Aminomethyl Pyridine Research Articles

Synthesis and functionalization of red-emissive carbon dots towards sensing of copper(II) and ATP in aqueous media

Red-emissive carbon dots, RCDs, were prepared in a bottom-up approach, from citric acid and urea, through a single solvothermal step, which were posteriorly surface-functionalized with di-(2-picolyl)amine (DPA) groups. The functionalized RCDs, henceforth named CD1, were analyzed through high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), dynamic light-scattering (DLS) and infrared spectroscopy (FTIR), and were found to be spherical, with diameter of circa 4 nm. UV-Vis and luminescence spectroscopic studies showed that CD1 display an absorption maximum at 550 nm, with emission maxima at around 640 nm. Fluorescence measurements indicated that Cu(II) induces the strongest changes in the emission of CD1 among eleven investigated metal ions, with a full quenching effect being observed. Further addition of an anionic species, adenosine 5-triphosphate (ATP), resulted in a recovery of the luminescence, which suggests that ATP is capable of sequestering metal ions from the surface of CD1. These results highlight the potential of simple and easy-to-make carbon nanomaterials as sensors for ions in aqueous media.

Synthesis and characterization of sulfonamide appended rigid phenyl-based and non-rigid 1,4-benzodioxan-based ring systems and their Pt(II) complexes towards potential therapeutic targets

Two novel non-rigid; 1,4-benzodioxan (bzd) based and rigid; 4-methylbiphenyl (4-Mebip) based di-(2-picolyl)amine derived sulfonamide ligands, and their cis-dichloroplatinum(II) complexes have been synthesized. The ligands; L1: N(SO2)(bzd)dpa and L2: N(SO2)(4-Mebip)dpa were synthesized via N-sulfonylation of di-(2-picolyl)amine in good yield. Their platinum(II) complexes; C1: [PtCl2(N(SO2)(bzd)dpa)], C2: [PtCl2(N(SO2)(4-Mebip)dpa)]·CH3CN were synthesized and characterized by 1H NMR, FTIR, UV–Vis and fluorescence spectroscopies. Structural studies revealed that the L1 and L2 ligands coordinate Pt(II) in a bidentate mode in C1 and C2 complexes, forming an eight-membered chelate ring. Interestingly, L1 possesses two conformations because the dioxan ring exists with a 95:5 occupancy ratio. The L2 ligand crystal undergoes a phase transition to triclinic form with twinning at 90 K whereas, at 150 K, the ligand exists in a monoclinic system; the populations of the two orientations for one pyridine substituent are approximately 78:22. The 1H NMR spectra of both Pt complexes obtained in DMSO‑d6 revealed two doublets (exo-CH2 and endo-CH2) for the magnetically inequivalent methylene protons, in contrast to their uncoordinated ligands, which show a singlet peak for the methylene protons. The NCI-H292 (non-small cell lung cancer cells) and MRC-5 (human normal lung fibroblast cells) were used to examine the in vitro cytotoxic activity of all synthesized compounds. All tested compounds demonstrated notable cytotoxicity against NCI-H292 cells, with the most pronounced cytotoxic effect being displayed by [PtCl2(N(SO2)(4-Mebip)dpa)]·CH3CN (C2). Docking studies strengthen in vivo antiproliferation activity where specific interactions with AKT1, BAX, STK-11, and BCL-2 were explored. Further predictions revealed that the compounds have inhibitory effects on COX-2 and PDE10A proteins.

Zinc N,N-bis(2-picolyl)amine Chelates Show Substitution-Dependent Cleavage of Phosphodiesters in Models as Well as of PNAzyme-RNA Bulges.

PNAzymes are a group of artificial enzymes which show promising results in selective and efficient cleavage of RNA targets. In the present study, we introduce a series of metal chelating groups based on N,N-bis(2-picolyl) groups (parent, 6-methyl and 6-amino substituted) as the active sites of novel PNAzymes. An improved synthetic route for the 6-amino analogues is described. The catalytic activity of the chelating groups for cleaving phosphodiesters were assessed with the model substrate 2-hydroxypropyl p-nitrophenyl phosphate (HPNPP), confirming that the zinc complexes have the reactivity order of parent < 2-methyl < 2-amino. The three ligands were conjugated to a PNA oligomer to form three PNAzymes which showed the same order of reactivity and some sensitivity to the size of the RNA bulge designed into the catalyst-substrate complex. This work demonstrates that the kinetic activity observed for the model substrate HPNPP could be translated onto the PNAzymes, but that more reactive Zn complexes are required for such PNAzymes to be viable therapeutic agents.

Synthesis, Spectroscopic Evaluations and UV-Vis Titration Studies of New Symmetrical Amide Compounds Derived from N-6-[(4-pyridylmethylamino)carbonyl]-pyridine-2-carboxylic Acid Methyl Ester

In this study, 2 flexible and pre-organized tetraamide compounds derived from N-6-[(4-pyridylmethylamino)carbonyl]-pyridine-2-carboxylic acid methyl ester namely 1,2-bis[N,N’-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]pentane (L1) and 1,2-bis[N,N’-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]hexane (L2) have been successfully synthesized when reacted with diamines in 1:2 ratio. These new compounds were built from combination of 3 main components, as a trend requires for anion receptor which are (i) 2,6-pyridine dicarboxamide moieties as targeted anion binding host, (ii) amino methyl pyridine pendants arms as the flexible moieties and (iii) pentyl (-C5H10-) and hexyl (-C6H12-) unit as the spacer. Compounds L1-L2 were fully characterized by using elemental analyzer, Fourier transform infrared (FTIR) spectroscopy, gas chromatography-mass spectroscopy (GC-MS), 1H, 2D NOESY and 13C Nuclear Magnetic Resonance (NMR) spectroscopies, and Ultraviolet-visible (UV-Vis) spectroscopies. In this study, anion titration methods were used to identify the affinity towards selected anions. The results showed that L1 (having a pentyl spacer) had the highest affinity towards phosphate anions as compared to L2, where the red shift changes were observed in the UV-vis spectrum at the amide region. HIGHLIGHTS Two novel amide compounds with flexible and pre-organized structure are designed for use as potential anion receptors The flexible moieties at the amide and the linker allow hydrogen bonding interaction of the molecules with variety anions with different geometries Anion titration studies revealed good affinities towards phosphate anions as suggested in Hofmeister trend GRAPHICAL ABSTRACT

Lead-Bromide Hybrid Perovskites with Different Dimensions due to NH&lt;sub&gt;2&lt;/sub&gt; Position Variation Pyridine Ligand Methylene Bridge-CH&lt;sub&gt;2&lt;/sub&gt;

The hybrid perovskites of amino(methyl) pyridines (AMP) and lead (II) bromide (PbBr2) were synthesised using a reflux method in 40% hydrobromic acid medium in a closed-nitrogen condition. The structural, chemical and optical properties of the as-synthesised compounds were analysed analytically using XRD, FT-IR and UV-Vis. Based on the XRD analysis, all compounds have distinct and evenly spaced diffraction peaks, indicating that they are strongly oriented and well-crystallised. The presence of aromatics and primary amines in mono-substituted pyridinium cation variations was confirmed by the FT-IR analysis. All compounds absorbed strongly in visible spectra at 430 nm, 427 nm and 355 nm, respectively. This study demonstrates that organic-tailoring effects in the shifting of aminomethyl position in the pyridine chain contribute to different dimensionalities of hybrid perovskite frameworks, even when synthesised under the same conditions. The as-synthesised low-dimensional hybrid perovskite can be further utilised as a light-harvester material in Perovskite Solar Cells (PSCs).

Zn(II)-complex-based hydrolytic nanozymes prepared by nanoprecipitation for the hydrolysis of carboxylic esters and methyl parathion

Zn(II)-complex-based nanozymes have been extensively used for the cleavage of carboxylic esters and phosphate esters. Cooperativity between neighboring Zn(II) complexes is of paramount importance for the development of Zn(II)-complex-based nanozymes with excellent efficiency. Here, we have developed a controllable synthetic strategy for the construction of Zn(II)-complex-based nanozymes by using the nanoprecipitation technique, which could bring Zn(II) complexes in close proximity and regulate their microenvironments. Linear copolymers containing di(2-picolyl)amine moieties were used for the preparation of Zn(II)-complex-based nanozymes by the coordination between di(2-picolyl)amine and Zn(II) ion. These Zn(II)-complex-based nanozymes displayed excellent catalytic performance in the hydrolysis of carboxylic esters. Moreover, hydrophobic Fe3O4 nanoparticles could be incorporated into Zn(II)-complex-based nanozymes via the one-step nanoprecipitation approach, enabling the recovery of nanozymes by using a permanent magnet. Such nanozymes effectively catalyzed the hydrolysis of methyl parathion, which is highly resistant to spontaneous hydrolysis and is extremely hazardous. These nanozymes may find application in the hydrolysis of hazardous carboxylic esters and phosphate esters.

Structural Characterization of Zinc(II)/Cobalt(II) Complexes of Chiral N-(Anthracen-9-yl)methyl-N,N-bis(2-picolyl)amine and Evaluation of DNA Photocleavage Activity.

We designed and synthesized a chiral ligand N-(anthracen-9-ylmethyl)-1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)ethanamine (APPE) DNA photocleavage agent to investigate the effects of chirality of bis(2-picolyl)amine on the DNA photocleavage activity of metal complexes. The structures of ZnII and CoII complexes in APPE were analyzed via X-ray crystallography and fluorometric titration. APPE formed metal complexes with a 1 : 1 stoichiometry in both the crystalline and solution states. Fluorometric titration was used to show that the ZnII and CoII association constants of these complexes (log Kas) were 4.95 and 5.39, respectively. The synthesized complexes were found to cleave pUC19 plasmid DNA when irradiated at 370 nm. The DNA photocleavage activity of the ZnII complex was higher than that of the CoII complex. The absolute configuration of the methyl-attached carbon did not affect DNA cleavage activity and, unfortunately, an achiral APPE derivative without the methyl group (ABPM) was found to perform DNA photocleavage more effectively than APPE. One reason for this may be that the methyl group suppressed the structural flexibility of the photosensitizer. These results will be useful for the design of new photoreactive reagents.

Efficient and Sustainable Bidentate Amines-Functionalized Resins for Removing Ag+, Cu2+, Pb2+, and Fe3+ from Water.

We evaluate the effectiveness of chelating resins (CR) derived from Merrifield resin (MR) and 1,2-phenylenediamine (PDA), 2,2'-dipyridylamine (DPA), and 2-(aminomethyl)pyridine (AMP) as adsorbent dosimeters for Ag+, Cu2+, Fe3+, and Pb2+ cations from water under competitive and noncompetitive conditions. MR-PDA, MR-DPA, and MR-AMP were obtained in a 95-97% yield and characterized by IR, fluorescence, and SEM. The ability of CRs as adsorbents was determined by batch and flow procedures. MR-PDA showed a batch adsorption capacity order of Fe3+ (29.8 mg/g) > Ag+ (2.7 mg/g) > Pb2+ (2.6 mg/g) at pH 3.4. The flow adsorption showed affinity towards the Ag+ cation at pH 7 (18.4 mg/g) and a reusability of 10 cycles. In MR-DPA, the batch adsorption capacity order was Ag+ (9.1 mg/g) > Pb2+ (8.2 mg/g) > Cu2+ (3.5 mg/g) at pH 5. The flow adsorption showed affinity to the Cu2+ cation at pH 5 (2.2 mg/g) and a reuse of five cycles. In MR-AMP, the batch adsorption capacity was Ag+ (17.1 mg/g) at pH 3.4. The flow adsorption showed affinity to the Fe3+ cation at pH 2 (4.3 mg/g) and a reuse of three cycles. The three synthesized and reusable CRs have potential as adsorbents for Ag+, Cu2+, Fe3+, and Pb2+ cations and showed versatility in metal removal for water treatment.

Synthesis of a new μ-chlorido-bridged tetra-nuclear copper(II) complex containing 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz), chlorido and perchlorato ligands: non-planar central pyrazine rings

A μ-chlorido-bridged tetra-nuclear copper(II) complex containing 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz), chlorido, and perchlorato ligands, starting from 2-aminomethyl pyridine (AMP) and Cu(OAc)2·H2O, was synthesized. The structure of the complex was determined by single-crystal X-ray diffraction (SCXRD), Fourier transform infrared spectroscopy (FT-IR), and electronic absorption spectroscopy (UV–Vis). The redox behavior of the complex was explored by cyclic voltammetry. The tetra-nuclear structure is formed by combining the di-nuclear copper complex of the two tppz ligands with a chloride bridge. The Cu(1) center adopts a distorted octahedral geometry, whereas the other three Cu centers adopt square pyramid geometries. Crystal data of the complex are monoclinic, P21/c, a = 13.602(4) Å, b = 13.438(4) Å, c = 29.412(8) Å, α = 90°, β = 95.258(8)°, γ = 90°, V = 5353(3) Å3, Z = 4. When the SCXRD structure was examined, it was determined that the two central pyrazine rings deviated from planarity, which is one of the four criteria for aromaticity. The aromaticity of the central pyrazine rings, whose planarity is disturbed, is decreased. Based on these bond lengths, the harmonic oscillator aromaticity model (HOMA) values of the non-planar central pyrazine rings were calculated as 0.964926 and 0.942886, respectively.

Crystal packing and photoelectric property of bis(2-picolyl)amine-functionalized triarylborane and its complexes

Organic crystalline materials are attracting increasing interest due to their promising applications in the fields of nonlinear optics (NLO), organic lasers, optical waveguides, and light-emitting transistors. In this paper, a photoelectric molecule QB was constructed through combining an electron-withdrawing unit, a triarylborane, and a metal-ligand unit of bis(2-picolyl)amine. The crystallization behavior and crystalline photoelectric properties of QB and its complexes were thoroughly studied. This compound exhibited polymorphism, and a green emitting block-like crystal and blue-emission lamellar crystal were obtained, respectively. Their different photoluminescence mechanisms were clarified through X-ray crystallographic analysis and theoretical calculations. Furthermore, the single-crystal structures of the complexes of QB coordinating with KCN and Zn(ClO4)2 were also determined. Crystal QB-KCN emitted strong blue fluorescence at 445 nm, owing to the formation of rigid 2-to-2 adduct, which could effectively suppress non-radiative transitions. Crystal QB-Zn(ClO4)2 showed very weak cyan emission due to its loose molecular packing. The electrochemical results illuminated that the metal coordination can effectively affect the electron-withdrawing ability of conjugated triarylborane, and further affect the monomolecular luminescent properties due to the intramolecular charge transfer. We believe that polymorphism and metal coordination are available means to obtain excellent crystalline photoelectric materials.

Multifunctional metallochaperone modifications for targeting subsite cavities in mutant p53-Y220C

The p53 protein, known as the ‘guardian of the genome’, plays an important role in cancer prevention. Unfortunately, p53 mutations result in compromised activity with over 50% of cancers resulting from point mutations to p53. There is considerable interest in mutant p53 reactivation, with the development of small-molecule reactivators showing promise. We have focused our efforts on the common p53 mutation Y220C, which causes protein unfolding, aggregation, and can result in the loss of a structural Zn from the DNA-binding domain. In addition, the Y220C mutant creates a surface pocket that can be stabilized using small molecules. We previously reported the bifunctional ligand L5 as a Zn metallochaperone and reactivator of the p53-Y220C mutant. Herein we report two new ligands L5-P and L5-O that are designed to act as Zn metallochaperones and non-covalent binders in the Y220C mutant pocket. For L5-P the distance between the Zn-binding di-(2-picolyl)amine function and the pocket-binding diiodophenol was extended in comparison to L5, while for L5-O we extended the pocket-binding moiety via attachment of an alkyne function. While both new ligands displayed similar Zn-binding affinity to L5, neither acted as efficient Zn-metallochaperones. However, the new ligands exhibited significant cytotoxicity in the NCI-60 cell line screen as well as in the NUGC3 Y220C mutant cell line. We identified that the primary mode of cytotoxicity is likely reactive oxygen species (ROS) generation for L5-P and L5-O, in comparison to mutant p53 reactivation for L5, demonstrating that subtle changes to the ligand scaffold can change the toxicity pathway.

A Novel D-π-A Type Fluorescent Probe for Cu2+ Based on Styryl-Pyridinium Salts Conjugating Di-(2-picolyl)amine (DPA) Units.

A novel D-π-A type fluorescent probe L(NO3) for Cu (II) sensing was designed and fully characterized. The probe consists of a styryl-pyridine cation fluorescent group and a di-(2-picolyl)amine (DPA) receptor unit, which are linked by a phenyl group to form an electron donor-π-acceptor (D-π-A) conjugate system, especially the introduction of a nitrate counter anion for significantly enhanced water solubility of the probe. Fluorescence titration studies of the probe L(NO3) showed a higher selectivity for Cu2+ than other metal ions, and the emission spectrum was strongly quenched upon binding. The competitive binding assay and the low detection limit (0.932 µM) showed that the probe L(NO3) had strong anti-interference ability and excellent Cu2+ detection performance. The binding ratio of probe L(NO3) and Cu2+ was determined from Job's plot to be 1:1, which is consistent with the results obtained from X-ray crystal structures. Meanwhile, the probe showed instantaneous chemical reversibility when titrated with EDTA solution, indicating potential recycling properties of the probe. In addition, the design of inexpensive fluorescent test strips can perform the on-site and real-time detection Cu2+ with a color recognition application.

A highly sensitive colorimetric and fluorogenic detection of copper(II) ion based on new picolylamine-armed calix[4]arene

In this study, two- and tetra-functionalized with bis(2-picolyl)amine calix[4]arene derivatives (2-PACX and 4-PACX) were synthesized, and their structures were confirmed by 1H NMR, 13C NMR, FT-IR and TOF-MS spectroscopies. Cation sensing behaviors of them were investigated towards several cations such as Fe2+, Al3+, Cr3+, Hg2+, Mn2+, Cu2+, Co2+, Cd2+, Zn2+, Ni2+, Ag+, Mg2+, Ca2+, Li+, Na+, and K+. The results showed that 4-PACX was an effective colorimetric sensor against Cu2+ ions. The binding constant (K) value of the complexation between 4-PACX and Cu2+ ion was calculated as 4.62x108 M−2 and the detection limit value of the sensor as 5.1 μM. Moreover, the fluorescence studies demonstrated that 4-PACX has great fluorogenic sensor potential with 0.16 μM of detection limit. As a result, good yield, large coupling constant with Cu2+ ion (Ka = 13.972), applicability to aqueous samples, low detection limit, and high sensitivity were some of the advantages of the obtained sensor.

Highly selective recovery of Ni(II) in neutral and acidic media using a novel Ni(II)-ion imprinted polymer.

In this work, an original ion-imprinted polymer (IIP) was synthetized for the highly selective removal of Ni(II) ions in neutral and acidic media. First a novel functional monomer (AMP-MMA) was synthetized through the amidation of 2-(aminomethyl)pyridine (AMP) with methacryloylchloride. Following Ni(II)/AMP-MMA complex formation study, the Ni(II)-IIP was produced via inverse suspension polymerization (DMSO in mineral oil) and characterized with solid state 13C CPMAS NMR, FT-IR, SEM and nitrogen adsorption/desorption experiments. The Ni(II)-IIP was then used in solid-phase extraction of Ni(II) exploring a wide range of pH (from neutral to strongly acidic solution), several initial concentrations of Ni(II) (from 0.02 to 1g/L), and the presence of competitive ions (Co(II), Cu(II), Cd(II), Mn(II), and Mg(II)). The maximum Ni(II) adsorption capacity at pH 2 and pH 7 reached values of 138.9mg/g and 169.5mg/g, that are among the best reported in literature. The selectivity coefficients toward Cd(II), Mn(II), Co(II), Mg(II) and Cu(II) are also very high, with values up to 38.6, 32.9, 25.2, 23.1 and 15.0, respectively. The Ni(II)-IIP showed good reusability of up to 5 cycles both with acidic and basic Ni(II) eluents.

A Near InfraRed Emissive Chemosensor for Zn2+ and Phosphate Derivatives Based on a Di-(2-picolyl)amine-styrylflavylium Push-Pull Fluorophore.

A new Near InfraRed (NIR) fluorescent chemosensor for metal ions and anions is herein presented. The fluorophore is based on a styrylflavylium dye, a synthetic analogue of the natural anthocyanin family, with a di-(2-picolyl)amine (DPA) moiety as the metal chelating unit. The substitution pattern of the styrylflavylium core (with tertiary amines on positions 7 and 4') shifts the optical properties of the dye towards the NIR region of the electronic spectra, due to a strong push-pull character over the π-conjugated system. The NIR chemosensor is highly sensitive to the presence of Zn2+, which induces a strong CHelation Enhanced Fluorescence (CHEF) effect upon binding to the DPA unit (2.7 fold increase). The strongest competing ion is Cu2+, with a complete fluorescence quenching, while other metals induce lower responses on the optical properties of the chemosensor. Subsequent anion screening of the Zn2+-chemosensor coordination compound has demonstrated a distinct selectivity towards adenosine 5'-triphosphate (ATP) and adenosine 5'-diphosphate (ADP), with high association constants (K ~ 106 M-1) and a strong CHEF effect (2.4 and 2.9 fold fluorescence increase for ATP and ADP, respectively). Intracellular studies with the Zn2+-complexed sensor showed strong luminescence in the cellular membrane of Gram- bacteria (E. coli) and mitochondrial membrane of mammalian cells (A659), which highlights its possible application for intracellular labelling.

Ether/Thioether-Functionalized Dianionic α-Iminopyridine Rare-Earth Metal Amido Complexes and Their Catalytic Activity toward Hydrophosphination of Alkenes

The double deprotonation of 2-aminomethyl pyridine by rare-earth metal triamido complexes was found to be an alternative strategy to anchor dianionic iminopyridine on rare-earth metal centers with the morpholinyl group previously. To verify the generality of the protocol with different appendant donor groups, reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with ether/thiotether-substituted 2-aminomethyl pyridine 2-(CH3DCH2CH2NHCH2)-6-R-C5H3N (D = O, R = H (1), Ph (2); D = S, R = H (3)) were performed, leading to the formation of ether/thioether-functionalized dianionic α-iminopyridine rare-earth metal amido complexes {μ-η2:σ1:κ1:κ1-2-[CH3ECH2CH2NCH]-6-R-C5H3N}2RE2[N(SiMe3)2]2 (D = O, R = H, RE = Dy (4a), Y (4b), Er (4c), Yb (4d), Lu (4e), R = Ph, RE = Dy (5a), Y (5b), Er (5c), Lu (5d); D = S, R = H, RE = Y (6a), Er (6b), Lu (6c)). These results supported the ability of oxygen or sulfur coordination in promoting the double deprotonation of 2-aminomethyl pyridine to construct new iminopyridine rare-earth metal complexes in the dianionic form. Further examination of these rare-earth metal amido complexes displayed good catalytic activity for hydrophosphination of alkenes, affording anti-Markovnikov addition products under solvent-free conditions.

Di(2-picolyl)amines as Modular and Robust Ligands for Nickel-Catalyzed C(sp2)-C(sp3) Cross-Electrophile Coupling.

Ni-catalyzed aryl-alkyl coupling reactions are reliant on using a limited set of commercially available bidentate nitrogenous ligands to enable the reaction, because noncommercial analogues usually entail challenging syntheses. In this work, di(2-picolyl)amines (DPAs) are explored as an alternative modular ligand class for the nickel-catalyzed aryl-alkyl cross-electrophile coupling. Novel DPA ligands were synthesized directly from inexpensive amine and pyridine building blocks in a single step. This facile synthetic route enabled the parallel synthesis of DPA ligands with varied steric and electronic properties. From this collection of ligands, a few robust ligands for C(sp2)-C(sp3) cross-electrophile coupling were identified and tested in the cross-coupling of a range of diverse molecules, including model examples for late-stage functionalization.

Insights into the Responding Modes of Highly Potent Gadolinium-Based Magnetic Resonance Imaging Probes Sensitive to Zinc Ions.

Zn ions (Zn2+) play an important biological role in many diseases; hence, an imaging method for monitoring the Zn2+ distribution in tissues could provide important clinical insights. Recently, we reported a potent Zn-sensitive probe based on the Gd-DO3A (DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylic acid), modified tyrosine. and di(2-picolyl)amine chelator for this metal cation, which generates an outstanding magnetic resonance imaging (MRI) response. Here we further explored the origin of this unprecedented response and expanded the choice of potential MRI probes by preparing the free acid version of the initial MRI sensor. We report a detailed investigation of the 1H NMR dispersion, 17O NMR, and isothermal titration calorimetry properties of these two MRI probes upon interaction with Zn2+. The performed experiments confirm selective interaction of the MRI probes and target metal cation, which causes substantial changes in the coordination sphere of the paramagnetic center. It also evidenced some aggregation, which enhances the relaxivity response. Interestingly, conversion of the methyl ester to the free carboxylic acid of the tyrosine moiety changes the nature of the aggregates and leads to a smaller relaxivity response. The probes interact with human serum albumin (HSA) in the absence of Zn2+, which leads to a possible modification of the coordination sphere of Gd3+ or a substantial change in the exchange rate of second-sphere water molecules. In the presence of Zn2+, the interaction with HSA is very weak, demonstrating the importance of the Zn2+ coordination sphere in the behavior of these systems.

An NIR Emissive Donor-π-Acceptor Dicyanomethylene-4H-Pyran Derivative as a Fluorescent Chemosensor System towards Copper (II) Detection

A novel donor-π-acceptor fluorescent dye as a chemosensor for Cu2+ ions is herein presented. The fluorophoric core consists of a 3,5-diphenyl-dicyanomethylene-4H-pyran (DCM), with extended styryl chains on positions 2 and 6, bearing terminal di-(2-picolyl)amine (DPA) groups for metal coordination. Optical characterization of the chemosensor dye reveals an absorption maximum at ca. 500 nm and a strong bathochromic shift in the emission, reaching ca. 750 nm in polar solvents. This solvatochromic behavior, which yields very large Stokes shifts (up to ~6700 cm−1), is characteristic of the strong intramolecular Charge Transfer (CT) nature of this chromophoric system. While the chemosensor has demonstrated no changes in its optical properties over a wide pH range (2–12), a strong quenching effect was observed upon Cu2+ coordination, with a 1:1 binding stoichiometry, indicating that only one DPA unit is capable of effectively chelating Cu2+, rendering the second DPA motif inactive. The binding constant was determined to be 7.5 × 107 M−1, indicating a very high sensitivity, and an LOD of 90.1 nM. Competition assays have demonstrated that the chemosensor is highly selective towards Cu2+, even in the presence of excesses of other mono- and di-valent cations. Co2+ and Ni2+ proved to be the strongest interferents, particularly in the luminescent response. Paper test-strips prepared with the embedded sensor showed a fluorometric response in the presence of different copper (II) concentrations, which attested to the potential of this chemosensor to be used in the determination of Cu2+ content in aqueous media, for in-field applications.

Sensor application of pyridine modified calix[4]arene Langmuir-Blodgett thin film

5,11,17,23–5,11,17,23-Tetra-(tert-butyl)− 25,27-di-(2-aminomethyl pyridine acetamide)− 26,28-dihydroxy calix[4]arene (C4P2T) molecule was transferred to gold coated glass substrate for the first time as a sensor active layer for the detection of volatile organic compounds (VOCs) such as acetone, benzene, chloroform, ethyl acetate and methanol. UV–visible spectroscopy and surface plasmon resonance (SPR) techniques were employed to monitor Langmuir-Blodgett (LB) thin film layer during the fabrication process of each sensor layers. In order to determine film thickness and refractive index values of C4P2T LB film, SPR measurements were performed using a Kretschmann’s prism configuration set-up system. Thickness and the refractive index values for the C4P2T LB thin films were determined to be 1.01 nm/layer and 1.59, respectively, by fitting the SPR curves using WINSPALL software based on the Fresnel formula. For the VOCs sensor application of the C4P2T LB thin film, reflected light intensity was recorded as a function of time by using SPR system. These measurements indicated that C4P2T LB thin film sensor layer was suitable for multiple usage with a fast response time (~ 3 s) and a recovery time (~ 3 s). The amount of C4P2T LB sensor responses against VOCs were followed by decreasing order acetone, chloroform, methanol, ethyl acetate and benzene. As a result, C4P2T LB film sensor has a sensitive and selective character and is suitable for VOCs sensor applications.