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11.
O'Neil-Cabello E Bryce DL Nikonowicz EP Bax A 《Journal of the American Chemical Society》2004,126(1):66-67
A new three-dimensional NMR experiment is described that yields five scalar or dipolar couplings from a single cross-peak between three spins. The method is based on the E.COSY principle and is demonstrated for the H1'-C1'-C2' fragment of ribose sugars in a uniformly 13C-enriched 24-nucleotide RNA stem-loop structure, for which a complete set of couplings was obtained for all nonmodified nucleotides. The values of the isotropic J couplings and the 13C1' and 13C2' chemical shifts define the sugar pucker. Once the sugar pucker is known, the five dipolar couplings between C1'-H1', C2'-H2', H1'-H2', C1'-H2', and C2'-H1', together with C1'-C2', C3'-H3', and C4'-H4' available from standard experiments, can be used to derive the five unknowns that define the local alignment tensor, thereby simultaneously providing information on relative orientation and dynamics of the ribose units. Data indicate rather uniform alignment for all stem nucleotides in the 24-nt stem-loop structure, with only a modest reduction in order for the terminal basepair, but significantly increased mobility in part of the loop region. The method is applicable to proteins, nucleic acids, and carbohydrates, provided 13C enrichment is available. 相似文献
12.
Zusammenfassung Ein neues Verfahren, das eine unmittelbare und kontinuierliche Registrierung des mechanischen Verlustwinkels über einen weiten
Temperaturbereich erm?glicht, wird beschrieben. Die Probe wird einer periodischen Biegung (f=2,5 Hz) unterworfen; die Zeit des Kraftnulldurchgangs relativ zur Bewegung ist dem Verlustwinkel proportional und wird elektronisch
ermittelt. Das Me\ergebnis ist weitgehend von der Probenform und deren ?nderung w?hrend der Messung (Krümmung der Probe, thermische
Ausdehnung usw). unabh?ngig.
Der Deutschen Forschungsgemeinschaft sei für die Unterstützung dieser Arbeit verbindlichst gedankt. 相似文献
13.
In a follow-up of the earlier characterisation of botulinum toxins type A and B (BTxA and BTxB) by mass spectrometry (MS), types C, D, E, and F (BTxC, BTxD, BTxE, BTxF) were now investigated. Botulinum toxins are extremely neurotoxic bacterial toxins, likely to be used as biological warfare agent. Biologically active BTxC, BTxD, BTxE, and BTxF are comprised of a protein complex of the respective neurotoxins with non-toxic non-haemagglutinin (NTNH) and, sometimes, specific haemagglutinins (HA). These protein complexes were observed in mass spectrometric identification. The BTxC complex, from Clostridium botulinum strain 003-9, consisted of a 'type C1 and D mosaic' toxin similar to that of type C strain 6813, a non-toxic non-hemagglutinating and a 33 kDa hemagglutinating (HA-33) component similar to those of strain C-Stockholm, and an exoenzyme C3 of which the sequence was in full agreement with the known genetic sequence of strain 003-9. The BTxD complex, from C. botulinum strain CB-16, consisted of a neurotoxin with the observed sequence identical with that of type D strain BVD/-3 and of an NTNH with the observed sequence identical with that of type C strain C-Yoichi. Remarkably, the observed protein sequence of CB-16 NTNH differed by one amino acid from the known gene sequence: L859 instead of F859. The BTxE complex, from a C. botulinum isolated from herring sprats, consisted of the neurotoxin with an observed sequence identical with that from strain NCTC 11219 and an NTNH similar to that from type E strain Mashike (1 amino acid difference with observed sequence). BTxF, from C. botulinum strain Langeland (NCTC 10281), consisted of the neurotoxin and an NTNH; observed sequences from both proteins were in agreement with the gene sequence known from strain Langeland. As with BTxA and BTxB, matrix-assisted laser desorption/ionisation (MALDI) MS provided provisional identification from trypsin digest peptide maps and liquid chromatography-electrospray (tandem) mass spectrometry (LC-ES MS) afforded unequivocal identification from amino acid sequence information of digest peptides obtained in trypsin digestion. 相似文献
14.
Ulmer TS Ramirez BE Delaglio F Bax A 《Journal of the American Chemical Society》2003,125(30):9179-9191
NMR measurements of a large set of protein backbone one-bond dipolar couplings have been carried out to refine the structure of the third IgG-binding domain of Protein G (GB3), previously solved by X-ray crystallography at a resolution of 1.1 A. Besides the commonly used bicelle, poly(ethylene glycol), and filamentous phage liquid crystalline media, dipolar couplings were also measured when the protein was aligned inside either positively or negatively charged stretched acrylamide gels. Refinement of the GB3 crystal structure against the (13)C(alpha)-(13)C' and (13)C'-(15)N dipolar couplings improves the agreement between experimental and predicted (15)N-(1)H(N) as well as (13)C(alpha)-(1)H(alpha) dipolar couplings. Evaluation of the peptide bond N-H orientations shows a weak anticorrelation between the deviation of the peptide bond torsion angle omega from 180 degrees and the angle between the N-H vector and the C'-N-C(alpha) plane. The slope of this correlation is -1, indicating that, on average, pyramidalization of the peptide N contributes to small deviations from peptide bond planarity ( = 179.3 +/- 3.1 degrees ) to the same degree as true twisting around the C'-N bond. Although hydrogens are commonly built onto crystal structures assuming the N-H vector orientation falls on the line bisecting the C'-N-C(alpha) angle, a better approximation adjusts the C(alpha)-C'-N-H torsion angle to -2 degrees. The (15)N-(1)H(N) dipolar data do not contradict the commonly accepted motional model where angular fluctuations of the N-H bond orthogonal to the peptide plane are larger than in-plane motions, but the amplitude of angular fluctuations orthogonal the C(alpha)(i-1)-N(i)-C(alpha)(i) plane exceeds that of in-plane motions by at most 10-15 degrees. Dipolar coupling analysis indicates that for most of the GB3 backbone, the amide order parameters, S, are highly homogeneous and vary by less than +/-7%. Evaluation of the H(alpha) proton positions indicates that the average C(alpha)-H(alpha) vector orientation deviates by less than 1 degrees from the direction that makes ideal tetrahedral angles with the C(alpha)-C(beta) and C(alpha)-N vectors. 相似文献
15.
16.
Stereodivergent Carbamate Synthesis by Selective in Situ Trapping of Organic Carbonate Intermediates 下载免费PDF全文
Dr. Eddy Martin Eduardo C. Escudero‐Adán Prof. Dr. Arjan W. Kleij 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(5):1722-1727
Trans carbamates have been prepared in a diastereoselective approach by a judicious one‐pot combination of organic carbonates, prepared in situ, and suitable amine reagents under appropriate reaction conditions. This unprecedented approach allows for stereodivergence from a single oxirane substrate with easy access to both cis and trans carbamate isomers with high stereoselectivity (>19:1 d.r.). Key to the control of the diastereoselective nature of the conversions that lead to the trans carbamates is the in situ formation of trans‐configured oligo/polycarbonates through Al catalysis, which provides the targeted products after aminolysis. The present results demonstrate the valorization of a renewable carbon‐based reagent (CO2) into new valuable scaffolds and an unusual stereocontrol exerted through carbonate intermediates. A series of control experiments support the proposed mechanistic rationale towards the trans carbamate products, which is based on the trapping of an in situ formed trans‐configured oligo/polycarbonate. 相似文献
17.
18.
Dr. Markus Lampimäki Dr. Veronika Zelenay Dr. Adéla Křepelová Dr. Zhi Liu Rui Chang Dr. Hendrik Bluhm Dr. Markus Ammann 《Chemphyschem》2013,14(11):2419-2425
Ozone adsorption and decomposition on metal oxides is of wide interest in technology and in atmospheric chemistry. Here, ozone‐adsorption‐induced band bending is observed on Ti‐ and Fe‐oxide model surfaces under dry and humid conditions. Photoelectron spectroscopic studies indicate the effect of charge transfer to O3, which limits the surface coverage of the precursor to decomposition reactions. This is also consistent with the negative pressure dependence observed in previous studies. These results contribute to our fundamental understanding of ozone adsorption and decomposition mechanisms on metal oxides of environmental and technological relevance. 相似文献
19.
Dr. Martha V. Escárcega‐Bobadilla Dr. Marta Martínez Belmonte Eddy Martin Eduardo C. Escudero‐Adán Prof. Dr. Arjan W. Kleij 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(8):2641-2648
A tetraoxo bis‐Zn(salphen) supramolecular host can bind various divalent metal salts, thereby providing access to trinuclear bifunctional systems that incorporate both Lewis acid sites and dynamically bound nucleophilic anions. The formation of these trinuclear species was investigated and their stability features were also determined. The application of these trinuclear complexes as bifunctional catalysts was evaluated in the formation of cyclic organic carbonates from epoxides and CO2. The catalytic data, in combination with control experiments, clearly demonstrate that these trinuclear compounds show much higher recycling potential compared to various control compounds and they can be used in up to five cycles without an observable loss in activity. Furthermore, this new recyclable catalytic system does not require any additives and can be applied under solvent‐free conditions. 相似文献
20.
do Nascimento Ticiano Gomes Borges Arthur Luy Tavares Ferreira de Almeida Lara Mendes Ribeiro Êurica Adélia Nogueira Silva Fernanda Geny Calheiros da Costa Silva Valdemir do Nascimento Prata Ana Paula Basílio-Júnior Irinaldo Diniz Goulart Marília Oliveira Fonseca Morilla Demetrius Peireira de Freitas Johnnatan Duarte Aragão Cícero Flávio Soares 《Journal of Thermal Analysis and Calorimetry》2022,147(21):11949-11963
Journal of Thermal Analysis and Calorimetry - This work prepared and characterized microcapsule of Uncaria tomentosa (UT) in order to standardize a spray-dryer Uncaria tomentosa extract. The UT... 相似文献