Controlling the Assembly of Cellulose-Based Oligosaccharides through Sequence Modifications

Peptides and nucleic acids with programmable sequences are widely explored for the production of tunable, self-assembling functional materials. Herein we demonstrate that the primary sequence of oligosaccharides can be designed to access materials with tunable shapes and properties. Synthetic cellulose-based oligomers were assembled into 2D or 3D rod-like crystallites. Sequence modifications within the oligosaccharide core influenced the molecular packing and led to the formation of square-like assemblies based on the rare cellulose IV_II allomorph. In contrast, modifications at the termini generated elongated aggregates with tunable surfaces, resulting in self-healing supramolecular hydrogels.     

A General Organophotoredox Strategy to Difluoroalkyl Bicycloalkane (CF2-BCA) Hybrid Bioisosteres**

Here, we report a general approach to the synthesis of the difluoroalkyl bicycloalkanes (CF₂-BCAs), as structural surrogates of aryl ketones and ethers. The chemistry is driven by a dihydrobenzoacridine photocatalyst, that engages in a catalytic electron-donor acceptor (EDA) complex, or directly reduces the fluorinated substrate. These two convergent manifolds lead to the generation of the R-CF₂ radical, that reacts with the [1.1.1]- or [3.1.1.]-propellane. The method is extremely general, and extendable to complex bioactive molecules (30 examples, up to 87 % yield). The structural features of the CF₂-BCP hybrid bioisostere were investigated by single crystal X-ray. Finally, we synthesised a CF₂-BCP analogue of a Leukotriene A₄ hydrolase inhibitor, replacing the original aryl ether motif. In silico docking studies indicated that this new analogue maintains the same arrangement within the enzyme pocket, profiling the use of the CF₂-BCA hybrid bioisostere in medicinal chemistry settings.     

Preparation of coatings via cationic photopolymerisation: influence of alcoholic additives

Coatings obtained through photopolymerisation of vinylethers, propenyl ethers and epoxy resins are described. The influence of alcohols and of comonomers bearing OH groups on the cationic mechanism of the curing process is discussed. The final properties of the coatings are evaluated and correlated to the structures of the additives.     

Visualizing Chiral Interactions in Carbohydrates Adsorbed on Au(111) by High-Resolution STM Imaging

Carbohydrates are the most abundant organic material on Earth and the structural “material of choice” in many living systems. Nevertheless, design and engineering of synthetic carbohydrate materials presently lag behind that for protein and nucleic acids. Bottom-up engineering of carbohydrate materials demands an atomic-level understanding of their molecular structures and interactions in condensed phases. Here, high-resolution scanning tunneling microscopy (STM) is used to visualize at submolecular resolution the three-dimensional structure of cellulose oligomers assembled on Au(1111) and the interactions that drive their assembly. The STM imaging, supported by ab initio calculations, reveals the orientation of all glycosidic bonds and pyranose rings in the oligomers, as well as details of intermolecular interactions between the oligomers. By comparing the assembly of D- and L-oligomers, these interactions are shown to be enantioselective, capable of driving spontaneous enantioseparation of cellulose chains from its unnatural enantiomer and promoting the formation of engineered carbohydrate assemblies in the condensed phases.     

Mechanisms and Synthetic Strategies in Visible Light-Driven [2+2]-Heterocycloadditions

The synthesis of four membered heterocycles usually requires multi-step procedures and prefunctionalized reactants. A straightforward alternative is the photochemical [2+2]-heterocycloaddition between an alkene and a carbonyl derivative, conventionally based on the photoexcitation of this latter. However, this approach is limited by the absorption profile of the carbonyl, requiring in most of the cases the use of high-energy UV-light, that often results in undesired side reactions and/or the degradation of the reaction components. The development of new and milder visible light-driven [2+2]-heterocycloadditions is, therefore, highly desirable. In this Review, we highlight the most relevant achievements in the development of [2+2]-heterocycloadditions promoted by visible light, with a particular emphasis on the involved reaction mechanisms. The open challenges will also be discussed, suggesting new possible evolutions, and stimulating new methodological developments in the field.     

ChemInform Abstract: Derivation of Force Field Parameters,and Force Field and Quantum Mechanical Studies of Layered α- and γ-Zirconium Phosphates.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

New Vistas in Frontal Polymerization

Frontal Polymerization is a technique for the synthesis of polymers that, by exploiting the heat liberated by the self-same reaction, generates a hot front that can sustain and propagate itself from one end of the reactor to the other converting monomer into polymer. After the activation and following formation of the front, it is not necessary to provide any other form of energy in order to carry out polymerization. In this article we will summarize some of the recent results we have obtained in the application of Frontal Polymerization to the preparation of polyurethanes, unsaturated polyester resins, and polyacrylates.