Stimuli-Responsive Poly‑<i>N</i>‑isopropylacrylamide: Phenylene Vinylene Oligomer Conjugate

Phenylene vinylene trimer (OPV) and PNIPAM conjugate with stimuli-responsive optical properties has been synthesized through the formation of amide linkage between PNIPAM and carboxylic-acid-terminated OPV. This material exhibits thermoresponsive optical properties as temperature exceeds the lower critical solution temperature (LCST), which is 32 °C for PNIPAM and the conjugate. This PNIPAM-trimer conjugate is fully characterized by using NMR, FT-IR, temperature-dependent UV–vis, and fluorescence spectroscopy. We have found that the polymer conjugate solution turns opaque as temperature exceeds lower critical solution temperature and a five-fold increase in fluorescence intensity as temperature increases from 20 to 70 °C. Such distinct increase in fluorescence intensity is likely due to the rigidchromism, that is, the change in optical properties due to confinement of the chromophores resulting from restriction of polymer conformational structures. The PNIPAM-trimer conjugate also shows a decrease in decay lifetime with increasing temperature, whereas OPV trimer alone shows no change in decay lifetime as a function of temperature. These unique optical properties are not observed in the trimer and PNIPAM mixture, suggesting that the stimuli-responsive optical properties can occur only in PNIPAM–trimer conjugate linked through covalent bond

Effect of Side-Chain Architecture on the Optical and Crystalline Properties of Two-Dimensional Polythiophenes

The present study reported here synthesis of three novel two-dimensional (2D) polythiophene derivatives with conjugated terthiophene–vinylene side chainpoly­{3-(5″-hexyl-2,2′:5′,2″-terthiophenyl-5-vinyl)­thiophene-alt-thiophene} (<b>P1</b>), poly­{3-(5,5″-dihexyl-2,2′:5′,2″-terthiophenyl-3′-vinyl)­thiophene-alt-thiophene} (<b>P2</b>), and poly­{3-(4,4″-dihexyl-2,2:5′,2″-terthiophene-3′-vinyl)­thiophene-alt-thiophene} (<b>P3</b>)that were synthesized via stille coupling reaction. The terthiophene side chain with different conformations conjugated to the polythiophene main chain via vinyl linkage provided the ability to control the molecular organization, hence affecting the optoelectronic and electrochemical properties of 2D polymers. TD-DFT calculation with the B3LYP/6-31+g­(d) function on electronic structures of the monomers was consistent with the experimental results. It suggested that the energetic states of HOMO and LUMO were highly dependent on the side-chain architectures. These polythiophene thin films fabricated by spin-casting show a broader absorption ranges from 300 to 700 nm which was significantly wider than the absorption of pure poly­(3-hexylthiophene). When comparing the solid-state absorption spectra of these polymers before and after thermal annealing, <b>P3</b> displayed the most red-shift in the wavelength range between 450 and 700 nm. It was presumably due to an extended conjugation length resulting from the linear conformation and preferred chain packing, as manifested in the X-ray diffraction. Molecular dynamics (MD) simulation on polymers with different side chains in isolated and packed states suggests planar conformation of the main chain was adopted and regulated by the side chains which were placed in parallel with the main-chain direction. Interestingly, <b>P1</b> solution revealed an excitation-dependent emission property, suggesting a structural inhomogeneity in solution. Contrary to <b>P1</b>, the PL spectra of <b>P2</b> and <b>P3</b> showed only one emission peak at 460 nm, regardless of the excitation energy. Orientation and regiochemistry of the terthiophene side chain had a major impact on the overall optical and electronic properties of the polymer. Moreover, the HOMO and LUMO of these three polymers had been determined through cyclic voltammetry. HOMO of the three polymers were in the following order: <b>P1</b> > <b>P2</b> > <b>P3</b>. It implied that the energy level was regiochemistry dependent and directly associated with the linked position between backbone and conjugated side chain. Most importantly, through mesogen-jacketed-like design strategy employed in the present study, the improved packing of these two-dimensional polymers offered insights into structure design to enhance properties that have strong ties to the electronic devices

Representation of the sequences flanking <i>fosA3</i>.

<p>Genes are shown as arrows with the direction of transcription indicated by the arrowheads.</p

Antibiotic resistant genes of the ESBL-producing <i>E</i>. <i>coli</i> human and pig isolates.

<p>a: TEM-1 was determined by sequencing.</p><p>Antibiotic resistant genes of the ESBL-producing <i>E</i>. <i>coli</i> human and pig isolates.</p

Evaluation of fosfomycin susceptibility in overexpressing wild type and mutant MurA.

<p>MIC, minimal inhibitory concentration.</p><p>^a MICs were determined in the presence of 1mM Isopropyl β-D-1-thiogalactopyranoside (IPTG) to induce MurA expression.</p><p>Evaluation of fosfomycin susceptibility in overexpressing wild type and mutant MurA.</p

A dendrogram of pulsotype relationships developed via the unweighted pair group method using arithmetic averages (UPGMA) with BioNumerics software version 6.5 (Applied Maths).

<p>Pulsotypes were assigned to the same clusters if they exhibited 80% similarity in the dendrogram. Three major clusters (XXIX, XXXIV, and XLIV) were found in two hospitals.</p

Characterization of Fosfomycin Resistant Extended-Spectrum β-Lactamase-Producing <i>Escherichia coli</i> Isolates from Human and Pig in Taiwan

<div><p>To investigate the efficacy of fosfomycin against extended-spectrum β-lactamases (ESBL) producing <i>Escherichia coli</i> in Taiwan and the resistance mechanisms and characterization of human and pig isolates, we analyzed 145 ESBL-producing isolates collected from two hospitals (n = 123) and five farms (n = 22) in Taiwan from February to May, 2013. Antimicrobial susceptibilities were determined. Clonal relatedness was determined by PFGE and multi-locus sequence typing. ESBLs, <i>ampC</i>, and fosfomycin resistant genes were detected by PCR, and their flanking regions were determined by PCR mapping and sequencing. The fosfomycin resistant mechanisms, including modification of the antibiotic target (MurA), functionless transporters (GlpT and UhpT) and their regulating genes such as <i>uhpA</i>, <i>cyaA</i>, and <i>ptsI</i>, and antibiotic inactivation by enzymes (FosA and FosC), were examined. The size and replicon type of plasmids carrying fosfomycin resistant genes were analyzed. Our results revealed the susceptibility rates of fosfomycin were 94% for human ESBL-producing <i>E</i>. <i>coli</i> isolates and 77% for pig isolates. The PFGE analysis revealed 79 pulsotypes. No pulsotype was found existing in both human and pig isolates. Three pulsotypes were distributed among isolates from two hospitals. IS<i>Ecp1</i> carrying <i>bla</i>_{CTX-M-group 9} was the predominant transposable elements of the ESBL genes. Among the thirteen fosfomycin resistant isolates, functionless transporters were identified in 9 isolates. Three isolates contained novel amino acid substitutions (Asn67Ile, Phe151Ser and Trp164Ser, Val146Ala and His159Tyr, respectively) in MurA (the target of fosfomycin). Four isolates had fosfomycin modified enzyme (<i>fosA3</i>) in their plasmids. The <i>fosA3</i> gene was harboured in an IncN-type plasmid (101 kbp) in the three pig isolates and an IncB/O-type plasmid (113 kbp) in the human isolate. In conclusion, we identified that 6% and 23% of the ESBL-producing <i>E</i>. <i>coli</i> from human and pigs were resistant to fosfomycin, respectively, in Taiwan. No clonal spread was found between human and pig isolates. Functionless transporters were the major cause of fosfomycin resistance, and the <i>fosA3</i>-transferring plasmid between isolates warrants further monitoring.</p></div

Tailored Electronic Structure and Optical Properties of Conjugated Systems through Aggregates and Dipole–Dipole Interactions

A series of PPVO (<i>p</i>-phenylene vinylene oligomer) derivatives with functional groups of varying electronegativity were synthesized via the Horner–Wadsworth–Emmons reaction. Subtle changes in the end group functionality significantly impact the molecular electronic and optical properties of the PPVOs, resulting in broadly tunable and efficient UV absorption and photoluminescence spectra. Of particular interest is the NO₂-substituted PPVO which exhibits photoluminescence color ranging from the blue to the red, thus encompassing the entire visible spectrum. Our experimental study and electronic structure calculations suggest that the formation of aggregates and strong dipole–dipole solute–solvent interactions are responsible for the observed strong solvatochromism. Experimental and theoretical results for the NH₂-, H-, and NO₂-substituted PPVOs suggest that the stabilization of ground or excited state dipoles leads to the blue or red shift of the optical spectra. The electroluminescence (EL) spectra of H-, COOH-, and NO₂-PPVO have maxima at 487, 518, and 587 nm, respectively, in the OLED device. This trend in the EL spectra is in excellent agreement with the end group-dependent PL spectra of the PPVO thin-films

Structural Design of Benzo[1,2‑<i>b</i>:4,5‑<i>b</i>′]dithiophene-Based 2D Conjugated Polymers with Bithienyl and Terthienyl Substituents toward Photovoltaic Applications

In this contribution, six conjugated polymers consisting of benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene–bithiophene (BDT-BT) and benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene–benzothiadiazle (BDT-BTD) as building blocks in the main chain were synthesized by coupling polymerization and utilized for photovoltaic applications. By directly attaching three kinds of alkylthienyl side chains to the conjugated main chain, the resulted two-dimensional configuration revealed a broader absorption range due to the ground state electron transition of their corresponding alkylthienyl units and polymer backbone. Temperature-dependent absorbance, emission spectra, and thermal annealing further verify that the shoulder band(s) were originated from the aggregated (crystalline) species of polymers. The photovoltaic properties of the donor–acceptor polymers revealed well-defined side chain geometries, physical, and electronic structures and showed the highest power conversion efficiency of 4.25% among polymer solar cells based on two-dimensional (2-D) bithienyl- or terthienyl-substituted benzodithiophene