Full-Field High-Strain Gradient Evaluation from Wrapped ESPI Data Using Phasors

Electronic Speckle Pattern Interferometry (ESPI) is a sensitive optical method commonly used for making full-field measurements of surface displacements. It would be very desirable to be able to extend the technique also to determine surface strains. This would provide a full-field, non-contact strain measurement method that avoids the substantial installation burden of strain gauges. A mathematical approach is described where the ESPI data from an in-plane interferometer are numerically differentiated to determine surface strains. This is a challenging process because numerical differentiation is very sensitive to the presence of noise and ESPI data are inherently noisy. In addition, the phase information from ESPI data are wrapped modulo-2π. The resulting phase discontinuities make it difficult to use local averaging to smooth the data. A technique is described here where phasors are used to avoid the need for phase unwrapping. The effect of noise is reduced by a localized multiple smoothing technique that is effective in preserving spatial resolution, even near very high strain concentrations. Example measurements are shown and the effectiveness of the proposed method is illustrated.     

Methods for the measurement of (1)J(NCalpha) and (2)J(NCalpha) from a simplified 2D (13)C(alpha)-coupled (15)N SE-HSQC spectrum

Two methods for the measurement of (2)J(NCalpha) and (1)J(NCalpha) in (15)N/(13)C-labeled small and medium-size proteins are described. The current approach is based on simplified (13)C(alpha)-coupled (15)N HSQC spectra, where the two (2)J(NCalpha) doublets are separated into two subspectra corresponding to the alpha and beta spin states of the residue's own alpha carbon. The displacement of the two (2)J(NCalpha) doublets between the two subspectra provides an accurate value for (1)J(NCalpha). The alpha/beta filtration is achieved by taking the sum and difference of the recorded complementary in-phase and antiphase J-coupled spectra. J-multiplication is utilized in one of the proposed methods. In this method, an additional coupling evolution period, which is incremented in concert with t(1), is included in the pulse sequence making it possible to scale the peak-to-peak separation.     

Diverting Hydrogenations with Wilkinson's Catalyst towards Highly Reactive Rhodium(I) Species

The addition of Barton's base has a dramatic effect on the classic rhodium(III)‐mediated hydrogenations promoted by Wilkinson′s catalyst. Following the initial oxidative addition, a barrierless reductive elimination of HCl from the traditional rhodium(III) intermediates instantly produces a rhodium(I) monohydride species, which is remarkably reactive in the hydrogenation of several internal alkynes and functionalized trisubstituted alkenes. The direct formation of this species is unprecedented upon addition of molecular hydrogen and its catalytic potential has been hitherto barely explored.     

Some aspects of quantitative 2D NMR

We have studied the application of 2D HSQC for quantitative measurements and propose some improvements to the previously published Q-HSQC method. Application of CPMG-INEPT for polarization transfer period suppresses the evolution of J(HH), and thus corrects the shape of the cross-peaks. The better cross-peak shape makes phase correction and integration of the cross-peaks easier. Further, the (13)C resonance offset dependency can have a significant influence to the results. The offset effects can be compensated either by correcting results with a proper coefficient, or using 90 degrees composite (13)C pulses in the pulse sequence. The results show that these modifications improve the applicability of 2D HSQC for quantitative analysis when studying molecules possessing large J(HH) couplings and wide (13)C chemical shift range.