مجال
التميز
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تميز دراسي و بحثي
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البحوث المنشورة
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البحث (1):
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عنوان البحث:
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An analytical ultracentrifugation based
study on the
conformation of lambda carrageenan in aqueous solution
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رابط البحث:
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here
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تاريخ النشر:
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14/08/2013
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موجز عن البحث:
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The conformation and heterogeneity of
lambda-carrageenan, a sulphonated galactan from red seaweed, solubilised in
aqueous solvent with the assistance of microwave irradiation, has been
assessed by a combination of analytical ultracentrifugation, size-exclusion
chromatography, light scattering and capillary viscometry. Preparations
appeared generally unimodal on the basis of sedimentation coefficient
distributions from sedimentation velocity although at the highest
concentrations a shoulder appears with a sedimentation coefficient
approximately 1.1 times greater than that of the main component. Even under
conditions commensurate with charge suppression simple linear regression was
insufficient to represent non-ideal concentration dependence and the extraction
of the Grálen concentration dependence parameter ks. A more general fitting
algorithm was therefore employed. Mark–Houwink–Kuhn–Sakurada analysis of the
change in intrinsic viscosity [η] with molecular weight, together with the
Wales–van Holde ratio (combination of ks with [η]) point to an extended
flexible conformation for lambda-carrageenan in the (weight average)
molecular weight range Mw = 340,000–870,000 g/mol. The origin of the larger
sedimentation coefficient component appearing at the higher concentrations is
considered
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البحث (2):
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عنوان البحث:
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Dilute Solution Viscometry Studies on a
Therapeutic Mixture of Non-digestible Carbohydrates
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رابط البحث:
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here
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تاريخ النشر:
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06/06/2012
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موجز عن البحث:
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Recent work has shown the beneficial effects of a proprietary
mixture of three non-digestible carbohydrates: konjac glucomannan, xanthan
and alginate and these effects have been linked with a synergistic
interaction observable with analytical ultracentrifugation, rheological and
NMR measurements. These observations have been supported by fundamental
dilute solution viscosity studies. Preparations of konjac glucomannan,
xanthan and alginate have been checked with regards their molecular integrity
(molar mass distribution) using a newly established method based on the
analytical ultracentrifuge. The intrinsic viscosity behaviour for each of the
individual polysaccharides were estimated at low ionic strength I (10-3M) and
found to be (2090±120) ml/g, (4430±340) ml/g and (3460±330) ml/g for konjac
glucomannan, xanthan and alginate respectively and at (10-1M) (2350±200)
ml/g, (3370±310) ml/g and (1210±50) ml/g respectively. The intrinsic
viscosity [η] was then determined for a proprietary mixture of the three
(known as “PGX®”) at both ionic strengths and compared with the
predicted values for a non-interacting mixture. In I=10-3 M solvent a significant
difference was observed (3090+250) ml/g compared with the predicted value
(2350+300) ml/g, although at higher ionic strength the interaction appears to
have gone: [η] = (1990+250) ml/g compared with the predicted value of
(2180+300) ml/g. This appears to reinforce the earlier observations that in
PGX® there is a synergistic interaction which is ionic strength sensitive
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البحث (3):
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عنوان البحث:
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SEDFIT-MSTAR:
Molecular weight and molecular weight distribution analysis of polymers by
sedimentation equilibrium in the ultracentrifuge.
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رابط الوصول إلى البحث:
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here
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تاريخ النشر:
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05 November 2013
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موجز عن البحث:
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Sedimentation
equilibrium (analytical ultracentrifugation) is one of the most inherently
suitable methods for the determination of average molecular weights and
molecular weight distributions of polymers, because of its absolute basis (no
conformation assumptions) and inherent fractionation ability (without the
need for columns or membranes and associated assumptions over inertness).
With modern instrumentation it is also possible to run up to 21 samples
simultaneously in a single run. Its application has been severely hampered
because of difficulties in terms of baseline determination (incorporating
estimation of the concentration at the air/solution meniscus) and complexity
of the analysis procedures. We describe a new method for baseline
determination based on a smart-smoothing principle and built into the highly
popular platform SEDFIT for the analysis of the sedimentation behavior of
natural and synthetic polymer materials. The SEDFIT–MSTAR procedure – which
takes only a few minutes to perform – is tested with four synthetic data sets
(including a significantly non-ideal system), a naturally occurring protein
(human IgG1) and two naturally occurring carbohydrate polymers (pullulan and
λ-carrageenan) in terms of (i) weight average molecular weight for the whole
distribution of species in the sample (ii) the variation in “point” average
molecular weight with local concentration in the ultracentrifuge cell and
(iii) molecular weight distribution.
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البحث (4):
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عنوان البحث:
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Hydrodynamic
characterisation of chitosan and its interaction with two polyanions: DNA and
xanthan
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رابط الوصول إلى البحث:
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here
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تاريخ النشر:
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25 September 2014
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موجز عن البحث:
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Chitosan,
a soluble polycationic derivative of insoluble chitin, has been widely
considered for use in the food, cosmetic and pharmaceutical industrials.
Commercial (“C”) and in-house laboratory (“L”) prepared chitosan samples
extracted from crustaceous shells with different molecular weight and degrees
of acetylation (25% and 15% respectively) were compared with regards to (i)
weight-average molecular weight (Mw); (ii) sedimentation coefficient (so20,w)
distribution, and (iii) intrinsic viscosity ([η]). These parameters were
estimated using a combination of analytical ultracentrifugation (AUC), size
exclusion chromatography coupled to multi-angle laser light scattering
(SEC–MALS) and differential pressure viscometry. Unimodal distributions were
seen from sedimentation coefficient distributions and elution profiles from
SEC-MALS. Mwvalues obtained for each sample by sedimentation equilibrium
measurements, and these were in excellent agreement with those obtained from
SEC-MALS. Mark–Houwink–Kuhn–Sakurada (MHKS) and Wales van Holde analyses of
the data all suggest a semi-flexible conformation, with chitosans having the
lowest degree of acetylation observed as more flexible.
The
principle of co-sedimentation was then used to monitor the interactions of
the two, different molecular weights of L chitosans with two polyanions, DNA
and xanthan (another double helical high molecular weight molecule).
Interactions were clearly observed and quantified from the changes in the
sedimentation coefficient distribution of the mixture compared to unmixed
controls using sedimentation velocity. The interactions appeared to show a
strong dependence on molecular weight. The relevance of this for DNA
condensation applications is indicated.
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المؤتمرات العلمية:
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المؤتمر (1):
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عنوان المؤتمر:
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EPNOE 2013: Polysaccharides and
Polysaccharide-Derived Products, From Basic Science to Applications.
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تاريخ الإنعقاد:
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October 2013
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مكان
الإنعقاد:
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Nice, France
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طبيعة المشاركة:
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Poster presentation
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عنوان المشاركة:
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Investigation of the oligomeric state of
the main classes of carrageenan (lambda, iota and kappa) using hydrodynamics.
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ملخص المشاركة:
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The oligomeric and
conformational state of the three main classes of carrageenan (lambda, iota
and kappa) in three different solvents NaI 0.1M (helix form),
phosphate-chloride buffer solution (PBS) 0.1M (coil form) and GuHCl 6.0M
(coil form) is investigated using analytical ultracentrifugation (AUC), size
exclusion chromatography coupled to multi angle light scattering (SEC-MALS)
and capillary viscometry. The sedimentation coefficient so20,w is determined
for all carrageenan samples under conditions which according to previous work
would promote either coil or helical
conformations and is compared with predicted values for double helix
formation. A significantly lower experimental value was observed for each
carrageenan compared with the expected value for a double chain helix
formation. Consequently, no sign of double helix formation was evident.
Furthermore, no doubling of the molecular weight MW was obtained using AUC,
and SEC-MALS measurements. Capillary viscometry results showed no increase in
intrinsic viscosity of carrageenans (lambda and iota) in helix form compared
to coil, whilst the highest intrinsic viscosity of kappa carrageenan
reflected a greater stiffness. These results appear to reinforce the view
that lambda, iota and kappa carrageenans are all in a single chain form adopt
single chain form when in ordered confirmation. However, the measurement of
carrageenans in GuHCl using AUC and capillary viscometry did not give any
reliable results. This might indicate GuHCl is not an appropriate solvent for
carrageenan.
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