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Rusli W, van Herk AM. Effect of salts on size and morphology of extruded dimethyldioctadecylammonium bromide or chloride vesicle for polymeric nanocapsules synthesis via templating emulsion polymerization. J Colloid Interface Sci 2021; 587:393-401. [PMID: 33370661 DOI: 10.1016/j.jcis.2020.11.116] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Accepted: 11/29/2020] [Indexed: 11/20/2022]
Abstract
In preparing polymer capsules by vesicle templated emulsion polymerization, the initial size and morphology of the biomimetic vesicle template dictate the final size and morphology of the capsules. The presence of salts (NaCl, NaBr and LiCl) influences the size, dispersity (PDI) and morphology of dimethyldioctadecylammonium bromide or chloride (DODAX, X = Br- or Cl-) vesicles, prepared via membrane extrusion. DODAX vesicles in pure water exhibit broad size distributions with PDI of 0.5 and 0.3 for DODAB and DODAC, respectively. Addition of salts in water before (pre-addition) and after (post-addition) extrusion reduces the size and PDI of the vesicles significantly and results in various morphology investigated with cryo-TEM. It is observed that at low salt concentration (≤0.5 mM) in pre-addition, DODAX exists as a nice quasi spherical unilamellar vesicle, suitable for vesicle templated polymerization whereas in post-addition of salt at any concentration, the morphology is dominated by structures not suitable for templating application. The information obtained here is crucial for vesicle templated emulsion polymerization and it will be shown that there is a relationship between vesicle template morphology and final polymer capsule morphology.
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Feitosa E, Lemos M, Adati RD. Mixed Cationic Surfactant Vesicles in (Dioctadecyldimethylammonium Bromide)/NaCl and (Dioctadecyldimethylammonium Chloride)/NaBr Aqueous Dispersions. J SURFACTANTS DETERG 2019. [DOI: 10.1002/jsde.12329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Eloi Feitosa
- Department of PhysicsSão Paulo State University, Rua Cristovao Colombo 2265 15.054‐000 São José do Rio Preto São Paulo Brazil
| | - Monique Lemos
- Department of PhysicsSão Paulo State University, Rua Cristovao Colombo 2265 15.054‐000 São José do Rio Preto São Paulo Brazil
| | - Renata D. Adati
- Department of Chemistry and BiologyFederal University of Technology ‐ Paraná (UTFPR) Curitiba Brazil
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Qiao W, Zheng Z, Qu W, Zhang S. Synthesis and Characterization of Carbamate-Linked Cationic Lipids with Hydroxyethyl Group. J AM OIL CHEM SOC 2012; 89:2121-5. [DOI: 10.1007/s11746-012-2115-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Alves FR, Loh W. Vesicles prepared with the complex salts dioctadecyldimethylammonium polyacrylates. J Colloid Interface Sci 2012; 368:292-300. [DOI: 10.1016/j.jcis.2011.11.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 11/09/2011] [Accepted: 11/09/2011] [Indexed: 11/25/2022]
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Goto M, Ishida S, Ito Y, Tamai N, Matsuki H, Kaneshina S. Thermotropic and barotropic phase transitions of dialkyldimethylammonium bromide bilayer membranes: effect of chain length. Langmuir 2011; 27:5824-5831. [PMID: 21520909 DOI: 10.1021/la200323h] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The bilayer phase transitions of dialkyldimethylammonium bromides (2C(n)Br; n = 12, 14, 16) were observed by differential scanning calorimetry and high-pressure light-transmittance measurements. Under atmospheric pressure, the 2C(12)Br bilayer membrane underwent the stable transition from the lamellar crystal (L(c)) phase to the liquid crystalline (L(α)) phase. The 2C(14)Br bilayer underwent the main transition from the metastable lamellar gel (L(β)) phase to the metastable L(α) phase in addition to the stable L(c)/L(α) transition. For the 2C(16)Br bilayer, moreover, three kinds of phase transitions were observed: the metastable main transition, the metastable transition from the metastable lamellar crystal (L(c(2))) phase to the metastable L(α) phase, and the stable lamellar crystal (L(c(1)))/L(α) transition. The temperatures of all the phase transitions elevated almost linearly with increasing pressure. The temperature (T)-pressure (p) phase diagrams of the 2C(12)Br and 2C(14)Br bilayers were simple, but that of the 2C(16)Br bilayer was complex; that is, the T-p curves for the metastable main transition and the L(c(2))/L(α) transition intersect at ca. 25 MPa, which means the inversion of the relative phase stability between the metastable phases of L(β) and L(c(2)) above and below the pressure. Moreover, the T-p curve of the L(c(2))/L(α) transition was separated into two curves under high pressure, and as a result, the pressure-induced L(c(2P)) phase appeared in between. Thermodynamic quantities for phase transitions of the 2C(n)Br bilayers increased with an increase in alkyl-chain length. The chain-length dependence of the phase-transition temperature for all kinds of transitions observed suggests that the stable L(c(1))/L(α) transition incorporates the metastable L(c(2))/L(α) transition in the bilayers of 2C(n)Br with shorter alkyl chains, and the main-transition of the 2C(12)Br bilayer would occur at a temperature below 0 °C.
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Affiliation(s)
- Masaki Goto
- Department of Life System, Institute of Technology and Science, The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan
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Goto M, Ito Y, Ishida S, Tamai N, Matsuki H, Kaneshina S. Hydrostatic pressure reveals bilayer phase behavior of dioctadecyldimethylammonium bromide and chloride. Langmuir 2011; 27:1592-1598. [PMID: 21261314 DOI: 10.1021/la104552z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Bilayer phase transitions of dioctadecyldimethylammonium bromide (2C(18)Br) and chloride (2C(18)Cl) were observed by differential scanning calorimetry and high-pressure light-transmittance measurements. The 2C(18)Br bilayer membrane showed different kinds of transitions depending on preparation methods of samples under atmospheric pressure. Under certain conditions, the 2C(18)Br bilayer underwent three kinds of transitions, the metastable transition from the metastable lamellar crystal (L(c(2))) phase to the metastable lamellar gel (L(β)) phase at 35.4 °C, the metastable main transition from the metastable L(β) phase to the metastable liquid crystalline (L(α)) phase at 44.5 °C, and the stable transition from the stable lamellar crystal (L(c(1))) phase to the stable L(α) phase at 52.8 °C. On the contrary, the 2C(18)Cl bilayer underwent two kinds of transitions, the stable transition from the stable L(c) phase to the stable L(β) phase at 19.7 °C and the stable main transition from the stable L(β) phase to the stable L(α) phase at 39.9 °C. The temperatures of the phase transitions of the 2C(18)Br and 2C(18)Cl bilayers were almost linearly elevated by applying pressure. It was found from the temperature (T)-pressure (p) phase diagram of the 2C(18)Br bilayer that the T-p curves for the main transition and the L(c(1))/L(α) transition intersect at ca. 130 MPa because of the larger slope of the former transition curve. On the other hand, the T-p phase diagram of the 2C(18)Cl bilayer took a simple shape. The thermodynamic properties for the main transition of the 2C(18)Br and 2C(18)Cl bilayers were comparable to each other, whereas those for the L(c(1))/L(α) transition of the 2C(18)Br bilayer showed considerably high values, signifying that the L(c(1)) phase of the 2C(18)Br bilayer is extremely stable. These differences observed in both bilayers are attributable to the difference in interaction between a surfactant and its counterion.
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Affiliation(s)
- Masaki Goto
- Department of Life System, Institute of Technology, and Science, University of Tokushima, 2-1 minamijosanjima-cho, Tokushima 770-8506, Japan
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Gonçalves LM, Kobayakawa TG, Zanette D, Chaimovich H, Cuccovia IM. Effects of Micelles and Vesicles on the Oximolysis of p‐Nitrophenyl Diphenyl Phosphate: A Model System for Surfactant‐Based Skin‐Defensive Formulations against Organophosphates. J Pharm Sci 2009; 98:1040-52. [DOI: 10.1002/jps.21506] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Feitosa E, Alves FR, Castanheira EMS, Oliveira MECDR. DODAB and DODAC bilayer-like aggregates in the micromolar surfactant concentration domain. Colloid Polym Sci 2009. [DOI: 10.1007/s00396-009-2008-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Feitosa E, Alves FR. The role of counterion on the thermotropic phase behavior of DODAB and DODAC vesicles. Chem Phys Lipids 2008; 156:13-6. [DOI: 10.1016/j.chemphyslip.2008.08.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Revised: 06/25/2008] [Accepted: 08/05/2008] [Indexed: 11/22/2022]
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Lopes A, Edwards K, Feitosa E. Extruded vesicles of dioctadecyldimethylammonium bromide and chloride investigated by light scattering and cryogenic transmission electron microscopy. J Colloid Interface Sci 2008; 322:582-8. [DOI: 10.1016/j.jcis.2008.03.015] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Revised: 03/02/2008] [Accepted: 03/04/2008] [Indexed: 11/17/2022]
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Abstract
his review highlights the relevant issues of spontaneous formation of vesicles. Both the common characteristics and the differences between liposomes and vesicles are given. The basic concept of the molecular packing parameter as a precondition of vesicles formation is discussed in terms of geometrical factors, including the volume and critical length of the amphiphile hydrocarbon chain. According to theoretical considerations, the formation of vesicles occurs in the systems with packing parameters between 1/2 and 1. Using common as well as new methods of vesicle preparation, a variety of structures is described, and their nomenclature is given. With respect to sizes, shapes and inner structures, vesicles structures can be formed as a result of self-organisation of curved bilayers into unilamellar and multilamellar closed soft particles. Small, large and giant uni-, oligo-, or multilamellar vesicles can be distinguished. Techniques for determination of the structure and properties of vesicles are described as visual observations by optical and electron microscopy as well as the scattering techniques, notably dynamic light scattering, small angle X-ray and neutron scattering. Some theoretical aspects are described in short, viz., the scattering and the inverse scattering problem, angular and time dependence of the scattering intensity, the principles of indirect Fourier transformation, and the determination of electron density of the system by deconvolution of p(r) function. Spontaneous formation of vesicles was mainly investigated in catanionic mixtures. A number of references are given in the review.
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Affiliation(s)
- Suzana Segota
- Department of Chemistry, University of Zagreb, Faculty of Science, Horvatovac 102a, P.O. Box 163, 10001 Zagreb, Croatia
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Feitosa E, Jansson J, Lindman B. The effect of chain length on the melting temperature and size of dialkyldimethylammonium bromide vesicles. Chem Phys Lipids 2006; 142:128-32. [PMID: 16574087 DOI: 10.1016/j.chemphyslip.2006.02.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2005] [Revised: 02/07/2006] [Accepted: 02/08/2006] [Indexed: 10/24/2022]
Abstract
Differential scanning calorimetry (DSC) and dynamic light scattering (DLS) were used to obtain the gel to liquid-crystalline phase transition temperature (Tm) and the apparent hydrodynamic radius (Rh) of spontaneously formed cationic vesicles of dialkyldimethylammonium bromide salts (CnH2n+1)2(CH3)2N+.Br-, with varying chain lengths. The preparation of cationic vesicles from aqueous solution of these surfactants, for n=12, 14, 16 and 18 (DDAB, DTDAB, DHDAB and DODAB, respectively), requires the knowledge of the surfactant gel to liquid-crystalline phase transition temperature, or melting temperature (Tm) since below this temperature these surfactants are poorly or not soluble in water. That series of cationic surfactants has been widely investigated as vesicle-forming surfactants, although C12 and C18, DDAB and DODAB are by far the most investigated from this series. The dependence of Tm of these surfactants on the number n of carbons in the surfactant tails is reported. The Tm obtained by DSC increases non-linearly with n, and the vesicle apparent radius Rh is about the same for DHDAB and DODAB, but much smaller for DDAB.
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Affiliation(s)
- E Feitosa
- Physics Department, Sao Paulo State University, IBILCE/UNESP, Rua Cristovao Colombo, 2265, Sao Jose do Rio Preto, CEP 15054-000, SP, Brazil.
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Feitosa E, Bonassi NM, Loh W. Vesicle-micelle transition in mixtures of dioctadecyldimethylammonium chloride and bromide with nonionic and zwitterionic surfactants. Langmuir 2006; 22:4512-7. [PMID: 16649757 DOI: 10.1021/la052923j] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We have investigated the effect of mixing spontaneously formed dispersions of the cationic vesicle-forming dioctadecyldimethylammonium chloride and bromide (DODAX, with X being anions Cl- (C) or Br- (B)) with solutions of the micelle-forming nonionic ethylene oxide surfactants penta-, hepta-, and octaethyleneglycol mono-n-dodecyl ether, C12E(n) (n = 5, 7, and 8), and the zwitterionic 3-(N-hexadecyl-N,N-dimethylammonio)propane sulfonate (HPS). We used for this purpose differential scanning calorimetry (DSC), turbidity, and steady-state fluorescence spectroscopy to investigate the vesicle-micelle (V-M) transition yielded by adding C12E(n) and HPS to 1.0 mM vesicle dispersions of DODAC and DODAB. The addition of these surfactants lowers the gel-to-liquid crystalline phase transition temperature (T(m)) of DODAC and DODAB, and the transition becomes less cooperative, that is, the thermogram transition peak shifts to lower temperature and broadens to disappear when the V-M transition is complete, the vesicle bilayer becomes less organized, and the T(m) decreases, in agreement with measurements of the fluorescence quantum yield of trans-diphenylpolyene (t-DPO) fluorescence molecules incorporated in the vesicle bilayer. Turbidity data indicate that the V-M transition comes about in three stages: first surfactants are solubilized into the vesicle bilayer; after saturation, the vesicles are ruptured, and, finally, the vesicles are completely solubilized and only mixed micelles are formed. The critical points of bilayer saturation and vesicle solubilization were obtained from the turbidity and fluorescence curves, and are reported in this communication. The solubility of DODAX is stronger for C12E(n) than it is for HPS, meaning that C12E(n) solubilizes DODAX more efficiently than does HPS. The surfactant solubilization depends slightly on the counterion, and varies according to the sequence C12E5 > C12E7 > C12E8 > HPS.
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Affiliation(s)
- Eloi Feitosa
- Departmento de Física, IBILCE/UNESP, São José do Rio Preto, SP, Brazil.
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Feitosa E, Karlsson G, Edwards K. Unilamellar vesicles obtained by simply mixing dioctadecyldimethylammonium chloride and bromide with water. Chem Phys Lipids 2006; 140:66-74. [PMID: 16494856 DOI: 10.1016/j.chemphyslip.2006.01.005] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Revised: 12/22/2005] [Accepted: 01/13/2006] [Indexed: 10/25/2022]
Abstract
Optically clear dispersions of dioctadecyldimethylammonium bromide and chloride (DODAX, X = Br-, Cl-) in water can be obtained by simply mixing the amphiphiles at low concentrations (1 mM) and at a temperature safely above the gel to liquid crystalline phase transition temperature (Tm approximately 45-48 degrees C) of DODAX in water. Under these conditions, dynamic light scattering shows that, at room temperature, the dispersions contain two well-defined populations of large vesicles with average hydrodynamic radii (R(H)) of 80 and 337 nm for DODAB and of 69 and 247 nm for DODAC. Cryo-transmission electron microscopy (cryo-TEM) micrographs show that DODAX vesicles are unilamellar and polydisperse with apparent radius up to 800 nm. The vesicles are stable for at least 1 month according to the ageing time-dependence of the turbidity and molar absorption coefficient.
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Affiliation(s)
- Eloi Feitosa
- Departamento de Física, IBILCE/UNESP, Rua Cristóvão Colombo 2265, 15054-000, São José do Rio Preto, SP, CEP: 15054-000, Brazil.
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Abstract
A series of pH-sensitive lipids, la-h [(2,3-bis-alkylcarbamoyloxy-propyl)-trialkylammonium halide] and 2a-d (1-di-methylamino-2,3-bis-alkylcarbamoyloxy-propane), with carbamate linkages between the hydrocarbon chains and an ammonium or tertiary amine head, were synthesized for liposome-mediated gene delivery. The variable length of the carbon chains and the quaternary ammonium or neutral tertiary amine heads allowed us to identify the structure-function relationship showing how these factors would affect cationic lipids in gene delivery performance.
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Affiliation(s)
- Dongliang Liu
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, China.
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Benatti CR, Feitosa E, Fernandez RM, Lamy-Freund MT. Structural and thermal characterization of dioctadecyldimethylammonium bromide dispersions by spin labels. Chem Phys Lipids 2001; 111:93-104. [PMID: 11457439 DOI: 10.1016/s0009-3084(01)00134-7] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Dioctadecyldimethylammonium bromide (DODAB) dispersions obtained by simply mixing the amphiphile in water, and by bath-sonication, were investigated by electron spin resonance (ESR) of stearic acids and their methyl ester derivatives, labeled at the 5th and 16th carbons of the acyl chain. The ESR spectra indicate that the non-sonicated dispersions are formed mainly by one population of DODAB vesicles, either in the gel (T<T(m)) or in the liquid-crystalline (T>T(m)) state. Around T(m) there is a co-existence of the two phases, with a thermal hysteresis of about 3.2 degrees C. In sonicated DODAB dispersions, spin labels indicate two different environments even for temperatures far below T(m): one similar to that obtained with non-sonicated samples, a gel phase, and another one in the liquid-crystalline state. The fluid phase domain present below T(m) could correspond to either the periphery of bilayer fragments, reported to be present in sonicated DODAB dispersions, or to high curvature vesicles.
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Affiliation(s)
- C R Benatti
- Physics Department, IBILCE/UNESP, Rua Cristóvão Colombo, 2265 SP, CEP 15054-000, Sao Jose do Rio Preto, Brazil
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Abstract
The anti-inflammatory, analgesic, and antipyretic drugs indomethacin (INDO) and acemetacin (ACE), extensively used for the treatment of diseases of degenerative or inflammatory character, exhibit marked gastric irritant action, have low water solubility at neutral pH, and decompose in alkali. Alternative formulations are being investigated to obtain products with lower toxicity and higher stability. Here we examine the effect of liposome charge on the rate of alkaline decomposition of INDO and ACE using micelles as reference. Binding of ACE and INDO to zwitterionic hexadecylphosphocholine (HDPC) micelles and phosphatidylcholine (PC) liposomes was analyzed using a two-phase separation model to quantify the effect of these aggregates on the rate of alkaline degradation. The substrate association constants to HDPC micelles were 1335 and 2192 M(-1) for INDO and ACE, respectively, whereas the corresponding values for PC vesicles were 612 and 3050 M(-1). The difference was attributed to the additional hydrophobicity of ACE. The inhibitory effect of HDPC micelles and PC vesicles was quantified by calculating the ratio between the rate constants in water (k(w)) and in the aggregate (k(m)). The values of the k(w)/k(m) ratios for INDO and ACE in HDPC micelles were, respectively, 80 and 42, and in PC liposomes these ratios were 21 and 3.7, respectively. Positively charged micelles of hexadecyltrimethylammonium chloride (CTAC) and vesicles containing varying proportions of dioctadecyldimethylammonium chloride (DODAC) and PC increase the rate of INDO and ACE alkaline decomposition. Vesicle effects were very sensitive to the DODAC/PC ratio, with rates increasing with the proportion of DODAC. The data were analyzed quantitatively using a pseudophase model with explicit consideration of ion exchange. The calculated second-order rate constants in micelles and vesicles were lower than that in water. The charge density in the liposome necessary to increase the entrapment efficiency and decrease drug decomposition can be modulated, by judicious choice of pH and ionic strength. These manipulations can lead to more stable formulation with increased efficiency in drug entrapment and controlled effects on drug stability.
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Affiliation(s)
- C Matos
- CEQUP/Departamento de Química-Física, Faculdade de Farmácia, Universidade do Porto, Portugal
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Affiliation(s)
- Paula C. A. Barreleiro
- Center for Chemistry and Chemical Engineering, Physical Chemistry 1, Lund University, P.O. Box 124, S-22100 Lund, Sweden, and Department of Chemical Engineering, State University of New York at Buffalo, Buffalo, New York 14260-4200
| | - Gerd Olofsson
- Center for Chemistry and Chemical Engineering, Physical Chemistry 1, Lund University, P.O. Box 124, S-22100 Lund, Sweden, and Department of Chemical Engineering, State University of New York at Buffalo, Buffalo, New York 14260-4200
| | - Paschalis Alexandridis
- Center for Chemistry and Chemical Engineering, Physical Chemistry 1, Lund University, P.O. Box 124, S-22100 Lund, Sweden, and Department of Chemical Engineering, State University of New York at Buffalo, Buffalo, New York 14260-4200
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Abstract
The gel to liquid crystalline phase transition of the double-chained cationic dioctadecyldimethylammonium chloride and bromide (DODAX, X = Cl- or Br-) in aqueous vesicle dispersions prepared by non-sonication. sonication and extrusion has been investigated using high-sensitivity differential scanning calorimetry (DSC). The transition temperature (Tm) is a function of the preparation method, amphiphile concentration, vesicle curvature and nature of the counterion. DSC thermograms for DODAB and DODAC non-sonicated vesicle dispersions exhibit a single endothermic peak at Tm roughly independent of concentration up to 10 mM. Extrusion broadens the transition peak and shifts Tm downwards. Sonication, however, broadens slightly the transition peak and tends to shift Tm upwards suggesting that extrusion and sonication form vesicles with different characteristics. DODAC always exhibits higher Tm than DODAB irrespective of the preparation method. Tm changes as follows: Tm (sonicated) > or = Tm (non-sonicated) > Tm (extruded). Hysteresis of about 7 degrees C was observed for DODAB vesicle dispersions.
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Affiliation(s)
- E Feitosa
- Department of Physics, IBILCE/UNESP, Saõ José do Rio Preto, SP, Brazil.
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