Circular Dichroism Of Molecules Research Articles

Magnetic and electric hotspots via fractal clusters of hollow silicon nanoparticles.

We show that fractal clusters of hollow Si nanoparticles provide both magnetic hotspots (MHs) and electric hotspots (EHs). The hollow size tailors the wavelength dependence of the field enhancement. In the wavelength window 400-750nm, magnetic field intensity enhancements of 10-3790 and electric field intensity enhancements of 10-400 are achievable. Wavelength-tuned MHs and EHs allow better enhancement of Raman optical activity, fluorescence and circular dichroism of molecules, and so on. Si nanoparticles overcome the limitations of metallic ones, which provide only EHs at the price of heat perturbations on a nearby quantum emitter due to metallic ohmic losses.

Dimers and Trimers of Hollow Silicon Nanoparticles: Manipulating the Magnetic Hotspots

We study magnetic and electric hotspots in the gaps of nanoparticle dimers and trimers composed of hollow silicon nanoparticles. We find that the hollow size markedly influences the overall shape of the field enhancement, in particular, the peak magnitude and the peak position. The peak shifts about 100–200 nm as the hollow size varies. Tuned magnetic hotspots allow one to better enhance the Raman optical activity and circular dichroism of molecules, the interaction of light and nanomagnets, and so on.

Circular dichroism of molecules requiring two substituents for chirality

A perturber that lies on a reflection plane of a chromophore gives no net helical character to transitions of that chromophore, and hence no circular dichroism spectrum. If, however, a molecule has two such substituents then it may in fact be chiral, with its circular dichroism resulting from the concerted coupling of both substituents to the transition of interest. In this paper the circular dichroism spectra of olefin and carbonyl molecules of this kind are analysed and related to the molecular geometry using an extended independent systems perturbation approach.

Circular dichroism of molecules in the continuous absorption region

The angular distribution of Photoelectrons with defined spin polarization ejected from oriented optically active molecules is derived. Circular dichroism in the angular distribution of photoelectrons from unoriented chiral molecules appears already in the electric dipole approximation.

Circular dichroism of molecules with isotopically engendered chirality

Circular dichroism of molecules with isotopically engendered chirality

The optical rotatory dispersion and circular dichroism of molecules containing interacting residues

We use a semiclassical formalism to derive expressions for the optical rotatory dispersion and circular dichroism associated with a dilute system of molecules represented as freely-rotating, rigid arrays of interacting residues. The relationship of the present approach to DeVoe's classical theory is discussed. Far from resonance, our results become equivalent to the equations of Moffitt, Fitts, and Kirkwood when the separation between adjacent residues is small compared to the wavelength of the light. In the resonance case, a calculation of the frequency-dependent circular dichroism per residue is carried out for a particular geometrical arrangement of the residues. These curves, for arrays both finite and infinite in extent, are compared with those obtained when a certain commonly used approximation to the orientational averaging is introduced. It is shown that this approximation is not always valid.

Circular dichroism of large molecules

AbstractThe circular dichroism of molecules, which are large compared to the wavelength of light, is considered. Explicit expressions are obtained for the circular dichroism and absorption of an exciton dimer and of a free particle on a helix. The dimensions are described for which the dipole approximation for the optical properties fails.

Dehydrated circular DNA: circular dichroism of molecules in ethanolic solutions.

AbstractWe have measured the ultraviolet CD spectra for covalently closed and linear forms of phage PM2 DNA in solution. We find that increased concentrations of salt or ethanol (up to 50% ethanol by weight) depress the long‐wavelength positive CD bands in the spectra of both forms of DNA, although the spectrum of the native covalently closed DNA always has a slightly larger magnitude of these bands than does the spectrum of the linear DNA. In addition, both DNAs are equally capable of undergoing a transition to the A conformation in 70–80% ethanol at low Na+ concentrations. Thus, the constraint imposed by the covalent closure of a DNA molecule does not seem to hinder its conformational response to these changing solution conditions. Lang [(1973) J. Mol. Biol. 78, 247–254] has found by electron microscopy that T7 DNA has an inherent ability to condense into compact particles, suggested to be supercoils of multiple order. Both covalently closed and linear forms of PM2 DNA also become condensed when the DNA, in 0.2M ammonium acetate and 1 mM EDTA, is exposed to ethanol and subsequent drying on specimen grids [Lang, D., Taylor, T. N., Dobyan, D. C. & Gray, D. M. (1976) J. Mol. Biol. 106, 97–107]. Under similar conditions, in solutions of 0.2M ammonium acetate and 1 mM EDTA to which ethanol is added, we have measured the CD spectra of both covalently closed and linear forms of DNA. Below ethanol concentrations at which the DNA obviously precipitates, the CD spectra of both forms have reduced long‐wavelength positive CD bands.

Circular dichroism of poly-D-glutamic acid adsorbed on air–water interfaces

A quartz cuvette was modified for use to determine the circular dichroism of molecules in thin films at airwater interfaces. By an application of the cuvette, circular dichroism spectra of poly-D-glutamic acid at air-water interfaces have been compared with circular dichroism spectra of the sample in aqueous solution. The results show that poly-D-glutamic acid is a beta structure on the surface of the solution in which the alpha helix or random coil is stable.