Functionalized heteropolyanions: high-valent metal nitrido fragments incorporated into a Keggin polyoxometalate structure

Three examples of nitrido-functionalized polyoxometalate species are reported, namely (n-Bu4N)4[PW11O39(OsN)] (1), (n-Bu4N)4[PW11O39(ReN)] (2), and (n-Bu4N)3[PW11O39(ReN)] (3), which feature the incorporation of [OsVI identical to N]3+, [ReVI identical to N]3+ and [ReVII identical to N]4+ fragments, respectively, into the framework of a Keggin-type heteropolyanion.     

Study on elution behavior of poly(amidoamine) dendrimers and their interaction with bovine serum albumin in asymmetrical flow field-flow fractionation

Polyamidoamine (PAMAM) dendrimers have an amine surface and an ethylenediamine core and are of great interest in various applications such as in drug delivery. Physiochemical properties of PAMAM dendrimers vary with pH. At neutral to basic pH, PAMAM dendrimers are either weakly charged or uncharged and tend to adsorb on to the neutral packing material, making chromatographic separation of the dendrimers difficult. Asymmetrical flow field-flow fractionation (AsFlFFF) was tested as an alternative to the chromatographic techniques for separation of the PAMAM dendrimers. AsFlFFF provided generation-based separation of the dendrimers even at neutral and basic pH. The elution time increased gradually as the generation number (and thus the size) increased. Separation of impurities such as generational or missing-arm impurities and aggregates from the main population was also achieved. Electrostatic and hydrophobic interactions (e.g., repulsive elecrostatic interaction among the dendrimer molecules or attractive hydrophobic interaction between the dendrimer molecules and the membrane) may result in an inaccurate size measurement. Careful optimization of experimental conditions such as the flow rate, pH, and the salt concentration may be required to minimize the interactions with the membrane. AsFlFFF was also tested for a study on the interaction between the PAMAM dendrimers and proteins. AsFlFFF was able to show the growth in the size of bovine serum albumin (BSA) when BSA is mixed with increasing amounts of PAMAM dendrimers. Results suggest that, with proper optimization, AsFlFFF could become a useful tool for separation and characterization of large charged molecules such as PAMAM dendrimers.     

A Diazoalkane Derivative of a Polyoxometalate: Preparation and Structure of [Mo6O18(NNC(C6H4OCH3)CH3)]2−

A new metathetical route to diazoalkane complexes is described which allows the introduction of such ligands into previously inaccessible environments. The method, which involves the exchange of oxo and [N₂CR₂] ligands, is illustrated by the preparation of the first diazoalkane–polyoxometalate complex 1 .     

Carboxymethylation of corn starch and characterization using asymmetrical flow field-flow fractionation coupled with multiangle light scattering

Asymmetrical flow field-flow fractionation (AsFlFFF) was coupled online with multiangle light scattering (MALS) to study the changes in the molecular weight and the size distribution of the corn starch during carboxymethylation. A corn starch was derivatized with sodium chloroacetate in alcoholic medium under alkaline condition to produce carboxymethyl starches (CMS) having various degrees of substitution (DS). The change in thermal characteristics and granule structure of the native corn starch and CMS were compared using Thermogravimetric analysis and scanning electron microscope. The ionic strength of the carrier liquid (water with 0.02% NaN₃) was optimized by adding 50 mM NaNO₃ to minimize the interactions among the starch molecules and between the starch molecules and the AsFlFFF membrane. A field-programmed AsFlFFF allowed determination of the molecular weight distribution (MWD) of starches within about 25 min. It was found that carboxymethylation of starch results in reduction in the molecular weight due to molecular degradation by the alkaline treatment. The weight-average molecular weight (M_w) was reduced down to about 4.4 × 10⁵ from about 7.2 × 10⁶ when DS was 0.14. It seems AsFlFFF coupled with MALS (AsFlFFF/MALS) is a useful tool for monitoring the changes taking place in the molecular weight and the size of starch during derivatization.     

Radiation-induced synthesis of vinyl copolymer based nanocomposites filled with reactive organic montmorillonite clay

Vinyl copolymer–clay nanocomposites were prepared by γ-irradiation-initiated radical polymerization using a mixture of styrene (St) and divinyl benzene (DVB) in the presence of reactive organic montmorillonite clay (OMMT) in methanol at room temperature. Reactive OMMT was synthesized by a cation exchange reaction of Na⁺-MMT and 1-[(4-ethylphenyl)methyl]-3-butyl-imidazolium chloride as a reactive organic modifier in an aqueous solution. The microstructures of the nanocomposites were confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal stability was examined by thermo gravimetric analysis (TGA). As a result, the reactive OMMT was a good additive material for preparing vinyl copolymer–clay nanocomposites.     

Implementation of splitter-less SPLITT fractionation and its application to large scale-fractionation of sea sediment

The split-flow thin cell fractionation (SF) is a useful tool for separating colloidal particles or macromolecules into two or more fractions in a preparative scale. In a conventional design, the SF channel is equipped with flow stream-splitters at the inlet and the outlet of the channel, which may cause deterioration of the resolution due to the disturbance in the flow stream by the imperfection of the splitter geometry. In this study, a new splitter-less SF channel was implemented, which was designed to operate only in the full-feed depletion (FFD) mode (FFD-SF). Without the splitters, it was possible to make the channel much larger than conventional ones (about 25 times larger in the channel volume), and thus obtain a much higher sample throughput (TP, amount of the sample that can be processed in a unit time period). The new splitter-less FFD-SF system was tested and optimized using polyurethane (PU) latex spheres, and then applied successfully to a large scale separation of sea sediment. A series of three steps of FFD-SF operations (with each step repeated, and there were 6 steps in total) yielded separation of the sea sediment into four fractions having diameter ranges of larger than 10 µm, between 5 and 10 µm, between 2 and 5 µm, and smaller than 2 µm. TP of the three FFD-SF operations were 37.3, 22.1, and 17.9 kg/h, and the fractionation efficiencies (FE) of the four size fractions were 80.5, 73.7, 79.1 and 86.1%. Results suggest the new splitter-less FFD-SF system could be a useful tool for large scale separation of complex particulates such as environmental particles.