A new benzo-annelated cryptand and a derivative with alkali cation-sensitive fluorescence

A Tool, an App and a Field: Fluorescent PET Sensors, Blood Electrolyte Analysis and Molecular Logic as Products of Supramolecular Photoscience from Northern Ireland and Sri Lanka

The general tool of fluorescent PET (photoinduced electron transfer) sensors/switches - a molecular design principle with engineering features - is outlined, with the aid of frontier orbital energy diagrams. Fluorophores such as anthracene, 1,3-diaryl-Δ² -pyrazolines and 4-amino-1,8-naphthalimides are employed within this system, alongside receptors such as amines, carboxylates, crown ethers and amino acids. This tool appealed to a multinational corporation for building a medical analyzer for electrolytes such as Na⁺ , K⁺ , Ca²⁺ and gases like CO₂ , which became a commercially successful application. Finally, the tool was a springboard for chemistry to cross into computer science. The field of molecular logic can elucidate how molecules inside us handle information. Molecular examples of the simplest logic gates such as YES, NOT, OR, AND are described. A case of a human-level computation - visual edge detection - is also included.

Synthesis and structures of three benzoannelated macrobicyclic diamides

We report the synthesis and structures of 9,10,20,21-tetrahydro-5,14-(ethanooxyethano)dibenzo[e,q][1,4,10,13,7,16]tetraoxadiazacyclooctadecine-6,13-dione [systematic name: 8,11,21,24,29-pentaoxa-1,18-diazatetracyclo[16.8.5.02,7.012,17]hentriaconta-2,4,6,12(17),13,15-hexaene-19,26-dione C24H28N2O8, I], 6,7,9,10,12,13,20,21-octahydro-5,14-(ethanooxyethano)dibenzo[e,q][1,4,10,13,7,16]tetraoxadiazacyclooctadecine-23,27-dione (8,11,21,24,29-pentaoxa-1,18-diazatetracyclo[16.8.5.02,7.012,17]hentriaconta-2,4,6,12,14,16-hexaene-27,31-dione; C24H28N2O7, II), and 9,10,20,21-tetrahydro-5,14-(ethanooxyethanooxyethano)dibenzo[e,q][1,4,10,13,7,16]tetraoxadiazacyclooctadecine-6,13-dione [8,11,21,24,29,32-hexaoxa-1,18-diazatetracyclo[16.8.8.02,7.012,17]tetratriaconta-2,4,6,12(17),13,15-hexaene-19,26-dione; C26H32N2O7, III]. All three compounds are made up of two tertiary diamides and are composed of two 15-membered rings with N2O3 donor sets and one 18-membered ring with an N2O4 donor set (compounds I and II) or three 18-membered rings with N2O4 donor sets (compound III). The solid-state structures of compounds I and II show little effects from the movement of the amide groups. However, compound III has a larger cavity and a different orientation of donor atoms in comparison to compounds I and II.

Molecular cages for biological applications

Artificial receptors able to recognise biologically relevant molecules or ions have gained interest in the chemical community because they offer a plethora of posibilities. Molecular cage compounds are polycyclic compounds with a cavity designed for the encapsulation of guest species. Once inside the host cavity, the substrate can be transported through membranes and protected from the action of enzymes or other reactive species, thus offering the possibility of interfering with biological systems. Commonly, enzymes have been an inspiration for chemists in the search and design of defined cavities for different purposes. However, the chemical preparation of molecular cages has struggled with many synthetic challenges but this effort is worthwhile as they are a very promising tool for many applications ranging from sensing, delivery, purification or even promotion of/prevention from chemical modifications. Since the early reports at the end of the 60s, this field has experienced a growing interest; this review summarises the progress in the preparation and study of cage-like compounds highlighting their importance in biological applications.

Lighting-up protein–ligand interactions with fluorescent PET (photoinduced electron transfer) sensor designs

Extending the versatile fluorescent PET sensing/switching system causes ‘off–on’ signalling when a ligand binds to its appropriate protein.

Recent progress in the design and applications of fluorescence probes containing crown ethers

Crown ethers, discovered by the winner of the Nobel Prize Charles Pedersen, are cyclic chemical compounds that consist of a ring or multiple rings containing several ether groups that are capable of binding various ions.

Fluorescent probes and bioimaging: alkali metals, alkaline earth metals and pH

All living species and life forms have an absolute requirement for bio-functional metals and acid-base equilibrium chemistry owing to the critical roles they play in biological processes. Hence, a great need exists for efficient methods to detect and monitor biometals and acids. In the last few years, great attention has been paid to the development of organic molecule based fluorescent chemosensors. The availability of new synthetic fluorescent probes has made fluorescence microscopy an indispensable tool for tracing biologically important molecules and in the area of clinical diagnostics. This review highlights the recent advances that have been made in the design and bioimaging applications of fluorescent probes for alkali metals and alkaline earth metal cations, including lithium, sodium and potassium, magnesium and calcium, and for pH determination within biological systems.

Mechanistic insights into excited state intramolecular proton transfer in isolated and metal chelated supramolecular chemosensors

Mechanistic studies of the excited state intramolecular proton transfer in a series of related and progressively more complex supramolecular chromophores.

Bright molecules for sensing, computing and imaging: a tale of two once-troubled cities

The circumstances in Colombo, Sri Lanka, and in Belfast, Northern Ireland, which led to a) the generalization of luminescent PET (photoinduced electron transfer) sensing/switching as a design tool, b) the construction of a market-leading blood electrolyte analyzer and c) the invention of molecular logic-based computation as an experimental field, are delineated. Efforts to extend the philosophy of these approaches into issues of small object identification, nanometric mapping, animal visual perception and visual art are also outlined.

Development of an Optical Nanosensor Incorporating a pH-Sensitive Quencher Dye for Potassium Imaging

One of the key challenges in the design of a sensor for measuring extracellular changes in potassium concentration is selectivity against the competing cation, sodium. Here, we present an optode-based nanosensor selective to potassium ions, owing to the addition of a pH-sensitive quencher molecule paired with a static fluorophore. The nanosensor was fabricated using emulsification and characterized in solution by absorbance and fluorescence spectroscopy. The resulting nanosensor detected potassium with nearly 1 order of magnitude higher selectivity compared to our chromoionophore-based optode nanosensors. In addition to the improved selectivity, the nanosensor has the following properties required for measurements in a biological environment: (1) a physiologically relevant dynamic range, (2) response to potassium ions at a physiological ionic strength, and (3) response to serum potassium in the presence of fouling biological components. The potassium nanosensor described in this study is envisioned to have application in cellular imaging and drug screening.

Metal ion induced fluorescence resonance energy transfer between crown ether functionalized quantum dots and rhodamine B: selectivity of K+ ion

A ratiometric fluorescent metal ion sensor based on the mechanism of fluorescence resonance energy transfer between 15-crown-5-ether capped CdSe/ZnS quantum dots and 15-crown-5-ether attached rhodamine B.

Integration of the 1,2,3-triazole "click" motif as a potent signalling element in metal ion responsive fluorescent probes

In a systematic approach we synthesized a new series of fluorescent probes incorporating donor-acceptor (D-A) substituted 1,2,3-triazoles as conjugative π-linkers between the alkali metal ion receptor N-phenylaza-[18]crown-6 and different fluorophoric groups with different electron-acceptor properties (4-naphthalimide, meso-phenyl-BODIPY and 9-anthracene) and investigated their performance in organic and aqueous environments (physiological conditions). In the charge-transfer (CT) type probes 1, 2 and 7, the fluorescence is almost completely quenched by intramolecular CT (ICT) processes involving charge-separated states. In the presence of Na(+) and K(+) ICT is interrupted, which resulted in a lighting-up of the fluorescence in acetonitrile. Among the investigated fluoroionophores, compound 7, which contains a 9-anthracenyl moiety as the electron-accepting fluorophore, is the only probe which retains light-up features in water and works as a highly K(+)/Na(+)-selective probe under simulated physiological conditions. Virtually decoupled BODIPY-based 6 and photoinduced electron transfer (PET) type probes 3-5, where the 10-substituted anthracen-9-yl fluorophores are connected to the 1,2,3-triazole through a methylene spacer, show strong ion-induced fluorescence enhancement in acetonitrile, but not under physiological conditions. Electrochemical studies and theoretical calculations were used to assess and support the underlying mechanisms for the new ICT and PET 1,2,3-triazole fluoroionophores.

Fluorescent sodium ion indicators based on the 1,7-diaza-15-crown-5 system

A series of novel sodium ion-sensitive fluorescent reagents suitable for biological applications is described. The chelator nitrogen atom substituents affect the selectivity and affinity of cation binding, while the nature of the fluorophore determines the type of fluorescent response to metal ion chelation.

Silver Ion Selective Fluoroionophores Based on Anthracene-Linked Polythiazaalkane or Polythiaalkane Derivatives

A dozen novel fluoroionophores have been synthesized which are polythiazaalkane and polythiaalkane derivatives coupled with an anthracene moiety by methyl, carbonyl, or methylphenylene bridging groups. The protonation and metal ion complexation behavior of analogues were examined in 1,4-dioxane-water solutions spectrophotometrically and spectrophotofluorometrically. The fluoroionophores, 1, 2, 5, and 6 contain basic nitrogen atoms and quench the fluorescence in the free forms because of photoinduced electron transfer (PET) from a nitrogen atom to a photoexcited anthracene unit. The fluorescence was recovered by the protonation on the nitrogen atom. The fluorescence intensities of the other fluoroionophores used here were not dependent on the pH of the solution. On the complexation of the protonated fluoroionophores 1, 2, 5, and 6 with metal ions under the acidic condition, the fluorescence intensities were decreased by the addition of silver ion selectively. Under the same conditions, the other fluoroionophores exhibited a decrease of the fluorescence intensity with the addition of silver ion selectively. These results imply that the fluoroionophores could form complexes and release a proton from the nitrogen atom of the protonated fluoroionophores. The quenching of the fluorescence of the complexed fluoroionophores 3, 4, 7, and 8-12 could be caused by the interaction of a silver ion with a pi-electron of the anthracene unit. The degree of spectral change on the complexation with silver ion is primarily dependent on the strength of the interaction of the bound silver ion with nitrogen atom, for 1, 2, 5, and 6, or with a pi-electron of the anthracene unit, for 3, 4, 7, and 8-12.