A highly selective fluorescent chemosensor for zinc ion and imaging application in living cells

A new 2,6-bis(5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazolin-6-yl)-4-methylphenol (1) serves as a highly selective and sensitive fluorescent probe for Zn(2+) in a HEPES buffer (50 mM, DMSO:water = 1:9 (v/v), pH = 7.2) at 25 °C. The increase in fluorescence in the presence of Zn(2+) is accounted for by the formation of dinuclear Zn(2+) complex [Zn(2)(C(35)H(25)N(6)O)(OH)(NO(3))(2)(H(2)O)] (2), characterized by X-ray crystallography. The fluorescence quantum yield of the chemosensor 1 is only 0.019, and it increases more than 12-fold (0.237) in the presence of 2 equiv of the zinc ion. Interestingly, the introduction of other metal ions causes the fluorescence intensity to be either unchanged or weakened. By incubation of cultured living cells (A375 and HT-29) with the chemosensor 1, intracellular Zn(2+) concentrations could be monitored through selective fluorescence chemosensing.     

Synthesis of Au nanoparticle-conductive polyaniline composite using H2O2 as oxidising as well as reducing agent

We report a new method of synthesis of an Au nanoparticle-conductive polyaniline composite by using H2O2 both for reduction of HAuCl4 and polymerization of aniline in the same aqueous medium: the electrical conductivity of the composite has been measured to be two orders of magnitude higher than the polymer itself.     

Syntheses and crystal structures of cadmium(II)X2-hexamethylenetetramine (X = Br/I/SCN) coordination polymers having different dimensionality

Four new coordination polymers of cadmium(II) with hexamethylenetetramine (htm) have been synthesized and characterized by routine physicochemical techniques as well as by X-ray single crystal structure analysis. They are [CdBr(htm)(SCN)(H₂O)₂·CH₃OH]_n (1), [CdI(htm)(SCN)(H₂O)₂·0.5(CH₃OH)]_n (2), [Cd₂(htm)₃(SCN)₄(H₂O)]_n·nH₂O (3) and [Cd₃Br₆(htm)₂(H₂O)₅·(htm)(H₂O)₆]_n (4). Complexes 1, 2 and 3 exhibit 1D polymeric structure and complex 4 shows a 2D undulated layered arrangement, containing Cd₆(htm)₆ hexagonal units as building block, which extended to a 3D supramolecular architecture through hydrogen bonding. Thorough thermal investigation suggest that as far as the thermal stability of Cd(II)-htm bond is concerned it attains the maximum in complex 1 and minimum in complex 4. In case of complex 3 the thermal study inferred that CdS end product was obtained at ∼730 °C, whereas in case of other complexes the thermally stable end product remained unidentified. Solid state fluorescence study shows that all the complexes are luminescent at room temperature except complex 3.     

Shape-dependent catalytic activity of copper oxide-supported Pd(0) nanoparticles for Suzuki and cyanation reactions

Palladium nanoparticles supported on different shapes of nanocrystalline CuO are prepared by the treatment of Cu(NO₃)₂ and Pd(OAc)₂ in polyethylene glycol (PEG-6000). The shapes of the CuO/Pd composite are dependent on the amount of PEG used. Suzuki coupling was catalyzed efficiently by the oval-shaped material, whereas the rod shape facilitates the cyanation reaction. The CuO/Pd catalyst is recovered and reused for subsequent Suzuki reactions; however, cyanation poisons the catalyst for further use. Both these reactions are very clean and high yielding.     

Copper(II) complexes of tetradentate N2S2 donor sets: Synthesis,crystal structure characterization and reactivity

Two mononuclear and one dinuclear copper(II) complexes, containing neutral tetradentate NSSN type ligands, of formulation [Cu^II(L¹)Cl]ClO₄ (1), [Cu^II(L²)Cl]ClO₄ (2) and [Cu^II₂(L³)₂Cl₂](ClO₄)₂ (3) were synthesized and isolated in pure form [where L¹ = 1,2-bis(2-pyridylmethylthio)ethane, L² = 1,3-bis(2-pyridylmethylthio)propane and L³ = 1,4-bis(2-pyridylmethylthio)butane]. All these green colored copper(II) complexes were characterized by physicochemical and spectroscopic methods. The dinuclear copper(II) complex 3 changed to a colorless dinuclear copper(I) species of formula [Cu^I₂(L³)₂](ClO₄)₂,0.5H₂O (4) in dimethylformamide even in the presence of air at ambient temperature, while complexes 1 and 2 showed no change under similar conditions. The solid-state structures of complexes 1, 2 and 4 were established by X-ray crystallography. The geometry about the copper in complexes 1 and 2 is trigonal bipyramidal whereas the coordination environment about the copper(I) in dinuclear complex 4 is distorted tetrahedral.     

Photophysics of norharmane in solution phase: From homogeneous to microheterogeneous environments

The photobehavior of norharmane (9H-pyrido[3,4-b]-indole) (NHM), one of the vastly used skeleton of drugs in therapeutic applications, has recently been the subject of increasing interest due to the finding of their phototoxic and photocarcinogenic properties. Its absorption and fluorescence behavior from different prototropic species show remarkable sensitivity towards the polarity, viscosity and local pH, exhibited by various microheterogeneous bio and biomimetic environments like micelles, reverse micelles, proteins, etc. The significant results obtained for NHM in homogeneous and a series of microheterogeneous environments is reviewed in this account. Much attention has been given to the properties of the excited states, location and biodistribution of NHM in different biological environments. The results can help in understanding the photophysics of the probe in biological environments and in assessing the correlation between different prototropic forms and biological activity.     

Synthesis,structure and magnetic properties of mono- and di-nuclear nickel(II) thiocyanate complexes with tridentate N3 donor Schiff bases

The 1:1 condensation of N-methyl-1,3-diaminopropane and N,N-diethyl-1,2-diminoethane with 2-acetylpyridine, respectively at high dilution gives the tridentate mono-condensed Schiff bases N-methyl-N′-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L¹) and N,N-diethyl-N′-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine (L²). The tridentate ligands were allowed to react with methanol solutions of nickel(II) thiocyanate to prepare the complexes [Ni(L¹)(SCN)₂(OH₂) (1) and [{Ni(L²)(SCN)}₂] (2). Single crystal X-ray diffraction was used to confirm the structures of the complexes. The nickel(II) in complex 1 is bonded to three nitrogen donor atoms of the ligand L¹ in a mer orientation, together with two thiocyanates bonded through nitrogen and a water molecule, and it is the first Schiff base complex of nickel(II) containing both thiocyanate and coordinated water. The coordinated water initiates a hydrogen bonded 2D network. In complex 2, the nickel ion occupies a slightly distorted octahedral coordination sphere, being bonded to three nitrogen atoms from the ligand L², also in a mer orientation, and two thiocyanate anions through nitrogen. In contrast to 1, the sixth coordination site is occupied by a sulfur atom from a thiocyanate anion in an adjacent molecule, thus creating a centrosymmetric dimer. A variable temperature magnetic study of complex 2 indicates the simultaneous presence of zero-field splitting, weak intramolecular ferromagnetic coupling and intermolecular antiferromagnetic interactions between the nickel(II) centers.     

Photoinduced properties of methyl ester of 2,6-dimethyl-1-amino-4-benzoic acid: Evidence of charge transfer emission from a weak primary amino donor

Photophysical properties of methyl ester of 2,6-dimethyl-1-amino-4-benzoic acid (M26DMB) have been investigated using steady state absorption and emission spectroscopy and time-resolved emission spectroscopy. Interestingly, not only in polar solvents, the molecule M26DMB having a weak primary amino donor group shows broad red-shifted emission band even in non-polar environment which in all probability arises from closely spaced local and charge transfer (CT) states. Clear dual fluorescence in polar protic solvents comprises of less intense local emission band and strong red-shifted CT band. The position of the red-shifted emission band is dependent on both the polarity and the hydrogen-bonding ability of the solvent.     

An easy and effective method for radiolabelling of solid lipid nanoparticles

Nanoparticle biodistribution study is of great importance in bringing nanomedicine to patients. In this article, solid lipid nanoparticle (SLN) with dimension less than 100 nm was successfully radiolabelled with ^99mTc by using sodium borohydride as a reducing agent (instead of stannous salts). Paclitaxel (PTX) was used as a model anticancer drug for the preparation of drug loaded SLN (PSLN). PSLN was characterized by standard methods. Encapsulation efficiency for PTX in PSLN was estimated by HPLC. PTX (Taxol formulation) and PSLN were radiolabelled separately and subsequent characterizations of these complexes were performed. Greater than 95 % radiolabelling efficiency was achieved and the labelling efficiency was calculated to be more than 90 % upto 24 h. Both the above-mentioned complexes passed the in vitro stability tests. PSLN achieved more brain concentration than Taxol as determined by biodistribution studies. This type of radiolabelling technique can be useful in preclinical evaluation of drug loaded SLN.