Schiff base addition to cyclic dicarboxylic anhydrides: an unusual concerted reaction. An MO and DFT theoretical study

The existing controversy as to whether dicarboxylic anhydride iminolysis by Schiff bases is a concerted [4 + 2] addition or a stepwise reaction following either a Perkin-like route or occurs as iminolysis via zwitterionic intermediates is solved computationally by DFT and MO theory. Both types of theory favor a concerted mechanism starting as bimolecular addition of imine to the carbonyl carbon of anhydride monoenol, accompanied by simultaneous elimination of carboxylate. The reaction proceeds further without forming any intermediate and completes as intramolecular charge transfer from enol HOMO to imine LUMO with ring closure.     

p-Moment exponential stability of Caputo fractional differential equations with noninstantaneous random impulses

Stability of Caputo fractional differential equations with impulses occurring at random moments and with non-instantaneous time of their action is studied. Using queuing theory and the usual distribution for waiting time, we study the case of exponentially distributed random variables between two consecutive moments of impulses. The p-moment exponential stability of the zero solution is defined and studied when the waiting time between two consecutive impulses is exponentially distributed and the length of the action of any impulse is initially given. The argument is based on Lyapunov functions. Some examples are given to illustrate our results.     

Stability of Gene Regulatory Networks Modeled by Generalized Proportional Caputo Fractional Differential Equations

A model of gene regulatory networks with generalized proportional Caputo fractional derivatives is set up, and stability properties are studied. Initially, some properties of absolute value Lyapunov functions and quadratic Lyapunov functions are discussed, and also, their application to fractional order systems and the advantage of quadratic functions are pointed out. The equilibrium of the generalized proportional Caputo fractional model and its generalized exponential stability are defined, and sufficient conditions for the generalized exponential stability and asymptotic stability of the equilibrium are obtained. As a special case, the stability of the equilibrium of the Caputo fractional model is discussed. Several examples are provided to illustrate our theoretical results and the influence of the type of fractional derivative on the stability behavior of the equilibrium.     

Homophtalonitrile for Multicomponent Reactions: Syntheses and Optical Properties of o-Cyanophenyl- or Indol-3-yl-Substituted Chromeno[2,3-c]isoquinolin-5-Amines

Malononitrile is a useful reagent for multicomponent reactions with hundreds of methods developed. In this paper, we suggest α-(cyano)-o-tolunitrile (homophtalonitrile) to work as a vinylogous malononitrile. Thus, a organocatalytic pseudo-three-component reaction of homopthalonitrile (2 equiv) and o-hydroxybenzaldehyde, leading to the diastereoselective formation of 5-amino-12H-chromeno[2,3-c]isoquinolin-12-yl)(cyano)methyl)benzonitriles, was discovered. The possibility to employ other nucleophiles was demonstrated for indoles, and a sequential three-component reaction of homophtalonitrile, o-hydroxybenzaldehyde, and (aza)indole, giving 12-(1H-Indol-3-yl)-12H-chromeno[2,3-c]isoquinolin-5-amines, was developed. The photophysical properties of the synthesized compounds have been studied, revealing high fluorescence quantum yields (42–70 %) for indol-3-yl substituted 12H-chromeno[2,3-c]isoquinolin-5-amines and reversible fluorescence quenching under acidic conditions.     

Electronic absorption and emission spectra and computational studies of some 2-aryl, 2-styryl, and 2-(4′-aryl)butadienyl quinazolin-4-ones

The relatively less popular group of quinazoline heterocyclic compounds is searched theoretically for compounds with promising classical and nonlinear optical properties, e.g. fluorescence and high (hyper)polarizabilities. Candidates for NLO materials are found among the general series of -4-(3H)-quinazolonyl-ω-aryl polyenes 1, 2, 3 and their fluorescence spectra are registered experimentally. CIS/6-31G* calculations provide no reliable predictions of observed UV/Vis and fluorescence spectra. However, semiempirical CISD PM3 calculations predict fairly well the observed bathochromic effects arising from extension of polyene chains (CHCH)_n, n=0–2, and donor substitution in the aryl fragments. The observed fluorescence is assigned to planar quinonoid S1 emissive states, while ground S0 state geometries of compounds with n=0 are nonplanar, and with n>0 are planar. We find high TDHF PM3 static polarizabilities for all studied molecules, as well as high hyperpolarizabilities β SHG and γ THG.     

Origins of stereoselectivity in the Diels-Alder addition of chiral hydroxyalkyl vinyl ketones to cyclopentadiene: a quantitative computational study

Modest basis set level MP2/6-31G(d,p) calculations on the Diels-Alder addition of S-1-alkyl-1-hydroxy-but-3-en-2-ones (1-hydroxy-1-alkyl methyl vinyl ketones) to cyclopentadiene correctly reproduce the trends in known experimental endo/exo and diastereoface selectivity. B3LYP theoretical results at the same or significantly higher basis set level, on the other hand, do not satisfactorily model observed endo/exo selectivities and are thus unsuitable for quantitative studies. The same is valid also with regard to subtle effects originating from, for example, conformational distributions of reactants. The latter shortcomings are not alleviated by the fact that observed diastereoface selectivities are well-reproduced by DFT calculations. Quantitative computational studies of large cycloaddition systems would require higher basis sets and better account for electron correlation than MP2, such as, for example, CCSD. Presently, however, with 30 or more non-hydrogen atoms, these computations are hardly feasible. We present quantitatively correct stereochemical predictions using a hybrid layered ONIOM computational approach, including the chiral carbon atom and the intramolecular hydrogen bond into a higher level, MP2/6-311G(d,p) or CCSD/6-311G(d,p), layer. Significant computational economy is achieved by taking account of surrounding bulky (alkyl) residues at 6-31G(d) in a low HF theoretical level layer. We conclude that theoretical calculations based on explicit correlated MO treatment of the reaction site are sufficiently reliable for the prediction of both endo/exo and diastereoface selectivity of Diels-Alder addition reactions. This is in line with the understanding of endo/exo selectivity originating from dynamic electron correlation effects of interacting pi fragments and diastereofacial selectivity originating from steric interactions of fragments outside of the Diels-Alder reaction site.     

Antimicrobial and Antioxidant Potential of Scenedesmus obliquus Microalgae in the Context of Integral Biorefinery Concept

Small-scale photobioreactors (PBRs) in the inoculum stage were designed with internal (red or green) and external white LED light as an initial step of a larger-scale installation aimed at fulfilling the integral biorefinery concept for maximum utilization of microalgal biomass in a multifunctional laboratory. The specific growth rate of Scenedesmus obliquus (Turpin) Kützing biomass for given cultural conditions was analyzed by using MAPLE software. For the determination of total polyphenols, flavonoids, chlorophyll “a” and “b”, carotenoids and lipids, UHPLC-HRMS, ISO-20776/1, ISO-10993-5 and CUPRAC tests were carried out. Under red light growing, a higher content of polyphenols was found, while the green light favoured the flavonoid accumulation in the biomass. Chlorophylls, carotenoids and lipids were in the same order of magnitude in both samples. The dichloromethane extracts obtained from the biomass of each PBR synergistically potentiated at low concentrations (0.01–0.05 mg/mL) the antibacterial activity of penicillin, fluoroquinolones or oregano essential oil against the selected food-borne pathogens (Staphylococcus aureus, Escherichia coli and Salmonella typhimurium) without showing any in vitro cytotoxicity. Both extracts exhibited good cupric ion-reducing antioxidant capacity at concentrations above 0.042–0.08 mg/mL. The UHPLC-HRMS analysis revealed that both extracts contained long chain fatty acids and carotenoids thus explaining their antibacterial and antioxidant potential. The applied engineering approach showed a great potential to modify microalgae metabolism for the synthesis of target compounds by S. obliquus with capacity for the development of health-promoting nutraceuticals for poultry farming.