Tarun Kumar Misra

Novel stationary phase for complexation gas chromatography originating from ionic liquid and metallomesogen

A metallomesogen of a polycatenar oxazoline copper(II) complex, [Cu(S-C(12))(2)], that exhibited a columnar mesophase with a helical organization was prepared and employed as the stationary phase for the GC separation with polycyclic aromatic hydrocarbons (PAHs) as model compounds. For introducing the mesogen into the capillary column, an ionic liquid (BeMIM-TfO) was used as the vehicle. The results of thermal analyses and UV-vis spectroscopy indicated that some beneficial interactions occurred between the metallomesogen and the ionic liquid. Various parameters affecting the separation efficiency were studied. Different ratios of BeMIM-TfO and Cu(S-C(12))(2) (1:0, 1:1, 1:2 and 1:3 (w/w)) were tested for the separation of the PAHs. As the amount of Cu(S-C(12))(2) was increased, complete separation could be achieved. The stationary phase with the ratio of 1:1 provided the most satisfactory result having average theoretical plate number of 5.2 x 10(3)plates/m. With an optimized temperature program, 11 PAH mixtures were completely separated within 27 min. The interaction between PAH and these fascinating and interesting stationary phases was discussed.

Synthesis of 28-membered macrocyclic polyammonium cations functionalized gold nanoparticles and their potential for sensing nucleotides.

A new synthesis of underivatized gold nanoparticles (Au-NPs) in water stabilized by the highly water soluble 28-membered macrocyclic polyammonium chloride, [28]ane-(NH(2)(+))(6)O(2)6Cl(-) (28-MCPAC) is reported. In addition to providing stability, 28-MCPAC with its cationic form functionalizes the Au-NPs for sensing anions in water. The 28-MCPAC-Au-NPs show a surface plasmon band in the visible region (>520 nm). By tuning the 28-MCPAC:HAuCl(4) ratio, Au-NPs with different core diameters ranging from 4 nm to 6 nm, as determined by TEM analysis, can be obtained. Particles are spherical, discrete, and appeared to have narrow size distributions. Raman spectroscopy confirms that the physisorption is responsible for the interaction between Au-NP surface and 28-MCPAC. The potential of the as-synthesized particles for sensing monophosphorylated nucleosides (nucleotides): 5-adenosine monophosphate (5-AMP), 5-cytosine monophosphate (5-CMP), 5-guanine monophosphate (5-GMP), and 5-uridine monophosphate (5-UMP) is investigated spectroscopically. Nucleotides-assisted agglomerations of 28-MCPAC-Au-NPs follow the order: 5-UMP>5-GMP>5-CMP>5-AMP. An attempt is taken to prepare Au-NPs in water at pH 4.55 without an added stabilizer. Particles without an added stabilizer are short lived, and the TEM image shows that the particles aggregate following a quasi-two-dimensional self-assembly array.

Capillary electrochromatographic separation of peptides using a macrocyclic polyamine for molecular recognition

A macrocyclic polyamine, 1,5,9,13,17,21,25,29‐octaazacyclodotriacontane ([32]ane‐N8), in the bonded phase was employed as a molecular receptor for CEC separation of oligopeptides. Parameters affecting the performance of the separations were considered. Baseline separation for the mixture of angiotensin I, angiotensin II, [Sar1, Thr8]‐angiotensin II, β‐casomorphin bovine, β‐casomorphin human, oxytocin acetate, tocinoic acid, vasopressin, and FMRF amide could be achieved using phosphate buffer (30 mM, pH 7) as the mobile phase. Column efficiency with average theoretical plate numbers of 69 000 plates/m and RSDs of <1% (n = 6) was achieved. [Met5]‐enkephalin and [Leu5]‐enkephalin, which have identical pI values and similar masses could be completely separated using acetate buffer (30 mM) with pH gradient (pH 3 inlet side and pH 4 outlet side). The results suggest that the mechanism for the peptide separation was mediated by a combination of electrophoretic migration and chromatographic retention involving anion coordination and anion exchange. After long‐term use, the deviation of the EOF of the column after more than 600 injections was still within 6.0% of that for a freshly prepared column.

Bioconjugation of 32-macrocyclic polyammonium cations-functionalized gold nanoparticles with BSA.

Water-dispersed, spherical, underivatized Au-NPs with particle size less than 5 nm were synthesized from an aqueous solution of 32-macrocyclic polyammonium chloride, [32]ane-(NH(2)(+))(8).8Cl(-) (32-MCPAC) using sodium borohydride (NaBH(4)) as the reducing agent. The bioconjugation of the synthesized Au-NPs at different pHs (3.6-5.6) with bovine serum albumin (BSA) protein was studied using UV-Vis, fluorescence, and Raman spectroscopy. These studies support that the Au-NPs were incorporated into the protein moiety and bound to it chemically. The binding constants (K(b)) and stoichiometries (n) (i.e., the number of Au-NPs bound by the proteins) of BSA protein to the Au-NPs at different pHs were determined by measuring the quenching of the fluorescence intensity of the tryptophan residues of the protein molecules after conjugation. The values for K(b) (n) were found to be 1.05 x 10(10) M(-1) (1.66), 2.09 x 10(10) M(-1) (2.30), and 1.86 x 10(10) M(-1) (1.75) at pH 3.60, 4.60, and 5.60 for BSA-Au-NPs conjugations, respectively. The results show that BSA binds to the Au-NPs strongly at pH 4.60, which is equivalent to its isoelectric point (pI 4.6).

Recognition of silver nanoparticles surface-adsorbed citrate anions by macrocyclic polyammonium cations: a spectrophotometric approach to study aggregation kinetics and evaluation of association constant.

In this report, we have studied the recognition of citrate anions adsorbed on the surface of silver nanoparticles (cit‐Ag‐NPs), by macrocyclic polyammonium cations (MCPACs): Me6[14]ane‐N4H84+ (Tet‐A/Tet‐B cations) and [32]ane‐N8H168+, which are well reputed anion recognizers and are treated as to mimic of biological polyamines. The study was monitored on ultraviolet–visible spectroscopy by performing a titration of the aqueous dispersion of the cit‐Ag‐NPs by the aqueous solution of MCPACs. The ultraviolet–visible time‐scan plots over the reduction of the absorption band of surface plasmon resonance of cit‐Ag‐NPs at 390 nm are well fitted with fourth‐order polynomial equation and are employed to determine the initial aggregation rate constants. It has been stated that the aggregation is the result in electrostatic attraction followed by H‐bond formation between the surface‐adsorbed citrate anions and added MCPACs. The atomic force microscopy results have evidenced aggregation of cit‐Ag‐NPs in presence of MCPACs. The evaluated H‐bonded association constant (Kasso) using Benesi–Hildebrand method reveals that [32]ane‐N8H168+ cations form stronger association complex, as expected, with the citrate anions than the Me6[14]ane‐N4H84+ cations. The study would thus provide the insight of molecular interactions involved in nanoparticle surface‐adsorbed anions with biological polyamines. Copyright

Hydrogen bonded networks based on Ni(II)-tetraazamacrocycle (tet-b) complexes: synthesis, isolation and structural characterization of α -[Ni(tet-b)(Cl)](ClO4) and α -[Ni(tet-b)(en)](ClO4)2

Five- and six-coordinate, α-[Ni(tet-b)(Cl)](ClO4) (1) and α-[Ni(tet-b)(en)](ClO4)2 (2) (tet-b = C-racemic-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) complexes have been synthesized and isolated from the reactions of α-[Ni(tet-b)](ClO4)2, which has trans-V (1R,4R,8R,11R,7S,14S or 1S,4S,8S,11S,7R,14R) conformation, with t-Bu4NCl and ethylenediamine (en), respectively. The complexes have been characterized by X-ray crystallography. The crystal structure of 1 shows a distorted trigonal bipyramidal (TBP) coordination geometry composed of four nitrogen atoms from tet-b and a chloro group with an N4Cl chromophore about the nickel(II) ion. The complex cations of 1 are assembled by the perchlorate ions via N–H ··· O hydrogen bonding to form 1-D zigzag chains along the [001] direction. The chains are linked through intermolecular hydrogen bonding where the coordinated chloro group of the complex cation forms two-center double hydrogen bonds with the adjacent N–H groups of the macrocyclic ligand along the [100] direction, resulting in a two-dimensional α-network. The crystal structure of 2 shows a distorted octahedral coordination environment consisting of four nitrogen atoms from tet-b and two from en with an N6 chromophore about nickel(II) ion. The crystal packing analysis shows that the complex cations, α-[Ni(tet-b)(en)]2+ are interconnected by perchlorate ions through conventional two-center (N)H ··· O, and bifurcated (N)H ··· O ··· H(N) hydrogen bonding.