Extremely Slow Dynamics of an Abiotic Helical Assembly: Unusual Relevance to the Secondary Structure of Proteins

Molecular Architectonics-guided Design of Biomaterials

The quest for mastering the controlled engineering of dynamic molecular assemblies is the basis of molecular architectonics. The rational use of noncovalent interactions to programme the molecular assemblies allow the construction of diverse molecular and material architectures with novel functional properties and applications. Understanding and controlling the assembly of molecular systems are daunting tasks owing to the complex factors that govern at the molecular level. Molecular architectures depend on the design of functional molecular modules through the judicious selection of functional core and auxiliary units to guide the precise molecular assembly and co-assembly patterns. Biomolecules with built-in information for molecular recognition are the ultimate examples of evolutionary guided molecular recognition systems that define the structure and functions of living organisms. Explicit use of biomolecules as auxiliary units to command the molecular assemblies of functional molecules is an intriguing exercise in the scheme of molecular architectonics. In this minireview, we discuss the implementation of the principles of molecular architectonics for the development of novel biomaterials with functional properties and applications ranging from sensing, drug delivery to neurogeneration and tissue engineering. We present the molecular designs pioneered by our group owing to the requirement and scope of the article while acknowledging the designs pursued by several research groups that befit the concept.

Architectonics: Design of Molecular Architecture for Functional Applications

The term architectonics has its roots in the architectural and philosophical (as early as 1600s) literature that refers to "the theory of structure" and "the structure of theory", respectively. The concept of architectonics has been adapted to advance the field of molecular self-assembly and termed as molecular architectonics. In essence, the methodology of organizing molecular units in the required and controlled configurations to develop advanced functional systems for materials and biological applications comprises the field of molecular architectonics. This concept of designing noncovalent systems enables to focus on different functional aspects of designer molecules for biological and nonbiological applications and also strengthens our efforts toward the mastery over the art of controlled molecular self-assemblies. Programming complex molecular interactions and assemblies for specific functions has been one of the most challenging tasks in the modern era. Meticulously ordered molecular assemblies can impart remarkable developments in several areas spanning energy, health, and environment. For example, the well-defined nano-, micro-, and macroarchitectures of functional molecules with specific molecular ordering possess potential applications in flexible electronics, photovoltaics, photonic crystals, microreactors, sensors, drug delivery, biomedicine, and superhydrophobic coatings, among others. The functional molecular architectures having unparalleled properties are widely evident in various designs of Nature. By drawing inspirations from Nature, intended molecular architectures can be designed and developed to harvest various functions, as there is an inexhaustible resource and scope. In this Account, we present exquisite designer molecules developed by our group and others with an objective to master the art of molecular recognition and self-assembly for functional applications. We demonstrate the tailor-ability of molecular self-assemblies by employing biomolecules like amino acids and nucleobases as auxiliaries. Naphthalenediimide (NDI), perylenediimide (PDI), and few other molecular systems serve as functional modules. The effects of stereochemistry and minute structural modifications in the molecular designs on the supramolecular interactions, and construction of self-assembled zero-dimensional (OD), one-dimensional (1D), and two-dimensional (2D) nano- and microarchitectures like particles, spheres, cups, bowls, fibers, belts, helical belts, supercoiled helices, sheets, fractals, and honeycomb-like arrays are discussed in extensive detail. Additionally, we present molecular systems that showcase the elegant designs of coassembly, templated assembly, hierarchical assembly, transient self-assembly, chiral denaturation, retentive helical memory, self-replication, supramolecular regulation, supramolecular speciation, supernon linearity, dynamic pathway complexity, supramolecular heterojunction, living supramolecular polymerization, and molecular machines. Finally, we describe the molecular engineering principles learnt over the years that have led to several applications, namely, organic electronics, self-cleaning, high-mechanical strength, and tissue engineering.

Morphogenesis and Optoelectronic Properties of Supramolecular Assemblies of Chiral Perylene Diimides in a Binary Solvent System

Chiral supramolecular structures are attracting great attention due to their specific properties and high potential in chiral sensing and separation. Herein, supramolecular assembling behaviors of chiral perylene diimides have been systematically investigated in a mixed solution of tetrahydrofuran and water. They exhibit remarkably different morphologies and chiral aggregation behaviors depending on the mixing ratio of the solvents, i.e., the fraction of water. The morphogenesis and optoelectronic properties of chiral supramolecular structures have been thoroughly studied using a range of experimental and theoretical methods to investigate the morphological effects of chiral supramolecular assemblies on the electrical performances and photogenerated charge-carrier behaviors. In addition, chiral perylene diimides have been discriminated by combining vibrational circular dichroism with theoretical calculations, for the first time. The chiral supramolecular nanostructures developed herein strongly absorb visible spectral region and exhibit high photoresponsivity and detectivity, opening up new opportunities for practical applications in optoelectronics.

Synthetic minimalistic tryptophan zippers as a chiroptical switch

Supramolecular helices with left and right handed chirality were designed and synthesized based on l-tryptophan that undergo helical inversion upon addition of H₂PO₄⁻.

Emergent Behaviors in Kinetically Controlled Dynamic Self-Assembly of Synthetic Molecular Systems

Living systems are categorically a kinetic state of matter that exhibits complex functions and emergent behaviors. By contrast, synthetic systems are relatively simple and are typically controlled by the thermodynamic parameters. To understand this inherent difference between the biological and synthetic systems, novel approaches are of vital importance. In this regard, we have designed a three-component molecular system (a triad) by conjugating an amino acid with two functional molecules (naphthalenediimide and pyrene), which facilitates kinetically controlled self-assemblies. Herein, we describe three different molecular aggregation states of triads (entitled State I, State II, and State III) and also the dynamic pathway complexities associated with their transformations from one state to another. By meticulously employing the triads of different molecular aggregation states and the stereochemical information of the amino acid, we report emergent behaviors termed "supramolecular speciation" and "supramolecular regulation". Further, we present a hitherto unknown emergent property in a self-assembled state under the majority-rules experiment, which has been termed "super-nonlinearity". This work provides novel insights into complex synthetic systems having unprecedented functions and properties. Such emergent behaviors of synthetic triads that involve an interplay among complex interactions may find relevance in the context of prebiotic chemical evolution.

Nanoarchitectonics of biomolecular assemblies for functional applications

The stringent processes of natural selection and evolution have enabled extraordinary structure-function properties of biomolecules. Specifically, the archetypal designs of biomolecules, such as amino acids, nucleobases, carbohydrates and lipids amongst others, encode unparalleled information, selectivity and specificity. The integration of biomolecules either with functional molecules or with an embodied functionality ensures an eclectic approach for novel and advanced nanotechnological applications ranging from electronics to biomedicine, besides bright prospects in systems chemistry and synthetic biology. Given this intriguing scenario, our feature article intends to shed light on the emerging field of functional biomolecular engineering.

Circularly Polarized Luminescence in Chiral Aggregates: Dependence of Morphology on Luminescence Dissymmetry

The self-assembly of a chiral perylene bisimide bichromophoric derivative possessing a 1,1'-binaphthalene bridge was investigated by adopting two different methodologies, leading to the formation of aggregates with dissimilar morphologies. The chiral nature of the aggregated structures was optically probed with the help of circular dichroism (CD), vibrational circular dichroism (VCD), and circularly polarized luminescence (CPL). The one-dimensional aggregates formed in methylcyclohexane (MCH) exhibited twice the value of luminescence dissymmetry factor (glum) when compared with the spherical aggregates formed in chloroform at higher concentration. The summation of excitonic couplings between the individual chromophoric units in an aggregated system is responsible for the remarkably high luminescence dissymmetry exhibited by the chiral aggregates. The nanostructures could be successfully embedded into polymer films, leading to the fabrication of solid-state materials with high CPL dissymmetry that can find novel applications in chiroptical sensing, memory, and light-emitting devices based on organic nanoparticles.