A designed receptor for pH-switchable ion binding in water

Cyanine Dyes Containing Quinoline Moieties: History, Synthesis, Optical Properties, and Applications

Cyanine dyes carrying quinoline moieties are an important class of organic molecules that are of great interest for applications in many fields like medicine, pharmacology, and engineering. Despite their exceptional properties, such as stability, high molar extinction coefficients, and high pH-sensitivity, this class of dyes has been less analyzed and reviewed in the last few decades. Therefore, this review article focuses on discussing the history of quinoline compounds, various synthetic routes to prepare quinolinium salts and symmetrical and asymmetrical mono-, di-, tri-, penta- and heptamethine cyanine dyes, containing quinoline moieties, together with their optical properties and applications as photosensitizers in photodynamic therapy, probes in biomolecules for labeling of nucleic acids, as well as imaging agents.

Environmentally responsive amino acid-bioconjugated dynamic covalent copolymer as a versatile scaffold for conjugation

A tyrosine-conjugated biodynamer with thermo/pH-responsive and adaptive features is constructed and modified by tyrosine-click reaction and HRP-mediated oxidative coupling reaction.

Novel ion-binding C3 symmetric tripodal triazoles: synthesis and characterization

Novel C3 symmetric tripodal molecules were synthesized from cyclohexane 1,3,5-tricarboxylic acid. Utilizing click and Sonogashira reactions, ion-binding triazole and pyridazin-3(2H)-one units were incorporated to form polydentate ligands for ion complexation. The structures of the novel C3 symmetric derivatives were extensively characterized by 1H, 13C and 2D NMR techniques along with HRMS and IR. The copper(I)-binding potentials of these ligands were investigated by using them as additives in model copper(I)-catalysed azide-alkyne cycloaddition (CuAAC) reactions. The copper(I) complexation ability of our compound was also proved by different spectroscopic methods, such as mass spectrometry, UV and NMR spectroscopy. Based on the mass spectrometric data all of the C3 symmetric ligands formed 1:1 complex with copper(I) ion. The specific role of C3 symmetric polydentate form in the complexation process was also discussed

Optically-gated self-calibrating nanosensors: monitoring pH and metabolic activity of living cells

Quantitative detection of biological and chemical species is critical to numerous areas of medical and life sciences. In this context, information regarding pH is of central importance in multiple areas, from chemical analysis, through biomedical basic studies and medicine, to industry. Therefore, a continuous interest exists in developing new, rapid, miniature, biocompatible and highly sensitive pH sensors for minute fluid volumes. Here, we present a new paradigm in the development of optoelectrical sensing nanodevices with built-in self-calibrating capabilities. The proposed electrical devices, modified with a photoactive switchable molecular recognition layer, can be optically switched between two chemically different states, each having different chemical binding constants and as a consequence affecting the device surface potential at different extents, thus allowing the ratiometric internal calibration of the sensing event. At each point in time, the ratio of the electrical signals measured in the ground and excited states, respectively, allows for the absolute concentration measurement of the molecular species under interest, without the need for electrical calibration of individual devices. Furthermore, we applied these devices for the real-time monitoring of cellular metabolic activity, extra- and intracellularly, as a potential future tool for the performance of basic cell biology studies and high-throughput personalized medicine-oriented research, involving single cells and tissues. This new concept can be readily expanded to the sensing of additional chemical and biological species by the use of additional photoactive switchable receptors. Moreover, this newly demonstrated coupling between surface-confined photoactive molecular species and nanosensing devices could be utilized in the near future in the development of devices of higher complexity for both the simultaneous control and monitoring of chemical and biological processes with nanoscale resolution control.

Fluorometric recognition of both dihydrogen phosphate and iodide by a new flexible anthracene linked benzimidazolium-based receptor

A new flexible anthracene linked benzimidazolium-based receptor 1 has been designed, synthesized and its binding properties have been studied by NMR, UV-vis and fluorescence spectroscopic techniques. While the receptor 1 exhibits a greater change in emission in the presence of tetrabutylammonium dihydrogenphosphate in CH(3)CN over the other anions studied, iodide is selectively preferred in CHCl(3) containing 0.1% CH(3)CN. Upon complexation of dihydrogen phosphate and iodide, the emission of 1 gradually decreased without showing any other characteristic change in the spectra. Hydrogen bonding and charge-charge interactions interplay simultaneously in a cooperative manner for selectivity in the binding process.

C-lysine conjugates: pH-controlled light-activated reagents for efficient double-stranded DNA cleavage with implications for cancer therapy

Double-stranded DNA cleavage of light-activated lysine conjugates is strongly enhanced at the slightly acidic pH (<7) suitable for selective targeting of cancer cells. This enhancement stems from the presence of two amino groups of different basicities. The first amino group plays an auxiliary role by enhancing solubility and affinity to DNA, whereas the second amino group, which is positioned next to the light-activated DNA cleaver, undergoes protonation at the desired pH threshold. This protonation results in two synergetic effects which account for the increased DNA-cleaving ability at the lower pH. First, lysine conjugates show tighter binding to DNA at the lower pH, which is consistent with the anticipated higher degree of interaction between two positively charged ammonium groups with the negatively charged phosphate backbone of DNA. Second, the unproductive pathway which quenches the excited state of the photocleaver through intramolecular electron transfer is eliminated once the donor amino group next to the chromophore is protonated. Experiments in the presence of traps for diffusing radicals show that reactive oxygen species do not contribute significantly to the mechanism of DNA cleavage at the lower pH, which is indicative of tighter binding to DNA under these conditions. This feature is valuable not only because many solid tumors are hypoxic but also because cleavage which does not depend on diffusing species is more localized and efficient. Sequence-selectivity experiments suggest combination of PET and base alkylation as the chemical basis for the observed DNA damage. The utility of these molecules for phototherapy of cancer is confirmed by the drastic increase in toxicity of five conjugates against cancer cell lines upon photoactivation.

Supramolecular Chemistry in Water

Supramolecular chemistry in water is a constantly growing research area because noncovalent interactions in aqueous media are important for obtaining a better understanding and control of the major processes in nature. This Review offers an overview of recent advances in the area of water-soluble synthetic receptors as well as self-assembly and molecular recognition in water, through consideration of the functionalities that are used to increase the water solubility, as well as the supramolecular interactions and approaches used for effective recognition of a guest and self-assembly in water. The special features and applications of supramolecular entities in aqueous media are also described.

Controlling a recognition-mediated reaction using a pH switch

The selective recognition-mediated reaction between a nitrone bearing a urea recognition site and a maleimide bearing a proton switchable recognition site can be turned 'on' and 'off' by the addition of base and acid respectively.