Post-Hartree-Fock ab initio quantum chemical calculations were performed for 5-fluorouracil in the gas phase and in a three-water cluster. Full geometry optimizations of the 5-fluorouracil-water complexes were carried out at the MP2/6-31+G(d,p) level of theory. MP4/6-31+G(d,p)//MP2/6-31+G(d,p) and MP4/6-31++G(d,p)//MP2/6-31+G(d,p) single-point calculations were performed to obtain more accurate energies. In water solution, 5-fluorouracil exists mainly in the 2,4-dioxo form (A). We propose that the populations of the 2-hydroxy-4-oxo (B) and 4-hydroxy-2-oxo (D) tautomers are 1 x 10(-4)% and 3.9 x 10(-8)%, respectively, on the basis of the relative stabilities of the tautomers calculated at the MP4/6-31++G(d,p)//MP2/6-31+G(d,p) level of theory. A profound difference between isolated and hydrated 5-fluorouracil is noted for the height of the tautomerization barrier. In the absence of water, the process of proton transfer is very slow. The addition of water molecules decreases the barrier by 2.3 times, making the process much faster. The minimum energy path (MP2/6-31+G(d,p)) for water-assisted proton transfer in trihydrated 5-fluorouracil was followed. CNDO/S-CI calculations predict singlet pi-pi(*) electron transitions at 312 nm for B and at 318 nm for D. The fluorescence spectrum of 5-fluorouracil in water confirms the presence of the hydroxy tautomer.

No abstract

No abstract

No abstract

No abstract

The synthesis of 3‐hetaryl substituted coumarin derivatives [7‐hydroxy‐2H‐chromen‐2‐on and 9‐hydroxy‐2H‐benzo(f)chromen‐2‐on] containing a hydroxyl group by reacting 2,4‐dihydroxybenzaldehyde and 2,4‐dihydroxynaphtaldehydes with 2‐cyanomethylbenzothiazole, 2‐cyanomethylbenzimidazole, 1‐methyl‐2‐cyanomethylbenzimidazole and 2‐cyanomethyl‐4‐phenylthiazole is presented. The absorption and steady‐state fluorescence characteristics of the synthesised 3‐hetaryl substituted 7‐hydroxy‐2H‐chromen‐2‐on and 9‐hydroxy‐2H‐benzo(f)chromen‐2‐on in a solution of ethanol and at different pH values are studied to assess their possible application as fluorescent probes for use in molecular biology and medicine.

We fabricated stable gold nanostars (AuNSs) with tunable extinction properties from the visible spectral region up to 1800 nm, depending on the average values of core size and branch length. The results of their UV-Vis and transmission electron microscopy characterization are compared with computational data from finite elements method, which makes use of an approximated model of the branched structures. The theoretical computations put in evidence the existence of hot spots located on the tips of the nanostars even up to 1800 nm wavelength, which opens the way to the improvement of diagnostics in the IR region. Preliminary Fourier transform Raman experiments performed after functionalization with a fluorescent dye bearing end thiol groups seem to confirm the field enhancing capability of the nanostructures at 1064 nm.

No abstract