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41.
Christopher Grieco Forrest R. Kohl Yuyuan Zhang Sangeetha Natarajan Lluís Blancafort Bern Kohler 《Photochemistry and photobiology》2019,95(1):163-175
The catechol functional group plays a major role in the chemistry of a wide variety of molecules important in biology and technology. In eumelanin, intermolecular hydrogen bonding between these functional groups is thought to contribute to UV photoprotective and radical buffering properties, but the mechanisms are poorly understood. Here, aggregates of 4‐t‐butylcatechol are used as model systems to study how intermolecular hydrogen bonding influences photochemical pathways that may occur in eumelanin. Ultrafast UV‐visible and mid‐IR transient absorption measurements are used to identify the photochemical processes of 4‐t‐butylcatechol monomers and their hydrogen‐bonded aggregates in cyclohexane solution. Monomer photoexcitation results in hydrogen atom ejection to the solvent via homolytic O‐H bond dissociation with a time constant of 12 ps, producing a neutral semiquinone radical with a lifetime greater than 1 ns. In contrast, intermolecular hydrogen bonding interactions within aggregates retard O‐H bond photodissociation by over an order of magnitude in time. Excited state structural relaxation is proposed to slow O‐H dissociation, allowing internal conversion to the ground state to occur in hundreds of picoseconds in competition with this channel. The semiquinone radicals formed in the aggregates exhibit spectral broadening of both their electronic and vibrational transitions. 相似文献
42.
43.
M. Nageshwari C. Rathika Thaya Kumari P. Sangeetha G. Vinitha M. Lydia Caroline 《Chinese Journal of Physics (Taipei)》2018,56(2):502-519
The efficient acentric L-ornithine monohydrochloride (LOMHCl), which belongs to the trait of semiorganic category and depicts nonlinear optical characteristics, was grown-up by the process of slow evaporation. The crystal structure and crystallinity of LOMHCl was established by the process of single crystal and powder X-ray diffraction. Single XRD affirm that LOMHCl crystallizes in the system of monoclinic with P21 as acentric space group. The examination of FTIR was done to ascertain the existence of various functional groups in LOMHCl. UV–Vis spectral analysis substantiates its optical quality and the optical constants were also assessed. Photoluminescence process elucidates its emission characteristics and its lifetime is also determined. LOMHCl discloses exquisite resistance to laser radiation having threshold up to 2.69 GW/cm2. The SEM analysis highlights its surface topography. The mechanical stability has been attested by the analysis of microhardness and several mechanical parameters are also estimated. The investigation of dielectric characteristics of LOMHCl was also accomplished. The studies on second and third order nonlinearity were established by the method of Kurtz–Perry and Z-scan which facilitates its utility in the field of nonlinear optics. 相似文献
44.
Adsorption of vanadium(V) from aqueous solution onto ZnCl2 activated carbon developed from coconut coir pith was investigated to assess the possible use of this adsorbent. The influence
of various parameters such as agitation time, vanadium concentration, adsorbent dose, pH and temperature has been studied.
First, second order, Elovich and Bangham’s models were used to study the adsorption kinetics. The adsorption system follows
second order and Bangham’s kinetic models. Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherms have been employed
to analyze the adsorption equilibrium data. Equilibrium adsorption data followed all the four isotherms—Langmuir, Freundlich,
D-R and Temkin. The Langmuir adsorption capacity (Q
0) was found to be 24.9 mg g− 1 of the adsorbent. The per cent adsorption was maximum in the pH range 4.0–9.0. The pH effect and desorption studies showed
that ion exchange mechanism might be involved in the adsorption process. Thermodynamic parameters such as ΔG
0, ΔH
0 and ΔS
0 for the adsorption were evaluated. Effect of competitive anions in the aqueous solution such as PO4
3 −, SO4
2−, ClO4
−, MoO4
2−, SeO3
2−, NO3
− and Cl− was examined. SEM and FTIR were used to study the surface of vanadium(V) loaded ZnCl2 activated carbon. Removal of vanadium(V) from synthetic ground water was also tested. Results show that ZnCl2 activated coir pith carbon is effective for the removal of vanadium(V) from water. 相似文献
45.
Photoelastic coatings can be cemented directly to actual structural components and tested under field conditions. This important advantage has made them relatively popular in industry. The information obtained, however, may be misinterpreted and lead to serious errors. A correct interpretation requires the separation of the principal strains and, so far, this operation has been found very difficult. Following a previous paper by one of the authors, it is proposed to drill small holes in the coating and record the birefringence at points removed from the edge of the holes. The theoretical background of the method is reviewed, the technique necessary to use it is explained and two applications are described. The precision of the method is evaluated and found satisfactory in contradiction to information previously published in the literature. 相似文献
46.
Sangeetha G. Bhat Girish Sharada Ramachandra Poornima Bhagavath Mahabaleshwara Subrao D. M. Potukuchi Srinivasulu Maddasani 《Journal of Thermal Analysis and Calorimetry》2018,132(2):989-1000
Two new series of liquid crystalline materials with non-mesomorphic fatty acids, viz. nonanoic (C9), capric (C10), undecanoic (C11), tridecanoic (C13), myristic (C14), palmitic (C16) and stearic acids (C18), are prepared with non-mesomorphic proton acceptors, viz. (4-pyridyl)-benzylidene-p-n-alkylanilines (PyBnA; n = 12 and 16). The smectic phase structures formed between the proton donor (fatty acid) and proton acceptor moieties are found due to the intermolecular hydrogen bonding (HB) and are monotropic. The presence of HB is confirmed by Fourier transform infrared spectroscopy in all the compounds. The characteristic optical textures of smectic phases are observed through polarizing optical microscope, provided with a hot stage and a camera. The phase transition temperatures and the enthalpy changes across the phase transitions are determined by differential scanning calorimetry. The smectic phase exhibited by the HB complexes is confirmed by miscibility studies as smectic-B. The π–π stacking interactions in layers are found to influence the mesomorphism in these HB complexes. 相似文献
47.
Four ring achiral ferroelectric liquid crystals of 1,2,4-oxadiazoles: synthesis and characterisation
Mahabaleshwara Subrao Poornima Bhagavath Sangeetha G. Bhat Girish Sharada Ramachandra D. M. Potukuchi 《Liquid crystals》2016,43(3):400-410
A novel series of four-ring achiral ferroelectric liquid crystals containing 1,2,4-oxadiazole cores with unsymmetrical substitutions at C-3 and C-5 positions are synthesised and characterised. A fluoro substituted biphenyl moiety is prepared by Suzuki coupling reaction and is directly attached to the oxadiazole core at the C-5 position for the first time in the literature. An octyl benzoate is attached to the oxadiazole core at the C-3 position of it. All the compounds exhibit polar smectic (B2) mesophases with ferroelectric switching along with the orthogonal smectic-A mesophases. These compounds possess high mesomorphic thermal ranges of polar smectic phases and are towards the ambient temperatures. The influence of a more electronegative fluorine substituent on the electron rich biphenyl moiety (at the C-5 position) of the oxadiazole core is analysed for the prevalence and abundance of polar smectic (ferroelectric) mesophases. 相似文献
48.
Sangeetha S Sathyaraj G Muthamilselvan D Vaidyanathan VG Nair BU 《Dalton transactions (Cambridge, England : 2003)》2012,41(19):5769-5773
We report two fluorophores with open coordination sites for specific sensing of Ni(2+) and Cu(2+) ions via a simple synthetic route. The fluorescence activity was completely quenched on coordination of the metal ions with the phenanthroline ring present in the fluorophore as is clearly evident from the photophysical studies. 相似文献
49.
The present study is focused on the development of single chamber microbial fuel cell (SCMFC) using sulfonated poly ether ether ketone (SPEEK) membrane to determine the biochemical oxygen demand (BOD) matter present in artificial wastewater (AW). The biosensor produces a good linear relationship with the BOD concentration up to 650 ppm when using artificial wastewater. This sensing range was 62.5% higher than that of Nafion®. The most serious problem in using MFC as a BOD sensor is the oxygen diffusion into the anode compartment, which consumes electrons in the anode compartment, thereby reducing the coulomb yield and reducing the electrical signal from the MFC. SPEEK exhibited one order lesser oxygen permeability than Nafion®, resulting in low internal resistance and substrate loss, thus improving the sensing range of BOD. The system was further improved by making a double membrane electrode assembly (MEA) with an increased electrode surface area which provide high surface area for electrically active bacteria. 相似文献
50.
Hydroxamic acid derivatives with metal ion binding properties were collected from the literature to generate a pharmacophore and 3D-QSAR model for HIV strand transfer inhibition. The derived pharmacophore model (AAAHRR) recognizes both metal ion binding site and hydrophobic group. The QSAR model generated using this hypothesis expressed statistical significance (r 2 = 0.971 for the training set and q 2 = 0.913 for the test set). The ability of this pharmacophore model to retrieve other metal ion binding inhibitors was examined by screening the ChemBank database (ligandinfo) incorporated with 10 known strand transfer inhibitors. The studied favourable and unfavourable contours of chemical features (H-bond donor, acceptor and hydrophobic sites) revealed the role of hydrophobic substitution at the fluorobenzene ring and cyclization of the metal ion binding hydroxamic acid in effective integrase inhibition. Analysis of the frontier orbitals, HOMO and LUMO revealed that the nucleophilic / electrophilic interactions depend on the significant overlapping observed at the azaindole and hydroxamic acid groups. In essence, the generated pharmacophore model is competent enough to disclose the essential site-specific interactions involved in the inhibition of HIV integrase, and hence can be used in virtual screening to identify novel scaffolds as leads with increased anti-viral potency. 相似文献