Shridhar P. Gejji

Synthesis, Electronic Structure, DNA and Protein Binding, DNA Cleavage, and Anticancer Activity of Fluorophore-Labeled Copper(II) Complexes

Two mononuclear fluorophore-labeled copper(II) complexes [Cu(nip)(acac)](+)(2) and [Cu(nip)2](2+) (3), where fluorophore is 2-(naphthalen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (nip) (1) and acac is acetylacetone, have been synthesized and characterized by various techniques. The ligand 1 and complex 2 are structurally characterized by single-crystal X-ray diffraction. The coordination geometries around the copper are square planar in solid as well as solution state as evidenced by electron paramagnetic resonance (EPR) spectroscopy. The density functional calculations carried out on 1-3 have shown that electron-rich regions in the highest occupied orbital are localized on the naphthalene and partly on the phenanthroline moiety. Both complexes 2 and 3 in dimethyl sulfoxide (DMSO) exhibit near square planar structure around the metal ion in their ground state. Time-dependent density functional theory (TD-DFT) calculations reveal that Cu(II) ion in complex 2 shows tetrahedral coordination around the metal while 3 retains its square planar geometry in the lowest excited state. The interaction of complexes with calf-thymus DNA (CT DNA) has been explored by using absorption, emission, thermal denaturation, and viscosity studies, and the intercalating mode of DNA binding has been proposed. The complexes cleave DNA oxidatively without any exogenous additives. The protein binding ability has been monitored by quenching of tryptophan emission in the presence of complexes using bovine serum albumin (BSA) as model protein. The compounds showed dynamic quenching behavior. Further, the anticancer activity of the complexes on MCF-7 (human breast cancer), HeLa (human cervical cancer), HL-60 (human promyelocytic leukemia), and MCF-12A (normal epithelial) cell lines has been studied. It has been observed that 3 exhibits higher cytotoxicity than 2, and the cells undergo apoptotic cell death.

Contact ion pair formation and ether oxygen coordination in the polymer electrolytes M[N(CF3SO2)2]2PEOn for M = Mg, Ca, Sr and Ba

The polymer electrolytes M[N(CF3SO2)2]2PEOn for M = Mg, Ca, Sr and Ba have been investigated using infra-red spectroscopy, differential scanning calorimetry and impedance spectroscopy. The effects of varying concentration (n = 6–40) and temperature (25–95°C) on the contact ion pair formation and cation coordination have been studied. Contact ion pairs are only found for the most concentrated samples (n < 9). Ion pairs occur with two types of structures: one type is found for samples containing Mg2+ and the other for samples with Ca2+, Sr2+ and Ba2+. The conductivities of the samples are discussed in terms of radii and coordination numbers of the cations.

Electronic Structure, Molecular Electrostatic Potential, and NMR Chemical Shifts in Cucurbit[n]urils (n = 5-8), Ferrocene, and Their Complexes

Electronic structure and molecular electrostatic potential (MESP) in ferrocene (FC), cucurbit[n]urils (CB[n]) with n = 5-8, and their host-guest complexes are obtained within the framework of density functional theory. MESP topography that is employed to gauge the dimensions of the CB[n] cavity estimates that the cavity height increases from 7.25 to 7.70 A along CB[n] homologue series, whereas the diameter of the CB[8] (8.57 A) cavity is larger than twice that of CB[5] (3.91 A). MESP investigations reveal deeper minima near ureido oxygens in CB[5] along with large electron-rich regions at its portal. A lateral interaction of the guest FC with hydrophilic exterior of the CB[n] portal and its encapsulation within hydrophobic cavity of the host are analyzed. The present calculations suggest that CB[5] does not yield stable complexes in either case. FC interacts laterally with CB[6], and inclusion of the guest occurs, both parallel as well as perpendicular to the CB[n] axis, in the cavity of higher homologue. Self-consistent reaction field studies indicate that, in the presence of water as a solvent, encapsulation of FC in parallel fashion is favored within CB[7] and CB[8] cavities. NMR chemical shifts (delta(H)) of CB[n] protons remain practically unchanged with an increase in the cavity size; however, they are influenced significantly by water. The spectra thus obtained in aqueous solution agree with those observed experimentally. The delta(H) values in FC-CB[n] complexes indicate deshielding of FC protons directed toward portals, while those pointing toward nitrogens exhibit up-shifts in the spectra.

Conformational analysis of poly(ethylene oxide) oligomers: diglyme

Abstract The changes in energy of the diethylene oxide dimethylether H 3 C(OCH 2 CH 2 ) 2 OCH 3 , oligomer of poly(ethylene oxide), as a function of rotation around CC and CO bonds have been analyzed by ab initio calculations. For the highest level calculations. MP2/6–31+ +G ** /HF/3–21 G a gauche conformation around a CC bond is nearly equal in energy with the all trans conformer. The torsional potentials for the CC and CO bonds are presented. The activation energy for the chain motion of a crystalline poly(ethylene oxide) derived from the NMR experiments is 28 kJ/mol. This implies that rotation around more than one bond must be involved in the associated conformational change.

Analysis of atomic electron momentum densities: Use of information entropies in coordinate and momentum space

Abstract The entropy maximization procedure has been extended to treat simultaneously the densities in coordinate and momentum space. The key quantity to be maximized is the sum of information entropies in complementary spaces rather than the entropy in one space alone. This modified procedure has been used to assess the quality of refined electron momentum densities for He, Be and H 2 . The momentum density which maximizes the entropy sum yields good estimates of Compton lineshape and related momentum space expectation values.

Density functional investigations on the charge distribution, vibrational spectra, and NMR chemical shifts in cucurbit[n]uril (n = 5-12) hosts.

Electronic structure, charge distribution, and vibrational frequencies of cucurbit[n]uril, CB[n] (n = 5-12), hosts have been derived using the density functional methods. CB[n] conformers with different orientations of methylene group connecting glycouril units have been investigated. The conformers that possess uniform CB[n] cavity turn out to be of lowest energy, and molecular electrostatic potential (MESP) herein engender shallow minima near ureido oxygens along the series. MESP topography has been utilized to estimate the cavity height and diameter; the ratio of which governs the shape (circular or elliptical) of the cavity. When this ratio is larger than unity (for CB[n] with n >or= 8), an elliptical host cavity is noticed. Calculated vibrational spectra reveal that carbonyl stretching frequency shift in successive CB[n] homologue decreases steadily from 1760 cm(-1) in CB[5] to 1742 cm(-1) in CB[12]. An increase in glycouril units along the CB[n] series influences significantly the intensity profile of C horizontal lineO and C-N stretching vibrations in the calculated infrared spectra. Furthermore, calculated (1)H chemical shifts predict that one of methylene protons directing outside the host cavity are deshielded, whereas the remaining proton near the carbonyl group exhibits downshifted signal in the NMR spectra.

Local coordination and conformation in polyether electrolytes: Geometries of M-triglyme complexes (M = Li, Na, K, Mg and Ca) from ab-initio molecular orbital calculations

Abstract We have performed ab-initio calculations on 1:1 complexes of triglyme (triethylene glycol dimethyl ether) with different metal ions. Several stable tetradentate complexes have been found for each cation. The energy difference between the least stable and the most stable conformations ranges from 18 kJ/mole for the Na + complex to 9 kJ/mole for the Mg 2+ complex. The considerable number of complexes obtained reflects the great flexibility of the oligomer chain.

Hydrogen Bond Energies and Cooperativity in Substituted Calix(n)arenes (n =4 , 5)

Hydrogen-bonded interactions in para-substituted calix[n]arenes (CX[n]) (n = 4, 5) and their thia analogues are analyzed using the recently proposed molecular tailoring approach. The cooperative contribution toward the hydrogen-bonding network within the CX[5] host is shown to be nearly 5 times larger than that in its thia analogue. Hydrogen bond strengths in the O-H···O network are enhanced on substitution of an electron-donating group. The cooperativity contributions are reflected in the electron density at the bond critical point in the quantum theory of atoms in molecules.

On the Binding of SF6 to Cucurbit[6]uril Host: Density Functional Investigations

Interactions of sulfur hexafluoride (SF(6)) with cucurbit[6]uril (CB[6]) have been investigated using the density functional calculations. An encapsulation of guest within CB[6] cavity as well as its binding to either exterior host protons or portal uredio oxygens have been analyzed. The present calculations predict that the complexes with the complete inclusion of SF(6) are favored over those possessing lateral or external interactions. The interactions between fluorine and ureido carbons (F---C) of the host contribute to lowering of energy of the complex. Normal mode analyses from the calculated vibrational spectra show a red-shifted stretching (approximately 928 cm(-1)) of S-F bonds perpendicular to the CB[6] cavity axis when SF(6) is encapsulated in the host cavity. On the other hand, S-F bonds parallel to the cavity axis exhibit a blue shift as compared to the corresponding vibration of the isolated guest. These frequency shifts of S-F bonds have further been analyzed by mapping the difference electron density on the bond critical point(s) (bcp) in molecular electron density (MED) topography and natural bond orbital (NBO) analyses. A depletion of electron density at the bcp along with an enhanced electron density in antibonding S-F* orbital engender weakening of the bond. Concomitant redistribution of electron density leads to the strengthening of S-F bonds parallel to the cavity axis (directing toward either portals). (1)H NMR reveals that the protons directing toward CB[n] portals are not influenced by encapsulation of the guest, which is in consonant with experimentally measured NMR spectra.

Methanol clusters (CH3OH)n, n = 3–6 in external electric fields: Density functional theory approach

Structural evolution of cyclic and branched-cyclic methanol clusters containing three to six molecules, under the influence of externally applied uniform static electric field is studied within the density functional theory. Akin to the situation for water clusters, the electric field is seen to stretch the intermolecular hydrogen bonds, and eventually break the H-bonded network at certain characteristic threshold field values of field strength in the range 0.009-0.016 a.u., yielding linear or branched structures with a lower energy. These structural transitions are characterized by an abrupt increase in the electric dipole moment riding over its otherwise steady nonlinear increase with the applied field. The field tends to rupture the H-bonded structure; consequently, the number of hydrogen bonds decreases with increasing field strength. Vibrational spectra analyzed for fields applied perpendicular to the cyclic ring structures bring out the shifts in the OH ring vibrations (blueshift) and the CO stretch vibrations (redshift). For a given field strength, the blueshifts increase with the number of molecules in the ring and are found to be generally larger than those in the corresponding water cluster counterparts.