3,278 research outputs found
Differentiation of HMBC Two- and Three-Bond Correlations: A Method to Simplify the Structure Determination of Natural Products
No full textThe structure elucidation of natural products, today, relies heavily on the application of proton-detected heteronuclear NMR experiments. Perhaps the most useful of these methods is the HMBC experiment, which provides correlations between protons and carbons over two and three bonds. The application of the HMBC method for the direct translation of H,C correlations to yield bonding information is limited, however, by the fact that it does not distinguish between (2)J(CH) and (3)J(CH) correlations. Reported here is an application of the recently described 1,1-ADEQUATE experiment that yields only two bond H,C connectivities in H-C-C moieties and therefore allows the differentiation of HMBC two- and three-bond correlations. The method is demonstrated on a 14 mg sample of a new marine natural product, 5,6-dihydro lamellarin H (1)
Rotaxane- and Catenane-based Molecular Machines and Motors
No full textThe concept of (macroscopic) machine can be extended to the molecular level. A molecular machine can be defined as an assembly of a discrete number of molecular components (i.e., a supramolecular system) in which the component parts can display changes in their relative positions as a result of some external stimulus. Rotaxanes and catenanes are promising systems for the construction of artificial molecular machines. The design, synthesis and investigation of chemical systems able to function as molecular machines and motors is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology. A few examples of molecular machines taken from our own research will be illustrated
Accurate Determination of 1H-15N Dipolar Couplings Using Inaccurate Settings of the Magic Angle in Solid-State NMR Spectroscopy
No full textMagic-angle spinning (MAS) is an essential ingredient in a wide variety of solid-state NMR experiments. The standard procedures to adjust the rotor angle are not highly accurate, resulting in a slight misadjustment of the rotor from the magic angle (θRL = tan-1 √2) on the order of a few millidegrees. This small missetting has no significant impact on the overall spectral resolution, but is sufficient to reintroduce anisotropic interactions. Shown here is that site-specific 1H-15N dipolar couplings can be accurately measured in a heavily deuterated protein. This method can be applied at arbitrarily high MAS frequencies, since neither rotor synchronization nor particularly high radiofrequency field strengths are required. The off-MAS method allows the quantification of order parameters for very dynamic residues, which often escape an analysis using existing methods
M. G. Stemmermann’s Correspondence and Materials on Monosodium Glutamate
No full textThis is a collection of various documents from the 1970s, including most predominately, the correspondence between two women: M.G. Stemmermann, MD and Liane Reif-Lehrer, PhD, as they collaborated on Monosodium Glutamate (MSG) research. Reif-Lehrer, a renowned scientist from Harvard Medical School, is also known for her history of resilience in fleeing Nazi occupied territory in 1939 and her dedication to sharing her story. Stemmermann and Reif-Lehrer worked together to author articles detailing their experiences with children suffering from MSG intolerance—from seizures to vision issues. Along with their correspondence, there are also newspaper clippings, manuscript copies, and contributions from other doctors and scientists on the effects of MSG in food.https://mds.marshall.edu/owen_clinic_institute/1026/thumbnail.jp
The Public Trust in Science Scale
No full textThe development and validation of the scale was published in:
Reif, A., Taddicken, M., Guenther, L., Schröder, J. T. & Weingart, P. (2025). The Public Trust in Science Scale: A Multilevel and Multidimensional Approach. Science Communication, 47(5), 670–701. https://doi.org/10.1177/1075547024130275
Cross Correlated Relaxation for the Measurement of Angles between Tensorial Interactions.
No full textTheory, experimental aspects, and use in structure calculation of cross-correlated relaxation rates measured on zero- and double-quantum coherences in liquid state NMR are presented. The relative size of the interaction depends on the projection angle between the two tensorial interactions. The tensorial interaction can be either a dipolar interaction or a chemical shift anisotropy relaxation mechanism (CSA). Effects of additional sources of relaxation on the cross-correlated relaxation rates are analyzed. Also, an easy-to-use formalism is given to manipulate different cross-correlated relaxation interactions. The application addresses measurement of the backbone angle psi in a protein by measuring dipole(N-15-H-1)-dipole(C-13(alpha)-H-1(alpha)) and CSA(N-15)- dipole(C-13(alpha)-H-1(alpha)) cross-correlated relaxation rates. It is shown that ambiguities due to the 3 cos(2)theta-1 dependence of one cross-correlated relaxation rate can be overcome by measuring additional cross-correlated relaxation rates. The use of cross-correlated relaxation rates is demonstrated in structure calculations. (C) 2000 Academic Press
Righting an injustice or American Taliban? the removal of Confederate statues
No full textIn recent years, several racial instances have occurred in the United States that have reinvigorated and demanded action concerning Confederate flags, statues and symbology. The Charleston massacre in 2015 prompted South Carolina to finally remove the Confederate battle flag from state grounds. The Charlottesville riots in 2017 accelerated the removal of Confederate statues from the public square. However, the controversy has broadened the discussion of how the Civil War monuments are to be viewed, especially in the public square. Many of the monuments were not built immediately following the Civil War, but later, during the era of Jim Crow and the disenfranchisement of African Americans during segregation in the South. Are they tributes to heroes or are they relics of a racist past that sought not to remember as much as to intimidate and bolster white supremacy?
This work seeks to break up the eras of Confederate monument building and demonstrate that different monuments were built at different times (and are still being built). The monuments reflect other events in the country happening at the time, as well as the thinking of those who built them. This author hopes that these nuances will add to the general discussion and the usual three responses toward the statues of either taking them down to either destroy them, keep them, but add context, or place them in museums, cemeteries or private property. These nuances are important, possibly rendering all three as valid decisions. This author will use multiple lenses, including Union, Confederate, and African American lenses as interpreters for the various eras discussed. (Author abstract)Reif, A.W. (2018). Righting an injustice or American Taliban? the removal of Confederate statues. Retrieved from http://academicarchive.snhu.eduMaster ArtsHistoryCollege of Online and Continuing Educatio
ADEQUATE, a New Set of Experiments to Determine the Constitution of Small Molecules at Natural Abundance
No full textThe RP-HPLC measurement and QSPR analysis of log Po/w values of several Pt(II) complexes
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