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Special Issue "Assembly Superstructures in Chemistry"

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Physical Chemistry and Chemical Physics".

Deadline for manuscript submissions: closed (30 September 2020).

Special Issue Editor

Prof. Dr. Luciano Galantini
E-Mail Website
Guest Editor
Department of Chemistry, La Sapienza University of Rome, 00185 Rome, Italy
Interests: aggregation of Bile Salts and derivatives; protein unfolding and effects of specific ligands; host-guest supramolecular polymers; colloid system investigation techniques
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Special Issue Information

Dear Colleagues,

The International Journal of Molecular Sciences (ISSN 1422-0067) is currently running a Special Issue entitled "Assembly Superstructures in Chemistry".

Based on your publication record in this area, we think it may be of interest to you to contribute a full research article or a comprehensive review for publication, following peer review, in this issue.

Nature suggests that functional materials results from a complex hierarchical organization of matter at different length scales. At the nano- and microscale, aggregates are formed by naturally driven interactions of elements like molecules, macromolecules, nano- and microparticles, with different features depending on the starting elements. This control over matter inspires state-of-the-art bottom–up nanotechnology exploited in modern chemistry and material science. Assembly can be rationalized through the fundamental knowledge of the association driving interactions, and of the effects of pivotal factors, such as composition and stability, in determining the properties of assembled structures. This knowledge allows researchers to explain naturally occurring phenomena and meanwhile to rationally direct aggregation in technologies employed in fields like food, medicine, nanomaterials, and several others.

The current Special issue of IJMS (International Journal of Molecular Sciences) represents an excellent platform for the discussion of recent developments in this field, focusing the attention on novel aspects of superstructures from assemblies of molecules, macromolecules, and nanoparticles. Studies on fundamental aspects and applications are welcome that can synergically merge in the platform to provide a comprehensive coverage of the field and the bases to boost the rational development of new systems.

Prof. Dr. Luciano Galantini
Guest Editor

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Keywords

  • Self-assembly
  • Polymers
  • Amphiphiles
  • Micelles
  • Nanoparticles
  • Nanostructures
  • Nanomedicine
  • Membranes
  • Liquid crystals
  • Supramolecular structures

Published Papers (14 papers)

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Research

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Article
Differential Interactions of Chiral Nanocapsules with DNA
Int. J. Mol. Sci. 2021, 22(2), 584; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22020584 - 08 Jan 2021
Cited by 2 | Viewed by 630
Abstract
(1) Background: Chiral nanoparticular systems have recently emerged as a compelling platform for investigating stereospecific behavior at the nanoscopic level. We describe chiroselective supramolecular interactions that occur between DNA oligonucleotides and chiral polyurea nanocapsules. (2) Methods: We employ interfacial polyaddition reactions between toluene [...] Read more.
(1) Background: Chiral nanoparticular systems have recently emerged as a compelling platform for investigating stereospecific behavior at the nanoscopic level. We describe chiroselective supramolecular interactions that occur between DNA oligonucleotides and chiral polyurea nanocapsules. (2) Methods: We employ interfacial polyaddition reactions between toluene 2,4-diisocyanate and lysine enantiomers that occur in volatile oil-in-water nanoemulsions to synthesize hollow, solvent-free capsules with average sizes of approximately 300 nm and neutral surface potential. (3) Results: The resultant nanocapsules exhibit chiroptical activity and interact differentially with single stranded DNA oligonucleotides despite the lack of surface charge and, thus, the absence of significant electrostatic interactions. Preferential binding of DNA on d-polyurea nanocapsules compared to their l-counterparts is demonstrated by a fourfold increase in capsule size, a 50% higher rise in the absolute value of negative zeta potential (ζ-potential), and a three times lower free DNA concentration after equilibration with the excess of DNA. (4) Conclusions: We infer that the chirality of the novel polymeric nanocapsules affects their supramolecular interactions with DNA, possibly through modification of the surface morphology. These interactions can be exploited when developing carriers for gene therapy and theranostics. The resultant constructs are expected to be highly biocompatible due to their neutral potential and biodegradability of polyurea shells. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Sequence of Polyurethane Ionomers Determinative for Core Structure of Surfactant–Copolymer Complexes
Int. J. Mol. Sci. 2021, 22(1), 337; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22010337 - 30 Dec 2020
Cited by 1 | Viewed by 1012
Abstract
The core of micelles self-assembled from amphiphiles is hydrophobic and contains little water, whereas complex coacervate core micelles co-assembled from oppositely charged hydrophilic polymers have a hydrophilic core with a high water content. Co-assembly of ionic surfactants with ionic-neutral copolymers yields surfactant–copolymer complexes [...] Read more.
The core of micelles self-assembled from amphiphiles is hydrophobic and contains little water, whereas complex coacervate core micelles co-assembled from oppositely charged hydrophilic polymers have a hydrophilic core with a high water content. Co-assembly of ionic surfactants with ionic-neutral copolymers yields surfactant–copolymer complexes known to be capable of solubilizing both hydrophilic and hydrophobic cargo within the mixed core composed of a coacervate phase with polyelectrolyte-decorated surfactant micelles. Here we formed such complexes from asymmetric (PUI-A2) and symmetric (PUI-S2), sequence-controlled polyurethane ionomers and poly(N-methyl-2-vinylpyridinium iodide)29-b-poly(ethylene oxide)204 copolymers. The complexes with PUI-S2 were 1.3-fold larger in mass and 1.8-fold larger in radius of gyration than the PUI-A2 complexes. Small-angle X-ray scattering revealed differences in the packing of the similarly sized PUI micelles within the core of the complexes. The PUI-A2 micelles were arranged in a more ordered fashion and were spaced further apart from each other (10 nm vs. 6 nm) than the PUI-S2 micelles. Hence, this work shows that the monomer sequence of amphiphiles can be varied to alter the internal structure of surfactant–copolymer complexes. Since the structure of the micellar core may affect both the cargo loading and release, our findings suggest that these properties may be tuned through control of the monomer sequence of the micellar constituents. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Aggregation Behavior, Antibacterial Activity and Biocompatibility of Catanionic Assemblies Based on Amino Acid-Derived Surfactants
Int. J. Mol. Sci. 2020, 21(23), 8912; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21238912 - 24 Nov 2020
Cited by 6 | Viewed by 779
Abstract
The surface activity, aggregates morphology, size and charge characteristics of binary catanionic mixtures containing a cationic amino acid-derived surfactant N(π), N(τ)-bis(methyl)-L-Histidine tetradecyl amide (DMHNHC14) and an anionic surfactant (the lysine-based surfactant Nα-lauroyl-Nεacetyl lysine (C12C3 [...] Read more.
The surface activity, aggregates morphology, size and charge characteristics of binary catanionic mixtures containing a cationic amino acid-derived surfactant N(π), N(τ)-bis(methyl)-L-Histidine tetradecyl amide (DMHNHC14) and an anionic surfactant (the lysine-based surfactant Nα-lauroyl-Nεacetyl lysine (C12C3L) or sodium myristate) were investigated for the first time. The cationic surfactant has an acid proton which shows a strong pKa shift irrespective of aggregation. The resulting catanionic mixtures exhibited high surface activity and low critical aggregation concentration as compared with the pure constituents. Catanionic vesicles based on DMHNHC14/sodium myristate showed a monodisperse population of medium-size aggregates and good storage stability. According to Small-Angle X-Ray Scattering (SAXS), the characteristics of the bilayers did not depend strongly on the system composition for the positively charged vesicles. Negatively charged vesicles (cationic surfactant:myristate ratio below 1:2) had similar bilayer composition but tended to aggregate. The DMHNHC14-rich vesicles exhibited good antibacterial activity against Gram-positive bacteria and their bactericidal effectivity declined with the decrease of the cationic surfactant content in the mixtures. The hemolytic activity and cytotoxicity of these catanionic formulations against non-tumoral (3T3, HaCaT) and tumoral (HeLa, A431) cell lines also improved by increasing the ratio of cationic surfactant in the mixture. These results indicate that the biological activity of these systems is mainly governed by the cationic charge density, which can be modulated by changing the cationic/anionic surfactant ratio in the mixtures. Remarkably, the incorporation of cholesterol in those catanionic vesicles reduces their cytotoxicity and increases the safety of future biomedical applications of these systems. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
A Matter of Size and Placement: Varying the Patch Size of Anisotropic Patchy Colloids
Int. J. Mol. Sci. 2020, 21(22), 8621; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21228621 - 16 Nov 2020
Cited by 1 | Viewed by 723
Abstract
Non-spherical colloids provided with well-defined bonding sites—often referred to as patches—are increasingly attracting the attention of materials scientists due to their ability to spontaneously assemble into tunable surface structures. The emergence of two-dimensional patterns with well-defined architectures is often controlled by the properties [...] Read more.
Non-spherical colloids provided with well-defined bonding sites—often referred to as patches—are increasingly attracting the attention of materials scientists due to their ability to spontaneously assemble into tunable surface structures. The emergence of two-dimensional patterns with well-defined architectures is often controlled by the properties of the self-assembling building blocks, which can be either colloidal particles at the nano- and micro-scale or even molecules and macromolecules. In particular, the interplay between the particle shape and the patch topology gives rise to a plethora of tilings, from close-packed to porous monolayers with pores of tunable shapes and sizes. The control over the resulting surface structures is provided by the directionality of the bonding mechanism, which mostly relies on the selective nature of the patches. In the present contribution, we investigate the effect of the patch size on the assembly of a class of anisotropic patchy colloids—namely, rhombic platelets with four identical patches placed in different arrangements along the particle edges. Larger patches are expected to enhance the bond flexibility, while simultaneously reducing the bond selectivity as the single bond per patch condition—which would guarantee a straightforward mapping between local bonding arrangements and long-range pattern formation—is not always enforced. We find that the non-trivial interplay between the patch size and the patch position can either promote a parallel particle arrangement with respect to a non-parallel bonding scenario or give rise to a variety a bonded patterns, which destroy the order of the tilings. We rationalize the occurrence of these two different regimes in terms of single versus multiple bonds between pairs of particles and/or patches. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Tunable Supramolecular Chirogenesis in the Self-Assembling of Amphiphilic Porphyrin Triggered by Chiral Amines
Int. J. Mol. Sci. 2020, 21(22), 8557; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21228557 - 13 Nov 2020
Cited by 1 | Viewed by 595
Abstract
Supramolecular chirality is one of the most important issues in different branches of science and technology, as stereoselective molecular recognition, catalysis, and sensors. In this paper, we report on the self-assembly of amphiphilic porphyrin derivatives possessing a chiral information on the periphery of [...] Read more.
Supramolecular chirality is one of the most important issues in different branches of science and technology, as stereoselective molecular recognition, catalysis, and sensors. In this paper, we report on the self-assembly of amphiphilic porphyrin derivatives possessing a chiral information on the periphery of the macrocycle (i.e., D- or L-proline moieties), in the presence of chiral amines as co-solute, such as chiral benzylamine derivatives. The aggregation process, steered by hydrophobic effect, has been studied in aqueous solvent mixtures by combined spectroscopic and topographic techniques. The results obtained pointed out a dramatic effect of these ligands on the morphology and on the supramolecular chirality of the final self-assembled structures. Scanning electron microscopy topography, as well as fluorescence microscopy studies revealed the formation of rod-like structures of micrometric size, different from the fractal structures formerly observed when the self-assembly process is carried out in the absence of chiral amine co-solutes. On the other hand, comparative experiments with an achiral porphyrin analogue strongly suggested that the presence of the prolinate moiety is mandatory for the achievement of the observed highly organized suprastructures. The results obtained would be of importance for unraveling the intimate mechanisms operating in the selection of the homochirality, and for the preparation of sensitive materials for the detection of chiral analytes, with tunable stereoselectivity and morphology. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
(R)-10-Hydroxystearic Acid: Crystals vs. Organogel
Int. J. Mol. Sci. 2020, 21(21), 8124; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21218124 - 30 Oct 2020
Cited by 2 | Viewed by 654
Abstract
The chiral (R)-10-hydroxystearic acid ((R)-10-HSA) is a positional homologue of both (R)-12-HSA and (R)-9-HSA with the OH group in an intermediate position. While (R)-12-HSA is one of the best-known low-molecular-weight organogelators, (R [...] Read more.
The chiral (R)-10-hydroxystearic acid ((R)-10-HSA) is a positional homologue of both (R)-12-HSA and (R)-9-HSA with the OH group in an intermediate position. While (R)-12-HSA is one of the best-known low-molecular-weight organogelators, (R)-9-HSA is not, but it forms crystals in several solvents. With the aim to gain information on the structural role of hydrogen-bonding interactions of the carbinol OH groups, we investigated the behavior of (R)-10-HSA in various solvents. This isomer displays an intermediate behavior between (R)-9 and (R)-12-HSA, producing a stable gel exclusively in paraffin oil, while it crystallizes in other organic solvents. Here, we report the X-ray structure of a single crystal of (R)-10-HSA as well as some structural information on its polymorphism, obtained through X-ray Powder Diffraction (XRPD) and Infrared Spectroscopy (IR). This case study provides new elements to elucidate the structural determinants of the microscopic architectures that lead to the formation of organogels of stearic acid derivatives. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Effect of the Cationic Head Group on Cationic Surfactant-Based Surfactant Mediated Gelation (SMG)
Int. J. Mol. Sci. 2020, 21(21), 8046; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21218046 - 28 Oct 2020
Cited by 1 | Viewed by 740
Abstract
The surfactant-mediated gelation (SMG) method allows us to formulate hydrogels using a water-insoluble organogelator. In this study, we formulated hydrogels using three cationic surfactants, hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and hexadecylpyridinium chloride (CPC)] and an organogelator (12-hydroxyoctadecanoic acid (12-HOA), and studied their [...] Read more.
The surfactant-mediated gelation (SMG) method allows us to formulate hydrogels using a water-insoluble organogelator. In this study, we formulated hydrogels using three cationic surfactants, hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and hexadecylpyridinium chloride (CPC)] and an organogelator (12-hydroxyoctadecanoic acid (12-HOA), and studied their structures and mechanical properties. A fiber-like structure similar to that found in the 12-HOA-based organogels was observed by optical microscopy. Small- and wide-angle X-ray scattering profiles showed Bragg peaks derived from the long- and short-spacing of the crystalline structures in the gel fibers and a correlation peak from the surfactant micelles in the small-angle region. Furthermore, the formation of micelles in the hydrogels was confirmed by UV-vis spectroscopic measurements of the gel samples in the presence of Rhodamine 6G. We concluded that the hydrogels prepared by the SMG method in the present systems are orthogonal molecular assembled systems in which two different molecular assembled structures coexist. Among the three surfactant systems, the CTAB system presented the lowest critical gelation concentration and highest sol-gel transition temperature and viscoelasticity. These differences in gel fiber formation and gel properties were discussed from the viewpoint of the degree of solubilization of the gelator molecules in micelles coexisting with gel fibers and diffusion of the gelator molecules in the gel formation process. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Slow Dissolution Kinetics of Model Peptide Fibrils
Int. J. Mol. Sci. 2020, 21(20), 7671; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21207671 - 16 Oct 2020
Cited by 2 | Viewed by 525
Abstract
Understanding the kinetics of peptide self-assembly is important because of the involvement of peptide amyloid fibrils in several neurodegenerative diseases. In this paper, we have studied the dissolution kinetics of self-assembled model peptide fibrils after a dilution quench. Due to the low concentrations [...] Read more.
Understanding the kinetics of peptide self-assembly is important because of the involvement of peptide amyloid fibrils in several neurodegenerative diseases. In this paper, we have studied the dissolution kinetics of self-assembled model peptide fibrils after a dilution quench. Due to the low concentrations involved, the experimental method of choice was isothermal titration calorimetry (ITC). We show that the dissolution is a strikingly slow and reaction-limited process, that can be timescale separated from other rapid processes associated with dilution in the ITC experiment. We argue that the rate-limiting step of dissolution involves the breaking up of inter-peptide β–sheet hydrogen bonds, replacing them with peptide–water hydrogen bonds. Complementary pH experiments revealed that the self-assembly involves partial deprotonation of the peptide molecules. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Effect of Vesicle Size on the Cytolysis of Cell-Penetrating Peptides (CPPs)
Int. J. Mol. Sci. 2020, 21(19), 7405; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21197405 - 07 Oct 2020
Cited by 2 | Viewed by 1102
Abstract
A specific series of peptides, called a cell-penetrating peptide (CPP), is known to be free to directly permeate through cell membranes into the cytosol (cytolysis); hence, this CPP would be a potent carrier for a drug delivery system (DDS). Previously, we proposed the [...] Read more.
A specific series of peptides, called a cell-penetrating peptide (CPP), is known to be free to directly permeate through cell membranes into the cytosol (cytolysis); hence, this CPP would be a potent carrier for a drug delivery system (DDS). Previously, we proposed the mechanism of cytolysis as a temporal and local phase transfer of membrane lipid caused by positive membrane curvature generation. Moreover, we showed how to control the CPP cytolysis. Here, we investigate the phospholipid vesicle’s size effect on CPP cytolysis because this is the most straightforward way to control membrane curvature. Contrary to our expectation, we found that the smaller the vesicle diameter (meaning a higher membrane curvature), the more cytolysis was suppressed. Such controversial findings led us to seek the reason for the unexpected results, and we ended up finding out that the mobility of membrane lipids as a liquid crystal is the key to cytolysis. As a result, we could explain the cause of cytolysis suppression by reducing the vesicle size (because of the restriction of lipid mobility); osmotic pressure reduction to enhance positive curvature generation works as long as the membrane is mobile enough to modulate the local structure. Taking all the revealed vital factors and their effects as a tool, we will further explore how to control CPP cytolysis for developing a DDS system combined with appropriate cargo selection to be tagged with CPPs. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Can the Isothermal Calorimetric Curve Shapes Suggest the Structural Changes in Micellar Aggregates?
Int. J. Mol. Sci. 2020, 21(16), 5828; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21165828 - 13 Aug 2020
Cited by 3 | Viewed by 922
Abstract
Inspired by the unusual shapes of the titration curve observed for many surfactants and mixed colloidal systems, we decided to extend the analysis to isothermal titration calorimetric curves (ITC) by paying special attention to potential structural changes in micellar aggregates. In this paper, [...] Read more.
Inspired by the unusual shapes of the titration curve observed for many surfactants and mixed colloidal systems, we decided to extend the analysis to isothermal titration calorimetric curves (ITC) by paying special attention to potential structural changes in micellar aggregates. In this paper, we used isothermal titration calorimetry in conjunction with Scanning Transmission Electron Microscopy (STEM), Small-Angle Neutron Scattering (SANS) and X-ray Scattering (SAXS) methods support by Monte Carlo and semiempirical quantum chemistry simulations to confirm if the isothermal calorimetric curve shape can reflect micelle transition phenomena. For that purpose, we analysed, from the thermodynamic point of view, a group of cationic gemini surfactants, alkanediyl-α,ω-bis(dimethylalkylammonium) bromides. We proposed the shape of aggregates created by surfactant molecules in aqueous solutions and changes thereof within a wide temperature range. The results provide evidence for the reorganization processes and the relationship (dependence) between the morphology of the created aggregates and the conditions such as temperature, surfactant concentration and spacer chain length which affect the processes. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Key Process and Factors Controlling the Direct Translocation of Cell-Penetrating Peptide through Bio-Membrane
Int. J. Mol. Sci. 2020, 21(15), 5466; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21155466 - 30 Jul 2020
Cited by 4 | Viewed by 1415
Abstract
Cell-penetrating peptide (CPP) can directly penetrate the cytosol (cytolysis) and is expected to be a potent vector for a drug delivery system (DDS). Although there is general agreement that CPP cytolysis is related to dynamic membrane deformation, a distinctive process has yet to [...] Read more.
Cell-penetrating peptide (CPP) can directly penetrate the cytosol (cytolysis) and is expected to be a potent vector for a drug delivery system (DDS). Although there is general agreement that CPP cytolysis is related to dynamic membrane deformation, a distinctive process has yet to be established. Here, we report the key process and factors controlling CPP cytolysis. To elucidate the task, we have introduced trypsin digestion of adsorbed CPP onto giant unilamellar vesicle (GUV) to quantify the adsorption and internalization (cytolysis) separately. Also, the time-course analysis was introduced for the geometric calculation of adsorption and internalization amount per lipid molecule consisting of GUV. As a result, we found that adsorption and internalization assumed to occur successively by CPP molecule come into contact with membrane lipid. Adsorption is quick to saturate within 10 min, while cytolysis of each CPP on the membrane follows successively. After adsorption is saturated, cytolysis proceeds further linearly by time with a different rate constant that is dependent on the osmotic pressure. We also found that temperature and lipid composition influence cytolysis by modulating lipid mobility. The electrolyte in the outer media is also affected as a chemical mediator to control CPP cytolysis by following the Hoffmeister effect for membrane hydration. These results confirmed the mechanism of cytolysis as temporal and local phase transfer of membrane lipid from Lα to Mesh1, which has punctured bilayer morphologies. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Controlling the Kinetics of an Enzymatic Reaction through Enzyme or Substrate Confinement into Lipid Mesophases with Tunable Structural Parameters
Int. J. Mol. Sci. 2020, 21(14), 5116; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21145116 - 20 Jul 2020
Cited by 2 | Viewed by 810
Abstract
Lipid liquid crystalline mesophases, resulting from the self-assembly of polymorphic lipids in water, have been widely explored as biocompatible drug delivery systems. In this respect, non-lamellar structures are particularly attractive: they are characterized by complex 3D architectures, with the coexistence of hydrophobic and [...] Read more.
Lipid liquid crystalline mesophases, resulting from the self-assembly of polymorphic lipids in water, have been widely explored as biocompatible drug delivery systems. In this respect, non-lamellar structures are particularly attractive: they are characterized by complex 3D architectures, with the coexistence of hydrophobic and hydrophilic regions that can conveniently host drugs of different polarities. The fine tunability of the structural parameters is nontrivial, but of paramount relevance, in order to control the diffusive properties of encapsulated active principles and, ultimately, their pharmacokinetics and release. In this work, we investigate the reaction kinetics of p-nitrophenyl phosphate conversion into p-nitrophenol, catalysed by the enzyme Alkaline Phosphatase, upon alternative confinement of the substrate and of the enzyme into liquid crystalline mesophases of phytantriol/H2O containing variable amounts of an additive, sucrose stearate, able to swell the mesophase. A structural investigation through Small-Angle X-ray Scattering, revealed the possibility to finely control the structure/size of the mesophases with the amount of the included additive. A UV–vis spectroscopy study highlighted that the enzymatic reaction kinetics could be controlled by tuning the structural parameters of the mesophase, opening new perspectives for the exploitation of non-lamellar mesophases for confinement and controlled release of therapeutics. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Article
Structure of Nanotubes Self-Assembled from a Monoamide Organogelator
Int. J. Mol. Sci. 2020, 21(14), 4960; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21144960 - 14 Jul 2020
Cited by 4 | Viewed by 936
Abstract
Some organic compounds are known to self-assemble into nanotubes in solutions, but the packing of the molecules into the walls of the tubes is known only in a very few cases. Herein, we study two compounds forming nanotubes in alkanes. They bear a [...] Read more.
Some organic compounds are known to self-assemble into nanotubes in solutions, but the packing of the molecules into the walls of the tubes is known only in a very few cases. Herein, we study two compounds forming nanotubes in alkanes. They bear a secondary alkanamide chain linked to a benzoic acid propyl ester (HUB-3) or to a butyl ester (HUB-4). They gel alkanes for concentrations above 0.2 wt.%. The structures of these gels, studied by freeze fracture electron microscopy, exhibit nanotubes: for HUB-3 their external diameters are polydisperse with a mean value of 33.3 nm; for HUB-4, they are less disperse with a mean value of 25.6 nm. The structure of the gel was investigated by small- and wide-angle X-ray scattering. The evolution of the intensities show that the tubes are metastable and transit slowly toward crystals. The intensities of the tubes of HUB-4 feature up to six oscillations. The shape of the intensities proves the tubular structure of the aggregates, and gives a measurement of 20.6 nm for the outer diameters and 11.0 nm for the inner diameters. It also shows that the electron density in the wall of the tubes is heterogeneous and is well described by a model with three layers. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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Review

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Review
Physiology and Physical Chemistry of Bile Acids
Int. J. Mol. Sci. 2021, 22(4), 1780; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22041780 - 10 Feb 2021
Cited by 11 | Viewed by 1843
Abstract
Bile acids (BAs) are facial amphiphiles synthesized in the body of all vertebrates. They undergo the enterohepatic circulation: they are produced in the liver, stored in the gallbladder, released in the intestine, taken into the bloodstream and lastly re-absorbed in the liver. During [...] Read more.
Bile acids (BAs) are facial amphiphiles synthesized in the body of all vertebrates. They undergo the enterohepatic circulation: they are produced in the liver, stored in the gallbladder, released in the intestine, taken into the bloodstream and lastly re-absorbed in the liver. During this pathway, BAs are modified in their molecular structure by the action of enzymes and bacteria. Such transformations allow them to acquire the chemical–physical properties needed for fulling several activities including metabolic regulation, antimicrobial functions and solubilization of lipids in digestion. The versatility of BAs in the physiological functions has inspired their use in many bio-applications, making them important tools for active molecule delivery, metabolic disease treatments and emulsification processes in food and drug industries. Moreover, moving over the borders of the biological field, BAs have been largely investigated as building blocks for the construction of supramolecular aggregates having peculiar structural, mechanical, chemical and optical properties. The review starts with a biological analysis of the BAs functions before progressively switching to a general overview of BAs in pharmacology and medicine applications. Lastly the focus moves to the BAs use in material science. Full article
(This article belongs to the Special Issue Assembly Superstructures in Chemistry)
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