Hexyl Esters Research Articles

‘Fuji’ apple (Malus domestica Borkh.) volatile production during high pCO2 controlled atmosphere storage

‘Fuji’ apple volatile compound dynamics were characterized during cold storage in air or at low pO2 controlled atmosphere (CA) with up to 5kPa CO2. Volatile compounds in storage chambers were adsorbed onto solid sorbent traps and analyzed by GC–MS. Fruit volatile production differed quantitatively by CO2 concentration. Production of butyl, hexyl, and propyl esters by apples stored in CA was lower compared with that by fruit stored in air, while methyl and ethyl ester contents increased during CA storage compared with air. CO2 injury incidence was highest in fruit stored in CA at 5kPa CO2, an atmosphere where methyl ester accumulation may provide an early indication of CO2 injury development.

Recent Patents on Lipase Catalyzed Vegetable and Fish Oil Modification

Lipase is an enzyme which catalyzes hydrolysis, esterification and transesterification processes. Type (origin) of lipase affects process conditions and final conversion. Use of these biocatalytic properties of lipase in modification of various vegetable oils is depicted in different patents, leading to varieties of beneficial products. Production and concentration of polyunsaturated fatty acids like eicosapentanoic acid, docosapentanoic acid and docosahexanoic acid were carried out through lipase catalyzed hydrolysis. Hydrolysis followed by reesterification was also employed in some patents to concentrate long chain polyunsaturated fatty acids in triacylglycerol fraction or free fatty acid fraction as per specific requirements. Ethanolysis of fish oil hexyl esters was also described in some studies to concentrate similar fatty acids. Combined ethanolysis and esterification, ethanolysis and transesterification were also conducted in some patents to concentrate these desirable fatty acids. Degumming using phospholipase and biodiesel production with lipase as catalyst were also carried out leading to some notable patents. Reactor configuration for maximizing conversion was also patented. Removal of diacylglycerols from their mixture with triacylglycerols led to specifically designed triacylglycerol mixture for catering certain purposes.

Chiral fluoroacetic acid: synthesis of (R)- and (S)-[2H1]-fluoroacetate in high enantiopurity

A two-step synthesis of (R)- and (S)-[2H1]-fluoroacetate (sodium salts) in high enantioselectivity is reported. The synthesis is the development of a previous one in which the enantioselectivity has been increased from ∼38% ee to >95% ee. The improvement in enantioselectivity applied Bio’s methodology, which involved a deoxyfluorination reaction with DAST on either enantiomer of [2H1]-benzyl alcohol, adding TMS-morpholine to the reaction. The additive promotes an SN2 inversion process, and suppresses a competing non-stereospecific SN1 reaction course, and as a result significantly improves the stereointegrity of the C–F bond formation. The intermediate [2H1]-benzyl alcohols, [2H1]-benzyl fluorides and the product [2H1]-fluoroacetates as their hexyl esters were separately assayed for their stereochemical integrity, using the Courtieu method. This method involved measuring their 2H NMR spectra in a chiral matrix of poly-γ-benzyl l-glutamate. The chiral assay demonstrated that there was no significant loss in stereointegrity during the deoxyfluorination reaction and showed that the enantiomers of [2H1]-fluoroacetate were generated with high enantiomeric purity (95% ee).

Impact of the Mediterranean fruit fly (Medfly) Ceratitis capitata on different peach cultivars: The possible role of peach volatile compounds

The relationship between susceptibility of different peach cultivars (cvs) to the Mediterranean fruit fly (medfly), Ceratitis capitata, and the volatile composition of ripe fruit of each cv has been investigated, since understanding the fruit-insect interaction mechanism is crucial for developing control strategies for such a pest. Volatile compounds were analyzed by SPME–GC–MS in three cvs highly susceptible to medfly attack (Fair Time, Flaminia, Sicilia Piatta), and in two less susceptible cvs (Percoca Romagnola 7 and Doctor Davis). Among the volatile compounds detected, 88 could be identified. The main differences found in the volatile composition of the cvs, concerned the relative abundance of esters. The least susceptible cvs, above all Percoca Romagnola 7, contained the higher amounts of hexenyl, hexyl, 3-methylbutyl, butyl and 2-methylpropyl esters; among these, some C6 derivatives detected, such as (Z)-3-hexenyl acetate, are known to act as priming agents, enhancing plant defence response to insects. Instead, a lower relative content of methyl esters, such as methyl hexanoate and methyl octanoate, known to act as medfly pheromone and attractant respectively, was found in the least susceptible cvs.

Analysis of CLA Isomer Distribution in Nutritional Supplements by Single Column Silver‐Ion HPLC

AbstractNutritional supplements containing conjugated linoleic acid (CLA) isomers, widely used to improve body composition and inhibit fat storage, should be thoroughly analyzed, as CLA effects are isomer specific. In this research, an improvement of silver‐ion high performance liquid chromatography (Ag+‐HPLC) was obtained by using a single‐column instead of the most commonly used multi‐columns. To develop the procedure, a standard CLA mixture has been derivatized with different chain length alcohols (from methanol to hexanol). Hexyl CLA showed better separation between CLA isomer pairs, in particular the resolution of the t10,c12: c9,t11 pair increased from 0.3 (methyl esters) to 0.8 (hexyl esters). Therefore, the CLA isomer composition of some commercial CLA products was determined by Ag+‐HPLC analysis of hexyl esters. The main isomers in all supplements turned out to be c9,t11‐CLA and t10,c12‐CLA, the most anti‐adipogenic isomer. t8,c10‐ and c11,t13‐CLA were not detected. The nutritional supplements were also analyzed by high resolution gas chromatography of methyl esters to evaluate the fatty acid % composition and total CLA % content. The total CLA ranged from 79.4 to 94.4 %, and the t,t isomer from 1.4 to 7.3 %.

Improved HRGC Separation of cis, trans CLA Isomers as Diels-Alder Adducts of Alkyl Esters

This paper reports the separation of four isomers of conjugated linoleic acid (CLA), c,t/t,c-8,10; c,t/t,c-9,11; c,t/t,c-10,12; c,t/t,c-11,13, after reaction of esterification with aliphatic alcohols of different chain length and adduct formation with 4-methyl-1,2,4-triazoline-3,5-dione (MTAD). The high resolution gas chromatographic analyses were carried out using a simple 50-m cyanopropyl polysiloxane capillary column both with a flame ionization detector and a mass spectrometer. The resolution between the two pair of isomers: c,t/t,c-9,11 and c,t/t,c-10,12 and between c,t/t,c-10,12 and c,t/t,c-11,13 isomers were good for all the investigated alkyl esters and increased with the chain length of alcohol esterified to carboxylic moiety of CLA isomers. The most interesting result was relative to the c,t/t,c-8,10 and c,t/t,c-9,11 isomers, critical pair of isomers also when analyzed with a 120-m cyanopropyl polysiloxane capillary column; their resolution also increased from methyl to hexyl esters of CLA isomers and reached an acceptable value (0.8) in the case of hexyl esters. The best resolutions of the four considered CLA isomers were obtained with the hexyl esters of MTAD adducts of the isomers, without excessive analysis time. This method was useful and simple to evaluate the profile of the four main c,t isomers in commercial CLA samples.

Composition of Diethyl Ether Flower Extracts of Lonicera fragrantissima Lindl. & Paxton (Caprifoliaceae)

GC and GC-MS analyses of two diethyl ether extracts of Lonicera fragrantissima flowers (extraction times 1 and 20 days) enabled the identification of 61 components that represented ca. 90% of the extract volatiles. 10-Nonacosanol (18.1-24.1%), nonacosane (14.4-15.0%) and the rather rare long-chained fatty acid hexyl esters (octadecanoate, eicosanoate, docosanoate, tetracosanoate, hexacosanoate, octacosanoate and triacontanoate, in total 19.1-19.5%) were among the main constituents of both extracts. However, a number of differences were observed in the chemical composition of the 1 and 20 day extracts, the relative percentage of the iridoid loganetin being the most striking (19.1 and 2.1%, respectively). To the best of our knowledge, this is the first report on the GC behavior of loganetin. It seems that this and the long-chain fatty acid hexyl esters could have chemotaxonomic significance at the generic level.

Practical Considerations in the Pharmaceutical Analysis of Methyl and Hexyl Ester Derivatives of 5-Aminolevulinic Acid

Photodynamic therapy (PDT) using topical 5-aminolevulinic acid (ALA), a water-soluble precursor of the potent endogenous photosensitiser, protoporphyrin IX (PpIX), is a treatment and diagnostic tool for premalignant and malignant skin cancers. However, to improve drug delivery to deeper skin lesions, more lipophilic ALA esters have been investigated. Owing to the necessity in drug delivery research for efficient and validated assays for ALA esters in solution, this paper aims to describe optimised protocols to quantify the methyl and hexyl esters of ALA. ALA esters were derivatised using acetyl acetone and formaldehyde reagents and analysed using reversed phase HPLC. For the first time, the significance of ALA-impurities in ester samples has been highlighted. Furthermore, it was shown that for a given concentration, peak areas obtained for ALA-esters were significantly smaller than those obtained for ALA (p m-ALA (38.3%) > h-ALA (33.9%). These findings may explain why, historically, some of the benefits seen with ALA-esters using cell culture models have not been demonstrated in vivo.

Synthesis of alkyl esters by cutinase in miniemulsion and organic solvent media

The main objective of this work was studying and testing the nature and influence of reaction media (organic solvent vs. miniemulsion system) on the synthesis of alkyl esters catalyzed by Fusarium solani pisi cutinase. Ester synthesis and cutinase selectivity for different chain length of acids and alcohols (ethyl and hexyl) were evaluated. In iso-octane, after 1 h of reaction, cutinase exhibits rates of esterification between 0.24 micromol x mg(-)1 x min(-1) for ethyl oleate and 1.15 micromol x mg(-)1 x min(-1) for ethyl butyrate, while in a miniemulsion system the rates were from 0.05 for ethyl heptanoate to 0.76 micromol x mg(-1) x min(-1) for ethyl decanoate. The reaction rate for the synthesis of hexyl esters in a miniemulsion system was from 0.19 for hexyl heptanoate to 1.07 micromol x mg(-)1 x min(-1) for hexyl decanoate. High conversion yields of 95% at equilibrium after 8 h of reaction in iso-octane for pentanoic acid (C(5)) with ethanol at equimolar concentration (0.1 M) was achieved. Additionally, this work showed that a significant and unexpected shift in cutinase selectivity occurred towards longer chain length carboxylic acids (C(8)-C(10)) in miniemulsion system as compared to organic solvent (iso-octane) and previous studies in reverse micellar systems. The possibility of working with higher concentration of substrates, without inhibitory effect on the enzyme, was another advantage of the miniemulsion system.

A Density Functional Theory (DFT) Study on Gas-Phase Proton Transfer Reactions of Derivatized and Underivatized Peptide Ions Generated by Matrix-Assisted Laser Desorption Ionization

In this study, classic molecular dynamics (MD) simulations followed by density functional theory (DFT) calculations are employed to calculate the proton transfer reaction enthalpy shifts for native and derivatized peptide ions in the MALDI plume. First, absolute protonation and deprotonation enthalpies are calculated for native peptides (RPPGF and AFLDASR), the corresponding hexyl esters and three common matrices alpha-cyano-4-hydroxycinnamic acid (4HCCA), 2,5-dihydroxybenzoic acid (DHB), and 6 aza-2-thiothymine (ATT). From the proton exchange reaction calculations, protonation and deprotonation of the neutral peptides are thermodynamically favorable in the gas phase as long as the corresponding protonated/deprotonated matrix ions are present in the plume. Moreover, the gain in proton affinity shown by the ester ions suggests that the increase in ion yield is likely to be related to an easier proton transfer from the matrix to the peptide.

Long-Term Storage of Pink Lady Apples Modifies Volatile-Involved Enzyme Activities: Consequences on Production of Volatile Esters

Pink Lady apples were harvested at commercial maturity and stored at 1 degrees C and 92% relative humidity under either air or controlled atmosphere conditions (2 kPa O 2:2 kPa CO 2 and 1 kPa O 2:1 kPa CO 2) for 27 weeks. Data on the emission of volatile compounds and on the activity of some related enzymes in both skin and flesh tissues were obtained during subsequent shelf life at 20 degrees C. Major effects of storage atmosphere and poststorage period were observed on the emission of volatile esters and their precursors. Changes in the production of volatile esters were partly due to alterations in the activity of alcohol o-acyltransferase, but the specific esters emitted by fruit after storage also resulted largely from modifications in the supply of the corresponding substrates. Samples stored under air were characterized by higher availability of acetaldehyde, whereas those stored under CA showed enhanced emission of the alcohol precursors ethanol and 1-hexanol (2 kPa O 2) and 1-butanol (1 kPa O 2), with accordingly higher production of ethyl, hexyl, and butyl esters. Multivariate analysis revealed that a large part of the observed differences in precursor availability arose from modifications in the activity of the enzymes considered. Higher pyruvate decarboxylase activity in air-stored fruit possibly accounted for higher acetaldehyde levels in these samples, while storage under 1 kPa O 2 led to significantly decreased lipoxygenase activity and thus to lessened production of 1-hexanol and hexyl esters. Low acetaldehyde availability together with enhanced hydroperoxide lyase and alcohol dehydrogenase levels in these fruits are suggested to have led to higher emission of 1-butanol and butyl esters.

Effect of Lipophilicity of Dispersed Drugs on the Physicochemical and Technological Properties of Solid Lipid Nanoparticles

A series of aliphatic esters of the NSAID naproxen (NAP) were synthesised and encapsulated in solid lipid nanoparticles (SLN) to evaluate the influence of lipophilicity on drug loading and release, as well as physicochemical properties and stability of SLN. The lipophilicity of esters mainly showed to influence their affinity for the solid lipid matrix, modifying the drug release profile compared to the parent drug, whereas drug encapsulation efficiency and the technological properties and stability of SLN were not affected. After storage at room temperature the in vitro release profiles of esters changed with respect to freshly prepared systems, depending on the lipophilicity of the dispersed derivative. In particular, the SLN containing the medium-chain hexyl and octyl esters showed a 70-80% increase of drug release after storage; SLN loaded with NAP or the lower ethyl and butyl esters did not show significant changes in the drug release rate. Such findings reveal that the affinity of NAP esters for the lipid network of the nanoparticles is strongly dependent on their lipophilicity and an excessive increase of the latter negatively influences the allocation and retention on these com- pounds in the nanoparticles.

Fungicidal Activities of Dihydroferulic Acid Alkyl Ester Analogues

The natural product dihydroferulic acid (DFA, 1) and the synthesized DFA methyl (4a), ethyl (4b), propyl (4c), hexyl (4d), octyl (4e), and decyl (4f) esters were examined for antifungal activity. Test fungi included Saccharomyces cerevisiae (wild type, and deletion mutants slt2 Delta and bck1 Delta), Aspergillus fumigatus, and A. flavus. Growth inhibition of S. cerevisiae treated with 5 mM DFA or the corresponding esters was 4a, 4b, and 4c >98%; 4d 18.8%; 1 6.4%; 4e 6.2%; and 4f 2.8%, relative to the control. The 50% minimum inhibitory concentrations for the more active propyl, methyl, and ethyl esters were 1.5, 2.1, and 4.0 mM, respectively. Compound 4c inhibited 100% growth of both aspergilli at 6.4 mM.

In vitro evaluation of quercetin-3- O-acyl esters as topical prodrugs

Quercetin-3- O-acyl esters (I–VI) were synthesized and their usefulness as quercetin topical prodrugs was evaluated. Quercetin esters were assayed to determine their water stability and solubility, their susceptibility to undergoing enzymatic hydrolysis and their permeation through excised human skin. Quercetin ethyl (I) and hexyl (IV) esters proved poorly stable in aqueous media and they were not assayed further. Among the derivatives tested, quercetin propyl (II) and butyl (III) esters were more water-soluble than the parent drug. Esters II, III and V were readily hydrolyzed by human plasma and esters II and III penetrated excised human skin better than quercetin from aqueous saturated solutions. On the basis of the results obtained, esters II and III could be regarded as promising quercetin topical prodrugs.

Theoretical study of 5-aminolevulinic acid (5ALA) and some pharmaceutically important derivatives

5-Aminolevulinic acid (5ALA) is the key synthetic building block in protoporphyrin IX (PpIX), the heme chromophore in mitochondria. The addition of extracorporeal 5ALA and its alkyl ester derivatives are in current clinical use in photodynamical diagnostics and photodynamic therapy of tumors and skin disorders. In the current study density functional theory calculations are performed on 5ALA and its methyl, ethyl, and hexyl esters, in order to explore the basic chemical properties of these species. It is concluded that even in aqueous media the zwitterionic form of 5ALA is less stable than the non-zwitterionic one, that the local environment (lipid vs water) affects the energetics of reaction considerably, and that the hexyl species is most prone to hydrolysis of the three alkyl ester derivatives.

An alcohol acyl transferase from apple (cv. Royal Gala), MpAAT1, produces esters involved in apple fruit flavor

Apple flavor is characterized by combinations of ester compounds, which increase markedly during fruit ripening. The final step in ester biosynthesis is catalyzed by alcohol acyl transferases (AATs) that use coenzyme A (CoA) donors together with alcohol acceptors as substrates. The gene MpAAT1, which produces a predicted protein containing features of other plant acyl transferases, was isolated from Malus pumila (cv. Royal Gala). The MpAAT1 gene is expressed in leaves, flowers and fruit of apple. The recombinant enzyme can utilize a range of alcohol substrates from short to medium straight chain (C3-C10), branched chain, aromatic and terpene alcohols. The enzyme can also utilize a range of short to medium chain CoAs. The binding of the alcohol substrate is rate limiting compared with the binding of the CoA substrate. Among different alcohol substrates there is more variation in turnover compared with K(m) values. MpAAT1 is capable of producing many esters found in Royal Gala fruit, including hexyl esters, butyl acetate and 2-methylbutyl acetate. Of these, MpAAT1 prefers to produce the hexyl esters of C3, C6 and C8 CoAs. For the acetate esters, however, MpAAT1 preference depends upon substrate concentration. At low concentrations of alcohol substrate the enzyme prefers utilizing the 2-methylbutanol over hexanol and butanol, while at high concentrations of substrate hexanol can be used at a greater rate than 2-methylbutanol and butanol. Such kinetic characteristics of AATs may therefore be another important factor in understanding how the distinct flavor profiles of different fruit are produced during ripening.

Esterification of phenylacetic and 2-phenylpropionic acids by mycelium-bound carboxylesterases

Lyophilized mycelia of Aspergillus oryzae and Rhizopus oryzae were used in phosphate buffer to study the hydrolysis of ethyl esters of phenylacetic and 2-phenylpropionic acids and in organic solvents to synthesize, by direct acylation, several esters of these acids, namely ethyl, propyl, butyl, pentyl, hexyl and isoamyl esters. Ethanol acylations with 2-phenylpropionic acid were also performed at different temperatures and in different solvents. In all cases, the conversion yield progressively increased with temperature and the best results were obtained at 50 °C in n-heptane. The use of A. oryzae led to the preferential formation of the ( S)-enantiomer of ethyl 2-phenylpropionate with enantiospecificity increasing with temperature, whereas R. oryzae behaved oppositely. The molar conversions of these reactions also increased with the alcohol molecular weight (MW), likely because of the higher hydrophobicity and chemical affinity of the products for the solvent. A. oryzae proved to be more effective and quicker than R. oryzae in all the esterifications, probably due to a more favorable microenvironment. The kinetics of direct ethanol acylations were also studied in various solvents, specifically dimethylsulfoxide, dioxane, acetonitrile, tetrahydrofurane, pyridine, diisopropyl ether, benzene, toluene, n-heptane, isooctane, and pentadecane. The starting formation rates of ethyl esters with either biocatalyst were shown to progressively increase with the ratio of log P to the solvent molecular weight.

New 2-naphthyloxyacetates for trunk sucker growth control on grapevine (Vitis vinifera L.)

Eighteen new hexyl esters of 2-naphthyloxyacetic acid (β-NOA) were synthesized and their efficiency on sucker control of grapevine was investigated. Different solutions (0.5, 1, and 2%, w/w concentrations) of each compound were sprayed on suckers and the wilting effect after 4, 10, and 30 days after treatment was evaluated. Esters derived from primary and secondary alcohols gave a rapid control of suckers, whereas tertiary alcohol derivatives showed milder activity. Moreover, all compounds proved to cause a long-lasting inhibition effect on the growth of new suckers even 1 year after treatment, especially when applied at a 2% concentration.

Production of volatile compounds by Fuji apples following exposure to high CO2 or low O2.

The emission of volatile compounds by Fuji apples following short- or long-term exposure to high CO(2) was studied. The production of ethanol, methyl and ethyl esters, octanal, nonanal, and decanal was enhanced while the production of C(3)-C(6) alcohols, propyl, butyl, pentyl, and hexyl esters and butanal decreased in fruit exposed to 10 kPa O(2) + 20 kPa CO(2) at 20 degrees C for up to 12 days. The impact of high CO(2) exposure on volatile production was dependent on fruit maturity at harvest. Apples stored for 8 months in an ultralow O(2)-controlled atmosphere (CA) (0.5 kPa O(2) + 0.05 kPa CO(2)) or high CO(2) CA (1.5 kPa O(2) + 3 kPa CO(2)) at 0.5 degrees C had reduced production of most volatiles, especially butyl and hexyl esters, as compared to fruit stored in air. Two exceptions were ethanol and ethyl acetate for which the production was enhanced by both CA regimes. Treatment with the antioxidant diphenylamine prior to storage prevented most of the high CO(2)-induced and ultralow O(2)-induced changes in volatile production. The results of this study do not indicate that changes in volatile production following the exposure of Fuji apples to high CO(2) are causally related to the development of CO(2) injury.

Studies on alkyl esters of carboxybenzotriazole as inhibitors for copper corrosion

A series of alkyl esters (methyl, butyl, hexyl, octyl) derived from carboxybenzotriazole (CBTAH) have been studied as inhibitors for copper. Coupon tests established that the inhibition efficiency (IE) is concentration, time and pH dependent. At pH∼0 the IEs of the octyl and hexyl esters are considerably higher than that for benzotriazole under similar conditions. As pH increases up to approximately 8 the IE of each ester is decreased, but is still sufficient for practical use. For the butyl and methyl esters an opposite trend was observed; IE increased with increased pH. In acidic sulphate solution (pH∼0) the IE was in the order: octyl>hexyl>butyl>methyl, whilst in the near-neutral solution (pH∼8) this order is reversed. It is proposed that the protonated species (CBTAH 2 +-R) is chemisorbed on the copper through an azole nitrogen and at low pH IE is determined by van der Waals' forces of attraction between adjacent alkyl chains oriented away from the copper surface, which are increased with the length of the alkyl chain. On the contrary it is proposed that at high pH a polymeric complex is formed and steric hindrance acts to make the film less protective. Polarisation, EIS and SERS studies confirm these hypotheses.