Electrical Conductivity and Thermoelectric Power of Silver Iododichromate Fast Ion Conducting Electrolytes

Fast ion conducting solid electrolytes are becoming increasingly important owing to their application in solid state ionic devices. The present work deals with the silver ion conducting x AgI – (1–x)Ag₂Cr₂O₇ electrolyte system. These electrolytes have been characterised by X-ray diffraction, electrical conductivity, electronic conductivity and thermoelectric power techniques. A high ionic conductivity of the order of 10⁻³ S/cm has been observed for the composition mol% 80 AgI–20 Ag₂Cr₂O₇, at room temperature. The electronic conductivity of this electrolyte is three orders of magnitude lower than the ionic conductivity.     

T lymphocyte migration to lymph nodes is maintained during homeostatic proliferation.

The immune system maintains appropriate cell numbers through regulation of cell proliferation and death. Normal tissue distribution of lymphocytes is maintained through expression of specific adhesion molecules and chemokine receptors such as L-selectin and CCR7, respectively. Lymphocyte insufficiency or lymphopenia induces homeostatic proliferation of existing lymphocytes to increase cell numbers. Interestingly, homeostatic proliferation of T lymphocytes induces a phenotypic change from na?ve- to memory-type cell. Na?ve T cells recirculate between blood and lymphoid tissues whereas memory T cells migrate to nonlymphoid sites such as skin and gut. To assess effects of homeostatic proliferation on migratory ability of T cells, a murine model of lymphopenia-induced homeostatic proliferation was used. Carboxyfluorescein diacetate, succinimidyl ester-labeled wild-type splenocytes were adoptively transferred into recombination activation gene-1-deficient mice and analyzed by flow cytometry, in vitro chemotactic and in vivo migration assays, and immunofluorescence microscopy. Homeostatically proliferated T cells acquired a mixed memory-type CD44high L-selectinhigh CCR7low phenotype. Consistent with this, chemotaxis to secondary lymphoid tissue chemokine in vitro was reduced by 22%-34%. By contrast, no differences were found for migration or entry into lymph nodes during in vivo migration assays. Therefore, T lymphocytes that have undergone homeostatic proliferation recirculate using mechanisms similar to na?ve T cells.     

Solvent dielectric delimited nitro–nitrito photorearrangement in a perylenediimide derivative

The discovery of vibrant excited-state dynamics and distinctive photochemistry has established nitrated polycyclic aromatic hydrocarbons as an exhilarating class of organic compounds. Herein, we report the atypical photorearrangement of nitro-perylenediimide (NO₂-PDI) to nitrito-perylenediimide (ONO-PDI), triggered by visible-light excitation and giving rise to linkage isomers in the polar aprotic solvent acetonitrile. ONO-PDI has been isolated and unambiguously characterized using standard spectroscopic, spectrometric, and elemental composition techniques. Although nitritoaromatic compounds are conventionally considered to be crucial intermediates in the photodissociation of nitroaromatics, experimental evidence for this has not been observed heretofore. Ultrafast transient absorption spectroscopy combined with computational investigations revealed the prominence of a conformationally relaxed singlet excited-state (S^CR₁) of NO₂-PDI in the photoisomerization pathway. Theoretical transition state (TS) analysis indicated the presence of a six-membered cyclic TS, which is pivotal in connecting the S^CR₁ state to the photoproduct state. This article addresses prevailing knowledge gaps in the field of organic linkage isomers and provides a comprehensive understanding of the unprecedented photoisomerization mechanism operating in the case of NO₂-PDI.

The unprecedented photorearrangement of nitro-perylenediimide (NO₂-PDI) to nitrito-perylenediimide (ONO-PDI) is shown to occur through a cyclic six-membered transition state triggered by visible-light excitation.     

A supramolecular ON-OFF-ON fluorescence assay for selective recognition of GTP

With the objective of developing small molecule based receptors for nucleosides and nucleotides, interactions of a cyclic donor-acceptor conjugate 1 with adenosine, AMP, ADP, CTP, UTP, ITP, ATP, and GTP have been investigated by absorption, steady-state, and time-resolved fluorescence, cyclic voltammetry (CV), NMR, and fluorescence indicator displacement techniques. Titration of 1 with the fluorescent indicator, 8-hydroxy-1,3,6-pyrene trisulfonate (HPTS), resulted in nearly complete fluorescence quenching of HPTS, along with 25% hypochromicity in its absorption spectrum. Benesi-Hildebrand analysis gave a 1:1 stoichiometry for the complex between the receptor 1 and HPTS with an association constant (Kass) of 4.66 x 104 M-1 in buffer. The driving force for such a complexation was evaluated to be the synergistic effects of pi-stacking and electrostatic interactions inside the cavity as confirmed by the effect of ionic strength, temperature, and the negative results obtained with the model compound 2. Titration of the nonfluorescent complex [1.HPTS] with various nucleosides and nucleotides resulted in revival of fluorescence of the indicator, HPTS. It was observed that GTP induces maximum displacement of HPTS from the complex [1.HPTS] with an overall fluorescence enhancement of ca. 150-fold. The addition of adenosine, AMP, ADP, CTP, and UTP showed negligible changes, whereas ca. 45- and 50-fold enhancement was observed with ATP and ITP, respectively. The competitive displacement of the indicator by various analytes is found to be in the order GTP (buffer) approximately GTP (biofluid) > ITP approximately ATP > UTP > CTP approximately ADP approximately AMP approximately Ade. By virtue of having a better pi-electron cloud, GTP undergoes effective electronic, pi-stacking, and electrostatic interactions inside the cavity and forms a stable complex with the receptor 1. The uniqueness of this assay is that it differentiates GTP from ATP and other nucleotides and signals the event through a visual "turn on" fluorescence mechanism in buffer as well as in biological fluids.     

Controlled reduction of the deleterious effects of photocatalytic activity of ZnO nanoparticles by PVA capping

Nanoparticles of uncapped and PVA (poly vinyl alcohol) capped zinc oxide were synthesized by precipitation method. The synthesized ZnO nanoparticles were characterized by fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric-differential thermal analysis. The photocatalytic activity of bare and modified ZnO nanoparticles was studied by monitoring the degradation of Rhodamine B. The results show that PVA capped ZnO nanoparticles has reduced photocatalytic activity than the bare ZnO nanoparticles. The reduction in the chemical oxygen demand and total organic carbon results also revealed the reduced photocatalytic activity of PVA capped ZnO. The UV-shielding property was evaluated by measuring the transmittance which shows that both bare and PVA capped ZnO nanoparticles possess good UV-shielding ability.     

Critical properties of superconducting Ba1−xKxFe2As2

Magnetisation and magneto-resistance measurements have been carried out on superconducting Ba_1?xK_xFe₂As₂ samples with x = 0.40 and 0.50. From high field magnetization hysteresis measurements carried out in fields up to 16 T at 4.2 K and 20 K, the critical current density has been evaluated using the Bean critical state model. The J_C determined from the high field data is >10⁴ A/cm² at 4.2 K and 5 T. The superconducting transitions were also measured resistively in increasing applied magnetic fields up to 12 T. From the variation of the T_C onset with applied field, dH_C2/dT at T_C was obtained to be ?7.708 T/K and ?5.57 T/K in the samples with x = 0.40 and 0.50.     

Hydrophobic self-assembly of a perylenediimide-linked DNA dumbbell into supramolecular polymers

The self-assembly of DNA dumbbell conjugates possessing hydrophobic perylenediimide (PDI) linkers separated by an eight-base pair A-tract has been investigated. Cryo-TEM images obtained from dilute solutions of the dumbbell in aqueous buffer containing 100 mM NaCl show the presence of structures corresponding to linear end-to-end assemblies of 10-30 dumbbell monomers. The formation of assemblies of this size is consistent with analysis of the UV-vis and fluorescence spectra of these solutions for the content of PDI monomer and dimer chromophores. Assembly size is dependent upon the concentration of dumbbell and salt as well as the temperature. Kinetic analysis of the assembly process by means of salt-jump stopped-flow measurements shows that it occurs by a salt-triggered isodesmic mechanism in which the rate constants for association and dissociation in 100 mM NaCl are 3.2 × 10(7) M(-1)s(-1) and 1.0 s(-1), respectively, faster than the typical rate constants for DNA hybridization. TEM and AFM images of samples deposited from solutions having higher concentrations of dumbbell and NaCl display branched assemblies with linear regions >1 μm in length and diameters indicative of the formation of small bundles of dumbbell end-to-end assemblies. These observations provide the first example of the use of hydrophobic association for the assembly of small DNA duplex conjugates into supramolecular polymers and larger branched aggregates.