Snehadrinarayan Khatua

Rapid and Highly Sensitive Dual-Channel Detection of Cyanide by Bis-heteroleptic Ruthenium(II) Complexes

Two new ruthenium complexes [Ru(bipy)(2)(PDA)](2+) (1) and [Ru(phen)(2)(PDA)](2+) (2) (PDA = 1,10-phenanthroline-4,7-dicarboxaldehyde) have been synthesized to detect cyanide based on the well-known formation of cyanohydrins. Both 1[PF(6)](2) and 2[PF(6)](2) were fully characterized by various spectroscopic techniques and their solid state structures determined by single-crystal X-ray diffraction. Their anion binding properties in pure and aqueous acetonitrile were thoroughly examined using two different channels, i.e., UV-vis absorption and photoluminescence (PL). After addition of only 2 equiv of CN(-), the PL intensity of 1[PF(6)](2) and 2[PF(6)](2) was enhanced ∼55-fold within 15 s along with a diagnostic blue shift of the emission by more than 100 nm. PL titrations of 1[PF(6)](2) and 2[PF(6)](2) with CN(-) in CH(3)CN furnished the very high overall cyanohydrin formation constants log β([CN(-)]) = 15.36 ± 0.44 (β([CN(-)]) = 2.3 × 10(15) M(-2)) and log β([CN(-)]) = 16.37 ± 0.53 (β([CN(-)]) = 2.3 × 10(16) M(-2)), respectively. For both probes, the second constant, K(2), is about 57-84 times less than K(1), suggesting that the cyanohydrin reaction is stepwise. The stepwise mechanism is further supported by results of a (1)H NMR titration of 2[PF(6)](2) with CN(-). The high selectivity of 2[PF(6)](2) for CN(-) was established by PL in the presence of other competing anions. Furthermore, the color change from orange-red to yellow and the appearance of a orange luminescence, which can be observed by the naked eye, provides a simple real-time method for cyanide detection. Finally, theoretical calculations were carried out to elucidate the details of the electronic structure and transitions involved in the ruthenium probes and their cyanide adducts.

A Single Molecular Light-up Sensor for Quantification of Hg2+ and Ag+ in Aqueous Medium: High Selectivity toward Hg2+ over Ag+ in a Mixture

A bis-heteroleptic Ru(II) complex (1) is presented that acts as a single molecular dual analyte sensor and quantifies Hg(2+) and Ag(+) by luminescence at two different wavelengths. The sensor has stronger binding to Hg(2+) than to its likely competitor Ag(+) allowing quantification of Hg(2+) in a sample with Ag(+) without a masking agent. 1 also selectively senses Ag(+) in the absence of Hg(2+) by enhancing the PL intensity at a different wavelength.

Bis-heteroleptic ruthenium(II) complex of a triazole ligand as a selective probe for phosphates.

A new bis-heteroleptic ruthenium(II) complex (1) of 2-(1-methyl-1H-1,2,3-triazol-4-yl) pyridine (L) ligand was extensively explored for anion sensing studies. 1[PF6]2 shows selective sensing of dihydrogen phosphate (H2PO4(-))/hydrogen pyrophosphate (HP2O7(3-)) among halides, HCO3(-), AcO(-), NO3(-), ClO4(-), HSO4(-), OH(-), BzO(-), H2PO4(-), and HP2O7(3-) in acetonitrile. Enhancement of emission intensity of 1[PF6]2 along with a 10 nm red shift of the emission maximum is observed in the presence of H2PO4(-)/HP2O7(3-) selectively. The photoluminescence (PL) titration experiment of 1[PF6]2 results in binding constants (K(a)) of 5.28 × 10(4) M(-1) and 4.67 × 10(4) M(-1) for H2PO4(-) and HP2O7(3-), respectively, which is in good agreement with the Ka values obtained from UV-vis titration experiments (2.97 × 10(4) M(-1) and 2.45 × 10(4) M(-1) for H2PO4(-) and HP2O7(3-), respectively). High selectivity of 1[PF6]2 toward these two anions in acetonitrile is further confirmed by PL intensity measurement of 1[PF6]2 upon addition of these two anions in the presence of a large excess of other competitive anions. Further, considerable changes in the lifetime (τ) as well as in the decay pattern of 1[PF6]2 in the presence of H2PO4(-)/HP2O7(3-) among all tested anions support the selective binding property of 1[PF6]2 toward these two anions. Significant downfield shift of the triazole -CH proton of 1[PF6]2 with 1 equiv of H2PO4(-) (Δδ = 0.26 ppm) and HP2O7(3-) (Δδ = 0.23 ppm) in deuterated dimethyl sulfoxide proclaim binding mechanism via C-H···anion interaction in solution state. Finally, single-crystal X-ray structural analysis confirms the first example of dihydrogen pyrophosphate (H2P2O7(2-)) recognition via solitary C-H···anion interactions.

A Chiral meso-ABC-Corrolatochromium(V) Complex

A chiral metallocorrole complex, oxo[5-(4-bromophenyl)-10-(pentafluorophenyl)-15-(2-thianaphthyl)corrolato]chromium(V) (7), was prepared and serves as the first example of an ABC-metallocorrole; meso substituents are of different electron-withdrawing capacity. An adaptation of a multistep protocol (D. T. Gryko) was made, followed by an aerobic oxidation using Cr(CO)(6) (Z. Gross). The X-ray crystal structure reveals the two enantiomers of 7. Electron paramagnetic resonance spectroscopy (g(iso) = 1.99) and cyclic voltammetry of 7 provide comparative data to that of the A(3)[tris(pfp)cCr(V)O] complex.

Direct dizinc displacement approach for efficient detection of Cu2+ in aqueous media: acetate versus phenolate bridging platforms

Two chiral and one racemic fluorescent dimeric zinc complex {[Zn2(slysH)2Cl2]·(CH3OH)2·(H2O)3 (1), [Zn2(slysH)2 (NO3)2]·(H2O)3 (2), [Zn2(rslysH)2(μ-OAc)2] (3)} are compared herein. Presently, 3 has been synthesized by a one-pot reaction in which the D-/L- lysine-based Schiff base ligand [slys = 6-amino-2-{(2-hydroxybenzylidene)amino}hexanoate] is generated in situ. These compounds have been characterized by single-crystal X-ray diffraction and by various spectroscopic techniques. The structures of previously reported compounds 1 and 2 are closely related in which two zinc centers possess two phenolate-bridges and an axial chloride or nitrate ligand. The novel compound 3 differs structurally through the presence and coordination mode of two bridging acetate groups spanning the dizinc core and formally releasing the phenolate bridging Schiff base ligands. These compounds (1–3) are highly blue fluorescent, either as solids or dissolved species. Under neutral and aqueous conditions (pH 7.4; 0.01 M HEPES buffer, H2O–MeOH = 9 : 1), the quantum yields are ΦF = 0.17 (1), 0.21 (2) (λex = 352 nm, λem = 452 nm), ΦF = 0.16 (3) (λex = 354 nm, λem = 452 nm). Complex 3 metal ion detection capability (i.e., Na+, K+, Ca2+, Mg2+, Co2+, Ni2+, Mn2+, Cu2+, Pb2+, Ag+, Hg2+, and Cd2+) was gauged in aqueous media at physiological pH facilitated by the similarity of its starting photophysical properties with those of 1 and 2. These dizinc species were all found to act as a highly selective fluorescent ON–OFF probes for Cu2+ through the direct displacement of two zinc ions in aqueous media at physiological pH range. The phenolate-bridged compounds 1 and 2, however, showed better selectivity towards Cu2+ over competitive ions, Ni2+ and Co2+ than the acetate-bridged compound 3.

Synthesis and structure of 1-D Na6 cluster chain with short Na-Na distance : Organic like aromaticity in inorganic metal cluster

A unique 1-D chain of sodium cluster containing (Na6) rings stabilized by a molybdenum containing metalloligand has been synthesized and characterized and the DFT calculations show striking resemblance in their aromatic behaviour with the corresponding hydrocarbon analogues.

A Cyanuric Acid Platform Based Tripodal Bis-heteroleptic Ru(II) Complex of Click Generated Ligand for Selective Sensing of Phosphates via C–H···Anion Interaction

A new bis-heteroleptic trinuclear Ru(II) complex (1[PF6]6) has been synthesized from electron deficient cyanuric acid platform based copper-catalyzed azide-alkyne cycloaddition, i.e., CuAAC click generated ligand, 1,3,5-tris [(2-aminoethyl-1H-1,2,3-triazol-4-yl)-pyridine]-1,3,5-triazinane-2,4,6-trione (L1). Complex 1[PF6]6 displays weak luminescence (ϕf = 0.002) at room temperature with a short lifetime of ∼5 ns in acetonitrile. It shows selective sensing of hydrogen pyrophosphate (HP2O7(3-)) through 20-fold enhanced emission intensity (ϕf = 0.039) with a 15 nm red shift in emission maxima even in the presence of a large excess of various competitive anions like F(-), Cl(-), AcO(-), BzO(-), NO3(-), HCO3(-), HSO4(-), HO(-), and H2PO4(-) in acetonitrile. Selective change in the decay profile as well as in the lifetime of 1[PF6]6 in the presence of HP2O7(3-) (108 ns) further supports its selectivity toward HP2O7(3-). UV-vis and photoluminescence titration profiles and corresponding Jobs plot analyses suggest 1:3 host-guest stoichiometric binding between 1[PF6]6 and HP2O7(3-). High emission enhancement of 1[PF6]6 in the presence of HP2O7(3-) has resulted in the detection limit of the anion being as low as 0.02 μM. However, 1[PF6]6 shows selectivity toward higher analogues of phosphates (e.g., ATP, ADP, and AMP) over HP2O7(3-)/H2PO4(-) in 10% Tris HCl buffer (10 mM)/acetonitrile medium. Downfield shifting of the triazole C-H in a (1)H NMR titration study confirms that the binding of HP2O7(3-)/H2PO4(-) is occurring via C-H···anion interaction. The single crystal X-ray structure of complex 1 having NO3(-) counteranion, 1[NO3]6 shows binding of NO3(-) with complex 1 via C-H···NO3(-) interactions.

Aromaticity in cyclic alkali clusters

Density functional calculations on a hexagonal 1D sodium cluster and a 2D potassium cluster show that the M6 (M = Na, K) rings in the chain present in 3D [Na2MoO3L(H2O)2]n (1) and 2D [K2MoO3L(H2O)3]n (2) are aromatic in character according to the nucleus independent chemical shift (NICS) and multicenter bond indices (MCI) values. The NICS values at the center of the Na6 rings and at the cage center of the K6 rings are comparable to the corresponding values of their polyacene analogues in most cases. The stability and reactivity patterns of the M6 rings also follow a similar trend as their organic analogues.

A coumarin based Schiff base probe for selective fluorescence detection of Al3 + and its application in live cell imaging

A new coumarin based Schiff base compound, CSB-1 has been synthesized to detect metal ion based on the chelation enhanced fluorescence (CHEF). The cation binding properties of CSB-1 was thoroughly examined in UV-vis and fluorescence spectroscopy. In fluorescence spectroscopy the compound showed high selectivity toward Al3+ ion and the Al3+ can be quantified in mixed aqueous buffer solution (MeOH: 0.01M HEPES Buffer; 9:1; v/v) at pH7.4 as well as in BSA media. The fluorescence intensity of CSB-1 was enhanced by ~24 fold after addition of only five equivalents of Al3+. The fluorescence titration of CSB-1 with Al3+ in mixed aqueous buffer afforded a binding constant, Ka=(1.06±0.2)×104M-1. The colour change from light yellow to colourless and the appearance of blue fluorescence, which can be observed by the naked eye, provides a real-time method for Al3+ sensing. Further the live cell imaging study indicated that the detection of intracellular Al3+ ions are also readily possible in living cell.

Highly Sensitive Bifunctional Probe for Colorimetric Cyanide and Fluorometric H2S Detection and Bioimaging: Spontaneous Resolution, Aggregation, and Multicolor Fluorescence of Bisulfide Adduct

A 4-methylbenzothiazole linked maleimide-based single molecular bifunctional probe 1 has been synthesized for the colorimetric and fluorometric detection of highly competitive H2S and cyanide ion in aqueous DMSO media. The probe 1 selectively detected CN- under the UV-vis spectroscopy through the rapid appearance of deep pink color. The bright pink color developed due to ICT in the moderately stable cyano substituted enolate intermediate. The absorbance titration of 1 with CN- revealed a new band at 540 nm and the nonlinear curve fitting analysis showed good fit with 1:1 model. In fluorescence channel, 1 was found to be highly selective to H2S in 50% aqueous buffer (pH 7). It exhibited ∼16-fold fluorescence intensity enhancement at 435 nm after reaction with 1 equiv of H2S due to the inhibition of PET. The 1-SH adduct showed TICT phenomenon and behaved like molecular rotor. It further displayed aggregation behavior at higher concentration and excitation wavelength dependent multicolor emission properties. Most interestingly, the spontaneous resolution of chiral S-isomer of the 1-SH adduct occurred during crystallization. The cell imaging study revealed the staining of the cell and multicolor emission in the presence of H2S.