Impact of Static-Oriented Electric Fields on the Kinetics of Some Representative Suzuki-Miyaura and Metal-Cluster Mediated Reactions.

In order to examine the effect of oriented (static) electric fields (OEF) on the kinetics of some representative Suzuki-Miyaura and metal-cluster mediated reactions at ambient temperatures, density functional theory-based calculations are reported herein. Results indicate that, in general, OEF can facilitate the kinetics of the concerned reactions when applied along the suitable direction (parallel or anti-parallel with respect to the reaction axis). The reverse effect happens if the direction of the OEF is flipped. OEF (when applied along the 'right' direction) helps to polarize the transition states in the desired direction, thereby facilitating favorable bonding interactions. Given the growing need for finding appropriate catalysts among the scientific community, OEF can prove to be a vital route for the same.

Conceptual density functional theory based electronic structure principles.

In this review article, we intend to highlight the basic electronic structure principles and various reactivity descriptors as defined within the premise of conceptual density functional theory (CDFT). Over the past several decades, CDFT has proven its worth in providing valuable insights into various static as well as time-dependent physicochemical problems. Herein, having briefly outlined the basics of CDFT, we describe various situations where CDFT based reactivity theory could be employed in order to gain insights into the underlying mechanism of several chemical processes.

Dynamics of Pyrene-Dimer Association and Ensuing Pyrene-Dimer Dissociation.

To address the possible role of pyrene dimers in soot, chemical dynamics simulations are reported to provide atomistic details for the process of collisional association of pyrene dimers and ensuing decomposition of pyrene dimers. The simulations are performed at 600, 900, 1200, 1600, and 2000 K temperatures (T) with different collisional impact parameters (b; 0-18 Å) using the all-atom optimized potentials for liquid simulations intermolecular force field. Corresponding to each b, ensembles of 1000 trajectories are computed up to a maximum time of 110 ps at each T. Microcanonical association rate constants for the pyrene-dimerization processes decrease with an increase in T. The ensuing dissociation of the pyrene dimers is statistical and could be well represented by the Rice-Ramsperger-Kassel-Marcus theory of unimolecular dissociation. Fits of the dissociation rate constants versus the harmonic Rice-Ramsperger-Kassel equation revealed that partial energy randomization occurs among the inter- and intramolecular vibrational modes during the dissociation of pyrene dimers, whereas rotational and translational modes play a significant role. Based on the low probability of association and short lifetime at 1600 (∼13.3 ps) and 2000 (∼12.8 ps) K, it is concluded that pyrene dimers are unlikely to play any major role in soot nucleation processes.

Bonding, Reactivity, and Dynamics in Confined Systems.

Confined systems often exhibit unusual behavior regarding their structure, stability, reactivity, bonding, interactions, and dynamics. Quantization is a direct consequence of confinement. Confinement modifies the electronic energy levels, orbitals, electronic shell filling, etc. of a system, thereby affecting its reactivity as well as various response properties as compared to the cases of corresponding unconfined systems. Confinement may force two rare gas atoms to form a partly covalent bond. Gas storage is facilitated through confinement and unprecedented optoelectronic properties are observed in certain cases. Some slow reactions get highly accelerated in an appropriate confined environment. In the current Feature Article we analyze these aspects with a special emphasis on the work done by our research group.

Confinement induced catalytic activity in a Diels-Alder reaction: comparison among various CB[n], n = 6-8, cavitands.

The impact of the size of the confining regime on the thermodynamic and kinetic outcome of a representative Diels-Alder reaction between ethylene and 1,3 butadiene has been investigated in silico. To this end, two organic hosts namely cucurbit[6]uril (CB[6]) and cucurbit[8]uril (CB[8]) have been considered in order to impose confinement on the reactants/transition state/product of the concerned reaction. The obtained results have been compared with the recently reported (Chakraborty et al. ChemPhysChem 18:2162-2170, 2017) corresponding case of the same reaction happening inside cucurbit[7]uril (CB[7]). Results indicate that as compared to the reaction of ethylene and 1,3 butadiene inside CB[7], both CB[6] and CB[8] cavitands slow down the same reaction at 298.15 K and 1 atm. It appears that the size of the cavitand plays a crucial role in affecting the kinetic outcome of the considered reaction. While CB[7] can enforce productive alignment of the reactants inside its cavity thereby facilitating the reaction, neither CB[6] nor CB[8] can perform the same task as effectively. This situation bears qualitative resemblance with the cases of enzyme catalyzed reactions.

Reactions involving some gas molecules through sequestration on Al12 Be cluster: An electron density based study.

The viability of sequestering gas molecules (CO, NO, CO2 , NO2 , N2 O, O2 , O3 , H2 O, NH3 , H2 , CH3 OH, CH3 F, C2 H5 F, C2 H2 , C2 H4 , HCN, and SO2 ) on the Al12 Be cluster is investigated by carrying out density functional theory based computations. Thermochemical as well as energetic considerations suggest that Al12 Be cluster adsorbs the chosen gas molecules in a favorable fashion. The gas molecules attain an activated state on getting adsorbed on the metal cluster as vindicated by Atoms-in-Molecule analysis. The possibility of CO oxidation, dissociative addition of CH3 F and C2 H5 F, NH bond decomposition in NH3 , dissociation of NO, and hydrogenation of C2 H2 reactions on Al12 Be cluster has been investigated. Results indicate that all the reactions take place in a thermodynamically favorable way at 298.15 K and one atmospheric pressure. The first five reactions aforementioned are kinetically favorable also and therefore are amenable to ambient temperature and pressure conditions. © 2017 Wiley Periodicals, Inc.

Confinement induced thermodynamic and kinetic facilitation of some Diels-Alder reactions inside a CB[7] cavitand.

The effect of geometrical confinement on the Diels-Alder reactions between some model dienes viz. furan, thiophene, cyclopentadiene, benzene, and a classic dienophile, ethylene has been explored by performing density functional theory-based calculations. The effect of confinement has been imposed by a rigid macrocyclic molecule cucurbit[7]uril (CB[7]). Results indicate that all the reactions become thermodynamically more favorable at 298.15 K temperature and one atmospheric pressure inside CB[7] as compared to the corresponding free gaseous state reactions. Moreover, the rate constants associated with the reactions experience manifold enhancement inside CB[7] as compared to the "unconfined" reactions. Suitable contribution from the entropy factor makes the concerned reactions more facile inside CB[7]. The energy gap between the frontier molecular orbitals of the dienes and dienophiles decrease inside CB[7] as compared to that in the free state reactions thereby allowing facile orbital interactions. The nature of interaction as well as bonding has been analyzed with the help of atoms-in-molecules, noncovalent interaction, natural bond orbital as well as energy decomposition analyses. Results suggest that all the guests bind with CB[7] in an attractive fashion. Primarily, noncovalent interactions stabilize the host-guest systems. © 2017 Wiley Periodicals, Inc.

Host-guest interactions between octa acid and cations/nucleobases.

The nature of host-guest interaction in between octa acid cavitand (OA) and some representative cationic guests (Li+ , Na+ , K+ , Be+2 , Mg+2 , Ca+2 , Li3 O+ , Na3 O+ , K3 O+ ) as well as heterocyclic moieties like [adenine (A), guanine (G), cytosine (C), thymine (T), uracil (U), and tetrathiafulvalene (TTF)] has been examined with the aid of density functional theory (DFT)-based computations. Thermochemical results indicate that all the guests bind with OA in a thermodynamically favorable fashion at 298.15 K temperature and one atmospheric pressure. OA exhibits high selectivity in binding the lighter cations/metal cluster cations as compared to the heavier congeners along each given series. Moreover, OA exhibits enhanced affinity as well as selectivity in binding A/G/TTF molecules as compared to C/T/U. Noncovalent interaction and energy decomposition analyses reveal that in addition to the van der Waals interaction, significant contribution from electrostatic as well as orbital interactions dictate the outcome in all the host-guest complexes. Time dependent DFT calculations have been carried out to assess the role of the guests in tuning the electronic properties as well as absorption spectrum of OA. © 2017 Wiley Periodicals, Inc.

Change in optoelectronic properties of ExBox+4 on functionalization and guest encapsulation.

The impact of functionalization as well as guest encapsulation on the optoelectronic properties of the ExBox+4 moiety has been investigated with the aid of density functional theory (DFT) based calculations. To this end, three functionalized variants of the ExBox+4 moiety have been modelled in silico, viz. NH2-ExBox+4-F, CN-ExBox+4-NH2 and NO2-ExBox+4-NH2, whereas coronene (Cor), B-doped coronene (BCor), N-doped coronene (NCor), tetrathiafulvalene (TTF), biphenyl (BiPh), tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) molecules have been employed as guests. The results indicate that as a result of functionalization, the ExBox+4 moiety can exhibit tangible non-linear optical (NLO) response properties as vindicated by the first static hyperpolarizability (ß). As a result of guest encapsulation, significant variation in the optoelectronic properties of the chosen hosts takes place. BCor/TCNQ/NCor molecules enhance the NLO activity of the hosts while TTF/TCNE suppresses the same. In particular, NCor@host moieties demonstrate very high ß values at the static field limit. Time dependent DFT results suggest that in general, the ability of the guest in tuning the transition energy associated with the pivotal electronic transitions of the host plays the dominant role in the observed variation in ß. In addition, BCor/NCor@host moieties demonstrate broadband optical absorption capability thereby elucidating the possibility of deriving multi-purpose optoelectronic features such as NLO activity as well as utility in photovoltaic systems. Thermochemical results suggest that all the guest@host systems are stable at 298.15 K. Non-covalent and electrostatic binding forces stabilize the studied systems.

Effect of functionalization of boron nitride flakes by main group metal clusters on their optoelectronic properties.

The possibility of functionalizing boron nitride flakes (BNFs) with some selected main group metal clusters, viz. OLi4, NLi5, CLi6, BLI7 and Al12Be, has been analyzed with the aid of density functional theory (DFT) based computations. Thermochemical as well as energetic considerations suggest that all the metal clusters interact with the BNF moiety in a favorable fashion. As a result of functionalization, the static (first) hyperpolarizability ([Formula: see text]) values of the metal cluster supported BNF moieties increase quite significantly as compared to that in the case of pristine BNF. Time dependent DFT analysis reveals that the metal clusters can lower the transition energies associated with the dominant electronic transitions quite significantly thereby enabling the metal cluster supported BNF moieties to exhibit significant non-linear optical activity. Moreover, the studied systems demonstrate broad band absorption capability spanning the UV-visible as well as infra-red domains. Energy decomposition analysis reveals that the electrostatic interactions principally stabilize the metal cluster supported BNF moieties.

Does Confinement Always Lead to Thermodynamically and/or Kinetically Favorable Reactions? A Case Study using Diels-Alder Reactions within ExBox+4 and CB[7].

The impact of geometrical confinement on the thermodynamic as well as kinetic aspects of a model cycloaddition reaction between 1,3-butadiene and ethylene have been investigated based on density functional theory calculations. To this end, organic hosts ExBox+4 and cucurbit[7]uril (CB[7]) were used to impose confinement effects on the reactants, transition state (TS), and product involved in the reaction. The results suggest that the shape of the host and thereby the nature of the confining regime dictates the thermodynamic outcome of the reaction. The reaction becomes thermodynamically more spontaneous inside CB[7] as compared with that in either ExBox+4 or in the "unconfined" gaseous state. Furthermore, the rate constant associated with the reaction increases manifold inside CB[7]. Atoms-in a-molecule, noncovalent interaction, natural bond orbital, as well as energy decomposition analyses suggest that the close geometrical proximity of the reactants inside CB[7] as well as extra stabilization of the TS in the encapsulated state may dictate the outcome.

Possible sequestration of polar gas molecules by superhalogen supported aluminum nitride nanoflakes.

The feasibility of having MF3 (where M = Rh, Ir, Pd, Pt, Ag, Au) supported AlN nanoflakes (AlNF) was investigated through density functional theory based calculations. The thermodynamic analysis reveals that the superhalogen MF3 molecules can bind with the host AlNF in a thermodynamically favorable way. The nature of interaction in between the metal centers and the host is of partly covalent type whereas the F centers bind with the host in a non-covalent fashion as vindicated by natural bond orbital and atoms-in a-molecule analyses. An ab initio molecular dynamics study carried out at 298 K temperature confirms the stability of the MF3@AlNF moieties in a dynamical context. The MF3 guests can reduce the HOMO-LUMO gaps of the host nanoflakes. In general, the MF3@AlNF complexes can sequestrate polar adsorbates such as CO, NO, and H2O in a thermodynamically favorable way in most of the cases. An ab initio molecular dynamics calculation illustrates that the MF3@AlNF can adsorb the chosen representative polar molecules in a more favorable way as compared to the corresponding adsorption scenario in the case of pristine AlNF.

Optical response and gas sequestration properties of metal cluster supported graphene nanoflakes.

The possibility of obtaining metal cluster (M3O(+), M = Li, Na, K) supported pristine, B-doped and BN-doped graphene nanoflakes (GR, BGR and BNGR, respectively) has been investigated by carrying out density functional theory (DFT) based calculations. Thermochemical analysis reveals the good stability of M3O(+)@GR/BGR/BNGR moieties. The dynamic stability of M3O(+)@GR/BGR/BNGR moieties is confirmed through an atom-centered density matrix propagation simulation at 298 K up to 500 fs. Orbital and electrostatic interactions play pivotal roles in stabilizing the metal-cluster supported graphene nanoflakes. The metal clusters lower the Fermi levels of the host nanoflakes and enable them to exhibit reasonably good optical response properties such as polarizability and static first hyperpolarizability. In particular, Na3O(+)/K3O(+)@BGR complexes exhibit very large first hyperpolarizability values at the static field limit. All the M3O(+)@BGR/BNGR moieties demonstrate broadband optical absorption encompassing the ultraviolet, visible as well as infrared domains. The metal-cluster supported graphene nanoflakes, in general, can sequestrate polar molecules, viz. CO, NO and CH3OH, in a thermodynamically more favorable way than GR, BGR and BNGR. In the adsorbed state, the CO, NO and CH3OH molecules, in general, attain an 'active' state as compared to their free counterparts.

Orbital free DFT versus single density equation: a perspective through quantum domain behavior of a classically chaotic system.

The orbital free density functional theory and the single density equation approach are formally equivalent. An orbital free density based quantum dynamical strategy is used to study the quantum-classical correspondence in both weakly and strongly coupled van der Pol and Duffing oscillators in the presence of an external electric field in one dimension. The resulting quantum hydrodynamic equations of motion are solved through an implicit Euler type real space method involving a moving weighted least square technique. The Lagrangian framework used here allows the numerical grid points to follow the wave packet trajectory. The associated classical equations of motion are solved using a sixth order Runge-Kutta method and the Ehrenfest dynamics is followed through the solution of the time dependent Schrodinger equation using a time dependent Fourier Grid Hamiltonian technique. Various diagnostics reveal a close parallelism between classical regular as well as chaotic dynamics and that obtained from the Bohmian mechanics.

In quest of a superhalogen supported covalent bond involving a noble gas atom.

The possibility of having neutral Xe-bound compounds mediated by some representative transition metal fluorides of general formula MX3 (where M=Ru, Os, Rh, Ir, Pd, Pt, Ag, Au and X=F) has been investigated through density functional theory based calculations. Nature of interaction between MX3 and Xe moieties has been characterized through detailed electron density, charge density and bond energy decomposition analyses. The feasibility of having compounds of general formula XeMX3 at 298 K has been predicted through thermodynamic considerations. The nature of interaction in between Xe and M atoms is partly covalent in nature and the orbital interaction is the dominant contributor toward these interactions as suggested by energy decomposition analysis.

Is there any role of mast cell density and microvessel density in cervical squamous cell carcinoma? A histologic study with special reference to CD-34 immunomarker staining.

BACKGROUND: Mast cells are involved in induction of angiogenesis in the early-stages of tumor development and in modulating blood vessel growth in the later stages of tumor progression. AIMS AND OBJECTIVES: This study was carried out to evaluate the association between mast cell density (MCD) and microvessel density (MVD) in carcinoma in situ (CIS), microinvasive carcinoma (CA) and invasive squamous cell CA of cervix. MATERIALS AND METHODS: Six cases of CIS, four cases of microinvasive CA and 38 cases of invasive CA were studied over a period of 2 years from August, 2011 to June, 2013. Ten control samples were included in the study. Routine histologic examination was done. Toluidine blue stain was used for MCD determination. Immunohistochemical analysis with CD-34 was done for assessing MVD. Student's t-test was used to calculate the statistical significance of MCD and MVD. RESULTS: Both MCD and MVD increased from normal samples through CIS to invasive cervical CA. In the four cases of microinvasive CA, the MCD and MVD were more than that of the control samples, but less than that of the six cases of CIS. CONCLUSION: There is a correlation between mast cell accumulation and angiogenesis in CIS, microinvasive CA and invasive cervical squamous cell CA. MCD and MVD in invasive CA exceed those in CIS and microinvasive CA. It gives us an opportunity to postulate that therapeutic strategies against mast cell mediators and angiogenesis may be of benefit in patients of early-stage cervical CA.

Neonatal sepsis: Role of a battery of immunohematological tests in early diagnosis.

BACKGROUND AND OBJECTIVE: Worldwide, many neonates with sepsis die due to lack of early diagnosis. In this study we attempt to analyze the value of various immunological and hematological parameters, singly and in combination, for the diagnosis of neonatal sepsis, with the aim being to formulate guidelines for the early diagnosis of the condition. MATERIALS AND METHODS: In this prospective study, 62 patients having clinical suspicion of neonatal sepsis were evaluated with a battery of investigations. Neonates admitted for other causes and without clinical suspicion of sepsis were selected as controls (n=40). The tests included blood culture, hemoglobin level, total and differential blood count, absolute neutrophil count, ratio of immature to total neutrophil count (I/T ratio), micro-erythrocyte sedimentation rate (m-ESR), C-reactive protein (CRP), platelet count, serum IgM level, and plasma fibrinogen level. Patients were divided into proven cases (positive blood culture) and probable cases (negative blood culture). RESULTS: Positive blood culture was seen in 38 cases (61.3%). Raised m-ESR (>8 mm in the first hour) was seen in 63.2% of proven and 66.7% of probable cases. I/T ratio of ≥0.2 was seen in 63.2% and 58.3% of proven and probable cases, respectively. Morphological changes in neutrophils were detected in 68.4% of proven cases and 91.7% of probable cases. Positive CRP test (≥6 mg/l) was found in 84.2% of proven cases and 100% of probable cases. Raised serum IgM, leucopenia, and neutropenia were seen in a small number of patients (11%-37%). Raised fibrinogen level (>400 mg/l) was seen in patients as well as in controls. CONCLUSIONS: The four useful tests that we identified were m-ESR, I/T ratio, morphological changes in neutrophils, and CRP; and role of these tests in early diagnosis of neonatal sepis were statistically significant (P<.05). The most sensitive test was CRP (84%) and the most specific test was m-ESR (94%). A combination of three or all of these four tests was highly specific (95%-100%).