Focusing effects in nonlinear resonant four-wave mixing (RFWM) MIR and FIR generation

Summary The influence of pump beam geometry in a NH₃ superradiant Raman FIR laser with RFWM generation of MIR emission has been analysed. We have observed that, in general, MIR radiation is emitted in a stimulated configuration, so pump and MIR beam overlap is basically important to exhibit an efficient RFWM. In particular, strong focusing, also in the presence of self-focusing, shows a lowering of the threshold of Raman FIR emission, as expected, plus a reduction of RFWM MIR emission. COMB-Arrich., CRE Frascati.     

A new HPLC method to determine glomerular filtration rate and effective renal plasma flow in conscious dogs by single intravenous administration of iohexol and p-aminohippuric acid

A high-performance liquid chromatography method to determine iohexol (IOX) and p-aminohippuric acid (PAH) in the plasma of dogs is evaluated according to recovery, reproducibility, and linearity utilizing a gradient pump. The mobile phase consists of 50mM sodium dihydrogen phosphate with 0.5mM tetrabutylammonium chloride, the pH is adjusted to 4.1, methanol is added to the final ratio of 90:10 (v/v), the flow rate is set at 1 mL/min, and separation is achieved with an ODS2 Luna column. The UV detector is set at 254 nm. IOX and PAH are used for evaluation of the effective renal plasma flow (ERPF) and glomerular filtration rate (GFR). The present method tested in three dogs demonstrates the accuracy in the evaluation of ERPF and GFR. Because of its precision and simplicity and low cost, it can be considered a good tool for ERPF and GFR in small animal practice.     

On a characterization of Clarke's tangent cone

For a subsetM of a normed vector spaceX, it is shown that, in the characterization given by Elster and Thierfelder of Clarke's tangent cone toM at a pointx ⁰X, there is a requirement which becomes superfluous whenx ⁰ belongs to the closure ofM.This research was supported by the Italian Ministry of University Scientific and Technological Research.     

Anion allosteric effect in the recognition of tetramethylammonium salts by calix[4]arene cone conformers.

Rigid calix[4]arene cone conformers, which are efficient receptors for quaternary ammonium salts, are usually obtained through the functionalization of their lower rim with suitable groups. Using flexible cone conformer of calix[4]arene, bearing four 4-hydroxybenzyl groups as cooperative and rigidifying structural elements at the upper rim of the calix, which act as anion binding groups, a new heteroditopic cavitand, 7, was synthesized. Whereas the tetramethoxy derivative 8 does not show any complexing ability, its tetrahydroxy analogue 7 recognizes tetramethylammonium salts with high efficiency. The binding abilities of this new receptor toward a series of tetramethylammonium salts (tosylate, chloride, acetate, trifluoroacetate, and picrate) have been investigated in CDCl(3) solution and compared to the monotopic and rigidified, through the lower rim, cone biscrown-3-calix[4]arene 9. The results obtained confirmed that in CDCl(3) ion pairing strongly affects binding. In particular, the rigid monotopic receptor 9 experiences good efficiency toward tetramethylammonium salts having anions with low ion-pairing ability such as trifluoroacetate or picrate. On the contrary, for the new heteroditopic cavitand 7, a reverse order of efficiency was found. In the latter case a different complexation mode was hypothesized in which the tetramethylammonium cation is deeply entrapped into the host cavity and its counteranion participates to the recognition process by coordination via hydrogen bonding by the four OH groups. To further support the role of the anion in the recognition process, a "dual host" approach, employing 7 or 9 in the presence of a specific receptor for chloride anion (10), was utilized. Molecular modeling studies confirmed that in the complexes formed by 7 and TMA salts the counteranion is involved in hydrogen bonding with the host OH groups and that the guests are bound as ligand-separated ion pairs.     

Alumina-supported vanadium nanoparticles: structural characterization and CO adsorption properties

Alumina-supported vanadium particles were prepared under ultrahigh vacuum (UHV) conditions and characterized with respect to their structural and CO adsorption properties. As supporting oxide, we used a thin, well-ordered alumina film grown on NiAl(110). This allows the application of scanning tunneling microscopy (STM), infrared reflection-absorption spectroscopy (IRAS), and X-ray photoelectron spectroscopy (XPS) without charging effects. Vanadium evaporation under UHV conditions leads to the growth of nanometer-sized particles which strongly interact with the alumina support. At very low vanadium coverages, these particles are partially incorporated into the alumina film and get oxidized through the contact to alumina. Low-temperature CO adsorption in this coverage regime permits the preparation of isolated vanadium carbonyls, of which we have identified mono-, di-, and tricarbonyls of the V(CO)(y)() type. A charge-frequency relationship was set up which allows one to quantify the extent of charge transfer from vanadium to alumina. It turns out that this charge transfer depends on the V nucleation site.     

Coordination properties of new bis(1,4,7-triazacyclononane) ligands: a highly active dizinc complex in phosphate diester hydrolysis

The synthesis and characterization of three new bis([9]aneN(3)) ligands, containing respectively 2,2'-bipyridine (L(1)), 1,10-phenanthroline (L(2)), and quinoxaline (L(3)) moieties linking the two macrocyclic units, are reported. Proton binding and Cu(II), Zn(II), Cd(II), and Pb(II) coordination with L(1)-L(3) have been studied by potentiometric titrations and, for L(1) and L(2), by spectrophotometric UV-vis measurements in aqueous solutions. All ligands can give stable mono- and dinuclear complexes. In the case of L(1), trinuclear Cu(II) complexes are also formed. The stability constants and structural features of the formed complexes are strongly affected by the different architecture and binding properties of the spacers bridging the two [9]aneN(3) units. In the case of the L(1) and L(2) mononuclear complexes, the metal is coordinated by the three donors of one [9]aneN(3) moiety; in the [ML(2)](2+) complexes, however, the phenanthroline nitrogens are also involved in metal binding. Finally, in the [ML(3)](2+) complexes both macrocyclic units, at a short distance from each other, can be involved in metal coordination, giving rise to sandwich complexes. In the binuclear complexes each metal ion is generally coordinated by one [9]aneN(3) unit. In L(1), however, the dipyridine nitrogens can also act as a potential binding site for metals. The dinuclear complexes show a marked tendency to form mono-, di-, and, in some cases, trihydroxo species in aqueous solutions. The resulting M-OH functions may behave as nucleophiles in hydrolytic reactions. The hydrolysis rate of bis(p-nitrophenyl)phosphate (BNPP) was measured in aqueous solution at 308.1 K in the presence of the L(2) and L(3) dinuclear Zn(II) complexes. Both the L(2) complexes [Zn(2)L(2)(OH)(2)](2+) and [Zn(2)L(2)(OH)(3)](+) and the L(3) complex [Zn(2)L(3)(OH)(3)](+) promote BNPP hydrolysis. The [Zn(2)L(3)(OH)(3)](+) complex is ca. 2 orders of magnitude more active than the L(2) complexes, due both to the short distance between the metal centers in [Zn(2)L(3)(OH)(3)](+), which could allow a bridging interaction of the phosphate ester, and to the simultaneous presence of single-metal bound nucleophilic Zn-OH functions. These structural features are substantially corroborated by semiempirical PM3 calculations carried out on the mono-, di-, and trihydroxo species of the L(3) dizinc complex.     

Protonation and Zn(II) coordination by dipyridine-containing macrocycles with different molecular architecture. A case of pH-controlled metal jumping outside-inside the macrocyclic cavity

The synthesis of the macrocyclic ligand 4,4'-(2,5,8,11,14-pentaaza[15])-2,2'-bipyridylophane (L3), which contains a pentaamine chain linking the 4,4'-positions of a 2,2'-dipyridine moiety, is reported. Protonation and Zn(II) complexation by L3 and by macrocycle L2, containing the same pentaamine chain connecting the 6,6'-positions of 2,2'-dipyridine, were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. While in L2 all the nitrogen donor atoms are convergent inside the macrocyclic cavity, in L3 the heteroaromatic nitrogen atoms are located outside. Both ligands form mono- and dinuclear Zn(II) complexes in aqueous solution. In the mononuclear Zn(II) complexes with L2, the metal is coordinated inside the macrocyclic cavity, bound to the heteroaromatic nitrogen donors and three amine groups of the aliphatic chain. As shown by the crystal structure of the [ZnL2](2+) complex, the two benzylic nitrogens are not coordinated and facile protonation of the complex takes place at slightly acidic pH values. Considering the mononuclear [ZnL3](2+) complex, the metal is encapsulated inside the cavity, not coordinated by the dipyridine unit. Protonation of the complex occurs on the aliphatic polyamine chain and gives rise to translocation of the metal outside the cavity, bound to the heteroaromatic nitrogens.     

Ligand hyperfine interactions and the model of the paramagnetic center Gd3+ in α-LiIO3 single crystals

The ligand hyperfine interaction (HFI) of Gd³⁺ ions in α-LiIO₃ single crystals is studied by the method of rf discrete saturation, and the tensor components of ligand HFI are determined. The model of a paramagnetic center is proposed on the basis of the analysis of the obtained results, and the mechanism of lattice distortion is discussed.