Terahertz Spectroscopy and Density Functional Theory Investigation of the Dipeptide L -Carnosine
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Terahertz Spectroscopy and Density Functional Theory Investigation of the Dipeptide L-Carnosine Jens Neu1
· Charles A. Schmuttenmaer2
Received: 28 June 2019 / Accepted: 17 October 2019 / © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Terahertz spectroscopy and density functional theory (DFT) calculations have been used to study the dipeptide L-carnosine. In this paper, we expand the range of materials described with THz measurements and DFT calculations from amino acids to dipeptides. Three clear resonances were detected in the experimental spectrum at 1.5 THz, 1.9 THz, and 2.3 THz. Additionally, we performed periodic boundary condition DFT calculations. The computational spectrum accurately reproduces the experimental one. Keywords Terahertz spectroscopy · Density functional theory · Peptides · Carnosine
1 Introduction In this paper, we present THz spectra of L-carnosine, a dipeptide. This dipeptide is naturally occurring in muscles where it acts as a pH buffer [1, 2]. Furthermore, Lcarnosine is explored for its potential in therapeutics, targeting age-related illnesses [3, 4]. As a dipeptide, it is an excellent model system to validate that DFT calculations which were previously used to describe amino acids are valid for larger systems. The range of materials that can be identified using THz spectroscopy is constantly expending: covering artificial metamaterials [5–10, 10, 11], illegal drugs [12–14], Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10762-019-00636-7) contains supplementary material, which is available to authorized users. Jens Neu
[email protected] Charles A. Schmuttenmaer [email protected] 1
Department of Molecular Biophysics and Biochemistry, and Molecular Science Institute, Yale University, West Haven, CT, 06516, USA
2
Department of Chemistry, and Energy Science Institute, Yale University, New Haven, CT, 06520-8107, USA
International Journal of Infrared and Millimeter Waves
explosives [13, 15], and organic molecular crystals [16–21]. Molecular crystals are of crucial importance in pharmaceutical products as the crystallinity can have an influence on the biochemical activity of these materials [22]. The measured spectral features can be used to identify the materials. However, in contrast to IR spectroscopy in which a spectral feature can easily be assigned a particular stretch or bend mode, THz resonances are delocalized over a large number of atoms within the unit cell. This delocalization makes it impossible to simply assign a resonance at a certain THz frequency to a particular movement. While this seems to be a disadvantage, it is actually one of the strengths of THz spectroscopy. A delocalized mode is intrinsically sensitive to small and minor changes in the material. For example, THz spectroscopy can be used to distinguish different polymorphs [18, 23], or single atom replacements which are hard to detect with crystallographic techniques [24]. Density functional theory (DFT) calculation
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