Luminescent Invertible Polymersome by Remarkably Stable Supramolecular Assembly of Naphthalene Diimide (NDI) π‑System

Self-assembly and photophysical properties of a trialkoxybenzhydrazide-functionalized naphthalene diimide (NDI)-appended amphiphilic polymer are reported. Hydrophobically assisted H-bonding among hydrazides in conjunction with π-stacking among NDI produced vesicles in aqueous medium with astonishingly high kinetic as well as thermodynamic stability which showed enhanced emission in the aggregated state. In benzene, rarely reported reverse vesicular assembly was formed with dual container property with almost identical photophysical properties and stability as observed in water. Both vesicular and reverse-vesicular assemblies were found to remain stable at the benzene–water interface

Multifaceted Synthetic Route to Functional Polyacrylates by Transesterification of Poly(pentafluorophenyl acrylates)

Synthesis of functional polyacrylates by 4-dimethylaminopyridine (DMAP) catalyzed trans-esterification of poly­(pentafluorophenyl acrylate) (polyPFPA) is reported. High fidelity and versatility of this strategy was exemplified by near quantitative conversion with diverse functional alcohols (primary, secondary as well as phenolic) featuring reactive groups like alkene, alkyne or acrylate, enabling further sequential functionalization using click chemistry. Co-integrating an equimolar mixture of allyl and propargyl alcohol produced an orthogonally clickable copolymer by thiol–ene and 1,3-cycloaddition reaction. Base catalyzed ester exchange allowed installation of acid labile Boc-l-serine to create amino acid pendent polymer keeping both NH₂- and COOH-group free, thereby providing a facile route toward zwitterionic polymers. Reaction with 2-dimethylaminoethanol conferred dual pH and CO₂ responsive polymers from the same reactive precursor. The synthetic strategy was further extended to attach alcohols obtained from natural resources such as geraniol, l-lactic acid or sesamol to engineer new renewable polymers. Even a graft copolymer with very high (93%) grafting density could be achieved utilizing PEG₃₅₀–OH. The trans-esterification was found to be highly selective for primary alcohols over secondary alcohols and also to the activated PFP-ester over a normal ester such as poly­(methyl acrylate). Using such selectivity, fluorescently tagged polymer could be synthesized by replacing only the PFP-ester of a poly­(methyl acrylate-<i>co</i>-PFPA) with 1-pyrenemethanol. Further, PFPA was polymerized with 2.0 mol % diacrylate to produce a cross-linked gel network. The PFP-ester groups of the cross-linked gel could be quantitatively replaced with Boc<i>-</i>l-serine, which upon deprotection of the Boc group resulted in a novel zwitterionic hydrogel exhibiting pH-dependent swelling properties. Time-dependent FTIR experiment suggested fast kinetics of the reaction, making this synthetic route practically applicable for postpolymerization modification. Mechanistic investigation exposed involvement of both DMAP and the nucleophilic solvent <i>N</i>,<i>N</i>-dimethylformamide (DMF) in catalyzing the reaction. This also explains the reason as to why near quantitative conversion was achieved in DMF and not in the non-nucleophilic solvent 1,4-dioxane

Supramolecularly Cross-Linked Nanogel by Merocyanine Pendent Copolymer

Directional dipole–dipole interaction mediated antiparallel dimerization of merocyanine dye (MD) has been explored for maneuvering supramolecular assembly of MD-conjugated flexible macromolecules leading to a cross-linked nanogel. The MD-functionalized copolymer was synthesized by a newly developed organocatalytic transesterification strategy for postpolymerization functionalization of poly­(pentafluorophenyl acrylate) (polyPFPA)-based reactive copolymer. Presence of ∼35% pendant MD attached to a coil-like polymer chain leads to spontaneous formation of highly emitting cross-linked nanogel with efficient container property and appreciable stability in toluene owing to strong dimerization propensity among the MD. Considering the significance of MD in the context of nonlinear optics and photovoltaics, these results not only enrich the toolbox for engineering macromolecular assembly, but also open up new possibilities for future organic materials

A Review on the Phylogeography of Potentially Chemoautotrophic Bacteria from Major Vent and Seep Fauna and Their Contribution to Primary Production

<p>Though geochemically and microbially well-defined, the phylogeographic data of microbial symbionts in these highly productive vent and seep systems require a closer examination and synthesis. QIIME analysis of 16S rDNA of bacterial associates of major fauna from 1995 to 2015 was thus undertaken to examine phylogeography of their microbial symbionts along with host specificity. While phylotypes were generally unrelated, bivalve <i>Calyptogena</i> exhibited vertical transmission sharing similar symbionts in geographically separated geosystems. Different species of tubeworms possessed identical symbionts through horizontal acquisition at geographically distinct Guaymas basin vent and the Arctic seep. Vents were more versatile with both mobile and sessile fauna hosting ecto- and endo-symbionts. Comparatively, seeps were more specialized with sessile animal hosts with endosymbionts. C-fixation rate measurements are still scanty for sediments, bedrocks and serpentine systems; vent, seep, anoxic and oxic basins were shown to fix up to 22, 325, 96, and 37,400 g C m⁻³ y⁻¹, respectively. Estimation of chemosynthetic primary production rates in chemoautotrophic ecosystems could endeavor to improve existing biogeographic models by coupling volcanism and plate-tectonics to global climate and phylogeography.</p

Chiral Structure of Thiolate-Protected 28-Gold-Atom Nanocluster Determined by X‑ray Crystallography

We report the crystal structure of a new nanocluster formulated as Au₂₈(TBBT)₂₀, where TBBT = 4<i>-tert-</i>butylbenzenethiolate. It exhibits a rod-like Au₂₀ kernel consisting of two interpenetrating cuboctahedra. The kernel is protected by four dimeric “staples” (-SR-Au-SR-Au-SR-) and eight bridging thiolates (-SR-). The unit cell of Au₂₈(TBBT)₂₀ single crystals contains a pair of enantiomers. The origin of chirality is primarily rooted in the rotating arrangement of the four dimeric staples as well as the arrangement of the bridging thiolates (quasi-<i>D</i>₂ symmetry). The enantiomers were separated by chiral HPLC and characterized by circular dichroism spectroscopy

Chiral Structure of Thiolate-Protected 28-Gold-Atom Nanocluster Determined by X‑ray Crystallography

We report the crystal structure of a new nanocluster formulated as Au₂₈(TBBT)₂₀, where TBBT = 4<i>-tert-</i>butylbenzenethiolate. It exhibits a rod-like Au₂₀ kernel consisting of two interpenetrating cuboctahedra. The kernel is protected by four dimeric “staples” (-SR-Au-SR-Au-SR-) and eight bridging thiolates (-SR-). The unit cell of Au₂₈(TBBT)₂₀ single crystals contains a pair of enantiomers. The origin of chirality is primarily rooted in the rotating arrangement of the four dimeric staples as well as the arrangement of the bridging thiolates (quasi-<i>D</i>₂ symmetry). The enantiomers were separated by chiral HPLC and characterized by circular dichroism spectroscopy

Five-Year Antimicrobial Resistance Patterns of Urinary <i>Escherichia coli</i> at an Australian Tertiary Hospital: Time Series Analyses of Prevalence Data

<div><p>This study describes the antimicrobial resistance temporal trends and seasonal variation of <i>Escherichia coli</i> (<i>E</i>. <i>coli)</i> urinary tract infections (UTIs) over five years, from 2009 to 2013, and compares prevalence of resistance in hospital- and community-acquired <i>E</i>. <i>coli</i> UTI. A cross sectional study of <i>E</i>. <i>coli</i> UTIs from patients attending a tertiary referral hospital in Canberra, Australia was undertaken. Time series analysis was performed to illustrate resistance trends. Only the first positive <i>E</i>. <i>coli</i> UTI per patient per year was included in the analysis. A total of 15,022 positive cultures from 8724 patients were identified. Results are based on 5333 first <i>E</i>. <i>coli</i> UTIs, from 4732 patients, of which 84.2% were community-acquired. Five-year hospital and community resistance rates were highest for ampicillin (41.9%) and trimethoprim (20.7%). Resistance was lowest for meropenem (0.0%), nitrofurantoin (2.7%), piperacillin-tazobactam (2.9%) and ciprofloxacin (6.5%). Resistance to amoxycillin-clavulanate, cefazolin, gentamicin and piperacillin-tazobactam were significantly higher in hospital- compared to community-acquired UTIs (9.3% versus 6.2%; 15.4% versus 9.7%; 5.2% versus 3.7% and 5.2% versus 2.5%, respectively). Trend analysis showed significant increases in resistance over five years for amoxycillin-clavulanate, trimethoprim, ciprofloxacin, nitrofurantoin, trimethoprim-sulphamethoxazole, cefazolin, ceftriaxone and gentamicin (P<0.05, for all) with seasonal pattern observed for trimethoprim resistance (augmented Dickey-Fuller statistic = 4.136; P = 0.006). An association between ciprofloxacin resistance, cefazolin resistance and ceftriaxone resistance with older age was noted. Given the relatively high resistance rates for ampicillin and trimethoprim, these antimicrobials should be reconsidered for empirical treatment of UTIs in this patient population. Our findings have important implications for UTI treatment based on setting of acquisition.</p></div

Total Structure and Optical Properties of a Phosphine/Thiolate-Protected Au₂₄ Nanocluster

We report the synthesis and total structure determination of a Au₂₄ nanocluster protected by mixed ligands of phosphine and thiolate. Single crystal X-ray crystallography and electrospray ionization mass spectrometry (ESI-MS) unequivocally determined the cluster formula to be [Au₂₄­(PPh₃)₁₀­(SC₂H₄Ph)₅­X₂]⁺, where X = Cl and/or Br. The structure consists of two incomplete (i.e., one vertex missing) icosahedral Au₁₂ units joined by five thiolate linkages. This structure shows interesting differences from the previously reported vertex-sharing biicosahedral [Au₂₅­(PPh₃)₁₀­(SC₂H₄Ph)₅­X₂]²⁺ nanocluster protected by the same type and number of phosphine and thiolate ligands. The optical absorption spectrum of Au₂₄ nanocluster was theoretically reproduced and interpreted

Dissociation of ribosomal subunits analyzed using fluorescence light scattering (at 20°C) and 5–20% sucrose density gradient centrifugation.

<p><b>(A)</b>Percent (%) dissociations of 70S are plotted as a function of time by: unfolded bovine carbonic anhydrase (UNP) (■); RRF+EFG-GTP+IF3 (●); decapeptide VGDANPALQK (▲); Native bovine carbonic anhydrase (▼). <b>(B)</b>Percent (%) dissociations of 70S by: RRF+EFG-GTP+IF3 (■); UNP+RRF+EFG-GTP+IF3 (●); UNP+EFG-GTP (▲); UNP+RRF (▼) are plotted against time. <b>(C)</b>Percent (%) dissociations of 70S by: UNP+EFG-GMPPNP (■); EFG-GMPPNP (●); EFG-GTP (▲) are plotted against time. <b>(D)</b>Dissociation rate constants (<i>k;</i> s^-1) are derived from the single exponential fits of the respective graphs and plotted as bar graphs against the corresponding combination of factors indicated in the figure. Error bars (s.d.) are propagated from three independent experiments for each combination of factors. <b>(E)</b> P-values for the dissociation rate constants (<i>k</i>) are calculated from three independent experiments for the respective combination of factors as indicated in Fig D and plotted here. Results showing statistical significance at <i>p</i>< 0.05. <b>(F)</b> Sucrose density gradient centrifugation showing dissociation of 70S by: unfolded protein (■); deca-peptide VGDANPALQK (●). The profile of 70S, 50S, 30S (▲) ran in a parallel sucrose gradient; and only untreated 70S (▼) ran in another gradient in parallel, are shown. <b>(G)</b> Sucrose density gradient centrifugation showing dissociation of 70S by: the combinations of RRF, EFG-GTP and IF3 (■);UNP, RRF, EFGGTP and IF3 (●); UNP and EFG-GTP (▲);UNP and RRF(▼).</p

Filter binding of tRNA^Glu to 70S.

<p><b>(A)</b> Percent (%) 70S (<i>E</i>.<i>coli</i> wild type) bound to the [α-³²P] UTP labeled tRNA are plotted in Y-axis against tRNA: 70S molar ratio. <b>(B)</b> After binding 70S to [α-³²P] UTP labeled tRNA at 25mM Mg²⁺, reaction mixture was diluted to7mM Mg²⁺ in the subunit dissociation buffer. Bar diagrams show percent (%) 70S bound by [α-³²P] UTP labeled tRNA before (bar 1) and after (bar 2) dilution. Error bars (s.d.) are propagated from 3 independent experiments for each of the bars.</p