Plant Antimicrobial Peptides Snakin‐1 and Snakin‐2: Chemical Synthesis and Insights into the Disulfide Connectivity

Antimicrobial peptides and proteins represent an important class of plant defensive compounds against pathogens and provide a rich source of lead compounds in the field of drug discovery. We describe the effective preparation of the cysteine‐rich snakin‐1 and ‐2 antimicrobial peptides by using a combination of solid‐phase synthesis and native chemical ligation. A subsequent cysteine/cystine mediated oxidative folding to form the six internal disulfide bonds concurrently gave the folded proteins in 40–50 % yield. By comparative evaluation of mass spectrometry, HPLC, biological data and trypsin digest mapping of folded synthetic snakin‐2 compared to natural snakin‐2, we demonstrated that synthetic snakin‐2 possesses full antifungal activity and displayed similar chromatographic behaviour to natural snakin‐2. Trypsin digest analysis allowed tentative assignment of three of the purported six disulfide bonds.     

Peptides as New Smart Bionanomaterials: Molecular‐Recognition and Self‐Assembly Capabilities

Biomolecules express exquisite properties that are required for molecular recognition and self‐assembly on the nanoscale. These smart capabilities have developed through evolution and such biomolecules operate based on smart functions in natural systems. Recently, these remarkable smart capabilities have been utilized in not only biologically related fields, but also in materials science and engineering. A peptide‐screening technology that uses phage‐display systems has been developed based on this natural smart evolution for the generation of new functional peptide bionanomaterials. We focused on peptides that specifically bound to synthetic polymers. These polymer‐binding peptides were screened by using a phage‐display peptide library to recognize nanostructures that were derived from polymeric structural features and were utilized for possible applications as new bionanomaterials. We also focused on self‐assembling peptides with β‐sheet structures that formed nanoscale, fibrous structures for applications in new bottom‐up nanomaterials. Moreover, nanofiber‐binding peptides were also screened to introduce the desired functionalities into nanofibers without the need for additional molecular design. Our approach to construct new bionanomaterials that employ peptides will open up excellent opportunities for the next generation of materials science and technology.     

Two‐Dimensional Polymers: Just a Dream of Synthetic Chemists?

In light of the considerable impact synthetic 2D polymers are expected to have on many fundamental and applied aspects of the natural and engineering sciences, it is surprising that little research has been carried out on these intriguing macromolecules. Although numerous approaches have been reported over the last several decades, the synthesis of a one monomer unit thick, covalently bonded molecular sheet with a long‐range ordered (periodic) internal structure has yet to be achieved. This Review provides an overview of these approaches and an analysis of how to synthesize 2D polymers. This analysis compares polymerizations in (initially) a homogeneous phase with those at interfaces and considers structural aspects of monomers as well as possibly preferred connection modes. It also addresses issues such as shrinkage as well as domain and crack formation, and briefly touches upon how the chances for a successful structural analysis of the final product can possibly be increased.     

Towards Sequence‐Controlled Antimicrobial Polymers: Effect of Polymer Block Order on Antimicrobial Activity

Synthetic polymers have shown promise in combating multidrug‐resistant bacteria. However, the biological effects of sequence control in synthetic antimicrobial polymers are currently not well understood. As such, we investigate the antimicrobial effects of monomer distribution within linear high‐order quasi‐block copolymers consisting of aminoethyl, phenylethyl, and hydroxyethyl acrylamides made in a one‐pot synthesis approach via photoinduced electron transfer–reversible addition–fragmentation chain transfer polymerisation (PET‐RAFT). Through different combinations of monomer/polymer block order, antimicrobial and haemolytic activities are tuneable in a manner comparable to antimicrobial peptides.     

Molecular imprinting of peptides and proteins in aqueous media

Molecular imprinting has received significant attention in recent years, as it provides a viable method for creating synthetic receptors capable of selectively recognizing specific target molecules. Despite significant growth within the field, the majority of template molecules studied thus far have been characterized by their low molecular weight and insolubility in aqueous systems. In biological systems, molecular recognition events occur in aqueous media. Therefore, in order to create molecularly imprinted polymers capable of mimicking biological processes, it is necessary to synthesize artificial receptors which can selectively recognize their respective target biological macromolecules such as peptides and proteins in aqueous media. In this review, we discuss the challenges associated with the imprinting of peptides and proteins in aqueous media. In addition, we discuss the significant progress which has been made within the field.     

Nucleic Acid/Organic Polymer Hybrid Materials: Synthesis,Superstructures, and Applications

Extensive efforts have been devoted to the development of hybrid structures consisting of biomacromolecules and organic polymers connected through covalent bonds. While the combination of proteins and peptides with synthetic macromolecules has been explored in depth, far fewer examples of nucleic acid/polymer hybrids are known. In this Review we give selected examples of this exciting class of materials which can be arranged as linear block copolymer architectures, as side‐chain polymers, or as cross‐linked networks. Emphasis is placed on the fabrication of these materials as well as on their potential applications in nanoscience, diagnostics, and biomedicine.     

Recent advances in the syntheses of radical‐containing macromolecules

Tailor‐made polymers containing specific chemical functionalities have ushered in a number of emerging fields in polymer science. In most of these next‐generation applications the focus of the community has centered upon closed‐shell macromolecules. Conversely, macromolecules containing stable radical sites have been less studied despite the promise of this evolving class of polymers. In particular, radical‐containing macromolecules have shown great potential in magnetic, energy storage, and biomedical applications. Here, the progress regarding the syntheses of open‐shell containing polymers are reviewed in two distinct subclasses. In the first, the syntheses of radical polymers (i.e., materials composed of non‐conjugated macromolecular backbones and with open‐shell units present on the polymer pendant sites) are described. In the second, polyradical (i.e., macromolecules containing stabilized radical sites either within the macromolecular backbone or those containing radical sites that are stabilized through a large degree of conjugation) synthetic schemes are presented. Thus, the state‐of‐the‐art in open‐shell macromolecular syntheses will be reported and future means by which to advance the current archetype will be discussed. By detailing the synthetic pathways possible for, and the inherent synthetic limitations of, the creation of these functional polymers, the community will be able to extend the bounds of the radical‐containing macromolecular paradigm. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1875–1894     

Advances in polymer precursors and bio‐based polymers synthesized from 5‐hydroxymethylfurfural

In recent years, considerable efforts have been made regarding the synthesis of renewable chemicals from natural resources. 5‐hydroxymethylfurfural (HMF) is an interesting platform chemical which has been widely exploited due to its rich chemistry and potential availability. The versatility of HMF has been demonstrated in several areas such as fine chemicals, biofuel precursors, and polymers. In particular, the potential to replace petroleum‐based analogues in the preparation of polymers associated with high performance has been observed owing to the structural rigidity of furan rings. This review aims at critically discuss the current research studies related to the derivatives of HMF, alongside with the synthesis and characterization of (co‐) polymers derived from HMF and its derivatives. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1478–1492     

Triazine‐Based Sequence‐Defined Polymers with Side‐Chain Diversity and Backbone–Backbone Interaction Motifs

Sequence control in polymers, well‐known in nature, encodes structure and functionality. Here we introduce a new architecture, based on the nucleophilic aromatic substitution chemistry of cyanuric chloride, that creates a new class of sequence‐defined polymers dubbed TZPs. Proof of concept is demonstrated with two synthesized hexamers, having neutral and ionizable side chains. Molecular dynamics simulations show backbone–backbone interactions, including H‐bonding motifs and pi–pi interactions. This architecture is arguably biomimetic while differing from sequence‐defined polymers having peptide bonds. The synthetic methodology supports the structural diversity of side chains known in peptides, as well as backbone–backbone hydrogen‐bonding motifs, and will thus enable new macromolecules and materials with useful functions.     

Evidence for coupling and decoupling of parts of macromolecules by temperature‐modulated calorimetry

Equilibrium crystals of linear macromolecules have an extended‐chain macroconformation. They can melt at the equilibrium melting temperature, whereas crystallization needs considerable supercooling, even in the presence of crystal nuclei, making the overall phase transition irreversible. The same molecules with a metastable, chain‐folded macroconformation may have a large amount of specific reversibility, that is, a fraction of the same polymer molecule that melts irreversibly may also show decoupled, reversible melting. The overall metastable, nanophase structure of such semicrystalline polymers may thus support local equilibria. The tool for the quantitative analysis is quasi‐isothermal temperature‐modulated calorimetry that can separate reversible from irreversible processes. A major review of the study of crystals of more than 20 polymers has been published. On the basis of this extensive body of information, a first discussion of decoupling of parts of macromolecules is attempted and linked to previous studies of phase equilibria. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1275–1288, 2004     

Synthetic Strategies for Constructing Two‐Dimensional Metal‐Organic Layers (MOLs): A Tutorial Review

Two‐dimensional (2D) metal‐organic layers (MOLs) are the 2D version of metal‐organic frameworks (MOFs) with nanometer thickness in one dimension. MOLs are also known as 2D‐MOFs, 2D coordination polymers, ultrathin MOF nanosheets (UMOFNs) or coordination nanosheets in literature. This new category of 2D materials has attracted a lot of interests because of the opportunity in combining molecular chemistry, surface/interface chemistry and material chemistry of low dimensional materials in these systems. Several synthetic strategies have been developed for the construction of 2D MOLs, but the general synthesis of MOLs still presents a challenge. This tutorial level review summarizes the recent progress in the fabrication of novel 2D MOLs and aims to highlight challenges in this field.     

Photoresponsive Circular Supramolecular Polymers: A Topological Trap and Photoinduced Ring‐Opening Elongation

Topological features of one‐dimensional macromolecular chains govern the properties and functionality of natural and synthetic polymers. To address this issue in supramolecular polymers, we synthesized two topologically distinct supramolecular polymers with intrinsic curvature, circular and helically folded nanofibers, from azobenzene‐functionalized supramolecular rosettes. When a mixture of circular and helically folded nanofibers was exposed to UV light, selective unfolding of the latter open‐ended supramolecular polymers was observed as a result of the curvature‐impairing internal force produced by the trans‐to‐cis photoisomerization of the azobenzene. This distinct sensitivity suggests that the topological features of supramolecular polymers define their mechanical stability. Furthermore, the exposure of circular supramolecular polymers in more polar media to UV irradiation resulted in ring opening followed by chain elongation, thus demonstrating that the circular supramolecular polymer can function as a topological kinetic trap.     

Reactive modifications of some chain‐ and step‐growth polymers with phosphorus‐containing compounds: effects on flame retardance—a review

This article reviews the recent developments in the synthetic strategies to chemically modify several chain‐growth polymers that were primarily developed in our laboratories, with a view to improve their flame retardance. In addition, it also incorporates the corresponding methodologies for the step‐growth thermoplastics and thermoset materials. For chain‐growth polymers, this involves primarily copolymerization reactions, under radical initiation, of acrylic or styrenic monomers with phosphorus‐containing comonomers, or optionally, by post‐modification reactions on preformed olefinic polymeric substrates with appropriate phosphorus‐containing reagents. In the case of step‐growth polymers, generally, an appropriate phosphorus‐bearing moiety is employed, as one of the reactive components, during the step‐growth synthetic process. The relative predominance of vapor‐ and condensed‐phase mechanisms of flame retardance in the modified systems was evaluated through a combination of various analytical techniques. It was found that incorporation of phosphorus, through chemical modification reactions, on to the various thermoplastics resulted in substantial increases in the flame retardation. Furthermore, mechanistic aspects of flame retardation revealed both vapor‐phase and condensed‐phase elements depending on the chemical nature of the parent polymer in question and to a lesser extent on the chemical environment of the phosphorus‐bearing moiety. Copyright © 2011 John Wiley & Sons, Ltd.     

GRAFT COPOLYMERIZATION OF CELLULOSE,CELLULOSE DERIVATIVES,AND LIGNOCELLULOSE

Abstract

The growth of polymer science has led to the development of new materials in direct competition with natural materials, many of which have been in use since earliest times. This has caused researchers to look more critically at both natural and synthetic macromolecules in order to learn more about their underlying structures and their relation to the properties exhibited by the macromolecules. In this regard, chemical modifications have been devised to impart certain desirable properties of both natural and synthetic macromolecules, and their applications have become an integral part of such chemical modifications. Various chemical modifications (e.g., change of functionality, oxidative degradation, inter- and intramolecular gelation, graft copolymerization), have been practiced to add improved properties to the base polymers. However, among all these methods, modification of polymers via graft copolymerization has been the subject of much interest and has made paramount contribution toward improved industrial and biomedical applications.     

Nano‐Star‐Shaped Polymers for Drug Delivery Applications

With the advancement of polymer engineering, complex star‐shaped polymer architectures can be synthesized with ease, bringing about a host of unique properties and applications. The polymer arms can be functionalized with different chemical groups to fine‐tune the response behavior or be endowed with targeting ligands or stimuli responsive moieties to control its physicochemical behavior and self‐organization in solution. Rheological properties of these solutions can be modulated, which also facilitates the control of the diffusion of the drug from these star‐based nanocarriers. However, these star‐shaped polymers designed for drug delivery are still in a very early stage of development. Due to the sheer diversity of macromolecules that can take on the star architectures and the various combinations of functional groups that can be cross‐linked together, there remain many structure–property relationships which have yet to be fully established. This review aims to provide an introductory perspective on the basic synthetic methods of star‐shaped polymers, the properties which can be controlled by the unique architecture, and also recent advances in drug delivery applications related to these star candidates.     

Recognition of proteins and peptides: Rational development of molecular imprinting technology

The creation of tailor-made receptors which are able to recognize molecular targets with high affinity and selectivity has attracted much attention in the field of chemistry, physics, and biology. Molecular imprinting has proved to be an effective technique for generating specific recognition sites in synthetic polymers. The synthesis of molecular imprinted polymers specific for proteins and peptides has been a focus for many scientists working in the area of molecular recognition, since the creation of synthetic polymers that can specifically recognize biomacromolecules is a very challenging but potentially extremely rewarding work. These polymers with specificity for biological macromolecules have considerable potential for applications in the areas of solid phase extraction, catalysis, medicine, clinical analysis, drug delivery, environmental monitoring, and sensors. In this review, the authors discuss the developed approaches associated with the imprinting of peptides and proteins, and provide an overview of the significant progress achieved within this field. Finally, the possible mechanism of the molecular imprinting and recognition has been discussed.     

Self‐assembly of supramolecular polymers into tunable helical structures

There is growing interest in the design of synthetic molecules that are able to self‐assemble into a polymeric chain with compact helical conformations, which is analogous to the folded state of natural proteins. Herein, we highlight supramolecular approach to the formation of helical architectures and their conformational changes driven by external stimuli. Helical organization in synthetic self‐assembling systems can be achieved by the various types of noncovalent interactions, which include hydrogen bonding, solvophobic effects, and metal‐ligand interactions. Since the external environment can have a large influence on the strength and configuration of noncovalent interactions between the individual components, stimulus‐induced alterations in the intramolecular noncovalent interactions can result in dynamic conformational change of the supramolecular helical structure thus, driving significant changes in the properties of the materials. Therefore, these supramolecular helices hold great promise as stimuli‐responsive materials. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1925–1935, 2008     

Strategies in two‐dimensional liquid chromatographic separation of complex polymer systems

Complex synthetic polymer systems as for example copolymers exhibit distributions in at least two of the three basic molecular characteristics which are molar mass, chemical structure/composition and molecular architecture. Size exclusion chromatography (SEC) separates macromolecules according to their size in solution which simultaneously depends on all molecular characteristics. Therefore, multi‐dimensional liquid chromatographic techniques are to be applied to independently assess all different distributions present in the sample. So far, two‐dimensional separations have been attempted. In the first dimension separation column, selected liquid chromatographic mechanisms are intentionally combined to suppress effects of all but one molecular characteristic. Consequently, polymer species are separated exclusively or at least predominantly according to one single parameter. In the second dimension separation column, macromolecules are separated according to another molecular characteristic. In this contribution the methods are briefly reviewed in which effect of polymer molar mass on polymer retention is suppressed. The resulting ”one parameter separation systems” can be on‐line or off‐line connected to another separation system such as SEC to provide more detailed characterization of complex polymers. Besides, selected procedures for the re‐concentration of diluted polymer solutions are concisely treated. These may be utilized for increasing the concentration of sample(s) leaving the first dimension separation column. Eventually, some arrangements for controlled sample re‐introduction into the second dimension separation column are outlined.     

Controlling open‐shell loading in norbornene‐based radical polymers modulates the solid‐state charge transport exponentially

Radical polymers are an emerging class of electronically active macromolecules; however, the fundamental mechanism by which charge is transferred in these polymers has yet to be established in full. To address this issue, well‐defined norbornene‐based nitroxide radical polymers were synthesized using the controlled ring‐opening metathesis polymerization technique. These polymers were blended in solution with a quenched, electrically insulating hydroxylamine derivative to dilute the radical content of the system. Electron paramagnetic resonance spectroscopy data were used to characterize the radical content as well as to reveal that hydrogen atom transfer occurred between the open‐shell and closed‐shell polynorbornene derivatives when they were blended in solution. Using these platform macromolecules, we demonstrate that the systematic manipulation of the radical content in open‐shell macromolecules leads to exponential changes in the macroscopic electrical conductivity. When coupled with the fact that these materials show a clear temperature‐independent charge transport behavior, a picture emerges that charge transfer in radical polymers is dictated by a tunneling mechanism between localized donor and acceptor sites within the redox‐active thin films. These results constitute the first experimental insight into the mechanism of solid‐state electrical conduction in radical polymers, and this provides a design paradigm for open‐shell macromolecular charge transport. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1516–1525