S. Egorov

Quenching of singlet molecular oxygen by carnosine and related antioxidants. Monitoring 1270-nm phosphorescence in aqueous media.

In order to elucidate the biochemical roles of imidazol‐containing dipeptides, we have studied quenching of singlet molecular oxygen (1O2) by carnosine (β‐alanyl‐L‐histidine), its structural components (L‐histidine, imidazole, and β‐alanine), and related natural free‐radical scavengers ‐ L‐anserine (β‐alanyl‐l‐methyl‐histidine), ergothioneine (2‐thiol‐ L‐histidine‐betaine), and taurine (2‐aminoethanesulfonic acid) in aqueous (D2O, pD 7) solutions by using monitoring of 1O2‐phosphorescence (1270‐nm). The rate constants of 1O2 quenching (Kq) by carnosine, anserine, and ergothioneine were shown to be similar [(3±1)×107 M‐1s‐1]. Their values resembled those of free L‐histidine [Kq=(4±1)×107 M‐1s‐1] and imidazole [Kq=(2±1)×107 M‐1s‐1]. Non‐aromatic amino acids ‐ taurine and β‐alanine ‐ showed very low quenching activities (Kq<3×103 M‐1c‐1). The Kq values did not correlate with the literature data on abilities of the tested compounds to stimulate muscle working capacities and inhibit myeloperoxidase‐catalyzed oxygenation. Thus, the dipeptides can be used as potent water‐soluble protectors against 102 attack whereas their natural biochemical functions are most probably determined by the processes of different nature.

Laser-induced luminescence of singlet molecular oxygen: generation by drugs and pigments of biological importance

The photon counting technique and flashlaser excitation were applied to the timeresolved measurement of photosensitized singlet oxygen luminescence in organic and aqueous media. The quantum yields for singlet oxygen generation have been measured in solutions of photosynthetic pigments synthetic and natural porphyrins porphyrins conjugated with monoclonal antibodies furocoumarins flavins fluorescein tetracycline and endogenous photosensitizers of human lens. The data obtained indicate that the measurement of the singlet oxygen luminescence is a reliable tool to study the photosensitizing activity of drugs and to elucidate primary mechanisms of photodynamic destruction. 1.

Kinetics of laser-induced phosphorescence of singlet molecular oxygen in aqueous porphyrin solutions

Kinetics of laser induced phosphorescence of singlet molecular oxygen was measured with nanosecond resolution at 1270 nm in air-saturated aqueous solutions of tetrakis(4- sulfonatophenyl)porphine, tetra sodium salt (TPPS). The phosphorescence kinetic curve comprised the rise and decay phases that are well described by exponentials with the rise time constant, (tau) r equals 2.16 +/- 0.08 microsecond(s) and decay time constant, (tau) d equals 3.15 +/- 0.15 microsecond(s) , the rise corresponding to the kinetics of energy transfer from triplet porphyrin to molecular oxygen, the decay - to deactivation of singlet oxygen. Within the accuracy of our measurements both (tau) r and (tau) d did not depend on pH in the range 5.8-9, laser powers in the range 0.32-1.6 W/cm2, the porphyrin concentrations in the range 13-48 (mu) M and the presence of phosphate buffer saline.

Method of assessing blood oxygenation in microcirculation vessels based on Doppler approach

Combination of laser Doppler flowmetry and pulse oximetry methods allows for the direct assessment of oxygen supply to tissues at the microcirculatory level, namely, in that part of the vascular network where the transcapillary exchange takes place that is responsible for saturating tissues with oxygen. The microcirculation system comprises arterial and venous microvascular parts that differ in blood flow velocities. Frequency separation of the photodetector signal components related to different velocity ranges makes possible to distinguish the hemodynamic processes in these two parts of the microvascular system. Moreover, numerous studies of collective oscillatory processes in hemodynamics reveal that cardio-oscillations are more pronounced in arterioles, whereas venous hemodynamics is mostly influenced by the breath rhythm. Taking account of the above phenomena allows developing a signal-filtration system for separate characterization of blood-oxygenation states in arterial and venous blood flows. Light absorbance in the skin depends on both light wavelength and blood-oxygenation level. Processing the signals obtained with a two-channel dual-wavelength (630 and 1115 nm) laser Doppler flowmeter provides information about blood oxygenation levels at the entrance and exit of the microvascular system and allows assessing the specific levels of oxygenation levels at the entrance and exit of the microvascular system and allows assessing the specific levels of oxygen consumption in tissues. In particular, this approach allows revealing pathogenic processes resulting from hyper- and hypo-oxygenation in tissues. For instance, rapidly growing malignant tumors are characterized by intensive metabolism, rapid formation of capillaries, and active transcapillary oxygen exchange that results in higher level of oxygen diffusion into tissue, while the level of oxygen is lowered in the microvascular veins.