Introduction: Although photophysical properties of Radachlorin photosensitizer (PS) were extensively studied in solutions and cells, no data is available on variations of its characteristics upon binding to serum albumins, which are major transporters in blood and nutrients in cell culture media. Objectives: The primary objective of this study was to analyze changes in photophysical properties of Radachlorin molecules upon their binding to human and bovine serum albumins at different microenvironment properties. Methods: Experiments were performed using time-resolved fluorescence spectroscopy and fluorescence recovery after photobleaching. Variations in fluorescence spectra and lifetime, fluorescence anisotropy, rotational and translational diffusion of PS molecules upon binding to albumins were studied in normal, basic and acidic conditions and at different concentrations of albumin and PS molecules. Results: Radachlorin molecules effectively bind to both types of serum albumins, which causes changes in photophysical properties of the PS. A minor red shift of the fluorescence spectrum, an increase in fluorescence lifetime and anisotropy and substantial decrease of translational and rotational mobility of PS molecules were observed upon their binding to albumins. The analysis of rotational diffusion time provided robust evaluation of the bound fraction of PS molecules. Both the highly acidic microenvironment and increase in alcohol concentration above 40% resulted in detachment of PS molecules from albumins. Photophysical properties of Radachlorin in complexes with BSA and HSA were found to be slightly different. Conclusions: Binding of Radachlorin photosensitizer to either BSA or HSA affects significantly its photophysical properties, which may also vary with microenvironment acidity and alcohol concentration.

We present a thorough experimental investigation of fluorescence properties of Radachlorin photosensitizer in solutions of different acidity, viscosity and polarity. Experiments were performed using time-resolved fluorescence lifetime imaging and time-resolved analysis of polarized fluorescence. Variations of solution acidity resulted in considerable changes of Radachlorin fluorescence quantum yield and lifetime in the pH range from 4 to 7, but did not affect the rotational diffusion time, and almost did not change the quantum yield and characteristic times of singlet oxygen phosphorescence. Variations of solution polarity and viscosity were achieved by changing ethanol or methanol fraction in aqueous solution. The decrease of solution polarity resulted in nonlinear rise of Radachlorin fluorescence quantum yield and lifetime up to alcohol concentration of 50%-65%, as well as in considerable rise of singlet oxygen quantum yield and significant changes in characteristic times of its phosphorescence. Variations of solution viscosity resulted in changes of rotational diffusion time of Radachlorin molecules, which appeared to be in perfect correlation with methanol solution viscosity. Good correspondence with ethanol solution viscosity was observed only up to 50% alcohol fraction. Deviations of rotational diffusion time of Radachlorin molecules from direct proportionality with solution viscosity at higher ethanol concentrations were suggested to be due to different solvation conditions. The data obtained can give important reference points for analysis of microenvironment of Radachlorin molecules, their intracellular localization and performance in singlet oxygen generation.

We studied quantum yield in biological coenzymes NADH and FAD in water-alcohol solutions. The analysis of the experimental results obtained allowed to separate the factors that influence on the fluorescence quenching in FAD and NADH: the role of molecular conformations in non-radiative relaxation processes in excited states, and solution viscosity and polarity.

We studied fast energy transfer processes in NADH excited states in water-l,2-propandiol solutions using recently developed polarization-sensitive modulation pump-probe technique. Linear dichroism in NADH excited states in 0% and 40% 1,2-propandiol were studied with a temporal resolution of about 0.3 ps and extremely high sensitivity. Fast picosecond anisotropic relaxation in NADH was observed at the first time. The effect observed was shown to be due to the rotation of the molecular transition dipole moment in the course of fast rearrangement of NADH nuclear configuration.

In this paper, experiments on measuring absorption of infrared laser radiation in the laser-produced plasma of Xe are described. An absorbed fraction of up to 65% was obtained when the gas-jet target was illuminated by a wide, defocused beam, whereas it barely reached 8.5% in the case of a sharply focused beam. The phenomenon is explained on the basis of a hypothesis of the plasma’s hydrodynamic expansion according to which the plasma leaves the illuminated area faster the smaller its size. This explains the similarity of extreme ultraviolet output and laser energy absorption as functions of the laser beam diameter. Based on the experimental results, an attempt to estimate the plasma parameters ( N, T, ) is undertaken, with the mean ion charge, , being calculated using ionization cross-sections for ions from +7 Xe to +14 Xe, which were obtained by means of a quantum-mechanical numeric simulation especially for the present work.

The fluorescence decay of Radachlorin photosensitizer in aqueous solution under two-photon excitation by femtosecond laser pulses at 810 nm has been studied. The major fluorescence parameters of the molecule including fluorescence decay time, rotational diffusion time and anisotropy have been determined.

Absorption of the laser pulse energy in the plasma has been shown to change from 8.5% at irradiation of a gas-puff target with a beam narrow-focused onto a near-central area of the jet up to 65% at the wide defocused irradiation. An analysis of this phenomenon is based on a hypothesis that plasma density decays significantly during the 10ns laser pulse due to hydrodynamic expansion of the hot plasma. A similarity of the EUV (Extreme UltraViolet) intensity and the laser light absorption as functions of the laser beam diameter suggests a revision of the conventional idea of a strong EUV radiation self-absorption in a cold peripheral shell of the laser plasma whereas the high absorptivity of the laser radiation by the plasma looks like a major feature to gain high efficiency of an EUV source.

Measurements of geometric parameters of a high-power infrared laser beam have been realized by three methods. The obtained results are in a satisfactory agreement with each other. When focusing the beam with wavelength of 1.064 μm with a specially designed non-aberrational objective, a focal spot of approximately 40 μm diameter could be obtained, with the waist length being 230−280 μm. The measured parameters give an idea of the size of a laser plasma generated by this beam on a Xe gas microjet.

A novel pump-probe method has been developed to study anisotropic relaxation and energy transfer in excited states of polyatomic molecules excited by femtosecond laser pulses. The method was used to study the rotational diffusion of NADH with a temporal resolution of about 0.6 ps. For the first time, absorption from the excited state of biological molecules pumped by laser pulses with energies of 1 nJ was detected

A novel ultrasensitive transient time-resolved monitoring method has been developed suitable for studying of fast anisotropic relaxation in electronic excited states of polyatomic and biologically relevant molecules under excitation with femtosecond laser pulses. The method is based on the modulation of a pump beam polarization with a photo-elastic modulator and highly sensitive balanced detection of mutually orthogonal polarization components of a probe beam with following recording of the differential transient signal with a lock-in amplifier. The method was used for the study of anisotropic relaxation in the first electronic excited state of coenzyme NADH in solutions with various viscosity and polarity.

A new pump–probe technique has been developed for investigation of anisotropic relaxation and energy transfer processes in excited states of polyatomic molecules excited by femtosecond laser pulses. The proposed method was applied for studying the rotational diffusion of NADH with a temporal resolution of about 0.6 ps. Linear dichroism in excited states of biological molecules induced by laser pulses with energy below 1 nJ has been detected for the first time.

We studied polarized fluorescence in biological coenzyme NADH in water-methanol solutions of various viscosity and polarity upon two-photon excitation with femtosecond laser pulses at 720 nm. Polarization anisotropy, fluorescence lifetimes, and rotational diffusion times have been determined. The results obtained are compared with the results reported elsewhere.

Measurements of geometric parameters of a powerful infrared laser beam have been realized by three methods. The results obtained are in a satisfactory agreement with each other. When focusing the beam with wavelength of 1.064 μm by means of a specially designed non-aberrational objective, a focal spot of ≈40μm diameter could been obtained, with the waist length being 230−280 μm. The measured parameters give an idea of the size of the laser plasma generated by this beam on the Xe gas microjet.

The decay of polarized fluorescence in coenzyme NADH in aqueous-methanol solution under two-photon excitation by femtosecond laser pulses within the spectral range of 720–780 nm has been studied. Molecular fluorescence parameters: decay times τ 1 and τ 2 , rotational diffusion time τ rot , and pre-exponential factor ratio a 2 / a 1 have been determined from experiment. The results obtained have been compared with those reported recently in NADH in aqueous solution.

We studied polarized fluorescence in biological coenzyme NADH in water-methanol solutions upon two-photon excitation with femtosecond laser pulses at 720 nm. The polarized fluorescence decay was recorded by a time correlated single photon counting (TCSPC) system. Fluorescence decay times, rotational diffusion time, fluorescence anisotropy, and the ratio of two pre-exponential factors have been determined and studied as a function of methanol concentration. The results obtained were interpreted on the basis of a model of NADH denaturation processes in solutions and can be used for modeling of NADH binding with various dehydrogenases in living cells.

The decay of polarized fluorescence in coenzyme NADH upon two-photon excitation by femtosecond laser pulses at the wavelength range of 720- 780 nm in water/methanol solution has been investigated. Decay fluorescence times tau_1 and tau_2, rotation diffusion time tau_rot, and preexponential factors a_1/a_2 ratio have been determined from experiment. The results obtained have been compared with previous results in NADH in aqueous solution. polarized fluorescence, NADH, adenine, nicotinamide, spectroscopy, time correlation single photon spectroscopy

AbstractA more than tenfold increase in the intensity of EUV radiation from a laser-produced plasma source is observed experimentally under the illumination of a Xe gas-jet target with a wide laser beam covering its densest part compared with the radiation intensity at the traditional geometry, when the beam is sharply focused on the jet axis. As an explanation, it is assumed that in this case almost the whole dense part of the jet is heated and ionized under the action of laser irradiation and becomes transparent to the quanta of the studied radiation. The thickness of the absorbing peripheral shell of a laser spark decreases accordingly, that leads to the increase in the radiation intensity reaching the observer.