Chaotropic-anion-induced supramolecular self-assembly of ionic polymeric micelles

Exploring the Depth-Dependent Microviscosity inside a Micelle Using Butterfly-Motion-Based Fluorescent Probes

The viscosity distribution of micellar interiors from the very center to the outer surface is dramatically varied, which has been distinguished in theoretical models, yet it remains highly challenging to quantify this issue experimentally. Herein, a series of fluorophore-substituted surfactants DPAC-Fn (n = 3, 5, 7, 9, 11, 13, and 15) are developed by functionalizing the different alkyl-trimethylammonium bromides with the butterfly motion-based viscosity sensor, N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC). The immersion depth of DPAC units of DPAC-Fn in cetrimonium bromide (C16TAB) micelles depends on the alkyl chain lengths n. From deep (n = 15) to shallow (n = 3), DPAC-Fn in C16TAB micelles exhibits efficient viscosity-sensitive dynamic multicolor emissions. With external standards for quantification, the viscosity distribution inside a C16TAB micelle with the size of ∼4 nm is changed seriously from high viscosity (∼190 Pa s) in the core center to low viscosity (∼1 Pa s) near the outer surface. This work provides a tailored approach for powerful micelle tools to explore the depth-dependent microviscosity of micellar interiors.

Hofmeister Effects Shine in Nanoscience

Hofmeister effects play a crucial role in nanoscience by affecting the physicochemical and biochemical processes. Thus far, numerous wonderful applications from various aspects of nanoscience have been developed based on the mechanism of Hofmeister effects, such as hydrogel/aerogel engineering, battery design, nanosynthesis, nanomotors, ion sensors, supramolecular chemistry, colloid and interface science, nanomedicine, and transport behaviors, etc. In this review, for the first time, the progress of applying Hofmeister effects is systematically introduced and summarized in nanoscience. It is aimed to provide a comprehensive guideline for future researchers to design more useful Hofmeister effects-based nanosystems.

Sequential acid/reduction response of triblock copolymeric nanomicelles to release camptothecin and toll-like receptor 7/8 agonist for orchestrated chemoimmunotherapy

Background

Immunosuppressive tumor immune microenvironment (TIME) lowers immunotherapy effectiveness. Additionally, low penetration efficiency and unpredictable drug release in tumor areas restrict tumor therapy.

Methods

A triblock copolymeric micelle (Nano^PCPT+PIMDQ) was developed to carry the chemotherapeutic drug camptothecin (CPT) and the TLR7/8 agonist 1-(4-(aminomethyl)benzyl)-2-butyl-1H-imidazo[4,5-c] quinoline-4-amine (IMDQ) to achieve deep tumor penetration and on-demand drug release by responding to acid and reduction stimuli sequentially. The synergistic antitumour efficacy of Nano^PCPT+PIMDQ was assessed both in vitro and in vivo.

Results

Nano^PCPT+PIMDQ is composed of a hydrophilic PEG(polyethylene glycol) outer layer, an acid-sensitive EPEMA middle layer, and a drug inner core. Upon intratumoral injection, (i) Nano^PCPT+PIMDQ first responds to the acidic tumor microenvironment and disintegrates to PIMDQ and PCPT, penetrating deep regions of the tumor; (ii) tumor cells are killed by the released CPT; (iii) DCs are activated by PIMDQ to increase the infiltration of cytotoxic T lymphocyte (CTL); and (iv) both downregulated Foxp3⁺ Tregs by CPT and repolarized M2 macrophages by PIMDQ can relieve the TIME.

Conclusion

This pH/GSH-responsive triblock polymer-drug conjugate reduces immunosuppression and enhances the infiltration of CTLs by codelivering CPT and IMDQ in a controllable manner, providing a promising platform for synergistic tumor chemoimmunotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01577-5.

Responsive Multivesicular Polymeric Nanovaccines that Codeliver STING Agonists and Neoantigens for Combination Tumor Immunotherapy

Immune checkpoint blockade (ICB) has significantly advanced cancer immunotherapy, yet its patient response rates are generally low. Vaccines, including immunostimulant-adjuvanted peptide antigens, can improve ICB. The emerging neoantigens generated by cancer somatic mutations elicit cancer-specific immunity for personalized immunotherapy; the novel cyclic dinucleotide (CDN) adjuvants activate stimulator of interferon genes (STING) for antitumor type I interferon (IFN-I) responses. However, CDN/neoantigen vaccine development has been limited by the poor antigen/adjuvant codelivery. Here, pH-responsive CDN/neoantigen codelivering nanovaccines (NVs) for ICB combination tumor immunotherapy are reported. pH-responsive polymers are synthesized to be self-assembled into multivesicular nanoparticles (NPs) at physiological pH and disassembled at acidic conditions. NPs with high CDN/antigen coloading are selected as NVs for CDN/antigen codelivery to antigen presenting cells (APCs) in immunomodulatory lymph nodes (LNs). In the acidic endosome of APCs, pH-responsive NVs facilitate the vaccine release and escape into cytosol, where CDNs activate STING for IFN-I responses and antigens are presented by major histocompatibility complex (MHC) for T-cell priming. In mice, NVs elicit potent antigen-specific CD8⁺ T-cell responses with immune memory, and reduce multifaceted tumor immunosuppression. In syngeneic murine tumors, NVs show robust ICB combination therapeutic efficacy. Overall, these CDN/neoantigen-codelivering NVs hold the potential for ICB combination tumor immunotherapy.

Effects of oppositely charged moieties on the self-assembly and biophysicochemical properties of polyurethane micelles

Gemini quaternary ammonium (GQA), a type of cationic surfactant, exhibits excellent micellization ability and acts as a cell internalization promoter to increase the permeability of the cell membrane. GQA is sensitive to ionic solutions, which disturb its stabilization and leads to the rapid degradation of its polymer micelles due to its unique hydrophilic N⁺ structure. However, the effect of negatively charged moieties in the polymer chains of GQA on its action in polymer micelles, typically with regard to its micellization and biological performance, remains unclear. In this work, a series of polyurethane micelles containing various ratios of oppositely charged moieties was prepared. We found that the interchain electrostatic interaction severely undermines the function of the GQA surfactant and hinders the self-assembly and stabilization of polyurethane micelles. Specifically, a hydrophilic corona with a longer length cannot completely overcome this effect. By regulating the ratio of oppositely charged moieties, micelles exhibited tunable biological properties, such as biocompatibility, cytotoxicity, cell internalization, and phagocytosis by macrophages. Based on our results, a moderate molecular weight of mPEG (Mn = 1900) and a slight positive surface potential (∼10 mV) are the best surface parameters for the comprehensive performance of the studied nanoplatforms. This study provides a further understanding of the electrostatic interaction effect on the properties of the cationic GQA, offering rational guidance for the design and fabrication of GQA polymer micelles.

Non-globular organic ionic plastic crystal containing crown-ether moiety - Tuning its behaviour using sodium salts

Organic ionic plastic crystals (OIPCs) are a class of soft materials showing positional order while still allowing orientational freedom. Due to their motional freedom in the solid state, they possess plasticity, non‐flammability and high ionic conductivity. OIPC behavior is typically exhibited by ‘simple’ globular molecules allowing molecular rotation, whereas the interactions that govern the formation of OIPC phases in complex non‐globular molecules are less understood. To better understand these interactions, a new family of non‐globular OIPCs containing a 15‐crown‐5 ether moiety was synthetized and characterized. The 15C5BA molecule prepared does not exhibit the sought‐after behavior because of its non‐globular nature and strong intermolecular H‐bonds that restrict orientational motion. However, the OIPC behavior was successfully obtained through complexation of the crown‐ether moiety with sodium salts containing chaotropic anions. Those anions weaken the interactions between the molecules, allowing rotational freedom and tuning of the thermal and morphological properties of the OIPC.

A Gradient pH-Sensitive Polymer-Based Antiviral Strategy via Viroporin-Induced Membrane Acidification

Lipid-membrane-targeting strategies hold great promise to develop broad-spectrum antivirals. However, it remains a big challenge to identify novel membrane-based targets of viruses and virus-infected cells for development of precision targeted approaches. Here, it is discovered that viroporins, viral-encoded ion channels, which have been reported to mediate release of hydrogen ions, trigger membrane acidification of virus-infected cells. Through development of a fine-scale library of gradient pH-sensitive (GPS) polymeric nanoprobes, the cellular membrane pH transitions are measured from pH 6.8-7.1 (uninfection) to pH 6.5-6.8 (virus-infection). In response to the subtle pH alterations, the GPS polymer with sharp response at pH 6.8 (GPS_6.8 ) selectively binds to virus-infected cell membranes or the viral envelope, and even completely disrupts the viral envelope. Accordingly, GPS_6.8 treatment exerts suppressive effects on a wide variety of viruses including SARS-CoV-2 through triggering viral-envelope lysis rather than affecting immune pathway or viability of host cells. Murine viral-infection models exhibit that supplementation of GPS_6.8 decreases viral titers and ameliorates inflammatory damage. Thus, the gradient pH-sensitive nanotechnology offers a promising strategy for accurate detection of biological pH environments and robust interference with viruses.

A transistor-like pH-sensitive nanodetergent for selective cancer therapy

Plasma membrane rupture is a promising strategy for drug-resistant cancer treatment, but its application is limited by the low tumour selectivity of membranolytic molecules. Here we report the design of 'proton transistor' nanodetergents that can convert the subtle pH perturbation signals of tumour tissues into sharp transition signals of membranolytic activity for selective cancer therapy. Our top-performing 'proton transistor' nanodetergent, P(C6-Bn₂₀), can achieve a >32-fold change in cytotoxicity with a 0.1 pH input signal. At physiological pH, P(C6-Bn₂₀) self-assembles into neutral nanoparticles with inactive membranolytic blocks shielded by poly(ethylene glycol) shells, exhibiting low toxicity. At tumour acidity, a sharp transition in its protonation state induces a morphological transformation and an activation of the membranolytic blocks, and the cation-π interaction facilitates the insertion of benzyl groups-containing hydrophobic domains into the cell membranes, resulting in potent membranolytic activity. P(C6-Bn₂₀) is well tolerated in mice and shows high anti-tumour efficacy in various mouse tumour models.

Effects of temperature on chaotropic anion-induced shape transitions of star molecular bottlebrushes with heterografted poly(ethylene oxide) and poly(N,N-dialkylaminoethyl methacrylate) side chains in acidic water

This article reports a study of the effects of temperature on chaotropic anion (CA)-induced star-globule shape transitions in acidic water of three-arm star bottlebrushes composed of heterografted poly(ethylene oxide) (PEO) and either poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMAEMA) or poly(2-(N,N-diethylamino)ethyl methacrylate) (PDEAEMA) (the brushes denoted as SMB-11 and -22, respectively). The brush polymers were synthesized by grafting alkyne-end-functionalized PEO and PDMAEMA or PDEAEMA onto an azide-bearing three-arm star backbone polymer using the copper(i)-catalyzed alkyne-azide cycloaddition reaction. Six anions were studied for their effects on the conformations of SMB-11 and -22 in acidic water: super CAs [Fe(CN)6]3- and [Fe(CN)6]4-, moderate CAs PF6- and ClO4-, weak CA I-, and for comparison, kosmotropic anion SO42-. At 25 °C, the addition of super and moderate CAs induced shape transitions of SMB-11 and -22 in pH 4.50 water from a starlike to a collapsed globular state stabilized by PEO side chains, which was driven by the ion pairing of protonated tertiary amine groups with CAs and the chaotropic effect. The shape changes occurred at much lower salt concentrations for super CAs than moderate CAs. Upon heating from near room temperature to 70 °C, the super CA-collapsed brushes remained in the globular state, whereas the moderate CA-collapsed brushes underwent reversible globule-to-star shape transitions. The transition temperature increased with increasing salt concentration and was found to be higher for SMB-22 at the same salt concentration, presumably caused by the chaotropic effect. In contrast, I- and SO42- had small effects on the conformations of SMB-11 and -22 at 25 °C in the studied salt concentration range, and only small and gradual size variations were observed upon heating to 70 °C. The results reported here may have potential uses in the design of stimuli-responsive systems for substance encapsulation and release.

Harnessing pH-Sensitive Polycation Vehicles for the Efficient siRNA Delivery

pH-sensitive hydrophobic segments have been certificated to facilitate siRNA delivery efficiency of amphiphilic polycation vehicles. However, optimal design concepts for these vehicles remain unclear. Herein, by studying the library of amphiphilic polycations mPEG-PAMA50-P(DEAx-r-D5Ay) (EAE5x/y), we concluded a multifactor matching concept (pKa values, "proton buffering capacities" (BCs), and critical micelle concentrations (CMCs)) for polycation vehicles to improve siRNA delivery efficiency in vitro and in vivo. We identified that the stronger BCs in a pH 5.5-7.4 subset induced by EAE548/29 (pKa = 6.79) and EAE539/37 (pKa = 6.20) are effective for siRNA delivery in vitro. Further, the stronger BCs occurred in a narrow subset of pH 5.5-6.5 and the lower CMC attributed to higher siRNA delivery capacity of EAE539/37 in vivo than EAE548/29 after intravenous administration and subcutaneous injection. More importantly, 87.2% gene knockdown efficacy was achieved by EAE539/37 via subcutaneous injection, which might be useful for an mRNA vaccine adjuvant. Furthermore, EAE539/37 also successfully delivered siRRM2 to tumor via intravenous administration and received highly efficient antitumor activity. Taken together, the suitable pKa values, strong BCs occurred in pH 5.5-6.5, and low CMCs were probably the potential solution for designing efficient polycationic vehicles for siRNA delivery.

pH- and chaotropic anion-induced conformational changes of tertiary amine-containing binary heterografted star molecular bottlebrushes in aqueous solution

Three-arm star-shaped, tertiary-amine-containing bottlebrushes exhibit star-globule shape transitions in response to pH changes and addition of sufficiently strong chaotropic anions.

100th Anniversary of Macromolecular Science Viewpoint: Biological Stimuli-Sensitive Polymer Prodrugs and Nanoparticles for Tumor-Specific Drug Delivery

The development of smart polymer vehicles to carry and release cytotoxic drugs to tumor tissues and cells while reducing the exposure of drugs in the blood and healthy organs is a highly challenging task with continuously growing interest from multiple fields, including polymer science, pharmaceutical science, nanotechnology, and clinical oncology. Inspired by the unique tumor microenvironment, such as mild acidity and overexpressed enzymes, functional polymer prodrugs and nanoparticles with reversible charge, detachable PEG shell, activatable ligand, and switchable size have been designed to enhance tumor deposition, tumor penetration, tumor cell uptake, and tumoral drug release. Utilizing biological signals inside tumor cells, such as acidic endo/lysosomal pH, elevated glutathione levels, and reactive oxygen species, responsive polymer prodrugs and nanoparticles with good extracellular stability but fast intracellular disintegration have been engineered for specific intracellular drug release. These biological stimuli-sensitive polymer prodrugs and nanoparticles have shown superior specificity and therapeutic efficacy to nonsensitive counterparts and, in certain cases, even clinically approved systems in varying tumor models. In this Viewpoint, design strategies and recent advances of biological stimuli-responsive polymer prodrugs and nanoparticles for tumor-specific drug delivery will be highlighted, and their challenges and future perspectives will be discussed.

Ionic effects on synthetic polymers: from solutions to brushes and gels

The ionic effects on synthetic polymers have attracted extensive attention due to the crucial role of ions in the determination of the properties of synthetic polymers. This review places the focus on specific ion effects, multivalent ion effects, and ionic hydrophilicity/hydrophobicity effects in synthetic polymer systems from solutions to brushes and gels. The specific ion effects on neutral polymers are determined by both the direct and indirect specific ion-polymer interactions, whereas the ion specificities of charged polymers are mainly dominated by the specific ion-pairing interactions. The ionic cross-linking effect exerted by the multivalent ions is widely used to tune the properties of polyelectrolytes, while the reentrant behavior of polyelectrolytes in the presence of multivalent ions still remains poorly understood. The ionic hydrophilicity/hydrophobicity effects not only can be applied to make strong polyelectrolytes thermosensitive, but also can be used to prepare polymeric nano-objects and to control the wettability of polyelectrolyte brush-modified surfaces. The not well-studied ionic hydrogen bond effects are also discussed in the last section of this review.

Self-Assembly Supramolecular Systems Based on Guanidinium Salts Modified Hyperbranched Polyamidoamine and Cationic Acrylamide Copolymers

Herein, novel hyperbranched polyamidoamine guanidinium salts (GS-h-PAMAM) and two cationic acrylamide copolymers P(AM-DAC-ABSM) and P(AM-DAC-AMTU) were successfully prepared. Then, self-assembly supramolecular systems were synthesized by directly mixing GS-h-PAMAM with copolymers in aqueous solution, and the mechanism of the self-assembly process was speculated. FT-IR, NMR, and SEM were used for structural confirmation. Furthermore, the excellent solution properties revealed that the supramolecular systems had potential application in clay hydration inhibitors. More importantly, utilizing functionalized hyperbranched polyamidoamine in the synthesis self-assembly supramolecular systems was an effective strategy for expanding their application fields and developing new functional materials, providing a powerful reference for the next study.

Guanidinium Can Break and Form Strongly Associating Ion Complexes

Guanidinium is one of nature's strongest denaturants and is also a motif that appears in several interfacial contexts such as the RGD sequence involved in cell adhesion, cell penetrating peptides, and antimicrobial molecules. It is important to quantify the origin of guanidinium's ion-specific interactions so that its unique behavior may be exploited in synthetic applications. The present work demonstrates that guanidinium ions can both break and form strongly associating ion complexes in a context-dependent way. These insights into guanidinium's behavior are elucidated using polyelectrolyte complexes (PECs), where interpolymer ion pairs between oppositely charged polymers play an important role in determining material stability. Different polycation-polyanion combinations can span a large range of association affinities, where more strongly associating complexes can remain insoluble in concentrated salt solutions and in extreme pH conditions. This high stability is desirable in several application contexts for PECs, but also renders them challenging to process and, therefore, to study since they cannot be dissolved into polymer solutions. Here we demonstrate that guanidinium salts are very effective in dissolving the poly(styrenesulfonate)/poly(allylamine) (PSS:PAH) complex, which has one of the highest reported polycation-polyanion association affinities. We also demonstrate the importance of charge identity in complexation phenomena by functionalizing guanidinium directly into poly(allylamine), resulting in a complex that remains stable under highly denaturing conditions. The model system of PSS:PAH is used to glean insights into guanidinium's denaturing activity, as well as to broadly comment on the nature of ion-specific interactions in charged macromolecules.

Recent Development of pH-Responsive Polymers for Cancer Nanomedicine

Cancer remains a leading cause of death worldwide with more than 10 million new cases every year. Tumor-targeted nanomedicines have shown substantial improvements of the therapeutic index of anticancer agents, addressing the deficiencies of conventional chemotherapy, and have had a tremendous growth over past several decades. Due to the pathophysiological characteristics that almost all tumor tissues have lower pH in comparison to normal healthy tissues, among various tumor-targeted nanomaterials, pH-responsive polymeric materials have been one of the most prevalent approaches for cancer diagnosis and treatment. In this review, we summarized the types of pH-responsive polymers, describing their chemical structures and pH-response mechanisms; we illustrated the structure-property relationships of pH-responsive polymers and introduced the approaches to regulating their pH-responsive behaviors; we also highlighted the most representative applications of pH-responsive polymers in cancer imaging and therapy. This review article aims to provide general guidelines for the rational design of more effective pH-responsive nanomaterials for cancer diagnosis and treatment.

Anion Specificity in Dimethyl Sulfoxide-Water Mixtures Exemplified by a Thermosensitive Polymer

In the present work, we have investigated the anion-specific upper critical solution temperature (UCST) behavior of polymer-supported borinic acid (PBA) in dimethyl sulfoxide-water (DMSO-H₂O) mixtures. An inverted V-shaped series CH₃COO^- < Cl^- < salt-free > NO₃^- > ClO₄^- > SCN^- is observed in terms of the anion-specific UCST of PBA in the DMSO-H₂O mixtures. Both direct anion-polymer interactions and indirect solvent-mediated anion-polymer interactions are involved in the specific anion effect on the UCST behavior of PBA. The direct binding of anions to the PBA surface generates a salting-in effect on PBA, causing the UCST for the different types of anions to increase from chaotropic to kosmotropic anions due to the stronger binding of the more chaotropic anions. On the other hand, the indirect anionic polarization of hydrogen bonding between PBA and DMSO molecules also produces a salting-in effect on PBA, leading the UCST for the different types of anions to increase from kosmotropic to chaotropic anions because of the stronger capability of the more kosmotropic anions to polarize the hydrogen bonding. Thus, the dominating anion-PBA interactions change from the direct anion binding to the indirect anionic polarization of hydrogen bonding as the anions change from chaotropes to kosmotropes. The observed inverted V-shaped series suggests that the specific anion effect on the UCST behavior of PBA in the DMSO-H₂O mixtures is determined by the combined effects of the binding of anions to the PBA surface and the anionic polarization of hydrogen bonding between PBA and DMSO molecules.

Cooperativity Principles in Self-Assembled Nanomedicine

Nanomedicine is a discipline that applies nanoscience and nanotechnology principles to the prevention, diagnosis, and treatment of human diseases. Self-assembly of molecular components is becoming a common strategy in the design and syntheses of nanomaterials for biomedical applications. In both natural and synthetic self-assembled nanostructures, molecular cooperativity is emerging as an important hallmark. In many cases, interplay of many types of noncovalent interactions leads to dynamic nanosystems with emergent properties where the whole is bigger than the sum of the parts. In this review, we provide a comprehensive analysis of the cooperativity principles in multiple self-assembled nanostructures. We discuss the molecular origin and quantitative modeling of cooperative behaviors. In selected systems, we describe the examples on how to leverage molecular cooperativity to design nanomedicine with improved diagnostic precision and therapeutic efficacy in medicine.

Ion-Hydrocarbon and/or Ion-Ion Interactions: Direct and Reverse Hofmeister Effects in a Synthetic Host

A combination of 1H NMR spectroscopy, DLS, and turbidity measurements reveal that polarizable anions engender both the Hofmeister and reverse Hofmeister effects in positand 2. Host 2 possesses two principal and distinctly different binding sites: a "soft" nonpolar pocket and a "hard" crown of ammonium cations. NMR spectroscopy reveals that anion affinity to both sites is comparable, with each site showing characteristic selectivities. NMR spectroscopy also reveals that anions competitively bind to the pocket and induce the Hofmeister effect in host-guest binding at very low concentrations (∼2 mM). Furthermore, the suite of techniques utilized demonstrates that anion binding to both sites leads to charge attenuation, aggregation, and finally precipitation (the reverse Hofmeister effect). Anion-induced precipitation generally correlated with affinity, and comparisons between the free host and its adamantane carboxylate (Ada-CO2-) complex reveals that the reverse Hofmeister effect is attenuated by blocking anion binding/charge attenuation at the nonpolar pocket.

Anion-coordination-directed self-assemblies

This review introduces the interplay of anion coordination and supramolecular self-assembly, presenting recent progress in anion-induced and anion-coordination-based self-assemblies.

Ion specific effects on the immobilisation of charged gold nanoparticles on metal surfaces

Since the pioneering work of F. Hofmeister, Arch. Exp. Pathol. Pharmakol., 1888, 24, 247, ion specific effects have been steadily reported in the context of colloidal or protein stabilisation in electrolyte solutions. Although the observed effects are omnipresent in chemistry and biology, their origin is still under ferocious discussion. Here, we report on ion specific effects affecting the self-assembly of amine and carboxylic acid functionalised gold nanoparticles on metal surfaces as well as in electrolyte solution as a function of the monovalent cations Li⁺, Na⁺, K⁺ and Cs⁺. Mercaptooctanoic acid and 1,8-amine-octanethiol functionalised gold nanoparticles were adsorbed on structured AuPd/Pt substrates under addition of the respective chloride salts. Furthermore, the influence of the same salts on the salt induced aggregation of these AuNP was investigated. Our results demonstrate that the assembly processes on the metal surface as well as in electrolyte solution are influenced by the addition of different cations. We attribute the observed effects to ion pairing of the functional end groups with the added cations. With these findings we introduce a new parameter to control the self-assembly of 2D AuNP arrays on solid supports or of 3D AuNP networks in solution, which could be of relevance for the fabrication of new tailor-made functional materials or for biomedical applications.

Different monovalent cations influence the immobilisation of carboxylic acid and amine terminated gold nanoparticles.

Ion specificities of artificial macromolecules

Artificial macromolecules are well-defined synthetic polymers, with a relatively simple structure as compared to naturally occurring macromolecules. This review focuses on the ion specificities of artifical macromolecules. Ion specificities are influenced by solvent-mediated indirect ion-macromolecule interactions and also by direct ion-macromolecule interactions. In aqueous solutions, the role of water-mediated indirect ion-macromolecule interactions will be discussed. The addition of organic solvents to aqueous solutions significantly changes the ion specificities due to the formation of water-organic solvent complexes. For direct ion-macromolecule interactions, we will discuss specific ion-pairing interactions for charged macromolecules and specific ion-neutral site interactions for uncharged macromolecules. When the medium conditions change from dilute solutions to crowded environments, the ion specificities can be modified by either the volume exclusion effect, the variation of dielectric constant, or the interactions between ions, macromolecules, and crowding agents.

Molecular basis of cooperativity in pH-triggered supramolecular self-assembly

Supramolecular self-assembly offers a powerful strategy to produce high-performance, stimuli-responsive nanomaterials. However, lack of molecular understanding of stimulated responses frequently hampers our ability to rationally design nanomaterials with sharp responses. Here we elucidated the molecular pathway of pH-triggered supramolecular self-assembly of a series of ultra-pH sensitive (UPS) block copolymers. Hydrophobic micellization drove divergent proton distribution in either highly protonated unimer or neutral micelle states along the majority of the titration coordinate unlike conventional small molecular or polymeric bases. This all-or-nothing two-state solution is a hallmark of positive cooperativity. Integrated modelling and experimental validation yielded a Hill coefficient of 51 in pH cooperativity for a representative UPS block copolymer, by far the largest reported in the literature. These data suggest hydrophobic micellization and resulting positive cooperativity offer a versatile strategy to convert responsive nanomaterials into binary on/off switchable systems for chemical and biological sensing, as demonstrated in an additional anion sensing model.

Understanding stimuli responsiveness on a molecular level can help with the rational design of nanomaterials with sharp responses. Here, Gao and co-workers have shown the molecular pathway of the supramolecular self-assembly of a series of ultra-pH sensitive block copolymers.

Non-covalent interactions in controlling pH-responsive behaviors of self-assembled nanosystems

Self-assembly and associated dynamic and reversible non-covalent interactions are the basis of protein biochemistry (e.g., protein folding) and development of sophisticated nanomaterial systems that can respond to and amplify biological signals. In this study, we report a systematic investigation of non-covalent interactions that affect the pH responsive behaviors and resulting supramolecular self-assembly of a series of ultra-pH sensitive (UPS) block copolymers. Increase of hydrophobic and π-π stacking interactions led to the decrease of pKa values. In contrast, enhancement of direct ionic binding between cationic ammonium groups and anionic counter ions gave rise to increased pKa. Moreover, hydration of hydrophobic surfaces and hydrogen bonding interactions may also play a role in the self-assembly process. The key parameters capable of controlling the subtle interplay of different non-covalent bonds in pH-triggered self-assembly of UPS copolymers are likely to offer molecular insights to understand other stimuli-responsive nanosystems. Selective and precise implementation of non-covalent interactions in stimuli-responsive self-assembly processes will provide powerful and versatile tools for the development of dynamic, complex nanostructures with predictable and tunable transitions.

Diblock- and triblock-copolymer based mixed micelles with high tumor penetration in vitro and in vivo

A series of self-assembled mixed micelles composed of TPGS and Pluronics were fabricated and their cellular uptake and exocytosis behaviors were studied in 2D cell and 3D tumor spheroid models.

Facile Construction of pH- and Redox-Responsive Micelles from a Biodegradable Poly(β-hydroxyl amine) for Drug Delivery

Here we demonstrate a type of pH and reduction dual-sensitive biodegradable micelles, which were self-assembled by a cationic polymer in an aqueous solution. Due to tumor cells or tissues showing low pH and high reduction concentration, these micelles possessed specific tumor targetability and maximal drug-release controllability inside tumor cells upon changes in physical and chemical environments, but presented good stability at physiological conditions. CCK-8 assay showed that the DOX-loaded micelles had a similar cytotoxicity for MCF-7 tumor cells as free DOX, and blank micelles had a very low cytotoxicity to the cells. Fluorescent microscopy observation revealed that the drug-loaded micelles could be quickly internalized by endosomes to inhibit cancer cell growth. These results indicated these biodegradable micelles, as a novel and effective pH- and redox-responsive nanocarrier, have a potential to improve drug delivery and enhance the antitumor efficacy.

A nanobuffer reporter library for fine-scale imaging and perturbation of endocytic organelles

Endosomes, lysosomes and related catabolic organelles are a dynamic continuum of vacuolar structures that impact a number of cell physiological processes such as protein/lipid metabolism, nutrient sensing and cell survival. Here we develop a library of ultra-pH-sensitive fluorescent nanoparticles with chemical properties that allow fine-scale, multiplexed, spatio-temporal perturbation and quantification of catabolic organelle maturation at single organelle resolution to support quantitative investigation of these processes in living cells. Deployment in cells allows quantification of the proton accumulation rate in endosomes; illumination of previously unrecognized regulatory mechanisms coupling pH transitions to endosomal coat protein exchange; discovery of distinct pH thresholds required for mTORC1 activation by free amino acids versus proteins; broad-scale characterization of the consequence of endosomal pH transitions on cellular metabolomic profiles; and functionalization of a context-specific metabolic vulnerability in lung cancer cells. Together, these biological applications indicate the robustness and adaptability of this nanotechnology-enabled 'detection and perturbation' strategy.