Time-Variable Chiroptical Vibrational Sum-Frequency Generation Spectroscopy of Chiral Chemical Solution.

Vibrational sum-frequency generation (VSFG) spectroscopy, a surface-specific technique, was shown to be useful even for characterizing the vibrational optical activity of chiral molecules in isotropic bulk liquids. However, accurately determining the spectroscopic parameters is still challenging because of the spectral congestion of chiroptical VSFG peaks with different amplitudes and phases. Here, we show that a time-variable infrared-visible chiroptical three-wave-mixing technique can be used to determine the spectroscopic parameters of second-order vibrational response signals from chiral chemical liquids.

Conformer-Specific Photodissociation Dynamics of CFICFI in Solution Probed by Time-Resolved Infrared Spectroscopy.

The photodissociation dynamics of CFICFI in solution was investigated from 0.3 ps to 100 μs, after the excitation of CFICFI with a femtosecond UV pulse. Upon excitation, one I atom is eliminated within 0.

Vibrational spectroscopy and imaging with non-resonant coherent anti-Stokes Raman scattering: double stimulated Raman scattering scheme.

We introduce a new coherent anti-Stokes Raman scattering (CARS) suppression scheme based on measuring a non-resonant CARS loss signal by three-beam (pump-Stokes-depletion) double stimulated Raman scattering (SRS) processes, which can be potentially of use for super-resolution Raman microscopy. In the converging configuration with employing both pump-depletion and Stokes-depletion SRS processes, we obtained approximately 94% suppression of non-resonant CARS signal, which is about 1.5 times more efficient than that with the parallel configuration with pump-Stokes and pump-depletion SRS processes.

Femtosecond Vibrational Sum-Frequency Generation Spectroscopy of Chiral Molecules in Isotropic Liquid.

Vibrationally resonant optically active (VOA) sum-frequency generation (SFG) is a second-order nonlinear process sensitive to the stereospecific vibrational structure of chiral molecules. We demonstrate that a femtosecond VOA SFG signal can be measured in the isotropic bulk of a chiral liquid. The chiral, achiral, and VOA SFG spectra of R- and S-limonene and their racemic mixture in the C-H stretching frequency region are characterized.

A Description of Vibrational Modes in Hexaphyrins: Understanding the Aromaticity Reversal in the Lowest Triplet State.

Aromaticity reversal in the lowest triplet state, or Baird's rule, has been postulated for the past few decades. Despite numerous theoretical works on aromaticity reversal, experimental study is still at a rudimentary stage. Herein, we investigate the aromaticity reversal in the lowest excited triplet state using a comparable set of [26]- and [28]hexaphyrins by femtosecond time-resolved infrared (IR) spectroscopy.

Ultrafast and Efficient Transport of Hot Plasmonic Electrons by Graphene for Pt Free, Highly Efficient Visible-Light Responsive Photocatalyst.

We report that reduced graphene-coated gold nanoparticles (r-GO-AuNPs) are excellent visible-light-responsive photocatalysts for the photoconversion of CO2 into formic acid (HCOOH). The wavelength-dependent quantum and chemical yields of HCOOH shows a significant contribution of plasmon-induced hot electrons for CO2 photoconversion. Furthermore, the presence and reduced state of the graphene layers are critical parameters for the efficient CO2 photoconversion because of the electron mobility of graphene.

Rebinding dynamics of NO to microperoxidase-8 probed by time-resolved vibrational spectroscopy.

Femtosecond vibrational spectroscopy was used to probe the rebinding kinetics of NO to microperoxidase-8 (Mp), an ideal model system for the active site of ligand-binding heme proteins, including myoglobin and hemoglobin, after the photodeligation of MpNO in glycerol/water (G/W) solutions at 294 K. The geminate rebinding (GR) of NO to Mp in viscous solutions was highly efficient and ultrafast and negligibly dependent on the solution viscosity, which was adjusted by changing the glycerol content from 65% to 90% by volume in G/W mixtures. The kinetics of the GR of NO to Mp in viscous solutions was well represented by an exponential function with a time constant of ca.

A very rapid electronic relaxation process in a highly conjugated Zn(II)porphyrin-[26]hexaphyrin-Zn(II)porphyrin hybrid tape.

The excited-state energy relaxation processes of a Zn(II)porphyrin–[26]hexaphyrin–Zn(II)porphyrin triply linked hybrid tape, FZn, have been investigated by femtosecond transient absorption spectroscopy (TA), using a directly meso–meso linked hybrid trimer, HZn, as a reference compound. FZn has a very small S1–S0 energy gap through the expansion of π-conjugation and the absorption band at 1897 nm corresponds to its lowest singlet excited-state as a consequence of enhanced transition dipole moment that lies parallel to the long molecular axis. In TA measurements, we observe an energy transfer process (0.

Picosecond dynamics of photoexcited DNO-bound myoglobin probed by femtosecond vibrational spectroscopy.

Like nitric oxide (NO), nitroxyl (HNO), a reduced form of NO, plays many biologically important roles including neurological function and vascular regulation. Although HNO is unstable in aqueous solution, it is exceptionally stable on binding to ferrous myoglobin (Mb) to form MbHNO. Various experimental and theoretical investigations has been carried out to unveil the structure of the active site and binding characteristics of MbHNO that can explain its functioning mechanism and the origin of its unusual stability.

Direct observation of the low-spin Fe(III)-NO(radical) intermediate state during rebinding of NO to photodeligated ferric cytochrome c.

Nitrosylated ferric heme is autoreduced readily to the more stable Fe(II)-NO adduct, but it is stabilized in NO-carrier heme proteins where maintaining the Fe(III) oxidation state is crucial for efficient NO delivery. Density functional theory calculations by Lehnert and co-workers have shown that a NO-bound ferric model heme has a low-spin (LS) Fe(III)-NO(radical) state that might be critical for efficient NO transport by NO-carrier heme proteins. Recently, the elusive LS Fe(III)-NO(radical) state was observed as an electronic intermediate state during geminate rebinding (GR) of NO to ferric myoglobin (Mb(III)).

Dynamics of geminate rebinding of CO to cytochrome c in guanidine HCl probed by femtosecond vibrational spectroscopy.

Femtosecond vibrational spectroscopy was used to probe the rebinding dynamics of CO to cytochrome c (Cytc) in 1.8 and 7 M guanidine HCl (GdnHCl) after photodeligation of the corresponding CO-bound protein in D2O buffer (pD = 7.4) at 283 K.

Geminate rebinding dynamics of nitric oxide to ferric hemoglobin in D2O solution.

Femtosecond mid-infrared (mid-IR) spectroscopy was used to probe geminate rebinding (GR) dynamics of photo-released nitric oxide (NO) to ferric hemoglobin (Hb(III)) in D2O solution at room temperature. Time-resolved vibrational spectra exhibit two overlapping NO bands for NO-bound Hb(III) (Hb(III)NO), a major band at 1925 cm(-1) (89%) and a minor one at 1905 cm(-1) (11%), suggesting that Hb(III)NO has at least two conformational substates. Both bands decay nonexponentially, each with a different time scale, and the decays are described by a stretched exponential function; the major band's decay is described by 0.

Photoexcitation dynamics of NO-bound ferric myoglobin investigated by femtosecond vibrational spectroscopy.

Femtosecond vibrational spectroscopy was used to investigate the photoexcitation dynamics of NO-bound ferric myoglobin (Mb(III)NO) in D2O solution at 294 K after excitation with a 575 nm pulse. The stretching mode of NO in Mb(III)NO consists of a major band at 1922 cm(-1) (97.7%) and a minor band at 1902 cm(-1) (2.

Dynamics of geminate rebinding of NO with cytochrome c in aqueous solution using femtosecond vibrational spectroscopy.

Using femtosecond vibrational spectroscopy, we investigated the rebinding dynamics of NO to cytochrome c (Cytc) and a model heme, microperoxidase-8 (Mp), after photodeligation of CytcNO in D(2)O solution and MpNO in an 81% glycerol/water (v/v) mixture at room temperature. Whereas the stretching mode of the NO band in MpNO was described by a Gaussian centered at 1653 cm(-1) with a full width at half-maximum (fwhm) of 41 cm(-1), that in CytcNO revealed an asymmetric structured band that peaked at 1619 cm(-1) with an fwhm of about 27 cm(-1). The structured NO band in CytcNO was well described by the sum of three Gaussians, and its shape did not evolve with time but its amplitude decayed exponentially with a time constant of 7 ± 1 ps.

Direct observation of ligand rebinding pathways in hemoglobin using femtosecond mid-IR spectroscopy.

The dynamics of NO rebinding in hemoglobin (Hb) was directly observed using femtosecond mid-IR spectroscopy after photodeligation of NO from HbNO in D(2)O at 283 K. Time-resolved spectra of bound NO appeared to have a single feature peaked at 1616 cm(-1) but were much better described by two Gaussians with equal intensities but different rebinding kinetics, where the feature at 1617 cm(-1) rebinds faster than the one at 1614 cm(-1). It is possible that the two bands each correspond to one of two subunit constituents of the tetrameric Hb.

Viscosity-dependent dynamics of CO rebinding to microperoxidase-8 in glycerol/water solution.

Rebinding kinetics of CO to microperoxidase-8 (Mp), an excellent model system for the active site of heme proteins such as myoglobin and hemoglobin, was measured after photolysis of MpCO in solutions with various viscosities and temperatures, using femtosecond vibrational spectroscopy. Whereas the geminate rebinding of CO to Mp in water is negligible, significant fractions of CO rebind nonexponentially within 1 ns at room temperature in a glycerol/water solution. The geminate yield of the CO rebinding increases and its rate accelerates as the viscosity of the solution increases either by increasing glycerol content in glycerol/water mixtures at 294 K or by decreasing temperature of the solution from 323 to 283 K.

Photodynamic therapy for steroid-associated central serous chorioretinopathy.

Purpose: To evaluate the short-term efficacy of photodynamic therapy (PDT) for steroid-associated chronic or recurrent central serous chorioretinopathy (CSC).

Design: Interventional case series.

Methods: Retrospective review of nine consecutive cases of steroid-associated CSC treated with PDT using half-fluence for fovea involving treatments (n=4) and full-fluence for extrafoveal treatments (n=5).

Unilateral scleral fixation of posterior chamber intraocular lenses in pediatric complicated traumatic cataracts.

Purpose: The purpose of this study was to evaluate the visual outcomes and complications of unilateral scleral fixation of posterior chamber intraocular lenses (SF-PCIOLs) in pediatric complicated traumatic cataracts without capsular support.

Methods: This study involved five eyes of five children who underwent unilateral SF-PCIOL. All patients had a unilateral complicated traumatic cataract associated with anterior or posterior segment injury.

Probing the role of hydration in the unfolding transitions of carbonmonoxy myoglobin and apomyoglobin.

We show that the equilibrium unfolding transition of horse carbonmonoxy myoglobin monitored by the stretching vibration of the CO ligand, a local environmental probe, is very sharp and, thus, quite different from those measured by global conformational reporters. In addition, the denatured protein exhibits an A(0)-like CO band. We hypothesize that this sharp transition reports penetration of water into the heme pocket of the protein.

Dynamics of ultrafast rebinding of CO to carboxymethyl cytochrome c.

Rebinding dynamics of CO to carboxymethyl cytochrome c (Ccytc), a chemically modified cytochrome c to bind ligands in its ferrous form, in D(2)O solution at 283 K after photodeligation, was investigated using femtosecond vibrational spectroscopy. The stretching mode of CO bound to the protein shows four stretching bands near 1962 cm(-1). Time-resolved spectra of the bound CO revealed a slight band-position-dependent rebinding kinetics, suggesting that the geminate rebinding of CO depends on the conformation of the protein.

Dynamics of ligand rebinding to unfolded MbCO by guanidine HCl.

Femtosecond vibrational spectroscopy was used to probe a functionally important dynamics and residual structure of myoglobin unfolded by 4 M guanidine HCl. The spectra of the dissociated CO indicated that the residual structure of unfolded myoglobin (Mb) forms a few hydrophobic cavities that could accommodate the dissociated ligand. Geminate rebinding (GR) of CO to the unfolded Mb is three-orders-of-magnitude faster and more efficient than the native Mb but similar to a model heme in a viscous solvent, suggesting that the GR of CO to heme is accelerated by the longer retention of the dissociated ligand near the Fe atom by the poorly-structured protein matrix of the unfolded Mb or viscous solvent.