Ho-Keui Han

Beta-azidoalanine dipeptide 1 was synthesized, and its azido stretching vibration in H2O and dimethyl sulfoxide (DMSO) was studied by using Fourier transform (FT) IR spectroscopy. The dipole strength of the azido stretch mode is found to be about 19 and 5 times larger than those of the CN and SCN stretch modes, respectively, which have been used as local environmental IR sensors. The azido stretch band in H2O is blue-shifted by about 14 cm(-1) in comparison to that in DMSO, indicative of its sen

An unprecedented high level of regioselectivities (up to 96%) in the intermolecular crossed acyloin condensations of various aromatic aldehydes with acetaldehyde was realized by an appropriate choice of N-heterocyclic carbene catalysts.

Vibrational chromophores that are sensitive to local electrostatic environment are useful probes of structural variations of proteins on subnanosecond time scales, but their short vibrational lifetimes often limit their applicability. Here we explore a possibility to increase the lifetime of nitrile probes by introducing heavy atoms between the probe and protein side chains. Stereoisomers of thiocyanato- and selenocyanato-derivatized prolines, Pro-SCN and Pro-SeCN, are synthesized, and their CN

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTTechnetium Complexes for the Quantitation of Brain AmyloidHogyu Han, Cheon-Gyu Cho, and Peter T. LansburyView Author Information Department of Chemistry Massachusetts Institute of Technology Cambridge, Massachusetts 02139 Cite this: J. Am. Chem. Soc. 1996, 118, 18, 4506–4507Publication Date (Web):May 8, 1996Publication History Received22 January 1996Published online8 May 1996Published inissue 1 January 1996https://pubs.acs.org/doi/10.1021/ja96020

Infrared (IR) probes based on terminally blocked β-isocyanoalanine (AlaNC) and p -isocyanophenylalanine (PheNC) amino acids were synthesized. These isonitrile (NC)-derivatized compounds were extensively characterized by FTIR and femtosecond IR pump–probe spectroscopies, and a direct comparison was made with popularly used nitrile (CN)- and azide (N 3 )-derivatized analogs. It is shown that the isonitrile stretch frequency exhibits extremely high sensitivity to hydrogen-bonding interactions. In a

An infrared (IR) probe based on isonitrile (NC)-derivatized alanine 1 was synthesized and the vibrational properties of its NC stretching mode were investigated using FTIR and femtosecond IR pump-probe spectroscopy. It is found that the NC stretching mode is very sensitive to the hydrogen-bonding ability of solvent molecules. Moreover, its transition dipole strength is larger than that of nitrile (CN) in nitrile-derivatized IR probe 2. The vibrational lifetime of the NC stretching mode is found

Infrared (IR) probes based on terminally blocked β-cyanamidoalanine (AlaNHCN) 1 and p -cyanamidophenylalanine (PheNHCN) 2 were synthesized, and the vibrational properties of their CN stretch modes were studied using Fourier transform infrared (FTIR) and femtosecond IR pump–probe spectroscopies in combination with quantum chemical calculations. From FTIR studies, it is found that the transition dipole strengths of the cyanamide (NHCN) group in 1 and 2 are much larger than those of the nitrile (CN

The infrared (IR) probe often suffers from an unexpected complex absorption profile due to the Fermi resonance and short vibrational lifetime, which restricts the application of time-resolved IR spectroscopy to investigate the site-specific structural dynamics of the protein. Researchers have found that isotope substitution to the IR probe not only removes the Fermi resonance but also extends the dynamic observation window with a prolonged vibrational lifetime. This method has been successfully

To study the azido gauche effect on the backbone conformation of β-azidoalanine (Aza) dipeptide (AAD, Ac-Aza-NHMe) and tripeptide (AAT, Ac-Aza-Aza-NH(2)), we used spectroscopic methods in combination with quantum chemistry calculations and molecular dynamics (MD) simulations. From the (1)H NMR coupling constants and (1)H,(1)H NOESY experimental data, we found that AAD in water mainly adopts a seven-membered cyclic (C(7)) rather than polyproline II (P(II)) backbone conformation and prefers the ga