Conducting 1D nanostructures from light-stimulated copper-metalated porphyrin-dibenzothiophene.

Control over the dimensionality of stimulated organic semiconductors has aroused significant interest in organic electronics; however, the design of such materials still remains to be decided. Herein, we have developed three dibenzothiophene-appended freebase, zinc-metalated and copper-metalated porphyrin derivatives (PFb-DBT, PZn-DBT and PCu-DBT) in which PCu-DBT leads to an anion-binding complex in chloroform upon the application of light, resulting in self-assembled 1D nanostructures with high electrical conductivity. Nevertheless, light-stimulated freebase and zinc-metalated P-DBT undergo protonation and demetalation. Electron microscopic images displayed the anion-binding-assisted 1D nanostructure using weak non-covalent interactions, which promotes enhancement in electrical conductivity among other things, as confirmed by electrochemical impedance spectra. Thus, the generation of well-defined nanostructures with improved electronic characteristics from stimuli-responsive organic dyes suggests the importance of developing various smart materials for efficient field effect transistors and sensors.

Effect of temperature and pH on the structure and stability of tumor-specific lectin jacalin and insights into the location of its tryptophan residues: CD, DSC and fluorescence studies.

Jacalin, the jackfruit seed lectin, exhibits high specificity for the tumor-specific T-antigen and is used in various biomedical and biotechnological applications. Here, we report biophysical studies on the thermal unfolding of jacalin and the effect of pH and temperature on its secondary structure. Differential scanning calorimetric (DSC) studies revealed that native jacalin unfolds at ∼60 °C and that carbohydrate binding stabilizes the protein structure. Circular dichroism spectroscopic studies indicated that the secondary structure of jacalin remains mostly unaffected over pH 2.0-9.0, whereas considerable changes were observed in the tertiary structure. DSC experiments demonstrated that jacalin exhibits two overlapping transitions between pH 2 and 5, which could be attributed to dissociation of the tetrameric protein into subunits and their unfolding. Interestingly, only one transition between pH 6 and 9 was observed, suggesting that the subunit dissociation and unfolding occur simultaneously. While quenching of the protein intrinsic fluorescence by acrylamide increased significantly upon carbohydrate binding, quenching by succinimide is essentially unaffected. We attribute this difference to increased exposure of Trp-123 in the α-chain as it is involved in carbohydrate binding. Both acrylamide and succinimide gave biphasic Stern-Volmer plots, consistent with differential accessibility of the two tryptophan residues of jacalin to them.

Narcissistic self-sorting in Zn(II) porphyrin derived semiconducting nanostructures.

The narcissistic self-sorted phenomenon is explicitly attributed to the structural similarities in organic molecules. Although such relevant materials are rarely explored, self-sorted structures from macrocyclic π-conjugated-based p- and n-type organic semiconductors facilitate the increase of exciton dissociation and charge separation in bulk heterojunction solar cells. Herein, we report two extended π-conjugated derivatives consisting of zinc-porphyrin-linked benzothiadiazole acting as an acceptor (PB) and anthracene as a donor (PA). Despite having the same porphyrin π-conjugated core in PA and PB, variations in donor and acceptor moieties make the molecular packing form one-dimensional (1D) self-assembled nanofibers via H- and J-type aggregates. Interestingly, a dissimilar aggregate of PA and PB exists as a mixture (PA + PB), promoting narcissistic self-sorted structures. Electrochemical impedance investigation reveals that the electronic characteristics of self-sorting assemblies are influenced by the difference in electrostatic potentials for PA and PB, resulting in a transitional electrical conductivity of 0.14 S cm-1. Therefore, the design of such materials for the fabrication of effective photovoltaics is promoted by these extraordinary self-sorted behaviors in comparable organic π-conjugated molecules.