Influence of Structural Properties of Oleic Acid-Capped CdSe/ZnS Quantum Dots in the Detection of Hg2+ Ions.

Oleic acid-capped CdSe/ZnS quantum dots (QDs) were used to investigate their photoluminescence (PL) response to Hg2+ ions as a function of the surface properties of QDs. Three distinctly-size CdSe/ZnS QDs were obtained by varying the molar ratio of shell precursors, which were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), Fourier-Transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), absorption spectroscopy, and time-resolved fluorescence spectroscopy. Results revealed the obtention of zinc blende nanocrystals with sizes ranging from 2.7 to 3.2 nm (± 0.5) and ZnS thickness between 0.3 and 1.0 monolayer (ML). The variation of the [S]/[Zn] molar ratio introduced chemical species that act as traps, affecting the PL properties differently. Depending on the thickness of the shell and chemical speciation on surface, Hg2+ ions could induce quenching or enhancement of PL. Detection of mercury ions was evaluated in terms of Stern-Volmer equation, where the limit of detection (LOD) for the PL quenching system was 11.2 nM, while for the PL enhancing systems were 8.98 nM and 10.7 nM. Results demonstrate the performance of oleic acid-capped CdSe/ZnS QDs to detect Hg2+ and their capacity to turn the PL on/off depending on surface properties.

A pH-Sensitive Fluorescent Chemosensor Turn-On Based in a Salen Iron (III) Complex: Synthesis, Photophysical Properties, and Live-Cell Imaging Application.

pH regulation is essential to allow normal cell function, and their imbalance is associated with different pathologic situations, including cancer. In this study, we present the synthesis of 2-(((2-aminoethyl)imino)methyl)phenol (HL1) and the iron (III) complex (Fe(L1)2Br, (C1)), confirmed by X-ray diffraction analysis. The absorption and emission properties of complex C1 were assessed in the presence and absence of different physiologically relevant analytes, finding a fluorescent turn-on when OH- was added. So, we determined the limit of detection (LOD = 3.97 × 10-9 M), stoichiometry (1:1), and association constant (Kas = 5.86 × 103 M-1). Using DFT calculations, we proposed a spontaneous decomposition mechanism for C1. After characterization, complex C1 was evaluated as an intracellular pH chemosensor on the human primary gastric adenocarcinoma (AGS) and non-tumoral gastric epithelia (GES-1) cell lines, finding fluorescent signal activation in the latter when compared to AGS cells due to the lower intracellular pH of AGS cells caused by the increased metabolic rate. However, when complex C1 was used on metastatic cancer cell lines (MKN-45 and MKN-74), a fluorescent turn-on was observed in both cell lines because the intracellular lactate amount increased. Our results could provide insights about the application of complex C1 as a metabolic probe to be used in cancer cell imaging.

Enhanced Host-Guest Association and Fluorescence in Copolymers from Copper Salphen Complexes by Supramolecular Internalization of Anions.

We describe the synthesis, crystallographic characterization of a new Cu-Salphen compound and its use as a host Lewis-acid against guest anions in two versions: a) free molecule, b) copolymerized with methyl methacrylate:n-butyl acrylate (1 : 4-wt.) as protective co-monomers. Higher contents in Cu-Salphen yielded larger and more homogeneous polymer sizes. Polymer size together with glass transitions, heat capacity, thermal degradation, guest-saturation degrees and host-guest species distribution profiles from spectrophotometric titrations explained growths of up to 630-fold in K11 and 180000-fold in K12 for the host's binding site attributable to a solvophobic protection from the macromolecular structure. Spectrofluorimetry revealed blue-shifted×13-16 larger luminescence for Cu-Salphen in the polymers (λem =488-498 nm) than that of the non-polymerized counterpart (λem =510-543 nm) and "turn-on" blue-shifted enhanced fluorescence upon guest association. We propose a cooperative incorporation of the guests occurring from the outer medium toward internally protected binding site pockets in the random coil polymer conformations.

Understanding the Deactivating/Activating Mechanisms in Three Optical Chemosensors Based on Crown Ether with Na+ /K+ Selectivity Using Quantum Chemical Tools.

The optical properties and transduction mechanisms in three reported optical chemosensors based on crown ether with selectivity turn-on luminescence toward Na+ over K+ , were investigated using Density Functional Theory/Time-Dependent Density Functional Theory (DFT/TD-DFT). The analysis of the structural stability of the conformers enables us to understand the optical properties of the sensors and their selectivity toward Na+ . The UV-Vis absorption and the radiative channels of the adiabatic S1 excited state were assessed. In these reported sensors, the Photoinduced Electron Transfer (PET) from the nitrogen and the oxygen (O-atoms of the substituted N-phenylaza group) lone pairs to fluorophore groups lead to a nonradiative deactivation process in the fluorophore to p-conjugated anilino-1,2,3-triazol ionophore. This Intramolecular Charge Transfer (ICT) deactivation produced the luminescence quenching in the free sensors and K+ /C1 complexes. The Na+ /sensor interaction produced a Chelation Enhanced Fluorescence (CHEF) due to the inhibition of the PET and ICT, which was confirmed via the calculated oscillator strength of the emission process. The K+ /sensor interaction displayed the possibility of PET in C3; however, this fact was inconclusive to affirm the quenching of luminescence, the CHEF in C2 and C3 and the selectivity toward Na+ over K+ in these systems. For this reason, simulation of the absorption and emissions spectra (calculated oscillator strength), calculation of the kinetic parameters (in charge transfers and radiative deactivations process), analysis of the metal-ligand interaction character, and the analysis of the structural stability of the conformers were determinant factors to understand the selectivity and the optical properties of these chemosensors. The results suggest that these theoretical tools can also be used to predict the optical properties and Na+ /K+ selectivity of optical chemosensors.

A "turn-off" fluorescent sensor based on electrospun polycaprolactone nanofibers and fluorene(bisthiophene) derivative for nitroaromatic explosive detection.

The preparation of fluorene(bisthiophene)-based fluorescent nanofibers for nitroaromatic explosive detection provides a convenient rapid and low-cost strategy aiming at forensic applications. Polycaprolactone (PCL) and fluorene(bisthiophene) derivative (FBT) nanofibers were obtained by electrospinning technique as a free-standing mat and characterized by SEM, FTIR, thermal analysis and fluorescence spectroscopy. The PCL/FBT nanofibers presented high sensitivity towards 2,4,6-trinitrotoluene (TNT) and picric acid (PA), with fluorescence quenching (turn-off mechanism), and selectivity to another kind of explosives. The free-standing mats were used as a cloth strip that was swiped on surfaces contaminated with TNT traces allowing its visual detection under UV light source. These findings are particularly important for the development of a facile and promising strategy to assembly portable optical devices for nitroaromatic explosive detection.

A multiple comparative study of putative endosymbionts in three coexisting apple snail species.

We here compare morphological and molecular characters of some putative endosymbiotic elements of the digestive gland of three ampullariid species (Pomacea canaliculata, Pomacea scalaris and Asolene platae) which coexist in Lake Regatas (Palermo, Buenos Aires). The putative endosymbionts were reported in these species and were identified as C and K corpuscles. The three species show tubuloacinar glands, each adenomere was constituted mainly by two distinct cell types (columnar and pyramidal). C and K corpuscles together occupied from one-fourth to one-fifth of the tissue area in the three host species, where C corpuscles were round and greenish-brown, were delimited by a distinct wall, stained positively with Alcian Blue and were associated with columnar cells. K corpuscles were oval, dark-brown multilamellar bodies and were associated with pyramidal cells. Under TEM, C corpuscles occurred within vacuoles of columnar cells and contained many electron-dense clumps and irregular membrane stacks and vesicles spread in an electron-lucent matrix. Sometimes a membrane appeared detached from the inner surface of the wall, suggesting the existence of a plasma membrane. In turn, K corpuscles were contained within vacuoles of pyramidal cells and were made of concentric lamellae, which were in turn made of an electron-dense fibrogranular material. No membranes were seen in them. Interspecifically, C corpuscles vary significantly in width and inner contents. K corpuscles were also variable in length and width. However, both C and K corpuscles in the three studied species hybridised with generalised cyanobacterial/chloroplast probes for 16S rRNA. Also, both corpuscle types (isolated from gland homogenates) were sensitive to lysozyme digestion, which indicates that bacterial peptidoglycans are an integral part of their covers. The reported data confirm and extend previous studies on P. canaliculata in which the endosymbiotic nature of C and K corpuscles were first proposed. We further propose that the endosymbiotic corpuscles are related to the Cyanobacteria/chloroplasts clade. Based on the known distribution of these corpuscles in the major clades of Ampullariidae, we hypothesise they may be universally distributed in this family, and that may constitute an interesting model for studying the co-evolution of endosymbionts and their gastropod hosts.

Recognition of Mg²âº by a new fluorescent "turn-on" chemosensor based on pyridyl-hydrazono-coumarin.

A new fluoroionophore PyHC bearing 2-pyridylhydrazone and 7-hydroxycoumarin moieties for selective detection of Mg(2+) was synthesized and characterized. This chemosensor exhibited "turn-on" fluorescence behavior and was sensitive to Mg(2+) concentrations as low as 105 nmol L(-1) in ethanol-water solution. Detailed spectroscopic studies revealed the binding mode of a 1:1 complex between PyHC and Mg(2+) that leads to a fluorescence enhancement.

A sensitive biosensor for the fluorescence detection of the acetylcholinesterase reaction system based on carbon dots.

The carbon dots (C-dots) with high fluorescence quantum yield were prepared using hydrothermal method. C-dots have been adopted as probes for the fluorescence turn-off detection of H2O2 based on the special sensibility for the hydroxyl radical. And then the biosensors for the detection of substrate and enzymes activities were established in the acetylcholinesterase reaction system, which were related to the production of H2O2. Specifically, the proposed fluorescent biosensor was successfully applied to detect the concentration of choline (in the range from 0.025 to 50 µM) and acetylcholine (in the range from 0.050 to 50 µM), and the activity of choline oxidase (in the range from 1 to 75 U/L) and acetylcholinesterase (1 to 80 U/L). These results showed a sensitive, universal, nontoxic and eco-friendly detecting technique has been developed.

Structure-activity relationship of Trp-containing analogs of the antimicrobial peptide gomesin.

Gomesin (Gm) has a broad antimicrobial activity making it of great interest for development of drugs. In this study, we analyzed three Gm analogs, [Trp(1) ]-Gm, [Trp(7) ]-Gm, and [Trp(9) ]-Gm, in an attempt to gain insight into the contributions of different regions of the peptide sequence to its activity. The incorporation of the tryptophan residue in different positions has no effect on the antimicrobial and hemolytic activities of the Gm analogs in relation to Gm. Spectroscopic studies (circular dichroism, fluorescence and absorbance) of Gm and its analogs were performed in the presence of SDS, below and above its critical micelle concentration (CMC) (~8 mM), in order to monitor structural changes induced by the interaction with this anionic surfactant (0-15 mM). Interestingly, we found that the analogs interact more strongly with SDS at low concentrations (0.3-6.0 mM) than close to or above its CMC. This suggests that SDS monomers are able to cover the whole peptide, forming large detergent-peptide aggregates. On the other hand, the peptides interact differently with SDS micelles, inserting partially into the micelle core. Among the peptides, Trp in position 1 becomes more motionally-restricted in the presence of SDS, probably because this residue is located at the N-terminal region, which presents higher conformational freedom to interact stronger with SDS molecules. Trp residues in positions 7 and 9, close to and in the region of the turn of the molecule, respectively, induced a more constrained structure and the compounds cannot insert deeper into the micelle core or be completely buried by SDS monomers.