Role of water and carbonates in photocatalytic transformation of CO2 to CH4 on titania

Using the electron paramagnetic resonance technique, we have elucidated the multiple roles of water and carbonates in the overall photocatalytic reduction of carbon dioxide to methane over titania nanoparticles. The formation of H atoms (reduction product) and (?)OH radicals (oxidation product) from water, and CO(3)(-) radical anions (oxidation product) from carbonates, was detected in CO(2)-saturated titania aqueous dispersion under UV illumination. Additionally, methoxyl, (?)OCH(3), and methyl, (?)CH(3), radicals were identified as reaction intermediates. The two-electron, one-proton reaction proposed as an initial step in the reduction of CO(2) on the surface of TiO(2) is supported by the results of first-principles calculations.     

Antiphytoviral activity of sesquiterpene-rich essential oils from four croatian teucrium species

The purpose of this study was to compare the essential oil profiles of four Croatian Teucrium species (Lamiaceae), as determined by GC and GC/MS, with their antiphytoviral efficiency. A phytochemical analysis showed that T. polium, T. flavum, T. montanum and T. chamaedrys are characterized by similar essential oil compositions. The investigated oils are characterized by a high proportion of the sesquiterpene hydrocarbons β-caryophyllene (7.1-52.0%) and germacrene D (8.7-17.0%). Other important components were β-pinene from T. montanum and α-pinene from T. flavum. The investigated essential oils were proved to reduce lesion number in the local host Chenopodium quinoa Willd. infected with Cucumber Mosaic Virus (CMV), with reductions of 41.4%, 22.9%, 44.3% and 25.7%, respectively.     

Novel Photochemical Synthesis of Spiro-1,2,6,8,9 Pentaza-4-thia(4,4)nonane via Rearrangement of Aliphatic Arylazo Compounds

Irradiation of N-phenyl-2-phenylazo-3-oxo-3-[(4-phenyl-5-aryl)-1,2,4-triazol-3-yl)thio]butanamides 4 _a–c gave the corresponding title spiro compounds 5 _a–c as end products via tandem rearrangement and cyclization of 4 _a–c in their excited states.     

SYNTHESIS AND REACTIONS OF TRIPHENYLPHOSPHONIMINOGLYOXALIC ACID ANILIDE ARYLHYDRAZONES

Abstract

A series of α-azidoglyoxatic acid anilide arylhydrazones 2 were prepared and converted to the corresponding phosphonimines 6 by reaction with triphenylphosphine. Treatment of the latter with acyl chlorides yielded the phosphonium salts 9 which afforded, upon treatment with triethylamine, 1, 5-disubstituted 1H-1, 2, 4-triazole-3-carboxylic acid anilides 11. Acid hydrolysis of 6 yielded the amidrazones 8.     

STUDIES ON ORGANOPHOSPHORUS COMPOUNDS VI1–5: Utility of Lawesson's Reagent for Synthesis of Thiaphosphorine,Thioxanthene, and Thiaphosphole Derivatives

Arylidene malonate derivatives 2a–c reacted with Lawesson's reagent (1) LR in equimolar ratio to yield the oxathiaphosphorine derivatives 3a–c. The behaviour of LR towards cyclic ketones was also examined and yielded the thioxanthene derivatives 5a,b. On the other hand, arylidene pyrazolone 8 reacted with LR to give the phosphole 10. Aminobenzenethiophene 11 reacted with LR under reflux to produce the corresponding thiazaphosphorine 12.     

Tuning the Stability of CaCO3 Crystals with Magnesium Ions for the Formation of Aragonite Thin Films on Organic Polymer Templates

Thin‐film growth of aragonite CaCO₃ on annealed poly(vinyl alcohol) (PVA) matrices is induced by adding Mg²⁺ into a supersaturated solution of CaCO₃. Both the growth rate and surface morphology of the aragonite thin films depend upon the concentration of Mg²⁺ in the mineralization solution. In the absence of PVA matrices, no thin films are formed, despite the presence of Mg²⁺. Molecular dynamics simulation of the CaCO₃ precursor suggests that the transition of amorphous calcium carbonate to crystals is suppressed in the presence of Mg²⁺. The role for ionic additives in the crystallization of CaCO₃ on organic templates obtained in this study may provide useful information for the development of functional hybrid materials.     

Optimization of Ultrasound-Assisted Extraction of Phenolics from Sideritis raeseri Using Response Surface Methodology

In this study we define the optimal conditions for ultrasound-assisted extraction of bioactive polyphenols from S. raeseri aerial parts using response surface methodology. The influence of ethanol concentration (10–90%), extraction temperature (20–80 °C), extraction time (10–60 min), and solid-to-solvent ratio (1:10–1:50) on total phenolic content as well as on content of individual flavonoids, and hypolaetin and isoscutellarein derivatives was studied. For the experimental design, a central composite design was chosen. In the obtained extracts, the following ranges of targeted compounds were detected: total phenol from 19.32 to 47.23 mg GAE/g dw, HYP from 1.05 to 11.46 mg/g dw, ISC 1 from 0.68 to 10.68 mg/g dw, and ISC 2 from 0.74 to 15.56 mg/g dw. The optimal extraction conditions were set as: ethanol concentration of 65%, extraction time of 50 min, extraction temperature of 63 °C, and solid-to-solvent ratio of 1:40. Contents of TP, HYP, ISC 1, and ISC 2 in optimal extracts were 47.11 mg GAE/g dw, 11.73 mg/g dw, 9.54 mg/g dw, and 15.40 mg/g dw, respectively. Experimentally set values were in good agreement with those predicted by the response surface methodology model, indicating suitability of the used model, as well as the success of response surface methodology in optimizing the conditions of the extraction.     

Isotope analyses of the lake sediments in the Plitvice Lakes,Croatia

The analyses of radioactive isotopes ¹⁴C, ¹³⁷Cs and ²¹⁰Pb, and stable isotope ¹³C were performed in the sediment cores, top 40 cm, taken in 2011 from karst lakes Pro??e and Kozjak in the Plitvice Lakes National Park, central Croatia. Frozen sediment cores were cut into 1 cm thick layers and dried. ¹⁴C activity in both carbonate and organic fractions was measured using accelerator mass spectrometry technique with graphite synthesis. ¹³⁷Cs, ²¹⁰Pb, ²¹⁴Pb and ²¹⁴Bi were measured by low level gamma spectrometry method on ORTECHPGe detector with the efficiency of 32%. Distribution of ¹⁴C activity from both lakes showed increase of the ¹⁴C activity in the top 10–12 cm in both carbonate and organic fractions as a response to thermonuclear bomb-produced ¹⁴C in the atmosphere in the sixties of the 20th century. Anthropogenically produced ¹³⁷Cs was also observed in sediment profiles. Sedimentation rates for both lake sediments were estimated based on the unsupported ²¹⁰Pb activity. Different ¹⁴C activity of the carbonate fraction (63–80 pMC, percent of modern carbon) and organic fraction (82–93 pMC) is the result of geochemical and biological processes of the sediment precipitation in the lake waters. This is also confirmed by the δ ¹³ C values of both fractions. Carbon isotope composition, a ¹⁴ C and δ ¹³ C, was compared with the lake sediments from the same lakes collected in 1989 and 2003.     

Analysis of High and Selective Uptake of CO2 in an Oxamide‐Containing {Cu2(OOCR)4}‐Based Metal–Organic Framework

The porous framework [Cu₂(H₂O)₂L] ? 4 H₂O ? 2 DMA (H₄L=oxalylbis(azanediyl)diisophthalic acid; DMA=N,N‐dimethylacetamide), denoted NOTT‐125, is formed by connection of {Cu₂(RCOO)₄} paddlewheels with the isophthalate linkers in L^4?. A single crystal structure determination reveals that NOTT‐125 crystallises in monoclinic unit cell with a=27.9161(6), b=18.6627(4) and c=32.3643(8) Å, β=112.655(3)°, space group P2₁/c. The structure of this material shows fof topology, which can be viewed as the packing of two types of cages (cage A and cage B) in three‐dimensional space. Cage A is constructed from twelve {Cu₂(OOCR)₄} paddlewheels and six linkers to form an ellipsoid‐shaped cavity approximately 24.0 Å along its long axis and 9.6 Å across its central diameter. Cage B consists of six {Cu₂(OOCR)₄} units and twelve linkers and has a spherical diameter of 12.7 Å taking into account the van der Waals radii of the atoms. NOTT‐125 incorporates oxamide functionality within the pore walls, and this, combined with high porosity in desolvated NOTT‐125a, is responsible for excellent CO₂ uptake (40.1 wt % at 273 K and 1 bar) and selectivity for CO₂ over CH₄ or N₂. Grand canonical Monte Carlo (GCMC) simulations show excellent agreement with the experimental gas isotherm data, and a computational study of the specific interactions and binding energies of both CO₂ and CH₄ with the linkers in NOTT‐125 reveals a set of strong interactions between CO₂ and the oxamide motif that are not possible with a single amide.     

The important role of tetrahedral Ti4+ sites in the phase transformation and photocatalytic activity of TiO2 nanocomposites

Highly photoactive, tetrahedral Ti4+ sites can be created, other than in zeolite cavities and on silica substrate, in mixed-phase TiO2 nanocomposites. The tetrahedral Ti4+ species was shown to be an intermediate formed during the thermally driven phase transformation from anatase to rutile.