Loss of CO from the molecular ions of o-, m- and p-anisoyl fluorides,CH3OC6H4COF,with fluorine atom migration

Loss of CO from the molecular ions ([CH₃OC₆H₄COF]⁺˙) of o-, m- and p-anisoyl fluorides has been investigated by mass-analysed ion kinetic energy (MIKE) spectrometry. This reaction involves fluorine atom migration from the carbonyl group to the benzene ring. In the cases of o- and p-anisoyl fluorides, the fluorine atom migrates via a three-membered transition state to form the molecular ions ([CH₃OC₆H₄F]⁺˙) of o- and p-fluoroanisoles, respectively. On the other hand, in the case of m-anisoyl fluoride, the fluorine atom migrates from the carbonyl group to the benzene ring via a three- or four-membered transition state.     

Spectroscopic and magnetic properties of Cu(II) complexes with selected biologically important ligands

The aim of this work was to study the spectroscopic and magnetic properties of copper(II) o-, m-, p-aminobenzoates, o-, m-, p-methoxybenzoates and o-, m- and p-nitrobenzoates. The complexes were synthesized and their compositions were evaluated by elementary analysis. The infrared and Raman spectra for Cu(II) aminobenzoates, methoxybenzoates and nitrobenzoates were recorded and assigned. The obtained data were compared with those previously published for aminobenzoic, methoxybenzoic and nitrobenzoic acids and their sodium salts. The structures of Cu(II) o-, m-, p-aminobenzoates, o-, m-, p-methoxybenzoates and o-, m- and p-nitrobenzoates as well as the change in the electronic charges distribution caused by Cu(II) complex formation were discussed.     

Electrochemical transformations of catecholate and <Emphasis Type="Italic">o</Emphasis>-amidophenolate complexes with triphenylantimony(V)

The electrochemical properties of catecholate and o-amidophenolate complexes with triphenylantimony(V) with various substituents in the aromatic ring were examined. Introduction of electron-donating groups into the catecholate ligand or replacement of an O atom (in catecholate) by a N atom (o-amidophenolate) stabilizes the monocationic forms of the complexes obtained by one-electron oxidation. Complexes with electron-withdrawing substituents undergo irreversible two-electron oxidation resulting in the elimination of o-quinone. Complexes containing electron-withdrawing ligands do not form o-semiquinones and are inert to atmospheric oxygen. According to electrochemical data, oxygen can be bound reversibly by catecholate complexes containing the electron-donating methoxy groups in the 3,6-di-tert-butylcatecholate ligand and o-amidophenolate derivatives with half-wave oxidation potentials lower than or equal to 0.70 V (vs. Ag/AgCl), which form relatively stable cationic complexes upon the oxidation.     

A pronounced ortho effect in the polymerization of o-substituted β-nitrostyrenes

It was shown in a previous paper that a number of m - and p-substituted β-nitrostyrenes would readily undergo polymerization via anionic initiation with alkoxide ions to yield high polymers, whereas, in all cases, the corresponding o-substituted isomers could not be induced to produce polymers under any conditions tried. This article reports a systematic study of this unexpected “ortho effect” based on the initial postulate that the effect was the result of steric inhibition of the propagation step that would ordinarily lead to polymer. Since the fluorine atom is only slightly larger than the hydrogen atom, the series o-, m-, and p-fluoro-β-nitrostyrenes was synthesized and its alkoxide ion-initiated polymerization studied. Although it was shown in all cases of o-substituted β-nitrostyrenes studied that initiation was rapid, only in the case of o-fluoro-β-nitrostyrene was a substantial amount of polymer obtained. With up to 3 mole % initiator a maximum of 26% polymer was obtained, whereas polymerization was rapid in cases of the meta and para isomers. The values of the propagation rate constants k_p were found to be 1.1 liters/mole-sec for the para isomer as compared with 4.8 × 10^?2 liter/mole-sec for the ortho isomer for a ratio k_p(p)/k_p(o) = 23, the magnitude of this ortho effect for the fluorine atom.     

Chelating Behaviour of Substituted 3-4 Aryl-Hydrazo-Pentane-2, 4-Dione: Part VI. Potentiometric and Infrared Studies of the Ligands and Their Divalent Metal Complexes

The dissociation constants of 3-phenylhydrazo-pentane-2, 4-dione and its o-, m-, p-carboxy derivatives, and the stability constants of complexes of divalent metal ions with the o-carboxy derivative are determined by pH-metric method. The ir-spectra of the ligands and some divalent metal complexes with the o-derivative are discussed.     

Factors that regulate the conformation of m-benziporphodimethene complexes: agostic metal-arene interaction, hydrogen bonding, and η2,π coordination

Group 12 and silver(I) tetramethyl‐m‐benziporphodimethene (TMBPDM) complexes with phenyl, methylbenzoate, or nitrophenyl groups as meso substituents were synthesized and fully characterized. The dimeric silver(I) complex displays an unusual η²,π coordination from the β‐pyrrolic C?C bond to the silver ion. All of the complexes displayed a close contact between the metal ion and the inner C(22)? H(22) on the m‐phenylene ring. The downfield chemical shifts of H(22) and large coupling constants between Cd^II and H(22) strongly support the presence of an agostic interaction between the metal ion and inner C(22)–H(22). Crystal structures revealed that the syn form is the predominant conformation for TMBPDM complexes. This is distinctively different from the exclusive anti conformation observed in m‐benziporphyrin and tetraphenyl‐m‐benziporphodimethene (TPBPDM) complexes. Evidently, intramolecular hydrogen‐bonding interactions between axial chloride and methyl groups stabilize syn conformations. Unlike the merely syn conformation observed in the solid‐state structures of TMBPDM complexes that contain an axial chloride, in solution these complexes display highly solvent‐ and temperature‐dependent syn/anti ratio changes. The observation of dynamic ¹H NMR spectroscopic scrambling between syn and anti conformations from the titration of chloride ion into the solution of the TMBPDM complex suggests that axial ligand exchange is a likely pathway for the conversion between syn and anti forms. Theoretical calculations revealed that intermolecular hydrogen‐bonding interactions between the axial chloride and CHCl₃ stabilizes the anti conformation, which explains the increased ratio for the anti form when dichloromethane or chloroform was used as the solvent.     

Covalent modification of mushroom tyrosinase with different amphiphic polymers for pharmaceutical and biocatalysis applications

Two different poly(ethylene glycol) derivatives (linear, mol wt 5000 and a branched form, mol wt 10000) and a new polymer (poly [acryloylmorfoline], mol wt 5500) were covalently bound to the enzyme tyrosinase. The polymer-protein conjugates were studied with a view to their potential pharmaceutical application and to their use for the bioconversion of phenolic substrates in organic solvents.V _max andK _m for the dopa-dopaquinone conversion, thermostability, stability toward inactivation by dopa oxidation products, half-life in blood circulation, and behavior in organic solvents for the different adducts were investi gated. Arrhenius plots for the dopa-dopaquinone conversion were also obtained in order to study the effects of temperature on the different enzyme forms. Covalent attachment of the polymers increased enzyme stability in aqueous solution and the solubility in organic solvents. However, organic solvent solubilization brought about loss of enzyme conformation as assessed by CD measurements, which is accompanied by a nonreversible loss of catalytic activity.     

Synthesis and characterisation of some new cyanonitrosyl chromium(l) complexes with phenetidines and anisidines

Summary A new series of cyano-substituted nitrosylchromium(I) complexes having octahedral stereochemistry around the metal ion, and of general formula, [CrNO(CN)₂(L)₂(H₂O)] (L =o-,m- andp-phenetidines oro-,m-, andp-anisidines) have been isolated in the solid state by interaction of potassium pentacy-anonitrosylchromate(I) monohydrate with the appropriately substituted aniline. The complexes, which have been characterised by elemental analysis, conductance, molecular weight determination, magnetic measurements, e.s.r. and i.r. spectral studies, contain chromium(I) in a low-spin d⁵-configuration.     

Synthesis of σ-(o-carboran-9-yl)- and σ-(m-carboran-9-yl)-π-cyclopentadienyldicarbonyliron and their rearrangement in reactions with bromine to π-(o-carboran-9-yl)cyclopentadienyl- and π-(m-carboran-9-yl)cyclopentadienyl-dicarbonylironbromides,respectively

9-o- and 9-m-carboranylcarboxylic acids were used to synthesize σ-(o-carboran-9-yl)- and σ-(m-carboran-9-yl)-π-cyclopentadienyldicarbonyliron. The latter complexes, in reactions with bromine, undergo rearrangement with the cleavage of the BFe σ-bond, involving migration of the 9-o- and 9-m-carboranyl groups into the cyclopentadienyl ring, to give π-(o-carboran-9-yl)cyclopentadienyl- and π-(m-carboran-9-yl)cyclopentadienyl-dicarbonyliron bromides, respectively. A simple method to obtain these acids by the oxidation of 9-alkyl-o- and 9-alkyl-m-carboranes with CrO₃ in CH₃COOH has been found.     

Synthesis and asymmetric polymerization of a series of methyl‐substituted triphenylmethyl methacrylate

Five novel ortho‐, meta‐, and para‐methyl‐substituted triphenylmethyl methacrylate monomers, such as o‐tolyldiphenylmethyl methacrylate (o‐MeTrMA), di‐o‐tolylphenylmethyl methacrylate (o‐Me₂TrMA), tris‐o‐tolylmethyl methacrylate (o‐Me₃TrMA), tris‐m‐tolylmethyl methacrylate (m‐Me₃TrMA), and tris‐p‐tolylmethyl methacrylate (p‐Me₃TrMA) have been synthesized. The methanolysis rates of these monomers were measured in CDCl₃‐CD₃OD (1:1, v/v) by ¹H NMR spectroscopy at 30 °C. It was found that the order of the methanolysis rates would be TrMA<o‐MeTrMA<o‐Me₂TrMA<o‐Me₃TrMA<m‐Me₃TrMA except p‐Me₃TrMA, which exhibited very good stability to methanolysis. The asymmetric polymerization of these monomers was investigated by chiral anionic complexes as initiators. The results showed that the ability to form a helical chain was effected not only by the types of chiral complex initiators, but also by the position and number of methyl‐substituted groups at the benzene rings of TrMA. The order of the ability of polymerization was o‐MeTrMA >o‐Me₂TrMA>o‐Me₃TrMA and m‐Me₃TrMA> p‐Me₃TrMA>o‐Me₃TrMA. These differences would be attributed to the different sizes and “propeller” steric structures of the bulky side groups. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 430–436, 2001     

Preparation and catalytic properties of chitosan bound Schiff base copper complexes

Chitosan, a natural polymer, bound Schiff base copper complexes CT‐She‐Cu, CT‐o‐Bel‐Cu, CT‐m‐Bel‐Cu were prepared and characterize by inductively coupled plasma (ICP), FT‐IR and X‐ray photoelectron spectroscopy (XPS). Their catalytic activity in the oxidation of cyclohexene with molecular oxygen was studied. All the complexes have catalytic activity and the main oxidation products are 2‐cyclohexene‐ol, 2‐cyclohexene‐one and cyclohexene hydroperoxide, which were measured by gas chromatography/mass spectroscopy (GC/MS) and GC/IR. CT‐m‐Bel‐Cu was selected to study the influence of reaction temperature, amount of catalyst and additives such as acid and base on the oxidation of cyclohexene systematically. Copyright © 2004 John Wiley & Sons, Ltd.     

Study on Inclusion Complex Formation of <Emphasis Type="Italic">m</Emphasis>-Aminobenzoic Acid with Native and Substituted <Emphasis Type="Italic">β</Emphasis>-Cyclodextrins

The complex formation of native and substituted β-cyclodextrins with m-aminobenzoic acid in water was characterized by calorimetry, ¹H NMR and UV spectroscopic studies. These studies showed that β-, hydroxypropyl-β- and methyl-β-cyclodextrins form 1:1 inclusion complexes with m-aminobenzoic acid. The thermodynamic properties of complex formation (K,Δ_c G ^o,Δ_c H ^o,Δ_c S ^o) were calculated. It was found that the processes of complexation are mainly favorable entropically. Introduction of hydroxypropyl- and methyl-substituents into the β-CD molecule results in negligible enhancement of stability of the complexes formed. The structure of these substituents has no influence on the stability constant values. The insertion of the carboxylic group of m-aminobenzoic acid into the cyclodextrin cavity was confirmed by ¹H NMR data.     

N-Glucosides of Aminobenzoic Acids and Aminophenols

N-o-, -m-, and -p-carboxyphenyl-D-glucosylamines and N-o-, -m-, and -p-hydroxyphenyl-D-glucosylamines were synthesized by reaction of D-glucose with o-, m-, and p-aminobenzoic acids and o-, m-, and p-aminophenols. It was demonstrated that both - and -anomers were formed by N-glycosylation of o-, m-, and p-aminobenzoic acids; only -anomers, by N-glycosylation of o-, m-, and p-aminophenols.     

Studies of the kinetics of the interaction between N-trifluoroacetlyl-D-tryptophan and α-chymotrypsin by pulsed nuclear magnetic resonance

The Carr-Purcell experiment first used by Allerhand and Gutowsky for the determination of chemical exchange rates has been applied to the study of an enzyme inhibitor complex. Chemical shift and relaxation time data obtained by analysis of pulsed fluorine NMR data collected at 51 MHz are shown to be consistent with high resolution results assembled at 94° 1 MHz. The rate constants for dissociation of the N-trifluoroacetyl-D -tryptophan-α-chymotrypsin complex were determined to be 1 × 10⁴ s^?1 at 26°C and 2 × 10³ s^?1 at 6·5°C. The resonance position of the fluorine nuclei of the inhibitor is shifted downfield ～1 ppm upon complexation to the enzyme, and the trifluoromethyl group suffers some restriction of molecular motion in the bound state as indicated by T₁ and T₂ data.     

Single-Point Mutant Inverts the Stereoselectivity of a Carbonyl Reductase toward β-Ketoesters with Enhanced Activity

Enzyme stereoselectivity control is still a major challenge. To gain insight into the molecular basis of enzyme stereo-recognition and expand the source of antiPrelog carbonyl reductase toward β-ketoesters, rational enzyme design aiming at stereoselectivity inversion was performed. The designed variant Q139G switched the enzyme stereoselectivity toward β-ketoesters from Prelog to antiPrelog, providing corresponding alcohols in high enantiomeric purity (89.1–99.1 % ee). More importantly, the well-known trade-off between stereoselectivity and activity was not found. Q139G exhibited higher catalytic activity than the wildtype enzyme, the enhancement of the catalytic efficiency (k_cat/K_m) varied from 1.1- to 27.1-fold. Interestingly, the mutant Q139G did not lead to reversed stereoselectivity toward aromatic ketones. Analysis of enzyme–substrate complexes showed that the structural flexibility of β-ketoesters and a newly formed cave together facilitated the formation of the antiPrelog-preferred conformation. In contrast, the relatively large and rigid structure of the aromatic ketones prevents them from forming the antiPrelog-preferred conformation.     

A theoretical study of the interactions between N,N-dimethylformamide and xylenes

The ab initio and density functional (DFT) methods were performed on binary systems of N,N-dimethylformamide (DMF) with xylenes (o-, or m-, or p-xylene), and seven stable configurations were obtained with no imaginary frequencies. To obtain the interaction energies of these complexes, single-point energy calculations with basis set superposition error (BSSE) correction were carried out at B3LYP/6-31G* and MP2/6-31G* levels. The structures, Chelpg (charges from electrostatic potentials using a grid-based method) charge distribution and bond characteristics of the mentioned complexes were calculated. The results indicated the presence of double C–H···O hydrogen bonds between DMF and xylenes in these complexes and the interaction energies of hydrogen bonding between DMF and xylene systems decreased in the following sequence: DMF–o-xylene: a1 > DMF–m-xylene: b1 > DMF–p-xylene: c1.     

Evaluation of Anisole‐Substituted Boron Difluoride Formazanate Complexes for Fluorescence Cell Imaging

Evaluation of three subclasses of boron difluoride formazanate complexes bearing o‐, m‐, and p‐anisole N‐aryl substituents (Ar) as readily accessible alternatives to boron dipyrromethene (BODIPY) dyes for cell imaging applications is described. While the wavelengths of maximum absorption (λ_max) and emission (λ_em) observed for each subclass of complexes, which differed by their carbon‐bound substituents (R), were similar, the emission quantum yields for 7 a – c (R=cyano) were enhanced relative to 8 a – c (R=nitro) and 9 a – c (R=phenyl). Complexes 7 a – c and 8 a – c were also significantly easier to reduce electrochemically to their radical anion and dianion forms compared to 9 a – c . Within each subclass, the o‐substituted derivatives were more difficult to reduce, had shorter λ_max and λ_em, and lower emission quantum yields than the p‐substituted analogues as a result of sterically driven twisting of the N‐aryl substituents and a decrease in the degree of π‐conjugation. The m‐substituted complexes were the least difficult to reduce and possessed intermediate λ_max, λ_em, and quantum yields. The complexes studied also exhibited large Stokes shifts (82–152 nm, 2143–5483 cm^?1). Finally, the utility of complex 7 c (Ar=p‐anisole, R=cyano), which can be prepared for just a few dollars per gram, for fluorescence cell imaging was demonstrated. The use of 7 c and 4′,6‐diamino‐2‐phenylindole (DAPI) allowed for simultaneous imaging of the cytoplasm and nucleus of mouse fibroblast cells.     

Complexes of cobalt(II) aryl carboxylates with quinoline and isoquinoline

Summary Several new complexes of cobalt(II) aryl carboxylates Co(O₂CC₆H₄R)₂ (R =o-Me;o,m-Cl:o,m-NO₂ andm-MeO) have been prepared by refluxing an ethanolic solution of the respective cobalt(II) aryl carboxylate with quinoline (Q) and isoquinoline (IQ). The quinoline complexes are green or purple while isoquinoline complexes are pink to reddish pink. All are neutral and soluble in common organic solvents. Analytical data indicate that quinoline complexes are of 1:1 stoichiometry. Magnetic and spectral studies show them to possess the usual copper(II) acetate monohydrate type dimeric carboxylate bridged structures. formulated as Co₂(O₂CC₆H₄R)₄Q₂, in which cobalt(II) is in a square pyramidal geometry. By contrast, isoquinoline yields monomeric bisamine complexes oftrans-octahedral configuration containing bidentate chelating carboxylate groups.     

Optical properties of inherently dissymmetric polyamides

A study of the optical rotatory dispersion (ORD), circular dichroism (CD), and ultraviolet spectra (UV) of polyamides derived from optically active biphenyl acid chlorides, and aromatic, and aliphatic diamines, was made. The optically active monomers were (–)-(S)-2,2′-dinitro-6,6′-dimethylbiphenyl-4,4′-dicarbonyl chloride and (–)-(S)-2,2′-dichloro-6,6′-dimethylbiphenyl-4,4′-dicarbonyl chloride. The diamines were o-, m-, and p-phenylenediamine, piperazine, trans-2,5-dimethylpiperazine, and 1,2-pyrazolidine. The ORD spectra of the o-phenylenediaminepolyamide taken in different solvents indicated the existence of some ordered structure in the least polar solvent. All other polyamides existed in a random coil conformation in the solvents employed.     

Coordinating Properties of Co(II) and Zn(II) Complexes with Sterically Hindered Porphyrins

Cobalt(II) and zinc(II) complexes with 5,15-di(o-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetra-n-buthylporphyrin and its capped analogues, where the MN₄ reaction site is shielded by bridging groups containing m-phenylene and dimethoxy-substitutedp-phenylene fragments, were synthesized. Equilibrium constants of additional coordination of pyridine and N-methylimidazole by these metalloporphyrins were determined at 298 K. It was found that steric distortion of the porphyrin core destabilizes extra complexes.