Search results for "Proton NMR"
showing 10 items of 324 documents
Experimental and theoretical NMR and IR studies of the side-chain orientation effects on the backbone conformation of dehydrophenylalanine residue
2011
Conformation of N-acetyl-(E)-dehydrophenylalanine N', N'-dimethylamide (Ac-(E)-ΔPhe-NMe(2)) in solution, a member of (E)-α, β-dehydroamino acids, was studied by NMR and infrared spectroscopy and the results were compared with those obtained for (Z) isomer. To support the spectroscopic interpretation, the Φ, Ψ potential energy surfaces were calculated at the MP2/6-31 + G(d,p) level of theory in chloroform solution modeled by the self-consistent reaction field-polarizable continuum model method. All minima were fully optimized by the MP2 method and their relative stabilities were analyzed in terms of π-conjugation, internal H-bonds and dipole interactions between carbonyl groups. The obtained…
1H nmr chemical shifts of [14]annulenes and their dianion salts
1987
Abstract The bridged (14]annulene 2 was reduced into its dianion and the structure of the dianion salt was proven by chemical and spectroscopic means. The 1H NMR spectroscopic properties of 2 are similar to those of the structurally related bridged [14]annulene 1 , whereas the corresponding dianions 2 2- and 1 2- are strikingly different. The geometries of 1 and 2 and their dianions were studied by means of a modified π-SCF force field approach. Almost planar perimeters without significant bond length alternation are obtained for the neutral annulenes 1 and 2 , whereas their dianions are characterized by structures with reduced symmetry. The 1H chemical shifts of the bridged [14]annulenes a…
Synthesis and structure verification of two previously uncharacterized pentachlorobiphenyls: PCB 108 and PCB 127
1992
Abstract The synthesis and structure verification of two previously uncharacterized polychlorinated biphenyl (PCB) congeners mono- ortho -substituted 2,3,3′,4,5′-pentachlorobiphenyl (PCB 108) and non- ortho -substituted 3,3′,4,5,5′-pentachlorobiphenyl (PCB 127) is described. The synthesis was done by the method of aromatic arylation in the presence of isopentyl nitrite. The purification and separation of the compounds was done by flash-chromatography on Al2O3- and charcoal columns. The structures were verified by 1H NMR, 13C NMR, IR and mass spectroscopy.
Tritylpyridinium tetrakis(pentafluorophenyl)borate as an efficient activator for “constrained-geometry” catalysts in ethylene polymerization
2004
Abstract Ethylene polymerization with linked amido-cyclopentadienyl or “constrained-geometry” titanium catalysts, Ti(η 5 :η 1 -C 5 Me 4 SiMe 2 N t Bu)X 2 (X=Me, Bz, Cl), activated by tritylpyridinium tetrakis(entafluorophenyl)borate, [Ph 3 C(NC 5 H 5 )] [B(C 6 F 5 ) 4 ], and silica-supported tritylpyridinium tetrakis(entafluorophenyl)borate (PySTB) was found to proceed with high activity. 1 H NMR spectra in CD 2 Cl 2 suggest that ([Ti(η 5 :η 1 -C 5 Me 4 ,SiMe 2 N t Bu)Me (NC 5 H 5 )] + is formed as the main cationic species. Using the heterogeneous cocatalyst PySTB in hexane, unexpectedly high ethylene polymerization activity was achieved, giving high molecular weight polyethylenes with exc…
ChemInform Abstract: Dissymmetric Calix(4)arenes with C4- and C2-Symmetry. Synthesis, X-Ray Structures, Conformational Fixation, and 1H NMR Spectrosc…
2010
Fluorescent Hg2+ Sensors: Synthesis and Evaluation of a Tren-Based Starburst Molecule Containing Fluorinated 1,2,4-Oxadiazoles.
2010
A new tren-based starburst molecule containing fluorinated 1,2,4-oxadiazoles as fluorophores has been synthesized and its sensing behavior toward several metal cations has been investigated by UV/Vis, fluorescence, 1 H NMR and 19 F NMR spectroscopy. Selective sensing for Hg 2+ ions through a PET-based mechanism was evidenced, suggesting application as fluorescent sensor for Hg 2+ of the off-on type.
Solid-liquid nuclear magnetic resonance relaxation and signal amplitude relationships with ranking of seasoned softwoods and hardwoods
2006
In 1H NMR (Nuclear Magnetic Resonance) relaxation measurements for a set of eight hardwood and softwood samples, each Free Induction Decay (FID) is fit by the sum of a “Solid” signal of the form A exp[−c(t/Ts)2] [1−g(t/Ts)2+h(t/Ts)4] plus a “Liquid” signal B exp(−t/T2 FID). Distributions of longitudinal (T1) relaxation times were computed separately for the Solid and Liquid components, giving also the Solid/Liquid 1H ratio α. From measurements on the samples dried, seasoned, and hydrated, the moisture content, (Liquid/Solid weight ratio) was found to be approximately 0.50/α. For each of the “Seasoned” samples (10-13% moisture content) a single T1 peak was found for the Solid and two for the…
Diastereoselective formation of homochiral flexible perylene bisimide cyclophanes and their hybrids with fullerenes†‡
2021
Cyclophanes of different ring sizes featuring perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) linked by flexible malonates were designed, synthesized, and investigated with respect to their structural, chemical and photo-physical properties. It is predominantly the number of PBIs and their geometric arrangement, which influence dramatically their properties. For example, two-PBI containing cyclophanes reveal physico-chemical characteristics that are governed by strong co-facial π–π interactions. This is in stark contrast to cyclophanes with either three or four PBIs. Key to co-facial π–π stackings are the flexible malonate linkers, which, in turn, set up the ways and means for diaster…
Isolation, purification and antibacterial effects of fusaproliferin produced by Fusariumsubglutinans in submerged culture.
2009
To evaluate the fusaproliferin (FUS) production, Fusariumsubglutinans ITEM 2404 was grown in a liquid medium of potato being this mycotoxin purified by high-performance liquid chromatography (HPLC) with a C18 semipreparative column using a mobile phase of acetonitrile/H(2)O using gradient conditions. The purity of the fusaproliferin was verified by analytical HPLC, ultraviolet absorbance measurements, LC/MS-MS, (1)H NMR spectroscopy. The isolated FUS was shown to be free of impurities and can be used as a standard for routine analysis. The pure fusaproliferin was utilized to study the biological activity on Escherichiacoli and Staphylococcusaureus. This study demostred that FUS not showed s…
Bis(imidazolium) salts derived from amino acids as receptors and transport agents for chloride anions
2015
The binding properties of bis(imidazolium) hosts 1a–c derived from amino acids towards different anions have been studied by 1H NMR titration experiments in 95 : 05 CD3CN : H2O at 303 K, ESI-MS and theoretical calculations. Among this family, the salt 1c showed a strong and high selectivity for chloride anions. Transmembrane chloride transport activity has also been studied for the three bis(imidazolium) based transporters in POPC liposome models, and compound 1a was identified as an active chloride/nitrate exchanger.