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Steffes VM, Zhang Z, Ewert KK, Safinya CR. Cryo-TEM Reveals the Influence of Multivalent Charge and PEGylation on Shape Transitions in Fluid Lipid Assemblies: From Vesicles to Discs, Rods, and Spheres. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:18424-18436. [PMID: 38051205 PMCID: PMC10799670 DOI: 10.1021/acs.langmuir.3c02664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
Lipids, and cationic lipids in particular are of interest as delivery vectors for hydrophobic drugs such as the cancer therapeutic paclitaxel, and the structures of lipid assemblies affect their efficacy. We investigated the effect of incorporating the multivalent cationic lipid MVL5 (+5e) and poly(ethylene glycol)-lipids (PEG-lipids), alone and in combination, on the structure of fluid-phase lipid assemblies of the charge-neutral lipid 1,2-dioleoyl-sn-glycero-phosphocholine (DOPC). This allowed us to elucidate lipid-assembly structure correlations in sonicated formulations with high charge density, which are not accessible with univalent lipids such as the well-studied DOTAP (+1e). Cryogenic transmission electron microscopy (cryo-TEM) allowed us to determine the structure of the lipid assemblies, revealing diverse combinations of vesicles and disc-shaped, worm-like, and spherical micelles. Remarkably, MVL5 forms an essentially pure phase of disc micelles at 50 mol % MVL5. At a higher (75 mol %) content of MVL5, short- and intermediate-length worm-like micellar rods were observed, and in ternary mixtures with PEG-lipid, longer and highly flexible worm-like micelles formed. Independent of their length, the worm-like micelles coexisted with spherical micelles. In stark contrast, DOTAP forms mixtures of vesicles, disc micelles, and spherical micelles at all studied compositions, even when combined with PEG-lipids. The observed similarities and differences in the effects of charge (multivalent versus univalent) and high curvature (multivalent charge versus PEG-lipid) on the assembly structure provide insights into parameters that control the size of fluid lipid nanodiscs, relevant for future applications.
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Affiliation(s)
- Victoria M. Steffes
- Materials Department, University of California, Santa Barbara, California 93106, USA
- Chemistry and Biochemistry Department, University of California, Santa Barbara, California 93106, USA
| | - Zhening Zhang
- The National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY 10027, USA
- Present Address: Biochemistry and Molecular Biophysics Department, Columbia University Medical Center, New York, NY 10032, USA
| | - Kai K. Ewert
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Cyrus R. Safinya
- Materials Department, University of California, Santa Barbara, California 93106, USA
- Molecular, Cellular, and Developmental Biology Department, University of California, Santa Barbara, California 93106, USA
- Physics Department, University of California, Santa Barbara, California 93106, USA
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Self-assembling properties of ionisable amphiphilic drugs in aqueous solution. J Colloid Interface Sci 2021; 600:701-710. [PMID: 34049025 DOI: 10.1016/j.jcis.2021.05.049] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 05/06/2021] [Accepted: 05/08/2021] [Indexed: 11/22/2022]
Abstract
HYPOTHESIS Common amphiphilic drug molecules often have a more rigid nonpolar part than conventional surfactants. The rigidity is expected to influence the self-assembling properties and possibly give rise to aggregation patterns different from that of regular surfactants. EXPERIMENTS We have investigated self-assembling properties of the hydrochloride salts of adiphenine (ADP), pavatrine (PVT), and amitriptyline (AMT) at concentrations up to 50 wt% using small-angle x-ray scattering, dynamic light scattering, cryo-transmission electron microscopy, and surface tension measurements. FINDINGS All drugs form small micelles of oblate spheroidal shape at concentrations above the critical micelle concentrations (CMC). The micelles grow weakly in size up to about 20 wt%, where the aggregation number reaches a maximum followed by a slight decrease in size at higher drug concentrations. We observe a correlation between the decrease in micelle size at high concentrations and an increasing charge of the micelles, as the degree of ionization increases with increasing drug concentration and decreasing pH. In contrast to what has previously been reported, the aggregation behavior of all studied drugs resembles the closed association behavior of conventional surfactants with a short aliphatic chain as hydrophobic tail group i.e. the micelles are always small in size and lack a second CMC. CMC values were determined with surface tension measurements, including also lidocaine hydrochloride (LDC) and chlorpromazine hydrochloride (CHL).
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Forooqi Motlaq V, Ortega-Holmberg M, Edwards K, Gedda L, Lyngsø J, Pedersen JS, Bergström LM. Investigation of the enhanced ability of bile salt surfactants to solubilize phospholipid bilayers and form mixed micelles. SOFT MATTER 2021; 17:7769-7780. [PMID: 34351343 DOI: 10.1039/d1sm00745a] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The self-assembly in mixtures of the anionic bile salt surfactant sodium deoxycholate (NaDC) and the zwitterionic phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) in physiological saline solution has been investigated using light scattering, small-angle X-ray scattering and cryo-transmission electron microscopy. Rather small tri-axial ellipsoidal NaDC-DMPC mixed micelles form at a high content of bile salt in the mixture, which increase in size as an increasing amount of DMPC is incorporated into the micelles. Eventually, the micelles begin to grow substantially in length to form long wormlike micelles. At higher mole fractions of DMPC, the samples become turbid and cryo-TEM measurements reveal the existence of large perforated vesicles (stomatosomes), coexisting with geometrically open disks. To our knowledge, stomatosomes have not been observed before for any bile salt-phospholipid system. Mixed micelles are found to be the sole aggregate structure in a very wide regime of bile salt-phospholipid compositions, i.e. up to about 77 mol% phospholipid in the micelles. This is much higher than the corresponding value of 25 mol% observed for the conventional surfactant hexadecyltrimethylammonium bromide (CTAB) mixed with DMPC in the same solvent. The enhanced ability of bile salt surfactants to solubilize phospholipid bilayers and form mixed micelles is rationalized using bending elasticity theory. From our theoretical analysis, we are able to conclude that amphiphilic molecules rank in the following order of increasing spontaneous curvature: phospholipids < conventional surfactants < bile salts. The bending rigidity of the different amphiphilic molecules increases according to the following sequence: bile salts < conventional surfactants < phospholipids.
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Affiliation(s)
- Vahid Forooqi Motlaq
- Department of Medicinal Chemistry, Pharmaceutical Physical Chemistry, Uppsala University, SE-751 23 Uppsala, Sweden.
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Twigg MS, Baccile N, Banat IM, Déziel E, Marchant R, Roelants S, Van Bogaert INA. Microbial biosurfactant research: time to improve the rigour in the reporting of synthesis, functional characterization and process development. Microb Biotechnol 2021; 14:147-170. [PMID: 33249753 PMCID: PMC7888453 DOI: 10.1111/1751-7915.13704] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 10/16/2020] [Accepted: 10/23/2020] [Indexed: 01/01/2023] Open
Abstract
The demand for microbially produced surface-active compounds for use in industrial processes and products is increasing. As such, there has been a comparable increase in the number of publications relating to the characterization of novel surface-active compounds: novel producers of already characterized surface-active compounds and production processes for the generation of these compounds. Leading researchers in the field have identified that many of these studies utilize techniques are not precise and accurate enough, so some published conclusions might not be justified. Such studies lacking robust experimental evidence generated by validated techniques and standard operating procedures are detrimental to the field of microbially produced surface-active compound research. In this publication, we have critically reviewed a wide range of techniques utilized in the characterization of surface-active compounds from microbial sources: identification of surface-active compound producing microorganisms and functional testing of resultant surface-active compounds. We have also reviewed the experimental evidence required for process development to take these compounds out of the laboratory and into industrial application. We devised this review as a guide to both researchers and the peer-reviewed process to improve the stringency of future studies and publications within this field of science.
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Affiliation(s)
- Matthew Simon Twigg
- School of Biomedical SciencesUlster UniversityColeraine, Co. LondonderryBT52 1SAUK
| | - Niki Baccile
- Centre National de la Recherche ScientifiqueLaboratoire de Chimie de la Matière Condensée de ParisSorbonne UniversitéLCMCPParisF‐75005France
| | - Ibrahim M. Banat
- School of Biomedical SciencesUlster UniversityColeraine, Co. LondonderryBT52 1SAUK
| | - Eric Déziel
- Centre Armand‐Frappier Santé BiotechnologieInstitut National de la Recherche Scientifique (INRS)531, Boul. Des PrairiesLavalQCH7V 1B7Canada
| | - Roger Marchant
- School of Biomedical SciencesUlster UniversityColeraine, Co. LondonderryBT52 1SAUK
| | - Sophie Roelants
- Centre for Industrial Biotechnology and Biocatalysis (InBio.be)Faculty of Bioscience EngineeringGhent UniversityGhentBelgium
- Bio Base Europe Pilot PlantRodenhuizenkaai 1Ghent9042Belgium
| | - Inge N. A. Van Bogaert
- Centre for Synthetic BiologyDepartment of BiotechnologyGhent UniversityCoupure Links 653Ghent9000Belgium
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5
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Endter LJ, Risselada HJ. Where are those lipid nano rings? J Colloid Interface Sci 2020; 587:789-796. [PMID: 33246654 DOI: 10.1016/j.jcis.2020.11.038] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Revised: 11/06/2020] [Accepted: 11/07/2020] [Indexed: 12/28/2022]
Abstract
Highly curved toroidal micelles with diameters as small as 100 nm have been successfully constructed by self-assembly of amphiphilic block copolymers. These structures may have potential applications in gene or drug delivery. Experimental observations suggest that toroidal micelles likely originate from spherical or disc-like micelles which are tricked into forming toroidal micelles upon external stimuli ('smart' materials). Since self-assembly of polymeric and lipid surfactants is guided by the same physical principles, we hypothesize that 'smart' lipid surfactants can be equivalently tricked into forming highly curved toroidal micelles that are tenfold smaller (≃10 nm diameter). Paradoxically, these 'nano rings' have never been observed. Using coarse-grained molecular dynamics (MD) simulations in conjunction with a state-of-the-art free energy calculation method (a string method), we illustrate how a thermo-responsive lipid surfactant is able to form toroidal micelles. These micelles originate from disc-like micelles that are spontaneously perforated upon heat shocking, thereby supporting a longstanding hypothesis on the possible origin of polymeric toroidal micelle phases observed in experiments. We illustrate that kinetically stable 'nano rings' are substantially shorter lived than their tenfold larger polymeric analogs. The estimated life-time (milliseconds) is in fact similar to the characteristic breaking time of the corresponding worm-like micelle. Finally, we resolve the characteristic finger print which 'nano rings' leave in time-resolved X-ray spectra and illustrate how the uptake of small DNA fragments may enhance their stability. Despite a shared kinetics of self-assembly, length scale dependent differences in the life-time of surfactant phases can occur when phases are kinetically rather than thermodynamically stable. This results in the apparent absence or presence of toroidal micelle phases on different length scales. Our theoretical work precisely illustrates that the universality of surfactants nevertheless remains conserved even at different length scales.
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Affiliation(s)
- Laura Josefine Endter
- Georg-August University Göttingen, Institute for Theoretical Physics, 37077 Göttingen, Germany
| | - Herre Jelger Risselada
- Georg-August University Göttingen, Institute for Theoretical Physics, 37077 Göttingen, Germany; Leiden University, Leiden Institute of Chemistry (LIC), 2311 Leiden, Netherlands.
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6
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Jiao W, Yang H, Wu Z, Liu J, Zhang W. Self-assembled block polymer aggregates in selective solution: controllable morphology transitions and their applications in drug delivery. Expert Opin Drug Deliv 2020; 17:947-961. [DOI: 10.1080/17425247.2020.1767582] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Weiqi Jiao
- Department of Pharmaceutics, China Pharmaceutical University, Nanjing, PR China
- Department of Biochemistry and Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, US
| | - Hu Yang
- Department of Chemical and Life Science Engineering, Virginia Commonwealth University, Richmond, VA, United States
| | - Zimei Wu
- School of Pharmacy, University of Auckland, Auckland, New Zealand
| | - Jianping Liu
- Department of Pharmaceutics, China Pharmaceutical University, Nanjing, PR China
| | - Wenli Zhang
- Department of Pharmaceutics, China Pharmaceutical University, Nanjing, PR China
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7
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Abstract
Vesicle structures primarily embody spherical capsules composed of a single or multiple bilayers, entrapping a pool of aqueous solution in their interior. The bilayers can be synthesised by phospholipids or other amphiphiles (surfactants, block copolymers, etc.). Vesicles with broad-spectrum applications in numerous scientific disciplines, including biochemistry, biophysics, biology, and various pharmaceutical industries, have attracted widespread attention. Consequently, a multitude of protocols have been devised and proposed for their fabrication. In this review, with a motivation to derive the basic conditions for the formation of vesicles, the associated thermodynamic and kinetic aspects are comprehensively appraised. Contextually, an all-purpose overview of the underlying thermodynamics of bilayer/membrane generation and deformation, including the chemical potential of aggregates, geometric packing and the concept of elastic properties, is presented. Additionally, the current review highlights the probable, inherent mechanisms of vesicle formation under distinct modes of manufacturing. We lay focus on vesicle formation from pre-existing bilayers, as well as from bilayers, which form when lipids from an organic solvent are transferred into an aqueous medium. Furthermore, we outline the kinetic effects on vesicle formation from the lamellar phase, with and without the presence of shearing force. Wherever required, the experimental and/or theoretical outcomes, the driving forces for vesicle size selection, and various scaling laws are also reviewed, all of which facilitate an overall improved understanding of the vesicle formation mechanisms.
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Affiliation(s)
- Chandra Has
- Department of Chemical Engineering, Indian Institute of Technology Bombay, Mumbai, India
| | - Sharadwata Pan
- School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany
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8
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Steffes VM, Zhang Z, MacDonald S, Crowe J, Ewert KK, Carragher B, Potter CS, Safinya CR. PEGylation of Paclitaxel-Loaded Cationic Liposomes Drives Steric Stabilization of Bicelles and Vesicles thereby Enhancing Delivery and Cytotoxicity to Human Cancer Cells. ACS APPLIED MATERIALS & INTERFACES 2020; 12:151-162. [PMID: 31820904 PMCID: PMC6984750 DOI: 10.1021/acsami.9b16150] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Poly(ethylene glycol) (PEG) is a polymer used widely in drug delivery to create "stealth" nanoparticles (NPs); PEG coatings suppress NP detection and clearance by the immune system and beneficially increase NP circulation time in vivo. However, NP PEGylation typically obstructs cell attachment and uptake in vitro compared to the uncoated equivalent. Here, we report on a cationic liposome (CL) NP system loaded with the hydrophobic cancer drug paclitaxel (PTX) in which PEGylation (i.e., PEG-CLPTX NPs) unexpectedly enhances, rather than diminishes, delivery efficacy and cytotoxicity to human cancer cells. This highly unexpected enhancement occurs even when the PEG-chains coating the NP are in the transition regime between the mushroom and brush conformations. Cryogenic transmission electron microscopy (TEM) of PEG-CLPTX NPs shows that PEG causes the proliferation of a mixture of sterically stabilized nanometer-scale vesicles and anisotropic micelles (e.g., bicelles). Remarkably, the onset of bicelles at sub-monolayer concentrations of the PEG coat has to our knowledge not been previously reported; it was previously thought that PEG-lipid in this composition regime was incorporated into vesicles but did not alter their shape. Confocal microscopy and flow cytometry reveal significantly greater PTX cell uptake from stabilized PEG-CLPTX NPs (vesicles and bicelles) in contrast to bare CLPTX NPs, which can aggregate in cell medium. This underscores the ability of steric stabilization to facilitate NP entry into cells via distinct size-dependent endocytic pathways, some of which cannot transport large NP aggregates into cells. This study highlights the value of understanding how PEGylation alters NP shape and structure, and thus NP efficacy, to design next-generation stealth drug carriers that integrate active cell-targeting strategies into NPs for in vivo delivery.
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Affiliation(s)
- Victoria M. Steffes
- Materials Department, University of California, Santa Barbara, California 93106, USA
- Chemistry and Biochemistry Department, University of California, Santa Barbara, California 93106, USA
| | - Zhening Zhang
- The National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY 10027, USA
- Present Address: Biochemistry and Molecular Biophysics Department, Columbia University Medical Center, New York, NY 10032, USA
| | - Scott MacDonald
- Physics Department, University of California, Santa Barbara, California 93106, USA
| | - John Crowe
- Physics Department, University of California, Santa Barbara, California 93106, USA
| | - Kai K. Ewert
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Bridget Carragher
- The National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY 10027, USA
| | - Clinton S. Potter
- The National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY 10027, USA
| | - Cyrus R. Safinya
- Materials Department, University of California, Santa Barbara, California 93106, USA
- Physics Department, University of California, Santa Barbara, California 93106, USA
- Molecular, Cellular, and Developmental Biology Department, University of California, Santa Barbara, California 93106, USA
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9
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Viitala L, Pajari S, Gentile L, Määttä J, Gubitosi M, Deska J, Sammalkorpi M, Olsson U, Murtomäki L. Shape and Phase Transitions in a PEGylated Phospholipid System. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:3999-4010. [PMID: 30789270 PMCID: PMC6727609 DOI: 10.1021/acs.langmuir.8b03829] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Revised: 02/18/2019] [Indexed: 05/23/2023]
Abstract
Poly(ethylene glycol) (PEG) polymers and PEG-conjugated lipids are widely used in bioengineering and drug transport applications. A PEG layer in a drug carrier increases hydrophilic repulsion, inhibits membrane fusion and serum opsonin interactions, and prolongs the storage and circulation time. It can also change the carrier shape and have an influence on many properties related to the content release of the carrier. In this paper, we focus on the physicochemical effects of PEGylation in the lipid bilayer. We introduce laurdanC as a fluorophore for shape recognition and phase transition detection. Together with laurdanC, cryogenic transmission electron microscopy, differential scanning calorimetry, molecular dynamics simulations, and small-angle X-ray scattering/wide-angle X-ray scattering, we acquire information of the particle/bilayer morphology and phase behavior in systems containing 1,2-dipalmitoyl- sn-glycero-3-phosphocholine:1,2-distearoyl- sn-glycero-3-phosphoethanolamine-PEG(2000) with different fractions. We find that PEGylation leads to two important and potentially usable features of the system. (1) Spherical vesicles present a window of elevated chain-melting temperatures and (2) lipid packing shape-controlled liposome-to-bicelle transition. The first finding is significant for targets requiring multiple release sequences and the second enables tuning the release by composition and the PEG polymer length. Besides drug delivery systems, the findings can be used in other smart soft materials with trigger-polymers as well.
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Affiliation(s)
- Lauri Viitala
- Department
of Chemistry and Materials Science, Aalto
University, P.O. Box 16100, FI-00076 Aalto, Finland
| | - Saija Pajari
- Department
of Chemistry and Materials Science, Aalto
University, P.O. Box 16100, FI-00076 Aalto, Finland
| | - Luigi Gentile
- Physical
Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
- Department
of Biology, MEMEG Unit, Lund University, Sölvegatan 37, SE-223 62 Lund, Sweden
- PRPDepartment
of Chemistry, University of Bari Aldo Moro, Via Orabona 4, 70126 Bari, Italy
| | - Jukka Määttä
- Department
of Chemistry and Materials Science, Aalto
University, P.O. Box 16100, FI-00076 Aalto, Finland
| | - Marta Gubitosi
- Physical
Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
| | - Jan Deska
- Department
of Chemistry and Materials Science, Aalto
University, P.O. Box 16100, FI-00076 Aalto, Finland
| | - Maria Sammalkorpi
- Department
of Chemistry and Materials Science, Aalto
University, P.O. Box 16100, FI-00076 Aalto, Finland
| | - Ulf Olsson
- Physical
Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
| | - Lasse Murtomäki
- Department
of Chemistry and Materials Science, Aalto
University, P.O. Box 16100, FI-00076 Aalto, Finland
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10
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Mortensen HG, Jensen GV, Hansen SK, Vosegaard T, Pedersen JS. Structure of Phospholipid Mixed Micelles (Bicelles) Studied by Small-Angle X-ray Scattering. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:14597-14607. [PMID: 30383384 DOI: 10.1021/acs.langmuir.8b02704] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Mixed phospholipid micelles (bicelles) are widely applied in nuclear magnetic resonance (NMR) studies of membrane proteins in solution, as they can solubilize these proteins and provide a membrane-like environment. In this work, the structure of bicelles of dihexanoyl phosphatidyl choline (DHPC) and dimyristoyl phosphatidyl choline (DMPC) at different ratios was determined by small-angle X-ray scattering (SAXS) at 37 °C. Samples with concentrations as applied for NMR measurements with 28 wt % lipids were diluted to avoid concentration effects in the SAXS data. The DMPC/DHPC ratio within the bicelles was kept constant by diluting with solutions of finite DHPC concentrations, where the concentration of free DHPC is the same as in the original solution. Absolute-scale modeling of the SAXS data using molecular and concentration constraints reveals a relatively complex set of morphologies of the lipid aggregates as a function of the molar ratio Q of DMPC to DHPC. At Q = 0 (pure DHPC lipids), oblate core-shell micelles are present. At Q = 0.5, the bicelles have a tablet-shaped core-shell cylindrical form with an ellipsoidal cross section. For Q = 1, 2, 3.2, and 4, the bicelles have a rectangular cuboidal structure with a core and a shell, for which the overall length and width increase with Q. At Q = ∞ (pure DMPC), there is coexistence between multilamellar structures and free bilayers. For Q = 1-4, the hydrocarbon core is relatively narrow and the headgroup thickness on the flat areas is larger than that of, respectively, pure DHPC and DMPC, suggesting some mixing of DHPC into these areas and staggering of the molecules. This is further supported by comparisons of the ratio of the areas of rim and flat parts and estimates of the composition of the flat areas.
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Affiliation(s)
- Henriette G Mortensen
- Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO) , Aarhus University , Gustav Wieds Vej 14 , 8000 Aarhus C , Denmark
| | - Grethe V Jensen
- Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO) , Aarhus University , Gustav Wieds Vej 14 , 8000 Aarhus C , Denmark
| | - Sara K Hansen
- Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO) , Aarhus University , Gustav Wieds Vej 14 , 8000 Aarhus C , Denmark
| | - Thomas Vosegaard
- Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO) , Aarhus University , Gustav Wieds Vej 14 , 8000 Aarhus C , Denmark
| | - Jan Skov Pedersen
- Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO) , Aarhus University , Gustav Wieds Vej 14 , 8000 Aarhus C , Denmark
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11
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12
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Asgari M. A molecular model for the free energy, bending elasticity, and persistence length of wormlike micelles. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2015; 38:98. [PMID: 26362658 DOI: 10.1140/epje/i2015-15098-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Revised: 07/15/2015] [Accepted: 08/05/2015] [Indexed: 06/05/2023]
Abstract
An expression for the elastic free-energy density of a wormlike micelle is derived taking into account interactions between its constituent molecules. The resulting expression is quadratic in the curvature and torsion of the centerline of micelle and thus resembles free-energy density functions for polymer chains and helical filaments such as DNA. The model is applied on a wormlike micelle in the shape of a circular arc, open or closed. Conditions under which linear chains in dilute systems transform into toroidal rings are analyzed. Two concrete anisotropic soft-core interaction potentials are used to calculate the elastic moduli present in the derived model, in terms of the density of the molecules and their dimensions. Expressions for the persistence length of the wormlike micelle are found based on the flexural rigidities so obtained. Similar to previous observations, our results indicate that the persistence length of a wormlike micelle increases as the aspect ratio of its constituent molecules increases. A detailed application of the model on wormlike micelles of toroidal geometry, along with employing statistical-thermodynamical concepts of self-assembly is performed, and the results are found to be well consistent with the literature. Steps to obtain the material parameters through possible experiments are discussed.
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Affiliation(s)
- Meisam Asgari
- Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, H3A0C3, Montreal, QC, Canada.
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13
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Bergström LM, Tehrani-Bagha A, Nagy G. Growth Behavior, Geometrical Shape, and Second CMC of Micelles Formed by Cationic Gemini Esterquat Surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:4644-4653. [PMID: 25835031 DOI: 10.1021/acs.langmuir.5b00742] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Micelles formed by novel gemini esterquat surfactants have been investigated with small-angle neutron scattering (SANS). The growth behavior of the micelles is found to differ conspicuously depending on the length of the gemini surfactant spacer group. The gemini surfactant with a long spacer form rather small triaxial ellipsoidal tablet-shaped micelles that grow weakly with surfactant concentration in the entire range of measured concentrations. Geminis with a short spacer, on the other hand, form weakly growing oblates or tablets at low concentrations that start to grow much more strongly into polydisperse rodlike or wormlike micelles at higher concentrations. The latter behavior is consistent with the presence of a second CMC that marks the transition from the weakly to the strongly growing regime. It is found that the growth behavior in terms of aggregation number as a function of surfactant concentration always appear concave in weakly growing regimes, while switching to convex behavior in strongly growing regimes. As a result, we are able to determine the second CMC of the geminis with short spacer by means of suggesting a rather precise definition of it, located at the point of inflection of the growth curve that corresponds to the transition from concave to convex growth behavior. Our SANS results are rationalized by comparison with the recently developed general micelle model. In particular, this theory is able to explain and reproduce the characteristic appearances of the experimental growth curves, including the presence of a second CMC and the convex strongly growing regime beyond. By means of optimizing the agreement between predictions from the general micelle model and results from SANS experiments, we are able to determine the three bending elasticity constants spontaneous curvature, bending rigidity, and saddle-splay constant for each surfactant.
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Affiliation(s)
- L Magnus Bergström
- †Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden
| | - Alireza Tehrani-Bagha
- ‡Department of Chemical and Petroleum Engineering, American University of Beirut, Beirut, Lebanon
| | - Gergely Nagy
- §Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, Villigen PSI, Switzerland
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14
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Bergström LM, Grillo I. Correlation between the geometrical shape and growth behaviour of surfactant micelles investigated with small-angle neutron scattering. SOFT MATTER 2014; 10:9362-9372. [PMID: 25342439 DOI: 10.1039/c4sm01800a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The correlation between the growth behaviour and geometrical shape for CTAB-rich mixed micelles formed by the cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) and the anionic surfactant sodium octyl sulphate (SOS) has been investigated with small-angle neutron scattering (SANS). Small tablet-shaped micelles formed by CTAB are found to grow only weakly in size with increasing surfactant concentration. The extent of growth becomes increasingly stronger as the fraction of SOS is increased. At higher fractions of SOS, a rather weak growth at low surfactant concentrations is followed by a sharp increase in aggregation numbers beyond a certain surfactant concentration. Such an abrupt transition from weakly to strongly growing micelles has been observed in the past for several micellar systems and is usually referred to as the second critical micelle concentration. The growth behaviour has been rationalized from a theoretical point of view by means of employing the recently developed general micelle model. The theory excellently predicts micellar growth behaviours as well as the observed correlation between the geometrical shape and micellar growth. In accordance, both width and length are found to slightly increase for weakly growing tablet-shaped micelles. On the other hand, strongly growing micelles that are observed above the second cmc display a completely different behaviour, according to which the length increases considerably while the width of the micelles decreases. Most interestingly, by means of optimizing the agreement between the general micelle model and experimentally determined aggregation numbers, we are able to determine the three bending elasticity constants: spontaneous curvature, bending rigidity and saddle-splay constant.
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Affiliation(s)
- L M Bergström
- KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, SE-10044 Stockholm, Sweden.
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Bergström LM. Explaining the growth behavior of surfactant micelles. J Colloid Interface Sci 2014; 440:109-18. [PMID: 25460696 DOI: 10.1016/j.jcis.2014.10.054] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 10/10/2014] [Accepted: 10/18/2014] [Indexed: 11/30/2022]
Abstract
The growth behavior of surfactant micelles has been investigated from a theoretical point of view. It is demonstrated that predictions deduced from the spherocylindrical micelle model, which considers micelles that are only able to grow in the length direction, are inconsistent with experimental measurements. Accordingly, the rise in aggregation numbers above a certain concentration, roughly corresponding to the second critical micelle concentration, appears to be much stronger than predicted by the spherocylindrical micelle model. On the other hand, predictions deduced from the general micelle model, which considers micelles that are able to grow with respect to both width and length, show excellent agreement with experimental observations. The latter theory is based on bending elasticity and it is demonstrated that the associated three parameters spontaneous curvature, bending rigidity and saddle-splay constant may all be determined for a micellar system from experimental measurements of the aggregation number as a function of surfactant concentration. The three parameters turn out to influence the appearance of a micellar growth curve rather differently. In accordance, the location of the second cmc is mainly determined by the saddle-splay constant and the bending rigidity. The shape of the growth curve, when going from the region of weakly growing micelles at low surfactant concentrations to strongly growing micelles above the second cmc, is mainly influenced by the bending rigidity.
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Affiliation(s)
- L Magnus Bergström
- KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, SE-10044 Stockholm, Sweden.
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Bergström LM, Skoglund S, Edwards K, Eriksson J, Grillo I. Spontaneous transformations between surfactant bilayers of different topologies observed in mixtures of sodium octyl sulfate and hexadecyltrimethylammonium bromide. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:3928-3938. [PMID: 24697326 DOI: 10.1021/la4042259] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The influence of adding salt on the self-assembly in sodium octyl sulfate (SOS)-rich mixtures of the anionic surfactant SOS and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) have been investigated with the two complementary techniques, small-angle neutron scattering (SANS) and cryo-transmission electron microscopy. We are able to conclude that addition of a substantial amount of inert salt, NaBr, mainly has three effects on the structural behaviors: (i) the micelles become much larger at the transition from micelles to bilayers, (ii) the fraction of bilayer disks increases at the expense of vesicles, and (iii) bilayer aggregates perforated with holes are formed in the most diluted samples. A novel form factor valid for perforated bilayer vesicles and disks is introduced for the first time and, as a result, we are able to directly observe the presence of perforated bilayers by means of fitting SANS data with an appropriate model. Moreover, we are able to conclude that the morphology of bilayer aggregates changes according to the following sequence of different bilayer topologies, vesicles → disks → perforated bilayers, as the electrolyte concentration is increased and surfactant mole fraction in the bilayer aggregates approaches equimolarity. We are able to rationalize this sequence of transitions as a result of a monotonous increase of the bilayer saddle-splay constant (k(c)(bi)) with decreasing influence from electrostatics, in agreement with theoretical predictions as deduced from the Poisson-Boltzmann theory.
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Affiliation(s)
- L Magnus Bergström
- School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, KTH Royal Institute of Technology , , SE-10044 Stockholm, Sweden
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Bergström LM, Skoglund S, Edwards K, Eriksson J, Grillo I. Self-assembly in mixtures of an anionic and a cationic surfactant: a comparison between small-angle neutron scattering and cryo-transmission electron microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:11834-11848. [PMID: 23984704 DOI: 10.1021/la401884k] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The self-assembly in SOS-rich mixtures of the anionic surfactant sodium octyl sulfate (SOS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) has been investigated with the complementary techniques small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). Both techniques confirm the simultaneous presence of open and closed bilayer structures in highly diluted samples as well as the existence of small globular and large elongated micelles at higher concentrations. However, the two techniques sometimes differ with respect to which type of aggregates is present in a particular sample. In particular, globular or wormlike micelles are sometimes observed with cryo-TEM in the vicinity of the micelle-to-bilayer transition, although only bilayers are present according to SANS and the samples appear bluish to the eye. A similar discrepancy has previously been reported but could not be satisfactorily rationalized. On the basis of our comparison between in situ (SANS) and ex situ (cryo-TEM) experimental techniques, we suggest that this discrepancy appears mainly as a result of the non-negligible amount of surfactant adsorbed at interfaces of the thin sample film created during the cryo-TEM specimen preparation. Moreover, from our detailed SANS data analysis, we are able to observe the unusually high amount of free surfactant monomers present in SOS-rich mixtures of SOS and CTAB, and the experimental results give excellent agreement with model calculations based on the Poisson-Boltzmann mean field theory. Our careful comparison between model calculations and experiments has enabled us to rationalize the dramatic microstructural transformations frequently observed upon simply diluting mixtures of an anionic and a cationic surfactant.
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Affiliation(s)
- L Magnus Bergström
- Department of Chemistry, Surface, and Corrosion Science, School of Chemical Science and Engineering, KTH Royal Institute of Technology , SE-10044 Stockholm, Sweden
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Abstract
We present a phase-field model to study the morphological transitions of surfactant micelles in supersaturated dilute solution. Simulations reveal that multiply connected micellar structure can be produced by interface branching instability of a growing micelle at relatively large supersaturation and intermediate spontaneous curvatures. Two branching mechanisms, i.e., a disk-to-cylinder shape transition and a tip bifurcation process, are identified for disklike and cylindrical micelles, respectively. We propose that dynamic branching at the micelle growth front provides an important kinetic pathway for the formation of branched wormlike micelles that are observed in many surfactant systems.
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Affiliation(s)
- Ming Tang
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
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Magnus Bergström L, Garamus VM. Structural behaviour of mixed cationic surfactant micelles: A small-angle neutron scattering study. J Colloid Interface Sci 2012; 381:89-99. [DOI: 10.1016/j.jcis.2012.05.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Revised: 05/09/2012] [Accepted: 05/10/2012] [Indexed: 11/26/2022]
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Bergström LM, Garamus VM. Geometrical shape of micelles formed by cationic dimeric surfactants determined with small-angle neutron scattering. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:9311-9321. [PMID: 22624499 DOI: 10.1021/la301190d] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The influence of spacer group on the geometrical shape of micelles formed by quaternary-bis dimeric (Gemini) surfactants C(12)H(25)N(CH(3))(2)(CH(2))(s)N(CH(3))(2)C(12)H(25) (12-s-12) has been investigated with small-angle neutron scattering (SANS). Dimeric surfactants with a short spacer unit (12-3-12 and 12-4-12) are observed to form elongated general ellipsoidal micelles with half axes a < b < c, whereas SANS data demonstrate that 12-s-12 surfactants with 6 ≤ s ≤ 12 form rather small spheroidal micelles rather than strictly spherical micelles. By means of comparing our present SANS results with previously determined growth rates using time-resolved fluorescence quenching, we are able to conclude that micelles formed by 12-6-12, 12-8-12, 12-10-12, and 12-12-12 are shaped as oblate rather than prolate spheroids. As a result, our present investigation suggests a never before reported structural behavior of Gemini surfactant micelles, according to which micelles transform from elongated ellipsoids to nonelongated oblate spheroids as the length of the spacer group is increased. The aggregation number of oblate micelles is observed to monotonously decrease with an increasing length of the surfactant spacer group, mainly as a result of a decreasing minor half axis (a), whereas the major half axis (b) is rather constant with respect to s. We argue that geometrically heterogeneous elongated micelles are formed by dimeric surfactants with a short spacer group mainly as a result of the surface charges becoming less uniformly distributed over the micelle interface. As the length of the spacer group increases, the distance between intramolecular charges become approximately equal to the average distance between charges on the micelle interface, and as a result, rather small oblate spheroidal micelles with a more uniform distribution of surface charges are formed by dimeric 12-s-12 surfactants with 6 ≤ s ≤ 12.
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Affiliation(s)
- L Magnus Bergström
- School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
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Balogh J. Determining scaling in known phase diagrams of nonionic microemulsions to aid constructing unknown. Adv Colloid Interface Sci 2010; 159:22-31. [PMID: 20537298 DOI: 10.1016/j.cis.2010.05.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Revised: 04/16/2010] [Accepted: 05/03/2010] [Indexed: 11/30/2022]
Abstract
Microemulsions based on nonionic surfactants of the ethylene oxide alkyl ether type C(m)E(n), have been studied thoroughly for around 30 years. Thanks to the considerable amount of published data available on these systems, it is possible to observe trends to make predictions of phase diagrams not yet determined. Strey and Kahlweit, and subsequently Sottmann and Strey, with coworkers have studied and published phase diagrams for systems with a fixed ratio of oil to water, varying the surfactant, the so-called Kahlweit fish-cut diagrams. Some properties of the phase diagrams can be scaled to become general and not system dependent. Here are shown two examples of scaling data from phase diagrams and the use of trends to determine phase diagrams, both inside and outside a dataset. The trends of microemulsions with fixed ratio of surfactant to oil, the so-called Lund-cut diagrams, are also investigated. The trends are used to determine a new phase diagram and this is compared with previously unpublished experimental data on C(12)E(5)-Octadecane-Water system. The scalings and trends make it possible to get good estimations of many of the important properties of the phase diagrams, both temperatures and surfactant concentrations of interest, by investigating one sample in the 3-phase region of the balanced fish-cut diagram.
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Affiliation(s)
- Joakim Balogh
- Department of Chemistry, University of Coimbra, Portugal.
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Lundberg D, Almgren M, Jarvoll P, Karlsson G. Structural evolution of oleyl betainate aggregates: in situ formation of small unilamellar vesicles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:7996-8001. [PMID: 20232921 DOI: 10.1021/la904889n] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Betaine esters prepared from long-chain alcohols are a class of hydrolyzable cationic surfactants that is interesting both because the compounds can be designed to give harmless products on degradation and that the hydrolysis products can induce potentially useful changes in the properties of systems where such surfactants are present. In this work, the evolution in structure of aggregates formed by oleyl betainate during hydrolysis of the compound has been investigated using (1)H NMR and cryo-transmission electron microscopy (cryo-TEM). With an increasing extent of hydrolysis, and thus an increasing fraction of oleyl alcohol in the aggregates, the aggregate structure changes in a sequence consistent with an increase in the average packing parameter of the surfactant-alcohol mixture, from spherical micelles, via wormlike micelles, to vesicles. An important result from this work is that it demonstrates a means of in situ production of small unilamellar vesicles with a rather narrow size distribution.
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Affiliation(s)
- Dan Lundberg
- Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
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Jiang N, Karlsson G, Almgren M. Perforated Vesicles as Intermediate Structures in the Transition from Vesicles to Micelles in Dilute Aqueous Systems Containing Long Chain Alcohols and Ionic Surfactants. J DISPER SCI TECHNOL 2009. [DOI: 10.1080/01932690802643394] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Kakehashi R, Karlsson G, Almgren M. Stomatosomes, blastula vesicles and bilayer disks: Morphological richness of structures formed in dilute aqueous mixtures of a cationic and an anionic surfactant. J Colloid Interface Sci 2009; 331:484-93. [DOI: 10.1016/j.jcis.2008.11.044] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Revised: 11/18/2008] [Accepted: 11/19/2008] [Indexed: 11/16/2022]
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Bergström LM. Bending elasticity of nonionic surfactant layers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:1949-1960. [PMID: 19199752 DOI: 10.1021/la802532n] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A novel approach to evaluate the bending elasticity of monolayers formed by nonionic surfactants with a rigid head group is introduced by means of considering head group repulsion as derived from the free energy of mixing rigid hydrophilic head groups with surrounding solvent molecules as well as contributions related to the hydrophobic tails. Explicit expressions for the spontaneous curvature (H0), bending rigidity (kc) and saddle-splay constant (kc) have been derived for the constraint of constant chemical potential of free surfactant (thermodynamically open layers) as well as the constraint of constant aggregation number (thermodynamically closed layers). Most interestingly, it is demonstrated that kc for thermodynamically open layers formed by a nonionic surfactant with rigid tail and head group always must be zero. However, kc for surfactants with a flexible tail as a function of the head group-to-tail volume ratio is found to go through a maximum at some large, positive value of kc and H0 approximately 0. Eventually, kc falls below zero as the head group volume increases above a certain value. Hence, we may conclude that nonionic surfactants with a rigid head group may form thermodynamically stable fluid layers or aggregates only insofar the hydrophobic part is flexible with respect to chain conformational degrees of freedom and the head group is not too voluminous. It is found that the head group repulsion contribution to kcH0 is always positive whereas the corresponding contribution to kc may be positive or negative depending on whether the hydrophobic layer of the film is thicker or thinner than the hydrophilic layer.
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Affiliation(s)
- L Magnus Bergström
- Department of Chemistry, Surface Chemistry, Royal Institute of Technology, Stockholm, Sweden.
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Lee J, Jha AK, Bose A, Tripathi A. Imaging new transient nanostructures using a microfluidic chip integrated with a controlled environment vitrification system for cryogenic transmission electron microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:12738-12741. [PMID: 18947241 DOI: 10.1021/la8027379] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Nanostructures (vesicles, micelles, bilayers) are important in nanomedicine and biochemical processes. They are agents for encapsulation and eventual release of drugs, flavors, and fragrances. The structural transition from micelles to vesicles through disk-like intermediate states has been demonstrated previously. Here, we disclose a new route for the micelle-vesicle transition, where micelles aggregate to first form long tubules that become unstable, and break up into vesicles. A simple theory, based on energy principles, is presented to explain the tubule-vesicle transition. Observation of this new tubular intermediate state has been facilitated by the development of an integrated microfluidic chip/cryogenic transmission electron microscopy (cryo-TEM) unit. Although this transition has been observed in a specific amphiphilic system where micellar solutions of cetyltrimethylammonium bromide (CTAB) and dodecylbenzene sulfonic acid (HDBS) are mixed to form vesicles, this new tool can be applied broadly to study transient structures in nanoscale systems under the very controlled conditions provided by microfluidics.
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Affiliation(s)
- Jinkee Lee
- Division of Engineering, Brown University, Providence, Rhode Island 02912, USA
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Bergström LM. Thermodynamics and bending energetics of toruslike micelles. J Colloid Interface Sci 2008; 327:191-7. [DOI: 10.1016/j.jcis.2008.08.025] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2008] [Revised: 08/07/2008] [Accepted: 08/12/2008] [Indexed: 11/24/2022]
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Johansson E, Sandström MC, Bergström M, Edwards K. On the formation of discoidal versus threadlike micelles in dilute aqueous surfactant/lipid systems. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:1731-1739. [PMID: 18215080 DOI: 10.1021/la702637h] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
In a recent study, we showed that the surfactant 1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000 (DSPE-PEG2000) induced mixed micelles of either threadlike or discoidal shape when mixed with different types of lipids. In this study, we have exchanged the PEG-lipid for the more conventional surfactants octaethylene glycol monododecyl ether (C12E8), hexadecyltrimethylammonium bromide (CTAB), and sodium dodecyl sulfate (SDS). Cryo-TEM investigations show that also these surfactants are able to induce the formation of long-lived discoidal micelles. Generally, the preference for either discoidal or threadlike micelles can be tuned by the choice of lipids and environmental conditions in much the same way as observed for the lipid/PEG-lipid system. Our investigation showed, furthermore, that the choice of surfactant may influence the type of mixed micelles formed. It is argued that the formation of discoidal rather than threadlike micelles may be rationalized as an effect of increasing bending rigidity. Our detailed theoretical model calculations show that the bending rigidity becomes significantly raised for aggregates formed by an ionic rather than a nonionic surfactant.
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Affiliation(s)
- Emma Johansson
- Department of Physical and Analytical Chemistry, Physical Chemistry, Uppsala University, Box 579, 751 23 Uppsala, Sweden.
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Bergström LM. Influence of bending energetics on the size, shape and polydispersity of droplet microemulsions. Colloids Surf A Physicochem Eng Asp 2008. [DOI: 10.1016/j.colsurfa.2007.08.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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