Initial example of a triangular single-molecule magnet from ligand-induced structural distortion of a [MnIII3O]7+ complex

The reaction of [Mn3O(O2CR)6(py)3](ClO4) (R = Me, Et) with methyl 2-pyridyl ketone oxime (mpkoH) in a 1:3 molar ratio in MeOH/MeCN leads to [Mn3O(O2CR)3(mpko)3](ClO4) in 80-90% isolated yield. Ferromagnetic exchange interactions between the three MnIII ions in the nonplanar [MnIII3O]7+ triangular core lead to a spin ground state of S = 6; single-crystal studies reveal the temperature and sweep rate dependent hysteresis loops expected for a single-molecule magnet.     

Modeling the coordination mode of hydroxamate inhibitors in urease: preparation,X-ray crystal structure and spectroscopic characterization of the dinuclear complex [Ni2(O2CMe)(LH)2(tmen)2](O2CMe) · 0.9H2O · 0.6EtOH (LH2 = benzohydroxamic acid; tmen = N,N, N′, N′-tetramethylethylenediamine)

Transition Metal Chemistry - Reaction of [Ni2(H2O)(O2CMe)4(tmen)2], (tmen = N, N, N′, N′-tetramethylethylenediamine) with two equivalents of benzohydroxamic acid (LH2) in H2O/EtOH gives...     

A new ionic strength adjustor for nitrate analysis in waters,soils and plants using ion-selective electrode

A new ionic strength adjustor, ISA (ISA-Pb) composed of 0.02M Pb(CH₃COO)₂–0.01M PbO–0.02M CH₃COOK–0.01M NH₂SO₃H, was tested for the rapid nitrate analysis of waters, soil and plant extracts by means of ion-selective electrode (ISE). It was found that nitrate can be determined accurately and precisely within the concentration range of 5 × 10^–2 M to 2 × 10^–6 M. The proposed ISA-Pb, with a pH of 6.8, controlled the interferences of Cl^–, HCO ₃ ^– , NO ₂ ^– , and organic anions effectively, and gave results comparable to those obtained by the commonly used ISA with Ag₂SO₄ (ISA-Ag) and to well established chemical methods as well. ISA-Pb is much cheaper than ISA-Ag, and can therefore economically replace the latter when ISE is used for nitrate determination.Part of the senior author's doctorate thesis     

Automated sample preparation based on the sequential injection principle. Solid-phase extraction on a molecularly imprinted polymer coupled on-line to high-performance liquid chromatography

A molecularly imprinted polymer (MIP) prepared using caffeine, as a template, was validated as a selective sorbent for solid-phase extraction (SPE), within an automated on-line sample preparation method. The polymer produced was packed in a polypropylene cartridge, which was incorporated in a flow system prior to the HPLC analytical instrumentation. The principle of sequential injection was utilised for a rapid automated and efficient SPE procedure on the MIP. Samples, buffers, washing and elution solvents were introduced to the extraction cartridge via a peristaltic pump and a multi-position valve, both controlled by appropriate software developed in-house. The method was optimised in terms of flow rates, extraction time and volume. After extraction, the final eluent from the extraction cartridge was directed to the injection loop and was subsequently analysed on HPLC. The overall set-up facilitated unattended operation, operation and improved both mixing fluidics and method development flexibility. This system may be readily built in the laboratory and can be further used as an automated platform for on-line sample preparation.     

Reactions of O-methyl o-quinone monoximes with methyl-, methylene- and methine- substituted aromatic compounds. Synthesis of benzo[d]oxazole and 1,4-benzoxazine derivatives

O-Methyl o-quinone monoxime 1 reacts thermally with compounds 2a-d or 6a,b or 7a,b to give mainly the corresponding 2-substituted phenanthroxazoles 3a-c and 8 . The reaction of 1 with aromatic methylene compounds lOa-c affords the ketones 13a-c in moderate to high yields. Similar products are also obtained from the reaction of monoximes 15a,b with some of the above reactants. The unexpected products 5 and 20 are obtained from the reaction of 1 with 2-methylimidazole ( 2d ) and with phenyloxirane ( 19 ) respectively, while the 4H-1,4-oxazine derivative 23 is obtained from the reaction of 1 with indene ( 21 ).     

Unusual reaction of N-aroyldihydrocyclopenta-pyrazolidinol with ketenes: formation of 1,3,4-oxadiazoles

1-Benzoyl-5-hydroxy-pyrazoline 1 was prepared and its reactions with ketenes, prepared in situ from the corresponding acid chlorides 3a-3d and the mixed anhydride 4, were studied. In all cases the 1,3,4-oxadiazoles 5 were isolated. In the case of compounds 3c and 3d a second diastereomeric oxadiazole 6 was obtained. In the case of 3a,3b and 4, an interesting aroyl migration product 7 was isolated. Structural assignments of the derived compounds were established by analysis of their IR, MS and NMR spectra (¹H, ¹³C, COSY, NOESY, HETCOR and COLOC). The proposed reaction mechanism is supported by semi-empirical (AM1) MO calculations.     

Complementary liposomes based on phosphatidylcholine: interaction effectiveness vs protective coating

A prospective targeted drug delivery system was prepared by the introduction of complementary and protective moieties at the external surfaces of liposomes. Thus recognition between hydrogenated phosphatidylcholine-cholesterol-based liposomes was achieved by the interaction of the complementary phosphate and guanidinium groups incorporated in separate liposomes while polyethylene glycol chains (PEG) protected both liposomes from environmental factors. In general, protective coating of liposomes in the range of 5% molar incorporation exerted an inhibitory effect on their recognition but it also permitted effective interaction between complementary liposomes.     

Aromatic gold and silver "rings": hydrosilver(I) and hydrogold(I) analogues of aromatic hydrocarbons

Quantum chemical calculations suggest that a series of molecules with the general formula cyclo-Mn(mu-H)n (M = Ag, Au; n = 3-6) are stable. All cyclo-MnHn species, except cyclo-Au(3)H(3), have the same symmetry with the respective aromatic hydrocarbons but differ in that the hydrogen atoms are in bridging positions between the metal atoms and not in terminal positions. The aromaticity of the hydrosilver(I) and hydrogold(I) analogues of aromatic hydrocarbons was verified by a number of established criteria of aromaticity, such as structural, energetic, magnetic, and chemical criteria. In particular, the nucleus-independent chemical shift, the relative hardness, Deltaeta, the electrophilicity index, omega, and the chemical reactivity toward electrophiles are indicative for the aromaticity of the hydrosilvers(I) and hydrogolds(I). A comprehensive study of the structural, energetic, spectroscopic (IR, NMR, electronic, and photoelectron spectra), and bonding properties of the novel classes of inorganic compounds containing bonds that are characterized by a common ring-shaped electron density, more commonly seen in organic molecules, is presented.     

Thionin-sensitized intrazeolite photooxygenation of trisubstituted alkenes: substituent effects on the regioselectivity as probed through isotopic labeling

The regioselectivity for the intrazeolite photooxygenation of several trisubstituted alkenes with geminal dimethyl groups was examined. The length of the alkyl chain at the lone position was varied, and as end groups, the phenyl or the cyclohexyl functionalities were chosen. The general trend for all alkenes is a significant increase of the reactivity at the twin position compared to the photooxygenation in solution. For the cyclohexyl-substituted alkenes, it was found that the regioselectivity is nearly independent of the alkyl chain length. However, for the phenyl-substituted alkenes, the ene reactivity of the allylic methylene hydrogen atoms at the lone position and the twix/twin regioselectivity depend significantly on the distance of the phenyl group from the double bond. These trends are discussed in terms of cation-pi interactions and conformational effects. Intramolecular and intermolecular isotope effects in the intrazeolite photooxygenation of deuterium-labeled alkenes suggest that a perepoxide-type intermediate is formed in the rate-determining step. Type I photooxygenation that involves reaction of the radical cations of the alkenes with superoxide ion are unlikely.     

Quantum chemical study of the coordination of glycolic acid conformers and their conjugate bases to [Ca(OH2)n] (n=0–4) ions

A detailed exploration of the configurational and conformational space of glycolic acid and their conjugate bases has been carried out with the aid of first principles quantum chemical techniques at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory. The most stable configuration among the eight possible glycolic acid conformers corresponds to the E-s-cis, s-trans configuration, while the highest energy E-s-trans, s-cis conformer was found at 10.88 and 12.17 kcal mol⁻¹ higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. Upon dissociation of glycolic acid the s-cis(syn), and s-trans(anti) configurations of the glycolate anion can be formed. The anti conformer was found to be less stable than the syn one by 14.20 and 16.87 kcal mol⁻¹ at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p)) levels of theory, respectively. The computed B3LYP/6-311+G(d,p) proton affinity of the syn conformer for the protonation process affording the more stable E-s-cis, s-trans conformer, in vacuum was found to be 325.35 kcal mol⁻¹ (ΔG⁰ value). From a methodological point of view, our results confirm the reliability of the integrated computational tool formed by the B3LYP density functional model. This model has subsequently been used to investigate the interaction of Ca²⁺ ions with the glycolic acid conformers and their conjugate bases in vacuum and in the presence of extra water ligands. For the complexes of glycolic acid conformers the η²–O,O–(COOH) coordination, that is the structure that arises from the coordination of the Ca²⁺ to the carboxylic group, is the global minimum of the PES, while the η²–O(OH),O–(COOH) coordination is a local minimum found at only 1.0 and 1.3 kcal mol⁻¹ higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. Moreover, the two isomers exhibit nearly the same binding affinities, which are predicted to be 89 and 85 kcal mol⁻¹ at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. The same holds also true for the complexes of the glycolate anion. The η²–O,O–(COO⁻) coordination involving the syn conformer of the glycolato ligand, is the global minimum, while the η²–O(OH),O–(COO⁻) one lies at 1.5 and 5.6 kcal mol⁻¹ higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. The other conformer with an η²–O,O–(COO⁻) coordination involving the anti conformer of the glycolato ligand, is less stable by only 0.2 kcal mol⁻¹ at both levels of theory. Noteworthy is the trend seen for the incremental binding energy due to the successive addition of water molecules to [HOCH₂C(O)O]Ca²⁺ species; the computed values are 30.4, 26.8, 22.9 and 16.2 kcal mol⁻¹ at the B3LYP/6-311+G(d,p) level of theory for the mono-, di-, tri- and tetraaqua complexes, respectively. This trend arising from the repulsion of the dipoles between the water ligands and from unfavorable many body interactions is in accordance with those anticipated from electrostatic considerations. The Ca(II)-water interaction weakens with increasing coordination of the metal. Obviously, it is the electrostatic nature of the Ca(II)-water interactions that accounts well for the computed coordination geometries of the cationic (aqua)(glycolato)calcium complexes. Calculated structures, relative stability and bonding properties of the conformers and their complexes with [Ca(OH₂)_n]²⁺ (n=0–4) ions are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution, harmonic vibrational frequencies and NMR chemical shifts.