Two asymmetrically structured model compounds for the hydrogen-generating [Fe-Fe]-hydrogenase active site were investigated to determine the ultrafast photodynamics, structural intermediates, and photoproducts compared to more common symmetric di-iron species. The bidentate-ligand-containing compounds studied were Fe2(μ-S2C3H6)(CO)4(bipy), 1, and Fe2(μ-S2C3H6)(CO)4(phen), 2, in dilute room temperature acetonitrile solution and low-temperature 2Me-THF matrix isolation using static FTIR difference and time-resolved infrared spectroscopic methods (TRIR). Ultraviolet-visible spectra were also compared to time-dependent density functional theory (TD-DFT) to ascertain the orbital origins of long wavelength electronic absorption features. The spectroscopic evidence supports the conclusions that only a propyl-bridge flip occurs in low-temperature matrix, while early time CO ejection leads to the formation of solvated isomeric species on the 25 ps time scale in room temperature solution.

Photolysis of RuCl3(eta(1)-NO)(PPh3)(2) in poly (vinyl chloride) (PVC) matrices at 85 K results in reversible linkage isomerism of the nitrosyl ligand to form the isonitrosyl complex RuCl3(eta(1)-ON)(PPh3)(2). Metal-to-ligand charge-transfer (MLCT) excitation of the isoelectronic phenylazo complex, RuCl3(eta 1-N2Ph) (PPh3)(2), has previously been shown to result in generation of the phenyl radical, presumably through decomposition a photogenerated diazenyl radical. Examination of this photolysis in a PVC matrix at cryogenic temperatures has permitted direct observation of an isotopically sensitive product band that may be assigned to a 17-electron ruthenium dinitrogen species, suggesting that this photochemical decomposition does not proceed through formation of a diazenyl intermediate but through homolytic cleavage of the parent diazonium complex to give the phenyl radical and the 17-electron RuCl3(eta(1)-N-2) (PPh3)(2).

Frozen-matrix photolysis studies of M(CO)(2)(N2Ph)(PPh3)(2) cations (M = Fe and Ru) have revealed end-on/side-on photochemical linkage isomerism of the phenylazo ligand. The previously reported solvent-dependent vibrational bands of the Ru(CO)(2)(N2Ph)(PPh3)(2) cation have now been identified as an equilibrium between the two linkage isomers. DFT calculations have been performed on the end-on and side-on isomers of the iron and ruthenium complexes.

Photolysis of the permanganate anion, MnO4-, in tetralkylammonium tetrafluoroborate matrices at 85 K results in formation of a single product, the metastable manganese(V) peroxo complex MnO2(eta(2)-O-2)(-). Although previously unobserved, this peroxo species has been postulated to be an intermediate in the photodecomposition of permanganate, yielding O-2 and MnO2. Results from variable-temperature and intensity-dependence photolysis experiments in solution, however, suggest that MnO2(eta(2)-O-2)(-) does not lose O-2 thermally or photochemically and is not an intermediate in the photodecomposition reaction. A mechanism is proposed in which MnO2(eta(2)-O-2)(-) is formed through vibrational relaxation of an excited [MnO4-]* species, which may also follow an alternative relaxation pathway that results in the formation of MnO2- and O-2(-) photodecomposition products.

The [FeFe]-hydrogenase model complexes [(μ-pdt){Fe(CO)3 }2 ], [(μ-edt){Fe(CO)3 }2 ], and [(μ-mdt){Fe(CO)3 }2 ], where pdt=1,3-propanedithiolate, edt=1,2-ethanedithiolate, and mdt=methanedithiolate, undergo wavelength dependent photodecarbonylation in hydrocarbon matrices at 85 K resulting in multiple decarbonylation isomers. As previously reported in time-resolved solution photolysis experiments, the major photoproduct is attributed to a basal carbonyl-loss species. Apical carbonyl-loss isomers are also generated and may undergo secondary photolysis, resulting in β-hydride activation of the alkyldithiolate bridge, as well as formation of bridging carbonyl isomers. For [(μ-bdt){Fe(CO)3 }2 ], (bdt=1,2-benzenedithiolate), apical photodecarbonylation results in generation of a 10 π-electron aromatic FeS2 C6 H4 metallacycle that coordinates the remaining iron through an η(5) mode.

Low energy photolysis of TpM(CO)2(η(3)-C3H4R), where Tp = tris(pyrazolyl)borate, M = Mo or W, and R = 2-H or 2-Me in PVC matrices at 85 K results in exo/gauche isomerism of the allyl ligand. This transformation comes in contrast to the behaviour observed in cyclopentadienyl analogues which undergo exo/endo isomerism. DFT computations reveal an η(3) → η(1)* → η(3) mechanism for the allyl rotameric interconversion where the η(1)*-allyl intermediate is generated upon MLCT excitation.

Successful catalytic dehydrogenation of aminoborane, H3NBH3, prompted questions as to the potential role of N-H oxidative addition in the mechanisms of these processes. N-H oxidative addition reactions are rare, and in all cases appear to involve initial dative bonding to the metal by the amine lone pairs followed by transfer of a proton to the basic metal. Aminoborane and its trimethylborane derivative block this mechanism and, in principle, should permit authentic N-H oxidative attrition to occur. Extensive experimental work failed to confirm this hypothesis. In all cases either B-H complexation or oxidative addition of solvent C-H bonds dominate the chemistry.

UV photolysis of the nitridoosmate(VIII) anion, OsO3 N(-) , in low-temperature frozen matrices results in nitrogen-oxygen bond formation to give the Os(II) nitrosyl complex OsO2 (NO)(-) . Photolysis of the Os(II) nitrosyl product with visible wavelengths results in reversion to the parent Os(VIII) complex. Formally a six-electron reductive elimination and oxidative addition, respectively, this represents the first reported example of such an intramolecular transformation. DFT modelling of this reaction proceeds through a step-wise mechanism taking place through a side-on nitroxyl Os(VI) intermediate, OsO2 (η(2) -NO)(-) .

The anodic oxidation mechanism of RhCp(CO)(PPh3), 1, has been studied in CH2Cl2/0.1 M [NBu4][PF6]. This complex and its analogue RhCp(PPh3)2 had been previously shown to form the fulvalenyl dirhodium complexes [Rh(2)FvL(2)(PPh3)(2)](2+) (Fv = (eta(5),eta(5)-C10H8), L = CO (2(2+)) or PPh3) upon chemical oxidation. The present work investigated the reaction of 1 by variable-temperature electrochemistry and IR spectroelectrochemistry. The radical cation 1(+) initially undergoes a radical-radical coupling reaction, giving the metal-metal bonded dimer dication [Rh2Cp2(CO)(2)(PPh3)(2)](2+) (5(2+)), which dominates at low temperatures. The room-temperature products are best accounted for by hydrogen atom transfer reactions of the dimer dication, affording 2(2+) and the metal hydride [RhCp(CO)(PPh3)H](+). The dimetalate complex [Rh-2(sigma:eta(5)-C5H4)(2)(CO)(2)(PPh3)(2)](2+) (7) may also be formed. The radical cation of the analogue RhCp(CO)(PPh2Me) (3) undergoes very rapid formation of a similar metal metal bonded dimer. A derivative with a large cone angle phosphine, RhCp(CO)((PPr3)-Pr-i) (4), does not show the same tendency toward oxidative dimerization. The monomer/dimer equilibrium [RhCp(CO)L](+) reversible arrow 1/2 [Rh2Cp2(CO)(2)L-2](2+) increasingly favors the dimer in the sequence L = (PPr3)-Pr-i < PPh3 < PPh2Me < PMe3, P(OPh)(3), the latter two being based on earlier work. The implied dinuclear hydrogen atom transfer reactions are not mechanistically well understood, but find analogies in the chemistry of second- and third-row early transition metal complexes.

Probing the specific hydrogen-bonding behavior of thermoplastic polyurethane (TPU) blends using vibrational spectroscopies remains the sin qua non for understanding the link between hydrogen-bonding and phase-segregation behavior. However, current literature holds to more traditional univariate approaches when studying the morphologically interesting normal molecular vibrations of TPUs. In the present study, multivariate analysis, including principal component analysis (PCA) and principal component regression (PCR), is used to scrutinize the relevant Raman bands acquired from a binary mixture of analogous TPU copolymer blends. Considering the near identical behavior of selected spectral regions, PCA was capable of isolating linear and nonlinear composition-dependent trends on PC-scores plots. From here, the PC scores, extracted from wavelengths comprising the carbonyl stretching region (1681-1764 cm(-1)), CH(2) deformations (1380-1500 cm(-1)), aromatic stretch from the hard segment (1617 cm(-1)), and amide II mixed band (1540 cm(-1)), were used to explicitly predict the mole fraction of hard segment present in each blend using PCR. Spectral preprocessing, wavelength selection, and variable scaling were major factors in PCR accurately predicting the weight fraction of each copolymer in spite of the clearly evident, blend-specific spectroscopic behavior.

A thorough analysis of the surface chemistry of silica nanowires has been performed by X-ray photoelectron spectroscopy to investigate unexpected surface changes. Examination of the Si 2p, O 1s, and C 1s core level states before and after exposure of the nanowires to various liquid media showed that silica nanowires are capable of much higher surface hydroxyl concentrations than planar native oxides. It is further demonstrated that the nanowire surface hydroxyl concentration corresponds to the pH of the aqueous media to which the nanowires are exposed. Spectral feature changes due to water exposure similar to those observed for fibronectin binding suggests that fibronectin binding is competitively inhibited by slow changes in surface chemistry resulting from water exposure. (C) 2011 Elsevier B. V. All rights reserved.

A novel fluorescent zinc sensor was designed and synthesized on ordered mesoporous silica material, MCM-41, with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide (QTEPA; 3) using a simple one-step molecular self-assembly of the silane. The solution and solid samples were characterized using solid-state nuclear magnetic resonance, transmission electron microscopy, diffuse-reflectance infrared Fourier transform, and thermogravimetric analysis techniques. The QTEPA-modified MCM-41 (4) shows 3-fold fluorescence emission enhancement and about a 55 nm red shift upon addition of 1 μM Zn(II) ions in a Tris-HCl (pH 7.22) aqueous buffer solution. The UV-vis absorption maximum is at 330 ± 5 nm, and the fluorescence emission maximum wavelength is at 468 nm, with an increase in quantum yield from 0.032 to 0.106 under the same conditions. The presence of other metal ions has no observable effect on the sensitivity and selectivity of 4. This system selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 μM. The MCM-41-based systems have the advantage that they can be employed in aqueous solutions without any aggregation.

Zinc is one of the most important transition metal of physiological importance, existing primarily as a divalent cation. A number of sensors have been developed for Zn(II) detection. Here, we present a novel fluorescent nanosensor for Zn(II) detection using a derivative of 8-aminoquinoline (N-(quinolin-8-yl)-2-(3 (triethoxysilyl)propylamino)acetamide (QTEPA) grafted on silica nanoparticles (SiNPs). These functionalized SiNPs were used to demonstrate specific detection of Zn(II) in tris-HCl buffer (pH 7.22), in yeast cell (Saccharomyces cerevisiae) suspension, and in tap water. The silane QTEPA, SiNPs and final product were characterized using solution and solid state nuclear magnetic resonance, Fourier transform infrared, ultraviolet-visible absorption spectroscopy, transmission electron microscopy, elemental analysis, thermogravimetric techniques, and fluorescence spectroscopy. The nanosensor shows almost 2.8-fold fluorescence emission enhancement and about 55 nm red-shift upon excitation with 330 ± 5 nm wavelength in presence of 1 μM Zn(II) ions in tris-HCl (pH 7.22). The presence of other metal ions has no observable effect on the sensitivity and selectivity of nanosensor. This sensor selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 μM. The sensor shows good applicability in the determination of Zn(II) in tris-HCl buffer and yeast cell environment. Further, it shows enhancement in fluorescence intensity in tap water samples.

Matrix isolation Fourier transform infrared spectroscopy (FTIR) in polyvinyl chloride film (PVC) at 90 K combined with density functional theory calculations (DFT) has been used to study the photochemical reactivity of 15-electron (S=3/2) [PPh4][CpCr(CN)(3)], Cp = eta(5)-C5H5. Photolysis (450 > lambda > 280 nm) results in loss of CN-. DFT calculations support the generation of neutral 13-electron S=3/2 CpCr(CN)(2). Photolysis of [PPh4][CpCr(CN)(3)] in CH2Cl2 under CO atmosphere and in the presence of excess phosphine afforded only recovery of the parent compound.

Full-range mid-infrared spectra were measured during the reaction of CpCo(CO) 2 with nitrosyl chloride by interfacing a rapid-mixing stopped-flow device with an ultra-rapid-scanning Fourier transform infrared (FT-IR) spectrometer having a temporal resolution of 5 ms. Changes to the data acquisition hardware of this spectrometer now allow a sequence of well over 2000 spectra to be collected without interruption. Two transient species were observed spectroscopically during the first 500 ms of the reaction of CpCo(CO) 2 with nitrosyl chloride. The shortest-lived species that was observed, [CpCo(CO) 2 (NO)] + , had a half-life of ∼20 ms at 25 °C and ∼70 ms at 10 °C. This intermediate transformed into a longer-lived (∼0.5 s) intermediate, CpCo(NO)Cl. Potential intermediate species with one CO and one NO ligand, such as [CpCo(CO)(NO)] + and CpCo(CO)(NO)Cl, were not observed, although the possibility that they exist cannot be ruled out.