Meso-mesityl dithia- and diselenarubyrins: existence of planar and inverted forms in solution

2002 ◽  
Vol 06 (06) ◽  
pp. 403-409
Author(s):  
Seenichamy Jeyaprakash Narayanan ◽  
Sundararaman Venkatraman ◽  
Venkatara-manarao G. Anand ◽  
Tavarekere K. Chandrashekar
Keyword(s):  
Spectroscopic Studies ◽  
Nmr Studies ◽  
H Nmr ◽  
Protonated Forms

Syntheses, characterization and spectroscopic studies of meso-mesityl substituted rubyrins are reported. Specifically, it has been shown that these rubyrins behave differently from the meso-phenyl containing rubyrins in their structure. 1 H NMR studies reveal the existence of both planar and inverted isomers in solution in different ratios both in the freebase and protonated forms.

Extraction of novel sulfated polysaccharides from Aphanothece sacrum (Sur.) Okada, and its spectroscopic characterization

2007 ◽  
Vol 79 (11) ◽  
pp. 2039-2046 ◽  
Author(s):  
Maiko Okajima-Kaneko ◽  
Masateru Ono ◽  
Kiyotaka Kabata ◽  
Tatsuo Kaneko
Keyword(s):  
Spectroscopic Characterization ◽  
Spectroscopic Studies ◽  
Environmentally Benign ◽  
Sulfated Polysaccharides ◽  
Nmr Studies ◽  
H Nmr ◽  
Elemental Analyses ◽  
Gelation Behavior ◽  
Long Time ◽  
Swelling Volume

We extracted polysaccharides (PS) from Aphanothece sacrum using a hot alkaline solution which degraded other biopolymers such as proteins and nucleotides. The spectroscopy and elemental analyses indicated the PS contain carboxyls and sulfate groups. The degree of sulfation was estimated as about 10 mol %. 1H NMR studies demonstrated that the PS of A. sacrum had a dimethylated fucose unit. The combination of sulfate group and fucose in the prokaryotic PS was first evidenced by the direct spectroscopic studies. The PS showed efficient gelation behavior, binding to metal ions abundant in soil, and the swelling volume of the gel was approximately 250 times the dry volume. These results imply that PS of A. sacrum, which has been mass cultivated in Japan for a long time, may have potential as an environmentally benign water absorbent.

1H NMR Conformational Studies in Water of Angiotensin II Analogues Modified at the N- and C-Termini: Interactions of the Aromatic Side Chains and Folding of the N-Terminal Domain

1994 ◽  
Vol 59 (11) ◽  
pp. 2523-2532 ◽  
Author(s):  
John Hondrelis ◽  
John Matsoukas ◽  
George Agelis ◽  
Paul Cordopatis ◽  
Ning Zhou ◽  
...  
Keyword(s):  
Shielding Effect ◽  
Resonance Spectroscopy ◽  
Nmr Studies ◽  
Previous Suggestion ◽  
Aminoisobutyric Acid ◽  
H Nmr ◽  
Neutral Ph ◽  
Angiotensin Ii Analogues ◽  
Proton Resonances ◽  
Cosy Nmr

The conformation of [Sar1]angiotensin II in water at neutral pH has been examined by proton magnetic resonance spectroscopy at 400 MHz and in particular by comparing its 1H NMR spectral data with those of analogues modified at positions 1,4 and 6, namely [Sar1,Cha8]ANGII, [Des Asp1,Cha8]ANGII, [Aib1,Tyr(Me)4]ANGII, [Aib1,Tyr(Me)4,Ile8]ANGII, [N-MeAib1,Tyr(Me)4]ANGII, [N-MeAib1,Tyr(Me)4,Ile8]ANGII, ANGIII and [Sar1,Ile8]ANGII. Assignment of all proton resonances in these analogues was made possible by 2D COSY NMR experiments. The H-2 and H-4 protons for the histidine ring in [Sar1]ANGII, ANGII and ANGIII were shielded compared with the same protons in [Sar1,Ile8]ANGII, [Sar1,Cha8]ANGII and [Des Asp1,Cha8]ANGII; this shielding effect was not disturbed upon methylation of the tyrosine hydroxyl and/or replacement of residue 1 (sarcosine or aspartic acid) with aminoisobutyric acid (Aib) or N-methyl aminoisobutyric acid (N-MeAib). These data are consistent with our previous suggestion based on NMR studies in neutral DMSO that a characteristic folded conformation for ANGII previously observed in non-polar solvents can also be detected in water at neutral pH, but to a lesser degree.

High field 1H NMR Studies of Sol-Gel Kinetics

1986 ◽  
Vol 73 ◽  
Author(s):  
Bruce D. Kay ◽  
Roger A. Assink
Keyword(s):  
Equilibrium Distribution ◽  
Sol Gel ◽  
Nmr Studies ◽  
H Nmr ◽  
Rate Limiting Step ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Product Species ◽  
Rate Limiting ◽  
Kinetics Of

ABSTRACTHigh resolution 1H NMR spectroscopy at high magnetic fields is employed to study the reaction kinetics of the Si(OCH3)4:CH3OH:H2O sol-gel system. Both the overall extent of reaction as a function of time and the equilibrium distribution of species are measured. In acid catalyzed solution, condensation is the rate limiting step while in base catalyzed solution, hydrolysis becomes rate limiting. A kinetic model in which the rate of hydrolysis is assumed to be independent of the adjacent functional groups is presented. This model correctly predicts the distribution of product species during the initial stages of the sol-gel reaction.

Equilibrium thermodynamic studies for the formation of 1:1 complexes of CO and ethene with a rhodium(II) porphyrin metallo-radical

2001 ◽  
Vol 79 (5-6) ◽  
pp. 854-856 ◽  
Author(s):  
Leah Basickes ◽  
Andrew G Bunn ◽  
Bradford B Wayland
Keyword(s):  
Carbon Monoxide ◽  
Complex Formation ◽  
Equilibrium Thermodynamic ◽  
Nmr Studies ◽  
Thermodynamic Studies ◽  
H Nmr ◽  
Porphyrin Ligand ◽  
The One ◽  
Paramagnetic Shifts

Tetra(2,4,6 triisopropropyl phenyl)porphyrinatorhodium(II) ((TTiPP)RhII·1) is a persistent metal-centered radical with the odd electron in the rhodium(II) dz2 orbital. (TTiPP)RhII· forms 1:1 complexes with CO and CH2CH2 where the porphyrin ligand steric properties inhibit further reactions of the one-electron activated substrates. 1H NMR paramagnetic shifts at a series of temperatures are used in evaluating the thermodynamics for CO complex formation with 1 to form [(TTiPP)RhII(CO)]·2 (ΔH° = -5.5 ± 0.5 kcal mol-1; ΔS° = -9 ± 1 cal K-1 mol-1). Related 1H NMR studies show that the bonding of 1 with ethene is less favorable than CO.Key words: rhodium porphyrin, carbon monoxide, ethene, thermodynamics, complex formation, metal-centered radical.

The synthesis of 11R- and 11S-HETE and of 11-R,S-HPETE methyl esters

1983 ◽  
Vol 61 (4) ◽  
pp. 712-717 ◽  
Author(s):  
George Just ◽  
Corinne Luthe ◽  
Minh Tan Phan Viet
Keyword(s):  
Methyl Esters ◽  
Nmr Studies ◽  
H Nmr ◽  
Conformational Properties

Methyl 11R- and 11S-hydroxyeicosa-5Z,8Z,12E,14Z-tetraenoate (17R, 17S) (11-HETE) and the corresponding 11-hydroperoxide 19 (11-HPETE) have been prepared from readily available starting materials. The yields were approximately 25% for 11R,S-HETE, and 5% each for 11R- and 11S-HETE.Extensive 400 MHz 1H nmr studies of 17 (nOe difference, 2D J-resolved) were undertaken to confirm the structure. Some conformational properties are discussed.

scholarly journals Darstellung und Charakterisierung von chiralen und achiralen exocyclischen π-enyl-Komplexen der Zusammensetzung (C8H13PdCl)2 / Synthesis and Characterization of Exocyclic π-Enyl Complexes of the Composition (C8H13PdCl)2

1979 ◽  
Vol 34 (4) ◽  
pp. 579-584 ◽  
Author(s):  
Richard Ratka ◽  
Manfred L. Ziegler ◽  
Gerhard Schilling
Keyword(s):  
Spectroscopic Studies ◽  
Synthesis And Characterization ◽  
Mechanism Of Formation ◽  
H Nmr ◽  
Cleavage Reactions

Abstract The mechanism of formation of the exocyclic dimeric π-enyl complex (C8H13PdCl)2 by reaction of 1,3-dimethylenecyclohexane, C8H12 with trans-PdCl2(C6H5CN)2 is discussed. Through UV, 1H NMR (90 MHz, 360 MHz) and 13C spectroscopic studies it was possible to show that the dimer is formed by the disproportionate of C8H12 to C8H14 and m-xylene, and further that it consists of diastereomeric products. The reaction of (-) R-3-methyl-1-methylencyclohexane, C8H14, with the Pd-salt confirms that during the reaction between C8H12 and trans-PdCl2(C6H5CN)2 no free C8H14 is formed in solution.Studies on cleavage reactions of the dimer are also described in this paper.

scholarly journals 1H NMR Studies of Surfactants in Aqueous Solutions

2003 ◽  
Vol 19 (07) ◽  
pp. 675-680 ◽  
Author(s):  
Mao Shi-Zhen ◽  
◽  
Du You-Ru
Keyword(s):  
Aqueous Solutions ◽  
Nmr Studies ◽  
H Nmr

ChemInform Abstract: (19)F- AND (1)H-NMR STUDIES OF RING-FLUORINATED IMIDAZOLES AND HISTIDINES

1975 ◽  
Vol 6 (42) ◽  
pp. no-no
Author(s):  
HERMAN J. C. YEH ◽  
KENNETH L. KIRK ◽  
LOUIS A. COHEN ◽  
JACK S. COHEN
Keyword(s):  
Nmr Studies ◽  
H Nmr

Chiral "basket handle" binaphthyl porphyrins: synthesis, catalytic epoxidation and NMR conformational studies

2010 ◽  
Vol 14 (07) ◽  
pp. 646-659 ◽  
Author(s):  
Eric Rose ◽  
Emma Gallo ◽  
Nicolas Raoul ◽  
Léa Bouché ◽  
Ariane Pille ◽  
...  
Keyword(s):  
Time Scale ◽  
Room Temperature ◽  
Conformational Equilibrium ◽  
Variable Temperature ◽  
Conformational Exchange ◽  
Iron Catalysts ◽  
Nmr Studies ◽  
Conformational Studies ◽  
H Nmr ◽  
Catalytic Epoxidation

Three "basket handle" porphyrins have been prepared by condensation of tetrakis-(α,β,α,β-2-aminophenyl)porphyrin atropoisomer with 1,1′-binaphthyl, 2,2′-dimethoxy, -3,3′-dicarbonylchloride, -3,3′-diacetylchloride and -3,3′-dipropanoylchloride. The epoxidation of styrene with the three iron catalysts, obtained after metalation of the free porphyrins, occurs with good yields and moderate ee up to 54%. These porphyrins showed unexpected conformational differences, as revealed by NMR spectroscopy. In particular, variable temperature NMR studies showed that the methoxy group in one of them undergoes intermediate conformational exchange on the 1H NMR time scale at room temperature. Lowering the temperature to -50 °C revealed the presence of four states in slow exchange on the NMR time scale. These results evidence a dynamic conformational equilibrium of the binaphthyl handles that adopt different, asymmetric positions with respect to the porphyrin plane.

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