A turn-on Schiff base fluorescence sensor for zinc ion

A simple Schiff base type fluorescent receptor 1 was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor 1 exhibits an ‘off-on-type’ mode with high selectivity in the presence of Zn²⁺ ion. The selectivity of 1 for Zn²⁺ is the consequence of combined effects of chelation-enhanced fluorescence (CHEF), CN isomerization, and inhibition of photoinduced electron transfer (PET).     

Reaction of Zn(II) with a BINOL-amino-acid Schiff base: An unusual off-on-off fluorescence response

An amino-acid based Schiff base (S)-2 is prepared from the condensation of (S)-3,3′-diformyl BINOL (BINOL?=?1,1′-bi-2-naphthol) with l-valine in the presence of tetrabutylammonium hydroxide in methanol. This compound is found to exhibit off-on-off fluorescence response toward Zn²⁺. The spectroscopic studies reveal that (S)-2 reacts with 1 equiv Zn²⁺ to form a dimeric [2+2] complex with greatly enhanced fluorescence. Excess amount of Zn²⁺ might cause dissociation of this dimeric complex to give significantly reduced fluorescence.     

Synthesis, fluorescence study and biological evaluation of three Zn(II) complexes with Paeonol Schiff base

The synthesis of three Paeonol Schiff base ligand and their Zn(II) complexes are reported. The complexes were fully characterized by IR, ¹H NMR, elemental analysis and molar conductivity. The experiment results show the three Zn(II) complexes can emit bright fluorescence at room temperature in DMF solution and solid state. The fluorescence quantum yields (Φ) of three Schiff base ligands and their Zn(II) complexes were calculated using quinine sulfate as the reference with a known Φ_R of 0.546 in 1.0N sulfuric acid. Furthermore, in order to develop these Zn(II) complexes’ biological value, the antioxidant activities against hydroxyl radicals (OH) were evaluated. The results show the three complexes possess excellent ability to scavenge hydroxyl radicals.     

Selective turn-on fluorescence for Zn and Zn + Cd metal ions by single Schiff base chemosensor

Chemosensor based on Schiff base molecules (1, 2) were synthesized and demonstrated the selective fluoro/colorimetric sensing of multiple metal ions (Mn²⁺, Zn²⁺ and Cd²⁺) in acetonitrile–aqueous solution. Both 1 and 2 showed a highly selective naked-eye detectable colorimetric change for Mn²⁺ ions at 10⁻⁷ M. Fluorescence sensing studies of 1 and 2 exhibited a strong fluorescence enhancement (36 fold) selectively upon addition of Zn²⁺ (10⁻⁷ M, λ_max = 488 nm). Fluorescence titration and single crystal X-ray analysis confirmed the formation of 1:1 molecular coordination complex between 1 and Zn²⁺. Interestingly, a rare phenomenon of strong second turn-on fluorescence (190 fold, λ_max = 466 nm) was observed by the addition of Cd²⁺ (10⁻⁷ M) into 1 + Zn²⁺ or Zn²⁺ (10⁻⁷ M) into 1 + Cd²⁺. Importantly both 1 and 2 exhibited different fluorescence λ_max with clearly distinguishable color for both Zn²⁺ and Cd²⁺.     

Spectrophotometric and spectrofluorimetric studies of novel heterocyclic Schiff base dyes

Novel heterocyclic Schiff base dyes were prepared by the reaction of salicylaldehyde/2-Hydroxy-1-naphthaldehyde with different heterocyclic amines. Results of the newly synthesized compounds established by FT-IR, ¹H-NMR, ¹³C-NMR and GC–MS spectroscopic experiments were consistent with their chemical structures. Resulted heterocyclic Schiff base dyes were found to be pure from data obtained by the elemental analysis. In addition, spectrophotometric and spectrofluorimetric studies showed that these dyes were good absorbent and fluorescent. Fluorescence polarity study data revealed that some of these compounds were sensitive to the polarity of the microenvironment provided by different solvents. Time-based fluorescence steady-state measurements also showed that these heterocyclic Schiff base dyes have high photostability against photobleaching.     

Pyrene based Schiff base ligand: A highly selective fluorescence chemosensor for the detection of Cu2+ ions

A Schiff base ligand L has been designed and synthesized by the condensation of 1′-Hydroxy-2′-acetonaphthonehydrazide with pyrene aldehyde for the detection of Cu²⁺ ions. The ligand was spectroscopically characterized by all possible techniques. Among different metal ions, Cu²⁺ ions give a tremendous enhancement of fluorescence intensity in 20% water with THF. The “Turn-On” fluorescence for Cu²⁺ ions utilizes the Photo-induced Electron Transfer (PET) mechanism. It has been observed that the presence of relevant cations and anions did not affect the probe's fluorescence intensity. The stoichiometric binding mode of the complex is confirmed using Job's method. The low detection limit and reversibility make it cost-effective.     

A Schiff base fluorescence probe for highly selective turn-on recognition of Zn2+

A simple Schiff base CTS, synthesized between 2-hydroxy-1-naphthaldehyde and 2-benzylthio-ethanamine, was found to be a good turn-on fluorescence probe for the detection of Zn²⁺, due to the restriction of the rotation of the bond between CN and naphthalene ring and/or the blocking of the photo-induced electron transfer (PET) mechanism of the nitrogen atom to naphthalene ring. Excellent selectivity for Zn²⁺ was evidenced, over many other competing ions, including Fe³⁺, Cr³⁺, Ni²⁺, Co²⁺, Fe²⁺,Mn²⁺, Ca²⁺, Hg²⁺, Pb²⁺, Cu²⁺, Mg²⁺, Ba²⁺, Cd²⁺, Ag⁺, Li⁺, K⁺, and Na⁺, in EtOH/HEPES buffer (95:5, v/v, pH = 7.4). It was noteworthy that Cd²⁺ had no interference with Zn²⁺. The stoichiometric complex of CTS-Zn²⁺ was determined to be 2:1 for CTS and Zn²⁺ in molar, based on the Job plot and single crystal X-ray diffraction data. The binding constant of the complex was 85.7 M^?2 with a detection limit of 5.03 × 10^?7 M. The fluorescence bio-imaging capability of CTS to detect Zn²⁺ in live cells was also studied. These results indicated that CTS could serve as a favorable probe for Zn²⁺.     

Synthesis, spectroscopy, electrochemistry and thermal study of vanadyl tridentate Schiff base complexes

The VO(IV) complexes of tridentate ONO Schiff ligands were synthesised and characterized by IR, UV–vis and elemental analysis. The electrochemical properties of the vanadyl complexes were investigated by cyclic voltammetry. A good correlation was observed between the oxidation potentials and the electron withdrawing character of the substituents on the Schiff base ligands, showing the following trend: MeO < H < Br < NO₂ and H < Cl. The thermogravimetry (TG) and differential thermoanalysis (DTA) of the VO(IV) complexes were carried out in the range of 20–700 °C. The VOL¹(OH₂) decomposed in two steps whereas the remaining six complexes decomposed in three steps. The thermal decomposition of these complexes is closely related to the nature of the Schiff base ligands and proceeds via first order kinetics.     

Isatin‐Schiff base copper(II) complexes—A DFT study of the metal‐ligand bonding situation

Herein, we report results of calculations based on density functional theory (BP86/TZVP) of a set of isatin‐Schiff base copper(II) and related complexes, 1‐12, that have shown significant pro‐apoptotic activity toward diverse tumor cells. The interaction of the copper(II) cation with different ligands has been investigated at the same level of theory. The strength and character of the Cu(II)‐L bonding was characterized by metal‐ligand bond lengths, vibrational frequencies, binding energies, ligand deformation energies, and natural population analysis. The metal‐ligand bonding situation was also characterized by using two complementary topological approaches, the quantum theory of atoms‐in‐molecules (QTAIM) and the electron localization function (ELF). The calculated electronic g‐tensor and hyperfine coupling constants present significant agreement with the EPR experimental data. The calculated parameters pointed to complex 10 as the most stable among the isatin‐Schiff base copper(II) species, in good agreement with experimental data that indicate this complex as the most reactive in the series. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Water soluble chromone Schiff base derivatives as fluorescence receptor for aluminium(III)

A novel water-soluble chromone Schiff base derivatives bearing polyhydroxylated moiety were prepared and applied for specific recognition of metal ions in aqueous medium. Their selective fluorescence response to Al(III) over a variety of other biologically important metal ions were demonstrated. Electronic parameters of the sensors were also studied by quantum chemical computations.     

Novel photoluminescent hemi-disclike liquid crystalline Zn(II) complexes of [N2O2] donor 4-alkoxy substituted salicyldimine Schiff base with aromatic spacer

A series of novel hemi-disclike four coordinated distorted square planar Zn(II) Schiff base complexes containing 4-substituted alkoxy chains on the side aromatic ring [Zn (4−C_nH_2n+1O)₂ salophen], n = 14, 16, 18 and salophen = N,N′-4-methyl phenylene bis (salicylideneiminato), have been prepared and their mesogenic, photophysical properties were investigated. The phase behavior of these compounds were characterized by differential scanning calorimetry, polarized optical microscopy and variable temperature PXRD study. The ligands are non-mesogenic but the complexes exhibited an unprecedented 2D-hexagonal columnar mesophase (Col_h) in the temperature 175–185 °C range. In the mesophase (Col_h), the molecules self assemble in a columnar stack in antiparallel fashion. All λ_max of the UV–Vis absorption and photoluminescence band occurred at ca. 291–425 and 504–524 nm, respectively. The ligands are non-emissive, but on coordination with Zn(II), the complexes show intense green emission at room temperature in dichloromethane solution (∼505 nm, Φ = 20%) as well as in solid (∼522 nm, Φ = 9%) at 360 nm excitation. The DFT calculations were performed using Dmol3 program at BLYP/DNP level to obtain the stable electronic structure of the complex. A small LUMO-HOMO band gap (∼2.1 eV), presumably suggests a rather strong electronic correlation among the molecules along the column.     

Synthesis,crystal structures and fluorescence properties of two new di- and polynuclear Cd(II) complexes with N2O donor set of a tridentate Schiff base ligand

Two new Cd(II) complexes, having one binuclear structure [Cd₂(L)₂(Cl)₂] (1) and another azido bridged one-dimensional zig-zag polynuclear network [Cd₃(μ_1,1-N₃)₄(L)₂{H₂N(CH₂)₂N(C₂H₅)₂} · H₂O]_n (2) have been synthesized from a tridentate N₂O donor Schiff base ligand LH, [LH = (OCH₃)(OH)C₆H₃CHN(CH₂)₂N(C₂H₅)₂], which is the condensation product of 2-hydroxy-4-methoxybenzaldehyde and 2-diethylaminoethylamine. Both the complexes 1 and 2 have been characterized by elemental analyses, IR & ¹H NMR spectroscopy, TGA and fluorescence studies. Finally their structures have been established by single crystal X-ray diffraction method. Structural study reveals that in the complex 1, two Cd(II) centers are held together by two μ₂-phenolato oxygen atoms and the terminal chlorine atom occupies the apical site of the square pyramidal environment of each metal center. In case of complex 2, the trinuclear asymmetric unit contains octahedral Cd(II) centers which are further held together by doubly end-on azido bridging to form a zig-zag polynuclear structure. It also displays intraligand ¹(π–π^∗) fluorescence and can potentially serve as photoactive material.     

Acidichromism in the LB film of bolaform Schiff base

A bolaform(BNC 10)and single-headed(HNOA)amphiphilic Schiff bases containing naphthyl group were designed and their Langmuir-Blodgett films were investigated.It was found that both the LB films show acidichromism,i.e.a reversible color change upon alternatively exposing the films to HCl and NH_3 gases,respectively.It was further found that the bolaform Schiff bases film could trap NH_3 gas during the acidichromic process.     

Antibacterial activity of transition metal complexes containing a tridentate NNO phenoxymethylpenicillin‐based Schiff base. An anti‐MRSA iron (II) complex

Transition metal complexes containing a phenoxymethylpenicillin‐derived Schiff base (HL) 3 obtained from the condensation of phenoxymethylpenicillin (PMP) 1 , with 1,2‐diaminobenzene 2 , were prepared. Spectroscopic and physicochemical techniques, namely, UV–Vis, FT‐IR, ¹H‐NMR, EPR, mass spectrometry, magnetic susceptibility, molar conductance, DFT studies, together with elemental and thermal analyses were used to characterize the synthesized complexes. Based on the characterization studies, the general formulae [ML (OAc)(H₂O)₂] where M = Fe 4 , Co 5 , Ni 6 , Cu 7 , and Zn 8 , were proposed for the complexes. The Schiff base ligand 3 behaved as a monoanionic tridentate NNO chelating agent. On the basis of magnetic and spectral data an octahedral geometry for all the complexes was suggested. Schiff base ligand 3 , and the metal complexes 4 – 8 were tested against G(+) or bactericidal activity by agar disc diffusion method and minimal inhibitory concentration (MIC). The results were compared with the activity of the standard drug PMP 1 . In vitro bacterial viability revealed that 3  had similar activity than 1 and exhibited modification in its bactericidal activity when formed metal complexes. It was found that the complexes 4 , 6 and 7 exhibited much better bactericidal activity than 1 against methicillin‐resistant Staphilococcus Aureus (MRSA) being complex 4 the most promising compound showing a MIC value of 0.042 μmol/ml.     

Synthesis and characterization of poly(p-arylene sulfide ketone/Schiff base) copolymers

Poly(p-arylene sulfide ketone/Schiff base) copolymers(PASK/SB) were prepared by solution polycondensation of 4,4’-diflurobenzophenone(DFBP) and N-phenyl(4,4’-diflurodiphenyl) ketimine(DFBI) with sodium sulfide in the presence of sodium hydroxide under normal pressure.Elemental analyses,FT-IR,NMR,DSC,TGA and XRD were used to characterize the resultant copolymers.It was found that the copolymers had good thermal properties with glass transition temperature(T_g) of 155.0-172.0°C,melting temperature(T_m) of 298-344°C,5%weight loss temperatures(T_d) of 471.0-501.5°C.These copolymers were almost amorphous with the content of DFBI beyond 30%.The polymer with 100% DFBI had excellent solubility,and it could dissolve in some solvents such as tetrahydrofuran(THF) and N-methyl-2- pyrrolidone(NMP).The processability of polymers was improved.Meantime the viscosity of PASK made from hydrolysis of PASK/SB(H-PASK/SB) was greatly improved from 0.135 dL/g to 0.605 dL/g.     

Design of end-on cyanato bridged trinuclear Cu(II) Schiff base complex with salen type Schiff base ligand: synthesis,structural investigation and DFT study

One ONNO-donor tetradentate Schiff base ligand LH₂ was derived from the condensation of salicylaldehyde and 1,3-diaminopropane and reacted with Cu(NO₃)₂·6H₂O and NaNCO to yield one trinuclear complex with molecular formula [Cu₃L₂(µ_1,1-NCO)₂]. The synthesized complex was characterized by IR, UV–vis spectroscopy, and electrochemical analysis. Single-crystal X-ray diffraction study explores that the two terminal copper atoms adopt square pyramidal geometry, whereas the central copper atom situated at the inversion center is surrounded by four phenoxo oxygens and two end-on cyanato anions to adopt an octahedral geometry. The ONNO-tetradentate Schiff base ligand coordinates with the copper(II) ion via two oxygen atoms of the phenoxo-group and two nitrogen atoms from the imine moiety. A theoretical density functional theory (DFT) calculation was also carried out to supplement the experimental results. All the DFT calculations were done in gas phase.     

Inhibitory study of some novel Schiff base derivatives on Staphylococcus aureus by microcalorimetry

The effect of a series of novel Schiff base compounds on Staphylococcus aureus was studied by microcalorimetric method at 37 °C The results showed that all of the organic compounds had the capacity to inhibit the growth of S. aureus in different extent. And the extent and duration of the inhibitory effect on the growth of S. aureus, judged from the rate constant (k), varied with the different structure of the Schiff base compounds. According to the power-time curves, the multiplication rate constant and inhibition ratio were calculated. The growth rate constant of S. aureus (in log phase) in the presence of Schiff base compounds decreased with the increasing of the concentrations of these compounds regularly. The experimental results revealed that the hydrophilicity of Schiff bases had a great influence on their antibacterial activity. Of these Schiff bases, the greater their hydrophilicity, the higher their antibacterial activity. The antibacterial structure-activity relationship (SAR) of Schiff base derivatives was also briefly discussed.     

Manganese (II) selective PVC based membrane sensor using a Schiff base

N,N′,N″,N′′′-1,5,8,12-tetraazadodecane-bis(salicylaldiminato)(H₂L) has been used as ionophore for preparing Mn²⁺ selective sensor. Membranes of different composition with regard to ratio of H₂L:PVC:NPOE:NaTPB have been prepared and investigated. The best performance was obtained with the membrane of composition 10:150:150:10 (H₂L:PVC:NPOE:NaTPB) (w/w; mg). This membrane generated linear potential response in the concentration range of 5.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a Nernstian slope of 30.0 mV/decade of activity and fast response time (10 s). Hydrogen ion does not effect to the performance of sensor in the pH range 3.0-6.5. The sensor was found to be sufficient selective for Mn²⁺ over a number of alkali, alkaline and heavy metal ions and could therefore be used for the determination of manganese in various samples by direct potentiometry.     

A study on the synthesis and characterization of Schiff base stabilized silver nanoparticles against propionic bacteria

Bacteriological contamination removing one of the most conservational problem in various environmental areas, predominantly in biomedical, effect of health care and disinfected applications. As synthesized optically transparent Schiff base stabilized silver nanoparticles (L-1AgNPs) of Schiff base ligand (N-(diphenylmethylene)-6-nitrobenzo[d]thiazol-2-amine) (L-1), has been successfully prepared, Schiff base stabilized silver nanoparticles were synthesized by easy process and straight forward protocol and using co-precipitation method. The synthesis of Schiff base stabilized silver nanoparticles using Schiff base ligand as a stabilizer. The synthesized Schiff base ligand (L-1) and its stabilized silver nanoparticles characterized were various spectroscopic technique, such as Fourier transform infrared (FT-IR), ¹H NMR, Electron Spray Ionization (ESI) Mass, and UV–Visible spectroscopy, P-XRD and Transmission Electron Microscopy (TEM). AgNPs using as shows antibacterial activities of pathogenic gram positive bacteria like Propionic bacteria by using disc diffusion method. Here disc diffusion methods used for comparative studies and found inhibition zone on culture plate. The antimicrobial enhancing efficiency for Ag-nanopartics and diminished the pathogenic behaviour as conservational problem. Here comparatively L-1 is less antimicrobial activity with comparatively L-1-AgNPs showing 14 mm zone of inhibition effect. There is no inhibition zone of pure AgNO₃. The microorganism for Propionic Bacteria against L-1-AgNPs show good activity as compared to L-1 and AgNO₃.     

Preparation of POSS-based organic–inorganic hybrid mesoporous materials networks through Schiff base chemistry

The synthesis of novel POSS-based organic–inorganic hybrid mesoporous materials networks functionalized with amine groups through Schiff base chemistry is reported. The material shows uniform mesoporous size. Nitrogen sorption analyses give high specific surface areas of 641–1103 m² g⁻¹ with pore volumes of 0.47–0.53 mL g⁻¹. The combined results of FTIR, solid ¹³C NMR and ²⁹Si NMR show that the POSS building blocks are successfully weaved in the porous structure without obvious alteration of the POSS structural characteristics. The hybrid materials show excellent thermal stability.