Nowadays, dynamically developing optical (photonic) technologies play an ever-increasing role in medicine. Their adequate and effective implementation in diagnostics, surgery, and therapy needs reliable data on optical properties of human tissues, including skin. This paper presents an overview of recent results on the measurements and control of tissue optical properties. The issues reported comprise a brief review of optical properties of biological tissues and efficacy of optical clearing (OC) method in application to monitoring of diabetic complications and visualization of blood vessels and microcirculation using a number of optical imaging technologies, including spectroscopic, optical coherence tomography, and polarization- and speckle-based ones. Molecular modeling of immersion OC of skin and specific technique of OC of adipose tissue by its heating and photodynamic treatment are also discussed.

Using the B3LYP/6-31G(d) method, calculations of the structure and the IR spectra of all-trans-β-carotene and its 15,15 ′ -cis-isomer have been performed. The effective harmonic force fields have been obtained and the observed IR bands have been interpreted. Vibrations of the β-ionic ring have been singled out. On the basis of the analogy between the molecular structure of stable radicals and carotenoids of natural origin we set up the hypothesis that the methyl groups of the β-carotene molecule stabilizing the biradical excited triplet state that arises in the process of triplet-triplet energy transfer play a protective, screening role. Introduction.Carotenoids are inseparable companions of chlorophyll in all photosynthesizing organisms. It has been reliably established [1, 2] that carotenoids perform a protective function from the photodynamic action of singlet oxygen that arises from collisions of O 2 molecules in the ground triplet state with chlorophyll molecules in the excited triplet state that are formed with a small quantum yield in the process of their photoexcitation. The deactivation channels of electron excitation in carotenoids are not known. Therefore, it is interesting to study in detail the vibrational states of these molecules by means of quantum-mechanical calculations.Of the wide class of carotenoids, the most comprehensive data on the resonant Raman scattering (RRS) and IR spectra have been obtained for β-carotene. The molecular structure of all-trans-β-carotene was determined in [3][4][5] by the method of single-crystal diffraction of X-rays. In [6], the IR spectra were registered, and in [7-9] the RRS spectra were investigated. In [10-16], using tunable lasers, RRS excitation profiles from the most intense bands in the spectrum were obtained. However, theoretical interpretation of the vibrational spectra of β-carotene has been the subject of only one paper [6], in which the normal vibrations for the model compound have been calculated with the use of the empirical force field. The results of more rigorous calculations for a fragment of the polyene chain of all-transspheroidine by the hybrid density-functional method with a 6-31G(d) basis set and an interpretation of its RRS-spectra are given in [17]. When combined with proteins of the photosynthetic apparatus some carotenoids take a cis-conformation due to the rotation about one of the polyene chain bonds [18,19].The aim of the present paper is to perform quantum-mechanical calculations of the structure and the vibrational spectrum of all-trans-β-carotene and its 15,15 ′ -cis isomer by the density-functional method, interpret their experimental IR spectra, and investigate the appearance of vibrations of β-ionone rings.Calculation Procedure. The quantum-mechanical calculations by the B3LYP/6-31G(d) method of the structure and the IR spectra of the molecules of all-trans-β-carotene (I) and 15,15 ′ -cis-β-carotene (II) were carried out using the Gaussian 03 program [20]. The geometry of molecule I was optimaized with symmetry limitation C i . ...

The interaction of six low-molecular tissue-clearing agents (1,2 and 1,3-propanediol, ethylene glycol, glycerol, xylitol, sorbitol) with the collagen mimetic peptide (GPH) was studied by applying the methods of classical molecular dynamics (GROMACS), molecular docking (AutoDock Vina) and quantum chemistry (PM6 and B3LYP). The spatial configurations of intermolecular complexes were determined and interaction energies calculated. The dependence of the volume occupied by the collagen peptide on the clearing agent concentration in an aqueous solution was calculated. This dependence is not linear, and has a maximum for almost all the agents in the study. The correlations between the optical clearing potential and intermolecular interactions parameters, such as the time of an agent being in a hydrogen-bonded state, and the relative probability of formation of double hydrogen bonds and interaction energies, were determined. Using the correlations determined, we predicted the numeric value of the optical clearing potential of dextrose molecules in rat skin, which correlates with experimental data. A molecular mechanism of tissue optical clearing within the post-diffusion stage is suggested. Graphical abstract The molecular modeling of the interaction between clearing agents and collagen.

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