Shape Control of Colloidal Semiconductor Nanocrystals

Shape control of inorganic nanocrystals is important for understanding basic size- and shape-dependent scaling laws, and may be useful in a wide range of applications. Methods for controlling the shapes of inorganic nanocrystals are evolving rapidly. This paper will focus on how we currently control the shape of semiconductor nanocrystals using CdSe as example.     

Surface and Structural Investigation of a MnOx Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions

Catalytically active MnO_x species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnO_x catalysts form without supports in situ under photocatalytic conditions. Our most active ⁴MnO_x catalyst (～0.84 mmol O₂ mol Mn^?1 s^?1) forms from a Mn₄O₄ bearing a metal–organic framework. ⁴MnO_x is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m²g^?1) and small regions of crystallinity and layer flexibility. In contrast, the ^SMnO_x formed from Mn²⁺ salt gives an amorphous species of lower surface area (80 m²g^?1) and lower activity (～0.15 mmol O₂ mol Mn^?1 s^?1). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p_3/2 core levels detects enriched Mn³⁺ and Mn²⁺ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.     

Phenanthroline-fluorescein molecular hybrid as a ratiometric and selective fluorescent chemosensor for Cu2+ via FRET strategy: synthesis,computational studies and in vitro applications

A FRET-based chemosensor L containing donor phenanthroline and acceptor fluorescein moiety was designed, synthesised and characterised for the ratiometric fluorescent detection of Cu²⁺ in organo-aqueous solution. Probe L showed high selectivity and excellent sensitivity towards Cu²⁺ ions by exhibiting both colorimetric and fluorometric changes due to opening of the spirolactum ring of fluorescein upon complexation with Cu²⁺. In presence of Cu²⁺ ions, probe L formed L-Cu²⁺ complex in 1:1 stoichiometric fashion which is established on the basis of Job’s plot and mass spectroscopy. We also performed DFT computational studies to know the binding nature and coordination feature of the complex. Furthermore, fluorescence imaging studies revealed that probe L was cell permeable and could be used to detect intracellular Cu²⁺ in living cells.     

Immobilization of bio-macromolecules on self-assembled monolayers: methods and sensor applications

Attachment of biomolecules on gold, silicon or glass surfaces has direct implications for the development of novel biosensors in the context of nanoscale detection of pathogens and other metabolites related to issues of human health. In this critical review, we have highlighted the current developments in various techniques of immobilization of biomolecules, specifically biological macromolecules on surfaces through the modification of a functional self-assembled monolayer. The utility of such immobilized biomolecules in the area of biosensing in nanoscale has been surveyed. Merits and demerits of some of the methods with reference to sensitivity of detection and practical use have been discussed (221 references).     

Reversible tunability of the near-infrared valence band plasmon resonance in Cu(2-x)Se nanocrystals

We demonstrate that colloidal Cu(2-x)Se nanocrystals exhibit a well-defined infrared absorption band due to the excitation of positive charge carrier oscillations (i.e., a valence band plasmon mode), which can be tuned reversibly in width and position by varying the copper stoichiometry. The value of x could be incrementally varied from 0 (no plasmon absorption, then a broad peak at 1700 nm) to 0.4 (narrow plasmon band at 1100 nm) by oxidizing Cu(2)Se nanocrystals (upon exposure either to oxygen or to a Ce(IV) complex), and it could be incrementally restored back to zero by the addition of a Cu(I) complex. The experimentally observed plasmonic behavior is in good agreement with calculations based on the electrostatic approximation.     

2-(2-Pyridyl) benzimidazole based Co(II) complex as an efficient fluorescent probe for trace level determination of aspartic and glutamic acid in aqueous solution: a displacement approach

A weakly fluorescent cobalt(II) complex is synthesized using 2-(2-pyridyl)-benzimidazole (PBI) as a chelating fluorescent ligand and characterized by single crystal X-ray structure. This complex serves as an efficient fluorescent probe for trace level determination of aspartic acid (AspA) and glutamic acid (GluA) in aqueous solution. Rest of the naturally occurring amino acids did not interfere. Both aspartic acid and glutamic acid replaces PBI from the coordination sphere of Co(II)-PBI complex resulting appearance of strong fluorescence signal for the released free PBI. The signal response is very fast and the interaction of both the AspA and GluA with the Co(II) is strong enough as evident from their displacement equilibrium constant values, viz. 4357.8 M(-1) and 8333.33 M(-1) respectively.     

Reactivity studies of a disilene with N2O and elemental sulfur

In a previous contribution, we have reported on a convenient and high yield synthesis of the disilene trans-[(TMS)(2)N(η(1)-Me(5)C(5))Si═Si(η(1)-Me(5)C(5))N(TMS)(2)] (2). Herein, we show the reactions of 2 with N(2)O and S(8). The former reaction affords two isomeric (cis- and trans-) dioxadisiletane ring compounds. To the best of our knowledge, this is the first report where both cis-and trans-isomers are isolated from the same disilene precursor and characterized structurally by single-crystal X-ray diffraction (XRD) studies. The reaction of 2 with elemental sulfur yields only the trans-isomer. To investigate this dissimilar reaction pattern exhibited by 2, computational studies were performed. Density functional theory (DFT) calculations showed that the two dioxadisiletane ring isomers are isoenergetic, with the trans isomer being slightly more stable than the cis counterpart, by 3.3 kcal/mol, while that is not the case with sulfur. All the isolated compounds are characterized by single-crystal XRD studies, multinuclear NMR spectroscopy, and electron ionization-mass spectrometry (EI-MS).     

Acid-responsive microcapsules: the loading-unloading processes

A simple and convenient method to prepare acid-responsive microcapsules by using functionalized single-walled carbon nanotubes and ytterbium triflate has been developed. Fluorescence active compounds were "pre-loaded" or "post-loaded" in the microcapsules and released later in acidic medium. An interesting "zip-unzip" phenomenon was observed while filming the action of acid on microcapsules under a microscope.