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Orthorhombic lepidocrocite-type lithium titanate hydrates (LTH), as one important member among two-dimensional (2D) materials, have drawn much attention due to their potential applications in nanoelectronics, energy conversion, and energy storage devices. However, only a few efforts have focused on an anisotropic growth mechanism that determines the formation kinetics of LTH and/or even their derivatives. In this context, in situ Raman observation was employed to the isothermal crystallization of LTH nanosheet crystals from amorphous precursor precipitates. During isothermal crystallization, the formation of monolayered LTH nuclei is controlled by oxygen diffusion with an activation energy of 0.72 eV; anisotropic growth along (010) planes induces an interblocking effect among LTH nanosheet crystals, which limits their size up to 50 nm. The nucleation-growth crystallization kinetics of LTH nanosheets were accurately interpreted by the modified Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, which considered their anisotropic 2D growth. Beyond LTH, the present study that combines in situ spectroscopic monitoring with kinetic modeling paves the way toward deeper comprehension and ultimate control of the growth kinetics of 2D titanate materials. [ABSTRACT FROM AUTHOR]

Microbial methylation and demethylation are two competing processes controlling the net production and bioaccumulation of neurotoxic methylmercury (MeHg) in natural ecosystems. Although mercury (Hg) methylation by anaerobic microorganisms and demethylation by aerobic Hg-resistant bacteria have both been extensively studied, little attention has been given to MeHg degradation by anaerobic bacteria, particularly the iron-reducing bacterium Geobacter bemidjiensis Bem. Here we report, for the first time, that the strain G. bemidjiensis Bem can mediate a suite of Hg transformations, including Hg(II) reduction, Hg(0) oxidation, MeHg production and degradation under anoxic conditions. Results suggest that G. bemidjiensis utilizes a reductive demethylation pathway to degrade MeHg, with elemental Hg(0) as the major reaction product, possibly due to the presence of genes encoding homologues of an organomercurial lyase (MerB) and a mercuric reductase (MerA). In addition, the cells can strongly sorb Hg(II) and MeHg, reduce or oxidize Hg, resulting in both time and concentration-dependent Hg species transformations. Moderate concentrations (10-500 μM) of Hg-binding ligands such as cysteine enhance Hg(II) methylation but inhibit MeHg degradation. These findings indicate a cycle of Hg methylation and demethylation among anaerobic bacteria, thereby influencing net MeHg production in anoxic water and sediments. [ABSTRACT FROM AUTHOR]

Identifying the structure of electrodes at atomic-scale remains a key challenge but is a fertile realm for groundbreaking fundamental research in the advanced Li-ion battery material field. In this context, the subtle structure evolution taking place during lithiation/delithiation in the bulk/surface of Li4Ti5O12 spinel (LTO) was probed using scanning transmission electron microscopy and found to undergo significant structure torque, namely Ti-- O bond stretching/shrinking at different state-of-charge (SOC), which is not identified previously. This kind of nanostructure change plays an important role in facilitating the formation of capturing centers for the electron/hole pairs in a 3.80 eV insulating material as is LTO. Furthermore, with the aid of electron energy loss spectroscopy, the spontaneous charge transfer process, Ti3+ ↔ e- + Ti4+, was confirmed in the fully lithiated Li7Ti5O12 surface as an essential step of the gas-releasing phenomenon. This new insight paves the way toward deeper comprehension and ultimately control of the electrochemical process for this and other important Li-ion battery materials. [ABSTRACT FROM AUTHOR]

The conditions present during enamel crystallite development change dramatically as a function of time, including the pH, protein concentration, surface type, and ionic strength. In this work, we investigate the role that two of these changing conditions, pH and ionic strength, have in modulating the interaction of the amelogenin, LRAP, with hydroxyapatite (HAP). Using solid-state NMR dipolar recoupling and chemical shift data, we investigate the structure, orientation, and dynamics of three regions in the N-terminus of the protein: L15 to V19, V19 to L23, and K24 to S28. These regions are also near the only phosphorylated residue in the protein pS16; therefore, changes in the LRAP-HAP interaction as a function of phosphorylation (LRAP(-P) vs LRAP(+P)) were also investigated. All of the regions and conditions studied for the surface immobilized proteins showed restricted motion, with indications of slightly more mobility under all conditions for L15(+P) and K24(-P). The structure and orientation of the LRAP-HAP interaction in the N-terminus of the phosphorylated protein is very stable to changing solution conditions. From REDOR dipolar recoupling data, the structure and orientation in the region L15V19(+P) did not change significantly as a function of pH or ionic strength. The structure and orientation of the region V19L23(+P) were also stable to changes in pH, with the only significant change observed at high ionic strength, where the region becomes extended, suggesting this may be an important region in regulating mineral development. Chemical shift studies also suggest minimal changes in all three regions studied for both LRAP(-P) and LRAP(+P) as a function of pH or ionic strength, and also reveal that K24 has multiple resolvable resonances, suggestive of two coexisting structures. Phosphorylation also alters the LRAP-HAP interface. All of the three residues investigated (L15, V19, and K24) are closer to the surface in LRAP(+P), but only K24S28 changes structure as a result of phosphorylation, from a random coil to a largely helical structure, and V19L23 becomes more extended at high ionic strength when phosphorylated. These observations suggest that ionic strength and dephosphorylation may provide switching mechanisms to trigger a change in the function of the N-terminus during enamel development. [ABSTRACT FROM AUTHOR]

2H and 15N solid-state NMR spectroscopic techniques were used to investigate both the side chain and backbone dynamics of wild-type phospholamban (WT-PLB) and its phosphorylated form (P- PLB) incorporated into I -palmitoyl-2-oleoyl-sn-glycerophosphocholine (POPC) phosphol ipid bilayers. 2H NMR spectra of site-specific CD3-labeled WT-PLB (at Leu51, Ala24, and Ala 15) in POPC bilayers were similar under frozen conditions (-25 °C). However, significant differences in the line shapes of the 2H NMR spectra were observed in the liquid crystalline phase at and above 0 °C. The 2H NMR spectra indicate that Leu51, located toward the lower end of the transmembrane (TM) helix, shows restricted side chain motion, implying that it is embedded inside the POPC lipid bilayer. Additionally, the line shape of the 2H NMR spectrum of CD3-Ala24 reveals more side chain dynamics, indicating that this residue (located in the upper end of the TM helix) has additional backbone and internal side chain motions. 2H NMR spectra of both WT-PLB and P-PLB with CD3-Ala15 exhibit strong isotropic spectral line shapes. The dynamic isotropic nature of the 2H peak can be attributed to side chain and backbone motions to residues located in an aqueous environment outside the membrane. Also, the spectra of 15N-labeled amide WT- PLB at Leu51 and Leu42 residues showed only a single powder pattern component indicating that these two 15N-labeled residues located in the TM helix are motionally restricted at 25 °C. Conversely, 15N- labeled amide WT-PLB at Ala11 located in the cytoplasmic domain showed both powder and isotropic components at 25 °C. Upon phosphorylation, the mobile component contribution increases at Ala11. The 2H and 15N NMR data indicate significant backbone motion for the cytoplasmic domain of WT-PLB when compared to the transmembrane section. [ABSTRACT FROM AUTHOR]

An 18-residue peptide, KWGAKIKIGAKIKIGAKI-NH2 was designed to form amphiphilic β-sheet structures when bound to lipid bilayers. The peptide possesses high antimicrobial activity when compared to naturally occurring linear antimicrobial peptides, most of which adopt an amphipathic α-helical conformation upon binding to the lipids. The perturbation of the bilayer by the peptide was studied by static 31P and 2H solid-state NMR spectroscopy using POPC and POPG/POPC (3/1) bilayer membranes with sn-1 chain perdeuterated POPC and POPG as the isotopic labels. 31P NMR powder spectra exhibited two components for POPG/POPC bilayers upon addition of the peptide but only a slight change in the line shape for POPC bilayers, indicating that the peptide selectively disrupted the membrane structure consisting of POPG lipids. 2H NMR powder spectra indicated a reduction in the lipid chain order for POPC bilayers and no significant change in the ordering for POPG/POPC bilayers upon association of the peptide with the bilayers, suggesting that the peptide acts as a surface peptide in POPG/POPC bilayers. Relaxation rates are more sensitive to the motions of the membranes over a large range of time scales. Longer 31P longitudinal relaxation times for both POPG and POPC in the presence of the peptide indicated a direct interaction between the peptide and the POPG/POPC bilayer membranes. 31P longitudinal relaxation studies also suggested that the peptide prefers to interact with the POPG phospholipids. However, inversion-recovery 2H NMR spectroscopic experiments demonstrated a change in the relaxation rate of the lipid acyl chains for both the POPC membranes and the POPG/POPC membranes upon interaction with the peptide. Transverse relaxation studies indicated an increase in the spectral density of the collective membrane motion caused by the interaction between the peptide and the POPG/POPC membrane. The experimental results demonstrate significant dynamic changes in the membrane in the presence of the antimicrobial peptide and support a carpet mechanism for the disruption of the membranes by the antimicrobial peptide. [ABSTRACT FROM AUTHOR]

A series of luminescent dinuclear gold(I) complexes with different crown ether pendants, [Au2(P∧P)(S-B15C5)2] [S-B15C5 = 4'-mercaptobenzo-15-crown-5, P∧P = bis(dicyclohexylphosphino)methane (dcpm) (1), bis(diphenylphosphino)methane (dppm) (2)] and [Au2(P∧P)(S-B18C6)2] [S-B18C6 = 4'-mercaptobenzo-18-crown-6, P∧P = dcpm (3), dppm (4)], and their related crown-free complexes, [Au2(P∧P)(SC6H3(OMe)2-3,4)2] [P∧P = dcpm (5), dppm (6)], were synthesized. The low-energy emission of the mercaptocrown ether-containing gold(I) complexes are tentatively assigned as originated from states derived from a S → Au ligand-to-metal charge transfer (LMCT) transition. The crown ether-containing gold(I) complexes showed specific binding abilities toward various metal cations according to the ring size of the crown pendants. Spectroscopic evidence was provided for the metal-ioninduced switching on of the gold···gold interactions upon the binding of particular metal ions in a sandwich binding mode. [ABSTRACT FROM AUTHOR]

Two novel ethynylcrown ether containing di- and tetranuclear gold(i) complexes have been synthesized and structurally characterized; their binding ability toward various metal ions has also been studied. [ABSTRACT FROM AUTHOR]

A series of platinum(ll) terpyridyl alkynyl complexes that have been derivatized with basic amino functionalities, [Pt(tpy)(C≡C-C6H4-NR2-4]X (X = Otf¯, R = CH3 1, R = CH2CH2OCH3 2, R = H 3; X = CI¯, R = CH3 4, R = CH2CH2OCH3 5, R = H 6) (tpy = 2,2′:6′,2″-terpyridine), have been synthesized and characterized. Their photophysical responses at various acid concentrations were studied. The abilities of the complexes to function as colorimetric and luminescence pH sensors were demonstrated with dramatic color changes and luminescence enhancement upon introduction of acid. [ABSTRACT FROM AUTHOR]