Today, the watchful gaze of scientists is drawn to all the new properties of various physicochemical systems, which are inexplicable from the point of view of classical theories. Highly diluted solutions are of particular interest among these systems. Important questions relating to this topic are still unresolved. Do molecular structures of the solvents form in such solutions? Do molecules of the active substance remain in such solutions? Scientists can answer these questions by using highly sensitive methods of spectral analysis. One such method is luminescent spectral analysis. It works as follows: a special device registers the luminescence of a substance which is excited by electromagnetic radiation.
Luminescence (from the Latin lumen - 'light' and -escent 'weak effect') is the non-thermal radiance of a substance that occurs after it absorbs excitation energy.
The Swiss scientist Louis Rey, for example, proposed a method of indirectly identifying hydrogen bonds in the structure of water using thermally stimulated luminescence (thermoluminescence). Crystals of 'heavy' water D2O were studied, as well as frozen samples of NaCl and LiCl solutions in D2O. The samples were exposed to x-rays. All solutions were prepared by multiple dilutions and mechanical succussion at each dilution step. According to Rey, the emergence of a new peak in the luminescence spectra of the samples is indirectly associated either with a change in the nature of the hydrogen bonds in the system or with the presence of structures formed due to such bonds. The decrease in the severity of this peak when sodium and lithium chlorides are present in the sample can be explained by the destruction of such structures. The author assigned great importance to the mechanical processing of the samples in the formation of these structures in highly diluted solutions, since this effect was not observed when succussion was not performed. Rey also observed the preservation of some properties of lithium and sodium chlorides, despite the ultra-low concentrations of the solutions.
The German scientist Wijk continued to study ultrahigh dilutions (up to 10-30g/cm3) of lithium chloride in deuterium oxide (D2O), also using the thermoluminescence spectral analysis method. The author confirmed the observations and conclusions made by Rey and concluded that thermoluminescence could become a promising tool for studying potentiated highly diluted solutions. The scientist noted that the presence of LiCl interferes with the process of stabilising structures based on the intermolecular hydrogen bonds of water molecules, but only for a limited time. He also observed a difference between a sample of water prepared with succussion and a control without succussion. This may indicate a change in the structural state of the water.
In her work, Russian scientist Belovolova considered the influence of impurities and oxygen dissolved in heavy water on its properties. For Belovolova, it is impurities and oxygen, together with external influences (for example, the Earth's geomagnetic radiation), that have a significant impact on the properties of tap water or 'natural' water. Due to hydrogen bonds, any changes occur almost immediately in the entire volume of water. Long-term changes from several hours to days, ultraviolet radiation and other effects were detected from the fluorescence and light scattering spectra of the solutions after succussion. It was also found that melted water was significantly more sensitive to physical effects as it contains less impurities.
The Swiss scientist Marschollek used ultraviolet spectroscopy to study the influence of various physical factors on highly diluted solutions of CuSO4 and sulphur. The solutions were irradiated with ultraviolet light and subjected to heating. After some time in storage, the UV-irradiated samples of CuSO4 solutions showed significantly lower UV-transmittance values than the pure water control. Incubation of the samples at 37°C increased this effect. According to the author, the obtained transmittance values may indicate that the solvent (water) becomes less structured after exposure to temperature or ultraviolet light.
The Swiss scientist Klein continued the use of ultraviolet spectroscopy to study highly diluted copper sulphate solutions. The researcher also found differences in the transmittance of ultraviolet radiation between the samples and the control. At the same time, the author ruled out the presence of possible contaminants or impurities in the samples that could have affected the results and also stressed the equal conditions for preparing and storing samples and controls. According to Klein, potentiated solutions are sensitive to the effects of heat and ultraviolet radiation, that is, the properties of such solutions may change under such exposure. This observation is important in the production, storage and processing of highly diluted drugs.
Cartwright, an English scientist, investigated highly diluted solutions using ultraviolet fluorescence spectroscopy and solvatochromic dyes. Solvatochromism refers to the ability of dye molecules to change their spectral characteristics when the polarity of a solvent changes. The author highlighted the following requirements for solvatochromic dyes that can be used to study the properties of highly diluted solutions: a large dipole moment, electron delocalisation, polarisability, and molecular rigidity. A combination of these properties of amino acids, which contain aromatic rings, has proven to be the most promising indicator of the properties of highly diluted solutions.
The advantages of spectroscopy methods are their availability, simplicity and high sensitivity. Modern devices allow the measurement procedure to be carried out with high accuracy and reproducibility. Due to this, the number of published scientific papers on studies into highly diluted solutions using these methods is increasing, and we can expect new data on the design of such systems soon.