Interaction of unmodified and partially silylated nanosilica with red blood cells

Interaction of red blood cells (RBCs) with unmodified and partially (50%) silylated fumed silica A-300 (nanosilica)was studied by microscopic, XRD and thermally stimulated depolarisation current (TSDC) methods. Nanosilica at a low concentration C _A-300 < 0.01 wt.% in buffered aqueous suspension is characterised by a weak haemolytic effect on RBCs. However, at C _A-300 = 1 wt% all RBCs transform into shadow corpuscles because of 100% haemolysis. Partial (one-half) hydrophobization of nanosilica leads to reduction of the haemolytic effect in comparison with unmodified silica at the same concentrations. A certain portion of the TSDC spectra of the buffered suspensions with RBC/A-300 is independent of the amounts of silica. However, significant portions of the low-and high-temperature TSDC bands have a lower intensity at C _A-300 = 1 wt% than that for RBCs alone or RBC/A-300 at C _A-300 = 0.01 wt.% because of structural changes in RBCs. Results of microscopic and XRD investigations and calculations using the TSDC-and NMR-cryoporometry suggest that the intracellular structures in RBCs (both organic and aqueous components) depend on nanosilica concentration in the suspension.      

UV-absorption studies of interaction of karanjin and karanjachromene with ds. DNA: Evaluation of binding and antioxidant activity

Two flavonoids, karanjin (Kj) and karanjachromene (Kc) have been investigated spectrophotometrically for their mode of interactions with double stranded (ds)-DNA at blood (7.4) and stomach (4.7) pH and at human body temperature (37°C). Benesi-Hildebrand equation was used to evaluate the binding constants, K _b . Binding constants at both pH values and at body temperature showed stronger binding of both the flavonoids and formation of 1:1 flavonoid-DNA complex via intercalative mode. However, K _b values for karanjin were evaluated to be comparatively greater than karanjachromene at both pH values. The highest value of binding constant (1.32×10⁵ M^?1) for karanjin at blood pH (7.4) demonstrated its comparatively stronger binding and greater effectiveness at this pH. Standard Gibbs free energy changes (ΔG) of flavonoid-DNA complexes were calculated as negative values and indicative of spontaneity of their binding. Both flavonoids showed significant DNA protection activity.      

Hydrogen Bonding and Solvent Effects on Complexation of Alkali Metal Cations by Lower Rim Calix[4]arene Tetra(O-[N-acetyl-D-phenylglycine methyl ester]) Derivative

Complexation of alkali metal cations with 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis(O-methyl-D-α-phenylglycylcarbonylmethoxy)calix[4]arene (L) was studied by means of spectrophotometric, conductometric and potentiometric titrations at 25 °C. The solvent effect on the binding ability of L was examined by using two solvents with different affinities for hydrogen bonding, viz. methanol and acetonitrile. Despite the presence of intramolecular NH···O=C hydrogen bonds in L, which need to be disrupted to allow metal ion binding, this calix[4]arene amino acid derivative was shown to be an efficient binder for smaller Li⁺ and Na⁺ cations in acetonitrile (lg K _LiL  > 5, lg K _NaL  = 7.66), moderately efficient for K⁺ (lg K _KL  = 4.62), whereas larger Rb⁺ and Cs⁺ did not fit in its hydrophilic cavity. The complex stabilities in methanol were significantly lower (lg K _NaL  =  4.45, lg K _KL  = 2.48). That could be explained by different solvation of the cations and by competition between the cations and methanol molecules (via hydrogen bonds) for amide carbonyl oxygens. The influence of cation solvation on complex stability was most pronounced in the case of Li⁺ for which, contrary to the quite stable LiL ⁺ complex in acetonitrile, no complexation was observed in methanol under the conditions used.     

Copper complexes formed by 3,5-bis(2,2′-bipyridin-4-ylethynyl)benzoic acid and its methyl and ethyl esters as studied by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry was used to study the complexes of ligands containing two bipyridine units, namely 3,5-bis(2,2-bipyridin-4-ylethynyl)benzoic acid (1) and its methyl and ethyl esters (2, 3), with copper cation, with CuCl₂ as a source of copper. It was found that the type of complexes formed strongly depends on CuCl₂ concentration. At lower CuCl₂ concentration, the detected complexes were rather simple and some of them were formed upon electrospray ionization conditions e.g. ions [2₂+Cu₂]²⁺ and [3₂+Cu₂]²⁺ (complexes ligand-Cu(I) of stoichiometry 2:2) which are analogical to the well known, for quaterpyridine, helical complexes. At higher CuCl₂ concentration, the detected complexes were more complicated, and most of them contained copper cations bridged by chlorides. The largest ions were [L₂+Cu₄Cl₆]²⁺. The CID MS/MS spectra of these ions allowed determination of their mass spectrometric fragmentation pathways and as a consequence their structure elucidation.      

Complexation of 4′-nitrobenzo-15-crown-5 with Li+, Na+, K+, and NH 4 + cations in acetonitrile–methanol binary solutions

The complexation processes between Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations with macrocyclic ligand, 4′-nitrobenzo-15C5, were studied in acetonitrile–methanol (AN–MeOH) binary mixtures at different temperatures using conductometric method. The conductance data show that the stoichiometry of the complexes formed between the ligand and Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations is 1:1(M:L). Addition of 4′-nitrobenzo-15C5 to these cations solution, causes a continuous increase in the molar conductivities which indicates that the mobility of the complexed cations is more than the uncomplexed ones. The values of stability constants of the complexes were determined from conductometric data using GENPLOT computer program. The obtained results show that the selectivity order of the ligand for Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations changes with the nature and composition of the binary mixed solvent. The values of thermodynamic parameters (ΔH°_c, ΔS°_c) for formation of the complexes were obtained from temperature dependence of the stability constants using the van’t Hoff plot. The results show that the complexes are both enthalpy and entropy stabilized. A non-linear behavior was observed between the stability constants (log K _f ) of the complexes and the composition of the AN–MeOH binary solution.     

Catalytic reduction of sulfuric acid to sulfur dioxide

The reduction of H₂SO₄ to SO₂ occurs with a relatively good efficiency only at high temperatures, in the presence of catalysts. Some experimental results, regarding conversion of sulfuric acid (96 wt.%) to sulfur dioxide and oxygen, are reported. The reduction has been performed at 800 ?C 900°C and atmospheric pressure, in a tubular quartz reactor. The following commercial catalysts were tested: Pd/Al₂O₃ (5 wt.% and 0.5 wt.% Pd), Pt/Al₂O₃ (0.1 wt.% Pt) and ??-Fe₂O₃. The fresh and spent catalysts were characterized by X-Ray diffraction and BET method. The highest catalytic activity was determined for 5 wt.% Pd/Al₂O₃, a conversion of 80% being obtained for 5 hours time on stream, at 9 mL h^?1 flow rate of 96 wt.% H₂SO₄. A conversion of 64% was determined for 0.5 wt.% Pd/Al₂O₃ and 0.1 wt.% Pt/Al₂O₃. For ??-Fe₂O₃, a less expensive catalyst, a conversion of 61% for about 60 hours was obtained.      

Dispersive evaluation and surface chemistry of advanced, multifunctional silica/lignin hybrid biomaterials

Advanced silica/lignin hybrid biomaterials were obtained using hydrated or fumed silicas (Aerosil®200) and Kraft lignin as precursors, which is a cheap and biodegradable natural polymer. To extend the possible range of applications, the silicas were first modified with N-2-(aminoethyl)-3-aminopropyltrimethoxsysilane, and then with Kraft lignin, which had been oxidized with sodium periodate. The SiO₂/lignin hybrids and precursors were characterised by means of determination of their physicochemical and dispersive-morphological properties. The effectiveness of silica binding to lignin was verified by FT-IR spectroscopy. The zeta potential value provides relevant information regarding interactions between colloid particles. Measurement of the zeta potential values enabled an indirect assessment of stability for the studied hybrid systems. Determination of zeta potential and density of surface charge also permitted the quantitative analysis of changes in surface charge, and indirectly confirmed the effectiveness of the proposed method for synthesis of SiO₂/lignin hybrid materials. A particularly attractive feature for practical use is their stability, especially electrokinetic stability. It is expected that silica/lignin hybrids will find a wide range of applications (polymer fillers, biosorbents, electrochemical sensors), as they combine the unique properties of silica with the specific structural features of lignin. This makes these hybrids biomaterials advanced and multifunctional.      

Synthesis of new (arylcarbonyloxy)aminopropanol derivatives and the determination of their physico-chemical properties

Eight hydrochlorides of 3-{2-[(2/4-fluorophenoxy)-ethylamino]}-2-hydroxypropyl-4-alkoxybenzoates and four hydrochlorides of 3-tert-butylamino-2-hydroxypropyl-4-butoxybenzoates were prepared as potential antagonists of the β₁-adrenergic receptor (beta-blockers). A multistep synthesis of these compounds is described as well as their detailed analytical characterization. The pharmacokinetic properties of these weak base compounds are significantly influenced by their acid-base dissociation constant, pK _a. The knowledge of this value is crucial for new drug development. This paper is aimed at developing a methodology that utilizes pH-dependent ¹H NMR spectroscopy for its routine analysis. The selected predicted physico-chemical parameters of the new (arylcarbonyloxy)aminopropanols (i.e., aryloxyaminopropanol derivatives) were compared with the model drugs esmolol and flestolol.      

Interaction of fibrinogen with nanosilica

Interaction of human plasma fibrinogen (HPF) with fumed nanosilica A-300 in a phosphate buffer solution (PBS) was studied using ¹H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial water in the temperature range of 210–273 K, TSDC (90 < T < 265 K), adsorption, FTIR, and UV spectroscopy methods. An increase in concentration of HPF in the PBS leads to a decrease in amounts of structured water (frozen at T < 273 K) because of coagulation of HPF molecules. Addition of nanosilica to the HPF solution strongly reduces the amounts of structured water because of adsorption interaction of HPF molecules with silica nanoparticles, self-association of HPF molecules, formation of denser packed hybrid agglomerates with HPF and silica, and lastly, because of conformational changes of HPF. A monolayer adsorption capacity of A-300 corresponds to 156 mg of HPF per gram of silica. The FTIR and UV spectra show that the HPF adsorption on silica leads to structural changes of the protein molecules. These changes and formation of hybrid HPF/A-300 aggregates can increase the rate of clotting that is of importance on nanosilica application as a component of tourniquet preparations.      

Phenylcopper(I) clusters in the gas phase obtained by laser desorption/ionization from bis(dibenzoylmethane)copper(II)

It has been demonstrated that phenylcopper(I)-containing clusters are generated in the gas phase from bis(dibenzoylmethane) copper(II) (Cu(dbm)₂) by laser desorption/ ionization (LDI) method. For example, the [Cu₅dbm₂(C₆H₅)₂]⁺ ion can be considered as consisting of two Cudbm molecules, two CuC₆H₅ molecules and a Cu⁺ cation. The [Cu₅(C₆H₅)₄]⁺ ion can be considered as phenylcopper(I) cluster (consisting of four phenylcopper molecules) ionized by additional Cu⁺ cation. Results from MS/MS (tandem mass spectrometry) experiments have confirmed the presence of phenylcopper molecules in the analyzed clusters. Ease of preparation of dibenzoylmethane-metal complexes and straightforward method to obtain LDI mass spectra offer a wide range of possibilities to study similar organometallic clusters in the gas phase.      

Thermodynamic protonation constants of vardenafil by the nonlinear regression of multiwavelength pH-spectrophotometric titration data

pH-spectrophotometric titration data were used to determine protonation constants of vardenafil at different ionic strengths I and temperatures of 25°C and 37°C. The use of two different multiwavelength and the multivariate treatment of spectral data, SPECFIT32 and SQUAD(84) nonlinear regression analyses and INDICES factor analysis is presented. The reliability of the protonation constants of the drug was proven with goodness-of-fit tests of the pH-spectra. The thermodynamic protonation constants log K _T ⁱ were estimated by a nonlinear regression of (log K, I) data using the Debye-Hückel equation, yielding log K ₄ ^T = 3.59(1) and 3.26(1), log K ₃ ^T = 5.64(1) and 5.81(1), log K ₂ ^T = 9.41(1) and 8.59(2), log K ₁ ^T = 10.92(2) and 10.05(1) at 25°C and 37°C, where the figure in brackets is the standard deviation in last significant digit. Concurrently, the experimental determination of four thermodynamic protonation constants was combined with the computational prediction of the MARVIN program based on knowledge of the chemical structures of the drug and was in good agreement with its experimental value. The factor analysis of spectra in the INDICES program predicts the correct number of light-absorbing components when the instrument error is known and when the signal-to-error ratio SER is higher than 10.      

Thermodynamic behavior of complexation process between benzo-15-crown-5 with Li+, Na+, K+, and NH4 + cations in acetonitrile–methanol binary media

The stability constants of 1:1 (M:L) complexes of benzo-15-crown-5 (B15C5) with Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations, the Gibbs standard free energies ( $ \Updelta {\text{G}}_{\text{c}}^{ \circ } $ ), the standard enthalpy changes ( $ \Updelta {\text{H}}_{\text{c}}^{ \circ } $ ) and standard entropy changes ( $ \Updelta {\text{S}}_{\text{c}}^{ \circ } $ ) for formation of these complexes in acetonitrile–methanol (AN–MeOH) binary mixtures have been determined conductometrically. The conductance data show that the stoichiometry of the complexes formed between the macrocyclic ligand and the studied cations is 1:1 (M:L). In most cases, addition of B15C5 to solutions of these cations, causes a continuous increase in the molar conductivities which indicates that the mobility of complexed cations is more than the uncomplexed ones. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, GENPLOT. The results show that the selectivity order of B15C5 for the metal cations changes with the nature and composition of the binary mixed solvent. The values of standard enthalpy changes ( $ \Updelta {\text{H}}_{\text{c}}^{ \circ } $ ) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard entropy ( $ \Updelta {\text{S}}_{\text{c}}^{ \circ } $ ) were calculated from the relationship $ \Updelta {\text{G}}_{{{\text{c}},298.15}}^{ \circ } = \Updelta {\text{H}}_{\text{c}}^{ \circ } - 298.15\Updelta {\text{S}}_{\text{c}}^{ \circ } $ . A non-linear behavior was observed between the stability constants (log K_f) of the complexes and the composition of the acetonitrile–methanol (AN–MeOH) binary solution. The results obtained in this study, show that in most cases, the complexes formed between B15C5 and Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations are both enthalpy and entropy stabilized and the values of these thermodynamic quantities change with the composition of the binary solution.     

A combined experimental and density functional theory study on the complexation ability of 15-crown-5 with Li+, Na+, K+, and NH4 + cations

The complexation processes among Li⁺, Na⁺, K⁺, and NH₄ ⁺ cations with the macrocyclic ligand, 15-crown-5 (15C5) have been studied in acetonitrile–methanol binary mixtures at different temperatures using conductometric method. The stability constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance–mole ratio data at various temperatures. The values of thermodynamic parameters ( $ \Updelta H_{\text{c}}^{^\circ } $ and $ \Updelta S_{\text{c}}^{^\circ } $ ) for the formation of the complexes were obtained from temperature dependence of the stability constants of complexes using van’t Hoff plots. In addition, a theoretical study has been carried out using density functional theory to obtain the stability of the complexes and the geometrical structure of the 15C5 and its complexes with Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations in the gas phase. We compared the experimental data with those obtained by quantum chemistry calculations to investigate the effect of the solvent on complexation process.     

Catalysis and compensation effect of K2CO3 in low-rank coal — CO2 gasification

The CO₂ gasification of a low rank coal catalysed by K₂CO₃ was studied, at 700–950°C and 1 atm. A two level full factorial design revealed that the gasification reaction was sensitive to the solid residence time, reaction temperature, CO₂ partial pressure and catalyst load. K₂CO₃ was an efficient catalyst at all temperatures studied, particularly during the second stage when the Boudouard reaction dominates. The gasification rate was increased continuously with increasing catalyst load up to a load of ～20% w/w K₂CO₃ concentration, following a sigmoid curve. Above this point, limited catalytic effect was observed, possibly due to the saturation of the lignite surface by K⁺. A correlation was found to exist between the catalytic gasification rate and the Alkali Index, which increased with the impregnation of the inorganic K₂CO₃ salt. When K₂CO₃ load increased, the Arrhenius parameters, E and k ₀, increased simultaneously exhibiting a compensation effect. The isokinetic temperature was found about 600 to 650°C corresponding to the minimum temperature required for the formation of catalytic active intermediates. At temperatures studied, the catalytic active intermediates seemed to be always present and the catalysis progresses unhindered due to the redox cycle, resulting in high rates and conversion.      

Stability prediction of Cu2+, Ni2+ and Zn2+ N-salicylidene-aminoacidato complexes by models based on connectivity index 3 χ v

This paper presents models for the estimation of stability constants (K ₁ and β ₂) of nickel(II), copper(II) and zinc(II) mono- and bis-complexes with 5 Schiff bases (salicylideneglycine, salicylidenealanine, salicylideneserine, salicylidenephenylalanine, and salicylidenetyrosine). The models were based on the molecular-graph theory and valence molecular connectivity index of the 3^rd order, ³χ ^v , derived from it. Univariate linear models were developed for each metal separately, while in the common models for two and three metals, the indicator variable, In, was introduced. The standard error of models for the log K ₁ constant was less than 0.12, while for log β ₂ models, the S.E. did not exceed 0.14.      

Synthesis of novel chromogenic azocalix[4]arenemonoquinones and their binding with alkali metal cations

Five new chromogenic azocalix[4]arenemonoquinones have been synthesized, characterized and examined for their interaction with alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) by UV-visible spectroscopic and cyclic voltammetric techniques. It has been determined that 4a selectively exhibits a significant bathochromic shift in its UV-visible spectrum on interaction with potassium ion in comparison to its treatment with other alkali metal cations. The binding stoichiometry of 4a and potassium ion was established to be 1:1 with an association constant of 3.27 × 10⁴ M^?1. Cyclic voltammetric experiments in 4:1 dichloromethane-acetonitrile also revealed a significant anodic shift (ΔE _(1/1′) = 115 mV) of the original redox waves of 4a on interaction with potassium ion.     

Implementation of chemometric techniques for evaluation of antioxidant properties of Camellia sinensis extracts

In this study, antioxidant properties of commercial green teas and dietary supplements containing Camellia sinensis extracts were evaluated. Extracts were examined using two antioxidant assays (DPPH^· radical method and ABTS^·+ cation radical method). A Folin-Ciocalteu assay was used to evaluate the total polyphenol content in the extracts. In order to compare and characterize the investigated Camellia sinensis extracts, chemometric techniques based on fingerprint chromatograms, antioxidant activity and total polyphenol content were applied. Application of chemometric methods allowed for reduction of multidimensionality of the data set and grouped the samples into differentiable clusters. The relationship between the antioxidant activity and total polyphenol content was also assessed. The results indicated that extracts with the higher polyphenolic content exhibited the stronger antiradical activity against both DPPH^· radicals and ABTS^·+ cation radicals. The multivariate calibration technique (such as a tree regression algorithm) can be a useful tool for rapid determining the antioxidant activity of a herbal product based on its fingerprint chromatogram      

Preparation, characterization and photocatalytic activity of Co3O4/LiNbO3 composite

The Co₃O₄/LiNbO₃ composites were synthesized by impregnation of LiNbO₃ in an aqueous solution of cobalt nitrate and next by calcination at 400°C. The activity of produced samples has been investigated in the reaction of photocatalytic hydrogen generation. The crystallographic phases, optical and vibronic properties were studied using X-ray diffraction (XRD), diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic techniques, respectively. The influence of cobalt content (range from 0.5 wt.% to 4 wt.%) on the photocatalytic activity of Co₃O₄/LiNbO₃ composites for photocatalytic hydrogen generation has been investigated. Co₃O₄/LiNbO₃ composites exhibited higher than LiNbO₃ photocatalytic activity for hydrogen generation. The highest H₂ evolution efficiency was observed for Co₃O₄/LiNbO₃ composite with 3 wt.% cobalt content. The amount of H₂ obtained in the presence of LiNbO₃ and Co₃O₄/LiNbO₃ (3 wt.% of cobalt content) was 1.38 µmol/min and 2.59 µmol min^?1, respectively.      

Spectroscopic study of associated systems formed between water-soluble cationic porphyrins or their copper (II) complexes and nucleic building blocks

The association process between two water soluble cationic porphyrins, 5,10,15,20-tetrakis[4-(trimethyl-ammonio)phenyl]-21H,23H-porphine tetra-p-tosylate (H₂TTMePP) and 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine tetra-p-tosylate (H₂TMePyP), as well as their Cu (II) complexes, with five series of nucleic agents has been studied using UV-VIS spectroscopy in aqueous solutions. During the titration with nucleic compounds the bathochromic effect of porphyrins absorption spectra can be observed as well as the hypochromicity of the Soret maximum. The association constants were calculated using a curve-fitting procedure (K_AC of the order of magnitude of 10³–10⁵ mol^?1). It has been shown that the interactions of H₂TTMePP with nucleic agents are much stronger than interactions of H₂TMePyP, which is most likely related to the kind and the size of the porphyrin substituent groups partaking in the process of stacking. The strength of the observed associated systems increases generally in a series: nucleic base < nucleoside < nucleotide.      

Spectrophotometric and voltammetric characterization of a novel selective electroactive chemosensor for Mg2+

A novel azocalix[4]arene derivative, 5,11,17,23-tetrakis[(acetophenone)azo]-25,26,27,28-tetrahydroxycalix[4]arene (APC4), containing acetophenone azo groups at the upper rim was synthesized as a chemosensor. Its binding and sensing properties with alkali and alkaline earth metal ions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) were investigated by UV-vis spectrophotometric and voltammetric techniques. The stoichiometric ratio and the association constant were determined spectrophotometrically as 1:1 and (1.94±0.31)×10⁵ L mol^?1 for the complex between Mg²⁺ and the chemosensor, respectively. Moreover, it was shown that the interaction between Mg²⁺ and the APC4 occurred by means of the phenol groups at the lower rim by voltammetric methods. The results of spectrophotometric and voltammetric experiments showed that the chromogenic chemosensor has high selectivity towards Mg²⁺ among the other used metal ions, especially the interfering Ca²⁺ ion.