We report on the synthesis of 4-hydroxycoumarin dimers 1–15 bearing an aryl substituent on the central linker and fused benzopyranocoumarin derivatives 16–20 and on their in vitro broad anti-DNA and RNA virus activity evaluations. The chemical identities and structure of compounds 1–20 were deduced from their homo- and heteronuclear NMR measurements whereas the conformational properties of 5, 14 and 20 were assessed by the use of 1D difference NOE enhancements. Unequivocal proof of the stereostructure of compounds 7, 9, 16 and 18 was obtained by single crystal X-ray diffraction method. The X-ray crystal structure analysis revealed that two 4-hydroxycoumarin moieties in the 4-trifluoromethylphenyl- and 2-nitrophenyl derivatives (compounds 7 and 9, respectively) are intramolecularly hydrogen-bonded between hydroxyl and carbonyl oxygen atoms. Consequently, the compounds 7 and 9 adopt conformations in which two 4-hydroxy-coumarin moieties are anti-disposed. Antiviral activity evaluation results indicated that the 4-bromobenzylidene derivative of bis-(4-hydroxycoumarin) (compound 3) possesses inhibitory activity against HSV-1 (KOS), HSV-2 (G), vaccinia virus and HSV-1 TK^- KOS (ACV^r) at a concentration of 9–12 μM and at a minimum cytotoxic concentration (MCC) greater than 20 μM. Compounds 4–6, 8, and 20 were active against feline herpes virus (50% effective concentration, EC₅₀ = 5–8.1 μM), that is at a 4-7-fold lower concentration than the MCC.

The conformational properties of 1,3-diindolylureas and thioureas were studied by a combination of heteronuclear NMR spectroscopy and quantum mechanics calculations. NOE experiments showed that the anti–anti conformer along the C7–N7α bonds was predominant in DMSO-d₆ solution in the absence of anions. Anion-induced changes in the ¹H and ¹⁵N chemical shifts confirm the weak binding of chloride anions with negligible conformational changes. Strong deshielding of ureido protons and moderate deshielding of indole NH was observed upon the addition of acetate, benzoate, bicarbonate and dihydrogen phosphate, which indicated that the predominant hydrogen bond interactions occurred at the urea donor groups. Binding of oxo-anions caused conformational changes along the C7–N7α bonds and the syn–syn conformer was preferred for anion–receptor complexes. The conformational changes upon anion binding are in good agreement with energetic preferences established by ab initio calculations.

A kinetic approach was used to determine the radical scavenging activities of sinapic acid and its derivatives: sinapine, 4-vinylsyringol, syringic acid, syringaldehyde, and ethyl, propyl and butyl sinapate. The responses were expressed as rates of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) scavenging (R_S), superoxide radical (O₂˙⁻) scavenging (R_FF), and β-carotene bleaching in the emulsion system (R_B). For R_S and R_B, the esters of sinapic acid showed the highest responses while, for R_FF, this was seen for syringic acid. The effectiveness of the selected compounds for scavenging these free radicals was also determined at a fixed endpoint. The early response parameters were demonstrated to be good discriminators in assessing differences for antioxidants with comparable fixed endpoint activity. The primary feature that ranks the kinetic data and the endpoint determinations is interpreted in terms of the mechanisms of the reactions involved in each of the assays conducted.

Due to their ability to inhibit viral DNA or RNA replication, nucleoside analogues have been used for decades as potent antiviral therapeutics. However, one of the major limitations of nucleoside analogues is the development of antiviral resistance. In that regard, flexible nucleoside analogues known as “fleximers” have garnered attention over the years due to their ability to survey different amino acids in enzyme binding sites, thus overcoming the potential development of antiviral resistance. Acyclic fleximers have previously demonstrated antiviral activity against numerous viruses including Middle East Respiratory Syndrome coronavirus (MERS-CoV), Ebola virus (EBOV), and, most recently, flaviviruses such as Dengue (DENV) and Yellow Fever Virus (YFV). Due to these interesting results, a Structure Activity Relationship (SAR) study was pursued in order to analyze the effect of the pyrimidine functional group and acyl protecting group on antiviral activity, cytotoxicity, and conformation. The results of those studies are presented herein.

In this work, fully polysaccharide based membranes were presented as self-standing, solid polyelectrolytes for application in anion exchange membrane fuel cells (AEMFCs). For this purpose, cellulose nanofibrils (CNFs) were modified successfully with an organosilane reagent, resulting in quaternized CNFs (CNF (D)), as shown by Fourier Transform Infrared Spectroscopy (FTIR), Carbon-13 (C13) nuclear magnetic resonance (¹³C NMR), Thermogravimetric Analysis (TGA)/Differential Scanning Calorimetry (DSC), and ζ-potential measurements. Both the neat (CNF) and CNF(D) particles were incorporated in situ into the chitosan (CS) membrane during the solvent casting process, resulting in composite membranes that were studied extensively for morphology, potassium hydroxide (KOH) uptake and swelling ratio, ethanol (EtOH) permeability, mechanical properties, ionic conductivity, and cell performance. The results showed higher Young’s modulus (119%), tensile strength (91%), ion exchange capacity (177%), and ionic conductivity (33%) of the CS-based membranes compared to the commercial Fumatech membrane. The addition of CNF filler improved the thermal stability of the CS membranes and reduced the overall mass loss. The CNF (D) filler provided the lowest (4.23 × 10⁻⁵ cm² s⁻¹) EtOH permeability of the respective membrane, which is in the same range as that of the commercial membrane (3.47 × 10⁻⁵ cm²s⁻¹). The most significant improvement (~78%) in power density at 80 °C was observed for the CS membrane with neat CNF compared to the commercial Fumatech membrane (62.4 mW cm⁻² vs. 35.1 mW cm⁻²). Fuel cell tests showed that all CS-based anion exchange membranes (AEMs) exhibited higher maximum power densities than the commercial AEMs at 25 °C and 60 °C with humidified or non-humidified oxygen, demonstrating their potential for low-temperature direct ethanol fuel cell (DEFC) applications.

The conformational analysis of four C2-amido and C7-ureido functionalised indole anion receptors was performed by a combination of heteronuclear NMR spectroscopy and ab initio quantum mechanical calculations. NOE experiments showed that anti–anti conformation across C2–C2α and C7–N7α bonds is predominant in acetone solution in the absence of anions. Upon anion binding to receptors, syn–syn conformation becomes predominant. The conformational changes upon anion binding are in good agreement with energetic preferences established by ab initio calculations. Chemical shift changes induced by interaction of anions suggest that binding of chloride and bromide anions occurs primarily to H1 and H7α protons. Nitrate anions favour interaction with H7α and H7γ ureido protons, whereas acetate anions interact strongly with all four available hydrogen bond donor groups.