Optical property modification of ZnO: Effect of 1.2 MeV Ar irradiation

We report a systematic study on 1.2 MeV Ar^8+ irradiated ZnO by x-ray diffraction (XRD), room temperature photoluminescence (PL) and ultraviolet-visible (UV-Vis) absorption measurements. ZnO retains its wurtzite crystal structure up to maximum fluence of 5 x 10^16 ions/cm^2. Even, the width of the XRD peaks changes little with irradiation. The UV-Vis absorption spectra of the samples, unirradiated and irradiated with lowest fluence (1 x 10^15 ions/cm^2), are nearly same. However, the PL emission is largely quenched for this irradiated sample. Red shift of the absorption edge has been noticed for higher fluence. It has been found that red shift is due to at least two defect centers. The PL emission is recovered for 5 x 10^15 ions/cm^2 fluence. The sample colour is changed to orange and then to dark brown with increasing irradiation fluence. Huge resistivity decrease is observed for the sample irradiated with 5 x 10^15 ions/cm^2 fluence. Results altogether indicate the evolution of stable oxygen vacancies and zinc interstitials as dominant defects for high fluence irradiation.Comment: Accepted in Physica Sattus Solidi (c

Development of Pressure-Temperature Integrated Multifunction Sensor Using Piezo-Resistive Element

A novel attempt was made to develop a multifunction sensor using piezo resistive material for sensing pressure and temperature simultaneously as because it is well known that piezo resistive material has better selectivity to both temperature and pressure or force variables. The advantage of use of piezo resistive material is that it occupies minimum space. The aggregated output, when excited by electrical signal varies with respect to temperature and pressure both. From the output, the temperature and pressure values are extracted with developed model using multiple regression technique and artificial neural network

Exploring the potential of 3′-O-carboxy esters of thymidine as inhibitors of ribonuclease A and angiogenin

In this study, compounds with a carboxy ester in lieu of the phosphate ester at the 3′-position have been employed to inhibit the ribonucleolytic activity of ribonuclease A (RNase A). Phosphates at the 3′-position of pyrimidine bases are well-known inhibitors of the protein. We have investigated the inhibition of RNase A by 3′-O-carboxy esters of thymidine. The compounds behave as competitive inhibitors with inhibition constants ranging from 42 to 95 μM. The mode of inhibition has also been confirmed by ¹H NMR studies of the active site histidines of RNase A. Docking studies have further substantiated the experimental results. The compounds are also found to inhibit the ribonucleolytic activity of angiogenin, a homologous protein and potent inducer of blood vessel formation

Synthesis and Determination of Absolute Configuration of α‑Pyrones Isolated from <i>Penicillium corylophilum</i>

The first total synthesis of (<i>S</i>)-6-(2,9-dihydroxy­nonyl)-4-hydroxy-3-methyl-2<i>H</i>-pyran-2-one, 4-hydroxy-3-methyl-6-((2<i>S</i>,4<i>R</i>)-2,4,11-trihydroxy­undecyl)-2<i>H</i>-pyran-2-one, and its unnatural 2<i>R</i>,4<i>R</i>-isomer starting from commercially available 1,8-octanediol is described. The synthesis led to the revision of the proposed structural assignment of the natural product as (<i>R</i>)-6-(2,9-dihydroxy­nonyl)-4-hydroxy-3-methyl-2<i>H</i>-pyran-2-one. The key steps include chiral auxiliary mediated asymmetric acetate aldol reaction, dianion addition, and base mediated cyclization to form an α-pyrone ring

Plasmonic Toroidal Metamolecules Assembled by DNA Origami

We show hierarchical assembly of plasmonic toroidal metamolecules that exhibit tailored optical activity in the visible spectral range. Each metamolecule consists of four identical origami-templated helical building blocks. Such toroidal metamolecules show a stronger chiroptical response than monomers and dimers of the helical building blocks. Enantiomers of the plasmonic structures yield opposite circular dichroism spectra. Experimental results agree well with the theoretical simulations. We also show that given the circular symmetry of the structures s distinct chiroptical response along their axial orientation can be uncovered via simple spin-coating of the metamolecules on substrates. Our work provides a new strategy to create plasmonic chiral platforms with sophisticated nanoscale architectures for potential applications such as chiral sensing using chemically based assembly systems

Programmable Multivalent DNA-Origami Tension Probes for Reporting Cellular Traction Forces

Mechanical forces are central to most, if not all, biological processes, including cell development, immune recognition, and metastasis. Because the cellular machinery mediating mechano-sensing and force generation is dependent on the nanoscale organization and geometry of protein assemblies, a current need in the field is the development of force-sensing probes that can be customized at the nanometer-length scale. In this work, we describe a DNA origami tension sensor that maps the piconewton (pN) forces generated by living cells. As a proof-of-concept, we engineered a novel library of six-helix-bundle DNA-origami tension probes (DOTPs) with a tailorable number of tension-reporting hairpins (each with their own tunable tension response threshold) and a tunable number of cell-receptor ligands. We used single-molecule force spectroscopy to determine the probes’ tension response thresholds and used computational modeling to show that hairpin unfolding is semi-cooperative and orientation-dependent. Finally, we use our DOTP library to map the forces applied by human blood platelets during initial adhesion and activation. We find that the total tension signal exhibited by platelets on DOTP-functionalized surfaces increases with the number of ligands per DOTP, likely due to increased total ligand density, and decreases exponentially with the DOTP’s force-response threshold. This work opens the door to applications for understanding and regulating biophysical processes involving cooperativity and multivalency

Programmable Multivalent DNA-Origami Tension Probes for Reporting Cellular Traction Forces

Mechanical forces are central to most, if not all, biological processes, including cell development, immune recognition, and metastasis. Because the cellular machinery mediating mechano-sensing and force generation is dependent on the nanoscale organization and geometry of protein assemblies, a current need in the field is the development of force-sensing probes that can be customized at the nanometer-length scale. In this work, we describe a DNA origami tension sensor that maps the piconewton (pN) forces generated by living cells. As a proof-of-concept, we engineered a novel library of six-helix-bundle DNA-origami tension probes (DOTPs) with a tailorable number of tension-reporting hairpins (each with their own tunable tension response threshold) and a tunable number of cell-receptor ligands. We used single-molecule force spectroscopy to determine the probes’ tension response thresholds and used computational modeling to show that hairpin unfolding is semi-cooperative and orientation-dependent. Finally, we use our DOTP library to map the forces applied by human blood platelets during initial adhesion and activation. We find that the total tension signal exhibited by platelets on DOTP-functionalized surfaces increases with the number of ligands per DOTP, likely due to increased total ligand density, and decreases exponentially with the DOTP’s force-response threshold. This work opens the door to applications for understanding and regulating biophysical processes involving cooperativity and multivalency