Encapsulation and controlled release of fragrances from functionalized porous metal-organic frameworks

Pore engineering of micro/mesoporous nanomaterials for encapsulation, controlled release and variegated applications of essential oils

Essential oils have become increasingly popular in fields of medical, food and agriculture, owing to their strongly antimicrobial, anti-inflammation and antioxidant effects, greatly meeting demand from consumers for healthy and safe natural products. However, the easy volatility and/or chemical instability of active ingredients of essential oils (EAIs) can result in the loss of activity before realizing their functions, which have greatly hindered the widely applications of EAIs. As an emerging trend, micro/mesoporous nanomaterials (MNs) have drawn great attention for encapsulation and controlled release of EAIs, owing to their tunable pore structural characteristics. In this review, we briefly discuss the recent advances of MNs that widely used in the controlled release of EAIs, including zeolites, metal-organic frameworks (MOFs), mesoporous silica nanomaterials (MSNs), and provide a comprehensive summary focusing on the pore engineering strategies of MNs that affect their controlled-release or triggered-release for EAIs, including tailorable pore structure properties (e.g., pore size, pore surface area, pore volume, pore geometry, and framework compositions) and surface properties (surface modification and surface functionalization). Finally, the variegated applications and potential challenges are also given for MNs based delivery strategies for EAIs in the fields of healthcare, food and agriculture. These will provide considerable instructions for the rational design of MNs for controlled release of EAIs.

Thermal/Redox-triggered release of pyrazinic functional molecules by coordination polymers with luminescence monitoring ability

Storage of volatile active molecules, along with the prolongation of their specific functions, requires the use of regulatable carriers. Pyrazine derivatives are highly volatile compounds with a broad application owing to their flavoring, pharmaceutical, antimicrobial, antiseptic, and insecticidal properties. In this study, pyrazines were stored by coordinating them with cuprous iodide to easily generate a series of luminescent coordination polymer (CP)-based carriers. The CPs could respond to thermal-redox stimuli and manipulate pyrazine release by breaking the labile Cu-N bonds when triggered by the two stimuli. Moreover, the release process could be visualized by decreased luminescence caused by the gradual decomposition of CP structures. The loading efficiencies ranged from 31% to 38%, and the controlled release behaviors accord with the zero-order kinetics. This work is the first to prove that CPs could function as dual stimuli-mediated delivery systems, which hold the potential to control the release and strengthen the usability of functional molecules.

Recent Advances in the Preparation of Delivery Systems for the Controlled Release of Scents

Scents are volatile compounds highly employed in a wide range of manufactured items, such as fine perfumery, household products, and functional foods. One of the main directions of the research in this area aims to enhance the longevity of scents by designing efficient delivery systems to control the release rate of these volatile molecules and also increase their stability. Several approaches to release scents in a controlled manner have been developed in recent years. Thus, different controlled release systems have been prepared, including polymers, metal-organic frameworks and mechanically interlocked systems, among others. This review is focused on the preparation of different scaffolds to accomplish a slow release of scents, by pointing out examples reported in the last five years. In addition to discuss selected examples, a critical perspective on the state of the art of this research field is provided, comparing the different types of scent delivery systems.

Copper(I)-Iodide Clusters as Carriers for Regulating and Visualizing Release of Aroma Molecules

Achieving the controlled release of functional substances is indispensable in many aspects of life. Especially for the aroma molecules, their effective delivery of flavor and fragrance is challenging. Here, selected pyridines, as highly volatile odorants, were individually coordinated with copper(I) iodide (Cu^II) via a straightforward one-pot synthesis method, rapidly forming pure or even crystalline Cu^II cluster-based profragrances at room temperature. The obtained profragrances enabled the stable and high loading of volatile fragrances under ambient conditions and guaranteed their long-lasting release during heating. Furthermore, the intrinsic emission luminescence of these solid-state profragrances decayed along with the aroma release, which can serve as an additional indicator for monitoring the delivery process. This research sets a precedent for using Cu^II clusters as dual-purpose release agents and greatly expands their potential applications.

Sponge-liked Silica Nanoporous Particles for Sustaining Release and Long-Term Antibacterial Activity of Natural Essential Oil

To improve the sustained release and long-term antibacterial activity of Chimonanthus nitens Oliv. essential oil (CEO), novel sponge-liked nanoporous silica particles (SNP) were synthesized via the soft template method, which was employed as a biocompatible carrier to prepare spong-liked nanoporous silica particles loading with CEO (CEO-SNP) through physical adsorption. The structure and properties of the samples were characterized via N2 adsorption/desorption measurements, thermogravimetry (TGA), Fourier transform infrared, SEM and TEM. The result showed that the SNP exhibited an excellent loading capability of CEO up to 76.3%. The thermal stability and release behavior of the CEO were significantly improved via the physical adsorption of the SNP materials. The release profile of CEO was in accordance with the first-order kinetic model, which meant that the release mechanism was drug Fick's diffusion. The antibacterial evaluation results demonstrated that the CEO-SNP exhibited strong antibacterial activity against S. aureus, E. coli and P. aeruginosa. The antibacterial results have shown that the CEO-SNP could destroy the cell structure of bacteria, and result in the generation of oxidative stress and the release of nucleic acid. After storage of 30 d at 25 °C, the CEO-SNP still had the stronger antibacterial activity towards S. aureus, E. coli and P. aeruginosa in comparison with CEO. Therefore, the sponge-like silica nanoporous particles seemed to be a promising carrier for long-term stability and antibacterial delivery of CEO.

Encapsulation of Volatile Monoterpene Fragrances in Mesoporous Organosilica Nanoparticles and Potential Application in Fruit Preservation

In this work, we synthesized mesoporous silica nanoparticles (MSNs) and periodic mesoporous organosilica nanoparticles containing bridging groups of ethylene (E-PMO) and phenylene (P-PMO) and compared their adsorption properties using D-limonene (Lim), myrcene (Myr), and cymene (Cym) as model guest molecules. For the selected nanoparticles of ~100 nm in diameter, the loading capacity to the volatile fragrances was in the order of P-PMO < E-PMO < MSN, consistent with the trend of increasing total pore volume. For example, P-PMO, E-PMO, and MSN had a Lim uptake of 42.2 wt%, 47.3 wt%, and 62.7 wt%, respectively, which was close to their theoretical adsorption capacity. Under isothermal thermogravimetric analysis conditions (30 °C, a N2 flow of 1 mL min−1), the lowest fragrance release of ~56% over 24 h was observed for P-PMO, followed by E-PMO (74−80%), and MSN (~89%). The release kinetics of the fragrant molecules from MSN and PMO materials can be well described by first-order and Weibull models, respectively. Moreover, the incorporation of Lim-loaded P-PMO NPs in an aqueous solution of regenerated silk fibroin provided a composite coating material suitable for perishable fruit preservation. The active layer deposited on fruit peels using dip coating showed good preservation efficacy, enabling the shelf-life of mangoes in a highly humid and hot atmosphere (30−35 °C, 75−85% RH) to be extended to 6 days.

Fabrication of γ-cyclodextrin-Based metal-organic frameworks as a carrier of cinnamaldehyde and its application in fresh-cut cantaloupes

Cinnamaldehyde (CA) is a promising antimicrobial agent for the preservation of fruits and vegetables due to its excellent antibacterial activity. The application is however, limited by its unstable and volatile properties. A biocompatible carbon dots hybrid γ-cyclodextrin-based metal organic framework (CD/MOF) was developed by the seed-mediated method to improve the encapsulation and sustained continuous release of CA. CD/MOF-0.5 exhibited a CA loading efficiency of 28.42% and a sustained release duration time of more than 15 days at 8 oC. The release kinetics results showed that the release behavior of CD/MOF-0.5 fitted well with the Korsmeyer-Peppas release kinetics model, indicating that its sustained release is mainly controlled by diffusion. Both the Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that CD/MOF-0.5 and CA molecules were linked by hydrogen bonds. Due to the high sustained release performance, CA-loaded CD/MOF-0.5 considerably inhibited the growth of Escherichia coli, hence preventing the spoilage of fresh-cut cantaloupes. CD/MOF-0.5/CA treatment also maintained the qualities of the fresh-cut cantaloupes, prolonging their edibility to five days. This work provides a promising strategy for the prevention of spoilage in food industry.

Heat Triggered Release Behavior of Eugenol from Tobacco Leaf

Fragrance is a commonly used substance in a number of commercial products, and fine control over the release behavior of the fragrance is essential for its successful application. Understanding the release behavior of the fragrance is the key to realizing the control of its release. Herein, we use tobacco leaf as the model substrate and investigate the mechanism of eugenol release from tobacco leaf. Our results show that interaction between eugenol and tobacco leaf is weak physical adsorption, and the eugenol release from tobacco leaf substrate is a temperature-dependent process. Further analysis on the release behavior reveals that eugenol release is closely associated with the morphology change of tobacco leaves under heating conditions. Our results provide insight into the release mechanism of fragrance from polymer substrate and may be useful for the future design of fragrance release systems.

Solidification of volatile D-Limonene by cyclodextrin metal-organic framework for pulmonary delivery via dry powder inhalers: In vitro and in vivo evaluation

D-Limonene (D-Lim), a volatile oil extracted from citrus fruits, has therapeutic effects on lung inflammation and cancer, whilst the deep delivery of D-Lim was challenging due to its physical instability for a long period of time. To prevent the volatilization of D-Lim and achieve efficient pulmonary delivery, herein, D-Lim was loaded into biodegradable γ-cyclodextrin metal-organic framework (γ-CD-MOF) with optimal loading efficiency achieving 13.79 ± 0.01% (molar ratio of D-Lim and γ-CD-MOF was 1.6:1), which possessed cubic shape with controllable particle size (1-5 μm). The experimental results indicated that γ-CD-MOF could improve the stability of D-Lim. A series of characterizations and molecular docking were used to reveal the interaction between D-Lim and γ-CD-MOF. The solidification of D-Lim by γ-CD-MOF played a crucial role in the exploitation of its inhalable dosage form, dry powder inhaler (DPI). Specifically, the aerosolization of D-Lim@γ-CD-MOF for inhalation was satisfactory with a fine particle fraction (FPF) of 33.12 ± 1.50% at 65 L/min of flow rate. Furthermore, in vivo study had shown a 2.23-fold increase in bioavailability of D-Lim solidified by γ-CD-MOF for inhalation compared to D-Lim for oral administration. Therefore, it is considered that γ-CD-MOF could be an excellent carrier for pulmonary drug delivery to realize solidification and lung therapeutic effects of volatile oils.

Encapsulation of Highly Volatile Fragrances in Y Zeolites for Sustained Release: Experimental and Theoretical Studies

Volatility is an inherent fragrance attribute and typically implies a reduced perception over time. One possibility to elongate odor perception is utilizing controlled fragrance-delivery systems. Herein, the Y type of faujasite with different extra-framework cations (abbreviated as ZY, where Z represents Na+, Ca2+, or La3+) was examined as potential carriers for fragrance entrapment and delivery. d-Limonene (Lim) and linalool (Lol) as model fragrances were loaded in the pore space of Y zeolites, yielding composites FG@ZY (FG = Lim, Lol). It was found that the fragrance release profiles correlate highly with the cationic species located in the nonframework. The retention of fragrances in matrices increases in the order NaY < CaY < LaY for either limonene or linalool. Interestingly, the release rate of limonene was significantly slower than that of linalool when encapsulated in the same zeolite, although neat limonene has a much higher saturated vapor pressure than linalool. For instance, the total fraction of aroma released from Lim@LaY over 30 days was about 10%, while the value was ∼20% for Lol@LaY. Based on the density functional theory calculations, the above results could be well rationalized by the electrostatic attraction and shape selectivity of microporous matrices to the dopant molecules.

Effect of mesoporous silica nanoparticles-based nano-fragrance on the central nervous system

Fragrances are widely used in our daily lives and can make us feel happy. However, traditional aromatic products release fragrance quickly and have a strong aroma. This not only worsens our scenting experience, but also severely shortens the useful life of fragrance products. In this study, nano-fragrances based on mesoporous silica nanoparticles with great encapsulation efficiency and slow-release function were designed and prepared. In addition, this nano-fragrances are applied to wallpapers. Open field tests showed that this nano-fragrance had significant stress relief and anti-depressant effects.

Chitosan-based nanofragrance with antibacterial function applied to wallpaper

Adding fragrances to the wallpaper can optimize our living environment and office environment. However, the poor adhesion and rapid release of fragrances on wallpapers have limited their application. In this study, vanillin was encapsulated in particles based on chitosan and poly(lactic-co-glycolic acid), thereby achieving a slow release of the fragrance. In addition, due to the addition of chitosan, the adhesion of the fragrance on the wallpaper was enhanced, and the wallpaper was given antibacterial properties.

Active Encapsulation in Biocompatible Nanocapsules

Co-precipitation is generally refers to the co-precipitation of two solids and is widely used to prepare active-loaded nanoparticles. Here, it is demonstrated that liquid and solid can precipitate simultaneously to produce hierarchical core-shell nanocapsules that encapsulate an oil core in a polymer shell. During the co-precipitation process, the polymer preferentially deposits at the oil/water interface, wetting both the oil and water phases; the behavior is determined by the spreading coefficients and driven by the energy minimization. The technique is applicable to directly encapsulate various oil actives and avoid the use of toxic solvent or surfactant during the preparation process. The obtained core-shell nanocapsules harness the advantage of biocompatibility, precise control over the shell thickness, high loading capacity, high encapsulation efficiency, good dispersity in water, and improved stability against oxidation. The applications of the nanocapsules as delivery vehicles are demonstrated by the excellent performances of natural colorant and anti-cancer drug-loaded nanocapsules. The core-shell nanocapsules with a controlled hierarchical structure are, therefore, ideal carriers for practical applications in food, cosmetics, and drug delivery.

Urea-Based Low-Molecular-Weight Pseudopeptidic Organogelators for the Encapsulation and Slow Release of (R)-Limonene

Low-molecular-weight compounds containing alkylurea fragments attached to the amino end of different miminalistic pseudopeptidic structures have been shown to be excellent organogelators in a variety of organic solvents and liquid organic compounds of different nature. The formation of gels in this work is defined through rheological measurements for those cases where G' > G''. Both the topology and the symmetry of the corresponding urea compounds play a role in defining their organogelator behavior. This can also be tuned by the presence of additional supramolecular guests, as is the case for suberic acid. These compounds also achieve the gelation of relevant active substances such as terpene natural oils and complex mixtures of flavors and fragrances. This provides a simple and mass-efficient supramolecular system for the quantitative encapsulation of active substances, without the need for any additional solvent or complex processes, and their consequent controlled release.

Thermal Triggered Release of Menthol from Different Carriers: A Comparative Study

The design of appropriate thermally responsive fragrance carrier systems is of significant importance for the application of fragrance in the food and tobacco industries. In this study, we investigate the potential of sorbitan monostearate and guar gum for the stabilization of menthol under ambient conditions and the thermally-induced release of menthol. Our results show that the sorbitan monostearate carrier could well stabilize the menthol for at least up to 15 days with neglectable menthol loss due to the favorable binding of menthol on the sorbitan monostearate carrier. In addition, rapid and controlled release of menthol could take place at a temperature of 80 °C in the sorbitan monostearate carrier system. As a comparison, guar gum could not stabilize menthol as a result of its poor compatibility. Our results suggest that sorbitan monostearate can be an ideal carrier material for the support of fragrance. In addition, our results also provide a useful guide for the tailored design of thermally responsive fragrance carriers.

A novel photothermo-responsive nanocarrier for the controlled release of low-volatile fragrances

We herein present a facile approach to create polydopamine (PDA) modified silica-based nanocarriers for use in the encapsulation and photothermally responsive release of the synthetic sandalwood odorant Sandalore (SA) as a low-volatile model fragrance. The method involves impregnating mesoporous silica nanoparticles with an ethanol solution of SA followed by surface functionalization via the in situ self-polymerization of dopamine under alkaline conditions. The resulted nanocomposites have high fragrance loading capacity with up to ∼85% by weight of SA relative to the silica matrix and are capable of effectively preserving the cargo in the dark or indoors. The aroma release was significantly accelerated upon illumination due to the photothermal heating effect of the PDA shell, which is proportional to the coating content and the irradiation intensity. Additionally, the emulated laundry tests showed that the composites exhibited a higher deposition efficiency on the fabric surface and better washing-resistance as compared to the control particles without PDA coating.

Polydopamine-modified nanocarriers were constructed for use in the encapsulation and photothermo-responsive release of the low-volatile synthetic odorant Sandalore.

Ti3 C2 MXene Paper for the Effective Adsorption and Controllable Release of Aroma Molecules

Olfactory sensing and perception play an important role in people's daily lives and greatly affects senses, emotions, and behavior. In particular, the development of the controlled release of aroma enhances human's well-being and strengthens interactions with surroundings through olfactory display, especial when combined with visual and audial cues. Here, Ti₃ C₂ MXene plays a dual-function role as the adsorption site of aroma molecules and the heating source for the controlled release of aroma molecules. Due to abundant termination groups on the surface and the metallic nature, Ti₃ C₂ MXene provides abundant active sites for the interaction with aroma molecules; simultaneously, MXene can be electrically heated to thermally desorb the aroma molecules from the interaction sites. This approach eliminates the interface incompatibility issues between the heating source and the molecular encapsulation layer in conventional olfactory display system. This work presents the controlled release of the aroma molecule phenethyl alcohol (PA) using Ti₃ C₂ MXene paper. Ti₃ C₂ MXene paper serves as the adsorption material and a heating source that achieves 100 °C within 1 s. The relative amount of PA released reaches nearly 100% after 1 min of heating.