Low angle laser light scattering-absolute calibration

Differential light scattering and the measurement of molecules and nanoparticles: A review

Within the past few decades, the application of light scattering techniques to a broad range of scientific disciplines has increased significantly, especially in the field of analytical chemistry. The resulting interest in and use of light scattering methods suggests the need for an easily understood introduction and review of material for those new to the method as well as for current users in need of a refresher. In many respects, the theory and its applications may appear so overwhelming for many studying the field for the first time, that they rarely can spend the time just needed to understand the basic measurements and their interpretations. A variety of applications in analytical chemistry especially have resulted in a greater understanding of many of the macromolecular processes themselves from molar mass distributions, to the macromolecular interactions responsible for aggregation processes, to determinations of structure and function. The use of such analytical processes to obtain a better understanding of nanoparticle structure and function has become almost universal.

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Deriving the distribution of fractionated macromolecules by light scattering.

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Deriving the distribution of fractionated nanoparticles by light scattering.

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Deriving the masses of fractionated macromolecules from their scattered light.

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Deriving the size of nanoparticles from the angular variation of scattered light.

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Deriving bacterial size and structure by light scattering.

Physicochemical Approach to Understanding the Structure, Conformation, and Activity of Mannan Polysaccharides

Extracellular polysaccharides are widely produced by bacteria, yeasts, and algae. These polymers are involved in several biological functions, such as bacteria adhesion to surface and biofilm formation, ion sequestering, protection from desiccation, and cryoprotection. The chemical characterization of these polymers is the starting point for obtaining relationships between their structures and their various functions. While this fundamental correlation is well reported and studied for the proteins, for the polysaccharides, this relationship is less intuitive. In this paper, we elucidate the chemical structure and conformational studies of a mannan exopolysaccharide from the permafrost isolated bacterium Psychrobacter arcticus strain 273-4. The mannan from the cold-adapted bacterium was compared with its dephosphorylated derivative and the commercial product from Saccharomyces cerevisiae. Starting from the chemical structure, we explored a new approach to deepen the study of the structure/activity relationship. A pool of physicochemical techniques, ranging from small-angle neutron scattering (SANS) and dynamic and static light scattering (DLS and SLS, respectively) to circular dichroism (CD) and cryo-transmission electron microscopy (cryo-TEM), have been used. Finally, the ice recrystallization inhibition activity of the polysaccharides was explored. The experimental evidence suggests that the mannan exopolysaccharide from P. arcticus bacterium has an efficient interaction with the water molecules, and it is structurally characterized by rigid-rod regions assuming a 14-helix-type conformation.

Light scattering by pure water and seawater: the depolarization ratio and its variation with salinity

We measured the linearly polarized light scattering of pure water and seawater at various salinities and estimated the depolarization ratio using five different methods of data analysis after removing the scattering due to contamination by residual nanoparticles. The depolarization ratio values (δ) estimated for pure water using these different methods are largely consistent with each other and result in a mean value of 0.039±0.001. For seawater, our results reveal a trend of a slight linear increase of δ with salinity (S), δ=0.039+a₁×S, where a₁ varies in the range of 1×10^-4 to 2×10^-4 between the methods.

Decoration of Chondroitin Polysaccharide with Threonine: Synthesis, Conformational Study, and Ice-Recrystallization Inhibition Activity

Several threonine (Thr)- and alanine (Ala)-rich antifreeze glycoproteins (AFGPs) and polysaccharides act in nature as ice recrystallization inhibitors. Among them, the Thr-decorated capsular polysaccharide (CPS) from the cold-adapted Colwellia psychrerythraea 34H bacterium was recently investigated for its cryoprotectant activity. A semisynthetic mimic thereof was here prepared from microbial sourced chondroitin through a four-step strategy, involving a partial protection of the chondroitin polysaccharide as a key step for gaining an unprecedented quantitative amidation of its glucuronic acid units. In-depth NMR and computational analysis suggested a fairly linear conformation for the semisynthetic polysaccharide, for which the antifreeze activity by a quantitative ice recrystallization inhibition assay was measured. We compared the structure-activity relationships for the Thr-derivatized chondroitin and the natural Thr-decorated CPS from C. psychrerythraea.

Substrate and Cofactor Dynamics on Guanosine Monophosphate Reductase Probed by High Resolution Field Cycling 31P NMR Relaxometry

Guanosine-5'-monophosphate reductase (GMPR) catalyzes the reduction of GMP to IMP and ammonia with concomitant oxidation of NADPH. Here we investigated the structure and dynamics of enzyme-bound substrates and cofactors by measuring 31P relaxation rates over a large magnetic field range using high resolution field cycling NMR relaxometry. Surprisingly, these experiments reveal differences in the low field relaxation profiles for the monophosphate of GMP compared with IMP in their respective NADP+ complexes. These complexes undergo partial reactions that mimic different steps in the overall catalytic cycle. The relaxation profiles indicate that the substrate monophosphates have distinct interactions in E·IMP·NADP+ and E·GMP·NADP+ complexes. These findings were not anticipated by x-ray crystal structures, which show identical interactions for the monophosphates of GMP and IMP in several inert complexes. In addition, the motion of the cofactor is enhanced in the E·GMP·NADP+ complex. Last, the motions of the substrate and cofactor are coordinately regulated; the cofactor has faster local motions than GMP in the deamination complex but is more constrained than IMP in that complex, leading to hydride transfer. These results show that field cycling can be used to investigate the dynamics of protein-bound ligands and provide new insights into how portions of the substrate remote from the site of chemical transformation promote catalysis.

Linear and nonlinear magneto-optics of ferritin

Measurements of Rayleigh light scattering and Cotton-Mouton (CM) effect are carried out at room temperature for 100 mM NaCl solutions of apoferritin/ferritin loaded with 0, 90, 100, 500, 700, and 1500 Fe atoms/molecule. Because of the spherical shape, ferritin macromolecule should not manifest magnetic anisotropy; however, in solution it shows the induced magnetic birefringence (CM effect) and changes in intensity of the scattered light components. The newly obtained data support the previously reported conclusions indicating that the deformation of linear optical polarizability induced in the ferritin by a magnetic field and the orientation of the induced magnetic dipole moment by this field are the main sources of the magneto-optical phenomena observed. Nevertheless, it is also found that the orientation of the permanent magnetic dipole moment contributes to both effects. The magnetic field induced changes in the light scattering and the CM effect theoretically depend on the linear magneto-optical polarizability, chi, on the nonlinear magneto-optical polarizability, eta, and square of the permanent magnetic dipole moment value of the macromolecule, mu(2). On the basis of the theory describing both effects as well as the experimental data, the values of the anisotropy of linear magneto-optical polarizabilities components, the values of the linear optical polarizability and its anisotropy, nonlinear magneto-optical polarizability and its anisotropy, are estimated. Also the magnetic dipole moment of the ferritin macromolecule is found. Interestingly, not all iron atoms in the ferritin are indicated to be in the superparamagnetic state, some of them occur in the diamagnetic form.

Comparison of Proutière and Carr−Zimm Theories for Static Light-Scattering Molecular Weight Determination: Application to Surfactants in Solution

Proutière's theory of molecular weight (M) determination by Rayleigh scattering has been tested on surfactants in solution, and it has been compared to the classical Carr-Zimm (CZ) method. Both methods make use of time-averaged scattering intensity, refractive index, and density measurements. Monoethers of poly(ethylene glycol) samples have been studied in the range 0.33-4.67 kg/mol of M. Under those conditions, it has been shown that Proutière's method leads to a far better agreement with formula weight (M) values than the CZ method because Proutière theory takes into account the specific mean polarizability of the solvent and derivative of the solution density with respect to the solute mass concentration, which is counter to CZ theory.

Comparison between Protein−Polyethylene Glycol (PEG) Interactions and the Effect of PEG on Protein−Protein Interactions Using the Liquid−Liquid Phase Transition

Phase transitions of protein aqueous solutions are important for protein crystallization and biomaterials science in general. One source of thermodynamic complexity in protein solutions and their phase transitions is the required presence of additives such as polyethylene glycol (PEG). To investigate the effects of PEG on the thermodynamic behavior of protein solutions, we report measurements on the liquid-liquid phase separation (LLPS) of aqueous bovine serum albumin (BSA) in the presence of relatively small amounts of PEG with an average molecular weight of 1450 g/mol (PEG1450) as a model system. We experimentally characterize two thermodynamically independent properties of the phase boundary: (1) the effect of PEG1450 concentration on the LLPS temperature, (2) BSA/PEG1450 partitioning in the two liquid coexisting phases. We then use a thermodynamic perturbation theory to relate the first property to the effect of PEG concentration on protein-protein interactions and the second property to protein-PEG interactions. As criteria to determine the accuracy of a microscopic model, we examine the model's ability to describe both experimental thermodynamic properties. We believe that the parallel examination of these two properties is a valuable tool for verifying the validity of existing models and for developing more accurate ones. For our system, we have found that a depletion-interaction model satisfactorily explains both protein-PEG interactions and the effect of PEG concentration on protein-protein interactions. Finally, due to the general importance of LLPS, we will experimentally show that protein-PEG-buffer mixtures can exhibit two distinct types of liquid-liquid phase transitions.

Light scattering and phase behavior of lysozyme-poly(ethylene glycol) mixtures

Measurements of liquid-liquid phase transition temperatures (cloud points) of mixtures of a protein (lysozyme) and a polymer, poly(ethylene glycol) (PEG) show that the addition of low molecular weight PEG stabilizes the mixture whereas high molecular weight PEG was destabilizing. We demonstrate that this behavior is inconsistent with an entropic lysozyme-PEG depletion interaction and suggest that an energetic lysozyme-PEG attraction is responsible. In order to independently characterize the lysozyme-PEG interactions, light scattering experiments on the same mixtures were performed to measure second and third virial coefficients. These measurements indicate that PEG induces repulsion between lysozyme molecules, contrary to the depletion prediction. Furthermore, it is shown that third virial terms must be included in the mixture's free energy in order to qualitatively capture our data.

Magneto-optics of Ferritin

Measurements of Rayleigh light scattering, nonlinear light scattering in DC magnetic fields, and the Cotton-Mouton effect were carried out for 15 mM NaCl and water solutions of ferritin at room temperature. The spherical geometry of the molecule implies that it is optically isotropic. Such a macromolecule should not manifest magnetic anisotropy; however, in solution it shows induced magnetic birefringence (Cotton-Mouton effect) and changes in the intensity of the scattered light components. The analysis of the obtained results indicates the deformation of linear optical polarizability induced in the ferritin by a magnetic field as the main source of the magneto-optical phenomena observed. Light scattering and the CM effects theoretically depend on the linear magneto-optical polarizability, chi, and the nonlinear magneto-optical polarizability, eta. Using the theory describing the phenomena as well as the experimental data, the values of the anisotropy of linear magneto-optical polarizability components, chi(parallel) - chi(perpendicular) = -(1.3 +/- 0.7) x 10(-22) [cm3] (in SI units chi(parallel) - chi(perpendicular) = -(2.0 +/- 1.2) x 10(-33) [m3]), the linear optical polarizability, alpha = (alpha(parallel) + 2alpha(perpendicular))/3 = (3.9 +/- 1.0) x 10(-20) [cm3] (in SI units alpha = (3.52 +/- 0.09)x10(-4) [Cm2 V(-1)]), and its anisotropy, kappa(alpha) = (alpha(parallel) - alpha(perpendicular))/3alpha = -(0.06+/-0.03), nonlinear magneto-optical polarizability, eta = (eta(parallel) + 2eta(perpendicular))/3 = -(4.7 +/- 0.9) x 10(-30) [cm3 Oe(-2)] (in SI units eta = -(6.7 +/- 1.3) x 10(-18) [Cm4 V(-1) A(-2)]) and its anisotropy, kappa(eta) = (eta[parallel) - eta(perpendicular))/3eta = -(0.15 +/- 0.10), were deduced. Here alpha(parallel), eta(parallel), alpha(perpendicular), eta(perpendicular) are the optical and magneto-optical polarizability components along the parallel and the perpendicular axes of the axially symmetric molecule, respectively.

Determination of pituitary and recombinant human growth hormone molecular weights by modern high-performance liquid chromatography with low angle laser light scattering detection

The determination of molecular weight for pituitary and recombinant human growth hormone (p-hGH/Crescormon and r-hGH/Protropin) has been performed. This has involved on-line coupling of size-exclusion chromatography (SEC) and gradient elution, reversed-phase high-performance liquid chromatography (RP-HPLC) with low-angle laser light scattering (LALLS) detection. A 5-microns, 300 A, Delta-bond octyl column was used. Traditional specific refractive index increment (dn/dc) and refractive index (n) measurements have been performed in order to derive absolute weight-average molecular weight (Mw) information for p-hGH and r-hGH. Known concentrations of each protein have been separated using reversed-phase gradients utilizing acetonitrile with on-line LALLS determination of excess Rayleigh scattering factors. Accurate Mw data has been obtained for both proteins under conventional RP-HPLC gradient elution conditions. SEC data of both hGHs were found to be concentration, mobile phase, and column dependent for the particular analyses. Both medium- and high-resolution SEC-LALLS studies were performed, and all of these determinations further confirmed our RP-HPLC results. On-line LALLs provides certain advantages in identifying aggregates that may be present, even in medium-resolution SEC, where incomplete resolution occurs. The on-line coupling of modern RP-HPLC for biopolymers with LALLS detection represents a major step forward in the ability of bioanalytical chemists to determine the nature (monomer versus higher-order aggregate) of such materials. Other classes of biopolymers should prove suitable for studies with the same RP-HPLC-LALLS-UV approaches.

Determination of biopolymer (protein) molecular weights by gradient elution, reversed-phase high-performance liquid chromatography with low-angle laser light scattering detection

The determination of molecular weights for certain proteins has been performed. This has involved the on-line coupling of gradient elution, reversed-phase high-performance liquid chromatography (RP-HPLC) with low-angle laser light scattering (LALLS) detection. A new 1.5-micron, non-porous, Monosphere RP-C8 column has been used in order to perform fast and conventional RP-HPLC gradients (5-45 min). Traditional specific refractive index increment (dn/dc) and refractive index (n) measurements have been performed in order to derive absolute weight-average molecular weight (Mw) information for ribonuclease A, lysozyme, and bovine serum albumin. Standard mixtures of known concentrations of each protein have been separated using reversed-phase gradients utilizing acetonitrile with on-line LALLS determination of excess Rayleigh scattering factors. Accurate Mw data have been obtained for all three proteins, but only under certain, conventional reversed-phase gradient elution conditions. Between 5-10 min of fast gradient elution, each protein appears to exhibit unusual Mw values, suggestive of aggregate formations. Methods have been developed to define the nature of such aggregates. The on-line coupling of modern RP-HPLC for biopolymers with LALLS represents a major step forward in the ability of bioanalytical chemists to determine the nature (monomer versus aggregate) of such materials. Other classes of biopolymers should prove suitable for studies with the same RP-HPLC-LALLS-UV approaches.

Mechanism of assembly of sea urchin egg tubulin

Tubulin purified from eggs of the sea urchin Strongylocentrotus purpuratus assembles efficiently in vitro to form microtubules at physiological (18 degrees C) and nonphysiological (37 degrees C) temperatures. MAPs, ring oligomers, and high concentrations of nonphysiological solvents are not required for the assembly reaction. At concentrations above 1.2 mg/ml at 18 degrees C and 0.5 mg/ml at 37 degrees C a concentration-dependent overshoot in turbidity and in light scattering at small angles was observed: turbidity and scattering increased rapidly to a peak, then decreased asymptotically toward a steady-state value. Electron microscopic analysis demonstrated that tubulin sheets were prevalent during the initial stages of overshoot assembly, whereas complete microtubules were present at steady state. Qualitative observations of solution birefringence suggested that the polymer became progressively more aligned during assembly. The overshoot cannot be explained by proteolysis or denaturation of tubulin, by depletion of GTP, by a decrease in assembled mass, or by redistribution of polymer lengths. Taken together, the results suggest that changes in the form and/or in the organization of the assembling polymer are responsible for the overshoots in turbidity and in light scattering at small angles. Our results are consistent with models of microtubule assembly that postulate nucleation by tubulin sheets and subsequent folding of the sheets to form mature microtubules.

Resolution of human mercapt- and nonmercaptalbumin by high-performance liquid chromatography

Gel-exclusion high-performance liquid chromatographic (HPLC) analysis of human serum albumin (HSA) on PGP 2000 column (0.10 M sodium phosphate buffer, 0.30 M NaCl, pH 6.86) showed at least two peaks, the principal component corresponding to human mercaptalbumin (HMA) and the second one to human nonmercaptalbumin (HNA). Mechanism for the separation of HMA and HNA might be due to weak resin-HSA interaction. HPLC analysis of bovine plasma albumin (BPA) showed a single peak on PGP 2000 column. The elution volume of HSA was larger than that of BPA, resulting in a clear resolution of HSA and BPA.