Time-resolved IR Spectra Research Articles

Visualization of the sequence of changes in the full wavenumber range by two-dimensional correlation spectroscopy

Two-dimensional correlation spectroscopy (2D-COS) is a powerful technique for analyzing changes in vibrational spectra. In this study, we propose a method that can easily visualize the order of changes at all the observed wavenumbers using 2D-COS. We applied it to time-resolved IR spectra of lysozyme subjected to a H–D exchange reaction to determine the order of the rates of the temporal changes associated with H–D exchange. The proposed method was also applied to IR absorption spectra of gas-phase pyrrole clusters. The agreement between the sizes of the experimentally determined clusters and the order of changes was successfully presented.

Meso-Oxoisocorroles: Tunable Antiaromaticity by Metalation and Coordination of Lewis Acids as Well as Aromaticity Reversal in the Triplet Excited State.

The corrole derivative meso-oxoisocorrole has been theoretically predicted to be antiaromatic, despite its formally cross conjugated electronic system. In this study, this prediction has been experimentally proven by the facile preparation of meso-oxoisocorrole via the oxidation of a meso free corrole with MnO2 and its comprehensive characterization using NMR, UV/vis absorption, FT-IR, and transient-absorption spectroscopy, cyclic voltammetry, and X-ray diffraction analysis. Furthermore, the free base meso-oxoisocorrole was metalated by treatment with Ni(acac)2, PdCl2(PhCN)2, and Zn(OAc)2 to give the corresponding metal complexes. These complexes are more strongly antiaromatic, and their degree of paratropicity depends on their planarity. Thus, fine tuning of their antiaromaticity was achieved with concomitant modulation of their HOMO-LUMO gaps. In the presence of tris(pentafluorophenyl)borane, their antiaromaticity is significantly enhanced due to the elongation of the C═O bond, which promotes the polarized C+-O- resonance state. Furthermore, a distinct frequency shift of the C═O vibrational mode in the triplet state was observed in the time-resolved IR spectra in accordance with the Baird rule, which indicates aromaticity reversal in the excited state.

Modeling the IR Spectra of Excited Quadrupole Molecules with Broken Symmetry in Polar Solvents

An approach is developed that allows estimation of excited quadrupole molecule parameters responsible for changes in vibration frequencies in states with symmetry breaking by charge transfer from time-resolved IR spectra. The approach is tested on a molecule like A-π-D-π-A composed of an electron-accepting group A coupled with electron-donating group D by means of π-conjugated bonds, a D pyrrolopyrrole core, and two cyanophenyl acceptors. The expression derived for the IR spectrum of a molecule with symmetry breaking is shown to perfectly describe experimental data. The numerical values of the parameters of asymmetry in a series of solvents with different polarities and the solvent-independent parameters of the molecule itself are determined.

Structure, photodynamic reaction and DNA photocleavage properties of a nitrosyl iron-sulfur cluster (Me4N)2[Fe2S2(NO)4]: A DFT calculation and experimental study.

Density functional theory calculations were performed on the structure of the nitrosyl iron-sulfur cluster (Me4N)2[Fe2S2(NO)4]. The IR spectra were assigned and the electronic ground-state properties in different solvents were analyzed. Dynamic conversion of [Fe2S2(NO)4]2- was analyzed quantitatively using the time-resolved IR spectra in different solvents. Photo irradiation and polarity of solvent obviously affect the reaction rates, which are faster in CH3CN and CH3OH than those in DMSO and water. The calculated orbital energies of HOMOs are higher and those of LUMO-HOMO gap are smaller in CH3CN and CH3OH than those in DMSO and water, which is consistent with the reaction rate and explains the experimental observation. Moreover, the photo-induced nitric oxide (NO) release and cluster conversion was identified using EPR spectra. The photocleavage of pBR322 DNA was observed, both NO and oxygen related free radicals play key roles in the process. The study provides an effective method to monitor the photodynamic reactions for better understanding of the physiological activity of nitrosyl iron-sulfur clusters.

Opening 2,2-diphenyl-2H-chromene to infrared light.

Time-resolved vibrational spectroscopy studies are reported on the photoinduced structural dynamics of 2,2-diphenyl-2H-chromene, a prototypical photochromic compound that undergoes ring opening upon UV radiation. The transient IR absorption measurements in combination with (TD-)DFT calculations have been used to understand in detail the life cycle of such compounds. Excited-state decay and ring opening was found to occur on an ultrafast time scale. Three species have been identified in the time-resolved IR spectra with two short-lived species (on a picosecond timescale) and a final long-lived species that remains after the measurable ns delay range. These species have been assigned to various open isomers using quantum chemical calculations of equilibrium structures and force fields. From the experiments and calculations key conclusions can be drawn on previously suggested models for the photocycle of such compounds, as well as on possible ways to controllably influence the performance of these compounds.

Ammonia Oxidation Reaction Mechanism on Pt-Ir Alloys: A Surface Enhanced Infrared Absorption Spectroscopy Study

Energy and environment are two of the most primary concerns of this century, thus leading to holistic research across numerous disciplines.1 Ammonia electro-oxidation reaction (AOR) is extremely crucial with regards to energy and environment as it holds spotlight in several fields such as wastewater remediation, analytical chemistry and as a source of renewable energy in direct ammonia fuel cells. In addition, AOR is also useful by being the producer of hydrogen via electrolysis.2 Ammonia has a greater promise compared to other compounds like ethanol and methanol due to its carbon-free nature, well-defined production, storage and transportation network and no net increase in carbon dioxide content of the environment.3 However, inadequate performance due to slow kinetics and expensive nature of electrocatalysts have impeded the utilization of ammonia oxidation technology on a large scale. Consequently, large amount of efforts have been put over the years to understand the mechanism properly which can assist in developing highly active and stable electrocatalysts. In this study, a powerful in-situ surface enhanced infrared absorption spectroscopy (SEIRAS) technique with the attenuated total reflection (ATR) was used to examine the mechanism and intermediates over Pt-Ir nanofilm deposited on a silicon hemispherical prism. Pt-Ir was chosen as it is the most promising alloy as electrocatalyst for AOR till date. Intermediates such as NO at 1478-1488 cm-1 previously found over Pt electrode6 and NO2 at 1331 cm-1 earlier found with CeO2-modified platinum catalyst7 were also observed in this study with Pt-Ir, thus establishing their presence at higher potential range. Most importantly, a weak band at 2140 cm-1 representing azide intermediate was also observed for the 1st time using FTIR, previously only seen using in-situ Raman spectroscopy.8 This work, confirming azide intermediate presence at higher potential and affirming the NO and NO2 for Pt-Ir too, provided much clearer understanding of the mechanism and intermediates within the most renowned Gerischer and Mauerer framework, henceforth opening pathway for further efficient AOR electrocatalyst design in future. Fig 1. Time-resolved IR spectra of the Pt-Ir nanofilm acquired simultaneously with the linear sweep voltammogram in 0.2 M NH3-10mM PBS buffer solution (pH 6.96). The reference spectrum was taken at 0.1V. References Liu, J., Liu, B., Ni, Z., Deng, Y., Zhong, C., & Hu, W., Electrochimica Acta 2014, 150, 146-150.Diaz, L. A., Valenzuela-Muñiz, A., Muthuvel, M., & Botte, G. G., Electrochimica Acta 2013, 89, 413-421.Zhong, C., Hu ,W. B., and Cheng Y. F., Journal of Materials Chemistry A 2013, 10, 3216-3238.Vitse, Frederic, Cooper, M., and Botte, G. G., Journal of Power Sources 2005, 1, 18-26.Satyapal, Sunita, et al. Catalysis Today 2007, 3, 246-256.Matsui, T., Suzuki, S., Katayama, Y., Yamauchi, K., Okanishi, T., Muroyama, H., and Eguchi, K.. Langmuir 2015, 31, 11717-11723.Katayama, Y., Okanishi, T., Muroyama, H., Matsui, T., and Eguchi, K., ACS Catalysis 2016, 3, 2026-2034.Vidal-Iglesias, F. J., Solla-Gullón, J., Pérez, J. M., and Aldaz, A.. Electrochemistry Communications 2006, 8, 102-106. Figure 1

Shedding Light on the Photoisomerization Pathway of Donor-Acceptor Stenhouse Adducts.

Donor–acceptor Stenhouse adducts (DASAs) are negative photochromes that hold great promise for a variety of applications. Key to optimizing their switching properties is a detailed understanding of the photoswitching mechanism, which, as yet, is absent. Here we characterize the actinic step of DASA-photoswitching and its key intermediate, which was studied using a combination of ultrafast visible and IR pump–probe spectroscopies and TD-DFT calculations. Comparison of the time-resolved IR spectra with DFT computations allowed to unambiguously identify the structure of the intermediate, confirming that light absorption induces a sequential reaction path in which a Z–E photoisomerization of C2–C3 is followed by a rotation around C3–C4 and a subsequent thermal cyclization step. First and second-generation DASAs share a common photoisomerization mechanism in chlorinated solvents with notable differences in kinetics and lifetimes of the excited states. The photogenerated intermediate of the second-generation DASA was photo-accumulated at low temperature and probed with time-resolved spectroscopy, demonstrating the photoreversibility of the isomerization process. Taken together, these results provide a detailed picture of the DASA isomerization pathway on a molecular level.

Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis

Summary The concept of excited-state aromaticity is receiving much attention in that completely reversed aromaticity in the excited state (so-called aromaticity reversal) provides crucial insight into photostability, photoreactivity, and its application to the photosynthetic mechanism and photoactive materials. Despite this significance, experimental elucidation of excited-state aromaticity is still unsolved, particularly for the excited singlet state. Here, as an unconventional approach, time-resolved IR (TRIR) spectroscopy on aromatic and anti-aromatic hexaphyrin congeners shed light on excited-singlet-state aromaticity. The contrasting spectral features between the Fourier transform IR and TRIR spectra reveal the aromaticity-driven structural changes, corroborating aromaticity reversal in the excited singlet states. Our paradigm for excited-state aromaticity, the correlation of IR spectral features with aromaticity reversal, provides another fundamental key to understanding the role of (anti)aromaticity in the stability, dynamics, and reactivity in the excited singlet state of π-conjugated molecular systems.

Mechanistic Study of Methanol Oxidation over Platinum Electrode in Alkaline Aqueous Solutions

Hydrogen is a clean fuel for stationary, mobile and transportation applications, particularly for fuel cells, but its storage and delivery are still major issues. To overcome these problems, hydrogen has been stored and transported via other chemical compounds, such as alcohols, hydrocarbons, ammonia, etc. Methanol is a promising hydrogen career due to its high volumetric energy density and ease in handling and storage. Direct methanol fuel cells (DMFCs) have been mainly studied with acidic electrolytes and the methanol oxidation mechanism has been clarified to some extent in recent years [1]. However, rare and expensive Pt–based electrocatalysts are normally used in DMFCs. One promising approach to improve this problem is using alkaline electrolytes because of the potential use of non–Pt catalysts. Nevertheless, there are few studies on the methanol oxidation mechanism in alkaline media. In this study, the electrochemical oxidation of methanol over Pt electrode in an alkaline solution was investigated using linear sweep voltammetry and in situ attenuated total reflection infrared (ATR–IR) spectroscopy. The oxidation current of methanol was observed at approximately 0.4–0.9 V in 0.25 M KOH–0.25 M CH3OH in the linear sweep voltammogram (LSV). In the time–resolved IR spectra acquired simultaneously with the LSV, two characteristic bands ascribable to the adsorbed formic acid species (HCOOad) were detected at 1800 cm–1 and 2000 cm–1 in the potential range of 0.1–0.3 V, and their intensity decreased with an increase in potential [2]. Alternatively, the new bands attributable to the aldehyde species (H x CHOad) appeared at 0.2 V in the same wavenumber range. These bands shifted to higher wavenumber with a rise in the potential probably due to the dipole–dipole coupling effect [3], and disappeared above 0.8 V. These results clarified that the formic acid species was oxidized in the initial step of methanol oxidation, followed by the aldehyde species. Therefore, aldehyde species and formic acid species were found to be the intermediates of the methanol oxidation. Since the aldehyde species existed over Pt electrode even at higher potential of 0.8 V, the development of the electrocatalysts active for the H x CHOad oxidation reaction will be required for the enhancement of methanol oxidation in alkaline media. REFERENCES [1] N. M. Markovic, H. A. Gasteiger, P. N. Ross Jr, Electrochim. Acta, 40 (1995) 91–98 [2] G. Samjeske, M. Osawa, Angew. Chem. Int. Ed., 117 (2005) 5840–5844. [3] Y. Y. Yang, J. Ren, H. X. Zhang, Z.Y. Zhou, S. G. Sun, W. B. Cai, Langmuir, 29 (2013) 1709–1716.

Isotopic transient studies of sodium promotion of Pt/Al2O3 for the water–gas shift reaction

The promotional effect of sodium on Pt/Al2O3 catalysts for the water–gas shift (WGS) reaction was investigated with operando FTIR during steady-state and isotopic transient experiments. The highest turnover frequency (TOF) promotion per surface Pt occurred on a 0.82wt.% Pt/Al2O3 catalyst with a 30:1molar ratio of Na:Pt. This catalyst exhibited a TOF of 0.35s−1 at 250°C and 7% CO, 11% H2O, 9% CO2, and 37% H2 compared to 0.43×10−2s−1 on Pt/Al2O3. Operando IR revealed that Na addition modifies CO adsorption on Pt to create more strongly bound, multiply-bonded CO species at 1768cm−1 and 1697cm−1 compared to predominantly linear CO on Na-free Pt/Al2O3 at 2060cm−1. Transient experiments with 12CO/13CO isotope switches showed that the number of carbon-containing active intermediates increased from less than 1% of the surface Pt for Na-free Pt/Al2O3 to nearly 100% of the surface Pt for 20Na:Pt/Al2O3, which indicates that only a small fraction of the Pt surface on the Na-free samples participates in the WGS reaction. From time-resolved IR spectra during transient WGS with 12CO/13CO and 12CO2/13CO2 isotope switches, we propose that surface formate species are spectators for all Na-promoted Pt/Al2O3 catalysts under these WGS conditions. The results suggest that Na promotes Pt/Al2O3 for WGS by modifying the local electronic properties of Pt and creating new H2O activation sites, which provide greater availability of surface OH/H species to react with nearly all CO on the metallic Pt surface through a non-formate pathway.

Ultrafast Structural Fluctuations of Myoglobin-Bound Thiocyanate and Selenocyanate Ions Measured with Two-Dimensional Infrared Photon Echo Spectroscopy.

Structural dynamics within the distal cavity of myoglobin protein is investigated using 2D-IR and IR pump-probe spectroscopy of the N≡C stretch modes of heme-bound thiocyanate and selenocyanate ions. Although myoglobin-bound thiocyanate group shows a doublet in its IR absorption spectrum, no cross peaks originating from chemical exchange between the two components are observed in the time-resolved 2D IR spectra within the experimental time window. Frequency-frequency correlation functions of the two studied anionic ligands are obtained by means of a few different analysis approaches; these functions were then used to elucidate the differences in structural fluctuation around ligand, ligand-protein interactions, and the degree of structural heterogeneity within the hydrophobic pocket of these myoglobin complexes.

Reversal of a Single Base-Pair Step Controls Guanine Photo-Oxidation by an Intercalating Ruthenium(II) Dipyridophenazine Complex.

Small changes in DNA sequence can often have major biological effects. Here the rates and yields of guanine photo‐oxidation by Λ‐[Ru(TAP)2(dppz)]2+ have been compared in 5′‐{CCGGATCCGG}2 and 5′‐{CCGGTACCGG}2 using pico/nanosecond transient visible and time‐resolved IR (TRIR) spectroscopy. The inefficiency of electron transfer in the TA sequence is consistent with the 5′‐TA‐3′ versus 5′‐AT‐3′ binding preference predicted by X‐ray crystallography. The TRIR spectra also reveal the differences in binding sites in the two oligonucleotides.

Reversal of a Single Base‐Pair Step Controls Guanine Photo‐Oxidation by an Intercalating Ruthenium(II) Dipyridophenazine Complex

AbstractSmall changes in DNA sequence can often have major biological effects. Here the rates and yields of guanine photo‐oxidation by Λ‐[Ru(TAP)2(dppz)]2+ have been compared in 5′‐{CCGGATCCGG}2 and 5′‐{CCGGTACCGG}2 using pico/nanosecond transient visible and time‐resolved IR (TRIR) spectroscopy. The inefficiency of electron transfer in the TA sequence is consistent with the 5′‐TA‐3′ versus 5′‐AT‐3′ binding preference predicted by X‐ray crystallography. The TRIR spectra also reveal the differences in binding sites in the two oligonucleotides.

Direct probing of photoinduced electron transfer in a self-assembled biomimetic [2Fe2S]-hydrogenase complex using ultrafast vibrational spectroscopy.

A pyridyl-functionalized diiron dithiolate complex, [μ-(4-pyCH2-NMI-S2)Fe2(CO)6] (3, py = pyridine (ligand), NMI = naphthalene monoimide) was synthesized and fully characterized. In the presence of zinc tetraphenylporphyrin (ZnTPP), a self-assembled 3·ZnTPP complex was readily formed in CH2Cl2 by the coordination of the pyridyl nitrogen to the porphyrin zinc center. Ultrafast photoinduced electron transfer from excited ZnTPP to complex 3 in the supramolecular assembly was observed in real time by monitoring the ν(C≡O) and ν(C═O)NMI spectral changes with femtosecond time-resolved infrared (TRIR) spectroscopy. We have confirmed that photoinduced charge separation produced the monoreduced species by comparing the time-resolved IR spectra with the conventional IR spectra of 3(•-) generated by reversible electrochemical reduction. The lifetimes for the charge separation and charge recombination processes were found to be τCS = 40 ± 3 ps and τCR = 205 ± 14 ps, respectively. The charge recombination is much slower than that in an analogous covalent complex, demonstrating the potential of a supramolecular approach to extend the lifetime of the charge-separated state in photocatalytic complexes. The observed vibrational frequency shifts provide a very sensitive probe of the delocalization of the electron-spin density over the different parts of the Fe2S2 complex. The TR and spectro-electrochemical IR spectra, electron paramagnetic resonance spectra, and density functional theory calculations all show that the spin density in 3(•-) is delocalized over the diiron core and the NMI bridge. This delocalization explains why the complex exhibits low catalytic dihydrogen production even though it features a very efficient photoinduced electron transfer. The ultrafast porphyrin-to-NMI-S2-Fe2(CO)6 photoinduced electron transfer is the first reported example of a supramolecular Fe2S2-hydrogenase model studied by femtosecond TRIR spectroscopy. Our results show that TRIR spectroscopy is a powerful tool to investigate photoinduced electron transfer in potential dihydrogen-producing catalytic complexes, and that way to optimize their performance by rational approaches.

Mixed IR/Vis Two‐Dimensional Spectroscopy: Chemical Exchange beyond the Vibrational Lifetime and Sub‐ensemble Selective Photochemistry

Two-dimensional exchange spectroscopy (2D EXSY) is a powerful method to study the interconversion (chemical exchange) of molecular species in equilibrium. This method has recently been realized in femtosecond 2D-IR spectroscopy, dramatically increasing the time resolution. However, current implementations allow the EXSY signal (and therefore the chemical process of interest) only to be tracked during the lifetime (T1 ) of the observed spectroscopic transition. This is a severe limitation, as typical vibrational T1 are only a few ps. An IR/Vis pulse sequence is presented that overcomes this limit and makes the EXSY signal independent of T1 . The same pulse sequence allows to collect time-resolved IR spectra after electronic excitation of a particular chemical species in a mixture of species with strongly overlapping UV/Vis spectra. Different photoreaction pathways and dynamics of coexisting isomers or of species involved in different intermolecular interactions can thus be revealed, even if the species cannot be isolated because they are in rapid equilibrium.

Two-Dimensional Infrared Spectroscopy of the Photoproduct of π-Cyclopentadienyliron Dicarbonyl Dimer

Equilibrium photoproduct of π-cyclopentadienyliron dicarbonyl dimer [CpFe(CO)2]2 in nonpolar solvent carbon tetrachloride (CCl4) is investigated using time-resolved 2D IR spectroscopy. One of the several possible visible-light-driven photoreaction pathways is confirmed and the product is found to contain a di-carbonyl group that exhibits quantum beating between two equivalent transitions in time-resolved 2D IR spectra, which turns out to be the anti-symmetric and symmetric stretching of the terminal carbonyl stretching modes of CpFe(CO)2Cl. This is the main product and its reaction pathway involves radical formation, followed by chloride addition. Quantum-chemistry computations support these experimental results. Our results indicate that 2D IR method can be used to identify in situ structures and dynamics of chemical species involved in condensed-phase chemical reactions.

Computational Study of the One‐ and Two‐Dimensional Infrared Spectra of a Proton‐Transfer Mode in a Hydrogen‐Bonded Complex Dissolved in a Polar Nanocluster

The signatures of nanosolvation on the one- and two-dimensional (1D and 2D) IR spectra of a proton-transfer mode in a hydrogen-bonded complex dissolved in polar solvent molecule nanoclusters of varying size are elucidated by using mixed quantum-classical molecular dynamics simulations. For this particular system, increasing the number of solvent molecules successively from N=7 to N=9 initiates the transition of the system from a cluster state to a bulk-like state. Both the 1D and 2D IR spectra reflect this transition through pronounced changes in their peak intensities and numbers, but the time-resolved 2D IR spectra also manifest spectral features that uniquely identify the onset of the cluster-to-bulk transition. In particular, it is observed that in the 1D IR spectra, the relative intensities of the peaks change such that the number of peaks decreases from three to two as the size of the cluster increases from N=7 to N=9. In the 2D IR spectra, off-diagonal peaks are observed in the N=7 and N=8 cases at zero waiting time, but not in the N=9 case. It is known that there are no off-diagonal peaks in the 2D IR spectrum of the bulk version of this system at zero waiting time, so the disappearance of these peaks is a unique signature of the onset of bulk-like behavior. Through an examination of the trajectories of various properties of the complex and solvent, it is possible to relate the emergence of these off-diagonal peaks to an interplay between the vibrations of the complex and the solvent polarization dynamics.

Protein Dynamics of Cytochrome C Oxidase: Analysis of Vibrational Components by Phase Sensitive Detection Applied to Modulated Excitation-Seiras

Cytochrome c oxidase (CcO) from R. sphaeroides was investigated by Modulated Excitation Surface-Enhanced IR-Absorption Spectroscopy (ME-SEIRAS). Sequential electron transfer (ET) within CcO was initiated by electrochemical excitation. During the modulated excitation by periodic potential pulses with frequencies between 20 Hz and 500 Hz, time-resolved IR spectra were measured by the Step-Scan technique with time-resolution in the millisecond time range. Conformational changes of the protein structure as a result of ET lead to rather complex SEIRA spectra with many overlapping bands embedded in a broad background signal. Phase sensitive detection (PSD) was used to separate single components within the broad band of overlapping structural bands in the amide region. PSD is able to extract the periodic response of single components with the same frequency as the excitation from noise or from static background and therefore enhances the signal-to-noise ratio. Moreover, PSD enables the validation of the fit model utilized for the deconvolution of overlapping bands by analyzing the phase lags of single components acquired at different stimulation frequencies. The phase lags between the evaluated vibrational components and the modulated excitation increase with increasing excitation frequencies, which is an inherent prerequisite of the evaluation method.

Determination of the Au active site and surface active species via operando transmission FTIR and isotopic transient experiments on 2.3 wt.% Au/TiO2 for the WGS reaction

The kinetics and the active site for the water gas shift (WGS) reaction were investigated by operando FTIR during steady state and isotopic transient experiments on a 2.3wt.% Au/TiO2 catalyst. The WGS rate at 120°C and activation energy measured in the operando IR reactor for the WGS reaction (7% CO, 11% H2O, 9% CO2, and 37% H2) on the Au/TiO2 catalyst were 1.1±0.1×10−2 (molH2) (mol−1Au) s−1 and 56±3kJmol−1, respectively. We have shown that the kinetics measured over a pressed wafer in a transmission FTIR were similar to those measured in a regular plug flow reactor (PFR). Operando IR data were used to follow the catalyst deactivation as a function of time, and the amount of CO adsorbed on metallic Au species (Au0, 2100cm−1) correlated with the WGS rates, while CO adsorbed on partially negatively charged Au species (Auδ−, 2040cm−1) did not. The rate loss did not correlate with the amounts of formate- and carbonate-like species measured by IR but was consistent with a loss of active sites by sintering.Measurements by isotopic transient experiments (13CO–12CO) on the Au/TiO2 catalyst with an average Au particle size of 3nm showed that less than 3% of the total surface Au atoms on the Au nanoparticles were responsible for the majority of the catalytic activity. Time-resolved IR spectra collected during the isotopic transient experiments showed that CO adsorbed on Au0 species were involved in the reaction pathway, while the surface formate and carbonate species were spectators under these WGS conditions. Based on these results, we conclude that metallic corner Au atoms are the dominant active sites for WGS on Au/TiO2 catalysts and that CO adsorbed on Au0 is an active intermediate. In addition, we present a detailed description of the design, construction, and operation of a transmission FTIR cell capable of performing operando kinetic measurements and isotope switching experiments with a signal decay time of about 95% in 1.5s.

Charge photoinjection in intercalated and covalently bound [Re(CO)3(dppz)(py)]+-DNA constructs monitored by time-resolved visible and infrared spectroscopy.

The complex [Re(CO)(3)(dppz)(py'-OR)](+) (dppz = dipyrido[3,2-a:2',3'-c]phenazine; py'-OR = 4-functionalized pyridine) offers IR sensitivity and can oxidize DNA directly from the excited state, making it a promising probe for the study of DNA-mediated charge transport (CT). The behavior of several covalent and noncovalent Re-DNA constructs was monitored by time-resolved IR (TRIR) and UV/visible spectroscopies, as well as biochemical methods, confirming the long-range oxidation of DNA by the excited complex. Optical excitation of the complex leads to population of MLCT and at least two distinct intraligand states. Experimental observations that are consistent with charge injection from these excited states include similarity between long-time TRIR spectra and the reduced state spectrum observed by spectroelectrochemistry, the appearance of a guanine radical signal in TRIR spectra, and the eventual formation of permanent guanine oxidation products. The majority of reactivity occurs on the ultrafast time scale, although processes dependent on slower conformational motions of DNA, such as the accumulation of oxidative damage at guanine, are also observed. The ability to measure events on such disparate time scales, its superior selectivity in comparison to other spectroscopic techniques, and the ability to simultaneously monitor carbonyl ligand and DNA IR absorption bands make TRIR a valuable tool for the study of CT in DNA.