The importance of stereochemically active lone pairs for influencing Pb(II) and As(III) protein binding

The toxicity of heavy metals, which is associated with the high affinity of the metals for thiolate rich proteins, constitutes a problem worldwide. However, despite this tremendous toxicity concern, the binding mode of As(III) and Pb(II) to proteins is poorly understood. To clarify the requirements for toxic metal binding to metalloregulatory sensor proteins such as As(III) in ArsR/ArsD and Pb(II) in PbrR or replacing Zn(II) in δ-aminolevulinc acid dehydratase (ALAD), we have employed computational and experimental methods examining the binding of these heavy metals to designed peptide models. The computational results show that the mode of coordination of As(III) and Pb(II) is greatly influenced by the steric bulk within the second coordination environment of the metal. The proposed basis of this selectivity is the large size of the ion and, most important, the influence of the stereochemically active lone pair in hemidirected complexes of the metal ion as being crucial. The experimental data show that switching a bulky leucine layer above the metal binding site by a smaller alanine residue enhances the Pb(II) binding affinity by a factor of five, thus supporting experimentally the hypothesis of lone pair steric hindrance. These complementary approaches demonstrate the potential importance of a stereochemically active lone pair as a metal recognition mode in proteins and, specifically, how the second coordination sphere environment affects the affinity and selectivity of protein targets by certain toxic ions.     

Efficient one-pot synthesis of cyclic β-enaminoamides by thermal Wolff rearrangement of cyclic 2-diazo-1,3-dicarbonyls and conversion to uracil derivatives

This paper describes simple and efficient approaches for the preparation of β-enaminoamides through thermal Wolff rearrangement of cyclic diazodicarbonyls followed by trapping with various amines. The synthesized β-enaminoamides were readily converted into uracil derivatives.     

A dual role of phenylboronic acid as a receptor for carbohydrates as well as a quencher for neighboring pyrene fluorophore

A simple amino acid based compound (1) containing a phenyl boronic group and pyrene fluorophore showed an enhanced fluorescence in aqueous solutions at physiological pH through suppression of the photoinduced electron transfer from pyrene to boronic acid on carbohydrate binding. The compound exhibited an interesting fluorescence change depending on pH with decreased emission intensity at acidic pH but enhanced emission intensity at basic pH unlike the fluorescent carbohydrate chemosensors using a PET process with amine and aryl-boronic acid. We have characterized a dual role of phenylboronic acid as a receptor for carbohydrates as well as a quencher for the fluorescence of pyrene fluorophore.     

Spin‐labeling of polymeric micelles and application in probing micelle swelling using EPR spectroscopy

Polymer structure and conformational dynamics are essential to polymer macroscopic properties, but are challenging to probe. We report here a synthetic pathway to chemically add a nitroxide moiety onto block polymers in a mild, aqueous environment and demonstrate its use in a series of polymeric micelles using Electron Paramagnetic Resonance (EPR) spectroscopy. The micelles were characterized with several analytical approaches and EPR findings were in general consistent with other approaches. Upon exposure to organic solvents, the line shape changes reflected the micelle swelling and EPR spectral simulations revealed structural information of the swelled micelles. The label introduced via our method can be cleaved and replaced with other probes to report different information site‐specifically. The mild conditions facilitate the future use of EPR in solving biopolymer problems. In combination with other labeling approaches, one can perform polymer spin labeling with different chemistry, so that various information about polymers can be obtained site‐specifically. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1770–1782     

Self-assembled cotton-like copper–molybdenum sulfide and phosphide as a bifunctional electrode for green energy storage and production

As the world's energy needs grow and environmental concerns intensify, there is an increasing need for research into developing new materials that may be used in energy production and storage. Herein, we developed copper-molybdenum (Cu–Mo) sulfide and phosphide-based cotton-like nanoarchitectures via hydrothermal strategy and they were characterized using various analytical techniques. The prepared sulfide and phosphide-based materials showed HER overpotentials of 207 mV and 147 mV, respectively, as well as Tafel slope values of 118 mV/dec and 109 mV/dec at 10 mA/cm². While OER at the same current density showed 270 mV and 213 mV overpotentials with 82 mV/dec and 48 mV/dec Tafel slope, respectively. In addition, the prepared sulfide and phosphide-based materials showed significant performance towards supercapacitors, displaying specific capacitances of 3.5 and 5.2 F/cm² at 3 mA/cm², and retaining their specific capacitances by 86.9 and 69.4%, respectively, after 4,000 cycles with 100% Coulombic efficiency. These materials have the potential to be employed for energy production and storage because of their excellent electrochemical characteristics and bifunctional performance.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.     

Warped compactification to de Sitter space

We explore in detail the prospects of obtaining a four-dimensional de Sitter universe in classical supergravity models with warped and time-independent extra dimensions, presenting explicit cosmological solutions of the (4+n)$(4+n)$-dimensional Einstein equations with and without a bulk cosmological constant term. For the first time in the literature we show that there may exist a large class of warped supergravity models with a noncompact extra dimension which lead to a finite 4D Newton constant as well as a massless 4D graviton localized on an inflating four-dimensional FLRW universe. This result helps establish that the ‘no-go’ theorem forbidding acceleration in ‘standard’ compactification of string/M-theory on physically compact spaces should not apply to a general class of warped supergravity models that allows at least one noncompact direction. We present solutions for which the size of the radial dimension takes a constant value in the large volume limit, providing an explicit example of spontaneous compactification.