Heteroarene-tethered Functionalized Alkyne Metamorphosis

Heteroarene-tethered functionalized alkynes are multipotent synthons in organic chemistry. This detailed Review described herein offers a thorough discussion of the metamorphosis of heteroarene-tethered functionalized alkynes, an area which has earned much attention over the past decade in the straightforward synthesis of architecturally complex heterocyclic scaffolds in atom and step economic manner. Depending upon the variety of functionalized alkynes, this Review is divided into multiple sections. Amongst the vast array of synthetic transformations covered, dearomatizing spirocyclizations and cascade spirocyclization/rearrangement are of great interest. Synthetic transformations involving the heteroarene-tethered functionalized alkynes with scope, challenges, limitations, mechanism, their application in the total synthesis of natural products and future perceptions are surveyed.     

Coumarin-based urea-amide scaffold in ratiometric fluorescence sensing of CN−

Coumarin-based urea and urea–amide scaffolds 1–3 have been designed and synthesized for the selective and naked eye detection of cyanide ion. Of the three, compound 3 exhibits ratiometric fluorescence change selectively in the presence of CN^? and validates the rationality in designing anion receptor. Upon interaction with CN^?, the color of the solution of 3 in CH₃CN under UV exposure becomes bright yellow, which is beneficial for its naked eye detection. Addition of CN^? of ～10^?4 M brings nice color change from colourless to yellow in ordinary light. The sensing event is supposed to be due to nucleophilic addition of CN^? to the coumarin unit enabling intramolecular charge transfer (ICT) mechanism.     

Turing pattern formation in anisotropic medium

Diffusion of reacting species in chemical and biochemical systems in anisotropic medium is markedly different from those occurring in isotropic medium, therefore approximating diffusion coefficients as constants may not be desirable as this has dynamical consequences. This paper is devoted to the analytical and numerical investigation of the development of spatial patterns in such systems. To this end we consider a general reaction–diffusion system with concentration-dependent diffusion and formulate a scheme to derive the general form of envelope equation for such systems. The theory is applied to the chlorite–iodide–malonic acid system, a standard paradigm for activator–inhibitor mechanism, to derive the instability condition in terms of the anisotropy parameters (\(\kappa _{i}, i = u, v\) that impart concentration-dependence to the diffusion coefficients) and identify the supercritical and subcritical Turing regions in the bifurcation diagram. The theoretical predictions are in good agreement with the numerical simulations.     

A differential evolution-based regression framework for forecasting Bitcoin price

This research proposes a differential evolution-based regression framework for forecasting one day ahead price of Bitcoin. The maximal overlap discrete wavelet transformation first decomposes the original series into granular linear and nonlinear components. We then fit polynomial regression with interaction (PRI) and support vector regression (SVR) on linear and nonlinear components and obtain component-wise projections. The sum of these projections constitutes the final forecast. For accurate predictions, the PRI coefficients and tuning of the hyperparameters of SVR must be precisely estimated. Differential evolution, a metaheuristic optimization technique, helps to achieve these goals. We compare the forecast accuracy of the proposed regression framework with six advanced predictive modeling algorithms- multilayer perceptron neural network, random forest, adaptive neural fuzzy inference system, standalone SVR, multiple adaptive regression spline, and least absolute shrinkage and selection operator. Finally, we perform the numerical experimentation based on—(1) the daily closing prices of Bitcoin for January 10, 2013, to February 23, 2019, and (2) randomly generated surrogate time series through Monte Carlo analysis. The forecast accuracy of the proposed framework is higher than the other predictive modeling algorithms.

     

Local lazy regression: making use of the neighborhood to improve QSAR predictions

Traditional quantitative structure-activity relationship (QSAR) models aim to capture global structure-activity trends present in a data set. In many situations, there may be groups of molecules which exhibit a specific set of features which relate to their activity or inactivity. Such a group of features can be said to represent a local structure-activity relationship. Traditional QSAR models may not recognize such local relationships. In this work, we investigate the use of local lazy regression (LLR), which obtains a prediction for a query molecule using its local neighborhood, rather than considering the whole data set. This modeling approach is especially useful for very large data sets because no a priori model need be built. We applied the technique to three biological data sets. In the first case, the root-mean-square error (RMSE) for an external prediction set was 0.94 log units versus 0.92 log units for the global model. However, LLR was able to characterize a specific group of anomalous molecules with much better accuracy (0.64 log units versus 0.70 log units for the global model). For the second data set, the LLR technique resulted in a decrease in RMSE from 0.36 log units to 0.31 log units for the external prediction set. In the third case, we obtained an RMSE of 2.01 log units versus 2.16 log units for the global model. In all cases, LLR led to a few observations being poorly predicted compared to the global model. We present an analysis of why this was observed and possible improvements to the local regression approach.     

Marginal states in a cubic autocatalytic reaction

Marginal steady state belongs to a special class of states in nonlinear dynamics. To realize this state we consider a cubic autocatalytic reaction A + 2B → 3B in a continuous-stirred-tank-reactor, where the flow rate of the reactant A can be controlled to manipulate the dynamical behavior of the open system. We demonstrate that when the flow rate is weakly noisy the autocatalytic reaction admits of a steady state which is marginal in nature and is surrounded by infinite number of periodic trajectories. When the uncatalyzed reaction A → B is included in the reaction scheme, there exists a marginal steady state which is a critical state corresponding to the point of transition between the flow branch and the equilibrium branch, similar to gas-liquid critical point of transition. This state loses its stability in the weak noise limit.     

Hydrogen atom abstraction from Piperazine by hydroxyl radical: a theoretical investigation

Dual level of quantum mechanical calculations have been carried out for hydrogen abstraction from Piperazine [HN(CH₂CH₂)₂NH] initiated by OH radical. Geometry optimisation and frequency calculations of all species involved in the titled reaction have been performed at M06-2X/6-31+G(d,p) level of theory. For the accuracy in the thermochemistry and kinetics data, single-point energy calculations have been further carried out at coupled cluster CCSD(T) method along with 6-311G(d,p) basis set. An energy profile diagram for the reaction has been plotted along with pre-reactive and post-reactive complexes at entrance and exit channels. Intrinsic reaction coordinates (IRCs) calculations have been performed for identification of real transition states that connect it via reactant to product. Our result shows that the H-atom abstraction takes place from the C–H position of Piperazine. The rate constant is calculated using canonical transition state theory (CTST) is found to be 2.86 × 10^?10 cm³ molecule^?1 s^?1 which is in good agreement with the reported experimental rate constant (2.38 ± 0.28) × 10^?10 cm³ molecule^?1 s^?1 at 298 K. We have also reported rate constant for the temperature range 300–500 K. Using group-balance isodesmic reaction, the standard enthalpies of formation for Piperazine and product radicals generated by hydrogen abstraction are reported. The branching ratios for both reaction channel (i.e. H-abstraction from –CH₂ and –NH position of Piperazine) are found to be 93% and 7%, respectively. The calculated atmospheric life time of Piperazine is found to be 0.97 hour.     

Frontispiece: Photocatalytic Terminal C−C Coupling Reaction Inside Water Soluble Nanocages

Developing methods that activate C−H bonds directly with high selectivity for C−C bond formation in complex organic synthesis has been a major chemistry challenge. Recently it has been shown that photoactivation of weakly polarized C−H bonds can be carried out inside a cationic water-soluble nanocage with visible light-mediated host-guest charge transfer (CT) chemistry. Using this novel photoredox activation paradigm, here we demonstrate C−C bond formation to photo-generate 1,3-diynes at room temperature in water from terminal aromatic alkynes for the first time. The formation of cavity-confined alkyne radical cation and the proton-removed neutral radical species highlight the unique C−C coupling step driven by supramolecular preorganization.     

Photocytotoxic and anaerobic DNA cleavage activity of binuclear 3,3′-dithiodipropionic acid cobalt(II) complexes having phenanthroline bases

Dicobalt(II) complexes [{(B)Co^II}₂(μ-dtdp)₂] (1–3) of 3,3′-dithiodipropionic acid (dtdp) and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3), have been prepared, characterized and their photo-induced anaerobic DNA cleavage activity studied. The elemental analysis and mass spectral data suggest binuclear formulation of the complexes. The redox inactive complexes have magnetically non-interacting dicobalt(II) core showing magnetic moment of ∼3.9 μ_B per cobalt(II) center. The complexes show good binding propensity to calf thymus DNA giving K_b values within 4.3 × 10⁵–4.0 × 10⁶ M⁻¹. Thermal melting and viscosity data predict DNA groove binding and/or partial intercalative nature of the complexes. The complexes show significant anaerobic DNA cleavage activity in green light under argon atmosphere possibly involving radical species generated from the disulfide moiety in a type-I pathway. The DNA cleavage reaction under aerobic medium in green light is found to involve hydroxyl radical species. The dppz complex 3 exhibits significant photocytotoxicity in HeLa cervical cancer cells with an IC₅₀ value of 2.3 μM in UV-A light of 365 nm, while it is essentially non-toxic in dark giving an IC₅₀ value of >200 μM. A significant reduction of the dark toxicity of the organic dppz base (IC₅₀ = 8.3 μM in dark) is observed on binding to the cobalt(II) center while essentially retaining its photocytotoxicity in UV-A light (IC₅₀ = 0.4 μM).     

A characterization of c-type subrings of C(X) of some kind

Positivity - A commutative ring with unity is of a c-type if it is (ring) isomorphic with C(X) for some space X. In this paper, we have described a structural representation of c-type subrings of...