Results on L-functions and certain uniqueness questions of Gross

In this paper, we study the value distribution of L-functions in the Selberg class and concentrate on the uniqueness questions of L-functions that share one or two sets with an arbitrary meromorphic function. The results obtained in this paper improve the recent results due to Q.-Q. Yuan, X.-M. Li, and H.-X. Yi [Value distribution of L-functions and uniqueness questions of F. Gross, Lith. Math. J., 58(2):249–262, 2018] and also extend a result due to B.Q. Li [A result on value distribution of L-functions, Proc. Am. Math. Soc., 138(6):2071–2077, 2010].

     

Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals

Abrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano‐emitters. Extended quantum‐confined nanostructures also undergo spatially heterogeneous blinking; however, there is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi‐level blinking of entire individual organo–lead bromide perovskite microcrystals (volume=0.1–3 μm³) under ambient conditions. Extremely high spatiotemporal correlation (>0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4 μm) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, which is rationalized by correlated and efficient migration of carriers to a few transient nonradiative traps, the nature and population of which determine blinking propensity. Observation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving long‐range (mesoscopic) electronic communication.     

Cytotoxic Oligomers and Fibrils Trapped in a Gel‐like State of α‐Synuclein Assemblies

α‐Synuclein (α‐Syn) aggregation is associated with Parkinson's disease (PD) pathogenesis. In PD, the role of oligomers versus fibrils in neuronal cell death is debatable, but recent studies suggest oligomers are a proximate neurotoxin. Herein, we show that soluble α‐Syn monomers undergo a transformation from a solution to a gel state on incubation at high concentration. Detailed characterization of the gel showed the coexistence of monomers, oligomers, and short fibrils. In vitro, the gel was highly cytotoxic to human neuroblastoma cells. The individual constituents of the gel are short‐lived species but toxic to the cells. They comprise a structurally heterogeneous population of α‐helical and β‐sheet‐rich oligomers and short fibrils with the cross‐β motif. Given the recent evidence of the gel‐like state of the protein associated with neurodegenerative diseases, the gel state of α‐Syn in this study represents a mechanistic and structural model for the in vivo toxicity of α‐Syn in PD.     

Bimetallic Ag‐Pt Sub‐nanometer Supported Clusters as Highly Efficient and Robust Oxidation Catalysts

A combined experimental and theoretical investigation of Ag‐Pt sub‐nanometer clusters as heterogeneous catalysts in the CO→CO₂ reaction (COox) is presented. Ag₉Pt₂ and Ag₉Pt₃ clusters are size‐selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first‐principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano‐aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O₂, and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species.     

Synthesis of hydroxy and methoxy perylene quinones, their spectroscopic and computational characterization, and their antiviral activity

Hydroxy and methoxy perylene quinones are synthesized in an attempt to isolate the essential spectroscopic and biological features of light-induced antiviral agents such as hypericin and hypocrellin. Unlike their naturally occurring counterparts, these synthetic quinones bear the carbonyl, hydroxyl, and methoxy groups in the "bay region." The hydroxy and methoxy compounds have rich absorption spectra with broad features in the visible (approximately 450-800 nm) and relatively more intense and narrow features at wavelengths < or = 350 nm. High-level ab initio quantum mechanical calculations assign the features in the absorption spectra to electronic transitions from S0 to S2 and to higher-lying electronic states. The calculations indicate that in the ground state the trans dihydroxy isomer is 12.5 kcal/mol lower in energy than the cis dihydroxy isomer and is thus the only species present. The lowest-energy trans methoxy ground state isomer and the lowest-energy cis methoxy ground state isomer are found to be degenerate. An additional cis methoxy isomer 6.3 kcal/mol higher in energy than the global minimum is assumed to contribute to the spectrum and is also considered. Finally, the synthetic compounds exhibit similar light-induced antiviral activity to each other, but significantly less than that of hypericin.     

pH‐Triggered Sustained Drug Delivery from a Polymer Micelle having the β‐Thiopropionate Linkage

The synthesis, micellar aggregation, and pH‐triggered intracellular drug delivery ability of an amphiphilic statistical copolymer (P2) are studied. Two methacrylate derivatives, one containing a hydrophilic pendant and the other containing a hydrophobic pendant chain, are copolymerized to produce P2. The hydrophobic pendant chain is linked to the polymer backbone by a β‐thiopropionate linkage, known to undergo slow hydrolysis at mild acidic pH. P2 forms a multimicellar cluster in water with a critical aggregation concentration of 0.02 mg mL⁻¹ and encapsulates a hydrophobic guest such as pyrene, Nile red, or the anti‐cancer drug doxorubicin (Dox). Sustained release of the entrapped Dox (80% after 100 h) is noticed at pH 5.2, while release is significantly slower (35% after 100 h) at pH 7.4. Acidic hydrolysis of the β‐thiopropionate linkage leading to the reduction of the hydrophobicity is established as the cause for micellar disassembly and triggered drug release. Cell‐culture studies with the human breast cancer cell line, MCF‐7, reveal biocompatibility of P2 (below 150 μg mL⁻¹). It is further tested for intracellular delivery of Dox. MCF‐7 cells remain healthy at pH 7.4 but become unhealthy at pH 5.2 when treated with a Dox‐loaded P2 micelles.

     

UV–Vis and NMR spectroscopic investigations on effective and selective non-covalent interactions between fullerenes and calix[6]arene

Ground state non-covalent interactions between a macro cyclic calixarene receptor, namely, 4-tert-butylcalix[6]arene (1), and fullerenes (C₆₀ and C₇₀) were studied in toluene medium by absorption spectrophotometric method. Absorption band due to the charge transfer (CT) transition have been observed in the visible region between fullerenes and 1. Utilizing the CT absorption bands, various important physicochemical parameters like oscillator strength, resonance energy, transition dipole strength of the fullerene-1 complexes and ionization potential of 1 is determined in present investigations. From Jobs method of continuous variation, it is observed that both C₆₀ and C₇₀ form stable 1:1 complexes with 1. The most fascinating feature of the present study is that 1 binds selectively C₇₀ compared to C₆₀ as obtained from binding constant (K) data of C₆₀–1 (K_C60–1) and C₇₀–1 (K_C70–1) complexes, i.e., K_C60–1 = 32,400 dm³·mol^? 1 and K_C70–1 = 110,000 dm³.mol^? 1 and selectivity (K_C70–1/K_C60–1) = 3.4. ¹H NMR analysis provides very good support in favor of strong binding between C₇₀ and 1.     

Dynamic solvation in imidazolium-based ionic liquids on short time scales

Steady-state and time-resolved Stokes shift data for the probe coumarin 153 in two imidazoles, six imidazolium-based ionic liquids, and several other solvents are presented. These results are consistent with our original suggestion (J. Phys. Chem. B 2004, 108, 10245-10255) that initial solvation is dominated by the organic moiety of the ionic liquid, and they show that for the imidazole-based liquids initial solvation is in all cases very rapid. Solvation by methylimidazole and butylimidazole is complete in 100 ps, and all of the imidazolium ionic liquids demonstrate similarly rapid initial solvation. Owing to the importance of determining the amount of initial solvation that is missed in a given experiment with finite time resolution, we discuss a method of estimating the intramolecular contribution to the reorganization energy. This method yields 2068 cm(-1) and is compared with an alternative method.     

Photophysical Investigations on Determination of Ionicity and Electronic Structures for the Non-covalent Complexes of Calix[4]resorcinarene with Fullerenes C<Subscript>60</Subscript> and C<Subscript>70</Subscript> in the Solution State

Ground state non-covalent interactions between a macrocyclic receptor, C-methylcalix[4]resorcinarene (1) and fullerenes (C₆₀ and C₇₀) have been studied in benzonitrile by an absorption spectrophotometric method. Absorption bands are located in the visible region due to the charge transfer (CT) transition between 1 and various electron acceptors (including fullerenes), namely, 2,3-dichloro-5,6-dicyano-p-benzoquinone, tetracyanoquinodimethane and p-chloranil. Utilizing the CT absorption bands, various important physicochemical parameters, including oscillator strength, resonance energy, transition dipole strength of all the acceptor-1 complexes and vertical ionization potential of 1 are determined. Job’s method of continuous variation reveals 1:1 stoichiometry between fullerenes and 1. The most fascinating feature of the present study is that 1 binds selectively to C₇₀ compared to C₆₀ as obtained from binding constant (K) data of C₆₀-1 (K_C60-1K_{\mathrm{C}60\mbox{-}\mathbf{1}}) and C₇₀-1 (K_C70-1K_{\mathrm{C}70\mbox{-}\mathbf{1}}) complexes, i.e., K_C60-1=190K_{\mathrm{C}60\mbox{-}\mathbf{1}}=190 dm³⋅mol⁻¹ and K_C70-1=5,800K_{\mathrm{C}70\mbox{-}\mathbf{1}}=5{,}800 dm³⋅mol⁻¹ and selectivity (K_C70-1 /K_C60-1 ) ∼30. Quantum chemical calculations based on hybrid density functional theory estimate the enthalpies of formation of the fullerene-1 complexes in vacuo and provide very good support for selectivity in the K values of the C₇₀ and C₆₀ complexes of 1. The exchange and correlation energies have been calculated using a hybrid DFT functional method. We have opted to use the hybrid DFT functional over the Hartree-Fock method, as it can account for correlation effects also. Molecular electrostatic potential map calculations give a clear picture on the electronic structures of the fullerene-1 complexes.