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Two b-d-glucopyranosidebased dendrimers, one incorporating three tetra-and the other three heptasaccharide wedges attached to a central trisfunctionalized nonsaccharide core component, have been synthesized. Branching at designated saccharide units of the tetra-and of the heptasaccharide wedges arises from (1 32)/ (1 33)/(1 36) and from (1 33)/(1 36) intersaccharide linkages, respectively, with the 1,2-trans configuration at all anomeric centers. Both oligosaccharide wedges were constructed by stepwise glycosylation strategies and have reactive primary amino groups at their focal points located at the termini of spacer arms connected to the reducing glucose residues. Amide bond formation between these amino groups and appropriate core components carrying three carboxylic acid functions afforded two dendrimers incorporating a total of 12 and 21 monosaccharide units when the tetra-and the heptasaccharide wedges were employed, respectively. These nanosized highly branched macromolecules possess molecular diameters of 5 ± 6 nm and molecular weights of 6195 and 10 008 Daltons for the 12-mer and 21-mer, respectively. The wedges and dendrimers were characterized and the intersaccharide connectivity elucidated by extensive mono-and bidimensional 1 H and 13 C NMR spectroscopic investigations. In addition, LSIMS and MAL-DI-TOFMS investigations were also performed and revealed molecular ion peaks generally as H, Na, or K adducts for all oligosaccharides.

Our recent work with cyclic and acyclic polyether self-assembled monolayers (SAMs) on gold is presented. A series of dithia-crowntetrathiafulvalene derivatives with one or two disulfide groups has been prepared, and their SAMs on gold have been characterized by electrochemistry and by reflection-absorption infrared spectroscopy. These SAMs are extremely stable on repeated electrochemical potential scans and can selectively recognize alkali metal ions. Acyclic polyether derivatives can also self-assemble on gold to yield selective metal ion recognition domains. Impedance spectroscopy data for these SAMs fit the Langmuir isotherm and allow the determination of ion association constants. Some of the SAMs prepared with new acyclic polyether derivatives are able to detect potassium cations selectively when templated in their presence. These structures are believed to be a consequence of ion ''imprinting'' during the process of SAM formation.T he easy preparation, stability, and versatility of self-assembled monolayers (SAMs) has resulted in considerable activity in this field since the first publication by Nuzzo and Allara (1). Molecular recognition is especially relevant on surfaces because it allows the control of the exchange of signals, structures, and energy through the interfaces (2-4). SAMs allow the introduction of functional groups in the adsorbates, thus offering a powerful way to develop systems that have applications as sensors, devices, and switches (5). Some recent articles have reported surface structures with hydrophobic and hydrophilic properties arranged in nano-strips and honeycomb or homogeneous structures (6), whereas others have detected photo and electrochemical conversion of cis to trans forms within the SAM (7). Other examples have shown the formation of chiral imprinted sites (8). SAM structures have also been prepared for the recognition and sensing of metal ions (9), some of which are electrochemically active (10-18).Relatively recently, and Bryce et al. (23,24) reported, almost simultaneously, the incorporation of crownether groups into SAMs and their use as potential metal ion sensors. The Reinhoudt group used electrochemical impedance spectroscopy (EIS) for SAM characterization and to study the ion recognition processes (19)(20)(21)(22). This technique enables the detection of interfacial ion recognition phenomena when both guest ion and host monolayer are electrochemically inactive, by detecting changes of the charge-transfer resistance induced by metal ion binding (see Fig. 1a; refs. 25 and 26). The report by Bryce et al. (23,24) described SAMs of crown-annelated tetrathiafulvalene (TTF) derivatives, which showed, by cyclic voltammetry (CV), a redox potential shift of the electroactive, surface-confined, crown-TTF group on ion complexation (23, 24). The first TTF-crown SAMs reported by this group were apparently unstable after several electrochemical scans (23). However, in a subsequent report they demonstrated that the stability and electrochemical behavior of the SAMs can be improv...

Two dendrimers, incorporating tetrasubstituted porphyrin units as their cores and, in one case, four perbenzoylated and, in the other case, twelve peracetylated β-D-glucopyranosyl residues at their peripheries, have been synthesized in yields of 39 and 16%, respectively. The deprotection of these dendrimers was achieved quantitatively under Zemplé n conditions. The protected and deprotected dendrimers were characterized by liquid secondary-ion or matrixassisted laser desorption ionization time-of-flight mass spec-

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