Electrochemical characteristics of the immobilization of calf thymus DNA molecules on multi-walled carbon nanotubes

Immobilization of DNA on carbon nanotubes plays an important role in the development of new types of miniature DNA biosensors. Electrochemical characteristics of the immobilization of calf thymus DNA molecules on the surfaces of multi-walled carbon nanotubes (MWNTs) have been investigated by cyclic voltammetry and electrochemical impedance analysis. The peak currents for Fe(CN)(6)(3-)/Fe(CN)(6)(4-) redox couple observed in the cyclic voltammograms decrease and the electron-transfer resistance (R(et)) obtained from the Nyquist plots increase due to the immobilization of DNA molecules (dsDNA or ssDNA) on the surfaces of MWNTs. Most of calf thymus DNA are covalently immobilized on MWNTs via diimide-activated amidation between the carboxylic acid groups on the carbon nanotubes and the amino groups on DNA bases, though the direct adsorption of the DNA molecules on MWNTs can be observed. Additionally, the interaction between DNA molecules immobilized on MWNTs and small biomolecules (ethidium bromide) can be observed obviously by cyclic voltammetry and electrochemical impedance analysis. This implies that the DNA molecules immobilized at the surface of MWNTs, with little structure change, still has the ability to interact with small biomolecules.     

Selective synthesis of fullerenol derivatives with terminal alkyne and crown ether addends

A series of isomerically pure alkynyl-substituted fullerenol derivatives such as C(60)(OH)(6)(O(CH(2))(3)CCH)(2) were synthesized through Lewis acid catalyzed epoxy ring opening and/or S(N)1 replacement reactions starting from the fullerene-mixed peroxide C(60)(O)(t-BuOO)(4). Copper-catalyzed azide-alkyne cycloaddition readily converted the terminal alkynyl groups into triazole groups. Intramolecular oxidative alkyne coupling afforded a fullerenyl crown ether derivative.     

Nonleaching antibacterial glass surfaces via "Grafting Onto": the effect of the number of quaternary ammonium groups on biocidal activity

Antimicrobial surfaces were prepared using the "grafting onto" technique. Well-defined block copolymers containing poly(2-(dimethylamino)ethyl methacrylate) and poly(3-(trimethoxysilyl)propyl methacrylate) segments (PDMAEMA/PTMSPMA) and corresponding random copolymers were prepared via atom transfer radical polymerization (ATRP), followed by covalent attachment to a glass surface through reaction of the trimethoxysilyl groups with surface silanol groups. The density of quaternary ammonium (QA) groups available to bind small molecules in solution increased with polymer solution concentration and immobilization time. For the PDMAEMA 97- b-PTMSPMA xdiblock copolymers with a fixed length of PDMAEMA segment (degree of polymerization (DP) = 97) and varied lengths of PTMSPMA segments, maximal available surface charge was observed when the ratio of DP PDMAEMA to DP PTMSPMA was 5:1. The tertiary amino groups in immobilized PDMAEMA segments were reacted with ethyl bromide to form QA groups. Alternatively, block copolymers with prequaternized PDMAEMA segments were attached to surfaces. Biocidal activity of the surfaces with grafted polymers versus Escherichia coli ( E. coli) increased with the density of available QA units on the surface. The number of bacteria killed by the surface increased from 0.06 x 10(5) units/cm2 to 0.6 x 10(5) units/cm2, when the density of surface QA increased from 1.0 x 10(14) unit/cm2 to 6.0 x 10(14) unit/cm2. The killing efficiency of QA on all surfaces was similar with approximately 1 x 10(10) units of QA needed to kill one bacterium. The AFM analysis indicated that grafting onto the surface resulted in small patches of highly concentrated polymer. These patches appear to increase the killing efficiency as compared to surfaces prepared by grafting onto with the same average polymer density but with a uniform distribution.     

Computational studies on the photophysical properties and NMR fluxionality of dinuclear platinum(II) A-frame alkynyl diphosphine complexes

The structural geometry, electronic structure, photophysical properties, and the fluxional behavior of a series of A-frame diplatinum alkynyl complexes, [Pt(2)(μ-dppm)(2)(μ-C≡CR)(C≡CR)(2)](+) [R = (t)Bu (1), C(6)H(5) (2), C(6)H(4)Ph-p (3), C(6)H(4)Et-p (4), C(6)H(4)OMe-p (5); dppm = bis(diphenylphosphino)methane], have been studied by density functional theory (DFT) and time-dependent TD-DFT associated with conductor-like polarizable continuum model (CPCM) calculations. The results show that the Pt···Pt distance strongly depends on the binding mode of the alkynyl ligands. A significantly shorter Pt···Pt distance is found in the symmetrical form, in which the bridging alkynyl ligand is σ-bound to the two metal centers, than in the unsymmetrical form where the alkynyl ligand is σ-bound to one metal and π-bound to another. For the two structural forms in 1-5, both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels show a dependence on the nature of the substituents attached to the alkynyl ligand. The energies of the HOMO and LUMO are found to increase and decrease, respectively, from R = (t)Bu to R = Ph and to R = C(6)H(4)Ph-p, because of the increase of the π- conjugation of the alkynyl ligand. On the basis of the TDDFT/CPCM calculations, the low-energy absorption band consists of two types of transitions, which are ligand-to-ligand charge-transfer (LLCT) [π(alkynyl) → σ*(dppm)]/metal-centered MC [dσ*(Pt(2)) → pσ(Pt(2))] transitions as well as interligand π → π* transition from the terminal alkynyl ligands to the bridging alkynyl ligand mixed with metal-metal-to-ligand charge transfer MMLCT [dσ*(Pt(2)) → π*(bridging alkynyl)] transition. The latter transition is lower in energy than the former. The calculation also indicates that the emission for the complexes originates from the triplet interligand π(terminal alkynyls) → π*(bridging alkynyl)/MMLCT [dσ*(Pt(2)) → π*(bridging alkynyl)] excited state. In terms of the fluxional behavior, calculations have been performed to study the details of the mechanisms for the three fluxional processes, which are the σ,π-alkynyl exchange, the ring-flipping, and the bridging-to-terminal alkynyl exchange processes.     

Adsorption and wetting characterization of hydrophobic SBA-15 silicas

This work describes adsorption and wetting characterization of hydrophobic ordered mesoporous silicas (OMSs) with the SBA-15 motif. Three synthetic approaches to prepare hydrophobic SBA-15 silicas were explored: grafting with (1) covalently-attached monolayers (CAMs) of C(n)H(2)(n+1)Si(CH(3))(2)N(CH(3))(2), (2) self-assembled monolayers (SAMs) of C(n)H(2)(n+1)Si(OEt)(3), and (3) direct ("one-pot") co-condensation of TEOS with C(n)H(2)(n+1)Si(OEt)(3) in presence of P123 (n=1-18). The materials prepared were characterized by nitrogen adsorption, TEM, and chemical analysis. The surface properties of the materials were assessed by water contact angles (CAs) and by BET C constants. The results showed that, while loadings of the alkyl groups (%C) were comparable, the surface properties and pore ordering of the materials prepared through different methods were quite different. The best quality hydrophobic surfaces were prepared for SBA-15 grafted with CAMs of alkylsilanes. For these materials, the water CAs were above ～120°/100° (adv/rec) and BET C constants were in the range of ～15-25, indicating uniform low-energy surfaces of closely packed alkyl groups on external and internal surfaces of the pores respectively. Moreover, surfaces grafted with the long-chained (C(12)-C(18)) silanes showed super-hydrophobic behavior (CAs～150-180°) and extremely low adhesion for water. The pore uniformity of parental SBA-15 was largely preserved and the pore volume and pore diameter were consistent with the formation of a single layer of alkylsilyl groups inside the pores. Post-synthesis grafting of SBA-15 with SAMs worked not as well as CAMs: the surfaces prepared demonstrated lower water CAs and higher BET C constants, thereby indicating a small amount of accessible polar groups (Si-OH) related to packing constrains for SAMs supported on highly curved surfaces of mesopores. The co-condensation method produced substantially more disordered materials and less hydrophobic surfaces than any of the grafting methods. The surfaces of these materials showed low water CAs and high BET C constants (～100-200) thereby demonstrating a non-uniform surface coverage and presence of unmodified silica. It is concluded that CAMs chemistry is the most efficient approach in preparation of the functionalized OMS materials with uniform surfaces and pores.     

Hydrolytic stability of organic monolayers supported on TiO2 and ZrO2

The hydrolytic stability of C18 monolayers supported on TiO2 and ZrO2 was studied. Three types of monolayers were prepared from the following octadecyl modifiers: (1) octadecyldimethylchlorosilane (C18H37Si(CH3)2Cl); (2) octadecylsilane (C18H37SiH3); and (3) octadecylphosphonic acid (C18H37P(O)(OH)2). The hydrolysis of the surfaces prepared was studied under static conditions at 25 and 65 degrees C at pH 1-10. On the basis of the loss of grafted material, the stability of the monolayers fall in the following range: C18H37P(O)(OH)2 > or = C18H37SiH3 > C18H37Si(CH3)2Cl. At 25 degrees C, monolayers from C18H37P(O)(OH)2 showed only approximately 2-5% loss in grafting density after one week at pH 1-10. The high stability of these monolayers was explained because of the strong interactions of the phosphonic acids with the substrates. Monolayers from C18H37Si(CH3)2Cl showed poor hydrolytic stability at any pH, which was explained because of the low stability of Ti-O-Si and Zr-O-Si bonds. Unlike monofunctional silanes, trifunctional silane (C18H37SiH3) yielded surfaces that showed good hydrolytic stability. This suggests that the stability of the monolayers from trifunctional silanes is primarily due to "horizontal" bonding (Si-O-Si or Si-OH...HO-Si) rather than due to bondingwith the matrix (M-O-Si). At 65 degrees C, all C18 surfaces become more susceptible to hydrolysis; however, the trend observed for 25 degrees C remained unchanged. Low-temperature nitrogen adsorption was used to study the adsorption properties of the monolayers as a function of their grafting density. The energy of adsorption interactions showed a significant increase as the grafting density of the monolayers decreased. The order of the alkyl groups in the monolayers, as assessed from CH2 stretching, decreased as the grafting density of the monolayers decreased.     

Carba-closo-dodecaborates with one or two alkynyl substituents bonded to boron

Salts of the carba-closo-dodecaborate anion with one or two phenyl- or trimethylsilylalkynyl substituents were synthesized by Pd-catalyzed Kumada-type cross-coupling reactions of the corresponding iodinated clusters with alkynyl Grignard reagents. Selective monofunctionalization in the 7- and 12-position of the {closo-CB(11)} cluster was achieved, resulting in salts of the anions: [1-R-12-R'C[triple bond]C-closo-CB(11)H(10)](-) (R = H, Ph; R' = Ph, Me(3)Si (1-4)), [12-Hal-7-PhC[triple bond]C-closo-CB(11)H(10)](-) (Hal = F (5), Cl (6), Br (7)), and [12-F-7-Me(3)SiC[triple bond]C-closo-CB(11)H(10)](-) (8). Furthermore, the disubstituted derivatives [7,12-(RC[triple bond]C)(2)-closo-CB(11)H(10)](-) (R = Ph (9), Me(3)Si (10)) are described. All salts were characterized by multi-NMR, IR, and Raman spectroscopy as well as by mass spectrometry (MALDI). The crystal structures of Cs(+)1 and [Et(4)N](+)6 were determined by single-crystal X-ray diffraction. The spectroscopic and structural properties are compared to values derived from DFT calculations and to data of related boron species with alkynyl groups.     

聚醚醚酮表面的亲水改性和胶原蛋白固定化

采用紫外光接枝法对聚醚醚酮(PEEK)表面进行化学修饰和生物分子固定化.首先向PEEK表面引入亲水性的丙烯酰胺,并以此为反应位点通过戊二醛将胶原和胶原蛋白固定在PEEK表面.用接触角测定仪、扫描电镜、荧光标记和X射线光电子能谱等对改性薄膜进行了表征.结果表明,PEEK上丙烯酰胺的接枝密度高达50.9μg/cm~2;改性薄膜表面浸润性显著提高,水接触角最低降至(22±3)°.荧光标记胶原固定的PEEK薄膜荧光发射光谱强度最高,并在X射线光电子能谱中检测到N元素,表明胶原已固定化,固定胶原蛋白的浓度为10.2μg/cm~2.     

Chemical modifications of Au/SiO2 template substrates for patterned biofunctional surfaces

The aim of this work was to create patterned surfaces for localized and specific biochemical recognition. For this purpose, we have developed a protocol for orthogonal and material-selective surface modifications of microfabricated patterned surfaces composed of SiO(2) areas (100 μm diameter) surrounded by Au. The SiO(2) spots were chemically modified by a sequence of reactions (silanization using an amine-terminated silane (APTES), followed by amine coupling of a biotin analogue and biospecific recognition) to achieve efficient immobilization of streptavidin in a functional form. The surrounding Au was rendered inert to protein adsorption by modification by HS(CH(2))(10)CONH(CH(2))(2)(OCH(2)CH(2))(7)OH (thiol-OEG). The surface modification protocol was developed by testing separately homogeneous SiO(2) and Au surfaces, to obtain the two following results: (i) SiO(2) surfaces which allowed the grafting of streptavidin, and subsequent immobilization of biotinylated antibodies, and (ii) Au surfaces showing almost no affinity for the same streptavidin and antibody solutions. The surface interactions were monitored by quartz crystal microbalance with dissipation monitoring (QCM-D), and chemical analyses were performed by polarization modulation-reflexion absorption infrared spectroscopy (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS) to assess the validity of the initial orthogonal assembly of APTES and thiol-OEG. Eventually, microscopy imaging of the modified Au/SiO(2) patterned substrates validated the specific binding of streptavidin on the SiO(2)/APTES areas, as well as the subsequent binding of biotinylated anti-rIgG and further detection of fluorescent rIgG on the functionalized SiO(2) areas. These results demonstrate a successful protocol for the preparation of patterned biofunctional surfaces, based on microfabricated Au/SiO(2) templates and supported by careful surface analysis. The strong immobilization of the biomolecules resulting from the described protocol is advantageous in particular for micropatterned substrates for cell-surface interactions.     

Copper(I) alkynyl clusters, [Cu(x+y)(hfac)(x)(C[triple chemical bond]CR)(y)], with Cu(10)-Cu(12) cores

The facile syntheses and the structures of five new Cu(I) alkynyl clusters, [Cu(12)(hfac)(8)(C[triple chemical bond]CnPr)(4)(thf)(6)]xTHF (1), [Cu(12)(hfac)(8)(C[triple chemical bond]CtBu)(4)] (2), [Cu(12)(hfac)(8)(C[triple chemical bond]CSiMe(3))(4)] (3), [Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(4)(diethyl ether)]/[Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(3)(C[triple chemical bond]CnPr)(diethyl ether)] (4) and [Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(4)(diethyl ether)] (5) are reported, in which hfacH=1,1,1,5,5,5-hexafluoropentan-2,4-dione. The first independent molecule found in the crystals of 4 (4 a) proved to be chemically identical to 5. The Cu(10) and Cu(12) cores in these clusters are based on a central "square" Cu(4)C(4) unit. Whilst the connectivities of the Cu(10) or Cu(12) units remain identical the geometries vary considerably and depend on the bulk of the alkynyl group, weak coordination of ether molecules to copper atoms in the core and CuO intramolecular contacts formed between Cu-hfac units on the periphery of the cluster. Similar intermolecular contacts and interlocking of Cu-hfac units are formed in the simple model complex [Cu(2)(hfac)(2)(HC[triple chemical bond]CtBu)] (6). When linear alkynes, C(n)H(2n+1)C[triple chemical bond]CH, are used in the synthesis and non-coordinating solvents are used in the workup, further association of the Cu(4)C(4) cores occurs and clusters with more than eighteen copper atoms are isolated.     

Effect of applied potential on arylmethyl films oxidatively grafted to carbon surfaces

Arylmethyl films have been grafted to glassy carbon surfaces and to pyrolyzed photoresist films (PPFs) by electrochemical oxidation of 1-naphthylmethylcarboxylate and 4-methoxybenzylcarboxylate. Atomic force microscopy (AFM) and electrochemistry were used to characterize the as-prepared films and to monitor changes induced by post-preparation treatments. Film thickness was measured by depth profiling using an AFM tip to remove film from the PPF surface. Surface coverage of electroactive modifiers was estimated from cyclic voltammetry, and monitoring the response of a solution-based redox probe at grafted surfaces gave a qualitative indication of changes in film properties. For preparation of the films, the maximum film thickness increased with the potential applied during grafting, and all films were of multilayer thickness. The apparent rate of electron transfer for the Fe(CN)(6)3-/Fe(CN)(6)4- couple was very low at as-prepared films. After film-grafted electrodes were transferred to pure acetonitrile-electrolyte solution and subjected to negative potential excursions, the response of the Fe(CN)(6)3-/Fe(CN)(6)4- couple changed and was consistent with faster electron-transfer kinetics, the film thickness decreased and the surface roughness increased substantially. Applying a positive potential to the treated film reversed changes in film thickness, but the voltammetric response of the Fe(CN)(6)3-/Fe(CN)(6)4- couple remained kinetically fast. After as-prepared films were subjected to positive applied potentials in acetonitrile-electrolyte solution, the apparent rate of electron transfer for the Fe(CN)(6)3-/Fe(CN)(6)4- couple remained very slow and the measured film thickness was the same or greater than that before treatment at positive potentials. Mechanisms are considered to explain the observed effects of applied potential on film characteristics.     

Covalent immobilization of chitosan on surfaces with anchoring layers of poly(glycidyl methacrylate) and maleic anhydride copolymers

The method for producing chitosan coatings on solid surfaces with anchoring layers of poly(glycidyl methacrylate) and maleic anhydride copolymers has been proposed. It is shown that, owing to a high reactivity of epoxy and anhydride groups, the efficiency of immobilization and the stability of the coatings are considerably higher than those prepared by the conventional method of chitosan grafting onto the surface modified by poly(acrylic acid). The properties of chitosan coatings are examined via atomic force microscopy, X-ray photoelectron spectroscopy, ellipsometry, and electrokinetic measurements. Depending on the anchoring layer used, the total thickness of the coatings is 6–16 nm with an rms roughness less than 1.2 nm, while the isoelectric points of the surfaces modified with chitosan are located in the pH range 5–6.     

Glass surfaces grafted with high-density poly(ethylene glycol) as substrates for DNA oligonucleotide microarrays

Surfaces carrying a dense layer of poly(ethylene glycol) (PEG) were prepared, characterized, and tested as substrates for DNA oligonucleotide microarrays. PEG bis(amine) with a molecular weight of 2000 was grafted onto silanized glass slides bearing aldehyde groups. After grafting, the terminal amino groups of the PEG layer were derivatized with the heterobifunctional cross-linker succinimidyl 4-[p-maleimidophenyl]butyrate to permit the immobilization of thiol-modified DNA oligonucleotides. The stepwise chemical modification was validated with X-ray photoelectron spectroscopy. Goniometry indicated that the PEG grafting procedure reduced surface inhomogeneities present after the silanization step, while atomic force microscopy and ellipsometry confirmed that the PEG layer was dense and monomolecular. Hybridization assays using DNA oligonucleotides and fluorescence imaging showed that PEG grafting improved the yield in hybridization 4-fold compared to non-PEGylated maleimide-derivatized surfaces. In addition, the PEG layer reduced the nonspecific adsorption of DNA by a factor of up to 13, demonstrating that surfaces with a dense PEG layer represent suitable substrates for DNA oligonucleotide microarrays.     

Surface modification of nanoporous alumina surfaces with poly(ethylene glycol)

Nanoporous alumina surfaces have a variety of applications in biosensors, biofiltration, and targeted drug delivery. However, the fabrication route to create these nanopores in alumina results in surface defects in the crystal lattice. This results in inherent charge on the porous surface causing biofouling, that is, nonspecific adsorption of biomolecules. Poly(ethylene glycol) (PEG) is known to form biocompatible nonfouling films on silicon surfaces. However, its application to alumina surfaces is very limited and has not been well investigated. In this study, we have covalently attached PEG to nanoporous alumina surfaces to improve their nonfouling properties. A PEG-silane coupling technique was used to modify the surface. Different concentrations of PEG for different immobilization times were used to form PEG films of various grafting densities. X-ray photoelectron spectroscopy (XPS) was used to verify the presence of PEG moieties on the alumina surface. High-resolution C1s spectra show that with an increase in concentration and immobilization time, the grafting density of PEG also increases. Further, a standard overlayer model was used to calculate the thickness of PEG films formed using the XPS intensities of the Al2p peaks. The films formed by this technique are less than 2.5 nm thick, suggesting that such films will not clog the pores which are in the range of 70-80 nm.     

Dissociation dynamics of asymmetric alkynyl(aryl)iodonium radicals: an ab initio DRC approach to predict the surface functionalization selectivity

The dissociation process of neutral open-shell [4-F-(C(6)H(4))-I-C≡C-(CH(2))(4)-Cl] and [4-NO(2)-(C(6)H(4))-I-C≡C-(CH(2))(4)-Cl] asymmetric iodonium radicals was studied theoretically. Vertical electron affinities and DRC (dynamic reaction coordinate) results were obtained and compared with experimental evidence. In particular, the fluorine and nitro substituent groups were selected because of (i) their opposite electron-withdrawing/electron-donating effects and (ii) experimental evidence that the grafting ability, in terms of alkynyl/aryl grafting ratio, increases with decreasing electron-withdrawing nature of the para-position substituent on the phenyl ring. DRC results show that the dissociation dynamics of the iodine-alkynyl carbon bond, for the nitro-substituted iodonium, occurs on a longer time scale than that of the fluorine-substituted iodonium. This finding is in agreement with the overall experimental results.     

Endohedral beryllium atoms in ten-vertex germanium clusters: effect of a small interstitial atom on the cluster geometry

Ten-vertex clusters are unusually versatile because polyhedra with 3-, 4-, and 5-fold symmetry are possible and are found in experimentally known structures. Such clusters therefore provide useful probes for subtle effects on cluster structure such as changing the electron count or introducing an interstitial atom. In this connection, DFT shows that one of the smallest possible interstitial atoms, namely beryllium, has relatively little effect on the structures of Be@Ge(10)(z) (z = +2, 0, -2, -4) clusters. Thus the same C(3v) and D(4d) polyhedra are found as the lowest energy structures for the isoelectronic pairs Be@Ge(10)(2+)/Ge(10) and Be@Ge(10)/Ge(10)(2-). Even for the more complicated potential energy surfaces of the Be@Ge(10)(2-)/Ge(10)(4-) and Be@Ge(10)(4-)/Ge(10)(6-) systems, the lowest energy structures are remarkably similar. Thus the same C(2v) structures are the global minima for both Be@Ge(10)(2-) and Ge(10)(4-). Similarly, the same slipped pentagonal prism structures are the global minima for both Be@Ge(10)(4-) and Ge(10)(6-).     

Detecting the chemoselective ligation of peptides to silicon with the use of cobalt-carbonyl labels

While fluorescent-based methods are generally used to detect the immobilization and the interactions of biomolecules to solid supports, recent studies have shown their limitations in the case of silicon surfaces. As an alternative, we investigated the synthesis of peptides labeled with a metal transition complex and their subsequent immobilization to the silicon surfaces. The feasibility of using such probes has been explored by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). By starting with hydrogen-terminated or oxidized silicon surfaces, we functionalized those surfaces with semicarbazide groups and showed the site-specific linkage of glyoxylyl peptides labeled with a Co2(CO)6 moiety.     

Aminocyclopentadienyl ruthenium complexes as racemization catalysts for dynamic kinetic resolution of secondary alcohols at ambient temperature

Aminocyclopentadienyl ruthenium complexes, which can be used as room-temperature racemization catalysts with lipases in the dynamic kinetic resolution (DKR) of secondary alcohols, were synthesized from cyclopenta-2,4-dienimines, Ru(3)(CO)(12), and CHCl(3): [2,3,4,5-Ph(4)(eta(5)-C(4)CNHR)]Ru(CO)(2)Cl (4: R = i-Pr; 5: R = n-Pr; 6: R = t-Bu), [2,5-Me(2)-3,4-Ph(2)(eta(5)-C(4)CNHR)]Ru(CO)(2)Cl (7: R = i-Pr; 8: R = Ph), and [2,3,4,5-Ph(4)(eta(5)-C(4)CNHAr)]Ru(CO)(2)Cl (9: Ar = p-NO(2)C(6)H(4); 10: Ar = p-ClC(6)H(4); 11: Ar = Ph; 12: Ar = p-OMeC(6)H(4); 13: Ar = p-NMe(2)C(6)H(4)). The tests in the racemization of (S)-4-phenyl-2-butanol showed that 7 is the most active catalyst, although the difference decreased in the DKR. Complex 4 was used in the DKR of various alcohols; at room temperature, not only simple alcohols but also functionalized ones such as allylic alcohols, alkynyl alcohols, diols, hydroxyl esters, and chlorohydrins were successfully transformed to chiral acetates. In mechanistic studies for the catalytic racemization, ruthenium hydride 14 appeared to be a key species. It was the major organometallic species in the racemization of (S)-1-phenylethanol with 4 and potassium tert-butoxide. In a separate experiment, (S)-1-phenylethanol was racemized catalytically by 14 in the presence of acetophenone.     

Synthesis of molecular brushes by "grafting onto" method: combination of ATRP and click reactions

Molecular brushes (densely grafted polymers or bottle-brush macromolecules) were synthesized by the "grafting onto" method via combination of atom transfer radical polymerization (ATRP) and "click" reactions. Linear poly(2-hydroxyethyl methacrylate) (PHEMA) polymers were synthesized first by ATRP. After esterification reactions between pentynoic acid and the hydroxyl side groups, polymeric backbones with alkynyl side groups on essentially every monomer unit (PHEMA-alkyne) were obtained. Five kinds of azido-terminated polymeric side chains (SCs) with different chemical compositions and molecular weights were used, including poly(ethylene glycol)-N3 (PEO-N3), polystyrene-N3, poly(n-butyl acrylate)-N3, and poly(n-butyl acrylate)-b-polystyrene-N3. All click coupling reactions between alkyne-containing polymeric backbones (PHEMA-alkyne) and azido-terminated polymeric SCs were completed within 3 h. The grafting density of the obtained molecular brushes was affected by several factors, including the molecular weights and the chemical structures of the linear SCs, as well as the initial molar ratio of linear chains to alkynyl groups. When linear polymers with "thinner" structure and lower molecular weight, e.g., PEO-N3 with Mn = 775 g/mol, were reacted with PHEMA-alkyne (degree of polymerization = 210) at a high molar ratio of linear chains to alkynyl groups in the backbone, the brush copolymers with the highest grafting density were obtained (Y(grafting) = 88%). This result indicates that the average number of SCs was ca. 186 per brush molecule and the average molecular weight of the brush molecules was ca. 190 kg/mol.     

High-nuclearity Pt-Tl-Fe complexes: structural, electrochemistry, and spectroelectrochemistry studies

A series of heteropolynuclear Pt-Tl-Fe complexes have been synthesized and structurally characterized. The final structures strongly depend on the geometry of the precursor and the Pt/Tl ratio used. Thus, the anionic heteroleptic cis-configured [cis-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and [Pt(bzq)(C≡CFc)(2)](-) (Fc = ferrocenyl) complexes react with Tl(+) to form discrete octanuclear (PPh(3)Me)(2)[{trans,cis,cis-PtTl(C(6)F(5))(2)(C≡CFc)(2)}(2)] (1), [PtTl(bzq)(C≡CFc)(2)](2) (5; bzq = benzoquinolate), and decanuclear [trans,cis,cis-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](2) (3) derivatives, stabilized by both Pt(II)···Tl(I) and Tl(I)···η(2)(alkynyl) bonds. By contrast, Q(2)[trans-Pt(C(6)F(5))(2)(C≡CFc)(2)] (Q = NBu(4)) reacts with Tl(+) to give the one-dimensional (1-D) anionic [(NBu(4)){trans,trans,trans-PtTl(C(6)F(5))(2)(C≡CFc)(2)}](n) (2) and neutral [trans,trans,trans-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](n) (4) polymeric chains based on [PtFc(2)](2-) platinate fragments and Tl(+) (2) or [Tl···Tl](2+) (4) units, respectively, connected by Pt(II)···Tl(I) and secondary weak κ-η(1) (2) or η(2) (4) alkynyl···Tl(I) bonding. The formation of 1-4 is reversible, and thus treatment of neutral 3 and 4 with PPh(3)MeBr causes the precipitation of TlBr, returning toward the formation of the anionic 1 and 2' (Q = PPh(3)Me). Two slightly different pseudopolymorphs were found for 2', depending on the crystallization solvent. Finally, the reaction of the homoleptic [Pt(C≡CFc)(4)](2-) with 2 equiv of Tl(+) affords the tetradecanuclear sandwich type complex [Pt(2)Tl(4)(C≡CFc)(8)] (6). Electrochemical, spectroelectrochemical, and theoretical studies have been carried out to elucidate the effect produced by the interaction of the Tl(+) with the Pt-C≡CFc fragments. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of 1-5 reveal that, in general, neutralization of the anionic fragments increases the stability of the fully oxidized species and gives higher E(1/2) (Fc) values than those observed in their precursors, increasing with the number of Pt-Tl bonding interactions. However, the electronic communication between Fc groups is reduced or even lost upon Tl(+) coordination, as confirmed by electrochemical (CVs and DPVs voltammograms, 1-5) and spectroelectrochemical (UV-vis-NIR, 2-4) studies. Complexes 2 and 4 still display some electronic interaction between the Fc groups, supported by the presence of an IVCT band in their UV-vis-NIR spectra of oxidized species and additional comparative DFT calculations with the precursor [trans-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and complex 3.