The directive of the protein: how does cytochrome P450 select the mechanism of dopamine formation?

Dopamine can be generated from tyramine via arene hydroxylation catalyzed by a cytochrome P450 enzyme (CYP2D6). Our quantum mechanical/molecular mechanical (QM/MM) results reveal the decisive impact of the protein in selecting the 'best' reaction mechanism. Instead of the traditional Meisenheimer-complex mechanism, the study reveals a mechanism involving an initial hydrogen atom transfer from the phenolic hydroxyl group of the tyramine to the iron-oxo of the compound I (Cpd I), followed by a ring-π radical rebound that eventually leads to dopamine by keto-enol rearrangement. This mechanism is not viable in the gas phase since the O-H bond activation by Cpd I is endothermic and the process does not form a stable intermediate. By contrast, the in-protein reaction has a low barrier and is exothermic. It is shown that the local electric field of the protein environment serves as a template that stabilizes the intermediate of the H-abstraction step and thereby mediates the catalysis of dopamine formation at a lower energy cost. Furthermore, it is shown that external electric fields can either catalyze or inhibit the process depending on their directionality.     

Tailoring the electrochemical charge storage properties of carbonaceous support by redox properties of heteropoly acids: where does the synergy come from?

Journal of Solid State Electrochemistry - The synergistic effects between two Keggin-type heteropoly acids (HPAs) and carbon surface were examined and elucidated. An improved high rate capability...     

Five-coordinate Fe(III)NO and Fe(II)CO porphyrinates: where are the electrons and why does it matter?

Recent years have seen dramatic growth in our understanding of the biological roles of nitric oxide (NO). Yet, the fundamental underpinnings of its reactivities with transition metal centers in proteins and enzymes, the stabilities of their structures, and the relationships between structure and reactivity remains, to a significant extent, elusive. This is especially true for the so-called ferric heme nitrosyls ([FeNO](6) in the Enemark-Feltham scheme). The Fe-CO and C-O bond strengths in the isoelectronic ferrous carbonyl complexes are widely recognized to be inversely correlated and sensitive to structural, environmental, and electronic factors. On the other hand, the Fe-NO and N-O bonds in [FeNO](6) heme complexes exhibit seemingly inconsistent behavior in response to varying structure and environment. This report contains resonance Raman and density functional theory results that suggest a new model for FeNO bonding in five-coordinate [FeNO](6) complexes. On the basis of resonance Raman and FTIR data, a direct correlation between the nu(Fe)(-)(NO) and nu(N)(-)(O) frequencies of [Fe(OEP)NO](ClO(4)) and [Fe(OEP)NO](ClO(4)).CHCl(3) (two crystal forms of the same complex) has been established. Density functional theory calculations show that the relationship between Fe-NO and N-O bond strengths is responsive to FeNO electron density in three molecular orbitals. The highest energy orbital of the three is sigma-antibonding with respect to the entire FeNO unit. The other two comprise a lower-energy, degenerate, or nearly degenerate pair that is pi-bonding with respect to Fe-NO and pi-antibonding with respect to N-O. The relative sensitivities of the electron density distributions in these orbitals are shown to be consistent with all published indicators of Fe-N-O bond strengths and angles, including the examples reported here.     

Preparation and characterization of the system NiMn2O4/TiO2 by sol–gel: application to the photodegradation of benzamide under visible light

Journal of Sol-Gel Science and Technology - Benzamide is successfully degraded on the novel heterosystem NiMn2O4/TiO2 under visible light. The nanosized spinel is synthesized by the sol–gel...     

The migration of styrene butadiene latex during the drying of coating suspensions: when and how does migration of colloidal particles occur?

Surface elemental compositions of model latex clay coatings on an impervious substrate consolidated under various conditions were measured using the XPS technique, in order to clarify when and how colloidal latex particles migrate to the surface during drying. Under similar drying conditions, surface carbon content decreased with the addition of a water-soluble polymer to the coating colors, while remaining virtually unchanged for coatings of different coat weights made with a given color, indicating that surface carbon content variation is mainly caused by migration of latex rather than of water-soluble polymer. The results also showed that for coatings made with a given suspension, surface carbon content decreased with increasing delay time between coating and heating. For coatings frozen during consolidation and dried by sublimation, surface carbon content increased with increasing drying time before freezing. These results suggest that for the model coatings studied, latex migration mainly occurs after coating application before capillary formation during the initial drying stage when coatings are in the liquid phase, contradicting both the conventional capillary transport and boundary wall migration mechanisms. An alternative mechanism which attributes latex migration to surface trapping effect and to higher Brownian mobility of the smaller latex particles compared with pigment appears to provide a systematically consistent explanation to those phenomena. The new particle migration mechanism implies that segregation of colloidal particles is a ubiquitous phenomenon that would occur not only during the drying of paper coatings but also during consolidation of colloidal films containing particles of different sizes. This is of great importance in the control of surface compositions of nanocomposite coatings.     

Magnetic criteria of aromaticity in a benzene cation and anion: how does the Jahn–Teller effect influence the aromaticity?

The aromatic/antiaromatic behavior of the Jahn–Teller (JT) active benzene cation and anion has been investigated using Density Functional Theory (DFT) calculations of Nuclear Independent Chemical Shifts (NICS) and magnetic susceptibility. NICS parameters have been scanned along the Intrinsic Distortion Path (IDP) for the benzene cation showing antiaromaticity which decreases with increasing deviation from D_6h to D_2h symmetry. Changes in NICS values along the IDP from D_6h to C_2v in the benzene anion revealed non-aromatic character.     

Size reduction of CdSe/ZnS core-shell quantum dots photosensitized by benzophenone: where does the Cd(0) go?

The size of core-shell CdSe/ZnS quantum dots can be decreased by using the combined action of an n,π* aromatic ketone and UVA light. Energy-dispersive X-ray spectroscopy as well as X-ray photoelectron spectroscopy techniques gave information on the photosensitization mechanism and the eventual destiny of Cd(2+) and Se(2-) core ions. Our data support the electron transfer from the BP ketyl radical to Cd(2+), leading to Cd(0) and H(+), as well as to the recovery of benzophenone. Elemental Cd remains on the core and, eventually, can be oxidized to CdO. In addition, Se(2-) counterions disperse inside the solution mainly attached to protonated amine ligands. The Se(2-) combines with H(+), leading to SeH(2), which is finally oxidized to Se(0) by oxygen. Therefore, quantum dots illumination in the presence of benzophenones brings about a profound nanoparticle reconstruction which takes place after dark storage; this agrees with the drastic quenching of the quantum dot emission detected immediately after illumination as well as the slow recovery in the dark.     

Rotational flexibility in NH4+-encapsulated 18-crown-6 studied by molecular dynamics and positron annihilation: where does the positron localize?

Conformational flexibility of the ammonium complex of macrocyclic 18-crown-6 at 100 K < or = T < or = 300 K is studied using a positron microprobe in conjunction with molecular dynamics simulations. The ammonium cation, encapsulated in a three-pointed hydrogen-bonding perching arrangement, undergoes unhindered facile rotation inside the crown cavity, and the ether backbone adopts itself to the dynamic cation conformation. Preferential localization of the positron in the vicinity of the encapsulated cation results in the positron sensing changes in the local electron density distribution arising from the unrestricted rotational motion of the cation as well as from the slow motion of the crown backbone and hence sensing only an average conformation of the complex.     

Copper(I) and nickel(II) complexes with 1:1 vs. 1:2 coordination of ferrocenyl hydrazone ligands: do the geometry and composition of complexes affect DNA binding/cleavage, protein binding, antioxidant and cytotoxic activities?

A new series of geometrically different complexes containing ferrocenyl hydrazone ligands were synthesised by reacting suitable precursor complex [MCl(2)(PPh(3))(2)] with the ligands HL(1) or HL(2) (where M = Cu(II) or Ni(II); HL(1) = [Cp(2)Fe(CH=N-NH-CO-C(6)H(5))] (1) and HL(2) = [Cp(2)Fe(CH=N-NH-CO-C(5)H(4)N)]) (2). The new complexes of the composition [Cu(L(1))(PPh(3))(2)], (3) [Cu(L(2))(PPh(3))(2)] (4), [Ni(L(1))(2)] (5) and [Ni(L(2))(2)] (6) were characterised by various spectral studies. Among them, complexes 3 and 5 characterised by single crystal X-ray diffraction showed a distorted tetrahedral structure for the former with 1:1 metal-ligand stoichiometry, but a distorted square planar geometry with 1:2 metal-ligand stoichiometry in the case of the latter. Systematic biological investigations like DNA binding, DNA cleavage, protein binding, free radical scavenging and cytotoxicity activities were carried out using all the synthesised compounds and the results obtained were explained on the basis of structure-activity relationships. The binding constant (K(b)) values of the synthesised compounds are found to be in the order of magnitude 10(3)-10(5) M(-1) and also they exhibit significant cleavage of supercoiled (SC) pUC19 DNA in the presence of H(2)O(2) as co-oxidant. The conformational changes of bovine serum albumin (BSA) upon binding with the above complexes were also studied. In addition, concentration dependent free radical scavenging potential of all the synthesised compounds (1-6) was also carried out under in vitro conditions. Assays on the cytotoxicity of the above complexes against HeLa and A431 tumor cells and NIH 3T3 normal cells were also carried out.     

Chemical mimicry: hierarchical 1D TiO2@ZrO2 core-shell structures reminiscent of sponge spicules by the synergistic effect of silicatein-α and silintaphin-1

In nature, mineralization of hard tissues occurs due to the synergistic effect of components present in the organic matrix of these tissues, with templating and catalytic effects. In Suberites domuncula, a well-studied example of the class of demosponges, silica formation is mediated and templated by an axial proteinaceous filament with silicatein-α, one of the main components. But so far, the effect of other organic constituents from the proteinaceous filament on the catalytic effect of silicatein-α has not been studied in detail. Here we describe the synthesis of core-shell TiO(2)@SiO(2) and TiO(2)@ZrO(2) nanofibers via grafting of silicatein-α onto a TiO(2) nanowire backbone followed by a coassembly of silintaphin-1 through its specifically interacting domains. We show for the first time a linker-free, one-step funtionalization of metal oxides with silicatein-α using glutamate tag. In the presence of silintaphin-1 silicatein-α facilitates the formation of a dense layer of SiO(2) or ZrO(2) on the TiO(2)@protein backbone template. The immobilization of silicatein-α onto TiO(2) probes was characterized by atomic force microscopy (AFM), optical light microscopy, and high-resolution transmission electron microscopy (HRTEM). The coassembly of silicatein-α and silintaphin-1 may contribute to biomimetic approaches that pursue a controlled formation of patterned biosilica-based biomaterials.     

Orientational effect of aryl groups in aryl selenides: how can 1h and 13c NMR chemical shifts clarify the effect?

Two sets of delta(H) and delta(C) are proposed by employing 9-(arylselanyl)anthracenes [9-(p-YC6H4Se)Atc: 1] and 1-(arylselanyl)anthraquinones [1-(p-YC6H4Se)Atq: 2] with various Y's. Structures of 1 and 2 are (A: pl) and (B: pd), respectively, for all Y examined in chloroform-d. After elucidation of the behavior of delta(H, C: 1) and delta(H, C: 2), they are applied to determine the structures in chloroform-d solutions for 1-(arylselanyl)naphthalenes (3), 1-(arylselanyl)-2-methylnaphthalenes (4), and 1-(arylselanyl)-8-bromonaphthalenes (5). Although the structure of 4 remains in (A: pl) in the solutions for all Y examined, that of 5 is (B: pd), except for Y = CN and NO2. On the other hand, 3 is shown to equilibrate between (A: pl) and (B: pd). Although the contributions of (B: pd) and (A: pl) are predominant for Y = NMe2 and NO2, respectively, the equilibrium constants change from Y to Y in the solutions. The results are supported by the quantum chemical calculations, containing the solvent effect of chloroform. These results demonstrate that delta(H, C: 1) and delta(H, C: 2), as well as delta(Se), serve as the practical standards for pl and pd, respectively, to analyze the structures of p-YC6H4ZR (Z = Se) in solutions.     

415 - Surface and/or Donnan potentials at the thylakoid membrane?: Part II. Calculation of light-induced surface potential changes and corresponding ion movement for a 1 : 1 electrolyte

The surface potential at the inner side of the thylakoid membrane in the dark and in the light state is calculated using the simple Gouy-Chapman theory, together with modifications to allow for proton binding to the surface. The corresponding transmembrane potential change and the ion transport, necessary for ion redistribution in the diffuse double layer, are formulated. the steady-state generalized Donnan potential is shown to be negligible. Finally, the surface potential representation is compared with the Donnan potential representation, given in the preceding paper. On the basis of the formula derived, measurements are discussed which will help to decide between the different concepts.     

A 1D double chains architecture based on the pyridine-2-sulfonate, 4,4′-Bipyridine and acetate-bridged of Zn(II) complex: Synthesis, spectral, thermal properties, and crystal structure

A new 1D double chains Zn(II) supramolecule framework, {[Zn₂(2-pSO₃)₂(Ac)₂(4,4??-Bipy)₂](4,4??-Bipy)} _n (I) (2-pSO₃H = pyridine-2-sulfonate, 4,4??-Bipy = 4,4??-bipyridine), was synthesized by reaction of Zn(CH₃COO)₂ · 2H₂O in methanol-water mixed solution and characterized by X-ray diffraction, elemental analysis, and IR spectrum. X-ray analysis indicates that I is a coordination polymer in which two deprotonated 2-pSO₃H through the aromatic nitrogens in trans positions, oxygens in cis positions and two N atoms of 4,4??-Bipy and two ??₂-Ac^? ligands, resulting in a ZnN₃O₃ distorted octahedral geometry. The 1D coordination polymer was connected to 2D and 3D supramolecule framework via ??-stacking and weak C-H??O contacts. The complex I also displays strong fluorescence property and good thermal stability.     

Structural determination of aspericins A?C,new furan and pyran derivates from the marine‐derived fungus Rhizopus sp. 2‐PDA‐61, by 1D and 2D NMR spectroscopy

Three new furan and pyran derivatives named aspericins A? C (1–3), as well as a known asperic acid (4), have been isolated from the marine‐derived fungus Rhizopus sp. 2‐PDA‐61. The complete ¹H and ¹³C NMR assignments for the new compounds were carried out using ¹H, ¹³C, DEPT, COSY, HMQC, HMBC, and NOESY NMR experiments. Compounds 1–3 were evaluated for their cytotoxic activities on P388, A549, HL‐60, and BEL‐7420 cell lines by the MTT and SRB methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Photoluminescence and photocatalytic properties of Er<Superscript>3+</Superscript>-doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films prepared by sol–gel: application to Rhodamine B degradation under solar light

The effect of Er³⁺ doping (1%) on the structural, optical and photocatalytic properties of In₂O₃ thin films deposited on quartz substrates by spin coating was investigated. The In₂O₃:1% Er³⁺ films, annealed in the temperature range 800–1000 °C, were characterized by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy, UV–Vis spectroscopy, ellipsometry and photoluminescence (PL). The films are polycrystalline with a cubic structure and the lattice parameter increases with the incorporation of Er³⁺ owing to its larger radius. The SEM images of the film show a granular morphology with large grains (~ 200 nm). The doped In₂O₃ film exhibits less transparency than In₂O₃ in the UV–visible region with band gaps of 3.42 and 3.60 eV, respectively. PL shows strong lines at 548 and 567 nm, assigned to Er³⁺ under direct excitation at 532 nm. The energy diagram of the junction In₂O₃:1% Er³⁺/Na₂SO₄ (0.1 M) solution plotted from physical and photoelectrochemical characterizations shows the feasibility of the films for Rhodamine B (RhB) degradation under solar light. The conduction band at 2.22 V deriving from the In³⁺:5s orbital is suitably positioned with respect to the O₂/O ₂ ^· level (~ 1.40 V_SCE), leading to oxidation of 32% of 10 ppm RhB within 40 min of solar irradiation.