Jukka-Pekka Jalkanen

The erratic emission of pyrene on gold nanoparticles.

Gold nanoparticles functionalized with chromophores are known to present unpredictable fluorescence as a function of their structure. Odd-even effects, based on the number of methylene units of the chain to which the fluorophore is attached, and the nature of the anchoring group on the gold surface have, in the past, been suggested to be responsible for the behavior. Here we investigate the fluorescence processes of two newly synthesized pyrene derivatives bound to gold nanoparticles. Two structurally identical ligands, differing only in the nature of the anchoring group (a thiolate in one case and an amine in the other), were newly synthetized and attached to the gold nanoparticles. The same changes in the fluorescence properties, namely, a red spectral shift with a moderate increase of the quantum yield and a shortening of the excited-state lifetime, are observed in the two cases and ascribed to the proximity of the gold core. By comparison with the results reported for other pyrene derivatives, it has been possible to draw the conclusions that (i) the nature of the binding group does not affect the fluorescence properties of the fluorophores attached to the nanoparticle surface and (ii) much stronger fluorescence is observed in the case of pyrene separated from the gold by short alkyl chain. The unusual behavior is explained in simple terms of competing chain-chain and chromophore-chromophore interactions and by means of proper energy diagrams.

Interaction energy surfaces of small hydrocarbon molecules

Nonbonding interactions of small alkane molecules were studied with ab initio methods. Previously reported energy data for ethane and propane dimers were supplemented with 1747 new configurations of dimers involving slightly larger hydrocarbons. The completed work provides interaction energy surfaces for all combinations of dimer pairs involving ethane, propane, isobutane, and neopentane and thus contains information of all chemical groups found in acyclic alkanes. The strongest attraction of the studied molecule pairs was encountered in isobutane C2h dimer, where an energy minimum of −1.784 kcal mol−1 at 4.28 A separation of centermost carbon atoms was observed. The composite data set was fitted with a modified Morse pair potential energy function representing each interatomic C–C, C–H, and H–H interaction for easy transfer to molecular dynamics simulation programs. The new generic parameter set was shown to describe the ab initio data for these small alkane molecules with good accuracy. Qualitative comp...

Ab initio potential energy surfaces of the propane dimer

The potential energy surface of a model propane dimer was systematically mapped with quantum chemical calculations. The calculations included approximately 12 separation distances between the monomers for each of 121 different relative geometries, or 1487 different configurations. The generated potential energy map reveals that the most attractive interactions are those having a maximum number of close contacts between carbon and hydrogen. The potential well depth of the most attractive orientation found was −1.625 kcal mol−1. The complete ab initio energy surface was fitted to a simple model consisting of pairwise-additive interatomic potentials, each modeled with a modified Morse function of interatomic distance. The resultant model accurately represents the entire propane dimer ab initio energy surface. The efficacy of the generated parameter set was tested with previously published ethane dimer energies and propane routes not included in fitting. The new parameter set is consistent with these results ...

Conformational properties and intramolecular hydrogen bonding of tetraethyl resorcarene: an ab initio study

Abstract The relative stability of the five extreme conformations of tetraethyl resorcarene was studied by ab initio calculations. The stabilizing effect of intramolecular hydrogen bonding was clearly observed. In addition, the directions of the hydrogen bonds affected the stability, the homodirectional orientation being favoured. The symmetrical C 4 ‘crown’ conformation, having a circular array of hydrogen bonds, was identified as the most stable conformational form of the resorcarene molecule.

Surface enhanced SHG from macrocycle, catenane and rotaxane thin films: experiments and theory.

Surface enhanced second harmonic generation experiments on supramolecules: macrocycles, catenanes and rotaxanes, monolayers and multilayers deposited by vacuum evaporation on silver layers are reported and described. The measurements show that the molecules are ordered in thin films. The highest order is observed in the case of macrocycles and the lowest in thin films of fumaramide [2] rotaxanes. Also a better ordering is observed in the case of monolayers. The observed second harmonic generation activity is interpreted in terms of electric field induced second harmonic generation. The electric field contributing to SHG signal is created by silver atoms on the surface of silver layers. The measured second order NLO susceptibilities for a fumaramide [2] rotaxane is compared with that obtained by considering only EFISH contribution to SHG intensities. The electric filed on the surface of silver layer is calculated using TINKER molecular mechanics/dynamics software and the Embedded Atom model. An excellent agreement is observed between the calculated and the measured SHG susceptibilities.

Computational study of adsorption and the vibrational properties of water on the Cu(110) surface

This work describes adsorption and internal vibrational motion of the water monomer on the Cu(110) surface. We have computed the vibrational wave numbers for the adsorbed water using anharmonic variational calculations previously applied to the gas phase molecule. The three-dimensional potential energy surface for the vibrational motion of the water molecule has been computed using density functional theory (DFT) with periodic boundary conditions, generalized gradient approximation (GGA), plane wave basis sets and projector augmented wave (PAW) potentials as implemented in the Vienna ab initio  simulation package (VASP). The data points on the potential energy surface have been fitted into an analytical model and the eigenvalues of the resulting Hamiltonian have been computed variationally.

Mapping the interaction energy surfaces of cyclic alkanes: Evaluating the transferability of an ab initio based potential model

Detailed interaction energy maps are computed for symmetric cyclopropane and tetrahedrane dimer systems using ab initio methods. Interaction energies of cubane and cyclohexane dimers are also reported. The global minimum energy structures of cyclopropane and tetrahedrane systems are both D(3d) structures with energies of -1.850 and -2.171 kcal mol(-1). The ability of NIPE potential model, based on ab initio nonbonding data of neopentane (N), isobutane (I), propane (P), ethane (E) and all their combinations to predict the pair interaction energies of these strained cyclic hydrocarbons is also investigated. The difference between the energies predicted by NIPE and those obtained from the ab initio calculations increases with ring strain In general, NIPE values are in close agreement with the ab initio results for alkane ring structures having low ring strain.

Alkali Metal Cation Binding of Tetraethyl Resorcarene: An Ab Initio and Mass Spectrometry Study

The complex formation between alkali metal cations (Li+, Na+, K+, Rb+, Cs+) and the most stable conformation of tetraethyl resorcarene, the C 4 crown, was studied by ab initio methods. The conformational change of the host resorcarene, the most favourable binding locations and the relative binding energies of the cations are reported. In addition, mass spectrometric H/D exchange reactions were carried out; the divergent results obtained for the lithium complex are well explained by the results obtained in the ab initio calculations.

Cleaner fuels for ships provide public health benefits with climate tradeoffs

We evaluate public health and climate impacts of low-sulphur fuels in global shipping. Using high-resolution emissions inventories, integrated atmospheric models, and health risk functions, we assess ship-related PM2.5 pollution impacts in 2020 with and without the use of low-sulphur fuels. Cleaner marine fuels will reduce ship-related premature mortality and morbidity by 34 and 54%, respectively, representing a ~ 2.6% global reduction in PM2.5 cardiovascular and lung cancer deaths and a ~3.6% global reduction in childhood asthma. Despite these reductions, low-sulphur marine fuels will still account for ~250k deaths and ~6.4 M childhood asthma cases annually, and more stringent standards beyond 2020 may provide additional health benefits. Lower sulphur fuels also reduce radiative cooling from ship aerosols by ~80%, equating to a ~3% increase in current estimates of total anthropogenic forcing. Therefore, stronger international shipping policies may need to achieve climate and health targets by jointly reducing greenhouse gases and air pollution.Aerosol pollution from shipping contributes to cooling but also leads to premature mortality and morbidity. Here the authors combine emission inventories, atmospheric models and health risk functions to show how cleaner marine fuels will reduce premature deaths and childhood asthma but results in larger warming.

Ammonium Ion Complexes of Tetraethyl Resorcarene: An Ab Initio Study

The complexation of various ammonium ions with a resorcarene host was evaluated by ab initio calculations. The approximations of the binding locations and the interaction energies for each guest are reported. The supramolecular complex formation also affects the conformation of the resorcarene host.