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The addition of thiol compounds to o-quinones, as exemplified by the biologically relevant conjugation of cysteine to dopaquinone, displays an anomalous 1,6-type regiochemistry compared to the usual 1,4-nucleophilic addition, for example, by amines, which has so far eluded intensive investigations. By means of an integrated experimental and computational approach, herein, we provide evidence that the addition of glutathione, cysteine, or benzenethiol to 4-methyl-o-benzoquinone, modeling dopaquinone, proceeds by a free radical chain mechanism triggered by the addition of thiyl radicals to the o-quinone. In support of this conclusion, DFT calculations consistently predicted the correct regiochemistry only for the proposed thiyl radical-quinone addition pathway. These results would prompt a revision of the commonly accepted mechanisms for thiol-o-quinone conjugation and stimulate further work aimed at assessing the impact of the free radical processes in biologically relevant thiol-quinone interactions.

The mechanism of the acid-dependent interring dehydrogenation in the conversion of the single-bonded 3-phenyl-2H-1,4-benzothiazine dimer 2 to the Δ2,2′-bi(2H-1,4-benzothiazine) scaffold of red hair pigments is disclosed herein. Integrated chemical oxidation and oxygen consumption experiments, coupled with electron paramagnetic resonance (EPR) analyses and DFT calculations, allowed the identification of a key diprotonated free-radical intermediate, which was implicated in a remarkable oxygen-dependent chain process via peroxyl radical formation and evolution to give the Δ2,2′-bi(2H-1,4-benzothiazine) dimer 3 by interring dehydrogenation. The critical requirement for strongly acidic conditions was rationalized for the first time by the differential evolution channels of isomeric peroxyl radical intermediates at the 2- versus 3-positions. These results offer for the first time a rationale to expand the synthetic scope of the double interring dehydrogenation pathway for the preparation of novel symmetric double-bond bridged captodative heterocycles.

Developing effective strategies to increase the chemical stability and to fine-tune the physico-chemical properties of melanin biopolymers by rational control of π-electron conjugation is an important goal in materials science for biomedical and technological applications. Herein we report that poly-1,8-dihydroxynaphthalene (pDHN), a non-nitrogenous, catechol-free fungal melanin mimic, displays a high degree of structural integrity (from MALDI-MS and CP/MAS 13 C NMR analysis), a strong radical scavenging capacity (DPPH and FRAP assays), and an unusually intense EPR signal (g=2.0030). Morphological and spectral characterization of pDHN, along with deassembly experiments in ionic liquids, indicated amorphous aggregates of small globular structures with an estimated stacking distance of 3.9 A and broadband absorption throughout the visible range. These results indicate that DHN-based melanins exhibit a high structural integrity and enhanced antioxidant and free-radical properties of potentially greater biomedical and technological relevance than for typical indole-based eumelanins.

Essential oils (EOs) are mixtures of volatile molecules endowed with health-promoting biological activities that go beyond their role as aromas and natural preservatives and can be exploited to develop functional foods and diet supplements. Their composition is briefly addressed along with regulatory aspects. The potential health benefit of human diet supplementation with EOs is outlined through a review of the recent literature on available clinical trials and preclinical research concerning EOs activity towards: (1) irritable bowel syndrome; (2) inflammatory bowel disease; (3) regulation of microbiota; (4) gastroprotection; (5) hepatoprotection; (6) protection of the urinary tract and diuresis; (7) management of metabolic disorders including hyperglycemia and hyperlipidemia; (8) anti-inflammatory and pain control; (9) immunomodulation and protection from influenza; and (10) neuroprotection and modulation of mood and cognitive performance. The emerging potential in such activities of selected EOs is given focus, particularly green and black cumin, bergamot, orange, myrtle, peppermint, sage, eucalyptus, lavender, thyme, lemon balm, ginger, and garlic.

The literature on coronaviruses counts more than 300,000 publications. Finding relevant papers concerning arbitrary queries is essential to discovery helpful knowledge. Current best information retrieval (IR) use deep learning approaches and need supervised training sets with labeled data, namely to know a priori the queries and their corresponding relevant papers. Creating such labeled datasets is time-expensive and requires prominent experts’ efforts, resources insufficiently available under a pandemic time pressure. We present a new self-supervised solution, called SUBLIMER, that does not require labels to learn to search on corpora of scientific papers for most relevant against arbitrary queries. SUBLIMER is a novel efficient IR engine trained on the unsupervised COVID-19 Open Research Dataset (CORD19), using deep metric learning. The core point of our self-supervised approach is that it uses no labels, but exploits the bibliography citations from papers to create a latent space where their spatial proximity is a metric of semantic similarity, for this reason, it can also be applied to other domains of papers corpora. SUBLIMER, despite is self-supervised, outperforms the Precision@5 (P@5) and Bpref of the state-of-the-art competitors on CORD19, which, differently from our approach, require both labeled datasets and a number of trainable parameters that is an order of magnitude higher than our.

Essential oils (EOs) have promising antioxidant activities which are gaining interest as natural alternatives to synthetic antioxidants in the food and cosmetic industries. However, quantitative data on chain-breaking activity and on the kinetics of peroxyl radical trapping are missing. Five phenol-rich EOs were analyzed by GC-MS and studied by oxygen-uptake kinetics in inhibited controlled autoxidations of reference substrates (cumene and squalene). Terpene-rich Thymus vulgaris (thymol 4%, carvacrol 33.9%), Origanum vulgare, (thymol 0.4%, carvacrol 66.2%) and Satureja hortensis, (thymol 1.7%, carvacrol 46.6%), had apparent kinh (30 °C, PhCl) of (1.5 ± 0.3) × 104, (1.3 ± 0.1) × 104 and (1.1 ± 0.3) × 104 M−1s−1, respectively, while phenylpropanoid-rich Eugenia caryophyllus (eugenol 80.8%) and Cinnamomum zeylanicum, (eugenol 81.4%) showed apparent kinh (30 °C, PhCl) of (5.0 ± 0.1) × 103 and (4.9 ± 0.3) × 103 M−1s−1, respectively. All EOs already granted good antioxidant protection of cumene at a concentration of 1 ppm (1 mg/L), the duration being proportional to their phenolic content, which dictated their antioxidant behavior. They also afforded excellent protection of squalene after adjusting their concentration (100 mg/L) to account for the much higher oxidizability of this substrate. All investigated EOs had kinh comparable to synthetic butylated hydroxytoluene (BHT) were are eligible to replace it in the protection of food or cosmetic products.

Symmetrical ditocopheryl disulfides (Toc)2 S2 and symmetrical and unsymmetrical ditocopheryl sulfides (Toc)2 S were simply prepared under remarkably mild conditions with complete control of the regiochemistry by using δ-, γ-, and β-tocopheryl-N-thiophthalimides (Toc-NSPht) as common starting materials. The roles of sulfur atom(s), H-bond and aryl ring substitution pattern on the antioxidant profile of these new compounds, which were assembled by linking together two tocopheryl units, are also discussed.

The autoxidation kinetics of stripped sunflower oil (SSO), squalene (SQ), and p-cymene (p-C) initiated by 2,2′-azobis(isobutyronitrile) at 303 K were investigated under controlled conditions by differential oximetry in order to build reference model systems that are representative of the natural variability of oxidizable materials, for quantitative antioxidant testing. Rate constants for oxidative chain propagation (kp) and chain termination (2kt) and the oxidizability (kp/2kt) were measured using 2,6-di-tert-butyl-4-methoxyphenol, 2,2,5,7,8-pentamethyl-6-chromanol, BHT, and 4-methoxyphenol as reference antioxidants. Measured values of kp (M-1 s-1)/2kt (M-1 s-1)/oxidizability (M-1/2 s-1/2) at 303 K in chlorobenzene were 66.9/3.45 × 106/3.6 × 10-2, 68.0/7.40 × 106/2.5 × 10-2, and 0.83/2.87 × 106/4.9 × 10-4, respectively, for SSO, SQ, and p-C. Quercetin, magnolol, caffeic acid phenethyl ester, and 2,4,6-trimethylphenol were investigated to validate calibrations. The distinctive usefulness of the three substrates in testing antioxidants is discussed.

Melanins are stable and non‐toxic biomaterials with a great potential as chemopreventive agents for diseases connected with oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), a well‐known synthetic melanin, becomes an excellent trap for alkylperoxyl radicals (ROO., typically formed during autoxidation of lipid substrates) in the presence of hydroperoxyl radicals (HOO.). The key reaction explaining this peculiar antioxidant activity is the reduction of the ortho‐quinone moieties present in PDA by the reaction with HOO.. This reaction occurs via a H‐atom transfer mechanism, as demonstrated by the large kinetic solvent effect of the reaction of a model quinone (3,5‐di‐tert‐butyl‐1,2‐benzoquinone) with HOO. (k=1.5×107 and 1.1×105 M−1 s−1 in PhCl and MeCN). The chemistry disclosed herein is an important step to rationalize the redox‐mediated bioactivity of melanins and of quinones., Polydopamine, a melanin analogue, is an excellent trap for alkylperoxyl radicals (ROO., typically formed during autoxidation of lipid substrates) only in the presence of hydroperoxyl radicals (HOO.). Activation of the ortho‐quinone moieties by HOO., and formation of exposed semiquinones are proposed as the reason of the peculiar antioxidant activity.

Helical shaped fused bis‐phenothiazines 1–9 have been prepared and their red‐ox behaviour quantitatively studied. Helicene radical cations (Hel.+) can be obtained either by UV‐irradiation in the presence of PhCl or by chemical oxidation. The latter process is extremely sensitive to the presence of acids in the medium with molecular oxygen becoming a good single electron transfer (SET) oxidant. The reaction of hydroxy substituted helicenes 5–9 with peroxyl radicals (ROO.) occurs with a ‘classical’ HAT process giving HelO. radicals with kinetics depending upon the substitution pattern of the aromatic rings. In the presence of acetic acid, a fast medium‐promoted proton‐coupled electron transfer (PCET) process takes place with formation of HelO. radicals possibly also via a helicene radical cation intermediate. Remarkably, also helicenes 1–4, lacking phenoxyl groups, in the presence of acetic acid react with peroxyl radicals through a medium‐promoted PCET mechanism with formation of the radical cations Hel.+. Along with the synthesis, EPR studies of radicals and radical cations, BDE of Hel‐OH group (BDEOH), and kinetic constants (kinh ) of the reactions with ROO. species of helicenes 1–9 have been measured and calculated to afford a complete rationalization of the redox behaviour of these appealing chiral compounds., Oxidation of differently substituted thia[4]helicenes: Single electron transfer and/or hydrogen atom transfer/proton‐coupled electron transfer processes operative on helical shaped fused bis‐phenothiazines are measured and studied rationalizing the role of substitution pattern and medium pH on the formation of Hel•+ radical cations and/or HelO• phenoxyl radicals.

The search for novel antioxidants inspired by the structure of vitamin E was made possible by rationalization of the physical-chemical properties at the basis of vitamin E bioactivity and has contributed significantly to such rationalization. Hundreds of novel compounds have been synthesized and tested, a representative selection of which (51 molecules) is illustrated and discussed in this chapter, highlighting the structure-activity relationships behind their antioxidant activity. Among them, BO-653, thiatocopherol and related compounds, selenotocopherol and related compounds, tellurophenols, N-tocopherol and related compounds, and Mito-Vitamin E are given special attention. The discussion focuses on the absolute rate constant for trapping peroxyl radicals in solution. When available, the performance in biomimetic models, like the protection of low density lipoproteins, along with the results of in vivo testing for pharmaceutical applications is also addressed. Some of the synthetic analogues largely outperformed the most active natural α-tocopherol, both in model systems and in vivo. However, none of these compounds has yet reached medical practice or is currently approved as a pharmaceutical, which calls for further research.

4-Hydroxynonenal (4-HNE) is a major product of the oxidation of ω-6-polyunstaturated lipids and an effector of radical-mediated oxidative damage, whose analytical determination requires chemical derivatization. In this work, its reactivity with fluorinated phenylhydrazines was explored both under preparative and analytical settings. A five-step synthesis of 4-HNE on gram-scale with an overall yield of 30 % is described. Reaction of 4-HNE with ortho-, meta-, or para-CF3-phenylhydrazine, as well as with the 3,5-di-CF3, 2,4-di-CF3, or pentafluoro analogues, in MeCN with 0.5 mM TFA yields the corresponding hydrazones with rate constants kf of 2.8 ± 0.4, 1.7 ± 0.1, 3.0 ± 0.2, 0.6 ± 0.1, 0.5 ± 0.1, and 3.5 ± 0.5 M–1 s–1, respectively at 298 K. At higher temperatures, the hydrazones undergo intramolecular cyclization to form 1,6-dihydropyridazines that, depending on the solvent and temperature, may further react with the hydrazine to yield tetrahydropyridazine adducts and their oxidation products. Other reaction products were isolated, depending on the reaction conditions, and the complex reactivity of 4-HNE with the above nucleophiles is discussed. Due to the good yield and rate of formation of the hydrazone adducts, their stability and favorable UV absorbance, 2-(trifluoromethyl)phenylhydrazine and 2,3,4,5,6-pentafluorophenylhydrazine are the most interesting candidates for the development of rapid and efficient analytical derivatizations of 4-HNE.

The incorporation of nitrogen atoms into the aryl rings of conventional diphenylamine antioxidants enables the preparation of readily accessible, air-stable analogues, several of which have temperature-independent radical-trapping activities up to 200-fold greater than those of typical commercial diphenylamines. Amazingly, the nitrogen atoms raise the oxidation potentials of the amines without greatly changing their radical-trapping (H-atom transfer) reactivity.

Solvent extracts from the aerial and root parts and seed oil from E. sativa (rocket salad) were assayed for anticancer activity against melanoma cells. The seed oil (isothiocyanates rich) significantly (p

Lactose intolerance is a common condition caused by intestinal lactase deficiency, and a lactose-free diet represents the simplest way to avoid gastrointestinal symptoms. The emerging use of dietary supplements requires analytical tools that are capable of assessing these analytes, particularly for those based on dry herbal extracts that contain lactose together with maltose and sucrose, because of cross-contamination and/or deliberate addition as excipient. Electrospray ionization mass spectrometry (ESI-MS) and MS/MS are valuable detection methods for underivatized disaccharides; however, the absence of distinctive ions and collision-induced dissociation (CID) fragmentation patterns does not allow discrimination of stereoisomers without good chromatographic resolution. We developed an ultrahigh performance liquid chromatography-ESI (U-HPLC-ESI) approach, based on porous graphitic carbon (PGC) columns, working at 5 °C to separate and detect the disaccharides in their anomeric forms as formate adducts obtained directly in-column by eluting with formate buffer/acetonitrile gradient mixtures. Using a Paul trap, we monitored the adducts [M + HCOO](-) at m/z 387 in ESI negative mode (MS(1)) as well as the CID fragment ion [M - H](-) at m/z 341 (MS(2)) and used MS(3) fragment ions at m/z 178 and 161 to confirm disaccharides identity in complex vegetable matrices. Complete resolution of lactose α- and β-anomers, maltose α- and β-anomers, and sucrose was obtained with R ≥ 2.0 for all peaks and selectivity α = 1.2 between α- and β-anomers of lactose. The limits of detection were in the range of 3-7 µg/l (ppb) for the target disaccharides. Because of the rapidity and good anomeric discrimination, the described method represents an alternative tool to investigate the mutarotation phenomenon for reducing disaccharides.

A series of amino acids analogous to tyrosine, but differing in the physicochemical properties of the aryl alcohol side chain, have been prepared and characterized. These compounds are expected to be useful in understanding the relationships between structure, thermodynamics, and kinetics in long-range proton-coupled electron transfer processes in peptides and proteins. Systematic changes in the acidity, redox potential, and O-H bond strength of the tyrosine side chain could be induced upon substituting the phenol for pyridinol and pyrimidinol moieties. Further modulation was possible by introducing methyl and t-butyl substitution in the position ortho to the phenolic hydroxyl. The unnatural amino acids were prepared by Pd-catalyzed cross-coupling of the corresponding halogenated aryl alcohol protected as their benzyl ethers with an organozinc reagent derived from N-Boc L-serine carboxymethyl ester. Subsequent debenzylation by catalytic hydrogenation yielded the tyrosine analogues in good yield. Spectrophotometric titrations revealed a decrease in tyrosine pK(a) of ca. 1.5 log units per included nitrogen atom, along with a corresponding increase in the oxidation (peak) potentials of ca. 200 mV, respectively. All told, the six novel amino acids described here have phenol-like side chains with pK(a)'s that span a range of 7.0 to greater than 10, and an oxidation (peak) potential range of greater than 600 mV at and around physiological pH. Radical equilibration EPR experiments were carried out to reveal that the O-H bond strengths increase systematically upon nitrogen incorporation (by ca. 0.5-1.0 kcal/mol), and radical stability and persistence increase systematically upon introduction of alkyl substitution in the ortho positions. The EPR spectra of the aryloxyl radicals derived from tyrosine and each of the analogues could be determined at room temperature, and each featured distinct spectral properties. The uniqueness of their spectra will be helpful in discerning one type of aryloxyl in the presence of other possible aryloxyl radicals in peptides and proteins with multiple tyrosine residues between which electrons and protons can be transferred.

The permeation of essential oils through SkinEthic reconstructed human epidermis, (RHE), was studied in vitro to establish a convenient tool to monitor the kinetics of release of active principles from cosmetic formulations. Twelve days old human epidermis held on polycarbonate disks was revitalized by addition of growth medium and incubated at 37 degrees C in 5% CO(2) atmosphere for five days prior to investigation. A system of six custom designed glass Franz-type diffusion cells were used for the permeation studies at 34 degrees C. The diffusion kinetic for 8 selected terpenes (camphor, carvone, 1,8-cineole, linalool, menthol, alpha-thujone, menthone, t-anethole), chosen as analytical markers of a mixture of plant essential oils contained in a cosmetic formulation, was probed by HS/SPME-GC-MS analysis and elaborated according to Fick's first law to obtain skin permeability coefficients (P(S) = 1.51, 1.47, 1.36, 0.80, 0.62, 0.40 and 0.14x10(-3) cm/h, respectively). The method proved to be sensitive, simple and reproducible, and RHE represents a convenient model for safety/quality assessment of cosmetic formulations.

Brassica vegetables are attracting major attention as healthy foods due to their content in glucosinolates (GLs) that release the corresponding isothiocyanates (ITCs) upon myrosinase hydrolysis. A number of studies have so far documented the chemopreventive properties of some ITCs. On the other hand studies focusing on single nutrients detached from food itself risk to be quite “reductive”, since plants contain several classes of compounds endowed with a polyhedral mechanism of action. Our recent finding that 4-methylthio-3-butenylisothiocyanate (GRH-ITC) and 4-methylsulfinyl-3-butenyl-isothiocyanate (GRE-ITC), released by the GLs purified from Japanese (Kaiware) Daikon (Raphanus sativus, L) seeds and sprouts, had selective cytotoxic/apoptotic activity on three human colon carcinoma cell lines, prompted further research on the potential chemopreventive role of a standardized Kaiware Daikon Extract (KDE), containing 10.5% w/w GRH and 3.8% w/w GRE, compared to its purified components. KDE administered in combination with myrosinase at doses corresponding to 50 M GRH-ITC plus 15 M GRE-ITC (50 M KDE-ITC) to 3 human cancer cell lines (LoVo, HCT-116 and HT-29) significantly reduced cell growth to only 4-6% of control in six days (p

Epidemiological evidence suggests a link between consumption of chlorinated drinking water and various cancers. Chlorination of water rich in organic chemicals produces carcinogenic organochlorine by-products (OBPs) such as trihalomethanes and haloacetic acids. Since the discovery of the first OBP in the 1970s, there have been several investigations designed to determine the biological effects of single chemicals or small artificial OBP combinations. However, there is still insufficient information regarding the general biological response to these compounds, and further studies are still needed to evaluate their potential genotoxic effects. In the current study, we evaluated the effect of three drinking water disinfectants on the activity of cytochrome P450 (CYP)-linked metabolizing enzymes and on the generation of oxidative stress in the livers of male and female Cyprinus carpio fish (carp). The fish were exposed in situ for up 20 days to surface water obtained from the Trasmene lake in Italy. The water was treated with 1-2 mg/L of either sodium hypochlorite (NaClO) or chlorine dioxide (ClO2) as traditional disinfectants or with a relatively new disinfectant product, peracetic acid (PAA). Micronucleus (MN) frequencies in circulating erythrocytes from the fish were also analysed as a biomarker of genotoxic effect. In the CYP-linked enzyme assays, a significant induction (up to a 57-fold increase in the deethylation of ethoxyresorufin with PAA treatment) and a notable inactivation (up to almost a 90% loss in hydroxylation of p-nitrophenol with all disinfectants, and of testosterone 2beta-hydroxylation with NaClO) was observed in subcellular liver preparations from exposed fish. Using the electron paramagnetic resonance (EPR) spectroscopy radical-probe technique, we also observed that CYP-modulation was associated with the production of reactive oxygen species (ROS). In addition, we found a significant increase in MN frequency in circulating erythrocytes after 10 days of exposure of fish to water treated with ClO2, while a non-significant six-fold increase in MN frequency was observed with NaClO, but not with PAA. Our data suggest that the use of ClO2 and NaClO to disinfect drinking water could generate harmful OBP mixtures that are able to perturb CYP-mediated reactions, generate oxidative stress and induce genetic damage. These data may provide a mechanistic explanation for epidemiological studies linking consumption of chlorinated drinking water to increased risk of urinary, gastrointestinal and bladder cancers.

Plant essential oils are lipid-soluble mixtures of volatile components obtained form the distillation or extraction of flowers, leaves, seeds or other plant organs and collect in concentrated form the typical scent of the plant itself. Although their chemical composition might be quite complex and differ from plant to plant, and even for each botanical species, according to climatic and environmental conditions, usually their components belong to well defined structural types, particularly terpeneoids and phenylpropanoids components, formed as plant secondary metabolites in the mevalonic acid pathway and in the shikimato pathway, respectively. Notable exceptions are the sulphur-containing volatiles from Alliaceae and Brassicaceae families. Essential oils have been used for thousands of years for religious, ornamental (cosmetic), dietary (spices and aromas) or medicinal purposes and possess a wealth of biological properties, among which the antimicrobial is certainly the more general and best documented by modern scientific literature. This chapter introduces their use as natural food additives by providing a brief overview on their history, composition, preparation, analysis, properties and safety for human use.

In the presence of micromolar peroxides or biometals (Fe(III)???, Cu(II)???, V(V) salts)???, and following a strong acid input, the stable 3-???phenyl-???2H-???1,???4-???benzothiazine is efficiently converted to a green-???blue ??2,???2'-???bi(2H-???1,???4-???benzothiazine) chromophore via dehydrogenative coupling of a 1,???4-???benzothiazinyl radical. The new system is of potential practical interest for colorimetric peroxide and redox biometal detection.

5-S-Lipoylhydroxytyrosol (1), the parent member of a novel group of bioinspired multidefense antioxidants, is shown herein to exhibit potent peroxyl radical scavenging properties that are controlled in a solvent-dependent manner by the sulfur center adjacent to the active o-diphenol moiety. With respect to the parent hydroxytyrosol (HTy), 1 proved to be a more potent inhibitor of model autoxidation processes in a polar solvent (acetonitrile), due to a lower susceptibility to the adverse effects of hydrogen bonding with the solvent. Determination of O-H bond dissociation enthalpies (BDE) in t-butanol by EPR radical equilibration technique consistently indicated a ca. 1.5 kcal/mol lower value for 1 relative to HTy. In good agreement, DFT calculations of the BDEOH using an explicit methanol molecule to mimic solvent effects predicted a 1.2 kcal/mol lower value for 1 relative to HTy. Forcing the geometry of the -S-R group to coplanarity with the aromatic ring resulted in a dramatic decrease in the computed BDEOH values suggesting a potentially higher activity than the reference antioxidant α-tocopherol, depending on geometrical constrains in microheterogeneous environments. These results point to sulfur substitution as an expedient tool to tailor the chain-breaking antioxidant properties of catechol derivatives in a rational and predictable fashion.

Topical bioavailability of lipid- and water-soluble vitamins is a critical issue for protecting or anti-ageing formulations. Using 17-day-old SkinEthic(®) reconstructed human epidermis, we investigated (at 34°C) the role of lemon EO in enhancing the penetration of α-tocopherol (E) and retinyl acetate (A), pyridoxine (B(6)) and ascorbic acid (C), released from O/W or W/O emulsions. D-limonene, α-pinene and p-cymene (65.9, 2.2 and 0.5%w/w of the oil) had skin permeability coefficients Ps (10(-3) cm h(-1)) of 0.56 ± 0.03 (or 0.73 ± 0.02), 0.72 ± 0.05 (or 0.98 ± 0.05) and 0.84 ± 0.04 (or 1.14 ± 0.04), respectively, when incorporated in a W/O (or O/W) emulsion. Vitamins B6, C and A had Ps values of (3.0 ± 0.4) × 10(-3), (7.9 ± 0.6) × 10(-3) and (0.37 ± 0.02) × 10(-5) cm h(-1), respectively, and their flux through the skin was enhanced by a factor of 4.1, 3.4 and 5.8, respectively, in the presence of lemon EO. The penetration of vitamin E was nine-fold enhanced. Lemon EO produced only reversible modification of TEWL, and it is a safe and effective penetration enhancer for topical administration of lipid- and water-soluble vitamins.

Verwendung einer Kombination aus einer Verbindung der allgemeinen Formel (I):in der R1 und R2 jeweils unabhängig voneinander Wasserstoff oder eine unverzweigte oder verzweigte C1-C20-Alkylgruppe ist, X -OR3 oder -NR3 2 ist, wobei R3 eine unverzweigte oder verzweigte C1-C20-Alkylgruppe oder eine C2-C4-Polyalkylenoxid-Gruppe ist, und einer Verbindung der allgemeinen Formel (II):in der R Wasserstoff, eine unverzweigte oder verzweigte C1-C18-Alkylgruppe oder -OR3 oder -NR3 2 ist, wobei R3 eine verzweigte oder unverzweigte C1-C20-Alkylgruppe ist, R' Wasserstoff, eine unverzweigte oder verzweigte C1-C18-Alkylgruppe ist und R'' eine unverzweigte oder verzweigte C1-C18-Alkylgruppe ist, zur Einstellung der Reaktivität und der Gelzeit von Harzmischungen auf Basis von radikalisch polymerisierbaren Verbindungen.