Synthesis of β-Cyclodextrin Metal Organic Framework for Loading of Hexanal

Abstract

Hexanal application is a recent strategy for enhancing the shelf-life of fruits and vegetables by inhibiting phospholipase D, a key enzyme responsible for plasma membrane degradation. Partial inhibition of phospholipase D increases shelf-life by preserving membrane stability. However, hexanal's low vapor pressure and high volatility pose challenges with temperature changes. Microwave-synthesized β-Cyclodextrin Metal Organic Framework (β-CDMOF) offers a promising solution as a delivery vehicle for hexanal due to its internal hydrophobic walls. In this study, we investigated thermal stability (TGA at 292°C), DSC, X-ray diffraction (XRD), and loading efficiency (24.

04%) to illustrate β-CDMOF as a potential template. UV-Vis (297nm) and FT-IR spectra studies confirmed β-CDMOF's ability to load hexanal.

Keywords:

Hexanal, β-CDMOF, Thermal Stability, Entrapment Efficiency

Introduction

Hexanal is a naturally occurring aldehyde responsible for the characteristic green flavor developed during the physical wounding process in vegetables like cucumbers and beans [1]. It remains in a liquid state at room temperature (25°C) with a low melting point of -20°C and a high boiling point of 120°C.

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Hexanal also exhibits a very low vapor pressure of 10mmHg at 20°C [2], making it volatile when exposed to elevated temperatures. Therefore, finding a suitable carrier material for hexanal that can release it in a controlled manner is essential to extend the shelf life of fruits and vegetables.

β-CDMOFs are widely used templates for entrapping volatile compounds due to their ability to form complexes with guest molecules within their hydrophobic cavities [3]. Cyclodextrin inclusion complexes are stable, held together by Vander Waals forces, and typically involve one cyclodextrin molecule entrapping a single guest molecule.

These complexes respond to humidity-triggered releases of volatiles, making them advantageous for preserving fruits during storage, where humidity levels often increase due to respiration rates.

Materials and Methods

Chemicals

• β-Cyclodextrin (Sigma-Aldrich, Bangalore, India) - 95% pure
• Potassium hydroxide pellets (SRL Laboratories, Mumbai) - 85% pure
• Carbinol (Finar Limited, Ahmedabad, India) - 99.7% pure
• Hexanal (Sigma-Aldrich, Bangalore, India) - 98.8% pure

β-Cyclodextrin Metal Organic Framework Synthesis

In the synthesis process of β-CDMOF, a (1:6) ratio of β-CD and KOH was dissolved in 9ml of distilled water and transferred to a 30ml glass vial in a Microwave synthesizer. 9ml of carbinol was added to the solution. White precipitation appeared in the vial, which was then placed in a Microwave synthesizer (Model Monowave 400, branded Anton Paar, Germany) with a magnetic bar. The sample was heated for 20 minutes at 100°C and 600rpm. After 20 minutes, a clear solution was obtained. The solution was cooled to room temperature, transferred to a 50ml beaker, and sealed with parafilm. Crystal initiation occurred after 8-9 hours, and complete harvesting of MOF crystals was done after 24 hours. The harvested crystals were washed with carbinol to remove impurities in β-CDMOF, followed by freeze-drying with a Lyophilizer (Model Penguin Classic, branded Lark Technologies, Chennai) at -80°C to remove moisture and activate the MOF.

Loading of Hexanal in β-Cyclodextrin Metal Organic Framework

For loading hexanal into β-CDMOF, a (1:3) ratio of activated β-CDMOF and hexanal were stirred together until a slurry formed. The slurry was placed in a vacuum desiccator to obtain dry samples.

Characterization of β-CDMOF and β-CDMOF loaded with Hexanal

Scanning Electron Microscope (SEM)

Morphology of β-CDMOF and β-CDMOF loaded with hexanal was analyzed using a Scanning Electron Microscope (SEM) (Quanta 250, FEI, Netherlands) with 10kV voltage. Samples were gold-coated with Emitech, SC7 620 sputter coater for clearer images [4]. β-CDMOF particles exhibited well-formed rod-shaped micro-crystals with lengths ranging from 40 to 90μm. In contrast, β-CDMOF loaded with hexanal displayed irregularly shaped crystals, indicating the embedding of hexanal within the β-CDMOF structure [10].

Thermogravimetry Analysis (TGA)

TGA provides insight into the physical and chemical properties of materials [11]. TGA analysis of β-CDMOF revealed two distinct thermal curves. The first curve at 153°C with a weight loss of 0.89% represented water loss, while the second curve at 292°C with a weight loss of 1.9% indicated sample decomposition [12] [13]. The overall mass loss during TGA analysis was 82.4% [14].

Differential Scanning Calorimetry (DSC)

DSC thermocurve of β-CDMOF is shown in Figure 3. DSC measures thermal properties such as enthalpy, melting point, and specific heat [15]. β-CDMOF's DSC provided two thermocurves. The first curve at 105°C indicated an exothermic event due to water loss, while the second curve at 285°C represented the solubilization of β-CDMOF [16].

X-ray Diffraction (XRD)

XRD peak patterns of pure β-CD, β-CDMOF, and β-CDMOF loaded with hexanal were shown in Figures 4a, 4b, and 4c. Pure β-CD exhibited characteristic peaks at a 2θ angle of 12.8°, matching JCPDS code number: 00.032-1626 for β-CD. β-CDMOF displayed dominant peaks at 2θ angles of 9.0° and 12.3°, confirming the formation of an inclusion complex [17]. XRD of β-CDMOF loaded with hexanal showed weaker peaks at 2θ angles of 12.4° and 19.3°, indicating the presence of hexanal within the structure [18].

UV-Vis Analysis

UV-Vis analysis revealed that pure hexanal had a peak at 291nm within the range of 280-330 nm [19]. Pure β-CD exhibited a weak peak near 295nm. β-CDMOF loaded with hexanal displayed an absorbance peak at 297 nm, indicating hexanal's conjugation with β-CDMOF, which shifted the maximum absorption to longer wavelengths (>291nm) [20]. The UV spectra of hexanal, β-CDMOF, and β-CD were shown in Figures 5a, 5b, and 5c.

FT-IR Analysis

FTIR spectroscopy was employed to study the chemical structure of the materials and confirm complex formation [21]. Hexanal's FT-IR spectrum showed C–H stretching vibrations at 2800–3000 cm-1 and C=O stretching vibrations at 1727 cm-1. β-CDMOF's FT-IR spectrum exhibited absorbance peaks at 3385 cm-1 representing O–H stretching vibrations and peaks around 2926 cm-1 indicating C–H stretching. FT-IR analysis of β-CDMOF loaded with hexanal showed C=O vibration stretching at 1727 cm-1, confirming hexanal's presence in β-CDMOF and the formation of the inclusion complex [22] [23]. The FT-IR absorbance of hexanal, β-CDMOF, and β-CDMOF loaded with hexanal was shown in Figures 6a, 6b, and 6c.

Entrapment Efficiency of β-CDMOF

Entrapment efficiency was estimated using Gas Chromatography-Mass Spectrometer (GC-MS) (Model QP2010 Ultra, Shimadzu, Japan) with a DB-5ms Capillary Standard Non–Polar Column. Helium served as the carrier gas at a rate of 1.0μL/min. 0.1g of β-CDMOF loaded with hexanal complex was dissolved in 10ml of carbinol, followed by complete dissolution with a water-bath sonicator. Debris was removed with a 0.2 µm micro filter to obtain a clear solution. The peak area of β-CDMOF loaded with hexanal was correlated with hexanal standards to calculate the entrapment efficiency of β-CDMOF, yielding a regression coefficient (R2) value of 0.95.

Results and Discussion

Scanning Electron Microscope (SEM)

The morphological study of β-CDMOF and β-CDMOF loaded with hexanal revealed that β-CDMOF particles were well-formed rod-shaped micro-crystals with lengths ranging from 40 to 90μm. In contrast, β-CDMOF loaded with hexanal exhibited irregularly shaped crystals, indicating the successful embedding of hexanal within the β-CDMOF structure.

Thermogravimetry Analysis (TGA)

TGA analysis of β-CDMOF showed two distinct thermal curves. The first curve at 153°C with a weight loss of 0.89% represented water loss, while the second curve at 292°C with a weight loss of 1.9% indicated sample decomposition. The overall mass loss during TGA analysis was 82.4%.

Differential Scanning Calorimetry (DSC)

DSC thermocurve of β-CDMOF indicated two significant points. The first curve at 105°C was attributed to an exothermic event due to water loss, while the second curve at 285°C represented the solubilization of β-CDMOF.

X-ray Diffraction (XRD)

XRD peak patterns of pure β-CD, β-CDMOF, and β-CDMOF loaded with hexanal confirmed the formation of an inclusion complex in β-CDMOF. β-CDMOF loaded with hexanal exhibited weaker peaks due to hexanal loading.

UV-Vis Analysis

UV-Vis analysis demonstrated that hexanal's peak at 291nm shifted to 297 nm when loaded into β-CDMOF, confirming the successful loading of hexanal into the framework.

FT-IR Analysis

FT-IR spectroscopy confirmed the presence of hexanal in β-CDMOF, indicating the formation of the inclusion complex.

Entrapment Efficiency

Entrapment efficiency was calculated to be 24% based on peak area comparisons with hexanal standards.

Conclusion

In conclusion, our study demonstrates that β-CDMOF serves as an effective template for entrapping guest molecules like hexanal. Characterization through XRD, TGA, and DSC thermocurves indicates that β-CDMOF can withstand temperatures up to 292°C, ensuring stability within the framework. UV-Vis, FTIR, and GC-MS analyses confirm the successful loading of hexanal into β-CDMOF. These findings highlight the potential of β-CDMOF as a delivery system for hexanal, offering a promising solution to extend the shelf life of fruits and vegetables.

References

1. Sekiya J, Hatanaka A. Cis-3-hexenal and n-hexanal formation from linolenic and linoleic acids in alfalfa cells cultured in vitro. Plant Science Letters 1977; 10: 165-9.
2. Jash A, Lim L-T. Triggered release of hexanal from an imidazolidine precursor encapsulated in poly (lactic acid) and ethylcellulose carriers. Journal of materials science 2018; 53: 2221-35.
3. Rekharsky MV, Inoue Y. Complexation thermodynamics of cyclodextrins. Chemical reviews 1998; 98: 1875-918.
4. Al-Ghamdi S, Kathuria A, Abiad M, Auras R. Synthesis of nanoporous carbohydrate metal-organic framework and encapsulation of acetaldehyde. Journal of Crystal Growth 2016; 451: 72-8.
5. Kohata S, Jyodoi K, Ohyoshi A. Thermal decomposition of cyclodextrins (α-, β-, γ-, and modified β-CyD) and of metal—(β-CyD) complexes in the solid phase. Thermochimica acta 1993; 217: 187-98.
6. Krishnaswamy K, Orsat V, Thangavel K. Synthesis and characterization of nano-encapsulated catechin by molecular inclusion with beta-cyclodextrin. Journal of food engineering 2012; 111: 255-64.
7. Yoshii H, Furuta T, Asada M, Sugisawa H. Quantitative analysis by X-ray diffraction of the inclusion complex formed by d-limonene in a β-cyclodextrin/maltodextrin mixed powder. Bioscience, biotechnology, and biochemistry 1992; 56: 384-7.
8. Bratu I, Hernanz A, Gavira J, Bora G. FT-IR spectroscopy of inclusion complexes of beta-cyclodextrin with fenbufen and ibuprofen. Romanian Journal of Physics 2005; 50: 1063.
9. Prasetyo S, Wientarsih I, Sajuthi D, Juniantito V. CHARACTERIZATION OF ANDROGRAPHOLIDE IN INCLUSION COMPLEX USING BETA CYCLODEXTRIN. INTERNATIONAL JOURNAL OF PHARMACEUTICAL SCIENCES AND RESEARCH 2018; 9: 1291-6.
10. Saini VK, Pires J. Development of metal organic framework-199 immobilized zeolite foam for adsorption of common indoor VOCs. Journal of Environmental Sciences 2017; 55: 321-30.
11. Zhao J, Lin D-Q, Yao S-J. Adsorption of rutin with a novel β-cyclodextrin polymer adsorbent: thermodynamic and kinetic study. Carbohydrate polymers 2012; 90: 1764-70.
12. Giordano F, Novak C, Moyano JR. Thermal analysis of cyclodextrins and their inclusion compounds. Thermochimica Acta 2001; 380: 123-51.
13. Zarif M, Afidah A, Abdullah J, Shariza A. Physicochemical characterization of vancomycin and its complexes with?-cyclodextrin. 2012.
14. Hădărugă DI, Ünlüsayin M, Gruia AT et al. Thermal and oxidative stability of Atlantic salmon oil (Salmo salar L.) and complexation with β-cyclodextrin. Beilstein journal of organic chemistry 2016; 12: 179-91.
15. Wang X, Luo Z, Xiao Z. Preparation, characterization, and thermal stability of β-cyclodextrin/soybean lecithin inclusion complex. Carbohydrate polymers 2014; 101: 1027-32.
16. Shah B, Khunt D, Bhatt H et al. Application of quality by design approach for intranasal delivery of rivastigmine loaded solid lipid nanoparticles: effect on formulation and characterization parameters. European Journal of Pharmaceutical Sciences 2015; 78: 54-66.
17. Roik N, Belyakova L. IR Spectroscopy, X Ray Diffraction and Thermal Analysis Studies of Solid b Cyclodextrin-Para Aminobenzoic Acid” Inclusion Complex. Фізика і хімія твердого тіла 2011: 168-73.
18. Tan K, Nijem N, Gao Y et al. Water interactions in metal organic frameworks. CrystEngComm 2015; 17: 247-60.
19. Tang Y, Zhu L. Wavelength-Dependent Photolysis of n-Hexanal and n-Heptanal in the 280− 330-nm Region. The Journal of Physical Chemistry A 2004; 108: 8307-16.
20. Jiménez E, Lanza B, Martínez E, Albaladejo J. Daytime tropospheric loss of hexanal and trans-2-hexenal: OH kinetics and UV photolysis. Atmospheric Chemistry and Physics 2007; 7: 1565-74.
21. Ge X, He J, Qi F et al. Inclusion complexation of chloropropham with β-cyclodextrin: Preparation, characterization and molecular modeling. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2011; 81: 397-403.
22. Zhang Y, Zhou Y, Cao S et al. Preparation, release and physicochemical characterisation of ethyl butyrate and hexanal inclusion complexes with β-and γ-cyclodextrin. Journal of microencapsulation 2015; 32: 711-8.
23. Wang J, Cao Y, Sun B, Wang C. Physicochemical and release characterisation of garlic oil-β-cyclodextrin inclusion complexes. Food chemistry 2011; 127: 1680-5.
24. Ram VR, Ram PN, Khatri TT et al. Thermal analytical characteristics by TGA-DTA-DSC analysis of Carica papaya leaves from Kachchh. International Letters of Natural Sciences 2014; 21.
25. Wang Y, Ha J. Determination of hexanal in rice using an automated dynamic headspace sampler coupled to a gas chromatograph–mass spectrometer. Journal of chromatographic science 2012; 51: 446-52.