Marcello Giomini

Infrared Characterization of Different Water Types inside Reverse Micelles

The three Gaussian components of the IR stretching band of OH for reverse micelles of egg yolk L-α-phosphatidylcholine in benzene have been characterized in frequency, bandwidth, and extinction coefficient. The different types of water identified inside the micelles correspond to hydration layers around the phospholipid polar heads, the first containing up to ∼11 water molecules per polar head, the second with a maximum of 10–12 water molecules per polar head.

Synthesis and spectroscopic studies (Mo¨ssbauer, IR and NMR) of [R2SnCl2bipym] (R = butyl or phenyl) and the crystal and molecular structure of [Ph2SnCl2bipym]

Abstract The complexes [R 2 SnCl 2 bipym] (R = phenyl or butyl, bipym = 2,2′,6,6′-bipyrimidine) were synthesized and studied in solution by 1 H- and 13 C-NMR spectroscopy and in the solid state by IR and Mo¨ssbauer spectroscopy. The latter was also performed in frozen ethanolic solution. The structure of the phenyl complex was determined by single crystal diffraction methods. The value obtained for the angle C-SN-C in the phenyl compound is 169.3(2)° (X-ray) and 151° (Mo¨ssbauer), but the assignment of an octahedral configuration by Mo¨ssbauer spectroscopy is consistent with the structure determined by diffraction. The butyl complex is also octahedral and the two techniques show better agreement. The value of the C-SN- C angle is 171° (Mo¨ssbauer in the solid state), 163° (Mo¨ssbauer in frozen solution) and 175.1(6)° (X-ray). The NMR coupling constant, 1 J ( 119 Sn- 13 C), was also used to estimate the C-SN-C angle. The 13 C-NMR spectrum for the butyl complex is markedly concentration-dependent. At the highest concentration, this angle is 138° (Lockhart) and 145° (Holecˇek); for less concentrated samples the angle tends to decrease. This suggests that the coordination number of tin in solution is less than six.

Interactions of small molecules with phospholipids in inverted micelles

Abstract NMR spectroscopy has been employed to study the effect of the presence of perturbing species in the internal aqueous cavity of inverted micelles. The perturbing species alter the dynamic behaviour and the relative amounts of the two water populations existing inside the micelles. Cross relaxation involving water plays an essential role in determining the relaxation rates in these systems.

A spectroscopic study of poly(dA–dT)·poly(dA–dT) in microemulsions

The behaviour of high molecular weight [poly(dA–dT)·poly(dA–dT)] (polyAT) [(0.9–1.9)×106 Da] in the quaternary water-in-oil microemulsion CTAB–n-pentanol–n-hexane–water has been studied as a function of temperature and NaCl concentration by means of UV and circular dichroism (CD) spectroscopy. Solubilization in the microemulsion stabilises the polymer double helix and no helix-to-coil thermal transition has been observed. At increasing NaCl concentration, the CD spectrum of polyAT exhibits dramatic changes and for salt concentrations 7.5×10−1 M the spectral pattern suggests the formation of aggregates of the ψ(−) type. Condensation is induced by the peculiar characteristics of the aqueous core of the microemulsion. The condensates seem to destabilise the microemulsive system and, with time, separate from it.

Synthesis, spectroscopic (Mössbauer, IR and NMR) and X-ray structural studies of diorganotin complexes of 2,2′-bipyrimidine and further NMR studies of diorganotin-pyrazine and — 2,2′-azopyridine complexes

Abstract The ligand 2,2′-bipyrimidine (bipym) was reacted with diorganotins R 2 SnCl 2 (R = methyl, ethyl) and complexes of the types R 2 SnCl 2 bipym, R 2 SnCl 2 bipym · bipym and (R 2 SnCl 2 ) 2 bipym were synthesized and studied by 1 H and 13 C NMR spectroscopy in solution, and by IR and Mossbauer spectroscopy in the solid state and frozen solutions. The complexes Et 2 SnCl 2 bipym · bipym and (Et 2 SnCl 2 ) 2 bipym were characterized by X-ray diffraction methods. In both complexes the tin environment is octahedral with chloro atoms in a cis disposition, the ethyl groups in a trans disposition and two N atoms from the ligand bipym. the second complex is a centrosymmetric binuclear species that has the ligand lone-pairs bound to two Et 2 SnCl 2 units, whereas the first has one Et 2 SnCl 2 species bound to the ligand and one ligand uncoordinated. The data obtained by 119 Sn Mossbauer spectroscopy for the solids and for frozen solutions indicate the presence of quadrivalent tin in an octahedral environment with trans alkyl groups, in keeping with the X-ray structures. The NMR spectra, however, reveal ligand lability in solution, and the CSnC angles calculated from coupling constants suggest a coordination number of between 5 and 6. These results together with the long SnN bond distances in crystals of Et 2 SnCl 2 bipym · bipym and (Et 2 SnCl 2 ) 2 bipym suggest that these complexes may have a potential antitumour activity.

INTERACTIONS OF ORGANOTIN(IV) HALIDES WITH REDUCED GLUTATHIONE IN AQUEOUS-SOLUTION

Abstract Glutathione (GSH) is a compound extremely common among many living organisms in which it plays a fundamental role in the processes of detoxification. Also, organotin(IV) derivatives are more and more commonly used in technological processes or as antitumor drugs. So it seemed interesting to investigate the possible interactions between GSH and organotin compounds in water. Particularly, it has been studied because of its role in the organic radicals linked to the tin center on the stoichiometry and the structure of the adducts. Information was obtained following the reaction between Me n SnCl 4-n (n = 1 to 3) and GSH by Mossbauer and NMR spectroscopies on the assumption that changes of the characteristic parameters such as the quadrupole splitting and the chemical shift and coupling constants, respectively, are closely related to modifications in the coordination of the tin atom. In the case of addition of GSH to a solution of CH 3 SnCl 3 in HEPES, complex equilibria are evidenced, while in the case of Me 2 SnCl 2 and of Me 3 SnCl only a single species is present. Mossbauer effect data together with point charge calculations and 1 H NMR results point to a 2:1 and a 1:1 complex, respectively; GSH is coordinated by the S thiolic ; atom and the coordination geometry around the tin center appears to be trigonal bipyramidal.

The influence of phosphate buffers on the 31P longitudinal relaxation time in inverted micelles

Abstract In inside-out micelles the 31P NMR chemical shift of the phosphate groups is insensitive to the pH of the aqueous internal compartment, while the longitudinal relaxation time follows the pH variations and can be used as an indicator when, as in this case, the chemical shift is uninformative because of the extensive hydrogen bond network.

Different factors affecting polyAT conformation in microemulsions: effects of variable P0 and KCl concentration

The behaviour of the synthetic polynucleotide polyAT entrapped in the inner core of a quaternary cationic microemulsion has been investigated by means of CD and UV spectroscopies in the presence of KCl (variable temperature at constant W0 = [H2O]/[CTAB] and P0 = [cosurfactant]/[CTAB]) and NaCl (variable P0 at constant W0 and temperature). While the presence of KCl gives rise to effects which are not substantially different from those already reported for NaCl (absence of thermal melting and formation of compact ψ(−) structures), the peculiar results obtained as a consequence of the progressive addition of cosurfactant (denaturation of the polymer at low [NaCl] and W0; transition from B- to A-form at intermediate [NaCl], formation of ψ(−) aggregates at high [NaCl]) can be attributed to the characteristics of the microemulsive system (restricted volume), of the micellar water (low dielectric constant and reduced activity) and of the interface (progressively higher cosurfactant concentration).

The interactions of Fe3+ ions with adriamycin studied by 57Fe Mössbauer and electronic spectroscopies☆

Abstract The interactions between ferric ions and the anticancer antibiotic adriamycin have been investigated by 57 Fe Mossbauer and electronic spectroscopies. The Mossbauer parameters are markedly dependent on the preparation procedure, the equilibration time, the metal-to-ligand ratio, and the concentration of the drug. At millimolar drug concentration, the 4.2 K Mossbauer spectra exhibit a broad Fe(III) magnetic sextet attributed to polynuclear aggregates of high magnetic anisotropy, and a quadrupole split Fe(III) doublet attributed to a species of lower magnetic anisotropy, which exhibits superparamagnetic behavior. The two species are in equilibrium, as indicated by the time evolution of both Mossbauer and electronic spectra. At 3.0 10 −5 M drug concentration, when adriamycin is mainly monomeric, the 4.2 K Mossbauer spectra exhibit a quadrupole split doublet, connected with a superparamagnetic system, as for the concentrated preparations, and a broad magnetic sextet whose relative area increases with aging. The species responsible for this sextet should be some polymerizable hydrolysis product of the Fe(III) ions present in the dilute solution. In addition, the presence of a transient Fe(II) quadrupole doublet, both in this preparation and when the [Fe] / [ADR] ratio is 1:5 at millimolar drug concentration, is explained with the known intramolecular one-electron redox reaction which ferric-adriamycin undergoes under anaerobic conditions. The present results confirm that adriamycin is markedly more reactive than daunomycin due to its hydroxymethyl side-chain, and suggest that the stacking of the drug molecules plays a role in the observed cooperative phenomena.

Acid Titrations of poly(dG-dC).poly(dG-dC) in Aqueous Solution and in a w/o Microemulsion

Abstract The model polynucleotide poly(dG-dC).poly(dG-dC) (polyGC) was titrated with a strong acid (HCl) in aqueous unbuffered solutions and in the quaternary w/o microemulsion CTAB/n-pentanol/n-hexane/water. The titrations, performed at several concentrations of NaCl in the range 0.005 to 0.600 M, were followed by recording the modifications of the electronic absorption and of the CD spectra (210≤ λ ≤350 nm) upon addition of the acid. In solution, the polynucleotide undergoes two acid-induced transitions, neither of which corresponds to denaturation of the duplex to single coil. The first transition leads to the Hoogsteen type synG.C+ duplex, while the second leads to the C+.C duplex. The initial B- form of polyGC was recovered by back-titration with NaOH. The apparent pKa values were obtained for both steps of the titration, at all salt concentrations. A reasonably linear dependence of pKa(1) and pKa(2) from p[NaCl] was obtained, with both pKa values decreasing with increasing ionic strength. In microemulsion, at salt concentrations ≤ 0.300 M, an acid-induced transition was observed, matching the first conformational transition recorded also in solution. However, further addition of acid led to denaturation of the protonated duplex. Renaturation of polyGC was obtained by back-titration with NaOH. At salt concentrations > 0.300 M, polyGC is present as a mixture of B-form and ψ(-) aggregates, that slowly separate from the microemulsion. The acid titration induces at first a conformational transition similar to the one observed at low salt or in solution, then denaturation occurs, which is however preceded by the appearance of a transient conformation, that has been tentatively classified as a left-handed Z double helix.