Practical Aspects of Carbon-13 Double Quantum NMR
We want to address an erroneous view that has recently been advanced on 13C double quantum NMR. A recent publication (I) introduced a modified version (I) of the original double quantum NMR experiments; this new version claims to offer an attractive increase in sensitivity by a factor of three, or a decrease in the size of the required data matrix by a factor of four. To avoid disappointment among spectroscopists we wish to make it clear that this modified version offers no gain in sensitivity whatsoever in comparison with the other double quantum experiments (2-6), provided they are properly optimized. It is shown here that the sensitivity of this modified experiment can be even slightly lower. The claim of a reduction of the size of the required data matrix is also shown to be incorrect. In the original two-dimensional double quantum “C experiments, the acquisition time t2 starts immediately after the final “read pulse” (Fig. 1), and the time during which the double quantum coherence evolves is labeled ti. The detected 13C-13C satellites (7) are modulated in amplitude as a function of tl with the double quantum frequencies (2). In the quadrature-Fi-detection version of this experiment (3), results are combined with those of a second experiment which contains a composite 45: pulse (8) in the evolution period. This allows the sign of the modulation frequency to be determined, which simplifies the interpretation of the results. A simpler and more sensitive alternative to obtain quadrature F, detection has been proposed more recently (6); an increase of the flip angle of the final “read pulse” to 135” provides directly satellite signals which are modulated in phase as a function oft,. In either case, data acquisition is started after the final read pulse and the coherence transfer echo (9) is detected (4, 6). The time domain signal of a carbon A, directly coupled to carbon X, is then given by sA(tl, t2) = c exp[-i(nA + &)t,] exp[i& + d&2]
Antibiotics from basidiomycetes. XXIX: Pilatin, a new antibiotically active marasmane derivative from cultures of Flagelloscypha pilatii agerer.
Pilatin, a new marasmane derivative, was isolated from fermentations of the cyphelloid fungus Flagelloscypha pilatii. Its structure was determined by chemical and physical methods. Pilatin inhibits the growth of bacteria and fungi at concentrations of 5-50 micrograms/ml. The compound is highly cytotoxic. The incorporation of thymidine and uridine into DNA and RNA in Ehrlich carcinoma ascitic cells is strongly inhibited by pilatin. Like marasmic acid pilatin causes frameshift mutations in Salmonella typhimurium TA98.
Explicit solutions for N-dimensional Schrödinger equations with position-dependent mass
With the consideration of spherical symmetry for the potential and mass function, one-dimensional solutions of nonrelativistic Schrodinger equations with spatially varying effective mass are successfully extended to arbitrary dimensions within the frame of recently developed elegant nonperturbative technique, where the BenDaniel-Duke effective Hamiltonian in one dimension is assumed like the unperturbed piece, leading to well-known solutions, whereas the modification term due to possible use of other effective Hamiltonians in one dimension and, together with the corrections coming from the treatments in higher dimensions, are considered as an additional term like the perturbation. Application of the model and its generalization for the completeness are discussed.