Synthesis,structure and magnetic properties of unsymmetrical dodecanuclear Mn–Ln clusters

Reaction of manganese acetate and lanthanide nitrates in the presence of excess of PhCOOH affords highly asymmetric dodecanuclear mixed-metal [Mn₁₀Ln₂(OH)(O)₈(PhCOOH)(PhCOO)₁₉] (Ln = Pr^III (1), Nd^III (2)) clusters. The similar reaction, but with only 2 equiv. of PhCOOH resulted in the compounds with higher nuclearity [Mn₁₁Eu₄(O)₈(OH)₈(PhCOO)₁₈(NO₃)₂(H₂O)₆]NO₃ · 4CH₃CN (3). Variable-temperature solid-state magnetic susceptibility of 1 and 2 in the temperature range 1.8–300 K were carried out, and for both complexes antiferromagnetic exchange interactions between the metal centers were observed, giving an estimated S = 17/2 ground state. AC magnetic susceptibility data have revealed out-of-phase signals, which suggest that these complexes exhibit a slow relaxation of magnetization as observed in single-molecule magnets.     

Simple methods to synthesize 2-pyridones: reactions of 2-aroyl-3,3-bis(alkylsulfanyl)acrylaldehydes and cyanoacetamide

5-Aroyl-6-(methylsulfanyl)-2-oxo-1,2-dihydro-3-pyridinecarbonitriles and 5-aroyl-4-(methylsulfanyl)-2-oxo-1,2-dihydro-3-pyridinecarbonitriles are synthesized effectively by the reaction of 2-aroyl-3,3-bis(alkylsulfanyl)acrylaldehydes and cyanoacetamide under two different conditions.     

Decomposition of dinuclear manganese complexes for the preparation of nanostructured oxide materials

The crystal structures of several dinuclear complexes of manganese are reported, and the decomposition and analysis of the nanostructured products derived from them are presented. 1,4,7,10-Tetraazacyclododecane (cyclen) forms dinuclear complexes 1-4 containing doubly oxo-bridged or oxo-acetato bridging ligands depending on the manganese salt used for the reaction. Doubly oxo-bridged 1 crystallizes in the orthorhombic space group Pnma, a = 22.3850(14) A, b = 9.1934(5) A, c = 13.2424(10) A, V = 2725.2(3) A(3). 2, containing [Mn(SCN)5](3-) conteranions, crystallizes in monoclinic space group I2/a with a = 18.2699(10) A, b = 11.2384(6) A, c = 18.6432(9) A, alpha = 90.00 degrees, beta = 114.510(6) degrees, gamma = 90.00 degrees, V = 3483.0(3) A(3). Oxo-acetato-bridged 3 crystallizes in orthorhombic space group Pca21, a = 13.9322(11) A, b = 16.2332(13) A, c = 14.6794(8) A, V = 3320.0(4) A(3). Compound 4 consists of a templated quasi-one-dimensional manganese oxalate crystallized in the triclinic space group P1, a = 9.5442(11) A, b = 10.3758(10) A, c = 21.851(2) A, alpha = 83.720(12) degrees, beta = 80.106(13) degrees, gamma = 85.457(13) degrees, V = 2114.9(4) A(3). Compounds 1, 3, and 4 decompose to nanostructured oxide materials, which may be isolated in bulk as lamellar-structured particles or microspheres or deposited on substrates.     

Anion-perturbed magnetic slow relaxation in planar {Dy4} clusters

Two planar tetranuclear dysprosium(III) complexes, [Dy(4)(mu(3)-OH)(2)(hmmpH)(2)(hmmp)(2)(Cl)(4)].3MeCN.MeOH (1) and [Dy(4)(mu(3)-OH)(2)(hmmpH)(2)(hmmp)(2)(N(3))(4)].4MeOH (2) {hmmpH(2) = 2-[(2-hydroxyethylimino)methyl]-6-methoxyphenol}, which exhibit an anion-dependent magnetic slow relaxation behavior, have been synthesized by in situ condensation of o-vanillin and 2-aminoethanol. The higher energy barrier observed in 2 could be the result of a more favorable crystal field and/or orientations of single-ion easy axes of magnetization of the Dy(III) ions.     

Development of liposomal immunosensor for the measurement of insulin with femtomole detection

The monitoring of insulin is of great relevance for the management of diabetes, the detection of pancreatic islet-cell malfunction, the definition of hypoglycemia, and the diagnosis of insulinoma. A liposomal immunosensing system for the determination of insulin was developed in this study. The insulin sensor was constructed by the immobilization of anti-insulin antibodies on the inner wall of the microcapillary immunoseparator. Liposomes tagged with anti-insulin and encapsulating a fluorescent dye were used as the detectable label. In the presence of insulin, sandwich immunocomplexes were formed between the immobilized antibodies in the column, the sample of insulin, and the antibody-tagged sulforhodamine B-dye-loaded liposomes. Signals generated by lysing the bound liposomes with 30 mM n-octyl-β-d-glucopyranoside were measured by a fluorescence detector. The detected signal was directly proportional to the amount of insulin in the test sample. The liposomal immunosensing system successfully detected as low as 136 attomole. MeOH (30%) was used for the regeneration of antibody-binding sites in the microcapillary after each measurement, which allowed the immunoseparator to be used for at least 70 repeated assays. The antibody activity in this proposed microcapillary immunoseparator could be well maintained for at least 1 week. The calibration curve for insulin in Tris-buffered saline had a linear dynamic range of 10 pM-10 nM, and the total assay time was less than 30 min. The coefficient of variation for triplicate measurements was <5.00%, which indicated that well-reproducible results can be obtained by this newly developed method.     

New Rh derivatives of s-indacene active in dehydrogenative silylation of styrene

The mono- and bimetallic complexes [(2,6-diethyl-4,8-dimethyl-s-indacenide){Rh(COD)}] (1), anti-[(2,6-diethyl-4,8-dimethyl-s-indacenediide){Rh(COD)}₂] (2a), syn-[(2,6-diethyl-4,8-dimethyl-s-indacenediide){Rh(COD)}₂] (2b) were synthesized and characterized spectroscopically and in the case of complex 2b, by means of X-ray diffraction. The ¹³C and ¹⁰³Rh NMR studies suggest that the bonding mode of the indacenediide ligand can be described as intermediate between η³- and η⁵-coordination. This result was confirmed by the crystal structure of 2b as evidenced by the slippage of the rhodium atom towards the periphery of the ligand. Cyclic voltammetry studies revealed a strong intermetallic communication through the fused ring ligand. This property was further illustrated by higher activity and selectivity of binuclear complexes 2 for the catalytic dehydrogenative silylation of styrene.     

Staudinger ligation of peptides at non-glycyl residues

The Staudinger ligation provides a means to form an amide bond between a phosphinothioester and azide. This reaction holds promise for the ligation of peptides en route to the total chemical synthesis of proteins. (Diphenylphosphino)methanethiol is the most efficacious of known reagents for mediating the Staudinger ligation of peptides, providing high (> 90%) isolated yields for equimolar couplings in which a glycine residue is at the nascent junction. Surprisingly, the yields are lower (< 50%) for non-glycyl couplings due to an aza-Wittig reaction that diverts the reaction toward a phosphonamide byproduct. Here, the partitioning of the reaction toward Staudinger ligation (and away from the aza-Wittig reaction) is shown to increase with increasing electron density on phosphorus. This electron density can be tuned either by installing functional groups on the phenyl substituents of (diphenylphosphino)methanethiol or by changing the polarity of the solvent. Installing p-methoxy groups and using a solvent of low polarity (such as toluene or dioxane) provide especially high (> 80%) isolated yields for the ligation of two non-glycyl residues. These conditions retain the high chemoselectivity of the reaction and do not lead to a substantial change in reaction rate. The traceless Staudinger ligation is now poised to enable the iterative ligation of peptides with little regard for their sequence, as well as the synthesis of amide bonds for other purposes.     

Profiling protein-surface interactions of multicomponent suspensions via flow cytometry

This study presents the use of flow cytometry as a high-throughput quantifiable technique to study multicomponent adsorption interactions between proteins and surfaces. Flow cytometry offers the advantage of high-throughput analysis of multiple parameters on a very small sampling scale. This enables flow cytometry to distinguish between individual adsorbent particles and adsorbate components within a suspension. As a proof of concept study, the adsorption of three proteins--bovine serum albumin (BSA), bovine immunoglobulin gamma (IgG) and fibrinogen--onto five surface-modified organosilica microsphere surfaces was used as a model multicomponent system for analysis. By uniquely labeling each protein and solid support type with spectrally distinguishable fluorescent dyes, the adsorption process could be "multiplexed" allowing for simultaneous screening of multiple adsorbate (protein) and adsorbent (particle surface) interactions. Protein adsorption experiments quantified by flow cytometry were found to be comparable to single-component adsorption studies by solution depletion. Quantitative distribution of the simultaneous competitive adsorption of BSA and IgG indicated that, at concentrations below surface saturation, both proteins adsorbed onto the surface. However, at concentrations greater than surface saturation, BSA preferentially adsorbed. Multiplexed particle suspensions of optically encoded particles were modified to produce a positively and negatively charged surface, a grafted 3400 MW poly(ethylene glycol) layer, or a physisorbed BSA or IgG layer. It was observed that adsorption was rapid and irreversible on all of the surfaces, and preadsorbed protein layers were the most effective in preventing further protein adsorption.     

Evidence of different stoichiometries for the limiting carbonate complexes across the lanthanide(III) series: a capillary electrophoresis-mass spectrometry study

The electrophoretic mobilities (mu ep,Ln) of twelve lanthanides (not Ce, Pr and Yb) were measured by CE-ICP-MS in 0.15 and 0.5 mol L(-1) Alk2 CO3 aqueous solutions for Alk+ = Li+, Na+, K+ and Cs+. In 0.5 mol L(-1) solutions, two different mu ep,Ln values were found for the light (La to Nd) and the heavy (Dy to Tm) lanthanides, which suggests two different stoichiometries for the carbonate limiting complexes. These results are consistent with a solubility study that attests the Ln(CO3)3(3-) and Ln(CO3)4(5-) stoichiometries for the heavy (small) and the light (big) lanthanides, respectively. The Alk+ counterions influence the mu ep,Ln Alk2 CO3 values, but not the overall shape of the mu ep,Ln Alk2 CO3 plots as a function of the lanthanide atomic numbers: the counterions do not modify the stoichiometries of the inner sphere complexes. The influence of the Alk+ counterions decreases in the Li+ > Na+ > K+ > Cs+ series. The K3,Ln stepwise formation constants of the Ln(CO3)3(3-) complexes slightly increase with the atomic numbers of the lanthanides while K4,Ln, the stepwise formation constants of Ln(CO3)4(5-) complexes, slightly decrease from La to Tb, and is no longer measurable for heavier lanthanides.