1,212 research outputs found
Determination of the Orientation of a Distant Bond Vector in a Molecular Reference Frame by Cross-Correlated Relaxation of Nuclear Spins
No full textDespite a separation of 7 Å the angles between C–H and H–H vectors (e.g., C3–H3/H25–H26) in 1 can be determined by NMR spectroscopy by the measurement of cross‐correlated double‐ and zero‐quantum relaxation rates in solution. As shown by comparison with a crystal structure of 1, the intervector projection angles can be measured with an error of at most ±3°
Direct measurement of angles between bond vectors in high-resolution NMR
No full textAngles between two interatomic vectors are measured for structure elucidation in solution nuclear magnetic resonance (NMR). The angles can be determined directly by using the effects of dipole-dipole cross-correlated relaxation of double-quantum and zero-quantum coherences. The measured rates can be directly related to the angular geometry without need for calibration of a Karplus-type curve, as is the case for scalar coupling measurements, and depend only on the rotational correlation time of the molecule as an empirical parameter. This makes the determination of torsional angles independent from the measurement of coupling constants. The two interatomic vectors can in principle be arbitrarily far apart. The method was demonstrated on the measurement of the peptide backbone angle psi in the protein rhodniin, which is difficult to determine in solution by NMR spectroscopy
Jahrestagung der Floristisch-soziologischen Arbeitsgemeinschaft (FlorSoz) in Freiburg im Breisgau 2013
No full textDie vier ausgewählten Exkursionen werden Sie in die wichtigsten Naturräume
Südbadens führen, von der hochmontanen Stufe im Feldbergbereich über die montan geprägte Waldvegetation des Mittleren Schwarzwaldes hin zur kollinen Hügellandschaft des Kaiserstuhls und der planaren Stufe der Rheinebene und –aue.
INHALT:
Vorwort
Exkursion 1: Der Feldberg im Schwarzwald. Von Arno Bogenrieder.
Exkursion 2: Geschichtsträchtige Vegetation und Landschaft im Schwarzwald - Einzigartige und repräsentative Fallbeispiele aus dem Zweribachgebiet. Von Thomas Ludemann.
Exkursion 3: Magerrasen im zentralen Kaiserstuhl und ihre Pflege. Von Oliver Karbiener und Bernd-Jürgen Seitz.
Exkursion 4: Auenentwicklung am südlichen Oberrhein - "Trockenaue" und rezente Rheinaue. Von Albert Reif, Stefanie Gärtner, Reinhard Zimmermann, Volker Späth, Jörg Lange.
Nachexkursion: Wutachschlucht. Von Albert Reif, Thomas Ludemann.
Autorenverzeichni
Differentiation of HMBC Two- and Three-Bond Correlations: A Method to Simplify the Structure Determination of Natural Products
No full textThe structure elucidation of natural products, today, relies heavily on the application of proton-detected heteronuclear NMR experiments. Perhaps the most useful of these methods is the HMBC experiment, which provides correlations between protons and carbons over two and three bonds. The application of the HMBC method for the direct translation of H,C correlations to yield bonding information is limited, however, by the fact that it does not distinguish between (2)J(CH) and (3)J(CH) correlations. Reported here is an application of the recently described 1,1-ADEQUATE experiment that yields only two bond H,C connectivities in H-C-C moieties and therefore allows the differentiation of HMBC two- and three-bond correlations. The method is demonstrated on a 14 mg sample of a new marine natural product, 5,6-dihydro lamellarin H (1)
Field and magic angle spinning frequency dependence of proton resonances in rotating solids.
No full textProton detection in solid state NMR is continuously developing and allows one to gain new insights in structural biology. Overall, this progress is a result of the synergy between hardware development, new NMR methodology and new isotope labeling strategies, to name a few factors. Even though current developments are rapid, it is worthwhile to summarize what can currently be achieved employing proton detection in biological solids. We illustrate this by analysing the signal-to-noise ratio (SNR) for spectra obtained for a microcrystalline α-spectrin SH3 domain protein sample by (i) employing different degrees of chemical dilution to replace protons by incorporating deuterons in different sites, by (ii) variation of the magic angle spinning (MAS) frequencies between 20 and 110 kHz, and by (iii) variation of the static magnetic field B0. The experimental SNR values are validated with numerical simulations employing up to 9 proton spins. Although in reality a protein would contain far more than 9 protons, in a deuterated environment this is a sufficient number to achieve satisfactory simulations consistent with the experimental data. The key results of this analysis are (i) with current hardware, deuteration is still necessary to record spectra of optimum quality; (ii) 13CH3 isotopomers for methyl groups yield the best SNR when MAS frequencies above 100 kHz are available; and (iii) sensitivity increases with a factor beyond B0 3/2 with the static magnetic field due to a transition of proton-proton dipolar interactions from a strong to a weak coupling limit
NMR spectroscopic determination of angles alpha and delta in RNA from CH-dipolar coupling, P-CSA cross-correlated relaxation
No full textA new method is introduced to measure the backbone torsion angles alpha and zeta in C-13-labeled oligonucleotides. The experiments relies on the quantification of the cross-correlated relaxation of C,P double and zero quantum coherence caused by the C,H dipolar coupling and the P chemical shift anisotropy. Two-dimensional surfaces that reveal the angular dependence of the cross-correlated relaxation rates depend on the backbone angles alpha and beta as well as epsilon and zeta and are interpreted using torsion angle information for the angles beta and epsilon from experiments measuring (3)J(H,P) and (3)J(C,P) coupling constants. The experiments have been carried out on the 10mer RNA 5'-CGCUUUUGCG-3' that forms a hairpin and in which the four uridine residues are C-13-labeled in the ribofuranoside moiety
Structure Determination of a Key Intermediate of the Enantioselective Pd Complex Catalyzed Allylic Substitution Reaction
No full textThe structure of a catalytic intermediate with important implications for the interpretation of the stereochemical outcome of the palladium complex catalyzed allylic substitution with phosphino-oxazoline (PHOX) ligands is determined by liquid state NMR. The complex displays a novel structure that is highly distorted compared with other palladium eta(2)-olefin complexes known so far. The structure has been determined from nuclear overhauser data (NOE), scalar coupling constants, and long range projection angle restraints derived from dipole dipole cross-correlated relaxation of multiple quantum coherence. The latter restraints have been implemented into a distance geometry protocol. The projection angle restraints yield a higher precision in the determination of the relative orientation of the two molecular moieties and are essential to provide an exact structural definition of the olefinic part of the catalytic intermediate with respect to the ligand
Determination of methyl order parameters using solid state NMR under off magic angle spinning.
No full textQuantification of dipolar couplings in biological solids is important for the understanding of dynamic processes. Under Magic Angle Spinning (MAS), order parameters are normally obtained by recoupling of anisotropic interactions involving the application of radio frequency pulses. We have recently shown that amide backbone order parameters can be estimated accurately in a spin-echo experiment in case the rotor spinning angle is slightly mis-calibrated. In this work, we apply this method to determine methyl order parameters in a deuterated sample of the SH3 domain of chicken a-spectrin in which the methyl containing side chains valine and leucine are selectively protonated
- …
