Reaction of carbon dioxide with a palladium-alkyl complex supported by a bis-NHC framework

The reactivity of a dimethyl palladium complex supported by a dicarbene chelate (MDC(Mes))PdMe(2) towards CO(2) has been investigated. In the presence of trace H(2)O, this reaction yields the corresponding methyl bicarbonate complex (MDC(Mes))PdMe(O(2)COH), which goes on to give the corresponding κ(2)-carbonato complex upon crystallization (MDC(Mes))Pd(CO(3)). This chemistry, as well as related protonolysis by acetic acid was monitored by a combination of techniques including React-IR spectroscopy.     

A flow cytometry-based dopamine transporter binding assay using antagonist-conjugated quantum dots

Here we present the development and validation of a flow cytometry-based dopamine transporter (DAT) binding assay that uses antagonist-conjugated quantum dots (QDs). We anticipate that our QD-based assay is of immediate value to the high throughput screening of novel DAT modulators.     

Bright white light emission from ultrasmall cadmium selenide nanocrystals

A simple treatment method using formic acid has been found to increase the fluorescence quantum yield of ultrasmall white light-emitting CdSe nanocrystals from 8% to 45%. Brighter white-light emission occurs with other carboxylic acids as well, and the magnitude of the quantum yield enhancement is shown to be dependent on the alkyl chain length. Additionally, the nanocrystal luminescence remains enhanced relative to the untreated nanocrystals over several days. This brightened emission opens the possibility for even further quantum yield improvement and potential for use of these white-light nanocrystals in solid-state lighting applications.     

Molecular vibration spectroscopy studies on novel trinuclear rhodium-7-hydride complexes of the general type {[Rh(PP*)X]3(μ(2-X)3(μ3-X)}(BF4)2 (X = H, D)

Novel trinuclear rhodium-hydride complexes with diphosphine ligands Tangphos, t-Bu-BisP*, and Me-DuPHOS which contain bridging μ(2)- and μ(3)-hydrides as well as terminal hydrides in one molecule have been reported recently. In this work, these different rhodium-hydride bonds are characterized by Raman spectroscopy and the results are compared with those obtained by means of the more commonly applied IR spectroscopy. Density functional theory (DFT) calculations have been carried out to support the experimental findings. The structure of the Rh(3)H(7) core is described in the context of their vibrational stretching modes.     

Visible light excitation of CdSe nanocrystals triggers the release of coumarin from cinnamate surface ligands

The photochemical properties of organic ligands on the surface of nanocrystalline CdSe particles were examined. A number of thiols carrying a substituted cinnamate tail was synthesized. In solution, these cinnamate compounds undergo light-induced (374 nm) E-Z isomerization, followed by a nonphotolytic lactonization to give highly fluorescent coumarin. The cinnamate-thiols were successfully exchanged onto the CdSe nanocrystal, and the photochemical behavior of these conjugates was studied. Upon aerobic photolysis at 374 nm, the surface cinnamates released coumarin accompanied by rapid nanocrystal degradation. This degradation was not observed under similar anaerobic conditions or when the organic ligands did not contain the cinnamate group. Surprisingly, very similar results were obtained upon irradiation at visible wavelengths at which the cinnamate has no absorption. With the aid of UV-visible absorption spectroscopy, fluorescence spectroscopy, and electrochemistry, a unified theory for both the increased photoinstability of the nanocrystal as well as the coumarin release was proposed. It involves cinnamate radical anions on the CdSe surface, formed upon electron transfer from the excited nanocrystal to the surface cinnamate, undergoing E-Z isomerization. Practically, this results in the remarkable ability to release coumarin from nanocrystal ligands simply by exciting the nanocrystal with visible light. This new photorelease protocol not only aids in the understanding of fundamental nanocrystal-ligand interactions but may also offer new opportunities in the areas of drug delivery and imaging.     

Reactions of Group 4 Metallocenes with Monosubstituted Acetonitriles: Keteniminate Formation versus CC Coupling

The reactions of the Group 4 metallocene dichlorides [Cp′₂MCl₂] ( 1 a : M=Ti, Cp′=Cp*=η⁵‐pentamethylcyclopentadienyl, 1 b : M=Zr, Cp′=Cp=η⁵‐cyclopentadienyl) with lithiated MesCH₂?C?N gave [Cp*₂TiCl(N=C=C(HMes))] ( 3 ; Mes=mesityl) in the case of 1 a . For compound 1 b , a nitrile–nitrile coupling resulted in a five‐membered bridge in 4 . The reaction of the metallocene alkyne complex [Cp*₂Zr(η²‐Me₃SiC₂SiMe₃)] ( 2 ) with PhCH₂?C?N led in the first step to the unstable product [Cp*₂Zr(η²‐Me₃SiC₂SiMe₃)(NC?CH₂Ph)] ( 5 ). After the elimination of the alkyne, a mixture of products was formed. By variation of the solvent and the reaction temperature, three compounds were isolated: a diazadiene complex 6 , a bis(keteniminate) complex 7 , and 8 with a keteniminate ligand and a five‐membered metallacycle. Subsequent variation of the Cp ligand and the metal center by using [Cp₂Zr] and [Cp*₂Ti] with Me₃SiC₂SiMe₃ in the reactions with PhCH₂?C?N gave complex mixtures.     

Amphiphilic membranes with controlled mesh dimensions for insulin delivery+

A series of amphiphilic networks (membranes), consisting of hydrophilic poly(N,N‐dimethylacrylamide) (PDMAAM) main chains crosslinked by hydrophobic telechelic polyisobutylene di‐ and trimethacrylates (MA‐PIB‐MA or ∅︁(PIB‐MA)₃) have been synthesized and used for the preparation of thin‐walled tubules suitable for the immunoisolation of porcine islets. The molecular weight cut‐off (MWCO) ranges, insulin and glucose diffusion coefficients and permeabilities of various membranes have been determined. The molecular weight of the PDMAAM moiety between two hydrophobic crosslinking points (M_{c,hydrophilic}) controls permeability, which in turn can be controlled by synthesis conditions. The strengths and elongations of water‐swollen membranes crosslinked with ∅︁(PIB‐MA)₃ are superior by a factor of about two to those prepared with MA‐PIB‐MA. Based on the values from these experiments, a well‐defined membrane prepared with ∅︁(PIB‐MA)₃ was selected and used to encapsulate porcine islet cells. Gratifyingly, the encapsulated islet cells remain functional and viable, and cells within the tubule release insulin upon glucose challenge. These in vitro experiments are sufficiently promising to encourage us to continue our studies to develop a bioartificial pancreas.