Reactions of the biologically active palladium complexes (H<Subscript>2</Subscript>A)<Subscript>2</Subscript>[PdCl<Subscript>4</Subscript>] with glutamic acid as a model of their transformations in blood plasma

Complexation in the systems Pd(II)-Cl⁻-HA-H₂Glu (HA is the l- or d-conformer of 2-methylamino-1-phenylpropanol; H₂Glu is glutamic acid) was studied using pH-metric titration, electronic absorption spectroscopy, and quantum-chemical modeling. It was found that the ratio of the complex species largely depends on pH and the amine, the crucial factor being stabilization of the structures by hydrogen bonding. This provides explanation to the previous data on the different radioprotective activities of the complexes (H₂A)₂[PdCl₄] containing the l- and d-conformers of the ligand HA.     

Catalytic reaction of 1-chloropropenyl butyl ethers with methyl diazoacetate

Catalytic reaction of trans- and cis-1-chloropropenyl butyl ethers with methyl diazoacetate catalyzed by either Rh₂(OAc)₃, or Cu(OTf)₂, or Cu(acac)₂ in the presence of the imidazolium salts [bmim]⁺ Cl^?, [bmim]⁺ BF ₄ ^? , and [bmim]⁺ PF ₆ ^? was studied. The composition and ratio of products formed was shown to depend on the reaction conditions and the nature and ratio of the components of the catalytic system.     

Micellization and surface properties of aqueous solutions of binary mixtures of tween-80 and bromide cetyltrimethylammonium

The physicochemical properties of solutions of mixtures of cationic (cetiltrimethylammonum bromide) and nonionic (polyoxyethylene (20) sorbitan monooleate) surfactant, i.e., Tween-80, have been studied. The critical concentration of micellization, adsorption at the interface of a mixture of surfactants solution/air, and the minimum area occupied by a surfactant molecule have been determined. It was shown that, in the whole region of ratios between surfactants, sinergic effects are observed for both micellization and for the process of adsorption at the interface of a mixture of surfactants solution/air. The results obtained have been analyzed according to the regular solution theory (RST).     

Caged glutathione - triggering protein interaction by light

Light, GSH, action! Glutathione (GSH) fulfills a universal role as redox factor, scavenger of reactive oxygen species, and as an essential substrate in the conjugation, detoxification, and reduction reactions catalyzed by glutathione S-transferase (GST). A photoactivatable glutathione allows the GSH-GST network to be triggered by light. GST fusion proteins can be assembled in situ at variable density and structures by laser-scanning activation.     

Reverse hydrogen spillover on and hydrogenation of supported metal clusters: insights from computational model studies

"Reverse" spillover of hydrogen from hydroxyl groups of the support onto supported transition metal clusters, forming multiply hydrogenated metal species, is an essential aspect of various catalytic systems which comprise small, highly active transition metal particles on a support with a high surface area. We review and analyze the results of our computational model studies related to reverse hydrogen spillover, interpreting available structural and spectral data for the supported species and examining the relationship between metal-support and metal-hydrogen interactions. On the examples of small clusters of late transition metals, adsorbed in zeolite cavities, we showed with computational model studies that reverse spillover of hydrogen is energetically favorable for late transition metals, except for Au. This preference is crucial for the chemical reactivity of such bifunctional catalytic systems because both functions, of metal species and of acidic sites, are strongly modified, in some cases even suppressed - due to partial oxidation of the metal cluster and the conversion of protons from acidic hydroxyl groups to hydride ligands of the metal moiety. Modeling multiple hydrogen adsorption on metal clusters allowed us to quantify how (i) the support affects the adsorption capacity of the clusters and (ii) structure and oxidation state of the metal moiety changes upon adsorption. In all models of neutral systems we found that the metal atoms are partially positively charged, compensated by a negative charge of the adsorbed hydrogen ligands and of the support. In a case study we demonstrated with calculated thermodynamic parameters how to predict the average hydrogen coverage of the transition metal cluster at a given temperature and hydrogen pressure.     

Ultrafast charge-transfer dynamics of donor-substituted truxenones

The photophysics of two donor-substituted truxenone derivatives has been studied by femtosecond time-resolved transient absorption spectroscopy. The systems consist of a central truxenone acceptor with three triarylamine (TARA) branches which act as electron donors. Upon excitation in the visible regime an electron is transferred from the donor to the acceptor, generating a charge-separated state. This state can be probed via the characteristic absorption of the TARA radical cation around 700 nm. A second absorption band around 420 nm exhibits the same kinetics and is assigned to an absorption of the radical anion of the truxenone moiety. The back electron transfer and the recovery of the ground state can be interpreted within the framework of Marcus theory. To study the dependence of the back electron transfer on the electronic coupling, the distance between the donor and the acceptor was adjusted. Two solvents were employed, dimethylsulfoxide and dichloroethane. A biexponential decay of the bands assigned to the charge-separated state was observed, with time constants in the picosecond range. Surprisingly, the rates for electron back transfer do not follow the simple picture of the donor-acceptor distance being the determining factor. The observations are explained within a model that additionally takes steric interactions between the donor and the acceptor into account.     

Hydrolytic Activity of Vanadate toward Serine-Containing Peptides Studied by Kinetic Experiments and DFT Theory

Hydrolysis of dipeptides glycylserine (Gly-Ser), leucylserine (Leu-Ser), histidylserine (His-Ser), glycylalanine (Gly-Ala), and serylglycine (Ser-Gly) was examined in vanadate solutions by means of (1)H, (13)C, and (51)V NMR spectroscopy. In the presence of a mixture of oxovanadates, the hydrolysis of the peptide bond in Gly-Ser proceeds under the physiological pH and temperature (37 °C, pD 7.4) with a rate constant of 8.9 × 10(-8) s(-1). NMR and EPR spectra did not show evidence for the formation of paramagnetic species, excluding the possibility of V(V) reduction to V(IV) and indicating that the cleavage of the peptide bond is purely hydrolytic. The pD dependence of k(obs) exhibits a bell-shaped profile, with the fastest hydrolysis observed at pD 7.4. Combined (1)H, (13)C, and (51)V NMR experiments revealed formation of three complexes between Gly-Ser and vanadate, of which only one complex, designated Complex 2, formed via coordination of amide oxygen and amino nitrogen to vanadate, is proposed to be hydrolytically active. Kinetic experiments at pD 7.4 performed by using a fixed amount of Gly-Ser and increasing amounts of Na(3)VO(4) allowed calculation of the formation constant for the Gly-Ser/VO(4)(3-) complex (K(f) = 16.1 M(-1)). The structure of the hydrolytically active Complex 2 is suggested also on the basis of DFT calculations. The energy difference between Complex 2 and the major complex detected in the reaction mixture, Complex 1, is calculated to be 7.1 kcal/mol in favor of the latter. The analysis of the molecular properties of Gly-Ser and their change upon different modes of coordination to the vanadate pointed out that only in Complex 2 the amide carbon is suitable for attack by the hydroxyl group in the Ser side chain, which acts as an effective nucleophile. The origin of the hydrolytic activity of vanadate is most likely a combination of the polarization of amide oxygen in Gly-Ser due to the binding to vanadate, followed by the intramolecular attack of the Ser hydroxyl group.     

A new metallostar complex based on an aluminum(iii) 8-hydroxyquinoline core as a potential bimodal contrast agent

A ditopic DTPA monoamide derivative containing an 8-hydroxyquinoline moiety was synthesized and the corresponding gadolinium(iii) complex ([Gd(H5)(H(2)O)](-)) was prepared. After adding aluminum(iii), the 8-hydroxyquinoline part self-assembled into a heteropolymetallic triscomplex [(Gd5)(3)Al(H(2)O)(3)](3-). The magnetic and optical properties of this metallostar compound were investigated in order to classify it as a potential in vitro bimodal contrast agent. The proton nuclear magnetic relaxation dispersion measurements indicated that the relaxivity r(1) of [Gd(H5)(H(2)O)](-) and [(Gd5)(3)Al(H(2)O)(3)](3-) at 20 MHz and 310 K equaled 6.17 s(-1) mM(-1) and 10.9 s(-1) mM(-1) per Gd(iii) ion respectively. This corresponds to a relaxivity value of 32.7 s(-1) mM(-1) for the supramolecular complex containing three Gd(iii) ions. The high relaxivity value is prominently caused by an increase of the rotational tumbling time τ(R) by a factor of 2.7 and 5.5 respectively, in comparison with the commercially used MRI contrast agent Gd(iii)-DTPA (Magnevist?). Furthermore, upon UV irradiation, [(Gd5)(3)Al(H(2)O)(3)](3-) exposes green broad-band emission with a maximum at 543 nm. Regarding the high relaxivity and the photophysical properties of the [(Gd5)(3)Al(H(2)O)(3)](3-) metallostar compound, it can be considered as a lead compound for in vitro bimodal applications.     

Compositional trends in low-temperature photoluminescence of heavily Er-doped GeS2–Ga2S3 glasses

The influence of temperature and glass composition on the photoluminescence (PL) efficiency of Er³⁺ ions embedded in (GeS₂)_100?x(Ga₂S₃)_x (x = 20, 25 and 33 mol%) glasses has been studied. The typical 4f–4f emission bands of Er³⁺ ions at around 830, 1000 and 1550 nm have been observed in the whole investigated temperature range from 300 K down to 10 K for all the compositions. New 4f–4f luminescence bands, in excess of the three basic ones, have been observed at 670, 870, 1120, 1260 and 1350 nm for (GeS₂)₇₅(Ga₂S₃)₂₅ glass composition, and are tentatively assigned to ²H_9/2 → ⁴I_11/2, ⁴G_11/2 → ⁴F_9/2, ²H_11/2 → ⁴I_11/2, ⁴F_7/2 → ⁴I_9/2 and ⁴F_3/2 → ⁴I_9/2 transitions, respectively. Thus a considerable influence of GeGaS host composition on the efficiency of 4f–4f transitions of embedded Er³⁺ ions is documented with the outcome that (GeS₂)₇₅Ga₂S₃)₂₅ composition appears near optimal for the emission efficiency of Er³⁺ ions. With decreasing temperature the PL efficiency is enhanced considerably with pronounced narrowing of all bands. In the case of the strongest PL band at ~ 1550 nm, corresponding to ⁴I_13/2 → ⁴I_15/2 transition, the narrowing at low temperature is further accompanied by the resolution of well pronounced fine structure due to “crystal field” splitting of corresponding electronic terms. The relationship between the photoluminescence and reflectance spectra as a function of Er content has been discussed.     

Epitaxially Grown Films of Standing and Lying Pentacene Molecules on Cu(110) Surfaces

This study investigates epitaxially oriented pentacene films grown on Cu(110) surfaces crystallizing either in the "thin film" phase with standing molecules or in the "single crystal" structure with molecules lying with their long axes parallel to the substrate.