Hydrophobic Flavonoids Research Articles

Scutellarein: a review of chemistry and pharmacology.

To get a better understanding of the scientific values of flavone scutellarein (SCT), and to encourage its applications in human health, the current review systematically summarizes the natural observation, biosynthesis, synthesis, pharmacology, pharmacokinetics, and recent synthetic advances. Scientific sources to search for references included Google Scholar, Scopus, Web of Science, PubMed, Sci-Finder, and journal websites. The references have been collected from the 1970s to the present. "Scutellarein" is the most meaningful keyword to search for publications, in which it was used alone or in combination with other keywords. SCT as a hydrophobic flavonoid can be found in various medicinal plants of the families Lamiaceae, Compositae, and Verbenaceae. Flavone SCT has drawn much interest due to its wide pharmacological effects, such as anticancer, anti-inflammation, antioxidant, antiobesity, and vasorelaxant. The SCT treatments also possessed a lot of positive results in the neuron, liver, heart, lung, kidney, bone, and skin protective experiments, and human sperm function enhancement. Its underlying mechanism of action may relate to the apoptotic program and cytokine inhibition by regulating a panel of the signaling pathway, e.g., NF-κB (nuclear factor kappa B)/MAPK (mitogen-activated protein kinase), IκBa (nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitors alpha)/NF-κB, TRAF2 (tumor necrosis factor receptor-associated factor 2)/NF-κB, and PTEN (phosphatase and tension homologue deleted on chromosome 10)/Akt (protein kinase B)/NF-κB. In addition, the metabolic actions and synthetic derivative promotions of SCT were mostly based on the substitution of hydroxyl groups. Collectively, the studies that aim to highlight the role of scutellarein in preclinical and clinical treatments are urgently needed. More and more experiments to improve its bioavailability are expected.

In situ ionic liquid-assisted mechanochemical extraction and aqueous two-phase system enrichment of hydrophobic flavonoids from rose

An effective in situ ionic liquid-assisted mechanochemical extraction (MCE) and aqueous two-phase system (ATPS) enrichment method was established. An ATPS can be formed to accomplish the enrichment of the compounds while realizing the MCE for medicinal crop, aiming to establish a pretreatment method for quantitative analysis of active compounds in complex matrices. The effects of ionic liquid amount, milling time, salt amount, vortex time and pH value were investigated, and the optimal conditions for the response surface method were obtained as follows: 1-butyl-3-methylimidazolium bromide amount of 250.37 mg, milling time of 1.99 min and salt amount of 4.38 g. After obtaining the optimal conditions, the method has the correlation coefficients of 0.9963–0.9996, and the limits of detection for the analytes were ranged from 0.05 to 0.08 ng/mL. Besides, the recoveries of rose samples were 84–119% at spiked levels of 0.1 and 1 µg/mL. Compared with other extraction methods, this method synchronously combines MCE and ATPS enrichment techniques, which is environmentally friendly and shortens the extraction time, and can effectively extract hydrophobic flavonoids from roses without any organic solvents.

Morus alba; A Ray of Hope for Psychiatric Illnesses

Purpose: Over the years, plants have been used in treatment of various health ailments. Morus alba also known as White Mulberry is a deciduous tree which belongs to family Moraceae. Mulberry is rich in antioxidants such as hydrophobic flavonoids, polyphenols, carotenoids, vitamin A, C and E.
 Materials and Methods: This study analyses the central nervous system activities including memory enhancement, learning abilities, changes in behavior, cognition, anxiety and depression. These effects will be studied on experimental mice, which will be distributed in control and test groups. Aqueous fruit extract prepared by Maceration extraction will be given to test group in three different doses per oral over a time period of 30 days, whereas control will be given water for injection for same duration.
 Findings: Afterwards, changes in aforementioned effects will be observed to determine the pharmacological effects of taken fruit. The obtained results suggest an antidepressant like effect of mulberry in the initial two weeks of dosing. Afterwards it shows anxiolytic effect at higher doses.
 Implications to Theory, Practice and Policy: All these tests can be repeated weekly while dosing the animals daily for 90 days for chronic toxicity analysis. Furthermore, we can add a brain biopsy/histopathology to evaluate the changes in chemical neurotransmitters.

Regulation Mechanism of Phenolic Hydroxyl Number on Self-Assembly and Interaction between Edible Dock Protein and Hydrophobic Flavonoids.

In this study, galangin (Gal), kaempferol (Kae), quercetin (Que), and myricetin (Myr) were chosen as the representative flavonoids with different phenolic hydroxyl numbers in the B-ring. The edible dock protein (EDP) was chosen as the new plant protein. Based on this, the regulation mechanism of the phenolic hydroxyl number on the self-assembly behavior and molecular interaction between EDP and flavonoid components were investigated. Results indicated that the loading capacity order of flavonoids within the EDP nanomicelles was Myr (10.92%) > Que (9.56%) > Kae (6.63%) > Gal (5.55%). Moreover, this order was consistent with the order of the hydroxyl number in the flavonoid's B ring: Myr (3) > Que (2) > Kae (1) > Gal (0). The micro morphology exhibited that four flavonoid-EDP nanomicelles had a core-shell structure. In the meantime, the EDP encapsulation remarkably improved the flavonoids' water solubility, storage stability, and sustained release characteristics. During the interaction of EDP and flavonoids, the noncovalent interactions including van der Waals forces, hydrophobic interaction, and hydrogen bonding were the main binding forces. All of the results demonstrated that the hydroxyl number of bioactive compounds is a critical factor for developing a delivery system with high loading ability and stability.

A stable core-shell metal-organic framework@covalent organic framework composite as solid-phase extraction adsorbent for selective enrichment and determination of flavonoids

Hydrophobization and stability is crucial for the practical application of most metal-organic frameworks (MOFs) in extraction technique. In this study, a stable core-shell MOF@COF composite (NH2-MIL-101(Fe)@TAPB-FPBA-COF) was successfully prepared by Schiff base reaction and applied to solid-phase extraction (SPE) of hydrophobic flavonoids. Notably, the TAPB-FPBA-COF shell acts as a hydrophobic "shield", which not only improves the hydrophobicity and stability of hydrophilic NH2-MIL-101(Fe), but also makes the extraction efficiency of flavonoids from MOF@COF composite significantly higher than that of pure NH2-MIL-101(Fe) and TAPB-FPBA-COF. In addition, a sensitive analytical method with excellent linearities (0.1–500 ng mL−1, R2 ≥ 0.9967), low limits of detection (0.02–0.04 ng mL−1 for water; 0.04–0.07 ng mL−1 for grape juice; 0.06–0.08 ng mL−1 for honey), good repeatability (intra-day/inter-day precision are 1.86–5.37%/1.82–7.79%, respectively) and only 5 mg of adsorbent per cartridge was established by optimizing the SPE process combined with high performance liquid chromatography with ultraviolet-visible detector (HPLC-UV). Meanwhile, selectivity study and comparative experiments with the commercial C18 adsorbent showed that the MOF@COF adsorbent exhibited satisfactory extraction efficiency for flavonoids due to multiple interactions such as hydrogen bonding, hydrophobic, and π-π interactions. Finally, the good recoveries in grape juice (84.5–102.5%) and honey (87.5–104.6%) samples further validated the applicability of the proposed method in complex samples.

Development of stable and functional encapsulated chrysin using casein–polysaccharide complexes for food applications

SummaryChrysin is a hydrophobic flavonoid with multiple health benefits. The various applications of chrysin are challenged by its poor solubility, instability and loss of bioactivity. Casein–chrysin complex and casein–polysaccharide–chrysin complexes have developed to overcome these limitations. Very high encapsulation efficiency of 98.23 ± 0.22% was achieved with casein–inulin–chrysin complex. The chrysin was able to form a stable casein–polysaccharide–chrysin complex suspension with a hydrodynamic diameter of 382.3 nm, zeta potential value of −12.3 mV and a Polydispersity Index (PDI) of 27.7. The antioxidant activity of chrysin increased about threefold after encapsulation. The release of chrysin from its encapsulated complexes to different buffers in the pH range of 3 to 10 was studied at 1:10 ratio. At the end of 48 h, only 6%–8% of chrysin was released in the pH range 3–4, 33%–58% at pH 5–9 and 62% at pH 10. The chrysin encapsulated in casein–inulin–chrysin complex was able to overcome the rapid release of chrysin from the casein–chrysin complex. The results indicate the successful development of a stable encapsulated chrysin complex which can overcome the various limitations of chrysin in its potential applications.

Separation and purification of target flavonoids using covalently connected MOFs@boronic acid-functionalized-COFs magnetic hybrids: Precise identification and enhanced stability

The magnetic boronate based sorbents have been widely used to separation of cis-diol containing flavonoids. However, It's still challenging due to its chemical structural fragility and low grafting efficiency. The major obstacles are low concentration, the hydrophobicity of flavoniods, and complexity of crude extract solutions. For solving these problems, a new kind of covalently connect MOF@boronic acid-functionalized-COFs core–shell hybrid composites based on magnetic colloidal nanocrystal clusters (MCNCs), MCNCs@NH2-UiO-66@BTCA-BA-COFs, with high surface area, abundant binding sites and excellent chemical and structurally stability were synthesized for enhancing the structure stability and selective recognition efficiency. The alkynylation COFs were not only to be facilely grated on the surface of magnetic microsphere@NH2-UiO-66 via Schiff-based reaction but also beneficial to the further modification of azide phenylboronic acid group via click reaction. Such mentioned advantages and covalently connect click strategy could generate highly structure stable and strong binding sites for the template flavonoids (Naringin, NRG). Adsorption equilibrium experiments were reached rapidly within 120 min, and the maximum equilibrium binding capacities of MCNCs@PDA@NH2-UiO-66@BTCA-BA-COFs were 31.20 µmol g−1 for NRG. Moreover, MCNCs@PDA@NH2-UiO-66@BTCA-BA-COFs exhibited a stronger selectivity towards NRG than other competitive targets (i.e rutin, catechol, hesperetin, o-nitrophenol). The MCNCs@PDA@NH2-UiO-66@BTCA-BA-COFs have shown outstanding reusability of 91.99 % loss in enrichment performance towards NRG after seven times repeatedly. The obtained MCNCs@PDA@NH2-UiO-66@BTCA-BA-COFs-based mass spectrum (MS) methods were applied to analyze the purity of NRG products. As excepted, a commercially available NRG with purity (approximately 60 %) could be effectively extracted and concentrated to 93.15 % purity. More interestingly, the separation performance of the sorbents was influenced by hydrophilic and hydrophobic performance. This approach provided an idea for constructing a new kind of hybrid sorbents with both enhanced functionality, suitable hydrophobic performance and fast magnetic-response behavior, which is of great significance to the field of separation and purification of hydrophobic flavonoids.

Thymoquinone induces apoptosis in temozolomide-resistant glioblastoma cells via the p38 mitogen-activated protein kinase signaling pathway.

Temozolomide (TMZ) can cross the blood-brain barrier (BBB) and deliver methyl groups to the purine (guanine) bases of DNA, leading to mispairing during DNA replication and subsequent cell death. However, increased expression of the repair enzyme methyl guanine methyltransferase (MGMT), which removes methyl groups from purine bases, counteracts methylation by TMZ. We evaluated the anticancer potential of thymoquinone (TQ), a hydrophobic flavonoid that inhibits resistance and induces apoptosis in various cancer cells, both in vitro and in vivo. In vitro experiments showed that compared with the Hs683 and M059J cell lines, U251 cells were more sensitive to TMZ. Compared to U251 cells, U251R cells, a TMZ drug-resistant strain established in this study, are characterized by increased expression of phosphorylated extracellular signal-regulated kinase (p-ERK) and MGMT. TQ treatments induced apoptosis in all cell lines. The p38 mitogen-activated protein kinase signal pathway was mainly activated in U251 and U251R cells; however, p-ERK and MGMT upregulation could not suppress TQ effects. Furthermore, si-p38 pretreatment of U251R cells in TQ treatments inhibited cell apoptosis. We speculate that TQ contributed to the phosphorylation and activation of p38, but not of ERK-induced apoptosis (irrespective of TMZ resistance). In vivo, U251R-derived tumors subcutaneously inoculated in nude mice exhibited significant tumor volume reduction after TQ or TQ + TMZ cotreatments. High-performance liquid chromatography assay confirmed the presence of TQ in murine brain tissues. Our findings demonstrate that TQ can effectively cross the BBB and function alone or in combination with TMZ to treat glioblastoma.

NANOEMULGEL BASED ON GUAR GUM AND PLURONIC® F127 CONTAINING ENCAPSULATED HESPERIDIN WITH ANTIOXIDANT POTENTIAL

Introduction: The development of antioxidant cosmetic products based on natural products added to nanotechnology is gaining more and more prominence. However, some of these actives are hydrophobic, which makes their placement in aqueous systems impossible. As a strategy to deliver hydrophobic actives in hydrophilic gels, nanoemulgels have been presented.
 Materials and Methods: The present study aimed to prepare an aqueous nanoemulgel based on guar gum and Pluronic® F127 as a strategy for the delivery of hesperidin, a hydrophobic flavonoid. A nanoemulsion was prepared and characterized to be incorporated into the gel. The formed nanoemulgel was evaluated for rheology and antioxidant activity.
 Results and Discussion: The nanoemulsion had a particle size of 192 ± 4 nm, a polydispersity index of 0.11 ± 0.01 and a zeta potential of -32.1 ± 0.9 mV. The encapsulation efficiency obtained was 99.35% and the rheological study of the nanoemulgel showed satisfactory gel characteristics for topical use. The antioxidant potential of nanoemulsions by the DPPH method presented an IC50 value of 14.4 ±1.3 μg mL-1 expressed in hesperidin equivalent to 17.4 mg mL-1 of the nanoemulgel. The formulated nanoemulgel delivered hesperidinsuccessfully without affecting its antioxidant properties, showing promise as a cosmetic for topical anti-aging use.

Maillard induced glycation of β-casein for enhanced stability of the self-assembly micelles against acidic and calcium environment

Bovine β-casein (β-CN) has attracted increasingly interest as biocompatible nanocarrier for hydrophobic flavonoid due to its self-assembly ability to form micelles. This paper reported Maillard induced glycation reaction of β-CN using dextran in order to improve stability of naringenin-loaded β-CN micelles under acidic and high calcium environments. Our results showed that solubility of β-CN-graft-dextran was remarkable increased at acidic pH and the conjugation with 20 kDa dextran had the highest level of graft degree. Glycation restrained β-CN from aggregating around pH 5.0 where was close to the isoelectric point, forming spherical micelles with irregular and rough surfaces, which were significantly larger than the micelles at pH 7.0. β-CN-graft-dextran also overcame destabilization of the micelles induced by excess calcium and had no impact on the chelating ability of calcium. These findings appeared to be promising for future applications of modified β-CN-graft-dextran based on Maillard reaction as fairly stable nanocarrier under extreme condition.

The Effect of pH and Sodium Caseinate on the Aqueous Solubility, Stability, and Crystallinity of Rutin towards Concentrated Colloidally Stable Particles for the Incorporation into Functional Foods.

Poor water solubility and low bioavailability of hydrophobic flavonoids such as rutin remain as substantial challenges to their oral delivery via functional foods. In this study, the effect of pH and the addition of a protein (sodium caseinate; NaCas) on the aqueous solubility and stability of rutin was studied, from which an efficient delivery system for the incorporation of rutin into functional food products was developed. The aqueous solubility, chemical stability, crystallinity, and morphology of rutin (0.1–5% w/v) under various pH (1–11) and protein concentrations (0.2–8% w/v) were studied. To manufacture the concentrated colloidally stable rutin–NaCas particles, rutin was dissolved and deprotonated in a NaCas solution at alkaline pH before its subsequent neutralisation at pH 7. The excess water was removed using ultrafiltration to improve the loading capacity. Rutin showed the highest solubility at pH 11, while the addition of NaCas resulted in the improvement of both solubility and chemical stability. Critically, to achieve particles with colloidal stability, the NaCas:rutin ratio (w/w) had to be greater than 2.5 and 40 respectively for the lowest (0.2% w/v) and highest (4 to 8% w/v) concentrations of NaCas. The rutin–NaCas particles in the concentrated formulations were physically stable, with a size in the range of 185 to 230 nm and zeta potential of −36.8 to −38.1 mV, depending on the NaCas:rutin ratio. Encapsulation efficiency and loading capacity of rutin in different systems were 76% to 83% and 2% to 22%, respectively. The concentrated formulation containing 5% w/v NaCas and 2% w/v rutin was chosen as the most efficient delivery system due to the ideal protein:flavonoid ratio (2.5:1), which resulted in the highest loading capacity (22%). Taken together, the findings show that the delivery system developed in this study can be a promising method for the incorporation of a high concentration of hydrophobic flavonoids such as rutin into functional foods.

Amphiphilic star block copolymer micelles in saline as effective vehicle for quercetin solubilization

There has been an enormous interest in improving the therapeutic efficacy of hydrophobic flavonoids through enhancement of their bioavailability. A carrier capable to effectively solubilize flavonoids is expected to support the chemical/structural integrity of flavonoid molecule, and hence, its antioxidant properties. In this paper, the effectiveness of saline solutions of an amphiphilic star block ethylene oxide-propylene oxide copolymer (Tetronic®T904) has been investigated for solubilizing quercetin (QN). T904 self-assembles in aqueous solution above its critical micellization temperature (CMT) that depends on solution concentration, temperature, pH and presence of salt. We have studied the solubilization of QN in T904 micelles at different temperature, concentration and salt (sodium chloride) concentration using scattering and spectral techniques. Our findings suggest that, at a given temperature, QN solubility is influenced by the concentration of salt and copolymer. When compared to its linear counterparts (the Pluronics®), T904 solutions offered superior solubilization. 2D NOESY NMR observations revealed that QN occupied the periphery of the hydrophobic core of micelles. Such an environment can protect the drug against oxidation in aqueous phase.

Design and evaluation of natural deep eutectic solvents system for chrysin to elicit its solubility, stability, and bioactivity

Natural deep eutectic solvents (NDESs) based on choline chloride (ChCl) together with glycerol (Gly), urea (U), and l-glutamine (L-Gln) were used for the improvement of solubility, stability, and bioactivity of chrysin (CHR). CHR is a promising flavonoid that has multifarious biological activities but a very low water solubility limits its clinical applications. A 21 different NDESs preparation were prepared and evaluated for solubility, pH, and kinematic viscosity. Among the different NDESs prepared, the ChCl: L-Gln: Gly combination gave the optimum solubility of CHR (10.13 ± 1.1 mg/mL). Motic microscopy and Differential scanning calorimetry revealed a transition in the crystalline nature of CHR in NDESs. Furthermore, FTIR and 1NMR were used to investigate the nature of molecular interaction exhibited by the selected NDESs-CHR preparation. The pH stability studies showed the protective effect of CHR in NDESs at simulated gastric conditions. The in vitro dissolution studies revealed an improvement in the dissolution rate of CHR presented in NDESs, compared to pure CHR. Besides, the in vitro cytotoxicity unveils a significant anti-proliferative activity of NDESs-CHR on Hep-G2 cells. The pharmacokinetic study revealed a 2.13-folds increment in oral bioavailability of CHR in selected NDESs preparation. Therefore, the presented study reports NDESs as a promising carrier considering their biosafety issues for hydrophobic flavonoids which could draw attention in pharmaceutical and food science.

Hydrophobic interaction and hydrogen bonding driving the self-assembling of quinoa protein and flavonoids

To improve the physicochemical stability of hydrophobic flavonoids, a series of protein-based nanomicelles have been developed in recent years. However, the quinoa protein (QP) nanomicelles and its interactions with different flavonoids were rarely reported. In this study, the QP nanomicelles (48.6 nm) were initially prepared. Then, quercetin (Que), curcumin (Cur), luteolin (Lut) and resveratrol (Res) were successfully assembled into the hydrophobic region of QP nanomicelles, giving the loading capacity of 33.9%, 8.0%, 17.8% and 6.4%, respectively. Moreover, this self-assembly significantly enhanced the solubility and stability of four flavonoids. The molecular interactions were further investigated. Results showed that hydrophobic interaction and hydrogen bonding were the main interaction driving forces between QP and hydrophobic flavonoids. The present work provided valuable evidences for the application of quinoa protein in functional foods.

Nanoencapsulation of food bioactives in supramolecular assemblies based on cyclodextrins and surfactant

The bioavailability of poorly soluble food ingredients can be achieved by their encapsulation into the 3D macrocyclic structure or self-assembled surfactant micelles. In this study, the mixed self-assembly of cyclodextrins (CDs) and cationic surfactant, 1-hexadecyl-4-(2-(1-methylpyridin-1-ium-4-yl)vinyl)pyridin-1-ium chloride, was studied by a set of physicochemical methods. It was shown using tensiometry and conductometry that the presence of CDs in the micellar medium of this surfactant increases the critical aggregation concentration. Moreover, NMR spectroscopy and spectrophotometry revealed the interaction between the alkyl tail of surfactant and the internal cavity of CDs. It is interesting to note that in the case of γ-CD and HP-β-CD there was additional binding by the vinyl group of surfactant. The observed patterns of aggregation behavior were confirmed by the method of solubilization of hydrophobic substances. Spectrophotometric monitoring of the solubilization of hydrophobic flavonoids (rutin and quercetin) demonstrated that mixed assemblies enriched with surfactant are capable of binding the flavonoid, while they show poor binding ability towards flavonol compound in the presence of a small amount of surfactant.. Variation of the component ratio in the supramolecular CD–surfactant system also allows adjusting the biological properties. Systems with an excess of CD are less toxic to the cells of test microorganisms, herewith, an increase of the surfactant content in a mixture with CD leads to an increase in both antimicrobial and hemolytic activities. Therefore, when using CD complex-based supramolecular approach for food safety, it is necessary to take into account the toxic properties of the base components of the supramolecular mixture.

Effects of genipin concentration on cross-linked β-casein micelles as nanocarrier of naringenin: Colloidal properties, structural characterization and controlled release

β-casein (β-CN), an amphiphilic protein from bovine milk, has attracted increasingly interest as biocompatible, non-toxic nanocarrier in foods due to its ability to form micellar nanostructures through self-assembling. In this study, the formation of genipin-crosslinked β-casein micelles (G-CNMs) was investigated for the delivery of naringenin, a hydrophobic flavonoid abundant in grapefruits. Our results showed that the degree of micellar crosslinking was dependent on the genipin concentration, as indicated by SDS-PAGE and GPC-MALLS. At the suitable genipin concentration (β-CN/genipin molar ratio of 1:20), the G-CNMs showed intra-micellar crosslinking with average hydrodynamic radius (9.35 nm) as measured by dynamic light scattering. We found that the degree of crosslinking has a significant influence on the aspects of stability and controlled release. G-CNMs overcame destabilization of micelles induced by acid pH (pH = 2) when β-CN/genipin molar ratio was 1:15 or 1:20, while the stability against the high NaCl concentration was not influenced. Specifically, as compared to untreated CNMs, all types of G-CNMs in phosphate buffered saline buffer (10 mM, pH 7.4) revealed slower releases of naringenin. With the increase of genipin amount, the controlled drug release properties was enhanced. Such findings appear to be promising for future applications of β-CN as controlled release nanocarrier for hydrophobic functional ingredient, whose characteristics can be modulated by tailored genipin crosslinking.

Bovine beta-casein micelles as delivery systems for hydrophobic flavonoids

The milk protein β-casein (β-CN) is an intrinsically unstructured amphiphilic protein that self-assembles into micelles. Naringenin is the main hydrophobic flavanone in grapefruit and has several beneficial biological effects: it exhibits, for example, antioxidant, anticancer and anti-inflammatory activity. This paper shows that naringenin can be encapsulated in β-CN micelles. Fluorescence spectroscopy, molecular docking modelling, dynamic light scattering (DLS), static light scattering (SLS) and isothermal titration calorimetry (ITC) were applied to characterize the effect of naringenin on the protein association behavior and properties of the resulting micelles. Naringenin binds to β-CN at both pH 7 and pH 2, promotes the formation of micelles with a well-defined size distribution and stabilizes the micelles. It was found that naringenin-containing β-CN micelles have a lower critical micelle concentration (CMC) and a larger aggregation number (Nagg) compared to pure β-CN micelles. SLS and multi-angle DLS results suggest considerable differences between the structures of pure β-CN micelles and naringenin-containing β-CN micelles. In the presence of naringenin spherical micelles were formed with a relatively loose core (“hollow sphere”), while the pure β-CN micelles are smaller and seem to be elliptic. Notably, by uptake of naringenin in the micelles, the concentration of naringenin in aqueous solution could be raised considerably. These findings lead to the conclusion that β-CN micelles are very promising as effective delivery nano-vehicles for hydrophobic bioactive compounds.

Interactions of flavonoids with α-amylase and starch slowing down its digestion.

Starch is digested to glucose in the intestine and absorbed into the body. If the increased blood concentrations of sugar after meals decrease slowly or are maintained for a long time, various adverse effects are induced. Therefore, it is important to decrease the rate of the digestibility of starch in the intestine in the patients of hyperglycemia. One of the ways to effect a decrease is the inhibition of α-amylase secreted from the pancreas. Flavonoids are a group of compounds that can inhibit this enzyme's activity, and many investigators have studied the flavonoid-dependent inhibition of this enzyme and presented mechanisms for the inhibition of its activity. Starch containing foods, however, cooked or ingested with flavonoid containing foods are mixed with saliva and gastric juice in the stomach. Thus, flavonoids in the foods can interact with starch and can react with nitrous acid derived from the oral cavity in the stomach before being transported to the intestine. This review mainly deals with: (i) the inhibition of α-amylase activity by flavonoids suggesting the mechanisms of the inhibition, (ii) suppression of starch digestion by flavonoids by forming starch-flavonoid complexes by hydrophobic interactions, and (iii) formation of starch not easily digested by α-amylase by the formation of covalent bonds between flavonoids and starch during cooking and in the stomach. In addition, the cooperation of flavonoids with fatty acids are discussed taking their binding to amylose into account.

Low vapor pressure deficit reduces glandular trichome density and modifies the chemical composition of cuticular waxes in silver birch leaves.

Cuticular wax layer is the first barrier against the outside environment and the first defense encountered by herbivores and pathogens. The effects of environmental factors on cuticular chemistry, and on the formation of glandular trichomes that account for the storage and secretion of lipophilic compounds to the leaf surface are poorly understood. Low vapor pressure deficit (VPD) has shown to reduce the nitrogen (N) status of plants. Thus, we studied the effects of elevated air humidity, indicated as VPD, and the effect of N fertilization on cuticular waxes and glandular trichome density in silver birch (Betula pendula Roth). Experiments were carried out in growth chambers with juvenile plants and in a long-term field experiment with older trees. Low VPD reduced the glandular trichome density in both experiments, in chamber and in field. The contents of the major triterpenoid and flavonoid aglycones correlated positively with glandular trichome density, which supports the role of trichomes in the exudation of secondary compounds to the leaf surface. A closer examination of the cuticular wax chemistry in the chamber experiment revealed that low VPD and N supply affected the composition of cuticular waxes, but not the total wax content. The deposition of different wax compounds followed a co-ordinated pattern in birch leaves, but different compound groups varied in their responses to N fertilization and low VPD. Low VPD reduced the hydrophobicity of cuticular waxes, as demonstrated by lower alkane content and less hydrophobic flavonoid profile in low VPD than in high VPD. Reduced hydrophobicity of the wax layer is presumed to increase leaf wettability. Together with reduced trichome density in low VPD it may enhance the susceptibility of trees to fungal pathogens and herbivores. High N supply under low VPD reduced the effect of low VPD on the cuticular wax composition. Total fatty acid content and the expression of β-amyrin synthase were lower under high N supply than under moderate N supply irrespective of VPD treatment. Nitrogen availability and decreasing VPD will modify leaf surface properties in silver birch and thereby affect tree defence against abiotic and biotic stress factors that emerge under climate change.

Study of the interaction of flavonoids with 3-mercaptopropionic acid modified CdTe quantum dots mediated by cetyltrimethyl ammonium bromide in aqueous medium

Flavonoids are polyphenols that help the maintenance of health, aiding the prevention of diseases. In this work, CdTe QDs coated with 3-mercaptopropionic acid (3MPA), with an average size of 2.7nm, were used as photoluminescence probe for flavonoids in different conditions. The interaction between 14 flavonoids and QDs was evaluated in aqueous dispersions in the absence and in the presence of cetyltrimethylammonium bromide (CTAB). To establish a relationship between photoluminescence quenching and the concentration of flavonoids, the Stern–Volmer model was used. In the absence of CTAB, the linear ranges for quercetin, morin and rutin were from 5.0×10−6molL−1 to 6.0×10−5molL−1 and from 1.0×10−5molL−1 to 6.0×10−4molL−1 for kaempferol. The sensibility of the Stern–Volmer curves (Ks) indicated that quercetin interacts more strongly with the probe: Ks quercetin>Ks kaempferol>Ks rutin>Ks morin. The conjugation extension in the 3 rings, and the acidic hydroxyl groups (positions 3ʹand 4ʹ) in the B-ring enhanced the interaction with 3MPA-CdTe QDs. The other flavonoids do not interact with the probe at 10−5molL−1 level. In CTAB organized dispersions, Ks 3-hydroxyflavone>Ks 7-hydroxyflavone>Ks flavona>Ks rutin in the range from 1.0×10−6molL−1 to 1.2×10−5molL−1 for flavones and of 1.0×10−6molL−1 to 1.0×10−5molL−1 for rutin. Dynamic light scattering, conductometric measurements and microenvironment polarity studies were employed to elucidate the QDs–flavonoids interaction in systems containing CTAB. The quenching can be attributed to the preferential solubility of hydrophobic flavonoid in the palisade layer of the CTAB aggregates adsorbed on the surface of the 3MPA CdTe QDs.