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Soft Matter Accepted Manuscript This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/softmatter Page 1 of 22 Soft Matter Chemical Society Review RSC Publishing ARTICLE Adaptive Soft Molecular Self-Assemblies a a a* a* Cite this: DOI: 10.1039/x0xx00000x Andong Wang, Wenyue Shi, Jianbin Huang , and Yun Yan ABSTRACT: Adaptive molecular self-assemblies provides possibility to construct smart and functional materials in a non-covalent bottom-up manner. Exploiting the intrinsic property of responsiveness of Received 00th January 2012, the non-covalent interactions, a great number of fancy self-assemblies have been achieved. In this Accepted 00th January 2012 review, we try to highlight the recent advances in this field. The following contents are focused: (1) DOI: 10.1039/x0xx00000x Environmental adaptiveness, including smart self-assemblies adaptive to pH, temperature, pressure, and moisture; (2) Special chemical adaptiveness, including nanostructures adaptive to important www.rsc.org/ chemicals, such as enzyme, CO 2, metal ions, redox agents, explosives, biomolecules; (3) Field adaptive- ness, including self-assembled materials that are able to be adaptive to external fields such as magnetic field, electric field, light irradiation, and shear forces. Introduction may respond to external stimuli and (2) to produce self- assembly of these building blocks through multiple non- The bottom-up method of soft molecular self-assembly 1-4 is covalent interactions. The building blocks and the non-covalent Manuscript becoming a powerful technique to construct complicated interactions run together to allow the whole system to respond nanostructures with relatively simple ingredients 5. Driven by a to different types of external stimuli. The orthogonal variety of inter-molecular non-covalent interactions such as combination of the two aspects is expected to produce artificial hydrophobic effect 6, hydrogen bonding 7-9, host-guest adaptive self-assembled materials with fascinating potentials 35 . recognition 10 , electrostatic interaction 11 , aromatic stacking 12, 13 , In this review, we briefly summarize recent progress in or metal-ligand coordination 14-16 , molecules can associate fabrication of advanced materials or molecular devices that are spontaneously into structurally well-defined, highly-ordered, adaptive to environments, special chemicals, and external and most important, functional nano or meso-scaled structures 17 . stimulus. Although single non-covalent interaction may not be as robust as covalent ones, the chorus of multiple non-covalent bonds can 1. Environment adaptive self-assemblies Accepted still construct robust systems 18 . Moreover, the dynamic nature of the non-covalent interactions can be exploited to design Environmental factors often affect the performance of many adaptive systems, since the environmental sensitivity of non- materials. Strictly speaking, any factor that is not involved in covalent bonds make the systems willingly to respond to the self-assembled structures is ‘environmental factor’. external stimuli 19 . These finally result in changes both in However, considering the mode of interaction, factors that structure and function for the supramolecular materials and don’t have special selectivity in acting on the self-assembling automatically bring the system to a state that is adaptive to the systems, such as pH, temperature, pressure, and moisture, are Matter environment. In contrast with their covalent counterparts, the classified as environmental factors in this review. Then it is non-covalent molecular self-assemblies also have unique and highly desired to understand how these factors affect a certain fascinating properties such as facility in fabrication and system and to employ these influences to design smart materials that may adaptive to environmental changes to lead to reversibility. These advantages make them very competitive Soft candidates for developing smart materials 20 in various fields potential applications. such as controlled-delivery 21-23 , sensors 24-26 , self-healing 1.1 pH adaptiveness materials 27-30 , piezoelectronic devices 31 , mechanochroism 32, 33 , or stimuli responsive devices 34 . Nature and biological systems employ pH variation to reach Actually, adaptive self-assembling systems are playing their functions. For instance, the seasoning change of colour for significant roles both in natural and artificial materials 1, 4, 5. leaves can be attributed to the variation of pH in cell liquid; Most life activities are realized through the adaptive behaviours tumour tissues usually have a lower pH than the normal ones. of cells to biological stimuli. The membrane structure and Artificial pH adaptive architectures either contain protonable function changes correspondingly when a signal arrives. For groups or pH cleavable chemical bonds. The most simple pH artificial materials, the general idea for construction of adaptive adaptive molecular self-assemblies are the vesicles formed by architectures is (1) to ingeniously design building blocks which fatty acids 36, 37 . These amphiphilic compounds dissolve slightly This journal is © The Royal Society of Chemistry 2013 J. Name ., 2013, 00 , 1-3 | 1 Soft Matter Page 2 of 22 ARTICLE Chemical Society Review at neutral and acidic pH but self-assemble into micelles in extremely basic solutions. Vesicles can be formed only at pH in between these two extreme conditions. The pH at which vesicle to micelle transition can be made the same or very close to that of the biological environment by tuning the number and structure of protonable groups 38, 39 . Such vesicles are ideal vehicles for controlled drug delivery. In addition to tuning the structure of protonable groups to design pH responsive vesicles, novel ideas are emerged to create advanced soft smart materials that exhibit pH adaptiveness. In this section, we briefly summarize some recent advances in this aspect. 1.1.1 pH responsiveness endowed by supramphiphiles Figure 1. pH-responsive dynamic amphiphiles. (A)Micelle formation. (B)Vesicle Specially designed pH responsive self-assemblies usually formation. (C) Wormlike micelles formed by dynamic gemini surfactants. Adapted with permission from ref. 44-46 . Copyright © 2009 and 2012, American formed by rather complicated molecules. The invention of 44, 46 40, 41 Chemical Society and © 2011, WILEY-VCH Verlag GmbH & Co. KGaA, supramphiphiles (SA) by Zhang et al. greatly simplified the Weinheim 45 . synthetic procedure toward this goal. For instance, they 42 utilized a dynamic covalent bond to fabricate a bola-form superamphiphile from 1-(10-(4- 1.1.2 pH responsiveness endowed by specially designed covalent compounds formylphenoxy)decyl)pyridinium (FDP) and 1-(10-(4- (ammoniomethyl)phenoxy)decyl)pyridinium (AMDP). At basic Molecular structure is very crucial in creating various conditions, the two molecules can be connected by a dynamic responsive nanostructures, this is also true for advanced pH benzoic imine bond to form a bola-like superamphiphile with a responsive materials 47-50 . For instance, Shen and co-workers 51 hydrophilic – hydrophobic – hydrophilic structure. Spherical reported an example of pH-responsive multifunctional three- Manuscript micellar nano-structure was formed by hydrophobic layered nanoparticles (3LNPs). The 3LNPs have a poly (e- interactions. As the pH was switched to slightly acidic values, caprolactone) (PCL) core, a pH-responsive poly [2-(N, N- the benzoic imine bond was hydrolyzed, thus the SA diethylamino)ethyl methacrylate] (PDEA) middle layer and a dissociated and resulted in disassembly of the micelles. polyethylene glycol (PEG) outer layer which consisted a core- Similar strategy was also adopted by them to fabricate a layer-layer structure. As a nanocarrier, hydrophobic drugs can toothbrush-type SA 43 . In this approach, methoxy- be loaded in the core, but the releasing performance can be poly(ethyleneglycol)114–block–poly(L-lysine controlled by the solubility of the PDEA layer which is pH hydrochloride)200 (PEG–b–PLKC) and 4- dependent. When the pH value is above 7 (approximately at (decyloxy)benzaldehyde (DBA) was chosen to be the two physiological pH), the drug release process is blocked by Accepted components of the supramolecular building block which was PDEA layer which covers the core. As the pH value drops also connected by benzoic imine bond. This SA is able to form below 6.5, the positively charged middle layer becomes soluble, spherical aggregates in water which disassemble reversibly which enables the drug release process. (Figure 2)

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