The Influence of the Leaving Tendency of the Phenoxy Group on the Ammonolysis and Hydrolysis of Substituted Phenyl Acetates

1960 ◽  
Vol 82 (12) ◽  
pp. 3067-3071 ◽  
Author(s):  
Thomas C. Bruice ◽  
Mahmood F. Mayahi
Keyword(s):  
Phenoxy Group ◽  
Hydrolysis Of

Synthesis, structure, and hydrolysis of esters of strained and unstrained N-phosphonylureas

1987 ◽  
Vol 65 (8) ◽  
pp. 1838-1844 ◽  
Author(s):  
Ronald Kluger ◽  
Gregory R. J. Thatcher ◽  
William C. Stallings
Keyword(s):  
Membered Ring ◽  
Equatorial Position ◽  
Alkyl Esters ◽  
Aqueous Acetonitrile ◽  
Phenoxy Group ◽  
X Ray Crystallography ◽  
Urea Group ◽  
Leaving Groups ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Compounds 1–5 were prepared to compare reactivity patterns of cyclic and acyclic phosphonylurea esters. The rates and products of reactions of phosphonylurea esters (1–3) with hydroxide in aqueous acetonitrile were analyzed. In these compounds the phosphonate moiety is in a strained five-membered ring, which also contains the ureido group. Structural determination of 1 by X-ray crystallography indicates that the five-membered ring is planar and the internal ring angle at phosphorus is 93.1°. The endocyclic N—C—N angle of the ureido group is 111°. The compounds undergo hydrolysis in alkaline aqueous acetonitrile at 35 °C with a rate about 106 times that of analogues (4, 5) in which the phosphonate group is exocyclic to the ureido ring. Compound 1 undergoes alkaline hydrolysis (k = 9.0 × 103 M−1 s−1) to release the phenoxy group to give 6. The hydrolysis of alkyl esters 2 (k = 2.4 × 104 M−1 s−1)and 3(k = 1.3 × 103 M−1 s−1) leads to cleavage of the endocyclic P—N bond, producing 7 and 8 respectively. The exocyclic alkyl esters (4 and 5) also cleave at the P—N bond with respective rate constants of 6.5 × 10−3 M−1 s−1 and 4.4 × 10−2 M−1 s−1. The data are consistent with a mechanism in which hydroxide adds to 1 to form a pentacoordinate phosphorus intermediate with the phenoxy group in an equatorial position and the ureido ring in apical and equatorial positions (with nitrogen apical). The departure of the urea group is slower than pseudorotation of the intermediate and expulsion of phenoxide. In the isomerized intermediate, phenoxy is apical but the methylene group of the ring, which has low apicophilicity, must also be apical. Reactions of 2 and 3, which have more basic oxygen leaving groups, occur with P—N cleavage because expulsion from the isomerized intermediate in those cases is not sufficiently fast. These results fit reaction patterns at phosphorus that are determined by ring strain and electronegativity of ligands. Contributions from effects due to antiperiplanar interactions between bonding and nonbonding electrons are not detected.

Fine Structural Localization of Acyltransferases Involved in Lipid Synthesis in Intestinal Mucosa.

1970 ◽  
Vol 28 ◽  
pp. 54-55
Author(s):  
R. J. Barrnett ◽  
J. A. Higgins
Keyword(s):  
Smooth Endoplasmic Reticulum ◽  
Lipid Synthesis ◽  
Mucosal Cell ◽  
Structural Localization ◽  
Morphological Studies ◽  
Mucosal Cells ◽  
Initial Appearance ◽  
Sh Group ◽  
Hydrolysis Of ◽  
Intestinal Mucosal Cells

The main products of intestinal hydrolysis of dietary triglycerides are free fatty acids and monoglycerides. These form micelles from which the lipids are absorbed across the mucosal cell brush border. Biochemical studies have indicated that intestinal mucosal cells possess a triglyceride synthesising system, which uses monoglyceride directly as an acylacceptor as well as the system found in other tissues in which alphaglycerophosphate is the acylacceptor. The former pathway is used preferentially for the resynthesis of triglyceride from absorbed lipid, while the latter is used mainly for phospholipid synthesis. Both lipids are incorporated into chylomicrons. Morphological studies have shown that during fat absorption there is an initial appearance of fat droplets within the cisternae of the smooth endoplasmic reticulum and that these subsequently accumulate in the golgi elements from which they are released at the lateral borders of the cell as chylomicrons.We have recently developed several methods for the fine structural localization of acyltransferases dependent on the precipitation, in an electron dense form, of CoA released during the transfer of the acyl group to an acceptor, and have now applied these methods to a study of the fine structural localization of the enzymes involved in chylomicron lipid biosynthesis. These methods are based on the reduction of ferricyanide ions by the free SH group of CoA.

Lattice imaging and pore structure of β ferric oxyhydroxide

1978 ◽  
Vol 36 (1) ◽  
pp. 264-265
Author(s):  
T. Baird ◽  
J.R. Fryer ◽  
S.T. Galbraith
Keyword(s):  
Electron Microscopy ◽  
Room Temperature ◽  
Bulk Material ◽  
Model Structure ◽  
Bulk Crystals ◽  
Lattice Imaging ◽  
Thin Sections ◽  
Ferric Oxyhydroxide ◽  
Resolution Electron ◽  
Hydrolysis Of

Introduction Previously we had suggested (l) that the striations observed in the pod shaped crystals of β FeOOH were an artefact of imaging in the electron microscope. Contrary to this adsorption measurements on bulk material had indicated the presence of some porosity and Gallagher (2) had proposed a model structure - based on the hollandite structure - showing the hollandite rods forming the sides of 30Å pores running the length of the crystal. Low resolution electron microscopy by Watson (3) on sectioned crystals embedded in methylmethacrylate had tended to support the existence of such pores.We have applied modern high resolution techniques to the bulk crystals and thin sections of them without confirming these earlier postulatesExperimental β FeOOH was prepared by room temperature hydrolysis of 0.01M solutions of FeCl3.6H2O, The precipitate was washed, dried in air, and embedded in Scandiplast resin. The sections were out on an LKB III Ultramicrotome to a thickness of about 500Å.

Elucidating cyclic AMP signaling in subcellular domains with optogenetic tools and fluorescent biosensors

2019 ◽  
Vol 47 (6) ◽  
pp. 1733-1747 ◽  
Author(s):  
Christina Klausen ◽  
Fabian Kaiser ◽  
Birthe Stüven ◽  
Jan N. Hansen ◽  
Dagmar Wachten
Keyword(s):  
Cyclic Amp ◽  
Adenosine Monophosphate ◽  
Adenylyl Cyclases ◽  
Temporal Precision ◽  
Fluorescent Biosensors ◽  
Subcellular Domains ◽  
Spatio Temporal ◽  
Hydrolysis Of ◽  
Shed Light ◽  
Cyclic Amp Signaling

The second messenger 3′,5′-cyclic nucleoside adenosine monophosphate (cAMP) plays a key role in signal transduction across prokaryotes and eukaryotes. Cyclic AMP signaling is compartmentalized into microdomains to fulfil specific functions. To define the function of cAMP within these microdomains, signaling needs to be analyzed with spatio-temporal precision. To this end, optogenetic approaches and genetically encoded fluorescent biosensors are particularly well suited. Synthesis and hydrolysis of cAMP can be directly manipulated by photoactivated adenylyl cyclases (PACs) and light-regulated phosphodiesterases (PDEs), respectively. In addition, many biosensors have been designed to spatially and temporarily resolve cAMP dynamics in the cell. This review provides an overview about optogenetic tools and biosensors to shed light on the subcellular organization of cAMP signaling.

Hydrolysis of glucuronide-based substrates mediated by tungsten, Cu2+, Fe2+, and Zn2+

1996 ◽  
Vol 96 (3) ◽  
pp. 484-490
Author(s):  
Chris A. Wozniak ◽  
Lowell D. Owens
Keyword(s):  
Hydrolysis Of
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