Intramolecular Ligation of Carbonyl Oxygen to Central Zinc in Synthetic Oligopeptide-Linked Zinc-Porphyrins

1994 ◽  
Vol 67 (9) ◽  
pp. 2478-2486 ◽  
Author(s):  
Hitoshi Tamiaki ◽  
Ayumu Kiyomori ◽  
Kazuhiro Maruyama
Keyword(s):  
Carbonyl Oxygen ◽  
Zinc Porphyrins ◽  
Intramolecular Ligation

Participation of 19-ester groups in the cleavage of 2α,3α- and 5α,6α-steroid epoxides. A case of competition between participation and external nucleophile attack

1979 ◽  
Vol 44 (5) ◽  
pp. 1496-1509 ◽  
Author(s):  
Pavel Kočovský ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Hydrobromic Acid ◽  
Ester Group ◽  
Carbonyl Oxygen ◽  
Cyclic Carbonate ◽  
Cyclic Ether ◽  
Normal Reaction ◽  
Neighboring Group ◽  
Ether Oxygen ◽  
The Difference

Acid cleavage of the acetoxy epoxide IIIa with aqueous perchloric acid or hydrobromic acid gave two types of products, i.e. the diol Va or the bromohydrin VIa, and the cyclic ether VIII. The latter compound arises by participation of ether oxygen of the ester group. On reaction with perchloric acid the epoxide IVa gave the diol XIIIa as a product of a normal reaction and the isomeric diol Xa as a product arising by intramolecular participation of the carbonyl oxygen of the 19-acetoxy group. Participation of the 19-ester group is confirmed by the formation of the cyclic carbonate XI when the 19-carbonate IVb is treated analogously. On reaction with hydrobromic acid, the epoxide IVa gave solely the bromohydrin XIVa as a product of the normal reaction course. Discussed is the similarity of these reactions with electrophilic additions to the related 19-acetoxy olefins I and II, the mechanism, the difference in behavior of both epoxides III and IV, the dependence of the product ratio on the nucleophility of the attacking species, and the competition between participation of an ambident neighboring group and an external nucleophile attack.

Conformation and electronic structure of aromatic chloroformates

1987 ◽  
Vol 52 (4) ◽  
pp. 970-979 ◽  
Author(s):  
Otto Exner ◽  
Pavel Fiedler
Keyword(s):  
Electronic Structure ◽  
Oxygen Atom ◽  
Strong Interaction ◽  
Electron Distribution ◽  
Room Temperature ◽  
Functional Group ◽  
Dipole Moments ◽  
Carbonyl Oxygen ◽  
Nonpolar Solvents ◽  
Single Method

Aromatic chloroformates Ib-Ie were shown to exist in the ap conformation, in agreement with aliphatic chloroformates, i.e. the alkyl group is situated cis to the carbonyl oxygen atom as it is the case in all esters. While 4-nitrophenyl chloroformate (Ie) is in this conformation in crystal, in solution at most several tenths of percent of the sp conformation may be populated at room temperature and in nonpolar solvents only. A new analysis of dipole moments explained the previous puzzling results and demonstrated the impossibility to determine the conformation by this single method, in consequence of the strong interaction of adjoining bonds. If, however, the ap conformation is once proven, the dipole moments reveal some features of the electron distribution on the functional group, characterized by the enhanced polarity of the C-Cl bond and reduced polarity of the C=O bond. This is in agreement with the observed bond lengths and angles.

Structure Investigations of Agonists of the Natural Neurotransmitter Acetylcholine, IV [1]. X-Ray Structure Analyses of Trimethylpentylammonium-chloride and (4-Acetoxybutyl) trimethylammonium-iodide

1986 ◽  
Vol 41 (5-6) ◽  
pp. 618-626
Author(s):  
Alfred Gieren ◽  
Michail Kokkinidis
Keyword(s):  
Structure Refinement ◽  
Pharmacological Action ◽  
Ammonium Nitrogen ◽  
Carbonyl Oxygen ◽  
Type B ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Structure Investigations ◽  
Automatic Diffractometer

The crystal structures of the title compounds which display cholinergic activity at the ganglionic receptor have been determined by X-ray structure analysis. [(CH3)3N+C5H11]Cl- (1) crystallizes in the orthorhombic space group Pbnm with half a formula unit per asymmetric unit, a = 11.381(14). b = 12.871(17), c = 7.316(4) Å. The intensities of 1106 independent reflections were collected with an automatic diffractometer. The structure refinement converged at R = 0.133 for the 355 observed reflections. The cation of 1 is disordered. [(CH3)3N + (CH2)4-O-C(O)-CH3]I- (2) crystallizes in the orthorhombic space group P212121 with four formula units per unit cell, a = 16.783(8), b = 10.276(6), c = 7.427(10) Å. The intensities of 1469 independent reflections were collected. The structure refinement converged at R = 0.071 for 1383 observed reflections. In both compounds the trimethylammonio methyl groups are coordinated nearly tetrahedrally by four anions in the first coordination sphere. Anions which occupy a special face type (B) of the tetrahedron of the (CH3)3N+ -CH2-group may be treated as a “model binding site” of the receptor. In the crystal structure of 2 the anions occupying B-type faces form together with the ammonium nitrogen and the carbonyl oxygen so called “Activity triangles”. The almost equal geometries of these activity triangles are correlated with the mode of pharmacological action.

scholarly journals Photoprotective Properties of Eumelanin: Computational Insights into the Photophysics of a Catechol:Quinone Heterodimer Model System

Photochem ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 26-37
Author(s):  
Victoria C. Frederick ◽  
Thomas A. Ashy ◽  
Barbara Marchetti ◽  
Michael N. R. Ashfold ◽  
Tolga N. V. Karsili
Keyword(s):  
Ground State ◽  
Sandwich Structure ◽  
Computational Study ◽  
Minimum Energy ◽  
Carbonyl Oxygen ◽  
Model System ◽  
Molecular Structures ◽  
Uv Damage ◽  
Chromosomal Dna ◽  
Relevant Model

Melanins are skin-centered molecular structures that block harmful UV radiation from the sun and help protect chromosomal DNA from UV damage. Understanding the photodynamics of the chromophores that make up eumelanin is therefore paramount. This manuscript presents a multi-reference computational study of the mechanisms responsible for the experimentally observed photostability of a melanin-relevant model heterodimer comprising a catechol (C)–benzoquinone (Q) pair. The present results validate a recently proposed photoinduced intermolecular transfer of an H atom from an OH moiety of C to a carbonyl-oxygen atom of the Q. Photoexcitation of the ground state C:Q heterodimer (which has a π-stacked “sandwich” structure) results in population of a locally excited ππ* state (on Q), which develops increasing charge-transfer (biradical) character as it evolves to a “hinged” minimum energy geometry and drives proton transfer (i.e., net H atom transfer) from C to Q. The study provides further insights into excited state decay mechanisms that could contribute to the photostability afforded by the bulk polymeric structure of eumelanin.

scholarly journals Crystal structure of atazanavir, C38H52N6O7

2020 ◽  
Vol 35 (2) ◽  
pp. 129-135
Author(s):  
James A. Kaduk ◽  
Amy M. Gindhart ◽  
Thomas N. Blanton
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Powder Diffraction ◽  
Density Functional ◽  
Carbonyl Oxygen ◽  
Hydroxyl Group ◽  
Amide Nitrogen ◽  
Classical Hydrogen Bond ◽  
Intramolecular Hydrogen ◽  
Atazanavir Sulfate

The crystal structure of atazanavir has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Atazanavir crystallizes in space group P21 (#4) with a = 15.33545(7), b = 5.90396(3), c = 21.56949(13) Å, β = 96.2923(4)°, V = 1941.134(11) Å3, and Z = 2. Despite being labeled as “atazanavir sulfate”, the commercial reagent sample consisted of atazanavir free base. The structure consists of an array of extended-conformation molecules parallel to the ac-plane. Although the atazanavir molecule contains only four classical hydrogen bond donors, hydrogen bonding is, surprisingly, important to the crystal energy. Both intra- and intermolecular hydrogen bonds are significant. The hydroxyl group forms bifurcated intramolecular hydrogen bonds to a carbonyl oxygen atom and an amide nitrogen. Several amide nitrogens act as donors to the hydroxyl group and carbonyl oxygen atoms. An amide nitrogen acts as a donor to another amide nitrogen. Several methyl, methylene, methyne, and phenyl hydrogens participate in hydrogen bonds to carbonyl oxygens, an amide nitrogen, and the pyridine nitrogen. The powder pattern is included in the Powder Diffraction File™ as entry 00-065-1426.

scholarly journals Crystal structure of (Z)-1-(3,4-dichlorophenyl)-3-methyl-4-[(naphthalen-1-ylamino)(p-tolyl)methylidene]-1H-pyrazol-5(4H)-one

2014 ◽  
Vol 70 (9) ◽  
pp. o955-o956 ◽  
Author(s):  
Naresh Sharma ◽  
Sanjay Parihar ◽  
R. N. Jadeja ◽  
Rajni Kant ◽  
Vivek K. Gupta
Keyword(s):  
Benzene Ring ◽  
Three Dimensional ◽  
Pyrazole Ring ◽  
Carbonyl Oxygen ◽  
Ring System ◽  
Dimensional Structure ◽  
Naphthalene Ring ◽  
Compound C ◽  
Schiff Base Compound ◽  
Base Compound

The title Schiff base compound, C28H21Cl2N3O, was synthesized by the condensation of 1-(3,4-dichlorophenyl)-3-methyl-4-(4-methylbenzoyl)-1H-pyrazol-5(4H)-one with 1-aminonaphthalene. Thep-tolyl ring is normal to the pyrazole ring, with a dihedral angle of 88.02 (14)°, and inclined to the naphthalene ring system by 78.60 (12)°. The pyrazole ring is inclined to the naphthalene ring system and the dichloro-substituted benzene ring by 63.30 (12) and 11.03 (13)°, respectively. The amino group and carbonyl oxygen atom are involved in an intramolecular N—H...O hydrogen bond enclosing anS(6) ring motif. There is also a short C—H...O contact involving the carbonyl O atom and the adjacent benzene ring. In the crystal, molecules are linked by C—H...π interactions, forming a three-dimensional structure.

scholarly journals The Fluorescence Quenching of Zinc Porphyrins with the ω-[4-(4-Pyridyl)pyridinio]alkyl Group

1989 ◽  
Vol 62 (10) ◽  
pp. 3069-3074 ◽  
Author(s):  
Kohshin Takahashi ◽  
Tetsuo Terashima ◽  
Teruhisa Komura ◽  
Hiroto Imanaga
Keyword(s):  
Fluorescence Quenching ◽  
Alkyl Group ◽  
Zinc Porphyrins

scholarly journals Mechanism of tubulin–colchicine recognition: a kinetic study of the binding of the colchicine analogues colchicide and isocolchicine

1997 ◽  
Vol 327 (3) ◽  
pp. 685-688 ◽  
Author(s):  
Chantal DUMORTIER ◽  
Qunying YAN ◽  
Susan BANE ◽  
Yves ENGELBORGHS
Keyword(s):  
Rate Constant ◽  
Total Concentration ◽  
Carbonyl Oxygen ◽  
Protein Fluorescence ◽  
Kinetic And Thermodynamic Parameters ◽  
Methoxy Groups ◽  
Displacement Experiments ◽  
Absorbance Changes ◽  
Initial Binding

Colchicide (IDE) is a colchicine (COL) analogue in which the C-10 methoxy group is replaced by a hydrogen atom. Its binding to tubulin is accompanied by a quenching of the protein fluorescence. The fluorescence decrease shows a monoexponential time dependence. The observed rate constant increases in a non-linear way with the total concentration of IDE, allowing the determination of a binding constant for an initial binding site (K1 = 5300±300 M-1) and the rate constant for the subsequent isomerization (k2 = 0.071±0.002 s-1) at 25 °C. The rate constant, k-2, for the reversed isomerization can be determined by displacement experiments. Despite the minor alteration of the C-ring substituent, the kinetic and thermodynamic parameters of binding are substantially different from those of COL itself, for both steps. In isocolchicine (ISO) the carbonyl oxygen atom and the methoxy groups of the C-ring have been interchanged. Its binding to tubulin only results in small fluorescence and absorbance changes. Therefore competition experiments with MTC [2-methoxy-5-(2ʹ,3ʹ,4ʹ-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-one] were performed. ISO competes rapidly and with low affinity with MTC. Fluorimetric titrations of tubulin with MDL (MDL 27048 or trans-1-(2,5 dimethoxyphenyl)-3-[4-(dimethylamino)phenyl]-2-methyl-2-propen-1-one) in the presence and absence of ISO give evidence for the existence of a second, slow-reacting low-affinity site for ISO that is not accessible to MTC or MDL. The relevance of these results for the recognition of COL is analysed.

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