An Optical Probe for Real-Time Monitoring of Self-Replicator Emergence and Distinguishing between Replicators.

Self-replicating systems play an important role in research on the synthesis and origin of life. Monitoring of these systems has mostly relied on techniques such as NMR or chromatography, which are limited in throughput and demanding when monitoring replication in real time. To circumvent these problems, we now developed a pattern-generating fluorescent molecular probe (an ID-probe) capable of discriminating replicators of different chemical composition and monitoring the process of replicator formation in real time, giving distinct signatures for starting materials, intermediates, and final products. Optical monitoring of replicators dramatically reduces the analysis time and sample quantities compared to most currently used methods and opens the door for future high-throughput experimentation in protocell environments.

Assessing changes in the expression levels of cell surface proteins with a turn-on fluorescent molecular probe.

Tri-nitrilotriacetic acid (NTA)-based fluorescent probes were developed and used to image His-tagged-labelled outer membrane protein C (His-OmpC) in live Escherichia coli. One of these probes was designed to light up upon binding, which provided the means to assess changes in the His-OmpC expression levels by taking a simple fluorescence spectrum.

A Metallosupramolecular Coordination Polymer for the 'Turn-on' Fluorescence Detection of Hydrogen Sulfide.

A coumarin based probe for the efficient detection of hydrogen sulfide in aqueous medium is reported. The investigated coumarine-based derivative forms spherical nanoparticles in aqueous media. In presence of Pd2+, a metallosupramolecular coordination polymer is formed, which is accompanied by quenching of the coumarin emission at 390 nm. Its Pd2+ complex could be used as a probe for chemoselective detection of monohydrogensulfide (HS-). Presence of HS- leads to a'turn-on' fluorescence signal, resulting from decomplexation of Pd2+ from the metallosupramolecular probe. The probe was successfully applied for qualitative and quantitative detection of HS- in different sources of water directly collected from sea, river, tap and laboratory drain water, as well as in growth media for aquatic species.

Switching the recognition ability of a photoswitchable receptor towards phosphorylated anions.

An azobenzene based photoswitchable macrocyclic receptor displays different binding affinities in its E and Z forms towards various phosphorylated coenzymes under physiological conditions with remarkable selectivity for ATP in the E-form and selectivity towards GTP in the photoisomerized Z-form. Linear discriminant analysis clearly separated the analytes using the E-form. An application of this method enabled monitoring the progress of enzymatic phosphorylation using a tyrosine kinase enzyme.

Multi-Stimuli-Responsive Supramolecular Polymers Based on Noncovalent and Dynamic Covalent Bonds.

Several modes of supramolecular assembly relying on noncovalent as well as dynamic covalent interactions were combined in a single molecule. The supramolecular self-assembly of 1 can be controlled by three stimuli, namely light, pH, and addition of metal ions, in both organic and aqueous media. The multi-stimuli-responsive nature of 1 was used successfully for the controlled encapsulation and on-demand release of hydrophobic molecules, such as dyes and drugs.

Diverse Properties of Guanidiniocarbonyl Pyrrole-Based Molecules: Artificial Analogues of Arginine.

The guanidinium moiety, which is present in active sites of many enzymes, plays an important role in the binding of anionic substrates. In addition, it was also found to be an excellent binding motif for supramolecular chemistry. Inspired by Nature, scientists have developed artificial receptors containing guanidinium scaffolds that bind to a variety of oxoanions through hydrogen bonding and charge pairing interactions. However, the majority of binding studies is restricted to organic solvents. Polyguanidinium based molecules can form efficient complexes in aqueous solvents due to strong electrostatic interactions. However, they only have moderate association constants, which are significantly decreased in the presence of competing anions and salts. Hence, to improve the binding affinity of the guanidinium moiety, our group developed the cationic guanidiniocarbonyl pyrrole (GCP) moiety. This rigid planar analogue binds efficiently to oxoanions, like carboxylates even in aqueous solvents. The lower p Ka value (7-8) of GCP compared to guanidinium derivatives (p Ka 13) favors the formation of strong, hydrogen bonded ion pairs. In addition, carboxylate binding is further enhanced by additional amide hydrogen bond donors located at the five position of the pyrrole core. Moreover, the design has allowed for introducing secondary interactions between receptor side chains and guest molecules, which allows for optimizing binding specificity and selectivity. The spectroscopic data confirmed stabilization of guanidiniocarbonyl pyrrole/oxoanion complexes through a combination of ion pairing and multiple hydrogen bonding interactions. The key role of the ionic interaction in a polar solvent, is demonstrated by a zwitterion derivative of the guanidiniocarbonyl pyrrole, which self-assembles in both dimethyl sulfoxide and pure water with association constants of K > 1010 M-1 and K = 170 M-1, respectively. In this Account, we discuss strategies for making GCP functionalized compounds, in order to boost their ability to bind oxoanions. Then we explore how these building blocks have been incorporated into different synthetic molecules and peptide sequences, highlighting examples that demonstrated the versatility of this binding scaffold. For instance, the high oxoanion binding property of GCP-based compounds was exploited to generate a detectable signal for sensing applications, thus improving selectivity and sensitivity in aqueous solution. Moreover, peptides and molecules containing GCP have shown excellent gene transfections properties. Furthermore, the self-assembly and zwitterionic behavior of zwitterionic GCP analogues was used to develop variety of supramolecular architectures such as stable supramolecular ß-helix structure, linear supramolecular oligomers, one-dimensional rods or two-dimension sheets, fibers, vesicles, soft nanospheres, as well as stimuli responsive supramolecular gels.

Analyzing Amyloid Beta Aggregates with a Combinatorial Fluorescent Molecular Sensor.

Different amyloid beta (Aß) aggregates can be discriminated by a combinatorial fluorescent molecular sensor. The unique optical fingerprints generated by the unimolecular analytical device provide a simple means to differentiate among aggregates generated from different alloforms or through distinct pathways. The sensor has also been used to track dynamic changes that occur in Aß aggregation states, which result from the formation of low molecular weight oligomers, high molecular weight oligomers, protofibrils, and fibrils.

Photoreversible assembly-disassembly of a polymeric structure by using an azobenzene photoswitch and Al3+ ions.

A nonmacrocyclic azobenzene-based photochromic receptor in its E isomer forms an extended polymeric assembly with Al(3+) ions. Exposure of the E form to UV light at λ = 366 nm causes a disassembly of the polymeric structure due to the change in the molecular geometry of the ligand. The linear polymeric structure was regenerated on exposure to visible light.

Altered selectivity of a dipicolylamine based metal ion receptor.

2,2-Dipicolylamine (DPA) based receptors detect Zn(2+) with high fidelity. A fluorescent sensor with thiocarbamate-linked DPA turns it into a highly selective module for Ag(+) with up to ~7-fold enhancement of fluorescence. The sensor exhibits a double ratiometric behavior. It also displays an interesting [Ag(+)] dependent aggregation induced emission.

A highly selective chemodosimeter for fast detection and intracellular imaging of Hg2+ ions based on a dithiocarbamate-isothiocyanate conversion in aqueous ethanol.

A new naphthalene diimide-dithiocarbamate based fluorescence probe was synthesized and its fluorogenic behavior towards various metal ions was studied. Upon addition of various metal ions, the probe afforded an irreversible change only with Hg(2+) ions in aqueous-ethanol media (4 : 1 v/v) with a fourfold enhancement of the fluorescence (Φ = 0.03 → 0.11) along with a distinct 43 nm blue shift of the emission maxima. The mechanism of the chemodosimetric behavior of the probe has been attributed to a Hg(2+) induced transformation of a weakly fluorescent dithiocarbamate to a highly fluorescent isothiocyanate which has been characterized by a number of spectroscopic techniques and a crystal structure. Intracellular detection of Hg(2+) ions was achieved using the probe.

Histidine based fluorescence sensor detects Hg2+ in solution, paper strips, and in cells.

A chemosensor having a bipodal thiocarbamate scaffold attached to histidine moieties senses Hg(2+) with a remarkable selectivity. The binding results in a 50 nm blue shift in the fluorescence spectra and a 19-fold enhancement of the fluorescence quantum yield of the ligand. In addition to the detection of Hg(2+) visually under UV light in solution, the chemosensor was used for fabrication of paper strips that detected Hg(2+) in aqueous samples. The sensor was also used for imaging Hg(2+) in adult zebrafish and in human epithelial carcinoma HeLa S3 cells.