Differential pulse polarographic determination of salicylaldehyde as its Girard-P derivative

A method for the determination of salicylaldehyde (2 × 10^–6–10^–4 M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.5% (ten determinations of 4 × 10^–5 M level). The applicability of this method was checked in synthetic samples containing salicyl alcohol,o-aminophenol, 2-methylphenol, salicylic acid and 4-aminobenzoic acid.     

The reaction of β-aminoenones with substituted acetonitriles. Regiospecific synthesis of 2(1H)-pyridones

Unsymmetrically substituted β-aminoenones react with malononitrile, cyanomethylphenylsulfone, benzoyl-acetonitrile and ethyl cyanoacetate, in very mild conditions, to yield regiospecifically 3-functionalized 2(1H)-pyridones in high yields.     

Solid state coordination chemistry of copper(II)/α-hydroxycarboxylato/2,2′-bipyridine systems

Four new two-ligand complexes of copper(II) with 2,2′-bipyridine and one of three different α-hydroxycarboxylic acids (lactic, H₂LACO; 2-methyllactic, H₂MLACO; and mandelic, H₂MANO) were prepared. Complexes 1–3 of general formula [Cu(HL)₂(bipy)]·nH₂O (HL=monodeprotonated acid), were characterized by elemental analysis, IR, electronic and EPR spectroscopy, magnetic measurements and thermogravimetric analysis. Complexes 1 (HL=HLACO, n=2), 2 (HL=HMLACO, n=1) and 3a (the result of attempted recrystallization of 3, of formula [Cu(HMANO)(bipy)₂](HMANO)·H₂MANO·CH₃CN were studied by X-ray diffractometry. The copper atom is in an elongated, tetragonally distorted octahedral environment in 1 and 2 and in 3a has a coordination polyhedron intermediate between a square pyramid and a trigonal bipyramid, as evaluated in terms of the parameter τ. In 1 and 2 the α-hydroxycarboxylato ligand is bidentate and monoanionic but in 3a there are three forms: a monodentate monoanion, a monoanionic counterion, and a neutral molecule.     

Preparation and characterization of individual peptide-wrapped single-walled carbon nanotubes

Two challenges for effectively exploiting the remarkable properties of single-walled carbon nanotubes (SWNTs) are the isolation of intact individual nanotubes from the raw material and the assembly of these isolated SWNTs into useful structures. In this study, we present atomic force microscopy (AFM) evidence that we can isolate individual peptide-wrapped SWNTs, possibly connected end-to-end into long fibrillar structures, using an amphiphilic alpha-helical peptide, termed nano-1. Transmission electron microscopy (TEM) and well-resolved absorption spectral features further corroborate nano-1's ability to debundle SWNTs in aqueous solution. Peptide-assisted assembly of SWNT structures, specifically in the form of Y-, X-, and intraloop junctions, was observed in the AFM and TEM images.     

A comparative XAS and X-ray diffraction study of new binuclear Mn(III) complexes with catalase activity. indirect effect of the counteranion on magnetic properties

Four new binuclear Mn(III) complexes with carboxylate bridges have been synthesized: [[Mn(nn)(H(2)O)](2)(mu-ClCH(2)COO)(2)(mu-O)](ClO(4))(2) with nn = bpy (1) or phen (2) and [[Mn(bpy)(H(2)O)](2)(mu-RCOO)(2)(mu-O)](NO(3))(2) with RCOO = ClCH(2)COO (3) or CH(3)COO (4). The characterization by X-ray diffraction (1 and 3) and X-ray absorption spectroscopy (XAS) (1-4) displays the relevance of this spectroscopy to the elucidation of the structural environment of the manganese ions in this kind of compound. Magnetic susceptibility data show an antiferromagnetic coupling for all the compounds: J = -2.89 cm(-1) (for 1), -8.16 cm(-1) (for 2), -0.68 cm(-1) (for 3), and -2.34 cm(-1) (for 4). Compounds 1 and 3 have the same cation complex [[Mn(bpy)(H(2)O)](2)(mu-ClCH(2)COO)(2)(mu-O)](2+), but, while 1 shows an antiferromagnetic coupling, for 3 the magnetic interaction between Mn(III) ions is very weak. The four compounds show catalase activity, and when the reaction stopped, Mn(II) compounds with different nuclearity could be obtained: binuclear [[Mn(phen)(2)](mu-ClCH(2)COO)(2)](ClO(4))(2), trinuclear [Mn(3)(bpy)(2)(mu-ClCH(2)COO)(6)], or mononuclear complexes without carboxylate. Two Mn(II) compounds without carboxylate have been characterized by X-ray diffraction: [Mn(NO(3))(2)(bpy)(2)][Mn(NO(3))(bpy)(2)(H(2)O)]NO(3) (5) and [Mn(bpy)(3)](ClO(4))(2).0.5 C(6)H(4)-1,2-(COOEt)(2).0.5H(2)O (8).     

A NMR method for the analysis of mixtures of alkanes with different deuterium substitutions

¹³C NMR at 125.76 MHz with ¹H and ²H decoupling, ²H NMR at 76.77 MHz with ¹H decoupling, and ¹H NMR at 500.14 MHz with ²H decoupling were employed as analytical tools to study the complex mixtures of deuterated ethanes resulting from the catalytic H–D exchange of normal ethane with gas-phase deuterium in the presence of a platinum foil. Reference samples consisting of 1:1 binary mixtures of pure normal ethane and ethane-d_n (n=1–6) were used to identify the peak positions in the ¹³C, ²H, and ¹H NMR spectra due to each individual isotopomer, and the effect of isotopic substitution on the chemical shifts was determined in each case. While the NMR of all three nuclei worked well for the identification of the individual components of the 1:1 standard mixtures, both ¹H and ²H NMR suffered from inadequate resolution when studying complex reaction mixtures because of the broadening of the lines due to ¹H–¹H (¹H NMR) and ²H–²H (²H NMR) couplings. ¹³C NMR was therefore determined to be the method of choice for the quantitative analysis of the reaction mixtures. Using the ¹³C NMR results, a correlation that takes into account the primary and secondary isotope substitution effects on chemical shifts was deduced. This equation was used for the identification of the individual components of the mixtures, and integration of the individual observed resonances was then employed for quantification of their composition. This study shows that ¹³C NMR with ¹H and ²H decoupling is a viable procedure for studying mixtures of deuterated ethanes. Furthermore, the additivity of the isotopic effects on chemical shifts and the transferability of the values obtained with ethane to other molecules makes this approach general for the analysis of other isotopomer mixtures.     

Can simple enones be useful partners for the catalytic stereoselective alkylation of indoles?

A new catalytic system for the first example of enantioselective Friedel-Crafts-type (FC) addition of indoles to simple enones is described. The use of an equimolar amount of chiral [Al(salen)Cl] and 2,6-lutidine (10 mol %) was found to be effective in promoting the conjugate addition of indoles to (E)-arylcrotyl ketones, furnishing the corresponding beta-indolyl ketones in excellent yield and high enantioselectivity (ee up to 89%). The role of the base was investigated through spectroscopic as well as computational analyses, which suggested that in situ formation of a new chiral (base.[Al(salen)]) complex was operating under our reaction conditions. In particular, a stable cationic [Al(salen)] hexacoordinate trans complex with the additive base and the enone is suggested as being responsible for the stereocontrolled reaction. Finally, detailed monitoring of the reaction course was carried out showing that a conventional FC pathway induced by [Al(salen)Cl] acting as a Lewis acid is operating.     

Platinum complexes of diazo ligands. Studies of regioselective aromatic ring amination, oxidative halogen addition and reductive halogen elimination reactions

2-(Arylazo)pyridine ligands, L1a-1c react with the salt K2[PtCl4] to give the mononuclear complexes [PtCl2(L1)](1), which readily react with ArNH2 to yield the monochloro complexes of type [PtCl(L2)](HL2= 2-[(2-(arylamino)phenyl)azo]pyridine)(2) via regioselective ortho-amine fusion at the pendent aryl ring of coordinated L1. Oxidative addition of the electrophiles Y2(Y = Cl, Br, I) to the square-planar platinum(II) complex, has led to syntheses of the corresponding octahedral platinum(IV) complexes, [PtY3(L2)](3) in high yields. Ascorbate ion reductions of the platinum(IV) complexes, , resulted in reductive halogen elimination to revert to the platinum(II) complexes almost quantitatively. Isolation of products and X-ray structure determination of the representative complexes followed all these chemical reactions. In crystal packing, the compound [PtCl2(L1c)](1c) forms dimeric units with a Pt...Pt distance of 3.699(1) A. In contrast, the crystal packing of 2b revealed that the molecules are arranged in an antiparallel fashion to form a noncovalent 1D chain to accommodate pi(aryl)-pi(pyridyl) and Pt-pi(aryl) interactions. Notably, the oxidation of [Pt(II)Cl(L2a)](2a) by I2 produced a mixed halide complex [Pt(IV)ClI2(L2a)](5), which, in turn, is reduced by ascorbate ion to produce [Pt(II)I(L2a)] with the elimination of ClI. All the platinum(II) complexes are brown, the platinum(IV) complexes, on the other hand, are green. Low-energy visible range transitions in the complexes of the extended ligand [L2]- are ascribed to ligand basedpi-pi* transitions. Cyclic voltammetric behaviour of the complexes is reported.     

Nickel(II) complexes of a thiosemicarbazone prepared from 2-Acetylpyridine

Summary The ligand 3-azabicyclo[3.2.2]nonane-3-thiocarboxylic acid 2-[1-(2-pyridinyl)ethylidene]hydrazide (HL), which is observed in an unusual tautomeric form in the solid state, and its selenium analogue (HLSe) have been used to prepare a series of nickel(II) complexes. Compounds of the general formula [NiLX] (X=Cl, Br, NCS, N₃, NO₂ or NCSe) as well as [Ni(LSe)Cl] have been found to be diamagnetic, planar complexes. A single crystal study of [NiL(NCS)] shows the deprotonated ligand bound in a tridentate mannervia its pyridyl nitrogen, imine nitrogen and the thione sulphur atom with the nitrogen atom of the thiocyanato-ligand occupying the fourth coordination position. The solids prepared from the nickel(II) salts having tetrafluoroborate, nitrate and iodide ions approximate to octahedral symmetry and have neutral HL ligands coordinated in a bidentate fashionvia the pyridine and imine nitrogens with the remaining coordination sites being occupied by the anions or water molecules. The [NiL₂] solid is also octahedral with the two deprotonated ligands bonding as tridentate groupsvia the same atoms as in the [NiLX] complexes.     

Interligand interactions controlling the mu-N7,N9-metal bonding of adenine (AdeH) to the N-benzyliminodiacetato(2-) copper(II) chelate and promoting the N9 versus N3 tautomeric proton transfer: molecular and crystal structure of [Cu2(NBzIDA)(2)(H2O)(2)(mu-N7,N9-Ade(N3)H)].(3)H2O

The reaction in water of the N-benzyliminodiacetate-copper(II) chelate ([Cu(NBzIDA)]) and the adenine:thymine base pair complex (AdeH:ThyH) with a Cu/NBzIDA/AdeH/ThyH molar ratio of 2:2:1:1 yields [Cu(2)(NBzIDA)(2)(H(2)O)(2)(mu-N7,N9-Ade(N3)H)].3H(2)O and free ThyH. The compound has been studied by thermal, spectral, and X-ray diffraction methods. In the asymmetric dinuclear complex units both Cu(II) atoms exhibit a square pyramidal coordination, where the four closest donors are supplied by NBzIDA in a mer-tridentate conformation and the N7 or N9 donors of AdeH, which is protonated at N3. The mu-N7,N9 bridge represents a new coordination mode for nonsubstituted AdeH, except for some adeninate(1-)-[methylmercury(II)] derivatives studied earlier. The dinuclear complex is stabilized by the Cu-N7 and Cu-N9 bonds and N6-H(exocyclic)...O(carboxyl) and N3-H(heterocyclic)...O(carboxyl) interligand interactions, respectively. The structure of the new compound differs from that of the mononuclear compound [Cu(NBzIDA)(Ade(N9)H)(H(2)O)].H(2)O, in which the unusual Cu-N3(AdeH) bond is stabilized by a N9-H...O(carboxyl) interligand interaction and where alternating benzyl-AdeH intermolecular pi,pi-stacking interactions produce infinite stacked chains. The possibility for ThyH to be involved in the molecular recognition between [Cu(NBzIDA)] and the AdeH:ThyH base pair is proposed.