Effect of complexation of oxidised corn starch with mineral elements on physicochemical properties

The objective of this study was to determine the effect of complexation of oxidised starch with mineral elements on its physicochemical properties. Corn starch was oxidised with sodium hypochlorite and, afterwards, modified with ions of potassium, magnesium and iron. Thus, native and modified starches were analysed for: contents of mineral elements, colour parameters (L*a*b*), water binding capacity and solubility in water at temperature of 60 and 80 °C. Thermodynamic characteristics of gelatinisation by DSC, molecular weight distribution by GPC, intrinsic viscosity and pasting properties by RVA were studied. The efficiency of incorporation of metal ions into oxidised corn starch was about 30%, 20% and 20% for potassium, magnesium and iron ions, respectively. The complexation with potassium ions caused the greatest changes in the molecular weight distribution and the intrinsic viscosity of starches and viscosity of starch pastes. Only modification of starch with iron ions affected the colour parameters of the starch. Incorporation of metal ions into starch resulted also in changes in its water binding capacity and solubility in water.     

Optically Tunable Nonlinearities in Polymers Based on Photoisomerizable Metal‐Based Coordination Complexes

The bottom‐up design of polymer films exhibiting quadratic nonlinear optical properties that can be tuned optically and chemically is described. The polymer matrices are doped with metal‐containing chromophores built around a Zn^II core and photoisomerizable ligands with two different geometries. These molecules possess specifically designed photophysical and nonlinear optical properties to be used towards all‐optical poling, an interference process between one‐ and two‐photon excitations that locally induces macroscopic second‐order effects in polymer films. It is shown that grafting the molecules onto the polymer chains improves the stability of the macroscopic photoinduced nonlinearity in the films.     

页岩油含氮化合物分离研究

探讨了用Lewis酸为络合剂除掉富集在页岩油中含氮化合物的最佳条件,考察了不同Lewis酸的脱氮效果;同时考察了Lewis酸的加入量、反应温度、反应时间、溶剂对脱氮效果的影响。实验表明,对于未经蒸馏分离的页岩油四氯化钛为主要成分的络合剂脱氮效果最好。     

CTAB—BPR作为EDTA滴定铋的金属指示剂的研究

溴化十六烷基三甲基铵（ＣＴＡＢ）和氟离子能够敏化溴邻苯三酚红（ＢＰＲ）作为ＥＤＰＡ滴定铋的指示剂变色反应，使终点颜色突变由原来的红色到橙色改变为由纯兰到粉红，清晰敏锐，滴定最佳ＰＨ范围为１．５－３氟离子的存在提高了方法的选择性，提出ＮａＦ－ＨＮＯ３分解试样快速测定锡铋合金中铋的分析方法。     

Characterization of copper complexation with natural dissolved organic matter (DOM)--link to acidic moieties of DOM and competition by Ca and Mg

We investigated Cu complexation by three dissolved organic matters (DOMs) collected by reverse osmosis (RO). Alkalimetric titration, pH-stat Cu and Ca titrations, pH edges of Cu–DOM complexation, and Ca/Mg–Cu exchange experiments were investigated at I=10⁻² M for DOM samples of 10 mg C/L. The proton and Cu binding characteristics indicated similarity for all three DOMs. All Cu titrations employed ion selective electrode measurement and indicated the presence of relatively small amounts of strong Cu-binding sites. Four distinct classes of Cu binding sites are required for FITEQL 4.0 to provide good fits to the entire curves. The estimated total Cu binding site density is 4.55 mmol/g C, much less than the total acidity but very close to the phenolic site content. Cu–DOM complexation increases approximately 10-fold per pH unit, even at relatively high pH (>8). We suggest that sites characterized as phenolic based on alkalimetric titration, not carboxyl sites, account for the majority of Cu complexation under natural water conditions, and Cu–DOM complexation is principally through the replacement of H⁺ by Cu²⁺ at the phenolic binding sites. The Cu–H exchange ratio is 1:1 for the first three sites and about 1:2 for the 4th site. This 4-site model describes well the pH dependency of Cu–DOM complexation and provides good estimates of free Cu concentrations throughout wide total copper (Cu_T) and pH ranges. Comparison between Ca–DOM and Cu–DOM complexation demonstrated that (i) Ca–DOM complexation increases much less than an order of magnitude per pH unit and decreases at higher Ca concentration, different from that of Cu–DOM complexation; and (ii) Cu–DOM complexation is highly non-linear, in contrast to the much reduced extent of non-linearity of Ca–DOM complexation. Ca/Mg–Cu exchange experiments showed small competition effect, less than expected by a simple competition model, and the competition tended to reduce with increasing Ca or Mg concentrations. The extent of the competition by Mg and Ca are essentially comparable. Put all together, it suggests that Ca and Mg are preferably bound by carboxyl sites, especially at relatively high concentrations, resulting in a weakened apparent competition effect.     

Effect of hydroxypropyl-beta-cyclodextrin on the solubility of an antibacterial isoxazolyl-naphthoquinone

The complexation of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (I) with a highly soluble cyclodextrin, hydroxypropyl-β-cyclodextrin (HP-β-CD) was studied in aqueous media by solubility methods. I is an antibacterial and trypanocidal agent that is undergoing preclinical testing. Unfortunately, I exhibits low water solubility, and it is therefore difficult to prepare the solutions for biological tests. I inclusion took place with 1:1 stoichiometry. The stability constants of the I complexes calculated from the slope and the intercept of the phase solubility diagrams are larger in the less ionized form, whereas greater overall solubility is obtained in basic media.     

Investigation of the piroxicam/hydroxypropyl-β-cyclodextrin inclusion complexation by means of a supercritical solvent in the presence of auxiliary agents

The complexation of piroxicam and 2-hydroxypropyl-β-cyclodextrin by means of supercritical CO₂ has been investigated. The experiments were carried out by varying the temperature, pressure and contact time and introducing two different auxiliary agents: polyvinyl pyrrolidone or l-lysine.Cyclodextrins, which are widely used to solubilize a large variety of poorly soluble drugs, are often used in combination with some auxiliary agents to enhance the complexation efficiency of the conventional techniques. While many recent literature works report that supercritical carbon dioxide is a clean, non-toxic alternative to organic solvents, the use of auxiliary agents in the supercritical complexation process has been scarcely examined and still needs to be investigated.The inclusion complexes obtained in this work were analysed by means of the ‘differential solubility method’, differential scanning calorimetry and Fourier transform infrared spectroscopy. The results showed that the supercritical treatment could be successfully employed below 140-150 °C without incurring thermal degradation of the samples. While 66% inclusion efficiency could be obtained at 140 °C and 30 MPa for a mixture of piroxicam/2-hydroxypropyl-β-cyclodextrin (1:2 molar ratio), higher percentages of complexation (95% in the ternary samples with polyvinyl pyrrolidone and 89-91% in those with l-lysine) could be obtained at a lower temperature (130 °C) when auxiliary agents were employed.     

Density functional complexation study of metal ions with poly(carboxylic acid) ligands. Part 1. Poly(acrylic acid) and poly(α-hydroxy acrylic acid)

We have studied metal ion complexation with poly(carboxylic acid) ligands using density functional methods and a continuum-solvation model (COSMO). Geometry optimisations have been carried out for metal complexes of poly(acrylic acid-co-maleic acid), poly(methyl vinyl ether-co-maleic acid), and poly(epoxy succinic acid) oligomers. The complexation energies for Mg²⁺, Ca²⁺, Mn²⁺, and Fe³⁺ have been calculated and they have been corrected with previously determined metal specific correction parameters. The most effective ligand for all the metal ions was found to be poly(epoxy succinic acid). With Ca²⁺, poly(epoxy succinic acid) was found to form 6-coordinated complex with three metal-coordinating carboxylate oxygen, two ether oxygens, and one hydroxyl oxygen atom. All the other metals favoured 5-coordinated complexation geometry with four metal-coordinating carboxyl oxygens and one ether oxygen atom.     

Effect of complexation on the zeta potential of silica powder

The present paper deals with the surface charge properties and dispersion stability of aqueous silica suspension. The zeta potential was measured versus barium acetate and zinc acetate concentration, at pH 6.0. EDTA was used to chelate the bivalent metal ions, so that the charge of counterion was reduced. The complexation of bivalent counterions favors the increase of the negative zeta potential and the dispersion stability of aqueous silica suspension.