Supramolecular Polymers: Inherently Dynamic Materials.

ConspectusSince its inception in the early 1990s, the field of supramolecular polymers (SPs) has grown into an interdisciplinary field of chemistry. It expanded from the self-assembly of molecular building blocks based on H-bonding into the realm of complex dynamic material, encompassing both supramolecular noncovalent and molecular covalent regimes. It has paved the path for a more diverse field of research into a new class of polymeric materials, coined dynamic polymers or dynamers. Dynamers are bringing a paradigm shift not only in material science research but also in a broad field of applications from self-healing materials to biocompatible polymeric materials. The present Account presents the evolution of supramolecular polymer chemistry from simple linear polymeric chains to complex dynamic polymers imparting novel functional properties, such as component exchange and self-healing. We explore how SPs led to materials of increasing complexity, starting from simple main-chain polymers to the formation of more complex columnar SPs and lateral SPs. The field has experienced three partially overlapping periods. The main goal was first the generation of polymeric entities from various molecular components connected through noncovalent interactions, especially complementary hydrogen bonding recognition patterns as well as stacked columnar SPs. Thereafter, attention was directed in parallel to the exploration of the properties of SPs and their applications as novel materials. In a third period, the dynamic properties of supramolecular polymers were explored, taking advantage of the lability of noncovalent interactions to perform component rearrangement and exchange. We illustrate how the field of SPs has emerged as a multidisciplinary field of chemistry, biology, and materials science with selected examples from the literature. The SPs, specifically dynamic owing to their inherent reversibility, also pave the path to easier sorting and recycling, as desired in the plastics industry.One of the biggest challenges that the plastics industry is facing today is the end-of-life fate of plastics. Plastics that cannot be recycled end up in landfills or are improperly disposed of in rivers and oceans, polluting and damaging the environmental balance irreversibly. Dynamic polymeric materials presenting inherent dynamicity could pave the way for addressing this long-standing challenge of nonrecyclability of plastics. Dynamers formed via noncovalent interactions or reversible covalent bonds can be broken into components that could be easily recycled and reused. Therefore, dynamers could play a pivotal role toward closing the loop for the plastics industry and provide a solution to an elusive circular economy with plastics being an integral part.

Molecular mapping of drought-responsive QTLs during the reproductive stage of rice using a GBS (genotyping-by-sequencing) based SNP linkage map.

BACKGROUND: In rice, drought stress at reproductive stage drastically reduces yield, which in turn hampers farmer's efforts towards crop production. The majority of the rice varieties have resistance genes against several abiotic and biotic stresses. Therefore, the traditional landraces were studied to identify QTLs/candidate genes associated with drought tolerance. METHODS AND RESULTS: A high-density SNP-based genetic map was constructed using a Genotyping-by-sequencing (GBS) approach. The recombinant inbred lines (RILs) derived from crossing 'Banglami × Ranjit' were used for QTL analysis. A total map length of 1306.424 cM was constructed, which had an average inter-marker distance of 0.281 cM. The phenotypic evaluation of F6 and F7 RILs were performed under drought stress and control conditions. A total of 42 QTLs were identified under drought stress and control conditions for yield component traits explaining 1.95-13.36% of the total phenotypic variance (PVE). Among these, 19 QTLs were identified under drought stress conditions, whereas 23 QTLs were located under control conditions. A total of 4 QTLs explained a PVE ≥ 10% which are considered as the major QTLs. Moreover, bioinformatics analysis revealed the presence of 6 candidate genes, which showed differential expression under drought and control conditions. CONCLUSION: These QTLs/genes may be deployed for marker-assisted pyramiding to improve drought tolerance in the existing rice varieties.

Small-Molecule Investigation of Diels-Alder Complexes for Thermoreversible Crosslinking in Polymeric Applications.

Combinations of dienes and dienophiles were examined in order to elicit possible combinations for thermoreversible crosslinking units. Comparison of experimental results and quantum calculations indicated that reaction kinetics and activation energy were much better prediction factors than change in enthalpy for the prediction of successful cycloaddition. Further testing on diene-dienophile pairs that underwent successful cycloaddition determined the feasibility of thermoreversibility/retro-reaction of each of the Diels-Alder compounds. Heating and testing of the compounds in the presence of a trapping agent allowed for experimental determination of reverse kinetics and activation energy for the retro-reaction. The experimental values were in good agreement with quantum calculations. The combination of chemical calculations with experimental results provided a strong insight into the structure-property relationships and how quantum calculations can be used to examine the feasibility of the thermoreversibility of new Diels-Alder complexes in potential polymer systems or to fine-tune thermoreversible Diels-Alder systems already in use.

An Easily Accessible Self-Healing Transparent Film Based on a 2D Supramolecular Network of Hydrogen-Bonding Interactions between Polymeric Chains.

Self-healing polymers hold great promise for the future, enhancing in particular the longevity of polymeric materials. We describe a self-healing covalent polymer, presenting an extensive array of hydrogen-bonding sites based on the combination of urea, urethane, and bis-acyl-hydrazine units. Solvent-cast thin-films prepared by polycondensation of a commercially available dihydrazide and a diisocyanate prepolymer exhibited excellent room temperature autonomous healing with almost full recovery of mechanical properties when two parts of a cut film were overlapped and gently pressed together. This autonomous healing upon damage may be attributed to the supramolecular dynamics of multiple lateral inter-chain hydrogen-bonding interactions between the polymer chains. The solid-state structure of a model compound incorporating the same structural backbone corroborates the existence of an extensive two-dimensional supramolecular hydrogen-bonding network.

DYNAMERS: dynamic polymers as self-healing materials.

Importing self-repair or self-healing features into inert materials is of great relevance to material scientists, since it is expected to eliminate the necessity of replenishing a damaged material. Be it material chemistry or more specifically polymer chemistry, such materials have attracted the imagination of both material scientists and chemists. A stroll down the memory lane 70 years back, this might have sounded utopian. However with the current progress in supramolecular chemistry and the emergence of dynamic covalent and non-covalent chemistries, novel perspectives have been opened up to materials science towards the development of dynamic materials (DYNAMATS) and in particular dynamic polymers (DYNAMERS), with the ability to produce such species by custom made designs. Chemistry took giant strides to gain control over the structure and features of materials and, besides basic progress, to apply it for tailor-making matter for applications in our daily life. In that applied perspective, materials science plays a paramount role in shaping our present and in contributing to a sustainable future. The goal is to develop materials, which would be dynamic enough to carry out certain functions as effectively as in biological systems with, however, the freedom to recruit the powers of chemistry on a wider scale, without the limitation imposed by life. Material scientists and in particular polymer chemists may build on chemistry, physics and biology for bridging the gap to develop dynamic materials presenting a wide range of novel functionalities and to convert dreams into reality. In this current review we will focus on developments in the area of dynamic polymers, as a class of dynamic materials presenting self-healing features and, more generally, the ability to undergo adaptation under the effect of physical and/or chemical agents, and thus function as adaptive polymers or ADAPTAMERS.

The tris-urea motif and its incorporation into polydimethylsiloxane-based supramolecular materials presenting self-healing features.

Materials of supramolecular nature have attracted much attention owing to their interesting features, such as self-reparability and material robustness, that are imparted by noncovalent interactions to synthetic materials. Among the various structures and synthetic methodologies that may be considered for this purpose, the introduction of extensive arrays of multiple hydrogen bonds allows for the formation of supramolecular materials that may, in principle, present self-healing behavior. Hydrogen bonded networks implement dynamic noncovalent interactions. Suitable selection of structural units gives access to novel dynamic self-repairing materials by incrementing the number of hydrogen-bonding sites present within a molecular framework. Herein, we describe the formation of a tris-urea based motif giving access to six hydrogen-bonding sites, easily accessible through reaction of carbohydrazide with an isocyanate derivative. Extension towards the synthesis of multiply hydrogen-bonded supramolecular materials has been achieved by polycondensation of carbohydrazide with a bis-isocyanate component derived from poly-dimethylsiloxane chains. Such materials underwent self-repair at a mechanically cut surface. This approach gives access to a broad spectrum of materials of varying flexibility by appropriate selection of the bis-isocyanate component that forms the polymer backbone.

Trivalent iron and ruthenium complexes with a redox noninnocent (2-mercaptophenylimino)-methyl-4,6-di-tert-butylphenolate(2-) ligand.

The 3,5-di-tert-butyl substituted N-(salicylidene)-o-mercaptoaniline (H(2)L) ligand reacted with equimolar amounts of FeBr(2) and 2 equiv of triethylamine in air affords [Fe(III)(L-L)Br](0) (1), where (L-L)(2-) is a pentacoordinate ligand formed from the oxidative dimerization of L(2-) via disulfide bridge formation. Reaction of H(2)L with RuCl(3) x H(2)O and NEt(3) gives a dark green-brown dinuclear complex, [Ru(III)(2)(L)(2)Cl(2)(NCCH(3))(2)](0) (2). Both complexes have been characterized by X-ray crystallography. A Ru-Ru single bond is evident in 2. Complex 1 has also been characterized by electron paramagnetic resonance and Mossbauer spectroscopies and magnetic susceptibility measurements that identify a high-spin Fe(III) (S = (5)/(2)) center. Diamagnetic 2 is successively twice reversibly one-electron oxidized to produce [Ru(III)(2)(L(*))(L)Cl(2)(NCCH(3))(2)](+), [2](+) (S = (1)/(2)), and [Ru(III)(2)(L(*))(2)Cl(2)(NCCH(3))(2)](2+), [2](2+) (S = 0). Spectroelectrochemical and electron paramagnetic resonance measurements identify these as ligand-based oxidations affording o-coordinated phenoxyl radicals. DFT calculations on the electron transfer series corroborate this result and that the Ru-Ru single bond is retained throughout this series.

Molecular and electronic structure of the square planar bis(o-amidobenzenethiolato)iron(III) anion and its bis(o-quinoxalinedithiolato)iron(III) analogue.

Crystalline purple [PPh4][FeIIIL2] (1), where L2- represents the closed-shell dianion of 4,6-di-tert-butyl-2-[(pentafluorophenyl)amino]benzenethiol, has been synthesized from the reaction of H2L and FeBr2 (2:1) in acetonitrile with excess NEt3, careful, brief exposure of the solution to air, and addition of [PPh4]Br. The monoanion has been shown by X-ray crystallography to be square planar. The oxidation of 1 with 1 equiv of iodine produces the neutral species [FeI(L*)2]0 (2) where (L*)1- represents the one-electron oxidized pi radical anion of L2-. The reaction of H2Land PtCl2 (2:1) and NEt3 in CH3CN in the presence of air produced green, crystalline [PtII(L*)2] (3). From temperature dependent(2-300 K) magnetic susceptibility measurements, it was established that 1 possesses a central intermediate spin ferric ion (SFe ) 3/2), whereas neutral 2 has a doublet ground state (St ) 1/2) comprising an intermediate spin ferric ion coupled antiferromagnetically to two ligand pi radicals (L*)1- (Srad ) 1/2). Complex 3 is diamagnetic. Almeida et al.'s complexes in ref 1, [N(n-Bu)4][FeIII(qdt)2] (A), and [PPh4]2[FeIII2(qdt)4] (B), have been revisited. It is shown here that the square planar anion in mononuclear [FeIII(qdt)2]- also possesses an SFe ) 3/2 ground state. The zero-field Mössbauer spectra of 1, 2, A, and B have been recorded and the molecular and electronic structures of all mononuclear iron species have been calculated by density functional theoretical methods.It is shown that the S ) 3/2 ground state in 1 and A is lower in energy by 8.5 and 16.6 kcal mol(-1), respectively,than the S ) 1/2 state.

EGFR gene regulation in colorectal cancer cells by garlic phytocompounds with special emphasis on S-Allyl-L-Cysteine Sulfoxide.

Colorectal cancer is one among the most common cancers in the world and a major cause of cancer related deaths. Similar to other cancers, colorectal carcinogenesis is often associated with over expression of genes related to cell growth and proliferation, especially Epidermal Growth Factor Receptor (EGFR). There is an increasing attention towards the plant derived compounds in prevention of colorectal carcinogenesis by downregulating EGFR. Among plants, garlic (Allium sativum L.) is emerging with anticancer properties by virtue of its organosulfur compounds. The present study was aimed to analyze the interaction ability of garlic compounds in the active region of EGFR gene by in silico molecular docking studies and in vitro validation. This was conducted using the Discovery studio software version 4.0. Among the tested compounds, s-allyl-l-cysteine-sulfoxide (SACS)/alliin showed higher affinity towards EGFR. Furthermore, wet lab analysis using cell viability test and EGFR expression analysis in colorectal cancer cells confirmed its efficacy as a potent anticancer agent.

Garlic Phytocompounds Possess Anticancer Activity by Specifically Targeting Breast Cancer Biomarkers - an in Silico Study.

BACKGROUND: Breast cancer (BC) is a serious lifestyle disease. There are several prognostic biomarkers like nuclear receptors whose over-expression is associated with BC characteristics. These biomarkers can be blocked by compounds with anti-cancer potential but selection must be made on the basis of no adverse side effects. This study is focused on finding of compounds from a plant source garlic. MATERIALS AND METHODS: Twenty compounds from garlic and five targets considered involved in BC were retrieved from Pubchem database and Protein Data Bank respectively. They were docked using Accelrys Discovery Studio (DS) 4.0. The compounds which showed interaction were checked for drug likeliness. RESULTS: Docking studies and ADMET evaluation revealed twelve compounds to be active against the targets. All the compounds displayed highly negative dock scores which indicated good interactions. CONCLUSIONS: The results of this study should help researchers and scientists in the pharmaceutical field to identify drugs based on garlic.

Plant Phenolics Ferulic Acid and P-Coumaric Acid Inhibit Colorectal Cancer Cell Proliferation through EGFR Down-Regulation.

BACKGROUND: Colorectal cancer (CRC) or bowel cancer is one of the most important cancer diseases, needing serious attention. The cell surface receptor gene human epidermal growth factor receptor (EGFR) may have an important role in provoking CRC. In this pharmaceutical era, it is always attempted to identify plant-based drugs for cancer, which will have less side effects for human body, unlike the chemically synthesized marketed drugs having serious side effects. So, in this study the authors tried to assess the activity of two important plant compounds, ferulic acid (FA) and p-coumaric acid (pCA), on CRC. MATERIALS AND METHODS: FA and pCA were tested for their cytotoxic effects on the human CRC cell line HCT 15 and also checked for the level of gene expression of EGFR by real time PCR analysis. Positive results were confirmed by in silico molecular docking studies using Discovery Studio (DS) 4.0. The drug parallel features of the same compounds were also assessed in silico. RESULTS: Cytotoxicity experiments revealed that both the compounds were efficient in killing CRC cells on a controlled concentration basis. In addition, EGFR expression was down-regulated in the presence of the compounds. Docking studies unveiled that both the compounds were able to inhibit EGFR at its active site. Pharmacokinetic analysis of these compounds opened up their drug like behaviour. CONCLUSIONS: The findings of this study emphasize the importance of plant compounds for targeting diseases like CRC.

Dynamic covalent chemistry: a facile room-temperature, reversible, Diels-Alder reaction between anthracene derivatives and N-phenyltriazolinedione.

A series of readily accessible, dynamic Diels-Alder reactions that are reversible at room temperature have been developed between anthracene derivatives as dienes and N-phenyl-1,2,4-triazoline-3,5-dione as the dienophile. The adducts formed undergo reversible component exchange to form dynamic libraries of equilibrating cycloadducts. Furthermore, reversible adduct formation allows temperature-dependent modulation of the fluorescent properties of anthracene components; a feature of potential interest for the design of optodynamic polymeric materials by careful selection and manipulation of these simple dienes and dienophiles.