Light activated simultaneous release and recognition of biological signaling molecule carbon monoxide (CO).

The therapeutic action of carbon monoxide (CO) is very well known and has been studied on various types of tissues and animals. However, real-time spatial and temporal tracking and release of CO is still a challenging task. This paper reported an amphiphilic CO sensing probe NP and phospholipid 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) based nanoscale vesicular sensing system Ves-NP consisting of NP. The liposomal sensing system (Ves-NP) showed good selectivity and sensitivity for CO without any interference from other relevant biological analytes. Detection of CO is monitored by fluorescence OFF-ON signal. Ves-NP displayed LOD of 5.94 µM for CO detection with a response time of 5 min. Further, in a novel attempt, Ves-NP is co-embedded with the amphiphilic CO-releasing molecule 1-Mn(CO)3 to make an analyte replacement probe Ves-NP-CO. Having a both CO releasing and sensing moiety at the surface of the same liposomal system Ves-NP-CO play a dual role. Ves-NP-CO is used for the simultaneous release and recognition of CO that can be controlled by light. Thus, in this novel approach, for the first time we have attached both the release and recognition units of CO in the vesicular surface, both release and recognition simultaneously monitored by the change in fluorescent OFF-ON signal.

Regulation of Nitric Oxide (NO) Release by Membrane Fluidity in Ruthenium Nitrosyl Complex-Embedded Phospholipid Vesicles.

Incorporating water-insoluble nitric oxide (NO)-releasing molecules into biocompatible vesicles may allow for the tunable control of NO release on a specific target site. In vesicles, membrane fluidity plays an important role and influences the final therapeutic efficiency of drugs loaded into the vesicles. Hence, we aimed to investigate the effect of lipid fluidity on the NO release behavior of the photo-controllable ruthenium nitrosyl (Ru-NO) complex. In this regard, a new photoactive ruthenium nitrosyl complex (L.Ru-NO) with amphiphilic terpyridine ligand was synthesized and characterized in detail. L.Ru-NO was incorporated with commercial phospholipids to form nanoscale vesicles L.Ru-NO@Lip. The photoactive {Ru-NO}6 type complex released NO in the organic solvent CH3CN and aqueous liposome solution by irradiating under low-intensity blue light (λ = 410 nm, 3 W). To demonstrate the effect of lipid structure and fluidity on NO release, four different liposome systems L.Ru-NO@Lip1-4 were prepared by using phospholipids such as DOPC, DSPC, DPPC, and DMPC having different chain lengths and saturation. The NO-releasing abilities of these liposomes in aqueous medium were studied by UV-vis spectrum, colorimetric Greiss, and fluorescent DAF assay. The results show that the rate of NO release could be easily tuned by varying the lipid fluidity. The effect of temperature and pH on NO release was also studied. Further, the complex L.Ru-NO and liposomes L.Ru-NO@Lip1 were assayed as an antibacterial agent against the strains of bacteria Escherichia coli and Staphylococcus aureus.

A simple colorimetric sensor for the detection of moisture in organic solvents and building materials: applications in rewritable paper and fingerprint imaging.

A simple off-the-shelf dye molecule, 1,4-dihydroxy-9,10-anthraquinone or quinizarin (1), has been investigated for the effective detection of moisture in organic solvents and building materials. Anion-induced deprotonation of 1 to 1.F followed by re-protonation with water is the working principle of the sensor system. Changes in colour, UV-Vis spectra and emission intensity indicate the moisture detection of 1.F in various organic solvents. The probe 1.F is more effective at the detection of water in acetonitrile and THF with a LOD of 0.0011 and 0.0026 wt%. Probe 1.F is reversible, reusable, highly selective, and sensitive and has a fast response time both in solution phase and in test papers. Probe 1.F is also applied for the detection of unknown moisture content in raw building materials such as cement, fly ash, foundry sand, and limestone. 1.F incorporated cellulose-based papers are applicable for inkless writing and stamping in the read-erase manner. Furthermore, these papers are also suitable for fingerprint imaging and sweat pore mapping by the simple colour change method.

Allosteric Regulation in Carbon Monoxide (CO) Release: Anion Responsive CO-Releasing Molecule (CORM) Derived from (Terpyridine)phenol Manganese Tricarbonyl Complex with Colorimetric and Fluorescence Monitoring.

A new CO-releasing terpyridine based manganese(I) tricarbonyl complex, [MnBr(CO)3(terpy-C6H4OH)] (1·Mn-OH) functioning via light has been reported. For the first time, we have demonstrated the allosteric regulation concept to control the CO-releasing properties of a CO-releasing molecule (CORM). Fluoride ion is reported to function as an allosteric activator to control the rate of CO release in the CORM. Complex 1·Mn-OH represents an interesting new class of CO-releasing system that releases CO upon irradiation with blue light (410 nm) over a period of 40 min with the half-time of 9.8 min. Fluoride ion selectively binds to the phenol moiety of the complex through hydrogen bonding and deprotonates to phenolate with a color change. Interestingly in the presence of fluoride ion, the rate of CO release is fast with the half-time of less than a minute. The rate of CO release is allosterically regulated by fluoride anion and can be monitored through a color change, fluorescence, and absorption based spectral changes along with IR studies and myoglobin assay.

Detection of Moisture by Fluorescent OFF-ON Sensor in Organic Solvents and Raw Food Products.

Copper complex based on a new class of fluorescence OFF-ON sensor 1.Cu has been reported for the detection of trace amounts of water in various organic solvents such as CH3OH, THF, CH3CN, and acetone by means of fluorescence emission intensity. The probe is highly responsive to water in THF (DL = 0.003 wt %). The dissociation of copper from probe 1.Cu in the presence of water is responsible for the fluorescence change and it was confirmed by electrospray ionization-mass spectrometry (ESI-MS), proton nuclear magnetic resonance (1H-NMR), and fluorescence lifetime studies. Real application of the probe was successfully applied for the detection of moisture content in commercial products such as salt, sugar, wheat, and washing powder.

Bis(phosphite) ligands with distal regulation: application in rhodium-mediated asymmetric hydroformylations.

Small amounts of achiral polyether binders are employed to enhance the enantioselectivity of the hydroformylation of an array of diversely substituted substrates (increase of up to 62% ee for vinyl acetate) mediated by chiral rhodium complexes derived from the α,ω-bis(phosphite)-polyether ligands 1. To the best of our knowledge, this study represents an unprecedented successful example of the positive regulation of enantioselectivity in hydroformylations.

Allosteric indicator displacement enzyme assay for a cyanogenic glycoside.

Indicator displacement assays (IDAs) represent an elegant approach in supramolecular analytical chemistry. Herein, we report a chemical biosensor for the selective detection of the cyanogenic glycoside amygdalin in aqueous solution. The hybrid sensor consists of the enzyme ß-glucosidase and a boronic acid appended viologen together with a fluorescent reporter dye. ß-Glucosidase degrades the cyanogenic glycoside amygdalin into hydrogen cyanide, glucose, and benzaldehyde. Only the released cyanide binds at the allosteric site of the receptor (boronic acid) thereby inducing changes in the affinity of a formerly bound fluorescent indicator dye at the other side of the receptor. Thus, the sensing probe performs as allosteric indicator displacement assay (AIDA) for cyanide in water. Interference studies with inorganic anions and glucose revealed that cyanide is solely responsible for the change in the fluorescent signal. DFT calculations on a model compound revealed a 1:1 binding ratio of the boronic acid and cyanide ion. The fluorescent enzyme assay for ß-glucosidase uses amygdalin as natural substrate and allows measuring Michaelis-Menten kinetics in microtiter plates. The allosteric indicator displacement assay (AIDA) probe can also be used to detect cyanide traces in commercial amygdalin samples.

A ruthenium nitrosyl complex-based highly selective colorimetric sensor for biological H2S and H2S-NO cross-talk regulated release of NO.

A ruthenium nitrosyl complex (1·NO) and 1·NO incorporated phospholipid-based liposomes (Lip-1·NO) were reported for highly selective colorimetric detection of H2S. The probe 1·NO "cross-talks" with H2S and releases nitric oxide (NO) in the process. The detection limit for H2S was found to be 0.31 µM and 0.45 µM in the cases of 1·NO and Lip-1·NO, respectively. The DAF-FM DA assay has been performed to confirm the H2S-induced NO release from 1·NO and Lip-1·NO. The sensing of H2S was also verified by ESI-MS and FT-IR spectroscopy. It was also observed that external stimuli, H2S and light worked in an almost similar way to release NO as observed by UV-Vis spectroscopy. A molecular logic gate operation "OR" was applied to the probe 1·NO in combination with inputs 'light' and 'H2S' to give the output 'NO release'. Hence, the probe 1·NO performs the dual work of sensing H2S with a colorimetric response, releasing NO upon cross-talk between NO and H2S.

Liposome Based Near-Infrared Sensors for the Selective Detection of Hydrogen Sulfide.

Cyanine dye-based new amphiphilic compound NIR-Amp has been synthesised. NIR-Amp was embedded with phospholipids DOPC and DPPC to form liposomes based nanoscale chemical sensors NIR-Lip1 and NIR-Lip2. Here, two different phospholipids were used to demonstrate the influence of lipid structure, composition and fluidity on sensing of nanosensors. Both the probes show NIR absorption maximum at 790 nm and emission maximum at 815 nm. H2 S-triggered thiolation resulted a remarkable change in color from green to pale yellow. A decrease in UV-Vis absorption and emission in the NIR region was observed only with H2 S. NIR-Lip1 and NIR-Lip2 are highly selective for H2 S with a LOD of 0.57 µM and 1.24 µM, respectively. It was observed that in a solid-like gel state, NIR-Lip1 is slightly more sensitive towards H2 S than fluid-like NIR-Lip2. The H2 S sensing mechanism was confirmed by ESI-mass and infrared (IR) spectroscopic analysis. Based on the high sensitivity and selectivity, NIR-Lip1 was employed to detect H2 S in vegetable samples. Further, the probes are found to be non-toxic and established for H2 S fluorescence imaging in live cells.

Multi analyte sensing of amphiphilic tridentate bis(benzimidazolyl)pyridine incorporated in liposomes and potential application in enzyme assay.

A liposome based nanosensor Lipo-1 for efficient detection of copper, cyanide (CN-) and ATP in a pure aqueous medium has been described. Lipo-1 shows a fluorescence ON-OFF response with copper. However, Lipo-1.Cu (Lipo-1 and copper ensemble) was used for the OFF-ON detection of ATP with nM and CN- with µM detection levels, lower than the WHO permissible level for safe drinking. Lipo-1 has better and enhanced binding properties over the counter organic amphiphilic compound Bzimpy-LC, which is not soluble in water. The significant changes in the emission spectra in the presence of Cu2+, CN- and ATP ions, as variable inputs, are used to construct INHIBIT and OR logic operations in a nano-scale environment. The fluorescent detection of CN- ions with Lipo-1.Cu was used to develop an enzyme assay for ß-glucosidase using amygdalin as the substrate. ß-Glucosidase enzymatic activity was monitored by the emission OFF-ON signal of the probe Lipo-1.Cu by CN- detection. This approach could be an efficient method for developing a fluorescence-based ß-glucosidase enzyme assay. A switch ON luminescence response, low detection limit, fast response, 100% aqueous solution, biocompatibility, multi-analyte detection, and improved sensitivity and selectivity of Bzimpy-LC in lipid bilayer membranes are the main features of the nanoprobe Lipo-1. These properties give it a clear advantage for analytical applications.

Polydiacetylene vesicles functionalized with N-heterocyclic ligands for metal cation binding.

Self assembled poly diacetylene (PDA) based blue vesicles LS-Terpy, LS-DPA, LS-DP and LS-DEA with metal chelating sites have been prepared and characterized. Their response to the presence of metal cations in buffered aqueous solution has been investigated by monitoring changes of colour, UV-Vis absorption and emission. The addition of zinc, manganese, cadmium, mercury or silver salts to solutions of the vesicles induces a colour change from blue to red observable by the naked eye, while the addition of other metal salts, containing ions like Li(+), Na(+), K(+), Mg(2+), Ca(2+), Cr(2+), Ni(2+), Fe(2+), Co(2+), Cu(2+) or Pb(2+), failed to show any changes. The metal ion coordination selectivity of the ligands is slightly different for the vesicle surface immobilized ligands compared to the reported metal cation binding of the corresponding ligands in solution, which may be due to the special environment at the lipid-solution interface. The vesicles aggregate upon metal ion coordination to the embedded ligands as shown by dynamic light scattering (DLS) particle size analysis. The functionalized PDA vesicles retain their response to the presence of aqueous solutions of metal ions if immobilized in transparent polyvinyl alcohol films or on paper.

Naked eye detection of moisture in organic solvents and development of alginate polymer beads and test cassettes as a portable kit.

New dabsyl-thiophene based receptor DABT and its mercury complex DABT-Hg is reported as a colorimetric sensor for rapid and sensitive detection of trace amount of water in aprotic solvents. Based on intramolecular charge transfer in the excited state, the receptor dabsyl-thiophene (yellow color) binds with the mercury ions (magenta color) to stimulate a colorimetric response. The mercury complex is used as a moisture sensor in THF, acetone, and acetonitrile due to its instability in moisture containing organic solvents. The probe exhibits higher sensitivity towards water in THF (LOD = 0.0041% w/w), acetone (LOD = 0.0144% w/w) and acetonitrile (LOD = 0.1008% w/w). The dissociation of mercury from probe DABT-Hg in the presence of water is accountable for the colorimetric response as proven by the 1H NMR and ESI-MS studies. DABT-Hg is the first mercury based complex for the detection of moisture in organic solvents. Test paper strip and PVA thin film doped with the probe were successfully used to detect moisture content in organic solvents. DABT-Hg incorporated alginate beads are prepared to determine the water content in triethylamine and ethylene glycol. Portable test cassettes are developed for the on-site detection of distilled and undistilled wet solvents in the chemical laboratory through naked-eye detection.

Nanoscale lipid vesicles functionalized with a nitro-aniline derivative for photoinduced nitric oxide (NO) delivery.

Nanoscale vesicles functionalized with a nitric oxide (NO) releasing molecule 4-nitro-3-(trifluoromethyl)aniline have been reported. The new NO-nano-vesicular donor material shows an effective photo-release of NO upon irradiation with blue light at 410 nm. The kinetics of NO release has been monitored by using simple spectroscopic techniques such as UV-Vis and fluorescence methods. Colorimetric Griess assay and fluorescence DAF assay have been used for the detection and quantification of NO released from vesicles. This new vesicular nanoscale NO donor has the advantages of facile preparation in water, capable of releasing NO in a pure aqueous medium, photo-controlled NO release, bio-compatibility and capacity to modulate the NO donor loading to achieve an essential amount of NO.

Sensing and Bioimaging of the Gaseous Signaling Molecule Hydrogen Sulfide by Near-Infrared Fluorescent Probes.

A fluorescent probe for the monitoring of H2S levels in living cells and organisms is highly desirable. In this regard, near-infrared (NIR) fluorescent probes have emerged as a promising tool. NIR-I and NIR-II probes have many significant advantages; for instance, NIR light penetrates deeper into tissue than light at visible wavelengths, and it causes less photodamage during biosample analysis and less autofluorescence, enabling higher signal-to-background ratios. Therefore, it is expected that fluorescent probes having emission in the NIR region are more suitable for in vivo imaging. Consequently, a considerable increase in reports of new H2S-responsive NIR fluorescent probes appeared in the literature. This review highlights the advances made in developing new NIR fluorescent probes aimed at the sensitive and selective detection of H2S in biological samples. Their applications in real-time monitoring of H2S in cells and in vivo for bioimaging of living cells/animals are emphasized. The selection of suitable dyes for designing NIR fluorescent probes, along with the principles and mechanisms involved for the sensing of H2S in the NIR region, are described. The discussions are focused on small-molecule and nanomaterials-based NIR probes.

Polydiacetylene-based colorimetric self-assembled vesicular receptors for biological phosphate ion recognition.

Self-assembled vesicular polydiacetylene (PDA) particles with embedded metal complex receptor sites have been prepared. The particles respond to the presence of ATP and PPi (pyrophosphate) in buffered aqueous solution by visible changes of their color and emission properties. Blue PDA vesicles of uniform size of about 200 nm were obtained upon UV irradiation from mono- and dinuclear zinc(II)-cyclen and iminodiacetato copper [Cu(II)-IDA] modified diacetylenes, embedded in amphiphilic diacetylene monomers. Addition of ATP and PPi to the PDA vesicle solution induces a color change from blue to red observable by the naked eye. The binding of ATP and PPi changes the emission intensity. Other anions such as ADP, AMP, H2PO4-, CH3COO-, F-, Cl-, Br- and I-, failed to induce any spectral changes. The zinc(II)-cyclen nanoparticles are useful for the facile detection of PPi and ATP in millimolar concentrations in neutral aqueous solutions, while Cu(II)-IDA modified vesicular PDA receptors are able to selectively discriminate between ATP and PPi.

Copper Complex-Embedded Vesicular Receptor for Selective Detection of Cyanide Ion and Colorimetric Monitoring of Enzymatic Reaction.

Detection of environmentally important ion cyanide (CN-) has been done by a new method involving displacement of both metal and indicator, metal indicator displacement approach (MIDA) on the vesicular interface. Terpyridine unit was selected as the binding site for metal (Cu2+), whereas Eosin-Y (EY) was preferred as an indicator. About 150 nm sized nanoscale vesicular ensemble (Lip-1.Cu) has shown good selectivity and sensitivity for CN- without any interference from other biologically and environmentally important anions. Otherwise, copper complexes are known for the interferences of binding with phosphates and amino acids. The Lip-1.Cu nanoreceptor also has the possibility to be used for real-time colorimetric scanning for the released HCN via enzymatic reactions. Lip-1.Cu has several superiorities over the other reported sensor systems. It has worked in 100% aqueous environment, fast response time with colorimetric monitoring of enzymatic reaction, and low detection limit.

Colorimetric sensor for triphosphates and their application as a viable staining agent for prokaryotes and eukaryotes.

The chromogenic complex 1 x Zn (where 1 is (E)-4-(4-dimethylamino-phenylazo)-N,N-bispyridin-2-ylmethyl-benzenesulfonamide) showed high affinity toward the phosphate ion in tetrabutylammonium phosphate in acetonitrile solution and could preferentially bind to adenosine triphosphate (ATP) in aqueous solution at physiological pH. This binding caused a visual change in color, whereas no such change was noticed with other related anions (adenosine monophosphate, adenosine diphosphate, pyrophosphate, and phosphate) of biological significance. Thus, 1 x Zn could be used as a staining agent for different biological cells through binding to the ATP, generated in situ by the mitochondria (in eukaryotes). For prokaryotes (bacteria) the cell membrane takes care of the cells' energy conversion, since they lack mitochondria. ATP is produced in their unique cell structure on the cell membrane, which is not found in any eukaryotes. These stained cells could be viewed with normal light microscopy. This reagent could even be used for distinguishing the gram-positive and the gram-negative bacteria (prokaryotes). This dye was found to be nonlipophilic in nature and nontoxic to living microbes (eukaryotes and prokaryotes). Further, stained cells were found to grow in their respective media, and this confirmed the maintenance of viability of the microbes even after staining, unlike with many other dyes available commercially.

Vesicles Functionalized with a CO-Releasing Molecule for Light-Induced CO Delivery.

In this paper, a new type of methodology to deliver carbon monoxide (CO) for biological applications has been introduced. An amphiphilic manganese carbonyl complex (1.Mn) incorporated into the 1,2-distearoyl-sn-glycero-3-phosphocholine lipid vesicles has been reported first time for the photoinduced release of CO. The liposomes (Ves-1.Mn) gradually released CO under light at 365 nm over a period of 50 min with a half-time of 26.5 min. The CO-releasing ability of vesicles appended with 1.Mn complexes has been confirmed by myoglobin assay and infrared study. The vesicles appended with 1.Mn have the advantages of biocompatibility, water solubility, and steady and slow CO release. This approach could be a rational approach for applying various water-insoluble photoinduced CO donors in aqueous media by using vesicles as a nanocarrier for CO release.

Colorimetric sensor for the detection of H2S and its application in molecular half-subtractor.

Azine based new colorimetric sensor 1 for the detection of gasotransmitter H2S has been reported. Sensor 1 used to detect the H2S with a remarkable red shift of 105 nm in the absorption spectra with a colour change from light yellow to brown red. Importantly, rare example of azine derivative has been used as a colorimetric probe for H2S detection using deprotonation mechanism. H2S induced deprotonation of one of the -OH proton followed by a change in resonance of 1 is responsible for the ratiometric spectral and colour change. The detection response was quick and the LOD calculated as 18.2 µM. Sensor 1 was also explored in the detection of H2S in biological fluids such as human serum and mouse serum. Moreover, for the first time, we have shown the applicability of H2S for the construction of half subtractor molecular logic gate.

Selective Detection of H2S by Copper Complex Embedded in Vesicles through Metal Indicator Displacement Approach.

A new approach for the detection of hydrogen sulfide (H2S) was constructed within vesicles comprising phospholipids and amphiphilic copper complex as receptor. 1,2-Distearoyl- sn-glycero-3-phosphocholine (DSPC) vesicles with embedded metal complex receptor (1.Cu) sites have been prepared. The vesicles selectively respond to H2S in a buffered solution and show colorimetric as well as spectral transformation. Other analytes such as reactive sulfur species, reactive nitrogen species, biological phosphates, and other anions failed to induce changes. The H2S detection is established through a metal indicator displacement (MIDA) process, where Eosin-Y (EY) was employed as an indicator. Fluorescence, UV-vis spectroscopy, and the naked eye as the signal readout studies confirm the high selectivity, sensitivity, and lower detection limit of the vesicular receptor. The application of vesicular receptors for real sample analysis was also confirmed by fluorescence live cell imaging.