β-Azidoalanine as an IR Probe: Application to Amyloid Aβ(16-22) Aggregation

Abstract

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 sensitivity to the electrostatic environment. To test the utility of beta-azidoalanine as an IR probe of the local electrostatic environment in proteins, azidopeptide 4 was prepared by its incorporation into Abeta(16-22) peptide of the Alzheimer's disease amyloid beta-protein at position Ala21. The amide I IR spectrum of 4 in D2O suggests that the azidopeptide thus modified forms in-register beta-sheets in aggregates as observed for normal Abeta(16-22). The azido peak frequency of 4 in aggregates is almost identical to that in DMSO, indicating that the azido group is not exposed to water but to the hydrophobic environment. We believe that beta-azidoalanine will be used as an effective IR probe for providing site-specific information about the local electrostatic environments of proteins.

2D attenuated total reflectance infrared spectroscopy reveals ultrafast vibrational dynamics of organic monolayers at metal-liquid interfaces

“…The azide group is a common vibrational probe in static and time-resolved infrared spectroscopy for the investigation of structural dynamics and environmental interactions. 38,40,[54][55][56][57] Formation of the monolayers results in a rather slow spectral diffusion for samples with two and 11 methylene groups between the azide group and the surface. Generally, an increase in length of the alkyl chain between the surface of immobilization and the vibrational probe also results in a smaller time-dependent inhomogeneity.…”

“…Different previous works explored the applicability of azide probes as reporters for ultrafast molecular dynamics. 38,[54][55][56][57] In these studies, spectral diffusion of azide groups covalently attached to different alkyl backbones in bulk solution and different polar and apolar environments generally occurred with rather short time constants in a range of ≈0.5-2 ps. 38,54,55,57 This indicates a generally rapid loss of correlation for the azide vibrational probe.…”

Solvation of fluoro-acetonitrile in water by 2D-IR spectroscopy: A combined experimental-computational study

“…10) or the CN − (Refs. 11 and 12) ion in water, the -C= =O group of N-methylacetamide (NMA) in water, 13,14 the phosphate group of hydrated phospholipids, 15 the OH/OD vibration of HOD in either D 2 O or H 2 O, [16][17][18][19] -C≡ ≡O, -C≡ ≡N, -N − 3 or -SCN ligands, [20][21][22][23][24] or as unnatural amino acids [25][26][27][28] inside proteins, to name just a few.…”

IR Probes of Protein Microenvironments: Utility and Potential for Perturbation

“…[1] Cyano (CN) groups had previously been proposed as probes of electrostatics, [2] and CN-derivatized amino acids have since been incorporated into model peptides [3][4][5][6][7][8][9][10] and proteins. [11][12][13][14][15][16][17][18][19] More recently, azide (N 3 ) groups have also been examined as probes and have been incorporated into peptides [20] and proteins. [21][22][23][24][25][26][27][28] The CN and N 3 probes have the advantage of being strong chromophores; however, unlike CÀD labels, CN and N 3 substituents are extrinsic probes that may introduce interactions that are not present in the native protein, and sensitivity to these artificial interactions may desensitize them to their native protein environment.…”