OFF-ON fluorescent detection of thymidine nucleotides by a zinc(II)-cyclen complex bearing two diagonal pyrenes

Argentivorous Molecules with Chromophores in Side Arms: Silver Ion-Induced Turn On and Turn Off of Fluorescence

The synthesis of argentivorous molecules (L¹ and L²) having two chromophores (4-(anthracen-9-yl)benzyl or 4-(pyren-1-yl)benzyl groups) and two benzyl groups and the fluorescence properties of their silver complexes in a solution and the solid state are reported. A crystallographic approach for the Ag⁺ complexes with L¹ and L² revealed that the observed fluorescence changes stem from the excimer formation and extinction of fluorescent. Furthermore, binding stabilities of L¹ and L² toward Ag⁺ ions were estimated by the Ag⁺-induced UV-vis and PL spectral changes.

Ratiometric Detection of ATP by Fluorescent Cyclophanes with Bellows-Type Sensing Mechanism

Pyrene-based cyclophanes have been synthesized with the aim to realize a bellows-type sensing mechanism for the ratiometric detection of nucleotide concentrations in a buffered aqueous solution. The sensing mechanism involves the encapsulation of a nucleobase between two pyrene rings, which affects the monomer-excimer equilibrium of the receptor in the excited state. The nature of the spacer and its connection pattern to pyrene rings have been varied to achieve high selectivity for ATP. The 1,8-substituted pyrene-based cyclophane with the 2,2'-diaminodiethylamine spacer demonstrates the best selectivity for ATP showing a 50-fold increase in the monomer-excimer emission ratio upon saturation with the nucleotide. The receptor can detect ATP within the biological concentrations range over a wide pH range. NMR and spectroscopic studies have revealed the importance of hydrogen bonding and stacking interactions for achieving a required receptor selectivity. The probe has been successfully applied for the real-time monitoring of creatine kinase activity.

Macrocyclic metal complexes for metalloenzyme mimicry and sensor development

Examples of proteins that incorporate one or more metal ions within their structure are found within a broad range of classes, including oxidases, oxidoreductases, reductases, proteases, proton transport proteins, electron transfer/transport proteins, storage proteins, lyases, rusticyanins, metallochaperones, sporulation proteins, hydrolases, endopeptidases, luminescent proteins, iron transport proteins, oxygen storage/transport proteins, calcium binding proteins, and monooxygenases. The metal coordination environment therein is often generated from residues inherent to the protein, small exogenous molecules (e.g., aqua ligands) and/or macrocyclic porphyrin units found, for example, in hemoglobin, myoglobin, cytochrome C, cytochrome C oxidase, and vitamin B12. Thus, there continues to be considerable interest in employing macrocyclic metal complexes to construct low-molecular weight models for metallobiosites that mirror essential features of the coordination environment of a bound metal ion without inclusion of the surrounding protein framework. Herein, we review and appraise our research exploring the application of the metal complexes formed by two macrocyclic ligands, 1,4,7-triazacyclononane (tacn) and 1,4,7,10-tetraazacyclododecane (cyclen), and their derivatives in biological inorganic chemistry. Taking advantage of the kinetic inertness and thermodynamic stability of their metal complexes, these macrocyclic scaffolds have been employed in the development of models that aid the understanding of metal ion-binding natural systems, and complexes with potential applications in biomolecule sensing, diagnosis, and therapy. In particular, the focus has been on "coordinatively unsaturated" metal complexes that incorporate a kinetically inert and stable metal-ligand moiety, but which also contain one or more weakly bound ligands, allowing for the reversible binding of guest molecules via the formation and dissociation of coordinate bonds. With regards to mimicking metallobiosites, examples are presented from our work on tacn-based complexes developed as simplified structural models for multimetallic enzyme sites. In particular, structural comparisons are made between multinuclear copper(II) complexes formed by such ligands and multicopper enzymes featuring type-2 and type-3 copper centers, such as ascorbate oxidase (AO) and laccase (Lc). Likewise, with the aid of relevant examples, we highlight the importance of cooperativity between either multiple metal centers or a metal center and a proximal auxiliary unit appended to the macrocyclic ligand in achieving efficient phosphate ester cleavage. Finally, the critical importance of the Zn(II)-imido and Zn(II)-phosphate interactions in Zn-cyclen-based systems for delivering highly sensitive electrochemical and fluorescent chemosensors is also showcased. The Account additionally highlights some of the factors that limit the performance of these synthetic nucleases and the practical application of the biosensors, and then identifies some avenues for the development of more effective macrocyclic constructs in the future.

A turn-on fluorescent chemosensor for selective responses of copper(ii) ion pairs

New piperazine-based aminonaphthalimide imidazolium podands as fluorescent chemosensor was designed and synthesized for selectively sensing Cu(ClO₄)₂ and Cu(NO₃)₂ over a wide range of tested metal ion pairs.

Deep-blue emitting pyrene–benzimidazole conjugates for solution processed organic light-emitting diodes

Pyrene–benzimidazole hybrids have been demonstrated as deep blue emitters for organic light-emitting diodes.

Dynamic cyclen-metal complexes for molecular sensing and chirality signaling

Structural dynamism plays important roles in artificial and biological systems, because it controls structures and functions of various molecules and assemblies. In this review, molecular recognition and self-assembling behavior of dynamic armed cyclen-metal complexes are discussed at the molecular and supramolecular levels. These metal complexes provide useful platforms for molecular receptors, supramolecules, and molecular assemblies that can respond rapidly to guest molecules and environments. Since armed cyclens have many structural and geometrical variations, they form a wide variety of metal complexes having specific sensing and signaling functions. The Lewis acidity of the metal cations plays an essential role in anion binding and in hydrolytic catalysis of phosphate esters. Characteristic luminescence and magnetic properties of lanthanides also enable techniques for effective bio-imaging. They also serve as chiral building blocks for self-assembled architectures, which offer chirality integration effective for chirality sensing and signaling at the supramolecular level.

Bis- and tris-naphthoimidazolium derivatives for the fluorescent recognition of ATP and GTP in 100% aqueous solution

Naphthoimidazolium groups can form unique ionic hydrogen bonds with anions as imidazolium moieties, and in addition, they are fluorescent, so no further elaborative synthesis is needed to introduce a fluorescent group. In this paper, three naphthoimidazolium derivatives were synthesized and studied for the recognition of nucleotides. Compound 1 composed of a single naphthoimidazolium group and quaternary ammonium group did not show any significant fluorescent changes with various anions and nucleotides, such as ATP, GTP, CTP, TTP, UTP, ADP and AMP. A tripodal compound 3 bearing three naphthoimidazolium groups and three quaternary ammonium groups, respectively, showed large fluorescence enhancements with UTP, CTP and TTP and moderate fluorescence enhancements with ATP and pyrophosphate and a fluorescence quenching effect with GTP. On the other hand, compound 2 bearing two naphthoimidazolium groups and two quaternary ammonium groups displayed a selective fluorescence enhancement with ATP and a selective fluorescence quenching effect with GTP in 100% aqueous solution.

Ratiometric fluorescent receptors for both Zn2+ and H2PO4(-) ions based on a pyrenyl-linked triazole-modified homooxacalix[3]arene: a potential molecular traffic signal with an R-S latch logic circuit

A ratiometric fluorescent receptor with a C(3) symmetric structure based on a pyrene-linked triazole-modified homooxacalix[3]arene (L) was synthesized and characterized. This system exhibited an interesting ratiometric detection signal output for targeting cations and anions through switching the excimer emission of pyrene from the "on-off" to the "off-on" type in neutral solution. (1)H NMR titration results suggested that the Zn(2+) center of receptor L·Zn(2+) provided an excellent pathway of organizing anion binding groups for optimal host-guest interactions. It is thus believed that this receptor has potential application in sensing, detection, and recognition of both Zn(2+) and H(2)PO(4)(-) ions with different optical signals. In addition, the fluorescence emission changes by the inputs of Zn(2+) and H(2)PO(4)(-) ions can be viewed as a combinational R-S latch logic circuit at the molecular level.

Fluorescent sensing of triphosphate nucleotides via anthracene derivatives

A nucleotide is composed of a nucleobase, a five-carbon sugar, and phosphate groups. Recognition of these three sites can provide useful information for the development of selective fluorescent receptors for a specific nucleotide. In this paper, anthracene derivatives with two imidazolium groups at the 1,8- and 9,10-positions, quaternary ammonium groups, or the boronic acid group were examined for the recognition of nucleotides, such as ATP, GTP, CTP, TTP, UTP, ADP, and AMP, via fluorescence changes. The anthracene group provides the interaction between the bases of the nucleotides. The imidazolium and quaternary ammonium groups induce hydrogen bonding interactions with the phosphate groups of the nucleotides. The boronic acid group can interact with the ribose of the nucleotides.

Fluorescent sensing and discrimination of ATP and ADP based on a unique sandwich assembly of pyrene-adenine-pyrene

It is still a challenging task to discriminate adenosine-5'-triphosphate (ATP) from various nucleoside triphosphates, such as GTP, CTP, UTP, and TTP. The ability to distinguish ATP from adenosine diphosphate (ADP) by fluorescent signals is also urgently desired. Herein, we report two pyrene-based zinc complexes as nucleoside polyphosphate receptors with high selectivity for ATP and ADP based on fluorescence and NMR studies. A unique pyrene-adenine-pyrene sandwich assembly was observed in the case of compound 1 with ATP or ADP, resulting in the increase of monomer fluorescence intensity; whereas the other bases of nucleoside triphosphates, such as GTP, CTP, UTP, and TTP were not sandwiched, resulting in a switch in the monomer-excimer fluorescence of pyrene. The different binding patterns of various nucleobases with a pyrene-pyrene assembly make 1 a highly selective fluorescent sensor for ANP (N=di, tri). In the case of compound 2, the first 0.5 equivalents of ATP induced a strong excimer emission, whilst ADP induced a large enhancement in the monomeric fluorescent peak. This fluorescence change makes 2 an efficient sensor to discriminate ATP from ADP.

Fluorescent and colorimetric chemosensors for detection of nucleotides, FAD and NADH: highlighted research during 2004-2010

Due to the biological importance of nucleotides and related species, such as XNP (where X = adenosine (A), uridine (U), cytidine (C), guanosine (G), and N = mono, di, tri), FAD and NADH, the development of optical probes for these molecules has recently been an active area of research. This tutorial review focuses on the contributions between 2004-2010 concerning the fluorescent or colorimetric sensors for these biomolecules, and is organized according to their target molecule's structural classification.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the year 2009

This critical review is focused on examples reported in the year 2009 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions (264 references).

Supramolecular chemical sensors based on pyrene monomer-excimer dual luminescence

The past ten years have seen a spectacular development of chemical sensors based on the monomer-excimer dual luminescence of aromatic systems, such as pyrene. Either in the form of integrated or multicomponent molecular devices these chemosensors have been attracting a high interest above all because of their unique ratiometric properties. This review will focus on the latter systems, which can be classified into two classes: Firstly, the assembly of receptor-effector conjugates is triggerred by the analyte of interest. As a result, the sensor shows monomer to excimer fluorescence switching upon substrate binding. Secondly, the supramolecular assembly that constitutes the sensor is perturbed by interaction with the analyte. This induces a conformational change or the exchange of a component of the system, which is the cause of the luminescence switch effect.

Mechanical tuning of molecular recognition to discriminate the single-methyl-group difference between thymine and uracil

Construction of enzyme-like artificial cavities is a complex and challenging subject. Rather than synthesizing complicated host molecules, we have proposed mechanical adaptation of relatively simple hosts within dynamic media to determine the optimum conformation for molecular recognition. Here we have applied this concept to one of the most challenging biomolecular recognition problems, i.e., that of discriminating thymine from uracil. We synthesized the novel cholesterol-armed triazacyclononane as a host molecule and subjected it to structural tuning by compression of its Langmuir monolayers in the absence and in the presence of Li(+) cations in the subphase. Experimental results confirm that the monolayer of triazacyclononane host selectively recognizes uracil over adenine (ca. 7 times based on the binding constant) and thymine (ca. 64 times) under optimized conditions ([LiCl] = 10 mM at surface pressure of 35 mN m(-1)). The concept of mechanical tuning of a host structure for optimization of molecular recognition offers a novel methodology in host-guest chemistry as an alternative to the more traditional molecular design strategies.

Zinc-cyclen coordination to UTP, TTP or pyrophosphate induces pyrene excimer emission

Pyrene labelled Zn(2+)-cyclen 1 and bis-Zn(2+)-bis-cyclen 2 complexes were synthesized. The reversible coordination at physiological pH of Zn(2+)-cyclens to phosphate anions and to imide moieties, as present in thymine and uracil nucleotides, is well known. In the presence of analytes bearing a phosphate and an imide or two phosphate groups the formation of a ternary complex consisting of two pyrene-labelled metal complexes and the analyte molecule, is observed. The close proximity of the pyrene labels in the complex induces pyrene excimer emission, which is observable by the unarmed eye. By this, the presence of UMP, UDP, UTP and TTP in buffered aqueous solution is signalled, while other nucleotides are not able to induce excimer emission. In the same way, Zn(2+)-cyclen-pyrene acts as luminescent chemosensor for PP(i) and fructose-1,6-bisphosphate in aqueous buffer.

Aminonaphthalimide-based imidazolium podands for turn-on fluorescence sensing of nucleoside polyphosphates

New aminonaphthalimide imidazolium podands, which worked as luminescence chemosensors for selectively sensing nucleoside polyphosphates through a "turn-on" manner, were prepared for fluorescent imaging of ADP and ATP in living cells.