Cyclohexanol dehydrogenation over Cu-loaded TiO2 photocatalyst under solar illumination

Abstract  

The liquid-phase selective dehydrogenation of cyclohexanol has been investigated using two classes of catalyst containing either Cu₂O or CuO on TiO₂ under solar light in deaerated conditions at room temperature using acetonitrile medium in a batch reactor. The effect on dehydrogenation of three conditions, cyclohexanol concentration, copper loading on TiO₂, and amount of catalyst, were investigated. The maximum yield of cyclohexanone obtained was 40%. The catalysts were characterized by XRD, UV–DRS, TEM, SEM–EDAX, and XPS. It was found that 1% (w/w) Cu₂O/TiO₂ was 100% selective for photocatalytic dehydrogenation of cyclohexanol.     

Quantification of binding affinities of essential sugars with a tryptophan analogue and the ubiquitous role of C-H···π interactions

The role of noncovalent interactions in carbohydrate recognition by aromatic amino acids has long been reported. To develop a molecular understanding of noncovalent interactions in the recognition process, we have examined a series of binary complexes between 3-methylindole (3-MeIn) and sugars. In particular, the geometries and binding affinities of 3-MeIn with α/β-D-glucose, β-D-galactose, α-D-mannose and α/β-L-fucose are obtained using the MP2(full)/6-31G(d,p) and the M06/TZV2D//MP2/6-31G(d,p) level of theories. The conventional hydrogen bonding such as N-H···O and C-H···O as well as nonconventional O-H···π and C-H···π type of interactions is, in general, identified as responsible for the moderately strong interaction energies. Large variations in the position-orientations of 3-MeIn with respect to saccharide are noticed, within the same sugar family, as well as across different sugar series. Furthermore, complexes with large differences in their geometries are recognized as capable of exhibiting very similar interaction energies, underscoring the significance of exhaustive conformation sampling, as carried out in the present study. These observations are readily attributed to the differences in the efficiency of the type of interactions enlisted above. The highest and lowest interaction energies, upon inclusion of 50% BSSE correction, are found to be -16.02 and -6.22 kcal mol(-1), respectively, for α-D-glucose (1a) and α-L-fucose (5j). While more number of prominent conventional hydrogen bonding contacts remains as a characteristic feature of the strongly bound complexes, the lower end of the interaction energy spectrum is dominated by multiple C-H···π interactions. The complexes exhibiting as many as four C-H···π contacts are identified in the case of α/β-D-glucose, β-D-galactose, and α/β-L-fucose with an interaction energy hovering around -8 kcal mol(-1). The presence of effective C-H···π interactions is found to be dependent on the saccharide configuration as well as the area of the apolar patch constituted by the C-H groups. The study offers a comprehensive set of binary complexes, across different saccharides, which serves as an illustration of the significance and ubiquitous nature of C-H···π interactions in carbohydrate binding in saccharide-protein complexes.     

Synthesis of high voltage (4.9 V) cycling LiNixCoyMn(1-x-y)O2 cathode materials for lithium rechargeable batteries

Layered mixed oxides LiNi(x)Co(y)Mn(1-x-y)O(2) (0 ≤x, y≤ 0.5) synthesized by a sol-gel method using tartaric acid as a chelating agent, and their structural and electrochemical properties are investigated by thermal analysis, XRD, SEM, FT-IR and XPS studies. The higher composition of Co leads to cation disorder and shrinks the cell volume. Electrochemical behaviour of the synthesized materials is evaluated by Galvanostatic charge/discharge studies using 2016 type coin cells. The cycling studies are carried out in the voltage limits of 2.7 to 4.6, 4.8 and 4.9 V at current rates of C/10 and C/5 respectively. The composition LiNi(0.4)Co(0.1)Mn(0.5)O(2) exhibits an average discharge capacity of 192 mA h g(-1) at the current density of 0.612 mA cm(-2) (C/5) in the voltage range of 2.7-4.9 V as compared to the discharge capacity of 155 and 175 mA h g(-1) in the potential range of 2.7-4.6 and 2.7-4.8 V over the 50 investigated cycles. The effect of higher charge voltage at 4.9 V on the electrochemical performance of LiNi(x)Co(y)Mn(1-x-y)O(2) oxide materials has not previously been reported.     

Different geometrical arrangements in carboxylate coordination polymers of flexible dicarboxylic acid

Dicarboxylate coordination polymers (1-5) of Mn(II), Ni(II), Cu(II), Zn(II) and Cd(II), respectively, derived from (7-carboxymethoxy-naphthalen-2-yloxy)-acetic acid (L₁H₂) are synthesized and characterized. Depending on the coordination sites around the metal centers and coordination mode of the ligand, dimensionality of these polymers varies. The dicarboxylates adopt three spatial orientations: in-plane linear coordination, out-of-plane cis coordination and out-of-plane trans coordination mode. Both the cis and trans out-of-plane coordination modes are found to exist only if the ancillary ligand pyridine is coordinated to the metal ion. When the aquoligand coordinates the in-plane linear coordination mode of L₁ predominates. The coordination polymers 4 and 5 show photoluminescence in solution. The dicarboxylate of (5-carboxymethoxy-naphthalen-1-yloxy)-acetic acid (L₂H₂) does not form coordination polymer under ambient conditions, but prefers to remain as uncoordinated anion providing hydrophobic confinement to hexa-aquometal(II) cation. Compound 3 crystallizes in P2₁ space group and it shows broadband ultra-violet fluorescence centered at 352.9 nm on focusing 632.8 nm He:Ne laser.     

Solid-phase extraction combined with headspace single-drop microextraction of chlorophenols as their methyl ethers and analysis by high-performance liquid chromatography-diode array detection

Solid-phase extraction (SPE) of phenol and chlorophenols, their derivatization to methyl ethers, headspace single-drop microextraction (HS-SDME) of methyl ethers using 1-butanol as extraction solvent, and direct transfer of the drop into the injector for high performance liquid chromatography with diode array detection (HPLC-DAD) have been reported. A flanged-end polytetrafluoroethylene sleeve, 3 mm × 0.5 mm, placed at the tip of the syringe needle, allowed the use of 10 μL solvent drop for extraction. The procedure has been optimized for variables involved in SPE and HS-SDME. A rectilinear relationship was obtained between the amount of chlorophenols and peak area ratio of their methyl ethers/internal standard (4-methoxyacetophenone) in the range 0.01-10 mg L⁻¹, correlation coefficient in the range 0.9956-0.9996, and limit of detection in the range 1.5-3.9 μg L⁻¹ when HS-SDME alone was used for sample preparation. When using coupled SPE and HS-SDME, the linear range obtained was 0.1-500 μg L⁻¹, correlation coefficient in the range 0.9974-0.9998, and the limit of detection in the range 0.04-0.08 μg L⁻¹. Spiked real samples have been analyzed with adequate accuracy, and application of the method has been demonstrated for the analysis of chlorophenols formed upon bamboo pulp bleaching.     

Self‐Assembled Helical Arrays for the Stabilization of the Triplet State

Room‐temperature phosphorescence of metal and heavy atom‐free organic molecules has emerged as an area of great potential in recent years. A rational design played a critical role in controlling the molecular ordering to impart efficient intersystem crossing and stabilize the triplet state to achieve room‐temperature ultralong phosphorescence. However, in most cases, the strategies to strengthen phosphorescence efficiency have resulted in a reduced lifetime, and the available nearly degenerate singlet‐triplet energy levels impart a natural competition between delayed fluorescence and phosphorescence, with the former one having the advantage. Herein, an organic helical assembly supports the exhibition of an ultralong phosphorescence lifetime. In contrary to other molecules, 3,6‐phenylmethanone functionalized 9‐hexylcarbazole exhibits a remarkable improvement in phosphorescence lifetime (>4.1 s) and quantum yield (11 %) owing to an efficient molecular packing in the crystal state. A right‐handed helical molecular array act as a trap and exhibits triplet exciton migration to support the exceptionally longer phosphorescence lifetime.