Peptide and protein fibrils have attracted an enormous amount of interests due to their relevance to many neurodegenerative diseases and their potential applications in nanotechnology. Although twisted fibrils are regarded as the key intermediate structures of thick fibrils or bundles of fibrils, the factors determining their twisting tendency and their handedness development from the molecular to the supramolecular level are still poorly understood. In this study, we have designed three pairs of enantiomeric short amphiphilic peptides: LI3LK and DI3DK, LI3DK and DI3LK, and LaI3LK and DaI3DK, and investigated the chirality of their self-assembled nanofibrils through the combined use of atomic force microscopy (AFM), circular dichroism (CD) spectroscopy, scanning electron microscopy (SEM), and molecular dynamic (MD) simulations. The results indicated that the twisted handedness of the supramolecular nanofibrils was dictated by the chirality of the hydrophilic Lys head at the C-terminal, while their characteristic CD signals were determined by the chirality of hydrophobic Ile residues. MD simulations delineated the handedness development from molecular chirality to supramolecular handedness by showing that the β-sheets formed by LI3LK, LaI3LK, and DI3LK exhibited a propensity to twist in a left-handed direction, while the ones of DI3DK, DaI3DK, and LI3DK in a right-handed twisting orientation.

•A new peptide and surfactant co-assembly system was studied.•This system was salt-free system which would be more stable.•Different nanostructures were formed during conversion the ratio of peptide and surfactant.•The solutions with different nanostructure behaved different rheological properties.The co-assembly behavior of a short tetrapeptide (I3E) and a zwitterionic surfactant (dodecyldimethylamine oxide, C14DMAO) in water have been systematically investigated. The microstructures and properties of the I3E/C14DMAO mixture were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and a HAAKE rotational rheometer. Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and circular dichroism (CD) were used to explore the formation of different microstructures. It was found that, with the increasing of C14DMAO, the co-assembly of the I3E/C14DMAO mixture changed from nanofibers to nanosheets, and then finally to wormlike micelles and spherical micelles. And the rheological properties of the mixtures also changed with the increasing of C14DMAO concentration accordingly.

Controllable self-assembly systems have attracted increasing attention in both the academic and industrial fields recently. Herein, we designed and synthesized a new photo-degradable anionic surfactant (PAS) with a coumarin group which could be degraded by both UV and NIR light. Thus, the micelles that are formed by sodium salts of PAS (PAS-Na) could be broken controllably under UV or NIR irradiation. Surface tension measurements, DLS, and Cryo-TEM were adopted to investigate the formation and disruption of PAS-Na micelles. PAS could also form wormlike micelles and vesicles when they co-assembled with common surfactant tetradecyldimethylamine oxide (C14DMAO). These wormlike micelles and vesicles could be degraded by UV and NIR irradiation due to the participation of PAS. Accordingly, the rheology properties of the wormlike micelles and vesicles were also changed significantly. Finally, the stimulus-responsive system was used to control the diffusion of hydrophobic and hydrophilic molecules. And it has shown controllable release effects on both the hydrophobic and hydrophilic molecules.

Spherical assemblies with core/shell configurations are prepared through C-terminal amidated short peptide mediated self-association of platinum nanocrystals. The interactions between the peptides might drive the self-assembly of platinum nanocrystals and determine their surface properties. Thus, the nanosize assemblies collapse and spread on a hydrophilic surface, whereas maintaining their spherical shapes on a hydrophobic surface.

•Hydrophobic interactions and steric conformation of Phes affect Aβ self-assembly.•When Phes replaced with Chas, Aβ(16–22) formed thin nanotubes morphologies.•When Phes replaced with Phgs, Aβ(16–22) formed thinner and twisted nanofibrils.•Equilibrium between lateral aggregation and twisting determines the morphologies.The effects of the two phenylalanine (Phe) residues in the blocked Aβ(16–22) peptide on its self-assembly have been investigated by replacing both of them with two cyclohexylalanines (Chas) or two phenylglycines (Phgs). TEM and SANS studies revealed that the flat and wide nanoribbons of Aβ(16–22) were transformed into thin nanotubes when replaced with Chas, and thinner and twisted nanofibrils when replaced with Phgs. The red-shifting degree of characteristic CD peaks suggested an increased twisting in the self-assembly of the derivative peptides, especially in the case of Ac-KLV(Phg)(Phg)AE-NH2. Furthermore, molecular dynamics (MD) simulations also indicated the increasing trend in twisting when Chas or Phgs were substituted for Phes. These results demonstrated that the hydrophobic interactions and spatial conformation between Cha residues were sufficient to cause lateral association of β-sheets to twisted/helical nanoribbons, which finally developed into nanotubes, while for Phg residue, the loss of the rotational freedom of the aromatic ring induced much stronger steric hindrance for the lateral stacking of Ac-KLV(Phg)(Phg)AE-NH2 β-sheets, eventually leading to the nanofibril formation. This study thus demonstrates that both the aromatic structure and the steric conformation of Phe residues are crucial in Aβ(16–22) self-assembly, especially in the significant lateral association of β-sheets.

Amphiphilic short peptides (ASPs) and surfactants (C14DMAO) were employed to prepare wormlike micelles. Herein, ASPs were used to induce wormlike micelle formation. The formation mechanism was investigated by cryo-TEM, FTIR, CD and a rheometer. C14DMAO could be protonated by a proton which was dissociated from the carboxyl headgroups of ASPs. The mean area of the headgroup would be reduced due to the interaction of protonated cationic surfactants and dissociated anionic ASPs which would lead to wormlike micelle formation. And the length of the wormlike micelles could be modulated by the size of the hydrophobic part of ASPs. The wormlike micelles could also respond to pH and metal ions, respectively. When the pH was regulated from 5.96 to 3.23, the wormlike micelles transformed into a nanofiber network. Nevertheless, when the pH was regulated to over 9, spherical micelles would be formed and the solution would lose its viscoelasticity. When a certain amount of metal salts were added into the wormlike micelle solution with a pH of 5.96, the viscosity of the solution increased significantly. The coordination interaction between metal ions and C14DMAO was considered as the responsive mechanism. Metal ions with high valence have more obvious effects on wormlike micelles.

Two amphiphilic catalysts (i.e., metal dodecylbenzenesulfonates, noted as C12BSNi and C12BSFe) were synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), element analysis (EA), atomic absorption spectroscopy (AAS), and thermogravimetric (TGA). Their interfacial activities were determined using a surface tensiometer and an interfacial tensiometer. Both catalysts are interfacial active and thermostable enough for heavy oil aquathermolysis. Their performance on heavy oil aquathermolysis was assessed in an autoclave. According to the viscosity reduction results, the synthesized amphiphilic catalysts are more effective than water-soluble or oil-soluble catalysts, with C12BSNi more efficient than C12BSFe. The average molecular weight, group compositions, and average molecular structure of heavy oil samples were analyzed using EA, FT-IR, and 1H nuclear magnetic resonance (1H NMR) before and after aquathermolysis reaction. And the results show that both catalysts caused the change of molecular structures in heavy oil. The change of asphaltene and resin molecular structures and decrease of their contents are crucially important to the reduction of viscosity. C12BSNi causes more changes of the asphaltene than C12BSFe, whereas C12BSFe is beneficial to the breakage of C–S bonds in asphlatenes and resins.

Lipopeptides are an important group of biosurfactants expressed by microorganisms. Because they are well-known for being biocompatible, biodegradable, and highly surface active, they are attractive for a wide range of applications. Natural lipopeptide surfactants are however impure; it is hence difficult to use them for exploring the structure–function relation. In this work, a series of cationic lipopeptide surfactants, C14Kn (n = 1–4), where C denotes the myristic acyl chain and K denotes lysine (Lys), have been synthesized, and their interfacial behavior has been characterized by studying their adsorption at the silicon/water interface (bearing a thin native oxide layer) using spectroscopic ellipsometry and neutron reflection (NR). The dynamic adsorption was marked by an initial fast step within the first 2–3 min followed by a slow molecular relaxation process over the subsequent 20–30 min. The initial rate of time-dependent adsorption and the equilibrated adsorbed amount showed a steady decrease with increasing n, indicating the impact of the molecular size, structure, and charge. NR revealed the formation of sandwiched bilayers from C14Kn, similar to conventional surfactants such as nonionic C12E6 and cationic C16TAB. However, the electrostatic attraction between K and the silica surface caused confinement of the K groups, forcing the head segments into a predominantly flat-on conformation. This characteristic structural feature was confirmed by the almost constant thickness of the headgroup regions ranging from 8 to 11 Å as determined from NR combined with partial deuterium labeling to the acyl tail. An increase in area per molecular pair with n resulted directly from increasing the footprint. As a result, the hydrophobic back-to-back tail mixing and acyl chain tilting rose with n. The extent of chain–head intermixing became so intensified that the C14K4 bilayer could be approximated to a uniform layer distribution.

The thermal reaction of Karamay residue was carried out in a micro batch reactor under nitrogen atmosphere. The oil was taken out through an online sampling tube. The asphaltene and coke contents of cracked residue at different reaction times were determined. The phase separation of residue oil was observed by an optical microscope, and the colloidal stability of residue oil was determined quantitatively by the mass fraction normalized conductivity method. The alkyl side chain length of resins and asphaltenes was analyzed by infrared spectroscopy, and their structure parameters were calculated via density method. The macroscopic phenomena of phase separation, coke formation and colloidal stability deterioration were correlated with micro molecular structure. The results showed that the increase of asphaltene condensation degree and the decrease of peptizing ability of resins were the essential reasons for phase separation and coking during thermal reaction. At the initial coke formation point, the condensation degree of resins and asphaltenes during low temperature reaction.was lower than that of high temperature reaction.

The functional groups on asphaltene surfaces of two kinds of Chinese residue oil were analyzed by X-ray photoelectron spectroscopy (XPS). The ζ potential and electrophoretic mobility of asphaltene solutions and residue solutions were measured through phase analysis light scattering (PALS) technique. The ability to stabilize asphaltenes of two typical ionic amphiphiles, dodecyl benzene sulfonic acid (DBSA) and dodecyl trimethyl ammonium bromide (DTAB), were investigated. Karamay asphaltenes contain large amount of carboxyl and calcium and are negatively charged; whereas Lungu asphaltenes are rich in nickel, vanadium, and pyrrolic structures and are positively charged. DBSA has good ability to stabilize Lungu asphaltenes but has no effect on Karamay asphaltenes. Differently, DTAB has good ability to disperse Karamay asphaltenes but has no obvious effect on Lungu asphaltenes. It is concluded from these results that the charges might derive from the dissociation of metal ions and the deprotonation of acid groups (such as COOH, OH, and SH) or basic groups (such as pyridinic groups) on asphaltene surface. The electric property of asphaltenes plays an important role in the interaction between asphaltenes and amphiphiles. The negatively charged asphaltenes tend to be dispersed by cationic amphiphiles, whereas the positively charged asphaltenes tend to be dispersed by anionic amphiphiles.