Biomedical subjects

Roberto Gobetto

Publications and source records attributed to Roberto Gobetto.

13 recordsLinked to original sources

PubMed2007

Polymorphism in crystalline cinchomeronic acid.

The structural relationship between the two crystal forms of cinchomeronic acid (CA 3,4-dicarboxypyridine) has been investigated by single crystal X-ray diffraction, IR and Raman spectroscopy and solid state NMR spectroscopy, showing that the two polymorphs form a monotropic system, with the orthorhombic form I being the thermodynamically stable form, while the monoclinic form II is unstable. In both forms CA crystallizes as a zwitterion and decomposes before melting. The crystal structure and spectroscopic analysis indicate that the difference in stability can be ascribed to the strength of the hydrogen-bonding patterns established by the protonated N-atom and the carboxylic/carboxylate O-atoms.

Journal Article↗

PubMed2007

A new tetrahydrated form of sodium naproxen.

The anhydrous sodium naproxen (ASN) can form several hydrated phases if maintained at different relative humidities (RH). The water uptake can promote crystallographic modifications, according to the amount of water. In a previous work, the authors showed that a dihydrated form could be obtained either by crystallization in water or by exposure of the anhydrous form to a RH of 55%. In the present work, the authors report about the formation and characterization of a new tetrahydrated form, obtained by exposing the ASN to RH >or= 75%. All the hydrated compounds were characterized by the combined use of several spectroscopic, thermal, and crystallographic techniques. The thermal stability of both the dihydrated and tetrahydrated compounds was also tested.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2006

The imidazole role in strontium beta-diketonate complexes formation.

A selection of new strontium beta-diketonate derivatives (imH2)2[Sr2(beta-dike)6] [where imH = imidazole and beta-dike = tfac (tfacH = 1,1,1-trifluoro-2,4-pentanedione), tfbz (tfbzH = 1,1,1-trifluoro-4-phenyl-2,4-butanedione), or hfac (hfacH = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione)], [Sr2(tfac)4(Meim)2(H2O)2], (MeimH)2[Sr(beta-dike)4] (where Meim = 1-methylimidazole and beta-dike = tfbz or hfac), [Sr2(thd)4(imH)2(EtOH)], and [Sr2(thd)4(Meim)2(EtOH)] (where thdH = 2,2,6,6-tetramethyl-3,5-heptanedione) have been synthesized and fully characterized. (imH2)2[Sr2(beta-dike)6] and (MeimH)2[Sr(beta-dike)4] are di- and mononuclear Sr anionic complexes, respectively, while [Sr2(tfac)4(Meim)2(H2O)2], [Sr2(thd)4(imH)2(EtOH)], and [Sr2(thd)4(Meim)2(EtOH)] are neutral dinuclear molecular derivatives. The derivative (imH2)2[Sr2(hfac)6] slowly decomposes in solution under aerobic conditions, giving (imH2)2[Sr(H2O)2(tfa)3](tfa) (tfaH = trifluoroacetic acid), which is an ionic compound containing polynuclear anionic chains composed of Sr(H2O)2(tfa)3 units. When a deficiency of imH is employed, the thdH proligand forms not only the dinuclear derivative [Sr2(thd)4(imH)2(EtOH)] but also an additional product with the formula [Sr(thd)2(H2O)2(EtOH)], in which the Sr atom is seven-coordinated. A complete solid-state characterization has been accomplished by comparing X-ray and solid-state 13C NMR data. Elucidation of the H-bond interaction between the heterocyclic rings and metal complexes by cross-polarization magic-angle-spinning 15N NMR is also reported.

Crystallography, X-Ray↗

PubMed2006

Chemicals from wastes: compost-derived humic acid-like matter as surfactant.

Compost humic acid-like (cHAL) polymeric matter (MW = 15610), isolated in 12% yield from food and green waste compost, exhibits very good surfactant properties in aqueous solution: i.e., critical micelle concentration (cmc) = 403 mg/L and surface tension at cmc = 36.1 mN/m. Values of cmc are confirmed also by conductivity and phenanthrene solubility measurements. These results, compared with those for other major commercial and research surfactants, propose cHAL as a competitive low-cost biosurfactant.

Humic Substances↗

PubMed2005

Hydrogen bonding and dynamic behaviour in crystals and polymorphs of dicarboxylic-diamine adducts: a comparison between NMR parameters and X-ray diffraction studies.

Fumaric, malonic, maleic, and hydromuconic (HOOCCH2(CH)2CH2COOH) acids were used to prepare a series of hydrogen-bonded adducts or salts, depending on whether acid-base proton transfer takes place, with the dibase [N(muCH2CH2)3N] in various stoichiometric ratios. The resulting compounds have been investigated by using the 1H MAS, 15N, and 13C cross polarisation magic-angle spinning (CPMAS) methods and discussed in relation to X-ray diffraction studies to ascertain the nature of the O-HO, NH-O, and N+-HO- hydrogen bonds between the various species. In addition, two polymorphic forms of the malonic compound and a hydrate in the maleic case were examined. We also present the correlations between the chemical shifts of the hydrogen-bonded protons and those from the proton transfer reaction (acid-to-base) with the heavy atom distances. The dynamic behaviour in the solid-state of the [N(muCH2CH2)3N] adducts with fumaric 2:1, maleic 1:1 hydrate, and hydromuconic acids, and a malonate 2:1 polymorph adduct have been investigated by using variable-temperature 1H spin-lattice relaxation times. A substantial agreement between the activation energies obtained from fitting the T1 data and the results of potential energy barrier calculations demonstrates that the facile reorientation of the [N(muCH2CH2)3N] molecule occurs in several of the adducts.

Journal Article↗

PubMed2005

Maya blue: a computational and spectroscopic study.

Maya Blue pigment, used in pre-Colombian America by the ancient Mayas, is a complex between the clay palygorskite and the indigo dye. The pigment can be manufactured by mixing palygorskite and indigo and heating to T > 120 degrees C. The most quoted hypothesis states that the dye molecules enter the microchannels which permeate the clay structure, thus creating a stable complex. Maya Blue shows a remarkable chemical stability, presumably caused by interactions formed between indigo and clay surfaces. This work aims at studying the nature of these interactions by means of computational and spectroscopic techniques. The encapsulation of indigo inside the clay framework was tested by means of molecular modeling techniques. The calculation of the reaction energies confirmed that the formation of the clay-organic complex can occur only if palygorskite is heated at temperatures well above the water desorption step, when the release of water is entropically favored. H-bonds between the clay framework and the indigo were detected by means of spectroscopic methods. FTIR spectroscopy on outgassed palygorskite and freshly synthesized Maya Blue samples showed that the presence of indigo modifies the spectroscopic features of both structural and zeolitic water, although no clear bands of the dye groups could be observed, presumably due to its very low concentration. The positions and intensities of delta(H2O) and nu(H2O) modes showed that part of the structural water molecules interact via a hydrogen bond with the C=O or N-H groups of indigo. Micro-Raman spectra clearly evidenced the presence of indigo both in original and in freshly synthesized Maya Blue. The nu(C=O) symmetric mode of Maya Blue red-shifts with respect to pure indigo, as the result of the formation of H-bonds with the nearest clay structural water. Ab initio quantum methods were applied on the indigo molecule, both isolated and linked through H-bonds with water, to calculate the magnitude of the expected vibrational shifts. Calculated and experimental vibrational shifts appeared to be in good agreement. The presence of a peak at 17.8 ppm and the shift of the N-H signal in the 1H MAS NMR spectrum of Maya Blue provide evidence of hydrogen bond interactions between indigo and palygorskite in agreement with IR and ab initio methods.

Journal Article↗

PubMed2005

Polarization transfer from para-hydrogen to heteronuclei: effect of H/D substitution. The case of AA'X and A2A2'X spin systems.

Upon hydrogenation from para-hydrogen (p-H(2)), hyperpolarization transfer toward a heteronucleus may be possible even if the two protons are chemically equivalent in the final product (but not magnetically equivalent), provided that J couplings with the heteronucleus exist. It is however shown (theoretically and experimentally) that this transfer effectively occurs if the spin system in the hydrogenated molecule is of the type AA'X (A and A' denoting the two protons originating from p-H(2) and X the heteronucleus) but does not occur for a spin system of the A(2)A(2)(')X type. A theory has been worked out for assessing the details of the X spectrum (multiplet patterns) in the case of ALTADENA and PASADENA experiments. Experimental verifications are provided.

Journal Article↗

PubMed2005

para-Hydrogenation of unsaturated moieties on poly(lysine) derived substrates for the development of novel hyperpolarized MRI contrast agents.

Four alkyne-functionalized poly(lysine) derivatives have been synthesized and characterized by 1H and 13C NMR spectroscopy. In the first poly(lysine) derivative, phenylpropiolate moieties are directly bound to the aminic arms, whereas in the other derivatives, propargylamine moieties are bound to the aminic poly(lysine) arms through glucaric acid and diethylene glycol (DG) chains, respectively. para-Hydrogenation of the alkyne-functionalized poly(lysine) compounds has been investigated and the results have been discussed in terms of spin lattice relaxation properties of the hydrogenated products. It is shown that the longer the mobile chain separating the unsaturation from the poly(lysine) backbone, the more intense the polarized signals when para-hydrogenation is carried out. This is due to (a) the maintenance of short reorientational times on the unsaturated ends, and therefore a sufficiently long T(1) of the protons added during hydrogenation, and (b) the minor effect of steric hindrance by the poly(lysine) backbone that decreases interaction of the unsaturation with the catalyst, allowing higher hydrogenation rates.

Alkynes↗

PubMed2005

[Os(bpy)2(CO)(enIA)][OTf]2: a novel sulfhydryl-specific metal-ligand complex.

The synthesis and physical-chemical characterization of the metal-ligand complex [Os(bpy)2(CO)(enIA)][OTf]2 (where enIA = ethylenediamine iodoacetamide) with a sulfhydryl-specific functional group is described. The UV and visible absorption and luminescence emission, including lifetime and steady-state anisotropy, are reported for the free probe and the probe covalently linked to two test proteins. The spectroscopic properties of the probe are unaffected by chemical modification and subsequent covalent linkage to the proteins. The luminescence lifetime in aqueous buffer is approximately 200 ns and the limiting anisotropy is greater than 0.125, suggesting a potentially useful probe for biophysical investigations.

Cysteine↗

PubMed2004

Supramolecular complexation of alkali cations through mechanochemical reactions between crystalline solids.

The organometallic zwitterion [Co(III)(eta(5)-C(5)H(4)COOH)(eta(5)-C(5)H(4)COO)] reacts quantitatively as a solid polycrystalline phase with a number of crystalline alkali salts MX (M = K(+), Rb(+), Cs(+), NH(4) (+); X = Cl(-), Br(-), I(-), PF(6)(-), although not in all cation/anion permutations) to afford supramolecular complexes of the formula [Co(III)(eta(5)-C(5)H(4)COOH)(eta(5)-C(5)H(4)COO)](2).M(+)X(-). In some cases, the mechanochemical complexation requires kneading of the two solids with a catalytic amount of water. The characterization of the solid-state products has been achieved by a combination of X-ray single-crystal and powder-diffraction experiments. The hydrogen-bonding interactions have been investigated by solid-state NMR spectroscopy. The mechanochemical reactions imply a profound solid-state rearrangement accompanied by breaking and forming of O-H...O hydrogen-bonding interactions between the organometallic molecules. All compounds could also be obtained by solution crystallization of the inorganic salts in the presence of the organometallic unit. The solid-state complexation of alkali cations by the organometallic zwitterion has been described as a special kind of solvation process taking place in the solid state.

Journal Article↗

PubMed2003

Spectroscopic and computational investigations of stable radical anions of triosmium benzoheterocycle clusters.

The variable temperature (1)H and (13)C NMR and EPR spectra of the stable radical anions [Os(3)(CO)(9)(micro(3)-eta(2)-L)(micro-H)] (LH=phenanthridine, 1; 5,6-benzoquinoline, 2), and [Os(3)(CO)(10)(micro(3)-eta(2)-L)(micro-H)] (LH=quinoxaline, 3) are reported. The radical anions 1(-), 2(-), and 3(-) can be prepared by both exhaustive electrolysis and partially by chemical reduction with cobaltocene and with sodium dispersion (only with sodium dispersion in the case of 3(-)). DFT calculations on 1-3 reveal that the LUMO for the electron-deficient compounds 1 and 2 involves significant contributions from both the heterocyclic ligand and the two metal atoms bridged by the ligand and the micro-hydride. The character of this orbital rationalizes the previously observed regioselective reactions of these complexes with nucleophiles. In contrast, the LUMO for the electron precise 3 involves only ligand-based orbitals. Partial chemical reduction of 1 and 2 requires an excess of either cobaltocene or sodium, and their (1)H and (13)C NMR spectra reveal selective line broadening of those proton resonances that are predicted by DFT calculations to bear the greatest amount of free spin density. The variable temperature behavior of the partially chemically reduced species of 1 and 2 indicates that electron transfer between the reduced/unreduced cluster pair and between the cobaltocene/cobaltocenium pair occurs on the NMR timescale. The radical anions of 1 and 2 prepared by exhaustive electrolysis show an EPR signal at room temperature, while the NMR signals are uniformly broadened. Compound 3 appears to be partially reduced by sodium at room temperature and shows uniformly broadened (1)H NMR resonances at room temperature that sharpen significantly at -80 degrees C. The temperature dependence of the spectra are discussed in terms of the effects of relative electron nuclear relaxation processes, chemical exchange, and the results of the DFT calculations.

Anions↗

PubMed2003

Mechanochemical preparation of hydrogen-bonded adducts between the diamine 1,4-diazabicyclo[2.2.2]octane and dicarboxylic acids of variable chain length: an X-ray diffraction and solid-state NMR study.

Mechanical mixing of solid dicarboxylic acids of variable chain length HOOC(CH(2))(n)COOH (n = 1-7) with solid 1,4-diazabicyclo[2.2.2]octane generates the corresponding salts or co-crystals of the formula [N(CH(2)CH(2))(3)N]-H-[OOC(CH(2))(n)COOH] (n=1-7). Preparation of the same systems from solution has been instrumental for a full characterization of the mechanochemical products by means of single-crystal and powder-diffraction X-ray analyses, as well as by solid-state NMR. The acid-base adducts, whether involving proton transfer from the COOH group to the N-acceptor, that is having ((-))O...H-N((+)) interactions, or the formation of neutral O-H...N hydrogen bonds, show a melting point alternation phenomenon analogous to that shown by the neutral carboxylic acids. The carbon chemical shift tensors of the COOH group obtained from the sideband intensity of low speed spinning NMR spectra provide a reliable criterion for assigning the protonation state of the adducts.

Journal Article↗

PubMed2002

Supramolecular gas-solid reaction between formic acid vapours and solid [CoIII(eta 5-C5H4COOH)(eta 5-C5H4COO)].

Exposure of the solid zwitterion [CoIII(eta 5-C5H4COOH)(eta 5-C5H4COO)] to vapours of formic acid quantitatively produces the co-crystal [CoIII(eta 5-C5H4COOH)(eta 5-C5H4COO)] [HCOOH] without proton transfer from formic acid to the deprotonated -COO- group on the zwitterion; formic acid can be quantitatively removed by mild thermal treatment, regenerating the starting material.

Journal Article↗