Complexation between oleanolic and maslinic acids with native and modified cyclodextrins

Oleanolic (OA) and maslinic (MA) acids are two natural triterpenoids with a wide range of beneficial effects for human health. However, their low solubility and permeability make their application in the food or industry difficult. The complexation of OA and MA with alpha- beta-, gamma-, HP-alpha-, HP-beta- and HP-gamma-CDs under different pH and temperature conditions has been studied. Neither alpha- nor HP-alpha-CDs formed inclusion complexes, while beta-, HP-beta- and HP-gamma-CDs provided AL type and gamma-CDs BS phase solubility diagrams. Complexation was shown to be more stable in the case of MA but complexation efficiency was greater for OA. Increasing the pH and temperature of the complexation media tended to improve the complexation process with triterpenic acids.Agencia de Ciencia y Tecnología de la Región de Murcia under the project PFEseneca/06/10Ciencias de la Alimentació

Chemically modified polysulfones for molecular imprinting. Synthesis and complexation with a fluorescent model template

Polysulfone (PSU) was chemically modified to prepare new molecular imprinted membranes (MIMs). Several amounts of amine and sulfonyl groups were introduced into the PSU chemical structure in order to create interactions with acid or base templates, such as biomolecules or biomacromolecules. A fluorescent dye, Acridine Orange base (AO), was used as a model template and its complexation with the prepared PSUs was monitored by spectroscopic techniques. This study showed an absence of complexation with the native PSU and a strong complexation with the aminated and the sulfonated PSUs. Partially allylated PSU bearing amine or sulfonyl groups were also synthesized. These compounds are expected to be used as precursors for designing new crosslinked molecular imprinting membranes (MIMs), exhibiting high stability of the template memory

Complexation of norfloxacin with DNA in the presence of caffeine

1H NMR spectroscopy (500 MHz) has been used to quantify the complexation of the antibacterial antibiotic Norfloxacin (NOR) with DNA in the presence of Caffeine (CAF). Separate studies have been made for the self-association of NOR, its hetero-association with CAF and complexation with a model self-complementary DNA tetramer, 5′-d(TpGpCpA), in order to determine the equilibrium parameters (induced chemical shifts, association constants, enthalpy and entropy) of the two-component mixtures to aid the analysis of the three-component systems. Investigations of the self-association of NOR and its hetero-association with CAF show that the aggregation of NOR molecules and association with CAF in solution are driven by the stacking of aromatic chromophores. The complexation of NOR with d(TGCA) has been analysed in terms of intercalation with the double-stranded form and non-intercalative binding with the single-stranded form of DNA. Investigations of the competitive binding of NOR and CAF with DNA show that at physiological concentrations of NOR (μM) and CAF (mM) the dominant mechanism influencing the affinity of NOR with DNA is the displacement of bound NOR molecules from DNA due to CAF–DNA complexation (i.e. the protector action of Caffeine)

Chemically modified polysulfones for molecular imprinting. Synthesis and complexation with a fluorescent model template

Polysulfone (PSU) was chemically modified to prepare new molecular imprinted membranes (MIMs). Several amounts of amine and sulfonyl groups were introduced into the PSU chemical structure in order to create interactions with acid or base templates, such as biomolecules or biomacromolecules. A fluorescent dye, Acridine Orange base (AO), was used as a model template and its complexation with the prepared PSUs was monitored by spectroscopic techniques. This study showed an absence of complexation with the native PSU and a strong complexation with the aminated and the sulfonated PSUs. Partially allylated PSU bearing amine or sulfonyl groups were also synthesized. These compounds are expected to be used as precursors for designing new crosslinked molecular imprinting membranes (MIMs), exhibiting high stability of the template memory

Protein-mediated dethreading of a biotin-functionalised pseudorotaxane

In this article, we describe the synthesis of new biotin-functionalised naphthalene derivatives 3 and 4 and their complexation behaviour with avidin and neutravidin using a range of analytical techniques. We have shown using 2-(4prime or minute-hydroxyazobenzene)benzoic acid displacement and ITC experiments{,} that compounds 3 and 4 have the propensity to form reasonably high-affinity bioconjugates with avidin and neutravidin. We have also demonstrated using 1H NMR{,} UV-vis and fluorescence spectroscopy that the naphthalene moiety of 3 and 4 facilitates the formation of pseudorotaxane-like structures with 1 in water. We have then investigated the ability of avidin and neutravidin to modulate the complexation between 1 and 3 or 4. UV-vis and fluorescence spectroscopy has shown that in both cases the addition of the protein disrupts complexation between the naphthalene moieties of 3 and 4 with 1

Poly(amidoamine)s synthesis, characterisation and interaction with BSA

Cationic poly(amidoamine)s (PAAs) were synthesised and characterised by NMR and gel permeation chromatography. Their thermal properties were investigated using thermogravimetric analysis and differential scanning calorimetry. Although poly(amidoamine)s have been used as endosomolytic polymers for protein intracellular delivery, the interaction of the polymers with the proteins still need to be investigated. BSA was used as a model protein and complexation with the different poly(amidoamine) s was investigated using gel retardation assays, fluorescence spectroscopy and high sensitivity differential scanning calorimetry. Our results indicate that the thermal stability of BSA was affected upon interaction and complexation with the poly(amidoamine)s, however these interactions did not seem to modify the structure of the protein. Polymer flexibility seemed to favour polymer/protein complexation and promoted thermal stability

RETRASO, a code for modeling reactive transport in saturated and unsaturated porous media

The code RETRASO (REactive TRAnsport of SOlutes) simulates reactive transport of dissolved and gaseous species in non-isothermal saturated or unsaturated problems. Possible chemical reactions include aqueous complexation (including redox reactions), sorption, precipitation-dissolution of minerals and gas dissolution. Various models for sorption of solutes on solids are available, from experimental relationships (linear KD, Freundlich and Langmuir isotherms) to cation exchange and surface complexation models (constant capacitance, diffuse layer and triple layer models). Precipitation-dissolution and aqueous complexation can be modelled in equilibrium or according to kinetic laws. For the numerical solution of the reactive transport equations it uses the Direct Substitution Approach. The use of the code is demonstrated by three examples. The first example models various sorption processes in a smectite barrier. The second example models a complex chemical system in a two dimensional cross-section. The last example models pyrite weathering in an unsaturated medium

Electrostatic colloid-membrane complexation

We investigate numerically and on the scaling level the adsorption of a charged colloid on an oppositely charged flexible membrane. We show that the long ranged character of the electrostatic interaction leads to a wrapping reentrance of the complex as the salt concentration is varied. The membrane wrapping depends on the size of the colloid and on the salt concentration and only for intermediate salt concentration and colloid sizes we find full wrapping. From the scaling model we derive simple relations for the phase boundaries between the different states of the complex, which agree well with the numerical minimization of the free energy.Comment: 7 page, 11 figure

Humic acid protein complexation

Interactions of purified Aldrich humic acid (PAHA) with lysozyme (LSZ) are investigated. In solution LSZ is moderately positively and PAHA negatively charged at the investigated pH values. The proton binding of PAHA and of LSZ is determined by potentiometric proton titrations at various KCl concentrations. It is also measured for two mixtures of PAHA¿LSZ and compared with theoretically calculated proton binding assuming no mutual interaction. The charge adaptation due to PAHA¿LSZ interaction is relatively small and only significant at low and high pH. Next to the proton binding, the mass ratio PAHA/LSZ at the iso-electric point (IEP) of the complex at given solution conditions is measured together with the pH using the Mütek particle charge detector. From the pH changes the charge adaptation due to the interaction can be found. Also these measurements show that the net charge adaptation is weak for PAHA¿LSZ complexes at their IEP. PAHA/LSZ mass ratios in the complexes at the IEP are measured at pH 5 and 7. At pH 5 and 50 mmol/L KCl the charge of the complex is compensated for 30¿40% by K+; at pH 7, where LSZ has a rather low positive charge, this is 45¿55%. At pH 5 and 5 mmol/L KCl the PAHA/LSZ mass ratio at the IEP of the complex depends on the order of addition. When LSZ is added to PAHA about 25% K+ is included in the complex, but no K+ is incorporated when PAHA is added to LSZ. The flocculation behavior of the complexes is also different. After LSZ addition to PAHA slow precipitation occurs (6¿24 h) in the IEP, but after addition of PAHA to LSZ no precipitation can be seen after 12 h. Clearly, PAHA/LSZ complexation and the colloidal stability of PAHA¿LSZ aggregates depend on the order of addition. Some implications of the observed behavior are discussed