Handedness-Inverted and Stimuli-Responsive Circularly Polarized Luminescent Nano/Micromaterials Through Pathway-Dependent Chiral Supramolecular Polymorphism

The precise manipulation of supramolecular polymorphs has been widely applied to control the morphologies and functions of self-assemblies, but is rarely utilized for the fabrication of circularly polarized luminescence (CPL) materials with tailored properties. Here, this work reports that an amphiphilic naphthalene-histidine compound (NIHis) readily self-assembled into distinct chiral nanostructures through pathway-dependent supramolecular polymorphism, which shows opposite and multistimuli responsive CPL signals. Specifically, NIHis display assembly-induced CPL from the polymorphic keto tautomer, which become predominant during enol-keto tautomerization shifting controlled by a bulk solvent effect. Interestingly, chiral polymorphs of nanofiber and microbelt with inverted CPL signals can be prepared from the same NIHis monomer in exactly the same solvent compositions and concentrations by only changing the temperature. The tunable CPL performance of the solid microbelts is realized under multi external physical or chemical stimuli including grinding, acid fuming, and heating. In particular, an emission color and CPL on-off switch based on the microbelt polymorph by reversible heating-cooling protocol is developed. This work brings a new approach for developing smart CPL materials via supramolecular polymorphism engineering.

Nanometrology based control: taming radical grafting reactions with attoliter precision

Precisely controlled micropatterning with organic moieties is a promising route for designing smart surfaces, enabling the development of microsensors and actuators with optimal usage of reactants. Such applications require fine control over the surface modification process, which in turn demands detailed knowledge about the surface modification process. As complex surface kinetics often emerge as a result of even slight modifications of the grafting entity, non-invasive, sensitive and precise closed loop control strategies are highly desirable. In this paper we demonstrate that a nanometrology approach based on quantitative phase imaging (QPI) fulfill all these requirements. We first use the technique to monitor surface photografting kinetics of aryl radicals, comprehensively analyzing the effect of substituents on surface addition reactions. We demonstrate that several aspects of the grafting process are affected in complex ways, rendering open-loop strategies impossible to implement precisely. Then, we show that the operando optical phase signal can be used as a direct feedback, guiding the grafting reaction process. Using relatively simple instrumentation, we demonstrate that general and precise control strategies can be designed and used to control the volume of the grafting material with attoliter precision, in spite of radically different surface modification kinetics spanning several orders of magnitude.

Polymorph control by designed ultrasound application strategy: The role of molecular self-assembly

Molecular self-assembly plays a vital role in the nucleation process and sometimes determines the nucleation outcomes. In this study, ultrasound technology was applied to control polymorph nucleation. For the first time, different ultrasonic application methods based on the nucleation mechanisms have been proposed. For PZA-water and DHB-toluene systems that the molecular self-assembly in solution resembles the synthon in crystal structure, ultrasound pretreatment strategy was conducted to break the original molecular interactions to alter the nucleated form. When the solute molecular self-associates can't give sufficient information to predict the nucleated polymorph like INA-ethanol system, the method of introducing continuous ultrasonic irradiation in the nucleation stage was applied. The induction of ultrasound during nucleation process can break the original interactions firstly by shear forces and accelerate the occurrence of nucleation to avoid the reorientation and rearrangement of solute molecules. These strategies were proved to be effective in polymorph control and have a degree of applicability.

Recognition in the Domain of Molecular Chirality: From Noncovalent Interactions to Separation of Enantiomers

It is not a coincidence that both chirality and noncovalent interactions are ubiquitous in nature and synthetic molecular systems. Noncovalent interactivity between chiral molecules underlies enantioselective recognition as a fundamental phenomenon regulating life and human activities. Thus, noncovalent interactions represent the narrative thread of a fascinating story which goes across several disciplines of medical, chemical, physical, biological, and other natural sciences. This review has been conceived with the awareness that a modern attitude toward molecular chirality and its consequences needs to be founded on multidisciplinary approaches to disclose the molecular basis of essential enantioselective phenomena in the domain of chemical, physical, and life sciences. With the primary aim of discussing this topic in an integrated way, a comprehensive pool of rational and systematic multidisciplinary information is provided, which concerns the fundamentals of chirality, a description of noncovalent interactions, and their implications in enantioselective processes occurring in different contexts. A specific focus is devoted to enantioselection in chromatography and electromigration techniques because of their unique feature as "multistep" processes. A second motivation for writing this review is to make a clear statement about the state of the art, the tools we have at our disposal, and what is still missing to fully understand the mechanisms underlying enantioselective recognition.

Polymorphic transient glycolipid assemblies with tunable lifespan and cargo release

HYPOTHESIS

In living systems, dynamic processes like dissipative assembly, polymorph formation, and destabilization of hydrophobic domains play an indispensable role in the biochemical processes. Adaptation of biological self-assembly processes to an amphiphilic molecule leads to the fabrication of intelligent biomaterials with life-like behavior.

EXPERIMENTS

An amphiphilic glycolipid molecule was engineered into various dissipative assemblies (vesicles and supramolecular nanotube-composed hydrogels) by using two activation steps, including heating-cooling and shear force in method-1 or boric acid/glycolipid complexation and shear force in method-2. The influence of number of activation steps on vesicle to nanotube phase transitions and activation method on the properties of hydrogels were investigated, where the morphological transformations and destabilization of hydrophobic domains resulted from a bilayer to a higher-order crystal structure.

FINDINGS

Hydrophobic and hydrophilic cargos encapsulated in the dissipative assemblies (vesicles and injectable hydrogels) can be released in a controlled manner via changing the activation method. The reported adaptive materials engineered by dual activation steps are promising self-assembled systems for programmed release of loaded cargos at a tunable rate.

Chiral Recognition of Self-Assembled Peptides on MoS2 via Lattice Matching

Chiral recognition of peptides on solid surfaces has been studied for a better understanding of their assembly mechanism toward its applications in stereochemistry and enantioselective catalysis. However, moving from small peptides such as dipeptides, understanding the chiral recognition of larger biomolecules such as oligopeptides or peptides with a larger sequence is challenging. Furthermore, their intrinsic mechanism for chiral recognition in liquid conditions was poorly investigated experimentally. Here, we used in/ex situ atomic force microscopy (AFM) to investigate the chiral recognition of self-assembled structures of l/d-type peptides on molybdenum disulfide (MoS₂). We chose single-layer MoS₂ with a triangular shape as a substrate for the self-assembly of peptides. The facet edges of MoS₂ were utilized as a landmark to identify the crystallographic orientation of their ordered structures. We found both peptide enantiomers formed nanowires on MoS₂ with a mirror symmetry according to the facet edges of MoS₂. From in situ AFM measurements, we found a dimension of a unit cell in the self-assembled structure and proposed a model of lattice matching between peptides and MoS₂ lattice. The lattice matching for chiral recognition was further investigated by changing peptide sequences and surface lattice from MoS₂ to graphite. This work further deepened the understanding of biomolecular chiral recognition and will lead us to rationally design specific morphologies and conformations of chiral self-assembled structures of peptides with expected functions in the future.

2D Self-assembled molecular networks and on-surface reactivity under nanoscale lateral confinement

Supramolecular self-assembly at surfaces provides a pathway for building chemically customized interfaces. Over the last three decades, research on the role of key parameters such as temperature, solute concentration, and molecular design has enabled a steady increase in the complexity of self-assembled molecular networks (SAMNs) that can thus be created. However, the structure and quality of SAMNs is often determined during the early stages of nucleation and growth. To study and influence self-assembly processes at this deterministic length scale, spatial confinement of molecular adsorbates to well-defined surface patterns with nanoscale lateral dimensions offers exciting possibilities. The aim of this tutorial review is to give an overview of the various ways in which confinement impacts SAMN formation, and how we can use that knowledge to direct assemblies towards desired structures. The possibility to exploit confinement for improved control over on-surface reactions is also contemplated.

Chirality from scratch: enantioselective adsorption in geometrically controlled lateral nanoconfinement

Chiral symmetry breaking in molecular adsorption at the solid/liquid interface by lateral geometric nanoconfinement is demonstrated. The chiral nanoconfinement is created at the interface of achiral covalently modified highly-oriented pyrolytic graphite and a racemate by in situ scanning probe lithography. Enantioselective adsorption of chiral molecules is achieved by adjusting the relative orientation between the nanoconfining walls and substrate symmetry direction.