摘要:

Base-pair and trimer formation between certain adenosine derivatives and anticancer agents has been studied by Fourier-transform infrared spectroscopy by determining hydrogen-bond association constants. The results indicate that the anticancer agents studied have a preference for Hoogsteen over Watson-Crick type base-pair formation and that they have an appreciable tendency for trimer formation. This might be the way in which they interfere with site recognition and hinder unwarranted protein formation.

ISSN:0144-235X    

DOI:10.1080/01442358609353377

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Hückel molecular orbital (HMO) theory is applied to (1) the bond lengths in phosphazenes arising from inhomogeneous substitution or complex formation, (2) conjugation between exocyclic groups and the ring and its consequences, and (3) chemical reactivity, carbanion stabilization and molecular rearrangements. Such bond characteristics as order, polarizability and electron localizability depend differently on relative orbital electronegativity. Ring size effects distinguish interactions of different symmetry types. Necessary theoretical improvements are briefly considered.

ISSN:0144-235X    

DOI:10.1080/01442358609353378

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The averaging-out of off-diagonal disorder effects in long-range, incoherent electronic energy transfer (EET) results in marginal dimensionalities for which, and beyond which, short-time transport ceases to be dispersive. For EET induced by multipolar interactions of the orders, the marginal dimensionalities ared*D=s– 2 andd*D=sfor the mean-square displacement and for the initial site survival probability, respectively, manifesting the interrogation of distinct aspects of spatial fluctuations.

ISSN:0144-235X    

DOI:10.1080/01442358609353379

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A summary of the mechanism for burning of non-photochemical holes in amorphous solids is presented. The universality of the technique and applications to vibrational spectroscopy and to studies of biologically significant molecules are reviewed and illustrated with examples of previously unpublished data. In addition, the various theories of optical dephasing in amorphous solids are summarized.

ISSN:0144-235X    

DOI:10.1080/01442358609353380

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Some aspects of the theory of arrays of rigid molecules are reviewed. Attention is focused on the orientation of the molecules. Quaternions are useful for non-linear molecules in determining the structure of the arrays and they may be adapted to give convenient vibrational displacement coordinates. Direction cosines play a similar role for linear molecules. The application of these ideas to molecular crystals is discussed and a preliminary analysis of molecular clusters is given.

ISSN:0144-235X    

DOI:10.1080/01442358609353381

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We investigate the effect of the internal modes of vibration of a molecular crystal on the diffuse X-ray diffraction pattern. Use is made of optical transform techniques to model the six in-plane modes of benzene. While the contribution of each mode to the scattering pattern is quite distinctive and characteristic of the particular mode, the combined effect of all the modes is of a form not easily separated from the scattering due to the external modes.

ISSN:0144-235X    

DOI:10.1080/01442358609353382

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A quantitative treatment of the frequencies and intensities of lines in infrared spectra of diatomic molecules is outlined, with particular reference to HC1. The relationship of classical and quantum-mechanical approaches to the analysis of such spectra and to ideas of molecular structure is discussed.

ISSN:0144-235X    

DOI:10.1080/01442358609353383

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The way in which localized ‘soliton states’ arise in systems with resonant energy transport is reviewed. This localization of energy in a mobile ‘packet’ arises from the coupling of internal states with molecular motions via a feedback mechanism. The connection between classical and quantum treatments of this process is discussed.

ISSN:0144-235X    

DOI:10.1080/01442358609353384

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The principal sources of errors in the determination of parameters of the spin hamiltonian by conventional electron paramagnetic resonance (E.P.R.) experiments are identified. It is possible to circumvent these errors by performing an E.P.R. experiment in zero magnetic field, scanning the frequency. The benefits of zero-field (electron paramagnetic) resonance (Z.F.R.) and of combining E.P.R. and Z.F.R. techniques in a variable-frequency, variable-field experiment are listed and discussed. Such an approach offers a challenge to theorists to calculate the higher-order parameters which can now be obtained with high accuracy. Experimental advantages are also discussed.

ISSN:0144-235X    

DOI:10.1080/01442358609353385

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A survey is presented of the lower excited states of the tetrahedral oxy-anions having a d0transition metal at the centre, with particular emphasis on the triplet states. The principal question addressed concerns the spin-orbit coupling mechanism in these ions. It appears that the symmetry of the molecular orbitals involved in the first excitation is such that—at least for the 3d compounds VO3-4, CrO2-4, MnO−4—the major spin-orbit coupling should occur on the oxygen ligands. Two quantitative problems are considered: the radiative lifetime of the3Ttstate, and the zero-field splitting of this multiplet if spin-orbit coupling is the dominant interaction determining the splitting. The results of the theoretical analysis are compared with recent information on the luminescent triplet states of K2Cr2O7, YVO4and CaMoO4obtained by E.P.R. The radiative lifetime of 4 ms calculated for VO3=4is in excellent agreement with the scarce experimental information. The spin orbit coupling, however, does not appear to be the dominant interaction determining the multiplet splitting of the 3d and 4d compounds. The tetrahedral ions, in accordance with the Jahn-Teller effect, suffer a distortion on excitation and a single orbital state lies lowest with a fine structure characteristic for a situation of low symmetry.

ISSN:0144-235X    

DOI:10.1080/01442358609353386

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor