Showing papers on "Bond cleavage published in 1977"
TL;DR: The relative paucity of AspPro bonds in proteins is both a limitation and an advantage of this specific cleavage procedure as the number of fragments obtained by application of the procedure can be advantageously small, which will simplify subsequent fractionation processes.
Abstract: Specific cleavage at AspPro bonds of a protein can be effected by exposure to acid at moderate temperature for periods up to 120 hr. The effectiveness of cleavage is usually increased by incorporating a denaturing agent in the acid solution. Some AspPro bonds are resistant to cleavage probably because of retention of protein folding even under the most vigorous conditions that have been employed, and under these circumstances some nonspecific peptide bond cleavage may occur, particularly if the exposure is prolonged.
It is very likely that cleavage at AspPro bonds will occur when acid procedures are employed in peptide bond scission or peptide separation and purification. With the larger peptides produced by cyanogen bromide cleavage it has been observed that partial cleavage at AspPro near the termini of the authentic peptide may yield fragments that copurify with the larger component, thus complicating subsequent sequence determinations.13
The relative paucity of AspPro bonds in proteins is both a limitation and an advantage of this specific cleavage procedure. The limitation is that many proteins do not contain any AspPro bonds but as the AspPro bond is never abundant the number of fragments obtained by application of the procedure can be advantageously small, which will simplify subsequent fractionation processes.
308 citations
TL;DR: The complete mass spectra of the trimethylsilyl derivatives of 46 amino acids are presented in this paper in terms of the common fragmentation pathways and factors controlling the fragment formation.
79 citations
62 citations
TL;DR: In this article, the configurations of 2-substituted 1,3,2-oxazaphospholidin(e)-2-ones, -2-thiones, and 2-selones derived from (−)-ephedrine have been established by spectroscopic and chemical methods.
Abstract: The configurations of the cis- and trans-isomers of 2-substituted 1,3,2-oxazaphospholidin(e)-2-ones, -2-thiones, and 2-selones derived from (–)-ephedrine have been established by spectroscopic and chemical methods. Displacements of the exocyclic 2-substituents occur with retention of configuration at phosphorus. With sodium alkoxides, the 1,3,2-oxazaphospholidine ring is opened by P–N rather than P–O bond cleavage, and inversion of configuration at phosphorus is observed. Under basic conditions the 2-methylamino-1-phenylpropyl phosphates derived from (–)-ephedrine rearrange to afford aziridines and phosphoric acid derivatives; in the cases of the sulphur- and selenium-containing derivatives optically active phosphorus thioacids and phosphorus selenoacids are formed and can be isolated as SMe and SeMe derivatives. These latter derivatives are converted into O-alkyl derivatives on treatment with alcohols in the presence of alkoxides or bromine or silver nitrate, and the stereoselectivities of these reactions have been determined. The optical purities of the title compounds have been measured by an n.m.r. method using chiral shift reagents.
61 citations
TL;DR: It is proved, by calculating electron density in each stage, that the change of the crystal of R-α-cyanoethyl (S- α-methylbenzylamine)-cobaloxime changes its unit cell dimensions by X-ray exposure without degradation of a single crystal form.
Abstract: DURING serial structure analysis of cobaloxime derivatives1, aimed at interpreting the catalytic capability of the asymmetric hydrogenation2–5, we have found that the crystal of R-α-cyanoethyl (S-α-methylbenzylamine)-cobaloxime changes its unit cell dimensions by X-ray exposure without degradation of a single crystal form. The rate of the change was so slow that it was possible to collect the intensity data for several intermediate stages. We have proved, by calculating electron density in each stage, that the change reflects the racemisation of the cyanoethyl group.
55 citations
TL;DR: In this paper, photolysis in the visible and the UV region of dialkyl metallocenes of the titanium group is studied by ESR and the primary process is homolytic cleavage of the metal-alkyl bond, with formation of paramagnetic metal species and organic free radicals.
47 citations
TL;DR: In this paper, a new type of oxidation of C 2 -C 5 olefins leading to the oxidative scissions of carbon skeletons was examined on the V 2 O 5 -MoO 3 catalyst in the presence of water vapor.
44 citations
TL;DR: In this article, the kinetics of the reaction of potassium phenyldimethylsilanolate with a series of linear trimethylsilyl-end-blocked dimethylsiloxane oligomers and with the series of cyclic cyclic dimethyl-siloxide oligomers was studied to clear mechanistic problems of anionic polymerization of siloxanes.
Abstract: The kinetics of the reaction of potassium phenyldimethylsilanolate (1) with the series of linear trimethylsilyl-end-blocked dimethylsiloxane oligomers and with the series of cyclic dimethylsiloxane oligomers was studied to clear some mechanistic problems of anionic polymerization of siloxanes.
The results indicate that the high reactivity of the siloxane bond in linear and higher cyclic oligomers—responsible for the large scope of chain redistribution and cyclization processes in the siloxane anionic polymerization system—is due to a mechanism involving multifunctional interaction of siloxane with silanolate, which gives assistance to the siloxane bond cleavage. This mechanism is impeded when strong cation solvating agents are present in the system.
43 citations
TL;DR: The hydrolysis of nitrazepam involves a two-step sequential mechanism, and the final products are glycine and 2-amino-5-ni-robenzophenone, the ring-opened compound resulting from scission of the azomethine bond.
38 citations
TL;DR: Enzymic hydrolysis of potassium (+)-octan-2-yl sulphate in the presence of H218O and analysis of Hydrolysis products for the presenceof 18O has confirmed that C-O bond scission (and not O-S bond scissions) occurs with both enzymes.
Abstract: The hydrolysis was studied of potassium (+)-octan-2-yl sulphate by two analogous, optically stereospecific, secondary alkylsulphohydrolases purified from two detergent-degrading micro-organisms, Comamonas terrigena and Pseudomonas C12B. Polarimetry studies have shown that (+)-octan-2-yl sulphate prepared from (+)-octan-2-ol is hydrolysed by both enzymes to yield (-)-octan-2-ol. This inversion of configuration implies that the enzymes are catalysing the scission of the C-O bond of the C-O-S linkage, a type of bond scission apparently not hitherto encountered among hydrolytic enzymes acting on ester bonds. Enzymic hydrolysis of potassium (+)-octan-2-yl sulphate in the presence of H218O and analysis of hydrolysis products for the presence of 18O has confirmed that C-O bond scission (and not O-S bond scission) occurs with both enzymes.
38 citations
TL;DR: In this paper, the base-induced decomposition of 4- and 5-phenylisoxazole and their derivatives to the corresponding cyanoenolate anions have been studied.
Abstract: The kinetics of the base-induced decomposition of 4- and 5-phenylisoxazole and their p-bromo- and p-nitrophenyl derivatives, and 3-deuterio-5-phenylisoxazole, to the corresponding cyanoenolate anions have been studied. The mechanism of reaction has been established as a one-stage concerted abstraction of the proton in position 3 and scission of the N–O bond. 4-Phenylisoxazole, previously synthesized by laborious methods, has been prepared by a simpler procedure.
TL;DR: In this article, a silyl-methyl group was used to give an unstable silaoxetane intermediate, which was followed by cleavage of both the silicon carbon and the silicon-oxygen bonds.
TL;DR: In this article, the effects of the acid-base character of catalysts and the feed of water vapor and gaseous oxygen on the reaction were investigated, and it was shown that, while acidic sites of the catalysts, water vapor, and GASO are all necessary for the reaction, the cut of its feed causing a total loss of reactivity of olefins at temperatures below 250 °C.
TL;DR: In this article, a rapid equilibrium between R 2 Te 2 and R 2 P + Te 2 was established in solution, which can satisfactorily be interpreted in terms of an initiation step involving photochemical cleavage of TeC bonds.
TL;DR: All three 8-amino guanosines exhibited log kobs - pH profiles clearly showing that both mono and di-base protonated nucleosides undergo hydrolysis, and the lack of anomerization of all substrates during the course of the reaction supports an A rather than a Schiff-base mechanism.
Abstract: The log kobs vs. pH profiles were determined in the intermediate acidity region for the glycosyl hydrolysis of guanosine and its 8-amino, 8-monomethylamino, 8-dimethylamino and 8-bromo derivatives. The decreased rate of the 8-amino and enhanced rate of the 8-bromo compound compared to guanosine support an A type mechanism: base protonation followed by glycosyl bond cleavage. All three 8-amino guanosines exhibited log kobs - pH profiles clearly showing that both mono and di-base protonated nucleosides undergo hydrolysis. The 700 fold rate acceleration of 8-N(CH3)-guanosine compared to 8-NHCH3-guanosine and the 110 fold rate acceleration of 8-N(CH3)2-adenosine compared to 8-NHCH3-adenosine could be unequivocally attributed to the fixed syn glycosyl conformation of both 8-dimethylamino compounds and relief of steric compression upon hydrolysis in these molecules. The lack of anomerization of all substrates during the course of the reaction supports an A rather than a Schiff-base mechanism.
TL;DR: In this article, it was shown that allylic carbon-oxygen bond scission with either bis(1,5-cyclopentadiene) or tetrakis(triethylphosphine) reagents accelerate the deoxygenation of epoxides bearing electron-withdrawing substituents and yield corresponding trans olefins.
TL;DR: In this article, a reaction scheme for the radical induced scission of the glycosidic bond of cellobiose was proposed, which involves hydrolysis and the rearrangements of radicals with the free spin next to the glyco-sensor and to the lactol bridge.
Abstract: In the γ-radiolysis of deoxygenated, N2O-saturated aqueous solutions of maltose, lactose, gentiobiose, melibiose, trehalose and sucrose carbohydrate products containing five or six carbon atoms have been identified and their G-values measured. These products originate from the OH radical induced scission of the glycosidic bond of the disaccharides. The nature of the products is in agreement with a reaction scheme proposed previously for the radical induced scission of the glycosidic bond of cellobiose. It involves hydrolysis and the rearrangements of radicals with the free spin next to the glycosidic bond and to the lactol bridge. The nature the glycosidic bond (α, β, 1-4, 1-6, 1-1, 1, 2) has only little influence on the G-values of its scission which range between about 1.9 and 3.5.
TL;DR: In this paper, the photochemical reaction mechanisms of several 2-isoxazolines have been studied using low-temperature technique and the results indicate the major differences in the chemical behaviors of the photolytically and thermally excited states for those heterocycles.
Abstract: In connection with photochemistry of the non-constrained Ph-C=N-0 system, those of several 2-isoxazoline derivatives containing cyclobutene, cyclobutane, cyclopropane and cyclohexane rings, have been investigated as the models of the rigid and constrained Ph-C=N-0 system. In most cases, such 2-isoxazolines, upon irradiation, underwent the nitrogen-oxygen bond fission as the primary process, and produced a variety of products depending on the structures of the starting materials. For instance, the irradiation of 4-aryl-2-oxa-3-azabicyclo [3.2.0] hepta-3, 6-dienes afforded 2-aryl-1, 3-oxazepines, sometimes accompanied by pyrrole aldehydes, whereas 2-isoxazolines fused with small ring yielded B-aminoaldehydes, oxazolines, azirine aldehydes, and small fragments such as benzonitrile. The photochemical reaction mechanisms of several 2-isoxazolines have been studied using low-temperature technique. In addition, the pyrolytic reactions of 4-phenyl-2-oxa-3-azabicyclo [3.2.0] heptadiene and 1, 3-oxazepines as well as their valence isomers have been examined to compare with their photochemical behavior. It was found that in pyrolysis of bicyclo [3.2.0] heptadiene derivatives containing the C=N-O or N=C-O group, the cyclobutene ring fission occurs prior to the nitrogen-oxygen or carbon-oxygen bond cleavage. Reaction mechanisms for the deep-seated rearrangements of the 1, 3-oxazepines and of 2-oxa-3-azabicyclo [3.2.0] hepta-3, 6-dienes to pyrrole aldehydes were discussed. The results indicate the major differences in the chemical behaviors of the photolytically and thermally excited states for those heterocycles.
TL;DR: In this paper, the first example of the vinyl-oxygen bond cleavage of diketene was presented, where the acid was isomerized to the conjugated acid, 4-trimethylsilyl-3-methyl-2-butenoic acid (2) by means of an excess LiN(SiMe3)2.
Abstract: The reaction of (CH3)3SiCH2MgCl with diketene yields 3-trimethylsilylmethyl-3-butenoic acid (1) in the presence of a catalytic amount of NiCl2(95%), PdCl2(68%), CoCl3(60%), or CuI(20%) under moderate conditions. The acid, 1, is isomerized to the conjugated acid, 4-trimethylsilyl-3-methyl-2-butenoic acid (2) by means of an excess LiN(SiMe3)2. The rearrangement proceeds stereoselectively to 2-(E) isomer by addition of diglyme or N,N,N′,N′-tetramethylethylenediamine. This is the first example of the vinyl-oxygen bond cleavage of diketene.
TL;DR: In this paper, a two carbon bridge π-cyclopentadienyl-σ-alkyl complex with CC bond cleavage was shown to have the same spectroscopic properties as the molybdenum complex.
TL;DR: Evidence is presented which strongly indicates that cleavage of aryl phosphates with electron donors may occur either by a one-electron or two-electrons pathway, and a rationale based on the intermediacy of a trigonal bipyramidal phosphate ester anion radical which either undergoes P-0 scission or is reduced further and undergoes C - 0 (0) scission.
Abstract: Evidence is presented which strongly indicates that cleavage of aryl phosphates with electron donors may occur either by a one-electron or two-electron pathway. Thus, high concentrations and greater reducing power of the electron donor favor production of arene (C-0 cleavage product) while low concentrations and/or lower reducing power of the electron donor favor production of phenol (P-0 cleavage product) from aryl phosphates. A rationale based on the intermediacy of a trigonal bipyramidal phosphate ester anion radical which either undergoes P-0 (a) scission or is reduced further and undergoes C - 0 (0) scission, is presented. Comparison is also made with the electron transfer chemistry of sulfonate esters.
TL;DR: In this article, simple alkyl sulfides and disulfides have been photolysed at 253.7nm in dilute rigid glasses of 3-methylpentane, and the reactions which occur both at 77 K and in the glass at higher temperatures have been studied using epr and optical spectroscopy.
Abstract: Simple alkyl sulfides and disulfides have been photolysed at 253.7 nm in dilute rigid glasses of 3-methylpentane, and the reactions which occur both at 77 K and in the glass at higher temperatures have been studied using epr and optical spectroscopy. The end products of photolysis have been determined using glc at room temperature. In sulfides, C—S bond cleavage leads to 'hot' radical pairs that react with each other giving rise to the main diamagnetic products observed, or react with nearby solvent molecules in the matrix by hydrogen abstraction yielding RSH and the solvent derived radicals (M•) which dominate the initial epr spectrum at 77 K. Thiyl radicals (RS•) are produced in significant amounts only after the sulfide glasses have been warmed slightly to allow the cage reaction,to occur. Pethiyl radicals (RS2•) are not ordinarily observed in sulfide photolyses. Photolysis of disulfide-containing glasses gives rise to S—S bond rupture and mainly diamagnetic products, or to C—S bond cleavage resulting ...
TL;DR: In this paper, the electrochemical properties of 2,4,5-triphenyl-imidazolyls have been analyzed from their electrochemical behavior, including reductive bond cleavage in an ē.c.
TL;DR: In this paper, cycloalkanones reacted with sodium pentacyanonitrosylferrate(II) (NP) to give red-brown or red-violet colored complexes under an alkaline condition.
Abstract: Cycloalkanones reacted with sodium pentacyanonitrosylferrate(II) (NP) to give red-brown or red-violet colored complexes under an alkaline condition. The solvolysis of the complexes gave ω-(hydroxyimino)alkanoic acids under a hot alkaline condition and gave ω-cyanoalkanoic acids or their esters in an acidic condition in good yields. These Products correspond to nitrosolysis products of cycloalkanones. The reaction mechanism was invesigated by use of 15N labeled NP. The complex was formed initially by an electrophilic attack of the nitrosyl ligand of NP to the active methylene of the cycloalkanone. Then a C–C bond cleavage of the resulting ligand, 2-(hydroxyimino) cycloalkanone, occurred by an action of the solvent species under the influence of the central ferrate ion. The solvolysis of the ligand occurred through Beckmann fission by an action of the acid in the coordination sphere.
TL;DR: Arylamines such as aniline, toluidine, anisidine, chloroaniline and nitroaniline in the presence of palladium(II) acetate have been found to give styrene derivatives as mentioned in this paper.