An improved error bound for a finite element approximation of a model for phase separation of a multi-component alloy

Using the approach of Rulla (1996 SIAM J. Numer. Anal. 33, 68-87)for analysing the time discretization error and assuming moreregularity on the initial data, we improve on the error boundderived by Barrett and Blowey (1996 IMA J. Numer. Anal. 16,257-287) for a fully practical piecewise linear finite elementapproximation with a backward Euler time discretization of amodel for phase separation of a multi-component alloy.     

Preparation of Re(I)- and (99m)Tc(I)-metallocarboranes in water under weakly basic reaction conditions

A new method for the preparation of Re- and (99m)Tc-metallocarboranes in water under mild reaction conditions was developed. Three nido-carborane ligands were reacted with [Re(CO)(3)Br(3)](2)(-) in the presence of aqueous potassium fluoride to give the corresponding eta(5)-Re(CO)(3)-carborane complexes. The use of KF as a base afforded the desired Re-metallocarboranes in good yields while avoiding the formation of Re clusters, which are byproducts commonly observed when reactions are carried out in the presence of strong aqueous bases. The reaction was also performed at the tracer level producing the first (99m)Tc-carborane complex, which was isolated in 80% radiochemical yield following a simple Sep-Pak purification process. The resulting organometallic complex was stable to cysteine and histidine challenges for more than 24 h.     

Microwave-assisted synthesis of tricarbonyl rhenacarboranes: steric and electronic effects on the 1,2 --> 1,7 carborane cage isomerization

A series of tricarbonyl rhenacarboranes {[M][Re(CO)3(RR'C2B9H9)]} (M = Na, K) were synthesized in water using microwave radiation with reaction times of less than 15 min. The novel complexes were isolated in good yields (57-94%) as either 3,1,2-(R = H: R' = CH2Pyr 6; R' = CH2Cy, 20) or 2,1,8-(R = H: R' = H, 4; R' = CH2PyrMe 12; R' = CH2PyrH, 13; R' = Pyr, 15; R' = Ph, 17; R = R' = Bn, 19) metallacarboranes and characterized by multinuclear (1H, 11B, 13C) and NOE NMR spectroscopy, IR spectroscopy, mass spectrometry, and X-ray crystallography in the case of compounds 12 and 13. Carborane cage isomerization from the original 1,2 configuration to the 1,7 orientation occurred in cases where significant steric crowding was present at the metal center. Incorporation of a methylene spacer between the carborane cage and the six-membered ring as in 7 and 20 decreased steric strain such that the 3,1,2 configuration was maintained. Conversion of the 3,1,2 complex 6 to the 2,1,8 isomers 12 and 13 takes place at room temperature upon methylation or protonation of the pyridyl ring, indicating that electronic effects also play a significant role in the isomerization process.     

A new strategy for preparing molecular imaging and therapy agents using fluorine-rich (fluorous) soluble supports

A convenient new strategy for producing radiolabeled compounds in high effective specific activity was developed using soluble fluorous supports. The reported methodology involves a fluorous linker group that is released from the substrate of interest upon reaction with radioiodine. The desired product can then be selectively separated from unreacted starting material and reaction byproducts using a simple fluorous solid-phase extraction procedure. The utility of this approach was demonstrated by labeling a series of benzoic acid derivatives which are commonly used to prepare molecular imaging agents. All compounds were produced in high radiochemical yields, purities, and effective specific activities. The strategy was further elaborated in that it was used to prepare a small collection of radiolabeled benzamides as a way of demonstrating the potential utility of this method for creating libraries of molecular imaging agents.     

Thermally induced phase transition of carborane-functionalized aliphatic polyester dendrimers in aqueous media

Three recently reported aliphatic polyester dendrimers of generations 3, 4, and 5, having 4, 8, and 16 carborane cages within their interior, respectively, were found to exhibit thermally induced, reversible precipitation in aqueous solution. The cloud-point temperatures for these molecules were observed to be between 40 and 80 degrees C, depending on the dendrimer generation. The three dendrimers investigated have a hydroxyl-to-carborane ratio of 8:1, which provides the ideal balance between the hydrophobic interior and the hydrophilic exterior to enable the thermally induced phase transition to occur. It was found that repeated heating/cooling cycles resulted in a decreasing cloud-point temperature and increased dendrimer solubility. Additionally, the effect of pH on the cloud point was investigated, indicating no significant changes as long as the dendrimers remained stable. Size-exclusion chromatography indicated that dendrimer degradation was occurring at pH above 7.0.     

Synthesis,Characterisation, and Biodistribution of Radioiodinated C‐Hydroxy‐Carboranes

The synthesis, radiolabelling and biodistribution of iodinated C‐hydroxy‐nido‐carborane ligands is described. Microwave heating by using NaF in aqueous ethanol was used to prepare {sodium [7‐hydroxy‐7,8‐dicarba‐nido‐undecaborate], nido‐carboranol} and {sodium [7‐hydroxy‐7,8‐dicarba‐nido‐undecaborate‐8‐carboxylic acid], nido‐salborin} in 97 and 90 % yield, respectively. Radioiodination of these nido‐carboranes was completed by using both ¹²⁵I and ¹²³I, and the products were obtained in high radiochemical purity (>99 %) and yield (72 to 87 %). The structures of the radiolabelled products were validated through comparison to authentic standards. Biodistribution studies in BALB/c mice showed low accumulation of the labelled compounds in the liver and intestines, which are sites where labelled carboranes typically localise. The labelled cluster bearing hydroxy and carboxylic acid groups on the two carbon vertices demonstrated preferential clearance through the kidneys and low thyroid uptake. This compound had substantially reduced non‐specific binding than the deshydroxy analogue making it an attractive bifunctional ligand for preparing targeted molecular imaging and therapy agents.     

Finite element approximation of a model for phase separation of a multi-component alloy with a concentration-dependent mobility matrix

We consider a model for phase separation of a multi-componentalloy with a concentration-dependent mobility matrix and logarithmicfree energy. In particular we prove that there exists a uniquesolution for sufficiently smooth initial data. Further, we provean error bound for a fully practical piecewise linear finiteelement approximation in one and two space dimensions. Finallynumerical experiments with three components in one space dimensionare presented.