Abstract

Layered double hydroxides (LDHs) are a group of natural and synthetic materials. They are structured as positively-charged layers mostly of divalent-trivalent metal combination between which anions are embedded. The container-like structure and the feasibility to vary the metallic and the interlayer components attracted attention to their use as potential carriers for biologically-active compounds for purposes such as preservation and storage, modulation of release, improving the solubility, targeted delivery, etc. This study aims at investigating the possibility to load different vitamins having different chemical characters into Zn-Al and Mg-Al LDHs of nitrate precursors, characterizing the produced vitamin-LDH hybrids and studying their release behavior. The preparation methods used entailed the co-precipitation and ion-exchange methods for the Zn-Al LDH and the co-precipitation, ion-exchange and reconstruction methods for the Mg-Al LDH system. Characterization of the pristine LDHs and the vitamin-LDH hybrid systems was carried out using XRD, FTIR, SEM and the interlayer arrangements of the vitamins were proposed. The loaded amount and release behavior were studied using UV spectroscopy. The characterization results indicated successful intercalation of vitamin B2 (medium to large neutral molecule) into Zn-Al and Mg-Al LDH systems by the co-precipitation method only, with loading amounts ≈ 55.1 and 53.2 (%w/w) respectively. The release from the Zn-Al system was more sustained where complete release was not reached within 20 minutes. The intercalation of vitamin B6 (small anionic molecule) was successful for all trials: co-precipitation and ion-exchange for Zn-Al LDH, with loading amounts ≈ 16.3 and 38.9 (%w/w), and co-precipitation, ion-exchange and reconstruction for Mg-Al LDH, with loading amounts ≈ 12.9, 17.2, 13.8 (%w/w). The release of the two B6-Zn-Al hybrid systems was more sustained (not complete within the 20-minute study period) with biphasic release observed for the anion-exchanged sample due to the intercalation of the vitamin adopting two different interlayer arrangements. On the other hand, complete release was noticed for the B6-Mg-Al hybrid systems within 15 minutes at most. Folic acid was successfully intercalated into Zn-Al LDH using the co-precipitation and ion-exchange methods with loading amounts of 36.5 and 36 (%w/w) respectively, while it failed for the Mg-Al LDH system by all routes. The release of the co-precipitated Zn-Al hybrid system was biphasic and significantly sustained with the release of only 50% of the intercalated vitamin within 20 minutes. This is attributed to the orientation of folic acid within the LDH layers promoting strong attractive forces with the LDH environment and hence hindering the immediate release. On the other hand, the ion-exchanged Zn-Al hybrid showed complete release within 10 minutes. Vitamin C was loaded into Zn-Al and Mg-Al LDHs by the co-precipitation and ion-exchange methods with loading amounts of 38 and 13 (% w/w) for the co-precipitated and ion-exchanged Zn-Al LDH hybrids respectively, 6 and 21.5 (% w/w) for the co-precipitated and ion-exchanged Mg-Al LDH hybrids respectively, while the intercalation failed by the reconstruction method. The release of the Zn-Al hybrid systems was more sustained and followed a biphasic behavior, while that of the Mg-Al hybrid systems was faster and reached completion in shorter time periods. In general, the intercalated vitamin amount was higher for the Zn-Al LDH systems as the Zn is more electronegative than Mg leading to more attraction between the LDH layers and the guest molecules. In addition, the release behavior depended on the vitamin-LDH interactions, as the attractive forces increased, the release was more sustained. Intercalation of vitamin B1 and B5 was unsuccessful for all trials: co-precipitation and ion-exchange to the Zn-Al LDH and co-precipitation, ion-exchange and reconstruction to the Mg-Al LDH system. In conclusion, nanostructured biocompatible LDH carriers for vitamins B2 , B6, folic acid and vitamin C were successfully synthesized using different methods. They showed significant vitamin loading and feasible release suggesting their potential use as vitamin storage carriers and delivery systems.

Department

Chemistry Department

Degree Name

MS in Chemistry

Graduation Date

Winter 1-31-2013

Submission Date

1-31-2013

First Advisor

Ramadan, Adham R.

Committee Member 1

Ramadan, Adham R.

Committee Member 2

Ragai, Jehane

Extent

189 p.

Document Type

Master's Thesis

Library of Congress Subject Heading 1

Vitamins.

Rights

The author retains all rights with regard to copyright. The author certifies that written permission from the owner(s) of third-party copyrighted matter included in the thesis, dissertation, paper, or record of study has been obtained. The author further certifies that IRB approval has been obtained for this thesis, or that IRB approval is not necessary for this thesis. Insofar as this thesis, dissertation, paper, or record of study is an educational record as defined in the Family Educational Rights and Privacy Act (FERPA) (20 USC 1232g), the author has granted consent to disclosure of it to anyone who requests a copy. The author has granted the American University in Cairo or its agents a non-exclusive license to archive this thesis, dissertation, paper, or record of study, and to make it accessible, in whole or in part, in all forms of media, now or hereafter known.

Institutional Review Board (IRB) Approval

Not necessary for this item

Comments

I cannot find words to express my immense gratitude to my research advisor and mentor, Dr. Adham Ramadan. This thesis would not have been possible without his continuous guidance and unconditional help and support. Since day one, I was deeply indebted to his exceptional planning and research skills that were incredibly helpful throughout the research project. His dedication, enthusiasm and passion about research made me very much like research and appreciate its value. Over the past three years, he taught me to pay attention to every small detail as well as to look at the overall picture. As a teacher, he is always incomparably generous with his knowledge, time and effort. During the hardest times of this research, his encouragement, understanding, patience and motivation gave me confidence. I consider it an honor to have been able to work with him as he transformed this educational experience into a time for personal growth as well. I would like to acknowledge the financial support of the American University in Cairo through the graduate student research grant and the laboratory instruction graduate fellowship. I would also like to express my sincere thanks to Mr. Islam Mohamed Mustafa for his great help with using the Gaussian software, Mr. Emad Farag and Mr. Mahmoud Abdel Moez for their invaluable technical help. I am deeply grateful to all my graduate professors in the Chemistry Department, AUC and undergraduate professors in the Faculty of Pharmacy, Cairo University. I have learnt a lot from all of them. Many thanks also go to my colleagues and friends for their family-like support. Last but not least, I am endlessly grateful to the most important people in my life, my dear parents. Without their unconditional love, prayers, support and guidance, I would have never reached anywhere. I am fortunate to have you in my life. I would also like to express heartfelt gratitude to my dear sister and brothers.

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