Biomedical subjects

D Polli

Publications and source records attributed to D Polli.

5 recordsLinked to original sources

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↗

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↗

PubMed1995

Rectal blood flow in ulcerative colitis.

OBJECTIVE: To determine the state of local blood flow in ulcerative colitis. METHODS: Rectal blood flow was measured by means of laser Doppler flowmetry during endoscopy in 20 patients with active or inactive ulcerative colitis and in 20 healthy controls. RESULTS: A significant (p < 0.01) reduction in the values of rectal perfusion was observed in ulcerative colitis patients both in active phase and in clinical and endoscopic remission. CONCLUSIONS: Impaired local blood flow may have a pathogenetic role in ulcerative colitis. Remission of the disease is not accompanied by normalization of local microcirculation, which may predispose to relapses.

Adult↗

PubMedDate not supplied

Measurement of rectal blood flow by laser Doppler flowmetry in inflammatory bowel disease.

BACKGROUND/AIMS: Vascular alterations have been suggested as pathogenic factors in inflammatory bowel disease, particularly Crohn's disease. The aim of our study was to assess rectal blood flow in patients with active inflammatory bowel disease involving the rectum. METHODOLOGY: Endoscopic measurement of rectal blood flow was performed by laser Doppler flowmetry in 45 subjects divided into three groups: healthy controls, ulcerative colitis and rectal Crohn's disease. RESULTS: Rectal perfusion was found to be significantly impaired in patients with ulcerative colitis, but not in those with Crohn's colitis. CONCLUSIONS: Our results confirm the role of local ischemia in ulcerative colitis, but do not support the theory that vascular factors play a key role in the pathogenesis of Crohn's disease.

Adult↗