Coding and decoding libraries of sequence-defined functional copolymers synthesized via photoligation

Kinetically Controlled Approach for One-Pot Synthesis of Poly(peptide-b-peptoid) Exhibiting Well-Defined Secondary Structure and Thermal Stability

Sequence-controlled polymerization aims to bridge the gap between biopolymers and synthetic macromolecules. In a kinetically controlled approach, the inherent reactivity differences among monomers determine the primary structure or sequence of the monomers linked within the resulting copolymer chains. This report outlines a one-pot synthesis of polypeptide-b-polypeptoid by choosing a suitable pair of N-carboxy anhydride (NCA) monomers with significant reactivity differences. We have demonstrated the preparation of well-defined block copolymers, including polyproline-b-polysarcosine (PLP-b-PSar) and poly(propargyl proline)-b-polysarcosine (PLPP-b-PSar) in a single step. 1H NMR kinetic studies confirmed the sequence-controlled primary structures of these block copolymers. The NMR analysis indicated a striking reactivity ratio difference (rPLP = 925 and rPSar = 0.0014; rPLPP = 860 and rPSar = 0.0015) between the selected monomer pairs, which was crucial for a one-pot block copolymer synthesis. Notably, these sequence-controlled copolymers' secondary structures and stability were remarkably similar to those of block copolymers synthesized through conventional sequential addition methods. This further underscores the practicality of this kinetically controlled approach.

Visible and near-infrared light-induced photoclick reactions

Photoclick reactions combine the advantages offered by light-driven processes, that is, non-invasive and high spatiotemporal control, with classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photocrosslinking, protein labelling and bioimaging. Despite these advances, most photoclick reactions typically require near-ultraviolet (UV) and mid-UV light to proceed. UV light can trigger undesirable responses, including cellular apoptosis, and therefore, visible and near-infrared light-induced photoclick reaction systems are highly desirable. Shifting to a longer wavelength can also reduce degradation of the photoclick reagents and products. Several strategies have been used to induce a bathochromic shift in the wavelength of irradiation-initiating photoclick reactions. For instance, the extension of the conjugated π-system, triplet-triplet energy transfer, multi-photon excitation, upconversion technology, photocatalytic and photoinitiation approaches, and designs involving photocages have all been used to achieve this goal. Current design strategies, recent advances and the outlook for long wavelength-driven photoclick reactions are presented.

New Wine in Old Bottle: Crown Ether-Functionalized Digital Polymer toward Efficient MALDI-TOF MS/MS Decoding via a Classical Supramolecular Interaction

Digital polymers (DPs), which serve as promising molecular-level storage media, have increasingly garnered interest. Their application significantly depends on the efficiency of the information writing (synthesis) and reading processes (sequencing). For reading, rational incorporation of weak bonds in the main chain was applied in most cases in order to improve readability of the tandem mass spectra (MS/MS), which would limit the chain length of DPs, thus reducing the information storage capacity. In this study, the introduction of commercially available crown ether (CE) at the terminus of digital oligo(γ-butyrolactone)s (DOBLs) significantly enhances the predictability and fidelity of matrix-assisted laser desorption/ionization time-of-flight tandem mass spectra (MALDI-TOF MS/MS), thus improving the decoding process. The use of crown ether, leveraging a well-established supramolecular interaction with alkali cations known since 1967, offers a strong affinity between ionization agents and CE motifs, to form a selective effect of the desired fragments during the tandem MS. This method is particularly effective for long-chain DPs, extending up to 32-mer, and allows for customizable fragmentation patterns. The incorporation of CE at the DP chain end presents a novel and efficient strategy for enhancing MS/MS readability and amplifying the information storage capacity of polymers.

Revealing the Effect of Stereocontrol on Intermolecular Interactions between Abiotic, Sequence-Defined Polyurethanes and a Ligand

The development of precision polymer synthesis has facilitated access to a diverse library of abiotic structures wherein chiral monomers are positioned at specific locations within macromolecular chains. These structures are anticipated to exhibit folding characteristics similar to those of biotic macromolecules and possess comparable functionalities. However, the extensive sequence space and numerous variables make selecting a sequence with the desired function challenging. Therefore, revealing sequence-function dependencies and developing practical tools are necessary to analyze their conformations and molecular interactions. In this study, we investigate the effect of stereochemistry, which dictates the spatial location of backbone and pendant groups, on the interaction between sequence-defined oligourethanes and bisphenol A ligands. Various methods are explored to analyze the receptor-like properties of model oligomers and the ligand. The accuracy of molecular dynamics simulations and experimental techniques is assessed to uncover the impact of discrete changes in stereochemical arrangements on the structures of the resulting complexes and their binding strengths. Detailed computational investigations providing atomistic details show that the formed complexes demonstrate significant structural diversity depending on the sequence of stereocenters, thus affecting the oligomer-ligand binding strength. Among the tested techniques, the fluorescence spectroscopy data, fitted to the Stern-Volmer equation, are consistently aligned with the calculations, thus validating the developed simulation methodology. The developed methodology opens a way to engineer the structure of sequence-defined oligomers with receptor-like functionality to explore their practical applications, e.g., as sensory materials.

Digital synthetic polymers for information storage

Digital synthetic polymers with uniform chain lengths and defined monomer sequences have recently become intriguing alternatives to traditional silicon-based information devices or natural biomacromolecules for data storage. The structural diversity of information-containing macromolecules endows the digital synthetic polymers with higher stability and storage density but less occupied space. Through subtly designing each unit of coded structure, the information can be readily encoded into digital synthetic polymers in a more economical scheme and more decodable, opening up new avenues for molecular digital data storage with high-level security. This tutorial review summarizes recent advances in salient features of digital synthetic polymers for data storage, including encoding, decoding, editing, erasing, encrypting, and repairing. The current challenges and outlook are finally discussed to offer potential solution guidance and new perspectives for the creation of next-generation digital synthetic polymers and broaden the scope of their applicability.

Digital micelles of encoded polymeric amphiphiles for direct sequence reading and ex vivo label-free quantification

Identification and quantification of synthetic polymers in complex biological milieu are crucial for delivery, sensing and scaffolding functions, but conventional techniques based on imaging probe labellings only afford qualitative results. Here we report modular construction of precise sequence-defined amphiphilic polymers that self-assemble into digital micelles with contour lengths strictly regulated by oligourethane sequences. Direct sequence reading is accomplished with matrix-assisted laser desorption/ionization (MALDI) tandem mass spectrometry, facilitated by high-affinity binding of alkali metal ions with poly(ethylene glycol) dendrons and selective cleavage of benzyl-carbamate linkages. A mixture of four types of digital micelles could be identified, sequence-decoded and quantified by MALDI and MALDI imaging at cellular, organ and tissue slice levels upon in vivo administration, enabling direct comparison of biological properties for each type of digital micelle in the same animal. The concept of digital micelles and encoded amphiphiles capable of direct sequencing and high-throughput label-free quantification could be exploited for next-generation precision nanomedicine designs (such as digital lipids) and protein corona studies.

Reading Information Stored in Synthetic Macromolecules

The storage of information in synthetic (macro)molecules provides an attractive alternative for current archival storage media, and the advancements made within this area have prompted the investigation of such molecules for numerous other applications (e.g., anti-counterfeiting tags, steganography). While different strategies have been described for storing information at the molecular level, this Perspective aims to provide a critical overview of the most prominent approaches that can be utilized for retrieving the encoded information. The major part will focus on the sequence determination of synthetic macromolecules, wherein information is stored by the precise arrangement of constituting monomers, with an emphasis on chemically aided strategies, (tandem) mass spectrometry, and nanopore sensing. In addition, recent progress in utilizing (mixtures of) small molecules for information storage will be discussed. Finally, the closing remarks aim to highlight which strategy we believe is the most suitable for a series of specific applications, and will also touch upon the future research avenues that can be pursued for reading (macro)molecular information.

Nondestructive Sequencing of Enantiopure Oligoesters by Nuclear Magnetic Resonance Spectroscopy

Sequence-defined synthetic oligomers and polymers are promising molecular media for permanently storing digital information. However, the information decoding process relies on degradative sequencing methods such as mass spectrometry, which consumes the information-storing polymers upon decoding. Here, we demonstrate the nondestructive decoding of sequence-defined oligomers of enantiopure α-hydroxy acids, oligo(l-mandelic-co-d-phenyl lactic acid)s (oMPs), and oligo(l-lactic-co-glycolic acid)s (oLGs) by 13C nuclear magnetic resonance spectroscopy. We were able to nondestructively decode a bitmap image (192 bits) encoded using a library of 12 equimolar mixtures of an 8-bit-storing oMP and oLG, synthesized through semiautomated flow chemistry in less than 1% of the reaction time required for the repetition of conventional batch reactions. Our results highlight the potential of bundles of sequence-defined oligomers as efficient media for encoding and decoding large-scale information based on the automation of their synthesis and nondestructive sequencing processes.

Microspheres from light-a sustainable materials platform

Driven by the demand for highly specialized polymeric materials via milder, safer, and sustainable processes, we herein introduce a powerful, purely light driven platform for microsphere synthesis – including facile synthesis by sunlight. Our light-induced step-growth precipitation polymerization produces monodisperse particles (0.4–2.4 μm) at ambient temperature without any initiator, surfactant, additive or heating, constituting an unconventional approach compared to the classically thermally driven synthesis of particles. The microspheres are formed via the Diels-Alder cycloaddition of a photoactive monomer (2-methylisophthaldialdehyde, MIA) and a suitable electron deficient dienophile (bismaleimide). The particles are stable in the dry state as well as in solution and their surface can be further functionalized to produce fluorescent particles or alter their hydrophilicity. The simplicity and versatility of our approach introduces a fresh opportunity for particle synthesis, opening access to a yet unknown material class.

Photopolymerization provides a safe and mild fabrication pathway towards polymeric particles but the implementation of photochemistry from solution to dispersed media to produce particles is far from trivial. Here, the authors demonstrate an additive-free step-growth photopolymerization with sunlight, exploiting the photoinduced Diels-Alder to fabricate micrometer sized polymeric particles.

Molecular data storage with zero synthetic effort and simple read-out

Compound mixtures represent an alternative, additional approach to DNA and synthetic sequence-defined macromolecules in the field of non-conventional molecular data storage, which may be useful depending on the target application. Here, we report a fast and efficient method for information storage in molecular mixtures by the direct use of commercially available chemicals and thus, zero synthetic steps need to be performed. As a proof of principle, a binary coding language is used for encoding words in ASCII or black and white pixels of a bitmap. This way, we stored a 25 × 25-pixel QR code (625 bits) and a picture of the same size. Decoding of the written information is achieved via spectroscopic (1H NMR) or chromatographic (gas chromatography) analysis. In addition, for a faster and automated read-out of the data, we developed a decoding software, which also orders the data sets according to an internal "ordering" standard. Molecular keys or anticounterfeiting are possible areas of application for information-containing compound mixtures.

Regioisomerism in Symmetric Dimethyl Dialdehydes Dictates their Photochemical Reactivity

We herein report the first light-driven selective monoderivatization (desymmetrization) of two chemically equivalent carbonyl groups in a single chromophore. By comparing of four symmetric regioisomers, featuring two equivalent ortho-methylbenzaldehyde units, we identify dimethyltherephtalaldehydes (DMTAs) which can be activated in a dual wavelength-selective fashion. Under visible light and UV-light irradiation, DMTAs undergo two consecutive Diels-Alder reactions exhibiting near-quantitative endo-selectivity (>99%) and provide excellent yields (96-98%). The influence of the regioisomerism of the dialdehydes on their photochemical behavior is profound, evidenced by an in-depth investigation of their photochemical performance. We exemplify the capability of the photosystems via the synthesis of complex Diels-Alder adducts with various dienophiles, including alkynes.

Sequencing of Uniform Multifunctional Oligoesters via Random Chain Cleavages

Sequence-defined polymers have been the object of many fascinating studies that focus on their implementation in both material and life science applications. In parallel, iterative synthetic methodologies have become more efficient, whereas the structure elucidation of these molecules is generally dependent on MS/MS analysis. Here, we report an alternative, simple strategy for the determination of the monomer order of uniform oligo(thioether ester)s. This approach, which relies on random cleavages of ester units within the macromolecular backbone via a basic treatment, enables the swift characterization of these macromolecules without the need for MS/MS. Consequently, this method can be used for decoding any information stored within the primary structure of oligoesters by means of ESI- or LC-MS. Finally, we speculate that a range of structurally diverse backbones could be susceptible towards this approach, which could promptly expand the library of chemically sequenceable macromolecules.

Switchable Polymerization Organocatalysis: From Monomer Mixtures to Block Copolymers

One-pot production of sequence-controlled block copolymer from mixed monomers is a crucial but rarely reached goal. Using a switchable Lewis-pair organocatalyst, we have accomplished sequence-selective polymerization from a mixture of O-carboxyanhydride (OCA) and epoxide. Polymerization of the OCA monomer occurs first and exclusively because of its exceedingly high polymerizability. When OCA is fully consumed, alternating copolymerization of epoxide and CO₂ liberated in OCA polymerization is triggered from the termini of the first block. The two polymerizations thus occur in tandem, both in chemoselective fashion, so that a sequence-controlled block polymer with up to 99 % CO₂ conversion is furnished in this one-pot protocol. Calculations and experimental results demonstrate a chemoselective and cooperative mechanism, where the high polymerizability of the OCA monomers guarantees exquisite sequence selectivity and the cooperative decarboxylation partly arose from the stabilization effect by triethylborane, which facilitates the smooth transformation of the chain end from carbonate to alkoxide.

Fabrication and Decryption of a Microarray of Digital Dithiosuccinimide Oligomers

Digital polymer with precisely arranged binary units provides an important option for information storage. This is especially true if the digital polymers are assembled in a device, as it would be of great benefit to data writing and reading in practice. Herein, inspired by DNA microarray technique, the programmable information storing and reading on a mass spectrometry target plate is proposed. First, an array of 4-bit sequence-coded dithiosuccinimide oligomers was efficiently built through sequential thiol-maleimide Michael couplings with good sequence readability by tandem mass spectrometry (MS/MS). Then, toward engineering microarray for information storage, a programmed robotic arm was specifically designed for precisely loading sequence-coded oligomers onto the target plate, and a decoding software was developed for efficient readout of the data from MS/MS sequencing. Notably, short sequence-coded oligomers chains can be used to write long strings of information, and extra error-correction codes are not required as usual due to the inherent concomitant fragmentation signals. Not only text but also bitimages can be automatically stored and decoded with excellent accuracy. This work provides a promising platform of digital polymers for programmable information storing and reading. This article is protected by copyright. All rights reserved.

Rewritable Macromolecular Data Storage with Automated Read-out

Rewriting data stored on synthetic macromolecules is an interesting feature, even though it is considered as being quite challenging within the area of digital macromolecules. In this context, we initially studied a strategy for modifying the position tag of sequence-encoded macromolecules in a reversible manner. The efficiency of this method, which relies on the orthogonal cleavage of a thioester moiety via aminolysis, was demonstrated by modifying parts of an exemplary sentence. Simultaneously, a novel algorithm was developed to ease the read-out of macromolecular information by means of MS/MS techniques. This program, Oligoreader, can identify potential information-containing macromolecules from a series of MS¹ spectra, analyze the corresponding MS² spectra, and finally decode the data. Consequently, the algorithm simplifies the entire read-out process by avoiding any interference from the operator, which increases the potential for blind sequencing of uniform macromolecules.

Semiautomated synthesis of sequence-defined polymers for information storage

Accelerated and parallel synthesis of sequence-defined polymers is an utmost challenge for realizing ultrahigh-density storage of digital information in molecular media. Here, we report step-economical synthesis of sequence-defined poly(l-lactic-co-glycolic acid)s (PLGAs) using continuous flow chemistry. A reactor performed the programmed coupling of the 2-bit storing building blocks to generate a library of their permutations in a single continuous flow, followed by their sequential convergences to a sequence-defined PLGA storing 64 bits in four successive flows. We demonstrate that a bitmap image (896 bits) can be encoded and decoded in 14 PLGAs using only a fraction of the time required for an equivalent synthesis by conventional batch processes. Accelerated synthesis of sequence-defined polymers could also contribute to macromolecular engineering with precision comparable to natural precedents.

Iterative Synthesis of Stereo- and Sequence-Defined Polymers via Acid-Orthogonal Deprotection Chemistry

Absolute control over polymer stereo- and sequence structure is highly challenging in polymer chemistry. Here, an acid-orthogonal deprotection strategy is proposed for the iterative synthesis of a family of unimolecular polymers starting with enantiopure serines, featuring precise sequence, stereoconfiguration and side-chain functionalities that cannot be achieved using traditional polymerization techniques. Acid-orthogonal deprotections proceed independently of one another by the selection of protecting groups that feature the respective acid-lability. Under p-toluenesulfonic acid, acidolysis of tert-butyloxycarbonyl can proceed exclusively, while low-dosage trifluoroacetic acid and low temperature only trigger the selective and quantitative cleavage of trityl. The pioneering use of this acid-orthogonal deprotection chemistry increases the compatibility with otherwise sensitive groups and opens up pathways to facilely introduce structural and functional diversity into stereo- and sequence-defined polymers, thus imparting their unique properties beyond natural biopolymers.

Discrete oligourethanes of sequence-regulated properties – impact of stereocontrol

Properties and functions of natural biopolymers such as proteins are strongly dependent on the sequence of amino acid monomers. The regulation of the properties of synthetic polymers by controlling monomer...

Using precision polymer chemistry for plastics traceability and governance

Resolving the anonymity of plastic materials is critical for safeguarding the well-being of our natural environments and human health.

Discrete, self-immolative N-substituted oligourethanes and their use as molecular tags

The depolymerization of N-substituted oligourethanes via an intramolecular cyclization event was studied in-depth, while the applicability of these macromolecules as anti-counterfeiting tags was demonstrated by labeling a polyurethane material.

Combining Hydroxyl-Yne and Thiol-Ene Click Reactions to Facilely Access Sequence-Defined Macromolecules for High-Density Data Storage

Through mimicking the synthesis of hereditary-information-containing nucleic acids, scientists are committed to synthesizing sequence-defined macromolecules. Herein, a protecting-group-free, metal-free, and atom-economical chemistry combining hydroxyl-yne and thiol-ene click reactions was developed to efficiently synthesize sequence-defined oligo(monothioacetals) (overall yield of 54% for an 11-step synthesis) from readily available starting compounds and monomers under ambient conditions. The sequences of linear oligo(monothioacetals) could be easily decoded via a tandem ESI-MS/MS technique, making them new kinds of digital macromolecules with a high data storage density (0.013 bit/Da). Moreover, star oligo(monothioacetals) could also be facilely generated through divergent and convergent strategies and their combination. An unprecedented sequence-defined miktoarm star oligo(monothioacetal) was obtained, which could serve as a new nonlinear digital macromolecule to achieve 2D information matrix encoding and hold great potential to be applied for information encryption, anticouterfeiting, secret communication, etc. Thus, this work provides a powerful stepwise iterative approach to facilely access sequence-defined linear and topological oligo(monothioacetals) for high-density data storage.

Polymers Strive for Accuracy: From Sequence-Defined Polymers to mRNA Vaccines against COVID-19 and Polymers in Nucleic Acid Therapeutics

Unquestionably, polymers have influenced the world over the past 100 years. They are now more crucial than ever since the COVID-19 pandemic outbreak. The pandemic paved the way for certain polymers to be in the spotlight, namely sequence-defined polymers such as messenger ribonucleic acid (mRNA), which was the first type of vaccine to be authorized in the U.S. and Europe to protect against the SARS-CoV-2 virus. This rise of mRNA will probably influence scientific research concerning nucleic acids in general and RNA therapeutics in specific. In this Perspective, we highlight the recent trends in sequence-controlled and sequence-defined polymers. Then we discuss mRNA vaccines as an example to illustrate the need of ultimate sequence control to achieve complex functions such as specific activation of the immune system. We briefly present how mRNA vaccines are produced, the importance of modified nucleotides, the characteristic features, and the advantages and challenges associated with this class of vaccines. Finally, we discuss the chances and opportunities for polymer chemistry to provide solutions and contribute to the future progress of RNA-based therapeutics. We highlight two particular roles of polymers in this context. One represents conjugation of polymers to nucleic acids to form biohybrids. The other is concerned with advanced polymer-based carrier systems for nucleic acids. We believe that polymers can help to address present problems of RNA-based therapeutic technologies and impact the field beyond the COVID-19 pandemic.

Nature-Inspired Circular-Economy Recycling for Proteins: Proof of Concept

The billion tons of synthetic-polymer-based materials (i.e. plastics) produced yearly are a great challenge for humanity. Nature produces even more natural polymers, yet they are sustainable. Proteins are sequence-defined natural polymers that are constantly recycled when living systems feed. Digestion is the protein depolymerization into amino acids (the monomers) followed by their re-assembly into new proteins of arbitrarily different sequence and function. This breaks a common recycling paradigm where a material is recycled into itself. Organisms feed off of random protein mixtures that are "recycled" into new proteins whose identity depends on the cell's specific needs. In this study, mixtures of several peptides and/or proteins are depolymerized into their amino acid constituents, and these amino acids are used to synthesize new fluorescent, and bioactive proteins extracellularly by using an amino-acid-free, cell-free transcription-translation (TX-TL) system. Specifically, three peptides (magainin II, glucagon, and somatostatin 28) are digested using thermolysin first and then using leucine aminopeptidase. The amino acids so produced are added to a commercial TX-TL system to produce fluorescent proteins. Furthermore, proteins with high relevance in materials engineering (β-lactoglobulin films, used for water filtration, or silk fibroin solutions) are successfully recycled into biotechnologically relevant proteins (fluorescent proteins, catechol 2,3-dioxygenase).

Photoclick Chemistry: A Bright Idea

At its basic conceptualization, photoclick chemistry embodies a collection of click reactions that are performed via the application of light. The emergence of this concept has had diverse impact over a broad range of chemical and biological research due to the spatiotemporal control, high selectivity, and excellent product yields afforded by the combination of light and click chemistry. While the reactions designated as "photoclick" have many important features in common, each has its own particular combination of advantages and shortcomings. A more extensive realization of the potential of this chemistry requires a broader understanding of the physical and chemical characteristics of the specific reactions. This review discusses the features of the most frequently employed photoclick reactions reported in the literature: photomediated azide-alkyne cycloadditions, other 1,3-dipolarcycloadditions, Diels-Alder and inverse electron demand Diels-Alder additions, radical alternating addition chain transfer additions, and nucleophilic additions. Applications of these reactions in a variety of chemical syntheses, materials chemistry, and biological contexts are surveyed, with particular attention paid to the respective strengths and limitations of each reaction and how that reaction benefits from its combination with light. Finally, challenges to broader employment of these reactions are discussed, along with strategies and opportunities to mitigate such obstacles.

Light-Triggered Click Chemistry

The merging of click chemistry with discrete photochemical processes has led to the creation of a new class of click reactions, collectively known as photoclick chemistry. These light-triggered click reactions allow the synthesis of diverse organic structures in a rapid and precise manner under mild conditions. Because light offers unparalleled spatiotemporal control over the generation of the reactive intermediates, photoclick chemistry has become an indispensable tool for a wide range of spatially addressable applications including surface functionalization, polymer conjugation and cross-linking, and biomolecular labeling in the native cellular environment. Over the past decade, a growing number of photoclick reactions have been developed, especially those based on the 1,3-dipolar cycloadditions and Diels-Alder reactions owing to their excellent reaction kinetics, selectivity, and biocompatibility. This review summarizes the recent advances in the development of photoclick reactions and their applications in chemical biology and materials science. A particular emphasis is placed on the historical contexts and mechanistic insights into each of the selected reactions. The in-depth discussion presented here should stimulate further development of the field, including the design of new photoactivation modalities, the continuous expansion of λ-orthogonal tandem photoclick chemistry, and the innovative use of these unique tools in bioconjugation and nanomaterial synthesis.

Sequence-Encoded Macromolecules with Increased Data Storage Capacity through a Thiol-Epoxy Reaction

Sequence-encoded oligo(thioether urethane)s with two different coding monomers per backbone unit were prepared via a solid phase, two-step iterative protocol based on thiolactone chemistry. The first step of the synthetic cycle consists of the thiolactone ring opening with a primary amine, whereby the in situ released thiol is immediately reacted with an epoxide. In the second step, the thiolactone group is reinstalled to initiate the next cycle. This strategy allows to introduce two different coding monomers per synthetic cycle, rendering the resulting macromolecules especially attractive in the area of (macro)molecular data storage because of their increased data storage capacity. Subsequently, the efficiency of the herein reported synthesis route and the applicability of the dual-encoded sequence-defined macromolecules as a potential data storage platform have been demonstrated by unraveling the exact monomer order using tandem mass spectrometry techniques.

Wavelength-Gated Photochemical Synthesis of Phenalene Diimides

Herein, we pioneer a wavelength‐gated synthesis route to phenalene diimides. Consecutive Diels–Alder reactions of methylisophthalaldehydes and maleimides afford hexahydro‐phenalene‐1,6‐diol diimides via 5‐formyl‐hexahydro‐benzo[f]isoindoles as the intermediate. Both photoreactions are efficient (82–99 % yield) and exhibit excellent diastereoselectivity (62–98 % d.r.). The wavelength‐gated nature of the stepwise reaction enables the modular construction of phenalene diimide scaffolds by choice of substrate and wavelength. Importantly, this synthetic methodology opens a facile avenue to a new class of persistent phenalenyl diimide neutral radicals, constituting a versatile route to spin‐active molecules.

High-Performance Reversed-Phase Flash Chromatography Purification of Peptides and Chemically Modified Insulins

Preparative reversed-phase HPLC is the established method for the purification of peptides, but has significant limitations. We systematically investigated the use of high-performance reversed-phase flash chromatography (HPFC) to rapidly purify laboratory-scale quantities of crude, synthetic peptides and chemically modified insulins. We demonstrated these methods for a diverse set of peptides, including short, medium, and long peptides. Depending on the purity profile of the peptide, HPFC can be used either as the sole purification method, or as a pre-purification method prior to final HPLC purification. Furthermore, HPFC is suitable for the purification of peptides that are not fully in solution. We provide guidelines for the HPFC of synthetic peptides and small proteins, including the choice of columns, eluents, and gradients. We believe that HPFC is a valuable alternative to HPLC purification of peptides and small proteins.

Applications of Discrete Synthetic Macromolecules in Life and Materials Science: Recent and Future Trends

In the last decade, the field of sequence-defined polymers and related ultraprecise, monodisperse synthetic macromolecules has grown exponentially. In the early stage, mainly articles or reviews dedicated to the development of synthetic routes toward their preparation have been published. Nowadays, those synthetic methodologies, combined with the elucidation of the structure-property relationships, allow envisioning many promising applications. Consequently, in the past 3 years, application-oriented papers based on discrete synthetic macromolecules emerged. Hence, material science applications such as macromolecular data storage and encryption, self-assembly of discrete structures and foldamers have been the object of many fascinating studies. Moreover, in the area of life sciences, such structures have also been the focus of numerous research studies. Here, it is aimed to highlight these recent applications and to give the reader a critical overview of the future trends in this area of research.

Protecting-Group-Free Iterative Exponential Growth Method for Synthesizing Sequence-Defined Polymers

As a main synthetic strategy for monodisperse sequence-defined polymers, the known iterative exponential growth (IEG) methods were all developed on protecting-group chemistry, where the additional deprotection reactions increased their synthetic steps and decreased their atom economy. In this study, we developed a protecting-group-free IEG method for the formation of sequence-defined polymers by combining three orthogonal click reactions of copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), sulfur-fluoride exchange reaction (SuFEx), and Ugi four-component reaction (Ugi-4CR). In this approach, oligomer synthesis began with three parallel CuAAC, SuFEx, and Ugi-4CR couplings among three monomers each with two orthogonal clickable end groups. By iteratively applying parallel CuAAC, SuFEx, and Ugi-4CR to couple three resultant oligomers, each having two orthogonal clickable terminals, this approach could exponentially grow three different sequence-defined polymers simultaneously with high efficiency, requiring no protecting-group chemistry. Additionally, each Ugi-4CR coupling reaction could introduce two external side groups to provide the molecular variation and side-chain functionalization for the resultant sequence-defined polymers.

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.

IrAAC-based construction of dual sequence-defined polytriazoles

One novel dual sequence-defined polytriazole structure was facilely achieved through an IrAAC-based iterative sequential growth strategy.

Reading mixtures of uniform sequence-defined macromolecules to increase data storage capacity

In recent years, the field of molecular data storage has emerged from a niche to a vibrant research topic. Herein, we describe a simultaneous and automated read-out of data stored in mixtures of sequence-defined oligomers. Therefore, twelve different sequence-defined tetramers and three hexamers with different mass markers and side chains are successfully synthesised via iterative Passerini three-component reactions and subsequent deprotection steps. By programming a straightforward python script for ESI-MS/MS analysis, it is possible to automatically sequence and thus read-out the information stored in these oligomers within one second. Most importantly, we demonstrate that the use of mass-markers as starting compounds eases MS/MS data interpretation and furthermore allows the unambiguous reading of sequences of mixtures of sequence-defined oligomers. Thus, high data storage capacity considering the field of synthetic macromolecules (up to 64.5 bit in our examples) can be obtained without the need of synthesizing long sequences, but by mixing and simultaneously analysing shorter sequence-defined oligomers.

Dual sequence definition increases the data storage capacity of sequence-defined macromolecules

Sequence-defined macromolecules offer applications in the field of data storage. Challenges include synthesising precise and pure sequences, reading stored information and increasing data storage capacity. Herein, the synthesis of dual sequence-defined oligomers and their application for data storage is demonstrated. While applying the well-established Passerini three-component reaction, the degree of definition of the prepared monodisperse macromolecules is improved compared to previous reports by utilising nine specifically designed isocyanide monomers to introduce backbone definition. The monomers are combined with various aldehyde components to synthesise dual-sequence defined oligomers. Thus, the side chains and the backbones of these macromolecules can be varied independently, exhibiting increased molecular diversity and hence data storage capacity per repeat unit. In case of a dual sequence-defined pentamer, 33 bits are achieved in a single molecule. The oligomers are obtained in multigram scale and excellent purity. Sequential read-out by tandem ESI-MS/MS verifies the high data storage capacity of the prepared oligomers per repeat unit in comparison to other sequence defined macromolecules.

Encoding Information into Polyethylene Glycol Using an Alcohol-Isocyanate "Click" Reaction

In this article, the capability of encoding information using a homologous series of monodisperse monomethoxypolyethylene glycols (mPEG), with a number of ethylene oxide units ranging from n_EO = 5 to 8, and monodisperse linear aliphatic isocyanates containing a number of CH₂ units from 3 to 7, is demonstrated. The “click” reaction of the two corresponding homologous series yielded 20 different isocyanate end-capped polyethylene glycol derivatives (mPEG-OCONHR) whose sodiated adduct ion’s nominal m/z values spanned from 360 to 548, providing an average ca. 8 m/z unit for the storage of one-bit information. These mPEG-OCONHR oligomers were then used to encode information in binary sequences using a 384-well MALDI sample plate and employing the common dried-droplet sample preparation method capable of encoding 20 bit, i.e., 2.5 byte information in one spot, was employed. The information stored in the spots was read by MALDI-TOF MS using the m/z value of the corresponding mPEG-OCONHR oligomers. The capability of the method to store data was demonstrated by writing and reading a text file, visualizing a small picture and capturing a short audio file written in Musical Instrument Digital Interface (MIDI) sequence. Due to the very large similarities in the chemical structures of the encoding oligomers and their “easy to be ionized” property, as well as their very similar ionization efficiencies, the MALDI-TOF MS signal intensities from each compound was so strong and unambiguous that complete decoding could be performed in each case. In addition, the set of the proposed encoding oligomers can be further extended to attain higher bit “densities”.

Engineering digital polymer based on thiol–maleimide Michael coupling toward effective writing and reading

Based on thiol–maleimide Michael coupling, a digital polymer allowing efficient message writing and reading was rationally designed.

Easily readable palindromic sequence-defined polymers built by cascade thiol-maleimide Michael couplings

The rational combination of cascade thiol-maleimide Michael couplings (CTMMC) with iterative exponential chain growth was demonstrated as an efficient way to synthesize palindromic sequence-defined polymers.

High-Throughput Tertiary Amine Deoxygenated Photopolymerizations for Synthesizing Polymer Libraries

The huge chemical space potential of synthetic polymers means that in many studies only a small parameter range can be realistically synthesized in a short time and hence the "best" formulations may not be optimum. Throughput is traditionally limited by the need for deoxygenation in radical polymerizations, but advances in photopolymerization now provide opportunities for "in-air" polymerizations. Here, we have developed a protocol using liquid handling robots (or multichannel pipettes) with blue light photolysis of reversible addition fragmentation chain transfer agents and tertiary amine deoxygenation to enable the synthesis of polymer libraries in industry-standard 96-well plates with no specialized infrastructure and no degassing step. The roles of solvents and amine deoxygenators are explored to optimize the polymerization, particularly to look at alternatives to dimethyl sulfoxide (DMSO) for hydrophobic monomer (co)polymerization. DMSO is shown to aid the degassing process but is not easy to remove and hence prevents isolation of pure polymers. In contrast, using dioxane in-plate evaporation or precipitation of the tertiary amine allowed isolation of polymers in-plate. This removed all reaction components yielding pure polymers, which is not easily achieved with systems using metal catalysts and secondary reductants, such as ascorbic acid. As an example of the throughput, in just under 40 h, 392 polymers were synthesized and subsequently analyzed direct from plates by a 96-well plate sampling size exclusion chromatography system to demonstrate reproducibility. Due to less efficient degassing in dioxane (compared to DMSO), the molecular weight and dispersity control were limited in some cases (with acrylates giving the lowest dispersities), but the key aim of this system is to access hundreds of polymers quickly and in a format needed to enable testing. This method enables easy exploration of chemical space and development of screening libraries to identify hits for further study using precision polymerization methods.