Interactions and Encapsulation of Vitamins C,B3, and B6 with Dendrimers in Water

Titrations of commercial diaminobutane (DAB) and polyamidoamine (PAMAM) dendrimers by vitamins C (ascorbic acid, AA), B₃ (nicotinic acid), and B₆ (pyridoxine) were monitored by ¹H NMR spectroscopy using the chemical shifts of both dendrimer and vitamin protons and analyzed by comparison with the titration of propylamine. Quaternarizations of the terminal primary amino groups and intradendritic tertiary amino groups, which are nearly quantitative with vitamin C, were characterized by more or less sharp variations (Δδ) of the ¹H chemical shift (δ) at the equivalence points. The peripheral primary amino groups of the DAB dendrimers were quaternarized first, but not selectively, whereas a sharp chemical‐shift variation was recorded for the inner methylene protons near the tertiary amines, thereby indicating encapsulation, when all the dendritic amines were quaternarized. With DAB‐G5‐64‐NH₂, some excess acid is required to protonate the inner amino groups, presumably because of basicity decrease due to excess charge repulsion. On the other hand, this selectivity was not observed with PAMAM dendrimers. The special case of the titration of the dendrimers by vitamin B₆ indicates only dominant supramolecular hydrogen‐bonding interactions and no quaternarization, with core amino groups being privileged, which indicates the strong tendency to encapsulate vitamins. With vitamin B₃, a carboxylic acid, titration of DAB‐G3‐16‐NH₂ shows that only six peripheral amino groups are protonated on average, even with excess vitamin B₃, because protonation is all the more difficult due to increased charge repulsion, as positive charges accumulate around the dendrimer. Inner amino groups interact with this vitamin, however, thus indicating encapsulation presumably with supramolecular hydrogen bonding without much charge transfer.     

Dynamic pricing and inventory control: robust vs. stochastic uncertainty models—a computational study

In this paper, we consider a variety of models for dealing with demand uncertainty for a joint dynamic pricing and inventory control problem in a make-to-stock manufacturing system. We consider a multi-product capacitated, dynamic setting, where demand depends linearly on the price. Our goal is to address demand uncertainty using various robust and stochastic optimization approaches. For each of these approaches, we first introduce closed-loop formulations (adjustable robust and dynamic programming), where decisions for a given time period are made at the beginning of the time period, and uncertainty unfolds as time evolves. We then describe models in an open-loop setting, where decisions for the entire time horizon must be made at time zero. We conclude that the affine adjustable robust approach performs well (when compared to the other approaches such as dynamic programming, stochastic programming and robust open loop approaches) in terms of realized profits and protection against constraint violation while at the same time it is computationally tractable. Furthermore, we compare the complexity of these models and discuss some insights on a numerical example.     

A theoretical introduction to “Combinatory SYBR®Green qPCR Screening”, a matrix-based approach for the detection of materials derived from genetically modified plants

The detection of genetically modified (GM) materials in food and feed products is a complex multi-step analytical process invoking screening, identification, and often quantification of the genetically modified organisms (GMO) present in a sample. “Combinatory qPCR SYBR®Green screening” (CoSYPS) is a matrix-based approach for determining the presence of GM plant materials in products. The CoSYPS decision-support system (DSS) interprets the analytical results of SYBR®GREEN qPCR analysis based on four values: the C _t- and T _m values and the LOD and LOQ for each method. A theoretical explanation of the different concepts applied in CoSYPS analysis is given (GMO Universe, “Prime number tracing”, matrix/combinatory approach) and documented using the RoundUp Ready soy GTS40-3-2 as an example. By applying a limited set of SYBR®GREEN qPCR methods and through application of a newly developed “prime number”-based algorithm, the nature of subsets of corresponding GMO in a sample can be determined. Together, these analyses provide guidance for semi-quantitative estimation of GMO presence in a food and feed product.     

HPLC direct purity assay using ultra-purified materials as primary standards

Reference materials certified for purity are essential to ensure harmonization of analytical measurements. LGC is currently certifying these materials using an indirect multi-method approach quantifying impurities: Related substances using high-performance liquid chromatography, gas chromatography (GC), differential scanning calorimetry; Residual solvents using headspace GC coupled to mass spectrometry; Inorganic content using ashing, acid digest ion couple plasma mass spectrometry or thermogravimetric analysis; Water using oven coulometric Karl Fischer/direct addition coulometric Karl Fischer. Related substances are not straightforward to quantify without an appropriate standard due to possible difference in response factor for the impurity relative to the main compound. In this article, existing LGC RMs certified for purity were purified further using semi-preparative HPLC. These ultra-purified organic substances were virtually free of related substances making their purity assessment faster and more straightforward, i.e., no need to identify impurities and subsequently quantify them. After characterization, these ultra-purified standards were used as calibrants to determine directly the mass fraction of the analyte in the original CRM using exact matching single-point HPLC calibration. This new approach opens the possibility of certifying the purity of low purity substances with a relative small uncertainty without the need of identifying the impurities present in the sample.     

Solvent effect on the singlet excited-state dynamics of 5-fluorouracil in acetonitrile as compared with water

The excited-state dynamics of 5-fluorouracil in acetonitrile has been investigated by femtosecond fluorescence upconversion spectroscopy in combination with quantum chemistry TD-DFT calculations ((PCM/TD-PBE0). Experimentally, it was found that when going from water to acetonitrile solution the fluorescence decay of 5FU becomes much faster. The calculations show that this is related to the opening of an additional decay channel in acetonitrile solution since the dark n/pi* excited state becomes near degenerate with the bright pi/pi* state, forming a conical intersection close to the Franck-Condon region. In both solvents, a S1-S0 conical intersection, governed by the out-of-plane motion of the fluorine atom, is active, allowing an ultrafast internal conversion to the ground state.     

Advancing understanding of actinide(iii) (Ac,Am, Cm) aqueous complexation chemistry

The positive impact of having access to well-defined starting materials for applied actinide technologies – and for technologies based on other elements – cannot be overstated. Of numerous relevant 5f-element starting materials, those in complexing aqueous media find widespread use. Consider acetic acid/acetate buffered solutions as an example. These solutions provide entry into diverse technologies, from small-scale production of actinide metal to preparing radiolabeled chelates for medical applications. However, like so many aqueous solutions that contain actinides and complexing agents, 5f-element speciation in acetic acid/acetate cocktails is poorly defined. Herein, we address this problem and characterize Ac³⁺ and Cm³⁺ speciation as a function of increasing acetic acid/acetate concentrations (0.1 to 15 M, pH = 5.5). Results obtained via X-ray absorption and optical spectroscopy show the aquo ion dominated in dilute acetic acid/acetate solutions (0.1 M). Increasing acetic acid/acetate concentrations to 15 M increased complexation and revealed divergent reactivity between early and late actinides. A neutral Ac(H₂O)₆₍₁₎(O₂CMe)₃₍₁₎ compound was the major species in solution for the large Ac³⁺. In contrast, smaller Cm³⁺ preferred forming an anion. There were approximately four bound O₂CMe¹⁻ ligands and one to two inner sphere H₂O ligands. The conclusion that increasing acetic acid/acetate concentrations increased acetate complexation was corroborated by characterizing (NH₄)₂M(O₂CMe)₅ (M = Eu³⁺, Am³⁺ and Cm³⁺) using single crystal X-ray diffraction and optical spectroscopy (absorption, emission, excitation, and excited state lifetime measurements).

Actinide complexation from aqueous acetic acid/acetate buffered solutions is described. The number of water ligands was directly correlated with the acetate concentration and characterized by X-ray absorption and optical spectroscopy.     

Synthesis and characterization of silica/poly (methyl methacrylate) nanocomposite latex particles through emulsion polymerization using a cationic azo initiator

Following a previous work (J. L. Luna-Xavier et al., Colloid Polym. Sci.279, 947 (2001)), silica-poly (methyl methacrylate) (PMMA) nanocomposite latex particles have been synthesized in emulsion polymerization using a cationic initiator, 2,2'-azobis (isobutyramidine) dihydrochloride (AIBA), and a nonionic polyoxyethylenic surfactant (NP30). Silica beads with diameters of 68, 230, and 340 nm, respectively, were used as the seed. Coating of the silica particles with PMMA was taking place in situ during polymerization, resulting in the formation of colloidal nanocomposites with a raspberry-like or a core-shell morphology, depending on the size and nature of the silica beads. The amount of surface polymer was quantified by means of ultracentrifugation and thermogravimetric analysis as extensively described in the first article of the series (see above reference). The influence of some determinant parameters such as the pH of the suspension, the initiator, silica, monomer, or surfactant concentration on the amount of coating polymer and on the efficiency of the coating reaction was investigated in details and discussed in light of the physicochemical properties of the seed mineral. Electrostatic attraction between the positive end groups of the macromolecules and the inorganic surface proved to be the driving force of the polymer assembly on the seed surface at high pH, while polymerization in adsorbed surfactant bilayers (so-called admicellar polymerization) appeared to be the predominant mechanism of coating at lower pH. Optimal conditions have been found to reach high encapsulation efficiencies and to obtain a regular polymer layer around silica.     

Mapping the cooperativity pathways in spin crossover complexes

Crystal packing energy calculations are applied to the [Fe(PM-L)₂(NCS)₂] family of spin crossover (SCO) complexes (PM-L = 4-substituted derivatives of the N-(2-pyridylmethylene)-4-aminobiphenyl ligand) with the aim of relating quantitatively the cooperativity of observed SCO transitions to intermolecular interactions in the crystal structures. This approach reveals a linear variation of the transition abruptness with the sum of the magnitudes of the interaction energy changes within the first molecular coordination sphere in the crystal structure. Abrupt transitions are associated with the presence of significant stabilising and destabilising changes in intermolecular interaction energies. While the numerical trend established for the PM-L family does not directly extend to other classes of SCO complex in which the intermolecular interactions may be very different, a plot of transition abruptness against the range of interaction energy changes normalised by the largest change shows a clustering of complexes with similar transition abruptness. The changes in intermolecular interactions are conveniently visualised using energy difference frameworks, which illustrate the cooperativity pathways of an SCO transition.

The abruptness of spin crossover (SCO) is related to intermolecular energy changes occurring over the course of an SCO transition. Crossover is abrupt when SCO-induced strain is accommodated synergistically in a few key interactions.