Self-Assembly of Supramolecular Architectures Using Chlorotetra(Pyrrole-2-Carboxylato)Diruthenium Molecules as Building Blocks

Two new complexes, based on the unit Ru₂Cl(μ-O₂CC₄H₄N)₄ (1) (O₂CC₄H₄N = pyrrole-2-carboxylate), Ru₂Cl(μ-O₂CC₄H₄N)₄(H₂O)·4H₂O [1(H ₂ O)·4H ₂ O], and Ru₂Cl(μ-O₂CC₄H₄N)₄(Me₂CO) [1(Me ₂ CO)], are synthesized and structurally characterized. The physical properties of these complexes are studied and compared with those previously reported for Ru₂Cl(μ-O₂CC₄H₄N)₄(thf)·thf·H₂O [1(thf)·thf·H ₂ O]. The nature of the solvent molecule bonded to the axial position of the dimetallic unit determines the supramolecular interactions leading to different arrangements in the solid state. The presence of NH groups in the pyrrolic rings favours the existence of hydrogen bond interactions that are present in the three complexes. In addition, complex 1(Me ₂ CO) shows π–π stacking interactions through pyrrolic rings of different dimetallic units. Dedicated to the memory of Prof. F. Albert Cotton.     

Coupling of a sheep anti-T3 IgG to a solid phase for a triiodothyronine radioimmunoassay

Optimal conditions for coupling sheep anti-T₃ IgG to a solid phase are presented. We found that the optimal activation of microcrystalline cellulose was achieved with 0.15M 1,1-carbonyldiimidazol (CDI) in acetone. We also found that using a 25 mg/cm³ anti-T₃ IgG solution, in barbitone buffer 0.05M, pH 8.0, we could get a reasonable yield of coupling and a remaining solution of anti-T₃ IgG (first supernatant) with a suitable concentration (10 mg/cm³) for another coupling. The solid phase anti-T₃ obtained in these two couplings present similar characteristics which make possible their use in a total T₃ RIA.     

MS-Xα study of the KCl: Cu− spectrum

We have interpreted the KCl:Cu^? spectrum in the context of the MS-X_α method. The results, considering only allowed electric-dipole transitions, are in good agreement with the experimental data. Four new absorption bands, peaking at 573, 390, ～324 and ～310nm, at room temperature, are reported.     

Single-crystal 55Mn NMR spectra of two Mn12 single-molecule magnets

The initial application is reported of single-crystal 55Mn NMR spectroscopy, and associated orientation dependence studies, to single-molecule magnets (SMMs). The studies were performed on two members of the Mn12 family of SMMs, [Mn12O12(O2CMe)16(H2O)4].2MeCO2H.4H2O (Mn12-Ac) and [Mn12O12(O2CCH2Br)16(H2O)4].4CH)Cl) (Mn12-BrAc). Single-crystal spectra give a dramatic improvement in the spectral resolution over oriented powder spectra, allowing the clear observation of quadrupolar splittings, the determination of quadrupole coupling parameters (e2qQ), and an assessment of the symmetry-lowering perturbation of the core of Mn12-Ac by hydrogen-bonding interactions with lattice solvate molecules of crystallization. The results emphasize the utility of single-crystal NMR studies to probe the cores of these magnetic molecules.     

A phenomenological model for the luminescence of hot electrons in the high excitation density regime

The departure from a Maxwellian behavior observed in the high energy part of the luminescence spectrum of a hot electron gas in a direct gap polar semiconductor in a regime of high density of excitation is shown to be a consequence of the out of equivalibrium steady state statistical distribution of carrier population in the conduction band. To do this we construct a phenomenological kinetic model of the time evolution of the distribution which incorporates the three important carrier collision mechanisms: recombination, electron-optical phonon and electron-electron. The model is non-linear due to the electron-electron terms. It has been solved numerically and in an approximate analytical way. This last method gives an explicit expression for the distribution function and the temperature of the hot electron gas in terms of the parameters of the system. Our calculations reproduce well the trends shown in the experimental data reported in the literature.     

Radiopharmaceuticals for renal studies: Evaluation of protein binding

Determination of total in vitro protein binding was evaluated for the following radiopharmaceuticals:^99mTc-diethylenetriaminepentaacetic acid (DTPA),^99mTc-dimercaptosuccinic acid (DMSA),^99mTc-glucoheptonate (GH) and^99mTc-fosfomycin (PHO). For that they were incubated wtih human serum at 37°C. After three and sixty minutes of incubation, the bound fraction was evaluated by two different methods: gel filtration and precipitation with trichloroacetic acid (TCA). The percentage of the^99mTc-kidney agents bound by human serum proteins is different for each one. Determination by TCA precipitation always leads to higher results. For renal imaging agents (DMSA, GH and PHO) the percentage of binding by each serum proteic constituent was also evaluated by electrophoretic analysis. All proteic constituents of human serum bind with those radiopharmaceuticals but the percentage of binding is different in accordance with both the radiopharmaceutical and the proteic constituent.