Albert Moscowitz

A simple technique for the inactivation of IgM antibodies using dithiothreitol.

Abstract. This report describes a simple method for inactivating 19S red cell antibodies using the odorless compound dithiothreitol (DTT). 30 sera which contained antiglobulin‐active red cell antibodies showed virtually no alteration in activity after DTT treatment, while 30 different sera containing cold‐active red cell antibodies showed almost total elimination of activity following DTT treatment. Six sera were separated into IgG and IgM fractions. All red cell activity was eliminated in the IgM fraction, but was unaffected by DTT treatment of the IgG fraction. This method of inactivating IgM antibodies should be of value in investigating cases of hemolytic disease of the newborn and in studying sera containing mixtures of warm and cold red cell antibodies.

Optical Activity of Vibrational Origin. I. A Model Helical Polymer

Measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) in the visible and ultraviolet region of the electromagnetic spectrum are common. Largely due to technical difficulties, however, few measurements of Cotton effects have yet been made at infrared frequencies. If the usefulness of such measurements could be demonstrated, it might be that the experimental difficulties would be overcome in the near future. It is such a demonstration which is undertaken in this paper. The model system studied is an infinite helical polymer of point masses each with an effective charge. The normal modes of vibration for the polymer are calculated using a valence‐force approximation, and using these normal‐modes expressions for molecular polarizability and optical rotatory dispersion are derived for infrared frequencies. It is seen that under certain conditions there will be normal vibrations which are not easily observed in the absorption spectrum but which should exhibit Cotton effects which are mor...

Low‐Lying Excited States of Mono‐olefins

Semiempirical calculations of energies, oscillator strengths, and rotational strengths for a number of singlet–singlet transitions of ethylene and of the twisted olefin trans‐cyclo‐octene are compared with experiments. The analysis shows that a minimum of three low‐lying singlet states are required to explain the data considered: a 1Bxu(πz → πz*) responsible for the strong, broad olefinic absorption, a 1Bzu(πz → σ*)3s Rydberg state responsible for the olefin band with e≅1000, and a 1Bxg(πz → πy*)3py Rydberg like state accounting for the low‐lying electric quadrupole‐allowed transition of ethylene and dominating the optical rotatory properties of the twisted double bond.

Optical Activity of Vibrational Origin. II. Consequences of Polymer Conformation

Calculations of absorption, circular dichroism, and optical rotatory dispersion spectra associated with vibrational transitions of several idealized helical polymers are reported. Although specific assumptions are made regarding the vibrational force field and the charge distribution within the polymer, these assumptions are applied consistently in an investigation of the effects of chain length and helical conformation upon the optical properties. Results obtained for an idealized model of polypropylene indicate that even rather short helical segments (5–10 residues) may have spectra rather similar to those calculated for an infinite helix. Calculations performed for several polypropylene oxide models indicate that the optical rotatory dispersion and circular dichroism spectra may, in some cases, be more sensitive to small changes in the helix geometry than the absorption spectra. Furthermore, in these instances a number of the partial ORD curves exhibit the characteristic triple‐extrema shape which may ...

A charge flow model for vibrational rotational strengths

The valence‐optical approach is used to construct a model applicable for the calculation of rotational strengths associated with fundamentals of vibrational transitions. It is shown that the model has the essential property of giving rotational strengths that are independent of the choice of origin.

Theorem Useful for Interpretation of Magnetic Circular Dichroism Spectra

It is shown that the magneto‐optical activity associated with a symmetry‐forbidden transition is of second or higher order in any perturbation and that the contributions to the magnetic rotational strengths of perturbations belonging to different irreducible representations are additive. This theorem can be useful in analyzing the vibrational structure of a forbidden spectral band and in elucidating the conformations of molecular systems. The problem of the origin dependence of the magnetic rotational strengths is also discussed.

The influence of an electric and magnetic field in chemical reactions

Abstract We have shown that a simultaneous application of uniform and constant electric and magnetic fields cannot affect the equality of the equilibrium enantiomeric populations in a racemic reaction mixture. Hence, whatever the sources of the rotations reported, they cannot have had their origin in uniform applied fields if the reactions have gone to completion.

Infrared circular dichroism associated with the C-H strecthing vibration of tartaric acid☆

The infrared circular dichroism associated with the C-H stretching vibration of tartaric acid-d4 [-CH(OD)COOD]2, has been measured. The observed CD spectra are most readily attributable to the chirality of the separate -CH(OD)COOD groups, rather than to a coupling between the groups.

THE USE OF CROSS-CORRELATION FUNCTIONS IN THE ANALYSIS OF CIRCULAR DICHROISM SPECTRA

Following Gordon, we show that the circular dichroism (CD) spectrum is proportional to the imaginary part of the Fourier transform of the cross-correlation function of the electric dipole moment and of the magnetic dipole moment. Such a result is useful in the study of CD band shapes, and also in obtaining a spectrum from a classical trajectory calculation, as was done for absorption by Noid, Koszykowski, and Marcus. For ergodic and multiperiodic regimes, the formula reduces to the Fourier cross spectrum of the two moment functions. As an application, we have run classical trajectories calculations for two coupled CH stretchings belonging to a chiral HCCH fragment, in the fixed partial charge approximation. Two sets of results are presented, relative to low and high total energy: Comments are made about the spectroscopic manifestation of normal, local, and chaotic modes.

Calculation of vibronic magnetic rotational strengths in formaldehyde

The magnetic rotational strengths (MRS) associated with the non‐totally‐symmetric vibrations in formaldehyde are calculated with CNDO/2 wave functions. The effects of configuration interaction are examined. We have also identified a single term that dominates the MRS. This raises the possibility of an economy of thought in attempts at correlating MRS data with molecular structure in the case of magnetic dipole allowed transitions.