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Excited state structural dynamics of 4-cyano-4 `-hydroxystilbene: deciphering the signatures of proton-coupled electron transfer using ultrafast Raman loss spectroscopy
No full textThe photo-initiated proton-coupled electron transfer (PCET) process plays a crucial role in the context of light harvesting in various biological and chemical systems. Molecular model systems are typically employed to understand the mechanisms underlying the functioning of complex biological systems. Some molecular dyads based on the PCET property have been particularly designed to achieve efficient sunlight-to-fuel production. Organic photoacids are potential sources for such applications since they exhibit an enhancement in their acidity upon photoexcitation, facilitating the mimicking of some of the biological processes. p-Hydroxybenzylideneimidazolinone (p-HBI), an organic photoacid, is a key chromophore in green fluorescent protein, which exhibits green emission due to excited state proton transfer. Herein, we investigate the structural changes and dynamics of 4-cyano-4 `-hydroxystilbene (CHSB), an analogue of p-HBI, in the presence of an external base, t-butylamine (TBA), using the techniques of ultrafast transient absorption, emission and ultrafast Raman loss spectroscopy. Femtosecond fluorescence up-conversion measurements of the CHSB-TBA adduct reveal a precursor-successor relationship between the similar to 420 and similar to 530 nm emission bands, which implies that the adduct evolves predominantly through an electron-proton transferred state. Further, Raman measurements show a clear distinction in the dynamics of the C & xe001;C stretch of CHSB in the presence and absence of TBA in terms of the amplitude growth (0.45 ps vs. instantaneous) and the central frequency (1584 vs. 1523 cm(-1))
Self-consistent theory of many-body localisation in a quantum spin chain with long-range interactions
No full textMany-body localisation is studied in a disordered quantum spin-1/2 chain with long-ranged power-law interactions, and distinct power-law exponents for interactions between longitudinal and transverse spin components. Using a self-consistent mean-field theory centring on the local propagator in Fock space and its associated self-energy, a localisation phase diagram is obtained as a function of the power-law exponents and the disorder strength of the random fields acting on longitudinal spin-components. Analytical results are corroborated using the well-studied and complementary numerical diagnostics of level statistics, entanglement entropy, and participation entropy, obtained via exact diagonalisation. We find that increasing the range of interactions between transverse spin components hinders localisation and enhances the critical disorder strength. In marked contrast, increasing the interaction range between longitudinal spin components is found to enhance localisation and lower the critical disorder
Performance improvement of cryosorption pump by enhancing thermal conductivity of epoxy-aluminum composite
No full textCryosorption pumps are only possible solution to pump helium gas in Tokamak. In this paper, we report the performance improvement of cryosorption pump, whose pumping speeds are increased by enhancing the thermal conductivity of epoxy by mixing fine aluminium powder as filler into it. From experimental studies it is found that 35% volume fraction of filler in epoxy adhesive is optimum for the improved thermal conductivity without reduction of the bonding strength. The pumping speed of cryosorption pump is increased by 3.60 times for helium gas when compared to identical commercial cryosorption pump
Synthesis of Naphthols by Rh(III)-Catalyzed Domino C-H Activation, Annulation, and Lactonization Using Sulfoxonium Ylide as a Traceless Directing Group
No full textSulfoxonium ylide directed C-H activation catalyzed by the Rh(III)-catalyst has been disclosed. In this study, sulfoxonium ylide functions as a traceless directing group, which reacts with an unsymmetrical alkyne, 4-hydroxy-2-alkynoate, to form the corresponding furanone-fused 1-naphthols. The application of the methodology has been illustrated by synthesizing bromo lactones, which are used as an intermediate in synthesizing photochromic dichroic materials. We have also demonstrated the synthesis of an analogue of fimbricalyx lactone A
Non-exponential decay of a giant artificial atom
No full textIn quantum optics, light-matter interaction has conventionally been studied using small atoms interacting with electromagnetic fields with wavelength several orders of magnitude larger than the atomic dimensions(1,2). In contrast, here we experimentally demonstrate the vastly different `giant atom' regime, where an artificial atom interacts with acoustic fields with wavelength several orders of magnitude smaller than the atomic dimensions. This is achieved by coupling a superconducting qubit(3) to surface acoustic waves at two points with separation on the order of 100 wavelengths. This approach is comparable to controlling the radiation of an atom by attaching it to an antenna. The slow velocity of sound leads to a significant internal time-delay for the field to propagate across the giant atom, giving rise to non-Markovian dynamics(4). We demonstrate the non-Markovian character of the giant atom in the frequency spectrum as well as non-exponential relaxation in the time domain
Treatment of household greywater laden with household chemical products in a multi-chambered anaerobic biofilm reactor
No full textAnaerobic treatment of greywater (GW) is challenging due to the presence of recalcitrant household chemical products (HCP) that inhibit the activity and growth of organic pollutant degrading anaerobic microbes. This research attempted to overcome this challenge through a novel, mull-chambered anaerobic biofilm reactor (AnBR) containing fluidized PVC media and packed bed lignocellulosic fiber (Cows nucifera) as biofilm support. The long-term effects of feeding HCP laden GW and effluent recycling on the performance of AnBR were corroborated with the bioconversion data and microbial community dynamics. The results indicated that the composition of wastewater and recycling both determine the rates of COD removal, microbial population, and diversity in AnBR. The inhibitory effects exhibited by GW constituents reduced the COD removal efficiencies by 74-94% in comparison to standard substrates (SS), while simultaneously reducing microbial population and diversity by 30-40%. Effluent recycling in GW and SS fed AnBR enhanced the rates of COD removal from 160 mg/L.day to 214 mg/L.day, and 627 mg/L.day to 3540 mg/L.day respectively, with the selective enrichment of Proteobacteria sp. and Methanogenic sp. The GW fed AnBR was dominated by aromatics degrading species of alpha-Proteobacteria, Synergistetes, etc., whereas, SS fed AnBR were inhabited by fermentative species of delta-Proteobacteria, Bacteroidetes, etc
Spatial distribution of decadal ice-thickness change and glacier stored water loss in the Upper Ganga basin, India during 2000-2014
No full textHimalayan glaciers have long been the focus of glaciologists across the world while trying to understand the contrasting patterns of elevation and mass changes. However, with limited number of ground observations, a comprehensive assessment of mass balance on a regional scale still remains elusive. Using the synoptic coverage of remote sensing data, we estimate a detailed spatial variation of glacier ice thickness change in the Central Himalaya of Uttarakhand using geodetic method, on a catchment scale. High resolution TerraSAR-X/TanDEM-X (12 m) and SRTM (30 m) digital elevation models (DEMs) have been utilized. The mean elevation change in the catchments is found to be -9.56 +/- 0.2 m (mean annual elevation change rate is -0.68 +/- 0.01 m a(-1)). To highlight the water potential of this region, the total ice mass loss has been estimated to be 16.0 +/- 1.2 Gigatonne (Gt) from 2000-2014 from eight identified catchments namely Yamunotri, Bhagirathi, Mandakini, Alaknanda, Dhauliganga, Pindar, Goriganga and Kali/Sarda. The estimated mass balance has been validated using reported observations on five selective glaciers and the coefficient of determination is 0.93. This spatial variation of ice thickness estimated in the eight catchments is critical, as the melt-water from these glaciers contribute to the upper Ganga basin
Role of Guanidinium-Carboxylate Ion Interaction in Enzyme Inhibition with Implications for Drug Design
No full textGuanidinium cation (Gdm(+)) interacts strongly with amino acids of different polarities modulating protein structure and function. Using density functional theory calculations and molecular dynamics simulations, we studied the interaction of Gdm(+) with carboxylate ions mimicking its interaction with acidic amino acids and explored its effect in enzymatic folding and activity. We show that, in low concentrations, Gdm(+) stabilizes carboxylate ion dimers by acting as a bridge between them, thereby reducing the electrostatic repulsion. We further show that this carboxylate-Gdm(+)-carboxylate interaction can have an effect on the structure-activity relationship in enzymes with active sites containing two acidic residues. Using five enzymes (hen egg white lysozyme, T4 lysozyme, HIV-1 protease, pepsin, and creatine kinase), which have two acidic amino acids in their active sites, we show that, in low concentrations (<0.5 M), Gdm(+) strongly binds to the enzyme active site, thereby potentially inhibiting its activity without unfolding it. This can lead to misleading conclusions in experiments, which infer the extent of enzyme unfolding from activity measurements. However, the carboxylate-Gdm(+)-carboxylate specific interaction can be exploited in drug discovery as drugs based on guanidinium derivatives are already being used to treat various maladies related to muscle weakness, cancer, diabetes etc. Guanidinium derivatives can be designed as potential drug molecules to inhibit activity or functioning of enzymes, which have binding pockets with two acidic residues in close vicinity
Furan Oxidation Strategy for the Synthesis of the Macrolactone Analogue of Migrastatin
No full textSynthesis of the 14-membered macrolide core of migrastatin is accomplished by the use of fury' carbinol in 13 linear steps from furfural with similar to 11% overall yield. Key strategies in the synthesis include the oxidative ring opening of furan and its use as a four-carbon synthon, S(N)2 displacement of a functionalized ally' bromide, and ring closing metathesis to obtain the macrolactone
Effect of N-2 dilution and preheat temperature on combustion dynamics of syngas in a reverse-flow combustor
No full textThe present study investigates the combustion dynamics of low-calorific value syngas in the reverse-flow configuration at P = 1 atm using OH* chemiluminescence (5 kHz), noise (50 kHz), and emissions (NOx and CO) measurements. The combustion dynamics have been investigated as a function of the global equivalence ratio (0.32-0.89), percentage O-2 in the coflow (7.6-21%), and the oxidizer preheat temperature (similar to 400-800 K). The variation of these parameters resulted in different operating conditions such as conventional, ultra-lean, transition, and MILD combustion modes. For all the cases, autoignition kernels were observed arid appear to be a possible mode of flame stabilization - highlighting the role of H-2 in reducing the ignition delay. The combustion chamber demonstrated stable operation over the range of equivalence ratio and percentage O-2 investigated, with the conventional mode displaying the highest SPL and fluctuations in the reaction zone (OH*). The most stable operation was obtained for the MILD case where the SPL decreased by similar to 6 dB caused by a suppression of the high-frequency (> 800 Hz) longitudinal modes. However, the operation of the combustion chamber became unstable as the oxidizer preheat temperature decreased from 603-547 K due to the emergence of very high-frequency (similar to 9-15 kHz) oscillations