Silicon Hydrofluoric Acid Research Articles

Synthesis, physico-chemical properties and biological activity of 3-(aminophenyl)propionic and 2-amino-2-phenyl butyric acid hexafluosilicates

It is known that dental caries is a serious problem for the health care systems of most countries of the world, and the search for new effective and safe means of treatment and prevention of caries remains an urgent task of modern pharmaceutical science. At the same time, fluoride preparations remain the most effective and widely used in the modern arsenal of means for fighting caries. In recent years, ammonium hexafluorosilicates have been actively studied as potential caries preventive agents due to some advantages compared to traditional means of fluoride caries therapy. The aim of the work, which continues the earlier research of ammonium hexafluorosilicates with aromatic amino acid cations, is the synthesis, establishment of physicochemical properties and biological activity of 3-(3-aminophenyl)propionic, 3-(4-aminophenyl)propionic, 2-amino-2- phenylbutyric acid hexafluorosilicates as potential caries preventive agents. 3-(3-Aminophenyl)propionic, 3-(4-aminophenyl)propionic, 2-amino-2-phenylbutyric acid hexafluorosilicates (I–III, respectively) were synthesized in near-quantitative yields by reacting methanolic solutions of the corresponding amino acids with excess 45% silicon hydrofluoric acid. The isolated complexes were identified using the methods of elemental analysis, IR, NMR, 19F and mass spectroscopy. The solubility of I–III in water was established, which is 0.11–0.32 mol. %. The researched compounds I–III and reference drugs – NaF and (NH4)2SiF6 – were introduced into gels based on the Na-salt of carboxymethylcellulose, which were applied to the teeth and gums of rats. In an experiment on an experimental caries model, it was established that the caries preventive efficiency (СPE) of NaF, (NH4)2SiF6, I–III is 30.3%, 44.7%, 23.7%, 38.5%, 26.3%, respectively, that is, only the СPE of compound II exceeds the corresponding indicator for the reference preparation NaF by 1.27 times, while the СPE values of compounds I and III are inferior to both reference preparations. All studied fluoride preparations effectively normalize the biochemical indicators of dental pulp and homogenate of the oral mucosa of rats (phosphatase, elastase, urease and lysozyme activities, malondialdehyde level) that were on a cariogenic diet, and hexafluorosilicates in some cases are more effective compared to NaF.

Change of Optical Properties of Carbon-Doped Silicon Nanostructures under the Influence of a Pulsed Electron Beam

In the work, porous silicon with observed photoluminescence was made from a p-type silicon substrate doped with boron and crystallographic orientation (100) using the method of electrochemical etching in a solution containing H2(SiF6) (silicon hydrofluoric acid) and ethyl alcohol. Thin carbon films were sprayed by high-frequency magnetron sputtering at room temperature onto the surface of porous silicon. The resulting carbon-doped thin films of porous silicon were irradiated on a pulsed electron booster and comparisons were made with nonirradiated films of porous silicon. To understand the effect of carbon on the properties of porous silicon films samples were analyzed by Raman spectroscopy, spectrophotometry, and scanning probe microscopy (SPM). The results of the SPM showed that the roughness of the samples increases after carbon doping on the surface of porous silicon. Thus, for the first time, experimental results were obtained on the effect of irradiation on carbon-doped porous silicon obtained in a solution containing hydrogen hexafluorosilicate H2(SiF6) and a significant change in its optical properties was shown. The results of the study showed that irradiated samples of carbon-doped porous silicon have better photoluminescence compared to nonirradiated samples.

Influence of dissolved oxygen on intensity modulated photocurrent spectroscopy (IMPS) at a silicon–hydrofluoric acid interface

The kinetic parameters of the cathodic reaction in a silicon–hydrofluoric acid system were measured using intensity modulated photocurrent spectroscopy (IMPS). The values and the potential dependences of the measured parameters were found to depend upon the concentration of dissolved oxygen. This is one of the reasons why photoelectrochemical measurements in this system have sometimes given poorly reproducible results. The effects of the presence of dissolved oxygen are discussed by considering the surface states and the relative energy levels of redox potentials in solution.

ChemInform Abstract: Inclusion Complexes of Siliconhydrofluoric Acid Transformation Products with the Crown Ethers

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Interference filters from porous silicon with laterally varying wavelength of reflection

Porous silicon reflection interference filters of Bragg type consists of up to 40 quarter wave layers with alternating high- and low-refraction index. The refraction index depends on the porosity of the silicon. The reflection wavelength can vary over a wide range and depends on the thickness and refraction index of the porous layers. A laterally continuously varying wavelength with linear profile of the filter can be achieved by manipulating the porosity and thickness of the silicon in the lateral direction. Our approach is to vary the Fermi level laterally by applying a potential parallel to the surface of the wafer. The slope of the Fermi level is easily controlled by the magnitude of the potential. The lateral current density and thus the porosity and thickness is related to the potential difference between the laterally varying Fermi level and the potential induced by the counter electrode. This relation is the well-known current–voltage characteristic of a Silicon hydrofluoric acid contact. The linearity of the etch profile across the wafer is demonstrated and the properties of preliminary reflection filters are shown.

A Water Rich Crystalline Hydrate Formed by 1,4,7,10-Tetraazacyclododecane, Siliconhydrofluoric Acid and Water: Structure and Properties

Novel complementary associations have been found in a crystalline ternarycomplex of the macrocyclic tetramine, [12]aneN4 (e.g. =1,4,7,10-tetraazacyclododecane, cyclen, L), hexafluorosilicate ions andwater (I). The final compound belongs to the host—guest type with themacrocycle as the host (H), the inorganic entity as a guest (G) and watermolecules. It was characterized by X-ray techniques, IR spectroscopy andthermogravimetric study. X-ray crystal analysis revealed that the structureis built of the charged entities, with a 3D-network uniting thequadriprotonated form of the macrocycle, hexafluorosilicate as counterionsand lattice water molecules viaN—H+...F-,N—H+...O(w),OH...F- and O—-H(w)...O(w)hydrogen bonds. The overall complex stoichiometry comprises fourSiF62- anions and seven water molecules per two[LH4]4+ cations. Crystals of (I) are monoclinic,space group P21/n with a = 14.585(3), b = 16.384(2), c =16.500(3) A, β = 92.84(3)°, V = 3938(1)A3 and Z = 8 forC8H31F12N4O3.5Si2.

An experimental and theoretical study of the formation and microstructure of porous silicon

We report a systematic study of the formation and properties of porous silicon formed by anodising silicon under a wide range of conditions. The current-voltage characteristics of the silicon-hydrofluoric acid system are presented. The detailed microstructure of the two types of porous silicon that form depending on the dopant concentration in the silicon, were determined by cross-sectional transmission electron microscopy. A theory for the formation of porous silicon is proposed which accounts for the dependence of the microstructure on the anodising conditions. The formation of porous gallium arsenide, analogous to porous silicon, is reported for the first time.