Two-photon photosensitized production of singlet oxygen in water

Singlet molecular oxygen (a(1)Delta(g)) has been produced and optically detected in time-resolved experiments upon nonlinear two-photon excitation of a photosensitizer dissolved in water. For a given sensitizer, specific functional groups that impart water solubility and that give rise to larger two-photon absorption cross sections are, in many cases, not conducive to the production of singlet oxygen in high yield. This issue involves the competing influence of intramolecular charge transfer that can be pronounced in aqueous systems; more charge transfer in the chromophore facilitates two-photon absorption but decreases the singlet oxygen yield. This phenomenon is examined in a series of porphyrins and vinyl benzenes.     

DsJ (2317) meson production at RHIC

We study the production of D _sJ (2317) mesons in relativistic heavy ion collisions using the quark coalescence model. The predicted D _sJ (2317) abundance depends sensitively on the quark structure of the D _sJ (2317) meson. We have also evaluated the absorption cross sections of the D _sJ (2317) meson by π, ρ, kaon and K* in a phenomenological hadronic model. We find that the final yield of D _sJ (2317) mesons remains sensitive to its initial number produced from the quark-gluon plasma, providing thus the possibility of studying the quark structure of the D _sJ (2317) meson and its production mechanism in relativistic heavy ion collisions.     

Azatrioxa[8]circulenes: Planar Anti‐Aromatic Cyclooctatetraenes

We describe herein the first synthesis of a new class of anti‐aromatic planar cyclooctatetraenes: the azatrioxa[8]circulenes. This was achieved by treating a suitably functionalised 3,6‐dihydroxycarbazole with 1,4‐benzoquinones or a 1,4‐naphthoquinone. We fully characterised the azatrioxa[8]circulenes by using optical, electrochemical and computational techniques as well as by single‐crystal X‐ray crystallography. The results of a computational study (NICS) suggest that the central planar cyclooctatetraene is anti‐aromatic when the molecules are in neutral or oxidised states (2+), and that the corresponding dianions are aromatic. We discuss the aromatic/anti‐aromatic nature of the planar cyclooctatetraenes and compare them with the isoelectronic tetraoxa[8]circulenes.     

Coordination‐Driven Switching of a Preorganized and Cooperative Calix[4]pyrrole Receptor

The study of preorganization in receptors, particularly in cooperative receptors, and their reversible control by external stimuli is important for elucidating design strategies that can lead to increased sensitivity and external control of molecular recognition. In this work we present the design, synthesis, and operation of an asymmetric tetrathiafulvalene (TTF)–calix[4]pyrrole receptor appended with a pyridine moiety. ¹H NMR spectroscopy was employed to demonstrate that intramolecular complexation between the receptor and the pyridine moiety leads to a preorganized receptor. Absorption and ¹H NMR spectroscopy along with a computational investigation were used to demonstrate the ability of the receptor to complex the substrate 1,3,5‐trinitrobenzene (TNB) and that the receptor can be reversibly modulated between negative and positive cooperativity by employing external stimuli in the form of Zn^II. Fitting procedures incorporating multiple datasets and fitting to multiple equilibria simultaneously have been employed to quantitatively determine the preorganization effects.     

Sulfonated hydrocarbon graft architectures for cation exchange membranes

A synthetic strategy to hydrocarbon graft architectures prepared from a commercial polysulfone and aimed as ion exchange membrane material is proposed. Polystyrene is grafted from a polysulfone macroinitiator by atom transfer radical polymerization, and subsequently sulfonated with acetyl sulfate to various degrees. Series of grafting densities and graft lengths are prepared, and membranes are solvent cast from DMSO. The membrane properties in aqueous environments are evaluated from their water swelling behavior, and their thermal properties and stability are investigated by thermogravimetric analysis and differential scanning calorimetry.     

Drug loading in cyclodextrin polymers: dexamethasone model drug

In pharmaceutical formulations cyclodextrins (CDs) are used to improve the aqueous solubility, stability, dissolution rate, bioavailability and/or local tolerance of drugs. Moreover, water-soluble polymers can be used to stabilize drug/CD complexes through formation ternary complexes. Alternative approach is to use CD-polymers, which can both enhance the aqueous solubility of a drug and result in sustained drug release. The aim of this work was to compare the solubilizing effects of ternary drug/CD/polymer complexes with two novel high molecular weight CD-polymers, i.e. poly(ethylene glycol) based ??-cyclodextrin (??CD) polymer (PEG/??CD) and epichlorohydrin-??-cyclodextrin polymer (EPI/??CD) using dexamethasone (Dex) as a model drug, as well as the drug loading capacity of those selected CD-polymers. Hydroxypropyl methylcellulose and carboxymethylcellulose sodium salt were shown to have negligible effect on the solubilizing efficacy of ??CD while hexadimethrine bromide increases the solubilization efficacy. The stability of the polymers was tested and it was adequate for the experimental conditions used. The solubilization efficacy of both CD-polymers was higher than that of the parent ??CD and these ??CD based polymers are able to load greater amount of Dex than the parent ??CD.     

Acid/base controllable molecular recognition

The study of controllable molecular recognition in supramolecular receptors is important for elucidating design strategies that can lead to external control of molecular recognition applications. In this work, we present the design and synthesis of an asymmetric (TTF) tetrathiafulvalene-calix[4]pyrrole receptor and show that its recognition of 1,3,5-trinitrobenzene (TNB) can be controlled by an acid/base input. The new receptor is composed of three identical TTF units and a fourth TTF unit appended with a phenol moiety. Investigation of the host-guest complexation taking place between the TTF-calix[4]pyrrole receptor and the TNB guests was studied by means of absorption and (1)H NMR spectroscopy; this revealed that the conformation of the molecular receptor can be switched between locked and unlocked states by using base and acid as the input. In the unlocked state, the receptor is able to accommodate two TNB guest molecules, whereas the guests are not able to bind to the receptor in the locked state. This work serves to illustrate how external control (acid/base) of a receptor may be used to direct the molecular recognition of guests (TNBs). It has led to a new controllable molecular recognition system that functions as an acid/base switch.