Colorimetric and Fluorescent Sensing of SCN- Based on meso-Tetraphenylporphyrin/meso-Tetraphenylporphyrin Cobalt(II) System

G-Quadruplex selectivity and cytotoxicity of a guanidine-encapsulated porphyrin-cyclodextrin conjugate

G-Quadruplex DNAs represent out-of-the-way nucleic acid conformations, frequently formed by guanine-rich sequences. They have emanated as cancer-associated targets for designed small molecules. The variation in the binding affinity of the synthesized compounds to duplex and quadruplex structures is an intriguing quest, solved by spectroscopic analysis. In this paper, we report the synthesis of a porphyrin-cyclodextrin conjugate, characterized by utilizing FT-IR, NMR, and mass spectrometry. Further, two benzimidazolylguanidines are synthesized which form host: guest complexes with the porphyrin-cyclodextrin conjugate. The structure of the complexes is optimized by analyzing their 2D ROESY spectra. The interactions of the host, guest, and the host: guest complexes with the duplex (calf thymus DNA) and quadruplex (kit22) nucleic acids are investigated employing UV-vis, fluorescence, circular dichroism, and DNA melting experiments. The calculated strengths of the compounds' binding with kit22 are in the order of 10⁶, which is larger than those observed for the duplex DNA binding. The significant G-quadruplex selectivity of the host: guest complex of anthracenyl-benzimidazolylguanidine is discussed in detail. Further, the in vitro cytotoxicity of the compounds on MCF-7 cell lines is examined. The host: guest complexes show enhanced half-maximal inhibitory concentration values compared to the un-complexed compounds.

Co(III)-tetra(4-sulfonatophenyl)porphyrin complexes with bidentate ligands in aqueous buffer media

The processes of hydrophilic Co(III)-tetra(4-sulfonatophenyl)porphyrin supramolecular assembly with 4,4-bipyridyl in aqueous buffer media have been studied by UV-vis, 1D and 2D 1H NMR-spectroscopy. In the case of 1,4-diazabicyclo[2.2.2]octane, pyrazine and piperazine in aqueous solutions, no assembly was observed. Interactions of the hydrophilic Co(III)-tetraarylporphyrin with ionic micelles (cationic surfactants with different alkyl tail lengths) in buffer media were investigated. These studies were performed by the UV-vis, 1D NOESY-spectroscopy and dynamic lightscattering (DLS) methods. The metalloporphyrins were incorporated into the hydrophobic part of micelles, which led to Co(III) reduction to Co(II) in the Co-porphyrinate composition. The rate of Co(III) reduction accompanied by detachment of additional ligands coordinated on Co(III)-porphyrins or disruption of supramolecular dimers and depends on the surfactant concentration and nature. The results obtained indicate the possibility of creating supramolecular porphyrin-based assemblies with the preprogrammed lifetime (from several hours to several days) and could be used in the creation of host-guest systems for recognition, selective binding and the prolonged release of bioactive substrates as the means in the designing of biomimetic systems with effective binding affinities to heterocycles, DNA base pairs and RNA.

Optical detection of thiocyanate in human saliva based on the colorimetric response of (2-(2-hydroxyphenyl)-1H-benzo[d]imidazol-5-yl)(phenyl) methanone (HBPM)/Co2+ ions conjugate

Simple colorimetric biosensor was designed for the quantification SCN^- ions based on the principle of colorimetric reactions between Co²⁺ and SCN^- ions reaction using synthesized chromophore (2-(2-hydroxyphenyl)-1H-benzo[d]imidazol-5-yl)(phenyl) methanone (HBPM)/Co²⁺ ions conjugate which was synthesized via greener ultrawave sonication method. The structural characterization of the HBPM chromophore was confirmed by using NMR, ESI-MASS spectral techniques and the photophysical properties, sensor studies were done by using UV-Vis Spectrophotometer. Our designed HBPM/Co²⁺ ions conjugates have selectively detected SCN^- ions qualitatively and quantitatively in the presence of other human salivary interferents. As per clinical point of view, three different ranges of SCN^- ions from 0.1 to 2 mM for normal, 3 to 10 mM for disease, and 100-600 µM for below normal ranges were tested successfully by our developed sensor and the LoD was calculated as 5.43 nM. The real potent application of the developed biosensor was tested in human salivary samples of both smokers and non-smokers under different ages and obtained results shown good agreement with existing clinical methods.

Isothiocyanate l-argininato copper(II) complexes - Solution structure, DNA interaction, anticancer and antimicrobial activity

l-argininato copper(II) complexes have been intensively investigated in a variety of diseases due to their therapeutic potential. Here we report the results of comprehensive structural studies (ESI-MS, NIR-VIS-UV, EPR) on the complexes arising in aqueous solutions of two ternary copper(II) complexes with molecular formulas from crystal structures, [Cu(l-Arg)₂(NCS)](NCS)·H₂O (1) and [Cu(l-Arg)(NCS)₂] (2) (l-Arg = l-arginine). Reference systems, the ternary Cu(II)/l-Arg/NCS^- as well as binary Cu(II)/NCS^- and Cu(II)/l-Arg, were studied in parallel in aqueous solutions by pH-potentiometric titration, EPR and VIS spectroscopy to characterize stability, structures and speciation of the formed species over the broad pH range. Comparative analysis of the obtained results showed that at a pH close to 7.0 mononuclear [Cu(l-Arg)₂(NCS)]⁺ is the only species in water solution of 1, while equilibrium between [Cu(l-Arg)(SCN)]⁺ and binary [Cu(l-Arg)₂]²⁺ was detected in water solution of 2. According to DNA binding studies, the [Cu(l-Arg)₂(NCS)]⁺, [Cu(l-Arg)(SCN)]⁺ and [Cu(l-Arg)₂]²⁺ species could be considered as strong minor groove binding agents causing, in the presence of H₂O_2, the involvement of ROS in plasmid damage. The human carcinoma cells (A549 cell line) were generally significantly more sensitive to cytotoxic and antiproliferative effect of compounds 1 and 2 than human normal cells. The studied compounds shown antimicrobial activity against bacteria belonging to Enterobacteriaceae family.

How to identify a smoker: a salient crystallographic approach to detect thiocyanate content

There is an increasing demand for monitoring environmental pollutants and the control requires new sensing materials with better sensitivity, selectivity and reliability. In this study, a series of Co₇ clusters incorporating various flexible polyhydroxyamine ligands are explored, with the first report of thiocyanate recognition triggered by crystal formation using a Co₇ crystal (1). For this, we have fortunately synthesized three new mixed metal Co₇ clusters with fascinating structural features. The clusters were characterized by spectroscopic and single crystal X-ray diffraction methods and later by DFT calculations. Due to its better emission spectrum, 1 was further utilized for evaluating its sensing ability towards various anions in water. Surprisingly, 1 shows better quenching ability towards the recognition of SCN⁻ with a better binding constant. The luminescence quenching towards SCN⁻ detection was further verified by the single crystal method, HSAB principle (symbiosis) and theoretical calculations such as DFT studies. The SCXRD data clearly suggest that the Co₇ (1) can be converted into Co₁₄ (1a) by direct reaction with NaSCN under ambient conditions. Besides the soft/hard acid–base concept (symbiosis), the energies of formation, and Co–NCS and Co–OH₂ bond energies (as unravelled by DFT) are responsible for this transformation. Therefore, 1 can be used as a selective and sensitive sensor for the detection of thiocyanate anions based on the fluorescence amplification and quenching method. Further, the designed cluster has also been utilized to detect anions in human blood samples to differentiate a smoker and a non-smoker. It has been concluded that the samples of smokers have a high degree of thiocyanate (∼12 or 9.5 mg L⁻¹) in comparison to those of non-smokers (2–3 mg L⁻¹). Thus, this kind of cluster material has high potentiality in the field of bio-medical science in future endeavours for identification of the extent of thiocyanate content in smokers.

A new Co based sensor for thiocyanate recognition by formation of the dimeric crystals is designed to distinguish a smoker from a non-smoker.

Inhibited oxidase mimetic activity of palladium nanoplates by poisoning the active sites for thiocyanate detection

In this work, a novel convenient colorimetric method for sensitive detection of thiocyanate (SCN^-) has been developed based on its suppression of the oxidase-like activity of palladium square nanoplates on reduced graphene oxide (Pd SP@rGO). SCN^- can be adsorbed onto the surface of Pd SP@rGO via binding with Pd atoms and blocks the active sites that mimic oxidase, thus inhibiting the corresponding chromogenic reaction of 3,3',5,5'-tetramethylbenzidine, which has been comprehensively revealed by the UV-vis spectra and X-ray photoelectron spectra. The color fading exhibits SCN^- concentration-dependent behavior and can be easily recorded by either UV-vis spectroscopy or naked-eye observation. Therefore, both quantitative detection via measurement of the decrease in absorbance and visual detection of SCN^- can be achieved. Owing to the intrinsic amplification of signals by the oxidase-like activity of Pd SP@rGO without resorting to unstable and destructive H₂O₂, this assay is straightforward, robust and sensitive enough for the detection of SCN^- in real samples. Furthermore, an "INH" logic gate is rationally constructed based on the proposed colorimetric SCN^- sensor.

The small silver nanoparticle-assisted homogeneous sensing of thiocyanate ions with an ultra-wide window based on surface-enhanced Raman-extinction spectroscopy

For the first time, we present an original sensing strategy with an ultra-wide detection window from 17 nM to 20 mM to detect SCN- ions. Initially, we investigated the clustering and optical properties of noble metal sol nanoparticles (NPs) due to the competitive interaction of thiocyanate ions (SCN-) and cetyltrimethylammonium bromide (CTAB) under weak acidic conditions, and found that different dimensions and scales of nanoclusters containing the alkyne-embedded Au@Ag NPs and relatively small Ag NPs could be achieved by the mediation of CTAB through electrostatic forces and hydrophobic interaction, in which SCN- could be covalently bonded with the silver surface of NPs to form a compact molecular layer (-Ag-S-C[triple bond, length as m-dash]N), and CTAB could only occupy remaining sites. In this process, we found that SCN- always runs counter to CTAB and tends to dissolve nanoclusters, so that they occupy the exposed surface of NPs in nanoclusters rather than the binding sites of one another. Remarkably, when the concentration of SCN- initially increased, two highly recognizable SERS emissions, which were assigned to alkyne reporter molecules (2208 cm-1) and C[triple bond, length as m-dash]N of SCN- (2110 cm-1), respectively, were rapidly detected, and their ratios (I2110/I2208) increased linearly proportional to the concentration of SCN- over a range of 17 nM to 172 μM, with a limit of detection (LOD) of 10 nM. With the further increase of SCN-, small Ag NPs started to desorb from the surface of individual Au@Ag NPs and dissociated in the solution but did not contribute to SERS signals. Instead, the surface plasmon resonance (SPR) peak of pure silver NPs at 385 nm increased gradually in the range from 0.5 to 20 mM with an LOD of 0.2 mM. Of particular significance, this simple sensor in conjunction with surface-enhanced Raman-extinction spectroscopy can be used for the rapid detection of extensive samples with an ultra-wide detection window, such as body fluids (saliva, urine, and serum) and food (milk powder and brassica vegetables), which is far superior to that of ion chromatography (IC).

Selective Fluorescent Sensing of Adenine Via the Emissive Enhancement of a Simple Cobalt Porphyrin

Porphyrins absorb strongly in the visible region and are also excellent fluorophores that emit in the visible region that make them excellent candidates for fluorescence sensing and in vivo imaging. This work describes the fluorescence determination of adenine using cobalt complex of a simple porphyrin. Tetraphenylporphyrin (TPP) and tetraphenylpophyrinatocobalt(II) (CoTPP) were synthesized and characterised. TPP on metallation with cobalt resulted in the red shift of fluorescence emission in the region 652 nm and 716 nm and showed an enhancement in the emission peaks with the addition of the nucleobase, adenine. CoTPP is found to be an efficient fluorescent sensor for adenine in DMF solvent. The fluorescence enhancement is due to the formation of the ground state complex formation between adenine and CoTPP, which is supported by experimental evidences from UV- visible spectra, time resolved fluorescence life time measurements etc. The detection limit of adenine was found to be 4.2 μM using the CoTPP fluorescent probe. The proposed sensor is found to be highly selective for adenine in presence of other nitrogen bases like guanine, cytosine, uracil, thymine, alanine, histidine etc. in 1:1 concentration.

Nano-fluorescent probes based on DNA-templated copper nanoclusters for fast sensing of thiocyanate

A fast and label-free fluorescent sensor was developed to determine SCN⁻via inhibiting the formation of DNA-templated copper nanoclusters (CuNCs).

Red-Emitting Fluorescence Sensors for Metal Cations: The Role of Counteranions and Sensing of SCN- in Biological Materials

The spatiotemporal sensing of specific cationic and anionic species is crucial for understanding the processes occurring in living systems. Herein, we developed new fluorescence sensors derived from tetrapyrazinoporphyrazines (TPyzPzs) with a recognition moiety that consists of an aza-crown and supporting substituents. Their sensitivity and selectivity were compared by fluorescence titration experiments with the properties of known TPyzPzs (with either one aza-crown moiety or two of these moieties in a tweezer arrangement). Method of standard addition was employed for analyte quantification in saliva. For K⁺ recognition, the new derivatives had comparable or larger association constants with larger fluorescence enhancement factors compared to that with one aza-crown. Their fluorescence quantum yields in the ON state were 18× higher than that of TPyzPzs with a tweezer arrangement. Importantly, the sensitivity toward cations was strongly dependent on counteranions and increased as follows: NO₃^- < Br^- < CF₃SO₃^- < ClO₄^- ≪ SCN^-. This trend resembles the chaotropic ability expressed by the Hofmeister series. The high selectivity toward KSCN was explained by synergic association of both K⁺ and SCN^- with TPyzPz sensors. The sensing of SCN^- was further exploited in a proof of concept study to quantify SCN^- levels in the saliva of a smoker and to demonstrate the sensing ability of TPyzPzs under in vitro conditions.

Studying the origin of fluorescence emissions of neodymium porphyrin based on the analysis of energy level structure

This paper studies the origin of fluorescence emissions of metalloporphyrins. The absorption spectrum of neodymium-coordinated hematoporphyrin monomethyl ether (Nd-HMME) was found to have four Q bands, which is different from the accepted knowledge (two Q bands). The absorbance of Nd-HMME was comparable to the corresponding absorbance of HMME at wavelengths of 538 nm and 572 nm, but the absorbance of Nd-HMME at wavelengths of 502 nm and 622 nm was approximately 1/30 of that at 572 nm. The doping of Nd[Formula: see text] enhanced the symmetry of HMME, and led to changes in energy level properties. Moreover, Nd-HMME still exhibited two fluorescence peaks at 624 nm and 686 nm, similar to HMME, which can be explained by the observation of a weak absorption peak of Nd-HMME at 622 nm.

White emission magnetic nanoparticles as chemosensors for sensitive colorimetric and ratiometric detection, and degradation of ClO⁻ and SCN⁻ in aqueous solutions based on a logic gate approach

Fluorescent chemosensors for detecting single anions have been largely synthesized. However, the simultaneous detection and degradation of multiple anions remain a major challenge. Herein we report the synthesis of a white emission nanoprobe on the basis of a Coumarin-Rhodamine CR1-Eu complex coordinated to dipicolinic acid (dpa)-PEG-Fe3O4 nanoparticles for the selective detection of ClO(-) and SCN(-) ions on controlling by a logic gate. The obtained nanoprobe exhibits three individual primary colors (blue, green, and red) as well as white emission at different excitation energies. Interestingly, this nanoprobe shows a marked rose red to violet emission color change in response to ClO(-), a reversible violet to rose red emission color change in response to SCN(-), and high ClO(-) and SCN(-) selectivity and sensitivity with a detection limit of 0.037 and 0.250 nM, respectively. Furthermore, the SCN(-) and ClO(-) can degrade simultaneously through the redox reaction between ClO(-) and SCN(-).

Pattern-Based Detection of Anion Pollutants in Water with DNA Polyfluorophores

Many existing irrigation, industrial and chemical storage sites are currently introducing hazardous anions into groundwater, making the monitoring of such sites a high priority. Detecting and quantifying anions in water samples typically requires complex instrumentation, adding cost and delaying analysis. Here we address these challenges by development of an optical molecular method to detect and discriminate a broad range of anionic contaminants with DNA-based fluorescent sensors. A library of 1296 tetrameric-length oligodeoxyfluorosides (ODFs) composed of metal ligand and fluorescence modulating monomers was constructed with a DNA synthesizer on PEG-polystyrene microbeads. These oligomers on beads were incubated with YIII or ZnII ions to provide affinity and responsiveness to anions. Seventeen anions were screened with the library under an epifluorescence microscope, ultimately yielding eight chemosensors that could discriminate 250 μM solutions of all 17 anions in buffered water using their patterns of response. This sensor set was able to identify two unknown anion samples from ten closely-responding anions and could also function quantitatively, determining unknown concentrations of anions such as cyanide (as low as 1 mM) and selenate (as low as 50 μM). Further studies with calibration curves established detection limits of selected anions including thiocyanate (detection limit ~300 μM) and arsenate (~800 μM). The results demonstrate DNA-like fluorescent chemosensors as versatile tools for optically analyzing environmentally hazardous anions in aqueous environments.

A dual-mode colorimetric and fluorometric “light on” sensor for thiocyanate based on fluorescent carbon dots and unmodified gold nanoparticles

A novel, highly sensitive and selective dual-readout (colorimetric and fluorometric) sensor based on fluorescent carbon dots (CDs) and unmodified gold nanoparticles (AuNPs) for the detection of thiocyanate (SCN⁻) was proposed.

A sensitive ratiometric fluorescent sensor for zinc(II) with high selectivity

A new fluorescent Zn²⁺ chemosensor (P1) based on a functionalized porphyrin was synthesized and characterized. P1 displayed dramatic ratiometric variations in absorption and fluorescent emission spectra upon exposure to Zn²⁺ due to the formation of a 1:1 Zn²⁺/P1 complex. The sensor also exhibited high selectivity and sensitivity toward Zn²⁺ over other common metal ions in the physiological pH range with a detection limit of 1.8 μM. The sensor showed fast response times and excellent reproducibility, thus confirming its potential applicability as a fluorescent sensor for Zn²⁺ sensing.

Optical fiber based methodology for assessment of thiocyanate in seawater

A new methodology for the assessment of thiocyanate (SCN(-)) is proposed based on optical fiber (OF) detection coupled to a liquid chromatography system (LC). The developed methodology showed an adequate performance for the analysis of SCN(-) comparable to a high performance liquid chromatography with UV detector (HPLC-UV) methodology: a detection limit of 3 µg L(-1), a linear range from 4 to 400 µg L(-1), and an analytical time of less than 6 min. The OF based methodology was of compact design and easy operation. This simple system has the potential to be used as a sensing approach for SCN(-) in seawater.