Dihydropyridine Fluorophores Allow for Specific Detection of Human Antibodies in Serum

Structure-activity relationship studies of tetrahydroquinolone derivatives as GPR41 modulators

GPR41, a G protein-coupled receptor, serves as a sensor for short-chain fatty acids and plays a crucial role in regulating multiple physiological processes such as the maintenance of metabolic and immune homeostasis. Therefore, the modulation of GPR41 has garnered attention as a potential strategy for the treatment of various disorders. We conducted a structure-activity relationship study on a lead tetrahydroquinolone derivative bearing a 2-(trifluoromethoxy)benzene group that displayed antagonistic activity toward GPR41. Modification of the aryl group attached to the furan moiety revealed that derivatives containing di- or trifluorobenzene, instead of 2-(trifluoromethoxy)benzene, exhibited agonistic activity toward GPR41, comparable with the reported agonistic modulator AR420626. These results suggest that the aryl group plays a pivotal role in regulating the activity of compounds toward GPR41, providing valuable insights for the design of GPR41 modulators.

Syntheses of novel pyridine-based low-molecular-weight luminogens possessing aggregation-induced emission enhancement (AIEE) properties

Novel pyridine-based fluorescing compounds, viz. pyrido[1,2-a]pyrrolo[3,4-d]pyrimidines 3a,b and N-methyl-4-((pyridin-2-yl)amino)maleimides 4a–e, were selectively prepared by a one-pot reaction between a functionalized maleimide and 2-aminopyridines with electron-donating or electron-withdrawing groups at position 5 and were investigated photophysically and computationally. The photophysical studies revealed that all the synthesized compounds exhibited fluorescence in organic solvents, while N-methyl-4-((pyridin-2-yl)amino)-substituted maleimide derivatives 4a–e, which are based on an acceptor–donor–acceptor (A–D–A) system, exhibited aggregation-induced emission enhancement (AIEE) properties in aqueous media. Compounds 4a and 4e, bearing electron-withdrawing groups (Br and CF₃, respectively) showed 7.0 and 15 times fluorescence enhancement. Time-dependent density functional theory (TD-DFT) calculations were performed to gain better insight into the electronic nature of the compounds with and without AIEE properties.

The nonlinear optical properties of two dihydropyridones derived from curcumin

Two dihydropyridone compounds are synthesized from curcumin using microwave radiation. Both compounds were identified by their melting points and ¹HNMR spectra. The nonlinear properties viz., nonlinear absorption coefficients and nonlinear refractive index of both compounds were calculated at wavelength 473 nm using the diffraction ring patterns and Z-scan techniques separately. The diffraction ring patterns evolved from circular symmetric to asymmetric due to convection current in the vertical direction. As a result of using Gaussian laser beam, the Fraunhofer approximation of the Fresnel-Kirchhoff diffraction, have led to successful simulation of the diffraction ring patterns with good quantitative and excellent qualitative agreements compared with experimental results. Optical limiting property has been tested in both compounds.

DNA Origami as Emerging Technology for the Engineering of Fluorescent and Plasmonic-Based Biosensors

DNA nanotechnology is a powerful and promising tool for the development of nanoscale devices for numerous and diverse applications. One of the greatest potential fields of application for DNA nanotechnology is in biomedicine, in particular biosensing. Thanks to the control over their size, shape, and fabrication, DNA origami represents a unique opportunity to assemble dynamic and complex devices with precise and predictable structural characteristics. Combined with the addressability and flexibility of the chemistry for DNA functionalization, DNA origami allows the precise design of sensors capable of detecting a large range of different targets, encompassing RNA, DNA, proteins, small molecules, or changes in physico-chemical parameters, that could serve as diagnostic tools. Here, we review some recent, salient developments in DNA origami-based sensors centered on optical detection methods (readout) with a special emphasis on the sensitivity, the selectivity, and response time. We also discuss challenges that still need to be addressed before this approach can be translated into robust diagnostic devices for bio-medical applications.

Structure-Activity Relationship Studies of Tetrahydroquinolone Free Fatty Acid Receptor 3 Modulators

Free fatty acid receptor 3 (FFA3, previously GPR41) is activated by short-chain fatty acids, mediates health effects of the gut microbiota, and is a therapeutic target for metabolic and inflammatory diseases. The shortage of well-characterized tool compounds has however impeded progress. Herein, we report structure-activity relationship of an allosteric modulator series and characterization of physicochemical and pharmacokinetic properties of selected compounds, including previous and new tools. Two representatives, 57 (TUG-1907) and 63 (TUG-2015), showed improved solubility and preserved potency. Of these, 57, with EC50 = 145 nM and a solubility of 33 μM, showed high clearance in vivo but is a preferred tool in vitro. In contrast, 63, with EC50 = 162 nM and a solubility of 9 μM, showed lower clearance and seems better suited for in vivo studies. Using 57, we demonstrate for the first time that FFA3 activation leads to calcium mobilization in murine dorsal root ganglia.

Complementary Oligonucleotide Conjugated Multicolor Carbon Dots for Intracellular Recognition of Biological Events

By using complementary DNA sequences as surface ligands, we selectively allow two individual diffusing "dual-color" carbon dots to interact in situ and in vitro. Spontaneous nanoscale oxidation of surface-abundant nitroso-/nitro-functionalities leads to two distinctly colored carbon dots (CD) which are isolated by polarity driven chromatographic separation. Green- and red-emitting carbon dots (gCD and rCD) were decorated by complementary single-stranded DNAs which produce a marked increase in the fluorescence emission of the respective carbon dots. Mutual colloidal interactions are achieved through hybridization of complementary DNA base pairs attached to the respective particles, resulting in quenching of their photoluminescence. The observed post-hybridization quenching is presumably due to a combined effect from an aggregation of CDs post duplex DNA formation and close proximity of multicolored CDs, having overlapped spectral regions leading to a nonradiative energy transfer process possibly released as heat. This strategy may contribute to the rational design of mutually interacting carbon dots for a better control over the resulting assembly structure for studying different biological phenomenon including molecular cytogenetics. One of the newly synthesized CDs was successfully used to image intracellular location of GAPDH mRNA using an event of change in fluorescence intensity (FI) of CDs. This selectivity was introduced by conjugating an oligonucleotide harboring complementary sequence to GAPDH mRNA. FI of this conjugated carbon dot, rCD-GAPDH, was also found to decrease in the presence of Ca2+, varied in relation to H+ concentrations, and could serve as a tool to quantify the intracellular concentrations of Ca2+ and pH value (H+) which can give important information about cell survival. Therefore, CD-oligonucleotide conjugates could serve as efficient probes for cellular events and interventions.

Formation and temporal evolution of diffraction ring patterns in a newly prepared dihydropyridone

A dihydropyridone has been prepared from butylamine and curcumin. A theoretical DFT study was conducted to determine the most stable conformer of the studied molecule (among three conformers) using the B3LYP/6-311+G(d,p) level of theory. This is assisted by the prediction of the ¹³C NMR chemical shifts of the conformers which then correlated with the observed ¹³C NMR chemical shifts. A TD-DFT study was conducted to analyze the electronic spectrum of the most stable conformer in order to determine the transitions responsible for the longer band in the electronic spectrum of the molecule. As well the frontier orbitals in the most stable conformer were analyzed to establish the density of donor and acceptor sites in the molecule that may be responsible for the nonlinear optical (NLO) properties of the studied molecule. Diffraction ring patterns were observed as a result of the use of visible, 473 nm, low power single mode laser beam traversed a thin cell containing solution of dihydropyridone. The nonlinear refractive index, n₂, was determined based on the number of diffraction rings per a pattern observed and by the Z-scan technique and both results are compared. The upward convection heat effect appears to be responsible for the asymmetries observed in the diffraction ring patterns. The use of convergent and divergent laser beams has led to new types of diffraction ring patterns. Temporal evolution of each diffraction ring patterns was registered. The diffraction ring patterns experimentally obtained are numerically calculated using the Fresnel-Kirchhoff diffraction integral, with good qualitative and reasonable quantitative agreements.