1. 17O MAS NMR Correlation Spectroscopy at High Magnetic Fields
Eric G Keeler, Vladimir K Michaelis, Michael T Colvin, Ivan Hung, Peter L Gor'kov, Timothy A Cross, Zhehong Gan, Robert G Griffin J Am Chem Soc. 2017 Dec 13;139(49):17953-17963. doi: 10.1021/jacs.7b08989. Epub 2017 Nov 30.
The structure of two protected amino acids, FMOC-l-leucine and FMOC-l-valine, and a dipeptide, N-acetyl-l-valyl-l-leucine (N-Ac-VL), were studied via one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy. Utilizing 17O magic-angle spinning (MAS) NMR at multiple magnetic fields (17.6-35.2 T/750-1500 MHz for 1H) the 17O quadrupolar and chemical shift parameters were determined for the two oxygen sites of each FMOC-protected amino acids and the three distinct oxygen environments of the dipeptide. The one- and two-dimensional, 17O, 15N-17O, 13C-17O, and 1H-17O double-resonance correlation experiments performed on the uniformly 13C,15N and 70% 17O-labeled dipeptide prove the attainability of 17O as a probe for structure studies of biological systems. 15N-17O and 13C-17O distances were measured via one-dimensional REAPDOR and ZF-TEDOR experimental buildup curves and determined to be within 15% of previously reported distances, thus demonstrating the use of 17O NMR to quantitate interatomic distances in a fully labeled dipeptide. Through-space hydrogen bonding of N-Ac-VL was investigated by a two-dimensional 1H-detected 17O R3-R-INEPT experiment, furthering the importance of 17O for studies of structure in biomolecular solids.
2. FMOC-amino acid surfactants: discovery, characterization and chiroptical spectroscopy
R Vijay, Prasad L Polavarapu J Phys Chem A. 2012 Nov 8;116(44):10759-69. doi: 10.1021/jp308134m. Epub 2012 Oct 25.
The sodium salts of amino acids with hydrophobic fluorenyl methyloxy carbonyl (FMOC) group and short alkyl side chains are found to have surfactant properties. This was ascertained first through visual observation of concentration dependent solution behavior and then confirmed by tensiometry measurements. The critical micelle concentrations (CMCs) for the sodium salts of FMOC-l-valine, FMOC-L-leucine, and FMOC-L-isoleucine have been determined to be ~0.1 M. The sodium salt of FMOC-l-norleucine forms a gel at >0.2 M. Powder X-ray diffraction measurements indicated that these surfactants adopt bilayer structures. Three different chiroptical spectroscopic properties, namely optical rotation, electronic circular dichroism, and vibrational circular dichroism, are presented for these surfactants. The specific rotation is found to exhibit an unprecedented increase with concentration beyond CMC. This observation opens up a new area of research relating the concentration dependent increase in specific rotation to the size and shape of aggregates formed by the surfactants.
