Saima Kint

Raman spectra of liquid n‐alkanes. III. Energy difference between trans and gauchen‐butane

The energy difference between the trans and gauche forms of liquid n‐butane has been determined from the temperature dependence of Raman band intensities. A value of 557±13 cal/mole was derived from the summed integrated intensities of six bands of each rotamer measured at nine temperatures between 0 and −127 °C. This value is considerably lower than those determined earlier from Raman spectra of the liquid and is in line with ΔE values for longer n‐alkanes in the liquid state. However, there is a large difference between the value reported here for liquid n‐butane and that reported for the gas (∼966 cal/mole).

Intermolecular coupling in liquid water

Changes in the Raman spectra of H2O from addition of OD oscillators indicate that there is significant intermolecular coupling of OH stretching vibrations in H2O at temperatures from −10 to 70°C. Measurements on solutions of KI in H2O indicate that the primary effect of salt addition on the spectrum of H2O is to diminish intermolecular coupling of OH oscillators. The disruption of intermolecular coupling by addition of a K+ and I− ion is about nine times more effective than addition of a single OD oscillator.

A Computer Controlled Raman Spectrometer System

We describe a software system and a hardware interface between a laser Raman spectrometer and a time-shared computer. This data acquisition system controls the wavelength drive of the spectrometer and the analyzer orientation using stepping motors and position sensors. With this method accurate depolarization ratios can be determined at every wavelength increment. Digitized photon counting gives good signal/noise ratios and a wide dynamic range for Raman intensity measurements. The software design permits automatic separation of isotropic and anisotropic spectra, repetitive counting periods, instant scope display of raw, reduced or integrated data, and numerous data refinement options.

Resonance Raman spectroscopy of iron (III) - ovotransferrin and iron (III) - human serum transferrin

Abstract We report the resonance Raman spectra in the frequency range 300–1800 cm−1 of Fe (III)-ovotransferrin and Fe (III)-human serum transferrin in aqueous solution at about 10−4M protein concentration. This is the first observation of resonance Raman scattering ascribable to amino acid ligand vibrational modes of a nonheme iron protein. The resonance Raman spectra of the transferrins are similar except that the resonance band near 1270 cm−1 is shifted to a higher frequency for Fe(III)-human serum transferrin than that for Fe(III)-ovotransferrin. The resonance Raman bands observed near 1170, 1270, 1500 and 1600 cm−1 may reflect resonance enhancement of p-hydroxy-phenyl frequencies of tyrosine residues and/or imidazolium frequencies of histidine residues.

Water in polymer membranes. Part III : Water sorption and pore volume in cellulose acetate films

Abstract Changes in waveguide properties of several cellulose acetate membranes and one polyimide membrane were measured as a function of their exposure to varying levels of relative humidity. The volume fraction of water in the films and the occupied pore volumes were determined from refractive index and thickness changes. The dependence of the refractive index on water absorption is related to a competition between two processes: one of filling pores with no film expansion and one of “free expansion” where the film expands to completely accommodate the added water volume. The term “pore” is taken to mean a volume with molecular and not macroscopic dimensions. The hydration properties of these dense cellulose acetate membranes were affected by degree of acetylation, casting temperatures and annealing treatments. Annealing CA398 membranes at 180°C decreased film water concentration by reducing the amount of free expansion. Annealed CA398 membranes that were tested in a reverse osmosis cell were found to have high salt rejection compared to unannealed films. The hydration characteristics of a polyimide membrane are compared to cellulose acetate membranes.

Analysis of cyclopropenoid fatty acids by raman spectroscopy

Abstract The cyclopropene fatty acids that occur in lipids of the cotton plant and other species of the order Malvales are responsible for a number of adverse biological effects subsequent to dietary consumption. Analyzing for these compounds in plant materials is complicated by their instability and lack of specific chemical reactivity. Raman spectroscopy, which takes advantage of an isolated strong band at 1870 cm −1 associated with the cyclopropene double bond, provides a direct method for determination of these cyclopropenoids as components of lipid mixtures at levels down to 0.03%. No derivatization or chemical treatment is required and sample preparation is uncomplicated.