The Experts below are selected from a list of 5010 Experts worldwide ranked by ideXlab platform
Rodney Croteau - One of the best experts on this subject based on the ideXlab platform.
-
Bifunctional abietadiene synthase: free diffusive transfer of the (+)-copalyl diphosphate intermediate between two distinct active sites.
Journal of the American Chemical Society, 2001Co-Authors: Reuben J. Peters, Robert M Coates, Matthew M. Ravn, Rodney CroteauAbstract:Abietadiene synthase (AS) catalyzes two sequential, mechanistically distinct cyclizations in the conversion of geranylgeranyl diphosphate to a mixture of abietadiene double bond isomers as the initial step of resin acid biosynthesis in grand fir (Abies grandis). The first reaction converts geranylgeranyl diphosphate to the stable bicyclic intermediate (+)-copalyl diphosphate via protonation-initiated cyclization. In the second reaction, diphosphate ester ionization-initiated cyclization generates the tricyclic perhydrophenanthrene-type backbone, and is directly coupled to a 1,2-methyl migration that generates the C13 Isopropyl Group characteristic of the abietane family of diterpenes. Using the transition-state analogue inhibitor 14,15-dihydro-15-azageranylgeranyl diphosphate, it was demonstrated that each reaction of abietadiene synthase is carried out at a distinct active site. Mutations in two aspartate-rich motifs specifically delete one or the other activity and the location of these motifs suggests ...
-
bifunctional abietadiene synthase free diffusive transfer of the copalyl diphosphate intermediate between two distinct active sites
Journal of the American Chemical Society, 2001Co-Authors: Reuben J. Peters, Robert M Coates, Matthew M. Ravn, Rodney CroteauAbstract:Abietadiene synthase (AS) catalyzes two sequential, mechanistically distinct cyclizations in the conversion of geranylgeranyl diphosphate to a mixture of abietadiene double bond isomers as the initial step of resin acid biosynthesis in grand fir (Abies grandis). The first reaction converts geranylgeranyl diphosphate to the stable bicyclic intermediate (+)-copalyl diphosphate via protonation-initiated cyclization. In the second reaction, diphosphate ester ionization-initiated cyclization generates the tricyclic perhydrophenanthrene-type backbone, and is directly coupled to a 1,2-methyl migration that generates the C13 Isopropyl Group characteristic of the abietane family of diterpenes. Using the transition-state analogue inhibitor 14,15-dihydro-15-azageranylgeranyl diphosphate, it was demonstrated that each reaction of abietadiene synthase is carried out at a distinct active site. Mutations in two aspartate-rich motifs specifically delete one or the other activity and the location of these motifs suggests ...
Reuben J. Peters - One of the best experts on this subject based on the ideXlab platform.
-
Bifunctional abietadiene synthase: free diffusive transfer of the (+)-copalyl diphosphate intermediate between two distinct active sites.
Journal of the American Chemical Society, 2001Co-Authors: Reuben J. Peters, Robert M Coates, Matthew M. Ravn, Rodney CroteauAbstract:Abietadiene synthase (AS) catalyzes two sequential, mechanistically distinct cyclizations in the conversion of geranylgeranyl diphosphate to a mixture of abietadiene double bond isomers as the initial step of resin acid biosynthesis in grand fir (Abies grandis). The first reaction converts geranylgeranyl diphosphate to the stable bicyclic intermediate (+)-copalyl diphosphate via protonation-initiated cyclization. In the second reaction, diphosphate ester ionization-initiated cyclization generates the tricyclic perhydrophenanthrene-type backbone, and is directly coupled to a 1,2-methyl migration that generates the C13 Isopropyl Group characteristic of the abietane family of diterpenes. Using the transition-state analogue inhibitor 14,15-dihydro-15-azageranylgeranyl diphosphate, it was demonstrated that each reaction of abietadiene synthase is carried out at a distinct active site. Mutations in two aspartate-rich motifs specifically delete one or the other activity and the location of these motifs suggests ...
-
bifunctional abietadiene synthase free diffusive transfer of the copalyl diphosphate intermediate between two distinct active sites
Journal of the American Chemical Society, 2001Co-Authors: Reuben J. Peters, Robert M Coates, Matthew M. Ravn, Rodney CroteauAbstract:Abietadiene synthase (AS) catalyzes two sequential, mechanistically distinct cyclizations in the conversion of geranylgeranyl diphosphate to a mixture of abietadiene double bond isomers as the initial step of resin acid biosynthesis in grand fir (Abies grandis). The first reaction converts geranylgeranyl diphosphate to the stable bicyclic intermediate (+)-copalyl diphosphate via protonation-initiated cyclization. In the second reaction, diphosphate ester ionization-initiated cyclization generates the tricyclic perhydrophenanthrene-type backbone, and is directly coupled to a 1,2-methyl migration that generates the C13 Isopropyl Group characteristic of the abietane family of diterpenes. Using the transition-state analogue inhibitor 14,15-dihydro-15-azageranylgeranyl diphosphate, it was demonstrated that each reaction of abietadiene synthase is carried out at a distinct active site. Mutations in two aspartate-rich motifs specifically delete one or the other activity and the location of these motifs suggests ...
Tayur N. Guru Row - One of the best experts on this subject based on the ideXlab platform.
-
Partial rotation of the Isopropyl Group in the solid state: single-crystal-to-single-crystal phase transformation in a carvacrol derivative
CrystEngComm, 2015Co-Authors: Umesh D. Pete, Amol G. Dikundwar, Vaishali Sharma, Shridhar P. Gejji, Ratnamala S. Bendre, Tayur N. Guru RowAbstract:A hitherto unseen rotation of the Isopropyl Group in the solid state, predicted to be forbidden based on theoretical investigations, is reported. This C–C rotation observed during the temperature dependent single-crystal-to-single-crystal transformation is attributed to the concomitant changes in molecular structure and intermolecular packing.
Ilona Turowska-tyrk - One of the best experts on this subject based on the ideXlab platform.
-
Structural Transformations in Crystals Induced by Radiation and Pressure. Part 7. Molecular and Crystal Geometries as Factors Deciding about Photochemical Reactivity under Ambient and High Pressures
Crystals, 2018Co-Authors: Krzysztof Konieczny, Julia Bąkowicz, Tomasz Galica, Arkadiusz Ciesielski, Ilona Turowska-tyrkAbstract:We studied the photochemical reactivity of salts of 4-(2,4,6-triIsopropylbenzoyl)benzoic acid with propane-1,2-diamine (1), methanamine (2), cyclohexanamine (3), and morpholine (4), for compounds (1), (3), and (4) at 0.1 MPa and for compounds (1) and (2) at 1.3 GPa and 1.0 GPa, respectively. The changes in the values of the unit cell parameters after UV irradiation and the values of the intramolecular geometrical parameters indicated the possibility of the occurrence of the Norrish–Yang reaction in the case of all the compounds. The analysis of the intramolecular geometry and free spaces revealed which o-Isopropyl Group takes part in the reaction. For (1), the same o-Isopropyl Group should be reactive at ambient and high pressures. In the case of (2), high pressure caused the phase transition from the space Group I2/a with one molecule in the asymmetric unit cell to the space Group P1¯ with two asymmetric molecules. The analysis of voids indicated that the Norrish–Yang reaction is less probable for one of the two molecules. For the other molecule, the intramolecular geometrical parameters showed that except for the Norrish–Yang reaction, the concurrent reaction leading to the formation of a five-membered ring can also proceed. In (3), both o-Isopropyl Groups are able to react; however, the bigger volume of a void near 2-Isopropyl may be the factor determining the reactivity. For (4), only one o-Isopropyl should be reactive.
-
Photoinduced Structural Changes as the Factor Influencing the Direction of the Photochemical Reaction in the Crystal
Crystal Growth & Design, 2017Co-Authors: Krzysztof Konieczny, Julia Bąkowicz, Renata Siedlecka, Tomasz Galica, Ilona Turowska-tyrkAbstract:The path of the Norrish–Yang reaction of methylammonium 4-(2,4,6-triIsopropylbenzoyl)benzoate was studied by means of X-ray structure analysis. The following parameters influenced by this photochemical reaction were monitored: (a) intramolecular distances and angles in the reaction center, (b) the size of the free space near the reactive atoms, (c) the mutual orientation of molecular fragments, (d) the cell parameters, and (e) the product content. Product molecules were created in two modes, namely, by the reaction of the 2-Isopropyl or 6-Isopropyl Group, which has not been revealed previously for other 2,4,6-triIsopropylbenzophenones. The 2-Isopropyl Group took part in the photochemical reaction during the whole crystal transformation, whereas the reaction of the 6-Isopropyl Group started with a delay and ceased before the total crystal conversion. The reason for such behavior was explained by the analysis of changes in the free space near both o-Isopropyl Groups with the crystal phototransformation.
Peter A. Beckmann - One of the best experts on this subject based on the ideXlab platform.
-
The quenching of Isopropyl Group rotation in van der Waals molecular solids
The Journal of chemical physics, 2008Co-Authors: Xianlong Wang, Arnold L. Rheingold, Antonio G. Dipasquale, Frank B. Mallory, Clelia W. Mallory, Peter A. BeckmannAbstract:X-ray diffraction experiments are employed to determine the molecular and crystal structure of 3-Isopropylchrysene. Based on this structure, electronic structure calculations are employed to calculate methyl Group and Isopropyl Group rotational barriers in a central molecule of a ten-molecule cluster. The two slightly inequivalent methyl Group barriers are found to be 12 and 15kJmol−1 and the Isopropyl Group barrier is found to be about 240kJmol−1, meaning that Isopropyl Group rotation is completely quenched in the solid state. For comparison, electronic structure calculations are also performed in the isolated molecule, determining both the structure and the rotational barriers, which are determined to be 15kJmol−1 for both the Isopropyl Group and the two equivalent methyl Groups. These calculations are compared with, and are consistent with, previously published NMR H1 spin-lattice relaxation experiments where it was found that the barrier for methyl Group rotation was 11±1kJmol−1 and that the barrier f...
