An average fock operator technique of approximate open-shell LCAO-MO-SCF calculation

The exchange part of the usual Hartree-Fock potential in the unrestricted Hartree-Fock (UHF) theory is suitablyaveraged to construct an, average one-electron model Hamiltonian which generates a set of spin-restricted one-electron orbitals in a self-consistent manner. These orbitals are then used to calculate the electronic energy of the open-shell system by using the proper functional form for the energy which handles the exchange terms correctly. The eigenvalues ofF ^av can be used for calculating either the spin-polarised or spin-averaged ionisation potentials of different orbitals at theKoopmans’ theorem level of approximation. Comparison ofE ^ac with the UHF-energy shows thatE _UHF<E ^ac in each case revealing some kind of an upper bound nature ofE ^ac. An approximate variational argument is given. Relationship of our model with the hyper-Hartree-Fock theory of slater is explored and the general problem of eliminating ‘self-interaction’ terms in average Fock-operator based theories is discussed.     

A Two‐Dimensional Coordination Compound as a Zinc Ion Selective Luminescent Probe for Biological Applications

A 2D coordination compound {[Cu₂(HL)(N₃)]?ClO₄}_∞ ( 1 ; H₃L=2,6‐bis(hydroxyethyliminoethyl)‐4‐methyl phenol) was synthesized and characterized by single‐crystal X‐ray diffraction to be a polymer in the crystalline state. Each [Cu₂(HL)(N₃)]⁺ species is connected to its adjacent unit by a bridging alkoxide oxygen atom of the ligand to form a helical propagation along the crystallographic a axis. The adjacent helical frameworks are connected by a ligand alcoholic oxygen atom along the crystallographic b axis to produce pleated 2D sheets. In solution, 1 dissociates into [Cu₂(HL)₂(H₃L)]?2H₂O ( 2 ); the monomer displays high selectivity for Zn²⁺ and can be used in HEPES buffer (pH 7.4) as a zinc ion selective luminescent probe for biological application. The system shows a nearly 19‐fold Zn²⁺‐selective chelation‐enhanced fluorescence response in the working buffer. Application of 2 to cultured living cells (B16F10 mouse melanoma and A375 human melanoma) and rat hippocampal slices was also studied by fluorescence microscopy.     

The spectrophotometry and solvent-extraction behaviour of iron(III), vanadium(IV and V) and titanium(IV) chelates of 1-(o-carboxyphenyl)-3-hydroxy-3-methyltriazene

l-(o-Carboxyphenyl)-3-hydroxy-3-methyltriazene is proposed as an excellent reagent for the spectrophotometric determination of iron(III) and titanium(IV), and also for the separation of titanium from a large quantity of iron as well as other cations and anions. Iron(III) forms an anionic violet 1:2 complex at pH 4.0–9.4, and a cationic green 1:1 complex at pH 1.5–2.0, with absorption maxima at 570 nm and 660 nm, respectively. The violet complex is quantitatively extracted in chloroform containing n-octylamine at pH 3.0–9.0. The green and the violet iron(III) complexes obey Beer's law, the respective optimal ranges being 8.9–35.8 and 3.9–11.2 p.p.m. The yellow titanium chelate extracted into chloroform (absorption maximum at 410 nm) between pH 1.0 and 3.5, can be re-extracted into concentrated sulphuric acid a violet colour being produced with absorption maximum at 530 nm. Beer's law is obeyed in the ranges 0.8–5.7 p.p.m. for the titanium complex in chloroform and 3.4–19.2 p.p.m. when extracted in concentrated sulphuric acid. Interferences from diverse ions are not severe. Procedures for the separation and determination of titanium in the presence of a large quantity of iron are given. The isolation of the iron(III) and vanadium(IV and V) complexes, and their properties, are described.     

Capillary electrophoresis in aqueous-organic media. Ionic strength effects and limitations of the Hubbard-Onsager dielectric friction model

The mobilities of three aromatic sulfonates, ranging in charge from -1 to -3, were investigated by capillary electrophoresis using buffers containing 0 to 75% ethanol or 2-propanol. Absolute mobilities were determined by extrapolation of the effective mobilities to zero ionic strength according to the Pitts' equation. For all buffers studied, ions of higher charge experienced larger ionic strength effects. The resulting ionic strength-induced selectivity alterations were more dramatic when organic solvents were present in the media. Furthermore, for different organic modifier types and contents, the magnitude of the ionic strength effect was governed to a large extent by the 1/(eta epsilon 1/2) dependence in the electrophoretic effect of the Pitts' equation. Addition of ethanol or 2-propanol to the electrophoretic media resulted in changes in the absolute mobilities of the ions. These solvent-induced mobility changes are attributed to dielectric friction. As predicted by the Hubbard-Onsager model, dielectric friction increased with increasing organic content and with increasing analyte charge. As a result, dramatic changes in the relative absolute mobilities were observed, such as a reversal in migration order between sulfonates of -1 and -3 charge in 75% 2-propanol. Within the alcohols, the Hubbard-Onsager model was successful at predicting the relative mobility trends upon changing solvent. However, the relative trends observed between acetonitrile-water and alcohol-water media were not consistent with the model. This may be explained by the continuum nature of the model, whereby the different ion-solvent interactions characteristic to each solvent class are not taken into account.     

Highly efficient recycling of a "sandwich" type polyoxometalate oxidation catalyst using solvent resistant nanofiltration

A "sandwich" type polyoxometalate catalyst ([MeN(n-C8H17)3]12[WZn3(ZnW9O34)2]) was very efficiently recycled by nanofiltration with almost quantitative retention, using an alpha-alumina supported mesoporous gamma-alumina membrane.     

A one-pot synthesis of novel sugar derived 5,6-dihydro-quinazolino[4,3-b]quinazolin-8-ones: an entry towards highly functionalized sugar-heterocyclic hybrids

An efficient and practical one-pot method for the synthesis of novel diversified sugar derived dihydro-quinazolino[4,3-b]quinazolin-8-ones has been reported. Various protected sugar hemiacetals were used to synthesize the hybrid tetracyclic ring system. The one-step reductive transformation of 2-(2-nitrophenyl)-3H-quinazolin-4-one with different sugar hemiacetals furnished the desired tetracyclic product in good yields and with high purity.     

Coordination chemistry of f-block elements with imine acids. Part IV. Synthetic and chiroptical studies on lanthanide(III) complexes of imine acids derived from L-alanine,L-valine,L-tyrosine and L-glutamic acid

Summary N-(orthovanillidene)L-alanine (OVAlaH₂), N-(salicylidene)L-valine (SValH₂), N-(orthovanillidene)L-valine (OVValH₂), N-(orthovanillidene)L-tyrosine (OVTyrH₃) and N-(salicylidene)L-glutamic acid (SGluH₃) react with La^III, Pr^III, Nd^III and Sm^III to yield new chiral complexes. Their dominant conformers were determined from c.d. spectra supported by¹H n.m.r. data, except for the L-glutamic acid derived complexes which were insoluble.     

Biyclo[2.2.1]heptane as cyclopentane precursor. Part 4 Stereocontrolled syhthesis of a potential intermediate to chromophycane dolastane and clavularane

The regio– and stereoselective synthesis of the keto-esters 20 and 22 are described, the latter being a potential intermediate to several diterpenes. The key steps involve the Diels-Alder cycloaddition between the benzocycloheptenone 5 and cyclopentadiene followed by a regioselective functionalisation of the adduct 6. A remarkable reversal of regioselectivity was observed during oxymercuration of the unsymmetric double bond in 6 and its reduced product 11 leading to 8 and 12 which were subsequently transformed to 20 and 22 respectively.     

Biomimetic studies on anti-thyroid drugs and thyroid hormone synthesis

The selenium analogues of anti-thyroid drugs exhibit their anti-thyroid action by a mechanism different from that of MMI. The selenium analogue of MMI and related selenium compounds exhibit high GPx activity, providing a novel method for the reversible inhibition of thyroid hormone biosynthesis.     

Synthesis and properties of a new member of the calixnaphthalene family: a C(2)-symmetrical endo-calix[4]naphthalene

The synthesis of a new endo-calix[4]naphthalene is described. The reaction sequence involves the cyclocondensation of a key bisnaphthylmethane intermediate (8) with formaldehyde. This key intermediate (8) is formed using a modified Suzuki-Miyaura Pd-catalyzed cross-coupling reaction between bromomethylnaphthyl (6) and naphthylboronic acid (7), both of which can be derived from 2-hydroxynaphthoic acid.