Control of nano-micrometric twist and helical ribbon formation with gemini–oligoalanine via interpeptidic β-sheet structure formation

Rational Design and Synthesis of Carboxylate Gemini Surfactants with an Excellent Aggregate Behavior for Nano-La2O3 Morphology-Controllable Preparation

A series of carboxylate gemini surfactants (CGS, C_n-Φ-C_n, n = 12, 14, 16, 18) with diphenyl ketone as a spacer group were prepared using a simple and feasible synthetic method. These CGS exhibited an excellent surface activity with extremely low critical micelle concentration (CMC) value (approximately 10^-5 mol/L), good performance in reducing surface tension (nearly 30 mN/m), and the ability of molecular self-assembly into different aggregate morphologies via adjusting the concentrations, which is attributed to the introduction of diphenyl ketone and carboxylic acid ammonium salt in the molecular structure. Moreover, the surface activity and self-assembly ability of CGS were further optimized by tuning the length of the tail chain. These excellent properties imply that CGS can be a soft template to prepare nanomaterials, especially in morphology-controllable synthesis. By adjusting the concentration of one of CGS (C₁₂-Φ-C₁₂), nano-La₂O₃ particles with diverse morphologies were obtained, including spherical shape, bead-chain shape, rod shape, velvet-antler shape, cedar shape, and bowknot shape. This work offers a vital insight into the rational design of template agents for the development of morphology-controllable nanomaterials.

Effect of counterions on the micellization and monolayer behaviour of cationic gemini surfactants

The effect of various inorganic and organic counterions on the aggregation behavior of gemini surfactants was examined to investigate the dominant influence of the anions on their micellization and aggregation behavior.

The influence of amino acid sequence on structure and morphology of polydiacetylene containing peptide fibres

A systematic study was performed on the influence of charge and steric hindrance on the assembly into fibres of a series of pentameric peptides based on the well-known β-sheet forming sequence Gly-Ala-Gly-Ala-Gly, which were N-terminally acylated with pentacosadiynoic acid. To investigate the effect of steric hindrance and charge repulsion on the fibre structure, either the N-terminal or the C-terminal amino acid in the sequence was replaced by a glutamic acid or lysine residue. Furthermore, peptide amphiphiles (PAs) with an amide or a free acid group at the C-terminus were compared. Steric hindrance and charge repulsion were addressed individually by varying the pH during and after fibre preparation. The self-assembled structures were examined with circular dichroism (CD) spectroscopy and transmission electron microscopy (TEM). UV spectroscopy was used to probe the diacetylene packing in the hydrophobic tail, both by polymerisation behaviour and chromatic properties of the polymers. In brief, the assembly was hindered more if the modification was close to the alkyl tail, and glutamic acid brought about a larger effect than lysine. PAs with two charges yielded assemblies which after polymerisation were found to be the most susceptible towards changes in pH, behaving as a colour-based pH sensor. Typically, TEM and UV showed the same trends, indicating that a distorted morphology as observed with TEM is indicative of a poorer molecular packing of the peptide amphiphile fibres, probed via the changes in absorption of the polydiacetylene backbone.

Chiral colloids: homogeneous suspension of individualized SiO2 helical and twisted nanoribbons

Finely tuned chiral nanometric silica fibers were synthesized based on sol-gel chemistry using organic self-assembly as a template. The optimization of the sol-gel process in acidic conditions allowed us to reduce the transcription time by a factor of 10. These nanohelices were successfully fragmented while preserving the fine internal structures from several micrometers to several hundreds of nanometers in length by a sonication method previously reported for carbon nanotubes. By carefully choosing the nature of the solvent, the sonication power, pH in the case of water, and densification of the silica walls by freeze-drying, the homogeneous and stable colloidal suspensions of individualized chiral nanometric silica ribbons with controlled length were obtained.

Morphology control between twisted ribbon, helical ribbon, and nanotube self-assemblies with his-containing helical peptides in response to pH change

pH-Responsive molecular assemblies with a variation in morphology ranging from a twisted ribbon, a helical ribbon, to a nanotube were prepared from a novel A3B-type amphiphilic peptide having three hydrophilic poly(sarcosine) (A block) chains, a hydrophobic helical dodecapeptide (B block), and two histidine (His) residues between the A3 and B blocks. The A3B-type peptide adopted morphologies of the twisted ribbon at pH 3.0, the helical ribbon at pH 5.0, and the nanotube at pH 7.4, depending upon the protonation states of the two His residues. On the other hand, another A3B-type peptide having one His residue between the A3 and B blocks showed a morphology change only between the helical ribbon and the relatively planar sheets with pH variation in this range. The morphology change is thus induced by one- or two-charge generation at the linking site of the hydrophilic and hydrophobic blocks of the component amphiphiles but in different ways.

Sperm trajectories form chiral ribbons

We report the discovery of an entirely new three-dimensional (3D) swimming pattern observed in human and horse sperms. This motion is in the form of ‘chiral ribbons’, where the planar swing of the sperm head occurs on an osculating plane creating in some cases a helical ribbon and in some others a twisted ribbon. The latter, i.e., the twisted ribbon trajectory, also defines a minimal surface, exhibiting zero mean curvature for all the points on its surface. These chiral ribbon swimming patterns cannot be represented or understood by already known patterns of sperms or other micro-swimmers. The discovery of these unique patterns is enabled by holographic on-chip imaging of >33,700 sperm trajectories at >90–140 frames/sec, which revealed that only ~1.7% of human sperms exhibit chiral ribbons, whereas it increases to ~27.3% for horse sperms. These results might shed more light onto the statistics and biophysics of various micro-swimmers' 3D motion.

Effect of Hofmeister and alkylcarboxylate anionic counterions on the Krafft temperature and melting temperature of cationic gemini surfactants

The effect of counterions was investigated to probe the principal ionic effects on the solubility in water and melting behavior of cationic gemini surfactants. We focused on two types of counterions: (1) small inorganic counterions that are typically taken from the Hofmeister series were studied to focus on the effect of ion type and (2) n-alkylcarboxylate counterions were studied to focus on the effect of the hydrophobicity of counterions. The Krafft temperature (Tk) and melting temperature (Tm) were obtained by conductivity measurements, calorimetric measurements, and optical microscopy observation. The results clearly indicate that Tk, which represents the solubility of surfactants, is not determined by a single parameter of ions such as the hydration free energy, as is too often assumed, but rather by the combined effects between the hydrophobicity of anions associated with other effects such as the polarizability, dehydrated ion size, and ionic morphology. In parallel, our observation demonstrated that all of the surfactants showed a transition from a crystalline phase to a thermotropic liquid-crystalline phase at around ca. 70 °C, which transformed to an isotropic liquid phase at around ca. 150 °C, and that the transition temperatures depended strongly on the counterion type. The counterion effects on the solubilization and melting behaviors were then compared with micellization properties that have been reported previously. These results provide new insight into understanding the effect of ions on the delicate balance of forces controlling the solution properties and aggregate morphology of charged amphiphilic molecules. Specifically, the solubilization properties of these cationic surfactants with various counterions were determined mainly by the subtle interplay between the hydration of counterions and the dissociation energies (stability of crystallinity) of the ion pair.

Counteranion effect on micellization of cationic gemini surfactants 14-2-14: Hofmeister and other counterions

The effect of counterions was investigated and analyzed to probe the principal ionic effects influencing the micellization behavior of dimeric cationic surfactant ethanediylbis(dimethyltetradecylammonium), referred to as gemini 14-2-14. The 30 counterions were classified to four different families depending on their nature: (1) small and inorganic counterions which are typically taken from the Hofmeister series were studied to focus on the effect of ion type; (2) n-alkyl carboxylate counterions were studied to focus on the effect of the hydrophobicity of counterions; (3) aromatic carboxylate counterions were included to focus on the effect of the position of substitutions; and (4) other counterions were included in order to shed light on other parameters. By investigating the critical micelle concentration (CMC), ionization degree of micelle (alpha), free energy of micellization (DeltaG(M)), and aggregation numbers N of the gemini surfactant with these different types of anions, we demonstrated the effect of different ion properties independently. This approach allowed us to describe the effect of counterions on the micellization behavior of the gemini surfactant in terms of complex interplay between hydrophobicity of anions and other ion properties such as counterion hydration, interfacial packing of ions, and ionic morphology. Indeed, our results clearly demonstrate that a counterion effect on micellization properties cannot be described as a result of one single parameter of ions, as is too often assumed, but rather the balancing effects cooperatively affect the propensity of counterions to form ion pairs with surfactant headgroups and the entropy gain upon micellization. These results provide new insight in understanding the effect of ions on the delicate balance of forces controlling aggregate morphology and solution properties of charged amphiphilic molecules.

Supramolecular structures generated by a p-tert-butylphenylamide derivative of deoxycholic acid. From planar sheets to tubular structures through helical ribbons

The formation of supramolecular structures initiated by a p-tert-butylphenylamide derivative of deoxycholic acid (Na-t-butPhDC) is investigated. At 1.18 mM concentration of Na-t-butPhDC and 37 degrees C, initial flat ribbons are observed which self-transform into helical ribbons (with a mean pitch angle of 47 +/- 6 degrees) which finally originate molecular tubes with an external diameter of 241 +/- 28 nm. Most of the molecular tubes show helical markings with a pitch angle value of 45 +/- 4 degrees, in full agreement with predictions of simple models based on chiral elastic properties of the membrane. A lateral association mechanism is proposed to account for the growth of the external diameter (from 225 +/- 32 to 546 +/- 59 nm) of tubes with time at 3.99 mM.

Nucleotide-promoted morphogenesis in amphiphile assemblies: kinetic control of micrometric helix formation

Anionic nucleotides adenosine monophosphate or guanosine monophosphate interact with cationic vesicles, exchange with the counteranions of the amphiphiles in situ, and organize themselves at the membrane surfaces. Such organized nucleotides reciprocally transfer their chirality to membranes of nonchiral amphiphiles to induce the formation of right-handed micrometric helices on the time scale of hours. The kinetics of the nucleotide molecular organization and the formation of supramolecular helices was followed. We have shown that helix formation is a kinetic-dependent process that does not primarily result from ion exchange but from conformational reorganization and formation of weak interactions between confined nucleotides.

Challenges and breakthroughs in recent research on self-assembly

The controlled fabrication of nanometer-scale objects is without doubt one of the central issues in current science and technology. However, existing fabrication techniques suffer from several disadvantages including size-restrictions and a general paucity of applicable materials. Because of this, the development of alternative approaches based on supramolecular self-assembly processes is anticipated as a breakthrough methodology. This review article aims to comprehensively summarize the salient aspects of self-assembly through the introduction of the recent challenges and breakthroughs in three categories: (i) types of self-assembly in bulk media; (ii) types of components for self-assembly in bulk media; and (iii) self-assembly at interfaces.

Self-assembly of nucleoamphiphiles: investigating nucleosides effect and the mechanism of micrometric helix formation

A new family of self-assembling systems based on nucleoamphiphiles is described. Nano to micrometric left-handed helix formation in aqueous solution was induced simply by complexing a GMP or an AMP with a nonchiral monocationic amphiphile. The assembling behavior such as micellar formation, monolayer at air-water interface, as well as the aggregates in solution of these nucleoamphiphiles are strongly influenced by the presence of nucleosides in solution. The observed effects depend on the properties of complexed nucleotides and nucleosides with a complex mixture of pi stacking, hydrophobicity of the bases, and hydrogen bonding.