Noncovalent complexation of glucosylthioureidocalix[4]arenes with carboxylates and their gas-phase characteristics: an ESI-FTICR mass spectrometric study

The noncovalent complexation of three glucosylcalix[4]arenes (1-3) towards 23 mono- and dicarboxylic acid anions were studied by ESI-FTICR mass spectrometry. Competitive complexation, collision-induced dissociation and gas-phase H/D-exchange experiments were performed to obtain information on selectivity of calixarenes towards carboxylates and characteristics of their complexes. The flexibility and number of glucose units of the host and the spatial disposition of the hydrogen bonding groups on the carboxylate guests were found to affect the selectivity of complexation strongly. The glucosylcalixarenes exhibited particular selectivity for dicarboxylic acid anions incorporating π-systems, and clear isomeric selectivity was observed for isophthalic among phthalic acid anions and for fumaric acid over maleic acid anion.     

Cationic intermediates in oxidative addition reactions of Cl2 to [PtCl2(cis-1,4-DACH)

Oxidative addition and reductive elimination are fundamental processes in transition-metal chemistry. New interest in this field has been generated by the exploitation of platinum(IV) complexes as antitumor drugs. The two extra ligands can be used to render these species more resistant to attack by biological nucleophiles compared to their platinum(II) counterparts, to anchor additional pharmacologically active moieties, or, finally, to target the drug to specific sites by conferring responsiveness to some type of chemotaxis. On the other hand, platinum(IV) species are considered to be prodrugs and to require reduction to Pt(II) to become active. Thus, reductive elimination promoted by biological reducing agents becomes an important issue and it too could be exploited for targeting purposes. In this paper, we investigated the oxidation step in more detail and shown that, independent of the solvent used, a solvent molecule assists the reaction by entering in a trans position with respect to the attacking oxidant. In the case of bifunctional solvent molecules, such as dimethylsulfoxide, both S- and O-coordinated species are formed, the latter being thermodynamically favored. The substitution of the axially coordinated solvent molecule by a free chloride ion is found to be quite slow in organic solvents, as well as in water. It is also shown that the intermediate solvato-species can be exploited for binding just one molecule of another substrate in the axial position.     

On Bifurcations in Nonlinear Consensus Networks

The theory of consensus dynamics is widely employed to study various linear behaviors in networked control systems. Moreover, nonlinear phenomena have been observed in animal groups, power networks and in other networked systems. These observations inspire the development in this paper of three novel approaches to define distributed nonlinear dynamical interactions. The resulting dynamical systems are akin to higher-order nonlinear consensus systems. Over connected undirected graphs, the resulting dynamical systems exhibit various interesting behaviors that we rigorously characterize.     

Perturbation method to calculate the interaction potentials and electronic excitation spectra of atoms in He nanodroplets

A method is proposed for the calculation of potential energy curves and related electronic excitation spectra of dopant atoms captured in/on He nanodroplets and is applied to alkali metal atoms. The method requires knowledge of the droplet density distribution at equilibrium (here calculated within a bosonic-He density functional approach) and of a set of valence electron orbitals of the bare dopant atom (here calculated by numeric solution of the Schr?dinger equation in a suitably parametrized model potential). The electron-helium interaction is added as a perturbation, and potential energy curves are obtained by numeric diagonalization of the resulting Hamiltonian as a function of an effective coordinate z(A) (here the distance between the dopant atom and center of mass of the droplet, resulting in a pseudodiatomic potential). Excitation spectra are calculated for Na in the companion paper as the Franck-Condon factors between the v = 0 vibrational state in the ground electronic state and excited states of the pseudodiatomic molecule. They agree well with available experimental data, even for highly excited states where a more traditional approach fails.     

Graphene solutions

Thermodynamics drive the spontaneous dissolution of a graphite intercalation compound (GIC) KC(8) in NMP to form stable solutions. Reduction potential of graphene is measured at +22 mV vs. SCE. Single layer graphene flakes (ca. 1 μm(2)) have been unambiguously identified by electron diffraction.     

Raman and computational study of solvation and chemisorption of thiazole in silver hydrosol

A SERS investigation combined with ab initio computational analysis involving Car-Parrinello molecular dynamics simulations and Density Functional Theory approach allows fundamental information to be obtained on the behaviour of thiazole in silver aqueous suspension where solvation and chemisorption processes competitively occur.     

Comment on “Factorizing of a concentration function for the mean activity coefficients of aqueous strong electrolytes into individual functions for the ionic species” by A. Ferse and H.O. Müller

A. Ferse and H.O. Müller have recently presented a mathematical method aimed at subdividing the activity coefficients of electrolytes into functions of individual ionic species; these functions are suggested to be the ionic activity coefficients. By examining the method, it is possible to verify that the peculiar mathematical structure of the functions in question really guarantees a unique result, unlike the usual subdivisions of electrolyte activity coefficients, which admit infinite possibilities for the ionic activity coefficients. But the subsequent step of the reasoning, i.e., that these functions have to be the activity coefficients of the ionic species, is an illation. And indeed, another kind of subdivision in individual functions can be exemplified, whose mathematical structure also guarantees results that are unique and perfectly compatible with all theoretical properties of the ionic activity coefficients. It is concluded that it is impossible to rely on mathematical method to pull the activity coefficients of ions out of the mean activity coefficients of the electrolytes. And hence, the individual functions for the ionic species determined by Ferse and Müller do not represent the ionic activity coefficients and do not have any particular utility.