Gadolinium(III) Complexes of dota‐Derived N‐Sulfonylacetamides (H4(dota‐NHSO2R)=10‐{2‐[(R)sulfonylamino]‐2‐oxoethyl}‐1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic Acid): A New Class of Relaxation Agents for Magnetic Resonance Imaging Applications

Four new ligands for lanthanide ions based on the H₃do3a (=1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid) structure and bearing one N‐sulfonylacetamide arm were synthesized, i.e., H₄dota‐NHSO₂R=10‐{2‐[(R)sulfonylamino]‐2‐oxoethyl}‐1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acids 1a – e . A ¹⁵N‐NMR study of the ¹⁵N‐labelled Eu³⁺ complex of one such ligands, 1d , showed that the coordination of the N‐sulfonylacetamide arm involves the carbonyl O‐atom rather than the N‐atom. The relaxometric properties of the corresponding Gd³⁺ complexes were investigated as a function of pH and temperature. These complexes have relaxivities in the range 4.5–5.3 mM ^?1 s^?1, at 20 MHz and 25°, and are characterized by a single H₂O molecule in their inner coordination sphere. The mean residence lifetime of this molecule is relatively long (500–700 ns) compared to other anionic complexes. The slow rate of H₂O exchange can be justified by the extensive delocalization of the negative charge on the N‐sulfonylacetamide arm. The long residence time of the coordinated H₂O allowed the observation of the effect of the prototropic exchange on the relaxivity. The study of the interaction between the complex [Gd( 1e )]‐ and HSA revealed a weak affinity constant highlighting the importance of a localized negative charge on the complex to promote a strong interaction with the protein.     

Structural researches on the chelating behaviour of the biguanide ligand. The crystal structures of Co(C2H6N5)3 · 2H2O and Cu(C2H7N5)2CO3·4H20

Summary Crystals of the title compounds are both monoclinic, with unit cell dimensions:a = 9.293(5),b = 10.122(5),c = 16.737(7) Å. = 103.44(3)°,Z = 4, space groupP2₁/c for the cobalt derivative;a = 13.1ß5(7),b = 17.546(ß),c = 6.871(3) Å, = 107.01(4)°Z = 4, space groupP2₁/n for the copper derivative. The structures were solved from diffractometer data by the heavy-atom technique for the first compound and by direct methods for the second compound. Refinement by block diagonal least-squares gaveR = 5.9% for 3511 independent reflections andR = 8.8% for 2885 independent reflections for the cobalt and copper compound respectively. In both compounds the biguanide moiety behaves as a bidentate chelating ligand in a symmetrical tautomeric form, but it is deprotonated in the octahedral cobalt compound and neutral in the square planar copper compound.     

Palladium-catalyzed reaction of aryl iodides with acetic anhydride. A carbon monoxide-free synthesis of acetophenones

[reaction: see text] The palladium-catalyzed reaction of aryl iodides with acetic anhydride provides a straightforward and experimentally simple carbon monoxide-free route to acetophenones. The reaction tolerates a wide range of functionalized aryl iodides. Acetophenones are isolated in excellent yield with a variety of neutral, slightly electron-rich, and slightly electron-poor aryl iodides, whereas moderate yields are obtained with aryl iodides containing strongly electron-withdrawing substituents.     

Structural characterization techniques for the analysis of semiconductor strained heterostructures

A combined method for structural characterization of strained epitaxial heterostructures involving different techniques such as Rutherford backscattering spectrometry (RBS), multiple crystal X-ray diffractometry (MCD) and transmission electron microscopy (TEM) is presented. In order to obtain a complete characterization of the analysed structure, three different quantities are measured independently: the epilayer thickness, the density of misfit dislocations which may appear at the interface, and the significant components of the strain tensor, mainly the tetragonal distortion, affecting the epilayer lattice. In this way the thermodynamic state and the mechanisms of plastic deformation of the structures can be fully investigated. In this contribution we present and discuss the experimental results concerning a set of InP/GaAs samples having different layer thicknesses ranging from 5 to 500 nm. The thickness of the samples has been determined by RBS. Measurements of in-plane strain and tetragonal distortion have been performed by MCD and RBS-channelling respectively, finally TEM has been used for determining the defects densities and distribution.     

High-intensity ultrasound and microwave, alone or combined, promote Pd/C-catalyzed aryl-aryl couplings

Pd-catalyzed homo- and cross-couplings of boronic acids and aryl halides were successfully carried out both in aqueous media under high-intensity ultrasound (US) and in DME under microwave (MW). Heterogeneous catalysis with Pd/C was employed, avoiding phosphine ligands and phase-transfer catalysts. In a trial series involving 15 different iodo- and bromoaryls and 7 boronic acids, both energy sources drastically reduced reaction times affording biaryls in acceptable to good yields. With palladium(II) acetate as catalyst, electron-deficient aryl chlorides also reacted, affording a few biaryls in acceptable yields. Ullmann-type zinc-mediated homocoupling of iodo- and bromoaryls in the presence of Pd/C under CO₂ atmosphere was achieved in aqueous media under US, though not under MW. Suzuki homo- and cross-couplings were also carried out in a new reactor developed in our laboratory, featuring combined US and MW irradiation, further improving a green synthetic method.     

Electrophilic cyclization of o-acetoxy- and o-benzyloxyalkynylpyridines: an easy entry into 2,3-disubstituted furopyridines

[reaction: see text] 2,3-Disubstituted furo[3,2-b]pyridines, 2,3-disubstituted furo[2,3-b]pyridines, and 2,3-disubstituted furo[2,3-c]pyridines are readily prepared under mild conditions via the palladium-catalyzed cross-coupling of 1-alkynes with o-iodoacetoxy- or o-iodobenzyloxypyridines, followed by electrophilic cyclization by I(2) or by PdCl(2) under a balloon of carbon monoxide.     

Synthesis, Structure, and Antimicrobial Activity of Complexes of Pt(II), Pd(II), and Ni(II) with the Condensation Product of 2-(Diphenylphosphino)benzaldehyde and Semioxamazide

Complexes of Pt(II), Pd(II), and Ni(II) with the condensation derivative of 2-(diphenylphosphino)benzaldehyde and semioxamazide were synthesized, characterized, and their antimicrobial activity was evaluated. The ligand and the complexes were characterized by spectroscopic methods with the particular accent on NMR spectral analysis. For the palladium(II) complex, the crystal structure was determined by X-ray analysis. In all the complexes the ligand is coordinated as a tridentate via a P, N, O donor set. The Pd(II) and Pt(II) complexes have a square planar geometry, whereas the geometry of the Ni(II) complex is tetrahedral. The ligand showed antibacterial and antifungal activity, which was enhanced upon complexation.     

Towards a rigorous treatment of the Jeans-Landau-Teller method for the energy exchanges of harmonic oscillators

For classical Hamiltonian systems containing an harmonic oscillator of high frequency, one has the problem of controlling the energy exchange between the oscillator and the remaining slow degrees of freedom; under very general conditions, such an exchange turns out to be exponentially small with the frequency of the oscillator. In the Jeans-Landau-Teller method, one aims to prove the exponential dependence, and to estimate the coefficient of the exponential, by exploiting the analyticity properties of the solution of the differential equations describing the motion of the system. However, in practice, since the exact solution is not known, such properties are inferred from those of an approximate solution, with no control of the difference; this fact might a priori even invalidate the exponential dependence itself. In the present paper a rigorous treatment is given, for a particular model of interest in the domain of atomic collisions, by keeping control of the difference between the exact and the approximate solution.     

Photochemistry of artificial photosynthetic reaction centers in liquid crystals probed by multifrequency EPR (9.5 and 95 GHz)

Photoinduced charge separation and recombination in a carotenoid-porphyrin-fullerene triad C-P-C(60)(1) have been followed by multifrequency time-resolved electron paramagnetic resonance (TREPR) at intermediate magnetic field and microwave frequency (X-band) and high field and frequency (W-band). The electron-transfer process has been characterized in the different phases of two uniaxial liquid crystals (E-7 and ZLI-1167). The triad undergoes photoinduced electron transfer, with the generation of a long-lived charge-separated state, and charge recombination to the triplet state, localized in the carotene moiety, mimicking different aspects of the photosynthetic electron-transfer process. Both the photoinduced spin-correlated radical pair and the spin-polarized recombination triplet are observed starting from the crystalline up to the isotropic phase of the liquid crystals. The W-band TREPR radical pair spectrum has allowed unambiguous assignment of the spin-correlated radical pair spectrum to the charge-separated state C(.+)-P-C(60)(.-). The magnetic interaction parameters have been evaluated by simulation of the spin-polarized radical pair spectrum and the spin-selective recombination rates have been derived from the time dependence of the spectrum. The weak exchange interaction parameter (J = +0.5 +/- 0.2 G) provides a direct measure of the dominant electronic coupling matrix element V between the C(.+)-P-C(60)(.-) radical pair state and the recombination triplet state (3)C-P-C(60). The kinetic parameters have been analyzed in terms of the effect of the liquid crystal medium on the electron-transfer process. Effects of orientation of the molecular triad in the liquid crystal are evidenced by simulations of the carotenoid triplet state EPR spectra at different orientations of the external magnetic field with respect to the director of the mesophase. The order parameter (S = 0.5 +/- 0.05) has been evaluated.