Ab initio and density functional theory studies on vibrational spectra of palladium (II) and platinum (II) complexes of methionine and histidine: effect of theoretical methods and basis sets

Investigation of the influence of chirality and halogen atoms on the anticancer activity of enantiopure palladium(ii) complexes derived from chiral amino-alcohol Schiff bases and 2-picolylamine

In order to evaluate the impact of chirality and halogen-substitution pattern on biological activity, four mixed-ligand enantiomeric pairs of Pd(ii) complexes were synthesized and characterized.

Heteroleptic enantiopure Pd(ii)-complexes derived from halogen-substituted Schiff bases and 2-picolylamine: synthesis, experimental and computational characterization and investigation of the influence of chirality and halogen atoms on the anticancer activity

To investigate the effect of chirality and different halogen substituents on the anticancer activity, seven enantiomeric pairs of palladium complexes were synthesized and characterized.

Geochemical behaviour of palladium in soils and Pd/PdO model substances in the presence of the organic complexing agents L-methionine and citric acid

Risk assessments of platinum group metal (PGE) emissions, notably those of platinum (Pt), palladium (Pd) and rhodium (Rh), have been mostly based on data regarding the metallic forms used in vehicular exhaust converters, known to be virtually biologically inert and immobile. To adequately assess the potential impacts of PGE, however, data on the chemical behaviour of these metals under ambient conditions post-emission is needed. Complexing agents with a high affinity for metals in the environment are hypothesized to contribute to an increased bioaccessibility of PGE. The purpose of this study is to examine the modulating effects of the organic complexing agents, L-methionine and citric acid, on the geochemical behavior of Pd in soils and model substances (Pd black and PdO). Batch experimental tests were conducted with soils and model substances to examine the impacts of the concentration of complexing agents, pH and length of extraction period on Pd solubility and its chemical transformation. Particle surface chemistry was examined using X-ray photoelectron spectroscopy (XPS) on samples treated with solutions under various conditions, including low and high O2 levels. Pd was observed to be more soluble in the presence of organic complexing agents, compared to Pt and Rh. Pd in soils was more readily solubilized with organic complexing agents compared to the model substances. After 7 days of extraction, L-methionine (0.1 M) treated soil and Pd black samples, for instance, had mean soluble Pd fractions of 12.4 ± 5.9% and 0.554 ± 0.024%, respectively. Surface chemistry analyses (XPS) confirmed the oxidation of metallic Pd surfaces when treated with organic complexing agents. The type of organic complexing agent used for experimental purposes was observed to be the most important factor influencing solubility, followed by solution pH and time of extraction. The results demonstrate that metallic Pd can be transformed into more bioaccessible species in the presence of organic complexing agents which are ubiquitous in the environment.

Synthesis, characterization, molecular modeling and antioxidant activity of Girard's T thiosemicarbazide and its complexes with some transition metal ions

The chelation behavior of N-{[(allylamino) thiomethyl] hydrazinocarbonylmethyl} trimethylammonium chloride (H3ATHC) towards VO(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+) and UO2(2+) ions have been studied. The structures of the complexes were elucidated using elemental analyses, spectral (IR, UV-visible, (1)H NMR and ESR and mass) as well as magnetic and thermal measurements. The ligand acted as ON bidentate, ONS tridentate donor forming mononuclear complexes. A tetrahedral geometry for Co(2+), square-planar for Ni(2+) and Cu(2+), an octahedral for Zn(2+) and a square-pyramidal arrangement for VO(2+) complexes were proposed, respectively. The EPR spectra of Cu(2+) and VO(2+) complexes confirmed the suggested geometries with values of α(2) and β(2) indicating that the in-plane σ-bonding and in-plane π-bonding are appreciably covalent, and were consistent with very strong in-plane σ bonding in the complexes. Also, the bond length, bond angle, HOMO, LUMO, dipole moment and charges on the atoms have been calculated. Also, the thermal behavior and kinetic parameters were determined using Coats-Redfern and Horowitz-Metzger methods. Furthermore, the synthesized compounds were screened for their superoxide-scavenging activity in the PMS/NADH-NBT system as well as their scavenging effect on ABTS (2,2'-azino-bis(3-ethyl benzthiazoline-6-sulfonic acid) and 2,2-diphenyl-1-picrylhydrazyl(DPPH) radicals. Among these compounds, the ligand and Zn(2+) complex, exhibited the potent ABTS (2,2'-azino-bis(3-ethyl benzthiazoline-6-sulfonic acid) radical scavenging activity, comparable to that of vitamin C.

Mono, bi- and trinuclear metal complexes derived from new benzene-1,4-bis(3-pyridin-2-ylurea) ligand. Spectral, magnetic, thermal and 3D molecular modeling studies

New bis (pyridylurea) ligand, H2L, was synthesized by the reaction of ethylpyridine-2-carbamate (EPC) and p-phenylenediamine. The ligand was characterized by elemental analysis, IR, (1)H NMR, electronic and mass spectra. Reaction of the prepared ligand with Co(2+), Ni(2+), Cu(2+), Fe(3+), VO(2+) and UO2(2+) ions afforded mono, bi- and trinuclear metal complexes. Also, new mixed ligand complexes of the ligand H2L and 8-hydroxyquinoline (8-HQ) with Co(2+), Ni(2+), Cu(2+) and Fe(3+) ions were synthesized. The ligand behaves as bi- and tetradentate toward the transition metal ions, coordination via the pyridine N, the carbonyl O and/or the amidic N atoms in a non, mono- and bis-deprotonated form. The complexes were characterized by elemental and thermal analyses, IR, electronic and mass spectra as well as conductance and magnetic susceptibility measurements. The results showed that the metal complexes exhibited different geometrical arrangements such as square planar, tetrahedral, octahedral and square pyramidal arrangements. The Coats-Redfern equation was used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. 3D molecular modeling of the ligand, H2L and a representative complex were studied.

New platinum-oxicam complexes as anti-cancer drugs. Synthesis, characterization, release studies from smart hydrogels, evaluation of reactivity with selected proteins and cytotoxic activity in vitro

The reaction of aqueous cis-[Pt(NH(3))(2)(H(2)O)(2)](NO(3))(2) with Na(+)HMEL(-) (H(2)MEL, meloxicam, 4-hydroxy-2-methyl-N-(5-methyl-1,3-thiazol-2-yl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide), and Na(+)HISO(-) (H(2)ISO, isoxicam, 4-hydroxy-2-methyl-N-(5-methylisoxazol-3-yl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide) at pH 7 produced micro-crystalline cis-[Pt(NH(3))(2)(N(1')-HMEL)(2)], 5 and cis-[Pt(NH(3))(2)(N(1')-HISO)(2)], 6. The X-ray diffraction structure of 5 shows two HMEL(-) anions donating through the thiazole nitrogen atoms and adopting a head-to-tail (HT) conformation. The (1)H NMR spectrum for 5 from DMSO-d(6) shows inertness of the complex up to at least 24h. Delivery studies for 5 and 6 from vinyl hydrogel based on L-phenylalanine (pH 6.5, 25 degrees C) show that concentrations of complexes ranging between 2.5 and 5 microM can be reached after a day. Compounds 5 and 6 show strong anti-proliferative effects on CH1 cells (ovarian carcinoma, human) in vitro, IC(50) values being 0.60 and 0.37 microM, respectively (0.16 microM for reference, cis-diamminodichloridoplatinum(II), cisplatin). ESI-MS measurements clearly documented that both 5 and 6 form adducts with the three model proteins ubiquitin (UBI), cytochrome c (CYT C) and superoxide dismutase (SOD), the HISO(-) complex being significantly more effective than the HMEL(-) one. Density functional methods help in finding rationale for the easiest dissociation of Pt-H(2)ISO/HISO bonds when compared to the Pt-N(1)(')-H(2)MEL/N(1)(')-HMEL linkages.

Cisplatin interaction with amino acids cysteine and methionine from gas phase to solutions with constant pH

This work is focused on the computational studies of reactions of hydrated forms of cisplatin with sulphur-containing amino acids cysteine and methionine. First, the appropriate model for solvation of the examined complexes was searched for. The suggested procedure employs the B3LYP density functional, 6-311++G(2df,2pd) basis set with Stuttgart-Dresden pseudopotentials on heavy atoms, the D-PCM solvation model and the UAKS cavity which uses more realistic NPA partial charges instead of formal partial charges for platinum ligands. In the second part this model is applied to the evaluation of the Legendre transformed reaction Gibbs free energy of cisplatin with cysteine and methionine in solution at constant pH.

Computational Studies on the Pt(II)-Catalyzed Cycloisomerization of 1,6-dienes into Bicyclopropanes: A Mechanistic Quandary Evaluated by DFT

The mechanism of the (bis(phosphanylethyl)phosphane)Pt(2+) catalyzed cyclo-isomerization reaction of 7-methyl-octa-1,6-diene to form 1-isopropylbicyclo[3.1.0]hexane was studied using computational methods. The cyclopropanation step was found to be the turnover-limiting step. The overall reaction proceeds via both a 5-exo and a 6-endo route. W conformations were shown to facilitate cyclopropanation, but do not have any influence on the rate of the 1,2-hydride shifts.

Stabilization of Platinum Clusters by Substitutional Boron Dopants in Carbon Supports

To stabilize platinum clusters on carbon supports, carbon substituted boron dopants were introduced in graphite and fullerene models, and the binding energies of Pt(1) to Pt(6) clusters on the carbon supports were investigated using first-principles density functional theory (DFT) calculations. The adsorption energies of the Pt clusters increased significantly in the presence of boron. The adsorption energies of Ru(1) and Au(1) were also found to dramatically increase in the presence of boron.

Cisplatin interaction with cysteine and methionine, a theoretical DFT study

Interactions of hydrated cisplatin complexes with sulphur-containing amino acids cysteine and methionine were explored. The square-planar cis-[Pt(NH3)2(H2O)X]+ complexes (where X=Cl- and OH-) were chosen as mono- and dihydrated reactants. Calculations using density functional theory (DFT) techniques with B3LYP functional were performed. The isolated molecules and the supermolecular approaches were employed for the determination of the reaction energies. Bond dissociation energies (BDE) were estimated in the model of isolated molecules and supermolecules were used for the determination of the association energies between the two interacting parts. Formation of monodentate complexes by replacing the aqua-ligand with the S, N, and O-sites of both amino acids represents an exothermic process. The highest BDE was found in cysteine structures for the Pt-S coordination. The bonding energy is about 114 kcal/mol, which is comparable with cisplatin-guanine adducts. Analogous BDE for methionine complexes is smaller by about 40 kcal/mol. This correlates well with the known fact that cysteine forms irreversible cisplatin adducts while similar adducts in the methionine case are reversible. The formation of chelate structures is an exothermic reaction only for the hydroxo-form of reactants in the supermolecular approach where additional association interactions between the released water and chelate molecules sufficiently stabilize the final product.