Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms - such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials - all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.

Biofilms: an emergent form of bacterial life.

▪ Abstract The Local Group dwarf galaxies offer a unique window to the detailed properties of the most common type of galaxy in the Universe. In this review, I update the census of Local Group dwarfs based on the most recent distance and radial velocity determinations. I then discuss the detailed properties of this sample, including (a) the integrated photometric parameters and optical structures of these galaxies, (b) the content, nature, and distribution of their interstellar medium (ISM), (c) their heavy-element abundances derived from both stars and nebulae, (d) the complex and varied star-formation histories of these dwarfs, (e) their internal kinematics, stressing the relevance of these galaxies to the “dark matter problem” and to alternative interpretations, and (f) evidence for past, ongoing, and future interactions of these dwarfs with other galaxies in the Local Group and beyond. To complement the discussion and to serve as a foundation for future work, I present an extensive set of basic observ...

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Dwarf galaxies of the local group

We have developed a transparent organic polymeric material that can repeatedly mend or "re-mend" itself under mild conditions. The material is a tough solid at room temperature and below with mechanical properties equaling those of commercial epoxy resins. At temperatures above 120 degrees C, approximately 30% (as determined by solid-state nuclear magnetic resonance spectroscopy) of "intermonomer" linkages disconnect but then reconnect upon cooling, This process is fully reversible and can be used to restore a fractured part of the polymer multiple times, and it does not require additional ingredients such as a catalyst, additional monomer, or special surface treatment of the fractured interface.

https://science.sciencemag.org/content/sci/295/5560/1698.full.pdf

A Thermally Re-mendable Cross-Linked Polymeric Material

Dynamic covalent chemistry relates to chemical reactions carried out reversibly under conditions of equilibrium control. The reversible nature of the reactions introduces the prospects of "error checking" and "proof-reading" into synthetic processes where dynamic covalent chemistry operates. Since the formation of products occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. In kinetically controlled reactions, however, it is the free energy differences between the transition states leading to the products that determines their relative proportions. Supramolecular chemistry has had a huge impact on synthesis at two levels: one is noncovalent synthesis, or strict self-assembly, and the other is supramolecular assistance to molecular synthesis, also referred to as self-assembly followed by covalent modification. Noncovalent synthesis has given us access to finite supermolecules and infinite supramolecular arrays. Supramolecular assistance to covalent synthesis has been exploited in the construction of more-complex systems, such as interlocked molecular compounds (for example, catenanes and rotaxanes) as well as container molecules (molecular capsules). The appealing prospect of also synthesizing these types of compounds with complex molecular architectures using reversible covalent bond forming chemistry has led to the development of dynamic covalent chemistry. Historically, dynamic covalent chemistry has played a central role in the development of conformational analysis by opening up the possibility to be able to equilibrate configurational isomers, sometimes with base (for example, esters) and sometimes with acid (for example, acetals). These stereochemical "balancing acts" revealed another major advantage that dynamic covalent chemistry offers the chemist, which is not so easily accessible in the kinetically controlled regime: the ability to re-adjust the product distribution of a reaction, even once the initial products have been formed, by changing the reaction's environment (for example, concentration, temperature, presence or absence of a template). This highly transparent, yet tremendously subtle, characteristic of dynamic covalent chemistry has led to key discoveries in polymer chemistry. In this review, some recent examples where dynamic covalent chemistry has been demonstrated are shown to emphasise the basic concepts of this area of science.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3773%2820020503%2941%3A9%3C1460%3A%3AAID-ANIE11111460%3E3.0.CO%3B2-N

Dynamic covalent chemistry.

/pdf/degradable-controlled-release-polymers-and-polymeric-1y322ha58z.pdf

Degradable Controlled-Release Polymers and Polymeric Nanoparticles: Mechanisms of Controlling Drug Release

Alginate is an elastic irreversible hydrocolloid, widely used for recording the impressions of dentulous arches, impressions for making models for diagnostic purposes, and for duplication of casts. Today, their use far exceeds the use of all other impression materials in general dental practice because of their hydrophilicity, ability to record finer details and sufficient elastic recovery. Over the years, several modifications have been done to improve their clinical performance. Modified alginates in form of dust
free, self-disinfectant and chromalginate have already been in the clinical practice and have shown their superiority over the conventional alginates. In addition to these modifications, other modifications have been introduced to further improve their clinical acceptance. This review is an overview of the evolution of dental alginate impression materials with an emphasis on the material aspects.

/pdf/terminology-for-biorelated-polymers-and-applications-iupac-3q2231bk35.pdf

Terminology for biorelated polymers and applications (IUPAC Recommendations 2012)

Styrene copolymers containing various amounts of a novel comonomer bearing a pendant furan ring were synthesized and characterized before being submitted to Diels−Alder reactions with either a monomaleimide or a bismaleimide. Spectroscopic evidence, supported by data from model compounds, indicated that the resulting linear and cross-linked products contained extensive percentages of adduct structures formed from the furan moieties. Both types of materials were then heated in a solvent containing a large excess of 2-methylfuran in order to induce the retro-Diels−Alder and the coupling of the released maleimides with the furanic additive. The reaction proceeded as expected and the original copolymers could be recovered from the treatment. The interest in the general strategy reported here resides in the possibility of recycling cross-linked polymers by a simple thermal treatment conducted in the presence of a suitable trap.

Application of the Diels−Alder Reaction to Polymers Bearing Furan Moieties. 2. Diels−Alder and Retro-Diels−Alder Reactions Involving Furan Rings in Some Styrene Copolymers

Entropically driven ring-opening polymerization of strainless organic macrocycles.

A number of liquid-crystalline siloxane derivatives based on the 4-(ω-alkenyloxy)-4′-cyanobiphenyl mesogenic unit have been prepared and their phase-transitional properties characterised. The compounds were synthesized by the addition of the 4-(ω-alkenyloxy)-4′-cyanobiphenyl moiety to pentamethyldisiloxane catalysed by a platinum divinyltetramethyldisiloxane complex. The materials are denoted ABs where A refers to the number of methylene groups in the 4-(ω-alkenyloxy)-4′-cyanobiphenyl and B refers to the number of silicon atoms in the siloxane unit. With the exception of 3/2 and 4/2, which exhibit only monotropic phase transitions, all these materials exhibit an enantiotropic smectic A phase. Preliminary X-ray results also support this. The thermal properties of this new series of thermotropic liquid-crystalline siloxanes were studied by differential scanning calorimetry (DSC) and polarising microscopy. The transitional properties for the AB series exhibit a pronounced odd–even effect with the length of the alkyl segment.

Synthesis and properties of low-molar-mass liquid-crystalline siloxane derivatives

The synthesis of organic compounds using polymer-supported catalysts, reagents, and/or scavengers, so that the required product is always in solution, has been of great interest in recent years, especially in connection with pharmaceutical research. To date, the reactions have almost always been carried out in batch mode. It is now timely to consider developing them further and carrying them out using flow systems. Advantages of flow systems typically include the following:  there is little or no reaction workup, the support suffers no physical damage in use, automation is relatively easy, and extension to continuous production, even on a large scale, is a possibility. This paper gives a brief background on previous work using polymer-supported catalysts, reagents, and/or scavengers and then reviews in detail the work that has been done to date using these reactants in flow systems. It identifies some of the problems encountered and indicates how they might be solved. Rapid progress requires collaboration...

Philip Hodge

Papers

Terminology for biorelated polymers and applications (IUPAC Recommendations 2012)

Application of the Diels−Alder Reaction to Polymers Bearing Furan Moieties. 2. Diels−Alder and Retro-Diels−Alder Reactions Involving Furan Rings in Some Styrene Copolymers

Entropically driven ring-opening polymerization of strainless organic macrocycles.

Synthesis and properties of low-molar-mass liquid-crystalline siloxane derivatives

Synthesis of Organic Compounds Using Polymer-Supported Reagents, Catalysts, and/or Scavengers in Benchtop Flow Systems†