Journal of Magnetic Resonance, Series B最新文献

General expressions involving Mathieu functions are derived for the magnetic field and stored energy associated with distributed currents, flowing, both azimuthally and axially, on the surface of an elliptic cylinder. These expressions can be used to design elliptical gradient coils of minimum inductance for MRI, as well as elliptical coils that will generate a uniform magnetic field or higher order shim fields.

A new design for a minimum inductance, distributed current, longitudinal (z) gradient coil, fabricated on the surface of an elliptic cylinder is proposed. By incorporating a small axial current, in addition to the purely azimuthal current which has been considered hitherto, this design greatly reduces the nonuniformity of the longitudinal magnetic field in transverse planes, which is associated with a purely azimuthal current flowing on the surface of an elliptic cylinder. For a coil with an axial ratio of the ellipse of 0.75, the deviation from gradient linearity along thezaxis is <0.1% out to 0.66awhereais the length of the semi-major axis. The nonuniformity of the field in the transverse directions is <0.1% out to 0.5a, over most of the target-field region |z| < 0.4a.

HCN, a new 3D NMR technique for stepwise coherence transfer from¹H to¹³C to¹⁵N and reverse through direct spin couplings¹J_CHand¹J_CN, is presented as a method for detection and assignment of histidine and tryptophan side-chain¹H,¹³C, and¹⁵N resonances in uniformly¹³C/¹⁵N-labeled proteins. Product-operator calculations of cross-peak volumes vs adjustable delay τ₃were employed for determination of optimal τ₃. For the phosphatidylinositol 3-kinase (PI3K SH3 domain, MW = 9.6 kD) at pH 6, H(C)N, the¹H/¹⁵N projection, produced observable cross peaks within 20 min. and was completely selective for the single tryptophan and single histidine. The 3D HCN experiment yielded well-defined cross peaks in 20 h for the¹³C/¹⁵N-labeled origin-specific DNA binding domain from simian virus 40 T-antigen (T-ag-OBD_131–259, MW = 15.4 kD) at pH 5.5. Resonances from all six histidines in T-ag-OBD were observed, and 11 of the 12¹H and¹³C chemical shifts and 10 of the 12¹⁵N chemical shifts were determined. The¹³C dimension proved essential in assignment of the multiply overlapping¹H and¹⁵N resonances. From the spectra recorded at a single pH, three of the imidazoles were essentially neutral and the other three were partially protonated (22–37%). HCN yielded strong cross peaks after 18 h on a 2.0 mMsample of phenylmethanesulfonyl fluoride (PMSF)-inhibited α-lytic protease (MW = 19.8 kD) at pH 4.4. No spectra have been obtained, however, of native or boronic acid-inhibited α-lytic protease after 18 h at various temperatures ranging from 5 to 55°C, probably due to efficient relaxation of active-site imidazole¹H and/or¹⁵N nuclei.

The ∼2.6 ppm aspartate multiplet ofN-acetyl aspartate (NAA) is considered a potential source of additional information onN-acetyl aspartatein vivo.Because the aspartate multiplet is the AB part of a strongly coupled ABX system it gives rise, as is shown in the analysis presented, to a significant field-strength dependence in the echo-time-dependent modulations of the response to typical spatial-localization sequences. The echo-time dependence of this response is developed analytically, not only for the STEAM and the PRESS localization sequences, but also for a spin-echo sequence. It is then verified experimentally at 2.35 T. The field-strength dependence of the response is demonstrated by evaluating the changes in the echo-time-dependent responses to each of the three sequences at field strengths of 1.5, 2.35, and 4.0 T. By means of these results, the preferred sequence (PRESS) can be optimized for the NAA aspartate multiplet at each field strength, as is illustrated with the human brain spectra obtainedin vivoat 1.5 T. Thesein vivospectra compare the optimal, long TE timing (163 ms) with a suboptimal TE (70 ms), for the observation of the ∼2.6 ppm aspartate resonances of NAA.