Electronic Fingerprint of the Protonated Imidazole Dimer Probed by X-ray Absorption Spectroscopy.

Protons in low-barrier superstrong hydrogen bonds are typically delocalized between two electronegative atoms. Conventional methods to characterize such superstrong hydrogen bonds are vibrational spectroscopy and diffraction techniques. We introduce soft X-ray spectroscopy to uncover the electronic fingerprints for proton sharing in the protonated imidazole dimer, a prototypical building block enabling effective proton transport in biology and high-temperature fuel cells. Using nitrogen core excitations as a sensitive probe for the protonation status, we identify the X-ray signature of a shared proton in the solvated imidazole dimer in a combined experimental and theoretical approach. The degree of proton sharing is examined as a function of structural variations that modify the shape of the low-barrier potential in the superstrong hydrogen bond. We conclude by showing how the sensitivity to the quantum distribution of proton motion in the double-well potential is reflected in the spectral signature of the shared proton.

Simulating Non-Adiabatic Dynamics of Photoexcited Phenyl Azide: Investigating Electronic and Structural Relaxation en Route to the Formation of Phenyl Nitrene.

Excited state molecular dynamics simulations of the photoexcited phenyl azide have been performed. The semi-classical surface hopping approximation has enabled an unconstrained analysis of the electronic and nuclear degrees of freedom which contribute to the molecular dissociation of phenyl azide into phenyl nitrene and molecular nitrogen. The significance of the second singlet excited state in leading the photodissociation has been established through electronic structure calculations, based on multi-configurational schemes, and state population dynamics. The investigations on the structural dynamics have revealed the N-N bond separation to be accompanied by synchronous changes in the azide N-N-N bond angle. The 100 fs simulation results in a nitrene fragment that is electronically excited in the singlet manifold.

Isolation and Identification of Cronobacter spp. from Fish and Shellfish Sold in Retail Markets.

In this study, we investigated the incidence of Cronobacter spp. in seafood collected from retail fish markets of Mumbai, India. A total of 50 samples comprising fresh finfish (n = 32), shellfish (n = 6), dried fish (n = 9) and water (n = 3) were analyzed for Cronobacter spp. by selective enrichment, isolation and biochemical tests. Of 145 isolates presumptively identified as Cronobacter spp. by biochemical tests, 37 were confirmed as Cronobacter spp. by Polymerase Chain Reaction (PCR) specific to the internal transcribed spacer (ITS) regions. Based on the partial ITS gene sequence analysis, 35 isolates were identified as Cronobacter malonaticus and two as Cronobacter sakazakii. The highest incidence of Cronobacter spp. was in dried fish (55.6%), followed by shellfish (33.3%). The virulence gene ompA was detected in two Cronobacter sakazakii isolates. This is the first report of the incidence of Cronobacter spp. in fresh and dried seafood from India, which highlights the need to focus on this emerging pathogen in tropical seafood.