Solid state water motions revealed by deuterium relaxation in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-zeolite A

Deuterium NMR relaxation experiments, low temperature deuterium NMR lineshape analysis, and FTIR spectra are consistent with a new model for solid state jump dynamics of water in (2)H(2)O-synthesized kanemite and (2)H(2)O-hydrated Na(+)-Zeolite A. Exchange occurs between two populations of water: one in which water molecules are directly coordinated to sodium ions and experience C(2) symmetry jumps of their OH bonds, and a population of interstitial water molecules outside the sodium ion coordination sphere that experience tetrahedral jumps of their OH bonds. For both samples the C(2) jump rate is much faster than the tetrahedral jump rate. (2)H NMR relaxation experiments match well with the fast exchange regime of the model over a wide range of temperatures, including room temperature and above. For hydrated Zeolite A, the kinetic activation parameters for the tetrahedral and C(2) symmetry jumps are Delta H tet++=+17 kJ/mol, Delta S tet++=-109 J/(mol K), Delta H C2++=+19 kJ/mol, and Delta S C2++=-20 J/(mol K). For kanemite, Delta H tet++ =+23 kJ/mol, Delta S tet++=-69 J/(mol K), Delta H C2++ =+23 kJ/mol, and Delta S C2++ =-11 J/(mol K).     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Multiple-Rotor-Cycle QPASS Pulse Sequences: Separation of Quadrupolar Spinning Sidebands with an Application to La NMR

The quadrupolar phase-adjusted spinning sidebands (QPASS) pulse sequence has been recently demonstrated as a useful method for obtaining quadrupolar parameters with magic-angle spinning NMR. The sequence separates spinning sidebands by order in a two-dimensional experiment. A sheared projection of the 2D spectrum effectively yields the infinite spinning rate second-order quadrupolar powder pattern, which can be analyzed to determine quadrupolar coupling constants and asymmetry parameters. The RF power and spinning speed requirements of the original QPASS sequence make it an experimentally demanding technique. A new version of the sequence is demonstrated here and is shown to alleviate many problems associated with the original sequence. New solutions to the determining equations, based on the use of multiple rotor cycles in the QPASS sequence, lead to longer delays between the nine π pulses, provide less chance of pulse overlap, and allow for use of weaker RF field strengths that excite only the central quadrupolar transition. A three-rotor-cycle version of the new experiment is demonstrated on the ¹³⁹La nucleus.     

Incorporating H chemical shift determination into C-direct detected spectroscopy of intrinsically disordered proteins in solution

Exclusively heteronuclear ¹³C-detected NMR spectroscopy of proteins in solution has seen resurgence in the past several years. For disordered or unfolded proteins, which tend to have poor ¹H-amide chemical shift dispersion, these experiments offer enhanced resolution and the possibility of complete heteronuclear resonance assignment at the cost of leaving the ¹H resonances unassigned. Here we report two novel ¹³C-detected NMR experiments which incorporate a ¹H chemical shift evolution period followed by ¹³C-TOCSY mixing for aliphatic ¹H resonance assignment without reliance on ¹H detection.     

Determination of loads applied perpendicularly to the outer boundary of a ring using coefficients of influence

A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used, following an approach similar to the one presented in a previous paper. Examples of application are given and the possible increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined.