Synthesis and NMR characterization of cationic rhodium(I) complexes containing phosphorus—sulfur bidentate ligands

The reaction of [Rh(diene)(acac)] (diene=cyclooctadiene or norbornadiene; acac=acetylacetonate) with bidentate ligands of the type Ph₂P(CH₂)_nSR (n=1, 2 or 3; R=Me, Et, Ph, not all combinations) or cis-Ph₂PCHCHPPh₂ leads to [Rh(diene)(LL)]⁺ or [Rh(LL)₂]⁺, depending on the stoichiometry of the reaction. The complexes were fully characterized by ¹H and ³¹P NMR spectroscopy.     

Kinetics of ligand substitution in platinum(II) complexes: A study on the concept of nucleophilic discrimination

Several platinum(II) complexes of the general type [Pt(OND)X] have been prepared and characterized, the ligand (OND) representing the phenolate anion of the tridentate Schiff bases N-(2- diethylaminoethyl)-salicylaldimine (D = NEt₂), N-(2- ethylaminoethyl)-salicylaldimine (D = NHEt) and N- (3-thia-n-pentyl)-salicylaldimine (D= SEt) and X= Cl, NO₃. As shown by conductimetric studies the nitrato complexes [Pt(OND)NO₃] dissociate completely in methanol according to:

Spectrophotometry (normal and stopped-flow) has been used to study the kinetics of solvent substitution according to

with a variety of neutral and anionic nucleophiles Y in methanol at 20 °C and constant ionic strength, I= 0.2 M (NaClO₄). The substitution follows a one- term rate law, v = k_obs[Pt(OND)(H₂O)⁺] = k_Y[Y]- [Pt(OND)(H₂O)⁺]. The k_Y data obtained for 13 (D = NEt₂) and 7 (D = NHEt; SEt) different nucleophiles Y cannot be adequately correlated with their n_pt⁰ values according to the well-known relationship log k_Y = sn_pt⁰ + log k_s. The deviations are strongest for large and bulky nucleophiles such as Y=Ph₃P, Bu₃P, Ph₃As, I^- and for D = NEt₂, from which it is concluded that steric crowding hinders the formation of the 5-coordinate transition state. The rate reducing steric cis-effect observed is of the order k_Y(D = NEt₂):k_Y(D = NHEt):k_Y(D = SEt) = 1:35:63 for small nucleophiles Y and as large as 1:192:2640 for Y = Ph₃P. The introduction of substituents X in the salicylaldehyde ring in ortho (X³), meta (X⁴) and para position (X⁵) to the phenolic oxygen proves the existence of rather small electronic effects (X⁴, X⁵) and much stronger steric effects of bulky substituents X³, neighboring the donor oxygen.With the standard substrate trans-[Ptpy₂Cl₂] some new n_pt⁰ values were determined, namely for N, N′- dimethylthiourea (n_pt⁰ = 7.02), N, N′ -diphenylthlourea (n_pt⁰ = 7.19), N, N, N′, N′-tetramethylthiourea (n_pt⁰ = 6.05) and for the pseudo-halide dicyanoamide ion, N(CN)₂^- (n_pt⁰= 3.05). The n_pt⁰ value for the pseudo-halide tricyanomethanide, ion, C(CN)₃^-, was estimated to be 3.03.     

Investigation of electron-transfer kinetics for bis(benzene) chromium(1+/0) redox couple in acetonitrile/dichloromethane binary mixtures at 298.15 K

The oxidation of bis(benzene) chromium(0) (Bz₂Cr) to bis(benzene) chromium(1+) (Bz₂Cr⁺) in acetonitrile (ACN), dichloromethane (DCM), and acetonitrile (ACN)/dichloromethane (DCM) binary mixtures with n-tetrabutylammonium hexafluorophosphate (TBAPF₆) as background electrolyte has been studied using the method of cyclic voltammetry at a temperature of 298.15 K. The diffusion coefficients (D) have been calculated using the Randles-Sevcik equation. The heterogeneous electron transfer rate constants (k_s) have been evaluated employing the electrochemical rate equation proposed by Nicholson. The one-electron oxidation of Bz₂Cr to produce Bz₂Cr⁺ was found to be either reversible or quasi-reversible and diffusion controlled in the investigated solvent media. The effect of the physical and chemical properties of the solvent medium on the electrochemical behavior of the Bz₂Cr⁺/Bz₂Cr couple has been examined.     

Interaction of tin methylchlorides SnMenCl4−n with molybdenum hydride bis(cyclopentadienyl)

The interaction between Cp₂MoH₂ (Cp=η⁵- C₅H₅) and SnMe_nCl_4−n (n=0−3) proceeds in aprotic solvent with the elimination of HCl and the formation of heterometallic complexes of the composition Cp₂Mo(H)SnMe_nCl_3−n (n=0−3) and Cp₂Mo(SnMe₂Cl)₂ which contains an MoSn σ-bond. It has been found that in all studied compounds the length of this bond is 0.20–0.30 Å less than the sum of the covalent radii of the Mo and Sn atoms.Based on analysis of the geometry of the Mo and Sn environment, the high values of the isomeric shifts (IS) in the Mössbauer spectra, the constants of the spin-spin interactions (SSI) J³_Cp-Sn and J²_HMoSn, and the considerably decreased values of the J²_Me-sn constants in ¹H NMR spectra, it was concluded that the decrease in the interatomic distance Mo-Sn is due to the high s-character of this bond. It is suggested that this effect, which is most pronounced in wedge-like complexes, is brought about by changing the orbital hybridization type of the tin atom from sp³ to s + 3p. This can explain the shorter interatomic distance M-Sn in heterometallic complexes of other types.     

The Effects of Solvent Environment on the Optical Rotatory Dispersion Parameters of Polypeptides: I. Studies on Poly-γ-Benzyl-l-Glutamate

The constancy of the Moffitt optical rotatory dispersion parameters for polypeptides in different solvents was tested by dispersion measurements on poly-γ-benzyl-L-glutamate in fifty-five solvents and solvent mixtures. b₀ was not constant but varied linearly with the refractive index of the solvent according to the equation -b₀ = 1701 - 730.3 n₈. This variation could not be explained by changes in configuration of the polypeptide. a₀ also showed a trend with solvent index but the values were widely scattered. λ₀ did not show a statistically significant dependence on solvent index. The variation in b₀ can be interpreted as an effect of solvent polarizability on the frequencies of optically active transitions.     

Synthesis, crystal structures, cytotoxicity and qualitative structure-activity relationship (QSAR) of cis-bis{5-[(E)-2-(aryl)-1-diazenyl]quinolinolato}di-n-butyltin(IV) complexes, (n)Bu2Sn(L)2

A series of cis-bis{5-[(E)-2-(aryl)-1-diazenyl]quinolinolato}di-n-butyltin(IV) complexes has been synthesized and characterized by ¹H-, ¹³C-, ¹¹⁹Sn NMR, ESI-MS (electrospray ionization mass spectrometry), IR and ^119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The structures of four di-n-butyltin(IV) complexes, viz., ⁿBu₂Sn(L³)₂ (3), ⁿBu₂Sn(L⁴)₂ (4), ⁿBu₂Sn(L⁵)₂ (5) and ⁿBu₂Sn(L⁷)₂ · 0.5C₆H₆ (7) (LH = 5-[(E)-2-(aryl)-1-diazenyl)quinolin-8-ol) were determined by single crystal X-ray diffraction. In general, the complexes were found to adopt a distorted cis-octahedral arrangement around the tin atom. These complexes retain their solid-state structure in non-coordinating solvent as evidenced by ¹¹⁹Sn and ¹³C NMR spectroscopic results. The in vitro cytotoxicity of di-n-butyltin(IV) complexes (3-8) is reported against seven well characterized human tumour cell lines. The basicity of the two quinolinolato donor N and O atoms of the ligands are discussed in relation to the cytotoxicity data.     

Reactions of platinum(IV) amine compounds with 9-methylhypoxanthine at high temperature result in both platinum(II) and platinum(IV) amine adducts

The products obtained from the reaction of Pt(IV)Cl₄(LL) compounds (LL denotes the chelating ligands ethylenediamine (en) and 2,2-dimethyl-1,3-diaminopropane (dmdap), or two cis- or trans-coordinated ammines) with 9-methylhypoxanthine (mHyp) at high temperature (80°C) have been characterized by proton NMR spectroscopy. It appeared that both platinum(II) and platinum(IV) adducts were present in the reaction mixtures. After cation-exchange chromatography, the Pt(II) compound could be characterized as Pt(II)(LL)(mHyp)₂, whereas the Pt(TV) fractions appeared to contain mainly one or two adducts for the chelating diamine compound but more adducts for the ammine compounds. A ³J(¹⁹⁵Pt-¹H) coupling was observed for the Pt(IV), but not for the Pt(II) compounds at the used spectrometer frequency. This supplies a useful tool to discriminate between these two types of platinum adducts.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

Synthesis, structures, electrochemistry and properties of dioxo-molybdenum(VI) and -tungsten(VI) complexes with novel asymmetric N2OS, and partially symmetric N2S2, NOS2N-capped tripodal ligands

A new class of asymmetric N-capped (dianionic/trianionic) tripodal proligands [H_x(Lⁿ)] (x = 2, n = 1-6; x = 3, n = 7, 8) which possess pendant arms with N₂OS, N₂S₂ or NOS₂ donor groups and with different chelate ring sizes {5,5,5} or {5,6,5} has been prepared. Treatment of these ligands with [WO₂Cl₂(dme)] (dme = 1,2-dimethoxyethane) in the presence of base (triethylamine or KOH) leads to the formation of cis-dioxotungsten(VI) complexes of the types [WO₂(Lⁿ)] (n = 1-6) and K[WO₂(Lⁿ)] (n = 7, 8). Reaction of these tetradentate ligands with [MoO₂(acac)₂] (acac = acetylacetonate) gives the corresponding Mo(VI) analogues [MoO₂(Lⁿ)] (n = 1-6) and K[MoO₂(Lⁿ)] (n = 7, 8). Moreover, a new five coordinate dioxomolybdenum(VI) complex with an NS₂ tridentate ligand [MoO₂(L⁹)] has been synthesised using similar procedure. All these compounds have been spectroscopically characterised and the molecular structures of [MoO₂(Lⁿ)] (n = 2, 6) and [WO₂(L⁶)] have been established by X-ray diffraction analysis. The electrochemistry and the catalytic activity for oxidation of allylic and benzylic alcohols of these dioxo complexes have also been investigated.     

Excited state relaxation in Cr(CN)6−n(H2O)nn−3 complexes

The emission spectra and excited state decay rates have been recorded for Cr(CN)_6−n(H₂O)_nⁿ⁻³ (n = 0-6) complexes. Both the transition energy and relaxation rates increase with n but the large changes in transition energies are not sufficient to account for the failure of the displaced coordinate to explain the relaxation rate results.     

Relationship of rapid light curves of variable fluorescence to photoacclimation and non-photochemical quenching in a benthic diatom

The response of rapid light–response curves (RLCs) of variable fluorescence to changes in short- and long-term photoacclimation status was studied in an estuarine benthic diatom. The diatom Nitzschia palea was grown under low- (LL, 20 μmol m⁻² s⁻¹) and high-light (HL, 400 μmol m⁻² s⁻¹) conditions, with the purpose of characterising the effects of long-term photoacclimation on (i) steady-state light–response curves (LC) of relative electron transport rate, rETR, (ii) the response of RLCs to changes in ambient irradiance (E, the irradiance to which the sample is acclimated to immediately before the RLCs), (iii) the relationship of RLCs to LC parameters and non-photochemical quenching (NPQ). Photoacclimation to LL and HL conditions induced distinct light–response patterns of rETR and NPQ. Higher growth light resulted in rETR vs. E curves with lower initial slopes (α, 0.591 μmol⁻¹ m² s vs. 0.661 μmol⁻¹ m² s, for HL and LL, respectively) and markedly higher maximum rates (rETR_m, 95.9 vs. 29.3), reached under higher E levels (higher light-saturation coefficient, E_k: 162.4 μmol m⁻² s⁻¹ vs. 44.3 μmol m⁻² s⁻¹). Acclimation to HL induced bi-phasic NPQ vs. E curves, with minimum values reached under low E levels (15–25 μmol m⁻² s⁻¹) and not on dark-acclimated samples. The response of RLCs to changes in ambient irradiance varied with the long-term photoacclimation status of the samples. The initial slope, α_RLC, decreased monotonically with E in LL cultures, from 0.68 to 0.25 μmol⁻¹ m² s, while varied bi-phasically in HL-acclimated samples. Typically, α_RLC of HL cultures increased under low E, reaching a maximum of 0.61 μmol⁻¹ m² s under 25–55 μmol m⁻² s⁻¹, and decreased gradually under higher E levels to 0.25 μmol⁻¹ m² s. RLC maximum rETR, rETR_m,RLC, and saturation coefficient E_k,RLC, increased with E following a saturation-like pattern, with the HL cultures presenting markedly higher values for all the E range (maximum rETR_m,RLC values were 108.6 and 33.4 for HL and LL cultures, respectively). An inverse relationship was consistently found between α_RLC and NPQ, both on LL and HL cultures, causing strong correlations (P < 0.001 in all cases) between NPQ and the high light-induced decrease of α_RLC, Δα_RLC. RLCs were confirmed to also provide information on the long-term photoacclimation status, as significant correlations (P < 0.001 both for HL and LL cultures) were verified between E_k and an index based on RLC parameters, Ê_k, both for LL and HL cultures. These results reinforce the usefulness of RLCs as a tool for inferring on the short- and long-term photoacclimation status of samples with different long-term light histories, through the estimation of LC parameters and the monitoring of NPQ levels.     

Mononuclear iron(III) complexes supported by tripodal N3O ligands: Synthesis, structure and reactivity towards DNA cleavage

A new synthetic route to the known tripodal tetradentate N₃O ligand L¹ (HL¹ = [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine) is reported. The related compounds HLⁿ (n = 2, 3) were prepared by a similar procedure. Treatment of HLⁿ (n = 1-3) with FeCl₃·6H₂O in hot methanol led to the mononuclear iron(III) complexes [Fe(Lⁿ)Cl₂] (1: n = 1, 2: n = 2, 3: n = 3). The solid-state structures of complexes 1 and 2 were determined by X-ray crystallography. [Fe(L¹)Cl₂] (1) showed effective nuclease activity in the presence of hydrogen peroxide, converting supercoiled plasmid DNA to its linear form.     

Reactions of cyanooxo-molybdates and -tungstates with picolinic acid, 2-pyridinecarboxaldehyde and 2,2′-pyridil: X-ray crystal structure of (PPh4)2[Mo(CN)4O(pic)] · 2.5H2O

The syntheses of (PPh₄)₂[M(CN)₃O(pic)] · nH₂O (M = Mo, W; n = 2.5, 4; pic = picolinate anion) as well as (PPh₄)₂[Mo(CN)₄O(apic)] · 3H₂O (apic = 2-pyridinecarboxaldehyde) are presented. The salts have been characterised by elemental analysis, IR and UV-Vis spectroscopy, cyclic voltammetry and X-ray crystal structure determination of (PPh₄)₂[Mo(CN)₃O(pic)] · 2.5H₂O. The anion in the latter salt is approximately octahedral with O and N donor atoms of pic situated in the trans and cis position to the MoO bond, respectively. The picolinate complexes have the characteristic MLCT bands in the visible spectra with the absorption maxima linearly dependent on the Reichardt’s E_T solvent parameter. These complexes are shown to exhibit the strongest solvatochromic effect of all studied tricyanooxo and hexacyano complexes of Mo(IV) and W(IV). The obtained values of E_1/2 in these salts [0.333 V (Mo) and 0.018 V (W) in 1,2-C₂H₄Cl₂] were found to be the highest of all [M(CN)₃O(LL)]²⁻ type complexes making these salts show reversibility in a remarkable variety of solvents. The oxidation of coordinated apic to pic has been demonstrated by means of electronic spectroscopy. The isolated salts were used to monitor the reaction of [M(CN)₄O(H₂O)]²⁻ with 2,2′-pyridil in water-ethanol solution. It was found that 2,2′-pyridil disproportionate to Hpic and apic in the first step and the other decomposition products of 2,2′-pyridil postulated in the literature were not observed.     

Occurrence of cellobiose residues directly linked to galacturonic acid in pectic polysaccharides

The study carried out in this work concerns the structural characterization of pectic polysaccharides from plum (Prunus domestica L.) and pear (Pyrus communis L.) cell walls and commercial pectic polysaccharides, obtained from Citrus. The α-(1 → 4)-d-galacturonic acid backbone was submitted to a selective hydrolysis with endo-polygalacturonase (EPG) and the fractions with low molecular weight (<1 kDa) obtained by size-exclusion chromatography were analysed by mass spectrometry using electrospray ionisation (ESI-MS). The ESI-MS spectra obtained revealed the presence of several [M+Na]⁺ ions of pectic oligosaccharides identified as belonging to different series, including oligosaccharides constituted only by galacturonic acid residues (GalA_n, n = 1-5) and galacturonic acid residues substituted by pentose residues (GalA₃Pent_n, n = 1-2). Surprisingly, it was also observed the occurrence of galacturonic acid residues substituted by hexose residues (GalA_nHex_m, n = 2-4, m = 1-2). The fragmentation of the observed [M+Na]⁺ ions, obtained under ESI-MS/MS and MSⁿ allowed to confirm the proposed structures constituent of these pectic oligosaccharides. Furthermore, the ESI-MSⁿ spectra of the ions that could be identified as GalA_nHex_m (n = 2-4, m = 1-2) confirmed the presence of Hex or Hex₂ residues linked to a GalA residue. Methylation analysis showed the presence, in all EPG treated samples, of terminally linked arabinose, terminally and 4-linked xylose, and terminally and 4-linked glucose. The occurrence of GalA substituted by Glc, and Glc-β-(1 → 4)-Glc are structural features that, as far as we know, have never been reported to occur in pectic polysaccharides.     

Kinetics of oxidation of ferrocene by tris-1,10-phenanthrolinecobalt(III) in t-butyl alcoholwater and acetonewater mixtures

Rate constants and activation parameters (ΔH^≠ and ΔS^≠)are reported for the oxidation of ferrocene by the tris-1,10-phenanthrolinecobalt(III) cation in t-butyl alcoholwater and in acetonewater solvent mixtures. Solvent effects on reactivity trends for these systems, for this same reaction in methanolwater mixtures, and for cobalt(II)-catalysed racemisation of Co(phen)_3³⁺ in t-butyl alcoholwater solvent mixtures are analysed into initial state and transition state contributions. The dependences of solubilities on solvent composition for ferrocene and for [Co(phen)₃](ClO₄)₃ in methanol, t-butyl alcohol, and acetonewater mixtures are also reported; these results are needed in order to establish solvent effects on the initial states of the reactions studied.     

Reversible ring opening and closure reactions of the triazine ligands derived from 1-phenylazo-2-naphthylamine and pyridine-2-aldehyde or quinoline-2-aldehyde - structure and reactivity of the palladium (II) complexes

New ligands containing a heterocyclic ring, L¹ (1-anilino-2-(2-pyridyl)-naphth[1,2-d]imidazol-1-io-3-ide), L² (2-phenyl-3-(2-pyridyl)-3,4-dihydro-naphtho[2,1-e][1,2,4]triazin-1-io-4-ide), and L³ (1-anilino-2-(2-quinolyl)-naphth[1,2-d]imidazol-1-io-3-ide), and their palladium (II) complexes have been prepared. Structures of the ligands and the complexes were determined by X-ray crystallography. The mononuclear square-planar complexes of [PdCl₂(Lⁿ)] (n = 1 (1), n = 2 (2) and n = 3 (3)) had didentate Lⁿ (n = 1-3) ligands. The Lⁿ (n = 1-3) ligands were stable and their absorption spectra did not change in dichloromethane and methanol. On the other hand, the absorption spectrum of [PdCl₂(L²)] (2) in dichloromethane changed rapidly when methanol was added to the solution, and [PdCl(L^4b)] (5) (L^4b = N-[methoxy(2-pyridyl)methyl]-1-(phenylazo)-2-naphthylamide) was obtained from the concentrated reaction mixture. In this reaction, the dihydrotriazine ring of the didentate L² ligand in complex 2 opened and the resulting tridentate L^4b ligand coordinated to the Pd atom in complex 5. When an excess amount of (ⁿBu)₄NCl was added to complex 5 in dichloromethane, the absorption spectrum reverted to that of complex 2. Thus, the reversible ring opening and closure reactions of the coordinating dihydrotriazine ligand were observed. We also prepared [PdCl₂(L⁵)] (9) (L⁵ = 1-(phenylazo)-N-[1-(2-pyridyl)ethylidene]-2-naphthylamine) and determined the structure. It is noted that neither the ring closure reaction nor the coordination of the azo nitrogen atom of the L⁵ ligand occurred in complex 9.     

Protective effects of complementary Ca2+ on low-light-induced oxidative damage in tall fescue

Low-light (LL) intensity is a primary abiotic stressor that negatively influences turf grass quality. In the present experiment, we studied the effect of exogenous Ca²⁺ (0, 10, 50, 100, and 200 mM) on the antioxidant system, the accumulation of MDA and proline, the content of photosynthetic pigments in plant leaves in order to investigate whether exogenous Ca²⁺ treatment improves LL tolerance in tall fescue (Festuca arundinacea Schreb.). We have found that LL significantly reduced a number of growth parameters (plant height, leaf width, leaf fresh weight, root fresh weight, leaf dry weight, and root dry weight), chlorophyll (Chl) a and Chl b contents, and carotenoid (Car) levels, while considerably enhancing electrolyte leakage (EL), MDA accumulation, calcium (Ca²⁺) concentration, and generation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide radical (O ₂ ^·? ). Moreover, LL significantly induced the activities of antioxidant enzymes, such as peroxidase (POD) and catalase (CAT), and slightly increased the activity of superoxide dismutase (SOD) in tall fescue leaves. In contrast, POD and SOD activities declined considerably while CAT activity significantly increased in plant roots under LL stress. The application of 50 mM Ca²⁺ significantly improved the aforementioned growth parameters, the content of photosynthetic pigments, and further enhanced the activities of POD, SOD, and CAT, but decreased electrolyte leakage and MDA and H₂O₂ levels in the leaves and roots of tall fescue under LL stress. These results suggest that Ca²⁺ is likely involved in a resistance to LL by regulating antioxidant enzyme action in tall fescue leaves and roots.     

The antitumor activity of di-n-butyltin(IV) glycylglycinate,and the correlation with the structure of dialkyltin(IV) glycylglycinates in solution

The in vivo activity of Bu₂ⁿSnGlyGly, Na(CI₂GaGlyGly), and CIGaGlyGly (GlyGly^2?- = glycylglycinate) has been investigated in connection with a number of tumors. Positive results have been obtained only for the Bu₂ⁿSn^IV complex in the case of leukemia P-388 In order to try to interpret the pharmacological data on a molecular basis, the nature of the species present in solutions of AIK₂Sn GlyGly complexes, as well as the reactivity of aqueous Me₂SnGlyGly, have been studied. The presence of chelated species (I), Figure 1, in organic solvents, and the equilibrium (I) ? (II), Figure 1, in water and mixed water-organic solvent systems, have been inferred from conductance measurements, as well as from studies by Mössbauer (in frozen solution), ¹H, ¹³C, and ¹¹⁹Sn NMR, and ir spectroscopy. Moreover, solvated (II) would release AlK₂Sn^IV moieties, as evidenced by the slow formation of (Me₂SnO)_n from aqueous Me₂Sn GlyGly. The involvement of (I) and (II) in the transportation of these drugs across cell membranes is discussed.     

Tetra-, penta- and hexacoordinate copper(II) complexes with N3 donor isoindoline-based ligands: Characterization and SOD-like activity

Reaction of 1,3-bis(2′-Ar-imino)isoindolines (HLⁿ, n = 1-7, Ar = benzimidazolyl, N-methylbenzimidazolyl, thiazolyl, pyridyl, 3-methylpyridyl, 4-methylpyridyl, and benzthiazolyl, respectively) with Cu(OCH₃)₂ yields mononuclear hexacoordinate complexes with Cu(Lⁿ)₂ composition. With cupric perchlorate square-pyramidal [Cu^II(HLⁿ)(NCCH₃)(OClO₃)]ClO₄ complexes (n = 1, 3, 4) were isolated as perchlorate salts, whereas with chloride Cu^II(HLⁿ)Cl₂ (n = 1, 4), or square-planar Cu^IICl₂(HLⁿ) (n = 2, 3, 7) complexes are formed. The X-ray crystal structures of Cu(L³)₂, Cu(L⁵)₂, [Cu^II(HL⁴)(NCCH₃)(OClO₃)]ClO₄, Cu^IICl(L²) and Cu^IICl(L⁷) are presented along with electrochemical and spectral (UV-Vis, FT-IR and X-band EPR) characterization for each compound. When combined with base, the isoindoline ligands in the [Cu^II(HLⁿ)(NCCH₃)(OClO₃)]ClO₄ complexes undergo deprotonation in solution that is reversible and induces UV-Vis spectral changes. Equilibrium constants for the dissociation are calculated. X-band EPR measurements in frozen solution show that the geometry of the complexes is similar to the corresponding X-ray crystallographic structures. The superoxide scavenging activity of the compounds determined from the McCord-Fridovich experiment show dependence on structural features and reduction potentials.