Experimental circular dichroic (CD) spectra of three proteins have been combined with estimates of the content of peptide-chain structural modes obtained from x-ray diffraction studies of the same proteins. Solution of the simultaneous equations at a series of wavelengths permits the construction of a CD spectrum for each of three structural modes: a-helix, j8-structure, and the so-called "random". The CD spectra thus obtained are compared with those obtained from polypeptide models. The a-helical spectra from the two approaches are nearly congruent, the 3-structure spectra are in fair agreement, and the third forms agree qualitatively, but are substantially different quantitatively. Comparisons are made between the present approach and earlier approaches to interpreting protein CD spectra. Certain advantages of the present approach are indicated.In recent years, much use has been made of circular dichroism (CD) and optical rotatory dispersion (ORD) to investigate the modes of polypeptide-chain folding in proteins. Without exception, earlier investigators have used synthetic polypeptides to calibrate the parameters employed in interpreting the ORD and CD of proteins (1-6). The degree of success of these attempts has been judged by comparison of the content of structural modes obtained by CD and/or ORD with the content found from structural solutions from x-ray diffraction studies of individual proteins.There are now several proteins for which the peptidechain structures are known from x-ray investigations. The structural content of these proteins can be linked with CD spectra for the same proteins in a set of simultaneous equations, whose solution yield the CD spectra of the structural modes as they are found in proteins. The same treatment can be applied to ORD data, although we have not done so here. We report the results of application of such a treatment to the x-ray structural and CD parameters of myoglobin, ribonuclease, and lysozyme. We have assumed that each of these three proteins contains only the structural modes commonly called "a-helix", ",8-structure (antiparallel)", and "random". The first two of these are obtained, not without uncertainties, from structural models derived from three-dimensional electron density maps constructed from single-crystal x-ray diffraction. The third, the so-called "random" structure, is surely not random in the usual structural sense of that word. It might better be called "without long-range order" or "remainder", since its fraction is defined as: third form = 1-(a + ().To determine (for a given wavelength) the mean residue ellipticities of the a-helix, (-structure, and the remainder, we write the following set of independent equations.[0]1 = X1 [0] [0]r, the intrinsic residue ellipticities of the three structural modes, at a number of wavelengths. When we plot these parameters against wavelength, we generate the CD spectra of the three structural modes as found in proteins. We used the data of Table 1 and Table 2 to evaluate the coefficients of these equation...

Quantum dots are under intense research, given their amazing properties which favor their use in electronics, optoelectronics, energy, medicine and other important applications. For many of these technological applications, quantum dots are used in their ordered self-assembled form, called superlattice. Understanding the mechanism of formation of the superlattices is crucial to designing quantum dots devices with desired properties. Here we review some of the most important findings about the formation of such superlattices that have been derived using grazing incidence scattering techniques (grazing incidence small and wide angle X-ray scattering (GISAXS/GIWAXS)). Acquisition of these structural information is essential to developing some of the most important underlying theories in the field.

Note: This paper is part of the JCP Special Topic on Time-resolved Vibrational Spectroscopy.