scholarly journals Separation and structural analysis of vinyl- and isovinyl-azobilirubin derivatives

1971 ◽  
Vol 125 (2) ◽  
pp. 585-597 ◽  
Author(s):  
F. H. Jansen ◽  
M. S. Stoll
Keyword(s):  
Proton Magnetic Resonance ◽  
Mass Spectra ◽  
Methyl Esters ◽  
Coupling Reaction ◽  
Azo Compounds ◽  
Side Chain ◽  
Diazonium Salts ◽  
Side Reactions ◽  
Group 2

The coupling reaction of bilirubin with the diazonium salts of ethyl anthranilate or of aniline yields two isomeric azopigments. These can be separated by t.l.c. as their methyl esters. The mass spectra of each pair of azopigments are very similar, showing that they are isomers. Proton-magnetic-resonance spectrometric studies show that they differ in the positions of the substituents on the pyrrolenone end ring; in one compound the methyl and vinyl groups are interposed compared with the other compound. These azo compounds were used as reference standards for determination of the site of conjugation in bilirubin monoglucuronide prepared enzymically. Analysis showed that conjugation occurs at the carboxyethyl side chain of both sides of the bilirubin molecule. During the preparation of the ethyl anthranilate reference compounds a series of minor azopigments were isolated by t.l.c. Analysis of the mass spectra of many of these showed that three side reactions can occur: (1) methylation of the imide carbonyl group; (2) addition of methanol or water to the vinyl substituent; (3) transmethylation of the ethoxycarbonyl group.

Spectroscopic Properties of the Methyl Esters of Chlorophenoxy Acid Herbicides

1975 ◽  
Vol 58 (5) ◽  
pp. 1001-1012 ◽  
Author(s):  
Carlos H Van Peteghem ◽  
Aubin M Heyndrickx
Keyword(s):  
Magnetic Resonance ◽  
Infrared Spectra ◽  
Proton Magnetic Resonance ◽  
Mass Spectra ◽  
Methyl Esters ◽  
Spectroscopic Properties ◽  
Chlorophenoxy Acid Herbicides ◽  
Acid Herbicides ◽  
Magnetic Resonance Spectra

Abstract The mass and infrared spectra of the methyl esters of 9 chlorophenoxy acid herbicides are presented. Ultraviolet data are discussed and proton magnetic resonance spectra are tabulated. Because of the sensitivity of the technique, the mass spectra are most useful for the identification of those compounds in residues, especially by combined gas chromatographymass spectrometry. The pure herbicides used for the recording of the spectra were obtained by synthesis and recrystallization.

Concerning the extension of the J method for internal barriers to six-bond couplings to 19F in the 4-fluorophenyl fragment

1978 ◽  
Vol 56 (18) ◽  
pp. 2442-2446 ◽  
Author(s):  
Ted Schaefer ◽  
Werner Danchura ◽  
Walter Niemczura ◽  
James Peeling
Keyword(s):  
Ground State ◽  
Proton Magnetic Resonance ◽  
Coupling Constants ◽  
Side Chain ◽  
Fluorine Nucleus ◽  
Proton Proton ◽  
Proton Coupling ◽  
Carbon Carbon Bond ◽  
Internal Barriers

The long-range coupling constants over six bonds from the side-chain protons to the fluorine nucleus on the ring are extracted from the proton magnetic resonance spectra of p-fluorobenzyl cyanide, chloride, and bromide; of p-fluorobenzal chloride; and of p-fluoroisopropylbenzene. On the assumption that these couplings are transmitted via a σ–π mechanism, a hindered rotor treatment yields the barriers to internal rotation about the carbon–carbon bond which attaches the substituent to the benzene ring. These barriers, when compared to those derived from the analogous proton–proton coupling constants, apparently are accurate enough for the determination of ground state conformations and for a rough assessment of the energetics of conformational interconversions.

Collision-Induced Dissociations of Deprotonated Dipeptide Methyl Esters Containing Serine or Threonine

1994 ◽  
Vol 47 (10) ◽  
pp. 1851 ◽  
Author(s):  
ST Steinborner ◽  
AM Bradford ◽  
RJ Waugh ◽  
JH Bowie ◽  
DL Vollmer ◽  
...  
Keyword(s):  
Methyl Ester ◽  
Mass Spectra ◽  
Methyl Esters ◽  
Side Chain ◽  
Backbone Cleavage ◽  
Sequencing Data ◽  
Deuterium Labelling ◽  
Product Ions

The collision-induced mass spectra (MS/MS) of (M - H)- ions derived from dipeptide methyl esters containing serine or threonine lack the characteristic backbone cleavage of the underivatized peptides (which provide primary sequencing data). Instead, competitive fragmentation occurs through the ester and α-side chain functions. For example, Ser methyl esters lose both CH2O (from the side chain) and MeOH ( MeO comes from the methyl ester). Isomeric dipeptides may be differentiated by competitive fragmentations; for example [ Gly Ser( OMe )-H]- fragments first by loss of CH2O, while [Ser Gly ( OMe )-H]-, in contrast, shows initial elimination of MeOH. The structures of the product ions in these spectra have been probed by deuterium labelling and MS/MS/MS studies.

scholarly journals Determination of Free Fatty Acids in Sausage Meat

2010 ◽  
Vol 67 (2) ◽  
Author(s):  
Codrean POP ◽  
Levente BARA ◽  
Elena HORJ ◽  
Andreea IORDACHE ◽  
Cornel LASLO ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Free Fatty Acids ◽  
Mass Spectra ◽  
Methyl Esters ◽  
Extraction Procedure ◽  
Internal Standard ◽  
Quadrupole Mass ◽  
Temperature Program ◽  
Separation Temperature

The aim of this work was to establish the extraction procedure, the derivatization method, the separation temperature program, the identification and quantitation of the free fatty acids from meat. A gas chromatography - mass spectrometric (GC/MS) technique was used. The fatty acids were obtained by grounding meat, water and sand and then extraction was performed by mixing chloroform:methanol (2:1) during 30 seconds, at room temperature. The fatty acids were derivatized to obtain methyl esters. A Trace DSQ ThermoFinnigan quadrupole mass spectrometer coupled with a Trace GC was used. Fatty acids were separated on a Rtx-5MS capillary column, 30m x 0.25mm, 0.25µm film thickness, using a suitable temperature program. The identification of fatty acids was obtained by comparison of fatty acids methyl esters (FAME) mass spectra with the mass spectra of FAME kits and of NIST library. Concentrations of fatty acids were calculated by using a proper internal standard.

scholarly journals Synthesis, characteristic fragmentation patterns, and antibacterial activity of new azo compounds from the coupling reaction of diazobenzothiazole ions and acetaminophen

2021 ◽  
Vol 27 (1) ◽  
pp. 79-89
Author(s):  
Joseph Tsemeugne ◽  
Pamela Kemda Nangmo ◽  
Pierre Mkounga ◽  
Jean De Dieu Tamokou ◽  
Iréne Chinda Kengne ◽  
...  
Keyword(s):  
Mass Spectra ◽  
Analytical Data ◽  
Coupling Reaction ◽  
Azo Compounds ◽  
Electrophilic Aromatic Substitution ◽  
Spectroscopic Techniques ◽  
Aromatic Substitution ◽  
Chemical Structures ◽  
Characteristic Fragmentation ◽  
Fragmentation Patterns

Abstract In this study, a series of azobenzothiazole dyes 4 were synthesized via diazotization of substituted benzothiazole derivatives followed by azo coupling with acetaminophen. The chemical structures of all synthesized compounds were confirmed using analytical data and spectroscopic techniques, including UV-visible, IR, mass spectra, and 1H- and 13C-NMR. The in situ formed diazobenzothiazole ions regiospecifically react with acetaminophen derivatives in the Hollemann-guided electrophilic aromatic substitution mechanism. The regio-orientations were established, on the one hand, by a rigorous interpretation of 1H-NMR spectra and, on the other hand, by the characteristic fragmentation patterns observed on the electrospray mass spectra. In the cases of 4a and 4b, multisubstitutions occurred. The antimicrobial activity of compound 4, along with all the starting materials, was investigated on Pseudomonas aeruginosa PA01, Staphylococcus aureus 18, Escherichia coli 64R, and S. aureus ATCC 25923. The results showed that this skeletal framework exhibited marked potency as antibacterial agents. The most active antibacterial agent against both targeted organisms was compound 4a′.

Simultaneous Spectrophotometric Determination of Salbutamol by Coupling with Diazotized 4-Aminobenzoic acid

2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Hind Hadi ◽  
Gufran Salim
Keyword(s):  
Pharmaceutical Preparations ◽  
Coupling Reaction ◽  
Dosage Forms ◽  
Water Soluble ◽  
Trace Determination ◽  
Aminobenzoic Acid ◽  
Optimum Conditions ◽  
Colored Product ◽  
Versus Concentration

A simple, rapid and sensitive spectrophotmetric method for trace determination of salbutamol (SAL) in aqueous solution and in pharmaceutical preparations is described. The method is based on the diazotization coupling reaction of the intended compound with 4-amino benzoic acid (ABA) in alkaline medium to form an intense orange, water soluble dye that is stable and shows maximum absorption at 410 nm. A graph of absorbance versus concentration indicates that Beer’s law is obeyed over the concentration range of 0.5-30 ppm, with a molar absorbtivity 3.76×104 L.mol-1 .cm-1 depending on the concentration of SAL. The optimum conditions and stability of the colored product have been investigated and the method was applied successfully to the determination of SAL in dosage forms.

Polypeptides Folding: Rules for the Calculation of the Backbone Dihedral Angles φ starting from the Amino Acid Sequence

2020 ◽  
Author(s):  
Michele Larocca
Keyword(s):  
Amino Acid ◽  
Amino Acid Sequence ◽  
Theoretical Approach ◽  
Polypeptide Chain ◽  
Hydrophobic Effect ◽  
Side Chain ◽  
Dihedral Angles ◽  
Mechanical Forces ◽  
Specific Chemical

<p>Protein folding is strictly related to the determination of the backbone dihedral angles and depends on the information contained in the amino acid sequence as well as on the hydrophobic effect. To date, the type of information embedded in the amino acid sequence has not yet been revealed. The present study deals with these problematics and aims to furnish a possible explanation of the information contained in the amino acid sequence, showing and reporting rules to calculate the backbone dihedral angles φ. The study is based on the development of mechanical forces once specific chemical interactions are established among the side chain of the residues in a polypeptide chain. It aims to furnish a theoretical approach to predict backbone dihedral angles which, in the future, may be applied to computational developments focused on the prediction of polypeptide structures.</p>

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