Exploring Strategies To Bias Sequence in Natural and Synthetic Oligomers and Polymers

Sequence-Controlled Electrochemical Immobilization of Catalyst-Photosensitizer Oligomers for Tuning Photoelectrochemical Behaviors

Immobilizing catalysts and photosensitizers on an electrode surface is crucial in interfacial energy conversion. However, their combination for optimizing catalytic performance is an unpredictable challenge. Herein, we report that catalyst and photosensitizer monomers are selectively grafted one-by-one addition onto the electrode surface by interfacial electrosynthesis to achieve composition and sequence-controlled oligomer photoelectrocatalytic monolayers. This electrosynthesis relies on the oxidative coupling reaction of carbazole and the reductive coupling reaction of vinyl on the catalyst and photosensitizer monomers, and it initiates on self-assembled monolayers and propagates with alternating positive and negative potentials. Each addition and completion of the target monomer can be quantitatively identified and monitored by optical and electrical responses and their linear coefficients as a function of reaction steps. The resulting composition and sequence-controlled monolayers exhibit tuning electrocatalytic behaviors including water splitting and CO2 reduction, indicating an efficient way to optimize the electro- and photocatalytic functions and performance of molecular materials.

Precision Sequence-Defined Polymers: From Sequencing to Biological Functions

Precise sequence-defined polymers (SDPs) with uniform chain-to-chain structure including chain length, unit sequence, and end functionalities represent the pinnacle of sophistication in the realm of polymer science. For example, the absolute control over the unit sequence of SDPs allows for the bottom-up design of polymers with hierarchical microstructures and functions. Accompanied with the development of synthetic techniques towards precision SDPs, the decoding of SDP sequences and construction of advanced functions irreplaceable by other synthetic materials is of central importance. In this Minireview, we focus on recent advances in SDP sequencing techniques including tandem mass spectrometry (MS), chemically assisted primary MS, as well as other non-destructive sequencing methods such as nuclear magnetic resonance (NMR) spectroscopy, circular dichroism (CD), and nanopore sequencing. Additionally, we delve into the promising prospects of SDP functions in the area of cutting-edge biological research. Topics of exploration include gene delivery systems, the development of hybrid materials combining SDPs and nucleic acids, protein recognition and regulation, as well as the interplay between chirality and biological functions. A brief outlook towards the future directions of SDPs is also presented.

Sequence Design of Random Heteropolymers as Protein Mimics

Random heteropolymers (RHPs) have been computationally designed and experimentally shown to recapitulate protein-like phase behavior and function. However, unlike proteins, RHP sequences are only statistically defined and cannot be sequenced. Recent developments in reversible-deactivation radical polymerization allowed simulated polymer sequences based on the well-established Mayo-Lewis equation to more accurately reflect ground-truth sequences that are experimentally synthesized. This led to opportunities to perform bioinformatics-inspired analysis on simulated sequences to guide the design, synthesis, and interpretation of RHPs. We compared batches on the order of 10000 simulated RHP sequences that vary by synthetically controllable and measurable RHP characteristics such as chemical heterogeneity and average degree of polymerization. Our analysis spans across 3 levels: segments along a single chain, sequences within a batch, and batch-averaged statistics. We discuss simulator fidelity and highlight the importance of robust segment definition. Examples are presented that demonstrate the use of simulated sequence analysis for in-silico iterative design to mimic protein hydrophobic/hydrophilic segment distributions in RHPs and compare RHP and protein sequence segments to explain experimental results of RHPs that mimic protein function. To facilitate the community use of this workflow, the simulator and analysis modules have been made available through an open source toolkit, the RHPapp.

Design of Abiological Digital Poly(phosphodiester)s

In biological systems, the storage and transfer of genetic information rely on sequence-controlled nucleic acids such as DNA and RNA. It has been realized for quite some time that this property is not only crucial for life but could also be very useful in human applications. For instance, DNA has been actively investigated as a digital storage medium over the past decade. Indeed, the "hard-disk of life" is an obvious choice and a highly optimized material for storing data. Through decades of nucleic acids research, technological tools for parallel synthesis and sequencing of DNA have been readily available. Consequently, it has already been demonstrated that different types of documents (e.g., texts, images, videos, and industrial data) can be stored in chemically synthesized DNA libraries. However, DNA is subject to biological constraints, and its molecular structure cannot be easily varied to match technological needs. In fact, DNA is not the only macromolecule that enables data storage. In recent years, it has been demonstrated that a wide variety of synthetic polymers can also be used for such a purpose. Indeed, modern polymer synthesis allows the preparation of synthetic macromolecules with precisely controlled monomer sequences. Altogether, about a dozens of synthetic digital polymers have already been described, and many more can be foreseen. Among them, sequence-defined poly(phosphodiester)s are one of the most promising options. These polymers are prepared by stepwise phosphoramidite chemistry like chemically synthesized oligonucleotides. However, they are constructed with non-natural building blocks and therefore share almost no structural characteristics with nucleic acids, except phosphate repeat units. Still, they contain readable digital messages that can be deciphered by nanopore sequencing or mass spectrometry sequencing. In this Account, we describe our recent research efforts in synthesizing and sequencing optimal abiological digital poly(phosphodiester)s. A major advantage of these polymers over DNA is that their molecular structure can easily be varied to tune their properties. During the last 5 years, we have engineered the molecular structure of these polymers to adjust crucial parameters such as the storage density, storage capacity, erasability, and readability. Consequently, high-capacity PPDE chains, containing hundreds of bits per chains, can now be synthesized and efficiently sequenced using a routine mass spectrometer. Furthermore, sequencing data can be automatically decrypted with the help of decoding software. This new type of coded matter can also be edited using practical physical triggers such as light and organized in space by programmed self-assembly. All of these recent improvements are summarized and discussed herein.

Geared Toward Applications: A Perspective on Functional Sequence-Controlled Polymers

Sequence-controlled polymers are an emerging class of synthetic polymers with a regulated sequence of monomers. In the past decade, tremendous progress has been made in the synthesis of polymers with the sophisticated sequence control approaching the level manifested in biopolymers. In contrast, the exploration of novel functions that can be achieved by controlling synthetic polymer sequences represents an emerging focus in polymer science. This Viewpoint will survey recent advances in the functional applications of sequence-controlled polymers and provide a perspective on the challenges and outlook for pursuing future applications of this fascinating class of macromolecules.

Effect of Poly(vinyl butyral) Comonomer Sequence on Adhesion to Amorphous Silica: A Coarse-Grained Molecular Dynamics Study

Modulating a comonomer sequence, in addition to the overall chemical composition, is the key to unlocking the true potential of many existing commercial copolymers. We employ coarse-grained molecular dynamics (MD) simulations to study the behavior of random-blocky poly(vinyl butyral-co-vinyl alcohol) (PVB) melts in contact with an amorphous silica surface, representing the interface found in laminated safety glass. Our two-pronged coarse-graining approach utilizes both macroscopic thermophysical data and all-atom MD simulation data. Polymer-polymer nonbonded interactions are described by the fused-sphere SAFT-γ Mie equation of state, while bonded interactions are derived using Boltzmann inversion to match the bond and angle distributions from all-atom PVB chains. Spatially dependent polymer-surface interactions are mapped from a hydroxylated all-atom amorphous silica slab model and all-atom monomers to an external potential acting on the coarse-grained sites. We discovered an unexpected complex relationship between the blockiness parameter and the adhesion energy. The adhesion strength between PVB copolymers with intermediate VA content and silica was found to be maximal for random-blocky copolymers with a moderately high degree of blockiness rather than for diblock copolymers. We attribute this to two main factors: (1) changes in morphology, which dramatically alter the number of VA beads interacting with the surface and (2) a non-negligible contribution of vinyl butyral (VB) monomers to adhesion energy because of their preference to adsorb to zones with low hydroxyl density on the silica surface.

Ring-Opening Alternating Copolymerization of O-Carboxyanhydrides of Lactic Acid and Malic Acid Using Hafnium Alkoxide Initiators with Different Stereo Selectivities and Activities

Monomer sequence controllable syntheses of copolymers, including copolyesters, remain a challenge in polymer science. Although alternating sequence-controlled copolymerization of O-carboxyanhydrides (OCAs) can be achieved via using syndioselective initiators, the alternating copolymerization of lactic acid-derived O-carboxyanhydride (LacOCA) with other monomers still suffers from a lack of highly syndioselective initiators. In this work, a highly syndioselective system for the ring-opening polymerization (ROP) of LacOCA was achieved using a bulky amine tris(phenolate) hafnium alkoxide initiator with a high P_r value of 0.91. However, the stereoselectivities of amine tris(phenolate) hafnium alkoxide initiators for the ROP of malic acid O-carboxyanhydride (MalOCA) change to be modestly or lowly isoselective. Interestingly, despite the different stereoselectivities of this system for the two different monomers, the high syndioselectivity of the initiator for the ROP of LacOCA and the low activity of MalOCA in the ROP allow comparatively high rates of cross-propagation; consequently, the ring-opening alternating copolymerization (ROAP) of LacOCA and MalOCA was achieved successfully.

Enabling technologies in polymer synthesis: accessing a new design space for advanced polymer materials

This review discusses how developments in laboratory technologies can push the boundaries of what is achievable using existing polymer synthesis techniques.

Emergence of Function and Selection from Recursively Programmed Polymerisation Reactions in Mineral Environments

Living systems are characterised by an ability to sustain chemical reaction networks far-from-equilibrium. It is likely that life first arose through a process of continual disruption of equilibrium states in recursive reaction networks, driven by periodic environmental changes. Herein, we report the emergence of proto-enzymatic function from recursive polymerisation reactions using amino acids and glycolic acid. Reactions were kept out of equilibrium by diluting products 9:1 in fresh starting solution at the end of each recursive cycle, and the development of complex high molecular weight species is explored using a new metric, the Mass Index, which allows the complexity of the system to be explored as a function of cycle. This process was carried out on a range of different mineral environments. We explored the hypothesis that disrupting equilibrium via recursive cycling imposes a selection pressure and subsequent boundary conditions on products. After just four reaction cycles, product mixtures from recursive reactions exhibit greater catalytic activity and truncation of product space towards higher-molecular-weight species compared to non-recursive controls.

One Step up the Ladder of Prebiotic Complexity: Formation of Nonrandom Linear Polypeptides from Binary Systems of Amino Acids on Silica

Evidence for the formation of linear oligopeptides with nonrandom sequences from mixtures of amino acids coadsorbed on silica and submitted to a simple thermal activation is presented. The amino acid couples (glutamic acid+leucine) and (aspartic acid+valine) were deposited on a fumed silica and submitted to a single heating step at moderate temperature. The evolution of the systems was characterized by X-ray diffraction, infrared spectroscopy, thermosgravimetric analysis, HPLC, and electrospray ionization mass spectrometry (ESI-MS). Evidence for the formation of amide bonds was found in all systems studied. While the products of single amino acids activation on silica could be considered as evolutionary dead ends, (glutamic acid+leucine) and, at to some extent, (aspartic acid+valine) gave rise to the high yield formation of linear peptides up to the hexamers. Oligopeptides of such length have not been observed before in surface polymerization scenarios (unless the amino acids had been deposited by chemical vapor deposition, which is not realistic in a prebiotic environment). Furthermore, not all possible amino acid sequences were present in the activation products, which is indicative of polymerization selectivity. These results are promising for origins of life studies because they suggest the emergence of nonrandom biopolymers in a simple prebiotic scenario.

Sequence-defined non-natural polymers: synthesis and applications

Sequence-defined polymer: A promising gateway for the next generation polymeric materials and vast opportunities for new synthetic strategies, functional diversity and its material and biomedical applications.

Synthesis of strictly alternating copolymers by living carbanionic copolymerization of diphenylethylene with 1,3-pentadiene isomers

The living carbanionic alternating copolymerizations of 1,3-pentadiene isomers with DPE are reported, and yield well-defined alternating and highly stereoregular amorphous copolymers with controllable M_n, low Đ_M and predominantly trans-1,4 units.

Benchtop flow-NMR for rapid online monitoring of RAFT and free radical polymerisation in batch and continuous reactors

A “Benchtop” NMR spectrometer is used for detailed monitoring of controlled and free radical polymerisations performed in batch and continuous reactors both offline and in real-time.

Recent Developments in Solid-Phase Strategies towards Synthetic, Sequence-Defined Macromolecules

Sequence-control in synthetic polymers is an important contemporary research area because it provides the opportunity to create completely novel materials for structure-function studies. This is especially relevant for biomimetic polymers, bioactive and information security materials. The level of control is strongly dependent and inherent upon the polymerization technique utilized. Today, the most established method yielding monodispersity and monomer sequence-definition is solid-phase synthesis. This Focus Review highlights recent advances in solid-phase strategies to access synthetic, sequence-defined macromolecules. Alternatives strategies towards sequence-defined macromolecules are also briefly summarized.