Modes of complexation of rutin with the flavonoid reagent diphenylborinic acid 2-aminoethyl ester

Abstract  

The interaction of the model flavonoid glycoside rutin with the flavonoid reagent diphenylborinic acid 2-aminoethyl ester (DPBA) was investigated using a combination of HPLC–DAD–ESI–MS analysis, UV–visible spectroscopy, and semiempirical calculations. Mass spectra and spectroscopic data made it possible to describe the complexation pathway as addition of diphenylboron groups to the two available 3′,4′-o-diphenolic and the 5-hydroxy-4-keto coordinating sites of rutin. Semiempirical calculations were carried out to obtain the conformation of the most stable DPBA/rutin adducts. The results showed that a number of complexation dynamics can occur as a function of the characteristics of the medium (type and pH of the solvent) and of the amount of DPBA. This work suggests the possibility of substantially improving existing procedures for recognition of flavonoid compounds by choice of suitable experimental conditions.     

Synthesis, characterization, and DNA binding of the biologically relevant novel cationic molybdenum(VI)–glutathione complex [Mo(GS)(Cl)(H2O)]Cl2

Abstract  

The complex [Mo(GS)(Cl)(H₂O)]Cl₂ (MoG) was synthesized in aqueous medium and its composition has been determined by elemental and thermogravimetric analysis. Binding modes were determined by ¹H NMR, ¹³C NMR, mass, and FT-IR spectrometry. The molecular formula was confirmed by mass spectral analysis. The molecular weight of the complex determined by the Rast camphor method also supports the formulation M _r = 525. This molecular formula demands the compound to be a 1:2 electrolyte, which is also supported by the conductance measurement, its value being 210 Ω⁻¹ cm². The compound is found to be diamagnetic, indicating that the molybdenum is in the +6 oxidation state (d⁰). The binding of MoG with calf thymus DNA was studied by spectroscopic titration. The interaction ratio was determined by monitoring the DNA 260 nm band as well as the S → Mo LMCT band of the complex observed at 225 nm. The interaction ratio calculated from the above studies was found to be 1:0.70 (DNA:MoG) in both cases, while the binding constant of DNA–MoG was found to be (4.8 ± 0.5) × 10⁵ M⁻¹. The binding constant data indicate that the binding nature is intercalative.     

Volumetric properties of aqueous solutions of quinic acid and its sodium salt

Abstract  

The apparent molar volume of quinic acid and its sodium salt were determined from the density data of aqueous solutions up to molality of 0.4 mol kg⁻¹ and in the temperature range from 293.15 to 328.15 K. The apparent molar volume of sodium quinate comprises the ionic and the associated ion-pair contributions. From the apparent molar volumes of quinic acid and the quinate ion, the molecular contributions to that of quinic acid are derived. At 298.15 K, the limiting apparent molar volume of quinic acid is 119.8 ± 0.5 cm³ mol⁻¹, and that of the quinic ion is 111.6 ± 0.3 cm³ mol⁻¹. Similarly, at 298.15 K, the limiting apparent molar expansibility of sodium quinate is 0.198 ± 0.003 cm³ mol⁻¹ K⁻¹, and that of quinic acid is 0.142 ± 0.003 cm³ mol⁻¹ K⁻¹. From these limiting ionic and molecular apparent molar volumes, the limiting volume change caused by ionization of quinic acid was calculated as −8.2 cm³ mol⁻¹ at 298.15 K. The coefficients of thermal expansion of these solutions were calculated from the density data, and from these the apparent molar expansibilities of quinic acid and its sodium salt were derived.     

N–H···O=P hydrogen-bonded dimers as the main structural motif of aminophosphonate diesters

Abstract  

Crystal and molecular structures of three aminophosphonate diesters, diethyl and dibutyl [α-(quinolin-3-ylamino)-N-benzyl]phosphonates (1 and 2) and dibutyl [α-anilino-(quinolin-3-yl)methyl]phosphonate (3) were reported and comparatively discussed. Characteristic structural features for these compounds are strong N–H···O=P hydrogen bonds that connect two organophosphorus molecules in cyclic centrosymmetric dimer. Phosphoryl oxygen forms additional interaction with a C–H donor from the nearby aromatic group. Dimer formation in solution was also confirmed using electrospray ionization mass spectrometry. Mass spectra of six structurally similar aminophosphonate derivatives, 1–3 along with diethyl [α-anilino-(quinolin-3-yl)methyl]phosphonate (4), diethyl and dibutyl [α-anilino-(quinolin-2-yl)methyl]phosphonates (5 and 6) were studied and dimolecular ions [2M + Na]⁺ and [2M + H]⁺ were observed.     

Formation of Aromatic and Other Unsaturated End Groups in Carboxymethyl Cellulose During Hot Alkaline Treatment

Carboxymethyl cellulose (CMC, DS 0.58) was treated in solutions of sodium hydroxide (0.001–1 M) at 95 °C. The treated (1–12 h) CMC samples were purified by dialysis and analyzed by UV spectroscopy and by UV resonance Raman spectroscopy (UVRRS) with excitation at 244 nm. A UV absorption maximum at 265 nm and a UVRR signal at 1650 cm⁻¹ were indicative of formation of -conjugated aldehyde end groups in CMC through -elimination. Another strong UVRR band at 1610 cm⁻¹ gave evidence on conversion of some of the -conjugated aldehyde end groups to alkali stable aromatic structures.     

Structure and chromotropic properties of mono- and binuclear mixed-ligand nickel(II) complexes containing 1,3-diketonate and polyamine ligands

Abstract  

Mixed-ligand Ni^II complexes have been synthesized with 1,3-diketonate and bulky tri- or tetra-amine ligands. Their structures were determined by X-ray crystallography, and solvatochromic behavior was examined by UV–vis–NIR spectroscopy. Steric effects of the bulky ligands on the coordination distances and spectral properties are discussed.     

Synthesis and characterization of novel thermally stable aromatic and semiaromatic polyamides derived from thiourea-based flexible diacid dichlorides

Abstract  

New diacid dichlorides bearing phenyl thiourea groups were prepared by a facile synthetic approach and characterized using spectroscopic and elemental analyses. A series of novel aromatic and semiaromatic polyamides were prepared via a condensation route from the synthesized diacid dichlorides with 4,4′-oxydianiline. The polymers were characterized by FT-IR, ¹H NMR, ¹³C NMR, and their physical properties, including their solution viscosities, solubilities and thermal properties, were studied too. Polyamides with phenyl thiourea moieties in the backbone showed good solubilities in amide solvents such as DMAc, DMF, DMSO, and NMP. All of the synthesized polymers had η _inh values of 0.042–0.053 dm³/g, and were obtained in quantitative yield. GPC measurements of the synthesized polyamides indicated M _w values of 64,759–86,172. The crystallinity of the polymers was evaluated via their X-ray diffraction patterns. Their glass transition temperatures were found to be 218–229 °C. Furthermore, thermogravimetric analysis indicated that the polymers were thermally stable in the range 300–398 °C in a N₂ atmosphere.     

Organo-modified mesoporous silica for sorption of carbon dioxide

Abstract  

Organo-modified mesoporous silica SBA-15 has been studied for sorption of carbon dioxide (CO₂). The SBA-15 sample was functionalized with a branched chain polymer, polyethylenimine (PEI), of different molecular weights (1,300 and 2,000 g mol⁻¹). Surface modification was carried out by impregnation of silica by PEI or by grafting with (3-chloropropyl)triethoxysilane, followed by substitution of chlorine atoms by PEI ligands. The prepared modified mesoporous materials were characterized by nitrogen adsorption/desorption at 77 K, high-resolution transmission electron microscopy, small-angle X-ray scattering, and thermal methods. Sorption of CO₂ was studied by gravimetric method at 303 K. The total amount of sorbed CO₂ varied between 0.19–0.67 mmol/g for respective samples. Regeneration of the materials after adsorption was achieved by thermal treatment at 343 K.     

ESI–IT–MSn and DFT calculation for electron affinities of bimetallic oxovanadium complexes

Abstract  

The MS ⁿ spectra of three bimetallic oxovanadium complexes were obtained using an ion trap. The fragmentation pathways were elucidated. Common features and major differences between ESI–QTOF–MS/MS and ESI–IT–MS ⁿ spectra were compared. Electron affinities of several radical molecular anions were calculated by DFT and these could be used as an indicator of the ions’ stability.     

Theoretical study on the complexation of the cesium cation with dibenzo-18-crown-6

Abstract  

By using quantum mechanical calculations, the most probable structures of free dibenzo-18-crown-6 ligand and the cationic complex species of Cs⁺ both with one and with two dibenzo-18-crown-6 ligands were derived. In these two complexes, the “central” cation Cs⁺ is bound by strong bond interactions to the corresponding ethereal oxygen atoms of the parent crown ligand.     

Determination of rutin using a CeO2 nanoparticle-modified electrode

CeO₂ nanoparticles approximately 12 nm in size were synthesized and subsequently characterized by XRD, TEM and UV-vis spectroscopy. Then, a gold electrode modified with CeO₂ nanoparticles was constructed and characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified electrode demonstrated strong catalytic effects with high stability towards electrochemical oxidation of rutin. The anodic peak currents (measured by differential pulse voltammetry) increased linearly with the concentration of rutin in the range of 5.0 × 10⁻⁷–5.0 × 10⁻⁴ mol · L⁻¹. The detection limit (S/N = 3) was 2.0 × 10⁻⁷ mol · L⁻¹. The relative standard deviation (RSD) of 8 successive scans was 3.7% for 5.0 × 10⁻⁶ mol · L⁻¹ rutin. The method showed excellent sensitivity and stability, and the determination of rutin in tablets was satisfactory.     

Theoretical study on the complexation of bambus[6]uril with the chloride, bromide, and iodide anions

Abstract  

By using quantum mechanical DFT calculations, the most probable structures of the bambus[6]uril·Cl⁻, bambus[6]uril·Br⁻, and bambus[6]uril·I⁻ anionic complex species were derived. In these three complexes, each of the considered univalent halide anions, included in the center of the macrocyclic cavity, is bound by 12 weak C–H⋯X⁻ (X⁻ = Cl⁻, Br⁻, I⁻) hydrogen bonds between methine hydrogen atoms on the convex face of the glycoluril units and the respective anion. The lengths of the C–H⋯X⁻ hydrogen bonds increase in the order Cl⁻ < Br⁻ < I⁻.     

Synthesis and biological activities of novel ethers of quinolinone linked with coumarins

Abstract  

A series of new ethers of quinolinone linked with different substituted coumarins and benzofurans were synthesized from 4-(bromomethyl)quinolinones. All newly synthesized compounds were screened for their in vitro antibacterial and antifungal activities. Most of the compounds with chloro substitution at the C-6 or C-7 position in quinolinone showed potent antibacterial and antifungal activities. In pharmacological evaluations, some of these chloroquinolinones also showed 70–77% inhibition of inflammation after 8 h, whereas the other compounds showed 51–55% inhibition. Most of the compounds showed potent analgesic activity compared to the standard and control. The structures of all newly synthesized compounds were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR, and EI-MS.     

Synthesis, Crystal Structure, Photophysical Properties, and DFT Calculations of a Bis(tetrathia-calix[4]arene) Tetracadmium Complex

Abstract  

Thiacalix[4]arenes are a unique family of polydentate ligands that offer a combination of four soft sulfur atoms together with four hard phenol oxygen atoms for binding to metal ions. In this study, the tetranuclear cadmium (II) complex Cd₄^II(tca)₂·1.5CH₂Cl₂ (tca⁴⁻ = tetra-anionic p-tert-butylthiacalix[4]arene) (1) was synthesized by reaction of a deprotonated p-tert-butylthiacalix[4]arene and various Cd^II salts. The structure of 1 was established by single crystal X-ray diffraction analysis. The neutral complex 1 contains a square arrangement of four cadmium (II) ions sandwiched between two tca⁴⁻ ligands that have a ‘cone’ conformation similar to that of the free ligand. The absorption and emission properties of the free ligand H₄tca and complex 1 have been recorded and explained by DFT calculations of the molecular orbitals and electronic transitions between them.     

Chiral separation of ofloxacin enantiomers by ligand exchange chromatography

Abstract  

The enantioseparation conditions of ligand exchange chromatography were examined using ofloxacin enantiomers. A C₁₈ column was used with the mobile phase consisting of a methanol–water solution (containing different concentrations of l-isoleucine and copper sulfate) at flow rate of 0.5 cm³ min⁻¹. The effect of different kinds and concentrations of ligands, bivalent ligand ions, and organic modifier, and temperature on enantioseparation were evaluated; the results showed that enantioselectivity was strongly affected by the ligand concentration of the mobile phase. Under the optimum conditions (methanol/water 20:80 v/v, containing 2.5 mmol dm⁻³ l-isoleucine and 0.6 mmol dm⁻³ Cu²⁺, room temperature), baseline separation of the two enantiomers was obtained with resolution of 1.32 in less than 30 min. The separation method was used to analyze the ofloxacin enantiomers in different commercial medicines.     

DFT and TD-DFT studies on symmetrical squaraine dyes for nanocrystalline solar cells

Abstract  

The ground-state geometries, electronic structures, and electronic absorption spectra of symmetrical squaraine dyes SQ1–SQ4 were investigated using density functional theory and time-dependent DFT at the B3LYP level. The calculated geometries indicate that strong conjugation effects occur in the dyes. The highest occupied molecular orbital energy levels were calculated to be −4.95, −5.22, −5.09, and −5.06 eV, and the lowest unoccupied molecular orbital energies were −2.72, −3.05, −2.80, and −2.80 eV for SQ1–SQ4, respectively. Taking the conduction band energy of TiO₂ into account, these data reveal the sensitized mechanism: the interfacial electron transfer between the semiconductor TiO₂ electrode and the dye sensitizers SQ1–SQ4 are electron-injection processes from excited dyes to the semiconductor conduction band. The intense calculated absorption bands are assigned to π → π* transitions, which exhibit appreciable blue-shift compared with the experimental absorption maxima due to the inherent approximations in the TD-DFT.     

Rapid solidification of cryolite and cryolite–alumina melts

Abstract  

Rapid solidification processing (with a cooling rate in the interval 10⁵–10⁶ K s⁻¹) was used to prepare deeply undercooled cryolite–alumina melts. These samples were analyzed by XRD, infrared, and Raman spectroscopy. Besides cryolite, the amorphous phase and a low amount of ι-Al₂O₃ were detected. Annealing of the quenched sample revealed the transformation of metastable amorphous phases into different products depending on the annealing conditions. The results obtained showed that all of the elements (Na, Al, O, and F) are probably present in the amorphous parts of the quenched samples.     

Beta-arrestin inhibits CAMKKbeta-dependent AMPK activation downstream of protease-activated-receptor-2

Background  

Proteinase-activated-receptor-2 (PAR₂) is a seven transmembrane receptor that can activate two separate signaling arms: one through Gαq and Ca²⁺ mobilization, and a second through recruitment of β-arrestin scaffolds. In some cases downstream targets of the Gαq/Ca²⁺ signaling arm are directly inhibited by β-arrestins, while in other cases the two pathways are synergistic; thus β-arrestins act as molecular switches capable of modifying the signal generated by the receptor.     

Synthesis and characterization of chitosan-based polyurethane elastomer dispersions

Abstract  

A number of aqueous polyurethane dispersions were synthesized by the reaction of poly(ε-caprolactone) and isophorone diisocyanate, extended with different mass ratios of chitosan and dimethylol propionic acid. Their chemical structures were characterized by using FTIR, ¹H NMR, and ¹³C NMR spectroscopy, and thermal properties were determined by TGA. Incorporation of chitosan into the polyurethane backbone improved thermal stability. The hydrophilicity of the prepared polymers was also examined by contact angle measurements. For all samples, the contact angles increased by increasing the amount of chitosan. The increased contact angle is ascribed to the decrease of the hydrophilicity of the polyurethanes, which is reduced by the increasing amount of chitosan with respect to dimethylol propionic acid chain extender.