Templated Atom‐Precise Galvanic Synthesis and Structure Elucidation of a [Ag24Au(SR)18]− Nanocluster

Synthesis of atom‐precise alloy nanoclusters with uniform composition is challenging when the alloying atoms are similar in size (for example, Ag and Au). A galvanic exchange strategy has been devised to produce a compositionally uniform [Ag₂₄Au(SR)₁₈]^? cluster (SR: thiolate) using a pure [Ag₂₅(SR)₁₈]^? cluster as a template. Conversely, the direct synthesis of Ag₂₄Au cluster leads to a mixture of [Ag_25?xAu_x(SR)₁₈]^?, x=1–8. Mass spectrometry and crystallography of [Ag₂₄Au(SR)₁₈]^? reveal the presence of the Au heteroatom at the Ag₂₅ center, forming Ag₂₄Au. The successful exchange of the central Ag of Ag₂₅ with Au causes perturbations in the Ag₂₅ crystal structure, which are reflected in the absorption, luminescence, and ambient stability of the particle. These properties are compared with those of Ag₂₅ and Ag₂₄Pd clusters with same ligand and structural framework, providing new insights into the modulation of cluster properties with dopants at the single‐atom level.     

Analytical approaches on some selected toxic heavy metals in the environment and their socio-environmental impacts: A meticulous review

Heavy metals are a group of metals and metalloids that have relatively high density and are toxic even at ppb levels. The excess intake of heavy metals in human bodies though the environment may cause various humans health problems. Analytical approaches of some selected toxic heavy metals in the environment and their socio-environmental impacts are discussed in this review. In this present investigation, we have also discussed the design and development of nanomaterials for the detection of metal ions along with kinetic approaches. The isolation or pre-concentration and determination of heavy metals from complex matrices become challenging for analytical chemists and researchers. The fundamentals on sample preparation and analysis of some selected heavy metals employing different analytical tools for qualitative and quantitative determination of these pollutants in real samples are also discussed. In addition, this compiled work enhanced our knowledge in learning about pathway mechanisms and the degree of their risk assessment.     

Peptide mapping with liquid chromatography using a basic mobile phase

A new peptide mapping with liquid chromatography (LC) using an ammonia-containing basic mobile phase was reported. As compared with a method under a traditional acidic condition with a mobile phase containing trifluoroacetic acid (TFA) or formic acid (FA), the new method exhibited excellent overall performance: it was advantageous over the TFA method in terms of the ultraviolet (UV) and mass spectrometry (MS) sensitivities and the sequence coverage for a tryptic map; it was superior to the FA method in terms of the UV sensitivity, the sequence coverage and the separation capacity. Due to a significant difference in the chromatographic selectivity, several important peptide mapping applications that were sometimes difficult to be conducted previously could now be carried out using the new method. For example, the baseline separation of peptides from the corresponding deamidated products could be achieved with confidence using the new method, a critical pre-requisite for definitive identification and quantification of the deamidation products with LC/MS. No on-column deamidation was observed with the conditions used for the separation. Complementary and confirmative information about a protein could be obtained by running its proteolytic digest under both the basic and acidic conditions.     

Design and development of a new pyrromethene dye with improved photostability and lasing efficiency: theoretical rationalization of photophysical and photochemical properties

In an attempt to develop a photostable and efficient pyrromethene compound for use in liquid dye lasers, three congeners of the commercially available pyrromethene 567 (PM567) laser dye were synthesized and their photophysical properties, lasing efficiencies, and photochemical stabilities were studied. In general the presence of an aryl group at C-8 of the pyrromethene chromophore increased the photostability. One of the congeners possessing a C-8 trimethoxyphenyl moiety showed significantly improved lasing parameters than PM567. Compared to PM567, the photochemical stability of the new dye was 2-fold, while it showed an equivalent lasing efficiency to that of PM567 at a significantly lower concentration. The increased photostability of these new dye molecules could be explained by theoretical calculation on their capacity to generate singlet oxygen ((1)O(2)) and probability of reaction with (1)O(2). Our calculations were in agreement with the experimental results and indicated that a systematic design of new derivatives of pyrromethene chromophore might lead to improved laser dye molecules.     

GdIII-19F Distance Measurements for Proteins in Cells by Electron-Nuclear Double Resonance

Studies of protein structure and dynamics are usually carried out in dilute buffer solutions, conditions that differ significantly from the crowded environment in the cell. The double electron-electron resonance (DEER) technique can track proteins’ conformations in the cell by providing distance distributions between two attached spin labels. This technique, however, cannot access distances below 1.8 nm. Here, we show that Gd^III-¹⁹F Mims electron-nuclear double resonance (ENDOR) measurements can cover part of this short range. Low temperature solution and in-cell ENDOR measurements, complemented with room temperature solution and in-cell Gd^III-¹⁹F PRE (paramagnetic relaxation enhancement) NMR measurements, were performed on fluorinated GB1 and ubiquitin (Ub), spin-labeled with rigid Gd^III tags. The proteins were delivered into human cells via electroporation. The solution and in-cell derived Gd^III-¹⁹F distances were essentially identical and lie in the 1–1.5 nm range revealing that both, GB1 and Ub, retained their overall structure in the Gd^III and ¹⁹F regions in the cell.     

Dimension Engineering of Stimuli-Responsive 1D Molecular Crystals into Unusual 2D and 3D Zigzag Waveguides

We demonstrate an innovative technique to achieve organic 2D and 3D waveguides with peculiar shapes from an acicular, stimuli-responsive molecular crystal, (2Z,2′Z)-3,3′-(anthracene-9,10-diyl)bis(2-(3,5-bis(trifluoromethyl)phenylacrylonitrile), Ant-CF₃. The greenish-yellow fluorescent (FL) Ant-CF₃ molecular crystals exhibit laser power-dependent permanent mechanical bending in 2D and 3D. Investigation of a single-crystal using spatially-resolved Raman/FL/electron microscopy, and theoretical calculations revealed photothermal (Z,E)/(E,E) isomerization-assisted transition from crystalline to amorphous phase at the laser-exposed regions. This phenomenon facilitates the dimension engineering of a 1D crystal waveguide into 2D waveguide on a substrate or a 3D waveguide in free space. The bends can be used as interconnection points to couple different optical elements. The presented technique has broader implications in organic photonics and other crystal-related photonic technologies.     

Impurity related optical properties in tuned quantum dot/ring systems

In this paper, we explore the linear, third-order nonlinear, and total optical absorption coefficient (OAC) and refractive index change coefficient (RICC) of a GaAs doped quantum dot/quantum ring (QD/QR) with parabolic-inverse squared potential in conjunction with modified Gaussian confinement and taking into account the presence of on-centre shallow donor and or acceptor impurity. Calculations are done via the compact density matrix formalism and the iterative method. The two-dimensional parabolic QD/QR is subjected to uniform magnetic field oriented perpendicularly to the plane of the structure. The energy levels and wave function are derived within the framework of effective-mass and parabolic band approximation. The results exhibit that the OACs and RICC are clearly affected by different parameters of the applied confinement, strength of magnetic field, and the presence of impurity. The variation of confinement potential, nature of impurity, dot radius, cyclotron frequency of the parabolic confinement potential, and geometric parameter of the on-centre repulsive potential lead to either a red-shift or a blue-shift of the resonant peaks of the OACs and of the maximum and minimum of the RICC together with significant variations of the magnitudes of these resonant structures.     

Tricoordinate Nontrigonal Pnictogen‐Centered Radical Anions: Isolation,Characterization, and Reactivity

The search for main‐group element‐based radicals is one of the main research topics in contemporary chemistry because of their fascinating chemical and physical properties. The Group 15 element‐centered radicals mainly feature a V‐shaped two coordinate structure, with a couple of radical cations featuring trigonal tricoordinated geometry. Now, nontrigonal compounds R₃E (E=P, As, Sb) were successfully synthesized by introducing a new rigid tris‐amide ligand. The selective one‐electron reduction of R₃E afforded the first stable tricoordinate pnictogen‐centered radical anion salts; the pnictogen atoms retain planar T‐shaped structures. EPR spectroscopy and calculations reveal that the spin density mainly resides at the p orbitals of the pnictogen atoms, which is perpendicular to the N₃E planes.     

Multifaceted nonlinear dynamics in $$\mathcal {PT}$$PT-symmetric coupled Liénard oscillators

Nonlinear Dynamics - We propose a generalized parity-time ($$\mathcal {PT}$$)-symmetric Liénard oscillator with two different orders of nonlinear position-dependent dissipation. We study the...