Flavonoid adsorption and stability on titania-functionalized silica nanoparticles

Epigallocatechin-3-gallate adsorbed on core-shell gold nanorod@mesoporous silica nanoparticles, an antioxidant nanomaterial with photothermal properties

Epigallocatechin-3-gallate (EGCG) exhibits several pharmacological activities with potential benefits for human health, however, it has low oral bioavailability. A promising approach is to transport EGCG in a nanostructured system to protect it until it reaches the site of action and also allow combining chemotherapy with phototherapy to improve its therapeutic efficiency. The aim of this work was to synthesize GNR@mSiO2-NH2/EGCG and characterize the adsorption process, its antioxidant activity, properties and photothermal stability, for its potential use in chemo-photothermal therapy. The nanosystem presented good encapsulation efficiency (19.2 %) and EGCG loading capacity (6.0 %). The DPPH• free radical scavenging capacity (RSA) and chelating activity of the nanosystem was 60.7 ± 6.9 % and 71.0 ± 6.4 % at an EGCG equivalent concentration of 1 µg/mL and 30 µg/mL, respectively. The core-shell NPs presented a good photothermal transduction efficiency of 17 %. EGCG free, as well as its RSA and chelating activity, remained stable after NIR irradiation (808 nm, 7 W/cm2). The morphology of GNR@mSiO2 remained intact after being irradiated with NIR, however, ultrasmall gold NPs could be observed, probably a product of photocracking of GNR. In summary, the nanosystem has good antioxidant activity, photothermal stability, and photothermal transduction ability making it potentially useful for chemo-photothermal therapy.

Preparation and characterization of quercetin@ZIF-L/GO@AgNPs nanocomposite film for room-temperature strawberry preservation

Fresh strawberries are easily contaminated by microorganisms after picking. Therefore, how to effectively store and keep fresh strawberries has been a hot topic for scientists to study. In this study, we prepared a leaf shaped metal organic framework nanomaterial loaded with quercetin (Quercetin@ZIF-L) at first, which can achieve effective loading of quercetin (96%) within 45 min and has a controlled release effect under acidic conditions. In addition, by cleverly combining satellite graphene oxide @ silver nanoparticles (GO@AgNPs) with slow precipitation performance, Quercetin@ZIF-L/GO@AgNPs nanocomposite film with larger pore size and larger specific surface area was prepared by scraping method. The characterization data of water flux, retention rate, flux recovery rate and water vapor permeability show that the composite film has good physical properties. The experiment of film packaging showed that the fresh life of strawberry could be extended from 3 to 8 days, which significantly improved the storage and freshness cycle of strawberry. At the same time, the metal migration test proved that the residual amount of silver ion in strawberry met the EU standard and zinc ions are beneficial to the health, enriching the types of high-performance fresh-keeping materials and broadening the application.

Morin loaded mesoporous molecular sieves as novel devices to the potential treatment of tumor pathologies

Morin is an antioxidant and anticancer flavonoid, extracted from natural sources, that may exert beneficial effects for several pathologies. Despite this, the administration of morin represents a challenge due to its low aqueous solubility. Mesoporous silica materials have emerged as biocompatible tools for drug delivery, as their pore size can be modulated for maximum surface area to volume ratio. In this contribution, we evaluate the ability of iron-modified mesoporous materials, for morin loading and controlled delivery. The SBA-15 and MCM-41 sieves were synthesized and modified with iron (metal content 4.02 and 6.27 % wt, respectivily). Characterization by transmission electron microscopy, XRD and UV-Vis revealed adequate pore size and agglomerates of very small metallic nanospecies (nanoclusters), without larger iron oxide nanoparticles. FT-IR spectra confirmed the presence of silanol groups in the solid hosts, which can interact with different groups present in morin molecules. SBA-15 materials were more efficient in terms of morin loading capacity (LC) due to their larger pore diameter. LC was more than 35% for SBA-15 materials when adsorptions studies were carried out with 9 mg of drug. Antioxidant activity were assayed by using DPPH test. Free iron materials presented a significate improvement as antioxidants after morin incorporation, reaching a scavenging activity of almost a 90%. On the other hand, in iron modified mesoporous materials, the presence of morin did not affect the scavenging activity. The results could be related with the formation of a complex between the flavonoid and the iron. Finally, biosafety studies using normal epithelial cells revealed that neither the loaded nor the unloaded materials exerted toxicity, even at doses of 1 mg/ml. These findings expand knowledge about mesoporous materials as suitable carriers of flavonoids with the aim of improving therapies for a wide range of pathologies.

The role of quercetin in the formation of titanium dioxide nanoparticles for nanomedical applications

The current work aimed to synthesize and characterize titanium dioxide nanoparticles (TiO₂NPs) using quercetin (QE) and evaluate their biological activities, i.e., anti-hemolytic, anti-inflammatory, and cytotoxicity effects. The crystallographic phase and morphology of biosynthesized QE-TiO₂NPs were characterized by XRD (X-Ray Diffraction) and TEM/FE-SEM (Transmission/Field-Emission Scanning Electron Microscopy) micrographs. Functional groups involved in the synthesis process were determined by FTIR spectroscopy (Fourier Transform-Infrared Spectroscopy). Based on the characterization results, selected QE-TiO₂NPs showed a rutile phase, spherical shape, and a size range of 7.3-39 nm. The QE-TiO₂NPs did not show a hemolytic effect. They indicated 95.3% red blood cells (RBCs) membrane stabilization activity and 82.6% inhibition of bovine serum albumin (BSA) denaturation, similar to a standard drug, which proved their anti-inflammatory effects. The attained results from cytotoxicity studies revealed the toxic effects of QE-TiO₂NPs with IC50 values below 100 and 50 μg/mL for human breast cancer cells of MCF-7 and melanoma cancer cells of A375, respectively. These NPs did not significantly affect normal skin fibroblast cells up to 50 μg/mL and only showed a 16% inhibition rate on the cell viability at 100 μg/mL. These NPs also induced excessive ROS generation. This work established the blood/biocompatibility and excellent nanomedical applications of biosynthesized QE-TiO₂NPs.

Mechanism of Mesoporous Silica Nanoparticle Interaction with Hairy Root Cultures during Nanoharvesting of Biomolecules

Cellular uptake and expulsion mechanisms of engineered mesoporous silica nanoparticles (MSNPs) are important in their design for novel biomolecule isolation and delivery applications such as nanoharvesting, defined as using nanocarriers to transport and isolate valuable therapeutics (secondary metabolites) out of living plant organ cultures (e.g., hairy roots). Here, temperature-dependent MSNP uptake and recovery processes in hairy roots are examined as a function of surface chemistry. MSNP uptake into hairy roots and time-dependent expulsion are quantified using Ti content (present for biomolecule binding) and fluorescence spectroscopy of fluorescently tagged MSNPs, respectively. The results suggest that functionalization and surface charge (regulated by amine group attachment) play the biggest role in the effectiveness of uptake and recovery. Comparison of MSNP interactions with hairy roots at 4 and 23 °C shows that weakly charged MSNPs functionalized only with Ti are taken up and expelled by thermally activated mechanisms, while amine-modified positively charged particles are taken up and expelled mainly by direct penetration of cell walls. Amine-functionalized MSNPs move spontaneously in and out of plant cells by dynamic exchange with a residence time of 20 ± 5 min, suggesting promise as a biomolecule nanoharvesting platform for plant organ cultures.

Nanoantioxidant-Based Silica Particles as Flavonoid Carrier for Drug Delivery Applications

Nanosystems used in pharmaceutical formulations have shown promising results in enhancing the administration of drugs of difficult formulations. In particular, porous silica nanoparticles have demonstrated excellent properties for application in biological systems; however, there are still several challenges related to the development of more effective and biocompatible materials. An interesting approach to enhance these nanomaterials has been the development of nanoantioxidant carriers. In this work, a hybrid nanoantioxidant carrier based on porous silica nanoplatform with rosmarinic acid antioxidant immobilized on its surface were developed and characterized. Techniques such as dynamic light scattering (DLS), zeta potential, transmission electron microscopy (TEM), N2 adsorption-desorption measurements, differential scanning calorimetry (DSC), Fourier transform-infrared spectroscopy (FT-IR), and 2,2-diphenyl-1-picrylhydrazyl (DPPH●) assay were used to characterize and evaluate the antioxidant activity of nanocarriers. In addition, drug release profile was evaluated using two biorelevant media. The antioxidant activity of rosmarinic acid was maintained, suggesting the correct disposition of the moiety. Kinetic studies reveal that more morin is released in the simulated intestinal fluid than in the gastric one, while an anomalous non-Fickian release mechanism was observed. These results suggest a promising antioxidant nanocarrier suitable for future application in drug delivery.

Nanoharvesting of bioactive materials from living plant cultures using engineered silica nanoparticles

Plant secondary metabolites are valuable therapeutics not readily synthesized by traditional chemistry techniques. Although their enrichment in plant cell cultures is possible following advances in biotechnology, conventional methods of recovery are destructive to the tissues. Nanoharvesting, in which nanoparticles are designed to bind and carry biomolecules out of living cells, offers continuous production of metabolites from plant cultures. Here, nanoharvesting of polyphenolic flavonoids, model plant-derived therapeutics, enriched in Solidago nemoralis hairy root cultures, is performed using engineered mesoporous silica nanoparticles (MSNPs, 165 nm diameter and 950 m2/g surface area) functionalized with both titanium dioxide (TiO2, 425 mg/g particles) for coordination binding sites, and amines (NH2, 145 mg/g particles) to promote cellular internalization. Intracellular uptake and localization of the nanoparticles (in Murashige and Skoog media) in hairy roots were confirmed by tagging the particles with rhodamine B isothiocyanate, incubating the particles with hairy roots, and quenching bulk fluorescence using trypan blue. Nanoharvesting of biologically active flavonoids was demonstrated by observing increased antiradical activity (using 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay) by nanoparticles after exposure to hairy roots (indicating general antioxidant activity), and by the displacement of the radio-ligand [3H]-methyllycaconitine from rat hippocampal nicotinic receptors by solutes recovered from nanoharvested particles (indicating pharmacological activity specific to S. nemoralis flavonoids). Post-nanoharvesting growth suggests that the roots are viable after nanoharvesting, and capable of continued flavonoid synthesis. These observations demonstrate the potential for using engineered nanostructured particles to facilitate continuous isolation of a broad range of biomolecules from living and functioning plant cultures.

Recovery of Polyphenols from Grape Pomace Using Polyethylene Glycol (PEG)-Grafted Silica Particles and PEG-Assisted Cosolvent Elution

Adsorption on a functionalized surface can be an effective way of purifying polyphenols from complex plant extracts. Polymeric resins that rely on hydrophobic interactions suffer from low selectivity, weak affinity towards polyphenols, and lack tunability therefore making the purification of polyphenols less efficient. In this study, a purification process for the recovery of polyphenols from grape pomace extract was successfully developed using hydrogen bonding affinity ligands grafted on silica particles and PEG-assisted elution solvents. Bare silica (SiO₂) and polyethylene glycol (mPEG)-grafted silica microparticles with molecular weights of 2000 and 5000 were tested to determine their polyphenol binding and release characteristics. Functionalizing the surface of bare silica with mPEG ligands increased the adsorption capacity by 7.1- and 11.4-fold for mPEG-2000 and mPEG-5000 compared to bare silica particles, respectively. This was likely due to the introduction of more polyphenol binding sites with mPEG functionalization. Altering the molecular weight (MW) of mPEG grafted on silica surfaces provided tunability in the adsorption capacity. A complete recovery of polyphenols (~99.9%) from mPEG-grafted silica particles was achieved by utilizing PEG–ethanol or PEG–water cosolvent systems. Recovered polyphenols showed up to ~12-fold antioxidant activity compared to grape pomace extract. This study demonstrates that mPEG-grafted silica particles and elution of polyphenols with PEG cosolvents can potentially be used for large-scale purification of polyphenols from complex plant extracts and simplify the use of polyphenols, as PEG facilitates remarkable solvation and is an ideal medium for the final formulation of polyphenols.

Preparation of novel molecularly imprinted magnetic graphene oxide and their application for quercetin determination

In this work, quercetin (Que) molecular imprinted polymer (MIP) material decorated on magnetic graphene oxide (MGO) with high performance was prepared for the first time using a surface-imprinting technique. Magnetic graphene oxide was synthesized using the solvothermal route. Methacrylic acid (MAA) was used as functional monomer, ethylene glycol dimethyl acrylate (EGDMA) as cross-linker; Que. was used as template, for the decoration with MIP. The prepared nanocomposite was examined by different characterization methods including fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM). The adsorption performance was investigated. MGO-MIP was found to have high loading (369 mg g^-1) and selective capacity making the nanomaterial more performant than previous similar reported nanomaterials. The determination of Que. was carried out by mean of magnetic solid phase extraction method coupled with high-performance liquid chromatography (HPLC) and the extraction conditions studies were also performed out. Under the optimized conditions, MGO-MIP showed great performance for the extraction, separation and determination of Que. in green tea and serum samples, compared to the flavonoid analogs luteolin (Lut) and rutin (Rut) in the same matrix samples.

Antioxidant Nanomaterial Based on Core⁻Shell Silica Nanospheres with Surface-Bound Caffeic Acid: A Promising Vehicle for Oxidation-Sensitive Drugs

The design of efficient, biocompatible, and easily prepared vehicles for drug delivery is a subject of great interest for medicine and pharmaceutical sciences. To achieve the above goals, surface functionalization is critical. Here, we report a hybrid nanocarrier consisting of core⁻shell silica nanospheres and the antioxidant caffeic acid linked to the surface, to evaluate their in vitro antioxidant capacity, their capability to protect oxidation-sensitive compounds incorporated in nanoparticles, and to study the interaction with bovine serum albumin protein. The results show that the radical-scavenging activity of immobilized caffeic acid is attenuated in the silica nanospheres; however, other antioxidant properties such as Fe2+-chelating activity and singlet oxygen quenching are enhanced. In addition, caffeic acid is protected from binding to proteins by the nanoparticle, suggesting that this nanosystem is more likely to maintain the antioxidant activity of caffeic acid in biological media. Finally, the natural antioxidant barrier on the nanocarrier is able to delay the degradation of a compound incorporated into this nanovehicle. Considering all findings, this work proposes a suitable tool for pharmaceutical and cosmetic industries as an antioxidant nanocarrier for oxidation-sensitive drugs.

Secondary Metabolites in the Green Synthesis of Metallic Nanoparticles

The ability of organisms and organic compounds to reduce metal ions and stabilize them into nanoparticles (NPs) forms the basis of green synthesis. To date, synthesis of NPs from various metal ions using a diverse array of plant extracts has been reported. However, a clear understanding of the mechanism of green synthesis of NPs is lacking. Although most studies have neglected to analyze the green-synthesized NPs (GNPs) for the presence of compounds derived from the extract, several studies have demonstrated the conjugation of sugars, secondary metabolites, and proteins in these biogenic NPs. Despite several reports on the bioactivities (antimicrobial, antioxidant, cytotoxic, catalytic, etc.) of GNPs, only a handful of studies have compared these activities with their chemically synthesized counterparts. These comparisons have demonstrated that GNPs possess better bioactivities than NPs synthesized by other methods, which might be attributed to the presence of plant-derived compounds in these NPs. The ability of NPs to bind with organic compounds to form a stable complex has huge potential in the harvesting of precious molecules and for drug discovery, if harnessed meticulously. A thorough understanding of the mechanisms of green synthesis and high-throughput screening of stabilizing/capping agents on the physico-chemical properties of GNPs is warranted to realize the full potential of green nanotechnology.

Adsorption and Recovery of Polyphenolic Flavonoids Using TiO2-Functionalized Mesoporous Silica Nanoparticles

Exploiting specific interactions with titania (TiO₂) has been proposed for the separation and recovery of a broad range of biomolecules and natural products, including therapeutic polyphenolic flavonoids which are susceptible to degradation, such as quercetin. Functionalizing mesoporous silica with TiO₂ has many potential advantages over bulk and mesoporous TiO₂ as an adsorbent for natural products, including robust synthetic approaches leading to high surface area, and stable separation platforms. Here, TiO₂-surface-functionalized mesoporous silica nanoparticles (MSNPs) are synthesized and characterized as a function of TiO₂ content (up to 636 mg TiO₂/g). The adsorption isotherms of two polyphenolic flavonoids, quercetin and rutin, were determined (0.05-10 mg/mL in ethanol), and a 100-fold increase in the adsorption capacity was observed relative to functionalized nonporous particles with similar TiO₂ surface coverage. An optimum extent of functionalization (approximately 440 mg TiO₂/g particles) is interpreted from characterization techniques including grazing incidence X-ray scattering (GIXS), high-resolution transmission electron microscopy (HRTEM), and nitrogen adsorption, which examined the interplay between the extent of TiO₂ functionalization and the accessibility of the porous structures. The recovery of flavonoids is demonstrated using ligand displacement in ethanolic citric acid solution (20% w/v), in which greater than 90% recovery can be achieved in a multistep extraction process. The radical scavenging activity (RSA) of the recovered and particle-bound quercetin as measured by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay demonstrates greater than 80% retention of antioxidant activity by both particle-bound and recovered quercetin. These mesoporous titanosilicate materials can serve as a synthetic platform to isolate, recover, and potentially deliver degradation-sensitive natural products to biological systems.

Elicitation as a tool to improve the profiles of high-value secondary metabolites and pharmacological properties of Hypericum perforatum

OBJECTIVES

In this review, we aim at updating the available information on the improvement of the Hypericum perforatum L. (Hypericaceae) phytochemical profile and pharmacological properties via elicitation.

KEY FINDINGS

Hypericum perforatum seedlings, shoots, roots, calli and cell suspension cultures were treated with diverse elicitors to induce the formation of secondary metabolites. The extracts of the elicitor-treated plant material containing naphthodianthrones, phloroglucinols, xanthones, flavonoids and other new compounds were quantitatively analysed and tested for their bioactivities. While hypericins were mainly produced in H. perforatum cultures containing dark nodules, namely shoots and seedlings, other classes of compounds such as xanthones, phloroglucinols and flavonoids were formed in all types of cultures. The extracts obtained from elicitor-treated samples generally possessed better bioactivities compared to the extract of control biomass.

SUMMARY

Although elicitation is an excellent tool for the production of valuable secondary metabolites in H. perforatum cell and tissue cultures, its exploitation is still in its infancy mainly due to the lack of reproducibility and difficulties in scaling up biomass production.

Adsorption kinetics and isotherms of bioactive antioxidant quercetin onto amino-functionalized silica nanoparticles in aqueous ethanol solutions

Nano-structural particles of silica were synthesized from low-cost rice husk by acid leaching and further annealing at different temperatures.

Morin Flavonoid Adsorbed on Mesoporous Silica, a Novel Antioxidant Nanomaterial

Morin (2´,3, 4´,5,7-pentahydroxyflavone) is a flavonoid with several beneficial health effects. However, its poor water solubility and it sensitivity to several environmental factors avoid its use in applications like pharmaceutical and cosmetic. In this work, we synthetized morin-modified mesoporous silica nanoparticles (AMSNPs-MOR) as useful material to be used as potential nanoantioxidant. To achieve this, we characterized its adsorption kinetics, isotherm and the antioxidant capacity as hydroxyl radical (HO•) scavenger and singlet oxygen (1O2) quencher. The experimental data could be well fitted with Langmuir, Freundlich and Temkin isotherm models, besides the pseudo-second order kinetics model. The total quenching rate constant obtained for singlet oxygen deactivation by AMSNPs-MOR was one order of magnitude lower than the morin rate constant reported previously in neat solvents and lipid membranes. The AMSNPs-MOR have good antioxidant properties by itself and exhibit a synergic effect with morin on the antioxidant property against hydroxyl radical. This effect, in the range of concentrations studied, was increased when the amount of morin adsorbed increased.