B. Andrews

Structural analyses of various Cu2+, Zn2+-superoxide dismutases by differential scanning calorimetry and Raman spectroscopy

The thermal denaturation profile of the Cu2+, Zn2+ metalloenzyme, bovine superoxide dismutase, consists of two primary components, the major component denatures irreversibly at Tm = 104 degrees C with a total enthalpy (delta Hcal) of 7.30 cal/g. Reduction of Cu(II) to Cu(I) with potassium ferrocyanide lowers Tm to 96 degrees C and delta Hcal to 6.96 cal/g. The apo-form of bovine superoxide dismutase (both Cu and Zn removed) denatures at 60 degrees C with an enthalpy only one-half that of the holo-form. The reduced thermal stability, which indicates a greater ability to change conformation, may explain the previously observed much greater membrane binding of the apo-enzyme. Reconstitution with Zn2+, Cu2+, or Zn2+ and Cu2+ raises Tm to 80, 89, or 102 degrees C, respectively, with corresponding increases in the enthalpy. Thus, the metal ions considerably stabilize the enzyme and must somewhat affect conformation. The effect of Cu2+ alone is greater than that of Zn2+, although both are needed for full stability. Raman spectroscopy indicates little difference in secondary structure between the apo- and holo-forms, implying that the increased stability due to metal binding is not caused by an extreme structural reorganization. The value of Tm of canine and yeast superoxide dismutase is also lowered by reduction of Cu(II). The reduced form of the yeast enzyme denatures irreversibly, as do all forms of the bovine and canine enzymes, but the oxidized form is unique in that it denatures reversibly. Thus, the copper ion must be oxidized for renaturation and appears to act as a nucleation site.

Raman and infrared spectra of crystalline dinitrogen tetroxide

Raman and infrared spectra of polycrystalline samples of N2O4 at low temperatures have been recorded. The number and activities of the fundamentals are compared with the predictions of group theory, based on the known molecular and crystal geometries. Several additional peaks are attributed to Fermi resonances of combinations with fundamentals. A new low frequency internal mode and five lattice modes have been observed.

Raman and infrared spectra of crystalline chloroform

Abstract Raman and far-infrared spectra of polycrystalline samples of chloroform at 20 and 80 K are reported. Crystal field spilttings of the intramolecular fundamentals are observed as well as nine Raman and six infrared lattice modes. Spectra are interpreted in terms of a group theoretical analysis based on the molecular and crystal symmetries.

Raman and infrared spectra of crystalline fluoroform

Abstract Raman and far-infrared spectra of crystalline fluoroform at temperatures between 20 and 106 K have been recorded. There is no evidence for any solid-state phase transitions, nor for hydrogen bonding. The rich lattice spectra and crystal field splittings suggest that the unit cell is rather large, and possible structures are discussed.

Spectroscopic studies of phase transitions in some organic crystals: C2H2, CHBr3 and CH3CN

Raman and infrared spectra of crystalline acetylene, bromoform and acetonitrile have been obtained. These three crystals and their fully deuterated analogues exhibit solid state phase transitions. Particular attention is given to the low frequency region (< 350 cm−1) where lattice vibrations and low-lying intramolecular fundamentals are observed. Such properties as frequency shifts on deuteration, relative intensities and moment of inertia values are used to aid in assignments. Changes in the observed spectra for crystals below and above the transition temperature are related to the types of transition involved, and, where possible, comparisons are made with inorganic crystals having similar structures.

Raman and infrared spectra of the solid phases of bromoform

Abstract Raman and infrared spectra of polycrystalline samples of bromoform and deuterated bromoform in the temperature ranpe 20–274 K are reported. Spectra in both the lattice and intramolecular regions are compared with earlier results and interpreted in terms of the known structures of the three phases of solid bromoform.

Lattice dynamics of cyanogen. I. Potential model and zone-centre phonons

Lattice dynamics calculations on crystalline cyanogen, C2N2, are reported. Lennard-Jones 12-6 potentials are used to represent the three types of atom-atom interactions N-N, C-C and C-N. Variation of six parameters involved and slight adjustment of the experimental values of the lattice constants lead to a satisfactory representation of both the lattice statics (equilibrium conditions and crystal energy) and lattice dynamics (frequencies and intensities of the zone-centre modes observed by Raman and infrared spectroscopy) for this crystal. The neglect of the contribution from molecular quadrupole-quadrupole interactions is briefly discussed.