Stereoselective reduction of arteannuin B and its chemical transformations

Absolute stereochemistry of dihydroarteannuin B 5 obtained by the reduction of arteannuin B 3 with Ni₂B, NaBH₄ or CdCl₂-Mg-MeOH-H₂O has been established by 2D NMR and single crystal X-ray diffraction studies. Some experiments aimed at the synthesis of dihydrodeoxyarteannuin B [C-4, 5 double bond isomer of 11] are also discussed.     

Acid-base thermochemistry of gaseous aliphatic α-aminoacids

Acid-base thermochemistry of isolated aliphatic amino acids (denoted AAA): glycine, alanine, valine, leucine, isoleucine and proline has been examined theoretically by quantum chemical computations at the G3MP2B3 level. Conformational analysis on neutral, protonated and deprotonated species has been used to identify the lowest energy conformers and to estimate the population of conformers expected to be present at thermal equilibrium at 298 K. Comparison of the G3MP2B3 theoretical proton affinities, PA, and ΔH(acid) with experimental results is shown to be correct if experimental thermochemistry is re-evaluated and adapted to the most recent acidity-basicity scales. From this point of view, a set of evaluated proton affinities of 887, 902, 915, 916, 919 and 941 kJ mol(-1), and a set of evaluated ΔH(acid) of 1433, 1430, 1423, 1423, 1422 and 1426 kJ mol(-1), is proposed for glycine, alanine, valine, leucine, isoleucine and proline, respectively. Correlations with structural parameters (Taft's σ(α) polarizability parameter and molecular size) suggest that polarizability of the side chain is the major origin of the increase in PA and decrease in ΔH(acid) along the homologous series glycine, alanine, valine and leucine/isoleucine. Heats of formation of gaseous species AAA, AAAH(+) and [AAA-H](-) were computed at the G3MP2B3 level. The present study provides previously unavailable Δ(f)H°(298) for the ionized species AAAH(+) and [AAA-H](-). Comparison with Benson's estimate, and correlation with molecular size, show that several experimental Δ(f)H°(298) values of neutral or gaseous AAA might be erroneous.     

Aromatic core-modified twisted heptaphyrins[1.1.1.1.1.1.0]: syntheses and structural characterization

[reaction: see text] First examples of aromatic core-modified twisted heptapyrrolic systems with six meso links have been obtained via a general [3 + 4] acid-catalyzed condensation method. Despite the twisted conformation, these heptaphyrins exhibit aromaticity in solution, unlike most of the all-aza analogues.     

LC Separation of Co-Existing Cetylpyridinium Chloride, Tetradecyltrimethylammonium Bromide and Dodecyltrimethylammonium Bromide on Silica TLC Plates with Aqueous-Organic Eluents

Thin-layer chromatography (TLC) of three cationic surfactants was performed on silica TLC plates with various solvent systems. The mutual separation of cetylpyridinium chloride (CPC), tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB) was achieved on silica TLC plates with ethanol: 1% aqueous ammonium chloride (4:6, v/v) as an eluent. Effects of cations and anions in the mobile phase on mobility and separation of CPC, TTAB and DTAB were examined. The interference due to the presence of metal cations as impurities on the resolution in the mixture of CPC, TTAB and DTAB was also examined. The limits of detection of CPC, TTAB and DTAB estimated were 0.015, 0.031 and 0.062 μg zone⁻¹, respectively. The developed method was utilized to identify these surfactants in different spiked water samples after their preliminary separation.     

Current advances in molecularly imprinted polymers and their release mechanisms in drug delivery systems

Molecularly imprinted polymer (MIP) has gained wide interest among researchers due to its unique molecular recognition of the template that is suitable as a drug carrier. Therefore, the preparation and formulation of the MIP are significant to suit the needs of the intended use. Due to its significance in drug delivery, this review aims to highlight various methods in the preparation of MIP, the composition for both controlled and stimuli-responsive drug delivery systems, and the release mechanism of the drugs. In drug delivery systems, MIP should have a sustained release performance as well as flexibility in surface modification for targeted delivery via a range of stimuli-responses, including  external stimuli (magnetic, light) and internal stimuli (pH, temperature, redox, biological). The properties of sustained release and targeted delivery of the MIP can improve the drug's therapeutic efficacy as well as the breakthrough for the tumor targeting application.     

Identification and Separation of Lead (II), Nickel (II), and Cobalt (II) on Silica Gel 60 F254 High-Performance Thin-Layer Chromatographic Plates with Mixed Aqueous Sodium Dodecyl Sulfate—Oxalic Acid Solvent System

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic separation of three metal cations was performed on high-performance thin-layer plates (silica gel 60F254) with...     

Molecular structure, vibrational spectra and HOMO, LUMO analysis of yohimbine hydrochloride by density functional theory and ab initio Hartree-Fock calculations

Yohimbine hydrochloride (YHCl) is an aphrodisiac and promoted for erectile dysfunction, weight loss and depression. The optimized geometry, total energy, potential energy surface and vibrational wavenumbers of yohimbine hydrochloride have been determined using ab initio, Hartree–Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set. A complete vibrational assignment is provided for the observed Raman and IR spectra of YHCl. The UV absorption spectrum was examined in ethanol solvent and compared with the calculated one in gas phase as well as in solvent environment (polarizable continuum model, PCM) using TD-DFT/6-31G basis set. These methods are proposed as a tool to be applied in the structural characterization of YHCl. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) with frontier orbital gap are presented.     

Figure-eight aromatic core-modified octaphyrins with six meso links: syntheses and structural characterization

The synthesis and structural characterization of the first examples of aromatic core-modified figure-eight octaphyrins with six meso links and their formation with and without acid catalysts are highlighted.     

Aromatic core modified decaphyrins with the largest two-photon absorption cross-sections: syntheses and characterization

[structure: see text] Core-modified aromatic decaphyrins with 42pi conjugated electrons exhibit the highest two-photon absorption cross-section value (sigma(2) = 108,000 GM) known for any organic molecule, suggesting possible device applications in the field of nonlinear optics.     

Design and synthesis of 4H-1,4-benzothiazines containing thiazole ring system for use as potential biopharmaceuticals

Synthesis of 4H-1,4-benzothiazines containing thiazole ring system is reported by condensation of substituted 2-amino-benzenethiols with N-(substituted benzothiazol-2-yl)-3-oxo-butyr-amides in the presence of DMSO.