Computational Modeling of the Amperometric Bioanalytical System for Lipase Activity Assay: a Time-Dependent Response

This paper presents computational modeling of response kinetics of bioelectroanalytical system based on the interfacial action of enzyme lipase. The model also assumes that the substrate of enzyme is located on the surface of micelles which are spread in the solution under study. Two distinct mathematical models have been developed and evaluated through computational simulation series. The results of simulation demonstrate that diffusion is important factor for the sensitivity of bioelectroanalytical system, and it is important to take this process of mass transfer into account in all system areas

Thermomyces lanuginosus lipase in the liquid-crystalline phases of aqueous phytantriol: X-ray diffraction and vibrational spectroscopic studies

The influence of Thermomyces lanuginosus lipase (TLL) on the phase behaviour of liquid-crystalline phases of aqueous phytantriol as well as conformational changes of TLL entrapped in the cubic Q(230) phase have been studied by small angle X-ray diffraction (SAXD), FT-Raman, and FT-IR techniques. It was found that the lipidic Q(230) Phase is able to accommodate up to 10 wt.% of TLL, and the temperature of phase transition to the inverted hexagonal phase H-11 increases indicating stabilizing effect of the protein. FT-Raman analysis of Trp amino acid marker band W3 revealed that the average rotation angle around the C-3 - C-beta bond of four TLL residues of TLL in the Q(230) phase increases. Reasoning from available TLL crystallographic data, this result is explained by structural transition of entrapped protein to so-called "open" and more related to the enzymaticallyactive conformation. TLL secondary structure analysis by amide I and amide III vibrational bands showed that content of alpha-helixes does not change, while a part of beta-sheet structures transforms to less ordered elements upon incorporation of protein into the Q230 phase of aqueous phytantriol. (c) 2008 Elsevier B.V. All rights served

Synthesis and aqueous phase behavior of 1-glyceryl monooleyl ether

Synthesis of 1-glyceryl monooleyl ether (GME) has been accomplished yielding material of high purity (99.6%). The aqueous phase behavior of synthesized lipid has been investigated by using polarized microscopy and small angle X-ray diffraction. As a result, a partial temperature-composition phase diagram has been constructed. GME forms a reversed micellar solution and reversed hexagonal liquid crystalline phase at low and high hydration, respectively. The hexagonal phase coexists with excess water and is stable up to about 63 degreesC. These findings make GME an interesting alternative to glycerol monoesters in various fields of applications. (C) 2004 Elsevier B.V. All rights reserved

Interactions of cyclic AMP and its dibutyryl analogue with a lipid layer in the aqueous mixtures of monoolein preparation and dioleoyl phosphatidylcholine as probed by X-ray diffraction and Raman spectroscopy

Interactions of adenosine 3':5'-cyclic monophosphate (cAMP) and N-6,2'-O-dibutyryl-adenosine 3':5'-cyclic monophosphate (dbcAMP) with a lipid layer composed of monoolein-based preparation and dioleoyl phosphatidylcholine ( DOPC) were investigated by small-angle X-ray diffraction (SAXD) and Raman spectroscopy. The reversed hexagonal (H-II) MO/DOPC/H2O phase of 65:15:20 wt.% composition was selected as a reference system. SAXD revealed that entrapment (at the expense of water) of 3 wt.% cAMP into the reference system did not change the polymorphic form and structural parameters of the phase. The same content of dbcAMP induced the transition from the HII phase to the reversed bicontinuous cubic phase of space group Ia3d. This transition is explained by the increase of lipid head-group area due to the penetration of the acylated adenine group of dbcAMP into the polar/apolar region of lipid layer. The conclusion is supported by Raman spectroscopy, showing the disruption/weakening of hydrogen bonding in the MO/DOPC-based matrix at the N1- and N3-sites of the dbcAMP adenine ring. As distinct from dbcAMP, cAMP remains mostly in the water channels of the HII phase, although the phosphate residue of nucleotide interacts with the quaternary ammonium group of DOPC. Both nucleotides increase the population of gauche isomers in the DOPC choline group

Towards redox active liquid crystalline phases of lipids: a monoolein/water system with entrapped derivatives of ferrocene

The phase and electrochemical behavior of the aqueous mixtures of monoolein (MO) and synthetic ferrocene (Fc) derivatives containing long alkyl chains -(Z)-octadec-9-enoylferrocene (1), (Z)-octadecen-9-ylferrocene (2), and ferrocenylmethyl (Z)-octadec-9-enoate (3)-were studied. At low hydration, the reversed micelles (L-2 phase) and cubic Q(230) phase of MO can accommodate relatively high amounts ( > 6 wt.%) of the Fc-derivative 2, whereas at high hydration, the pseudoternary cubic phase Q(224) is destabilized even at about 2 wt.% of this Fc. Increasing the Fc-derivative content induces L-alpha L-2 and L-alpha --> reversed bicontinuous cubic phase (Q(II)) H-II transitions depending upon hydration. A rough study of the MO system containing compounds I and 3 indicates very similar phase behavior to that of the MO/2/H2O system. Compound 2 apparently has no effect on the lipid monolayer thickness in the pseudoternary L-alpha, H-II and Q(II) liquid crystalline phases of MO. Within a 3D-structure of the Q224 phase, derivatives 1-3 exhibit electrochemical activity on the gold electrode. The one-electron redox conversion processes are electro-chemically quasi-reversible and controlled by diffusion. The values of apparent diffusion coefficient (D-app) and heterogeneous electron-transfer rate constant (k(s)) of Fcs are significantly lo er in the cubic,phase matrix when compared to the acetonitrile solution. By contrast, the MO H-II phase with entrapped Fc-derivatives does not exhibit electrochemical activity on the electrode surface. It is suggested that the diffusional anisotropy and/or localized aggregation of compounds 1-3 within a 2D-structure of the H-II phase account(s) for the latter observation. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved