Biomedical subjects

Rene A Nome

Publications and source records attributed to Rene A Nome.

5 recordsLinked to original sources

PubMed2006

Field-resolved coherent Raman spectroscopy of high frequency vibrational resonances.

Electric fields of coherent Raman signals are resolved with sensitivity for high-frequency vibrational resonances utilizing a four-pulse, trapezoidal beam geometry in a diffractive optic-based interferometer. Our experiments show that the heterodyne detected signal phase is stabilized for particular terms in the third-order response function by the cancellation of inter-pulse phases. The C-H stretching modes of cyclohexane and benzene are studied under two polarization conditions. The temporal profiles of signal fields for cyclohexane exhibit a low-frequency recurrence due to the interference between the signals associated with the symmetric and asymmetric C-H stretching modes. In contrast, the electronically nonresonant polarizability response of benzene gives rise to a significant broadband signal component in addition to that associated with its C-H vibrational resonance. Time-frequency shapes of the Raman signal fields are strongly dependent on the properties of the liquid and the polarizations of the laser pulses.

Letter↗

PubMed2006

Resolving the emission times of solute and solvent four-wave mixing signals by spectral interferometry.

Electric field-resolved transient grating measurements are used to distinguish the four-wave mixing signal emission from a resonant solute and a non-resonant solvent. The two components of the solution (i.e., solute and solvent) emit signal fields at different times with respect to the arrival of the probe pulse to the sample. This gives rise to a recurrence in the temporal profile of the total signal field. We show that the origin of this interference is the difference in relaxation time scales of the holographic gratings associated with the solute and solvent. The grating of the resonant solute relaxes on the time scale of a few picoseconds due to depopulation of its excited electronic state, whereas the electronic polarizability response of the solvent relaxes on the femtosecond time scale. This separability of responses is a general phenomenon that is particularly useful for studying weakly absorbing solute dynamics in polarizable solvents.

Journal Article↗

PubMed2006

Single-molecule detection of structural changes during Per-Arnt-Sim (PAS) domain activation.

The Per-Arnt-Sim (PAS) domain is a ubiquitous protein module with a common three-dimensional fold involved in a wide range of regulatory and sensory functions in all domains of life. The activation of these functions is thought to involve partial unfolding of N- or C-terminal helices attached to the PAS domain. Here we use atomic force microscopy to probe receptor activation in single molecules of photoactive yellow protein (PYP), a prototype of the PAS domain family. Mechanical unfolding of Cys-linked PYP multimers in the presence and absence of illumination reveals that, in contrast to previous studies, the PAS domain itself is extended by approximately 3 nm (at the 10-pN detection limit of the measurement) and destabilized by approximately 30% in the light-activated state of PYP. Comparative measurements and steered molecular dynamics simulations of two double-Cys PYP mutants that probe different regions of the PAS domain quantify the anisotropy in stability and changes in local structure, thereby demonstrating the partial unfolding of their PAS domain upon activation. These results establish a generally applicable single-molecule approach for mapping functional conformational changes to selected regions of a protein. In addition, the results have profound implications for the molecular mechanism of PAS domain activation and indicate that stimulus-induced partial protein unfolding can be used as a signaling mechanism.

Anisotropy↗

PubMed2006

Optical coherence and theoretical study of the excitation dynamics of a highly symmetric cyclophane-linked oligophenylenevinylene dimer.

Optoelectronic properties of a polyphenylenevinylene-based oligomer and its paracylophane-linked dimer are studied using a variety of experimental and theoretical techniques. Despite the symmetrical structure and redshifted absorption of the dimer versus the monomer, an exciton picture is not the most appropriate. Electronic structure calculations establish changes in charge density upon optical excitation and show localized excitations that cannot be accounted for by a simple Frenkel exciton model. Visible frequency pump-probe anisotropy measurements suggest that the dimer should be considered as a three-level system with a fast, approximately 130 fs, internal conversion from the higher to lower energy excited electronic state. Signatures of nuclear relaxation processes are compared for electric field-resolved transient grating and two-dimensional photon echo spectra. These measurements reveal that nuclear relaxation occurs on similar time scales for the monomer and dimer. The connection between the spectral phase of four-wave mixing signals and the time dependent width of a nuclear wave packet is discussed. Semiempirical electronic structure and metropolis Monte Carlo calculations show that the dominant line broadening mechanisms for the monomer and dimer are associated with inter-ring torsional coordinates. Together, the theoretical calculations and electric field-resolved four-wave mixing experiments suggest that while the structure of dimer is more rigid than that of monomer, the difference in their rigidities is not sufficient to slow down excited state relaxation of dimer with respect to the monomer.

Journal Article↗

PubMed2005

Distribution of hexavalent Cr species across the clay mineral surface-water interface.

The adsorption isotherms of Cr(VI) on kaolinite, montmorillonite, and alumina were adequately treated with Langmuir model showing behavior characteristic of single-layer adsorption. The efficiency of the adsorbents in removing Cr(VI) from water follows the order alumina > kaolinite > montmorillonite > silica. Speciation studies indicate that hydrogen chromate ions were the major adsorbed species and simultaneous adsorption of dichromate ion occurred at concentrations greater than approximately 10(-3) mol L(-1). It is most probable that the mechanism of adsorption of the hydrogen chromate ion at the surface of alumina is predominantly electrostatic adsorption, with outer sphere complex formation.

Journal Article↗