The r-mean curvature and rigidity of compact hypersurfaces in the Euclidean space

Annals of Global Analysis and Geometry - In this paper, we characterize round spheres in the Euclidean space under some suitable conditions on the r-mean curvature.     

Weak exchange interaction supported by a biologically relevant long chemical bridge in a Cu-peptide model compound

The copper complex of the dipeptide L-alanyl-L-phenylalanine, catena-(L-alaninate-L-phenylalaninate-copper(II) monohydrate), identified as Cu(II)Ala-Phe, provides a convenient system to study a weak exchange interaction between unpaired spins transmitted through a biologically relevant long chemical bridge (18.34 A). In this complex, the copper ions are arranged in two symmetry-related anisotropic layers parallel to the ab plane at 13.17 A, separated by a double layer of water molecules. The equatorial-equatorial bridge considered as the most relevant path for exchange interactions between copper ions in neighbor layers contains 11 diamagnetic atoms (including three hydrogens), with two covalent amidate bridges plus three weak and moderate H bonds that go across the water layer. This interaction was studied using electron paramagnetic resonance in single-crystal samples, at 9.5 and 34.5 GHz. The measured magnitude of the interlayer interaction, |J3|/kB = 1.7(2) x 10(-3) K, is discussed in terms of values obtained for similar paths in other model compounds and in proteins. These results in model systems provide information that may be important in understanding biological functions at the molecular level.     

Synthesis, structural characterization and ex vivo biological properties of a new complex [Cu(propranolol)2]·2H2O, a potential beta-blocker

The synthesis and spectroscopic characterization (UV–Vis, IR, EPR) of a new copper complex with a beta-blocker propranolol (1-(isopropylamino)-3-(1-naphthyloxy)-2-propanol) are presented. Besides, the X-ray crystal structure of [Cu(propranolol)₂]·2H₂O is determined, showing two different copper ions, one coordinated through two S propranolol isomers and the other through two R isomers. The effect on the heart contraction force and on the heart rate plus the block of response to adrenaline of the complex and the free ligand, were studied. The effect of [Cu(propranolol)₂]·2H₂O on contractility was very similar to that of the free propranolol while the reduction on the heart rate is approximately 30% of the reduction obtained with the free ligand. This is an encouraging result since the search of new beta-blocker drugs that have lesser effect on heart rate is one of the important topics in cardiac pharmacology. The block of the response to adrenaline is at least similar for both ligand and complex.     

Interaction of Cu-dipeptide complexes with Calf Thymus DNA and antiproliferative activity of [Cu(ala-phe)] in osteosarcoma-derived cells

In this work the study of Calf Thymus DNA interaction with several Cu(l-dipeptide) complexes was reported. The binding stoichiometry (Cu(mmol)/DNAmol base) was determined and in an attempt to clarify the binding mode, EPR and CD experiments were performed. All the studied complexes interacted with DNA, in a more selective way than [Cu(H₂O)₆]²⁺, being the [Cu(ala-phe)] the complex with the highest interaction. The EPR experiments suggested that the monomeric species formed in solution were coordinated through a nitrogen atom of the DNA bases (inner-sphere binding) and the CD studies showed structural changes upon the DNA–complex interaction. Besides, the ratio Cu(mmol)/DNAmol base obtained by the binding stoichiometry experiments was close to that found by EPR and CD determinations. The effect on cell proliferation determined by the crystal violet bioassay on UMR106 rat osteosarcoma-derived cells showed that the [Cu(ala-phe)] complex exerted an antiproliferative action against this tumor line.     

Two-dimensional ELDOR in the study of model and biological membranes

Recent studies on model and biological membranes by two-dimensional (2-D) electronelectron double resonance (ELDOR) are reviewed and discussed. The studies include (1) the phase behavior of dispersions of phospholipid-cholesterol membrane vesicles; (2) the effect of the ion-channel-forming peptide gramicidin A on the lipid membrane; and (3) the effects of stimulation by antigen of the immunoglobulin E receptors in plasma membrane vesicles upon the lipid structure. In the first studies it is shown that the 2-D ELDOR spectra enable clear distinctions amongst the different phases, and this leads to a reliable temperature and composition-dependent phase diagram. In the second studies it is possible to distinguish bulk and boundary lipids and to describe their different dynamic structures. In the third studies we could distinguish both liquid-ordered and liquid-disordered spectral components, and one finds that the fraction of the latter increases as a result of stimulation. Emphasis is placed on the new “full Sc — method” of processing the 2-D ELDOR data to significantly enhance spectral resolution, which is particularly important in studying the spectra from coexisting phases or components. In the full Sc — method, one utilizes both the real and imaginary parts of the signal, instead of their magnitude; the needed phase corrections are obtained as part of the nonlinear least-squares fitting of the 2-D ELDOR data.     

X-ray structure and EPR behavior of a new dimeric copper(II) complex with 4-amino-N-(5-methoxy-2-pyrimidinyl)benzenesulfonamide

A new complex, [Cu₂(sulfameter)₄]₃ · 2.5H₂O (sulfameter = 4-amino-N-(5-methoxy-2-pyrimidinyl)benzenesulfonamide), has been synthesized. Its structure has been determined by single-crystal X-ray diffraction and its spectroscopic properties (EPR, IR, Raman, UV–Vis) have been analyzed. The structure presented three different dimeric units in the unit cell and the EPR spectra, characteristic of antiferromagnetically coupled dimers, revealed two magnetically different dimeric environments.