PtCl

The ionic complex [PtCl(3)(C(2)H(4))](-)[(S,S)-(PhMeCH)(2)NH(2)](+) containing a chiral secondary amine is a new and versatile chiral derivatizing agent (CDA) for the determination of the enantiomeric composition of several unsaturated compounds including simple olefins: the diastereoisomeric mixtures arising from the exchange of ethylene by the unsaturated analytes are easily detected by (195)Pt NMR spectroscopy.     

Asymmetric induction by the cholestanic moiety on tropos species: synthesis and stereochemical characterization of bile acid-based biphenyl phosphites

Three different bile acid-derived biphenyl phosphites were synthesized, starting from cholic and deoxycholic acids and biphenol, and their stereochemical features were checked by CD and NMR spectroscopies. On the basis of the spectroscopic results, the capability of the cholestanic system to induce a prevalent sense of twist on the biphenyl moiety of the bile acid-derived phosphites as well as their tropos nature was inferred.     

NMR Investigation of the Interaction of Three Non-Steroidal Anti-Inflammatory Drugs with Human Serum Albumin

The understanding of the interaction between non-steroidal anti-inflammatory drugs and human serum albumin plays a fundamental role in the development of new drugs and new therapeutic strategies. Several studies have been performed, nevertheless, the interaction phenomena are still not fully understood. In this work, high-field solution Nuclear Magnetic Resonance (NMR) spectroscopy was applied to compare the strength of the interaction of diclofenac sodium salt, ketorolac tris salt and flurbiprofen sodium salt toward albumin. To this aim, mono- and bi-selective relaxation rate measurements were performed by applying selective π-pulses at the selected frequencies and by following magnetization recovery. On the basis of the dependence of relaxation parameters on albumin concentration, normalized affinity indexes were calculated for several protons of the drugs. Affinity indexes for diclofenac were about five-fold higher in comparison with ketorolac and flurbiprofen. Aromatic moieties of the three drugs and methine protons at the chiral centers of ketorolac and flurbiprofen were more involved in the interaction with albumin. In conclusion, NMR spectroscopy allows not only for the comparison of drug-to-protein affinities but also points out the nature of the drug sites that are more extensively involved in the interaction.     

Restricted rotation of the olefin and amine ligands in cis-dichloro(p-toluidine)(ethyl vinyl ether)platinum(II)

cis-Dichloro(p-toluidine)(olefin)platinum(II) complexes, in which the olefin is either ethyl vinyl ether or ethylene, have been investigated by ¹H NMR spectroscopy over a range of temperatures (+50 to ?60° C) in order to study the rotation of the olefin ligand.The results give no evidence of rotation of the amine or vinyl ether ligands even at the highest temperature investigated, +50°C; only one of the two possible rotational isomers is present, and this is attributed to the presence of intramolecular hydrogen bonding between the oxygen atom of the vinyl ether and the -NH- group of the amine.In contrast, the amine and vinyl ligands in the ethylene complex rotate freely at room temperature, coalescence being observed above ?25° C for the ethylene protons.     

PtCl3(C2H4)]-[AmH]+ complexes containing chiral secondary amines: use as chiral derivatizing agents for the enantiodiscrimination of unsaturated compounds by 195Pt NMR spectroscopy and NMR stereochemical investigation.

Ionic complexes [PtCl3(C2H4)]-[AmH]+, containing chiral secondary amines, constitute a versatile class of chiral derivatizing agents (CDAs) for the enantiomeric purity determination of chiral unsaturated compounds via 195Pt NMR spectroscopy. The NMR conformational analysis allows us to search for the stereochemical basis of their enhanced versatility.     

A new platinum vapor-derived highly efficient hydrosilylation catalyst: NMR structural investigation

The structural features of a highly efficient hydrosilylation catalyst generated by reaction of Pt vapor and a mixture of mesitylene and 1,3-divinyltetramethyldisiloxane (DVS) were investigated by mono- and bidimensional NMR analyses. The structure around the Pt atoms was highlighted and compared with a commercial sample (Karstedt catalyst) and previously reported Pt vapor-derived system.     

Different enantioselective interaction pathways induced by derivatized quinines

The stereochemistries in solution of the diastereoisomeric complexes formed by quinines modified at the hydroxyl site (9-O-acetylquinine; 9-O-(3,5-dimethoxyphenylcarbamate)quinine) or quinuclidine nitrogen (N-benzylquininium chloride) and each enantiomer of 2-(3', 5'-dinitrobenzamido)-1-phenylethanol have been compared to those of the free compounds by (1)H NMR investigations. Completely different interaction models, also involving changes of the free state conformations, have been obtained.     

Nuclear magnetic resonance approaches to the rationalization of chromatographic enantiorecognition processes

NMR spectroscopy represents a valuable tool for obtaining information about structure and dynamics at a molecular level on the diastereoisomeric complexes formed by enantiomeric substrates and chromatographic chiral selectors or modifiers. Some examples collected from the literature show the potentialities of solution NMR spectroscopy in the rationalization of chromatographic enantiorecognition processes and the different NMR approaches needed according to the chiral selector features.     

The control of the growth of Pt clusters in solution: A way to prepare Pt particles of tailored size

The growth of Pt particles in mesitylene-solvated metal atoms, obtained by metal vapour synthesis (MVS), has been followed at two temperatures (−40 and 25 °C) by NMR DOSY technique. The addition of 1,3-divinyltetramethyldisiloxane (DVS) at different time allows to quench the growth process and to make the resulting thermally stable solutions suitable for the evaluation of the Pt particles size at that moment. These solutions can be conveniently used to prepare supported Pt systems containing Pt particles of tailored size.     

Synthesis and host-guest studies of chiral N-linked peptidoresorc[4]arenes

Four cone resorc[4]arene octamethyl ethers (10, 11, ent-10, and ent-11) tetrafunctionalized at the feet with valyl-leucine [LL- (6); DD- (ent-6)] and leucyl-valine [LL- (9); DD- (ent-9)] methyl esters have been synthesized. These compounds, obtained by conjugation of macrocycle tetracarboxylic acid chlorides with the appropriate terminal amino groups of the above dipeptides, are N-linked peptidoresorc[4]arenes. We found that these macrocycles (M) are capable of recognizing the homologue dipeptides as guests (G), both in solution and in the gas phase, by forming relatively stable host-guest complexes ([M.G]), resistant to chromatographic purification but not to heating. Complexation phenomena between M and G in solution were investigated by NMR methods, including NMR DOSY experiments, for the detection of translational diffusion. Heteroassociation constants of 2030 and 186 M(-1) were obtained by the Foster-Fyfe method for the complexes [10.6] and [10.ent-6], respectively, the latter being comparable to the self-association constant of dipeptide itself. Conversely, the structural features of the proton-bound complexes [M.H.Gn]+ (n = 1, 2), generated in the gas phase by electrospray ionization mass spectrometry (ESI-MS), were investigated by collision-induced dissociation (CID) experiments. In both cases, the four N-linked peptidoresorc[4]arenes were shown to act as synthetic receptors and to recognize the homologue dipeptide by means of hydrogen bonds.