Separation techniques used in radiochemical procedures

After summarising the techniques available generally in analytical chemistry for the separation and pre-concentration of trace elements, reasons are given why some of these procedures have achieved greater prominence in particular radiochemical separations. Examples of contemporary practice and current trends in a wide variety of radiochemical separation problems are then illustrated by reference to papers that have appeared in recent literature. Adapted from a Plenary Lecture delivered at the 4th Symposium on Recent Developments in Neutron Activation Analysis, 4–7th August 1975, Cambridge, England.     

Dynamic mechanism of photochemical induction of turing superlattices in the chlorine dioxide-iodine-malonic acid reaction-diffusion system

We study the mechanism of development of superlattice Turing structures from photochemically generated hexagonal patterns of spots with wavelengths several times larger than the characteristic wavelength of the Turing patterns that spontaneously develop in the nonilluminated system. Comparison of the experiment with numerical simulations shows that interaction of the photochemical periodic forcing with the Turing instability results in generation of multiple resonant triplets of wave vectors, which are harmonics of the external forcing. Some of these harmonics are situated within the Turing instability band and are therefore able to maintain their amplitude as the system evolves and after illumination ceases, while photochemically generated harmonics outside the Turing band tend to decay.     

Preparation of Neutral Ionophores for Alkali and Alkaline Earth Metal Cations and their application in ion selective membrane electrodes

The preparation of a series of non-cyclic, uncharged ligands able to selectively complex alkali and alkaline earth metal cations is described. These molecules are designed to be used as carriers for cations through membranes. Some of the compounds show high Ca²⁺ and Na⁺ selectivity, respectively, in liquid membrane electrodes.     

Interaction of urea with poly(2-hydroxyethyl methacrylate) hydrogels

The interaction of poly(2-hydroxyethyl methacrylate) [poly(HEMA)] and other similar hydrogels with dilute urea solution has been studied by a variety of techniques, including swelling experiments, fluorescence quenching, near infrared spectroscopy and fundamental band infrared spectroscopy. The results obtained indicate that the anomalous swelling behavior of poly(HEMA) gels in the presence of such dilute urea solutions is probably not due to the disruption of a secondary hydrophobic bond structure as has been generally believed. Although poly(HEMA) gels do contain sites that can participate in hydrophobic bonding, the evidence gathered indicates that dilute urea solutions have no effect on such bonds. A plausible model that does fit all the data involves the interaction of urea with a secondary structure composed of hydrogen-bonded hydroxyl groups, stabilized by the exclusion of water molecules from the regions containing the bonds.     

KINETIC STUDIES OF THE TWO LIGHT REACTIONS IN PHOTOSYNTHESIS

Abstract— The decay kinetics of the photo-induced absorbance changes in red and green algae are very sensitive to the wavelength of the actinic light. A four to tenfold increase in half-decay time is noted in going from short wavelength (550–650 mμ) to long wavelength (> 700 mμ) excitation. The slow decay rates produced by long wavelength light can be enhanced with a steady background of short wavelength light. A relationship between initial decay rates and O₂ evolution rates is described. This relationship allows a direct correspondence between these spectroscopic studies and the 'red-drop' and 'enhancement' experiments of Emerson.     

The proton affinity of proline analogs using the kinetic method with full entropy analysis

The proton affinity of proline analogs, L-azetidine-2-carboxylic acid (Aze), L-proline (Pro), and L-pipecolic acid (Pip), have been measured using the Armentrout modification of the extended kinetic method in a quadrupole ion trap instrument. Experimental values of 223.0 +/- 1.5, 224.9 +/- 1.6, and 225.6 +/- 1.6 kcal/mol have been determined for the 298K proton affinities of Aze, Pro, and Pip respectively. High level theoretical calculations using both MP2 and B3LYP methods at a variety of basis sets were carried out in order to give theoretical predictions for the 298 K proton affinity and gas phase basicity of all three analogs. Recommended values for the gas phase basicity and proton affinity for proline based on our work and other recent determinations are 216 +/- 2 and 224 +/- 2 kcal/mol.     

Palladium salicylaldimine complexes containing boronate esters

Reactions of salicylaldehydes with boronate ester derivatives of aniline have been examined. Addition of these Schiff base ligands to palladium acetate or Na₂PdCl₄ afforded novel boron-containing trans-bis(N-arylsalicylaldiminato) palladium complexes.Condensation of salicylaldehyde (2-HOC₆H₄C(O)H) with H₂NC₆H₄Bpin (pin=1,2-O₂C₂Me₄) afforded the boron-containing Schiff bases, 2-HOC₆H₄C(H)=NC₆H₄Bpin (1–3a). Similar reactivity with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy-1-naphthaldehyde gave the corresponding Schiff bases (1-3b) and (1-3c), respectively. Reaction of Schiff bases (2) and (3) with palladium acetate or Na₂PdCl₄ afforded complexes of the type PdL₂ (4,5), where L=deprotonated Schiff base. The molecular structure of the nitro-salicylaldehyde 4-Bpin palladium complex (5b) was characterized by an X-ray diffraction study. All new palladium compounds have been characterized fully and tested for their antifungal activity against Aspergillus niger and Aspergillus flavus.     

CombiDOCK: Structure-based combinatorial docking and library design

We have developed a strategy for efficiently docking a large combinatorial library into a target receptor. For each scaffold orientation, all potential fragments are attached to the scaffold, their interactions with the receptor are individually scored and factorial combinations of fragments are constructed. To test its effectiveness, this approach is compared to two simple control algorithms. Our method is more efficient than the controls at selecting best scoring molecules and at selecting fragments for the construction of an exhaustive combinatorial library. We also carried out a retrospective analysis of the experimental results of a 10×10×10 exhaustive combinatorial library. An enrichment factor of approximately 4 was found for identifying the compounds in the library that are active at 330 nM.     

Highly selective tritium-from-deuterium isotope separation by pulsed NH3 laser multiple-photon dissociation of chloroform

Infrared multiple-photon dissociation of CTCl₃ was investigated using a pulsed CO₂ laser-pumped NH₃ laser at 12.08 μm. No evidence of any CDCl₃ depletion or decomposition product was observed in photolyzed CTCl₃/CDCl₃ mixtures. A lower limit of the single-step T/D enrichment factor, β, was found to be ≈ 165, based on the sensitivity in measuring CDCl₃ depletion. The low-fluene CTCl₃/CDCl₃ optical selectivity in absorptions is > 9000 at the 835 cm^?1 CTCl₃ ν₄ peak.