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Biomedical subjects

G Cerullo

Publications and source records attributed to G Cerullo.

At least 19 recordsLinked to original sources
PubMed2006

Cis and trans regulatory elements in NPHS2 promoter: implications in proteinuria and progression of renal diseases.

Podocin (NPHS2) expression in podocytes is associated with variable degrees of proteinuria and progression to renal failure in different glomerular diseases that suggests different expression profiles in NPHS2 promoter. Three functional polymorphisms in NPHS2 promoter (-51T, -116T, and -535 insCTTTTTT(3)) were found determining strong downregulation (-73, -59, and -82%, respectively) of the reporter gene expression when transfected in podocytes. Electrophoretic mobility shift assay experiments showed that all wild-type variants (-51G, -116C, and -535 insCTTTTTT(2)) formed specific DNA-protein complexes with podocyte nuclear extracts that were abolished by the presence of the rare forms (-51T, -116T, and -535 insCTTTTTT(3)). In the case of -51G, upstream stimulatory factor-1 (USF1) was identified as the specific trans element in accord to binding inhibition experiments and USF1 RNAi silencing. Haplotype analysis of 204 normal controls and 545 patients with renal diseases (308 immunoglobulin (Ig)A nephropathy and 237 focal segmental glomerulosclerosis) evidenced that -116/-51 and -535/P2OL formed two blocks in strong linkage disequilibrium in both normal and pathological cohorts. The high NPHS2 promoter profile -116C/-51G haplotype was more frequent in patients with IgA nephropathy (P-value=0.005) and was associated with a better clinical outcome in terms of proteinuria and creatinine levels. Overall our study describes functional variants of NPHS2 promoter and characterizes trans-acting elements that modulate podocin expression in the kidney. High producer NPHS2 promoter haplotypes seem protective in patients with chronic glomerular diseases.

Adolescent↗
PubMed2006

Imaging of Bloch oscillations in erbium-doped curved waveguide arrays.

We report a direct observation of Bloch-like dynamics of light in curved waveguide arrays manufactured in Er:Yb-doped phosphate glass by femtosecond laser writing. The green upconversion fluorescence emitted by excited erbium ions is exploited to image the flow of the guided pump light at approximately 980 nm along the array. Direct and clear evidence of periodic light breathing for single-waveguide excitation, closely related to Bloch oscillations, is reported.

Journal Article↗
PubMed2006

Generation of high-energy self-phase-stabilized pulses by difference-frequency generation followed by optical parametric amplification.

We produce ultrabroadband self-phase-stabilized near-IR pulses by a novel approach where a seed pulse, obtained by difference-frequency generation of a hollow-fiber broadened supercontinuum, is amplified by a two-stage optical parametric amplifier. Energies up to 20 microJ with a pulse spectrum extending from 1.2 to 1.6 microm are demonstrated, and a route for substantial energy scaling is indicated.

Journal Article↗
PubMed2005

Intersubband exciton relaxation dynamics in single-walled carbon nanotubes.

We study exciton (EX) dynamics in single-walled carbon nanotubes (SWNTs) included in polymethylmethacrylate by two-color pump-probe experiments with unprecedented temporal resolution. In the semiconducting SWNTs, we resolve the intersubband energy relaxation from the EX2 to the EX1 transition and find time constants of about 40 fs. The observation of a photoinduced absorption band strictly correlated to the photobleaching of the EX1 transition supports the excitonic model for primary excitations in SWNTs. We also detect in the time domain coherent oscillations due to the radial breathing modes at approximately 250 cm(-1).

Journal Article↗
PubMed2005

Ultrafast intrachain photoexcitation of polymeric semiconductors.

We report on excited state dynamics in isolated poly(9,9-dioctylfluorene) chains obtained by embedding the polymer in an inert plastic matrix. Early events (<300 fs) of intrachain photophysics are detected by pump-probe spectroscopy using tunable UV 25-fs pump pulses and sub-10-fs visible probe pulses. We show that higher-lying optical states, reached by multiphoton transitions, give rise to on-chain charge separation on the ultrafast time scale. The intrachain charge pair decays geminately within 500 fs to the lowest singlet state. Characteristic time scales for internal conversion and intramolecular vibrational redistribution are also determined.

Journal Article↗
PubMed2004

Er:Yb-doped waveguide laser fabricated by femtosecond laser pulses.

Laser action is demonstrated in a 20-mm-long waveguide fabricated on an Er:Yb-doped phosphate glass by femtosecond laser pulses. An output power of 1.7 mW with approximately 300 mW of pump power coupled into the waveguide is obtained at 1533.5 nm. Waveguides are manufactured with the 520-nm radiation from a frequency-doubled, diode-pumped, cavity-dumped Yb:glass laser operating at a 166-KHz repetition rate, with a 300-fs pulse duration.

Journal Article↗
PubMed2004

Conjugation length dependence of internal conversion in carotenoids: role of the intermediate state.

We report on a sub-20-fs transient absorption study of the S2(1(1)B(+)(u))-->S1(2(1)A(-)(g)) internal conversion in a series of carotenoids with a number of conjugated double bonds (N) ranging from 5 to 15. For the longer carotenoids (N>or=9), the measurements reveal the existence of an additional intermediate excited state lying between the optically allowed S2 state and the lower-lying forbidden S1 state. This state enables us to explain the nonmonotonic dependence of the S2-->S1 conversion rate on N and is expected to play an important role in photosynthetic light harvesting.

Carotenoids↗
PubMed2004

Highly efficient second-harmonic nanosource for near-field optics and microscopy.

A nanometric source of second-harmonic (SH) light with unprecedented efficiency is demonstrated; it exploits the grazing-incidence illumination of a metal tip, which is conventionally used for atomic force microscopy, by 25-fs laser pulses of a high-energy Ti:sapphire oscillator. Tip scanning around the beam focus shows that the SH generation is strongly localized at its apex. The polarization dependence of the SH light complies with the model of an on-axis nonlinear oscillating dipole.

Journal Article↗
PubMed2003

Understanding fundamental processes in poly(9,9-dioctylfluorene) light-emitting diodes via ultrafast electric-field-assisted pump-probe spectroscopy.

Femtosecond electric-field-assisted pump-probe measurements are a new approach to the study of fundamental processes within organic optoelectronic devices. Here we report a detailed study of organic light-emitting diodes based on poly(9,9-dioctylfluorene), using both temporal and spectral information to investigate polaron generation, due to field-induced singlet dissociation, and their subsequent recombination. The fundamental event in electroluminescence is time resolved: we find that initially free polarons coalesce into intermediate pairs of both singlets and triplets multiplicity which subsequently decay into the neutral state. Our results indicate that the efficiency of singlet formation, beta approximately 0.7, is much higher than expected from simple state degeneracy arguments (beta approximately 0.25).

Journal Article↗
PubMed2003

Time domain investigation of the intrachain vibrational dynamics of a prototypical light-emitting conjugated polymer.

Coherent nuclear motion of the carbon backbone is monitored in real time in substituted poly(phenylene)-vinylene in both excited and ground electronic state using sub-10-fs light pulses. Characteristic features of the intrachain vibrational dynamics are obtained. We observe vibrational dephasing in the excited state within 1 ps (time constant T(2e) approximately 300 fs). These findings are in agreement with the molecular picture for photoexcitation in conjugated polymers.

Journal Article↗
PubMed2002

Photosynthetic light harvesting by carotenoids: detection of an intermediate excited state.

We present the first direct evidence of the presence of an intermediate singlet excited state (Sx) mediating the internal conversion from S2 to S1 in carotenoids. The S2 to Sx transition is extremely fast and is completed within approximately 50 femtoseconds. These results require a reassessment of the energy transfer pathways from carotenoids to chlorophylls in the primary step of photosynthesis.

Carotenoids↗
PubMed2002

Time-resolved charge carrier generation from higher lying excited states in conjugated polymers.

Sub-ps three-pulse transient differential transmission spectroscopy using two excitation pulses is used to directly investigate the generation of charge carriers in ladder-type poly(para)phenyl in bulk film. The role of higher excited singlet states of both even and odd symmetry is examined and the dynamics of the major processes involved is described quantitatively. The charge generation efficiency is found to depend strongly on the delay between the two excitation pulses. This is explained by the interplay between internal conversion, excitation energy migration, and on-site vibronic relaxation.

Journal Article↗
PubMed2002

High-brightness high-order harmonic generation by truncated bessel beams in the sub-10-fs regime.

Low-divergence, high-brightness harmonic emission has been generated by using a fundamental beam with a truncated Bessel intensity profile. Such a beam is directly obtained by using the hollow-fiber compression technique, which indeed allows one to optimize both temporal and spatial characteristics of the high-order harmonic generation process. This is particularly important for the applications of radiation, where extreme temporal resolution and high brightness are required.

Journal Article↗
PubMed2001

Coherent dynamics of photoexcited green fluorescent proteins.

The coherent dynamics of vibronic wave packets in the green fluorescent protein is reported. At room temperature the nonstationary dynamics following impulsive photoexcitation displays an oscillating optical transmissivity pattern with components at 67 fs (497 cm(-1)) and 59 fs (593 cm(-1)). Our results are complemented by ab initio calculations of the vibrational spectrum of the chromophore. This analysis shows the interplay between the dynamics of the aminoacidic structure and the electronic excitation in the primary optical events of green fluorescent proteins.

Green Fluorescent Proteins↗
PubMed2001

ACE gene polymorphism and IgA nephropathy: an ethnically homogeneous study and a meta-analysis.

BACKGROUND: Conflicting results have implicated the angiotensin-converting enzyme (ACE) D allele in the progression of renal damage in patients with IgA nephropathy (IgAN). Most of these findings have been obtained by heterogeneous studies. METHODS: We investigated the ACE insertion/deletion (I/D) gene polymorphism by polymerase chain reaction (PCR) amplification of genomic DNA in an ethnically homogeneous sample size of IgAN patients from Southern Italy. The association between ACE I/D gene polymorphism and the development of the disease was examined in 247 biopsy-proven IgAN patients and 205 healthy subjects. The association with the progression of renal damage was evaluated in 136 patients with a follow-up of > or =3 years according to the slope of the creatinine clearance against time, and in 221 patients with a follow-up of > or =1 year assessing by univariate and multivariate analyses of renal survival. These associations were further estimated in a meta-analysis of seven studies retrieved in the Medline database. The meta-analysis was performed according to the Mantel-Haenszel-Peto method when homogeneity of the studies was established using the chi(2) test by Breslow-Day. RESULTS: No difference in the ACE I/D gene distribution between patients and controls and between patients with stable and those with deteriorating renal function was found in our study. A meta-analysis performed separately for Caucasian and Asian studies showed that the ACE I/D gene polymorphism did not contribute to the genetic susceptibility of the development of IgAN (total OR 0.93, 95% CI, 0.71 to 1.23; and 0.95, 95% CI, 0.64 to 1.42, respectively) or the progression of the renal damage (total OR 1.12, 95% CI, 0.67 to 1.88; and 2.26, 95% CI, 0.75 to 6.79, respectively) in both groups. CONCLUSIONS: Our study and meta-analysis suggest caution in the interpretation of results from association studies enrolling heterogeneous populations. Further studies using new tests, which are free of the bias due to population stratification and ethnicity, are warranted.

Adolescent↗
PubMed2000

Spectral features and modeling of high-order harmonics generated by sub-10-fs pulses

Harmonic radiation generated in a neon gas jet by sub-10-fs laser pulses was investigated both experimentally and theoretically. The spectral profile of the harmonics with respect to the order, their intensity and relative spectral shifts were measured as a function of the position of the gas jet. The results point out spectral features typical of the quasi-single-cycle excitation regime. A nonadiabatic three-dimensional numerical model was developed, which provides harmonic spectra in remarkable agreement with the experiments.

Journal Article↗