New Properties of a Bioinspired Pyridine Benzimidazole Compound as a Novel Differential Staining Agent for Endoplasmic Reticulum and Golgi Apparatus in Fluorescence Live Cell Imaging

Accurate measurement of sequential Ar desorption energies from the dispersion-dominated Ar1-3 complexes of aromatic molecules

We present experimental determination of the energies associated with the gradual desorption of Ar atoms from the aromatic molecular surface. Non-covalently bound 2,2'-pyridylbenzimidazole-Ar_1-3 complexes were produced in the gas phase and characterized using resonant two-photon ionization (R2PI) spectroscopy. The single Ar desorption from the PBI-Ar, PBI-Ar₂ and PBI-Ar₃ complexes were measured as 581 ± 18, 656 ± 30 and 537 ± 31 cm^-1, respectively. The energies were bracketed between the last observed band in the respective R2PI spectra and the disappeared intramolecular modes of PBI. The Ar_n dissociation energies in the S₁ state were measured as 581 ± 18, 1237 ± 48 and 1774 ± 79 cm^-1, respectively, for n = 1, 2 and 3. The calculated dissociation energies of the respective complexes, obtained using three computational methods, show excellent agreement with the experimental data. The ground state dissociation energies were estimated by subtracting the Δν shift of the origin band, and the respective values are 541 ± 18, 1160 ± 48 and 1634 ± 79 cm^-1. Overall, the calculated values resulted in scaling factors ranging from 0.956 to 1.017, which depict the predictive power of the methods to determine dispersion energies. The current investigation describes a unique methodology to accurately determine the dissociation and desorption energies of Ar atoms from the surfaces of bio-relevant aromatic molecules.

β-Cyclodextrin-Grafted Chitosan Enhances Intestinal Drug Absorption and Its Preliminary Mechanism Exploration

β-Cyclodextrin (CD) and chitosan (CS) have attracted great attention due to their unique properties and structures. β-Cyclodextrin-grafted chitosan (CD-CS) has been widely used as a drug carrier to prepare nano-formulations for drug delivery. However, few researches have been conducted to investigate the effect of CD-CS as an excipient on cellular uptake and intestinal absorption. Herein, Caco-2 cells were used to investigate the influence of CD-CS on cellular uptake. The MTT assay showed that CD-CS was non-toxic to Caco-2 cells in concentrations ranging from 15.62 to 125 μg/mL. Confocal laser microscopy and flow cytometry measurements indicated that the uptake ability of Caco-2 cells was significantly enhanced after being treated with CD-CS at a concentration of 31.25 μg/mL or incubation for 0.5 h, and the uptake enhancement gradually increased with increasing CD-CS concentration and incubation time. The Caco-2 monolayer cell model and the everted intestinal sac method were employed to preliminarily explore the mechanism of the improved intestinal absorption. The results demonstrated that CD-CS might open the tight junctions and enhance the clathrin-dependent endocytosis, macro-pinocytosis, and phagocytosis of the intestinal epithelial cells. Such findings can serve as references and inspiration for the design of absorption enhancers.

A combined spectroscopic and computational investigation on dispersion-controlled docking of Ar atoms on 2-(2'-pyridyl)benzimidazole

The dispersion-controlled docking of inert Ar atoms on the face of polycyclic 2-(2'-pyridyl)-benzimidazole (PBI) was studied experimentally aided by computational findings. The PBI-Ar_n (n = 1-3) complexes were produced in a supersonically jet-cooled molecular beam and probed using resonant two-photon ionization coupled with a time-of-flight mass spectrometric detection scheme and laser-induced fluorescence spectroscopy. The ground state vibrational frequencies were obtained from single vibronic level fluorescence spectroscopy. The formation of multiple isomers was verified using UV-UV hole-burning spectroscopy. The geometries of PBI-Ar_n (n = 1-3) complexes were derived by mutual agreement between experimental findings and computational results such as vibrational frequencies in the ground and excited electronic states, Franck-Condon factors and spectral shift of the S₁← S₀ transitions. All the above analyses provided good agreement between the experimental and simulated spectrum with the most stable PBI-Ar_n (n = 1-3) clusters. The highest intermolecular interaction between PBI and Ar was obtained with the Ar atom positioned above the imidazolyl ring. A second Ar atom was preferably docking on the other side of the imidazolyl ring than the pyridyl ring. The subsequent addition of the third Ar atom preferred the position above the pyridyl ring. The current investigation can be useful to investigate the preferential docking of dispersion-controlled interacting partners in multifunctional aromatic side chains present in biological systems.

New Cationic fac-[Re(CO)3(deeb)B2]+ Complex, Where B2 Is a Benzimidazole Derivative, as a Potential New Luminescent Dye for Proteins Separated by SDS-PAGE

Sodium-dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) can be used to separate proteins based mainly on their size such as in denaturing gels. Different staining methods have been reported to observe proteins in the gel matrix, where the most used dyes are generally anionic. Anionic dyes allow for interactions with protonated amino acids, retaining the dye in the proteins. Fluorescent staining is an alternative technique considered to be sensitive, safe, and versatile. Some anionic complexes based on d⁶ transition metals have been used for this purpose, where cationic dyes have been less explored in this context. In this work, we synthesized and characterized a new monocationic rhenium complex fac-[Re(CO)₃(deeb)B2]⁺ (where deeb is 4,4′-bis(ethoxycarbonyl)-2,2′-bpy and B2 is 2,4-di-tert-butyl-6-(3H-imidazo[4,5-c]pyridine-2-yl)phenol). We carried out a structural characterization of this complex by MS⁺, FTIR, ¹H NMR, D₂O exchange, and HHCOSY. Moreover, we carried out UV-Vis, luminescence, and cyclic voltammetry experiments to understand the effect of ligands on the complex’s electronic structure. We also performed relativistic theoretical calculations using the B3LYP/TZ2P level of theory and R-TDDFT within a dielectric continuum model (COSMO) to better understand electronic transitions and optical properties. We finally assessed the potential of fac-[Re(CO)₃(deeb)B2]⁺ (as well as the precursor fac-Re(CO)₃(deeb)Br and the free ligand B2) to stain proteins separated by SDS-PAGE. We found that only fac-[Re(CO)₃(deeb)B2]⁺ proved viable to be directly used as a luminescent dye for proteins, presumably due to its interaction with negatively charged residues in proteins and by weak interactions provided by B2. In addition, fac-[Re(CO)₃(deeb)B2]⁺ seems to interact preferentially with proteins and not with the gel matrix despite the presence of sodium dodecyl sulfate (SDS). In future applications, these alternative cationic complexes might be used alone or in combination with more traditional anionic compounds to generate counterion dye stains to improve the process.

Lighting-Up Tumor for Assisting Resection via Spraying NIR Fluorescent Probe of γ-Glutamyltranspeptidas

For the precision resection, development of near-infrared (NIR) fluorescent probe based on specificity identification tumor-associated enzyme for lighting-up the tumor area, is urgent in the field of diagnosis and treatment. Overexpression of γ-glutamyltranspeptidase, one of the cell-membrane enzymes, known as a biomarker is concerned with the growth and progression of ovarian, liver, colon and breast cancer compared to normal tissue. In this work, a remarkable enzyme-activated NIR fluorescent probe NIR-SN-GGT was proposed and synthesized including two moieties: a NIR dicyanoisophorone core as signal reporter unit; γ-glutamyl group as the specificity identification site. In the presence of γ-GGT, probe NIR-SN-GGT was transformed into NIR-SN-NH₂, the recovery of Intramolecular Charge Transfer (ICT), liberating the NIR fluorescence signal, which was firstly employed to distinguish tumor tissue and normal tissues via simple “spraying” manner, greatly promoting the possibility of precise excision. Furthermore, combined with magnetic resonance imaging by T2 weight mode, tumor transplanted BABL/c mice could be also lit up for first time by NIR fluorescence probe having a large stokes, which demonstrated that probe NIR-SN-GGT would be a useful tool for assisting surgeon to diagnose and remove tumor in clinical practice.