Abnormal Nucleophilic Substitution on Methoxytropone Derivatives: Steric Strategy to Synthesize 5-Substituted Azulenes

Azulene is a non-alternant non-benzenoid aromatic system, and in turn, it possesses unusual photophysical properties. Azulene-based conjugated systems have received increasing interest in recent years as optoelectronic materials. Despite the routes available for the preparation of substituted azulene derivatives, there remain few methods that allow regioselective substitution on the seven-membered ring of azulenes due to the subtle reactivity difference among the various positions. This report explores the reactivity of substituted tropolones as the azulene precursors and also provides a new method to create 5-substituted azulenes. The reaction of cyanoacetate enolate with unsubstituted 2-methoxytropone affords azulene through the attack of the nucleophile on the C-2 center (normal pathway). We have observed that 3-substituted 2-methoxytropones undergo steric-guided nucleophilic addition at the C-7 center (abnormal pathway) to afford 5-substituted azulene derivatives. Based on this observation and DFT calculation, a new synthetic strategy is devised for the regioselective synthesis of 5-substituted multifunctional azulenes, which cannot be accessed by any other method.     

Electronic and ligating properties of carbocyclic carbenes: A theoretical investigation

Carbocyclic carbenes (CCCs) are a class of nucleophilic carbenes which are very similar to N-heterocyclic carbenes (NHCs) in terms of their reactivity, but they do not contain a stabilizing heteroatom in their cyclic ring system. In this study, 17 representative known CCCs and 34 newly designed CCCs are evaluated using quantum chemical methods, and the results are compared in terms of their stability, nucleophilicity, and proton affinity (PA) parameters. The results are divided on the basis of ring size of the known and reported CCCs. The stability, nucleophilicity, PA, complexation energy, and bond strength–related parameters were estimated using M06/6-311++G(d,p) method. The results indicated that the CCCs known in the literature are strong σ-electron donating species and have considerable π-accepting properties. This study led to the design and identification of a few new CCCs with dimethylamine and diaminomethynyl substituents which can be singlet stable and are substantially nucleophilic. © 2018 Wiley Periodicals, Inc.     

Ageratum conyzoides L. and Its Secondary Metabolites in the Management of Different Fungal Pathogens

Ageratum conyzoides L. (Family—Asteraceae) is an annual aromatic invasive herb, mainly distributed over the tropical and subtropical regions of the world. It owns a reputed history of indigenous remedial uses, including as a wound dressing, an antimicrobial, and mouthwash as well as in treatment of dysentery, diarrhea, skin diseases, etc. In this review, the core idea is to present the antifungal potential of the selected medicinal plant and its secondary metabolites against different fungal pathogens. Additionally, toxicological studies (safety profile) conducted on the amazing plant A. conyzoides L. are discussed for the possible clinical development of this medicinal herb. Articles available from 2000 to 2020 were reviewed in detail to exhibit recent appraisals of the antifungal properties of A. conyzoides. Efforts were aimed at delivering evidences for the medicinal application of A. conyzoides by using globally recognized scientific search engines and databases so that an efficient approach for filling the lacunae in the research and development of antifungal drugs can be adopted. After analyzing the literature, it can be reported that the selected medicinal plant effectively suppressed the growth of numerous fungal species, such as Aspergillus, Alternaria, Candida, Fusarium, Phytophthora, and Pythium, owing to the presence of various secondary metabolites, particularly chromenes, terpenoids, flavonoids and coumarins. The possible mechanism of action of different secondary metabolites of the plant against fungal pathogens is also discussed briefly. However, it was found that only a few studies have been performed to demonstrate the plant’s dosage and safety profile in humans. Considered all together, A. conyzoides extract and its constituents may act as a promising biosource for the development of effective antifungal formulations for clinical use. However, in order to establish safety and efficacy, additional scientific research is required to explore chronic toxicological effects of ageratum, to determine the probability of interactions when used with different herbs, and to identify safe dosage. The particulars presented here not only bridge this gap but also furnish future research strategies for the investigators in microbiology, ethno-pharmacology, and drug discovery.     

Catalytic Three‐Component Machinery: Control of Catalytic Activity by Machine Speed

Three supramolecular slider‐on‐deck systems DS1 – DS3 were obtained as two‐component aggregates from the sliders S1 – S3 and deck D with its three zinc porphyrin (ZnPor) binding sites. The binding of the two‐footed slider to the deck varies with the donor qualities of and the steric hindrance at the pyridine/pyrimidine (pyr) feet, and was effected by two N_pyr→ZnPor interactions. Accordingly, the sliders move over the three zinc porphyrins in the deck at different speeds, namely with 32.2, 220, and 440 kHz at room temperature. The addition of N‐methylpyrrolidine as an organocatalyst to DS1 – DS3 generates catalytic three‐component machineries. By using a conjugate addition as a probe reaction, we observed a correlation between the operating speed of the slider‐on‐deck systems and the yields of the catalytic reaction. As the thermodynamic binding of the slider decreases, both the frequency of the sliding motion and the yield of the catalytic reaction increase.     

Proton/Metal–Ligand Stability Constants of Complexes of Sr(II), Cr(II), and Al(III) with N-Phthaloyl Aminoacid and Benzimidazole Derivatives in Dioxane–Water Mixture

Russian Journal of Physical Chemistry A - Formation of complexes Sr(II), Cr(II), and Al(III) with ligands (1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)acetic acid (L1),...     

PNIPAAM Grafted Polymeric Monoliths Synthesized by the Reactive Gelation Process and their Swelling/Deswelling Characteristics

The production of macroporous monoliths functionalized with a thermo‐responsive polymer (PNIPAAM) is described. The surface functionalization was achieved by copolymerization of acrylic end capped atom transfer radical polymerization initiator (BPOEA) with divinylbenzene with or without styrene. Monoliths were generated by swelling them with styrene, BPOEA and divinylbenzene followed by gelation with salt and post polymerization. Subsequent grafting of these monoliths with PNIPAAM was achieved by atom transfer radical polymerization and their swelling deswelling characteristics quantified. The grafted monoliths provide a unique chromatographic stationary phase where adsorption/desorption can be driven by the use of temperature only.

     

Adsorption of basic fuchsin using waste materials--bottom ash and deoiled soya--as adsorbents

Basic fuchsin, a triaminotriphenylmethane dye, was removed by adsorption utilizing two waste materials--"bottom ash," a power plant waste material, and "deoiled soya," an agriculture waste product. The adsorbents were characterized through IR spectroscopy and differential thermal analysis (DTA). Batch adsorption experiments were carried out by measuring effects of pH, adsorbate concentration, sieve size, amount of adsorbent, contact time, temperature, etc. The results have been verified on the basis of Langmuir and Freundlich adsorption isotherm models and data obtained have been applied to calculate thermodynamic parameters. Specific rate constants for the processes were calculated by kinetic measurements and a pseudo-second-order adsorption kinetics was observed in each case. To identify whether the ongoing process is particle diffusion or film diffusion, the treatment given by Boyd and Reichenberg was employed. To assess the practical utility of the adsorbent, the aqueous adsorbate samples were eluted through fixed-bed columns of respective adsorbents. Attempts were also made to recover the adsorbed dyes by passing suitable solvent through the columns.     

Physical adsorption of organic molecules on the surface of layered silicate clay platelets: a thermogravimetric study

Physical adsorption of various adsorbents on the surface of premodified montmorillonite platelets was performed to fully organophilize the inorganic platelets for the purpose of their easy nanoscale dispersion in the polymer matrices during compounding. Different extents of adsorption could be achieved owing to the nature and the functionality of the adsorbents. High molecular weight adsorbents not only enhanced the organic coverage of the platelets but also were observed to contribute toward the thermal stability improvement of the organic modification, thus further fitting the use of such clays for high temperature compounding. The amount of adsorption could also be quantified with respect to the initial amount of adsorbent used in the process. The importance of a clean surface free from any excess surface modification or adsorbent molecules was emphasized. The adsorption process is an effective means to generate such high potential montmorillonites and is much simpler in technique than the common methods of grafting of polymer chains from the clay surface.     

Evidence for Multiple Binding Modes in the Initial Contact Between SARS-CoV-2 Spike S1 Protein and Cell Surface Glycans**

Infection of host cells by SARS-CoV-2 begins with recognition by the virus S (spike) protein of cell surface heparan sulfate (HS), tethering the virus to the extracellular matrix environment, and causing the subunit S1-RBD to undergo a conformational change into the ‘open’ conformation. These two events promote the binding of S1-RBD to the angiotensin converting enzyme 2 (ACE2) receptor, a preliminary step toward viral-cell membrane fusion. Combining ligand-based NMR spectroscopy with molecular dynamics, oligosaccharide analogues were used to explore the interactions between S1-RBD of SARS CoV-2 and HS, revealing several low-specificity binding modes and previously unidentified potential sites for the binding of extended HS polysaccharide chains. The evidence for multiple binding modes also suggest that highly specific inhibitors will not be optimal against protein S but, rather, diverse HS-based structures, characterized by high affinity and including multi-valent compounds, may be required.