Biomedical subjects

Cristian Manzoni

Publications and source records attributed to Cristian Manzoni.

5 recordsLinked to original sources

PubMed2006

300 microJ noncollinear optical parametric amplifier in the visible at 1 kHz repetition rate.

We demonstrate an order-of-magnitude energy scaling of a white-light seeded noncollinear optical parametric amplifier in the visible. The generated pulses, tunable between 520 and 650 nm with sub-25-fs duration, had energies up to 310 microJ with 20% blue-pump-to-signal energy conversion efficiency at 540 nm. This new ultrafast source will make possible numerous extreme nonlinear optics applications. As a first application, we demonstrate the generation of tunable vacuum ultraviolet pulses.

Journal Article↗

PubMed2006

Observation of terahertz vibrations in Pyrococcus furiosus rubredoxin via impulsive coherent vibrational spectroscopy and nuclear resonance vibrational spectroscopy--interpretation by molecular mechanics.

We have used impulsive coherent vibrational spectroscopy (ICVS) to study the Fe(S-Cys)(4) site in oxidized rubredoxin (Rd) from Pyrococcus furiosus (Pf). In this experiment, a 15 fs visible laser pulse is used to coherently pump the sample to an excited electronic state, and a second <10 fs pulse is used to probe the change in transmission as a function of the time delay. PfRd was observed to relax to the ground state by a single exponential decay with time constants of approximately 255-275 fs. Superimposed on this relaxation are oscillations caused by coherent excitation of vibrational modes in both excited and ground electronic states. Fourier transformation reveals the frequencies of these modes. The strongest ICV mode with 570 nm excitation is the symmetric Fe-S stretching mode near 310 cm(-1), compared to 313 cm(-1) in the low temperature resonance Raman. If the rubredoxin is pumped at 520 nm, a set of strong bands occurs between 20 and 110 cm(-1). Finally, there is a mode at approximately 500 cm(-1) which is similar to features near 508 cm(-1) in blue Cu proteins that have been attributed to excited state vibrations. Normal mode analysis using 488 protein atoms and 558 waters gave calculated spectra that are in good agreement with previous nuclear resonance vibrational spectra (NRVS) results. The lowest frequency normal modes are identified as collective motions of the entire protein or large segments of polypeptide. Motion in these modes may affect the polar environment of the redox site and thus tune the electron transfer functions in rubredoxins.

Fourier Analysis↗

PubMed2006

Ultrafast pump-probe study of excited-state charge-transfer dynamics in umecyanin from horseradish root.

We have applied femtosecond pump-probe spectroscopy to investigate the excited-state dynamics of umecyanin from horseradish roots, by exciting its 600-nm ligand-to-metal charge-transfer band with a 15-fs pulse and probing over a broad range in the visible region. The decay of the pump-induced ground-state bleaching is modulated by clearly visible oscillations and occurs exponentially with a time constant depending on the observed spectral component of the transmission difference signal, ranging from 270 fs up to 700 fs. The slower decaying process characterizes the spectral component corresponding to the metal-to-ligand charge-transfer transition. The excited-state decay rate is significantly lower than in other blue copper proteins, probably because of the larger energy gap between ligand- and metal-based orbitals in umecyanin. Wavelength dependence of the recovery times could be due to either the excitation of several transitions or the occurrence of intramolecular vibrational relaxation within the excited state. We also find evidence of a hot ground-state absorption, at 700 nm, persisting for several picoseconds. The vibrational coherence induced by the ultrashort pump pulse allows vibrational activity to be observed, mainly in the ground state, as expected in a system with fast excited-state decay. However, we find evidence of a rapidly damped oscillation, which we assign to the excited state. Finally, the Fourier transform of the oscillatory component of the signal presents additional bands in the low-frequency region which are assigned to collective motions of the protein.

Armoracia↗

PubMed2006

Group-velocity control by quadratic nonlinear interactions.

We give direct experimental evidence that the group velocity of ultrashort pulses can be controlled through chi(2)-cascaded interactions, under the condition of large group-velocity mismatch. The group velocity can be finely tuned by acting on pulse intensity and phase mismatch. Group-delay shifts up to 50 fs are achieved by propagating 40 fs pulses around 1400 nm in a 25 mm long periodically poled stoichiometric lithium tantalate crystal.

Journal Article↗

PubMed2005

Study of mechanisms of light-induced dissociation of Ru(dcbpy)(CO)2I2 in solution down to 20 fs time resolution.

Mechanisms of the light-induced ligand exchange reaction of (trans-I) Ru(dcbpy)(CO)2I2 (dcbpy = 4,4'-dicarboxylic acid-2,2'-bipyridine) in ethanol have been studied by transient absorption spectroscopy. Ultraviolet 20 fs excitation pulses centered at 325 nm were used to populate a vibrationally hot excited pi bipyridyl state of the reactant that quickly relaxes to a dissociative Ru-I state resulting in the release of one of the carbonyl groups. Quantum yield measurements have indicated that about 40% of the initially exited reactant molecules form the final photoproduct. A 62 fs rise component in the transient absorption (TA) signal was observed at all probe wavelengths in the visible region for the ongoing reaction, while the rise for the photoproduct was pulse limited (20 fs). We assign the observed 62 fs time component to the depopulation of the repulsive CO dissociative state. Vibrational coherences of the TA signals were observed at a wavenumber of 90 cm(-1). The resolved frequency, typical of I-Ru-I vibrational modes, is assigned to trans-cis isomerization of the iodines of the five-coordinated intermediate and damping of this oscillation in 500 fs to simultaneous solvent coordination. Cooling of the hot reactant and the product molecules occurs on a much slower time scale from 4 to 270 ps (Lehtovuori, V.; Aumanen, J.; Myllyperkiö, P.; Rini, M.; Nibbering, E. T. J.; Korppi-Tommola, J. J. Phys. Chem. A 2004, 108, 1644).

Journal Article↗