Macroscopic recognition of iodide by polymer appended calix[4]amidocrown resin

ABSTRACT

The current study reveals the synthesis of polymer appended Calix[4]amidocrown-5 with specific binding affinity for iodide at ppm-level. The low detection limits are observed via UV-vis and fluorescence spectroscopy. The time-dependent solution and solid-state ¹²⁷I NMR studies with 18.8 and 19 ppm shifts, indicate a strong sensing nature of resin towards iodide ion. A significant reduction in surface area and pore volume with higher thermostability of resin after iodide uptake indicated iodide inclusion in the amidocrown cavity. The mechanism of iodide sensing may be governed by noncovalent interactions of NH and OH protons present in amidocrown and phenyl ring as observed in terms of emission enhancement in fluorescence spectroscopy. The binding affinity and stoichiometric determinations are determined by Benesi-Hildebrand and Jobs plots, respectively.     

Ultrafast spectroscopy and computational study of the photochemistry of diphenylphosphoryl azide: direct spectroscopic observation of a singlet phosphorylnitrene

The photochemistry of diphenylphosphoryl azide was studied by femtosecond transient absorption spectroscopy, by chemical analysis of light-induced reaction products, and by RI-CC2/TZVP and TD-B3LYP/TZVP computational methods. Theoretical methods predicted two possible mechanisms for singlet diphenylphosphorylnitrene formation from the photoexcited phosphoryl azide. (i) Energy transfer from the (π,π*) singlet excited state, localized on a phenyl ring, to the azide moiety, thereby leading to the formation of the singlet excited azide, which subsequently loses molecular nitrogen to form the singlet diphenylphosphorylnitrene. (ii) Direct irradiation of the azide moiety to form an excited singlet state of the azide, which in turn loses molecular nitrogen to form the singlet diphenylphosphorylnitrene. Two transient species were observed upon ultrafast photolysis (260 nm) of diphenylphosphoryl azide. The first transient absorption, centered at 430 nm (lifetime (τ) ～ 28 ps), was assigned to a (π,π*) singlet S(1) excited state localized on a phenyl ring, and the second transient observed at 525 nm (τ ～ 480 ps) was assigned to singlet diphenylphosphorylnitrene. Experimental and computational results obtained from the study of diphenyl phosphoramidate, along with the results obtained with diphenylphosphoryl azide, supported the mechanism of energy transfer from the singlet excited phenyl ring to the azide moiety, followed by nitrogen extrusion to form the singlet phosphorylnitrene. Ultrafast time-resolved studies performed on diphenylphosphoryl azide with the singlet nitrene quencher, tris(trimethylsilyl)silane, confirmed the spectroscopic assignment of singlet diphenylphosphorylnitrene to the 525 nm absorption band.     

Ab initio quantum chemical investigation of intramolecular magnetic interaction in some diradical derivatives of imino nitroxide and nitronyl nitroxide

The magnetic properties of the monoradicals 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl (1) and 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide (2) and the diradicals 2,2'-(1,2-ethynediyldi-4,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (3), 2,2'-(1,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (4), and 2,2'-(1,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide] (5) are investigated by ab initio quantum chemical methods. The rule of spin alternation in the unrestricted Hartree-Fock (UHF) method clearly shows that the radical sites are antiferromagnetically coupled in 3 and ferromagnetically coupled in 4 and 5, which is consistent with a previous experiment. The molecular geometries are optimized at Hartree-Fock levels. This is followed by single-point calculations using the density functional (UB3LYP) treatment and the multiconfigurational complete active space self-consistent field (CASSCF) methodology. Magnetic exchange coupling constants are determined from the broken-symmetry approach. The calculated J values, -3.60 cm(-1) for 3, 0.16 cm(-1) for 4, and 0.67 cm(-1) for 5, are in excellent agreement with the observed values. Because of the very large size of the diradicals 3-5, the CASSCF (10,10) calculations cannot yield realistic J values. Nevertheless, the CASSCF calculations support the antiferromagnetic nature of the magnetic coupling in 3 and the ferromagnetic nature of the coupling in 4 and 5. The existence of an intramolecular magnetic coupling in 3-5 is also confirmed through computations of the isotropic hyperfine coupling constants for monoradicals 1 and 2 as well as diradicals 3-5.     

Alkyne Versus Ynamide Reactivity: Regioselective Radical Cyclization of Yne‐Ynamides

Ynamides are typically more reactive than simple alkynes and olefins. However, a serendipitous observation revealed a rare case where the reactivity of simple alkynes exceeds that of ynamides. This led to the development of a unique sulfur‐radical‐triggered cyclization of yne‐tethered ynamides, which involves attack of the alkyne by a thiyl radical followed by cyclization with the ynamide. A wide range of novel 4‐thioaryl pyrroles that could tolerate common functional moieties and N‐protecting groups were expediently constructed by this strategy. The current method contrasts with the typical cyclization of yne‐ynamides, which involves the attack of the alkyne moiety by the ynamide core. Control experiments and DFT calculations supported the participation of the sulfur radical in the reaction and the regioselective cyclization. The synthetic potential of the substituted pyrroles is also discussed.     

Spontaneous translation of nanodroplet over a heterogeneous surface due to thermal cycles: role of solid–liquid interfacial fluctuations

ABSTRACT

We study the molecular-scale features of the solid surface that result in the spontaneous motion of a nanodroplet due to the periodic variation of temperature. We first employ a thermodynamic model to predict the variation of solid–fluid interfacial properties that can result in the above motion. The model identifies a composite (surface couple) made of two surfaces that are characterised by a large difference between the entropic parts of the solid–liquid interfacial free energies. In order to understand the molecular-scale features of the two surfaces that may form a surface couple, we performed grand canonical Monte Carlo simulations of Lennard Jones fluid and crystalline surfaces made of Lennard Jones-like atoms. We then used the cumulant expansions of the perturbation formulas to divide the interfacial entropy into two parts: The one that is directly affected by the solid–fluid attraction (direct part), and the other (indirect part) that is indirectly affected by the solid–fluid attraction via the alteration of interfacial fluctuations. Our results indicate that two surfaces form a surface couple if the differences between their chemical natures lead to large differences in the indirect part of the interfacial entropy, while the direct part remains relatively unaffected.     

Exploration of pyrazole based aldo-x bifunctional building blocks for the synthesis of pyrazole annulated molecular architectures

Over the last decade, the synthetic chemist's community has attracted attention towards aldo-x precursors due to their versatility to afforded variety of heterocyclic frameworks. The aldo-x bifunctional building blocks (AXB3s) contain two or more reactive sites with different reactivity, which may offer new opportunities for the introduction of diversity in core skeleton, which may be of great biological and medicinal relevance. In this context, pyrazole based AXB3s such as 4-iodopyrazole-3/5-carbaldehyde may be explored for achieving pyrazole fused/linked heterocyclic skeletons by employing different organic transformations. Specifically, iodo substituted pyrazoles provide a new platform for the installation of desired pattern via transition-metal catalyzed approaches. Herein, we have assembled the strategies towards the development of pyrazole substituted and fused molecular architectures by using 4-iodopyrazole-3/5-carbaldehydes and pyrazole C-3)/C5- carbaldehydes. The photophysical data of some fluorescent pyrazole derivatives have also been discussed.     

Luminescence studies of diopside doped with various concentrations of Dysprosium (III)

Research on Chemical Intermediates - Diopside doped with various concentration (0.5, 1.0, 1.5, 2.0 and 2.5 mol%) of Dysprosium were prepared using solid-state reaction technique....     

Regioselective Difunctionalization and Annulation of Ynamide

The use of ynamides in organic synthesis has gained significant attention due to their ability to provide access to complex molecular structures through transformations such as 1,2-difunctionalization and annulation reactions. These reactions enable the formation of highly functionalized N-bearing olefins and unusual N-bearing heterocycles. In this minireview, we present a systematic overview of the regioselective difunctionalization and annulation reactions of ynamides. We discuss the multi-component reactions, and radical-triggered functionalizations across the ynamides carbon–carbon multiple bonds and the use of bifunctional reagents in annulation of ynamides, highlighting their potential in expanding the substrate scope. Furthermore, we provide insights into the mechanistic breakthroughs that have been achieved in recent years in the development of these reactions. Finally, we emphasize the promising future prospects of ynamides as versatile building blocks for the synthesis of complex molecular architectures.     

Sterically-Hindered Molecular p-Dopants Promote Integer Charge Transfer in Organic Semiconductors

Molecular p-dopants designed to undergo electron transfer with organic semiconductors are typically planar molecules with high electron affinity. However, their planarity can promote the formation of ground-state charge transfer complexes with the semiconductor host and results in fractional instead of integer charge transfer, which is highly detrimental to doping efficiency. Here, we show this process can be readily overcome by targeted dopant design exploiting steric hindrance. To this end, we synthesize and characterize the remarkably stable p-dopant 2,2′,2′′-(cyclopropane-1,2,3-triylidene)tris(2-(perfluorophenyl)acetonitrile) comprising pendant functional groups that sterically shield its central core while retaining high electron affinity. Finally, we demonstrate it outperforms a planar dopant of identical electron affinity and increases the thin film conductivity by up to an order of magnitude. We believe exploiting steric hindrance represents a promising design strategy towards molecular dopants of enhanced doping efficiency.