14N overtone NMR spectra under magic angle spinning: experiments and numerically exact simulations

It was recently shown that high resolution (14)N overtone NMR spectra can be obtained directly under magic angle spinning (MAS) conditions [L. A. O'Dell and C. I. Ratcliffe, Chem. Phys. Lett. 514, 168 (2011)]. Preliminary experimental results showed narrowed powder pattern widths, a frequency shift that is dependent on the MAS rate, and an apparent absence of spinning sidebands, observations which appeared to be inconsistent with previous theoretical treatments. Herein, we reproduce these effects using numerically exact simulations that take into account the full nuclear spin Hamiltonian. Under sample spinning, the (14)N overtone signal is split into five (0, ±1, ±2) overtone sidebands separated by the spinning frequency. For a powder sample spinning at the magic angle, the +2ω(r) sideband is dominant while the others show significantly lower signal intensities. The resultant MAS powder patterns show characteristic quadrupolar lineshapes from which the (14)N quadrupolar parameters and isotropic chemical shift can be determined. Spinning the sample at other angles is shown to alter both the shapes and relative intensities of the five overtone sidebands, with MAS providing the benefit of averaging dipolar couplings and shielding anisotropy. To demonstrate the advantages of this experimental approach, we present the (14)N overtone MAS spectrum obtained from L-histidine, in which powder patterns from all three nitrogen sites are clearly resolved.

Estimating internuclear distances between half-integer quadrupolar nuclei by central-transition double-quantum sideband NMR spectroscopy

We demonstrate the estimation of homonuclear dipolar couplings, and thereby internuclear distances, between half-integer spin quadrupolar nuclei by central-transition (CT) double-quantum (2Q) sideband nuclear magnetic resonance (NMR) spectroscopy. It is shown that the rotor-encoded sideband amplitudes from CT 2Q coherences in the indirect dimension of the two-dimensional NMR spectrum are sensitive probes of the magnitude of the homonuclear dipolar coupling, but are significantly less affected by other NMR parameters such as the magnitudes and orientations of the electric field gradient tensors. Experimental results of employing the [Formula: see text] recoupling sequence to the 11B spin pair of bis(catecholato)diboron resulted in an estimation of the internuclear B–B distance as (169.6 ± 3) pm, i.e., with a relative uncertainty of ±2%, and in excellent agreement with the distance of 167.8 pm determined by single-crystal X-ray diffraction.

Quantitative CT imaging of the spatio-temporal distribution patterns of vasa vasorum in aortas of apoE-/-/LDL-/- double knockout mice

OBJECTIVE

To investigate the distribution of vasa vasorum (VV) relative to advanced atherosclerotic lesions (calcified, fibrotic or hemorrhaged) along the aortic wall of apoE-/-/LDL-/- mice at the age of 25 and 80 weeks using high-resolution nano-CT.

METHODS

Aortas from male apoE-/-/LDL-/- mice at the age of 25 weeks (n=4) and 80 weeks (n=7) were infused in situ with contrast agent and harvested for scanning with nano-CT. The spatial distribution of vasa vasorum [number and area/cross-section (mm2)] was compared to aortic luminal cross-sectional area and plaque cross-sectional area in the ascending aorta, aortic arch and descending aorta. Results were complemented with co-localized histology.

RESULTS

The number and total luminal cross-sectional area of VV showed a significant decrease in the ascending aorta and aortic arch from 25 to 80 weeks but not in the descending aorta. The number and cross-sectional area of VV showed significant local differences depending on whether it was near a fibrotic, and hemorrhaged or calcified plaque in animals at the age of 80 weeks. Area of VV progressively increased along the aorta from least in the ascending aorta<aortic arch<descending aorta in animals at the age of 80 weeks and is inverse in animals aged 25 weeks.

CONCLUSION

Atherosclerotic lesion type is correlated to the number and cross-sectional area of VV in different aortic segments in apoE-/-/LDL-/- mice. The chronological development of VV along the aorta proceeds distally from the ascending aorta and aortic arch.

Symmetry-based recoupling in double-rotation NMR spectroscopy

In this contribution, we extend the theory of symmetry-based pulse sequences of types CN(n) (nu) and RN(n) (nu) in magic-angle-spinning nuclear resonance spectroscopy [M. H. Levitt, in Encyclopedia of Nuclear Magnetic Resonance, edited by D. M. Grant and R. K. Harris (Wiley, Chichester, 2002), Vol. 9]. to the case of rotating the sample simultaneously around two different angles with respect to the external magnetic field (double-rotation). We consider the case of spin-1/2 nuclei in general and the case of half-integer quadrupolar nuclei that are subjected to weak radio frequency pulses operating selectively on the central-transition polarizations. The transformation properties of the homonuclear dipolar interactions and J-couplings under central-transition-selective spin rotations are presented. We show that the pulse sequence R2(2) (1)R2(2) (-1) originally developed for homonuclear dipolar recoupling of half-integer quadrupolar nuclei under magic-angle-spinning conditions [M. Eden, D. Zhou, and J. Yu, Chem. Phys. Lett. 431, 397 (2006)] may be used for the same purpose in the case of double rotation, if the radio frequency pulses are synchronized with the outer rotation of the sample. We apply this sequence, sandwiched by central-transition selective 90 degrees pulses, to excite double-quantum coherences in homonuclear spin systems consisting of (23)Na and (27)Al nuclei.

[Patient surveys as an element of quality management in outpatient care: development and assessment of a questionnaire]

OBJECTIVE

The present study was designed to develop and assess a questionnaire measuring all relevant quality dimensions of general practice care from the patients' perspective. Furthermore, the study aimed to evaluate the implementation of a patient survey in outpatient care.

METHODS

Based on the Kölner Patientenfragebogen (KPF) and by developing some additional new items, we created the new questionnaire KPF-A (Kölner Patientenfragebogen-ambulant) which covers all relevant aspects of outpatient care. The questionnaire was distributed to the patients of 41 GP's and specialists in ambulatory care from different regions of Germany. N=3188 patients were included in the sample. We used these data to assess some selected psychometric characteristics of the KPF-A. Factor analysis was used to examine the underlying factor structure. A qualitative study was conducted to evaluate the implementation of the patient survey. Therefore, all N=41 doctors involved were asked to complete five open questions concerning their experience.

RESULTS

Most scales of the KPF-A showed good psychometric characteristics in the present study. Factor analysis revealed a two-factors solution for the new items representing the dimensions "professional competence" and "medical equipment". We have not yet been able to find a sound factor solution for those items representing the dimension "Staff and Organisation". The results of the qualitative study revealed a satisfying implementation of the patient survey in daily routine from the doctors' perspective. The length of the questionnaire was criticised by some participants. In the design of the study patients were supposed to fill in the questionnaires after consultation. This turned out to be difficult. We therefore modified the KPF-A so that patients can fill it in either before or after consultation.

Antikörperkontrollierte zytostatische Therapie des malignen Thymoms bei begleitender Myasthenia gravis

In a 46-year-old female patient with malignant thymoma and concomitant myasthenia gravis relapse with gravitational metastases occurred 6 1/2 years after the first operation. Metastases could be removed surgically only partially and were subsequently irradiated with 50 Gy. After 3 1/2 years renewed metastatic growth occurred. Until then the concomitant myasthenia had been stable during treatment with pyridostigmine and azathioprin and intermittent prednisone; acetylcholine receptor antibody titres had remained largely stable. Combined cytostatic treatment with vincristine, cyclophosphamide, prednisone and doxorubicin or cisplatin led to regression of metastases during the observation period of 1 1/2 years and at the same time to stabilisation of the myasthenia. Acetylcholine receptor antibody titres decreased and this was roughly paralleled by clinical improvement. Whereas there is no obvious correlation of antibodies against acetylcholine-receptor protein and tendency of tumour growth there is good agreement with the course of the accompanying myasthenia.

Environmentally friendly flame retardants. A detailed solid-state NMR study of melamine orthophosphate

We used solid-state NMR spectroscopy to gain detailed information about the proton positions, proximities and the hydrogen-bonding network in the environmentally friendly flame retardant melamine orthophosphate (MP). High-resolution proton one- and two-dimensional solid-state NMR spectra were obtained at high external magnetic field in combination with fast magic angle spinning of the sample. Furthermore, we recorded homo- and heteronuclear correlation spectra of types (15)N–(15)N, (1)H–(13)C, (1)H–(15)N and (1)H–(31)P. In addition, we determined the geometry of the NH and NH(2) groups in MP by (15)N–(1)H heteronuclear recoupling experiments.We were able to completely assign the different isotropic chemical shifts in MP. Furthermore, we could identify the protonation of the melamine and orthophosphate moieties. The experimental results are discussed in connection with the structural model obtained by powder X-ray diffraction together with a combined molecular modeling-Rietveld refinement approach (De Ridder et al. Helv. Chim. Acta 2004; 87: 1894). We show that the geometry of the NH2 groups can only be successfully estimated by solid-state NMR.

[Management of the operation room in an university hospital]

The heart of any surgical department is the operation room area. Any disturbances in the daily routine will affect the work flow of the whole hospital. As an example the major complaints of a university surgical department regarding workflow and communication are outlined. To solve these problems a team "OR organization" was established, which started the work based on a new developed OR statute. Within a short period the contentment of the employees as well as the workflow improved. But as a matter of fact, even in the following years of central OR management there is still the need to further stabilize the system and carefully improve the controlling system.

Proton-Selective17O−1H Distance Measurements in Fast Magic-Angle-Spinning Solid-State NMR Spectroscopy for the Determination of Hydrogen Bond Lengths

We present a proton-selective method to determine 17O-1H distances in organic, biological, and biomimetic materials by fast magic-angle-spinning solid-state NMR spectroscopy. This method allows the determination of internuclear distances between specific (17O, 1H) spin pairs selectively. It enables the estimation of medium-range 17O...1H distances across hydrogen bonds in the presence of short-range 17O-1H contacts sharing the same 17O site. The method employs the newly developed symmetry-based radiofrequency pulse sequence SR%@mt;sys@%4%@sx@%1%@be@%2%@sxx@%%@mx@% applied to the protons to achieve heteronuclear dipolar recoupling, while simultaneously decoupling the homonuclear proton dipolar interactions. Fast MAS (50 kHz) and high static magnetic fields (18.8 T) achieve the required proton spectral resolution.

Sensitivity Enhancement and Heteronuclear Distance Measurements in Biological 17O Solid-State NMR

In this contribution we present a comprehensive approach to study hydrogen bonding in biological and biomimetic systems through 17O and 17O-1H solid-state NMR combined with density functional theory calculations of 17O and 1H NMR parameters. We explore the signal enhancement of 17O in L-tyrosine.HCl using repetitive double-frequency swept radio frequency pulses in solid-state NMR. The technique is compatible with high magnetic fields and fast magic-angle spinning of the sample. A maximum enhancement by a factor of 4.3 is obtained in the signal-to-noise ratio of the selectively excited 17O central transition in a powdered sample of 17Oeta-L-tyrosine.HCl at an external field of 14.1 T and a spinning frequency of 25 kHz. As little as 128 transients lead to meaningful 17O spectra of the same sample at an external field of 18.8 T and a spinning frequency of 50 kHz. Furthermore we employed supercycled symmetry-based pulse sequences on the protons to achieve heteronuclear longitudinal two-spin-order (IzSz) recoupling to determine 17O-1H distances. These sequences recouple the heteronuclear dipolar 17O-1H couplings, where dipolar truncation is absent, while decoupling the homonuclear proton dipolar interactions. They can be applied at fast magic-angle-spinning frequencies up and beyond 50 kHz and are very robust with respect to 17O quadrupolar couplings and both 17O and 1H chemical shift anisotropies, which makes them suitable for the use at high external magnetic fields. The method is demonstrated by determining the 17Oeta-1H distance in L-tyrosine.HCl at a spinning frequency of 50 kHz and an external field of 18.8 T.

Microcoil High-Resolution Magic Angle Spinning NMR Spectroscopy

We report the construction of a dual-channel microcoil nuclear magnetic resonance probehead allowing magic-angle spinning for mass-limited samples. With coils down to 235 mum inner diameter, this allows high-resolution solid-state NMR spectra to be obtained for amounts of materials of a few nanoliters. This is demonstrated by the carbon-13 spectrum of a tripeptide and a single silk rod, prepared from the silk gland of the Bombyx mori silkworm. Furthermore, the microcoil allows for radio frequency field strengths well beyond current probe technology, aiding in getting the highest possible resolution by efficiently decoupling the observed nuclei from the abundantly present proton nuclei.