Search

Hypothesis Doxorubicin hydrochloride (DX) is widely used as a chemotherapeutic agent, though its severe side-effects limit its clinical use. A way to overcome these limitations is to increase DX latency through encapsulation in suitable carriers. However, DX has a high solubility in water, hindering encapsulation. The formulation of DX with sodium cholate (NaC) will reduce aqueous solubility through charge neutralization and hydrophobic interactions thus facilitating DX encapsulation into poloxamer (F127) micelles, increasing drug latency. Experiments DX/NaC/PEO-PPO-PEO triblock copolymer (F127) formulations with high DX content (DX-PMs) have been prepared and characterized by scattering techniques, transmission electron microscopy and fluorescence spectroscopy. Cell proliferation has been evaluated after DX-PMs uptake in three cell lines (A549, Hela, 4T1). Cell uptake of DX has been studied by means of confocal laser scanning microscopy and flow cytometry. Findings DX-PMs formulations result in small and stable pluronic micelles, with the drug located in the apolar core of the polymeric micelles. Cell proliferation assays show a delayed cell toxicity for the encapsulated DX compared with the free drug. Data show a good correlation between cytotoxic response and slow DX delivery to nuclei. DX-PMs offer the means to restrict DX delivery to the cell interior in a highly stable and biocompatible formulation, suitable for cancer therapy.

Anthracyclines self-assemble in water into dimers. In the presence of sufficiently high salt (NaCl) concentrations, solutions of the antibiotic doxorubicin, but not those of the closely related molecules daunomycin and epirubicin, turn into gels barely compatible with the presence of small oligomers. The use of spectroscopic, scattering, imaging and computational techniques, allowed light to be shed on the self-assembly process that triggered doxorubicin gelification. A complex picture emerged, with doxorubicin molecules assembled into long, highly chiral, supramolecular aggregates made of hundreds of units, showing redshifted fluorescence spectra, very short fluorescence lifetimes and small-angle X-ray scattering profiles compatible with long cylinders. The involvement of specific chemical groups and the need for a specific stereochemistry of the monomers in the formation of a hydrogen-bond network to stabilise the supramolecular aggregates was supported by molecular dynamics calculations. A salt-induced, temperature-dependent, cooperative nucleation-elongation supramolecular polymerisation of the doxorubicin molecules is deduced.

Hypothesis Doxorubicin hydrochloride (DX) is one of the most powerful anticancer agents though its clinical use is impaired by severe undesired side effects. DX encapsulation in nanocarrier systems has been introduced as a mean to reduce its toxicity. Micelles of the nonionic triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) (PEO-PPO-PEO), are very promising carrier systems. The positive charge of DX confines the drug to the hydrophilic corona region of the micelles. The use of mixed micelles of PEO-PPO-PEO copolymers and a negatively charged bile salt should favour the solubilization of DX in the apolar core region of the micelles. Experiments We studied the DX uptake in the micellar systems formed by sodium cholate (NaC) and the PEO100PPO65PEO100 (F127) copolymer, prepared with different mole ratios (MR = nNaC/nF127) in the range 0 ÷ 1. The systems were characterized by small angle X-ray scattering (SAXS) and dynamic light scattering (DLS); DX encapsulation was followed by steady-state and time-resolved fluorescence spectroscopy. Findings The successful solubilization of DX in the host micellar systems did not affect their structure, as evidenced by both SAXS and DLS data. In the presence of NaC, DX experiences a more apolar environment as indicated by its characteristic fluorescent behaviour. The almost complete uptake of the drug occurred shortly after the sample preparation; however, time resolved fluorescence revealed a slow partition of DX between corona and core regions of the micelles. DX degradation in the mixed micellar systems was markedly reduced relative to aqueous DX solutions.

The self-association equilibria of doxorubicin hydrochloride (DX), at high drug and NaCl concentrations, are studied by temperature scan fluorescence spectroscopy, with the support of molecular dynamics (MD) calculations. Even though all anthracyclines show dimerization equilibria, DX only can further associate into long polymeric chains according to DXmon ⇄ DXdim ⇄ DXpol. This is reflected not only in the mechanical properties of DXpol solutions (behaving as thixotropic gels) but also in their spectroscopic behaviour. Fluorescence, in particular, is the technique of election to study this complex set of equilibria. Upon increasing the temperature, DXpol melts into DXdim, which in turn is in equilibrium with DXmon. Since DXdim is non fluorescent, with a fluorescence temperature scan experiment the DXpol⇄ DXmon equilibrium is probed. However, also information on the DX dimerization equilibrium can be derived together with the relevant thermodynamic parameters ruling the dimerization process ( Δ H d i m ° = - 56 k J m o l - 1 ; Δ S d i m ° = - 97 J m o l - 1 K - 1 ). The residence time of DX molecules in the dimer (74.7 μs), as well as the monomers mutual orientation in the dimer, are characterized by means of theoretical and computational modelling.

The interaction of doxorubicin (DX) with model polynucleotides poly(dG-dC)·poly(dG-dC) (polyGC), poly(dA-dT)·poly(dA-dT) (polyAT), and calf thymus DNA has been studied by several spectroscopic techniques in phosphate buffer aqueous solutions. UV-vis, circular dichroism, and fluorescence spectroscopic data confirm that intercalation is the prevailing mode of interaction, and also reveal that the interaction with AT-rich regions leads to the transfer of excitation energy to DX not previously documented in the literature. Moreover, the DX affinity for AT sites has been found to be on the same order of magnitude as that reported for GC sites.

When the model polynucleotide poly(dG-dC)∙poly(dG-dC) [polyGC] is titrated with a strong acid (HCl) in unbuffered aqueous solutions containing the chlorides of the alkali metals in the concentration range 0.010 M-0.600 M, two transitions in the absorbance vs. pH plots are evidenced, characterized by the constants pK(a(₁)) and pK(a(₂)). The limiting values at infinite saline concentrations of these two constants, namely pK(∞)(a(₁)) and pK(∞)(a(₂)) obtained making use of the "one site saturation constant" equation or, in turn, of the double logarithmic plot: pK(a) vs. log([salt]⁻¹), exhibit a clear dependence on the nature of the cations. The effects of the different alkali cations on the pK(∞)(a) values follow the Hofmeister series. In fact, the pK(∞)(a(₁)) and the pK(∞)(a(₂)) values are smaller for Li+ and Na+ than for Rb+ and Cs+, with K+ at the border between the two, showing that the transitions require higher concentrations of protons to occur in the presence of high concentrations of the cosmotropic ions.

Two metal complexes of 2,2′:6′,2′′-terpyridine (terpy), i.e. Cd(terpy)Cl2 and Ni(terpy)Cl2·3H2O, have been prepared and extensively characterized. The interaction of Cd(terpy)Cl2 with synthetic DNA models, poly(dA-dT)·poly(dA-dT) (polyAT) and poly(dG-dC)·poly(dG-dC) (polyGC), has been studied by CD, fluorescence and UV-vis electronic absorption spectroscopy at several metal/polynucleotide–phosphate ratios and for different NaCl concentrations. All the experimental results indicate an intercalative mechanism of interaction. The optimized geometry of the cadmium complex intercalated between the sixth and seventh base pairs of (AT) and (GC) dodecanucleotide duplexes, obtained by quantum mechanics/molecular mechanics (QM/MM) calculations, lends support to the proposed mechanism. The calculated models provide some additional structural details of the intercalation complex at the molecular level. To evidence the influence of the charge and geometry of the metal complex on the mechanism of interaction with polynucleotides, the nickel complex–polyAT system has been studied to some extent by means of CD and UV-vis spectroscopy, and by thermal melting experiments. The results suggest that the octahedral complex cation [Ni(terpy)(H2O)2Cl]+ interacts with polyAT by partial intercalation assisted by electrostatic interaction with the negative charges of the backbone phosphate groups.

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 (210or = lambdaor =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 pKa1 and pKa2 from p[NaCl] was obtained, with both pKa values decreasing with increasing ionic strength. In microemulsion, at salt concentrationsor = 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 concentrations0.300 M, polyGC is present as a mixture of B-form and psi- 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.

CD and uv absorption data showed that high molecular weight poly(dA-dT) . poly(dA-dT), at 298 K, undergoes an acid-induced transition from B-double helix to random coil in NaCl solutions of different concentrations, ranging from 0.005 to 0.600M. Similarly, titration of the polynucleotide with a strong base causes duplex-to-single strands transition. The base- and acid-induced transitions were both reversible by back-titration (with an acid or, respectively, with a base): the apparent pKa were the same in both directions. However, the number of protons per titratable site (adenine N1) required to reach half-denaturation was in great excess over the stoichiometric value; to a much larger extent, the same effect was observed also for the deprotonation of the N3H sites of thymine. Moreover, in the basic denaturation experiments, at low salt concentrations ([NaCl]< or =0.300M) less acid than calculated was needed to back-titrate the base excess to half-denaturation. Both effects could be qualitatively justified on the basis of the counterion condensation theory of polyelectrolytes and considering the energy barrier created by the negatively charged phosphodiester groups to the penetration of the OH- ions inside the double helix and the screening effect of the Na+ ions on such charges, in the deprotonation experiments.

CD and UV spectroscopies have been used to investigate the effects caused by the addition of either strong acid-or base-containing microemulsions on the behaviour of the synthetic polynucleotide polyAT entrapped in the aqueous core of a cationic quaternary water-in-oil microemulsion (μE). The titrations were performed in the presence of variable concentrations of NaCl, in the range 0.00 to 0.60 M. In both cases, the primary effect was the reversible transition from B-double helix to random coil of the guest polynucleotide. However, in the microemulsive medium, the number of moles of protons (RH) and hydroxide ions (ROH) per mole of titrable sites are independent of the salt concentration but larger than 0.5, the value predicted on the basis of the stoicheiometry of the protonation-deprotonation processes. This result is in contrast with that obtained in aqueous solution (higher RH and ROH values and strongly dependent on NaCl concentration) and is explained with the presence of the cationic micellar wall (CTAB polar heads) acting as a ionic strength buffer.

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).

Several novel diorgano- and triorgano-tin(IV) derivatives of orotic acid, (2,6-dihydroxypyrimidine-4-carboxylic acid; H 3 or) have been synthesized. In the diorganotin(IV) derivatives, the orotic acid behaved either as a monoanionic or as a dianionic ligand, yielding R 2 Sn(H 2 or) 2 and R 2 SnHor (R = Me, Bu) species, respectively, while in the triorganotin(IV) orotates only monodeprotonation of the orotic acid occurred, giving R 3 SnH 2 or (R = Me, Bu) derivatives. Structural hypotheses are proposed and discussed for the solid state based on Mossbauer and IR spectroscopic data, and for solution on 1 H and 1 C NMR results. Finally, investigations have been carried out in vivo, showing the inhibitor properties of all of the newly synthesized derivatives towards Ciona intestinalis embryos. In particular, in order to test the cytotoxicity in vivo of Me 2 SnHor, Bu 2 SnHor, Me 3 SnH 2 or and Bu 3 SnH 2 or, exposure to these chemicals of C. intestinalis embryos at the 2-4-blastomere stage has been studied. The compound which exerts the highest cytotoxic effect is Bu 3 SnH 2 or at 10 5 M concentration because it blocks embryo development immediately. Me 3 SnH 2 or at 10 -5 M concentration inhibits cell cleavage in the embryos at the 32-blastomere stage, while Bu 2 SnHor at the same concentration gives rise to abnormal embryos. Me 2 SnHor, is less toxic than the trimethyl, dibutyl and tributyl analogues, since 40% of the total number of treated embryos resulted in normal larvae. The ligand does not affect embryonic development significantly. The results seem to indicate that the chemical species under investigation, especially Bu 3 Sn-H 2 or, interfere with polymerization of tubulin during the process of cell division in early embryo development.

Diorgano- and triorgano-tin(IV) derivatives of meso-tetra(4-sulfonatophenyl)porphine (H4TPPS) with general formula (R2Sn)2TPPS and (R3Sn)4TPPS (TPPS4−=[meso-tetra(4-sulfonatophenyl)porphinate]4−, R=Me, Bu, Ph) have been obtained and their solid-state configuration inferred on the basis of IR and Mossbauer spectroscopy, while solution-phase studies have been carried out by 1H and 13C NMR in DMSO-d6, together with determination of the in vivo cytotoxicity of the new derivatives towards embryonic development of Ciona intestinalis. In particular, octahedral and trigonal-bipyramidal eq-R3Sn polymeric configurations are proposed, in the solid state, respectively for (R2Sn)2TPPS and (R3Sn)4TPPS complexes, with the arylsulfonate groups behaving as monoanionic bidentate bridging ligands. The 1H and 13C NMR data lead to the conclusion that the metal-to-ligand ratio (2:1 or 4:1), binding site (the sulfonato-group oxygens), and the coordination polyhedron around the metal (trans-octahedral or trigonal-bipyramidal) found in the solid state are preserved in solution. © 1997 John Wiley & Sons, Ltd.

Several new triorganotin(IV) derivatives of L-homocysteic acid (L-HCAH) with formula R3Sn(L-HCA) (R=Me, nBu, Ph) have been synthesized. Their solid-state configurations were determined by IR and Mossbauer spectroscopy. The tin(IV) atom is five-coordinated in all the complexes, with the L-homocysteic acid behaving as a monoanionic bidentate ligand coordinating the tin(IV) atom through a chelating or bridging carboxylate group. The sulfonate (SO3−) and NH3+ groups of L-homocysteic acid maintain their free acid configuration and hence do not participate to the coordination of the tin(IV) atom. Coordination hypotheses have been checked through the correlation between the Mossbauer parameter isomer shift, δ, and partial atomic charge on the tin atoms, QSn, performed, for all the new organotin(IV) compounds, on the basis of an equalization procedure applied to idealized trigonal-bipyramidal structures for R3Sn(L-HCA). 1H and 13C NMR spectra of the complexes show that pentacoordination of the tin atom, with R groups in the equatorial plane of a trigonal bipyramid, is retained in DMSO solution. The NMR data confirm also that the uncoordinated NH3+ group of the ligand is still present in solution. Results gathered after exposure of two- to four-cell embryos of the sea urchin Paracentrotus lividus (Echinodermata) to the triorganotin(IV) L-homocysteate derivatives as well as to the parent triorganotin(IV) chlorides document cytotoxicity of the complexes, while free L-homocysteic acid exerts no significant toxic activity. The trimethyltin(IV) L-homocysteate derivative seems to exert a lower cytotoxicity than the tributyl- and triphenyl-tin(IV) ones. Different structural lesions have been identified by comparative analysis of mitotic chromosomes from untreated embryos (negative controls) and embryos treated with triorganotin(IV) L-homocysteate derivatives, such as (1) suppression of the stretch among sister chromatids at the beginning of anaphase stage; (2) deeply stained zones mainly located at the telomeric regions of chromosomes; (3) arm breakages; and (4) chromosome bridges among daughter chromosomes at anaphase stage. A colchicine-like effect of triorganotin(IV) L-homocysteate derivatives was observed. © 1997 John Wiley & Sons, Ltd.

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.

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.

The molecular dynamics of the complexes Sn(SPyN)4 (1), SnCl2(SPyN)2 (2), MeSn(SPy)3 (3), MeSnCl(SPyN)2 (4), Me2Sn(TCy)2 (5), Me2SnCl(TOx) (6), and Me2Sn(TUr) (7) [HSPy = 2-mercaptopyridine; HSPyN = 2-mercaptopyrimidine; HTCy = 2-thiocytosine; HTOx = 8-thioquinoline; H2TUr = 2-thiouracil] has been investigated by variable temperature 119Sn Mossbauer spectroscopy. The area under the resonant peaks has been determined as function of temperature, from which Debye temperatures and cut-off frequencies, as well as recoil-free fractions (Lamb Mossbauer factor) and mean square displacements of 119Sn, have been calculated. By fingerprint procedures on the basis of literature data, monomeric structures are attributed to complexes (1)–(4) and (6), while (5) and (7) lie in the borderline monomersmonodimensional polymers. The results are discussed on the basis of known crystal and molecular structures. The nature of the environment of tin atoms has been simulated by point-charge model calculations of nuclear quadrupole splitting parameters; molecular structures are proposed for complexes (5)–(7), where no X-ray diffractometric data are available.

The dynamics of tin nuclei in the condensates SnR2(DNA monomer)2 and SnR3(DNA monomer)(R = Me or Et), freeze-dried, has been investigated by variable-temperature 119Sn Mossbauer spectroscopy. Linear functions In (At/A77.3)(T), In farel,abs(T) and 〈x2〉(T)(At= total area under the resonant peaks, fa the relative and the absolute estimates of Lamb-Mossbauer factors, and 〈x2〈 the mean-square displacements of the Mossbauer nucleus extracted from farel and faabs respectively) have been found at T 77.3 K, which indicate harmonic motions and the lack of phase transitions. The latter is also suggested by the temperature-invariant hyperfine parameters, isomer shift, nuclear quadrupole splitting (ΔE) and peak widths. From the slopes of the functions In At(T) and In farel(T), the dynamics of tin in alkyltin(IV)–DNA condensates is found to be analogous to that in organotin(IV) salts and complexes, on the assumption of effective vibrating masses, corresponding to molecular groups. The coincidence between farel,abs, as well as the related 〈x2〉, data, indicates that the negative charge on the DNA backbone phosphodiester groups is fully neutralized by alkyltin(IV) cations in SnR2(DNA monomer)2(R = Me or Et) as well as in SnEt3(DNA monomer), while only partially in SnMe3(DNA monomer) and in SnMe2(DNA monomer)2 obtained by standard procedures for DNA condensation. From the magnitude of the functions, as well as of the Debye temperatures, on fingerprint criteria, SnIVR2 moieties are assumed to bridge phosphodiester groups in toroidal condensates through interstrand bonding, while SnIVR3 would be appended to the double helix. Motions would involve SnR2(mononucleotide)2 and SnR3(mononucleotide) units as the effective vibrating masses. Two tin co-ordination sites occur for SnIVR2 moieties at the DNA surface, both trans-octahedral, and a single trigonal-bipyramidal site for SnIVR3, the organometal moieties being co-ordinated by phosphodiester and water oxygen atoms, according to ΔE rationalization by point-charge model structure simulations, as well as to Mossbauer–Zeeman spectra of the SnIVEt2– and SnIVEt3–DNA condensates.

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.

The present work is dedicated to the study of the interactions of CdCl(2) with the synthetic polynucleotides polyAT and polyGC confined in the nanoscopic aqueous compartment of the water-in-oil microemulsion CTAB/pentanol/hexane/water, with the goal to mimic in vitro the situation met by the nucleic acids in vivo. In biological structures, in fact, very long strings of nucleic acids are segregated into very small compartments having a radius exceedingly smaller than the length of the encapsulated macromolecule. For comparison, the behaviour of polyGC was also studied in aqueous solutions of matched composition. The conformational and thermal stabilities of both polynucleotides enclosed in the inner compartment of the microemulsion are scarcely affected by the presence of CdCl(2), whereas in solution immediate and large effects were observed also at room temperature. The lack of effects of CdCl(2) on the properties of the biopolymers entrapped in the aqueous core of the microemulsion has been attributed to the peculiar characteristics of the medium (low dielectric constant, in particular) which cause a total repression of the CdCl(2) dissociation that is not complete even in water. In fact, several of the numerous effects of CdCl(2) observed on the conformational stability of polyGC in aqueous solutions have also been ascribed to the limited dissociation of the cadmium salt.

The compounds R2SnCl2 and R3SnCl (RMe, Et, nBu, nOct, Ph, in ethanol solution) as well as the aqueous species [Me2Sn(OH2)n]2+ and [Me3Sn(OH2)2]+, react with aqueous native DNA, yielding solid phases. According to the pointcharge model treatment of the 119Sn Mossbauer parameter nuclear quadrupole splitting, trans-octahedral R2Sn(O2PXY)2, and trigonalbipyramidal R3Sn(O2PXY), (RMe, Et, nBu), would occur in the pellets, the tin atoms being coordinated by phosphodiester groups of the nucleic acid. The precipitates from Ph2SnIV would consist of the DNA complex as well as of the Ph2SnIV distannoxane obtained by hydrolysis of the reactant, whilst nOct2SnCl2, nOct3SnCl and Ph3SnCl would mainly yield stannoxanes and hydroxides. The water-soluble hydrolyzed species [Me2Sn(OH)(OH2)n]+, Me2Sn(OH)2 and Me3Sn(OH)(OH2) do not show any interaction with native DNA, although they are possibly coordinated by phosphate oxygen atoms in model aqueous systems, in the presence of excess ligand. These trends have been rationalized by QSAR approach (Quantitative Structure-Activity Relationships) in terms of electronic factors related to tin-oxygen (phosphate) Coulomb interactions, as well as the lipophilicity of R in the RnSnIV moieties.

The mono and bis dipyrido[3,2-a:2',3'-c]phenazine (dppz) adducts of iron(III) chloride, i.e. [Fe(dppz)]Cl(3) and [Fe(dppz)(2)]Cl(3), have been synthesized and characterized. The interaction of the Fe(III)dppz hydrolyzed aquo complex with native calf thymus DNA has been monitored as a function of the metal complex-DNA molar ratio, by variable temperature UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The results obtained in solution at various ionic strength values give support for a tight intercalative binding of the Fe(III)dppz cation with DNA. In particular, the appearance of induced CD bands, caused by the addition of Fe(III)dppz, indicate the existence of a rigid metal complex-DNA-binding leading to dominating chiral organization of Fe(III)dppz species within the DNA double helix. The trend of selected CD bands with the molar concentration of Fe(III)dppz emphasizes that the presence of high amounts of metal complex induces also the formation of DNA-Fe(III)dppz supramolecular aggregates in solution. The analysis of fluorescence measurements allowed us to calculate a value of the intercalative binding constant comparable to that obtained by UV spectrophotometric titration. Finally, the temperature dependence of the absorbance at 258nm shows that the metal complex strongly increases the DNA melting temperature already at metal complex-DNA molar ratio equal to 0.25 suggesting that metal complex intercalation effectively hinders DNA denaturation. Overall, the results of the present study point out that the Fe(III)dppz aquo complex has DNA-binding properties analogous to those previously reported for the tris-chelate Fe(II)(phen)(2)dppz complex (phen=1,10-phenantroline).

Truncated driven nuclear Overhauser effect difference spectra have been used to ascertain the conformational characteristics of the glycosidic linkage of Adriamycin in aqueous solution. The “two-spin approximation” has been employed to evaluate the cross-relaxation rates between nearby protons and to obtain the relative internuclear distances. The rotational angles φ1 = C(7)−O(7)−C(1′)−(H1′) and φ2 = H(7)−C(7)−O(7)−C(1′) have also been calculated.

The thermal behavior of the synthetic, high molecular weight, double stranded polynucleotides poly(dA-dT)·poly(dA-dT) [polyAT] and poly(dG-dC)·poly(dG-dC) [polyGC] solubilized in the aqueous core of the quaternary water-in-oil cationic microemulsion CTAB|n-pentanol|n-hexane|water in the presence of increasing amounts of NiCl2 at several constant ionic strength values (NaCl) has been studied by means of circular dichroism and electronic absorption spectroscopies. In the microemulsive medium, both polynucleotides show temperature-induced modifications that markedly vary with both Ni(II) concentration and ionic strength. An increase of temperature causes denaturation of the polyAT duplex at low nickel concentrations, while more complex CD spectral modifications are observed at higher nickel concentrations and ionic strengths. By contrast, thermal denaturation is never observed for polyGC. At low Ni(II) concentrations, the increase of temperature induces conformational transitions from B-DNA to Z-DNA form, or, more precisely, to left-handed helical structures. In some cases, at higher nickel concentrations, the CD spectra suggest the presence of Z′-type forms of the polynucleotide. Chirality, 2008. © 2008 Wiley-Liss, Inc.

PolyGC was titrated with a strong base in the presence of increasing concentrations of NaCl (from 0.00 to 0.60M) either in water solution or with the polynucleotide solubilized in the aqueous core of reverse micelles, i.e., the cationic quaternary water-in-oil microemulsion CTAB/n-hexane/n-pentanol/water. The results for matched samples in the two media were compared. CD and UV spectroscopies and, for the solution experiments, pH measurements were used to follow the course of deprotonation. In both media the primary effect of the addition of base was denaturation of the polynucleotide, reversible by back-titration with a strong acid. In solution, the apparent pK(a) of the transition decreases with increasing the salt concentration and a roughly linear dependence of pK(a) on p[NaCl] has been found. A parallel monotonic decay with ionic strength has been found in solution for R(OH), defined as the number of hydroxyl ions required per monomeric unit of polyGC to reach half-transition. By contrast, in microemulsion, R(OH) has been found to be independent of the NaCl concentration (and 10 to 50 times lower than in solution). This result is proposed as an indirect evidence of the independence of pK(a) on the salt concentration in microemulsion, where the pH cannot be measured. A sort of buffering effect of the positive charges on the micellar wall and of their counter-ions on the ionic strength could well explain this discrepancy of behavior in the two media.

The first study of the interaction of tin(IV) with the anticancer antibiotic doxorubicin in N,N-dimethylformamide (dmf) solution is reported. Electronic absorption spectroscopy showed that reaction of the drug with SnCl4 is time dependent and involves the initial formation of a 1∶1 complex. The strong binding was also shown by 119Sn NMR spectroscopy. Reactions with modified anthracyclines show that the α-ketol side chain at C9 is essential for interaction, while the quinone chromophore is not involved in binding, as inferred from optical spectroscopy. Proton NMR data suggest that binding to the C9 side chain involves enolization at C13–C14. The two-dimensional total correlation spectra indicate that the daunosamine moiety of doxorubicin can be involved in SnIV binding with formation of several time-dependent species. This was verified by 1H and 119Sn NMR studies of SnIV–daunosaminide hydrochloride systems. These findings suggest that SnIV can bind to doxorubicin at two sites: the C9 α-ketol chain, probably after enolization, and the sugar ring at the 4′-OH and 3′-NH2 positions. This is the first report of metal binding to doxorubicin at the C9 side chain.

In this review some aspects of the interactions of organized structures of amphiphiles with natural or synthetic DNAs are briefly considered. In particular DNAs encapsulated in closed cavities of amphiphiles, specifically giant vesicles and water-in-oil droplets and reverse micelles, are dealt with. Two main applications of giant vesicles are reviewed in detail, namely their use as microreactors where reactions can be followed by optical microscopy on a single vesicle and in synthetic biology as protocell models or as potential semi-synthetic ‘‘living’’ cells. Water-in-oil droplets uses for rapid and relatively low-cost DNA amplification by PCR reaction are described as well as for in vitro transcription and translation. A large variety of non-Watson–Crick conformations of polynucleotides observed in the aqueous inner core of reverse micelles is illustrated and compared with those observed in matched water solutions.

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.

Thixotropic and thermally reversible gels have been prepared from doxorubicin—lecithin association products (DL12) by addition of salts to their aqueous solutions. The gel formation and the melting profiles have been followed by several spectroscopic techniques ( 1 H NMR, UV-Vis, Circular Dichroism). The transition temperatures increase as the concentration of both the salt and the DL12 is increased, suggesting a progressive closer approach of the gel forming species. The process of the gel formation is cooperative and causes immobilization of the doxorubicin molecules of DL12.

Physicochemical investigations on the aggregation of phospholipids (mainly phosphatidylcholines) in organic solvents are reviewed and compared with the aggregation behaviour of phospholipids in aqueous medium. In particular we review the data showing that phosphatidylcholines (lecithins) form reverse micellar structures in certain apolar solvents. In these systems not only low molecular weight compounds but also catalytically active enzymes and entire cells can be solubilized. In addition, highly viscous phosphatidylcholine gels can be obtained in organic solvents upon solubilizing a critical amount of water. Generally, phospholipid-based reverse micelles can be regarded as thermodynamically stable models for inverted micellar lipid structures possibly occurring in biological membranes.

The interaction of organotin(IV) moieties SnIVR2 and SnIVR3(R = Me, Et, Bun, C8H17 or Ph) with calf thymus deoxyribonucleic acid (DNA) has been studied. The experimental conditions have been determined for the formation of condensates SnIVR2– and SnIVR3–DNA by the reaction of ethanolic organotins [SnR2Cl2(EtOH)2 and SnR3Cl(EtOH)], as well as aqueous SnIVMe3 species, with aqueous DNA. The nature of the condensates has been investigated by 119Sn Mossbauer spectroscopy. The species SnEt2(DNA phosphate)2 and SnR3(DNA phosphate)(R = Me or Et) have been assumed to occur, where the environment of the tin atoms would be trans octahedral and trigonal bipyramidal respectively. In the reaction with aqueous DNA of SnR2Cl2(EtOH)2 and SnR3Cl(EtOH)(R = Bun, C8H17 or Ph), stannoxanes (SnR2Cl)2O and hydroxides SnR3(OH) would form too, being possibly the main reaction products for the moieties SnIV(C8H17)2, SnIV(C8H17)3 and SnIVPh3. Possible bonding situations have been advanced for SnIVRn–DNA condensates, involving e.g. two vicinal phosphodiester groups (from the DNA double strand)cis-co-ordinated giving an octahedral geometry, as well as a phosphodiester residue axially binding SnIVR3 to give a trigonal-bipyramidal structure.

The interaction of ferrocene and ruthenocene with proton donors has been investigated by NMR spectroscopy in a broad range of protic media, including such weakly protic agents as chloroform, moderately acidic systems such as TFA, and more strongly acidic systems such as conc. H2SO4. The results indicate that these metallocenes undergo two kinds of interactions with acidic media, viz., π-hydrogen bonding in which the Cp ring is the electron donor and, in the most strongly protic solvents, metal protonation. The (H0) 1 2 of ruthenocene and a group of ferrocene derivatives have been determined by a combined extractive-spectrophotometric technique. These values show that the metal atom acts as a very weak base. The H/D exchange rate of ruthenocene in conc. D2SO4 decreases on increasing acid concentration, which rules out the metal-protonated species as an intermediate in the reaction.

Dipotassium hexahalogeno-osmates, K 2 OsX 6 (X = Cl, Br) dissolved in non-aqueous inert organic solvents (benzene, o -dichlorobenzene, bromo-benzene) by addition of dicyclohexyl-18-crown-6 ether (C 20 H 36 O 6 ) are catalytic precursors for the multiple double bond shift in olefins. Studies on the interaction between K 2 OgX 6 and several olefins (1-heptene, 1-heptene-3d 2 , 1-pentene, cis -stilbene, 3,3-dimethyl-l-butene) support an osmium hydride species, probably [OsHX 5 ] = , as the true catalyst, which affords the olefin isomerization through successive 1,2-addition-elimination steps to the CC double bond. Such an alleged osmium hydride species is formed by allylic hydrogen atom abstraction from the olefin with formation of the corresponding conjugate diolefin.

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.

CNDO/2 Calculations on NN′-dimethylthiourea, NNN′-trimethylthiourea, and the methyl ester of dithiocarbazic acid are reported. The results are in satisfactory agreement with experimental data (n.m.r. spectra) on the equilibrium conformations found in solutions of these systems.

The ligand behaviour of the esters of dithiocarbazic acid NHRNHC(S)SR′ in intensely coloured complexes containing the doubly deprotonated ligands [Pt{NRNC(S)SR′}2](R = H, R′= CH2Ph; R = CH2Ph, R′= Me or CH2Ph; R = Pri, R′= Me; R = hexyl, R′= Me or CH2Ph) has been investigated by electronic, i.r., and 1H n.m.r. spectroscopy and electrochemistry. The crystal and molecular structure of [Pt{N(CH2Ph)NC(S)SMe}2] has also been determined. All the complexes have a square-planar trans-PtN2S2 chromophore; they are dithiolene-like and show electron-transfer properties.

Four novel cyanocarbon dyes derived from tetracyanoethylene (TCNE) have been studied. They are carbanions isolated as tetraphenylarsonium salts of formula C11N7H2–(1), C15N6H3–(2), C14N7H2–(3), and C13N8H–(4). Compound (1) was obtained by a condensation reaction of TCNE promoted by Ti(bpy)3 and its structure has already been reported. Compounds (2)–(4) are the 1,3-bistricyanovinyl derivatives of cyclopentadienyl, pyrrolyl, and imidazolyl anions, respectively. The tetraphenylarsonium salt of anion (3) gives crystals isomorphorus with the crystals of the analogous salts of anions (2) and (4), whose crystal structures are reported here. Structural and electronic properties of the four anions are discussed on the basis of 13C n.m.r., i.r., u.v., and electrochemical data; electrical and magnetic properties of their radical salts with the tetrathiafulvalenium cation (TTF˙+) are also reported and discussed.

N.m.r. spectra of some potentially bidentate thiosemicarbazones, NR3H·CS·NH·N:CR2R1(L: R1,R2= H, Me, Ph, or R1R2= C6H11; R3= H or Ph), and their complexes [ZnCl2L] or [ZnCl2L2] have been measured. The results are compared with semiempirical CNDO/2 total-energy calculations. Only one conformer, containing an intramolecular hydrogen bond, is present in solution. All the zinc(II) complexes are tetrahedral. The possible formation of complexes in which the ligand is bidentate is discussed.

In recent years the use of NMR for clinical purposes has been increasing. Magnetic resonance imaging has great diagnostic potential, despite the many problems and drawbacks involved in its practice (1). More controversial is the possibility to exploit NMR spectroscopy as a diagnostic tool in clinical practice. Its applications seem to be restricted to the study of phosphorus containing metabolites (2), in particular to muscle energetics and to the viability of organs. However, some very recent research, based on 1H (3) and 13C (4,5) NMR, opens new fields in the applications of in vivo NMR to clinical problems.