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Phase Diagram and Dielectric Properties of MA(1-x)FA(x)PbI(3)
No full textWith the help of 10 different compositions (x) between 0.0 and 0.4 for MA(1-x)FA(x)PbI(3) and about 20 temperature points between 15 and 310 K for each composition, we establish a rich temperature composition phase diagram in terms of structural variations determined by powder and single-crystal X-ray diffraction. Four crystallographic phases are found to exist for this solid solution series, namely, cubic (Pm-3m), tetragonal (I4/mcm), orthorhombic (Pnma), and large-cell cubic (Im-3). Variable-temperature dielectric measurement reveals qualitative changes in dielectric properties of these materials driven by the observed structural phase transitions; it establishes that with an increasing FA content the high-temperature-dominant Curie-like behavior in dielectric constant of MAPbI(3) gets suppressed and an unusually prominent glassy behavior evolves in direct correlation with the structural evolution. This reveals a strong structure-property correlation existing in these solid solutions, qualitatively modifying properties of MAPbI(3) with FA substitution
Journey of Electroactive beta-Polymorph of Poly(vinylidenefluoride) from Crystal Growth to Design to Applications
No full textElectroactive polymers are ideal candidates for dielectric and piezoelectric applications due to their very high breakdown strength, good flexibility, and ease of processing. Among the various polymers, poly(vinylidenefluoride) (PVDF) is of special interest due to potential applications in sensors, capacitors, actuators, etc. PVDF exists in four different crystalline phases (alpha-, beta-, gamma-, and delta-phases). Among these, the electroactive beta-phase is very important for dielectric and piezoelectric applications. In the recent past, research has been focused on obtaining the maximum amount of electroactive beta-polymorph in PVDF. The piezoelectric and dielectric properties of PVDF are influenced by the amount and the possible orientation of the polar beta-phase. However, the effect of orientation on the electroactive beta-phase in the field direction toward improving dielectric and piezoelectric applications is still not clear. This review attempts to bring in mechanistic insights into various processes that induce the electroactive beta-phase, orientation, and correlation with dielectric and piezoelectric properties in PVDF-based composites. Some of the challenges and possible solutions for the future fabrication of piezoelectric materials are also emphasized
Gate Tunable Cooperativity between Vibrational Modes
No full textCoupling between a mechanical resonator and optical cavities, microwave resonators, or other mechanical resonators have been used to observe interesting effects from sideband cooling to coherent manipulation of phonons. Here we demonstrate strong coupling between different vibrational modes of MoS2 drum resonators at room temperature. We observe intermodal as well as intramodal coupling. Cooperativity, a measure of coupling between the two modes, can be tuned by more than an order of magnitude by changing the direct current gate bias. The large measured cooperativity of about 900 at room temperature indicates that the phonon population can be coherently transferred between the modes for more than 500 cycles. This coherent oscillation is of great interest in studying quantum effects in macroscopic objects
Mannopyranoside Glycolipids Inhibit Mycobacterial and Biofilm Growth and Potentiate Isoniazid Inhibition Activities in M. smegmatis
No full textLipomannan and lipoarabinomannan are integral components of the mycobacterial cell wall. Earlier studies demonstrated that synthetic arabinan and arabinomannan glycolipids acted as inhibitors of mycobacterial growth, in addition to exhibiting inhibitory activities of mycobacterial biofilm. Herein, it is demonstrated that synthetic mannan glycolipids are better inhibitors of mycobacterial growth, whereas lipoarabinomannan has a higher inhibition efficiency to biofilm. Syntheses of mannan glycolipids with a graded number of mannan moieties and an arabinomannan glycolipid are conducted by chemical methods and subsequent mycobacterial growth and biofilm inhibition studies are conducted on Mycobacterium smegmatis. Growth inhibition of (73 +/- 3) % is observed with a mannose trisaccharide containing a glycolipid, whereas this glycolipid did not promote biofilm inhibition activity better than that of arabinomannan glycolipid. The antibiotic supplementation activities of glycolipids on growth and biofilm inhibitions are evaluated. Increases in growth and biofilm inhibitions are observed if the antibiotic is supplemented with glycolipids, which leads to a significant reduction of inhibition concentrations of the antibiotic
Emerging technologies for antibiotic susceptibility testing
No full textSuperbugs such as infectious bacteria pose a great threat to humanity due to an increase in bacterial mortality leading to clinical treatment failure, lengthy hospital stay, intravenous therapy and accretion of bacteraemia. These disease-causing bacteria gain resistance to drugs over time which further complicates the treatment. Monitoring of antibiotic resistance is therefore necessary so that bacterial infectious diseases can be diagnosed rapidly. Antimicrobial susceptibility testing (AST) provides valuable information on the efficacy of antibiotic agents and their dosages for treatment against bacterial infections. In clinical laboratories, most widely used AST methods are disk diffusion, gradient diffusion, broth dilution, or commercially available semi-automated systems. Though these methods are cost-effective and accurate, they are time-consuming, labour-intensive, and require skilled manpower. Recently much attention has been on developing rapid AST techniques to avoid misuse of antibiotics and provide effective treatment. In this review, we have discussed emerging engineering AST techniques with special emphasis on phenotypic AST. These techniques include fluorescence imaging along with computational image processing, surface plasmon resonance, Raman spectra, and laser tweezer as well as micro/nanotechnology-based device such as microfluidics, microdroplets, and microchamber. The mechanical and electrical behaviour of single bacterial cell and bacterial suspension for the study of AST is also discussed
Conformational Sensors and Domain Swapping Reveal Structural and Functional Differences between beta-Arrestin Isoforms
No full textDesensitization, signaling, and trafficking of G-protein-coupled receptors (GPCRs) are critically regulated by multifunctional adaptor proteins, beta-arrestins (beta arrs). The two isoforms of beta arrs (beta arr1 and 2) share a high degree of sequence and structural similarity; still, however, they often mediate distinct functional outcomes in the context of GPCR signaling and regulation. A mechanistic basis for such a functional divergence of beta arr isoforms is still lacking. By using a set of complementary approaches, including antibody-fragment-based conformational sensors, we discover structural differences between beta arr1 and 2 upon their interaction with activated and phosphorylated receptors. Interestingly, domain-swapped chimeras of beta arrs display robust complementation in functional assays, thereby linking the structural differences between receptor-bound beta arr1 and 2 with their divergent functional outcomes. Our findings reveal important insights into the ability of beta arr isoforms to drive distinct functional outcomes and underscore the importance of integrating this aspect in the current framework of biased agonism
Rh(III)-Catalyzed Distal C-H Alkenylation of Weakly Coordinating Acetamides Via Desilylation Pathway
No full textRh(III)-Catalyzed distal ortho-C-H alkenylation of arylacetamides have been reported employing acetamide, a weak coordinating group, as a directing group. This challenging C-H alkenylation of arylacetamides has been achieved by using arylalkynyl silanes as a surrogate for terminal alkynes under redox neutral process through desilylation pathway. The control experiments suggest that the in situ generatedRh-species is likely to be Lewis acidic, which is playing a vital role in the desilylation step
New Members of SHG Active Dugganite Family, A(3)BC(3)D(2)O(14) (A = Ba, Pb; B = Te, Sb; C = Al, Ga, Fe, Zn; D = Si, Ge, P, V): Synthesis, Structure, and Materials Properties
No full textA family of compounds, A(3)BC(3)D(2)O(14) (A = Ba, Pb; B = Te, Sb; C = Al, Ga, Fe, Zn; D = Si, Ge, P, V), with the Dugganite structure was prepared employing traditional solid-state chemistry methods. PXRD and Rietveld refinement studies indicate that the compounds are stabilized in P321 space group (no. 150). The compounds are found to be SHG active with values ranging from 1.9 to 15.0 x KDP. The compounds exhibit high dielectric constants and low loss in our studies. The noncentrosymmetry related properties of the new Dugganites were understood by band structure calculations. We also explored the present Dugganite-structured oxides for the development of new inorganic colored materials by substituting Co2+, Ni2+, Cu2+, and Fe3+ in place of Zn2+. Thus, substitution of Co2+ and Fe3+ together tunes the blue color of the cobalt compound to blue-green color arising from metal-to-metal charge transfer (MMCT) of Fe3+ and Co2+ ions. The tetrahedrally coordinated Ni2+ in the Dugganite imparts a magenta color
Omega 76: A designed antimicrobial peptide to combat carbapenem- and tigecycline-resistant Acinetobacter baumannii
No full textDrug resistance is a public health concern that threatens to undermine decades of medical progress. ESKAPE pathogens cause most nosocomial infections, and are frequently resistant to carbapenem antibiotics, usually leaving tigecycline and colistin as the last treatment options. However, increasing tigecycline resistance and colistin's nephrotoxicity severely restrict use of these antibiotics. We have designed antimicrobial peptides using a maximum common subgraph approach. Our best peptide (Omega 76) displayed high efficacy against carbapenem and tigecycline-resistant Acinetobacter baumannii in mice. Mice treated with repeated sublethal doses of Omega 76 displayed no signs of chronic toxicity. Sublethal Omega 76 doses co-administered alongside sublethal colistin doses displayed no additive toxicity. These results indicate that Omega 76 can potentially supplement or replace colistin, especially where nephrotoxicity is a concern. To our knowledge, no other existing antibiotics occupy this clinical niche. Mechanistically, Omega 76 adopts an a-helical structure in membranes, causing rapid membrane disruption, leakage, and bacterial death
Aggregation behavior in naphthalene-appended diketopyrrolopyrrole derivatives and its gas adsorption impact on surface potential
No full textDiketopyrrolopyrrole derivatives containing phenyl and thiophene units adorned with alkoxynaphthalene (Naph-PDPP and Naph-TDPP) were synthesized by a Suzuki cross-coupling reaction. The effect of the phenyl/thiophene units on the aggregation behavior and detailed photophysical properties were investigated by UV-visible, steady-state, and time-resolved fluorescence spectroscopy. The absorption and fluorescence spectra of Naph-PDPP and Naph-TDPP in the solid-state exhibit red-shifted spectral patterns due to strong intermolecular interactions. The concentration-dependent photophysical properties reveal the formation of J-type aggregates at higher concentrations and in the solid state. The extent of aggregate formation is higher for Naph-TDPP. DFT and TD-DFT studies showed that Naph-TDPP containing a thiophene ring in the backbone adopts a more planar geometry than Naph-PDPP and undergoes strong pi-pi stacking interactions that favor the formation of J-aggregates. Scanning Kelvin probe measurements on the thin films of Naph-PDPP and Naph-TDPP were performed (both in the dark and under visible light) upon exposure to different volatile organic vapors (ethanol and triethylamine). The study reveals that under visible light illumination, the Naph-PDPP thin film has significant gas adsorption towards ethanol vapors and alters its sign of response