Visible Absorptions of Potential Diffuse ISM Hydrocarbons: C9H9 and C9H5 Radicals

The laboratory detection of previously unobserved resonance-stabilized C9H5 and C9H9 radicals in the supersonic expansion of a hydrocarbon discharge source is reported. The radicals are tentatively assigned as acetylenic-substituted cyclopentadienyl C9H5 and vinyl-substituted benzyl C9H9 species. They are found to feature visible absorption bands that coincide with a few very weak diffuse interstellar bands toward HD183143 and HD204827

Electronic spectra of linear HC5_5H and cumulene carbene H2_2C5_5

The $1 ^3\Sigma_u^- \leftarrow X^3\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B).Comment: 7 pages, 4 figures, 5 table

Gas Phase Detection of Benzocyclopropenyl

The gas phase detection of benzocyclopropenyl is reported. In this aromatic resonance stabilized radical, a large angular strain is present due to a three-membered ring annelated to a benzene. The resonant two-color two-photon ionization technique is used to record the D1(2A2) ← D0(2B1) electronic transition of this radical after the in situ synthesis in a discharge source. The spectrum features absorptions up to 3300 cm–1 above the origin band at 19 305 cm–1. Benzocyclopropenyl is possibly the major product of the bimolecular reaction of benzene and an atomic carbon at low temperatures

Spectroscopic characterization of the complexes of 2-(2′-pyridyl)-benzimidazole and (H2O)1,2, (CH3OH)1,2, and (NH3)1,2 isolated in the gas phase

The hydrogen-bonded docking preferences of small solvent molecules on 2-(2′-pyridyl)-benzimidazole (PBI) were studied experimentally aided by computational findings. The PBI–S1,2 complexes (S = H2O, CH3OH, and NH3) were produced in a supersonically jet-cooled molecular beam and probed using resonant two-photon ionization and laser-induced fluorescence spectroscopy, with multiple isomers confirmed by UV–UV hole-burning spectroscopy. Two distinct isomers of PBI–H2O and PBI–(H2O)2 complexes were identified, while PBI–CH3OH and PBI–NH3 each formed a single 1 : 1 and 1 : 2 complex. Computational results with experimental findings revealed PBI–S-a as the most stable structure, with a solvent molecule forming a hydrogen-bonded bridge between imidazolyl-NH (NIH) and pyridyl-N (NP) at site-a. The site-a isomers exhibit higher S1 state stability compared to the S0 state, resulting in red-shifted S0 → S1 band origin for PBI–S-a and a further red-shift for the PBI–(S)2-aa isomers. In contrast, the PBI–S-b isomer, with a hydrogen bond between imidazolyl-N (NI) and pyridyl-CH (CPH) at site-b opposite to site-a, showed a blue-shifted band origin transition. A unique PBI–(H2O)2-ab isomer was detected with solvent molecules bound at both sites a and b, displaying a smaller red-shift in the band origin transition than the aa-isomer. The energy barrier for solvent-to-chromophore proton transfer varies with isomeric configuration. PBI–H2O-b isomers show significantly higher barriers (&gt;800 cm−1), while PBI–(H2O)-aa has a slightly increased barrier (&gt;436 cm−1) compared to the PBI–H2O-a (420 ± 10 cm−1) isomer. This study explores the potential landscape of PBI, enhancing our understanding of stabilization effects, spectral shifts, and their impact on chromophore excited-state dynamics in various environments.<br/

Salivary Metabolomics for Oral Precancerous Lesions: A Comprehensive Narrative Review

Oral submucous fibrosis (OSMF) is a chronic, potentially malignant disorder of the oral cavity, primarily associated with the consumption of areca nut products and other risk factors. Early and accurate diagnosis of OSMF is crucial to prevent its progression to oral cancer. In recent years, the field of metabolomics has gained momentum as a promising approach for disease detection and monitoring. Salivary metabolomics, a non-invasive and easily accessible diagnostic tool, has shown potential in identifying biomarkers associated with various oral diseases, including OSMF. This review synthesizes current literature on the application of salivary metabolomics in the context of OSMF detection. The review encompasses a comprehensive analysis of studies conducted over the past decade, highlighting advancements in analytical techniques, metabolomic profiling, and identified biomarkers linked to OSMF progression. The primary objective of this review is to provide a critical assessment of the feasibility and reliability of salivary metabolomics as a diagnostic tool for OSMF, along with its potential to differentiate OSMF from other oral disorders. In conclusion, salivary metabolomics holds great promise in revolutionizing OSMF detection through the identification of reliable biomarkers and the development of robust diagnostic models. However, challenges such as sample variability, validation of biomarkers, and standardization need to be addressed before its widespread clinical implementation. This review contributes to a comprehensive understanding of the current status, challenges, and future directions of salivary metabolomics in the realm of OSMF detection, emphasizing its potential impact on early intervention and improved patient outcomes

Electronic Spectroscopy of Resonantly Stabilized Aromatic Radicals : 1-Indanyl and Methyl Substituted Analogues

The gas-phase electronic spectra of two resonantly stabilized radicals, 1-indanyl (C9H9) and 1-methyl-1-indanyl (C10H11), have been recorded in the visible region using a resonant two-color two-photon ionization (R2C2PI) scheme. The D1(A″) ← D0(A″) origin bands of 1-indanyl and 1-methyl-1-indanyl radicals are observed at 21157 and 20565 cm–1, respectively. The excitation of a′ vibrations in the D1 state is observed up to ∼1500 cm–1 above the origin band in both cases. The experimental assignments are in agreement with DFT and TD-DFT calculations. The R2C2PI spectrum recorded at m/z = 131 amu (C10H11) features three additional electronic transitions at 21433, 21369, and 17989 cm–1, which are assigned to the origin bands of 7-methyl-1-indanyl, 2,3,4-trihydronaphthyl, and methyl-4-ethenylbenzyl radicals, respectively

Investigation on the Origin of Dispersion Interaction in Weakly Bound Phenylacetylene•CnHm clusters using dispersion corrected density functional calculations

Dispersion interaction is the attractive forces between an instantaneous dipole and induced dipole, generated due to the correlated movement of electrons in interacting molecules. Dispersion dominated intermolecular interaction has been the topic of interest among scientific communities to describe physical, chemical, and biological phenomena of diverse chemical systems such as crystal packing, protein folding, conformations and configurations of many biomolecules and polymers. Understanding the nature and origin of the interaction requires both experimental and theoretical investigations and a mutual agreement between them. In this project, we are going to investigate the dispersion interaction of PHA-CnHm clusters, where PHA is a non-polar S molecule with π-electron density which can form C-H/π bound complexes which are significantly different than the conventional hydrogen bonds like O-H/π or N-H/π. We have used density functional theory with dispersion correction using B3LYP-D3, PBE0-D3 functionals with def2-TZVPP and aug-cc-pVDZ basis sets to calculate the electronic structures and stabilization energies with the help of TURBOMOLE software. The intermolecular dispersion terms are calculated using two different numerical models as functions of (i) molecular dispersion and (ii) total dispersion by atomic polarizability. The model with total dispersion energy providing a good correlation with the binding energy of the cluster than molecular dispersion model. Success of this method, lead us to propose a novel numerical method based on the contribution by whole sets of atoms, which is able to determine the origin of C-H/π interaction

Microsolvation of Pyridylbenzimidazole Isomers and Its Effect on Excited State NH···N Proton Transfer

The excited state proton/hydrogen transfer (ESPT/ESHT) is one of the most important reaction pathways to many chemicals, biological phenomena such as DNA damage, radiation-induced cell damages, etc. In this, a molecule absorbs a UV-VIS photon, and in the excited electronic state, it exhibits a proton migration process within the molecular system. Understanding the ESPT mechanism is far from complete as many eminent research groups proposed different pathways for identical systems. In this project, I have been computationally investigating NH•••N proton transfer pathways in 2-(2’/3’/4’)-peridylbenzimidazole molecules in the excited state via hydrogen bonded clusters with a water molecule. We have been using B3LYP method with the def2-TZVPP basic set to calculate ground and first excited states of the monomer and their isomers (M) as well as the hydrogen bonded clusters with one and two water molecules M-(H2O) and M-(H2O)2. Here we aim to investigate the ESPT pathways at the molecular level by studying isolated hydrogen-bonded molecular clusters in the excited state