Mario P. Marzocchi

Resonance Raman spectrum of crystal violet

The preresonance Raman spectra, taken under various conditions, of crystal violet have been obtained using the exciting lines of an Ar+ laser. The analysis of the Raman data and of the IR and UV visible absorption spectra allowed us to determine the structure of the ion (propeller-like in shape with D3 symmetry), to characterize the unstable single protonated dye cation, and to propose a detailed vibrational assignment in terms of coupled vibrations of the substituted benzenes. In addition, the measurements of the Raman excitation profiles furnished information on the vibronic couplings and provided evidence for a close correlation in the resonance mechanisms between crystal violet and benzene and its monosubstituted derivatives.

The Quantum Mixed-Spin Heme State of Barley Peroxidase:A Paradigm for Class III Peroxidases

Electronic absorption and resonance Raman (RR) spectra of the ferric form of barley grain peroxidase (BP 1) at various pH values, at both room temperature and 20 K, are reported, together with electron paramagnetic resonance spectra at 10 K. The ferrous forms and the ferric complex with fluoride have also been studied. A quantum mechanically mixed-spin (QS) state has been identified. The QS heme species coexists with 6- and 5-cHS hemes; the relative populations of these three spin states are found to be dependent on pH and temperature. However, the QS species remains in all cases the dominant heme spin species. Barley peroxidase appears to be further characterized by a splitting of the two vinyl stretching modes, indicating that the vinyl groups are differently conjugated with the porphyrin. An analysis of the currently available spectroscopic data for proteins from all three peroxidase classes suggests that the simultaneous occurrence of the QS heme state as well as the splitting of the two vinyl stretching modes is confined to class III enzymes. The former point is discussed in terms of the possible influences of heme deformations on heme spin state. It is found that moderate saddling alone is probably not enough to cause the QS state, although some saddling may be necessary for the QS state.

Intramolecular hydrogen bonding and excited state proton transfer in hydroxyanthraquinones as studied by electronic spectra, resonance Raman scattering, and transform analysis

The scheme of energy levels previously proposed to describe dual excitation and emission associated to excited state intramolecular proton transfer (ESIPT) of some hydroxyanthraquinones (HAQ’s) has been made more quantitative in the present paper. The zero-point energy and the frequency of the νOH mode for the HAQ’s have been calculated on the basis of the Lippincott–Schroeder double-minimum potential for the O–H⋯O hydrogen bond. The second derivative absorption (D2) spectra show that the vibrational structures of the electronic excited state of HAQ’s giving rise to ESIPT are characterized by the progression of the νOH stretching mode. The νOH mode in the ground state is observed as a very strong band in the vibrational structure of the short wavelength emission for HAQ’s showing ESIPT. The combined resonance Raman band assignment of four hydroxyanthraquinones and transform analysis show that the visible transition involves the hydrogen bonded cycle and induces proton transfer in the excited state in most...

Absorption, fluorescence and resonance Raman spectra of adriamycin and its complex with DNA

Abstract Absorption, fluorescence and resonance Raman spectra of adriamycin and of its complex with DNA have been measured. These results together with the analysis of the excitation profiles of the solid drug were used to interpret the complex pattern of the absorption spectra as due to the vibronic structure of a single electronic state. In addition a surplus band, depending on the concentration, was attributed to self-association. Further support was given for the intercalation nature of the drug-DNA complex. In particular it was found that the monomer form of adriamycin interacts with the nucleic acid and that interaction involves the whole chromophore framework.

Raman Spectrum of a Single Crystal of Benzene

The Raman spectrum of a single crystal of benzene at 140°K has been obtained using an argon ion laser source. The single crystals were oriented with the aid of a polarizing microscope. This technique was found suitable for low temperature work. Despite some cracking of the sample, the polarization was defined well enough to make the assignment of most librational lattice modes certain. The internal vibrations were also investigated, and for ν6, ν9, and ν10 the observed peaks have been assigned to their proper factor group species. The agreement between observed frequencies and those calculated in this laboratory is extremely good for the lattice vibrations, and acceptable for the internal modes.

Infrared Spectra in Polarized Light of Crystalline Benzene and Benzene‐d6

The high‐resolution spectra in polarized light of oriented polycrystalline films of C6H6 and C6D6 at 85°K have been obtained. The observation of two different crystal faces allowed the classification of the Davydov components, according to their polarization character, into three different sets, which correspond to the three infrared‐active factor‐group symmetry species. The complications which arise from the presence of isotopic impurities (13C12C5H6 in 12C6H6, 13C12C5D6 and 12C6D5H in 12C6D6) are removed thanks to the use of polarized light, the aid of the correlation between C6H6 and C6D6 spectra, and solid solution information. Therefore, a complete assignment of all the observed peaks has been possible. The experimental results have been compared with exciton splittings and crystal shifts calculated by other authors.

Resonance Raman and polarized light infrared spectra of 1,4-dihydroxyanthraquinone. vibrational studies of the ground and excited electronic states

Abstract The resonance Raman scattering and the infrared spectrum in polarized light of solid 1,4-dihydroxyanthraquinone have been measured. These data together with the low temperature the deuterated analog infrared spectra allowed us to propose a detailed vibrational assignment of the ground electronic state and to obtain information for the excited state analysis. Pronounced fine structures were in fact observed in the absorption and fluorescence spectra of both the hydrogenated and deuterated compounds. The patterns have been interpreted in terms of vibronic transitions involving the totally symmetric modes associated with the CO bending, skeletal stretching and OH bending motions. The large change of the equilibrium coordinate of the latter mode in the excited electronic state accounts for the distorted mirror image relationship between absorption and emission.

Raman excitation profiles and second‐derivative absorption spectra of β‐carotene

The absorption and second‐derivative spectra of β‐carotene in n.hexane, isopentane, and CS2, as well as the Raman excitation profiles for six modes in n.hexane and isopentane have been measured. The combined analysis of the absorption and second‐derivative spectra in terms of model summing over the vibronic excited states furnished reliable values of the excited state displacement parameters. The input parameters for the calculation of the full spectra were taken from the Raman band relative intensities, while the line shape functions and their widths were determined by the second‐derivative absorption spectra. The Raman excitation profiles were then calculated in terms of the transform theory, both the observed and calculated absorption spectra being transformed. Very good fits with the experimental profiles were found by including a small contribution of inhomogeneous broadening to the total width. It was concluded that the homogeneous broadening mainly derives from dephasing of nondegenerate low‐freque...

Infrared Spectra of Crystalline Cyclopentane and Cyclopentane‐d10

Infrared spectra of crystalline cyclopentane and cyclopentane‐d10 have been measured at different temperatures between 4000 and 200 cm−1. Spectroscopic evidence shows that form I (− 120°C) and form II (− 140°C) have the same degree of disorder as the liquid. In the ordered crystal form III (− 180°C) the molecule has a rigid bent conformation. By the mixed‐crystal technique the nature of the observed splittings has been established. This has permitted us to show that the site symmetry of the molecule in form III is C1, and packing concepts together with the spectroscopic data led to the choice of C2h5 as the possible space group of the lowest‐temperature form.

Infrared Spectrum of Crystalline CH2I2. Crystal Structure and Phase Transition

The infrared spectra of two crystalline modifications, I and II of CH2I2, have been measured at various temperatures ranging from 3° to −196°C between 4000 and 400 cm−1. The transition between the two crystal forms I→II has been demonstrated to be monotropic.The absence of the A2 fundamental in Form I allows a C2v site symmetry to be established, while for Form II the activity of the A2 fundamental and the observed factor‐group splitting for A1, B1, and B2 fundamentals is consistent only with trivial site symmetry.Among the multiplicity of factor groups consistent with the observed crystal spectra, a choice is possible using packing considerations. Orthorhombic, (D2h5) or (D2h13), and monoclinic (C2h5) structure are proposed for Forms I and II, respectively, which are consistent with the ir crystal spectra and densities of the two crystalline solids.