Phenolic Aldehyde Research Articles

Identification and quantification of free and bound phenolic compounds contained in the high-molecular weight melanoidin fractions derived from two different types of cocoa beans by UHPLC-DAD-ESI-HR-MSn

The aim of the present study was to establish the profiles of soluble free phenolics (SFPs) and bound phenolics (BPs) in high molecular weight (HMW) melanoidin fractions isolated from raw and roasted beans of two Theobroma cacao L. varieties. Samples were prepared using three methods (saline treatment and acidic and alkaline hydrolysis) to obtain different forms of phenolic compounds. A total of fifteen phenolics, including three flavan-3-ols, seven phenolic acids, one phenolic aldehyde, and four N-phenylpropenoyl-L-amino acids (NPAs), were identified using ultra-high-performance liquid chromatography coupled to diode array detection and electrospray ionization high-resolution mass spectrometry (UHPLC-DAD-ESI-HR-MSn). In HMW fractions from both studied cocoa types, the main SFPs were N-caffeoyl-L-Asp and procyanidin B2, whereas the main BPs were catechin, epicatechin, ellagic acid, protocatechualdehyde, and N-caffeoyl-L-Asp. The concentrations of individual BPs were much higher than the content of total SFPs. It was also found that, as compared to alkaline hydrolysis, acid hydrolysis released a significantly higher amount of BPs from HMW melanoidin fractions. A comprehensive quantitative analysis indicated significant variation in the investigated phenolic compounds depending on the cocoa type and roasting conditions. An increase in treatment temperature from 110 to 150 °C led to a decline in SFPs and an increment in BPs. The HMW fractions of unroasted Criollo beans exhibited the highest content of SFPs and the lowest content of BPs. The highest BP concentrations were obtained for both cocoa bean varieties roasted at 150 °C. The present study revealed that HMW melanoidin fractions from cocoa beans of different varieties roasted at higher temperatures are a good source of phenolic compounds that can be released under both acidic and alkaline conditions.

Volatility and thermodynamic stability of vanillin

Vanillin is a naturally occurring phenolic aldehyde that is world-wide known for its flavouring properties. This work reports an extensive experimental and computational study of its thermodynamic properties. The vapour pressures of crystalline and liquid phases of vanillin were measured in the following temperature ranges T = (321.0–350.7) K and (324.9–382.3) K respectively, using a static method based on diaphragm capacitance gauge. Additionally, the crystalline vapour pressures were also measured in the temperature interval T = (303.1–325.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization, at selected reference temperatures, were derived from the vapour pressure measurements. The enthalpies of vaporization and of sublimation, at T = 298.15 K, were also determined using Calvet microcalorimetry and the standard (p° = 105 Pa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, was calculated and compared with the values estimated by employing quantum chemical calculations. To analyse the thermodynamic stability of vanillin, the standard Gibbs energies of formation in crystalline and gaseous phases were calculated. The molar enthalpy of fusion determined using DSC is compared with indirect results determined using Calvet microcalorimetry and vapour pressure measurements.

Probing the binding of phenolic aldehyde vanillin with bovine serum albumin: Evidence from spectroscopic and docking approach

The interactions of bovine serum albumin (BSA) with vanillin (VAN) were studied using UV–vis absorption, fluorescence, synchronous fluorescence, three dimensional fluorescence spectroscopy (3D), Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), and molecular docking techniques. The results revealed that VAN causes the static quenching of BSA by forming BSA-VAN complex. The thermodynamic parameters obtained using isothermal titration calorimetry (ITC) showed that the interaction between BSA and VAN is spontaneous and hydrogen bonding, van der Waals forces are mainly involved in stabilizing the complex. The distance between the donor and the acceptor was analyzed using fluorescence resonance energy transfer (FRET) which showed Forster distance of 2.58 nm. Molecular docking technique was applied to study the modes of interaction between BSA-VAN system and it was found that VAN bound to the sub-domain IIA of BSA. Structural analysis using 3D, synchronous fluorescence FTIR, and CD showed that upon binding of VAN, BSA exhibits small micro-environmental changes around tryptophan amino acid residue.

A comprehensive LC–MS/MS method validation for the quantitative investigation of 37 fingerprint phytochemicals in Achillea species: A detailed examination of A. coarctata and A. monocephala

The current study aims to optimize and validate a comprehensive LC–MS/MS method for the quantification of 37 phytochemicals (15 phenolic acids, 17 flavonoids, 3 non-phenolic organic acids, 1 phenolic aldehyde and 1 benzopyrene) in Achillea species. Though Achillea species were chosen as real life samples, the current method is applicable to a wide range of plant species. The developed method was fully validated in terms of linearity, accuracy (recovery), inter-day and intra-day precision (repeatability), limits of detection and quantification (LOD/LOQ) and relative standard uncertainty (U% at 95% confidence level (k = 2)). Reversed-phase ultrahigh performance liquid chromatography was optimized to achive optimum separation for 37 phytochemical compounds and to overcome the suppression effects. MS detection was performed using a triple quadrupole mass spectrometer and negative or positive ionization modes were optimized for each analyte. Multiple reaction monitoring (MRM) was used to quantify the analytes, related molecular ions and transition ions were optimized. Phytochemical screening of ethanol and methanol-chloroform extracts of root and aerial parts of A. coarctata and A. monocephala were performed by using the developed and validated LC–MS/MS method. Root and aerial parts of both species have considerable amounts of certain phenolic-nonphenolic acids (quinic, malic, fumaric, chlorogenic and vanillic acids) and flavonoids (rutin, hesperidin, isoquercitrin, apigetrin, luteolin, apigenin). Additionally, total phenolic and flavonoid amounts, antioxidant (DPPH free radical scavenging assay, ABTS radical cation decolorization assay, β-carotene lipid peroxidation test system and CUPRAC cupper reduction capacity methods), anticholinesterase, tyrosinase, urease inhibition and cytotoxic activities (on HeLa (Human Cervical Carcinoma Cell Line) of A. coarctata and A. monocephala were also investigated. It has been determined that the studied Achillea species, that are rich in total phenolic-flavonoid and chlorogenic acid contents, have high antioxidant and cytotoxic potential at the same time. According to the results of LC–MS/MS, antioxidant and cytotoxic activity studies, after detailed chemical investigation and toxicity studies on these species, A. coarctata and A. monocephala may be promoted as promising sources of natural agents and used for the development of nutraceuticals or functional food ingredients in future.

Identification and Quantification of Avenanthramides and Free and Bound Phenolic Acids in Eight Cultivars of Husked Oat ( Avena sativa L) from Finland.

Finland is the second largest oat producer in Europe. Despite the existing knowledge of phenolics in oat, there is little information on the phenolic composition of oats from Finland. The aim of the study was to investigate the concentrations of free and bound phenolic acids, as well as avenanthramides in eight Finnish cultivars of husked oat (Avena sativa L.). Seven phenolic acids and one phenolic aldehyde were identified, including, in decreasing order of abundance: p-coumaric, ferulic, cinnamic, syringic, vanillic, 2,4-dihydroxybenzoic, and o-coumaric acids and syringaldehyde. Phenolic acids were mostly found as bound compounds. Significant varietal differences (p < 0.05) were observed in the cumulative content of phenolic acids, with the lowest level found in cv. ‘Viviana’ (1202 ± 52.9 mg kg–1) and the highest in cv. ‘Akseli’ (1687 ± 80.2 mg kg–1). Avenanthramides (AVNs) 2a, 2p, and 2f were the most abundant. Total AVNs levels ranged from 26.7 ± 1.44 to 185 ± 12.5 mg kg–1 in cv. ‘Avetron’ and ‘Viviana’, respectively.

Synthesis of Fluorine-Containing Derivatives of 5-Arylisoxazoles and 4,5-Dichlorothiazole

Alkylation of fluorophenols and phenolic aldehydes with 5-phenyl(p-tolyl)-3-chloromethylisoxazole under the Williamson reaction conditions afforded the corresponding ethers. Condensation of the resulting phenolic aldehyde derivatives and 5-phenyl(p-tolyl)isoxazole-3-carbaldehydes with p-fluoroaniline resulted in fluorine-containing azomethines. Acylation of fluorinated amines with 5-(p-tolyl)isoxazole- and 4,5- dichloroisothiazole-3-carbonyl chlorides gave rise to fluorinated amides bearing isoxazole and isothiazole fragments, representatives of which showed a synergistic effect in compositions with insecticides.

FCS and ECH dependent production of phenolic aldehyde and melanin pigment from l-tyrosine in Escherichia coli.

In this study, we engineered E. coli cells to express l-tyrosine converting enzymes, including tyrosine ammonia-lyase (TAL), p-coumarate 3-hydroxylase (C3H), feruloyl-CoA synthetase (FCS), and enoyl-CoA hydratase/aldolase (ECH). A catabolic circuit, which consisted of the protocatechualdehyde and p-hydroxybenzaldehyde production pathways, was reconstituted through combinatorial production of discrete enzymes. First, cells expressing FCS and ECH could convert each 5mM of caffeic acid and ferulic acid into protocatechualdehyde (70.5%) and vanillin (96.5%), respectively. Second, TAL and C3H were co-expressed with FCS and ECH. This strain converted l-tyrosine into caffeic acid, which was then converted into protocatechualdehyde. Ascorbic acid was used as an inhibitor of catechol aldehyde-based melanin formation, and the production yields of protocatechualdehyde and p-hydroxybenzaldehyde were 31.0±5.6 and 24.0±4.2mg/L, respectively. Finally, caffeic acid-based melanin formation was observed with higher production rate of 40.9±6.2mg/L/h by co-expressing FCS and ECH in the presence of caffeic acid.

酚醛比对特辛基苯酚甲醛树脂结构的影响

以对特辛基苯酚和甲醛为原料，通过调整酚醛的物质的量比，合成了具有不同分子量的酚醛树脂。通过软化点、凝胶渗透色谱、核磁共振氢谱对其结构进行了表征。在酚醛比例相同的情况下，制得了软化点为93.1℃，重均分子量为1050，分子量分布相对集中的树脂。研究结果表明，通过控制酚醛的物质的量比，可以得到预期分子量、分子量分布和分子结构的树脂。 Phenolic resins with different molecular weight were synthesized by the adjustment of phenolic aldehyde, with p-tert-octyl phenol and formaldehyde as materials. Softening point, gel permeation chromatography and 1H NMR Spectroscopy were used to characterize its structure. With the same molar ratio of p-tert-octyl phenol and formaldehyde, a resin with the softening point of 93.1˚C, the mean molecular weight of 1050 and relatively concentrated distribution of molecular weight was made. Results indicate that the expected molecular weight, molecular weight distribution and structure of resin can be made by the control of molar ratio of p-tert-octyl phenol and formaldehyde.

MoS2-decorated coaxial nanocable carbon aerogel composites as cathode materials for high performance lithium-sulfur batteries

MoS2-decorated coaxial nanocable carbon aerogel (MoS2/CNCA) has been successfully prepared by phenol aldehyde reaction on the substrate of multi-walled carbon nanotube with catalysis of ammonium molybdate followed pyroprocessing with sulfur. The as-prepared samples were characterized by transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, X-ray powder diffraction, and X-ray photoelectron spectroscopy. The MoS2-decorated carbon aerogel (CA) with carbon nanotube as fine wire presents narrow distribution of pore size, interconnected structure and high conductance. The MoS2/CNCA/S composites exhibit improved electrochemical performances as cathode of lithium-sulfur batteries. Especially, the MoS2-8/CNCA/S composite delivers a discharge capacity of 1343 mAh g−1 at 0.2 C with the capacity retention of 81% after 200 cycles. Even at 5 C, the electrode presents high discharge capacity of 723 mAh g−1. These improved results can be attributed to the contribution of entangled network as electronic conductive channel, large surface area, small pore size and special anchoring action of molybdenum disulfide.

Efficient synthesis of rottlerin and its two subunits

Rottlerin, a natural product isolated from Mallotus philippensis, is associated with a range of biological activities. Its chemical structure is featured by two different substituted phloroglucinol units linked by a methylene group. In this study, we accomplished a total synthesis of rottlerin using phenol–aldehyde condensation as the key reaction. By our method, gram-scale preparation of the two structural subunits was achieved, and rottlerin was obtained in a longest eight linear step with 20% overall yield. Our study provides a practical solution for obtaining the sample of rottlerin in an efficient way.

Substituent Effect of Phenolic Aldehyde Inhibition on Alcoholic Fermentation by Saccharomyces cerevisiae

Phenolic compounds significantly inhibit microbial fermentation of biomass hydrolysates. To understand the quantitative structure–inhibition relationship of phenolic aldehydes on alcoholic fermentation, the effect of 11 different substituted benzaldehydes on the final ethanol yield was examined. The results showed that the degree of phenolic benzaldehyde inhibition was strongly associated with the position of phenolic hydroxyl groups but not the number of phenolic hydroxyl groups. It was observed that ortho-substituted 2-hydroxybenzaldehyde resulted in 15–20-fold higher inhibition than the meta- or para-substituted analogues of 3- and 4-hydroxybenzaldehydes. From the correlation of the molecular descriptors to inhibition potency in yeast fermentation, we found a strong relationship between the octanol/water partition coefficient (log P) of aldehydes and the EC50 value. The most inhibitory 2-hydroxybenzaldehyde has the highest log P and possesses an ortho −OH group capable of forming an intramolecular hydr...

Preparation and characterization of epoxy/slag composite for cement slurry applications

ABSTRACTIn this study, epoxy/slag composites (ESCs) were prepared by using diglycidyl ether of bisphenol‐A epoxy resin, water‐quenched granulated blast furnace slag as filler, phenolic aldehyde amine as hardener, and titanate as coupling agent. The properties of ESC, including chemical structure, thermal stability, wetting properties, and morphological structure, were investigated by using Fourier transform infrared spectroscopy, thermogravimetric analysis, a contact angle meter, scanning electron microscopy, and energy dispersive spectrometry. The results show that ESCs possess excellent thermal stability, hydrophilicity, and good compatibility with cement slurry compared to pure epoxy. In addition, the applications of ESC in a cement slurry were also investigated. It was found that the fluidity, free water, fluid loss, and content of Ca(OH)2 decreased, while the compressive strength increased with the incorporation of slag into the epoxy matrix. These features were attributed to the pozzolanic reaction of slag by consumption of Ca(OH)2 to form calcium silicate hydrate (C‐S‐H) gel which contributed more to the compressive strength of set cement. Finally, lightweight cement containing ESCs exhibited high strength without affecting the density of the light cement slurry under curing pressure and at high mixing rate compared with lightweight cement made of floating beads. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43359.

The ADH7 Promoter of Saccharomyces cerevisiae is Vanillin-Inducible and Enables mRNA Translation Under Severe Vanillin Stress.

Vanillin is one of the major phenolic aldehyde compounds derived from lignocellulosic biomass and acts as a potent fermentation inhibitor to repress the growth and fermentative ability of yeast. Vanillin can be reduced to its less toxic form, vanillyl alcohol, by the yeast NADPH-dependent medium chain alcohol dehydrogenases, Adh6 and Adh7. However, there is little information available regarding the regulation of their gene expression upon severe vanillin stress, which has been shown to repress the bulk translation activity in yeast cells. Therefore, in this study, we investigated expression patterns of the ADH6 and ADH7 genes in the presence of high concentrations of vanillin. We found that although both genes were transcriptionally upregulated by vanillin stress, they showed different protein expression patterns in response to vanillin. Expression of Adh6 was constitutive and gradually decreased under vanillin stress, whereas expression of Adh7 was inducible, and, importantly, occurred under severe vanillin stress. The null mutants of ADH6 or ADH7 genes were hypersensitive to vanillin and reduced vanillin less efficiently than the wild type, confirming the importance of Adh6 and Adh7 in vanillin detoxification. Additionally, we demonstrate that the ADH7 promoter is vanillin-inducible and enables effective protein synthesis even under severe vanillin stress, and it may be useful for the improvement of vanillin-tolerance and biofuel production efficiency via modification of yeast gene expression in the presence of high concentrations of vanillin.

Transcriptome analysis of Zymomonas mobilis ZM4 reveals mechanisms of tolerance and detoxification of phenolic aldehyde inhibitors from lignocellulose pretreatment.

BackgroundPhenolic aldehydes generated from lignocellulose pretreatment exhibited severe toxic inhibitions on microbial growth and fermentation. Numerous tolerance studies against furfural, 5-hydroxymethyl-2-furaldehyde (HMF), acetate, and ethanol were reported, but studies on inhibition of phenolic aldehyde inhibitors are rare. For ethanologenic strains, Zymomonas mobilis ZM4 is high in ethanol productivity and genetic manipulation feasibility, but sensitive to phenolic aldehyde inhibitors. Molecular mechanisms of tolerance for Z. mobilis toward phenolic aldehydes are not known.ResultsWe took the first insight into genomic response of Z. mobilis ZM4 to the phenolic aldehyde inhibitors derived from lignocellulose pretreatment. The results suggest that the toxicity to cells is caused by the functional group of phenolic aldehyde, similar to furfural and HMF, rather than aromatic groups or phenolic hydroxyl groups. Transcriptome response against 4-hydroxybenzaldehyde, syringaldehyde, and vanillin, representing phenolic groups H, S, and G, respectively, was investigated. The atlas of the important genes responsible for significantly enhanced and repressed genes at the genomic level was illustrated. 272 genes with twofold greater expressions than non-treated controls and 36 gene clusters in response to challenges of these phenolic aldehydes were identified. Several reductases encoded by ZMO1116, ZMO1696, and ZMO1885 were found to play the key roles in reducing phenolic aldehydes into the corresponding phenolic alcohols. Reduction of phenolic aldehydes by overexpression of ZMO1116, ZMO1696, and ZMO1885 in Z. mobilis ZM4 resulted in the increased inhibitor conversion and ethanol productivity, especially for 4-hydroxybenzaldehyde and vanillin. Several transporter genes such as ZMO0282, ZMO0283, ZMO0798, ZMO0799, and ZMO0800 was also displayed significantly increased expressions against the phenolic aldehydes.ConclusionsThe genes encoding reductases are with potentials on phenolic aldehydes-tolerant genes contributing to the reduction of phenolic aldehydes into the corresponding phenolic alcohols forms for Z. mobilis ZM4. Overexpression of the key genes improved the conversion ratio and ethanol productivity of 4-hydroxybenzaldehyde and vanillin with high toxicity. New knowledge obtained from this research aids understanding the mechanisms of bacterial tolerance and the development of the next-generation biocatalysts for advanced biofuels production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0333-9) contains supplementary material, which is available to authorized users.

Antioxidant and Anti-inflammatory Compounds in Nutmeg (Myristica Fragrans) Pericarp as Determined byin vitroAssays

Nutmeg, Myristicafragrans, is known for its culinary and medicinal values. The nutmeg pericarp, abundant during the production of the seed, is also used in food and beverage preparations. In this study, the pericarp of M. fragrans was evaluated for its bioactive components using in vitro antioxidant and antiinflammatory assays. The hexane, ethyl acetate and methanolic extracts inhibited lipid peroxidation (LPO) by 82.5, 70.1 and 73.2%, and cyclooxygenase enzymes COX-1 by 44, 44 and 42% and COX-2 by 47, 41 and 36%, respectively, at 100 microg/mL. The bioassay-guided purifications of extracts yielded 20 compounds belonged to neolignans (0.13%), phenylpropanoids (0.28%), phenolic aldehyde (0.35%), triterpenoids (0.06%), triglycerides (0.20%), sugars (10.2%) and steroids (0.49%). Pure isolates 1-5 inhibited LPO by 70-99% and 3-12 inhibited COX-1 and -2 enzymes by 37-49%. This is the first report on the bioassay-guided characterization of constituents in nutmeg pericarp. Our results support the medicinal claims of nutmeg pericarp.

Simultaneous determination of phenolic acids in Guanxinning injection by HPLC

This paper was aim to determine five phenolic acids, sodium danshensu (SD), protocatechuic aldehyde (PA), rosmarinic acid (RA), lithospermic acid (LA) and salvianolic acid B (SAB), in Guanxinning injection. In the test, Kromasil C18 column (4.6 mm x 250 mm, 5 µm) was adopted, with acetonitrile-3% formic acid solution as the mobile phase for gradient elution. The flow rate was 1 mL · min, the column temperature was 30 °C and the detection wavelength was 280 nm. According to the results of the test, SD, PA, RA, LA and SAB showed good linear relations between peak areas and sample sizes in 0.006 06-4.04 (r = 0.999 3), 0.006 15-4.10 (r = 0.999 4), 0.005 94-3.96 (r = 0.999 3), 0.006 06-4.04(r = 0.999 1) and 0.006 09-4.06 (r = 0.999 2) µg, respectively. The average recoveries (n = 6) were 98.9% (RSD 0.75%), 98.1% (RSD 1.2%), 100% (RSD 0.77%), 98.7% (RSD 1.7%), 102% (RSD 0.68%), respectively. The above 5 components were determined in 13 batches of samples by using the established method. The method was simple, accurate and highly reproducible that it could be used for quality control of the components in Guanxinning injection.

Low temperature wafer level conformal polymer dielectric spray coating for through silicon vias with 2:1 aspect ratio

This paper presents a detailed study to perform low temperature spray coating polymer dielectric process with good conformal deposition on aspect ratio features (2:1) through silicon via (TSV) CMOS image sensor (CIS) wafer-level-packaging. In this study, one kind of phenolic aldehyde polymer is deposited on the sidewall of though silicon via by spray coating process. Individual conditions that affect the weak-point of polymer dielectric on the TSV sidewall and step coverage such as nitrogen gas pressure, polymer so lution flow rate and temperature are investigated. The optimal condition is used to deposit into TSVs by spray coating process. The results turn to give excellent step coverage and satisfied weak-point (>2 µm) on the sidewall of though silicon via with the diameter of 65 µm and depth of 130 µm.

G protein-coupled estrogen receptor-1 is involved in the protective effect of protocatechuic aldehyde against endothelial dysfunction.

Protocatechuic aldehyde (PCA), a phenolic aldehyde, has therapeutic potency against atherosclerosis. Although PCA is known to inhibit the migration and proliferation of vascular smooth muscle cells and intravascular thrombosis, the underlying mechanism remains unclear. In this study, we investigated the protective effect of PCA on endothelial cells and injured vessels in vivo in association with G protein-coupled estrogen receptor-1 (GPER-1). With PCA treatment, cAMP production was increased in HUVECs, while GPER-1 expression was increased in both HUVECs and a rat aortic explant. PCA and G1, a GPER-1 agonist, reduced H2O2 stimulated ROS production in HUVECs, whereas, G15, a GPER-1 antagonist, increased ROS production further. These elevations were inhibited by co-treatment with PCA or G1. TNFα stimulated the expression of inflammatory markers (VCAM-1, ICAM-1 and CD40), phospho-NF-κB, phospho-p38 and HIF-1α; however, co-treatment with PCA or G1 down-regulated this expression significantly. Likewise, increased expression of inflammatory markers by treatment with G15 was inhibited by co-treatment with PCA. In re-endothelization, aortic ring sprouting and neointima formation assay, rat aortas treated with PCA or G1 showed accelerated re-endothelization of the endothelium and reduced sprouting and neointima formation. However, aortas from G15-treated rats showed decelerated re-endothelization and increased sprouting and neointima formation. The effects of G15 were restored by co-treatment with PCA or G1. Also, in the endothelia of these aortas, PCA and G1 increased CD31 and GPER-1 and decreased VCAM-1 and CD40 expression. In contrast, the opposite effect was observed in G15-treated endothelium. These results suggest that GPER-1 might mediate the protective effect of PCA on the endothelium.

High-Throughput Screening of Inhibitory Compounds on Growth and Ethanol Production of Saccharomyces cerevisiae

A high-throughput screening experiment to establish the individual and mixture effects of various common inhibitors found in lignocellulosic hydrolysates on the growth kinetics and ethanol production of Saccharomyces cerevisiae was carried out. Fermentations were performed utilizing 96-well microtiter plates to allow for carrying out fermentations in parallel, around which a central composite design of experiments was used to select inhibitor concentrations in each well. The individual and interaction effects of six common inhibitors were quantified using response surface fits of the growth rate, as determined by optical absorbance measurements and final cell density. For growth rate, 4-hydroxy-methylbenzaldehyde (phenol aldehyde) was found to be the strongest inhibitor of growth rate over the concentration range studied, while m-cresol (phenolic) had the least effect on growth rate and the largest inhibitory effect on final cell density. Both positive and negative interactions between inhibitors were found to affect both growth rate and maximum cell density. For example, both furfural and guaiacol when combined with m-cresol were found to have a positive effect on cell growth (less inhibitory), while guaiacol and m-cresol had a negative interaction with 4-hydroxy-methylbenzaldehyde. At all conditions studied, S. cerevisiae produced identical or higher ethanol yields compared to the inhibitor-free control fermentation which was attributed to the effects of physiological stress cause by the some inhibitors. These results quantify both the interactions of various inhibitors as well as their individual effects in a rapid and easy-to-perform experiment which can be easily expanded to include further inhibitors. Such a design can also be used for rapid and efficient screening of different pretreatments and feedstocks in the emerging field of lignocellulosic biofuels.

DOSY-NMR and raman investigations on the self-aggregation and cyclodextrin complexation of vanillin.

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is a phenolic aldehyde with limited solubility in water; in this work, we investigate its self-aggregation, as well as its complexation equilibria with β-cyclodextrin by using nuclear magnetic resonance (NMR) and vibrational spectroscopy. In particular, diffusion-ordered NMR (DOSY) measurements allowing to detect diffusional changes caused by aggregation/inclusion phenomena lead to a reliable estimate of the equilibrium constants of these processes, while Raman spectroscopy was used to further characterize some structural details of vanillin self-aggregates and inclusion complexes. Although the self-association binding constant of vanillin in water was found to be low (K(a) ∼10), dimeric species are not negligible within the investigated range of concentration (3-65 mM); on the other hand, formation of β-cyclodextrin self-aggregates was not detected by DOSY measurements on aqueous solutions of β-cyclodextrin at different concentrations (2-12 mM). Finally, the binding of vanillin with β-cyclodextrin, as measured by the DOSY technique within a narrow range of concentrations (2-15 mM) by assuming the existence of only the monomeric 1:1 vanillin/β-CD complex, was about an order of magnitude higher (K(c) ∼ 90) than self-aggregation. However, the value of the equilibrium constant for this complexation was found to be significantly affected by the analytical concentrations of the host and guest system, thus indicating that K(c) is an "apparent" equilibrium constant.