Observation of dynamic oxygen release in hemoglobin using surface enhanced Raman scattering

Photoinduced oxygen dynamics in hemoglobin is monitored by surface enhanced resonant Raman spectroscopy (SERRS) using silver colloids. The spectra are characterized by massive transient amplifications which we assign to a charge-transfer mechanism during the opening of the heme-pockets in the release of oxygen. This transient lifts the selection rule specificity of normal Raman active modes and allows for the full density of states of the hemes to be observed. The amplification of specific forbidden modes is controlled by the orientation alignment of individual molecules in proximity with the colloid surface. We propose that the technique can be used to monitor oxygen release in single proteins.     

Photoluminescence and Raman scattering of ZnO nanorods

Zinc oxide (ZnO) nanorods were synthesized by a simple microemulsion method. The photoluminescence (PL) spectra at room temperature were measured. The strong UV excitonic emission indicates the good optical properties, and the weak deep-level emission reveals very limited structural defects in the crystals. The multiple peaks in the PL spectrum obtained at 15 K are assigned to the donor-bound exciton (DBE), free to bound transition (FB) and FB–LO phonon replicas. The temperature dependence of energy, intensity, and linewidth of each emission band confirms the effect of thermal ionization progress of excitons and nonradiative recombination activated thermally. The nonresonant Raman scattering spectra at room temperature were excited by He–Ne laser (wavelength ～632.8 nm). The perfect wurtzite structure in ZnO nanorods has been verified by the intense E₂ modes, which include low and high frequency vibrations. The possible reasons for the red shift and broadening of vibration modes were studied by the resonant Raman scattering spectra at room temperature. The power-dependence of Raman shift and FWHM shows the laser irradiation effect on the vibrational modes.     

Influence of electronic resonances on mode selective excitation with tailored laser pulses

Femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) gives access to ultrafast molecular dynamics. However, the gain of the temporal resolution entails a poor spectral resolution due to the inherent spectral width of the femtosecond excitation pulses. Modifications of the phase shape of one of the exciting pulses results in dramatic changes of the mode distribution reflected in coherent anti-Stokes Raman spectra. A feedback-controlled optimization of specific modes making use of phase and/or amplitude modulation of the pump laser pulse is applied to selectively influence the anti-Stokes signal spectrum. The optimization experiments are performed under electronically nonresonant and resonant conditions. The results are compared and the role of electronic resonances is analyzed. It can be clearly demonstrated that these resonances are of importance for a selective excitation by means of phase and amplitude modulation. The mode selective excitation under nonresonant conditions is determined mainly by the variation of the spectral phase of the laser pulse. Here, the modulation of the spectral amplitudes only has little influence on the mode ratios. In contrast to this, the phase as well as amplitude modulation contributes considerably to the control process under resonant conditions. A careful analysis of the experimental results reveals information about the mechanisms of the mode control, which partially involve molecular dynamics in the electronic states.     

Resonant Raman spectroscopy of PAH--Os self-assembled multilayers

We present a resonant Raman scattering study of (PAH--Os/PVS)n and (PAH--Os/GOx)m self-assembled multilayers (n=1-11 and m=1-3). These Os polymer multilayers can be used in electrodes as efficient molecular wires for biomolecular recognition. The Raman intensity dependence on the number of self-assembly cycles provides information on the deposition process. The spectra are identical to that observed for PAH--Os in aqueous solution, indicating that the PAH--Os metal complex structure is conserved in the multilayers. We observe at approximately 500 nm incoming and outgoing Raman resonances of osmium and bipyridine vibrational modes. These resonances are associated to the metal-to-ligand charge transfer (MLCT) transition. We study the evolution of these Raman modes as a function of the Os oxidation state during in situ electrochemistry. During the oxidation process, Os(II)-->Os(III), the Raman resonance related to the MLCT disappears and the bipyridine related modes harden by approximately 10 cm(-1). These results are correlated with optical transmission measurements which show the disappearance of the visible region absorption when the Os complex is oxidized. We also find partial quenching of the Raman mode intensity after in situ voltamperometric cycles which demonstrates the existence of photo-electro-chemical processes.     

A new ultrafast technique for measuring the terahertz dynamics of chiral molecules: the theory of optical heterodyne-detected Raman-induced Kerr optical activity

Optical heterodyne-detected Raman-induced Kerr optical activity (OHD-RIKOA) is a nonresonant ultrafast chiroptical technique for measuring the terahertz-frequency Raman spectrum of chirally active modes in liquids, solutions, and glasses of chiral molecules. OHD-RIKOA has the potential to provide much more information on the structure of molecules and the symmetries of librational and vibrational modes than the well-known nonchirally sensitive technique optical heterodyne-detected Raman-induced Kerr-effect spectroscopy (OHD-RIKES). The theory of OHD-RIKOA is presented and possible practical ways of performing the experiments are analyzed.     

FM spectroscopy: Raman scattering and luminescence

This paper describes a new method of light scattering spectroscopy which involves modulation of the optical frequency of a cw laser. The experiments are shown to yield accurate Raman data while suppressing sample luminescence and reducing contamination by background laser luminescence. The laser FM technique also shows promise for studying certain properties of luminescing systems.     

Resonance multiplex cars of fluorescing acridines

Resonance enhanced coherent anti-Stokes Raman scattering (CARS) spectra have been obtained for the highly fluorescing acridine dyes, acridine orange and proflavine, in dilute methanol solutions at submillimolar concentrations. Spectra have also been taken in the multiplex mode by the use of a broad-band Stokes laser and a Vidicon OMA detection system. Several Raman bands are observed in the 1100–1600 cm^?1 region originating from the acridine ring modes. Upon decreasing the beam crossing angle a continuous transition from the normal CARS spectrum to a negative spectrum in the nonresonant background is observed.     

Towards quantum optics and entanglement with electron spin ensembles in semiconductors

We discuss a technique and a material system that enable the controlled realization of quantum entanglement between spin-wave modes of electron ensembles in two spatially separated pieces of semiconductor material. The approach uses electron ensembles in GaAs quantum wells that are located inside optical waveguides. Bringing the electron ensembles in a quantum Hall state gives selection rules for optical transitions across the gap that can selectively address the two electron spin states. Long-lived superpositions of these electron spin states can then be controlled with a pair of optical fields that form a resonant Raman system. Entangled states of spin-wave modes are prepared by applying quantum-optical measurement techniques to optical signal pulses that result from Raman transitions in the electron ensembles.     

Transition rates between selected vibrational states in methyl halides; influence of anharmonicities

A semiclassical model of collision induced vibrational relaxation is discussed in terms of an effective collision mass for different values of vibrational energy release. Selected one, two and three quantum transitions of the methyl halides upon collision with rare gases are evaluated in the presence of resonant and nonresonant anharmonic couplings. It is found, that due to the anharmonic coupling the rates between CH stretching modes and the overtones of the CH bending modes become as large as the transfer rates between two CH stretching modes. This is in qualitative agreement with experiments. Without the anharmonic coupling they differ by two orders of magnitude.     

Resonant Raman scattering characterization of carbon nanotubes grown with different catalysts

Single-walled carbon nanotube samples produced in the presence of different combinations of metal catalysts have been studied by resonant Raman spectroscopy. The diameter distribution of different samples has been determined by analysis of the laser excitation energy dependence of the tangential modes associated with metallic nanotubes. These modes are resonantly enhanced over a narrow range of the exciting energies, which shifts for different samples. The Raman cross-section expression has been used to fit the experimental Raman excitation profiles. This procedure was used to determine the mean value and the width of the distribution of diameters within each sample.     

Elucidating the spectral and temporal contributions from the resonant and nonresonant response to femtosecond coherent anti-Stokes Raman scattering

A theoretical expression is developed for femtosecond coherent anti-Stokes Raman scattering (CARS) to quantitatively account for the vibrational line shape in the presence of nonresonant signal. The contributions of the resonant and nonresonant components are extracted from the emitted signal line shape as a function of Stokes wavelength and as a function of the temporal overlap of the two pump pulses (for spectrally resolved femtosecond CARS). The theory is compared to the measured spectra of the oxygen vibrational transition DeltaG(01)=1556.4 cm(-1) for temporal detunings of 0 and 700 fs.     

Laser Linewidth and Spectral Resolution in Infrared Scanning Sum Frequency Generation Vibrational Spectroscopy System

Sum frequency generation vibrational spectroscopy (SFG-VS) is a robust technique for interfacial investigation at molecular level. The performance of SFG-VS mostly depends on the spectral resolution of the SFG system. In this research, a simplified function was deduced to calculate the spectral resolution of picosecond SFG system and the lineshape of SFG spectra based on the Guassian shaped functions of IR beam and visible beam. The function indicates that the lineshpe of SFG spectra from nonresonant samples can be calculated by the Guassian widths of both IR beam and visible beam. And the Voigt lineshape of SFG spectra from vibrational resonant samples can be calculated by the Homogeneous broadening (Lorentzian width) and Inhomogeneous broadening (Guassian width) of vibrational modes, as well as the Guassian widths of both IR beam and visible beam. Such functions were also applied to verify the spectral resolution of the polarization-resolved and frequency-resolved picosecond SFG-VS system which was developed by our group recently. It is shown that the linewidths of IR beams that generated from current laser system are about 1.5 cm^-1. The calculated spectral resolution of current picosecond IR scanning SFG-VS system is about 4.6 cm^-1, which is consist with he spctral resolution shown in the spectra of cholesterol monolayer (3.5-5 cm^-1).     

Heme reactivity is uncoupled from quaternary structure in gel-encapsulated hemoglobin: a resonance Raman spectroscopic study

Encapsulation of hemoglobin (Hb) in silica gel preserves structure and function but greatly slows protein motion, thereby providing access to intermediates along the allosteric pathway that are inaccessible in solution. Resonance Raman (RR) spectroscopy with visible and ultraviolet laser excitation provides probes of heme reactivity and of key tertiary and quaternary contacts. These probes were monitored in gels after deoxygenation of oxyHb and after CO binding to deoxyHb, which initiate conformational change in the R-T and T-R directions, respectively. The spectra establish that quaternary structure change in the gel takes a week or more but that the evolution of heme reactivity, as monitored by the Fe-histidine stretching vibration, ν(FeHis), is completed within two days, and is therefore uncoupled from the quaternary structure. Within each quaternary structure, the evolving ν(FeHis) frequencies span the full range of values between those previously associated with the high- and low-affinity end states, R and T. This result supports the tertiary two-state (TTS) model, in which the Hb subunits can adopt high- and low-affinity tertiary structures, r and t, within each quaternary state. The spectra also reveal different tertiary pathways, involving the breaking and reformation of E and F interhelical contacts in the R-T direction but not the T-R direction. In the latter, tertiary motions are restricted by the T quaternary contacts.     

Optical waveguide techniques for structural and chemical analysis in thin film and interfacial systems

This review considers some of the problems with which analytical chemists interested in thin-film and interfacial structures must deal. It is advocated that the types of classical spectroscopies which have served so well for so long in the solution regime are not particularly well suited to attacking these problems and that entirely new approaches are required. One such approach uses the generation of resonant optical waveguide modes in thin-film structures as the basis for spectroscopic excitation. The details of the waveguiding process are discussed and the properties important for spectroscopic experiments emphasized. The power of the technique for generating qualitative spectroscopic information is demonstrated by considering some specific Raman and resonance Raman experiments, and the implementation of an optical depth profiling capability is discussed. Finally, some recent four-wave mixing experiments are detailed to demonstrate both the breadth of capabilities and the vitality of research in the area. It should be noted that several fairly extensive efforts have not been covered. Notable among these is the use of resonant optical modes for thin-film absorption spectroscopy in which active research is ongoing (D. A. Stephens and P. W. Bohn, unpublished results).     

The role of tunnelling in light atom diffusion in metals: A comparison of resonant and non-resonant theoretical approaches

We are concerned here with the question of the applicability of resonant (energy splitting) and nonresonant (transmission coefficient) tunnelling theories to the problem of symmetric double well transfer. We apply a recently developed method of the former type, the Generalized Method of Beats (GMOB), to the calculation of interstitial hydrogen and deuterium diffusion in the metals niobium, vanadium and palladium and compare our results to both experiment and earlier calculations using a nonresonant theory. Both theories can be parametrised so as to fit approximately the experimental temperature dependence of the diffusion coefficients, but the parameters differ markedly. For fixed barrier height, the mean jump distance needed to fit a given rate using the resonant theory is jump distance in the resonant approach is 2.0 Å, which is close to an experimental value; in a nonresonant approach by Weiner a very much smaller distance, 1.166 Å, was required. It is noted, however, that the appropriateness of the underlying model assumptions to the interpretation of hydrogen/deuterium migration dynamics in metal requires further investigation.     

Imaging receptor-mediated endocytosis with a polymeric nanoparticle-based coherent anti-stokes Raman scattering probe

Coherent anti-Stokes Raman scattering (CARS) microscopy was used to visualize receptor-mediated endocytosis and intracellular trafficking with the aid of a CARS probe. The probe was made of 200-nm polystyrene particles encapsulated in folate-targeted liposomes. By tuning (omega(p) - omega(s)) to 3045 cm(-1), which corresponds to the aromatic C-H stretching vibration, the polystyrene nanoparticles with a high density of aromatic C-H bonds were detected with a high signal-to-noise ratio, while the epi-detected CARS signal from cellular organelles was cancelled by the destructive interference between the resonant contribution from the aliphatic C-H vibration and the nonresonant contribution. Without any photobleaching, the CARS probe allowed single-particle tracking analysis of intracellular endosome transport. No photodamage to cells was observed under the current experimental conditions. These results show the advantages and potential of using a CARS probe to study cellular processes.     

The nature of in-plane skeleton Raman modes of P3HT and their correlation to the degree of molecular order in P3HT:PCBM blend thin films

The nature of main in-plane skeleton Raman modes (C=C and C-C stretch) of poly(3-hexylthiophene) (P3HT) in pristine and its blend thin films with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) is studied by resonant and nonresonant Raman spectroscopy and Raman simulations. Under resonant conditions, the ordered phase of P3HT with respect to its disordered phase is identified by (a) a large shift in the C=C mode peak position to lower wavenumber (~21 cm(-1) shift), (b) a narrower fwhm of the C=C mode (~9 cm(-1) narrower), (c) a larger intensity of the C-C mode relative to the C=C mode (~56% larger), and (d) a very small Raman dispersion (~5 cm(-1)) of the C=C mode. The behavior of the C=C and C-C modes of the ordered and disordered phases of P3HT can be explained in terms of different molecular conformations. The C=C mode of P3HT in P3HT:PCBM blend films can be reproduced by simple superposition of the two peaks observed in different phases of P3HT (ordered and disordered). We quantify the molecular order of P3HT after blending with PCBM and the subsequent thermal annealing to be 42 ± 5% and 94 ± 5% in terms of the fraction of ordered P3HT phase, respectively. The increased molecular order of P3HT in blends upon annealing correlates well with enhanced device performance (J(SC), -4.79 to -8.72 mA/cm(2) and PCE, 1.07% to 3.39%). We demonstrate that Raman spectroscopy (particularly under resonant conditions) is a simple and powerful technique to study molecular order of conjugated polymers and their blend films.     

Photo-acoustic measurements of gas and aerosol absorption with diode lasers

The results of designing multipurpose high-sensitive photo-acoustic (PA) detectors and their application to high-resolution diode laser spectroscopy of molecular gases, gas analysis, and aerosol absorption measurements are summarized in this paper. The hardware and software of the diode laser spectrometer with a Helmholtz resonant PA detector providing an absorption sensitivity limit of better than 10(-7)Wm(-1)Hz(-1/2) are described. A procedure is proposed for an experiment involving the measurements of the rotational structure of hot vibrational bands of molecules. The results of the application of the nonresonant PA cell with temporal resolution of signals to measurements of weak nonresonant absorption of gases and soot aerosols are presented, and the possibility of creating a broad-band PA laser diode aerosol-meter is discussed.     

Ligand binding intermediates of nitrosylated human hemoglobin induced at low temperature by X-ray irradiation

Under prolonged X-ray irradiation, the ferrous heme of nitrosylated human adult hemoglobin derivative (HbNO) undergoes a reversible transition generating a 5-coordinate species, due to release of the Fe-NO bond. The overall process can be investigated using X-ray absorption near edge structure (XANES) spectroscopy. In this work, Fe K-edge XANES spectra were measured at T < 15 K, pH 9.2, i.e., on a high-affinity state (R-HbNO) where all the hemes are 6-coordinate, and at pH 6.5 in the presence of inositol hexakis-phosphate (IHP), i.e., on a low-affinity ligated state (T-HbNO) where the iron-hemes of the α-chains are 5-coordinate due to breaking of the Fe-proximal histidine bond. Under X-ray irradiation, 5-coordinate Fe-hemes are populated in both R-HbNO and T-HbNO, the Fe-NO bond lysis induced in T-HbNO involving rebinding of the proximal histidine to the transiently populated 4-coordinate hemes of the α-chains. A detailed analysis of the spectra confirms that different intermediate states in the ligand binding cooperative process of hemoglobin can be populated by X-ray irradiation, and that the part of the energy associated to the R-T quaternary transition, that is transmitted to the heme site, can be monitored by XANES spectroscopy.