Diffusion-ordered two-dimensional nuclear magnetic resonance spectroscopy

Abstract

diamide's behavior on the basis of spectroscopic data should be more straightforward than for 1. Previously reported variabletemperature 'H NMR measurements (A5(NH)/Ar) indicated that the intramolecularly hydrogen-bonded and non-hydrogen-bonded6 states of 2 are of very similar enthalpy in CD2Cl2.2a In contrast, when an attempt was made to account for solvation by including three CH2C12 molecules in a "supermolecule" calculation, AMI predicted the minimum energy intramolecularly hydrogen-bonded conformation of 2 to be 1.9 kcal/mol more enthalpically favorable than the minimum energy non-hydrogen-bonded conformation.3In order to provide a more quantitative comparison with the calculations, we have now carried out an IR-based van't Hoff analysis of the intramolecular hydrogen bonding equilibrium occurring in a 1 mM CH2C12 solution of 2 over the temperature range -69 to 23 °C. Figure 1 shows the N-H stretch region of the IR spectra obtained at high and low temperatures. Both hydrogen-bonded (3340-50 cm"1) and non hydrogen-bonded6 (3443-8 cm"1) bands are observed at each temperature. No hydrogen-bonded N-H stretch band can be detected at any temperature for a 1 mM sample of iV-methylcyclohexylacetamide (3) in CH2C12; therefore, we used this compound to estimate the extinction coefficient of the non-hydrogen-bonded N-H stretch band of 2 as a function of temperature, van't Hoff analysis (intramolecularly hydrogen-bonded vs non-hydrogen-bonded states; each "state" comprises a set of conformations) indicated that the internally hydrogen-bonded state of 2 is 0.25 ± 0.06 kcal/mol less enthalpically favorable and 0.67 ± 0.48 eu more entropically favorable than the non-hydrogen-bonded state.7 (CHE-9157510), the Eastman Kodak Company, and the Upjohn Company for support. The FT-IR spectrometer was purchased with funds provided by the Office of Naval Research (N00014-90-1902).Supplementary Material Available: Representative van't Hoff plot for intramolecular hydrogen bonding of 2 in CH2C12 (1 page). Ordering information is given on any current masthead page.(10) (a) Baker, E.

Progressive Structuring of a Branched Antimicrobial Peptide on the Path to the Inner Membrane Target

“…Lipid Phase Partition of B2088 and Monomer Peptide-To characterize the affinity of B2088 and its monomeric precursors for the lipid phase, translational diffusion coefficients (D S ) for free peptides and peptide micelle complexes were measured using DOSY experiments (40). Pure DPC and mixed DPC-POPG micelles were used to represent mammalian and bacterial cell membranes, respectively.…”

Real-life applications of the MULVADO software package for processing DOSY NMR data

“…The main idea of DOSY is to separate the pure components of a mixture by introducing a new dimension to a conventional NMR spectrum. 1 The new dimension is constructed by the diffusion coefficients of the components, which are dependent on their individual physical properties such as size and shape (the hydrodynamic radius) of the molecule, temperature and viscosity. 2 A DOSY data set is obtained by measuring a series of stimulated echo spectra with different gradient strengths.…”

“…where N is the number of components in the sample and D n is the diffusion coefficient of the nth component m 2 s 1 .  0 is an effective diffusion time (s), which is the correction of a real diffusion time  to  υ/3 for experiments with a single gradient pulse each for diffusion encoding and decoding, where υ is the duration of gradient pulses (s).…”

“…Both υ and  0 are experimental constants. K is the product of υ, , the gyromagnetic ratio of the nuclei under study rad s 1 T 1 , and g, the gradient strength T m 1 . I 0 n is the intensity at a gradient strength g equal to zero.…”

Structure-Activity Relationship of the N-terminal Helix Analog of Papiliocin, PapN

“…18,19 The duration of the gradient pulse was 1.5 ms to obtain a 2 % residual signal with the maximum gradient strength. The 2D data sets were processed using BIOSPIN software.…”