Electrochemical behavior of heterometallic chalcogenide clusters

The electrochemical properties of sixteen tri- and tetranuclear chalcogenide-bridged heterometallic clusters in comparison with the tetrahedral clusters Cp′₄M₄S₄ (M = Cr, V; Cp′ = CH₃C₅H₄) simulating ferredoxins were studied. For complexes with μ₄-coordination of the chalcogen, only reduction processes involving the metal-heterometal bonds are reversible. For complexes with μ₃-coordination of the chalcogen, the oxidation processes are reversible except for triiron-chalcogen-pnicogenide clusters having an easily and reversibly oxidizable E-Fe(CO)₂C₅H₄Bu-t bond (E = Sb, Bi) at the pnicogen atom. The electron-compensating role of the lone pair at the bridging chalcogen atom in the stabilization of the oxidation products of the clusters is discussed.     

Energetics of the binding of Cu(II) ions by thermosensitive copolymers of N-vinylcaprolactam and N-vinylimidazole in different conformational states of macromolecules

Random and protein-like copolymers based on N-vinylcaprolactam and N-vinylimidazole are synthesized by free radical polymerization in an aqueous solution. The above copolymers show a different thermal behavior in aqueous media at pH 7.2. At 45°C, the solution of a random copolymer experiences phase separation, whereas a protein-like copolymer undergoes a transition from the unfolded conformation to the compact conformation without any phase separation. The method of isothermal titration calorimetry is used to study the binding of Cu(II) ions by protein-like and random copolymers of N-vinylcaprolactam and N-vinylimidazole at 25 and 45°C, which correspond to different conformational states of macromolecules. The standard enthalpy and constant of binding are estimated. For both copolymers, the enthalpies of binding are negative and similar. When temperature is increased from 25 to 45°C, the constant of binding of copper ions by a protein-like copolymer increases by more than three orders of magnitude, whereas the corresponding constant of a random copolymer remains almost unchanged. Therefore, the transition of protein-like copolymer from the coiled conformation to the compact conformation noticeably facilitates the formation of an imidazole quasi-receptor, which is characterized by a certain spatial configuration and by a high affinity for the functional ligand. This effect is provided by an entropy gain no less than 50 J/(mol K).     

Advances towards using finger/toenail dosimetry to triage a large population after potential exposure to ionizing radiation

Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the emergency medical response to a large-scale radiological/nuclear event. One technique that has the potential for rapid and accurate dosimetry measurements is electron paramagnetic resonance (EPR) spectroscopy of relatively stable radiation-induced signals (RIS) in fingernails and toenails. Two approaches are being developed for EPR nail dosimetry. In the approach using ex vivo measurements on nail clippings, accurate estimation of the dose-dependent amplitude of the RIS is complicated by the presence of mechanically-induced signals (MIS) that are generated during the nail clipping. Recent developments in ex vivo nail dosimetry, including a thorough characterization of the MIS and an appreciation of the role of hydration and the development of effective analytic techniques, have led to improvements in the accuracy and precision of this approach. An in vivo nail dosimetry approach is also very promising, as it eliminates the problems of MIS from the clipping and it has the potential to be an effective and efficient approach for field deployment. Two types of EPR resonators are being developed for in vivo measurements of fingernails and toenails.     

A Deployable In Vivo EPR Tooth Dosimeter for Triage After a Radiation Event Involving Large Populations

In order to meet the potential need for emergency large-scale retrospective radiation biodosimetry following an accident or attack, we have developed instrumentation and methodology for in vivo electron paramagnetic resonance spectroscopy to quantify concentrations of radiation-induced radicals within intact teeth. This technique has several very desirable characteristics for triage, including independence from confounding biologic factors, a non-invasive measurement procedure, the capability to make measurements at any time after the event, suitability for use by non-expert operators at the site of an event, and the ability to provide immediate estimates of individual doses. Throughout development there has been a particular focus on the need for a deployable system, including instrumental requirements for transport and field use, the need for high throughput, and use by minimally trained operators.Numerous measurements have been performed using this system in clinical and other non-laboratory settings, including in vivo measurements with unexposed populations as well as patients undergoing radiation therapies. The collection and analyses of sets of three serially-acquired spectra with independent placements of the resonator, in a data collection process lasting approximately five minutes, provides dose estimates with standard errors of prediction of approximately 1 Gy. As an example, measurements were performed on incisor teeth of subjects who had either received no irradiation or 2 Gy total body irradiation for prior bone marrow transplantation; this exercise provided a direct and challenging test of our capability to identify subjects who would be in need of acute medical care.     

A novel approach to the determination of the crosslink density in rubber materials with the dipolar correlation effect in low magnetic fields

We present a novel NMR approach to the determination of crosslink densities in rubber materials. The method is based on the dipolar correlation effect (DCE) on the stimulated echo examined in a series of rubber samples and linear polyisoprene. The parameter evaluated from the echo attenuation curves is the mean‐squared dipolar fluctuation associated with anisotropic reorientations of macromolecular backbones. The contributions to the DCE of the constraints due to excluded volume effects and chemical crosslinks are estimated. A strong dependence of the mean‐squared dipolar fluctuation on the crosslink density of rubber combined with the simplicity of performing the measurements with inexpensive low‐field instruments suggests that the DCE is a useful tool for routine applications. The potential and problems of performing DCE measurements in low‐magnetic‐field conditions are discussed in detail. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2207–2216, 2001     

Synthesis, structure and redox properties of new cobalt(II) and nickel(II) complexes with 6-ferrocenyl-2,2′-bipyridyl

New ionic complexes [ML₂(MeCN)₂]?2Otf (M = Co or Ni; L = 6-ferrocenyl-2,2′-bipyridyl) were synthesized and characterized by single-crystal X-ray diffraction. Cyclic voltammograms of the compounds [ML₂(MeCN)₂]?2Otf in CH₂Cl₂ show good cycle stability over 100 cycles in the quasi-reversible oxidation potential range (from −0.25 to 0.5 V).     

Ueber Elementaranalyse von Kohlen

Ohne Zusammenfassung(Mittheilung aus dem Chemisch-technischen Institut der Technischen Hochschule zu Karlsruhe.)     

Time-resolved streak camera system with solid state laser and optical parametric generator in different spectroscopic applications

Apparatus to study time-evolution of emission spectra over very wide time and spectral range is described. Excitation part of the equipment consists of solid state Nd:YAG laser and optical parametric generator. The heart of the detection system consists of spectrograph and streak camera. The significance of optics and electronics built in the system for proper, fast and convenient measurements is underlined. The results of donor-acceptor energy transfer in a rigid polyvinyl alcohol matrix serve here as an example of application our equipment to study complex systems.