1,354,579 research outputs found
Use of nonradiative decays of extrinsic fluorophores as structural and dynamical probes in protein environments: Fluorescence quenching
No full textIn this work a combined pulsed-laser, time-resolved photoacoustic calorimetry (PAC) and fluorescence study is presented on two widely used covalent protein probes, fluorescein-5-isothiocyanate (FITC) and 6-acryloyl-2-dimethylaminonaphtalene (acrylodan). Three proteins that contain a single free thiol, namely carbonic anhydrase, bovine serum albumin (BSA) and papain, have been selectively labelled with FITC and acrylodan, and their fluorescence emission was quenched with KI. Nonradiative decays of the excited states of FITC are used to complement the information usually obtained by monitoring the quenching of fluorescence emssion. Data analysis evidences the dependence of the nonradiative quenching constants on the exposure of the dye to the solvent, and shows the involvement of a triplet state of FITC in the non radiative deexcitation. The shielding of the binding sites from the solvent is demonstrated also by the fluorescence emission of acrylodan and by the Stern-Volmer analysis of fluorescence quenching by KI. From photoacoustic data, an estimate of the fluorescent quantum yield of bound FITC is obtained. This work demonstrates the complete equivalence of quenching data obtained by fluorescence and photoacoustics measurements and shows that this combined approach allows a better control of the photophysics of the dyes involved in the quenching process
A novel targeting approach for melanoma cancer treatment based on photodynamic therapy
No full textPhotosensitizing molecules have been at the basis of photodynamic therapy (PDT) since its early development in the 1950s. The therapy is a selective treatment method based on the administration of a photosensitizer to diseased cells: when irradiated with visible light of suitable wavelength, the photoactivated molecule starts a cascade of molecular transitions leading to cytotoxic effects in the targeted cells. The achievement of effective bio-compounds with photosensitizing capabilities and increased selectivity towards specific tumors is at the heart of the current research in the field. The aim of the herein project is to create an all-in-one multifunctional bio-molecule to be used in PDT treatments for melanoma cancer cells and holding targeting, imaging and photosensitizing potential
Photoinduced structural volume changes in aqueous solutions of blepharismin
No full textEmploying time-resolved photoacoustics we measured the structural volume changes (ΔVri) occurring after photo-excitation of blepharismin (BPR) aqueous solutions; an expansion occurring in the subnanosecond timescale is followed by a back contraction within some hundreds of nanoseconds. The magnitude of the ΔVri strongly depends on pH, allowing the determination of the pKa of BPR with this method. The values so measured are very close to those found by means of UV-visible absorption spectroscopy. The presence of water-soluble electron acceptors or donors (hexacyanoferrate [III] hexacyanofer-rate [II]) as well as the concentration of oxygen do not affect the magnitude or the kinetics of the structural volume changes. On the contrary, we detect a strong deuterium effect; this suggests that the observed ΔVri are related to an altered hydrogen bond pattern of the excited state of the pigment with respect to the ground state. Comparative measurements with the parent compound hypericin are also reported, suggesting that the photo-induced expansion-contraction pattern is a general characteristic of polyhydroxylated quinones
Reaction volume of water formation detected by time resolved photoacoustics: photoinduced proton transfer between o-nitrobenzaldehyde and hydroxyls in water
No full textThe structural volume changes accompanying light-induced proton transfer reactions in aqueous solutions of o-nitrobenzaldehyde have been investigated using time-resolved photoacoustics. The solvation of the newly formed ions is accopanied by a contraction of the medium of about −5.2 ± 0.2 ml/mol. At a pH above 9.5, the formation of water molecules leads to an expansion of 24.5 ± 0.4 ml/mol. The apparent rate constant for the protonation of hydroxyls is k = (4.9 ± 0.4) X 1010 M− s−. This is the first direct time-resolved measurement of the extent of the structual volume changes accompanying water formation
Method for acquiring extended real-time kinetics in nanosecond laser flash photolysis experiments
No full textWe report a data acquisition method for detecting transient absorbance signals extended in time which require nanosecond resolution and need to span several decades in time up to the hundreds of milliseconds. A microprocessor is used to generate a sequence of up to 100, 2.120 μs wide radio frequency signals at 500 MHz which are used to trigger the analog-to-digital conversion on a digital oscilloscope, operating in the external clock mode. During these radio frequency bursts the data are sampled at a sampling rate of 500 Ms/s. The delay of each sampling burst can be set at arbitrary values with respect to the first signal, with a minimum delay of 0.96 μs for the second pulse, and 1.2 μs for all other pulses. The microprocessor provides accessory synchronization outputs for laser triggering and for shutter opening and closing. This data acquisition system allows measuring the complete time course of extended kinetics after each laser shot, thus reducing acquisition times and data size. We prove the complete equivalence of the proposed acquisition method with standard methods, where several time bases are acquired to cover the complete kinetic trace for the ligand rebinding to myoglobin after photolysis of a gel embedded myoglobin-CO complex. © 2004 American Institute of Physics
Reaction volume and rate constants for the Excited State Proton Transfer in aqueous solutions of Naphthols
No full textIn this Letter we report the time-resolved determination of the volume changes for the excited-state deprotonation of 1-naphthol, 2-naphthol and 1-naphthol-3,6-disulphonate and the neutralization of the ground-state naphtholate anions with the protons free in solution. Photoexcitation of the naphthols leads to a fast contraction of the solution due to the solvation of the newly formed ions and is followed by an expansion of equal extent, due to the back recombination reaction. The apparent rate constant of the recombination reaction depends on the concentration of protons free in solution in accordance with a pseudo-first-order reaction model
Time-Resolved Photoacoustic-Spectroscopy - New developments of an old idea
No full textAcoustic waves generated by heat emission in radiationless transitions from photoexcited molecules can be detected by suitable transducers. Their study allows the investigation of thermal relaxations, thus providing thermodynamic and kinetic data on short-lived species produced by the absorption of pulses of light.
In this field of research the best technique has proved to be the so-called pulsed-laser, time-resolved photoacoustic spectroscopy, which is based on piezoelectric detection of pressure waves in the time domain. Deconvolution processing of the transient signals gives both the lifetimes of excited states and the energy content of the transitions, provided that decay times are in the range 5 ns-5 mu s Moreover, when compared with proper theoretical models emphasizing the energy balance, the photoacoustic results can help to build a complete picture of the deactivation pathways, including photochemical events.
The biophysical applications, although numerous and widespread both in basic and applied research, offer the real possibility of giving information on photobiological processes in conditions very close to the living state.
Among the more significant contributions obtained in this area, the results on photosynthesis and photosensitivity of plants and photosynthetic micro-organisms, structural and functional dynamics of respiratory proteins, photocycles of rhodopsin and bacteriorhodopsin and photophysical properties of several natural pigments are particularly relevant, together with some medical and biotechnological applications.
Another promising field of application of photoacoustics concerns photoactive drugs and,the photophysics of fluorescent probes for conformational studies of proteins, nucleic acids and membranes. In general terms, time-resolved photoacoustic spectroscopy promises to become one of the most powerful techniques in photobiophysics, provided that some limitations in data analysis and time resolution are removed by technical improvements
Treatment with natural anti-oxidants from vitis vinifera decreases lipid peroxidation in non insulin-dependent diabetics
No full textTime-resolved photothermal methods : accessing time-resolved thermodynamics of photoinduced processes in chemistry and biology
No full textPhotothermal methods are currently being employed in a variety of research areas, ranging from materials science to environmental monitoring. Despite the common term which they are collected under, the implementations of these techniques are as diverse as the fields of application. In this review, we concentrate on the recent applications of time-resolved methods in photochemistry and photobiology
Study of proton transfer processes in solution using the laser induced pH-jump: a new experimental setup and an improved data analysis based on genetic algorithms
No full textWe present an experimental setup for studying proton transfer reactions in solution and an innovative data analysis based on a genetic algorithm. We have used o-nitrobenzaldehyde to irreversibly release protons in an aqueous solution upon photolysis with an intense UV nanosecond laser pulse. Reactions of the photodetached protons with pH indicators have been followed by monitoring the changes in absorbance at 632.8 nm with a He–Ne laser and a Si avalanche photodiode. The setup has laser-limited time resolution and single shot sensitivity. The pH jump established with the laser shot lasts ∼30 ms, during which proton transfer reactions can be followed. The proposed methodology represents a simplification in the kinetic schemes with respect to the previous protocols based on the use of reversible caged protons.© 1998 American Institute of Physics
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