Heterogeneous enantioselective epoxidation catalyzed by Mn(salen) complexes grafted onto mesoporous materials by phenoxy group

Three chiral Mn(salen) complexes were immobilized into different mesoporous material via phenoxy group by a simplified method and they show high activity and enantioselectivity for asymmetric epoxidation of various substituted unfunctional olefins. The heterogeneous Mn(salen) catalysts show comparable ee values for asymmetric epoxidation of styrene and 6-cyano-2,2-dimethylchromene and much higher ee values for epoxidation of a-methylstyrene (heterogeneous 79.7% ee versus homogeneous 26.4% ee) and cis-beta-methylstyrene (heterogeneous 94.9% ee versus homogeneous 25.3% ee for cis-epoxide) than the homogeneous catalysts. These heterogeneous catalysts also remarkably alter the cis/trans ratio of epoxides for asymmetric epoxidation of cis-beta-methylstyrene (heterogeneous 21 versus homogeneous 0.38). The axial tether group does not make a big effect on ee values and the increase in ee value and change in cis/trans ratio are mainly attributed to the axial immobilization mode and the support effect of heterogeneous catalysts. The catalysts keep constant ee values for the recycle tests of eight times for asymmetric epoxidation of a-methylstyrene. And several possibilities were proposed to elucidate the difference in ee values of heterogeneous catalysts from homogeneous catalysts. (c) 2005 Elsevier B.V. All rights reserved.

Synthesis and structural characterization of (pyrazolyl)alkenyl Fischer carbene complexes of chromium and tungsten

Michael addition of substituted pyrazoles 2 to 1-alkynyl Fischer carbene complexes (CO)(5)M=C(OEt)(CdropCPh) (1) (a, M = Cr and b M = W) afforded (pyrazolyl)alkenyl Fischer carbene complexes (CO)(5)M=C(OEt)(CH=C(R(1)R(2)R(3)pz)Ph) (R(1)R(2)R(3)pz = pyrazolyl) 3 (M = Cr) and 4 (M = W), respectively, with an exclusive (E)-configuration in mild to excellent yields. The reaction of la and 3,5-dimethylpyrazole (2b) was monitored to demonstrate the formation and decomposition of complex 3b by H-1 NMR measurements in CDCl3 at 23degreesC. Complexes 3 and 4 were characterized with H-1, C-13{H-1} NMR, IR spectroscopies and elemental analysis. When the substituted pyrazoles were 3-methylpyrazole (2a) and 3,5-di-tert-butylpyrazole (2d), molecular structures of the corresponding (pyrazolyl)alkenyl Fischer carbene complexes 3a and 4d were characterized by X-ray crystallographic study. (C) 2004 Elsevier Ltd. All rights reserved.

Application of gold complexes in the development of sensors for volatile organic compounds

Two different kinds of sensors have been developed by using the same kind of vapochromic complexes. The vapochromic materials [Au2Ag2(C6F5)(4)L-2](n) have different colours depending on the ligand L. These materials change, reversibly, their optical properties, colour and fluorescence, in the presence of the vapours of volatile organic compounds (VOCs). For practical applications, two different ways of fixing the vapochromic material to the optical fibre have been used: the sol-gel technique and the electrostatic self-assembly method (ESA). With the first technique the sensors can even be used to detect VOCs in aqueous solutions, and using the second method it has been possible to develop nanosensors.

Protein Docking by the Underestimation of Free Energy Funnels in the Space of Encounter Complexes

Similarly to protein folding, the association of two proteins is driven by a free energy funnel, determined by favorable interactions in some neighborhood of the native state. We describe a docking method based on stochastic global minimization of funnel-shaped energy functions in the space of rigid body motions (SE(3)) while accounting for flexibility of the interface side chains. The method, called semi-definite programming-based underestimation (SDU), employs a general quadratic function to underestimate a set of local energy minima and uses the resulting underestimator to bias further sampling. While SDU effectively minimizes functions with funnel-shaped basins, its application to docking in the rotational and translational space SE(3) is not straightforward due to the geometry of that space. We introduce a strategy that uses separate independent variables for side-chain optimization, center-to-center distance of the two proteins, and five angular descriptors of the relative orientations of the molecules. The removal of the center-to-center distance turns out to vastly improve the efficiency of the search, because the five-dimensional space now exhibits a well-behaved energy surface suitable for underestimation. This algorithm explores the free energy surface spanned by encounter complexes that correspond to local free energy minima and shows similarity to the model of macromolecular association that proceeds through a series of collisions. Results for standard protein docking benchmarks establish that in this space the free energy landscape is a funnel in a reasonably broad neighborhood of the native state and that the SDU strategy can generate docking predictions with less than 5 � ligand interface Ca root-mean-square deviation while achieving an approximately 20-fold efficiency gain compared to Monte Carlo methods.

Multi-Area Visuotopic Map Complexes in Macaque Striate and Extra-striate Cortex

We propose that a simple, closed-form mathematical expression--the Wedge-Dipole mapping--provides a concise approximation to the full-field, two-dimensional topographic structure of macaque V1, V2, and V3. A single map function, which we term a map complex, acts as a simultaneous descriptor of all three areas. Quantitative estimation of the Wedge-Dipole parameters is provided via 2DG data of central-field V1 topography and a publicly available data set of full-field macaque V1 and V2 topography. Good quantitative agreement is obtained between the data and the model presented here. The increasing importance of fMRI-based brain imaging motivates the development of more sophisticated two-dimensional models of cortical visuotopy, in contrast to the one-dimensional approximations that have been in common use. One reason is that topography has traditionally supplied an important aspect of "ground truth", or validation, for brain imaging, suggesting that further development of high-resolution fMRI will be facilitated by this data analysis. In addition, several important insights into the nature of cortical topography follows from this work. The presence of anisotropy in cortical magnification factor is shown to follow mathematically from the shared boundary conditions at the V1-V2 and V2-V3 borders, and therefore may not causally follow from the existence of columnar systems in these areas, as is widely assumed. An application of the Wedge-Dipole model to localizing aspects of visual processing to specific cortical areas--extending previous work in correlating V1 cortical magnification factor to retinal anatomy or visual psychophysics data--is briefly discussed.

Synthesis of iminophosphine and phosphinoiminol cyclometallated Pt (II) and Pt (IV) chloro complexes and studies into their biological and photophysical properties

This thesis focuses on the synthesis and analysis of novel chloride based platinum complexes derived from iminophosphine and phosphinoamide ligands, along with studies on their reactivity towards substitution and oxidation reactions. Also explored here are the potential applications of these complexes for biological and luminescent purposes. Chapter one provides an extensive overview of platinum coordination chemistry with examples of various mixed donor ligands along with the history of platinum anticancer therapy. It also looks at metals in medicine, both for biological functions as well as for therapeutic purposes and gives a background to some other applications for platinum complexes. Chapter two outlines the design and synthetic strategies employed for the development of novel platinum (II) chloride complexes from iminophosphine and phosphinoamide ligands. Also reported is the cyclometallation of these complexes to form stable tridentate mixed donor platinum (II) compounds. In Chapter three the development of a direct method for displacing a chloride from a platinum metal centre with a desired phosphine is reported. Numerous methods for successful oxidation of the platinum (II) complexes will also be explored, leading to novel platinum (IV) complexes being reported here also. The importance of stabilisation of the displaced anion, chloride, by the solvent system will also be discussed in this chapter. Chapter four investigates the reactivity of the platinum (II) complexes towards two different biomolecules to form novel platinum bio-adducts. The potential application of the platinum (II) cyclometallates as chemotherapeutics will also be explored here using in-vitro cancer cell testing. Finally, luminescence studies are also reported here for the ligands and platinum complexes reported in chapter two and three to investigate potential applications in this field also. Chapter five provides a final conclusion and an overall summary of the entire project as well as identifying key areas for future work.

Reductive elimination of hypersilyl halides from zinc (II) complexes. Implications for electropositive metal thin film growth

Treatment of Zn(Si(SiMe3)3)2 with ZnX2 (X = Cl, Br, I) in tetrahydrofuran (THF) at 23 °C afforded [Zn(Si(SiMe3)3)X(THF)]2 in 83–99% yield. X-ray crystal structures revealed dimeric structures with Zn2X2 cores. Thermogravimetric analyses of [Zn(Si(SiMe3)3)X(THF)]2 demonstrated a loss of coordinated THF between 50 and 155 °C and then single-step weight losses between 200 and 275 °C. The nonvolatile residue was zinc metal in all cases. Bulk thermolyses of [Zn(Si(SiMe3)3)X(THF)]2 between 210 and 250 °C afforded zinc metal in 97–99% yield, Si(SiMe3)3X in 91–94% yield, and THF in 81–98% yield. Density functional theory calculations confirmed that zinc formation becomes energetically favorable upon THF loss. Similar reactions are likely to be general for M(SiR3)n/MXn pairs and may lead to new metal-film-growth processes for chemical vapor deposition and atomic layer deposition.

Ab initio investigation of C2H2/X Van der Waals complexes (X=Noble gas, CO2, N2O)

info:eu-repo/semantics/nonPublished

Characterisation of bifunctional ruthenium(ii) complexes, potential DNA photo-probes. Presence of folded and unfolded conformers

Novel bifunctional ruthenium(n) complexes, [Ru(TAP)2(POQ-Nmet)]2+ and [Ru(BPY)2(POQ-Nmet)]2+(la, 2a), containing a metallic and an organic moiety, have been prepared as photoprobes and photoreagents of DNA(TAP = 1,4,5,8-tetraazaphenanthrene, POQ-Nmet = 5-[6-(7-chloroquinolin-4-yl)-3-thia-6-azaheptanamido]-l,10phenanthroline). The ES mass spectrometry and 'H NMR data in organic solvents indicate that the quinoline moiety exists in both the protonated and non-protonated form. Moreover, the comparison of the NMR data with those of the corresponding monofunctional complexes(without quinoline) evidences that [Ru(TAP).2(POQ-Nmet)]2+ and [Ru(BPY)J(POQ-Nmet)]2+ are unfolded when the quinoline unit is protonated whereas deprotonation permits folding of the molecule. In the folded state the spatial proximity of the electron donor(the organic moiety) and electron acceptor(the metallic moiety) in [Ru(TAP)2(POQ-Nmet)]2+ favours intramolecular photo-induced electron transfer, which has been shown in a previous study to be responsible for the very low luminescence of la in non-protonating solutions. The restoration of the luminescence by protonation of the quinoline moiety as observed previously is in agreement with the unfolding of the molecule demonstrated in this work. The existence of such folding-unfolding processes related to protonation is crucial for studies of la with DNA. © The Royal Society of Chemistry 2000.

EPR spectroscopy of nitrite complexes of methemoglobin.

The chemical interplay of nitrogen oxides (NO's) with hemoglobin (Hb) has attracted considerable recent attention because of its potential significance in the mechanism of NO-related vasoactivity regulated by Hb. An important theme of this interplay-redox coupling in adducts of heme iron and NO's-has sparked renewed interest in fundamental studies of FeNO(x) coordination complexes. In this Article, we report combined UV-vis and comprehensive electron paramagnetic resonance (EPR) spectroscopic studies that address intriguing questions raised in recent studies of the structure and affinity of the nitrite ligand in complexes with Fe(III) in methemoglobin (metHb). EPR spectra of metHb/NO(2)(-) are found to exhibit a characteristic doubling in their sharper spectral features. Comparative EPR measurements at X- and S-band frequencies, and in D(2)O versus H(2)O, argue against the assignment of this splitting as hyperfine structure. Correlated changes in the EPR spectra with pH enable complete assignment of the spectrum as deriving from the overlap of two low-spin species with g values of 3.018, 2.122, 1.45 and 2.870, 2.304, 1.45 (values for samples at 20 K and pH 7.4 in phosphate-buffered saline). These g values are typical of g values found for other heme proteins with N-coordinated ligands in the binding pocket and are thus suggestive of N-nitro versus O-nitrito coordination. The positions and shapes of the spectral lines vary only slightly with temperature until motional averaging ensues at approximately 150 K. The pattern of motional averaging in the variable-temperature EPR spectra and EPR studies of Fe(III)NO(2)(-)/Fe(II)NO hybrids suggest that one of two species is present in both of the alpha and beta subunits, while the other is exclusive to the beta subunit. Our results also reconfirm that the affinity of nitrite for metHb is of millimolar magnitude, thereby making a direct role for nitrite in physiological hypoxic vasodilation difficult to justify.