Molecular Recognition Driven Bioinspired Directional Supramolecular Assembly of Amphiphilic (Macro)molecules and Proteins

Alternating vs. random amphiphilic polydisulfides: aggregation, enzyme activity inhibition and redox-responsive guest release

Herein, we report the synthesis of an alternating copolymer (ACP) with a bio-reducible amphiphilic polydisulfide backbone and highlight the impact of the alternating monomer connectivity on the self-assembly, morphology, chain-exchange dynamics, drug-release kinetics, and enzyme activity inhibition. Condensation polymerization between hydrophobic 1,10-bis(pyridin-2-yldisulfaneyl)decane and hydrophilic 2,3-mercaptosuccinic acid (1.04 : 1.00 ratio) generated amphiphilic ACP P1 (Mw = 8450 g mol-1, Đ = 1.3), which exhibited self-assembly in water, leading to the formation of an ultra-thin (height <5.0 nm) entangled fibrillar network. In contrast, structurally similar amphiphilic random copolymer P2 exhibited a truncated irregular disc-like morphology under the same conditions. It is postulated that due to the perfect alternating sequence of the hydrophobic and hydrophilic segments in P1, its immiscibility-driven aggregation in water leads to a pleated structure, which further assembles and forms the observed long fibrillar structures, similar to crystallization-driven self-assembly. In fact, wide-angle X-ray diffraction (WXRD) analysis of a lyophilized P1 sample showed sharp peaks, indicating its crystalline nature (approximately 37% crystallinity), and these were completely missing for P2. The effect of such distinct self-assembly on the chain-exchange dynamics was probed by fluorescence resonance energy transfer (FRET) using 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO) and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) as the FRET-donor and -acceptor, respectively. For DiI- and DiO-entrapped solutions of P1, when mixed, no prominent FRET appeared even after 24 h. In sharp contrast, for P2, intense FRET emission occurred, and the FRET ratio (approximately 0.9) reached saturation in approximately 15 h, indicating the greatly enhanced kinetic stability of P1 aggregates. Glutathione-induced release of encapsulated Nile red showed much slower kinetics for P1 compared to that of P2, which was corroborated by the observed slow chain-exchange dynamics of the highly stable alternating copolymer assembly. Furthermore, the well-ordered assembly of P1 exhibited an excellent surface-functional group display (zeta potential of -32 mV compared to -14 mV for P2), which resulted in the effective recognition of the α-chymotrypsin (Cht) protein surface by electrostatic interaction. Consequently, P1 significantly (>70%) suppressed the enzymatic activity of Cht, while in the presence of P2, the enzyme was still active with >70% efficacy.

Hydrogen-Bonding-Regulated Morphology Control and the Impact on the Antibacterial Activity of Cationic π-Amphiphiles

This manuscript describes the synthesis, self-assembly, and antibacterial properties of naphthalene-diimide (NDI)-derived cationic π-amphiphiles. Three such asymmetric NDI derivatives with a nonionic hydrophilic wedge and a guanidine group in the two opposite sides of the NDI chromophore were considered. They differ by a single functional group (hydrazide, amide, and ester for NDI-1, NDI-2, and NDI-3, respectively), located in the linker between the NDI and the hydrophilic wedge. For NDI-1, the H-bonding among the hydrazides regulated unilateral stacking and a preferential direction of curvature of the resulting supramolecular polymer, producing an unsymmetric polymersome with the guanidinium groups displayed at the outer surface. NDI-3, lacking any H-bonding group, exhibits π-stacking without any preferential orientation and generates spherical particles with a relatively poor display of the guanidium groups. In sharp contrast to NDI-1, NDI-2 exhibits an entangled one-dimensional (1D) fibrillar morphology, indicating the prominent role of the H-bonding motif of the amide group and flexibility of the linker. The antibacterial activity of these assemblies was probed against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). NDI-1 showed the most promising antibacterial activity with a minimum inhibitory concentration (MIC) of ∼7.8 μg/mL against S. aureus and moderate activity (MIC ∼ 125 μg/mL) against E. coli. In sharp contrast, NDI-3 did not show any significant activity against the bacteria, suggesting a strong impact of the H-bonding-regulated directional assembly. NDI-2, forming a fibrillar network, showed moderate activity against S. aureus and negligible activity against E. coli, highlighting a significant impact of the morphology. All of these three molecules were found to be compatible with mammalian cells from the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) and hemolysis assay. The mechanistic investigation by membrane polarization assay, live/dead fluorescence assay, and microscopy studies confirmed the membrane disruption mechanism of cell killing for the lead candidate NDI-1.

Seed-Induced Living Two-Dimensional (2D) Supramolecular Polymerization in Water: Implications on Protein Adsorption and Enzyme Inhibition

In biological systems, programmable supramolecular frameworks characterized by coordinated directional non-covalent interactions are widespread. However, only a small number of reports involve pure water-based dynamic supramolecular assembly of artificial π-amphiphiles, primarily due to the formidable challenge of counteracting the strong hydrophobic dominance of the π-surface in water, leading to undesired kinetic traps. This study reveals the pathway complexity in hydrogen-bonding-mediated supramolecular polymerization of an amide-functionalized naphthalene monoimide (NMI) building block with a hydrophilic oligo-oxyethylene (OE) wedge. O-NMI-2 initially produced entropically driven, collapsed spherical particles in water (Agg-1); however, over a span of 72 h, these metastable Agg-1 gradually transformed into two-dimensional (2D) nanosheets (Agg-2), favoured by both entropy and enthalpy contributions. The intricate self-assembly pathways in O-NMI-2 enable us to explore seed-induced living supramolecular polymerization (LSP) in water for controlled synthesis of monolayered 2D assemblies. Furthermore, we demonstrated the nonspecific surface adsorption of a model enzyme, serine protease α-Chymotrypsin (α-ChT), and consequently the enzyme activity, which could be regulated by controlling the morphological transformation of O-NMI-2 from Agg-1 to Agg-2. We delve into the thermodynamic aspects of such shape-dependent protein-surface interactions and unravel the impact of seed-induced LSP on temporally controlling the catalytic activity of α-ChT.

Donor-acceptor complex formation by social self-sorting of polycyclic aromatic hydrocarbons and perylene bisimides

Self-assembly versus complexation with polycyclic aromatic hydrocarbon (PAH) guest molecules is studied for a series of perylene bisimides (PBIs). Bulky imide substituents at the PBI guide their self-assembly into dimer aggregates with null-type exciton coupling. Host-guest titration experiments with perylene and triphenylene PAHs afford 1 : 1 and 1 : 2 complexes whose properties are studied by single crystal X-ray analysis and UV/Vis and fluorescence spectroscopy.

Kaleidoscope megamolecules synthesis and application using self-assembly technology

The megamolecules with high ordered structures play an important role in chemical biology and biomedical engineering. Self-assembly, a long-discovered but very appealing technique, could induce many reactions between biomacromolecules and organic linking molecules, such as an enzyme domain and its covalent inhibitors. Enzyme and its small-molecule inhibitors have achieved many successes in medical application, which realize the catalysis process and theranostic function. By employing the protein engineering technology, the building blocks of enzyme fusion protein and small molecule linker can be assembled into a novel architecture with the specified organization and conformation. Molecular level recognition of enzyme domain could provide both covalent reaction sites and structural skeleton for the functional fusion protein. In this review, we will discuss the range of tools available to combine functional domains by using the recombinant protein technology, which can assemble them into precisely specified architectures/valences and develop the kaleidoscope megamolecules for catalytic and medical application.

Density functional theory computation of the intermolecular interactions of Al2@C24 and Al2@Mg12O12 semiconducting quantum dots conjugated with the glycine tripeptide

The nature of intermolecular forces within semiconductor quantum dot systems can determine various physicochemical properties, as well as their functions, in nanomedical applications. The purpose of this study has been to investigate the nature of the intermolecular forces operating between Al₂@C₂₄ and A_l2@Mg₁₂O₁₂ semiconducting quantum dots and the glycine tripeptide (GlyGlyGly), and also consider whether permanent electric dipole–dipole interactions play a significant role vis-à-vis these molecular systems. The energy computations, including the Keesom and the total electronic interactions and the energy decomposition, together with the quantum topology analyses were performed. Our results demonstrate that no significant correlation is found between the magnitude and orientation of the electrical dipole moments, and the interaction energy of the Al₂@C₂₄ and A_l2@Mg₁₂O₁₂ with GlyGlyGly tripeptide. The Pearson correlation coefficient test revealed a very weak correlation between the quantum and the Keesom interaction energies. Apart from the quantum topology analyses, the energy decomposition consideration confirmed that the dominant share of the interaction energies was associated with the electrostatic interactions, yet both the steric and the quantum effects also made appreciable contributions. We conclude that, beside the electrical dipole–dipole interactions, other prominent intermolecular forces, such as the polarization attraction, the hydrogen bond, and the van der Waals interactions can also influence the interaction energy of the system. The findings of this study can be utilized in several areas in the field of nanobiomedicine, including the rational design of cell-penetrating and intracellular drug delivery systems using semiconducting quantum dots functionalized with a peptide.

The nature of intermolecular forces within semiconducting quantum dot systems can determine various physicochemical properties, as well as their functions, in nanomedical applications.

Impact of the Hydrogen-Bonding Functional Group on Hydrogelation of Amphiphilic Naphthalene-diimide Derivatives and Nonspecific Protein Adsorption

This manuscript reports the effect of hydrogen-bonding functionality on the supramolecular assembly of naphthalene-diimide (NDI)-derived amphiphilic building blocks in water. All the molecules contain a central NDI chromophore, functionalized with a hydrophilic oligo-oxyethylene (OE) wedge in one arm and a phenyl group on the opposite arm. They differ by a single H-bonding functionality, which links the NDI chromophore and the phenyl moiety. The H-bonding functionalities are amide, thioamide, urea, and urethane in NDI-A, NDI-TA, NDI-U, and NDI-UT, respectively. All of these molecules exhibit π-stacking in water, as evident from their distinct UV/vis absorption spectra when compared to that of the monomeric dye in THF. However, among these four, only NDI-A and NDI-TA show hydrogelation, while the other two precipitate out of the medium. The NDI-A hydrogel also exhibits transient stability and leads to a crystalline precipitate within ∼5 h. Only NDI-TA produces stable transparent hydrogel with the entangled fibrillar morphology that is typical for gelators. Both NDI-A and NDI-TA showed a thermoresponsive property with a lower critical solution temperature of about 41-42 °C. Powder XRD studies show a parallel orientation for NDI-A and an antiparallel orientation for NDI-TA. Computational studies support this experimental observation and indicate that the NDI-A assembly is highly stabilized by strong H-bonding among the amide groups and π-stacking interaction in the parallel orientation. On the other hand, due to weak H-bonding among the thioamide groups, the binding energy of the parallelly oriented NDI-TA was significantly lower and the optimized structure was disordered. Instead, its antiparallel orientation was more stable, with criss-cross aligned H-bonding interactions and π-π interactions between adjacent aromatic rings. The NDI-TA hydrogel with less ordered OE chains on the surface showed prominent adsorption of serum protein BSA. In sharp contrast, NDI-A did not exhibit any notable interaction with BSA, as evident from the ITC studies.

Biomolecule-mimetic nanomaterials for photothermal and photodynamic therapy of cancers: Bridging nanobiotechnology and biomedicine

Nanomaterial-based phototherapy has become an important research direction for cancer therapy, but it still to face some obstacles, such as the toxic side effects and low target specificity. The biomimetic synthesis of nanomaterials using biomolecules is a potential strategy to improve photothermal therapy (PTT) and photodynamic therapy (PDT) techniques due to their endowed biocompatibility, degradability, low toxicity, and specific targeting. This review presents recent advances in the biomolecule-mimetic synthesis of functional nanomaterials for PTT and PDT of cancers. First, we introduce four biomimetic synthesis methods via some case studies and discuss the advantages of each method. Then, we introduce the synthesis of nanomaterials using some biomolecules such as DNA, RNA, protein, peptide, polydopamine, and others, and discuss in detail how to regulate the structure and functions of the obtained biomimetic nanomaterials. Finally, potential applications of biomimetic nanomaterials for both PTT and PDT of cancers are demonstrated and discussed. We believe that this work is valuable for readers to understand the mechanisms of biomimetic synthesis and nanomaterial-based phototherapy techniques, and will contribute to bridging nanotechnology and biomedicine to realize novel highly effective cancer therapies.

Amphiphilic Polymers for Color Dispersion: Toward Stable and Low-Viscosity Inkjet Ink

Amphiphilic random and block copolymers were synthesized as potential inkjet inks. This study evaluated the potential of these polymers for color dispersion by examining the following factors: surface tension, zeta potential, viscosity, and particle size. Acrylic acid and (ethoxyethoxy)ethyl acrylate were used as the hydrophilic molecular units. Styrene, butyl acrylate, and phenoxyethyl acrylate were used as hydrophobic units. Color dispersions were prepared by using organic dye and these amphiphilic polymers. The color dispersions containing random copolymers exhibited low viscosity, which is preferable for jetting, but the dye particles tended to sediment after the thermal aging test. In contrast, those containing block copolymers showed high viscosity, which was unsuitable for jetting. However, they retained their initial dispersion state after the aging test. The advantages and disadvantages of each monomer arrangement (random or block) were demonstrated, providing a future outlook on the molecular design of polymer dispersants for color dispersions.

Self-assembly of fullerene C60-based amphiphiles in solutions

Fullerene C₆₀ is an all-carbon cage molecule with rich physicochemical properties. It is highly symmetric and hydrophobic, which can be used as a building block for the preparation of amphiphiles that self-assemble into diverse supramolecular structures in aqueous solutions. Meanwhile, C₆₀ is also lipophobic, which is different from the alkyl chains in traditional surfactants. By attaching alkyl chains to the C₆₀ sphere, a new type of lipophobic-lipophilic amphiphiles can be constructed which undergo self-assembly in n-alkanes. When inorganic clusters such as polyoxometalate are linked to the C₆₀ sphere, organic-inorganic hybrids will be obtained which can self-assemble in polar organic solvents. Pristine C₆₀ has also been modified by polar groups such as hydroxy and carboxy, which are linked to hydrophobic moieties and form a new class of amphiphiles. In this review, the self-assembly of C₆₀-based amphiphiles in aqueous and nonaqueous solutions will be summarized. The characteristics exhibited by C₆₀-based amphiphiles during the self-assembly will be discussed with close comparison to traditional surfactants, and the influences of the aggregate formation on the physicochemical properties of the C₆₀ sphere will be described. Finally, a brief summary will be given together with a promising perspective in near future.

Boosting the Discovery of Small Molecule Inhibitors of Glucose-6-Phosphate Dehydrogenase for the Treatment of Cancer, Infectious Diseases, and Inflammation

We present an overview of small molecule glucose-6-phosphate dehydrogenase (G6PD) inhibitors that have potential for use in the treatment of cancer, infectious diseases, and inflammation. Both steroidal and nonsteroidal inhibitors have been identified with steroidal inhibitors lacking target selectivity. The main scaffolds encountered in nonsteroidal inhibitors are quinazolinones and benzothiazinones/benzothiazepinones. Three molecules show promise for development as antiparasitic (25 and 29) and anti-inflammatory (32) agents. Regarding modality of inhibition (MOI), steroidal inhibitors have been shown to be uncompetitive and reversible. Nonsteroidal small molecules have exhibited all types of MOI. Strategies to boost the discovery of small molecule G6PD inhibitors include exploration of structure-activity relationships (SARs) for established inhibitors, employment of high-throughput screening (HTS), and fragment-based drug discovery (FBDD) for the identification of new hits. We discuss the challenges and gaps associated with drug discovery efforts of G6PD inhibitors from in silico, in vitro, and in cellulo to in vivo studies.

Programmed Macromolecular Assembly by Dipole-Dipole Interactions with Aggregation-Induced Enhanced Emission in Aqueous Medium

Self-assembling polymers by bioinspired directional supramolecular interactions currently hold great scientific and technological interests. Herein, we report an unorthodox strategy based on a dipole-dipole interaction-mediated extended antiparallel dipolar assembly of a model merocyanine (MC) dye for maneuvering the self-assembly of a highly water-soluble MC-functionalized block copolymer (P2). Unlike traditional amphiphilic block copolymers featuring distinct hydrophobic segments (flexible aliphatic hydrocarbon chains or rigid nonpolar aromatic scaffolds), P2 comprises polyethylene glycol monomethyl ether (PEG) as a hydrophilic block and an unconventional structure-directing acrylate block functionalized with polar MC-dyes in the side chains of every repeat unit. In the absence of any additional hydrophobic assistance, P2 spontaneously self-assembles in water through the continuous opposite alignment of its pendant MCs by multiple dipole-dipole interactions to cancel out their ground state dipole moments, which initially generates an H-aggregated species with ill-defined morphology (Aggregate 1). Upon thermal annealing, Aggregate 1 reorganizes into higher-order core-shell nanodisc-like structures (Aggregate 2) driven by the orthogonal π-stacking interactions of the rigid aromatic framework derived from the extended cofacial MC-stacks. The aromatic interiors of the nanodiscs gain colloidal stability from the externally decorated hydrophilic PEG chains. While the initially formed Aggregate 1, predominantly by dipole-dipole interactions, showed remarkable thermal stability due to the cooperative effect of the polymer chain, the hierarchical assembly guided by relatively weaker dispersion forces of the MC-stacked π-surfaces could be tailored by dilution or thermal treatment. Such organized packing of pendant MCs by the dual effect of dipole-dipole interactions and π-stacking conferred several exciting properties to the P2 assembly in water. Long-range ordered antiparallel stacking of the pendant MCs rendered outstanding aggregation-induced enhanced emission (AIEE) properties to the resultant nanostructures in water with increased fluorescence lifetime, quantum yield, and Stokes shift compared to nonaggregating P2 in CHCl₃. The remarkable thermal and kinetic stability of the nanodiscs, their guest loading ability, and very low critical aggregation concentration (CAC) were demonstrated by Förster resonance energy transfer (FRET) studies with an encapsulated donor-acceptor dye pair.

Deep-blue-emitting nanoaggregates from carbazole-based dyes in water

New amphiphilic carbazole-based dyes assemble in water into deep-blue-emitting, highly fluorescent helical aggregates as observed by transmission electron microscopy and atomic force microscopy. Single crystal X-ray diffraction and NMR spectroscopy reveal that self-complementary, antiparallel H-bonding and π-π stacking interactions are the driving forces for the formation of these dye aggregates.

Shape-Dependent Cellular Uptake of Nanostructures Produced from Supramolecular Structure-Directing Unit-Appended Hydrophilic Polymers

Cellular uptake is an important event in drug delivery and other biomedical applications. Amphiphilic polymers produce aggregates of different size and shape depending on the intrinsic structural differences and the packing parameter. Although they have been explored for various biomedical applications with immense interest, the relationship between the shape of the aggregate and cellular uptake has been studied only in limited examples. This work reports two polymers (P1 and P2), both of which contain a hydrophobic supramolecular structure-directing unit (SSDU) at the chain-end of a fluorescence dye-labeled hydrophilic polymer. Depending on the difference in the structure of the single H-bonding functional group (hydrazide or amide) of the SSDU, P1 and P2 produce polymersomes (NS1) and spherical micelles (NS2), respectively. An aged solution of P2 produces cylindrical micelles (NS3). Confocal microscopy studies reveal that the uptake of these nanostructures in HeLa cells greatly depends on the shape of the aggregate. Spherical NS1 and NS2 show appreciable uptake at 1 or 4 h of incubation, whereas NS3 shows negligible uptake. Temperature-dependent cellular uptake studies reveal an energy-dependent endocytosis pathway. Kinetic studies show gradual increase in the cellular uptake with time, and at 24 h the relative uptake ratio (NS1:NS2:NS3) is 1.0:0.2:<0.1, implying the polymersome morphology (NS1) is most efficient for cellular uptake compared to the spherical or cylindrical micelles. The same trend was also noticed for MDA-MB 231 cells. Confocal microscopy studies further reveal cellular internalization and intracellular location of NS1, which showed maximum cellular uptake. As the intrinsic difference in the chemical structure of the two polymers is negligible, the observed difference can be explicitly assigned to their difference in shape.

Precise control over supramolecular nanostructures via manipulation of H-bonding in π-amphiphiles

Self-assembled supramolecular architectures are ubiquitous in nature. A synchronized combination of dynamic noncovalent interactions is the major driving force in forming unique structures with high-precision control over the self-assembly of supramolecular materials. Herein, we have achieved programmable nanostructures by introducing single/multiple H-bonding units in a supramolecular building block. A diverse range of nanostructures can be generated in aqueous medium by subtly tuning the structure of π-amphiphiles. 1D-cylindrical micelles, 2D-nanoribbons and hollow nanotubes are produced by systematically varying the number of H-bonding units (0-2) in structurally near identical π-amphiphiles. Spectroscopic measurements revealed the decisive role of H-bonding units for different modes of molecular packing. We have demonstrated that a competitive self-assembled state (a kinetically controlled aggregation state and a thermodynamically controlled aggregation state) can be generated by fine tuning the number of noncovalent forces present in the supramolecular building blocks. The luminescence properties of conjugated dithiomaleimide (DTM) provided insight into the relative hydrophobicity of the core in these nanostructures. In addition, fluorescence turn-off in the presence of thiophenol enabled us to probe the accessibility of the hydrophobic core in these assembled systems toward guest molecules. Therefore the DTM group provides an efficient tool to determine the relative hydrophobicity and accessibility of the core of various nanostructures which is very rarely studied in supramolecular assemblies.

Self-Assembly of a Pyridine-Based Amphiphile Complexed with Regioisomeric Dihydroxy Naphthalenes into Supramolecular Nanotubes with Different Inner Diameters

A pyridine-based amphiphile complexed with 1,5-, 1,6-, 2,6-, or 2,7-dihydroxy naphthalene self-assembled in water to form nanotubes with inner diameters of 46, 38, 24, 18, and 11 nm in which the naphthalene molecules formed J-type aggregates. In contrast, the amphiphile complexed with 1,2-, 1,3-, 1,4-, 1,7-, 1,8-, or 2,3-dihydroxy naphthalene formed nanofibers in which the naphthalene molecules formed H-type aggregates. The inner diameter of the nanotubes strongly depended on the regioisomeric dihydroxy naphthalene. UV-vis, fluorescence, infrared spectroscopy, X-ray diffraction analysis, and differential scanning calorimetry showed that nanotubes with smaller inner diameters had weaker intermolecular hydrogen bonds between the tilted amphiphiles complexed with the naphthalene molecules within the membrane walls and showed larger Stokes shifts in the excimer fluorescence of the naphthalene moiety. These findings should be useful not only for fine-tuning the inner diameters of supramolecular nanotubes but also for controlling the aggregation states of functional aromatic molecules to generate nanostructures with useful optical and electronic properties in water.