4-methoxybenzyl Alcohol Research Articles

A comparative study of organic electron transfer redox mediators: electron transfer kinetics for triarylimidazole and triarylamine mediators in the oxidation of 4-methoxybenzyl alcohol

The triarylimidazoles (TAIs) constitute a promising class of organic electron transfer redox mediators that have been used to achieve indirect electrochemical C-H bonds activation and functionalization. Herein we report the diffusion and electron transfer rates for the oxidation of 4-methoxybenzyl alcohol using TAI and compare its electrochemical behavior with that of tris(4-bromophenyl)amine (TBPA). The results contribute to our understanding of the electron transfer process of electrocatalytic oxidation using TAIs, and offer useful guidelines for their further development and use.

Molecular characterization and expression of a novel alcohol oxidase from Aspergillus terreus MTCC6324.

The alcohol oxidase (AOx) cDNA from Aspergillus terreus MTCC6324 with an open reading frame (ORF) of 2001 bp was constructed from n-hexadecane induced cells and expressed in Escherichia coli with a yield of ∼4.2 mg protein g−1 wet cell. The deduced amino acid sequences of recombinant rAOx showed maximum structural homology with the chain B of aryl AOx from Pleurotus eryngii. A functionally active AOx was achieved by incubating the apo-AOx with flavin adenine dinucleotide (FAD) for ∼80 h at 16°C and pH 9.0. The isoelectric point and mass of the apo-AOx were found to be 6.5±0.1 and ∼74 kDa, respectively. Circular dichroism data of the rAOx confirmed its ordered structure. Docking studies with an ab-initio protein model demonstrated the presence of a conserved FAD binding domain with an active substrate binding site. The rAOx was specific for aryl alcohols and the order of its substrate preference was 4-methoxybenzyl alcohol >3-methoxybenzyl alcohol>3, 4-dimethoxybenzyl alcohol > benzyl alcohol. A significantly high aggregation to ∼1000 nm (diameter) and catalytic efficiency (kcat/Km) of 7829.5 min−1 mM−1 for 4-methoxybenzyl alcohol was also demonstrated for rAOx. The results infer the novelty of the AOx and its potential biocatalytic application.

Reversible Chemical and Electrochemical Dehydrogenation/Hydrogenation of Primary Alcohols Catalyzed By Iridium Complexes

Development of efficient electrocatalysts for both dehydrogenation and hydrogenation of organic fuels is critical to the realization of regenerative liquid fuel cells (RLFCs). Alcohols are convenient fuels currently utilized in direct alcohol fuel cells (DAFCs) and are capable of undergoing reversible partial dehydrogenation without CO2 emission in a RLFC.1 An Ir-diaminodiolefin complex, [Ir(trop2DACH)][OTf] (trop2DACH = N,N’-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-diaminocyclohexane) (1) was proposed by Grützmacher et al.2 as a catalyst for alcohol oxidation with benzoquinone. Previously we demonstrated that 1 also catalyzes chemical dehydrogenation of 4-methoxybenzyl alcohol to p-anisaldehyde with one-electron oxidants in the presence of a base as well as electrochemical dehydrogenation at a low applied potential with high selectivity and Faradaic efficiency.3 In this presentation we report both chemical and electrochemical dehydrogenation of primary alcohols and hydrogenation of the corresponding aldehydes using 1 or an analogous iridium complex [Ir(trop2DAD)]OTf (trop2DAD = N,N’-bis(5H-dibenzo[a,d]cycloheptene-5-yl)-1,4-diazabuta-1,3-diene) (2) as a single homogeneous catalyst. In the chemical processes the same acid/conjugate base pair (substituted phenols/phenolates) is used with an appropriate one electron reductant (e.g. cobaltocene) for hydrogenation or oxidant (e.g. ferrocene) for dehydrogenation. In the electrochemical processes 1 and 2 catalyze dehydrogenation and hydrogenation with high faradaic efficiency and excellent selectivity though hydrogenation produced smaller yields. Further details on the effects of the base, solvent and electrolysis conditions on chemical and electrochemical catalysis will be provided. This work is supported as part of the Center for Electrocatalysis, Transport Phenomena, and Materials (CETM) for Innovative Energy Storage, an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001055.1. Kariya, N. F., Fukuoka, A.; Ichikawa, M., Phys. Chem. Chem. Phys. 2006, 8, 17242. Königsmann, M.; Donati, N.; Stein, D.; Schönberg, H.; Harmer, J.; Sreekanth, A.; Grützmacher, H., Angew. Chem. Int. Ed. 2007, 46, 3567.3. Bonitatibus, P. J.; Rainka, M. P.; Peters, A. J.; Simone, D. L.; Doherty, M. D., Chem. Communs 2013, 49, 10581.

ChemInform Abstract: A Practical Method for p‐Methoxybenzylation of Hydroxy Groups Using 2,4,6‐Tris(p‐methoxybenzyloxy)‐1,3,5‐triazine (TriBOT‐PM).

A new acid-catalyzed p-methoxybenzylating reagent, 2,4,6-tris(p-methoxybenzyloxy)-1,3,5-triazine (TriBOT-PM), has been developed. The reaction of acid- and alkali-labile alcohols with TriBOT-PM in the presence of a catalytic amount of various acids (TfOH, BF3·OEt2, CSA, etc.) afforded the corresponding p-methoxybenzyl ethers in good yields. Since TriBOT-PM is an air-stable crystalline solid and can be prepared from inexpensive materials, i.e. cyanuric chloride and anisyl alcohol, this route is of practical use.

Comparing the catalytic efficiency of ring substituted 1-hydroxybenzotriazoles as laccase mediators

A series of ring substituted 1-hydroxybenzotriazoles (6-X-HBTs) have been tested as mediators in the laccase-promoted oxidation of 4-methoxybenzyl alcohol, 3,4-dimethoxybenzyl alcohol, and the dimeric lignin model 1-(3,4-dimethoxyphenyl)-2-phenoxyethanol. The effect of the aryl substituents on the yields of oxidation products is remarkable. The catalytic mediation efficiency increases as the electron releasing (ER) properties of the substituent increases up to a maximum value for 6-CH3-HBT, which resulted a very efficient mediator. Both the oxidation of the 6-X-HBTs to the N-oxyl radicals (6-X-BTNO) by laccase and the hydrogen atom transfer (HAT) process from the benzylic C–H to the 6-X-BTNO contribute to the overall reactivity. The former process is favored by ER substituents that lower the mediator redox potentials. On the other hand, ER substituents decrease the 6-X-BTNO reactivity in the HAT process due to a decrease in the NO–H BDE value, as assessed in this study through a radical equilibration technique.

ChemInform Abstract: Highly Selective Electrocatalytic Dehydrogenation at Low Applied Potential Catalyzed by an Ir Organometallic Complex.

A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde at a very low applied potential with remarkably high selectivity and Faradaic efficiency. In the chemical catalysis, when stoichiometric oxidant and anionic base were used to separately accept electrons and protons, aldehyde selectivity was in agreement with electrolysis results.

Ochrobactrum sp. Pv2Z2 exhibits multiple traits of plant growth promotion, biodegradation and N-acyl-homoserine-lactone quorum sensing

Rhizosphere bacteria play a vital role in plant growth, pathogen control, biodegradation and rhizosphere signaling. A motile, rod-shaped bacterium, Pv2Z2, isolated from the nodules of the common bean grown in Tanzanian soil was characterized using a polyphasic approach. The traits assessed included the production of indole-3-acetic acid and N-acyl homoserine lactone (AHL) molecules, solubilization of insoluble phosphate and zinc compounds and biodegradation of a number of toxic compounds. The 16S rRNA sequence of Pv2Z2 (EU399793) showed 99 % homology to Ochrobactrum anthropi isolates (Accession no. AJ867292, AJ867291, AJ867290) from soil samples of wheat root. Phylogenetic analysis showed relatedness to nodulating strain Ochrobactrum cytisi rather than to the clinical/pathogenic type strain of O. anthropi. Moreover, it showed unique fingerprints in the randomly amplified polymorphic DNA (RAPD) and two primers-RAPD assays which were different from those of the pathogenic type strain of O. anthropi. The bacterium produced 6.68 μg/mL-1 indoleacetic acid in the presence of tryptophan, released 25.7 μg/mL-1 phosphorus from inorganic tri-calcium phosphate in the Pikoviskaya’s medium and solubilized zinc sulphate and zinc oxide in the LG1 medium. The production of AHLs (e.g. 3O-C7-HSL, 3OH-C7-HSL) was detected with biosensor strains CV026 using reverse phase thin layer chromatography. The bacterium was able to grow in minimal salt medium supplemented with 100 mg/L each of phenol, 2-bromophenol, 2,4-diamino phenol hydrochloride, 3,4-dimethoxy benzyl alcohol and 4-methoxy benzyl alcohol. Phenol degradation was recorded up to a level of 94 % within 12 days. Inoculation of common bean plants resulted in a significant increase in plant height, fresh/dry weight and nitrogen uptake as compared to non-inoculated plants. The data suggest that the plant growth-promoting and biodegradation potential of this bacterium may be exploited on a large scale. The capacity to produce AHL molecules by members of the Ochrobactrum genus has not been previously reported and needs to be explored in detail.

Regioselective syntheses of [13C]4-labelled sodium 1-carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate and sodium 2-carboxy-1-(2-ethylhexyloxycarbonyl)ethanesulfonate from [13C]4-maleic anhydride.

The entitled monohydrolysis products, also known as α-ethylhexyl and β-ethylhexyl sulfosuccinate (EHSS), of the surfactant diisooctyl sulfosuccinate (DOSS) were synthesized in stable isotope-labelled form from [(13)C]4 -maleic anhydride. Sodium [(13)C]4 -1-carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate (α-EHSS) was prepared by the method of Larpent by reaction of 2-ethylhexan-1-ol with [(13)C]4 -maleic anhydride followed by regioselective conjugate addition of sodium bisulfite to the resulting monoester (38% overall yield). The regiochemical outcome of bisulfite addition was confirmed by a combination of (13)C/(13)C (incredible natural abundance double quantum transfer) and (1)H/(13)C (heteronuclear multiple-bond correlation (HMBC)) NMR spectral correlation experiments. Sodium [(13)C]4 -2-carboxy-1-(2-ethylhexyloxycarbonyl)ethanesulfonate (β-EHSS) was prepared in four steps by reaction of 4-methoxybenzyl alcohol with [(13)C]4 -maleic anhydride, regioselective sodium bisulfite addition, N,N'-dicyclohexylcarbodiimide-mediated esterification with 2-ethylhexan-1-ol, and p-methoxybenzyl ester deprotection with trifluoroacetic acid (13% overall yield). The regiochemical outcome of the second synthesis was confirmed by a combination of (1)JCC scalar coupling constant analysis and (1)H/(13)C (HMBC) NMR spectral correlation. The materials prepared are required as internal standards for the liquid chromatography-mass spectrometry (LC-MS)/MS trace analysis of the degradation products of DOSS, the anionic surfactant found in Corexit, the oil dispersant used during emergency response efforts connected to the Deepwater Horizon oil spill of April 2010.

Facile two-step preparation of polystyrene/anatase TiO2 core/shell colloidal particles and their potential use as an oxidation photocatalyst

Titania and materials containing titania have received considerable attention due to their technological importance in many areas. In this study, anatase crystalline titania (TiO2) coated polystyrene (PS) colloidal particles were successfully prepared in two easy steps. First, a one pot synthesis of the colloidal particles was produced via an emulsifier-free emulsion copolymerization of styrene (S) and 2-(dimethylamino)ethyl methacrylate (DMA) at pH 4.0. In the second step, the synthesized particles were coated by titania using a sol–gel process in-situ hydrolysis and a condensation reaction of titanium(IV) isopropoxide in an acidic aqueous solution. In this way, anatase crystalline titania, rather than the usual amorphous form, was obtained as a shell on the PS colloidal particles. Both the PS colloidal particles and the polystyrene/anatase titania (PS/TiO2) core/shell colloidal particles had monodisperse morphology and were characterized using SEM, Zetasizer, FTIR, XRD and TGA techniques or measurements. In addition, the photocatalytic activity of the PS/TiO2 core/shell particles was tested for the first time in an oxidation reaction, in the oxidation of 4-methoxybenzyl alcohol (MBA) with O2 in water. Much higher selectivities of the target product, p-anisaldehyde (AA), were obtained with the PS/TiO2 core/shell particles than with a commercial anatase crystalline TiO2.

Mechanistic Insight into Peroxo-Shunt Formation of Biomimetic Models for Compound II, Their Reactivity toward Organic Substrates, and the Influence ofN-Methylimidazole Axial Ligation

High-valent iron-oxo species have been invoked as reactive intermediates in catalytic cycles of heme and nonheme enzymes. The studies presented herein are devoted to the formation of compound II model complexes, with the application of a water soluble (TMPS)Fe(III)(OH) porphyrin ([meso-tetrakis(2,4,6-trimethyl-3-sulfonatophenyl)porphinato]iron(III) hydroxide) and hydrogen peroxide as oxidant, and their reactivity toward selected organic substrates. The kinetics of the reaction of H2O2 with (TMPS)Fe(III)(OH) was studied as a function of temperature and pressure. The negative values of the activation entropy and activation volume for the formation of (TMPS)Fe(IV)=O(OH) point to the overall associative nature of the process. A pH-dependence study on the formation of (TMPS)Fe(IV)=O(OH) revealed a very high reactivity of OOH(-) toward (TMPS)Fe(III)(OH) in comparison to H2O2. The influence of N-methylimidazole (N-MeIm) ligation on both the formation of iron(IV)-oxo species and their oxidising properties in the reactions with 4-methoxybenzyl alcohol or 4-methoxybenzaldehyde, was investigated in detail. Combined experimental and theoretical studies revealed that among the studied complexes, (TMPS)Fe(III)(H2O)(N-MeIm) is highly reactive toward H2O2 to form the iron(IV)-oxo species, (TMPS)Fe(IV)=O(N-MeIm). The latter species can also be formed in the reaction of (TMPS)Fe(III)(N-MeIm)2 with H2O2 or in the direct reaction of (TMPS)Fe(IV)=O(OH) with N-MeIm. Interestingly, the kinetic studies involving substrate oxidation by (TMPS)Fe(IV)=O(OH) and (TMPS)Fe(IV)=O(N-MeIm) do not display a pronounced effect of the N-MeIm axial ligand on the reactivity of the compound II mimic in comparison to the OH(-) substituted analogue. Similarly, DFT computations revealed that the presence of an axial ligand (OH(-) or N-MeIm) in the trans position to the oxo group in the iron(IV)-oxo species does not significantly affect the activation barriers calculated for C-H dehydrogenation of the selected organic substrates.

Temperature and Pressure Effects on C–H Abstraction Reactions Involving Compound I and II Mimics in Aqueous Solution

The presented results cover a comparative mechanistic study on the reactivity of compound (Cpd) I and II mimics of a water-soluble iron(III) porphyrin, [meso-tetrakis(2,4,6-trimethyl-3-sulfonatophenyl)porphinato]iron(III), Fe(III)(TMPS). The acidity of the aqueous medium strongly controls the chemical nature and stability of the high-valent iron(IV) oxo species. Reactivity studies were performed at pH 5 and 10, where the Cpd I and II mimics are stabilized as the sole oxidizing species, respectively. The contributions of ΔH(‡) and ΔS(‡) to the free energy of activation (ΔG(‡)) for the oxidation of 4-methoxybenzaldehyde (4-MB-ald), 4-methoxybenzyl alcohol (4-MB-alc), and 1-phenylethanol (1-PhEtOH) by the Cpd I and II mimics were determined. The relatively large contribution of the ΔH(‡) term in comparison to the -TΔS(‡) term to ΔG(‡) for reactions involving the Cpd II mimic indicates that the oxidation of selected substrates by this oxidizing species is clearly an enthalpy-controlled process. In contrast, different results were found for reactions with application of the Cpd I mimic. Depending on the nature of the substrate, the reaction at room temperature can be entropy-controlled, as found for the oxidation of 4-MB-alc, or enthalpy-controlled, as found for 1-PhEtOH. Importantly, for the first time, activation volumes (ΔV(‡)) for the oxidation of selected substrates by both reactive intermediates could be determined. Positive values of ΔV(‡) were found for reactions with the Cpd II mimic and slightly negative ones for reactions with the Cpd II mimic. The results are discussed in the context of the oxidation mechanism conducted by the Cpd I and II mimics.

Synthesis, characterization and applications of highly active and robust sulfated Fe–TiO2 catalyst (ICT-3) with superior redox and acidic properties

A novel multifunctional sulfated Fe–TiO2 catalyst with different Fe loading, leading to the introduction of both redox and superacidic properties (designated as ICaT-3), was developed. Chorosulfonic acid was used to create super acidity in the catalyst matrix. The catalyst was characterized by FT-IR, XRD, TG-DTA, surface area measurements, NH3-TPD, XPS, SEM and EDX analysis with reference to its superior redox and acidic properties. The catalyst was found to be very active and selective as compared to unsulfated catalyst for industrially important oxidation reaction of benzyl alcohol to benzaldehyde and its efficacy was tested in a variety of substrates such as 4-methoxy benzyl alcohol, 4-chlorobenzyl alcohol, styrene, p-bromostyrene, and methyl phenyl sulfide. This induced acidity increases the oxidation activity by twofold as compared to conventional TiO2 catalyst. Its superior acidic properties were also evaluated in the alkylation of toluene with benzyl alcohol. The catalyst was reused repeatedly to find it as stable and reusable.

Molecularly imprinted polymeric Cu(II) catalysts with modified active centres mimicking oxidation enzymes

In this paper the preparation of surface molecularly imprinted Cu(II) catalysts with modified active centres is described. The resins were synthesized using suspension polymerization of 1-vinylimidazole, acrylonitrile, 1,1,1-tris(hydroxymethyl)propane trimethacrylate and 4-vinyloxybutylstearate in the presence of Cu(II) ions and 4-methoxybenzyl alcohol as the template. The resins obtained in the form of polymer beads posses diameters ranging from 30 μm to 300 μm and specific surface areas up to 315 m2/g depending on sonication mode. The resins, after copper removal, were modified in a two-step reaction: bromoalkylation with four alkyl bromides and subsequent exchange of bromide for tetrafluoroborate and trifluoroacetate anions. Non-modified and modified polymers bearing imidazole ligands inside the active centres were complexed with Cu(II) ions, leading to various copper content and applied as heterogeneous catalysts. The formed Cu(II) complexes were subsequently characterized by electron paramagnetic resonance (EPR) spectroscopy. A comparison of the EPR parameters, obtained by computer simulations of the experimental spectra of different Cu2+-catalysts allows to propose structures of the Cu(II) active centres as mostly N2O2 type (similar to the enzymatic ones). The catalytic activity of the Cu(II) loaded polymers without and with ionic liquids analogues inside active centres was tested using hydrogen peroxide in model oxidation reaction of hydroquinone. Protonation of imidazole nitrogen and introduction of additional free groups possessing strong electrostatic properties resulted in significant increase of catalytic activity in comparison to non-modified samples (oxidation degrees from 50 % to 90 %, selectivity up to 100 %). Trifluoroacetic anion has stronger effect than other studied anions.

A Green Approach for Producing Solvent-free Anisyl Acetate by Enzymecatalyzed Direct Esterification in Sponge-like Ionic Liquids Under Conventional and Microwave Heating

The biocatalytic synthesis of anisyl acetate fragrance was carried out by direct esterification of acetic acid with anisyl alcohol in sponge-like ionic liquids (SLILs), e.g. N,N,N,N-hexadecyltrimethylammonium bis(trifluoromethylsulfonyl) imide ([C16tma][NTf2], N,N,N,N-octadecyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([C18tma] [NTf2]), etc. as reaction/separation media under conventional and microwave (MW) heating. These SLILs are temperatureswitchable ionic liquid/solid phases that behave as sponges. As liquid phases, they are excellent monophasic reaction media for the lipase-catalyzed synthesis of anisyl acetate, the product yield being improved up to 100% for 2 hour reaction under the appropriate reaction conditions (i.e. SLIL concentration, alcohol: acid molar ratio, enzyme amount, dehydrating molecular sieves, temperature and MW heating). As a function of the phase behaviour of different SLIL/anisyl acetate mixtures, a new clean separation protocol based on the centrifugation of the solid IL/flavour ester through nylon membranes was proposed, which provided a nearly full separation of the solid SLIL and the easy recovery of the reaction mixture. The enzymatic synthesis of anisyl acetate in [C16tma] [NTf2] under MW assistance, followed by the separation step of the solid SLIL, provided a nearly solvent-free fragrance product with up to 0.89 g/mL concentration. The catalytic activity of the enzyme / SLIL system remained unchanged for ten consecutive operational cycles. This work reports a straightforward and sustainable approach for producing anisyl acetate as a natural flavour and demonstrates to be suitable for scaling-up, providing a high potential for practical application. Keywords: Anisyl acetate, anisyl alcohol, biocatalysis, biocatalytic process, clean process, enzymatic synthesis, esterification, flavours, fragrances, green chemistry, ionic liquids, lipase, neoteric solvents, pure products, solvent-free, sponge-like ionic liquids, sustainable chemistry, switchable ionic liquids.

The influence of the anatase nanoparticles boundaries on the titania activity performance

Metal oxides structures, formed by ordered self-assembling of crystalline nanoparticles aggregates, are attracting growing attention in fields such as catalysis or solar cells. The properties of these structures are influenced not only by their morphology and nanoparticles composition but also by the assembled particles boundaries. In order to determine the influence of these boundaries on the structures properties, the present investigation has been devoted to study the characteristics of anatase nanoparticles boundaries in titania aggregates prepared by TiCl4 hydrolysis at low temperature. Proton magic angle spinning nuclear magnetic resonance and high resolution transmission electron microscopy show that these samples mainly contain amorphous TiO2 strongly bound to specific faces of anatase particles. This amorphous titania-mediated attachment induces the ordered self-assembling of the anatase particles, with favored formation of mesopores in the nanoparticles boundaries. Photocatalytic degradation of 4-methoxybenzyl alcohol in water, test reaction used as a method to get information on the boundaries properties, indicates that the mesoporous amorphous TiO2 offers active sites for the alcohol catalytic partial oxidation, but it strongly hampers inter-particles electron transfer. These effects, characteristic of amorphous oxide chain morphology, can be expected when low dispersed dopants or promoters are incorporated to metal oxides.

Influence of crystallinity and OH surface density on the photocatalytic activity of TiO2 powders

Abstract The aim of the work was to study the influence of crystallinity and OH surface density on the photocatalytic activity of two commercial and two home-prepared TiO 2 powders. The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG) and electron paramagnetic resonance (EPR) measurements. The photoactivity of the powders was tested employing the photodegradation of 4-nitrophenol (4-NP) and the selective oxidation of 4-methoxybenzyl alcohol (4-MBA) to 4-methoxybenzaldehyde ( p -anisaldehyde) under UV irradiation. An anti-correlation between oxidant power and selectivity of the various samples was found. A higher rate of 4-NP degradation was exhibited by the most crystalline commercial samples, whereas the highest selectivity toward the synthesis of p -anisaldehyde was obtained in the presence of the least crystalline and most hydroxylated home-prepared powders.

A Practical Method for p-Methoxybenzylation of Hydroxy Groups Using 2,4,6-Tris(p-methoxybenzyloxy)-1,3,5-triazine (TriBOT-PM)

A new acid-catalyzed p-methoxybenzylating reagent, 2,4,6-tris(p-methoxybenzyloxy)-1,3,5-triazine (TriBOT-PM), has been developed. The reaction of acid- and alkali-labile alcohols with TriBOT-PM in the presence of a catalytic amount of various acids (TfOH, BF3·OEt2, CSA, etc.) afforded the corresponding p-methoxybenzyl ethers in good yields. Since TriBOT-PM is an air-stable crystalline solid and can be prepared from inexpensive materials, i.e. cyanuric chloride and anisyl alcohol, this route is of practical use.

Identification of the Key Odorants in Tahitian Cured Vanilla Beans (Vanilla tahitensis) by GC-MS and an Aroma Extract Dilution Analysis

The key odorants of Tahitian vanilla beans (Vanilla tahitensis) were characterized by a sensory evaluation, aroma extract dilution analysis (AEDA), quantification, and aroma reconstitution. Vanillin and anisaldehyde were identified in the same highest flavor dilution (FD) factor as the most characteristic odor-active compounds in Tahitian vanilla beans, followed by anisyl alcohol and anisyl acetate. Vanillin and anisyl alcohol were by far the most abundant odorants present with the highest concentration in the beans, followed by acetic acid, anisaldehyde, and anisyl acetate. A sensory evaluation of Tahitian vanilla beans and its reconstitute aroma concentrate characterized both samples as similar. These results indicated vanillin, anisaldehyde, anisyl alcohol, and anisyl acetate to be the key odorants in Tahitian vanilla beans. 3-Methylnonane-2,4-dione were identified for the first time in vanilla beans. β-Damascenone and phenylacetic acid were identified for the first time in Tahitian vanilla beans.

Photoresponsive two-component organogelators based on trisphenylisoxazolylbenzene

Photochromic tris(phenylisoxazolyl)benzene 1 and bispyridine derivatives 2a–e were mixed in a certain ratio to generate stable gels in benzyl alcohol, 4-methoxybenzyl alcohol, and aniline. Supramolecular assembly of 1 in solution was confirmed by 1H NMR study. The Tgel value was saturated in a 2 : 3 ratio of 1 and 2c. The intermolecular hydrogen bonds OH···N and salt bridge O(−)···H(–)N(+) between 1 and 2c coexisted evidently, and these hydrogen bonds contributed to the stabilization of the gel networks. The lengths of alkyl chains of 2a–e governed the stabilities of the gels. The gel formations were driven by the morphological transition of 1 before and after the addition of 2a–e. Mixtures of 1 and 2a–e led to the well developed fibrillar networks, generating a lot of voids that are responsible for immobilizing solvent molecules. When the benzyl alcohol gel was irradiated at 360 nm, the gel turned to the sol. The sol was reversed to the gel by warming. This gel-to-sol phase transition was completely reversible.

Polymer Catalysts Imprinted with Metal Ions as Biomimics of Metalloenzymes

This work presents the preparation and properties of molecularly imprinted polymers (MIPs) with catalytic centers that mimic the active sites of metalloenzymes. The MIP synthesis was based on suspension polymerization of functional monomers (4-vinylpyridine and acrylonitrile) with trimethylolpropane trimethacrylate as a crosslinker in the presence of transition metal ions and 4-methoxybenzyl alcohol as a template. Four metal ions have been chosen for imprinting from among the microelements that are the most essential in the native enzymes: Cu2+, Co2+, Mn2+, and Zn2+. To prepare catalysts, the required loading of metal ions was obtained during sorption process. The catalysts imprinted with Cu2+, Co2+, and Zn2+were successfully used for hydroquinone oxidation in the presence of hydrogen peroxide. The Mn2+-imprinted catalyst showed no activity due to the insufficient metal loading. Cu2+MIP showed the highest efficiency. In case of Cu- and Co-MIP catalysts, their activity was additionally increased by the use of surface imprinting technique.