Tatiana A. Dolenko

Raman and IR spectroscopy research on hydrogen bonding in water–ethanol systems

Vibrational spectroscopy provides invaluable information about hydrogen bonding in aqueous solutions. To study changes in H-bonding due to increase of ethanol concentration in water, we perform research on water–ethanol binary mixtures with various mixing ratios using a combination of Raman scattering and IR absorption techniques. We study Raman spectra from 200 to 4000 cm−1 excited at 488 nm and IR spectra from 500 and 4000 cm−1 for solutions with different ethanol concentrations from pure water to pure ethanol. Using the intensity ratio of OH stretching band taken at 3200 and 3420 cm−1 for Raman spectra and at 3240 and 3360 cm−1 for IR spectra we evaluate the strength of H-bonding. Maximal strength of H-bonding in water–ethanol mixture corresponds to ethanol concentration 15–20% w/w. We explain it by the presence of transient ethanol hydrates similar in composition to gaseous clathrates with stoichiometric water/ethanol ratio 5:1. Further weakening of H-bonding with ethanol concentration is caused by the formation of chain aggregates from ethanol/water molecules. In addition, we apply other approaches, such as multivariate curve resolution-alternating least squares analysis, decomposition of water Raman stretching band, and comparison of water Raman stretching band in ethanol solutions to that of gas clathrates to support this hypothesis.

Valence band of liquid water raman scattering: some peculiarities and applications in the diagnostics of water media

A short analysis of the results of our research on peculiarities of water Raman scattering spectra and of their applications in the diagnostics of water media is presented. The results of using a new approach for research on water Raman scattering spectra, i.e. the method of artificial neural networks for spectra treatment and for the solution of inverse problems in water media diagnostics, are also presented. This technique allowed us to improve the accuracy of water temperature determination (error 0.3 °C) by exploiting the temperature dependence of valence band parameters. However, no peculiarities of this dependence in the vicinity of 20, 36 and 76 °C, reported by others, were discovered. Copyright

Core-shell designs of photoluminescent nanodiamonds with porous silica coatings for bioimaging and drug delivery I: fabrication

A multifunctional core-shell nanocomposite platform consisting of a photoluminescent nanodiamond (ND) core with uniform porous silica coatings is presented. This design intended for drug delivery applications allows simultaneous stable fluorescent imaging with high loading capacity of bioactive molecules. Despite irregularly shaped starting cores, well-dispersed and uniformly shaped nanocomposite particles can be produced. Moreover, after optimization of the silica source-to-diamond ratio, the thickness of the porous layer can be tuned by adjusting the ethanol amount, allowing rational nanoparticle size control. The ND key property, photoluminescence, is not quenched regardless of coating with thick silica layers. The high loading capacity for incorporation of active agents, provided by the introduced porous layer, is demonstrated by adsorption of a hydrophobic model drug to the composite particles. The loading degree, as compared to a pure ND, increased by two orders of magnitude from 1 wt% for the ND to >100 wt% for the composite particles. Combining these two material classes, which both have well-documented excellent performance especially in biomedical applications, for the NDs with emphasis, but not exclusively, on imaging and mesoporous silica (MSN) on drug delivery, the advantages of both are shown here to be synergistically integrated into one multifunctional nanocomposite platform.

Saturation spectroscopy as a method for determining the photophysical parameters of complicated organic compounds

A fundamentally new approach to the fluorescence diagnostics of complicated organic compounds and complexes has been proposed. The method is based on in vivo and in situ measurements of the photophysical parameters of organic molecules from saturation curves. The results obtained for the solution of the relevant inverse problem are presented.

Fluorescence diagnostics of oil pollution in coastal marine waters by use of artificial neural networks

We discuss the problems with and the real possibilities of determining oil pollution in situ in coastal marine waters with fluorescence spectroscopy and of using artificial neural networks for data interpretation. In general, the fluorescence bands of oil and aquatic humic substance overlap. At oil concentrations in water from a few to tens of micrograms per liter, the intensity of oil fluorescence is considerably lower than that of humic substances at concentrations that typically are present in coastal waters. Therefore it is necessary to solve the problem of separating the small amount of oil fluorescence from the humic substance background in the spectrum. The problem is complicated because of possible interactions between the components and variations in the parameters of the fluorescence bands of humic substances and oil in water. Fluorescence spectra of seawater samples taken from coastal areas of the Black Sea, samples prepared in the laboratory, and numerically simulated spectra were processed with an artificial neural network. The results demonstrate the possibility of estimating oil concentrations with an accuracy of a few micrograms per liter in coastal waters also in cases in which the contribution from other organic compounds, primarily humic substances, to the fluorescence spectrum exceeds that of oil by 2 orders of magnitude and more.

The effect of hydration of ions of inorganic salts on the shape of the raman stretching band of water

The shape of the Raman stretching band of water molecules in aqueous solutions of electrolytes KBr, KCl, KI, NaCl, and NaI is studied. It is confirmed that the characteristics of the stretching band strongly depend on the concentration and type of salt. The behavior of different parameters of the band is explained in terms of the theory of hydration of salts.

Decomposition of water Raman stretching band with a combination of optimization methods

In this study, an investigation of the behaviour of stretching bands of CH and OH groups of water–ethanol solutions at alcohol concentrations ranging from 0 to 96% by volume has been performed. A new approach to decomposition of the wide structureless water Raman band into spectral components based on modern mathematical methods of solution of inverse multi-parameter problems–combination of Genetic Algorithm and the method of Generalized Reduced Gradient–has been demonstrated. Application of this approach to decomposition of Raman stretching bands of water–ethanol solutions allowed obtaining new interesting results practically without a priori information. The behaviour of resolved spectral components of Raman stretching OH band in binary mixture with rising ethanol concentration is in a good agreement with the concept of clathrate-like structure of water–ethanol solutions. The results presented in this paper confirm existence of essential structural rearrangement in water–ethanol solutions at ethanol concentrations 20–30% by volume.

High‐Pressure Synthesis of Boron‐Doped Ultrasmall Diamonds from an Organic Compound

The first application of the high-pressure-high-temperature (HPHT) technique for direct production of doped ultrasmall diamonds starting from a one-component organic precursor is reported. Heavily boron-doped diamond nanoparticles with a size below 10 nm are produced by HPHT treatment of 9-borabicyclo [3,3,1]nonane dimer molecules.

Application of artificial neural networks to solve problems of identification and determination of concentration of salts in multi-component water solutions by Raman spectra

In this paper, the results of elaboration and comparative analysis of approaches concerned with application of neural network algorithms for effective solution of problem of pattern recognition (inverse problem with discrete output) along with inverse problem with continuous output are presented. Consideration is carried out at the example of problem of identification and determination of concentrations of inorganic salts in multi-component water solutions by Raman spectra. The studied approach is concerned with solution of both problems (classification and determination of concentrations) using a single neural network trained on experimental or quasi-model data.

Time-Resolved Fluorimetry of Two-Fluorophore Organic Systems Using Artificial Neural Networks

Abstract In this paper, we study the ability of determining the lifetimes τ 1,2 of fluorophores excited states and the ratio of their fluorescent contributions in a two-fluorophore system with the help of time-resolved fluorimetry in its modification when the lifetimes τ 1,2 may be smaller than the exciting pulse duration τ p and the receiver gate duration τ g . The investigation has been performed under the assumption that there are no intermolecular interactions that could influence the times of fluorescence decay. The described three-parameter inverse problem was solved with the help of artificial neural networks (ANN). Numerical modeling and physical experiment with binary dyes solution have been performed. Both have demonstrated that the ANN algorithm can determine with acceptable precision the lifetimes τ 1,2 down to 1 ns at τ p and τ g values equal to 10 ns (the gate delay being changed in 2 ns steps). Practical stability of the ANN algorithms to noise in the input data and to non-controlled variations of shape and duration of the exciting radiation pulse has been investigated. It is shown that for actual level of noise in kinetic curves, the ANN algorithms give significantly better results in solving the studied three-parameter inverse problem than the variational algorithms. It is intended that the considered modification of time-resolved fluorimetry will be used to build the future complex method of fluorimetry of composite multi-fluorophore compounds.