Slow interconversion of enantiomeric conformers or atropisomers of anilide and urea derivatives of 2-substituted anilines

N-Acylated 2-substituted anilines undergo slow Ar-N bond rotation, allowing in some cases isolation of enantiomeric or diastereoisomeric atropisomers and in others the determination of the rate of Ar-N bond rotation by NMR. 2-Iodoanilides bearing a branched N-substituent demonstrate sufficient enantiomeric stability to be resolvable, either by HPLC or by formation of diastereoisomeric lactanilide derivatives. For the first time, the rates of Ar-N rotation in 2-substituted N,N'-diarylureas have been established: they mainly fall in the region of 50-70 kJ mol(-1) with a relatively weak dependence on substituent size.     

Photoelectrochemical sensing of tannic acid based on the use of TiO<Subscript>2</Subscript> sensitized with 5-methylphenazinium methosulfate and carboxy-functionalized CdTe quantum dots

The article describes a method for determination of tannic acid in extracts of medicinal plants. Tannic acid (TA) is an antioxidant and has anticancer and antimicrobial properties. Titanium dioxide nanoparticles (TiO₂) were co-sensitized with 5-methylphenazinium methosulfate (PMS) and carboxy-functionalized cadmium telluride quantum dots (CdTe QDs), and immobilized on a fluorine-doped tin oxide electrode. The surface morphology and electrochemical properties of the modified electrode were investigated by scanning electron microscopy and amperometry, respectively. A composite consisting of TiO₂, PMS and CdTe QDs in a nafion film has a response to TA under LED light higher than that observed for each separate component. Under optimized experimental conditions and at an applied voltage of +0.4 V vs Ag/AgCl, the photoelectrochemical sensor has a linear response in the 0.2 to 200 μmol L^?1 TA concentration range and a detection limit of 60 nmol L^?1. The sensor was successfully applied to the determination of TA in spiked extracts from three medicinal plants, with recovery values between 98.3 and 103.9 %.

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Graphical abstract Schematic diagram for photoelectrochemical detection of tannic acid based on a fluorine doped tin oxide electrode modified with titanium oxide, 5-methylphenazinium methosulfate and carboxy-functionalized cadmium telluride quantum dots

     

Improved high performance liquid chromatographic determination of ginsenosides in Panax ginseng-based pharmaceuticals using a diol column

A reversed-phase high-performance liquid chromatographic assay for the simultaneous quantitative determination of seven ginsenosides, Rb(1), Rb(2), Rc, Rd, Rg(1), Re and Rf in pharmaceutical preparations is described. Chromatographic separation was achieved in less than 20 min using a 250 x 4 mm Lichrospher, 5 microm, 100 A diol column with detection at 203 nm. The method was validated over the range of 2.5-20 ng/microL using a 20 microL sample volume. The average accuracy at five concentrations was 90-100%, and the within-day and between-day precision ranged from 1 to 7% expressed as coefficient of variation. The detection limit and the quantitation limit of the method were 20 and 50 ng injected for each ginsenoside, respectively.     

Hinge Distortion in Platinum(II) Dimers with a Pt(2)S(2) Ring. An ab Initio Molecular Orbital Study

Ab initio calculations have been carried out for Pt(II) dimers with S(2)(-) and/or RS(-) bridging ligands in order to elucidate the factors governing the structural preference, planar or hinged, of these complexes. Calculations have been performed for systems which model all structurally characterized Pt(II) binuclear complexes. All possible determinants of the hinge angle have been taken into account in the ab initio calculations. These show that electronic rather than steric effects govern the geometry of the central Pt(2)S(2) ring. Only one minimum of energy has been found for each complex, but the energetic cost of the hinge motion is low. Complexes with two S(2)(-), or with one S(2)(-) and one RS(-), bridging ligands are hinged; the decrease of the through-ring antibonding interaction between the in-plane sulfur p orbitals with folding appears to be the determinant for hinging. Complexes with two RS(-) bridging ligands can be planar or hinged depending on the relative orientation, syn or anti, of the R groups, on the nature, L(4) or L(2)L(2)', of the terminal ligands, and in the latter case on their disposition, cis or trans. However, the aromatic or aliphatic nature of bridging thiolates does not influence the geometry of the Pt(2)S(2) ring significantly. Conclusions drawn from platinum dimers can be extended to the palladium analogs.     

Simultaneous separation of the enantiomers of cizolirtine and its degradation products by capillary electrophoresis

The simultaneous enantioselective separation of (±)-cizolirtine and its impurities: (±)-N-desmethylcizolirtine, (±)-cizolirtine-N-oxide and (±)-5-(-hydroxybenzyl)-1-methylpyrazole was investigated by capillary electrophoresis. Electrokinetic chromatography with carboxymethyl-β-CD (CM-β-CD) and sulfobutyl-ether-β-CD was tried, showing good enantioseparation but poor chemical selectivity. The four racemic pairs were baseline separated, in a single run, by cyclodextrin-modified micellar electrokinetic chromatography. The migration buffer composition was: (60 mM hydroxypropyl-β-cyclodextrin–150 mM sodium dodecyl sulfate–50 mM disodium tetraborate, pH 9.2, in water)–butanol (95:5, v/v). Work was done to determine the effect of buffer components and their optimal concentration on selectivity. The method was validated with respect to enantioselectivity of cizolirtine as well as its degradation products and separation selectivity between the different components. Linearity, limit of detection, limit of quantitation and precision were also determined. This method is suitable for the enantiomeric purity determination and stability control of cizolirtine (racemic mixture or enantiomers) and its degradation products. Examples of electropherograms of (R)-cizolirtine degraded under stressed conditions are shown.     

Syntheses of both the putative and revised structures of aeruginosin EI461 bearing a new bicyclic alpha-amino acid

[structure: see text] The putative structure of the naturally occurring aquatic peptide aeruginosin EI461 has been prepared from d-tyrosine. A corrected structure for aeruginosin EI461 is proposed, and the structure is proven by synthesis, which was accomplished using the new alpha-amino acid (2S,3aR,6R,7aR)-6-hydroxy-2-carboxyoctahydroindole, prepared from l-tyrosine. Succesive couplings of the dipeptide d-Leu-3a,7a-diepi-l-Choi with l-Hpla and NH(4)OH and a deprotection step gave aeruginosin EI461.     

A first-principles analysis of the magnetism of CuII polynuclear coordination complexes: the case of [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4.2.5H2O

The magnetic structure of the [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4.2.5 H2O crystal -- using fractional coordinates determined at room-temperature -- has been analysed in detail. This analysis has been carried out by extending our first principles bottom-up theoretical approach, which was initially designed to study through-space magnetic interactions, to handle through-bond magnetic interactions. The only input data required by this approach are the values of the computed J(AB) exchange parameters for all the unique pairs of spin-containing centres. The results allow the magnetic structure of the crystal, which presents two types of isolated tetranuclear CuII clusters, to be defined in quantitative terms. Each of these clusters presents ferro and antiferromagnetic interactions, the former being stronger, although outnumbered by the latter. The computed magnetic susceptibility curve shows the same qualitative features as the experimental data. However, there are small differences that are presumed to be associated with the use of room-temperature crystal coordinates.     

Synthesis,resolution, and reactivity of benzylmesitylphenylphosphine: a new p-chiral bulky ligand

The synthesis of P,P'-dimesityl-P,P'-diphenyldiphosphine and benzylmesitylphenylphosphine is described as well as the resolution of the latter ligand by means of homochiral organometallic complexes. The absolute configuration of the phosphine is assigned by NMR spectra, using the homochiral palladacycle as a reference point. The configuration has been confirmed by single crystal X-ray diffraction. Molecular mechanics calculations were performed in [PdCl-(R)-(+)-C10H6CH(Me)NH2(PBnMesPh)], and showed that the rotation around the Pd-P bond is restricted in this complex. [Pd(eta3-2-MeC3H4)Cl(PBnMesPh)] was obtained and used as a precursor in the catalytic hydrovinylation of styrene. Benzylmesitylphenylphosphine has a strong tendency to form phosphapalladacycles by activation of one of the ortho-methyl groups. The formation of this metallacycle from cyclopalladated N-donor derivatives by a ligand-exchange reaction is also described.     

2D copper(II) complex built from N-methyl-1,3-diamino-2-propanolate and azide ligands: structure, magnetic, and DFT studies

The synthesis, structural characterization, and magnetic behavior of a new 2D copper(II) compound with formula {[Cu2(mu-O2CMe)(mu-MedapO)(mu1,1-N3)2]n (CH3OH)n} 1, in which MedapOH is N-methyl-1,3-diamino-2-propanol is reported herein. 1 crystallizes in the triclinic system, space group P1, with unit cell parameters a = 6.688(5) A, b = 10.591(6) A, c = 12.100(7) A, alpha = 113.01(3) degrees, beta = 105.08(4) degrees, gamma = 93.93(3) degrees, Z = 2. The structure of 1 consists of neutral alternate 1D chains formed by the sequence of [Cu(1)-(mu1,1-N3)2-Cu(1)-(MedapO/acetate)-Cu(2)-(mu1,1-N3)2-Cu2)]. Each dinuclear [Cu(1)-Cu(2)] unit interacts with similar dinuclear units of neighbor chains in basis to large Cu-N(azido) distances to give a 2D arrangement. The magnetic behavior of 1 has been checked giving a net ferromagnetic coupling. The fit of the chiM versus T data as dinuclear compound affords a J value of 53.0 cm(-1) as a consequence of the orbital countercomplementarity phenomenon. The exchange pathways have been justified by density functional calculations.     

Synthesis,characterization and X-ray crystal structure determination of cyclopalladated [Csp2,N,N′]−, zwitterionic and chelated compounds in the reaction of 3,5-diphenyl-N-alkylaminopyrazole derived ligands with Pd(II)

The synthesis of two N-alkylaminopyrazole ligands, 1-[2-(diethylamino)ethyl]-3,5-diphenylpyrazole (L1) and 1-[2-(dioctylamino)ethyl]-3,5-diphenylpyrazole (L2), is reported. These ligands present, a priori, one pyrazole nitrogen and one amine nitrogen as potential donor atoms. However, in the reaction of the ligands (L1 and L2) with [PdCl₂(CH₃CN)₂] one of the C_phenyl atoms can also behave as a donor atom. As a result, we have obtained the formation of three different compounds for each one of the ligands: chelated ([PdCl₂(L)] L = L1 (1a), L2 (2a)), zwitterionic ([PdCl₃(LH)] LH = LH1 (1b), LH2 (2b)), and cyclopalladated compounds ([PdCl(LC)] (LC = LC1 (1c), LC2 (2c)). The solid-state structures for 1a, 1b and 1c were determined by single crystal X-ray diffraction methods. The potentially [C,N,N′]^? ligand is coordinated through the N_pz and the N_amino to the metal atom for 1a, through the N_pz for 1b, and through the N_pz, the N_amino and a C_phenyl for 1c.