Highly-Ordered Selective Self-Assembly of a Trimeric Cationic Surfactant on a Mica Surface

Novel trimeric cationic surfactant tri(dodecyldimethylammonioacetoxy)diethyltriamine trichloride (DTAD) has been synthesized, and its self-assembly morphology on a mineral surface has been studied. From its micelle solution, highly ordered bilayer patterns are obtained on a mica surface, whereas randomly distributed bilayer patches are formed on a silica substrate. The highly ordered bilayer patterns on mica are first caused by the matching of the special structure of DTAD headgroups with the negative charge sites on mica, which leads to the specific nucleation of DTAD on the mica surface via electrostatic interaction. Furthermore, hydrophobic interaction among the DTAD hydrocarbon chains results in the formation of the bilayer structure, and intermolecular hydrogen-bonding among the DTAD headgroups promotes the directional growth of such bilayer structures

Modulation of Fibrillogenesis of Amyloid β(1−40) Peptide with Cationic Gemini Surfactant

Modulation of the fibrillogenesis of amyloid peptide Aβ(1−40) with the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) has been studied. Both UV−vis and AFM results show that C12C6C12Br2 monomers can promote the fibrillogenesis of Aβ(1−40) while its micelles inhibit this process. The electrostatic/hydrophobic force balance plays important roles in determining the Aβ(1−40) aggregation style and the secondary structures. When the surfactant positive charges are close to the Aβ(1−40) negative charges in number, the hydrophobic interaction is highly enhanced in the system. Both the nucleation rate and the lateral association between fibrils are greatly promoted. However, when the surfactant positive charges are in excess of the Aβ(1−40) negative charges, the electrostatic interaction is strengthened. In this case, the lateral association is inhibited and the α-helix to β-sheet transition in the secondary structure is prevented. Simultaneously, another assembly pathway is induced to give the amorphous aggregates. Moreover, the size and surface roughness of the Aβ(1−40) aggregates also vary upon increasing C12C6C12Br2 concentration

Modulation of Fibrillogenesis of Amyloid β(1−40) Peptide with Cationic Gemini Surfactant

Modulation of the fibrillogenesis of amyloid peptide Aβ(1−40) with the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) has been studied. Both UV−vis and AFM results show that C12C6C12Br2 monomers can promote the fibrillogenesis of Aβ(1−40) while its micelles inhibit this process. The electrostatic/hydrophobic force balance plays important roles in determining the Aβ(1−40) aggregation style and the secondary structures. When the surfactant positive charges are close to the Aβ(1−40) negative charges in number, the hydrophobic interaction is highly enhanced in the system. Both the nucleation rate and the lateral association between fibrils are greatly promoted. However, when the surfactant positive charges are in excess of the Aβ(1−40) negative charges, the electrostatic interaction is strengthened. In this case, the lateral association is inhibited and the α-helix to β-sheet transition in the secondary structure is prevented. Simultaneously, another assembly pathway is induced to give the amorphous aggregates. Moreover, the size and surface roughness of the Aβ(1−40) aggregates also vary upon increasing C12C6C12Br2 concentration

Amino Acid-Mediated Synthesis of the ZIF‑8 Nanozyme That Reproduces Both the Zinc-Coordinated Active Center and Hydrophobic Pocket of Natural Carbonic Anhydrase

The zeolitic imidazolate framework-8 (ZIF-8) nanozyme has been synthesized using hydrophobic amino acid (AA) to regulate crystal growth. The as-synthesized ZIF-8 reproduces both the structural and functional properties of natural carbonic anhydrase (CA). Structurally, Zn2+/2-methylimidazole coordinated units mimic very well the active center of CA while the hydrophobic microdomains of the adsorbed AA simulate the CA hydrophobic pocket. Functionally, the nanozymes show excellent CA-like esterase activity by giving specific enzyme activity of 0.22 U mg–1 at 25 °C in the case of Val–ZIF-8. More strikingly, such nanozymes are superior to natural CA by having excellent hydrothermal stability, which can give highly enhanced esterase activity with increasing temperature. The specific enzyme activity of Val–ZIF-8 at 80 °C is about 25 times higher than that at 25 °C. In addition, AA–ZIF-8 also shows an excellent catalytic efficiency toward carbon dioxide (CO2) hydration. This study puts forward the important role of hydrophobic microdomains in biomimetic nanozymes for the first time and develops a facile and mild method for the synthesis of nanozymes with controlled morphology and size to achieve excellent catalytic efficiency

Facile Disassembly of Amyloid Fibrils Using Gemini Surfactant Micelles

The accumulation of a peptide of 38−43 amino acids, in the form of fibrillar plaques, was one of the essential reasons for Alzheimer’s disease (AD). Discovering an agent that is able to disassemble and clear disease-associated Aβ peptide fibrils from the brains of AD patients would have critical implications not only in understanding the dynamic process of peptide aggregation but also in the development of therapeutic strategies for AD. This study reported a new finding that cationic gemini surfactant C12C6C12Br2 micelles can effectively disassemble the Aβ(1−40) fibrils in vitro. Systematic comparisons with other surfactants using ThT fluorescence, AFM, and FTIR techniques suggested that the disassembly effectiveness of gemini surfactant micelles arises from their special molecular structure (i.e., positively bicharged head and twin hydrophobic chains). To track the disassembly process, systematic cryoTEM characterization was also done, which suggested a three-stage disassembly process: (i) Spherical micelles are first absorbed onto the Aβ fibrils because of attractive electrostatic interaction. (ii) Elongated fibrils then disintegrate into short pieces and form nanoscopic aggregates via synergistic hydrophobic and electrostatic interactions. (iii) Finally, complete disaggregation of fibrils and dynamic reassembly result in the formation of peptide/surfactant complexes

Dissolution of the Calcite (104) Face under Specific Calcite–Aspartic Acid Interaction As Revealed by in Situ Atomic Force Microscopy

In the presence of aspartic acid (Asp), the calcite (104) face shows distinct dissolution pit morphology, presumably resulting from the surface reaction between calcite and Asp. However, the specific nature of this interaction and the influence of solution hydrodynamics remain unclear. To this end, we have followed the calcite (104) surface dissolution using in situ fluid cell atomic force microscopy (AFM). The results showed that at pH 4.5 and in 100 mM Asp the surface reactions were controlled by diffusion under static conditions and that trapezoidal etch pits were formed. In contrast, elliptical etch pits were rapidly developed upon flowing due to the increased transfer of Asp to the [010] step edge and the dissolution of Asp-surface complexes away from the step edge. The occurrence of the [010], [461̅], and [4̅11] steps of trapezoidal etch pits was attributed to the stabilization of the (001), (1̅12), and (01̅1) faces by Asp through bridging between the two carboxyl groups and two adjacent Ca atoms, with the α-NH₃⁺ group forming a hydrogen bond with the oxygen of the H₂O from the bulk solution and the surface CO₃ groups from the (1̅12) and (01̅1) faces. The mirror images of the etch pits formed in d-Asp and l-Asp solutions resulted from the enantio-specific interaction, supporting the tripodal contact of Asp with the crystal surface. Thus, the etch pit morphology is affected by Asp concentration, mass transfer, and specific surface reaction

Core–Shell Structures from the Coassembly of Lipoprotein-like Nanoparticles and Plasmid DNA for Gene Delivery

We reported self-assembled core–shell nanoparticles (NPs) based on lipoprotein-like NPs and plasmid DNA (pDNA). Lipoprotein-like NPs were prepared using cholic acid (CA)-modified lipopeptides. We designed six different lipopeptides with different peptide segments to construct a series of NPs. It was proven that these NPs have different positive surface charges. These NPs could bind pDNA through electrostatic interaction to form core–shell complexes. The interactions between NPs and pDNA were systematically investigated. The number of NP charges determines the strength of the interaction between NPs and pDNA. Thus, various types of core–shell structures, such as loose and dense core–shell NPs, were found in this system. Cytotoxicity test confirmed that the carriers had no toxicity. We also proved that the core–shell structures have a good cell transfection effect. This study would expand the application of lipopeptide assemblies in the gene delivery field, which may lead to the development of peptide-based gene vectors for therapeutic application

Molecular Modulation of Calcite Dissolution by Organic Acids

Dissolution of the calcite (104) surface in aqueous solution in the presence of 10 organic acids has been studied using fluid-cell atomic force microscopy (AFM) in vitro. Etch pit morphology varies as species conformation changes. [421̅] steps appeared in the presence of each of Gly, l-Glu, l-Lys, malonate, and succinate. The overall shape of etch pits became hexagonal in Gly, malonate, and succinate, while a pseudotriangular shape in l-Glu solution and a sectorial shape in l-Lys solution were observed, primarily as a result of molecular chirality. Unexpectedly, [010] instead of [421̅] steps emerged in l-Asp solution, giving a trapezoidal pit shape. Despite the differences in molecular structure of 6-aminohexanoate, acetate, oxalate, and glutarate, these molecules did not show any influence on pit morphology, revealing that solid/fluid recognition must depend on the geometry of additives, especially the distance between functional groups. We show that both the ammonium and the carboxylate groups are active in surface binding and that the organic acids tend to bind through more than one functional group to the calcite face. Our AFM results confirm the crucial role of geometrical matching between calcite and modifiers and show that step edge reactivity, stereochemical correspondence, electrostatic attraction, and molecular chirality play a secondary role in surface modification. This conclusion will give guidelines for synthesizing bioinspired materials with specific shape

Enhanced Molecular Recognition between Nucleobases and Guanine-5′-monophosphate-disodium (GMP) by Surfactant Aggregates in Aqueous Solution

Only specific base pairs on DNA can bind with each other through hydrogen bonds, which is called the Watson–Crick (W/C) pairing rule. However, without the constraint of DNA chains, the nucleobases in bulk aqueous solution usually do not follow the W/C pairing rule anymore because of the strong competitive effect of water and the multi-interaction edges of nucleobases. The present work applied surfactant aggregates noncovalently functionalized by nucleotide to enhance the recognition between nucleobases without DNA chains in aqueous solution, and it revealed the effects of their self-assembling ability and morphologies on the recognition. The cationic ammonium monomeric, dimeric, and trimeric surfactants DTAB, 12–3–12, and 12–3–12–3–12 were chosen. The surfactants with guanine-5′-monophosphate-disodium (GMP) form micelles, vesicles, and fingerprint-like and plate-like aggregates bearing the hydrogen-bonding sites of GMP, respectively. The binding parameters of these aggregates with adenine (A), uracil (U), guanine (G), and cytosine­(C) indicate that the surfactants can promote W/C recognitions in aqueous solution when they form vesicles (GMP/DTAB) or plate-like aggregates (GMP/12–3–12) with proper molecular packing compactness, which not only provide hydrophobic environments but also shield non-W/C recognition edges. However, the GMP/12–3–12 micelles with loose molecular packing, the GMP/12–3–12 fingerprint-like aggregates where the hydrogen bond sites of GMP are occupied by itself, and the GMP/12–3–12–3–12 vesicles with too strong self-assembling ability cannot promote W/C recognition. This work provides insight into how to design self-assemblies with the performance of enhanced molecule recognition