Knowledge Sharing in Knowledge Economy: An integrated framework for decision making
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The synthesis of the first halogen bonding [3]rotaxane host system containing abis-iodo triazolium-bis-naphthalene diimide four station axle component is reported. Proton NMR anion binding titration experiments revealed the halogen bonding rotaxane is selective for nitrate over the more basic acetate,hydrogen carbonate and dihydrogen phosphate oxoanions and chloride,and exhibits enhanced recognition of anions relative to ah ydrogen bonding analogue.T his elaborate interlocked anion receptor functions via an ovel dynamic pincer mechanism where upon nitrate anion binding,b oth macrocycles shuttle from the naphthalene diimide stations at the periphery of the axle to the central halogen bonding iodotriazolium station anion recognition sites to form aunique 1:1 stoichiometric nitrate anion-rotaxane sandwich complex. Molecular dynamics simulations carried out on the nitrate and chloride halogen bonding [3]rotaxane complexes corroborate the 1 HNMR anion binding results.The prevalence of negatively charged species in biology and in the environment has deemed the development of synthetic anion receptors capable of their strong and selective recognition an important field of chemical research. [1][2][3] Thenitrate anion in particular is an environmental pollutant when leeched into lakes and rivers resulting from anthropogenic overuse of fertilizers or by acid rain.[4] Medically,a no ver exposure to nitrate via contaminated drinking water is associated with the formation of carcinogenic nitrosamines and ar ange of diseases such as methemoglobinemia (blue baby syndrome) in infants. [5] Thedesign of synthetic receptors capable of the selective recognition of nitrate is ac hallenge because of the anions inherent low affinity for hydrogen bonds and high energy of solvation.[6] To date only arelatively small number of nitrateselective tripodal acyclic,m acrocyclic and cage-like host systems have been reported that utilise convergent hydrogen bonding (HB) and/or anion-p interactions to recognise the oxoanion in polar organic solvents. [7][8][9][10][11][12][13][14][15][16][17][18][19] Thec hallenge of developing synthetic receptors that can rival the anion recognition properties of biotic systems relies upon the arrangement of at hree-dimensional convergent array of numerous HB donor groups in an optimized geometry for recognition of the complementary guest. [20,21] To meet this challenge we have exploited anion-templation to construct interlocked host structures [22,23] whose unique threedimensional cavities encapsulate anionic guest species.While during the past two decades HB has been widely exploited in anion receptor design, halogen bonding (XB), [24][25][26][27] the attractive highly directional interaction between an electron-deficient halogen atom and aL ewis base,h as only recently begun to be utilised for anion recognition. Of the relatively few examples of XB anion receptors reported to date,i ti sn oteworthy that all display promising,a nd significantly contrasting, anion recognition behaviour when compared ...
The synthesis of the first halogen bonding [3]rotaxane host system containing abis-iodo triazolium-bis-naphthalene diimide four station axle component is reported. Proton NMR anion binding titration experiments revealed the halogen bonding rotaxane is selective for nitrate over the more basic acetate,hydrogen carbonate and dihydrogen phosphate oxoanions and chloride,and exhibits enhanced recognition of anions relative to ah ydrogen bonding analogue.T his elaborate interlocked anion receptor functions via an ovel dynamic pincer mechanism where upon nitrate anion binding,b oth macrocycles shuttle from the naphthalene diimide stations at the periphery of the axle to the central halogen bonding iodotriazolium station anion recognition sites to form aunique 1:1 stoichiometric nitrate anion-rotaxane sandwich complex. Molecular dynamics simulations carried out on the nitrate and chloride halogen bonding [3]rotaxane complexes corroborate the 1 HNMR anion binding results.The prevalence of negatively charged species in biology and in the environment has deemed the development of synthetic anion receptors capable of their strong and selective recognition an important field of chemical research. [1][2][3] Thenitrate anion in particular is an environmental pollutant when leeched into lakes and rivers resulting from anthropogenic overuse of fertilizers or by acid rain.[4] Medically,a no ver exposure to nitrate via contaminated drinking water is associated with the formation of carcinogenic nitrosamines and ar ange of diseases such as methemoglobinemia (blue baby syndrome) in infants. [5] Thedesign of synthetic receptors capable of the selective recognition of nitrate is ac hallenge because of the anions inherent low affinity for hydrogen bonds and high energy of solvation.[6] To date only arelatively small number of nitrateselective tripodal acyclic,m acrocyclic and cage-like host systems have been reported that utilise convergent hydrogen bonding (HB) and/or anion-p interactions to recognise the oxoanion in polar organic solvents. [7][8][9][10][11][12][13][14][15][16][17][18][19] Thec hallenge of developing synthetic receptors that can rival the anion recognition properties of biotic systems relies upon the arrangement of at hree-dimensional convergent array of numerous HB donor groups in an optimized geometry for recognition of the complementary guest. [20,21] To meet this challenge we have exploited anion-templation to construct interlocked host structures [22,23] whose unique threedimensional cavities encapsulate anionic guest species.While during the past two decades HB has been widely exploited in anion receptor design, halogen bonding (XB), [24][25][26][27] the attractive highly directional interaction between an electron-deficient halogen atom and aL ewis base,h as only recently begun to be utilised for anion recognition. Of the relatively few examples of XB anion receptors reported to date,i ti sn oteworthy that all display promising,a nd significantly contrasting, anion recognition behaviour when compared ...
Thiazole‐Based σ1 Receptor Ligands: Diversity by Late‐Stage C−H Arylation of Thiazoles, Structure–Affinity and Selectivity Relationships, and Molecular Interactions
Spirocyclic thiophene derivatives represent promising σ ligands with high σ affinity and selectivity over the σ subtype. To increase ligand efficiency, the thiophene ring was replaced bioisosterically by a thiazole ring, and the pyran ring was opened. Late-stage diversification by regioselective C-H arylation of thiazoles 9 a-c resulted in a set of 53 compounds with high diversity. This set of compounds was analyzed with respect to σ affinity, σ /σ selectivity, lipophilicity (logD ), lipophilicity-corrected ligand efficiency (LELP), and molecular target interactions. The most promising candidates were pyridyl-substituted thiazole derivatives 33 c (2-(1-benzyl-4-ethoxypiperidin-4-yl)-5-(pyridin-3-yl)thiazole) and 34 c (2-(1-benzyl-4-ethoxypiperidin-4-yl)-5-(pyridin-4-yl)thiazole), possessing low-nanomolar σ affinity (K =1.3 and 1.9 nm), high σ /σ selectivity (>1500-fold), low lipophilicity (logD =1.8) and very good ligand efficiency (LELP=5.5), indicating promising pharmacodynamics and pharmacokinetics. Molecular simulation studies, including docking and deconvolution of the free binding energy into its major components, led to decreased hydrophobic stabilization of pyridyl derivatives 33 c and 34 c, which was compensated by lower desolvation energy.
Role of the Chalcogen (S, Se, Te) in the Oxidation Mechanism of the Glutathione Peroxidase Active Site
The oxidation by H O of the human phospholipid hydroperoxide glutathione peroxidase (GPx4), used as a model peroxidase selenoenzyme, as well as that of its cysteine (Cys) and tellurocysteine (Tec) mutants, was investigated in silico through a combined classic and quantum mechanics approach to assess the role of the different chalcogens. To perform this analysis, new parameters for selenocysteine (Sec) and tellurocysteine (Tec) were accurately derived for the AMBER ff14SB force field. The oxidation represents the initial step of the antioxidant activity of GPx, which catalyzes the reduction of H O and organic hydroperoxides by glutathione (GSH). A mechanism involving a charge-separation intermediate is feasible for the Cys and Sec enzymes, leading from the initial thiol/selenol form to sulfenic/selenenic acid, whereas for the Tec mutant a direct oxidation pathway is proposed. Activation strain analyses, performed for Cys-GPx and Sec-GPx, provided insight into the rate-accelerating effect of selenium as compared to sulfur and the role of specific amino acids other than Cys/Sec that are typically conserved in the catalytic pocket.
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