High-fidelity Recognition of Organotrifluoroborate Anions (R−BF3−) as Designer Guest Molecules

The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF₃⁻). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF₃⁻, by cyanostar macrocycles that are size-complementary to the inorganic BF₄⁻ progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K⁺ salts of R−BF₃⁻ anions.     

On the Fundamental Polymer Chemistry of Inverse Vulcanization for Statistical and Segmented Copolymers from Elemental Sulfur

In this concept review, the fundamental and polymerization chemistry of inverse vulcanization for the preparation of statistical and segmented sulfur copolymers, which have been actively developed and advanced in various applications over the past decade is discussed. This concept review delves into a discussion of step-growth polymerization constructs to describe the inverse vulcanization process and discuss prepolymer approaches for the synthesis of segmented sulfur polyurethanes. Furthermore, this concept review discusses the advantages of inverse vulcanization in conjunction with dynamic covalent polymerization and post-polymerization modifications to prepare segmented block copolymers with enhanced thermomechanical and flame retardant properties of these materials.     

Galactose-Grafted 2D Nanosheets from the Self-Assembly of Amphiphilic Janus Dendrimers for the Capture and Agglutination of Escherichia coli

High aspect ratio, sugar-decorated 2D nanosheets are ideal candidates for the capture and agglutination of bacteria. Herein, the design and synthesis of two carbohydrate-based Janus amphiphiles that spontaneously self-assemble into high aspect ratio 2D sheets are reported. The unique structural features of the sheets include the extremely high aspect ratio and dense display of galactose on the surface. These structural characteristics allow the sheet to act as a supramolecular 2D platform for the capture and agglutination of E. coli through specific multivalent noncovalent interactions, which significantly reduces the mobility of the bacteria and leads to the inhibition of their proliferation. Our results suggest that the design strategy demonstrated here can be applied as a general approach for the crafting of biomolecule-decorated 2D nanosheets, which can perform as 2D platforms for their interaction with specific targets.     

Highly Efficient Ir(III)-Coumarin Photo-Redox Catalyst for Synergetic Multi-Mode Cancer Photo-Therapy

Four photo-catalysts of the general formula [Ir(CO6/ppy)₂(L)]Cl where CO6=coumarin 6 ( Ir1 – Ir3 ), ppy=2-phenylpyridine ( Ir4 ), L=4′-(3,5-di-tert-butylphenyl)-2,2′ : 6′,2′′-terpyridine ( Ir1 ), 4′-(3,5-bis(trifluoromethyl)phenyl)-2,2′ : 6′,2′′-terpyridine ( Ir2 and Ir4 ), and 4-([2,2′ : 6′,2′′-terpyridin]-4′-yl)-N,N-dimethylaniline ( Ir3 ) were synthesized and characterized. These photostable photo-catalysts ( Ir1 – Ir3 ) showed strong visible light absorption between 400–550 nm. Upon light irradiation (465 and 525 nm), Ir1 – Ir3 generated singlet oxygen and induced rapidly photo-catalytic oxidation of cellular coenzymes NAD(P)H. Ir1 – Ir3 showed time-dependent cellular uptake with excellent intracellular retention efficiency. Upon green light irradiation (525 nm), Ir2 provided a much higher photo-index (PI=793) than the clinically used photosensitizer, 5-aminolevulinicacid (5-ALA, PI>30) against HeLa cancer cells. The observed necro-apoptotic anticancer activity of Ir2 was due to the Ir2 triggered photo-induced intracellular redox imbalance (by NAD(P)H oxidation and ROS generation) and change in the mitochondrial membrane potential. Remarkably, Ir2 showed in vivo photo-induced catalytic anticancer activity in mouse models.     

Boron-Thioketonates: A New Class of S,O-Chelated Boranes as Acceptors in Optoelectronic Devices

Development of new n-type semiconductors with tunable band gap and dielectric constant has significant implication in dissociating bound charge carrier relevant for demonstrating high performance optoelectronic devices. Boron-β-thioketonates (MTDKB), analogues to boron-β-diketonates containing a sulfur atom in the framework of β-diketones were synthesized. Bulk transport measurement exhibited an outstanding bulk electron mobility of ≈0.003 cm² V⁻¹ s⁻¹, which is among the best values reported till date in these class of semiconducting materials and correspondingly a single junction photo responsivity of upto 6 mA W⁻¹ was obtained. This new family of O,S-chelated boron compounds exhibited luminescence in the far red/near-infrared region. The remarkable red shift of 89 nm (fluorescence) observed for 4 a in comparison with analogues boron-β-diketonate signifies the importance of sulfur in these molecules. MTDKBs with amine functionality have also been investigated as an ON/OFF fluorescent sensor.     

Sterically Allowed H-type Supramolecular Polymerizations

The functionalization of π-conjugated scaffolds with sterically demanding substituents is a widely used tactic to suppress cofacial (H-type) stacking interactions, which may even inhibit self-assembly. Contrary to expectations, we demonstrate herein that increasing steric effects can result in an enhanced thermodynamic stability of H-type supramolecular polymers. In our approach, we have investigated two boron dipyrromethene (BODIPY) dyes with bulky phenyl ( 2 ) and mesityl ( 3 ) meso-substituents and compared their self-assembly in nonpolar media with that of a parent meso-methyl BODIPY 1 lacking bulky groups. While the enhanced steric demand induces pathway complexity, the superior thermodynamic stability of the H-type pathways can be rationalized in terms of additional enthalpic gain arising from intermolecular C−H⋅⋅⋅F−B interactions of the orthogonally arranged aromatic substituents, which overrule their inherent steric demand. Our findings underline the importance of balancing competing non-covalent interactions in self-assembly.     

The first polymorph in the family of nucleobases: a second form of cytosine

A new polymorph of cytosine, C₄H₅N₃O, is reported half a century after the report of its first known crystal structure [Barker & Marsh (1964). Acta Cryst. 17 , 1581–1587]. Cytosine thus provides the first polymorphic example in the category of parent nucleobases. The new form, denoted (Ib), was observed unexpectedly during an attempt to cocrystallize cytosine with catechol. Form (Ib) crystallizes in the orthorhombic centrosymmetric space group Pccn with two molecules in the asymmetric unit. The previously known form, denoted (Ia), crystallizes in the orthorhombic noncentrosymmetric space group P2₁2₁2₁. The cytosine molecule is planar in both forms. Hydrogen‐bonding interactions are also similar for both forms. Infinite one‐dimensional ribbons composed of cytosine base‐pair dimers in R₂²(8) arrangements are observed in both (Ia) and (Ib). However, the way that the ribbons are packed differs in (Ia) and (Ib). This appears to guide the centrosymmetric versus noncentrosymmetric space‐group selection through the formation of an inversion‐related motif in polymorph (Ib) and a helical propagation in polymorph (Ia). A few selected polymorphic systems have been gathered from the Cambridge Structural Database to understand possible structural features responsible for achiral molecules adopting centro‐ and noncentrosymmetric space groups.     

Four oxoindole‐linked α‐alkoxy‐β‐amino acid derivatives

Four structures of oxoindolyl α‐hydroxy‐β‐amino acid derivatives, namely, methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐methoxy‐2‐phenylacetate, C₂₄H₂₈N₂O₆, (I), methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐ethoxy‐2‐phenylacetate, C₂₅H₃₀N₂O₆, (II), methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐[(4‐methoxybenzyl)oxy]‐2‐phenylacetate, C₃₁H₃₄N₂O₇, (III), and methyl 2‐[(anthracen‐9‐yl)methoxy]‐2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐phenylacetate, C₃₈H₃₆N₂O₆, (IV), have been determined. The diastereoselectivity of the chemical reaction involving α‐diazoesters and isatin imines in the presence of benzyl alcohol is confirmed through the relative configuration of the two stereogenic centres. In esters (I) and (III), the amide group adopts an anti conformation, whereas the conformation is syn in esters (II) and (IV). Nevertheless, the amide group forms intramolecular N—H...O hydrogen bonds with the ester and ether O atoms in all four structures. The ether‐linked substituents are in the extended conformation in all four structures. Ester (II) is dominated by intermolecular N—H...O hydrogen‐bond interactions. In contrast, the remaining three structures are sustained by C—H...O hydrogen‐bond interactions.