NMR Structure of a Triangulenium‐Based Long‐Lived Fluorescence Probe Bound to a G‐Quadruplex

An NMR structural study of the interaction between a small‐molecule optical probe (DAOTA‐M2) and a G‐quadruplex from the promoter region of the c‐myc oncogene revealed that they interact at 1:2 binding stoichiometry. NMR‐restrained structural calculations show that binding of DAOTA‐M2 occurs mainly through π–π stacking between the polyaromatic core of the ligand and guanine residues of the outer G‐quartets. Interestingly, the binding affinities of DAOTA‐M2 differ by a factor of two for the outer G‐quartets of the unimolecular parallel G‐quadruplex under study. Unrestrained MD calculations indicate that DAOTA‐M2 displays significant dynamic behavior when stacked on a G‐quartet plane. These studies provide molecular guidelines for the design of triangulenium derivatives that can be used as optical probes for G‐quadruplexes.     

A Range-Compaction Heuristic for Graph Coloring

This paper presents a novel heuristic for graph coloring that works on a range of colors and iteratively tries to make this range more compact. This range-compaction heuristic also has a pressure component and an annealing schedule for it. The value of this component is empirically quantified. This algorithm is evaluated on a wide range of DIMACS benchmark graphs, and found to be competitive with state-of-the-art algorithms in terms of solution quality and run time.     

Transition metal complexes of amidinourea and related ligands part III. Infrared spectra and thermal decomposition studies on metal complexes of O-alkyl-1-amidinoureas

Summary The i.r. spectral data on O-methyl-l-amidinourea hydrochloride,O-ethyl-1-amid inourea hydrochloride and the metal complexes [M = copper(H), nickel(II), palladium(II), zinc(II) and oxovanadium(IV)] ofO-methyl-l-amid inourea andO-ethyl-l-amidinourea are reported. The spectral results suggest that secondary amine nitrogens are the donor atoms inO-alkyl-1-amid inourea. The free ligands and the complexes exhibit a characteristic band at ca. 1100 cm^–1 due to the C-OR group. The i.r. and electronic spectral data on the hydrated and anhydrous uncharged metal complexes indicate that the hydrated uncharged metal complexes ofO-alkyl-l-amidinourea may be represented as [M(AAU)_n]] · xH₂0 and not as [M(AAUII)_n](OH)_n · xH₂O [where AAU = H₂NC(=NH)NC(=NH)OR and AAUH = H₂NC(=NH)NHC(=NH)OR, R = Me, Et]. The use of the term anhydrobase is confusing and suitable names for various metal complexes ofO-alkyl-l-amid inourea are suggested. The main decomposition stage in metal complexes ofO-ethyl-l-amidinourea occurs at lower temperatures than for the corresponding biguanide complexes indicating that the former are less stable than the latter.     

Conversion of colloidal aggregates into polymer networks on aging

After long-term aging, surfactant-mediated colloidal aggregates of sulfonated polyaniline (S-PANI) and poly(vinylidene fluoride) (PVF₂) converted into three-dimensional polymer networks, whereas colloidal crystals prepared from pure PVF₂ remained unaltered. A model, where the surfactant tails anchored from the colloidal particles interdigitate with time resulting in coalescence of the particles to form the network morphology, has been proposed. X-ray photoelectron spectroscopy (XPS) revealed higher relative abundances of carbon atoms on the surface of the polymer networks than those of the colloidal aggregates, which adequately supports the proposed model.     

Interactive influence and optimization of reaction parameters in the hydrolysis of olive and coconut triacylglycerols byC. cylindracea andR. javanicus lipases in reverse micellar media

The four reaction parameters—pH, reaction temperature, molar ratio (R) of water to surfactant, and Aerosol-OT concentration—have significant linear, quadratic., and interactive effects on the initial rate and the degree of hydrolysis for lipase-mediated hydrolysis of triacylglycerols (TAG) in Aerosol-OT/iso-octane reverse micellar media. Reaction temperature and pH had the most significant influence on the rate and the degree of hydrolysis, whereas Aerosol-OT concentration had the least influence on those parameters. The initial rate was most influenced by the interactive effect of pH with all other variables, whereas the degree of hydrolysis was the most influenced by the interactive effect of reaction temperature with other variables. Lowerlevel variable combinations were favorable over higher-level variable combinations to TAG hydrolysis in reverse micellar media. Regression models, developed for the initial rate and the degree of hydrolysis as a function of reaction variables, accounted for up to 96% of the variation in the two responses. The optimum reaction condition ranges were determined based on maximization of both the rate and the degree of hydrolysis. The differences in the physicochemical characteristics of substrates had no significant effect on the optimum condition ranges. However, the noticeable differences were observed for these ranges between the systems withRhizopus javanicus andCandida cylindracea lipases. Lipase-catalyzed hydrolysis of TAG in Aerosol-OT/iso-octane reverse micellar media was optimum at about 22‡C, 140 mM Aerosol-OT concentration, pH 6.8, andR value of 14.     

Synthesis of covalent probes for the radiolabeling of the cannabinoid receptor

The main psychoactive constituent of marijuana, (-)-Delta(9)-tetrahydrocannabinol, produces most of its physiological effects by interacting with the CB1 cannabinoid receptor, a membrane protein belonging to the large superfamily of G-protein coupled receptors. The 3-D structure of the receptor binding site is of value in the design of novel medications for a variety of therapeutic indications. To obtain information on the amino acid residues associated with this binding site, we have designed and synthesized a cannabinergic CB1 ligand prototype carrying an electrophilic isothiocyanato group capable of reacting covalently with amino acid residues bearing thiol or unprotonated amino groups. The ligand also incorporates an iodide atom, which can serve as a high-activity radiolabel. The key step in our synthesis involves a rapid intramolecular Diels-Alder reaction of a transiently formed o-quinone methide, which proceeds stereospecifically with the formation of the tricyclic cannabinoid template. Introduction of the iodo group is the last step in the sequence and is compatible with the use of (125)I-radiolabel.     

Chromatographic separation of ions in presence of oxalate,tartrate and citrate,with aqueous ethanol as solvent

The paper Chromatographic separation of Ag, Hg, Pb, Bi, Cu, Cd, Co, As(III), Sb(III) and Sn(II) in mixtures of 3, 4 or 5 of these ions has been studied in the absence and presence of oxalate, citrate and tartrate with aqueous ethanol as solvent.     

Size extensive modification of local multireference configuration interaction

We recently developed a reduced scaling multireference configuration interaction (MRCI) method based on local correlation in the internal (occupied) and external (virtual) orbital spaces. This technique can be used, e.g., to predict bond dissociation energies in large molecules with reasonable accuracy. However, the inherent lack of size extensivity of truncated CI is a disadvantage that in principle worsens as the system size grows. Here we implement an a priori size-extensive modification of local MRCI known as the averaged coupled pair functional (ACPF) method. We demonstrate that local MR-ACPF recovers more correlation energy than local MRCI, in keeping with trends observed previously for nonlocal ACPF. We test the size extensivity of local ACPF on noninteracting He atoms and a series of hydrocarbons. Basis set and core correlation effects are explored, as well as bond breaking in a variety of organic molecules. The local MR-ACPF method proves to be a useful tool for investigating large molecules and represents a further improvement in predictive accuracy over local MRCI.     

Alkyne-Tagged Apigenin,a Chemical Tool to Navigate Potential Targets of Flavonoid Anti-Dengue Leads

A flavonoid is a versatile core structure with various cellular, immunological, and pharmacological effects. Recently, flavones have shown anti-dengue activities by interfering with viral translation and replication. However, the molecular target is still elusive. Here we chemically modified apigenin by adding an alkyne moiety into the B-ring hydroxyl group. The alkyne serves as a chemical tag for the alkyne-azide cycloaddition reaction for subcellular visualization. The compound located at the perinuclear region at 1 and 6 h after infection. Interestingly, the compound signal started shifting to vesicle-like structures at 6 h and accumulated at 24 and 48 h after infection. Moreover, the compound treatment in dengue-infected cells showed that the compound restricted the viral protein inside the vesicles, especially at 48 h. As a result, the dengue envelope proteins spread throughout the cells. The alkyne-tagged apigenin showed a more potent efficacy at the EC₅₀ of 2.36 ± 0.22, and 10.55 ± 3.37 µM, respectively, while the cytotoxicities were similar to the original apigenin at the CC₅₀ of 70.34 ± 11.79, and 82.82 ± 11.68 µM, respectively. Molecular docking confirmed the apigenin binding to the previously reported target, ribosomal protein S9, at two binding sites. The network analysis, homopharma, and molecular docking revealed that the estrogen receptor 1 and viral NS1 were potential targets at the late infection stage. The interactions could attenuate dengue productivity by interfering with viral translation and suppressing the viral proteins from trafficking to the cell surface.