Enhanced Host-Guest Association and Fluorescence in Copolymers from Copper Salphen Complexes by Supramolecular Internalization of Anions

We describe the synthesis, crystallographic characterization of a new Cu-Salphen compound and its use as a host Lewis-acid against guest anions in two versions: a) free molecule, b) copolymerized with methyl methacrylate:n-butyl acrylate (1 : 4-wt.) as protective co-monomers. Higher contents in Cu-Salphen yielded larger and more homogeneous polymer sizes. Polymer size together with glass transitions, heat capacity, thermal degradation, guest-saturation degrees and host-guest species distribution profiles from spectrophotometric titrations explained growths of up to 630-fold in K₁₁ and 180000-fold in K₁₂ for the host's binding site attributable to a solvophobic protection from the macromolecular structure. Spectrofluorimetry revealed blue-shifted×13-16 larger luminescence for Cu-Salphen in the polymers (λ_em =488-498 nm) than that of the non-polymerized counterpart (λ_em =510-543 nm) and "turn-on" blue-shifted enhanced fluorescence upon guest association. We propose a cooperative incorporation of the guests occurring from the outer medium toward internally protected binding site pockets in the random coil polymer conformations.

Designing Excess Electron Compounds by Substituting Alkali Metals to a Small and Versatile Tetracyclic Framework: A Theoretical Perspective

Organic compound-based nonlinear optical (NLO) materials have sparked a lot of attention due to their multitude of applications and shorter optical response times than those of inorganic NLO materials. In the present investigation, we designed exo-exo-tetracyclo[6.2.1.1^3,6.0^2,7]dodecane (TCD) derivatives, which were obtained by replacing H atoms of methylene bridge carbon with alkali metals (Li, Na, and K). It was observed that upon the substitution of alkali metals at bridging CH₂ carbon, absorption within the visible region occurred. Moving from 1 to 7 derivatives, the maximum absorption wavelength of the complexes exhibited a red shift. The designed molecules showed a high degree of intramolecular charge transfer (ICT) and excess electrons in nature, which were responsible for rapid optical response time and significant large molecular (hyper)polarizability. Calculated trends also inferred that the crucial transition energy decreased in order that also played a key role in the higher nonlinear optical response. Furthermore, to examine the effect of the structure/property relationship on the nonlinear optical properties of these investigated compounds (1-7), we calculated the density of state (DOS), transition density matrix (TDM), and frontier molecular orbitals (FMOs). The largest first static hyperpolarizability (β_tot) of TCD derivative 7 was 72059 au, which was 43 times greater than that of the prototype p-nitroaniline (β_tot = 1675 au).

Molecular tweezers with a rotationally restricted linker and freely rotating porphyrin moieties

The effect of the degree of conformational rigidity and/or flexibility on preorganisation in artificial molecular receptors continues to be actively explored by supramolecular chemists. This work describes a bis-porphyrin architecture, linked via a rigid polycyclic backbone, in which a sterically bulky 2,3,5,6-tetramethylphenyl diimide core restricts rotation to afford two non-interconvertible tweezer conformations; syn- and anti-. After separation, the host-guest chemistry of each conformation was studied independently. The difference in host geometry allows only the syn-conformation to form a strong 1 : 1 bis-porphyrin complex with the diamino ligand 1,4-diazabicyclo[2.2.2]octane (DABCO) (K11 = 1.25 × 108 M-1), with the anti-conformation adopting a 2 : 2 sandwich complex with DABCO (K22 = 5.57 × 1017 M-3).

Norbornene chaotropic salts as low molecular mass ionic organogelators (LMIOGs)

Phenylalanine functionalised norbornene (9:Na) functions as a potent, low molecular-mass (MW = 333 Da) ionic organogelator with a minimum gelating concentration of 0.5 wt% in THF, i-PrOH, 1,4-dioxane and n-BuOH. Fibrous crystals form in the gel and X-ray crystallography identified a cation mediated helical assembly process controlled by the chirality of the phenylalanine. In addition to excellent gelating properties 9:Na readily forms aqueous biphasic and triphasic systems.

Using steric bulk for selective recognition; blocking the binding site to differentiate guests

Amenable to bendable: blocking the binding cleft enhances selectivity for flexible guests.

Synthesis and evaluation of cationic norbornanes as peptidomimetic antibacterial agents

A series of structurally amphiphilic biscationic norbornanes have been synthesised as rigidified, low molecular weight peptidomimetics of cationic antimicrobial peptides. A variety of charged hydrophilic functionalities were attached to the norbornane scaffold including aminium, guanidinium, imidazolium and pyridinium moieties. Additionally, a range of hydrophobic groups of differing sizes were incorporated through an acetal linkage. The compounds were evaluated for antibacterial activity against both Gram-negative and Gram-positive bacteria. Activity was observed across the series; the most potent of which exhibited an MIC's ≤ 1 μg mL(-1) against Streptococcus pneumoniae, Enterococcus faecalis and several strains of Staphylococcus aureus, including multi-resistant methicillin resistant (mMRSA), glycopeptide-intermediate (GISA) and vancomycin-intermediate (VISA) S. aureus.

Synthesis of Norbornane Bisether Antibiotics via Silver-mediated Alkylation

A small series of norbornane bisether diguanidines have been synthesized and evaluated as antibacterial agents. The key transformation-bisalkylation of norbornane diol 6-was not successful using Williamson methodology but has been accomplished using Ag2O mediated alkylation. Further functionalization to incorporate two guanidinium groups gave rise to a series of structurally rigid cationic amphiphiles; several of which (16d, 16g and 16h) exhibited antibiotic activity. For example, compound 16d was active against a broad range of bacteria including Pseudomonas aeruginosa (MIC = 8 µg/mL), Escherichia coli (MIC = 8 µg/mL) and methicillin-resistant Staphylococcus aureus (MIC = 8 µg/mL).

Modular synthesis of linear bis- and tris-monodentate fused [6]polynorbornane-based ligands and their assembly into coordination cages

A modular approach has been developed for the synthesis of rigid linear di- and tritopic ligands based on a fused [6]polynorbornane scaffold. The design provides up to three sites for installing functionality, including both "ends" and a "central" position with the advantage that each region can be independently addressed during synthesis. To illustrate the utility of the approach, both pyridyl and picolyl units were incorporated to provide six new ligands, with centers and ends either matched or mismatched. Indeed, both [M2L4] cages with endohedral functionality and [M3L4] complexes were cleanly produced from these ligands with assembled structures confirmed by using (1)H NMR spectroscopy, HRMS, and molecular modelling.

Solid-state NMR as a probe of anion binding: molecular dynamics and associations in a [5]polynorbornane bisurea host complexed with terephthalate

A suite of solid-state NMR experiments is used to study a supramolecular complex consisting of a [5]polynorbornane bisurea host and terephthalate dianion guest, revealing information on the dynamics of both the host and guest species.

A simple donor–acceptor probe for the detection of Cr3+ cations

A probe exhibits fluorescence enhancement upon exposure to Cr(iii) in a THF–water (v/v = 9/1) Tris–HCl buffer solution. Fluorescence imaging experiments of the exciplex in human glioma cells evidenced its potential application in biological systems.