Synthesis, inclusion capabilities, and electrical properties of some asymmetrical cyclophanes

For the first time, we announce the synthesis of cyclo(bis-paraquat-p-phenylene-p-phenylene-carbonyl)tetrakis(hexafluorophosphate), named ‘CETOBOX’. This compound exists in three tautomeric forms. These forms were evidenced by NMR data (¹H NMR, TOCSY, COSY, and NOESY), UV-vis spectra coupled with pH measurements, and by synthesis. As the ‘CETOBOX’ gives ‘in situ’ only the corresponding monoylide, the synthesis of a new fluorescent indolizine cyclophane has been performed by a 3+2 cycloaddition. This cycloadduct, in an amidation reaction with 6-amino-β-cyclodextrin, furnishes the final two-cavity sensor with good yields. All structures of the new compounds presented herein have been established by NMR spectroscopy. Also, theoretical methods (MM3, AM1, AM1 (COSMO), and B88LYPDFT) have been used to determine the most stable conformer structures. For the fluorescent indolizine cycloadduct, we evaluated its inclusion capabilities and for the two-cavity sensor, we measured some of its electrical properties that make it suitable for use in VOCs detection and energy conversion.     

Characterization of mycobacterial triacylglycerols and monomeromycolyl diacylglycerols from Mycobacterium smegmatis biofilm by electrospray ionization multiple-stage and high-resolution mass spectrometry

The storage of triacylglycerols (TAGs) is essential for non-replicating persistence relevant to survival and the re-growth of mycobacteria during their exit from non-replicating state stress conditions. However, the detailed structures of this lipid family in mycobacteria largely remain unexplored. In this contribution, we describe a multiple-stage linear ion-trap mass spectrometric approach with high resolution mass spectrometry toward direct structural analysis of the TAGs, including a novel lipid subclass previously defined as monomeromycolyl diacylglycerol (MMDAG) isolated from biofilm of Mycobacterium smegmatis, a rapidly growing, non-pathogenic mycobacterium that has been used as a tool for molecular analysis of mycobacteria. Our results demonstrate that the major isomer in each of the molecular species of TAGs and MMDAGs consists of the common structure in which Δ⁹18:1- and 16:0-fatty acyl substituents are exclusively located at sn-1 and sn-2, respectively. Several isomers were found for most of the molecular species, and thus hundreds of structures are present in this lipid family. More importantly, this study revealed the structures of MMDAG, a novel subclass of TAG that has not been previously reported by direct mass spectrometric approaches.     

Total assignment and structure in solution of tetrandrine by NMR spectroscopy and molecular modelling

High-resolution 1- and 2D NMR spectra of tetrandrine and molecular modelling were employed to characterise its structure in solution. Complete and unambiguous assignment of all proton and carbon resonance signals is reported. Scalar couplings were determined from dihedral angles with the Karplus equation. Inter-proton distances were evaluated from NOE correlation peaks. Comparison of simulated and X-ray conformations of tetrandrine reveals only small differences.     

Complexation of tetrandrine with calcium ion probed by various spectroscopic methods and molecular modeling

The formation of the complex between tetrandrine and the calcium ion, in solution, was studied using FTIR, UV-Vis, ¹H NMR, ¹³C NMR and electrospray mass spectroscopy spectroscopic methods and molecular modeling. The calcium salts used were: Ca(ClO₄)₂·4H₂O and Ca(Picrate)₂ in the solvents: acetonitrile (CH₃CN), deuterated acetonitrile (CD₃CN) and tetrahydrofurane (THF). The determined complex stability constant was: 20277±67 dm³ mol⁻¹ and corresponding free energy ΔG₀=−5.820±0.002 kcal mol⁻¹. The molecular simulation of the complex formation with the MM3 Augmented force field integrated in CAChe provided useful data about its energy. Combining the experimental results and molecular modeling we propose a model for the structure of tetrandrine-Ca complex with an eight coordinated geometry.     

Evaluation of losses and group effective refractive index of Er3+:Ti:LiNbO3 optical waveguides

In this paper, we report some experimental results concerning several types of loss measurements of Er³⁺:Ti:LiNbO₃ optical waveguides by using optical methods. Using the Fabry-Pérot interferometry method, we evaluated the attenuation coefficient of an optical waveguide resonator for a laser radiation having λ = 1.55 μm. We also evaluated the insertion losses, polarization dependent losses, and coupling with external losses. Additionally, from the transmitted spectra of the symmetrical monomode Fabry-Pérot optical waveguide resonator, we were able to evaluate the value of the group effective refractive index.     

Theoretical study of free-radical ring-opening polymerization of 2-(o-chlorophenyl)-4-methylene-1,3-dioxolane. A molecular and quantum mechanics approach

The methylene derivatives of 1,3-dioxolane were proved to yield homo- and binary or ternary copolymers via free-radical polymerization, depending on initiation type and reaction conditions. While different authors reported experimental data on these compounds, no explanation of such polymerization behaviour was provided. The present paper is aimed to propose, through molecular mechanics and quantum mechanics approaches, a valid explanation of the already published experimental results.     

Identification of Novel Antistaphylococcal Hit Compounds Targeting Sortase A

Staphylococcus aureus (S. aureus) is a causative agent of many hospital- and community-acquired infections with the tendency to develop resistance to all known antibiotics. Therefore, the development of novel antistaphylococcal agents is of urgent need. Sortase A is considered a promising molecular target for the development of antistaphylococcal agents. The main aim of this study was to identify novel sortase A inhibitors. In order to find novel antistaphylococcal agents, we performed phenotypic screening of a library containing 15512 compounds against S. aureus ATCC43300. The molecular docking of hits was performed using the DOCK program and 10 compounds were selected for in vitro enzymatic activity inhibition assay. Two inhibitors were identified, N,N-diethyl-N′-(5-nitro-2-(quinazolin-2-yl)phenyl)propane-1,3-diamine (1) and acridin-9-yl-(1H-benzoimidazol-5-yl)-amine (2), which decrease sortase A activity with IC₅₀ values of 160.3 µM and 207.01 µM, respectively. It was found that compounds 1 and 2 possess antibacterial activity toward 29 tested multidrug resistant S. aureus strains with MIC values ranging from 78.12 to 312.5 mg/L. These compounds can be used for further structural optimization and biological research.     

LC-MS and FT-IR characterization of amber artifacts

This work focuses on using analytical methods, such as Fourier transform Infrared spectroscopy (FTIR) and high performance liquid chromatography (HPLC) with mass spectrometry (MS) detection to assess archaeological and geological amber. The main goal of this study is to apply the previously developed and optimized analytical methods in verifying criteria to ascribe and characterize the origin of materials found in archaeological sites. The proposed LC-MS method was successfully applied for the quantification of succinic acid content both in geological and archaeological samples of amber and offers excellent linearity between 0.1 and 5??g mL^?1. The developed FTIR method provided some criteria which is able to differentiate between Baltic and Romanian amber (Romanite) that furthermore validates on archaeological amber artefacts.      

Hyers–Ulam Stability of Euler’s Differential Equation

We obtain a result on generalized Hyers–Ulam stability for Euler’s differential equation in Banach spaces. Our result extends and improves some recent results of Mortici, Jung and Rassias concerning the stability of Euler’s equation on a bounded domain.