Straightforward synthesis of bioconjugatable azo dyes. Part 2: Black Hole Quencher-2 (BHQ-2) and BlackBerry Quencher 650 (BBQ-650) scaffolds

Bicyclic-Ammonium-Incorporated Ylidic Nitrogen Groups for Strong π-Electron Donation in Push-Pull Benzene π-Conjugated Systems

Ylidic nitrogen-based π-electron-donating groups, (quinuclidinio)amidyl (QA) and (1-azanorbornanio)amidyl (ANA) groups, were developed to shift the absorption of push-pull benzenes toward longer wavelengths. Changing the pyrrolidinyl group to the QA or ANA group achieved a bathochromic shift of 45-100 nm in the maximum absorption wavelength, depending on the push-pull π-conjugated system investigated (p-nitrobenzene, 1,8-naphthalimide, and an azo dye).

Molecular folding governs switchable singlet oxygen photoproduction in porphyrin-decorated bistable rotaxanes

Rotaxanes are mechanically interlocked molecules where a ring (macrocycle) is threaded onto a linear molecule (thread). The position of the macrocycle on different stations on the thread can be controlled in response to external stimuli, making rotaxanes applicable as molecular switches. Here we show that bistable rotaxanes based on the combination of a Zn(II) tetraphenylporphyrin photosensitizer, attached to the macrocycle, and a black-hole-quencher, attached to the thread, are capable of singlet oxygen production which can be switched on/off by the addition of base/acid. However, we found that only a sufficiently long linker between both stations on the thread enabled switchability, and that the direction of switching was inversed with regard to the original design. This unexpected behavior was attributed to intramolecular folding of the rotaxanes, as indicated by extensive theoretical calculations. This evidences the importance to take into account the conformational flexibility of large molecular structures when designing functional switchable systems.

The continuous flow synthesis of azos

Azo compounds find use in many areas of science, displaying crucial properties for important applications as photoconductive organic pigments, fluorescent quenchers, paints, cosmetics, inks, and in the large and valuable dye industry. Due to the unstable intermediates, and the exothermic and fast reactions used in their synthesis, high value azo compounds are excellent candidates for continuous flow manufacturing. This comprehensive review covers the progress made to date on developing continuous flow systems for azo synthesis and reflects on the main challenges still to be addressed, including scale up, conversion, product purity, and environmental impact. The further development of integrated continuous flow processes has the potential to help tackle these challenges and deliver improved methods for azo compound generation.

Ultrasensitive detection of Staphylococcus aureus using a non-fluorescent cDNA-grafted dark BBQ®-650 chromophore integrated hydrophilic upconversion nanoparticles/aptamer system

A highly structured fluorometric bioassay has been proposed for screening Staphylococcus aureus (S. aureus). The study exploits (i) the spectral attributes of the hexagonal NaYF₄:Yb,Er upconversion nanoparticle (UCNP)-coated 3-aminopropyl)triethoxysilane; (ii) the intrinsic non-fluorescent quenching features of the highly stable dark blackberry (BBQ®-650) receptor; (iii) the aptamer (Apt-) biorecognition and binding affinity, and (iv) the complementary DNA hybridizer-linkage efficacy. The principle relied on the excited state energy transfer between the donor Apt-labeled NH₂-UCNPs at the 3' end, and cDNA-grafted BBQ®-650 at the 5' end, as the effective receptors. The donor moieties in proximity (< 10.0 nm) trigger hybridization with the cDNA-grafted dark BBQ®-650, as the receptors of energy from the ²F_5/2 level of Yb³⁺ ions to initiate the Förster resonance energy transfer pathway. This was confirmed by the decline in the excited-state lifetimes from 223.52 μs (τ₁) to 179.26 μs (τ₂). The existence of the target S. aureus in the bioassay attracts the Apt- resulting in the detachment of the acceptor, and disintegration of the complex configuration via conformation reversal. The re-activated fluorescence monitored at λex/em = 980/652 nm, as a function of the logarithmic concentration of S. aureus (42 to 4.2 × 10⁸ CFU mL^-1), yielded an ultra-low detection response of 2.0 CFU mL^-1. The bioassay screening of S. aureus in real samples revealed satisfactory recoveries (92.44-107.82%) and validation results (p > 0.05). Hence, the comprehensive Apt-labeled NH₂-UCNPs-cDNA-grafted dark BBQ®-650 bioassay offered fast and precise S. aureus screening in food and environmental settings.

Fluorogenic sydnonimine probes for orthogonal labeling

A FRET-based fluorescence turn-on probe is designed, which employs a sydnonimine as the linker to match specific fluorophore and quencher pairs and releases the fluorescence after the "click-and-release" reaction. Furthermore, we realized selective fluorescence labeling by exploiting the mutual orthogonality between sydnonimine-DIBAC and tetrazine-1,3-Cp cycloaddition pairs.

Preparation of carbon-based AuAg alloy nanoparticles by using the heterometallic [Au4Ag4] cluster for efficient oxidative coupling of anilines

We herein report the preparation of unique heteroatom-doped and carbon-based AuAg alloy nanoparticles (NPs) via the pyrolysis of a structurally defined octanuclear heterometallic Au(i)-Ag(i) cluster [Au4Ag4(Dppy)4(Tab)4(MeCN)4](PF6)8 (2, Dppy = diphenylphosphine-2-pyridine and Tab = 4-(trimethylammonio)benzenethiolate). This cluster-precursor approach exerts a fine control over the spatial arrangement, size and uniformity of the AuAg alloy NPs as well as the doped heteroatoms (P, N, F and S). The optimized material prepared at 450 °C efficiently catalyzes the oxidative coupling of anilines to yield azobenzenes under mild conditions.