Nitrile IR intensities characterize electric fields and hydrogen bonding in protic, aprotic, and protein environments

Nitriles are widely used as vibrational probes; however, the interpretation of their IR frequencies is complicated by hydrogen bonding (H-bonding) in protic environments. We report a new vibrational Stark effect (VSE) that correlates the electric field projected on the nitrile bond to the transition dipole moment and, by extension, the nitrile peak area or integrated intensity. This linear VSE applies to both H-bonding and non-H-bonding interactions. It can therefore be generally applied to determine electric fields in all environments. Additionally, it allows for semi-empirical extraction of the H-bonding contribution to the blueshift of the nitrile frequency. Nitriles were incorporated at H-bonding and non-H-bonding protein sites using amber suppression, and each nitrile variant was structurally characterized at high resolution. We exploited the combined information now available from variations in frequency and integrated intensity and demonstrate that nitriles are a generally useful probe for electric fields.

AC/DC analysis of infrared intensities by means of QTAIM and Hirshfeld atomic charges and dipoles

Infrared intensities of water were partitioned using the AC/DC analysis employing QTAIM and Hirshfeld atomic charges and dipoles. By including atomic dipoles, both models are superior to those based solely on point charges, but their descriptions of the IR intensity profiles are still remarkably different. Whereas QTAIM points towards opposite charge and dipole contributions to the dipole, Hirshfeld indicates these contributions to be aligned to one another, and this is propagated into the Atomic and Dynamic Contributions for the asymmetric stretch of water. Therefore an earlier demonstration on the need of atomic polarizations for achieving accurate descriptions of IR intensities must be further refined to find out the best polarization model, i.e. the one which will provide the most meaningful interpretations to IR intensities. The Atomic Contributions recently developed by our group seem to be a valuable tool for pursuing this systematic study on charge models featuring atomic polarizations, not only employing QTAIM and Hirshfeld partitions but any other scheme delivering charges or charges and dipoles.

Formation of C4H4 from photolysis of icy C2H2 with 175 nm at 60 K

ABSTRACT The absorption spectrum of solid acetylene (C2H2) at 10 K was measured in wavelength range 107–250 nm with UV light from a synchrotron source. Based on the absorption spectrum, we irradiated at 175 nm the icy acetylene at 60 K; the results yielded a new set of IR absorption lines with similar temporal profiles of production during the photolysis periods. From icy 12C2H2, these new features were recorded at 3276.8, 1598.7, 963.0, 936.3, and 671.3 cm−1, which are assigned to modes ν1, ν6, ν14, ν15, and ν11 (mixing with ν17), respectively, of vinylacetylene (C4H4) based on the results of 13C- and D-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP/6–311++G**) predict vibrational wavenumbers and IR intensities of vinylacetylene that agree satisfactorily with our experimental results. This work enhances our understanding of the photochemistry of icy acetylene in cold astronomical environments; for instance, the present result can be applied directly to the photochemical processes on Titan's surface.

Deterrence of Aspergillus Flavus Regrowth and Aflatoxin Accumulation on Shelled Corn Using Infrared Heat Treatments

HighlightsInfrared heating was used to deactivate Aspergillus flavus.Treating samples for 150 s at the 3.24 kW/m2 intensity resulted in complete deactivation of A. flavus.Adding a tempering step at 70°C for 4 h significantly increased deactivation of A. flavus.Corn treated at IR intensity =3.24 kW/m2 showed no potential for A. flavus regrowth or aflatoxin persistence.The study demonstrated a non-chemical approach to deactivate mycotoxigenic fungi on corn.Abstract.The objectives of this study were to determine the suitable combinations of infrared (IR) heating duration and intensity, followed by tempering treatments to maximize the deactivation of aflatoxin-producing mold spores, specifically Aspergillus flavus (A. flavus). Corn samples at moisture content of 24% wet basis were inoculated with spore suspension of A. flavus and incubated to allow microbial attachment on the kernels. Corn samples were then heated using IR energy and then tempered for 4 h. Following the treatments, the samples were placed in conditions favorable for mold regrowth. Treatments of non-tempered samples for 210 s at the lowest intensity (1.27 kW/m2) resulted in A. flavus load reductions of 5.9 Log CFU/g. Treatments of non-tempered samples at the medium (3.24 kW/m2) and highest intensity (6.9 kW/m2) for 210 s resulted in complete deactivation of A. flavus. No fungal regrowth or aflatoxin persistence was observed on samples treated for 210 s at the lowest, medium, and highest IR intensities. Keywords: Aflatoxins, Aspergillus flavus, Infrared heating, Shelled corn, Tempering.

The hydrogen bond – practice and QTAIM theory

IR intensities in the spectra of H-complexes as a source of electron-density data ρ(rc) (e a−3) = 10−2(ΔA1/2) (A, 10−4 cm mmol−1/2).