed (mixed electronic parentage) as opposed to pure (non-spectroscopic) vibronic states.
132 citations
130 citations
TL;DR: Weak, broad, Raman bands have been observed from water and heavy water at shifts above and below those corresponding to the intramolecular bending and stretching vibrations of D2O and H2O molecules that are either partially, or fully hydrogen bonded.
Abstract: Weak, broad, Raman bands have been observed from water and heavy water at shifts above and below those corresponding to the intramolecular bending and stretching vibrations. Bands near Δv = 1190 cm−1 for D2O and Δv = 1625 cm−1 for H2O, in addition to relatively sharp bands at 1210 cm−1 for D2O and 1640 cm−1 for H2O are thought to arise from intramolecular bending vibrations of D2O and H2O molecules that are either partially, or fully hydrogen bonded. Other weak bands can be explained as combinations of known intra‐ and intermolecular vibrations, in particular, librations.
97 citations
TL;DR: In this article, an experimental study of the proton spin-lattice relaxation time T1 has been made for H2O over the temperature interval from −16 to 145°C, and the experimental T1 behavior can be represented by the double exponential form of the rate expression used to treat the relaxation for the quadrupolar nuclei 2H and 17O in water.
Abstract: An experimental study of the proton spin‐lattice relaxation time T1 has been made for H2O over the temperature interval from −16 to 145°C. It is found that after correction for spin‐rotational interaction, the experimental T1 behavior can be represented by the double exponential form of the rate expression used to treat the relaxation for the quadrupolar nuclei 2H and 17O in water. The oxygen‐17 data are used to calculate the intramolecular contribution to the proton T1. The activation energies E1=9.4± 0.8 kcal/mole and E2=3.6± 0.1 kcal/mole for the two contributions to the intermolecular relaxation are in sufficiently good agreement with those for the intramolecular relaxation to indicate that the relaxation mechanism is the same in both cases. This mechanism involves two processes. The data indicate the process dominant at high temperature can be described as a rotational diffusion where the amplitude of angular motion increases with increasing temperature.
93 citations
TL;DR: In this article, LCAO-SCF calculations with an extended basis set are used to predict the geometry and various vibrational properties of the hydrogen bonded complex between HCN and HF.
83 citations
72 citations
70 citations
TL;DR: Evidence is presented that the interaction of the uncomplexed antibiotic with polar solvent molecules leads to conformational rearrangements which can be characterized by a step-wise opening of a closed structure stabilized by intramolecular hydrogen bond formation.
Abstract: The 13C nuclear magnetic resonance spectra of the membrane-active antibiotic valinomycin and its alkali-ion complexes are interpreted. From the 13C chemical shifts and infrared absorptions of the highly stable K+, Rb+ and Cs+ complexes in methanol it is concluded that the ligand conformations of these complexes must be similar. The essential features are the coordination of all ester carbonyl groups with the cation in addition to the formation of intramolecular hydrogen bonds between the amide groups. In contrast to these results the weaker Na+ complex of the antibiotic exhibits different spectral properties which are more similar to those of the uncomplexed antibiotic in polar solvents thus indicating the existence of a considerably different ligand conformation in this complex. The structure of the Na+ complex can be characterized by a reduced number of coordinated ester carbonyl groups and intramolecular hydrogen bonds between the amide groups as compared to the complexes with larger cations.
The conformational rearrangements occurring during the complexation of cations are compared to those observed for the uncomplexed valinomycin in solvent systems of different polarities. Evidence is presented that the interaction of the uncomplexed antibiotic with polar solvent molecules leads to conformational rearrangements which can be characterized by a step-wise opening of a closed structure stabilized by intramolecular hydrogen bond formation.
TL;DR: In this paper, an iterative method is used to obtain, within the framework of the transition state theory, sets of force constants from experimental kinetic isotope effect data for the reaction system H2 + Cl → [H-H-Cl] → H+HCl.
Abstract: An iterative method is used to obtain, within the framework of the transition state theory, sets of force constants from experimental kinetic‐isotope‐effect data for the reaction system H2 + Cl → [H–H–Cl]‡ → H+HCl. Two sets of force constants, describing quite different transition‐state structures, are found to be equally compatible with all available rate data for the reactions of chlorine atoms with H2, HD, HT, DT, D2, and T2. These force fields are compared with force fields derived by semiempirical methods. Measurements of the intramolecular kinetic isotope effect, i.e., the relative rate of production of HCl/DCl in the reaction HD+Cl, are shown to be especially suited for selecting compatible transition‐state models.
TL;DR: Iodine-cyclohexa-amylose tetrahydrate (C6H10O5)6 ·I2·d4H2O] was solved by heavy-atom techniques and refined by least-squares methods to a conventional discrepancy index R 0.148 for the 2872 observed data as mentioned in this paper.
TL;DR: In this article, it was shown that arabinofuranose side-groups can be incorporated into the ordered assembly and contribute to the optical rotation shift, and they therefore have an unusual role compared with other polysaccharide side-chains.
TL;DR: In this article, the first example of intramolecular oxidative addition of an 'ortho' B-H bond of a coordinated phosphine to a transition metal was presented.
Abstract: : When (Ir(C8H14)2Cl)2 is allowed to react at room temperature with 6 moles of 1-(Me2P)-1,2-C2B10H11 in cyclohexane and then heated at reflux for two hours, IrHCl(C2B10H10P(CH3)2)(CH3)2)(C2B10H11P(CH3)2)2 is formed in nearly quantitative yield. This is the first example of intramolecular oxidative addition of an 'ortho' B-H bond of a coordinated phosphine to a transition metal. (Author)
TL;DR: In this paper, a study of the i.r. spectra of dilute solutions of α, ω-dials in carbon tetrachloride has given information on the thermodynamics of formation of the intramolecular H bond by cyclisation.
TL;DR: The physical and chemical properties of the yellow crystalline products suggest that organotitanium(IV) derivatives are formed by an intramolecular "redox" process.
02 Oct 1973
TL;DR: In this article, the sum-and-difference bands of the OH stretch with other fundamentals, 14 summation modes were observed extending in frequency to over 5000 cm -1 and involving most of the fundamentals below 1500 cm −1.
Abstract: Infrared spectra are reported of methanol, ethanol, propan-2-ol, 2-methylpropan-2-ol, 2, 2, 2-trifluoroethanol, 2, 2, 3, 3-tetrafluoropropan-1-ol and 1, 1, 1, 3, 3, 3-hexafluoropropan-2-ol in the vapour phase in a 1 m path-length cell at pressures up to the s. v. p. of the alcohol. Also reported are 40 m path-length vapour and argon matrix spectra of trifluoroethanol. Dimer absorptions are identified for all the alkanols and for trifluoroethanol, and some estimates of ∆ H provided. Trifluoroethanol exhibits a striking series of sum-and-difference bands of the OH stretch with other fundamentals, 14 summation modes being observed extending in frequency to over 5000 cm -1 and involving most of the fundamentals below 1500 cm -1 . Other fluoroalcohols with fluorines substituted on β carbon atoms exhibit similar sum-and-difference modes. The alkanols exhibit only one such pair of bands due to the OH stretch plus or minus the OH torsion, and this provides a convenient method of measuring the torsional frequencies. The different behaviour of the fluoroalcohols is attributed to intramolecular hydrogen bonding.