• Bhattacharyya

Articles written in Journal of Chemical Sciences

• Chemical approaches of penicillin allergy—III - Isolation of the penicillin-free carrier receptor protein (CRP) on a polymeric 7-deoxy penicillin analogue template and its role in penicillin immunogeneses in rabbit and man

Specific penicillin-carrier receptor proteins (CRP) have been isolated from the sera of penicillin allergic rabbits and human subjects in the unconjugated native state in electrophoretically homogeneous form by employing a synthetic polymeric affinity template containing the 7-deoxy analogue of penicillin G. The synthesis of the 7-deoxy analogue has been described. In this affinity system the antipenicillin-antibody is desorbed by 0·9M thiourea and the CRP in 8M urea. The CRP after incubation with penicillin is converted into the full-fledged antigen. Studies on the origin of CRP and the nature of antibody as well as comparative studies on the properties of the rabbit antibody and those of antibodies elicited by a BSA-BPO conjugate are reported.

• Chemical approaches to penicillin allergy—IV. Binding of carrier receptor protein with penicillin and its analogues

The availability of electrophoretically homogeneous rabbit penicillin carrier receptor protein (CRP) by affinity chromatography afforded an idealin vitro system to calculate the thermodynamic parameters of binding of penicillin and analogues with CRP as well as competitive binding of such analogues with CRP in presence of14C-penicillin G. The kinetics of association of CRP with 7-deoxy penicillin which does not bind covalently with CRP have been studied through equilibrium dialysis with14C-7-deoxybenzyl penicillin and found to be K=2·79×106M−1.−ΔG=8·106 k cal/mole as well as fluorescence quenching studies with exciter λ 280 K=3·573×106M−1,−ΔG=8·239 k cal/mole. The fluorescence quenching studies have been extended to CRP-benzyl penicillin and CRP-6-aminopenicillanic acid (6APA) systems also. The fluorescence data with benzyl penicillin indicate two conformational changes in CRP—a fast change corresponding to the non-covalent binding to CRP with 7-deoxy penicillin and a slower change due to covalent bond formation. With 6-APA the first change is not observed but the conformational change corresponding to covalent binding is only seen.

Competitive binding studies indicate that the order of binding of CRP with the analogues of penicillin is as follows: methicillin &gt; 6APA &gt; carbenicillin &gt;o-nitrobenzyl penicillin &gt; cloxacillin ≈ benzyl penicillin ≈ 6-phenyl acetamido penicillanyl alcohol ≈ 7 phenyl acetamido desacetoxy cephalosporanic acid ≈p-amino benzyl penicillin ≈p-nitro benzyl penicillin &gt; ticarcillin &gt;o-amino benzyl penicillin &gt; amoxycillin &gt; 7-deoxy benzyl penicillin &gt; ampicillin.

From these data it has been possible to delineate partially the topology of the penicillin binding cleft of the CRP as well as some of the functional groups in the cleft responsible for the binding process.

• Chemical approaches to penicillin allergy—V. Nature of reaction between rabbit antigen (CRP-penicillin conjugate) and rabbit antipenicillin antibody

The availability of an electrophoretically homogeneous rabbit penicillin carrier receptor protein (CRP) and rabbit antipenicillin antibody afforded an idealin vitro system to calculate the thermodynamic parameters of the binding of14C benzyl penicillin CRP conjugate (antigen) to the purified rabbit antipenicillin antibody. The thermodynamic parameters of this antigen-antibody reaction has been studied by radio-active assay method by using millipore filter. Equilibrium constant (K) of this reaction has been found to be 2·853×109M−2 and corresponding free energy (ΔG) at 4°C and 37°C has been calculated to be −12·02 and −13·5 kcal/mole, enthalpy (ΔH) and entropy (ΔS) has been found to be 361 kcal/mole and +30 eu/mole respectively.

Competitive binding studies of CRP-analogue conjugates with the divalent rabbit antibody has been carried out in the presence of14C-penicilloyl CRP. It was found that 7-deoxy penicillin-CRP complex and 6-amino penicilloyl CRP conjugate binds to the antibody with energies stronger than that with the14C-penicilloyl CRP. All the other analogue conjugates are much weaker in interfering with the binding of the penicilloyl CRP with the antibody. The conjugate of methicillin,o-nitro benzyl penicillin and ticarcillin with CRP do not materially interfere in the process.

• CNDO bonding parameters in transition metal atoms

The method of calculating CNDO bonding parameters developed recently is extended to transition metal atoms. It is shown that one of the approximations introduced earlier can also be deduced by a more complete treatment of the imbalance problem in CNDO-MO theory. The conventionally calibrated bonding parameters indirectly incorporate important contributions from two-particle interactions. The parameters developed are used to compute the coefficients of metal-to-ligand transfer of spin in many hexafluro metallate ions of transition metals. The results are compared with those obtained by conventional CNDO-MO calculation. Comparison of the computed bonding parameters with other available values is also made.

• Change of molecular structure in the excited states: A (CNDO/2) hole-potential study on phosphine

Molecular structure of phosphine in a number of excited electronic states is studied using the method of hole-potential within the basic framework of CNDO/2 theory. Effects of including 3d-functions of phosphorus in the basis set on computed molecular geometries, transition energies and inversion barriers in the excited states have been investigated. An attempt is made to rationalise qualitatively the structural changes in the excitedstate in terms of Walsh-type correlation diagram constructed with the eigenvalues of the Fock operator in theVN-1 potential model. A simple orbital model for predicting the nature of structural changes in the excited states is proposed.

• Substituent effect on ionisation potential in a series of related molecules: A theoretical study in a molecular orbital framework

The effect of replacing the hydrogen atoms in thioformaldehyde by halogen atoms (F, Cl) on the ionisation potential of the non-bonding electron is analysed by using the Hellman-Feynman theorem, regarding the nuclear charge of the substituent as a parameter in the many-electron Hamiltonian. The trends predicted by our theory nicely agree with the relevant ionisation potentials computed either by applying Koopmans’ theorem or by the ΔESCF method. For the carbonyls, avaible experimental data indicate the reliability of our prediction.

• Chemical probes into the active centre of a heme thiolate monoxygenase

Linalool-8-monoxygenase, a typical bacterial P-450 heme thiolase, shows a high degree of substrate specificity towards linalool. The active site of the pure enzyme has been probed with a large number of substrate analogues with systematic alterations or conformational variations in the linalool molecule. The comparison of three parameters, the mo→mos conversion of the enzyme as a result of substrate binding monitored at 392 nm, theKD of the analogues giving information about energies of association and the relative turnover as substrate have given information about the space-filling characteristics of the substrates in the enzyme cleft, the number of contacts the molecules make with the respective domains of the enzyme and the distance of the site undergoing hydroxylation from the oxygen site, respectively. The data permit the conclusion that linalool makes contact with the enzyme by hydrogen bonding with the hydroxyl group as well through hydrophobic association with all the eight carbons carrying hydrogen in the molecules.

• Applications of a novel algorithm for the calculation ofMCSCF wavefunction: a look into possible avenues of convergence acceleration

The efficacy of a method based on the direct inversion in the iterative subspace (DIIS) in accelerating the approach to self consistency in the calculation of theMCSCF wavefunction using a novel algorithm developed earlier, is compared with that of a simple damping technique. Although the ‘damping’ turns out to be ineffective in the ‘quadratic region’, it accelerates remarkably in the rate of descent on the energy hypersurface in the early stages of the iterative process which leads to an impressive overall increase in the rate of approach to self consistency. TheDIIS based procedure turns out to be ineffective when coupled to the present method and is plagued by ill conditioning problems. Calculations are done to compute the equilibrium geometrical parameter, charge density on different atoms, and dipole moment of HNO molecule in the lowest1,3nπ* states at theINDO/2-MCSCF level.

• Semi-empirical calculation of static molecular polarizability using CHFT: some benzene derivatives and aromatic heterocycles

The static polarizability of fifteen organic molecules (point group symmetry:C2v; number of electrons ≥ 26) have been theoretically calculated using the CNDO/S-CHFT scheme and the results have been compared with other available data.

• The scaled one-electron Hamiltonian model for open-shelllcao-mo-scf calculations: further corrections to thesoeh energy

The wavefunction generated by the scaled one-electron Hamiltonian (soeh) model has been modified further by including all single excitations from the space of thesoeh function. A perturbation-variation ansatz has been invoked for obtaining the corresponding energy correction (ΔE2). [E(soeh)+ΔE2] is shown to reproduceE(Roothaan) very closely. It has been demonstrated that by making ΔE2 stationary with respect to change in μ results. The correctedsoeh [E(soeh)+ΔE2] is shown to be quite useful for the calculation of geometrical parameters of open-shell systems even though it lacks the ‘upper-boundedness’ exhibited byE(soeh).

• On the use of generalized Euler transformation in handling divergent series

A parametrized version of the Euler transformation, introduced fairly recently, is employed to study the behaviour of functions, given their formal power-series (alternating) expansions in λ with finite radii of convergence, in the limit λ»∞. The strategy requires only the first few low-order data. Results are tested with quite a few known cases and found remarkably satisfactory. The role of some other methods in this context are briefly discussed.

• Radiative interactions in diatomic molecules

Radiative interactions which give rise to allowed and forbidden radiative transitions in diatomic molecules are presented as tensor operators. A translational expansion of these interaction operators from the centre of mass of the molecule to the atomic centres is discussed. It is found that the expansion of the magnetic dipole interaction operator generates an extra gradient operator which may contribute significantly towards the transition probability. The expansion of atomic orbitals from one centre to the other is also discussed and analytical expressions of the two-centre integrals which one may encounter in radiative processes are presented.

• On the use of dipole moment as a collective coordinate in constrained variational calculations

The dipole moment function of a diatomic molecule may be viewed as a continuous collective coordinate which encodes a lot of information about sharing of electrons between the atoms concerned. By its very nature it takes cognizance of certain many-body effects and should shape the constrained wavefunction or the one electron density in much the same way as would explicit inclusion of the same many-body effects. A case study of the problem with lithium hydride as the model system has been presented and the long range behaviour of the constrained density analysed. The spectrum of the constrained Fock operator is compared with that of the unconstrained one.

• Theoretical studies on hydrogen bonding inπ-electron systems: A note on the structural features of diacetylene-hydrogen fluoride complexes

Ab initio supermolecular SCF calculations at the STO-3G level are reported for the diacetylene-hydrogen fluoride complexes. The reverse σ-complex is predicted to have somewhat higher stability and H-bond strength than the π-complexes.

• Cation-inert gas atom interactions: A look into charge transfer energetics

The charge-transfer energetics of interactions in a series of closed-shell cation-inert gas pairs is studied by using a model based on the electronegativity equalization principle. These results arc compared with those obtained from SCF calculations carried out at the STO-3G level. A model interaction potential is tested for these systems. The possible effect of an additional electrostatic factor in the charge transfer process is investigated.

• Macroscopic solvation of molecules in excited states: An MCSCF model including solvent polarization effects-I

An MCSCF model including the effects of solvent polarization is developed. The model is applied within the limitations of INDO approximations to look into the dominant effects of solvent polarization on the electronic structure in the excited states of a model system (e.g.* states of H2CO). Important features of macroscopic solvation-induced reorganization of electron density and some consequence thereof are noted.

• Reactivity of the Re-NO centre: Proton induced oxidation of Re(NO)2+ to Re(NO)3+. Synthesis and characterisation of some Re(II) thiocyanato-halogenonitrosyl complexes

The Re(NO)2+ moiety as [Re(NO)(NCS)3H2O] or [Re(NO)(NCS)2(L-L)H2O]· [L-L = phen (1,10-phenanthroline) or bipy (2,2′-bipyridine)] undergoes proton-induced oxidation reaction with HX (X = Cl, Br) to produce a Re(NO)3+ moiety. The spectral and physico-chemical data suggest that the anionic complex is 5 coordinate and the neutral one is 6 coordinate with axial NO group and two NCS ligands intrans-equatorial positions. The complex, [Re(NO)(NCS)2(phen)Br]·H2O shows complicated magnetic behaviour which is discussed in the paper. The ESR spectrum of this compound shows typical rhenium hyperfines and &lt;g&gt;-tensor anisotropy compatible with the loss of axial symmetry. However, the spectrum of [Re(NO)(NCS)2Br2] quite reasonably shows axial symmetry, other features being grossly comparable to the L-L compounds. The anionic species and the neutral L-L complex show irreversible one-electron oxidation waves at different voltages. This may correspond to a conversion of Re(NO)3+ to Re(NO)4+ in both the cases. Interestingly enough, only the neutral complexes exhibit an irreversible reduction wave due probably to a conversion of Re(NO)3+ to Re(NO)2+.

• On the usefulness of generalised quantum chemical valence parameters in monitoring the course of a chemical reaction: A case study of the photochemical decomposition of HNO in excited states

A variant of the orthogonal gradient method of orbital optimization in the INDO-MCSCF framework has been used to study the photochemical decomposition of the HNO molecule into H + NO in the lowest1.3A″ states. A complete geometry optimization has been carried out at all points of the reaction path which appears to be almost barrierless. The one-electron density matrix extracted from the optimized wavefunction at each point has been used to generate the relevant sets of quantum chemical valence parameters. A sharp transition is noted in the N-H bond order and hydrogen free valence index when plotted as functions of rNH. This enables us to locate the transition region easily.

• One- and two-photon spectra of some selected molecules: A comparative study

The complementarity of one- and two-photon spectroscopy has been utilised for throwing light on the following problems of chemical interest: (1) Weak interaction between identical chromophores separated by insulating bridges gives rise to split states of different symmetries. Two-photon spectroscopy (TPA), in conjunction with one-photon absorption (OPA), has been used to identify the states and hence to estimate the magnitude of interaction in bimolecules and trimolecules. From the shifts between the one- and the two-photon spectra, the splittings have been estimated. Calculations confirm that the dominant interaction is the through-bond one. (2) The second type of problem is the identification ofg andu vibrations in molecules. We have initiated studies on three molecules in jet-cooled conditions: 9,10-dihydro-anthracene (DHA). 9,10-dihydro-phenanthrene (DHP) and octa-fluoronaph-thalene (OFN). Only the one-photon fluorescence excitation spectra have so far been obtained by us and the TPA spectra are under investigation. (3) The third class of molecules discussed here are the Ln3+ complexes wherefn⇒ fn transitions are intrinsically two-photon allowed. We have studied two GD3+ single crystals. The CF-splittings, observed clearly in TPA, have been fitted with a parametric model. Some of our observations on the variations of TPA intensity patterns from crystal to crystal, such as circular:linear polarisation ratios, relative intensities of transitions to differentJ-states, do not quite fit in with the Axe-Judd-Downer model. The discrepancies call for a reappraisal of the role of ligand in the TPA process.

• Closed shell-closed shell S, S-bridged heteropolymetallic aggregates: Synthesis and characterisation

[Cu(CN)x]1−x in the presence of excess of KCN reacts with MS42− and M02S22− (M = W, Mo) producing [NC−CuS2MS2]2− and hitherto unknown [NC−CuS2−M02]2− respectively as PPh4 salts. Complexes have been characterised by typicalvCN,v(M=S), v(M-S-M′) andv(M=0) vibrations in appropriate cases. In their electronic spectra the intraligand (MS42− or M02S22−) transitions are interestingly perturbed. Cd2+ affords [Cd(WS4)2]2− and [Cd(W02S2)2]2− but Hg2+ is reduced by WS42− and W02S22−affording [S2WS2HgHgS2WS2]2− and [02WS2HgHgS2W02]2− respectively. Besides LMCT transitions, the softer Cd and Hg complexes presumably also show MLCT type transitions. Pb2+ affords [Pb2[WS4)4]4− which is isostructural with the Sn-analogue. The copper-tungsten complexes show irreversible reduction waves in their cyclic voltammograms, indicating the reduction of W(VI) to W(V). The corresponding Mo complexes show quasi-reversibility whereby Mo(VI) is reduced to Mo(V) and then MoS43− is reversibly oxidised. The Hg(I) centres in the mercury complexes are also reduced to Hg(0). [NC−CuS2WS2]2− reacts with NiCl2·6H20 probably forming [CuS2WS2NiS2WS2Cu]2− and [NC−CuS2W02]2− reacts with UO22+ presumably affording [NCCuS2W02U02(H20)02·WS2 CuCN]2− providing evidence that besides the W=S bond, the W=0 bond can also show nucleophilic character.

• Abstracts

• Basicity of some proto-typical carbonyls in the ground and some low lying excited states: Application of the orthogonal gradient method of orbital optimization in an INDO-MC-SCF framework-I

Gas phase proton affinities of formaldehyde and fluoroformaldehyde in the ground,1,3* (lowest) and3ππ* (lowest) states have been theoretically studied within the framework of the INDO-MC-SCF orthogonal gradient method developed earlier. Complete geometry optimization has been carried out for both the protonated and unprotonated bases in the ground and relevant excited states. Computed proton affinities (PA) of H2CO in different electronic states are in the following order:$$PA({}^1S_0 ) &gt; PA({}^3\pi \pi ^ * ) \sim PA({}^1n\pi ^ * ) &gt; PA({}^3n\pi ^ * )$$ In F2CO, however, the ordering turns out to be different viz PA(1S0)&gt;PA(1*)&gt;PA(3*)&gt;PA(3ππ*) for protonation at the carbonyl oxygen. For protonation at the F atom the ordering is PA(1S0)&gt;PA(3*)&gt;PA(1*)&gt;PA(3ππ*). Protonation at the oxygen atom is predicted to be energetically more favourable than protonation at one of the F atoms by approximately 30 kcal/mole in all the states studied. The role of Fermi correlation in shaping the difference in proton affinities of the singlet and triplet* states of H2CO is discussed.

• Time-dependent Fourier grid Hamiltonian method for modelling real-time quantum dynamics: Theoretical models and applications

A local grid method for modelling real-time quantum dynamical events is formulated. The formulation is straightforward for 1-D systems. For more than one dimension, appeal has to be made to mean-field approximation of the appropriate kind. The simplest mean-field model results in time-dependent Hartree-Fourier grid method. The relationship of the proposed method with some other methods available in the literature is examined. A few examples of numerical applications dealing with (i) the dynamics of dissociation and ionization processes in diatoms and atoms respectively and (ii) tunnelling dynamics in the intramolecular H-atom transfer phenomenon are presented.

• Synthesis, characterization and reactivity of oxomolybdenum(V) complexes with ONS and NNS donors

The monomeric oxomolybdenum(V) complexes, [MoOLCl2]1a-1d [HL = S-benzyl/methyl 3-(2-pyridyl)methylenedithiocarbazate (1a and1b), or N-methyl-S-benzyl/methyl 3-(2-hydroxy phenyl)methylenedithiocarbazate (1c and1d) are synthesized by the reaction of MoOCl52− with HL ligands. All these complexes show magnetic moment of about 1.7 B.M. The complexes,1a and1b, exhibit rhombicg-tensor anisotropy (like xanthine oxidase) whilst1c and1d show axial spectrum. The above complexes undergo irreversible electrochemical reduction furnishing Mo(IV) species and the potentials are dependent on the S-substituents. Reactions of MoOX5 (X = Cl or Br) with H2L1 [H2L1 = S-methyl 3-(5-R-2-hydroxyphenyl)methylenedithiocarbazate] (R = H, CH3, Cl, Br) produce complexes of thiolatobridged dimers, [Mo2O2L21X2], which show sub-normal magnetic moments at room temperature. The metal-centred irreversible oxidation and reduction of these complexes show expected dependence on the R-substituents of the salicyl phenyl ring of the ligands.

• Ligand control on the synthesis and redox aspects of mononuclear manganese-(III) and -(IV) complexes with tridentate ONS-coordination

MnCl2·4H2O reacts with benzohydroxamic acid (BHAH2) in aqueous/non-aqueous solution (alkaline) forming manganese(IV) complexes of the type (PPh4)2[Mn(BHA)3]·3H2O. Its IR data suggest the hydroximato mode of coordination (O, O). This complex in frozen solution exhibits axial spectra with strong zero field splitting giving rise to ag≈4 signal which is more intense than that forg≈2. The solid, however, shows rhombic spectra. A probable reason for this difference is assigned. Trifunctional (ONS) Schiff bases H2L1 and H2L2 (5-R-salicylaldehyde thiosemicarbazone and 5-R-salicyl aldehyde-4-phenyl thiosemicarbazone, respectively; R=H, Me or Br) furnish Mn(IV) complexes of the type [MnL2](L=L1 or L2), whereas H2L3 and H2L4 (H2L3=S-methyl 3-(5-R-2-hydroxyphenyl) methylene dithiocarbazate; H2L4=S-benzyl 3-(5-R-2-hydroxyphenyl) methylene dithiocarbazate; R=H, Me or Br) afford manganese(III) complexes of the type [MnL(O2CMe)] or [MnL(acac)] (acac=acetylacetonate, L=L3 or L4), when treated with MnII (O2CMe)2·4H2O or [MnIII(acac)3] in ethanol medium in air. The EPR spectra of the manganese(IV) complexes in frozen dimethyl formamide (dmf)-methanol solution show weak and strong signals at 〈g〉≈4·0 and ≈2·0 respectively, implying a small zero field splitting. The 〈g〉≈2·0 shows hyperfine (55Mn) as well as forbidden lines. Cyclic voltammograms of these complexes scanned in DMF show reversible and quasi-reversible MnIV-MnIII couple, theE2980 values of which are significantly affected by the electronic effects of the R-substituents in the salicyl phenyl ring and those attached to the carbon atom bound to the thiolate functionality of the ligands. The HammettσP values of the R-substituents are linearly correlated with theE2980 values.

• Transcription of the results of quantum chemical calculations in terms of the classical notion of molecular structures: The cases of some small carbonyls in the ground and excited states

Quantum chemical valence parameters of several carbonyl molecules in the ground and excited states are calculated by invoking the INDO-orthogonal gradient method in an MC-SCF framework. These parameters are then used to construct state-specific structural descriptions of these molecules in terms of superposition of several canonical structures. Photochemical reactivities of some of these molecules are sought to be explained on the basis of the picture that emerges.

• Oxygen-rich molybdenum and chromium complexes: Synthesis, structure and catalysis

• Relaxation in binary mixtures: Non-ideality, heterogeneity and re-entrance

Binary mixtures show many kinds of fascinating dynamical behaviour which has eluded microscopic description till very recently. In this work we show that much of the anomalous behaviour can be explained by building suitable models and carrying out theoretical and simulation studies. Specifically, three well-known problems have been addressed here. (a) Non-ideality in composition dependence of viscosity, (b) re-entrant behaviour of orientational relaxation, and (c) heterogeneity in supercooled binary mixtures. The physical origin of the dynamical behaviour of binary mixtures can be understood in terms of composition fluctuation, a study of which has also been presented in this paper.

• Photoisomerization of merocyanine 540 in polymer-surfactant aggregate

Photoisomerization of merocyanine 540 (MC540) in a polymer-surfactant aggregate is studied using picosecond time resolved emission spectroscopy. The aggregate consists of the polymer, poly(vinylpyrrolidone) (PVP) and the surfactant, sodium dodecyl sulphate (SDS). With increase in the concentration of SDS in an aqueous solution of MC540 containing PVP, the emission quantum yield and lifetime of MC540 increase markedly. This indicates marked retardation in the nonradiative photoisomerization process of MC540, when it binds to the polymer-surfactant aggregate. The critical association concentration of SDS for binding to PVP has been found to be 0.5 mM. This is about 16 times lower than the CMC of SDS in pure water (8 mM).

• Isomerization and fluorescence depolarization of merocyanine 540 in polyacrylic acid. Effect ofpH

Dynamics of isomerization and fluorescence depolarization of merocyanine 540 (MC540) in an aqueous solution of polyacrylic acid (PAA) have been studied using picosecond time resolved fluorescence spectroscopy. It is observed that the dynamics of isomerization and depolarization are sensitive enough to monitor the uncoiling of PAA at high pH (&gt; 6). At low pH (&lt; 3), when the polymer remains in a hypercoiled form, polymer bound MC540 experiences very high microscopic friction and, hence, the isomerization and depolarization processes are very slow. At high pH (&gt; 6) a polyanion is formed and the polymer assumes an extended configuration due to electrostatic repulsion. At high pH (&gt; 6), the anionic probe MC540 is expelled from the polyanion to bulk water and the dynamics of isomerization and fluorescence depolarization become faster by 12 and 5 times respectively, compared to those at low pH.

• Ultrafast chemistry in complex and confined systems

Self-organized molecular assemblies play a crucial role in many natural and biological processes. Recent applications of ultrafast laser spectroscopy and computer simulations revealed that chemistry in a confined environment is fundamentally different from that in ordinary solutions. Many recent examples of slow dynamics in constrained environments and their biological implications are discussed

• Diagonalization of a real-symmetric Hamiltonian by genetic algorithm: A recipe based on minimization of Rayleigh quotient

A genetic algorithm-based recipe involving minimization of the Rayleigh quotient is proposed for the sequential extraction of eigenvalues and eigenvectors of a real symmetric matrix with and without basis optimization. Important features of the method are analysed, and possible directions of development suggested

• Excited-state proton transfer from pyranine to acetate in methanol

Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate ($k_1$) is calculated to be $\sim 1 \times 10^9$ M-1 s-1. This is slower by about two orders of magnitude than that in bulk water ($8 \times 10^{10}$ M-1 s-1) at 4 M acetate.

• On the origin of the anomalous ultraslow solvation dynamics in heterogeneous environments

Many recent experimental studies have reported a surprising ultraslow component (even &gt;10 ns) in the solvation dynamics of a polar probe in an organized assembly, the origin of which is not understood at present. Here we propose two molecular mechanisms in explanation. The first one involves the motion of the buried water’ molecules (both translation and rotation), accompanied by cooperative relaxation (‘local melting’) of several surfactant chains. An estimate of the time is obtained by using an effective Rouse chain model of chain dynamics, coupled with a mean first passage time calculation. The second explanation invokes self-diffusion of the (di)polar probe itself from a less polar to a more polar region. This may also involve cooperative motion of the surfactant chains in the hydrophobic core, if the probe has a sizeable distribution inside the core prior to excitation, or escape of the probe to the bulk from the surface of the self-assembly. The second mechanism should result in the narrowing of the full width of the emission spectrum with time, which has indeed been observed in recent experiments. It is argued that both the mechanisms may give rise to an ultraslow time constant and may be applicable to different experimental situations. The effectiveness of solvation as a dynamical probe in such complex systems has been discussed.

• Ultrafast fluorescence resonance energy transfer in a bile salt aggregate: Excitation wavelength dependence

Fluorescence resonance energy transfer (FRET) from Coumarin 153 (C153) to Rhodamine 6G (R6G) in a secondary aggregate of a bile salt (sodium deoxycholate, NaDC) is studied by femtosecond up-conversion. The emission spectrum of C153 in NaDC is analysed in terms of two spectra-one with emission maximum at 480 nm which corresponds to a non-polar and hydrophobic site and another with maximum at ∼ 530 nm which arises from a polar hydrophilic site. The time constants of FRET were obtained from the rise time of the emission of the acceptor (R6G). In the NaDC aggregate, FRET occurs in multiple time scales -4 ps and 3700 ps. The 4 ps component is assigned to FRET from a donor (D) to an acceptor (A) held at a close distance ($R_{\text{DA}} \sim 17$ Å) inside the bile salt aggregate. The 3700 ps component corresponds to a donor-acceptor distance ∼ 48 Å. The long (3700 ps) component may involve diffusion of the donor. With increase in the excitation wavelength ($\lambda_{\text{ex}}$) from 375 to 435 nm, the relative contribution of the ultrafast component of FRET (∼ 4 ps) increases from 3 to 40% with a concomitant decrease in the contribution of the ultraslow component (∼3700 ps) from 97 to 60%. The $\lambda_{ex}$ dependence is attributed to the presence of donors at different locations. At a long $\lambda_{\text{ex}}$ (435 nm) donors in the highly polar peripheral region are excited. A short $\lambda_{\text{ex}}$ (375 nm) selects’ donor at a hydrophobic location.

• Oximato bridged Rh$^{\text{III}}_2$MII and RhIIIMI species (MII = Mn, Co, Ni; MI = Cu, Ag)

The reaction of [RhCl2(HPhL)(PhL)] with MII(ClO4)2.6H2O in presence of alkali has furnished trinuclear [RhCl2(PhL)2]2M(H2O)$_2.$H2O (HPhL is phenylazobenzaldoxime; M = Mn, Co, Ni). A similar reaction with MI(PPh3)2NO3 yielded binuclear [RhCl2(PhL)2]M(PPh3)2 (M = Cu, Ag). In these molecules the oximato group acts as a bridge between RhIII (bonded at N) and MII or MI (bonded at O). In structurally characterized [RhIIICl2(PhL)2]2Mn(H2O)2.H2O the centrosymmetric distorted octahedral MnO6 coordination sphere is spanned by four oximato oxygen atoms and two water molecules lying in trans position. In the lattice the neighbouring molecules are held together by H2O$\cdots$H2O$\cdots$H2O hydrogen bonds generating infinite zigzag chains. The manganese atoms lie parallel to the C-axis, the shortest Mn…Mn distance being 7.992 Å. Magnetic exchange interactions if any are small as seen in room temperature magnetic moments. The manganese system displays a strong EPR signal near 𝑔 = 2.00. In the complex [RhCl2(PhL)2]Cu(PPh3)2 the copper atom is coordinated to two oximato oxygen atoms and the two phosphorus atoms in a distorted tetrahedral geometry. The softness of the phosphine ligand is believed to sustain the stable coordination of hard oximato oxygen to soft CuI. The coordination sphere of the RhIII atom in both the complexes is uniformly trans-RhN4Cl2.

• Pressure effect on rate of production of glucose-equivalent in plant cells

The rate of glucose equivalent production in C4 green plants is investigated as a function of the intercellular partial pressure of CO2, so as to find the precise physical chemistry of photosynthesis. Expressions are first formulated for the dependence of photochemical efficiency and of rubisco activation on pressure. Then a pressure-dependent rate law is derived. The latter is successfully tested for two specific C4 plants, namely, Panicum antidotale and Panicum coloratum.

• Graham’s law of diffusion: Quantum analogy and non-ideality

We focus attention on two equivalent forms of Graham’s law of diffusion that is valid for an ideal gas mixture. This equivalence is shown to be lost by the empirical equations of state in presence of an attractive nonideality. The modified forms are noted. We then construct a simple quantum mechanical model to simulate these results and obtain a one-to-one correspondence. We see how these equations of interest may be extended to 𝐷-dimensions. By employing the quantum model, we next observe the equivalence of the results found above with those obtained via statistical mechanics. As an added advantage, we demonstrate that the virial theorem for confined quantum stationary states retains its validity in the statistical domain too, though here the averaging scheme is correspondingly different.

• On optimal designing of low frequency polychromatic fields for facile photo-dissociation of model diatomic molecules

The dissociation of a diatomic molecule in low frequency polychromatic fields of moderate intensities is studied. Genetic Algorithm is invoked to search out a set of four optimal non-resonant frequencies ($\omega_1$ - $\omega_4$), intensities ($\epsilon_1$ - $\epsilon_4$) the and phase angles ($\delta_1 - \delta_4$), for achieving a facile photo dissociation. Time-dependent Hellmann-Feynman theorem is used to gain insight into the frequency resolved energy absorption pattern. The ‘quantum phase space’ structures indicate occurrence of bond breaking dynamics akin to the classical one.

• Synthesis, structure and ionic conductivity in scheelite type Li0.5Ce$_{0.5−x}$Ln$_x$MoO4 ($x = 0$ and 0.25, Ln = Pr, Sm)

Scheelite type solid electrolytes, Li0.5Ce$_{0.5−x}$Ln$_x$MoO4 ($x = 0$ and 0.25, Ln = Pr, Sm) have been synthesized using a solid state method. Their structure and ionic conductivity (𝜎) were obtained by single crystal X-ray diffraction and ac-impedance spectroscopy, respectively. X-ray diffraction studies reveal a space group of $I4_1/a$ for Li0.5Ce$_{0.5−x}$Ln$_x$MoO4 ($x = 0$ and 0.25, Ln = Pr, Sm) scheelite compounds. The unsubstituted Li0.5Ce0.5MoO4 showed lithium ion conductivity $\sim 10^{−5}-10^{−3} \Omega^{−1}$cm-1 in the temperature range of 300-700°C ($\sigma = 2.5 \times 10^{−3} \Omega^{−1}$cm-1 at 700°C). The substituted compounds show lower conductivity compared to the unsubstituted compound, with the magnitude of ionic conductivity being two (in the high temperature regime) to one order (in the low temperature regime) lower than the unsubstituted compound. Since these scheelite type structures show significant conductivity, the series of compounds could serve in high temperature lithium battery operations.

• Dynamics of atom tunnelling in a symmetric double well coupled to an asymmetric double well: The case of malonaldehyde

The quantum dynamics of intramolecular H-atom transfer in malonaldehyde is investigated with a model two-dimensional Hamiltonian constructed with the help of available ab initio theoretical data on the relevant portion of the potential energy surface. At zero temperature, the H-atom transfer takes place by tunnelling leading to cis-cis isomerization while the cis-trans channel remains closed. Local excitation of the cis-trans mode by an external field is predicted to quench cis-cis tunnelling isomerization while excitation of the cis-cis mode is found to enhance the isomerization by tunnelling.

• Electrochemical sensing and photocatalysis using Ag-TiO2 microwires

Anatase Ag-TiO2 microwires with high sensitivity and photocatalytic activity were synthesized via polyol synthesis route followed by a simple surface modification and chemical reduction approach for attachment of silver. The superior performance of the Ag-TiO2 composite microwires is attributed to improved surface reactivity, mass transport and catalytic property as a result of wiring the TiO2 surface with Ag nanoparticles. Compared to the TiO2 microwires, Ag-TiO2 microwires exhibited three times higher sensitivity in the detection of cationic dye such as methylene blue. Photocatalytic degradation efficiency was also found to be significantly enhanced at constant illumination protocols and observation times. The improved performance is attributed to the formation of a Schottky barrier between TiO2 and Ag nanoparticles leading to a fast transport of photogenerated electrons to the Ag nanoparticles.

• Synthesis, characterization and superoxide dismutase activity of bi-copper(II)-bisacetato-𝜇−phthalicacid[bis(benzyloxy)ethyl]ester

A new binuclear copper(II) complex, bridged by the ligand phthalicacid[bis(benzyloxy)ethyl]ester, where each copper(II) is coordinated to one carboxylate (from ligand) and one acetate in square planar mode is reported. The ligand synthesized by the reaction of phthalic anhydride and ethylene glycol, has been characterized by FT-IR, 1HNMR and LCMS. The binuclear Copper(II) complex has been characterized by UV/visible spectra, FTIR spectra, EPR spectra, ESI-MS spectra, magnetic moment measurement and thermogravimetric analysis. DFT calculation has shown a Z type structure for the complex. Excellent superoxide dismutase activity with IC50 value 8.6 × 10−6 M for the complex has been observed.

• Effect of external electric field on Cyclodextrin-Alcohol adducts: A DFT study

Effect of external electric fields on the interaction energy between cyclodextrin and alcohol was analyzed in the light of density functional theory (DFT) and density functional reactivity theory (DFRT). Stability of the cyclodextrin-alcohol adducts was measured in terms of DFT based reactivity descriptor, global hardness, electrophilicity, and energy of the HOMO. Stability of adducts was observed to be sensitive towards the strength as well as direction of the applied external electric field. In addition, reactivity pattern follows the maximum hardness and minimum electrophilicity principles.

• Does oligomerization in fused thiophene affect reactivity and aromaticity?

Reactivity and aromaticity of a few fused thiophene oligomers and their conformers are discussed in the light of density functional theory (DFT) and conceptual density functional theory. Reactivity parameters, such as hardness (𝜂) and electrophilicity (𝜔), chemical potential (𝜇) and energy of the HOMO (highest occupied molecular orbital) have been studied. Oligomerization raises the 𝐸HOMO of the species, which in turn increases the reactivity of the oligomers. The absorption spectra of the species are analysed using TDDFT (time dependent density functional theory). The absorption peaks show red shift with increasing size of the oligomers. Aromaticity of the species is gauged by nucleus independent chemical shift (NICS). The out-of-plane component, (NICSzz) values advocate higher aromatic character at longer distance whereas, NICS supports the reverse.

• Reactivity of chitosan derivatives and their interaction with guanine: A computational study

The present study delves into the reactivity of a few chitosan derivatives (CSDs) and their interactionwith guanine in vacuum and in different phases. Increase in the polarity of the solvent lowers reactivityof the chosen derivatives (evaluated by using reactivity descriptors). Interaction between the CSDs and guanine(measured by interaction energy) weakens in solvent media and CSD-guanine interaction is weaker thanthe interaction between guanine and unmodified chitosan (CS). Chemical stability of CSD-guanine adductsremains similar to that of CS-guanine adduct in both polar and non-polar media. Moreover, CSD-guanineadducts exhibit comparable thermodynamic stability (quantified by free energy of solvation, δGsol) to that ofunmodified CS-guanine adduct in non-polar solvent but in polar medium they are immensely destabilized incomparison to CS-guanine adduct. Observed theoretical results are expected to provide guidance for futurerelevant experimental research on gene delivery by CS derivatives.

• Spatial inhomogeneity in spectra and exciton dynamics in porphyrin micro-rods and micro-brushes: Confocal microscopy

In an aqueous acidic solution, the porphyrin meso-tetra(4-sulfonatophenyl) porphyrin tetrasodium salt (TPPS) forms different kinds of assembly (micro-rods and micro-brush) depending on condition of evaporation. The exciton dynamics and emission spectra of the micro-rods and micro-brushes depend on spatialinhomogeneity. This is elucidated by time-resolved confocal microscopy.

• On the effect of external perturbation on amino acid salt bridge: a DFT study

Effect of external perturbation (in terms of external electric field and solvents) on the stability of lysine-aspartic acid salt bridge was analyzed by density functional theory. Because of solvation, interaction energy in the aqueous phase is much lower as compared to gas phase. Interaction energy as well as stability (measured in terms of global hardness, HOMO energy and total electronic energy) are observed to be sensitive towards the strength and direction of the applied electric field. Gap between HOMO energy of the acids and salt bridge also points towards the feasibility of hydrogen bonding.

• Validity of the Rosenfeld relationship: A comparative study of the network forming NTW model and other simple liquids

In this paper we explore the validity of the Rosenfeld and the Dzugutov relation for the Lennard- Jones (LJ) system, its repulsive counterpart, the WCA system and a network forming liquid, the NTW model. We find that for all the systems both the relations are valid at high temperature regime with an universalexponent close to 0.8. Similar to that observed for the simple liquids, the LJ and the WCA systems show a breakdown of the scaling laws at the low temperature regime. However for the NTW model, which is a simple liquid, these scaling laws are valid even at lower temperature regime similar to that found for ionic melts. Thus we find that the NTW model has mixed characteristics of simple liquids and ionic melts. Our study further reveals a quantitative relationship between the Rosenfeld and the Arrhenius relations. For strong liquids, the validity of the Rosenfeld relation in the low temperature regime is connected to it following the Arrhenius behaviour in that regime. Finally we explore the role of pair entropy and residual multiparticle entropy in the dynamics as a function of fragility of the systems.

• Size and Structure of Cytochrome-c bound to Gold nano-clusters: Effect of Ethanol

Size and structure of cytochrome c (Cyt C) bound to gold nano-clusters (AuNC) were studied using fluorescence correlation spectroscopy (FCS) and circular dichroism (CD) spectroscopy. The CD spectra of Cyt C indicate that the ellipticity is almost completely lost on binding to AuNC which indicates unfolding.Addition of ethanol causes partial restoration of ellipticity and hence, structure of Cyt C. FCS data indicate that size (hydrodynamic radius, rH) of free Cyt C is 17Å which increases to 24Å on binding to AuNC. This too suggests unfolding of Cyt C upon binding to AuNCs. Both the size and conformational relaxation time of Cyt C bound to AuNC vary non-monotonically with increase in ethanol content.

• A density functional study on synthetic polymer–amino acid interaction

Interaction of four synthetic polymers viz., poly-ε-caprolactone (PCL), polyglycolide (PGA), polylactic acid (PLA) and Poly(lactic-co-glycolic) acid (PLGA) used as protein delivery vectors with a few amino acids have been studied by using density functional theory. Association geometries of polymer–amino acid adduct are modelled in a vacuum and in four solvents. Nature and strength of interaction have been analyzed in terms of interaction energy and thermochemical parameters of adducts as well as vibrational frequencyshifts upon adduct formation. Results suggest comprehensive stability of adducts in the gas phase. Progressive destabilization of adducts with increasing polarity of solvent is observed. Redshifts in vibrational frequencies of X-H bonds (X=H donor in hydrogen bonding) upon adduct formation are noticed. The study asserts the potentiality of the considered synthetic polymers as an amino acid carrier

• Photoinduced electron transfer processes of (E)-9-(4-nitrostyryl)anthracene in non-polar solvent medium: generation of long-lived charge-separated states

In the present study, photoinduced electron transfer (PET) dynamics between N,N-diethylaniline (DEA) and (E)-9-(4-nitrostyryl)anthracene (An-NO2) in a non-polar solvent medium {methylcyclohexane (MCH)}, has been investigated. The rate constant of back electron transfer (kKBT) for the An-NO2 – DEA pair was 3.8×105s -1 which is ca. 2 orders of magnitude less compared to the anthracene (An)-DEA (control) system. The results indicate that long-lived charge separated species can be generated using the design strategy used herein by achieving resonance stabilization of the excited state (acceptor) radical via conjugation.

• Syntheses and structures of chalcogen-bridged binuclear group 5 and 6 metal complexes

Syntheses and structural elucidations of a series of chalcogen stabilized binuclear complexes of group 5 and 6 transition metals have been described. Room temperature reaction of [Cp*CrCl]2 (Cp* = h5- C5Me5) with Li[BH3(SePh)] afforded a Se inserted binuclear chromium complex, [(Cp*Cr)2(m-Se2SePh)2], 1.In an attempt to make the analogous complexes with heavier group 6 metals, reactions of [Cp*MCl4] (M = Mo and W) with Li[BH3(SePh)] were carried out that yielded Se inserted binuclear complexes [(Cp*M)2(m-Se)2(m-SePh)2], 2 and 3 (2: M = Mo and 3: M = W) along with known [(Cp*M)2B5H9], 4a–b (4a: M = Mo and 4b: M = W). Similarly, the reactions of [Cp*NbCl4] with Li[BH3(EPh)] (E = S or Se)followed by thermolysis led to the formation of binuclear chalcogen complexes [(Cp*Nb)2(m-E2)2], 5 and 6 (5: E = S and 6: E = Se) and known [(Cp*Nb)2(B2H6)6], 7. All these complexes have been characterized by 1H and 13C NMR spectroscopy and mass spectrometry. The structural integrity of complexes 1, 3, 5 and 6 was established by the X-ray diffraction studies. The DFT studies further exemplify the bonding interactions present in these complexes, especially the multiple bond character between the metals in 1–3.

• Correction to: Syntheses and structures of chalcogen-bridged binuclear group 5 and 6 metal complexes

• Luminescent metal–organic frameworks and their potential applications

The metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are a class of porous, crystalline material with numerous possibilities of real-world applications including storage, separation, catalysis, sensing etc. The possibility of intrinsic crystallinity and virtually infinite metal/metal-oxo node and organic linker combination make it a perfect material for photophysical studies. In the last decade, luminescent MOFs have emerged as an excellent modular material for various optical applications, and here, we have discussed about its design strategies. In this review, with relevant examples we have highlighted the rational design approach, possible applications (light emitting diodes, sensing) and future directions in luminescent MOFs

• Investigation of lanthanide complexation with acetohydroxamic acid in nitrate medium: experimental and DFT studies

Complexation study of acetohydroxamic (AHA) ligand with La(III), Nd(III), Eu(III), Er(III), andLu(III), as representative of lanthanide (Ln) series, has been described, in presence of pure nitrate andcombination of nitrate and perchlorate ions using various spectroscopic analysis and density functional theory(DFT) calculations. Nuclear magnetic resonance (NMR) spectroscopy reports the bidentate mode of coordinationof Z-Keto tautomer of AHA monomer with La(III). Formation of 1:3 Nd(III)-AHA complexes inpresence of pure nitrate and a combination of nitrate and perchlorate ions has been observed from ultravioletvisible(UV-Vis) spectroscopy analysis. The geometrical parameter analysis exhibit the bidentate modecoordination fashion of the AHA monomer which corroborates the NMR results. The geometrical parameter,frontier orbital(HOMO-LUMO), global reactivity descriptors and local reactivity descriptors analysis supportsthe findings of the spectroscopy titration methods that stability of Ln-AHA complexes decreases in thepresence of pure nitrate ions than in presence of both perchlorate and nitrate ions. The trend of theoreticalNMR chemical shifts of AHA and La(III)-AHA complexes support the experimental NMR chemical shifts.This work helps to measure subtle differences in complexation behaviour of AHA with Ln in presence of purenitrate and a combination of nitrate and perchlorate ions quantitatively, providing information about the Ln-AHA structural environment.

Various spectroscopic methods (UV-Vis, NMR, and Fluorescence spectroscopy) and density functional theory (DFT) calculations have been implemented for structural characterization of lanthanides (Ln(III))-acetohydroxamic acid(AHA) complexes in the presence of a combination of both perchlorate and nitrate ions and in pure nitrate ions. The Ln(III)-AHA complexes show more stability in the presence of a combination of both perchlorate and nitrate ions than in the presence of nitrate ions which is supported by DFT calculations.

• Correction to: Investigation of lanthanide complexation with acetohydroxamic acid in nitrate medium: experimental and DFT studies

In this article Snehanshu Pal at affiliation Departmentof Metallurgical and Materials Engineering,National Institute of Technology Rourkela, Rourkela,Odisha, India-769008 was missing from the authorlist.

The affiliation Department of Metallurgical andMaterials Engineering, Indian Institute of TechnologyKharagpur, Kharagpur 721302, West Bengal, India forAuthor T. K. Kundu was missing.The original article has been corrected.

• # Journal of Chemical Sciences

Volume 134, 2022
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019