Bicyclomycin generates ROS and blocks cell division in Escherichia coli.

The role of reactive oxygen species (ROS) in the killing exerted by antibiotics on bacteria is debated. Evidence attributes part of toxicity of many antibiotics to their ability to generate ROS by interfering with cellular metabolism, but some studies dismiss the role of ROS. Bicyclomycin (BCM) is a broad-spectrum antibiotic that is the only known compound to inhibit E. coli transcription terminator factor Rho with no known other cellular targets. In the present study, we addressed this question by checking whether the induction of oxidative stress could explain the increased sensitivity to Bicyclomycin in the hns deleted strain even in Δkil background in E. coli. BCM evoked the generation of ROS in E. coli cells. BCM is known to cause the cell filamentation phenotype in E. coli. Performing fluorescence microscopic analysis, we show that bicyclomycin-dependent cell filamentation is associated with SOS response. RecA-GFP filaments were found to colocalize with the damaged DNA sites in the cell. Further analysis revealed that the genomic DNA was partitioned but the cell septum formation was severely affected under BCM treatment. Furthermore, we observed biofilm formation by E. coli after BCM treatment. We hypothesize that ROS production after BCM treatment could lead to cell filamentation in bacteria. A better understanding of the mode of toxicity of BCM will help us design better antibiotic treatment regimes for clinical practices, including combinatorial drug therapies. The cell filamentation phenotype observed after BCM treatment makes this antibiotic a promising drug for phage-antibiotic synergy (PAS) therapy.

Proton Conductivity in a Metal-Organic Cube-Based Framework and Derived Hydrogel with Tubular Morphology.

The hydrogels, formed by self-assembly of predesigned, discrete metal-organic cubes (MOCs), have emerged as a new type of functional soft material whose diverse properties are yet to be explored. Here, we explore the proton conductivity of a MOC-based supramolecular porous framework {(Me2NH2)12[Ga8(ImDC)12]·DMF·29H2O} (1) (ImDC = 4,5-imidazole dicarboxylate) and derived hydrogel (MOC-G1). The intrinsic charge-assisted H-bonded (between anionic MOC {[Ga8(ImDC)12]12-} and dimethylammonium cations) framework 1 exhibits an ambient condition proton conductivity value of 2.3 × 10-5 S cm-1 (@40% RH) which increases with increasing temperature (8.2 × 10-4 S cm-1 at 120 °C and 40% RH) and follows the Grotthuss type of mechanism of proton conduction. Self-assembly of the MOCs in the presence of ammonium cations, as molecular binders, resulted in a hydrogel (MOC-G1) that shows directional H-bonded 1D nanotubular morphology. While guest water molecules are immensely important in deciding the proton conductivity of both 1 and MOC-G1, the presence of additional proton carriers, such as DMA and ammonium cations, resulted in at least 1 order increment in the proton conductivity of the latter (1.8 × 10-2 S cm-1) than the former (1.4 × 10-3 S cm-1) under 25 °C and 98% RH condition. The values of proton conductivity of 1 and MOC-G1 are comparable with those of the best proton conduction reports in the literature. This work may pave the way for the development of proton conductors with unique architecture and conductivity requisite for the state-of-the-art technologies by selecting appropriate MOC and molecular binders.

Rho-dependent termination enables cellular pH homeostasis.

The termination factor Rho, an ATP-dependent RNA translocase, preempts pervasive transcription processes, thereby rendering genome integrity in bacteria. Here, we show that the loss of Rho function raised the intracellular pH to >8.0 in Escherichia coli. The loss of Rho function upregulates tryptophanase-A (TnaA), an enzyme that catabolizes tryptophan to produce indole, pyruvate, and ammonia. We demonstrate that the enhanced TnaA function had produced the conjugate base ammonia, raising the cellular pH in the Rho-dependent termination defective strains. On the other hand, the constitutively overexpressed Rho lowered the cellular pH to about 6.2, independent of cellular ammonia levels. Since Rho overexpression may increase termination activities, the decrease in cellular pH could result from an excess H+ ion production during ATP hydrolysis by overproduced Rho. Furthermore, we performed in vivo termination assays to show that the efficiency of Rho-dependent termination was increased at both acidic and basic pH ranges. Given that the Rho level remained unchanged, the alkaline pH increases the termination efficiency by stimulating Rho's catalytic activity. We conducted the Rho-mediated RNA release assay from a stalled elongation complex to show an efficient RNA release at alkaline pH, compared to the neutral or acidic pH, that supports our in vivo observation. Whereas acidic pH appeared to increase the termination function by elevating the cellular level of Rho. This study is the first to link Rho function to the cellular pH homeostasis in bacteria. IMPORTANCE The current study shows that the loss or gain of Rho-dependent termination alkalizes or acidifies the cytoplasm, respectively. In the case of loss of Rho function, the tryptophanase-A enzyme is upregulated, and degrades tryptophan, producing ammonia to alkalize cytoplasm. We hypothesize that Rho overproduction by deleting its autoregulatory DNA portion increases termination function, causing excessive ATP hydrolysis to produce H+ ions and cytoplasmic acidification. Therefore, this study is the first to unravel a relationship between Rho function and intrinsic cellular pH homeostasis. Furthermore, the Rho level increases in the absence of autoregulation, causing cytoplasmic acidification. As intracellular pH plays a critical role in enzyme function, such a connection between Rho function and alkalization will have far-reaching implications for bacterial physiology.

Unraveling the mechanistic insights of sophorolipid-capped gold nanoparticle-induced cell death in Vibrio cholerae.

IMPORTANCE: Vibrio cholerae, a Gram-negative bacterium, is the causative agent of a fatal disease, "cholera." Prevention of cholera outbreak is possible by eliminating the bacteria from the environment. However, antimicrobial resistance developed in microorganisms has posed a threat and challenges to its treatment. Application of nanoparticles is a useful and effective option for the elimination of such microorganisms. Metal-based nanopaticles exhibit microbial toxicity through non-specific mechanisms. To prevent resistance development and increase antibacterial efficiency, rational designing of nanoparticles is required. Thus, knowledge on the exact mechanism of action of nanoparticles is highly essential. In this study, we explore the possible mechanisms of antibacterial activity of AuNPs-SL against V. cholerae. We show that the interaction of AuNPs-SL with V. cholerae enhances ROS production and membrane depolarization, change in permeability, and leakage of intracellular content. This action leads to the depletion of cellular ATP level, DNA damage, and subsequent cell death.

An Intrinsic Alkalization Circuit Turns on mntP Riboswitch under Manganese Stress in Escherichia coli.

The trace metal manganese in excess affects iron-sulfur cluster and heme-protein biogenesis, eliciting cellular toxicity. The manganese efflux protein MntP is crucial to evading manganese toxicity in bacteria. Recently, two Mn-sensing riboswitches upstream of mntP and alx in Escherichia coli have been reported to mediate the upregulation of their expression under manganese shock. As the alx riboswitch is also responsive to alkaline shock administered externally, it is intriguing whether the mntP riboswitch is also responsive to alkaline stress. Furthermore, how both manganese and alkaline pH simultaneously regulate these two riboswitches under physiological conditions is a puzzle. Using multiple approaches, we show that manganese shock activated glutamine synthetase (GlnA) and glutaminases (GlsA and GlsB) to spike ammonia production in E. coli. The elevated ammonia intrinsically alkalizes the cytoplasm. We establish that this alkalization under manganese stress is crucial for attaining the highest degree of riboswitch activation. Additional studies showed that alkaline pH promotes a 17- to 22-fold tighter interaction between manganese and the mntP riboswitch element. Our study uncovers a physiological linkage between manganese efflux and pH homeostasis that mediates enhanced manganese tolerance. IMPORTANCE Riboswitch RNAs are cis-acting elements that can adopt alternative conformations in the presence or absence of a specific ligand(s) to modulate transcription termination or translation initiation processes. In the present work, we show that manganese and alkaline pH are both necessary for maximal mntP riboswitch activation to mitigate the manganese toxicity. This study bridges the gap between earlier studies that separately emphasize the importance of alkaline pH and manganese in activating the riboswitches belonging to the yybP-ykoY family. This study also ascribes a physiological relevance as to how manganese can rewire cellular physiology to render cytoplasmic pH alkaline for its homeostasis.

Free spermidine evokes superoxide radicals that manifest toxicity.

Spermidine and other polyamines alleviate oxidative stress, yet excess spermidine seems toxic to Escherichia coli unless it is neutralized by SpeG, an enzyme for the spermidine N-acetyl transferase function. Thus, wild-type E. coli can tolerate applied exogenous spermidine stress, but ΔspeG strain of E. coli fails to do that. Here, using different reactive oxygen species (ROS) probes and performing electron paramagnetic resonance spectroscopy, we provide evidence that although spermidine mitigates oxidative stress by lowering overall ROS levels, excess of it simultaneously triggers the production of superoxide radicals, thereby causing toxicity in the ΔspeG strain. Furthermore, performing microarray experiment and other biochemical assays, we show that the spermidine-induced superoxide anions affected redox balance and iron homeostasis. Finally, we demonstrate that while RNA-bound spermidine inhibits iron oxidation, free spermidine interacts and oxidizes the iron to evoke superoxide radicals directly. Therefore, we propose that the spermidine-induced superoxide generation is one of the major causes of spermidine toxicity in E. coli.

A novel plant lectin, NTL-125, interferes with SARS-CoV-2 interaction with hACE2.

COVID-19 caused by SARS-CoV-2 virus has had profound impact on the world in the past two years. Intense research is going on to find effective drugs to combat the disease. Over the past year several vaccines were approved for immunization. But SARS-CoV-2 being an RNA virus is continuously mutating to generate new variants, some of which develop features of immune escape. This raised serious doubts over the long-term efficacy of the vaccines. We have identified a unique mannose binding plant lectin from Narcissus tazetta bulb, NTL-125, which effectively inhibits SARS-CoV-2 replication in Vero-E6 cell line. In silico docking studies revealed that NTL-125 has strong affinity to viral Spike RBD protein, preventing it from attaching to hACE2 receptor, the gateway to cellular entry. Binding analyses revealed that all the mutant variants of Spike protein also have stronger affinity for NTL-125 than hACE2. The unique α-helical tail of NTL-125 plays most important role in binding to RBD of Spike. NTL-125 also interacts effectively with some glycan moieties of S-protein in addition to amino acid residues adding to the binding strength. Thus, NTL-125 is a highly potential antiviral compound of natural origin against SARS-CoV-2 and may serve as an important therapeutic for management of COVID-19.

Structure-Guided Designing and Evaluation of Peptides Targeting Bacterial Transcription.

The mycobacterial RNA polymerase (RNAP) is an essential and validated drug target for developing antibacterial drugs. The ß-subunit of Mycobacterium tuberculosis (Mtb) RNAP (RpoB) interacts with an essential and global transcription factor, CarD, and confers antibiotic and oxidative stress resistance to Mtb. Compromising the RpoB/CarD interactions results in the killing of mycobacteria, hence disrupting the RpoB/CarD interaction has been proposed as a novel strategy for the development of anti-tubercular drugs. Here, we describe the first approach to rationally design and test the efficacy of the peptide-based inhibitors which specifically target the conserved PPI interface between the bacterial RNAP ß/transcription factor complex. We performed in silico protein-peptide docking studies along with biochemical assays to characterize the novel peptide-based inhibitors. Our results suggest that the top ranked peptides are highly stable, soluble in aqueous buffer, and capable of inhibiting transcription with IC50 > 50 µM concentration. Using peptide-based molecules, our study provides the first piece of evidence to target the conserved RNAP ß/transcription factor interface for designing new inhibitors. Our results may hence form the basis to further improve the potential of these novel peptides in modulating bacterial gene expression, thus inhibiting bacterial growth and combating bacterial infections.

MoSx on Nitrogen-Doped Graphene for High-Efficiency Hydrogen Evolution Reaction: Unraveling the Mechanisms of Unique Interfacial Bonding for Efficient Charge Transport and Stability.

Functional nanostructures with abundant exposed active sites and facile charge transport through conductive scaffolds to active sites are pivotal for developing an advanced and efficient electrocatalyst for water splitting. In the present study, by coating ∼3 nm MoSx on nitrogen-doped graphene (NG) pre-engrafted on a flexible carbon cloth (MNG) as a model system, an extremely low Tafel slope of 39.6 mV dec-1 with cyclic stability up to 5000 cycles is obtained. The specific fraction of N on the NG framework is also analyzed by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy with synchrotron radiation light sources, and it is found that the MoSx particles are selectively positioned on the specific graphitic N sites, forming the unique Mo-N-C bonding state. This Mo-N-C bonding is founded to facilitate highly effective charge transfer directly to the active sulfur sites on the edges of MoSx, leading to a highly improved hydrogen evolution reaction (HER) with excellent stability (95% retention @ 5000 cycles). The functional anchoring of MoSx by such bonding prevents particle aggregation, which plays a significant role in maintaining the stability and activity of the catalyst. Furthermore, it has been revealed that MNG samples with adequately high amounts of both pyridinic and graphitic N result in the best HER performance. This work helps in understanding the mechanisms and bonding interactions within various catalysts and the scaffold electrode.

Nanocatalyst-Assisted Fine Tailoring of Pore Structure in Holey-Graphene for Enhanced Performance in Energy Storage.

Nanoporous holey-graphene (HG) shows potential versatility in several technological fields, especially in biomedical, water filtration, and energy storage applications. Particularly, for ultrahigh electrochemical energy storage applications, HG has shown promise in addressing the issue of low gravimetric and volumetric energy densities by boosting of the ion-transport efficiency in a high-mass-loaded graphene electrode. However, there are no studies showing complete control over the entire pore architecture and density of HG and their effect on high-rate energy storage. Here, we report a unique and cost-effective method for obtaining well-controlled HG, where a copper nanocatalyst assists the predefined porosity tailoring of the HG and leads to an extraordinary high pore density that exceeds 1 × 103 µm-2. The pore architectures of the hierarchical and homogenous pores of HG were realized through a rationally designed nanocatalyst and the annealing procedure in this method. The HG electrode with a high mass loading results in improved supercapacitor performance that is at least 1 order of magnitude higher than conventional graphene flakes (reduced electrochemically exfoliated graphene (rECG)) in areal capacitance (∼100% retention of capacitance until 15 000 cycles), energy density, and power density. The diffusion coefficient of the HG electrode is 1.5-fold higher than that of rECG at a mass loading of 15 mg cm-2, indicating excellent ion-transport efficiency. The excellent ion-transport efficiency of HG is further proved by nearly 4-fold magnitude lowering of its Rion (the ionic resistance in the electrolyte-filled pores) value as compared with rECG when estimated for equivalent high-mass-loaded electrodes. Furthermore, the HG exhibits a packing density that is 2 orders of magnitude higher than rECG, revealing the utility of the maximum electrode mass and possessing higher volumetric capacitance. The perfect tailoring of HG with optimized porosity allows the achievement of high areal capacitance and excellent cycling stability due to the facile ion- and charge-transport at high-mass-loaded electrodes, which could open a new avenue for addressing the long-existing issue of practical application of graphene-based energy storage devices.

HflX protein protects Escherichia coli from manganese stress.

The ribosome-binding GTPase HflX is required for manganese homeostasis in E. coli. While under normal conditions ΔhflX cells behave like wild type E. coli with respect to growth pattern and morphology, deletion of hflX makes E. coli cells extremely sensitive to manganese, characterized by arrested cell growth and filamentation. Here we demonstrate that upon complementation by hflX, manganese stress is relieved. In phenotypic studies done in a manganese-rich environment, ΔhflX cells were highly sensitive to antibiotics that bind the penicillin binding protein 3 (PBP3), suggesting that the manganese stress led to impaired peptidoglycan biosynthesis. An irregular distribution of dark bands of constriction along filaments, delocalization of the dark bands from midcell towards poles and subpoles, lack of septum formation and arrested cell division were observed in ΔhflX cells under manganese stress. However, chromosome replication and segregation of nucleoids were unaffected under these conditions, as observed from confocal microscopy imaging and FACS studies. We conclude that absence of HflX leads to manganese accumulation in E. coli cells, affecting cell septum formation, probably by modulating the activity of the cell division protein PBP3 (FtsI), a major component of the divisome apparatus. We propose that HflX acts as a gatekeeper, regulating the influx of manganese into the cell.

Revisiting graphene-polymer nanocomposite for enhancing anticorrosion performance: a new insight into interface chemistry and diffusion model.

Graphene is impermeable to all molecules and has high chemical stability, which makes it an excellent anticorrosion coating for metals. However, current studies have indicated that galvanic coupling between graphene and a metal actually accelerates corrosion at the interface. Due to the insulating nature of polymers, graphene-polymer composite coatings with a strong interaction between the filler and the polymer matrix are an alternative means of addressing this issue. Nevertheless, such coatings require well-dispersed graphene flakes to lengthen the diffusion paths of gases or liquids, while preventing the formation of a conducting network from graphene to the metal. The difficulty in preparing such coatings was mainly due to problems with the control of the assembled phase during interfacial reactions. Herein, the interactions between the filler and the polymer were found to be a key factor governing anticorrosion performance, which has scarcely been previously reported. The advantage of graphene as a filler in anticorrosion coatings lies in its dispersibility and miscibility with both the casting solvent and the polymer. Electrochemically exfoliated graphene (EC-graphene) with appropriate surface functionalities that allow high miscibility with waterborne polyurethane (PU) and hydrophobic epoxy has been found to be an ideal filler that outperforms other graphene materials such as graphene oxide (GO) and reduced graphene oxide (rGO). Furthermore, a bilayer coating with EC-graphene additives for PU over epoxy has been found to reduce the corrosion rate (CR) to 1.81 × 10-5 mm per year. With a graphene loading of less than 1%, this represents the lowest CR ever achieved for copper and steel substrates and a diffusion coefficient that is lower by a factor of nearly 2.2 than that of the pristine polymer. Furthermore, we have shown that by controlling the amount of graphene loaded in the polymer galvanic corrosion favored by the formation of an interconnected graphene percolation network can successfully be limited. The present study, together with a facile and eco-friendly method of nanocomposite synthesis, may pave the way toward practical applications in the development of graphene-based anticorrosion coatings.

Escherichia coli ß-clamp slows down DNA polymerase I dependent nick translation while accelerating ligation.

The nick translation property of DNA polymerase I (Pol I) ensures the maturation of Okazaki fragments by removing primer RNAs and facilitating ligation. However, prolonged nick translation traversing downstream DNA is an energy wasting futile process, as Pol I simultaneously polymerizes and depolymerizes at the nick sites utilizing energy-rich dNTPs. Using an in vitro assay system, we demonstrate that the ß-clamp of the Escherichia coli replisome strongly inhibits nick translation on the DNA substrate. To do so, ß-clamp inhibits the strand displacement activity of Pol I by interfering with the interaction between the finger subdomain of Pol I and the downstream primer-template junction. Conversely, ß-clamp stimulates the 5' exonuclease property of Pol I to cleave single nucleotides or shorter oligonucleotide flaps. This single nucleotide flap removal at high frequency increases the probability of ligation between the upstream and downstream DNA strands at an early phase, terminating nick translation. Besides ß-clamp-mediated ligation helps DNA ligase to seal the nick promptly during the maturation of Okazaki fragments.

Controlled multimodal hierarchically porous electrode self-assembly of electrochemically exfoliated graphene for fully solid-state flexible supercapacitor.

Supercapacitors constructed from three-dimensional (3D) graphene electrodes with high ion-accessible surface area and durable mechanical flexibility have great potential for wearable devices. For the development of a highly efficient graphene electrode for electrical double layer capacitors (EDLCs), proper control over not only the specific surface area but also the type of pore (macro-, meso- and micro-porous networks) adapted for an appropriate type of electrolyte is crucial to ensure an ideal performance in terms of both energy density and power delivery rate. However, there is still a lack of technology to create graphene structures that combine macro-, meso- and micro-pores by a one-step and facile method. In addition, the ion/electron transport of a solid state electrolyte among such multimodal pore structures is not fully investigated. Here, we report a novel cost-effective technique of concentration dependent self-assembly of electrochemically exfoliated graphene (EC-graphene) to obtain a 3D architecture with controllable macropores (0.39-4.99 µm) and multimodal hierarchical meso- and micro-pores. The better performance of the 3D architecture is obtained due to its optimum micron-sized macropore diameter (∼5 µm) that serves as an ion buffering reservoir, followed by facile ion diffusion kinetics through the well-modulated combination of macro-, meso- and micro-pores. The binder and conductive carbon additive free supercapacitor constructed from the 3D graphene electrode exhibited a specific capacitance of 45.40 F g-1 (6 M KOH) and 23.89 F g-1 (1 M H2SO4 gel electrolyte). A capacitance retention of above 90% (up to 180° folding angle) after 50 bending-relaxing cycles is obtained, implying the superior durability of the device and the worthiness of the synthesis procedure. The method reported here may pave the way for the development of an environment friendly, large scale producible and controlled porous graphene-based architecture for the high performance next generation flexible, all-solid-state and binder-free energy storage devices.

Cobalt and nickel impair DNA metabolism by the oxidative stress independent pathway.

The oxidative stress that evolves under cobalt and nickel exposure is thought to exert toxicity, though the exact routes of such metal poisoning remain ambiguous. We revisited the metal toxicity in Escherichia coli to show that cobalt and nickel exposure at levels as low as 0.5 and 1 mM, respectively, visibly inhibits growth. We also observed that acidic conditions aggravated, while alkaline conditions alleviated the metal toxicity. Besides, 1 mM manganese, which is non-cytotoxic, as judged by the growth of E. coli, synergistically elevated cobalt and nickel stress. However, the metal toxicity did not lead to oxidative stress in E. coli. On the other hand, we show that cobalt and nickel, but not manganese, reduced the rate of DNA replication to 50% within 2 hours. Interestingly, the metal ions promoted DNA double-strand breaks but did not induce SOS repair pathways, indicating that the metal ions could block SOS induction. To test this, we show that cobalt and nickel, but not manganese, suppressed the nalidixic acid-induced SOS response. Finally, using an in vitro assay system, we demonstrated that cobalt and nickel inhibit RecBCD function, which is essential for SOS induction. Therefore, our data indicate that cobalt and nickel affect DNA replication, damage DNA, and inhibit the SOS repair pathway to exert toxicity.

Affected energy metabolism under manganese stress governs cellular toxicity.

Excessive manganese exposure is toxic, but a comprehensive biochemical picture of this assault is poorly understood. Whether oxidative stress or reduced energy metabolism under manganese exposure causes toxicity is still a debate. To address this, we chose Δmnt P Escherichia coli, a highly manganese-sensitive strain, in this study. Combining microarray, proteomics, and biochemical analyses, we show that the chronic manganese exposure rewires diverse regulatory and metabolic pathways. Manganese stress affects protein and other macromolecular stability, and envelope biogenesis. Most importantly, manganese exposure disrupts both iron-sulfur cluster and heme-enzyme biogenesis by depleting cellular iron level. Therefore, the compromised function of the iron-dependent enzymes in the tricarboxylic acid cycle, and electron transport chain impede ATP synthesis, leading to severe energy deficiency. Manganese stress also evokes reactive oxygen species, inducing oxidative stress. However, suppressing oxidative stress does not improve oxidative phosphorylation and cell growth. On the contrary, iron supplementation resumed cell growth stimulating oxidative phosphorylation. Therefore, we hypothesize that affected energy metabolism is the primal cause of manganese toxicity.

Spectroscopic and computational investigations on the origin of charge transfer between included neutral guest molecules and a functionalized anionic layered host.

Layered double hydroxides (LDHs) or anionic clays are an important class of ion-exchange materials, well known for drug and gene delivery and several other applications including catalysis, bioactive nanocomposite, electroactive and photoactive materials. Their structure is based on positively charged brucite-like inorganic sheets with the interlamellar space being occupied by charge-compensating exchangeable anions. In spite of having a vast scope many of the applications of LDHs are restricted as their host-guest chemistry is limited to ion-exchange reactions. Recently we have shown for the first time that charge-transfer interactions can be used as a driving force for the insertion of neutral guest molecules (ortho- and para-chloranil) within the galleries of an Mg-Al LDH by forming a charge-transfer complex with aniline pre-intercalated as p-aminobenzoate anion. Here, we have performed quantum chemical calculations in combination with molecular dynamics simulations to elucidate the nature of interactions, arrangement and the evaluation of electronic and Raman spectral signatures of the chloranil charge-transfer complex included within the galleries of the Mg-Al LDH. The natural bond orbital (NBO) analysis has been used to understand the nature and origin of the unidirectional charge-transfer that lead to the unusual insertion of chloranil in the galleries of the Mg-Al LDH. The NBO analysis reveals that a considerable amount of electronic charge redistribution occurs from the p-aminobenzoate to the chloranil during latter's insertion within the LDH galleries with a very negligible amount of back donation. This work is expected to pave the way for understanding the host-guest chemistry and targeted and controlled delivery of poorly soluble drugs.

Probing the pseudo-1-D ion diffusion in lithium titanium niobate anode for Li-ion battery.

Comprehensive understanding of the charge transport mechanism in the intrinsic structure of an electrode material is essential in accounting for its electrochemical performance. We present here systematic experimental and theoretical investigations of Li(+)-ion diffusion in a novel layered material, viz. lithium titanium niobate. Lithium titanium niobate (exact composition Li0.55K0.45TiNbO5·1.06H2O) is obtained from sol-gel synthesized potassium titanium niobate (KTiNbO5) by an ion-exchange method. The Li(+)-ions are inserted and de-inserted preferentially into the galleries between the octahedral layers formed by edge and corner sharing TiO6 and NbO6 octahedral units and the effective chemical diffusion coefficient, is estimated to be 3.8 × 10(-11) cm(2) s(-1) using the galvanostatic intermittent titration technique (GITT). Calculations based on density functional theory (DFT) strongly confirm the anisotropic Li(+)-ion diffusion in the interlayer galleries and that Li(+)-ions predominantly diffuse along the crystallographic b-direction. The preferential Li(+)-ion diffusion along the b-direction is assisted by line-defects, which are observed to be higher in concentration along the b-direction compared to the a- and c-directions, as revealed by high resolution electron microscopy. The Li-Ti niobate can be cycled to low voltages (≈0.2 V) and show stable and satisfactory battery performance over 100 cycles. Due to the possibility of cycling to low voltages, cyclic voltammetry and X-ray photoelectron spectroscopy convincingly reveal the reversibility of Ti(3+) ↔ Ti(2+) along with Ti(4+) ↔ Ti(3+) and Nb(5+) ↔ Nb(4+).

Characterization of the autophosphorylation property of HflX, a ribosome-binding GTPase from Escherichia coli.

Escherichia coli HflX belongs to the widely distributed but poorly characterized HflX family of translation factor-related GTPases that is conserved from bacteria to humans. A 426-residue polypeptide that binds 50S ribosomes and has both GTPase and ATPase activities, HflX also exhibits autophosphorylation activity. We show that HflX(C), a C-terminal fragment of HflX, has an enhanced autophosphorylation activity compared to the full-length protein. Using a chemical stability assay and thin layer chromatography, we have determined that phosphorylation occurs at a serine residue. Each of the nine serine residues of HflX(C) was mutated to alanine. It was found that all but S211A retained autophosphorylation activity, suggesting that S211, located in the P-loop, was the likely site for autophosphorylation. While the S211A mutant lacked the autophosphorylation site, it possessed strong GTP binding and GTPase activities.

N7-(carboxymethyl)guanine-Lithium Crystalline Complex: A Bioinspired Solid Electrolyte.

Electrochemical device with components having direct significance to biological life processes is a potent futuristic strategy for the realization of all-round green and sustainable development. We present here synthesis design, structural analysis and ion transport of a novel solid organic electrolyte (G7Li), a compound reminiscent of ion channels, derived from regioisomeric N7-guanine-carboxylate conjugate and Li-ions. G7Li, with it's in-built supply of Li(+)-ions, exhibited remarkably high lithium-ion transference number (= 0.75) and tunable room temperature ionic conductivity spanning three decades (≈10(-7) to 10(-3) Ω(-1) cm(-1)) as a function of moisture content. The ionic conductivity show a distinct reversible transition around 80-100 °C, from a dual Li(+) and H(+) (<100 °C) to a pure Li(+) conductor (>100 °C). Systematic studies reveal a transition from water-assisted Li-ion transport to Li hopping-like mechanism involving guanine-Li coordination. While as-synthesized G7Li has potential in humidity sensors, the anhydrous G7Li is attractive for rechargeable batteries.