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Cristofoli M, Kung CP, Hadgraft J, Lane ME, Sil BC. Ion Pairs for Transdermal and Dermal Drug Delivery: A Review. Pharmaceutics 2021; 13:909. [PMID: 34202939 PMCID: PMC8234378 DOI: 10.3390/pharmaceutics13060909] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2021] [Revised: 06/16/2021] [Accepted: 06/18/2021] [Indexed: 11/21/2022] Open
Abstract
Ion pairing is a strategy used to increase the permeation of topically applied ionised drugs. Formation occurs when the electrostatic energy of attraction between oppositely charged ions exceeds their mean thermal energy, making it possible for them to draw together and attain a critical distance. These ions then behave as a neutral species, allowing them to partition more readily into a lipid environment. Partition coefficient studies may be used to determine the potential of ions to pair and partition into an organic phase but cannot be relied upon to predict flux. Early researchers indicated that temperature, size of ions and dielectric constant of the solvent system all contributed to the formation of ion pairs. While size is important, this may be outweighed by improved lipophilicity of the counter ion due to increased length of the carbon chain. Organic counter ions are more effective than inorganic moieties in forming ion pairs. In addition to being used to increase permeation, ion pairs have been used to control and even prevent permeation of the active ingredient. They have also been used to stabilise solid lipid nanoparticle formulations. Ion pairs have been used in conjunction with permeation enhancers, and permeation enhancers have been used as counter ions in ion pairing. This review attempts to show the various ways in which ion pairs have been used in drug delivery via the skin. It also endeavours to extract and consolidate common approaches in order to inform future formulations for topical and transdermal delivery.
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Affiliation(s)
- Mignon Cristofoli
- School of Human Sciences, London Metropolitan University, 166-220 Holloway Road, London N7 8DB, UK;
| | - Chin-Ping Kung
- School of Pharmacy, University College London, 29-39 Brunswick Square, London WC1N 1AX, UK; (C.-P.K.); (J.H.); (M.E.L.)
| | - Jonathan Hadgraft
- School of Pharmacy, University College London, 29-39 Brunswick Square, London WC1N 1AX, UK; (C.-P.K.); (J.H.); (M.E.L.)
| | - Majella E. Lane
- School of Pharmacy, University College London, 29-39 Brunswick Square, London WC1N 1AX, UK; (C.-P.K.); (J.H.); (M.E.L.)
| | - Bruno C. Sil
- School of Human Sciences, London Metropolitan University, 166-220 Holloway Road, London N7 8DB, UK;
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Song X, Ding T, Yao L, Lin M, Siew Tan RL, Liu C, Sokol K, Yu L, Lou XWD, Chen H. On the Origin and Underappreciated Effects of Ion Doping in Silica. Small 2015; 11:4351-4365. [PMID: 26068983 DOI: 10.1002/smll.201500539] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Revised: 05/14/2015] [Indexed: 06/04/2023]
Abstract
The origin of selectivity in the hollowing of silica nanoparticles is investigated to further understand silica. It is realized that, during the synthesis, the silica precursors are essentially ion-paired polyelectrolytes, whose nucleation depends on the concentration of the counter ions, and most importantly, the size/length of the poly(silicic acid). Thus, the "silica" that nucleates out at the different stages of synthesis has different degrees of ion doping, which explains its solubility in water, its microporosity, and the selective etching phenomena. The etching of silica in water is shown to be a matter of silica solubility, which correlates to the relative amounts of solvent and to the solvent quality (the water/isopropanol ratio). Hollowing does not occur when the silica nanoparticles are incubated in solutions presaturated with "silica," ruling out surface reposition and Ostwald ripening as the hollowing mechanism. The embedded ions in silica are confirmed by elemental analysis (CHNS) and inductively coupled plasma-mass spectrometry. The high ionic doping ratios (N/Si = 2.3% for NH3 -catalyzed silica; Na/Si = 11.2% for NaOH-catalyzed silica) explain the unusual solubility of silica in neutral water. The new view of silica with the ionic impurities on the central stage allows for insights in silica properties and versatility in synthetic design.
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Affiliation(s)
- Xiaohui Song
- Division of Chemistry and Biological Chemistry, Nangyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Tao Ding
- Division of Chemistry and Biological Chemistry, Nangyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Lin Yao
- Division of Chemistry and Biological Chemistry, Nangyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Ming Lin
- Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore, S117602, Singapore
| | - Rachel Lee Siew Tan
- Division of Chemistry and Biological Chemistry, Nangyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Cuicui Liu
- Division of Chemistry and Biological Chemistry, Nangyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Katarzyna Sokol
- Division of Chemistry and Biological Chemistry, Nangyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Le Yu
- School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore, 637459, Singapore
| | - Xiong Wen David Lou
- School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore, 637459, Singapore
| | - Hongyu Chen
- Division of Chemistry and Biological Chemistry, Nangyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
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