Computations on Three Isomers of La@C 74

ABSTRACT: Density-functional theory calculations are presented for La@C 74 , where C 74 is either the IPR (isolated pentagon rule) cage or two cages with a pentagon-pentagon junction. Their relative thermodynamic production yields are evaluated using the calculated terms, and it is shown that the IPR-based endohedral prevails at relevant temperatures in agreement with the observation

Lix@C60: Calculations of the Encapsulation Energetics and Thermodynamics

Li@C60 and Li@C70 can be prepared and thus, their calculations at higher levels of theory are also of interest. In the report, the computations are carried out on Li@C60, Li2@C60 and Li3@C60 with the B3LYP density-functional theory treatment in the standard 3-21G and 6-31G* basis sets. The computed energetics suggests that Lix @C60 species may be produced for a few small x values if the Li pressure is enhanced sufficiently. In order to check the suggestion, a deeper computational evaluation of the encapsulation thermodynamics is carried out

Finite-Size Effects in Simulations of Chemical Reactions

To study macroscopic systems with coarse grained simulations one typically simulates a micro- scopic part of this macroscopic system. By reducing the size of the simulated system one introduces finite size effects. In this work we study the finite-size effects in the reaction ensemble, which is used to simulate reactive system. We calculate the finite-size effects in a non-interacting systems by explicitly calculating the partition function. This approach provides high precision data at low computational costs. For a grand canonical insertion/deletion of a pair of particles our results reproduces previously published results, validating our approach. Further, we show that a sim- ple isomerization reaction is not affected by finite size effects. For a decomposition reaction we show that previous estimates were overestimating the finite-size effects, and one can simulate much smaller systems while avoiding the finite-size effects. For previously studied acid-base equilibria the finite-size effects are only relevant at extreme conditions. The tool we provide allows to a priori estimate the finite-size effects and find the limits of the applicability of the reaction ensemble

Intramolecular micellization and nanopatterning in pH- and thermo-responsive molecular brushes

International audienceConformational transitions and nanoscale self-organization triggered in double pH- and thermo-responsive molecular brushes by varying environmental conditions are studied by means of analytical mean-field theory and numerical Scheutjens–Fleer self-consistent field modelling. Such molecular brushes are composed of multiple thermo-responsive side chains end-grafted onto the main chain (backbone) and are capable of acquiring ionic charges via reversible (de)protonation of the monomer units. Competition of long-range Coulomb repulsion with short-range solvophobic interactions leads to complex patterns in the intramolecular self-organization of molecular brushes. In particular, we observed formation of pearl necklace-like structures with multiple dense nanodomains formed by weakly ionized collapsed side chains and stabilized by a fraction protruding into the solution and strongly ionized ones. Such structures are thermodynamically stable in a certain parameter range and can be termed as intramolecular micelles. The stimuli-induced intramolecular nanopatterning occurs via a sequence of quasi-first order phase transitions corresponding to splitting/fusion of collapsed domains accompanied by jumps in the average degree of ionization and macromolecular dimensions. A re-entrant sequence of transitions is observed when the salt concentration is used as a control parameter. These theoretical predictions provide guidelines for design of smart unimolecular devices, for example multicompartment nanocarriers of active substances or nanosensors

Eu@C72: Computed Comparable Populations of Two Non-IPR Isomers

Relative concentrations of six isomeric Eu@C 72 —one based on the IPR C 72 cage (i.e., obeying the isolated-pentagon rule, IPR), two cages with a pentagon–pentagon junction (symmetries C 2 and C 2 v ), a cage with one heptagon, a cage with two heptagons, and a cage with two pentagon–pentagon fusions—are DFT computed using the Gibbs energy in a broad temperature interval. It is shown that the two non-IPR isomers with one pentagon–pentagon junction prevail at any relevant temperature and exhibit comparable populations. The IPR-satisfying structure is disfavored by both energy and entropy

Computed stabilization for a giant fullerene endohedral: Y2C2@C1(1660)-C108

24 month embargo; published online: 23 August 2018This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Eu@C88 Isomers: Calculated Relative Populations

Relative populations of three energy-lowest IPR (isolated-pentagon-rule) isomers of Eu@C88 are computed using the Gibbs energy based on characteristics from density functional theory and MP2 calculations (M06-2X/3-21G∼SDD entropy term, and the MP2=FU/6-31G*∼SDD or B2PLYPD=FU/6-31 + G*∼SDD energetics). The calculations predict coexistence of three isomers, in agreement with extraction using a polar solvent, and offer a possible explanation why the Eu@C 2(27)-C88 species should prevail with a non-polar solvent. Role of extraction solvents and catalysis is thus pointed out.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]