A simple chemical model for clathrate hydrate inhibition by polyvinylcaprolactam.

A dimeric model compound gives structural insight into the mode of interaction of low dosage hydrate inhibitors with water.

Anion tuning and polymer templating in a simple low molecular weight organogelator.

A simple triethoxysilane appended bis(urea) low molecular weight gelator (LMWG) affords strong gels in organic solvents that are susceptible to fine tuning by anion binding, while the gel structure can be rigidified into a porous hybrid polymer material by hydrolysis of the triethoxysilane end groups.

Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth.

We describe the use of low-molecular-weight supramolecular gels as media for the growth of molecular crystals. Growth of a range of crystals of organic compounds, including pharmaceuticals, was achieved in bis(urea) gels. Low-molecular-weight supramolecular gelators allow access to an unlimited range of solvent systems, in contrast to conventional aqueous gels such as gelatin and agarose. A detailed study of carbamazepine crystal growth in four different bis(urea) gelators, including a metallogelator, is reported. The crystallization of a range of other drug substances, namely sparfloxacin, piroxicam, theophylline, caffeine, ibuprofen, acetaminophen (paracetamol), sulindac and indomethacin, was also achieved in supramolecular gel media without co-crystal formation. In many cases, crystals can be conveniently recovered from the gels by using supramolecular anion-triggered gel dissolution; however, crystals of substances that themselves bind to anions are dissolved by them. Overall, supramolecular gel-phase crystallization offers an extremely versatile new tool in pharmaceutical polymorph screening.

A water soluble, anion-binding zwitterionic capsule based on electrostatic interactions between self-complementary hemispheres.

A water soluble anion receptor is reported that binds bromide in aqueous solution via CH...Br(-) interactions in a dimeric capsule.

Metal ion and anion-based "tuning" of a supramolecular metallogel.

A bis(pyridylurea) ligand (1) forms metallogels in methanol in the presence of up to 0.5 equiv of copper(II) chloride. The metallogel has been characterized using powder X-ray diffraction, SEM, and MAS NMR spectroscopic techniques. The addition of further copper(II) chloride gives the unusual crystalline 4:3 coordination polymer [Cu3(1)4Cl4]Cl2 x nH2O (2). In the presence of 0.5 equiv of copper(II) nitrate, the 2:1 crystalline coordination polymer [Cu(1)2](NO3)2 x H2O x MeOH (5) is isolated. Both 2 and 5 have been characterized by single-crystal X-ray diffraction. Complex 5 represents a possible model for the gelator and highlights key interactions with counteranions that suggest a means to tune gel properties using anion binding. The influence of chloride and acetate anions (as their NBu4+ salts) on the rheological properties of the copper(II) chloride metallogels of 1 are investigated. The rheology of the anion-containing mixtures shows complex behavior with the gel structure apparently evolving over time.

Gelation is crucially dependent on functional group orientation and may be tuned by anion binding.

The gelation ability of a series of chiral bis(urea) gels alternates between even and odd chain length and for the even numbered spacers the rheological characteristics can be tuned by the addition of anions according to the anion binding constant.

Dynamics of the size distribution of CdTe quantum dot ensembles during growth in liquid and crystalline phases.

We recently reported that the growth rate of colloidal CdTe nanoparticles decreases by orders of magnitude when the particles undergo a phase transition from liquid to crystal. The dynamics of nanoparticle growth are dominated by this factor rather than the size dependence of the chemical potential. Herein we discuss how the phase transition affects the size distribution and photoluminescence quantum efficiency of the nanoparticles. We suggest that the absorption linewidth is a better monitor of size distribution than the photoluminescence linewidth because the photoluminescence quantum efficiency, which affects the latter via energy transfer, varies substantially with reaction time. We find that the size distribution broadens in the early stages of growth possibly because of inhomogeneities in the phase transition radius or because particles nucleated at later times coalesce with nanocrystals. The quantum efficiency is enhanced when tellurium is depleted in the reaction solution, giving a cadmium-enriched surface. Batches with high initial tellurium and cadmium concentrations show a substantial amount of delayed nucleation, lower quantum efficiency and some anisotropic growth.

Growth dynamics of CdTe nanoparticles in liquid and crystalline phases.

Normally the size dependence of the chemical potential is used to explain the growth dynamics of semiconductor nanoparticles. Instead we show that very small CdTe nanoparticles continue to grow at high dilution, the growth rate is virtually independent of monomer concentration, nucleation continues after the growth of larger particles has saturated, and the growth rate has a much greater nonlinear dependence on particle size than predicted by theory. We suggest that nanoparticle growth is fast in the liquid phase and then saturates as the particles change phase from liquid to crystal at a threshold size which depends on the growth temperature and not the monomer concentration. The photoluminescence quantum efficiency becomes high when tellurium is depleted in the reaction solution giving a cadmium enriched surface.

A low-temperature synthesis for organically soluble HgTe nanocrystals exhibiting near-infrared photoluminescence and quantum confinement.

A new low-temperature, one-pot method is introduced for the preparation of organically passivated HgTe nanocrystals, without the use of highly toxic precursors. The nanocrystals show bright photoluminescence in the infrared telecommunication windows about 1300 and 1550 nm with quantum efficiencies between 55 and 60%. They have a zinc blende structure with a mean particle diameter of 3.4 nm, thus exhibiting quantum confinement effects. Particle growth is self-limited by temperature quenching, so a narrow size distribution is obtained. The measured size of the particles agrees with calculations using the pseudopotential method.