Activity

Superconcentrated aqueous electrolytes (“water-in-salt” electrolytes, or WiSEs) enable various aqueous battery chemistries beyond the voltage limits imposed by the Pourbaix diagram of water. However, their detailed structural and transport properties remain unexplored and could be better understood through added studies. Here, we report on our observations of strong acidity (pH 2.4) induced by lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) at superconcentration (at 20 mol/kg). Multiple nuclear magnetic resonance (NMR) and pulsed-field gradient (PFG) diffusion NMR experiments, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations reveal that such acidity originates from the formation of nanometric ion-rich structures. The experimental and simulation results indicate the separation of water-rich and ion-rich domains at salt concentrations ≥5 m and the acidity arising therefrom is due to deprotonation of water molecules in the ion-rich domains. As such, the ion-rich domain is composed of hydrophobic -CF3 (of TFSI-) and hydrophilic hydroxyl (OH-) groups. At 20 m concentration, the tortuosity and radius of water diffusion channels are estimated to be ∼10 and ∼1 nm, respectively, which are close to values obtained from hydrated Nafion membranes that also have hydrophobic polytetrafluoroethylene (PTFE) backbones and hydrophilic channels consisting of SO3- ion cluster networks providing for the transport of ions and water. Thus, we have discovered the structural similarity between WiSE and hydrated Nafion membranes on the nanometer scale.Techniques to probe molecular mechanistic events occurring at a single catalytic site of multi-subunit enzymes in real time are few and are still under development. Here time-resolved information is extracted from measurements of the extensive oxygen exchange that occurs at an intermediate stage of adenosine triphosphate (ATP) synthesis during photophosphorylation by chloroplast thylakoids. A stochastic process-based approach for modeling exchange reactions is formulated that provides a physical basis for the kinetic theory. Compatible with the assumptions made in such a model of randomness, the formulation is shown to lead to a Poisson-type theory that enables kinetic analysis of oxygen-exchange data and offers novel physical insights. selleck chemicals llc Parameters such as the apparent rate constant of exchange and the average lifetime of the exchanging intermediates during the synthesis of ATP by the chloroplast F1FO-ATP synthase have been determined over a 5000-fold range of ADP concentration. Experimental isotopomer distributions of [18O]ATP at high (0.5 mM), intermediate (10 μM), and low (0.2 μM) ADP concentrations have been quantified and compared to expected distributions from the theory. The observed distributions are shown to closely match the predicted distributions. A wealth of novel mechanistic insights such as the number of sites/pathways of oxygen exchange, the order of substrate binding steps at the enzyme catalytic site, and regulation of the process of energy coupling have been deduced, and the results are interpreted with the help of available high-resolution X-ray structures. The various biological implications for models of energy coupling have been discussed. Permutation of oxygen ligands about the phosphorus center is proposed as a possible and general but not well-recognized mechanism for oxygen exchange that is consistent with the principal results of this work, and several suggestions for future research are offered.Perylenediimide (PDI) derivatives are essential organic semiconductor materials in a variety of photofunctional devices. By virtue of the large energy gap between the singlet and triplet excited states (ΔEST = 1.1 eV), augmentation of the triplet state population in monomeric PDI is a challenging task. We report the metal atom-free approach in engendering a near-quantitative triplet yield in perbromoperylenediimide/octabromoperylenediimide (OBPDI), absorbing in the visible region of the electromagnetic spectrum. Perbromination of PDI causes significant out-of-plane distortion (θ = 39°) in the aromatic core of OBPDI as compared to the planar PDI (θ = 0°). A substantial decrease (ΔE0red = 0.377 V) in the reduction potential of OBPDI, E1/2(OBPDI/OBPDI·-) = -0.170 V, when compared to the reduction potential, E1/2 (PDI/PDI·-) = -0.547 V, of bare PDI makes OBPDI a promising electron acceptor. As a consequence of incorporating eight bromine atoms, the fluorescence quantum yield of a bare PDI chromophore (ϕf = 97 ± 1%; τf = 4.54 ns) decreases to a very low value in OBPDI (ϕf = 3 ± 1%; τf = 13.78 ps). Femtosecond transient absorption measurements of OBPDI reveal intersystem crossing (ISC) occurring at an ultrafast time scale (τISC = 14.20 ps), leading to a near-quantitative triplet population (ϕT = 97 ± 1%). Theoretical investigations performed to decode the excited state dynamics in OBPDI propose that (i) cumulative addition of eight bromine atoms enhances the magnitude of spin-orbit coupling (SOC) and (ii) twist on the perylene core moderately reduces the energy gap between the singlet-triplet states. Understanding the structural alterations that control the electronic parameters in accessing the triplet excited states of organic chromophores, like PDI, can lead to the design and fabrication of efficient optoelectronic devices and energy storage materials.Minidumbbell (MDB) is a newly discovered DNA structure formed by native sequences, which serves as a possible structural intermediate causing repeat expansion mutations in the genome and also a functional structural motif in constructing DNA-based molecular switches. Until now, all the reported MDBs containing two adjacent type II tetraloops were formed by pyrimidine-rich sequences 5′-YYYR YYYR-3′ (Y and R represent pyrimidine and purine, respectively), wherein the second and sixth residues folded into the minor groove and interacted with each other. In this study, we have conducted a high-resolution nuclear magnetic resonance (NMR) spectroscopic investigation on alternative MDB-forming sequences and discovered that an MDB could also be formed stably with a purine in the minor groove, which has never been observed in any previously reported DNA type II tetraloops. Our refined NMR solution structures of the two MDBs formed by 5′-CTTG CATG-3′ and 5′-CTTG CGTG-3′ reveal that the sixth purine residue was driven into the minor groove via base-base stacking with the second thymine residue and adenine stacked better than guanine.