Layer-by-Layer Self-Assembly of Cationic and Anionic Supramolecular Polymers

Supramolecular phenanthrene polymers with a negative charged phosphate backbone have been synthesized in our group. These assembled oligomers can act as light harvesting antennas. Herein we replaced the negative charged phosphate backbone by a positive charged amine one and analyzed the aggregation behavior and light harvesting properties. The self-assembly of 1,8-disubstituted amine-linked phenanthrene trimers in aqueous solution formed mono- and even multilayered vesicles based on atomic-force microscopy. The incorporation of pyrene into the vesicles allows aninvestigation of light harvesting properties.

Conventional amphiphilic block copolymers are macromolecules consisting of at least a hydrophilic segment covalently attached to a hydrophobic segment. They are unique and versatile building blocks in supramolecular polymer chemistry, both for the generation of highly organized, self-assembled structures and for the structural control of material interfaces. In the absence of solvents, the phase-behavior of block-copolymers is sparingly described. In aqueous solutions block copolymers self-assemble into nanoscopic objects. These structures are gaining more and more attention for technical formulations. Self-assembly is simply induced by dissolving dry powder of amphiphilic copolymers in water. This self-assembly process, however, cannot be described solely based on bulk phase behavior and very few experimental phase diagrams of block copolymer/water mixtures have been reported. In order to control, predict and eventually achieve a comprehensive understanding of this process and in particular the formation of vesicles, worm/rod-like micelles and spherical micelles it is important to systematically investigate the phase behavior of block copolymers across the whole water concentration range. We therefore undertook investigations of the self-assembly of two block copolymers. Preliminary encapsulation studies reveal their potential for applications relevant for drug delivery. 
\nThe concentration profile of the identified amphiphilic block-copolymers diluted in aqueous solution was examined across the whole concentration range with four poly(ethylene oxide)-block-poly(γ-methyl-ε-caprolactone) (PEO-b-PMCL) block copolymers keeping the hydrophilic block length constant but varying the hydrophobic lengths. Bulk polymers did not display any ordered morphology. With increasing water concentrations the polymers underwent transitions from lamellar phases to packed vesicles and eventually all polymers self-assembled into vesicles in dilute aqueous solutions. At high concentration the largest polymer organized further into an inverse hexagonal phase prior to self-assembly into a lamellar phase. The smallest block-copolymer also self-aggregated into rod-like micelles and exhibited a hexagonal phase between the packing of the rod-like micelles/vesicles and the lamellar phase.
\nThe concentration profile of phases assembled by amphiphilic block-copolymers diluted in aqueous solution was examined as well across the whole concentration range with three poly(isobutylene)-block-poly(ethylene oxide) block copolymers having the same hydrophobic block length but varying in their hydrophilic lengths. In contrast to PEO-b-PMCL these polymers self-aggregated depending on the hydrophilic length into micelles, worm-like micelles and for the shortest polymer into vesicles. Thus, increasing the polymer concentration lead to a different phase behavior. The largest polymer which solely formed micelles, underwent transitions from packed micelles with a few packed worm-like micelles to a hexagonal phase and finally into a lamellar phase, in contrary to the middle length polymer, which self-aggregated into worm-like micelles. The best to our knowledge, it is the first time that an experimental phase diagram is built such that it displays the formation of worm/rod-like micelles. With the composition studied in here, the worms, with increasing polymer concentration, pack and undergo afterwards into a hexagonal and finally a lamellar phase has been observed. For the shortest polymer the phase behavior was similar to that of vesicles self-assembled by PEO-b-PMCL. In contrast, the pure polymer formed an inverse hexagonal phase.
\nIt was eventually shown that PEO23-PMCl32 can be used to encapsulate both small and large molecules. By adjusting the pH towards acidic conditions the responsiveness of the vesicles could be triggered to release the encapsulated material.

Exciton-polarons in self-assembling helical aggregates: relating optical properties to supramolecular structure

Inspired by the vast array of assemblies present in nature, supramolecular chemistry has attracted significant attention on account of its diverse supra-structures, which include micelles, vesicles, and fibers, in addition to its extensive applications in luminescent materials, sensors, bioimaging, and drug delivery over the past decades. Supramolecular polymers, which represent a combination of supramolecular chemistry and polymer science, are constructed by non-covalent interactions, such as host-guest interactions, hydrogen bonding, hydrophobic or hydrophilic interactions, metal-ligand interactions, π-π stacking, and electrostatic interactions. To date, numerous host-guest recognition systems have been reported, including crown ethers, cyclodextrins, calixarenes, cucurbituril, pillararenes, and other macrocyclic hosts. Among them, crown ethers, as the first generation of macrocyclic hosts, provide a promising and facile alternative route to supramolecular polymers. In addition, the incorporation of fluorophores into supramolecular polymers could endow them with multiple properties and functions, thereby presenting potential advantages in the context of smart materials. Thus, this review focuses on the fabrication strategies, interesting properties, and potential applications of fluorescent supramolecular polymers based on crown ethers. Typical examples are presented and discussed in terms of three different types of building blocks, namely covalently bonded low-molecular-weight compounds, polymers modified by hosts or guests, and supramolecular coordination complexes.

Owing to the mastery exhibited by Nature in integrating both covalent and noncovalent interactions in a highly efficient manner, the quest to construct polymeric systems that rival not only the precision and fidelity but also the structure of natural systems has remained a daunting challenge. Supramolecular chemists have long endeavored to control the interplay between covalent and noncovalent bond formation, so as to examine and fully comprehend how function is predicated on self-assembly. The ability to reliably control polymer self-assembly is essential to generate "smart" materials and has the potential to tailor polymer properties (i.e., viscosity, electronic properties) through fine-tuning the noncovalent interactions that comprise the polymer architecture. In this context, supramolecular polymers have a distinct advantage over fully covalent systems in that they are dynamically modular, since noncovalent recognition motifs can be engineered to either impart a desired functionality within the overall architecture or provide a designed bias for the self-assembly process. In this Account, we describe engineering principles being developed and pursued by our group that exploit the orthogonal nature of noncovalent interactions, such as hydrogen bonding, metal coordination, and Coulombic interactions, to direct the self-assembly of functionalized macromolecules, resulting in the formation of supramolecular polymers. To begin, we describe our efforts to fabricate a modular poly(norbornene)-based scaffold via ring-opening metathesis polymerization (ROMP), wherein pendant molecular recognition elements based upon nucleobase-mimicking elements (e.g., thymine, diaminotriazine) or SCS-Pd(II) pincer were integrated within covalent monofunctional or symmetrically functionalized polymers. The simple polymer backbones exhibited reliable self-assembly with complementary polymers or small molecules. Within these systems, we applied successful protecting group strategies and template polymerizations to enhance the control afforded by ROMP. Main-chain-functionalized alternating block polymers based upon SCS-Pd(II) pincer-pyridine motifs were achieved through the combined exploitation of bimetallic initiators and supramolecularly functionalized terminators. Our initial design principles led to the successful fabrication of both main-chain- and side-chain-functionalized poly(norbornenes) via ROMP. Utilizing all of these techniques in concert led to engineering orthogonality while achieving complexity through the installation of multiple supramolecular motifs within the side chain, main chain, or both in our polymer systems. The exploitation and modification of design principles based upon functional ROMP initiators and terminators has resulted in the first synthesis of main-chain heterotelechelic polymers that self-assemble into A/B/C supramolecular triblock polymers composed of orthogonal cyanuric acid-Hamilton wedge and SCS-Pd(II) pincer-pyridine motifs. Furthermore, supramolecular A/B/A triblock copolymers were realized through the amalgamation of functionalized monomers, ROMP initiators, and terminators. To date, this ROMP-fabricated system represents the only known method to afford polymer main chains and side chains studded with orthogonal motifs. We end by discussing the impetus to attain functional materials via orthogonal self-assembly. Collectively, our studies suggest that combining covalent and noncovalent bonds in a well-defined and precise manner is an essential design element to achieve complex architectures. The results discussed in this Account illustrate the finesse associated with engineering orthogonal interactions within supramolecular systems and are considered essential steps toward developing complex biomimetic materials with high precision and fidelity.

Recent advances in DNA nanotechnology led to the development of biocompatible functional materials targeting different applications, including delivery, precise scaffolding, computation, etc. However, a standard toolbox of building blocks used by chemists is largely limited to canonical nucleobases. To further develop the functional potential of synthetic DNA systems, the use of sequence-specific DNA-polymer conjugates has emerged as an exciting alternative approach. Herein, we demonstrate the synthesis and self-assembly properties of monodisperse DNA-pyrene polyphosphate oligomers as essential units for DNA-grafted supramolecular polymers. Such systems become increasingly important for the creation of dynamic and stimuli-responsible materials. The unique self-recognition properties of oligonucleotides laid the foundation of modern DNA nanotechnology. Over the last two decades, man-made DNA assemblies led to the development of numerous biocompatible functional materials, including drug carriers, nanorobots, and scaffolding platforms. A standard toolbox of building blocks used by chemists in the field is largely limited to four units – A, G, C, T. To further develop the functional potential of synthetic DNA systems, the use of DNA-chromophore conjugates emerges as an exciting approach. Following our previous findings, we demonstrate herein the synthesis of the DNA-pyrene oligomers and the temperature-induced self-assembly of these conjugates into DNA-grafted supramolecular polymers. (see Figure 1). Such systems become increasingly important for the creation of dynamic and stimuli-responsible materials targeting various applications such as delivery and precise scaffolding.

A low optical bandgap and fullerene-like electron affinity of functionalized cyclopenta[hi]aceanthrylene (cypac) was reported and potential applications as electron acceptors in organic solar cells are suggested among others.[1] In this work, a water-soluble, bolaamphiphilic cypac derivative with a low-lying LUMO and intense absorption bands over an extended range of the UV-visible spectral region has been synthesized.[2] Self-assembly of cypac-bis-phosphate in aqueous medium leads to the formation of a supramolecular polymer with a vesicular morphology. The electronic properties of the monomer remain largely intact upon supramolecular polymer formation, as evidenced by UV-vis and cyclic voltammetry measurements.

The work presented in this thesis entails the synthesis and characterisation of new iron(II) tris(dioxime) clathrochelate complexes functionalised with apical capping groups suitable for supramolecular applications, and their subsequent incorporation into self-assembled structures. These complexes possess a number of desirable characteristics as supramolecular building blocks, such as their synthetic accessibility and broad scope for structural and functional modification, which are highlighted throughout. Chapter 1 introduces certain key concepts and background literature relevant to this thesis. Clathrochelate-based 4,4'-bipyridyl metalloligands are presented in Chapter 2. Simple complexes bearing 4-pyridyl capping groups were prepared from commercially available starting materials and their potential as building blocks for supramolecular architectures demonstrated through the preparation of a discrete molecular square and a 3D coordination polymer (CP). Furthermore, bent and extended linear 4,4'-bipyridyl metalloligands up to 5.4 nm in length were prepared by two distinct homologation strategies. Clathrochelate-based 3,3'-bipyridyl metalloligands are presented in Chapter 3. Simple complexes were prepared from commercially available starting materials and subsequently combined with Pd(II) ions to give unprecedented [Pd6L12]12+ octahedral cage structures by coordination-driven self-assembly. These assemblies were shown to bind the large, non-coordinating anion BPh4- in aqueous solvent mixtures. Furthermore, linear and bent bis(clathrochelate) complexes bearing 3-pyridyl apical capping groups were also prepared by a one-pot approach. Clathrochelate complexes bearing carboxylic acid-functionalised capping groups are presented in Chapter 4. Ditopic and tetratopic metalloligands were synthesised in good yields. A heterometallic 2D CP was prepared through combination of Zn(II) ions with a clathrochelate complex functionalised with phenyl-4-carboxylic acid groups and the structure of this material determined by single crystal X-ray diffraction. Clathrochelates bearing functional groups suitable for imine-based self-assembly are presented in Chapter 5. Complexes functionalised with amine or aldehyde moieties as well as complexes functionalised with 3-pyridine-4-carboxaldehyde groups, were prepared in either one or two steps. Preliminary investigations into the preparation of metal-organic cage architectures through a well-established subcomponent self-assembly approach combining imine-based DCC and coordination-driven self-assembly gave promising results, including the synthesis of an [Fe4L6]8+ cage, which was characterised by single crystal X-ray crystallography.

Brassinosteroid alleviates phenanthrene and pyrene phytotoxicity by increasing detoxification activity and photosynthesis in tomato

ConspectusSince its inception in the early 1990s, the field of supramolecular polymers (SPs) has grown into an interdisciplinary field of chemistry. It expanded from the self-assembly of molecular building blocks based on H-bonding into the realm of complex dynamic material, encompassing both supramolecular noncovalent and molecular covalent regimes. It has paved the path for a more diverse field of research into a new class of polymeric materials, coined dynamic polymers or dynamers. Dynamers are bringing a paradigm shift not only in material science research but also in a broad field of applications from self-healing materials to biocompatible polymeric materials. The present Account presents the evolution of supramolecular polymer chemistry from simple linear polymeric chains to complex dynamic polymers imparting novel functional properties, such as component exchange and self-healing. We explore how SPs led to materials of increasing complexity, starting from simple main-chain polymers to the formation of more complex columnar SPs and lateral SPs. The field has experienced three partially overlapping periods. The main goal was first the generation of polymeric entities from various molecular components connected through noncovalent interactions, especially complementary hydrogen bonding recognition patterns as well as stacked columnar SPs. Thereafter, attention was directed in parallel to the exploration of the properties of SPs and their applications as novel materials. In a third period, the dynamic properties of supramolecular polymers were explored, taking advantage of the lability of noncovalent interactions to perform component rearrangement and exchange. We illustrate how the field of SPs has emerged as a multidisciplinary field of chemistry, biology, and materials science with selected examples from the literature. The SPs, specifically dynamic owing to their inherent reversibility, also pave the path to easier sorting and recycling, as desired in the plastics industry.One of the biggest challenges that the plastics industry is facing today is the end-of-life fate of plastics. Plastics that cannot be recycled end up in landfills or are improperly disposed of in rivers and oceans, polluting and damaging the environmental balance irreversibly. Dynamic polymeric materials presenting inherent dynamicity could pave the way for addressing this long-standing challenge of nonrecyclability of plastics. Dynamers formed via noncovalent interactions or reversible covalent bonds can be broken into components that could be easily recycled and reused. Therefore, dynamers could play a pivotal role toward closing the loop for the plastics industry and provide a solution to an elusive circular economy with plastics being an integral part.

Irreversible transformation of the porphyrin supramolecular structures under a water vapor environment

The ability of a broad range of N-heterocycles to act as very effective and stable complexation agents for several transition metal ions, such as cobalt(II), copper(II), nickel(II), and ruthenium(II), has long been known in analytical chemistry. This behavior was later utilized in supramolecular chemistry for the construction of highly sophisticated architectures, such as helicates, racks, and grids. The discovery of macromolecules by Staudinger in 1922 opened up avenues towards sophisticated materials with properties hitherto completely unknown. In the last few decades, the combination of macromolecular and supramolecular chemistry has been attempted by developing metal-complexing and metal-containing polymers for a wide variety of applications that range from filtration to catalysis. The stability of the polymer-metal complex is a fundamental requirement for such applications. In this respect, the use of bi- and terpyridines as chelating ligands is highly promising, since these molecules are known to form highly stable complexes with interesting physical properties with transition-metal ions. A large number of different structures have been designed for many different applications, but polymers based on the application of coordinative forces have been prepared in a few cases only. Furthermore, the synthetic procedures applied frequently resulted in low yields. During the last few years, strong efforts have been made in the direction of self-assembling and supramolecular polymers as novel materials with "intelligent" and tunable properties. In this review, an overview of this active area at the interface of supramolecular and macromolecular chemistry is given.

Supramolecular chemistry continues to experience widespread growth, as fine-tuned chemical structures lead to well-defined bulk materials. Previous literature described the roles of hydrogen bonding, ionic aggregation, guest/host interactions, and π-π stacking to tune mechanical, viscoelastic, and processing performance. The versatility of reversible interactions enables the more facile manufacturing of molded parts with tailored hierarchical structures such as tissue engineered scaffolds for biological applications. Recently, supramolecular polymers and additive manufacturing processes merged to provide parts with control of the molecular, macromolecular, and feature length scales. Additive manufacturing, or 3D printing, generates customizable constructs desirable for many applications, and the introduction of supramolecular interactions will potentially increase production speed, offer a tunable surface structure for controlling cell/scaffold interactions, and impart desired mechanical properties through reinforcing interlayer adhesion and introducing gradients or self-assembled structures. This review details the synthesis and characterization of supramolecular polymers suitable for additive manufacture and biomedical applications as well as the use of supramolecular polymers in additive manufacturing for drug delivery and complex tissue scaffold formation. The effect of supramolecular assembly and its dynamic behavior offers potential for controlling the anisotropy of the printed objects with exquisite geometrical control. The potential for supramolecular polymers to generate well-defined parts, hierarchical structures, and scaffolds with gradient properties/tuned surfaces provides an avenue for developing next-generation biomedical devices and tissue scaffolds.

In the Central Anatolian Crystalline Complex (CACC), besides the ophiolitic bodies with more or less recognisable sequence and preserved magmatic pseudostratigraphy, there are many massive and layered gabbroic masses occurring as isolated outcrops. Most of these mafic rocks were interpreted as dismembered parts of an allochthonous ophiolitic assemblage (Yaliniz et al, 2000), derived from the northerly located Izmir-Ankara branch of the Alpine Neotethys. An overall supra-subduction zone genesis has been envisaged for the Central Anatolian Ocean (CAO). However, remarkable differences in the geochemical characteristics of different isolated outcrops suggest differences in the source areas and tectonic settings within the intra-oceanic subduction zone. One of these gabbro units, the Kurancali Metagabbro, occurs as an isolated body in the central part of CACC. It is thrust along a steep south vergent thrust-plane onto the uppermost units of the Central Anatolian Metamorphics (CAM). The main body of the Kurancali Metagabbro is characterised by a distinct compositional layering. The layered gabbros are represented by pyroxene and hornblende gabbros. Phlogopite-rich plagioclase-hornblende gabbro occurs mainly as pegmatitic dikes intruding the layered gabbro sequence. The layered gabbros in general consist mainly of diopsidic augites, brown hornblendes, plagioclase. Secondary phases are phlogopitic mica, brownish green hornblende replacing clinopyroxenes, and fibrous greenish actinolitic hornblende partially or completely replacing brown hornblende. The primary dark micas display phlogopitic composition within the range of annite30.13-42.60 and plogopite 69.9-57.4 The analysed pyroxenes are diopsidic (En32.3Fs18.5Wo49.1 - En34.9Fs17.9Wo48.2). The whole-rock geochemistry of the gabbros indicates the presence of two distinct groups of rocks; a subordinate group of phlogopite gabbro with island arc calc-alkaline affinity and a dominating layered gabbro sequence with island arc tholeiite characteristics. They are extremely enriched in LIL elements, indicative of an alkaline metasomatism in the source region and they display geochemical features of transitional back arc basin basalts (BABB)/island arc basalts (IAB)- and IABtype oceanic crust. Based on their geochemical similarities with modern island arc basements, we suggest that the Kurankali Metagabbro may represent the basement of an initial island arc, generated in a supra-subduction zone setting within the Izmir-Ankara branch of Neotethys.

Determination of polycyclic aromatic hydrocarbons in urine of coke oven workers by headspace solid phase microextraction and gas chromatography–mass spectrometry