Constraints on the structure of (CUG)97 RNA from magic-angle-spinning solid-state NMR spectroscopy.
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Biomedical subjects
Christian Herbst
Publications and source records attributed to Christian Herbst.
Tailoring broadband inversion pulses for MAS solid state NMR.
A simple approach is demonstrated for designing optimised broadband inversion pulses for MAS solid state NMR studies of biological systems. The method involves a two step numerical optimisation procedure and takes into account experimental requirements such as the pulse length, resonance offset range and extent of H(1) inhomogeneity compensation needed. A simulated annealing protocol is used initially to find appropriate values for the parameters that define the well known tanh/tan adiabatic pulse such that a satisfactory spin inversion is achieved with minimum RF field strength. This information is then used in the subsequent stage of refinement where the RF pulse characteristics are further tailored via a local optimisation procedure without imposing any restrictions on the amplitude and frequency modulation profiles. We demonstrate that this approach constitutes a generally applicable tool for obtaining pulses with good inversion characteristics. At moderate MAS frequencies the efficacy of the method is experimentally demonstrated for generating double-quantum NMR spectra via the zero-quantum dipolar recoupling scheme RFDR.
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Solid state NMR at high magic angle spinning frequencies: dipolar chemical shift correlation with adiabatic inversion pulse based RF pulse schemes.
The efficacy of hetero- and homonuclear dipolar recoupling employing tanh/tan adiabatic inversion pulse based RF pulse schemes has been examined at high magic angle spinning (MAS) frequencies via numerical simulations and experimental measurements. An approach for minimising the recoupling RF power level is presented, taking into consideration the spinning speed, the range of resonance offsets and H(1) inhomogeneities and the available RF field strength. This involves the tailoring of the frequency and amplitude modulation profiles of the inversion pulses. The applicability of tanh/tan pulse based dipolar recoupling schemes to spinning speed regimes where the performance with conventional rectangular pulses may not be satisfactory is demonstrated.
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A comparison of different methods to measure the EGG contact quotient.
The results from six published electroglottographic (EGG-based) methods for calculating the EGG contact quotient (CQEGG) were compared to closed quotients derived from simultaneous videokymographic imaging (CQKYM). Two trained male singers phonated in falsetto and in chest register, with two degrees of adduction in both registers. The maximum difference between methods in the CQEGG was 0.3 (out of 1.0). The CQEGG was generally lower than the CQKYM. Within subjects, the CQEGG co-varied with the CQkym, but with changing offsets depending on method. The CQEGG cannot be calculated for falsetto phonation with little adduction, since there is no complete glottal closure. Basic criterion-level methods with thresholds of 0.2 or 0.25 gave the best match to the CQKYM data. The results suggest that contacting and de-contacting in the EGG might not refer to the same physical events as do the beginning and cessation of airflow.
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