Femtosecond fluorescence studies of DNA/RNA constituents

International audienceIn this overview, femtosecond fluorescence studies of various DNA constituents are presented, ranging from the monomeric chromophores to different model helices. In order to interpret the experimental results in terms of fundamental processes on the molecular scale they are discussed in the light of recent theoretical calculations. The ultrafast fluorescence decay observed for the monomers is explained by the involvement of highly efficient conical intersections (CI) between the first singlet excited state and the ground state. For the model helices, the picture is more complex, but fluorescence anisotropy data reveal collective effects

Assessing solvent effects on the singlet excited state lifetime of uracil derivatives: a femtosecond fluorescence upconversion study in alcohols and D2O

The excited state lifetimes of uracil, thymine and 5-fluorouracil have been measured using femtosecond UV fluorescence upconversion in various protic and aprotic polar solvents. The fastest decays are observed in acetonitrile and the slowest in aqueous solution while those observed in alcohols are intermediate. No direct correlation with macroscopic solvent parameters such as polarity or viscosity is found, but hydrogen bonding is one key factor affecting the fluorescence decay. It is proposed that the solvent modulates the relative energy of two close-lying electronically excited states, the bright ΠΠ and the dark nΠ states. This relative energy gap controls the non-radiative relaxation of the ΠΠ state through a conical intersection close to the Frank-Condon region competing with the ultrafast internal conversion to the ground state. In addition, an inverse isotope effect is observed in D2O where the decays are faster than in H2O

Singlet excited state dynamics of uracil and thymine derivatives: A femtosecond fluorescence upconversion study in acetonitrile

The excited state properties of uracil, thymine and four analogous uracil compounds have been studied in acetonitrile by steady-state and time-resolved spectroscopy. The excited state lifetimes were measured using femtosecond UV fluorescence upconversion. The excited state lifetimes of uracil and its 1- and 3-methyl substituted derivatives are well described by one ultrafast (6100 fs) component. Five substituted compounds show a more complex behavior, exhibiting longer excited state lifetimes and bi-exponential fluorescence decays. These longer decays are substantially faster in acetonitrile than in aqueous solution showing that the excited state deactivation mechanism is in part governed by the solvent

Optical Properties of Guanine Nanowires: Experimental and Theoretical Study

International audienceLong nanowires formed by ca. 800 guanine tetrads (G4-wires) are studied in phosphate buffer containing sodium cations. Their room temperature optical properties are compared to those of the monomeric chromophore 2-deoxyguanine monophosphate (dGMP). When going from dGMP to G4-wires, both the absorption and the fluorescence spectra change. Moreover, the fluorescence quantum yield increases by a factor of 7.3 whereas the average fluorescence lifetime increases by more than 2 orders of magnitude, indicating emission associated with weakly allowed transitions. The behavior of G4-wires is interpreted in the light of a theoretical study performed in the frame of the exciton theory combining data from molecular dynamics and quantum chemistry. These calculations, carried out for a quadruplex composed of three tetrads, reveal the existence of various exciton states having different energies and oscillator strengths. The degree of delocalization of the quadruplex Franck−Condon excited states is larger than those found for longer duplexes following the same methodology. The slower excited-state relaxation in G4-wires compared to dGMP is explained by emission from exciton states, possibly limited on individual tetrads, whose coherence is reserved by the reduced mobility of guanines due to multiple Hoogsteen hydrogen bonds

Lean Six Sigma Approach to Implement a Femur Fracture Care Pathway at “San Giovanni di Dio e Ruggi d’Aragona” University Hospital

Timeliness in the treatment of fracture of the femur, through surgery, is crucial in the elderly patient as it reduces the risk of mortality and disability. Here we propose a Lean Six Sigma (LSS) approach to reduce the preoperative length of stay for patients with femur fracture. Through the LSS, a tailored Diagnostic Therapeutic Assistance Path (DTAP) for these has been implemented and monitored over time. In particular, through the analysis, based on the application of the DMAIC cycle conducted on data extrapolated from the information system of the “San Giovanni di Dio e Ruggi d’Aragona” University Hospital of Salerno, the new DTAP was designed and implemented. After the introduction of the DTAP, a significant reduction in the average length of hospital stay was observed, with a preoperative length of stay within 48 h in 65% cases (compared to the previous 9%). In particular, the most significant reduction (over 55%) is obtained for patients aged over 65 years old. Such a result reflects not only the improvement in the care process but it is also compliant with the guidelines of the Italian Ministry of Health, as reported in the New Guarantee System for monitoring the quality of care. © 2021, Springer Nature Switzerland AG