Determination of bismuth in pharmaceutical products using phosphoric acid as molecular probe by resonance light scattering

A novel method for the sensitive determination of bismuth(III) in pharmaceutical products using phosphoric acid as a molecular probe by resonance light scattering (RLS) is discussed. In 0.5 mol/L phosphoric acid (H₃PO₄) medium, bismuth(III) reacted with PO₄^3? to form an ion association compound, which resulted in the significant enhancement of RLS intensity and the appearance of the corresponding RLS spectral characteristics. The maximum scattering peak of the system existed at 364 nm. Under optimal conditions, there was linear relationship between the relative intensity of RLS and concentration of bismuth(III) in the range of 0.06–10.0 µg/mL for the system. A low detection limit for bismuth(III) of 3.22 ng/mL was achieved. The relative standard deviations (RSD) for the determination of 0.40 and 0.80 µg/mL bismuth(III) were 2.1% and 1.1%, respectively, for five determinations. Based on this fact, a simple, rapid, and sensitive method was developed for the determination of bismuth(III) at nanogram level by RLS technique with a common spectrofluorimeter. This analytical system was successfully applied to determine the trace amounts of bismuth(III) in pharmaceutical products, which was in good agreement with the results obtained by atomic absorption spectrometry (AAS). Copyright © 2011 John Wiley & Sons, Ltd.     

Molecular weight of scleroglucan and other extracellular microbial polysaccharides by size-exclusion chromatography and low angle laser light scattering

High-performance aqueous size-exclusion chromatography coupled to a low angle laser light scattering detector has been applied to the analysis of scleroglucan and various other extracellular microbial polysaccharides. Emphasis has been focused on three main findings. (1) The molecular weight of these macromolecules is not very sensitive to changes in fermentation conditions. This is specially true in the case of scleroglucan and related (1 → 3)-β- -glucans including schizophyllan, which all exhibited a constant weight-average molecular weight of 5·7×10⁶±5%. (2) In contrast to plant polysaccharides, polydispersity is very low, usually near unity. (3) The molecular weight levels off quickly during biosynthesis since the molecular weight is constant from the middle of fermentation, if not before.     

Dynamic light scattering investigation of sodium caseinate and xanthan mixtures

Aqueous solutions of sodium caseinate and xanthan at pH 7 and containing 0.1 M NaCl, and their mixtures were investigated using dynamic light scattering. Sodium caseinate solutions showed a bimodal distribution of relaxation rates; with the aggregate peak distribution predominating. Xanthan solutions showed a single distribution at low concentrations (≤0.06 wt.%) and a bimodal distribution at higher concentrations. The sodium caseinate–xanthan mixture modes were independent of the total biopolymer concentration, and behaved as a superposition of sodium caseinate solution alone and xanthan solution alone. This indicates that there is no interaction between xanthan and sodium caseinate in the range of concentrations considered in this study.     

Insight into molecular imprinting in precipitation polymerization systems using solution NMR and dynamic light scattering

Molecular imprinting is a powerful synthetic technique for generating template-defined binding sites in cross-linked polymers. One scientific challenge in molecular imprinting research is to understand the intermolecular interactions leading to molecular complexation and the process of binding site formation during polymerization. In this work, we present a novel method for studying the molecular imprinting process in precipitation polymerization systems. This method employs solution (1) H NMR and dynamic light scattering (DLS) to investigate the association of template molecules with colloidal particles and the dynamic process of particle growth. Under precipitation polymerization conditions, the colloidal particles formed did not interfere with NMR signals from the soluble components, allowing unreacted monomers and free template to be easily quantified. To examine the process of particle nucleation and growth, DLS was used to measure the hydrodynamic particle size at different reaction times. To corroborate the interpretation of the NMR and DLS results, imprinted nanoparticles were collected at different reaction times and their binding characteristics were evaluated using radioligand-binding analysis. Our experimental results provide new insights into the molecular imprinting process that will be useful in the development of new imprinted nanoparticles.     

Light scattering and hydrodynamic properties of linear and circular bacteriophage lambda DNA

Low-angle light scattering, sedimentation velocity, and intrinsic viscosity measurements have been made on circular and linear forms of lambda (λ) bacteriophage DNA. Available equations, used to relate hydrodynamic parameters of both forms to the molecular weight, give relatively consistent values of particle weights which essentially agree with the light-scattering results. An average molecular weight of (34 ± 3) × 10⁶ for λ DNA was obtained in good agreement with literature values of (31–33) × 10⁶. The linear λ DNA has a larger root-mean-square radius than the circular molecule, when determined by light scattering, but the difference does not appear to be us large as expected from hydrodynamic data. The two forms also show significantly different angular distrbutions of scattered light intensities which agree only qualitatively with those derived from existing theory. The light-scattering results suggest that further experiments and modifications of available theories should be undertaken.     

Determination of the concentrations of separate species of microorganisms in mixtures by the light scattering spectra of the suspensions

A possibility of number determination of microorganisms in cultures mixture according to the spectra light transmission is shown.     

An investigation of the dissociation and denaturation of legumin by salts using laser light scattering and circular dichroism spectroscopy

The dissociation of legumin, a 12 S seed storage globulin from Pisum sativum, has been studied by laser light scattering and circular dichroism spectroscopy. Salts from the Hofmeister series, in particular sodium perchlorate, were used as dissociating agents. The Mr 360,000 hexameric protein was found to dissociate first to trimers and further to monomers and the number of amino acids involved in the trimer-trimer interaction estimated to be 23(+/-4). Native legumin appears to be more strongly bound together than some analogous seed storage globulins from other plant species such as Arachis hypogaea or Sesamum indicum and the dissociation process was accompanied by some changes in conformation.     

Determination of molecular weight by neutron scattering

Theoretical and practical advantages of neutron scattering for the determination of molecular weights of particles in solution are discussed. The method presented does not use known particles for calibration and is applicable to a wide molecular weight range (10⁴–10⁹); it is not sensitive to assumptions about the partial specific volume of the particles, and the experiments are performed quite easily in standard spectrophotometer cells using 100–500 μg of material. The method is nondestructive and the sample can be recovered totally. The use of D₂O in solvents has particular advantages especially for multicomponent particles, for which the in situ molecular weight of each component can be determined separately.     

Determination of urinary adenosine using resonance light scattering of gold nanoparticles modified structure-switching aptamer

A novel sensitive method has been developed for the detection of adenosine (AD) in human urine by using enhanced resonance light scattering (RLS). This method is based on the specific recognition and signal amplification of adenosine aptamer (Apt) coupled with gold nanoparticles (GNPs) via G-quartet-induced nanoparticle assembly, which was fabricated by triggering a structure switching of the 3′ terminus G-rich sequence and aptamer duplex. RLS signal linearly correlated with the concentration of adenosine over the range of 6-115 nM. The limit of detection (LOD) for adenosine is 1.8 nM with relative standard deviations (RSD) of 2.90-4.80% (n = 6). The present method has been successfully applied to determination of adenosine in real human urine, and the obtained results were in good agreement with those obtained by the HPLC method. Our investigation shows that the combination of the excellent selectivity of aptamer with the high sensitivity of the RLS technique could provide a promising potential for aptamer-based small molecule detection, and be beneficial in extending the application of RLS.     

Comparative study of small linear and branched alpha-glucans using size exclusion chromatography and static and dynamic light scattering

A series of synthesized small linear and branched alpha-glucans has been studied by dynamic light scattering and combined size exclusion chromatography, refractive index measurement and static light scattering. The alpha-glucan molecules studied were maltose, maltotriose, maltopentaose, maltohexaose, maltoheptaose, panose, 6'-alpha-maltosyl-maltotriose, methyl 6'-alpha-maltosyl-maltotrioside, 6' '-alpha-maltosyl-maltotetraose, 6' '-alpha-maltotriosyl-maltohexaose, and 6,6' ' '-bis(alpha-maltosyl)-maltohexaose. The alpha-glucan oligosaccharides appeared to be very flexible molecules having a variety of conformations and self-associating into noncovalent dimers and trimers (referring to the single molecule). The size distributions were narrow (compared to pullulan) indicating that the alpha-glucan oligosaccharides are relatively compact molecules. The branched oligomers that include one or more flexible alpha-(1 --> 6) linkages exhibit size distributions corresponding to more compact conformations than their linear counterparts. This observation may be explained by intermolecular interactions or water bridges facilitated by the additional flexibility of these molecules. For the branched maltohexaose, a significant noncovalent trimer formation was observed, whereas in all other cases, noncovalent dimers were formed. Model calculations suggest that both the linear and branched oligomers containing 5-10 alpha-glucose units exist predominantly in a partial or full single turn helix in agreement with the glycosidic linkage preferences derived for these molecules.     

Determination and differentiation in the light of molecular genetics

A review of the data obtained by the author and his collaborators in studying tissue specific esterase of Drosophila males. Patterns were established for molecular-genetic regulation of synthesis of this isozyme.     

Conformation of intercalated DNA plasmids investigated by circular dichroism and dynamic light scattering

Two DNA plasmids, pEGF and pACL29, intercalated with ethidium bromide (EB), have been examined by circular dichroism (CD) and dynamic light scattering (DLS). CD and DLS data show significant changes when the EB/DNA (phosphates) ratio reaches a value of r approximately equal to 0.13. The translational and rotational diffusion coefficients, predicted assuming that plasmids can be described by a string of beads, and the CD spectrum, suggest that a transition from an interwound to a toroidal conformation is likely to occur.     

Structure of hyperacetylated chromatin: light scattering and flow linear dichroism study

Cation-induced folding of 10 nm chromatin filament to 30 nm fiber was studied with hyperacetylated chromatin using light scattering at 90 degrees and flow linear dichroism. Acetylated chromatin folded in a way indistinguishable from that of the control chromatin: both the compactness of chromatin and the orientation of nucleosomes relative to the fiber axis were identical at a given salt concentration.     

Measurements of Euglena motion parameters by laser light scattering.

Measurements of Euglena gracilis motion parameters have been performed by the spectral analysis of the scattered laser light. Samples were oriented by a radiofrequency field to obtain easily interpretable spectra. Cell rotation frequency and flagellar beating frequency distributions were obtained from the homodyne spectra, whereas the Doppler lines obtained at small observation angles by heterodyne detection yielded the swimming speed distributions. We discuss the broadening of the heterodyne spectra at large angles of observation. An application of this method to the study of the photo-kinetic effect is also described.     

Determination of carbohydrate contents from excess light scattering.

In the light scattering technique, glycosylation gives rise to excess light scattering for glycoproteins. Assuming additivity of refractive index and using an appropriate refractive index increment for carbohydrate, one can determine the degree of glycosylation from the excess light scattering. Here we have used size-exclusion chromatography in combination with online light scattering, UV absorbance, and refractive index. The results show that the technique accurately determines the carbohydrate content of recombinant stem cell factor.     

Conformational studies of BSA using laser light scattering

The usefulness of laser light scattering as a technique for determining protein conformation has been investigated by studying the self-association and drug binding of bovine serum albumin (BSA). The diffusion coefficients of BSA monomers and dimers have been measured and the ratio of these two quantities indicates that in the dimer, the subunit separation is 2.2 times the monomeric hydrodynamic radius. The binding of salicylate to BSA causes an increase in its diffusion coefficient corresponding to a reduction in the frictional drag of the solvent on the protein molecules. It has been found that data obtained using laser light scattering may be interpreted confidently only when proper care has been taken in sample preparation and the scattered intensity autocorrelation function has been appropriately analyzed.     

Determination of phase transition temperatures of lipids by light scattering

Various techniques have been proposed to specify the phase transition temperatures of surfactant molecules. The work reported herein deals with a new general method of T(c) determination based on the optical properties' modifications of aqueous surfactant solutions when the phase transitions occur in the phospholipid membrane. The shape alteration of supramolecular systems induced by the phase transition was correlated with the refraction and absorption coefficients of their aqueous dispersion. The mean count rate (average number of photons detected per second) measured with a Zetasizer Nano-S model ZEN1600 Dynamic Light Scattering Instrument, is representative of an emerging macroscopic phenomenon, but not directly size dependent and has been adapted to our expectations. Changes in the measured scattering intensity reflect changes in the optical properties of the material during temperature variations. Thus, this method allowed to specify the phase transition temperature of many natural or synthetic surfactants independently of their polar head or hydrophobic part.