No abstract

The 1-substituted tris(2-thioimidazolyl)hydroborate ligands Tt(R) were prepared as the potassium salts from KBH(4) and the corresponding 1-R-2-thioimidazole for R = t-Bu and C(6)H(4)-p-CH(CH(3))(2) (Cum). Their reactions with zinc salts yielded the tetrahedral complexes Tt(R)Zn-X with X = F, Cl, ONO(2) and (Tt(t)()(-)(Bu))(2)Zn. With zinc perchlorate the labile perchlorate complexes Tt(R)Zn-OClO(3) were obtained. They served as starting materials for the incorporation of substrates which are relevant for the chemistry of horse liver alcohol dehydrogenase: Ethanol led to [Tt(t)()(-Bu)Zn.EtOH] ClO(4).EtOH, p-nitrophenol (NitOH) yielded Tt(Cum)Zn-ONit. Pyridine-2-carbaldehyde and salicylic aldehyde were incorporated as N(pyridine) and O(phenolate) coligands with possible additional O(aldehyde) coordination. Substituted pyridyl methanols (R-PyCH(2)OH) yielded the trinuclear complexes [(Tt(t)()(-Bu))(2)Zn(3)(R-PyCH(2)O)(2)] (ClO(4))(2) with bridging Tt and pyridylmethoxide ligands. Preliminary experiments on the functional modeling of alcohol dehydrogenase have shown that TtZn complexes promote both the dehydrogenation of 2-propanol and the hydrogenation of pentafluorobenzaldehyde.

pH-responsive systems are promising in their applicability to many areas, e.g., in drug delivery. Herein, we report a novel versatile pH−responsive system based on the coordination bonding of metal ions and functional groups in mesopores. Organic group functionalized mesoporous silica nanoparticles were employed as typical carriers for hosting metal ion binders and guest molecules to form a “host−metal−guest” architecture. The cleavage of either the “host−metal” or the “metal−guest” coordination bond, in response to pH variations, gives rise to a significant release of guest molecules under designated pH conditions. Using amino group functionalized mesoporous silica and choosing proper metal ions, the successful release of anticancer drugs bearing coordination binding groups was achieved at pH 5.0−6.5. Furthermore, a vector bearing pH-responsive binding functional groups is designed to assist in the release of drugs without significant binding capabilities. This route opens up a facile but powerful avenue for the design of various pH-responsive systems and new opportunities for their application in drug delivery.

Nine new tripodal NS 2 ligands of the bis(mercaptoimidazolyl)(pyrazolyl)borate type with varying 3-R-mercaptoimidazolyl moieties were prepared as their potassium salts. Treatment with zinc salts yielded the complex types L·Zn−Cl, L·Zn−I, L·Zn−ONO 2 , L·Zn−OClO 3 and [L·Zn(imidazole)]ClO 4 . Attempts at the formation of L·Zn−OH or cationic L·Zn complexes resulted in dismutation and formation of ZnL 2 complexes. Hydrolytic destruction yielded one [OZn 4 (thiooimidazolate) 6 ] complex. The ZnS 2 NO coordination which is pre-

We report the use of helicene with an intrinsic helical molecular structure to prepare covalent organic cages via imine condensation. The organic cages revealed a [3+2]-type architecture containing a triple-stranded helical structure with three helicene units arranged in a propeller-like fashion with the framework integrally twisted. Such structural chirality was retained upon dissolution in organic solvents, as indicated by a strong diastereotopy effect in proton NMR and unique Cotton effects in circular dichroism spectra. Further study on chiral adsorption showed that the chiral organic cages possess considerable enantioselectivity toward a series of aromatic racemates.