Sven Macholl

Dynamic Nuclear Polarization of [1-13C]pyruvic acid at 4.6 tesla.

Dynamic Nuclear Polarization (DNP) of the (13)C nucleus has been investigated for [1-(13)C]pyruvic acid, doped with the trityl radical OX063Me, at 4.64 T and 1.15K. The dependence of the polarization on microwave frequency, radical concentration and electron saturation was studied. For optimized conditions, a (13)C polarization equal to 64+/-5% was obtained, an increase by more than a factor of two compared with earlier results at 3.35 T of the same system. It was furthermore observed that the addition of gadolinium, which resulted in a twofold polarization increase at 3.35 T, only resulted in a minor improvement at 4.64 T. The dependence of the electron saturation on microwave frequency and microwave power was quantified by first moment measurements which were obtained by nucleus-electron double resonance (NEDOR) experiments. Complete electron saturation was observed for a microwave frequency close to the centre frequency of the ESR line, and by using maximum power of the microwave source. The DNP build-up time at 4.64 T (approximately 3000 s) was prolonged by approximately a factor three over the build-up time at 3.35 T (approximately 1200 s). However, after approximately 20 min of microwave irradiation the polarization at 4.64 T exceeded the polarization at 3.35 T.

Trityl biradicals and 13C dynamic nuclear polarization.

The objective of this study is to investigate if trityl biradicals could lead to more efficient dynamic nuclear polarization (DNP) for low gamma nuclear spins at low temperature (approximately 1 K) than a trityl monoradical. Three novel trityl biradicals of different size are synthesized, characterized and employed for hyperpolarization of [1-(13)C]pyruvic acid at 3.35 T and 4.64 T. Intramolecular electron-electron distances are obtained via dipolar couplings from electron paramagnetic resonance (EPR) spectroscopy at X-band and W-band that match well with calculated molecular structures. Steady-state DNP levels and build-up times are measured as function of radical concentration, magnetic field strength and microwave frequency for each biradical. Similar maximal DNP is obtained with all studied biradicals whereas a twice as high polarization is achievable with the monoradical. Both the biradicals and the monoradical show approximately a doubling of the polarization when increasing the field strength from 3.35 T to 4.64 T. Biradical concentrations at maximum polarization are several times lower than the optimum monoradical concentration, but the penalty is a much longer build-up time. Adding a small amount of Gd(3+) to the samples (molar fraction of typically 100 ppm) has the same effect on DNP with the biradicals as with the monoradical. The electron longitudinal relaxation time T(1e) is found to be independent of the radical type and the field strength in this study. The same dependence of T(1e) on the trityl concentration is observed for all radicals. A considerable shortening of the (13)C longitudinal relaxation time is observed for biradicals which agrees with the shortened build-up time compared to the monoradical at the same trityl concentration. This is probably the reason for lower DNP levels with trityl biradicals.

In vivo pH imaging with (99m)Tc-pHLIP.

PurposeA novel molecular imaging agent has been developed recently, which stains tissues of low extracellular pH [pH (low) insertion peptide, pHLIP®]. A pH-dependent process of peptide folding and insertion into cell membranes has been found in vitro. Targeting of acidic solid tumours has been demonstrated in vivo using fluorescence and PET labels. Here, we present proof of feasibility studies of pHLIP with a single-photon emission computed tomography (SPECT) label, 99mTc-AH114567, with focus on preclinical efficacy and imageability.ProceduresLewis lung carcinoma, lymph node carcinoma of the prostate and prostate adenocarcinoma tumour xenografts were grown in mice and characterised by the angiogenesis marker 99mTc-NC100692 and by extracellular pH measurements with 31P-MRS of 3-aminopropyl phosphonate. Biodistribution was assessed and CT/SPECT imaging performed. Oral administration of bicarbonate served as control.Results and ConclusionTc-AH114567 can be obtained via a robust synthesis with good radiolabelling profile and improved formulation. The tracer retains the pH-dependent ability to insert into membranes and to target tumours with similar pharmacokinetics and efficacy that had been demonstrated earlier for pHLIP with optical or 64Cu PET labels. Despite the inherent challenges of SPECT compared to optical and PET imaging, e.g., in terms of lower sensitivity, 99mTc-AH114567 shows adequate image quality and contrast. The main development need for transitioning SPECT labelled pHLIP into the clinic is more rapid background signal reduction, which will be the focus of a subsequent optimisation study.

Contrast agent and radiation dose reduction in abdominal CT by a combination of low tube voltage and advanced image reconstruction algorithms

AbstractObjectivesTo assess image quality in abdominal CT at low tube voltage combined with two types of iterative reconstruction (IR) at four reduced contrast agent dose levels.MethodsMinipigs were scanned with standard 320xa0mg I/mL contrast concentration at 120xa0kVp, and with reduced formulations of 120, 170, 220 and 270xa0mg I/mL at 80xa0kVp with IR. Image quality was assessed by CT value, dose normalized contrast and signal to noise ratio (CNRD and SNRD) in the arterial and venous phases. Qualitative analysis was included by expert reading.ResultsProtocols with 170xa0mg I/mL or higher showed equal or superior CT values: aorta (278–468xa0HU versus 314xa0HU); portal vein (205–273xa0HU versus 208xa0HU); liver parenchyma (122–146xa0HU versus 115xa0HU). In the aorta, all 170xa0mg I/mL protocols or higher yielded equal or superior CNRD (15.0–28.0 versus 13.7). In liver parenchyma, all study protocols resulted in higher SNRDs. Radiation dose could be reduced from standard CTDIvolu2009=u20097.8xa0mGy (6.2xa0mSv) to 7.6xa0mGy (5.2xa0mSv) with 170xa0mg I/mL.ConclusionCombining 80xa0kVp with IR allows at least a 47xa0% contrast agent dose reduction and 16xa0% radiation dose reduction for images of comparable quality.Key Points• There is a balance between image quality, contrast dose and radiation dose.n • Iterative reconstruction has a major, positive impact on this balance.n • Both contrast dose and radiation dose can be reduced in abdominal CT.n • The trade-off can be quantitatively described by a 3D model.n • Contrast and radiation dose can be tailored according to specific safety concerns.

2H MAS NMR of strongly dipolar coupled deuterium pairs in transition metal dihydrides : extracting dipolar coupling and quadrupolar tensor orientations from the lineshape of spinning sidebands

A selectively D2 labeled transition metal dihydride, Os(D2)(Cl)2(CO)(PiPr3)2, was synthesized and studied by 2H magic angle spinning (MAS) NMR spectroscopy. It was found that the interference between the n quadrupolar and homonuclear dipolar interaction results in a characteristic lineshape of the MAS sidebands. n The basic properties of the interference of homonuclear dipolar and quadrupolar coupling on the 2H NMR n lineshape were elucidated, using average Hamiltonian theory, and exact simulations of the experiments were achieved by stepwise integration of the equation of motion of the density matrix. These simulations show that it n is possible to determine the size of the dipolar interaction and thus the D–D distance from the lineshape of the sidebands.

[18F]Fluciclatide in the in vivo evaluation of human melanoma and renal tumors expressing αvβ3 and αvβ5 integrins

Purpose[18F]Fluciclatide is an integrin-targeted PET radiopharmaceutical. αvβ3 and αvβ5 are upregulated in tumor angiogenesis as well as on some tumor cell surfaces. Our aim was to use [18F]fluciclatide (formerly known as [18F]AH111585) for PET imaging of angiogenesis in melanoma and renal tumors and compare with tumor integrin expression.MethodsEighteen evaluable patients with solid tumors ≥2.0xa0cm underwent [18F]fluciclatide PET/CT. All patients underwent surgery and tumor tissue samples were obtained. Immunohistochemical (IHC) staining with mouse monoclonal antibodies and diaminobenzidine (DAB) was applied to snap-frozen tumor specimens, and additional IHC was done on formalin-fixed paraffin-embedded samples. DAB optical density (OD) data from digitized whole-tissue sections were compared with PET SUV80% max, and Patlak influx rate constant (Ki) data, tumor by tumor.ResultsTumors from all 18 patients demonstrated measurable [18F]fluciclatide uptake. At the final dynamic time-point (55xa0min after injection), renal malignancies (in 11 patients) demonstrated an average SUV80% max of 6.4u2009±u20092.0 (range 3.8xa0–xa010.0), while the average SUV80% max for metastatic melanoma lesions (in 6 patients) was 3.0u2009±u20092.0 (range 0.7xa0–xa06.5). There was a statistically significant difference in [18F]fluciclatide uptake between chromophobe and nonchromophobe renal cell carcinoma (RCCs, with SUV80% max of 8.2u2009±u20091.8 and 5.4u2009±u20091.4 (Pu2009=u20090.020) and tumor-to-normal kidney (T/N) ratios of 1.5u2009±u20090.4 and 0.9u2009±u20090.2, respectively (Pu2009=u20090.029). The highest Pearsons correlation coefficients were obtained when comparing Patlak Ki and αvβ5 OD when segregating the patient population between melanoma and RCC (ru2009=u20090.83 for Ki vs. melanoma and ru2009=u20090.91 for Ki vs. RCC). SUV80% max showed a moderate correlation with αvβ5 and αvβ3 OD.Conclusion[18F]Fluciclatide PET imaging was well tolerated and demonstrated favorable characteristics for imaging αvβ3 and αvβ5 expression in melanoma and RCC. Higher uptake was observed in chromophobe than in nonchromophobe RCC. [18F]Fluciclatide may be a useful radiotracer to improve knowledge of integrin expression.

Revealing CSA tensors and hydrogen bonding in methoxycarbonyl urea: A combined 13C, 15N and 13C14N2 dipolar chemical shift NMR and DFT study

Abstract Methoxycarbonyl urea (MCU), a potential long-term nitrogen fertilizer, is studied by 13C and 15N dipolar chemical shift NMR spectroscopy and ab initio calculations. Employing a combination of dipolar chemical shift NMR, selective isotope labeling and ab initio gas phase calculations, possible molecular structures and chemical shielding tensors of all 15N nuclei and of two out of the three 13C nuclei were revealed. Four possible stable configurations of the molecule with different energies were found in the calculations. The CSA tensors were calculated for these configurations. While the calculated 13C(urea) CSA tensor orientation of the configuration with the lowest energy is in good agreement with the experimental tensor orientation, there are pronounced differences between calculated and experimental tensor eigenvalues. These differences are a clear indication of the presence of intermolecular hydrogen bonds in the experimental sample, which are neglected in the gas phase calculations. Four different possible orientations of the experimental 13C(urea) CSA tensor exist, due to symmetry. This ambiguity is solved by comparison with results from GIAO calculations of the 13C CSA tensor, employing the minimum energy configuration (EEZ). It is found that the orientation, where δ11 points approximately in direction of N(imide), δ22 approximately in direction of the C=O bond, and δ33 is oriented perpendicular to the molecular frame, is adopted in the molecule.

NMR Study of Blue-Shifting Hydrogen Bonds Formed by Fluoroform in Solution

Abstract Low-temperature (193 K) 1H, 13C and 15N NMR spectra of blue- and red-shifting H-bonded complexes formed by fluoroform with various proton acceptors were measured. Experimental NMR parameters were plotted versus the ab initio calculated H-bond strength (MP2/6–31+G(d, p); interaction energy varies from ~5 up to 25 kJ · mol−1 in the series). We show that experimental 1H and 15N shieldings, as well as the H/D isotope effect on 13C shielding change monotonously with the calculated H-bond strengthening. The 13C chemical shift and the CH scalar coupling change non-monotonously and the extremum points are situated approximately in the region of transformation from blue- to red-shifting H-bonds. The most informative NMR feature is the H/D isotope effect on 15N shielding which changes its sign upon transformation from blue- to red-shifting H-bonds. To rationalize these observations, ab initio calculations of 13C and 15N shieldings as functions of C···H and C···N distances were performed for complexes of CHF3 with acetonitrile (blue-shifting) and pyridine (red-shifting). The coupling of the vibrations of the covalent and hydrogen bonds has been accounted for by direct computation of the distance C···N = f(C···H) dependence. We demonstrate that the unusual sign of the H/D isotope effect on 15N chemical shift across a blue-shifting H-bond can be explained as a result of the inversion of the dynamic coupling of two vibrations.

NMR crystallography of amides, peptides and protein–ligand complexes

NMR crystallography, the combination of solid-state NMR techniques, chemical modelling, quantum chemical calculations and other characterization techniques, allows the determination of molecular and supramolecular structures which are not amenable to standard X-ray crystallography. The method is demonstrated on a set of application examples. First the principles and practical considerations of NMR crystallography based on dipolar NMR spectroscopy are outlined in conformational studies of polymorphs of N-octyl-gluconamide and of methoxycarbonyl urea. Then structural studies of two substrate–inhibitor complexes, human manganese superoxide dismutase with azide and nickel superoxide dismutase with cyanide, are reviewed. Finally an example of ongoing developments in the related field of EPR crystallography is reported.