Biosynthetic Approaches towards the Design of Artificial Hydrogen-Evolution Catalysts

Hydrogen is a clean and sustainable form of fuel that can minimize our heavy dependence on fossil fuels as the primary energy source. The need of finding greener ways to generate H₂ gas has ignited interest in the research community to synthesize catalysts that can produce H₂ by the reduction of H⁺. The natural H₂ producing enzymes hydrogenases have served as an inspiration to produce catalytic metal centers akin to these native enzymes. In this article we describe recent advances in the design of a unique class of artificial hydrogen evolving catalysts that combine the features of the active site metal(s) surrounded by a polypeptide component. The examples of these biosynthetic catalysts discussed here include i) assemblies of synthetic cofactors with native proteins; ii) peptide-appended synthetic complexes; iii) substitution of native cofactors with non-native cofactors; iv) metal substitution from rubredoxin; and v) a reengineered Cu storage protein into a Ni binding protein. Aspects of key design considerations in the construction of these artificial biocatalysts and insights gained into their chemical reactivity are discussed.     

Phase behaviour of the discotic mesogen 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT) under hydrostatic pressure

The phase behaviour of the discotic mesogen 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT) was investigated under hydrostatic pressures up to 500 MPa using high pressure optical and DTA measurements. The known enantiotropic phase transitions of HHTT, i.e. crystal (Cr)-helical phase (H), H-hexagonal columnar phase (Col_h) and Col_h-isotropic liquid (I) were observed up to 32 MPa. Application of hydrostatic pressures above 32 MPa results in the H and Col_h phases becoming monotropic, depending upon the applied pressure. The H phase was observed as a monotropic phase in the pressure region between 32 and about 180 MPa. Thus, the I →Col_h →H →Cr transition sequence appeared only on cooling under these pressures, while the Cr →Col_h →I transition occurred on heating. Further increases in pressure above a second limiting value leads to the Col_h phase becoming monotropic. Thus the I →Col_h →Cr transition sequence appeared on cooling, while the Cr →I transition was observed on heating. The T vs. P phase diagram based on the data obtained in the heating mode contains two triple points; one is estimated as 40 MPa, 77.2°C for the Cr-H-Col_h triple point and the other is extrapolated as 285 MPa, 118.3°C for the Cr-Col_h-I triple point. These triple points define the upper limits for the appearance of the stable H and Col_h phases, respectively.     

Calcium Borohydride

Calcium borohydride reduces both aliphatic and aromatic esters to alcohols completely in the presence of alkene catalysts. The intermediate borates formed during the reduction of aromatic esters are converted to aldehydes with aqueous NaOC1 in good yields.     

Synthesis of achiral four-ring unsymmetrically substituted toluene derived liquid crystals with a polar end group

Achiral four-ring unsymmetrically substituted toluene-derived liquid crystals have been designed and synthesised by known and straightforward methods. All these compounds exhibit nematic phase over wide temperatures.     

l-Proline-accelerated,eco-friendly synthesis of 9-substituted-2,3,4,9-tetrahydro-1H-xanthen-1-ones under mild conditions

An efficient l-proline-accelerated synthesis of 9-substituted-2,3,4,9-tetrahydro-1H-xanthen-1-one derivatives has been accomplished via one-pot condensation of dimedone or 1,3-cyclohexanedione with substituted salicylaldehydes under mild reaction conditions. This protocol demonstrates several notable advantages, including operational simplicity, short reaction times, environmentally friendly conditions, no necessity of extraction and chromatographic purification steps, and high yields of the target products.     

Synthesis,Photophysical Properties and Application of New Porphyrin Derivatives for Use in Photodynamic Therapy and Cell Imaging

New derivatives of tetrakis(4-carboxyphenyl) porphyrin were designed, synthesized and characterized by IR, proton NMR and mass spectroscopy. The ground and excited state nature of new derivatives were examined using UV-Vis. absorption and fluorescence spectroscopy, fluorescence quantum yield and fluorescence lifetime studies. The singlet oxygen quantum yield of each synthesized derivative of porphyrin was estimated for their further efficacy as potential photosensitizer in biological studies. The significant photophysical data of all synthesized derivatives was supplementary accessed to examine the cell imaging and cytotoxicity against two cancer cell lines viz. MBA-MD-231 and A375. The fluorescence lifetime, fluorescence quantum yield and efficiency of singlet oxygen generation suggests alkyl amine and alkyl hydrazide linked new porphyrin photosensitizers can be useful for PDT agent in cancer treatment.     

Stepwise Oxidations in a Cofacial Copper(II) Porphyrin Dimer: Through-Space Spin-Coupling and Interplay between Metal and Radical Spins

cis and trans-copper(II) porphyrin dimers have been synthesized, in which two Cu^II porphyrin macrocycles are bridged through a rigid ethene linker for possible through-space and through-bond spin-couplings between the paramagnetic Cu^II centers. It has been found that the two macrocycles come closer after 1 e⁻ oxidation, however, they move far apart upon further 1 e⁻ oxidation leading to transformation of the cis to the trans isomer. Detailed investigations are performed here on the interactions between the two porphyrin macrocycles, between two unpaired spins of closely spaced Cu^II centers, and also between the unpaired spins of metal and porphyrin π–cation radicals. Spectroscopic investigations along with the X-ray structure of the 2 e⁻-oxidized complex displayed strong electronic communications through the bridge between two porphyrin π–cation radicals. The counterion I₉⁻ is stabilized in an unusual trigonal-pyramidal structure in the 2 e⁻-oxidized complex in which the central iodide ion is bound with four iodine (I₂) molecules. Variable-temperature magnetic study revealed strong antiferromagnetic coupling between the two porphyrin π–cation radical spins (J_r–r) in the 2 e⁻-oxidized complex. DFT calculations suggest stabilization of the triplet state, which is also in good agreement with the experiment. Ab initio molecular dynamics allowed the variation of the structural details to be followed upon stepwise oxidations and also the final isomerization process including its associated energy barrier.     

Electro-kinetically driven route for highly sensitive blood pathology on a paper-based device

Enhancing the sensitivity of colorimetric detection in paper-devices is a quintessential step in achieving frugal diagnosis. Here, we demonstrate an effective way of improving the detection sensitivity of paper-based devices, as mediated by electro-kinetic mechanisms. By directly employing blood plasma, we investigate the electro-kinetic clustering of glucose, a neutral molecule in paper devices. Under the influence of uniform electric field, dispersed glucose gets accumulated in the paper strips. Due to the combination of EOF and electrophoretic migration, we achieve twofold increase in the colour intensity for both normal and diabetic samples. This approach is robust and possesses better sensitivity than conventional colorimetric assays and can be easily extended to other body fluid based diagnosis. These results may turn out to be of profound importance in improving the quality of pathological diagnosis in low-cost paper-based point-of-care devices deployed in resource-limited settings.     

Detection of nitrobenzene using transition metal doped C24: A DFT study

Structural Chemistry - First principles calculations have been used to verify the ability for sensing nitrobenzene by the host systems, pristine C24 and transition metal (TM) doped C24, viz.,...     

Dichiral [4.4.3.01,5]tridecane copper(II) cluster derived from a tripodal ligand having unsymmetrical podands and the linker: Synthesis,structure, surface grafting and catalytic aspects

Pseudo‐atranes have a significant role in catalysis; however, obtaining chiral pseudo‐atranes for covalent functionalization of heterogeneous catalytic surfaces is very challenging. Herein, synthesis of a chiral tripodal amine [N{CH (CH₂Ph)CH₂OH}{CH₂(4? Br? C₆H₃OH)}{CH₂(2? CHO? 4? Me? C₆H₂OH)}] ( 1 ) and a dichiral [4.4.3.0^1,5]tridecane copper(II) cluster, that is, (Cu[N{CH (CH₂Ph)CH₂OH}{CH₂(4? Br? C₆H₃O)}{CH₂(2? CHO? 4? Me? C₆H₂O)}])₂ ( 2 ) is described. The compounds are characterized by elemental analyses, Fourier transform infrared (FT‐IR) spectroscopy, mass spectrometry and single‐crystal X‐ray crystallography (for 2 ). The compound 2 is the first example of chiral pseudo‐copper(II)atrane in which three unsymmetrical arms (two phenolic and a chiral ethanolic arm) are fused via Cu? N transannular bond. The free ? CHO group present in one of the tricyclic arms of the 2 is tested as a linker to load it on 3‐aminopropyltriethoxysilane‐functionalized magnetic nanosilica for catalytic applications. The loading of 2 on magnetic nanosilica through ? CHO was confirmed by FT‐IR spectroscopy, and the 2 ‐loaded magnetic nanosilica ( Fe ₃ O ₄ @SiO ₂ /2 ) was characterized by powder X‐ray diffraction, vibrating sample magnetometry, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and elemental mapping. The Fe ₃ O ₄ @SiO ₂ /2 was found highly efficient, retrievable, eco‐friendly and green catalyst for obtaining β‐amino alcohols in excellent yields in an aqueous medium. Overall, present work is the first report on synthetic, structural and catalytic aspects of dichiral cluster of copper(II)atrane possessing unsymmetrical tricyclic arms.