Chemistry of 1,1-bis(acylamido)-1-deoxyalditols. Base-catalyzed,intramolecular O,N-transacylation of per-O-acyl-1,1-bis(benzamido)-1-deoxy-d-glucitols in aprotic solvents

Penta-O-acetyl and penta-O-propanoyl derivatives of 1,1-bis(benzamido)-1-deoxy-d-glucitol are transformed into 1-acetamido-1-benzamido-1-deoxy-d-glucitol and 1-benzamido-1-deoxy-1-propanamido-d-glucitol, respectively, by heating with a suspension of potassium cyanide in acetonitrile, and subsequently O-deacylating with sodium methoxide in methanol. The reaction was also studied in the presence of a crown ether. When other nucleophiles (HO^? and CH³O^?) or other aprotic solvents (propanonitrile, benzene) were employed, the yields of transacylation products diminished noticeably; likewise, the use of sodium as the counter-ion significantly affected this reaction. These results are qualitatively discussed in terms of the solvent effects on the reactivity of the nucleophiles employed.     

Toward charge-neutral ‘soft scorpionates’: Coordination chemistry and Lewis acid promoted isomerization of tris(1-organo-imidazol-2-ylthio)methanes

Two tris(1-organo-imidazol-2-ylthio)methanes, HC(S-tim^R)₃ (R = organo = methyl, tert-butyl), have been prepared by a triphasic reaction between chloroform, the appropriate heterocycle, and saturated aqueous solutions of Na₂CO₃, in the presence of a phase transfer agent, (NBu₄)(Br). These ligands have been characterized both spectroscopically and by single crystal X-ray diffraction. The reaction chemistry of these potentially N,N,N-tripodal ligands with AgBF₄ was also explored where simple 1:1 coordination complexes could be isolated from reactions performed in THF solution at room temperature. The derivative {Ag[HC(S-tim^Me)₃]}(BF₄) was structurally characterized which showed that the ligand binds in a μ-κ²N,κ¹N-mode to give a coordination polymer with an interesting layered supramolecular structure. Surprisingly, heating CH₃CN solutions of the silver complexes at reflux resulted in decomposition of the complex and concomitant isomerization of the ligands to give metal-free tris(3-organo-1-imidazole-2-thione)methane, HC(N-imt^R)₃; the heretofore elusive charge-neutral analogues of the well-studied ‘soft scorpionate’ Tm^R− anions. The solution isomerization of HC(S-tim^R)₃ to HC(N-imt^R)₃ was found to be general, occurring in a variety of solvents with any of a host of different Lewis acids [para-toluenesulfonic acid, KPF₆, and M(CO)₅Br (M = Mn, Re)] but did not occur by heating in the absence of Lewis acid. The compound HC(N-imt^Me)₃ exhibited unusually low solubility in common organic solvents. Single crystal X-ray diffraction of HC(N-imt^Me)₃ revealed a remarkable honeycomb supramolecular structure with ca. 5 Å channels filled with solvent. The robust nature of this solid is a result of strong dipolar stacking interactions of molecules into polymer chains bolstered by concerted π-π and CH-π interactions involving the heterocycles, holding the chains together in the remaining two dimensions.     

Microwave-assisted enzymatic resolution of (R,S)-2-octanol in ionic liquid

Combination use of microwave irradiation (MW) as heating mode and ionic liquid (IL) as reaction medium in enzymatic resolution of (R,S)-2-octanol with vinyl acetate as the acyl donor through transesterification by Novozym 435 was investigated. A synergistic effect of MW and IL [EMIM][NTf2], which was screened as the best reaction medium for this reaction, on improving enzyme activity and enantioselectivity was observed. The activity and enantioselectivity of Novozym 435 in [EMIM][NTf2] under MW were much higher than that in solvent free system under conventional heating, in solvent free system under MW, and in [EMIM][NTf2] under conventional heating, respectively. A systematic screening and optimization of the reaction parameters in [EMIM][NTf2] under MW were performed. Under the optimum conditions, 50% yield of (S)-2-octanol with 99% enantiomeric excess was obtained in 6 h. Furthermore, increased thermal stability and reusability of Novozym 435 under the combination use of MW and IL condition were also observed.     

Cellulose esters from waste cotton fabric via conventional and microwave heating

The esterification of cellulose from waste cotton fabric in a N,N-dimethylacetamide/lithium chloride solvent system was carried out using different types of fatty acid chloride including butyryl chloride, capryloyl chloride, and lauroyl chloride as esterifying agents, and N,N-dimethyl 1-4-aminopyridine as a catalyst under conventional and microwave activation. Microwave esterification was performed under 2.45 GHz with power varying from 90 to 450 W. The optimum conditions for esterification of cotton cellulose with various esterifying agents were investigated in terms of reaction time and temperature to attain appropriate %weight increase and degree of substitution of esterified-cellulose. The degree of substitution, functional group and chemical structure, and thermal stability of cellulose ester powder were characterized by ¹H NMR, FTIR, and TGA/SDTA analysis. Morphologies, crystallinity, and solubility of modified cellulose by two different heating methods were compared.     

Clostridium acetobutylicum Mutants That Produce Butyraldehyde and Altered Quantities of Solvents

Spontaneous mutants of Clostridium acetobutylicum NRRL B643 that were resistant to allyl alcohol (AA) were selected and characterized. These mutants contained 10- to 100-fold reduced activities of butanol and ethanol alcohol dehydrogenase. The AA mutants formed two groups and produced no ethanol. Type 1 AA mutants produced significant amounts of a new solvent, butyraldehyde, and contained normal levels of the coenzyme A-dependent butyraldehyde dehydrogenase (BAD). Type 2 AA mutants produced no significant butyraldehyde and lower levels of all solvents, and they contained 45- to 100-fold lower activity levels of BAD. Following ethyl methanesulfonate mutagenesis, low-acid-producing (Acid⁻) mutants were selected and characterized as superinduced solvent producers, yielding more than 99% of theoretical glucose carbon as solvents and only small amounts of acetate and butyrate. Following ethyl methanesulfonate mutagenesis, 13 sporulation-negative (Spo⁻) mutants were characterized; and 3 were found to produce only butyrate and acetate, a minor amount of acetone, and no alcohols. These Spo⁻ mutants contained reduced butanol dehydrogenase activity and no BAD enzyme activity. The data support the view that the type 2 AA, the Acid⁻, and the Spo⁻ mutants somehow alter normal regulated expression of the solvent pathway in C. acetobutylicum.     

Comparative study of the influence of the metal centres: Fe(III), Cu(II) and Zn(II), on the ring opening and oxidative dehydrogenation reactions occurring in a coordinated imidazolidine ligand

Condensation of 2-pyridinecarboxaldehyde and 1,9-bis-(2′-pyridyl)-2,5,8-triazanonane, L¹, yields 1-[3-aza-4-(2-pyridyl)butyl]-2-(2-pyridyl)-3-[(2-pyridyl)methyl]imidazolidine, L², as proven by NMR solution spectra. When L² is reacted with Fe(III) in different alcohols, an imidazolidine ring opening and an oxidative dehydrogenation reaction occur resulting in new complexes of the type: [Fe^IIL^n′]²⁺. Compound 1 with a coordinated L^3′ ligand was obtained in n-propanol as a solvent. Compounds 2, 3 and 4 were obtained with L^4′, L^5′ and L^6′ when iso-propanol, n-butanol and iso-butanol were used as solvent, respectively. The structures for 1, 2, 3 and 4 were determined by NMR solution spectra and additionally by X-ray crystallography in the case of the n-butoxy derivative 3. When Cu(II) was used, the hexadentate ligand L² undergoes also an imidazolidine ring opening reaction on complex formation, however, now generating the well-known pentadentate ligand L¹ that is coordinated to the metal ion, 7. Evidence is again provided by the corresponding X-ray structure. With Zn(II) the initial structure of L² is maintained and in this case L² functions as a tetradentate, 5, or bis-tridentate ligand, 6, depending on whether the stoichiometric ratio M:L was 1:1 or 2:1, respectively. This has been proven by a solid-state X-ray structure analysis as well as by NMR solution spectra. The ring opening reaction in the presence of Fe(III) can be explained as a result of a higher Lewis acidity of this metal centre, which decreases the electronic density on the nitrogen atom of the imidazolidinic cycle, thus weakening the nitrogen-carbon bond, favouring the nucleophilic attack on the carbon atom by alcohols and producing a more stable hexacoordinated species. Electrochemical evidence is provided in order to support this reaction mechanism.     

Tuning redox and spin state properties of Fe(II) N-heterocyclic complexes via electronic/steric influence on metal-ligand binding

A series of complexes with the general formula [Fe(L)₂]²⁺, where L represents the tridentating 6-(N-3,5-dimethylpyrazolyl)2,2^′-bipyridine (L⁴); 6-(N-pyrazolyl-1-ylmethyl)-2,2^′-bipyridine (L⁵); and 6-(N-3,5-dimethylpyrazolyl-1-ylmethyl)-2,2^′-bipyridine (L⁶), were prepared and characterized. The room temperature solution magnetic susceptibility and redox properties of these compounds were investigated as a function of stepwise variation in the ligand structure. The Fe(III/II) couple was characterized by way of cyclic voltammetry using aprotic solvent conditions (acetonitrile) where each complex was observed to have reversible behavior. NMR methodology was used for measuring the magnetic susceptibilities where both [Fe(L⁴)₂]²⁺ and Fe(L⁵)₂]²⁺ exhibited diamagnetic low spin behavior; however, [Fe(L⁶)₂]²⁺ measured a μ_eff of 4.1 Bohr-magnetons indicating spin equilibrium predominantly in the high spin state.     

Kinetics of the complexation of nickel(II) with 1,10-phenanthroline and its derivatives in acetonitrile-water mixed solvents

The kinetics of the complexation of Ni(II) with 1,10-phenanthroline(phen), 4,7-dimethyl-1,10-phenanthroline(dmphen), and 5-nitro-1,10-phenanthroline(NO₂phen) in acetonitrile-water mixed solvents of acetonitrile mole fraction x_AN = 0, 0.05, 0.1, 0.2 and 0.3 at 288, 293, 298 and 303 K have been studied by stopped-flow method at ionic strength of 1.0 (NaClO₄) and pH 7.4. The corresponding activation enthalpy, entropy, and free energy were determined from the observed rate constants. The complexation of Ni(II) with the three ligands has comparable observed rate constants; in pure water the observed rate constants are (×10³ dm³ mol⁻¹ s⁻¹) 2.31, 2.57, and 1.38 for phen, dmphen and NO₂phen, respectively. The corresponding activation parameters for the three ligands are, however, considerably different; in pure water the ΔH^‡/ΔS^‡ (kJ mol⁻¹/J K⁻¹ mol⁻¹) are 44.7/−30.2, 19.5/−114.1, and 32.2/−76.9 for phen, dmphen, and NO₂phen, respectively. The effects of solvent composition on the kinetics are also markedly different for the three ligands. The ΔH^‡ and ΔS^‡ showed a minimum at x_AN = 0.1 for phen; for dmphen and NO₂phen, however, maxima at x_AN = 0.2 were observed. Nevertheless, there is an effective enthalpy-entropy compensation for the ΔH^‡/ΔS^‡ of all the three ligands, demonstrating the significant effects of the changes in solvation and solvent structure on the complexation kinetics. As the rate-determining step of Ni(II) complexation is the dissociation of a water molecule from Ni(II), the solvent and ligand dependencies in the Ni(II) complexation kinetics are ascribed to the change in solvation status of the ligands and the altered solvent structures upon changing solvent composition.     

Polymerization study of o-Si(OH)4 and complexation with Am(III), Eu(III) and Cm(III)

The stability constants of Am⁺³, Cm³⁺ and Eu³⁺ with ortho silicate, were measured at pH 3.50 and in ionic strengths of 0.20-1.00 M (NaClO₄) by the solvent extraction method. The Am⁺³, Cm³⁺ and Eu³⁺ forms 1:1 complex with ortho silicate ion at pH 3.60 with the stability constant (log β₁) value of 8.02 ± 0.10, 7.78 ± 0.08 and 7.81 ± 0.11, respectively. The stability of these metal ions decrease with increased ionic strength from 0.20 to 1.00 M (NaClO₄) for silicic acid concentrations of 0.002-0.020 M. Increasing silicic acid concentration above 0.02 M increased the amount of M³⁺ extracted into the organic phase, contrary to the trend usually observed for increased ligand concentration in solvent extraction. This reversed trend is likely due to the extraction of cationic species of silicic acid by HDEHP. Aging time (60-300 min) had no effect on the stability constant of these metal ions for 0.002-0.020 M silicic acid at pH 3.50 and I = 0.20 M (NaClO₄).The fraction of polymeric silicic acid present in solutions of 0.20-4.50 M NaClO₄ solutions at pH 3.0-10.0, T = 0-60 °C and aging time = 5-300 min was measured for determination of the silicomolybdate reaction to ascertain the proper conditions to study metal-silicate complexation.     

Synthesis and characterization of 2-quinoxalinol Schiff-base metal complexes

The reaction of uranyl acetate with (2,2′-(1E,1′E)-(2-benzyl-3-hydroxyquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene) diphenol) (H₂L1) at room temperature in methanol and chloroform yields the UO₂L1 complex. Crystals were grown through solvent diffusion of the ligand-metal complex in dimethyl formamide with diethyl ether to prepare: UO₂L1 · DMF (1). Complexes with 2,2′-(1E,1′E)-(2-benzyl-3-hydroxyquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dibenzene-1,4-diol (H₂L2) and 2,2′-(1E,1′E)-(2-hydroxy-3-isopropylquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)diphenol (H₂L3) were also prepared, and crystals of the uranyl complexes (UO₂L2 · DMF (2) and (3)) grown from DMF/ether. A fourth complex UO₂L4 · H₂O (4) was prepared through layering a solution of the tetra-tert-butyl substituted 2-quinoxalinol salen ligand H₂L4 in acetone with an aqueous solution containing uranyl acetate. The complexes exhibit a symmetric core featuring a slightly distorted bicapped pentagonal geometry around the uranium center with two oxo-groups and two imine groups from the ligand chelating the ligand and the fifth site in the coordination plane of the ligand occupied by a solvent molecule. These compounds have been characterized using solution (NMR and UV-Vis) and solid-state (IR, X-ray crystallography) techniques. Complexes of H₂L4 with early transition metals; Mn²⁺, Co²⁺, Ni²⁺, and Cu²⁺ are also prepared and characterized for comparison of solution and spectroscopic characteristics.     

Homogeneous green catalysts for olefin oxidation by mono oxovanadium(V) complexes of hydrazone Schiff base ligands

Three mono oxovanadium(V) complexes of tridentate Schiff base ligands [VO(OMe)L¹] (1), [VO(OMe)L²] (2) and [VO(OMe)L³] (3) obtained by monocondensation of 3-hydroxy-2-naphthohydrazide and aromatic o-hydroxyaldehydes have been synthesized (H₂L¹ = (E)-3-hydroxy-N′-(2-hydroxy-3-methoxybenzylidene)-2-naphthohydrazide, H₂L² = (E)-3-hydroxy-N′-(2-hydroxybenzylidene)-2-naphthohydrazide and H₂L³ = (E)-N′-(5-bromo-2-hydroxybenzylidene)-3-hydroxy-2-naphthohydrazide). The complexes were characterized by spectroscopic methods in the solid state (IR) and in solution (UV-Vis, ¹H NMR). Single crystal X-ray analyses were performed with 1 and 2. The catalytic potential of these complexes has been tested for the oxidation of cyclooctene using H₂O₂ as the terminal oxidant. The effects of various parameters including the molar ratio of oxidant to substrate, the temperature, and the solvent have been studied. The catalyst 2 showed the most powerful catalytic activity in oxidation of various terminal, cyclic and phenyl substituted olefins. Excellent conversions have been obtained for the oxidation of cyclic and bicyclic olefins.     

cis-Dioxo-molybdenum(VI)-oxazoline complex catalyzed epoxidation of olefins by tert-butyl hydrogen peroxide

A new efficient catalytic system was investigated for the epoxidation of various olefins by cis-dioxo-bis[2-(2′-hydroxyphenyl)-oxazolinato]molybdenum(VI), cis-[MoO₂(phox)₂], and TBHP as oxidizing agent. Using this system as catalyst for the oxidation of aliphatic substrates at 80 °C gives the epoxide as the sole product with yields up to 100% and turnover frequency up to 5000 h⁻¹. The efficiency of the catalyst is strongly influenced by the nature of solvent, reaction time and temperature, and a significant increase in the epoxide yields is observed in higher temperatures and longer reaction times.     

Solvent Effect on the Photolysis of Riboflavin

The kinetics of photolysis of riboflavin (RF) in water (pH 7.0) and in organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol, ethyl acetate) has been studied using a multicomponent spectrometric method for the assay of RF and its major photoproducts, formylmethylflavin and lumichrome. The apparent first-order rate constants (k_obs) for the reaction range from 3.19 (ethyl acetate) to 4.61 × 10⁻³ min⁻¹ (water). The values of k_obs have been found to be a linear function of solvent dielectric constant implying the participation of a dipolar intermediate along the reaction pathway. The degradation of this intermediate is promoted by the polarity of the medium. This indicates a greater stabilization of the excited-triplet states of RF with an increase in solvent polarity to facilitate its reduction. The rate constants for the reaction show a linear relation with the solvent acceptor number indicating the degree of solute–solvent interaction in different solvents. It would depend on the electron-donating capacity of RF molecule in organic solvents. The values of k_obs are inversely proportional to the viscosity of the medium as a result of diffusion-controlled processes.KEY WORDS: dielectric constant, kinetics, photolysis, riboflavin, solvent effect, viscosity     

Synthesis and characterization of an N-coordinated amidate copper(II) complex of deprotonated N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide

The title ligand, N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide (DIPMAE-H), was prepared by a nucleophilic substitution reaction between N-(2,6-diisopropyl)phenyl-2-bromoethanamide and bis-(2-pyridylmethyl)amine. An analogous ligand (TBPMAE-H) in which the 2,6-diisopropylphenyl group was substituted for a tert-butyl group was also prepared in this manner. Then, [(DIPMAE-H)CuBr]⁺Br⁻ and [(TBPMAE-H)CuBr]⁺Br⁻ were prepared by heating one equivalent of ligand and CuBr₂ in CH₃CN. In both compounds the geometry about the copper center is square pyramidal with distortions due to the geometrical constraints of the ligand. The amide oxygen occupies the axial position, and the three amine nitrogens and the bromide ligand form the basal plane of the square pyramid. Pairs of complexes in the unit cell are associated via weak donation of a lone pair on the bromide ligand of one complex to the copper center of another (Cu?Br distances in the range of 3.3576-3.4022 Å).The title compound, (DIPMAE)CuBr, was prepared by deprotonation of [(DIPMAE-H)CuBr]⁺Br⁻ using NaH. The key feature of (DIPMAE)CuBr is the amidate group η¹- and N-coordinated to the copper center. The compound also exhibits distorted trigonal bipyramidal coordination geometry with the bromide and tertiary amine donors occupying the axial sites and the amidate and pyridyl donors occupying the equatorial positions. The copper atom is displaced from the trigonal plane towards the bromide donor apex due to the geometrical demands of the ligand.     

Synthesis, X-ray crystal structure, DFT- and TDDFT-based spectroscopic property investigations on a mixed-ligand chromium(III) complex, bis[2-(2-hydroxyphenyl)benzimidazolato]-(1,10-phenanthroline)chromium(III) isophthalate

A mixed-ligand Cr(III) complex with 2-(2-hydroxyphenyl)benzimidazole, 1,10-phenanthroline and isophthalic acid, [Cr(pbm)₂(phen)]X_0.5 (1X_0.5) (Hpbm = 2-(2-hydroxyphenyl)benzimidazole; phen = 1,10-phenanthroline; H₂X = isophthalic acid) has been prepared by heating in aqueous solution and characterized, and the geometric structure and spectroscopic properties, investigated experimentally and theoretically by using the density functional theory level (DFT) and the time-dependent density functional theory level (TDDFT). The theoretical-experimental agreement is satisfactory. Further theoretical analyses of electronic structure and molecular orbitals have demonstrated that the low-lying absorption bands in UV-Vis spectrum are mainly π → π∗ ligand-to-ligand charge transfer transition (LLCT) and or π → (d_z²-d_x²-y²-d_yz) ligand-to-metal charge transfer transition (LMCT) in nature.     

Purification and characterisation of 6G-fructosyltransferase from the roots of asparagus (Asparagus officinalis L.)

A fructosyltransferase that catalyses the transfer of the terminal (2 → 1)-β-linked d-fructosyl group of fructo-oligosaccharides [1^F(1-β-d-fructofuranosyl)_msucrose, m > 0] to HO-6 of the glucosyl group of similar saccharides [1^F(1-β-d-fructofuranosyl)_nsucrose, n > 0] has been purified (760-fold) from an extract of the roots of asparagus (Asparagus officinalis L.) by successive fractionation with ammonium sulfate, treatment with calcium phosphate gel, and then chromatography on octyl-Sepharose, DEAE-cellulose, Sephadex G-200, and raffinose-coupled Sepharose 6B. The enzyme, tentatively termed 6^G-fructosyltransferase, was homogeneous in disc electrophoresis, had a mol. wt. of ~69,000 and an optimum pH of ~5.5, was stable at pH 5.0–6.0 on heating for 20 mins at 45° and for 10 min at 20–37°, and was inhibited by Hg²⁺, p-chloromercuribenzoate, and Ag⁺.     

Metabolism of Cytokinin : DEPHOSPHORYLATION OF CYTOKININ RIBONUCLEOTIDE BY 5'-NUCLEOTIDASES FROM WHEAT GERM CYTOSOL

Two forms (F-I and F-II) of 5′-nucleotidases (5′-ribonucleotide phosphohydrolase, EC 3.1.3.5) which catalyze the dephosphorylation of N⁶-(Δ²-isopentenyl)adenosine 5′-monophosphate and AMP to form the corresponding nucleosides were partially purified from the cytosol of wheat (Triticum aestivum) germ. Both the F-I (molecular weight, 57,000) and F-II (molecular weight, 110,000) 5′-nucleotidases dephosphorylate the ribonucleotides at an optimum pH of 7. The K_m values for the cytokinin nucleotide are 3.5 micromolar (F-I enzyme) and 12.8 micromolar (F-II enzyme) in 100 millimolar Tris-maleate buffer (pH 7) at 37 C. The F-I enzyme is less rapidly inactivated by heating than is the F-II enzyme. Both nucleotidases hydrolyze purine ribonucleoside 5′-phosphates, AMP being the preferred substrate. N⁶-(Δ²-isopentenyl)Adenosine 5′-monophosphate is hydrolyzed at a rate 72 and 86% that of AMP by the F-I and F-II nucleotides, respectively. Phenylphosphate and 3′-AMP are not substrates for the enzymes. It is proposed that dephosphorylation of cytokinin nucleotide by cytosol 5′-nucleotidases may play an important role in regulating levels of “active cytokinin” in plant cells.     

Investigation on Crude and High-Temperature Heated Coffee Oil by ATR-FTIR Spectroscopy along with Antioxidant and Antimicrobial Properties

The coffee oil has a promising potential to be used in food industry, but an efficient use, especially in products that required high-temperature heating, depends on its chemical composition and the changes induced by processing. Since there is little information on this topic, the aim of our study was to investigate the crude green and roasted coffee oil (GCO, RCO) and heated (HGCO, HRCO) for 1 h at 200°C, by Fourier Transform Infrared (FTIR) spectroscopy and in terms of antioxidant and antimicrobial properties. The results of FTIR spectroscopy revealed that no statistically significant differences (one-way ANOVA, p>0.05) in the oxidative status of GCO and RCO were found. The coffee oils heating induced significant spectral changes in the regions 3100–3600 cm^–1, 2800–3050 cm^–1 and 1680–1780 cm^–1 proved by the differences in the absorbance ratios A 3009 cm⁻¹/A 2922 cm⁻¹, A 3009 cm⁻¹/A 2853 cm⁻¹, A 3009 cm⁻¹/A 1744 cm⁻¹, A 1744 cm⁻¹/A 2922 cm⁻¹. These alterations were related to the reduction of the unsaturation degree due to primary and secondary oxidation processes of the lipid fraction. The radical scavenging ability of oils investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay revealed that the IC50 value of GCO was significantly lower than of RCO (p<0.05). The IC50 values of crude coffee oils were lower than those of heated samples. The antioxidant activity of oils was attributed to both antioxidant compounds with free-radical scavenging capacity and to lipids oxidation products generated by heating. In the first 6 h of incubation, the inhibitory activity of crude oils against E. coli and E. faecalis was not significantly different to the control (p>0.05). Also, HGCO and HRCO showed significantly different inhibitory potential related to the control (p<0.05). The heating induced statistically significant decreases in the effectiveness of coffee oils against the tested bacteria. GCO proved to be the most effective among investigated coffee oils against the tested bacteria.     

Escherichia coli Heat Shock Protein DnaK: Production and Consequences in Terms of Monitoring Cooking

Through use of commercially available DnaK proteins and anti-DnaK monoclonal antibodies, a competitive enzyme-linked immunosorbent assay was developed to quantify this heat shock protein in Escherichia coli ATCC 25922 subjected to various heating regimens. For a given process lethality (F₇₀¹⁰ of 1, 3, and 5 min), the intracellular concentration of DnaK in E. coli varied with the heating temperature (50 or 55°C). In fact, the highest DnaK concentrations were found after treatments at the lower temperature (50°C) applied for a longer time. Residual DnaK after heating was found to be necessary for cell recovery, and additional DnaK was produced during the recovery process. Overall, higher intracellular concentrations of DnaK tended to enhance cell resistance to a subsequent lethal stress. Indeed, E. coli cells that had undergone a sublethal heat shock (105 min at 55°C, F₇₀¹⁰ = 3 min) accompanied by a 12-h recovery (containing 76,786 ± 25,230 molecules/cell) resisted better than exponentially growing cells (38,500 ± 6,056 molecules/cell) when later heated to 60°C for 50 min (F₇₀¹⁰ = 5 min). Results reported here suggest that using stress protein to determine cell adaptation and survival, rather than cell counts alone, may lead to more efficient heat treatment.     

[60]Fullerene displacement from fac-(dihapto-[60]fullerene)(dihapto-1,2-bis-(1,10-phenanthroline) tricarbonyl tungsten(0)

The Lewis bases triphenyl phosphine and tricyclohexyl phosphine (L) displace [60]fullerene (C₆₀) from fac-(η²-C₆₀)(η²-phen)W(CO)₃ (phen=1,10-phenanthroline) to produce fac-(η²-phen)(η¹-L)W(CO)₃. Under flooding conditions, the reactions were first order with respect to fac-(η²-C₆₀)(η²-phen)W(CO)₃. The order with respect to C₆₀ and L depends on the reaction conditions i.e., whether [C₆₀]/[L] ≈ 0 or 0?It [C₆₀]/[L] ≈ 1. Two limiting cases of an interchange displacement of [60]fullerene from fac-(η²-C₆₀)(η²-phen)W(CO)₃, whose relative contributions to the overall mechanism depend on the nature of the solvent, are proposed based on the rate law and on the activation parameters. The mechanism involves an initial [60]fullerene dissociation to produce (i) the electronically unsaturated intermediate (η²-phen)W(CO)₃ for the dissociative displacement and (ii) the solvated intermediate fac-(solvent)(η²-phen)W(CO)₃ for the solvent-assisted [60]fullerene dissociation. The W-C₆₀ bond energy in fac-(η²-C₆₀)(η²-phen)W(CO)₃ was estimated to be in the vicinity of 105 kJ/mol based on the enthalpy of activation of the step where presumably [60]fullerene dissociates from fac-(η²-C₆₀)(η²-phen)W(CO)₃ to produce (η²-phen)W(CO)₃.