Complex dielectric constants have been measured at frequencies from below 20 c/s to 5 mc/s over the temperature range −40° to −75°C in glycerol, −45° to −90° in propylene glycol, and −80° to −140° in n‐propanol. The results for n‐propanol are described by the Debye equation, but the values for the other two require a modified equation corresponding to a broader range of dispersion at higher frequencies. In all three liquids, evidence is found for a second dispersion region at still higher frequencies, which accounts for much of the difference between the radio frequency and optical dielectric constant. The relaxation times are quantitatively described over wide ranges by an empirical rate equation of a form which also fits viscosity data. The significance of the various results is discussed.

Dielectric Relaxation in Glycerol, Propylene Glycol, and n-Propanol

The α-dispersion in many polymer systems is the process to be associated with the glass transition temperature where many physical properties undergo drastic changes. We have measured and analyzed the complex dielectric behavior of the α-dispersions for five polymers [i.e., polycarbonate and polyisophthalate esters of bisphenol A, isotactic poly-(methyl methacrylate), poly(methyl acrylate), and a copolymer of phenyl methacrylate and acrylonitrile] and have found that the usual methods of analysis cannot be used to represent the data. However, it is possible to represent the relaxation process as the sum of two dispersions but there is no evidence to support this contention. An empirical expression is proposed to represent the data. This expression which takes the form of 



appears to be a general representation for the three known dispersions, i.e., Debye, circular arc, and skewed semicircle. The complex dielectric constants calculated with the aid of this expression and the parameters for each polymer system which was determined graphically were found to be in excellent agreement with the experimental complex dielectric constants. This method of representation was extended to sixteen α-dispersions reported in the literature always with excellent results.

A complex plane analysis of α‐dispersions in some polymer systems

Publisher Summary The chapter reviews the results obtained from measurements of hydrogen exchange (H–H, H–D, and H–T) in proteins and related compounds. The slowness of the rate of hydrogen exchange in a protein, relative to the exchange rate observed with simple peptides under the same experimental conditions is closely related to the conformation of the protein molecule in aqueous solution. Quantitative measurements of the rate of hydrogen exchange in a given protein, under specified experimental conditions, provide a multiparameter characterization of the protein conformation (or distribution of conformations) present under these conditions. Moreover, the chapter discusses the experimental techniques that have been used to measure quantitatively the rate of hydrogen exchange. The chapter also discusses arguments that support case, as the mechanism of exchange of the slowly exchanging hydrogen atoms.

Hydrogen exchange in proteins.

Spherical nanoparticles can be assembled into periodic, closepacked layers using sedimentation or slow crystallization procedures, 4,5 and these arrays act as Bragg gratings and diffract light of specific wavelengths. 6 Such materials could be developed into diffractive optics and photonic band gap materials. Other nanoparticle assembly methods have been investigated, including the use of DNA conjugates, 7-9 assembly onto monolayer surfaces, 10,11

Preparation of Structurally Well-Defined Polymer−Nanoparticle Hybrids with Controlled/Living Radical Polymerizations

Diffraction from a photonic crystal material composed of a hydrolyzed polymerized crystalline colloidal array (PCCA) can be used to sense pH and ionic strength. The PCCA is a polyacrylamide hydrogel which embeds a polystyrene crystalline colloidal array (CCA). The diffracted wavelength of the PCCA changes as the PCCA volume changes due to the alterations in the CCA lattice constant. We examine the pH and ionic strength dependence of the hydrolyzed PCCA volume by monitoring the Bragg diffracted wavelength. We also develop a zero free parameter quantitative model to describe the pH and ionic strength dependence of the hydrogel volume.

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Photonic Crystal Chemical Sensors: pH and Ionic Strength

The bridge described has been developed for reasonably accurate measurement by direct balance of capacitance and conductance in the frequency range 50 c/sec. to 5 mc/sec., and over most of this range is essentially direct reading in the two admittance components with negligible unbalance from lead effects or guard circuits of the unknown. These properties are realized by using two circuits developed from the work of others. The first employs inductively coupled ratio arms to minimize residual impedance effects and unbalance by guard circuits, the second, a conductance shifter wye network with good high frequency properties and an essentially linear conductance reading. Design considerations and limitations of these circuits are discussed, as are suitable test cells and auxiliary equipment.

A Wide Range Capacitance‐Conductance Bridge

The association and polar character of various carboxylic acids have been studied in the solvents benzene and heptane by means of measurements of the electric polarization in very dilute solutions. The data have been analyzed by assuming an equilibrium between dimers and monomers of the acid molecules. A rather large anomalous contribution to the polarization of the dimer has been found. Possible origins of this polarization have been briefly considered.

Electric Polarization of Carboxylic Acids in Dilute Solutions of Nonpolar Solvents I. The Relation of Electric Polarization to the Association of Carboxylic Acids in Hydrocarbon Solvents

The Dielectric Constants of Water, Hydrogen Peroxide and Hydrogen Peroxide—Water Mixtures1,2

Identity of coleonol with forskolin: structure revision of a base-catalysed rearrangement product

The structure of the title compound has been established by single-crystal X-ray analysis. Crystals are orthorhombic, space group Pna21, a= 13.85(1), b= 9.83(1), c= 13.39(1)A, Z= 4. The structure was solved by the heavy-atom method and atomic paramters were refined by full-matrix least-squares calculations tyo R 0.043 for 1 394 stattistically significant reflections from diffractometer measurements. The copper atom has a tetragonally distorted octahedral co-ordination in which four imidazole nitrogen atoms define the basal plane, mean Cu–N 2.011 A, and unidentatate nitrato-oxygen atoms occupy the axial sites, mean Cu–O 2.566 A. The mean copper atom displacement from the nitrato-group planes is 0.80A. The imidazole N–H groups all participate in an extensive N–H ⋯ O hydrogen bonded network involving one the nitrato-oxgen atoms. The single-crystal e.s.r. and polarised electronic spectra are also reported and the electronic structure of the chromophore discussed with reference to these and the crystallographic data.

Paul M. Gross

Papers

A Wide Range Capacitance‐Conductance Bridge

Electric Polarization of Carboxylic Acids in Dilute Solutions of Nonpolar Solvents I. The Relation of Electric Polarization to the Association of Carboxylic Acids in Hydrocarbon Solvents

The Dielectric Constants of Water, Hydrogen Peroxide and Hydrogen Peroxide—Water Mixtures1,2

Identity of coleonol with forskolin: structure revision of a base-catalysed rearrangement product

Crystal and molecular structure, electron spin resonance, and electronic spectrum of tetrakis(imidazole)dinitratocopper(II)