Crystal and molecular structure of nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides

Comprehensive structural analyses were performed for o-, m-, and p-nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides. Single-crystal X-ray diffraction data were collected and revealed that meta isomer undergoes temperature-dependent polymorph transition (crystal structures of two polymorphs were obtained). This transition was verified by differential scanning calorimetry. The number of molecules in the independent part of the crystal unit cells of the compounds under investigation was in agreement with the number of resonances in solid-state ¹³C and ¹⁵N NMR spectra. The o- and p-nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides exist as single polymorph at room temperature, as confirmed by powder X-ray diffraction measurements.     

Photosensitized oxidation of methionine derivatives. Laser flash photolysis studies

The early events in the triplet 4-carboxybenzophenone (CB)-induced oxidation of N-acetyl-methionine methyl ester (N-Ac-Met-OCH₃) are investigated in aqueous solution. Upon electron transfer from the methionine residue of N-Ac-Met-OCH₃ to ³CB*, the resulting sulfur radical cation undergoes further reactions: (1) back electron transfer, (2) escape of the radical ions from the solvent cage, or (3) proton transfer and escape of the radicals. The yields and paths of these reactions are shown to depend strongly on the pH of the solution, and, similar to the previously reported results for dipeptides (Met-Gly and Gly-Met), on the structural nature of the methionine substituents. In the experiments performed in this work, low quencher concentrations were used to avoid formation of intermolecular transients (e.g., dimeric sulfur-centered radical cation (S∴S)⁺). Under these experimental conditions, the one-electron oxidized sulfur does not seem to become stabilized in an (S∴N)⁺ three-electron bonded intramolecular complex. The proposed mechanism is further supported by the stable products analysis. A detailed mechanism involving characterization of the transients is discussed and compared to that of methionine and methionine-containing dipeptides (Met-Gly and Gly-Met). Moreover, a newly installed transient absorption laser system is described in details.     

Application of HPLC-DAD for In Vitro Investigation of Acetylcholinesterase Inhibition Activity of Selected Isoquinoline Alkaloids from Sanguinaria canadensis Extracts

Isoquinoline alkaloids may have a wide range of pharmacological activities. Some of them have acetylcholinesterase activity inhibition. Nowadays, neurodegenerative disorders such as Alzheimer’s disease have become a serious public health problem. Searching for new effective compounds with inhibited acetylcholinesterase activity is one of the most significant challenges of modern scientific research. The aim of this study was the in vitro investigation of acetylcholinesterase activity inhibition of extracts obtained from Sanguinaria canadensis collected before, during and after flowering. The acetylcholinesterase activity inhibition of these extracts has not been previously tested. The aim was also to quantify selected alkaloids in the investigated extracts by high performance liquid chromatography (HPLC). The analyses of alkaloid content were performed using HPLC in reversed phase (RP) mode using Polar RP column and mobile phase containing acetonitrile, water and ionic liquid (IL). The acetylcholinesterase activity inhibition of the tested plant extracts and respective alkaloid standards were examined using high performance liquid chromatography with diode-array detector (HPLC-DAD) for the quantification of 5-thio-2-nitro-benzoic acid, which is the product of the reaction between the thiocholine (product of the hydrolysis of acetylthiocholine reaction) with Ellman reagent. The application of the HPLC method allowed for elimination of absorption of interfering components, for example, alkaloids such as sanguinarine and berberine. It is revealed that the HPLC method can be successfully used for the evaluation of the acetylcholinesterase inhibitory activity in samples such as plant extracts, especially those containing colored components adsorbing at wavelength in the range 405–412 nm. The acetylcholinesterase inhibition activity synergy of pairs of alkaloid standards and mixture of all investigated alkaloids was also determined. Most investigated alkaloids and all Sanguinaria canadensis extracts exhibited very high acetylcholinesterase activity inhibition. IC₅₀ values obtained for alkaloid standards were from 0.36 for berberine to 23.13 µg/mL for protopine and from 61.24 to 89.14 µg/mL for Sanguinaria canadensis extracts. Our investigations demonstrated that these plant extracts can be recommended for further in vivo experiments to confirm their acetylcholinesterase activity inhibition.     

Electromagnetic simulations of tunable terahertz metamaterial infiltrated with highly birefringent nematic liquid crystal

In this article electromagnetic simulations of tunable terahertz metamaterial infiltrated with nematic liquid crystal are described. A full-wave analysis technique based on the finite-difference time-domain (FDTD) method was done by employing QuickWave 3D electromagnetic solver. Scattering parameter analysis shows a resonant frequency shift of 0.8 THz obtained by reorienting the layered highly birefringent nematic liquid crystal. Effective refractive index for operation frequency varies from negative to positive values.     

Inclusion Compounds of Nitrosobenzenes with Cholic Acid and Deoxycholic Acid

The crystalline inclusion compounds of cholic acid (CA) and deoxycholic acid (DCA) with several nitrosobenzenes were prepared. The IR spectra and crystal structures of these compounds confirmed inclusion of the monomeric form of the C-nitroso compounds. The DCA compounds have 2 : 1 host:guest stoichiometry and P2₁ symmetry. Guest molecules are enclosed in channels and disordered. In the CA-nitrobenzene inclusion compound (1·CA) the host:guest stoichiometry is 1 : 1. The host molecules form typical CA bilayer aggregates and guest molecules are accommodated in helicoidal channels. The guest nitroso group is not coplanar with the phenyl ring; the torsion angle on the C–N bond is 8.6(8)°. The solid-state circular dichroism spectrum of 1·CA shows the negative Cotton effect at 780 nm corresponding to the n–^* electronic transition that can be associated with the P helicity of the guest molecule. The extremely weak magnitude of the Cotton effects exhibited by the DCA complexes points to a nearly planar arrangement of the NO group and the phenyl ring in the guest molecules.     

Visible‐Light Photoactive,Highly Efficient Triplet Sensitizers Based on Iodinated Aza‐BODIPYs: Synthesis,Photophysics and Redox Properties

A series of novel iodinated NO₂‐substituted aza‐BODIPYs have been synthesized and characterized. Highly desirable photophysical and photochemical properties were induced in NO₂‐substituted aza‐BODIPYs by iodination of the pyrrole rings. In particular, high values of singlet oxygen quantum yields (Φ_Δ) ranging from 0.79 to 0.85 were measured. The photooxygenation process proceeds via a Type II mechanism under the experimental conditions applied. The compounds studied exhibited an absorption band within the so‐called “therapeutic window”, with λ_max located between 645 nm to 672 nm. They were non‐fluorescent at room temperature with excited singlet‐state lifetimes within the picosecond range as measured by femtosecond transient absorption. Nanosecond laser flash photolysis experiments revealed T₁→T_n absorption spanning from ca. 400 nm to ca. 500 nm and allowed determination of the triplet‐state lifetimes. The estimated triplet lifetimes (τ_T) in deaerated acetonitrile ranged between 2.74 μs and 3.50 μs. As estimated by CV/DPV measurements, all iodinated aza‐BODIPYs studied exhibited one irreversible oxidation and two quasi‐reversible reductions processes. Estimation of the E_HOMO gave the value of ?6.06 to ?6.26 eV while the E_LUMO was found to be located at ca. ?4.6 eV. Thermogravimetric (TGA) analysis revealed that iodinated aza‐BODIPYs were stable up to approximately 300 °C. All compounds studied exhibit high photostability in toluene solution.     

Complete π-Facial Stereoselectivity in the TiCl4-Mediated [4 + 2] Cycloaddition of Cyclopentadiene to N,N′-fumaroyldi[(2R)-bornane-10,2-sultam]

Under the co-operative influence of two prosthetic groups, and independent of the TiCl₄ concentration, complete and constant diastereofacial π-selection was achieved during the [4 + 2] cycloaddition of cyclopentadiene to N,N′-fumaroyl-di[(2R)-bornane-10,2-sultam] ((?)- 1c ); reactive conformations are discussed.     

Column Chromatography and Preparative TLC for Isolation and Purification of Coumarins from Peucedanum verticillare L. Koch ex DC

JPC – Journal of Planar Chromatography – Modern TLC - Preparative separation and isolation of coumarins from petroleum ether and methanol extracts of the fruits and roots of Peucedanum...