Wyniki wyszukiwania - Biblioteka Nauki

1

The stoichiometry and stability of beta-cyclodextrin complexes of some aromatic ketones and thioketones

100%

Milewski M. , Urjasz W. , Maciejewski A. , Augustyniak W.

Polish Journal of Chemistry

|

1998

|

tom Vol. 72, nr 11

2405-2417

EN

Stoichiometry and stability constants of beta-cyclodextrin (beta-CD) complexes of several aromatic ketones and the corresponding thioketones were determined by the spectrophotometric and solubility methods. The solubility method with high-performance liquid chromatography (HPLC) detection of the solute concentration proved to be very convenient in determination of the stability constant for the least soluble thioketone. The formation constants were correlated with 1-octanol-water partition cefficients, which vary over more than five orders of magnitude for compounds studied. The hydrophobic interaction and dispersion forces were found to be the most important sources of the complex stability. Relatively strong hydrogen bonds between the ketone molecules and water destabilize their beta-cyclodextrin complexes. Stoichiometry of all beta-cyclodextrin complexes studied was found to be 1:1. The synthesis of a new alkyl derivative of 4H-1-benzopyran-4-one and 4H-1-beznopyran-4-thione was described.

2

Heat and SDS insensitive NDK dimers are largely stabilised by hydrophobic interaction to form functional hexamer in Mycobacterium smegmatis

86%

Arumugam M. , Ajitkumar P.

Acta Biochimica Polonica

|

2013

|

tom 60

|

nr 2

EN

The primary structure and function of nucleoside diphosphate kinase (NDK), a substrate non-specific enzyme involved in the maintenance of nucleotide pools is also implicated to play pivotal roles in many other cellular processes. NDK is conserved from bacteria to human and forms a homotetramer or hexamer to exhibit its biological activity. However, the nature of the functional oligomeric form of the enzyme differs among different organisms. The functional form of NDKs from many bacterial systems, including that of the human pathogen, Mycobacterium tuberculosis (MtuNDK), is a hexamer, although some bacterial NDKs are tetrameric in nature. The present study addresses the oligomeric property of MsmNDK and how a dimer, the basic subunit of a functional hexamer, is stabilized by hydrogen bonds and hydrophobic interactions. Homology modeling was generated using the three-dimensional structure of MtuNDK as a template; the residues interacting at the monomer-monomer interface of MsmNDK were mapped. Using recombinant enzymes of wild type, catalytically inactive mutant, and monomer-monomer interactive mutants of MsmNDK, the stability of the dimer was verified under heat, SDS, low pH, and methanol. The predicted residues (Gln17, Ser24 and Glu27) were engaged in dimer formation, however the mutated proteins retained the ATPase and GTPase activity even after introducing single (MsmNDK- Q17A, MsmNDK-E27A, and MsmNDK-E27Q) and double (MsmNDK-E27A/Q17A) mutation. However, the monomer-monomer interaction could be abolished using methanol, indicating the stabilization of the monomer-monomer interaction by hydrophobic interaction.

3

Polymer-Surfactant Interaction and Physico-Chemical Properties of Polymethacrylic Acid-Triton X-100 and Polymethacrylic Acid-Poly(ethylene)oxide Aqueous Systems

86%

Tugay A. , Zakordonskiy V. , Sołtys M.

Polish Journal of Chemistry

|

2006

|

tom Vol. 80, nr 6

957-974

EN

The interaction of both Triton X-100 and poly(ethylene)oxide (PEO-2000) with polymethacrylic acid (PMAA) in aqueous solutions has been investigated by different methods: tensiometry, conductivity, viscometry, pH- and optical density measurement. The obtained results testify, that interaction of PMAA with the nonionic surfactants of different nature is accompanied by non-additive changes of physico-chemical properties and phase separation of binary systems. Thus, the character of influence of nonionic component depends on its nature. These changes take place in the clearly defined concentration ranges (1x10-4-1x10-3 M for Triton X-100 and 1x10-2-1x10-1 M for more high-molecular PEO-2000) and they are caused by intramolecular PMAA-surfactant complex formation. The experimental results clearly reveal, that important role in complex formation is played by hydrogen bonds. For investigated systems both the critical aggregation concentration (CAC) and the saturation concentration (C2) were calculated, and the idealized schema of the mechanism of polymer-surfactant interaction was proposed.

4

Proposition of a bubble-particle attachment model based on DLVO van der Waals and electric double layer interactions for froth flotation modelling

86%

Buchmann M. , Öktem G. , Rudolph M. , Boogaart K. G. v. d.

Physicochemical Problems of Mineral Processing

|

2022

|

tom Vol. 58, iss. 5

art. no. 154812

EN

The attachment of bubbles and particles represents one of the sub-processes in froth flotation among others (e.g. collision and detachment). The main interactions present at short distances in such a bubble-particle system are the van der Waals and electrostatic double layer interactions combined in the DLVO theory. In this study, the special features of the attachment process were discussed with a focus on flotation. For the van der Waals interactions, the Hamaker constants were calculated with the help of Lifshitz´ macroscopic theory as a function of the separation distance for specific material combinations. A specific material system (PbS-Water-Air) was used to demonstrate the implementation of bubble-particle attachment of the proposed modelling framework. The effects of additional surfactant/collector and air layers on the solid interface were presented. This framework of layered systems showed that the sign of van der Waals interaction could be turned from repulsive to attractive without the need to extend the DLVO theory. The thickness of the layer as a function of collector adsorption between a particle and a bubble is suggested as a modelling parameter in bubble-particle attachment efficiency.

5

Inhibition study of adenosine deaminase by caffeine using spectroscopy and isothermal titration calorimetry

86%

Saboury A. A. , Divsalar A. , Ataie G. , Amanlou M. , Moosavi-Movahedi A. A. , Hakimelahi G. H.

Acta Biochimica Polonica

|

2003

|

tom 50

|

nr 3

EN

Kinetic and thermodynamic studies were made on the effect of caffeine on the activity of adenosine deaminase in 50 mM sodium phosphate buffer, pH 7.5, using UV spectrophotometry and isothermal titration calorimetry (ITC). An uncompetitive inhibition was observed for caffeine. A graphical fitting method was used for determination of binding constant and enthalpy of inhibitor binding by using isothermal titration microcalorimetry data. The dissociation-binding constant is equal to 350 uM by the microcalorimetry method, which agrees well with the value of 342 uM for the inhibition constant that was obtained from the spectroscopy method. Positive dependence of caffeine binding on temperature indicates a hydrophobic interaction.

6

A novel matrix for hydrophobic interaction chromatography and its application in lysozyme adsorption

72%

Gedikli M. , Ceylan S. , Erzengin M. , Odabasi M.

Acta Biochimica Polonica

|

2014

|

tom 61

|

nr 4

7

Heat and SDS insensitive NDK dimers are largely stabilised by hydrophobic interaction to form functional hexamer in Mycobacterium smegmatis

72%

Arumugam M. , Ajitkumar P.

Acta Biochimica Polonica

|

2013

|

tom 60

|

nr 2

199-207

EN

The primary structure and function of nucleoside diphosphate kinase (NDK), a substrate non-specific enzyme involved in the maintenance of nucleotide pools is also implicated to play pivotal roles in many other cellular processes. NDK is conserved from bacteria to human and forms a homotetramer or hexamer to exhibit its biological activity. However, the nature of the functional oligomeric form of the enzyme differs among different organisms. The functional form of NDKs from many bacterial systems, including that of the human pathogen, Mycobacterium tuberculosis (MtuNDK), is a hexamer, although some bacterial NDKs are tetrameric in nature. The present study addresses the oligomeric property of MsmNDK and how a dimer, the basic subunit of a functional hexamer, is stabilized by hydrogen bonds and hydrophobic interactions. Homology modeling was generated using the three-dimensional structure of MtuNDK as a template; the residues interacting at the monomer-monomer interface of MsmNDK were mapped. Using recombinant enzymes of wild type, catalytically inactive mutant, and monomer-monomer interactive mutants of MsmNDK, the stability of the dimer was verified under heat, SDS, low pH, and methanol. The predicted residues (Gln17, Ser24 and Glu27) were engaged in dimer formation, however the mutated proteins retained the ATPase and GTPase activity even after introducing single (MsmNDK- Q17A, MsmNDK-E27A, and MsmNDK-E27Q) and double (MsmNDK-E27A/Q17A) mutation. However, the monomer-monomer interaction could be abolished using methanol, indicating the stabilization of the monomer-monomer interaction by hydrophobic interaction.

8

Aspects of the physical properties and the visco-elastic features of the sea water - oil system

58%

Khalifa S. S. , Pogorzelski S. , Linde B. , Sliwinski A.

Oceanologia

|

1992

|

tom 32

9

Inhibitory and activatory effects of various compounds on cholesterol sulphate sulphohydrolase of human placenta microsomes

58%

Gniot-Szulzycka J. , Wieczorek B. , Tronowska B.

Bulletin of the Polish Academy of Sciences. Biological Sciences

|

1999

|

tom 47

|

nr 1