Side Reactions in the Formation of Polyurethanes: Model Reactions Between Phenylisocyanate and 1-Butanol

The following side reactions occurring in the formation of polyurethanes were modeled: a reaction of excess phenyl isocyanate either with 1-butanol in 1, 4-dioxane and in bulk, or with n-butylphenyl urethane or water in dioxane catalyzed with dibutyltin dilaurate that leads to the formation of n-butyl-α, γ-diphenyl allophanate N, N-diphenylurea, and 1, 3, 5-triphenylbiuret. The reaction products were determined quantitatively by means of liquid chromatography. The rate and equilibrium constants were calculated at various temperatures and various initial ratios of functional groups. Biuret is formed from N, N'-diphenylurea much more quickly than allophanate from urethane, and the equilibrium constant of its formation is also higher.     

The synthesis and characterization of an expansive admixture for M-type cements I. The influence of free CaO to the formation of ettringite

The hydration process of expansive admixtures for M-type of expansive or shrinkage compensation cements was studied by thermal analysis supplemented by infrared spectroscopy and X-ray diffraction. The main attention was focused on ettringite formation and on the influence of lime content upon the process. The behaviour of expansive admixture during hydration is significantly affected by the content of lime. The increasing content of lime slows down the rate of ettringite formation and supports the formation of monosulphate (AFm phase) that can be transformed afterwards into ettringite during hardening process. This process may produce better expansion effect because of better transfer of expansion stress after the setting of the paste.     

Study of Bi2O3 doped by rare-earth element

A series of novel environmentally inorganic pigments based on Bi₂O₃ doped by metal ion Dy³⁺ has been developed and characterized using methods of thermal analysis, X-ray powder diffraction and by reflectance spectral data. The new pigments have been synthesized from mixtures containing Bi₂O₃ and Dy₂O₃ by traditional solid-state route. The incorporation of Dy³⁺ into crystal lattice Bi₂O₃ changes the colour from yellow-orange to orange. The band gap of phases with formula Bi_2?xDy_xO₃, where x = 0.8, increases from 2.30 to 2.38 eV with growth of calcination temperature. The pigment Bi_1.2Dy_0.8O₃ was also evaluated from the standpoint of influence of milling time on the colour properties and particle size. The simultaneous TG–DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. The results confirm the positive effect of lanthanide ions into Bi₂O₃ on thermal stability of prepared phases.     

Photoelectrochemistry of silicon in HF solution

Photoelectrochemical, photoelectrocatalytic, and electrochemical processes of silicon anodic oxidation and hydrogen evolution in aqueous HF solution are discussed in terms of thermodynamic stability of Si, oxides SiO, SiO₂, and Si surface hydrides. It is shown that photoelectrochemical oxidation of n-type low-resistivity silicon to SiO₂ is catalyzed by Si $^{+}$ photo-hole formation, whereas in the case of p-type Si, the feasibility of this reaction is predetermined by p-type conductivity. It is suggested that anodic oxidation of Si goes through the stage of SiO oxide formation and its subsequent oxidation to SiO₂. Such mechanism accounts for chemical inertness of Si phase in HF solutions as well as for selective, anisotropic, and isotropic etching of Si within E ranges from $-0.5$ to 0.35 V, $0.35-0.8~V,$ and $E > 0.8$ V, respectively. Hydrogen evolution reaction on Si surface proceeds at very large overpotential ( $\geq 0.5$ V) through the stage of surface Si hydride formation: $\mathrm {Si + H_{2}O + e^{-} \rightarrow (SiH)_{surf} + OH^{-}}$ (the rate determining step) and $\mathrm {(SiH)_{surf} + H_{2}O + e^{-} \rightarrow Si + H_{2} + OH^{-}}$ . Illumination-related effects of surface reactions relevant to selective and anisotropic etching and nano/micro-structuring of Si surface are discussed.     

Structural Differences Between Copolymers of Acryl‐ and Methacryl‐dicyclohexylurea with Ethylene Glycol Dimethacrylate and their Thermal Degradation Products

The present paper describes structural characteristics of crosslinked copolymers of acryl‐dicyclohexylurea (A‐DCU) and methacryl‐dicyclohexylurea (MA‐DCU) with ethylene glycole dimethacrylate (EDMA). Both copolymers decompose when heated at temperatures between 180–250°C under the separation cyclohexylisocyanate (C₆H₁₁NCO) yielding nanoporous copolymers of poly(A‐CHA‐co‐EDMA) and poly(MA‐CHA‐co‐EDMA). The comparison was also made between structural characteristics of crosslinked nanoporous copolymers of poly(A‐CHA‐co‐EDMA) and poly(MA‐CHA‐co‐EDMA) and nonporous crosslinked model compounds poly(A‐CHA‐co‐EDMA) and poly(MA‐CHA‐co‐EDMA).     

Redox reactions: inconsistencies in their description

The paper is aimed at defining reduction, oxidation, and redox reactions based both on the oxidation number and charge changes in reacting species. It is rationalized that the processes of oxidation and reduction, usually occurring simultaneously, can occur also as independent processes. It is explained that in balancing chemical equations of redox reactions the “gain” or “loss” of electrons should be understood as changes in oxidation number. A formal expressions “+n e^?” and “?n e^?” represent in reality a decrease and increase in oxidation number by n units, respectively.     

Effect of plasma treatment on cellulose fiber

Cotton cellulose fibers were modified in inert plasma. Surface morphology of the modified fibers was studied by SEM and changes in the surface composition by XPS and FTIR. Standard goniometry was used for determination of contact angle as a function of modified fiber aging. Absorptivity of modified fibers was determined by gravimetry and fiber width in physiological solution, simulating body liquids, by confocal microscopy. Antibacterial effect of pristine and plasma treated samples was examined by following growth of Escherichia coli. Plasma treatment led to surface ablation, changes in surface morphology and fiber width. Surface of the plasma modified fibers was oxidized and their water absorptivity was reduced. The plasma modification did not affect E. coli growth substantially.     

Inactivation of cholinesterases by silver and gold ions in vitro

The main goal of the present study was to investigate the effects of silver and gold ions on cholinesterases (ChEs) activity due to increasing application of these metals in a wide variety of nanomaterials. A chromogenic assay using the substrate o-nitrophenyl acetate/butyrate made it possible to conclude unmistakably that both metals inhibit ChEs. Addition of bovine serum albumin (BSA) indicates that binding of metal ions to albumin could serve to scavenge metals and consequently reduce their amount for reaction with ChEs. The effects of metal ions on ChE should be taken into consideration when using this enzyme as an environmental biomarker.      

Use of electrophoretic techniques and MALDI–TOF MS for rapid and reliable characterization of bacteria: analysis of intact cells, cell lysates, and “washed pellets”

In this study electrophoretic and mass spectrometric analysis of three types of bacterial sample (intact cells, cell lysates, and “washed pellets”) were used to develop an effective procedure for the characterization of bacteria. The samples were prepared from specific bacterial strains. Five strains representing different species of the family Rhizobiaceae were selected as model microorganisms: Rhizobium leguminosarum bv. trifolii, R. leguminosarum bv. viciae, R. galegae, R. loti, and Sinorhizobium meliloti. Samples of bacteria were subjected to analysis by four techniques: capillary zone electrophoresis (CZE), capillary isoelectric focusing (CIEF), gel IEF, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–TOF MS). These methods are potential alternatives to DNA-based methods for rapid and reliable characterization of bacteria. Capillary electrophoretic (CZE and CIEF) analysis of intact cells was suitable for characterization of different bacterial species. CIEF fingerprints of “washed pellets” and gel IEF of cell lysates helped to distinguish between closely related bacterial species that were not sufficiently differentiated by capillary electrophoretic analysis of intact cells. MALDI–TOF MS of “washed pellets” enabled more reliable characterization of bacteria than analysis of intact cells or cell lysates. Electrophoretic techniques and MALDI–TOF MS can both be successfully used to complement standard methods for rapid characterization of bacteria.