The results of in vivo optical immersion clearing of human skin under the effect of aqueous solutions of some immersion agents (monosaccharides of ribose, glucose and fructose, as well as glycerol, a triatomic alcohol) were obtained with the use of the OCT method. Values of average velocity of scattering coefficient change, obtained through an averaged Ascan of the OCT signal in the region of derma with the depth of 350 to 700 μm, were determined to evaluate the optical clearing efficiency. The velocity of scattering coefficient change and the optical clearing potential value appeared to be well correlated. The complex molecular modeling of a number of immersion clearing agents with a mimetic peptide of collagen (GPH)3, carried out with the use of the methods of classical molecular dynamics and quantum chemistry, allowed to identify correlations between the optical clearing efficiency and such a property as the energy of intermolecular interaction of clearing agents with a collagen peptide fragment.
The Raman spectra of five samples of sunflower seed oil and five samples of cold-pressed olive oil of various brands are recorded in the range of 500–2000 cm–1. Within the framework of the B3LYP/631G(d)/6-31G(d,p)/6-31+G(d,p)/6- 311G(d)/6-311G(d, p)/6-311+G(d,p) methods, the structural models of eight fatty acids (oleic, linoleic, palmitic, stearic, α-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic) are constructed, and also within the framework of the B3LYP/6-31G(d) method, the structural models of triglycerides of the first four of the above acids are obtained. The vibrational wavenumbers and intensities in the IR and Raman spectra are calculated. The Raman spectra of olive oil and sunflower seed oil were simulated by using the supermolecular approach. We investigated the dependence of the relative intensity of the vibrational bands νexp = 1660 and 1445 cm–1 on the concentration of triglycerides in oils of oleic and linoleic acids and the dependence of the intensity of these bands on the degree of saturation of fatty acids. Experimental and empirical dependences are constructed to estimate the relative concentration of triglycerides of oleic and linoleic acids in a mixture of olive oil and sunflower seed oil. The applicability of the density functional theory together with the vibrational spectroscopy for the identification of mixtures of vegetable oils is discussed.
FT-IR spectra of grape seed oil and glycerol were registered in the 650-4000 cm-1 range. Molecular models of glycerol and some fatty acids that compose the oil under study – linoleic, oleic, palmitic and stearic acids – as well as their triglycerides were developed within B3LYP/6-31G(d) density functional model. A vibrating FT-IR spectrum of grape seed oil was modeled on the basis of calculated values of vibrating wave numbers and IR intensities of the fatty acids triglycerides and with regard to their percentage. Triglyceride spectral bands that were formed by glycerol linkage vibrations were revealed. It was identified that triglycerol linkage has a small impact on the structure of fatty acids and, consequently, on vibrating wave numbers. The conducted molecular modeling became a basis for theoretical interpretation on 10 experimentally observed absorption bands in FT-IR spectrum of grape seed oil.
The interaction of glycerol immersion agent with collagen mimetic peptide ((GPH)9)3 and a fragment of the microfibril 5((GPH)12)3 was studied by the classical molecular dynamics method using the GROMACS software. The change in geometric parameters of collagen α-chains at various concentrations of an aqueous solution of glycerol is analyzed. It is shown that these changes nonlinearly depend on the concentration and are limited to a certain level, which correlates with the experimental data on optical clearing efficiency of human skin. A hypothesis on the cause of the decreased efficiency of optical skin clearing at high immersion agent concentrations is put forward. The molecular mechanism of immersion optical clearing of biological tissues is discussed.
The interaction of three tissue-clearing agents (1,2-1,3-propanediol, 1,2-ethanediol) with the collagen mimetic peptide ((GPH)3)9 was studied by applying the method of classical molecular dynamics. The complete conformational analysis of the clearing agents under study was performed using the DFT/B3LYP/6-311+G method (d, p), the most energetically favorable spatial configurations were determined, the values of the Mulliken atomic charges were calculated which were used for the simulation. The research showed that there is a good correlation between the time of the hydrogen binding of a clearing agent with a collagen peptide and the potential of optical clearing. The paper also discusses that the interaction of the tissue-clearing agents with a collagen peptide in a water solution results in the 6% average enlargement of the distance between the alpha peptide chains. It has been suggested that such changes in a collagen structure can affect the refraction index and as a consequence the optical clearing of a biotissue. The dependences of the average distance changing between the alpha chains of a collagen peptide and the concentration of clearing agents in water solution were determined.
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