Vibrational IR spectrum in the area (900-4000 cm-1) and Raman spectrum in the area (600-1900 cm-1) of cold-pressed cottonseed oil were recorded. Structural and dynamic models of fatty acids, including linoleic, oleic, palmitic, stearic acids and their triglycerides as well as gossypol molecules, were calculated using the DFT/B3LYP/6-31G(d) method. Theoretical IR and Raman spectra of cottonseed oil are constructed and the experimental spectra are interpreted in detail. The application of vibrational spectroscopy for percentage determination of gossypol content in cottonseed oil is discussed.
Measurements and modeling of the optical properties of adipose tissue and its components in the terahertz range with a change in tissue temperature were carried out. It was shown that the optical density (OD) of adipose tissue samples decreases with increasing temperature, which can be mainly associated with dehydration of the sample. We can also expect some contribution to the decrease in the OD of suppression of THz wave scattering when matching the refractive indices of scatterers and their environment due to the intake of free fatty acids secreted by adipocytes due to thermally induced cell lipolysis. It is shown that in the experimental model, the difference between the THz absorption spectra of water and oil allows us to estimate the water content in adipose tissue. A comparison of the measurement results and molecular modeling in the terahertz region confirmed the hypothesis about the reasons for the change in the optical properties of heated adipose tissue.
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.
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.
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.
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.
The T-matrix method together with the approximate theories such as the Rayleigh-Gans and anomalous diffraction approximations are used for the refractive index determination of bacterial cells from spectral extinction measurements. The water suspension of Escherichia coli K12 cells in exponential phase of growth is modeled as a system of randomly oriented homogeneous circular cylinders with identical radii and different lengths. In the case of length monodispersity the results of the approximate theories are compared with those obtained by the exact T-matrix method. Assuming the gamma distribution of bacterial lengths, the influence of the length polydispersity on the refractive index is investigated using the Rayleigh-Gans approximation. It is shown that the effect of the length polydispersity degree upon the refractive index of rod-shaped bacteria is negligible. The wavelength dependence of the refractive index of E. coli cells obtained gives the value of 1.397 at 589 nm what is in a good agreement with the result of immersion refractometry (1.395±0.005).
A simple modification of the Rayleigh-Gans approximation for homogeneous prolate cylinders are presented. It is shown that the structure of the phase function, calculated by the modified Rayleigh-Gans approximation, is more close to that, obtained by the T-matrix method, then do the classical Rayleigh-Gans approximation.
Experimental values of the extinction of Escherichia coli cells water suspension by Bryant et al. are used for the refractive index determination of these bacteria. The real suspension of E. coli cells is modeled as a system of identical randomly oriented homogeneous circular cylinders. This model permits one to determine the volume average value of the refractive index of the optically soft particles with a narrow size distribution. The discrete Shifrin method is used to calculate the extinction cross section of the finite cylinders. The results indicate that the relative refractive index is practically independent of the wavelength of the incident radiation in the range from 0.4 micrometers to 0.8 micrometers . The mean value of 1.0387 in this range corresponds to the absolute refractive index value equal to 1.384 at 0.589 micrometers . The obtained value of refractive index of E. coli cells is somewhat lower than the result of immersion refractometry measured by Bryant et al.
The description of the discrete Shifrin's method (DShM) is presented. This method is based on representation of monochromatic Maxwell's equations in integral form. Using a simple discretization scheme the corresponding integral equation is converted to a system of simultaneous algebraic equations which is solved by the successive approximation method. The accuracy and the worked area of the DShM were investigated by comparison with Mie theory for homogeneous sphere. It was shown that this method converges rapidly for optically soft particle, whose equivolumetric radius is of the incident radiation wavelength order. Two normalized scattering matrix elements, S12/S11 and S34/S11, for randomly oriented homogeneous finite cylinders are also presented as a practical example.
The paper is devoted to computer simulation of elastic light scattering on reagent mixture during the immune reaction process in vitro. The immune reaction was analyzed in the limits of the 3-stages process of antigen-antibody complexes aggregation. Antibodies were treated as bivalent biomolecules, antigens were performed by 2, 3-valent biomolecule or polyvalent cells. Two variants of the problem solution of light scattering on the biological objects chosen were analyzed-Rayleigh-Gans-theory, the approach, and Mie theory, the preference was given to the first one. The optimum of the immune reaction output was revealed at quite a definite ratio of initial reagents concentrations. This optimum is analog of experimentally a well known phenomenon -- the 'zone of equivalence.' It's shown that the form of the 'zone of equivalence' both depends upon the kind of experimental procedure and the ratio of the antigen, antibody sizes. This result is preferably to take into consideration while one tries to optimize the medical diagnostic procedure based on the immune approach. It was revealed that the scattered light power correlates with the immunochemical kinetics not adequately sometimes. That fact may be useful to interpret the experimental investigations and at the same time it may give a principal possibility to use nephelometry for the aims of immune metrology.
On the base of computer simulation the immune kinetic processes for in vitro analysis was carried out for two cases: (1) antigen (Ag) was polyvalent, antibody (Ab)- monovalent; and (2) both Ag and Ab were bivalent. The problem was solved by calculation of the differential equations system minding limitations naturally. The immune reaction was treated as a combination of two competing processes: the antigen-antibody aggregation and synchronous disaggregation of immune complexes. Such a combination is to be described by a system of nonlinear differential equations but for simplicity the equations were linearized. The solution of the differential equation system was carried out minding some limitations naturally. The kinetic curves of immune reaction were obtained for different initial Ag, Ab concentrations and two experimental procedures. Partially, the concentrational curves obtained occurred for some cases analogous to the well known experimental results -- 'zone of equivalence.' The results of in vitro immune reaction simulation were used for computer analysis of one of the widely used methods of immune biomedical diagnosis -- light beam scattering (nephelometry). The light beam scattering by the 'Ag-Ab-complex' mixture during immune reaction was treated as a single light scattering on the spheres of different diameters less than the wavelength. So the scattering medium was the polydisperse system, when the scattering centers concentration and sizes were changing in time. The expression for intensity of scattered light induced by the immune reaction process for different experimental conditions was derived.
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