A series of monodispersed oligo( p-phenyleneethynylene)s were synthesized bearing intramolecular hydrogen bonds between side chains of adjacent phenylene units in the backbone. Thus, all repeating units of the molecules are constrained in a coplanar orientation. Such planarized conformation is considered favorable for single-molecule conductance. Photophysical characterization results show narrowed bandgaps and extended conjugation lengths, consistent with a rigid, planar backbone framework as a result of intramolecular hydrogen bonding.

Low molecular weight protein-tyrosine phosphatases (LMWPTPs) are small enzymes that ubiquitously exist in various organisms and play important roles in many biological processes. In Escherichia coli, the LMW-PTP Wzb dephosphorylates the autokinase Wzc, and the Wzc/Wzb pair regulates colanic acid production. However, the substrate recognition mechanism of Wzb is still poorly understood thus far. To elucidate the molecular basis of the catalytic mechanism, we have determined the solution structure of Wzb at high resolution by NMR spectroscopy. The Wzb structure highly resembles that of the typical LMW-PTP fold, suggesting that Wzb may adopt a similar catalytic mechanism with other LMW-PTPs. Nevertheless, in comparison with eukaryotic LMW-PTPs, the absence of an aromatic amino acid at the bottom of the active site significantly alters the molecular surface and implicates Wzb may adopt a novel substrate recognition mechanism. Furthermore, a structure-based multiple sequence alignment suggests that a class of the prokaryotic LMW-PTPs may share a similar substrate recognition mechanism with Wzb. The current studies provide the structural basis for rational drug design against the pathogenic bacteria.Low molecular weight protein-tyrosine phosphatases (LMW-PTPs) 3 are small cytoplasmic enzymes (ϳ18 kDa) that are widely distributed in prokaryotes and eukaryotes (1, 2). In eukaryotes, LMW-PTPs specifically dephosphorylate and down-regulate many tyrosine kinase receptors, such as platelet-derived growth factor receptor (3, 4), insulin receptor (5), or ephrin receptor (6). The reaction mechanism of eukaryotic LMW-PTPs has been structurally, thermodynamically, and kinetically characterized (7). In contrast, very limited knowledge is available for prokaryotic LMW-PTPs thus far. All LMW-PTPs share a highly conserved C(X) 5 RS motif, where X can be any amino acid. This motif adopts a loop structure, where the phosphate group of the substrate binds to, and is known as the P-loop (1). In addition, some amino acids required for the catalysis are also highly conserved, such as an aspartate residue that acts as a general acid (8). Based on the structures of mammalian LMW-PTPs in complex with exogenous substrates or serendipitous ligands, determinants for substrate specificity were proposed, including the ring stacking around the targeted phosphotyrosine provided by two aromatic side chains of the LMW-PTPs (9, 10).Many bacterial species harbor a layer of capsular polysaccharides and surface-associated exopolysaccharides (EPS). In Escherichia coli, the group 1 capsular polysaccharides and the colanic acid EPS are assembled in a Wzy-dependent polymerization system (11). The ca gene cluster contains one tyrosine autokinase (Wzc) and one LMW-PTP (Wzb) that function as a pair of kinase/phosphatase in the regulation of colanic acid production (12, 13). As a consequence, colanic acid is only produced after the dephosphorylation of the phosphorylated Wzc by Wzb (14). Wzc was identified to regulate the activity of UDPglucose dehydrogenase b...

A series of conjugated oligo(p-phenylene-ethynylene) (OPE) molecules with backbone conformations (that is, the relative orientations of the contained phenylene units) controlled by competitive intramolecular hydrogen bonds to be either co-planar or random were synthesised and studied. In these oligomers, carboxylate and amido substituents were attached to alternate phenylene units in the OPE backbone. These functional groups were able to form intramolecular hydrogen bonds between neighbouring phenylene units. Thereby, all phenylene units in the backbone were confined in a co-planar conformation. This planarised structure featured a more extended effective conjugation length than that of regular OPEs with phenylene units adopting random orientation due to a low rotational-energy barrier. However, if a tri(ethylene glycol) (Tg) side chain was appended to the amido group, it enabled another type of intramolecular hydrogen bond, formed by the Tg chain folding back and the contained ether oxygen atom competing with the ester carbonyl group as the hydrogen-bond acceptor. The outcome of this competition was proven to depend on the length of the alkylene linker joining the ether oxygen atom to the amido group. Specifically, if the Tg chain folded back to form a five-membered cyclic structure, this hydrogen-bonding motif was sufficiently robust to overrule the hydrogen bonds between adjacent phenylene units. Consequently, the oligomers assumed non-planar conformations. However, if the side chain formed a six-membered ring by hydrogen bonding with the amido NH group, such a motif was much less stable and yielded in the competition with the ester carbonyl group from the adjacent phenylene unit. Thus, the hydrogen bonds between the phenylene units remained, and the co-planar conformation was manifested. In our system, the hydrogen bonds formed by the back-folded Tg chain and amido NH group relied on a single oxygen atom as the hydrogen-bond acceptor. The additional oxygen atoms in the Tg chain made a negligible contribution. A bifurcated hydrogen-bond motif was unimportant. From our results, in combination with the results from an independent study by Meijer et al., it is evident that intramolecular hydrogen bonds involving back-folded oligo(ethylene glycol) moieties may differ in their structural details. Absorption spectroscopy served as a convenient yet sensitive technique for analysing hydrogen-bonding motifs in our study.

An oligo( o-phenyleneethynylene- alt- p-phenyleneethynylene) was synthesized to create a conjugated molecule capable of adopting a helical secondary structure. A special feature of such a folded molecule is that the effective directions of energy/charge transport via covalent conjugation and through pi-pi stacking are converged to be along the helix axis. The transition from random conformations to the helix, driven by solvophobic and aromatic stacking interactions, was controlled by solvent properties. UV-vis and fluorescence spectroscopies gave supportive evidence for the folding process.

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Pure yttrium aluminum garnet (YAG) phosphor doped with Eu2+ has been successfully synthesized by a facile sol–gel method. The use of hydrogen iodide aimed to get Eu2+ ions, confirmed by X‐ray absorption near‐edge structure (XANES) analysis. Nearly spherical and well dispersed particles were synthesized. The produced YAG:Eu2+ phosphor powder had a broad emission band in the range of 400–600 nm with a peak at 480 nm, attributed to the allowed 4f7–4f65d1 transition of electrons in Eu2+ ions. The proposed method could also be expanded to prepare many other Eu2+‐doped phosphors with a solution method.

One of the major challenges in using upconversion nanoparticles (UCNPs) is to improve their brightness. This is particularly true for in vivo studies, as the low power excitation is required to prevent the potential photo toxicity to live cells and tissues. Here, we report that the typical NaYF4:Yb0.2,Er0.02 nanoparticles can be highly doped, and the formula of NaYF4:Yb0.8,Er0.06 can gain orders of magnitude more brightness, which is applicable to a range of mild 980 nm excitation power densities, from 0.005 W/cm2 to 0.5 W/cm2. Our results reveal that the concentration of Yb3+ sensitizer ions plays an essential role, while increasing the doping concentration of Er3+ activator ions to 6 mol % only has incremental effect. We further demonstrated a type of bright UCNPs 12 nm in total diameter for in vivo tumor imaging at a power density as low as 0.0027 W/cm2, bringing down the excitation power requirement by 42 times. This work redefines the doping concentrations to fight for the issue of concentration quenching, so that ultrasmall and bright nanoparticles can be used to further improve the performance of upconversion nanotechnology in photodynamic therapy, light-triggered drug release, optogenetics, and night vision enhancement.

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