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PubMed1997

Organisation and association of kappa-carrageenan helices under different salt conditions.

Mixtures of the added salts NaI and CsI can be used to gradually 'tune' the propensity of kappa-carrageenan (KC) helices to aggregate in solution. We show that this method can be used to resolve the molecular events by which helix formation, under certain conditions, leads to gelation. We also present an overview of the various states of aggregation and organisation that appear for helical KC (non-degraded or ultrasonically degraded) when the NaI/CsI ratio and the concentration of KC are varied. A transition to rigid, superhelical rods is found above a well-defined fraction of cesium. This transition is reflected in a range of experimental measurements, such as cryo-transmission electron microscopy, optical rotation, viscometry and small deformation oscillatory measurements. The superhelical-rod state also seems essential for the association of KC with locust bean gum, and locust bean gum is found to stabilise this state. Novel states of KC alone have been found at cesium contents below the transition threshold. Non-degraded KC forms weak gels at sufficiently high concentrations (> ca. 1%). In contrast, ultrasonically degraded KC forms a chiral nematic liquid crystalline phase at sufficiently high concentrations (> ca. 5%) under these salt conditions.

Carbohydrate Conformation↗
PubMed1997

On the specific role of coions and counterions on kappa-carrageenan conformation.

The role of the nature and concentration of counterions and coions on the conformation of kappa-carrageenan is discussed; particularly, that of iodide compared with chloride based on the results obtained from optical rotation, viscometry and microcalorimetry. Iodide gives a more stable helical conformation, with a larger degree of order; at the same time, it represses aggregation of the helices and the gelation ability. Concerning the ordered conformation obtained in the presence of iodide coions, the results obtained are not conclusive. From the enthalpy of the conformational change, it seems that, even in the presence of iodide, the ordered conformation remains a double helix. On the other hand, no doubling of molecular weight was obtained by MALLS/GPC. Thus, this aspect remains still under discussion.

Calorimetry↗
PubMed1999

Comparison between the physicochemical behaviour of two microbial polysaccharides: RMDP17 and rhamsan.

This paper concerns the properties of two ionic polysaccharides with very close chemical structures. pH metric and conductimetric measurements showed that they behave similarly from a polyelectrolytic point of view. From optical rotation and differential scanning calorimetry (DSC) measurements, the two polymers probably adopt a double helical conformation which is destabilised by deacetylation. The main differences concern the stability of this ordered conformation and the ability of these double helices to associate to form gels. The results support a higher thermal stability of the ordered conformation for deacetylated RMDP17 (about 8 degrees C), whereas deacetylated rhamsan has a better ability to form gels.

Acetylation↗
PubMed2000

A new bacterial polysaccharide (YAS34). I. Characterization of the conformations and conformational transition.

This paper concerns the study of the conformational transition of a new exopolysaccharide (YAS34) using experimental techniques such as optical rotation, conductimetric and microcalorimetric measurements as a function of temperature. The behaviors of this polysaccharide in the acid or sodium salt form are compared; a deacetylated sample is also prepared to demonstrate the role of substituents. For the native structure (never heated), a conformational transition is observed but the deacetylated polysaccharide exhibits no ordered conformation. Multidetection size exclusion chromatography (SEC) analyses and conductimetric experiments allowed to determine the nature of each conformation and the molecular dimensions. From these results, it is suggested that the native conformation is a double helix which by heating over T(m) (temperature corresponding to half conformational transition) dissociates into disordered single chains. In the acid and sodium salt forms, by cooling below T(m), an ordered conformation is restored. This conformation seems to be an intramolecular double helix 'hairpin-like turn' (called renatured conformation). Nevertheless an irreversible denaturation is obtained progressively in the sodium salt form when the time of heating over T(m) increases. The conformation of the deacetylated polysaccharide corresponds to that of a single flexible chain (disordered conformation). The conformational transition for the native conformation was studied also in relation to the polyelectrolytic character of the polysaccharide: stability as a function of salt nature and salt and polymer concentrations was investigated for the polymer initially in the sodium and acid forms.

Carbohydrate Conformation↗
PubMed1985

Physicochemical and immunological studies of the renatured alpha 1(II) chains and isolated cyanogen bromide peptides of type II collagen.

The alpha 1(II) and cyanogen bromide (CB)1-generated peptides of chick type II collagen were isolated, purified, renatured and examined for their physicochemical and immunological properties. The alpha 1(II) chains and peptides CB-6 through CB-12 (3,000 to 40,000 daltons) formed renatured thermostable products as determined by measurements of reduced viscosity, optical rotation and Stokes radius. Moreover, renatured alpha 1 (II) chains and CB-10 were observed to form segment-long-spacing (SLS) crystallites under appropriate conditions. When examined for immunoreactivity with defined rat polyclonal and mouse monoclonal antibodies to chick type II collagen, conformation-dependent epitopes were detected on renatured alpha 1(II) chains and renatured peptides, CB-8, CB-10 and CB-11. Conformation-independent epitopes were also detected on all CB-peptides in their denatured form. These studies demonstrate that the alpha 1 (II) chains and CB-peptides of chick type II collagen can be efficiently renatured and that the renatured products retain some conformation-dependent epitopes present on the naive molecule.

Animals↗
PubMed2003

An NMR and circular dichroism study of the interaction of thiocyanate with human and cross-linked hemoglobin: identification of Lys-alpha-99 as a possible dissociation linked binding site.

The interaction of thiocyanate with human native and cross-linked oxyhemoglobin (oxyHb), and methemoglobin (metHb) has been investigated by optical spectroscopy, circular dichroism (CD) and nuclear spin lattice relaxation rate measurements. The interaction of thiocyanate anion with human hemoglobin has been investigated by NMR measurements of the nuclear spin lattice relaxation rate of N(15) labeled thiocyanate in the presence of cyanomethemoglobin and cross-linked cyanomethemoglobin. Results show that thiocyanate is located approximately 8.9 and 6.2 A away from the heme group in cyanomethemoglobin and cross-linked cyanomethemoblobin, respectively. These results are consistent with the binding of SCN(-) at the lys-alpha-99 in the unmodified hemoglobin. Since this site is blocked in the cross-linked hemoglobin, the binding site is different. Results show that one mole of SCN(-) is binding to one mole of oxyhemoglobin suggesting that binding at the lys-alpha-99 is linked to dissociation of the hemoglobin tetramer into dimers due to its location at the alpha(1)beta(2) interface. Circular dichroism studies show that the interaction of thiocyanate with oxyHb decreases the optical rotation at 240 nm indicating a conformational change of the protein, which influences the electronic transitions of a number of peptide bonds or (and) a few aromatic side chains.

Binding Sites↗
PubMed1990

Enantiomer analysis of E- and Z-10-hydroxyamitriptyline in human urine.

E- and Z-10-hydroxyamitriptyline (E- and Z-10-OH-AT) are racemic alcoholic metabolites of the antidepressant amitriptyline. Their enantiomers were separated by high-performance liquid chromatography as diastereomeric derivatives using R-(+)-alpha-methoxy-alpha-trifluoromethylphenylacetyl chloride (Mosher's reagent). Although E-10-hydroxyamitriptyline excreted in patient urine in free form or as the O-glucuronide consisted primarily of the (-)-enantiomer, the N-glucuronide contained similar amounts of the two enantiomers. Z-10-OH-AT was analysed in one patient and an excess of the (+)-isomer was found in the unconjugated, total conjugated and N-glucuronidated metabolite. The specific optical rotation of (-)-E-10-OH-AT was determined.

Amitriptyline↗
PubMed1998

Chiral chromatographic method to determine the enantiomers of halofantrine and its main chiral desbutyl metabolite in erythrocytes.

We describe a direct liquid chromatographic method with spectrofluorimetric detection to quantify the two enantiomers of halofantrine and the two enantiomers of its main chiral N-monodesbutylated metabolite in erythrocyte pellets. The method involves a Chiralpak AD column and a rapid one-step extraction procedure with acetonitrile. The method was validated for the four enantiomers within the range 0-1000 ng/ml. The absence of stereoconversion was studied in samples stored frozen for up to eight months. The optical rotation of the halofantrine and metabolite enantiomers was determined after separation on a semi-preparative Chiralcel OD column with polarimetric detection.

Administration, Oral↗
PubMed2001

LC determination of the enantiomeric purity of levamisole using stationary phase with bonded naphthylethylcarbamoylated-beta-cyclodextrin.

A direct enantioselective high-performance liquid chromatography was employed successfully for determination of the enantiomeric purity of levamisole. The elaborated method used S-naphthylethylcarbamoylated beta-cyclodextrin stationary phase in reversed-phase mode. The optimized mobile phase composition was acetonitrile-0.5% triethylammonium acetate buffer, pH 5.0 (2:8, v/v). Linearity, precision, accuracy, and the quantitation limit were determined. The method proved to be capable of determining 0.05% (w/w) of dexamisole (the enantiomeric impurity) contrary to the pharmacopoeial optical rotation measurement, in which only amounts of dexamisole higher than 2.2% (w/w) caused the test to fail. The enantiomeric purity of three different levamisole substances and levamisole tablets was assessed with the use of the method. The content of dexamisole impurity was found to be in the range 0.66-1.60% (w/w).

Antinematodal Agents↗
PubMed2003

Quantification of 5-HMF and dextrose in commercial aqueous dextrose solutions.

5-Hydroxymethylfurfural (5-HMF) is the major thermal decomposition product formed in aqueous dextrose solutions during sterilization and upon storage. Current compendial tests employ a spectrophotometric assay for 5-HMF and a separate assay based on optical rotation for dextrose. Efforts herein focused on identification of approaches to simultaneously quantify both 5-HMF and dextrose in aqueous solutions. Initial studies employed anion exchange chromatography with pulsed amperometric detection (PAD). These studies showed that the low anion exchange column loading capacity and concentration mismatch of dextrose and 5-HMF in typical commercial solutions makes simultaneous quantitation impractical at a single sample concentration. However, mixed modes of detection for each analyte using refractive index (RI) detection for dextrose and UV detection for 5-HMF proved viable for simultaneous quantitation. The performance of both approaches was evaluated and extremely high sensitivity for 5-HMF demonstrated (30-50 ppb). The formation of 5-HMF upon the forced thermal decomposition of dextrose was monitored and compared with results from the USP spectrophotometric assay.

Chromatography, High Pressure Liquid↗
PubMed1997

Optimization of a polarized photometric detector equipped with a split-type flow cell and its analytical application to oligo-saccharides.

A novel, non-modulated polarimeter called a polarized photometric detector (PPD) was previously described by the authors. The PPD enables the measurement of the optical rotation of chiral compounds as a change in absorbance by placing two linear polarizers on either side of a flow cell of a conventional photometric detector. The present study describes the optimization of the conditions of PPD for highly sensitive detection of saccharides. To maximize the light intensity, the light balancing filter and slit were removed from the detector (Shimadzu model SPD-10AV). These modifications resulted in an approximately 15-fold increase in the incident light intensity when the maximum current was applied to the lamp. When this intense light was transmitted through the polarizers, the signal intensity followed the theoretical equation for phase angles up to around 1 rad. If the energy of the transmitted light was less than 700 mV, however, the baseline noise was too great to determine the chiral analyte accurately. Setting the phase angle between two polarizers at 50 degrees and the detection wavelength at 400 nm provided the most suitable conditions. This detector was applicable for the determinations of oligosaccharides in foodstuffs separated by HPLC using gradient elution.

Flow Injection Analysis↗
PubMed1998

Determination of fluoxetine hydrochloride enantiomeric excess using high-performance liquid chromatography with chiral stationary phases.

Chromatographic methods using chiral stationary phases have been developed for the separation of fluoxetine hydrochloride enantiomers. Ovomucoid and tris(3,5-dimethylphenyl carbamate) cellulose stationary phases were used in the reversed- and normal-phase modes, respectively. Acceptable isomer separation was achieved at pH 3.5 with the ovomucoid phase. Isopropyl alcohol and methyl-tert- butyl ether mobile phase modifiers each provide complete resolution using the derivatized cellulose column. Better separation robustness was obtained with a column temperature of 1 degree C the isopropyl alcohol modifier. The methyl-tert-butyl ether system was robust at room temperature. Differences in relative enantiomer amounts of as little as 2% could be determined. The chromatographic conditions provided a much more discriminating test compared to an optical rotation method proposed for pharmacopeial use which had difficulty distinguishing individual enantiomers. The chiral chromatographic conditions were also applied to capsule formulations to demonstrate the presence of racemic fluoxetine hydrochloride.

Chromatography, High Pressure Liquid↗
PubMed2003

Potent antibacterial activity of halogenated metabolites from Malaysian red algae, Laurencia majuscula (Rhodomelaceae, Ceramiales).

Red algae genus Laurencia (Rhodomelaceae, Ceramiales) are known to produce a wide range of chemically interesting secondary halogenated metabolites. This investigation delves upon extraction, isolation, structural elucidation and antibacterial activity of inherently available secondary metabolites of Laurencia majuscula Harvey collected from two locations in waters of Sabah, Malaysia. Two major halogenated compounds, identified as elatol (1) and iso-obtusol (2) were isolated. Structures of these compounds were determined from their spectroscopic data such as IR, 1H-NMR, 13C-NMR and optical rotation. Antibacterial bioassay against human pathogenic bacteria was conducted using disc diffusion (Kirby-Bauer) method. Elatol (1) inhibited six species of bacteria, with significant antibacterial activities against Staphylococcus epidermis, Klebsiella pneumonia and Salmonella sp. while iso-obtusol (2) exhibited antibacterial activity against four bacterial species with significant activity against K. pneumonia and Salmonella sp. Elatol (1) showed equal and better antibacterial activity compared with tested commercial antibiotics while iso-obtusol (2) only equaled the potency of commercial antibiotics against K. pneumonia and Salmonella sp. Further tests conducted using dilution method showed both compounds as having bacteriostatic mode of action against the tested bacteria.

Anti-Bacterial Agents↗
PubMed1999

Production of D-lyxose from D-glucose by microbial and enzymatic reactions.

D-arabitol was first prepared from D-glucose using Candida famata R28. The reaction gave 5.0% D-arabitol from 10.0% D-glucose. D-arabitol was then almost completely converted to D-xylulose using Acetobacter aceti IFO 3281. Finally, D-lyxose was prepared from D-xylulose enzymatically using L-ribose isomerase from toluene-treated cells of Acinetobacter sp. strain DL-28. The isomerization reaction progressed steadily and the concentration of D-xylulose increased from 1.0 to 10.0%. About 70% of D-xylulose was converted to D-lyxose in all cases. Separation of residual D-xylulose from the reaction mixture is very difficult to achieve by column chromatography, but D-xylulose could be selectively degraded easily using Saccharomyces cerevisiae IFO 0841. The product was crystallized and was confirmed to be D-lyxose by HPLC, 13C-NMR spectra, IR spectra analysis, and optical rotation measurement.

Journal Article↗
PubMed1999

Preparation of L-talose and D-gulose from L-tagatose and D-sorbose, respectively, using immobilized L-rhamnose isomerase.

L-rhamnose isomerase of Pseudomonas sp. LL172 immobilized on BCW 2603 Chitopearl beads was used to produce L-talose and D-gulose. At equilibrium, the production yields of L-talose and D-gulose were determined to be 12 and 10% from L-tagatose and D-sorbose, respectively. The crystallized products were confirmed by HPLC, IR and NMR spectra, and optical rotation measurement analyses.

Journal Article↗
PubMed2004

A novel enzymatic approach to the massproduction of L-galactose from L-sorbose.

Wild-type strain of Pseudomonas cichorii ST-24 was unable to grow on D -psicose and inductively produced D -tagatose 3-epimerase (D -TE) with D -tagatose as an inducer. We have isolated a constitutive mutant, designated strain Ka75, which had acquired a new ability to grow on a mineral salts medium containing D -psicose as a sole carbon source. The D -psicose-metabolizing mutant synthesized a high level of D -TE. When grown on the culture medium supplemented with Mn(2+), the mutant strain produced around 250-fold higher activity than did the parent strain. Enzymatic properties of the constitutive enzyme were similar to those of the wild-type. Using the immobilized D -TE and recombinant L-rhamnose isomerase (L-RhI) from Escherichia coli strain JM109, a two-step enzymatic reaction was performed for massproduction of a rare aldo-hexose monosaccharide, L-galactose, from a common one, L-sorbose. In the first step, L-sorbose was epimerized to L-tagatose in a yield of 28%. The L-tagatose obtained was utilized as a starting material for L-galactose preparation by the immobilized L-RhI. At equilibrium, approximately 30% L-tagatose was isomerized to L-galactose. Finally, 7.5 g of L-galactose was obtained from 100 g of L-sorbose, viz an overall yield of 7.5%. The product obtained was purified and identified to be L-galactose by specific optical rotation and high performance liquid chromatography (HPLC) analysis, and was ultimately confirmed by (13)C nuclear magnetic resonance ((13)C NMR) and IR spectra.

Journal Article↗
PubMed1999

Production of D-iditol from D-sorbose by Rhodotolura rubra RY10 isolated from miso paste.

The yeast strain RY10 that can convert D-sorbose to D-iditol was isolated from miso paste and identified as Rhodotolura rubra. The cells grown on D-fructose were found to have relatively high conversion potential. Addition of ethanol to the reaction mixture significantly accelerated the conversion rate of D-sorbose to D-iditol. During the conversion reaction, ethanol was added to the reaction mixture at 48 h intervals to maintain the concentration of ethanol at 1.0%. The final conversion ratios were 82.7%, 95.0%, 93.7%, and 78.0% using washed cells when the concentration D-sorbose were 1.0%, 2.0%, 3.0% and 5.0%, respectively. The product produced from D-sorbose was identified as D-iditol by high performance liquid chromatography analysis, infrared spectrum, optical rotation and melting point measurements.

Journal Article↗