Refractive Increment Research Articles

Conformation changes in stiff‐chain poly‐n‐butyl isocyanate. The dilute regime

AbstractA change of conformation of the rod‐like poly‐n‐butyl isocyanate (PBIC), in the dilute regime, was induced by temperature and observed via an abrupt change of index of refraction increment, Δn, and of viscosity, η. PBIC was dissolved in carbon tetrachloride where it exhibits its most extended conformation, with persistence length of 15 nm. The index of refraction increment Δn and viscosity η were measured as a function of temperature in the dilute regime, that is, the concentration range below the threshold concentration c* where intermolecular interactions are negligible. Strikingly, increasing the temperature an abrupt change of Δn was observed, at a given solution concentration. The change of Δn is associated to a change in macromolecular size per the Clausius‐Mossotti relation. At the same solution concentration and temperature range, the shear viscosity also exhibited an abrupt increase Δη. This investigation showed that the conformation transition temperature Ttr is independent of the wavelength utilized to measure Δn, and it is an increasing function of the solution concentration and of PBIC molecular weight. Static light scattering confirmed that the sudden changes of Δn and η are not associated to macromolecular aggregation. Finally, the magnitude of the change of Δn and Δη was gradually reduced when increasing the solution concentration c, that is, when c > c*, therefore suggesting that the conformation transition was screened by intermolecular interactions.

SEDNTERP: a calculation and database utility to aid interpretation of analytical ultracentrifugation and light scattering data.

Proper interpretation of analytical ultracentrifugation (AUC) data for purified proteins requires ancillary information and calculations to account for factors such as buoyancy, buffer viscosity, hydration, and temperature. The utility program SEDNTERP has been widely used by the AUC community for this purpose since its introduction in the mid-1990s. Recent extensions to this program (1) allow it to incorporate data from diffusion as well as AUC experiments; and (2) allow it to calculate the refractive index of buffer solutions (based on the solute composition of the buffer), as well as the specific refractive increment (dn/dc) of proteins based on their composition. These two extensions should be quite useful to the light scattering community as well as helpful for AUC users. The latest version also adds new terms to the partial specific volume calculations which should improve the accuracy, particularly for smaller proteins and peptides, and can calculate the viscosity of buffers containing heavy isotopes of water. It also uses newer, more accurate equations for the density of water and for the hydrodynamic properties of rods and disks. This article will summarize and review all the equations used in the current program version and the scientific background behind them. It will tabulate the values used to calculate the partial specific volume and dn/dc, as well as the polynomial coefficients used in calculating the buffer density and viscosity (most of which have not been previously published), as well as the new ones used in calculating the buffer refractive index.

Optical Properties of Glycated and Non-Glycated Hemoglobin – Raman/Fluorescence Spectroscopy and Refractometry

In this study, the optical properties of glycated (HbA1c) and non-glycated (Hb) hemoglobin are compared using Surface-enhanced Raman spectroscopy (SERS), spectrofluorimetry, and refractometry. Analysis of the spectral shift of SERS spectra showed good discrimination between two hemoglobins indicating differences in their molecular structure. The fluorescence spectra measured at excitation wavelengths of 260, 270, and 280 nm also indicate differences in the molecular structure of these hemoglobins. For the first time refractive index temperature increments were measured for HbA1c in a wide wavelength range in the visible and NIR as –(1.35 ± 0.11) x 10–4 °C–1 and compared with normal hemoglobin (dn/dT = –(1.02 ± 0.12) x 10–4 °C–1). The comparison of temperature RI increments for hemoglobin obtained from the whole blood of healthy volunteers and diabetic patients is also done. The data obtained can serve as a basis for further study of the optical properties of glycated hemoglobin and other glycated proteins.

Dual-wavelength angle-resolved light scattering used in the analysis of particles by scanning flow cytometry

For the first time, a scanning flow cytometer (SFC) was applied for the analysis of individual particles using angle-resolved light scattering at two wavelengths simultaneously. The SFC was equipped with three lasers with wavelengths of 405, 444 and 660 nm. The performance of dual-wavelength angle-resolved light-scattering (DWARLS) flow cytometry was demonstrated by the analysis of polymer beads, spherized red blood cells (RBCs) and blood platelets. The main advantage of dual-wavelength flow cytometry relates to an increment in the precision of the inverse light-scattering problem solution. The solution allows one to retrieve the characteristics of individual particles by measuring the light-scattering profiles of these particles. DWARLS has allowed us to measure diameters and refractive indices (RIs) of polystyrene beads with record precision: a median error of 12 nm and a few thousandths for diameter and RI, respectively. Analysis of spherized RBCs with DWARLS flow cytometry has provided record precision in the sizing of spherized RBCs, with a median error of 16 nm for diameter, and an adequate value of the specific refraction increment for hemoglobin. By means of DWARLS, we have formed a numerical criterion for shape separation of blood platelets, which can be described by an oblate spheroid model to increase the precision of the distribution parameters of the platelet fractions.

Enhanced reflection chiroptical effect of planar anisotropic chiral metamaterials placed on the interface of two media**Project supported by the National Natural Science Foundation of China (Grant No. 11604227).

The strong chiroptical effect is highly desirable and has a wide range of applications in biosensing, chiral catalysis, polarization tuning, and chiral photo detection. In this work, we find a simple method to enhance the reflection circular dichroism (CDR) by placing the planar anisotropic chiral metamaterials (i.e., Z-shaped PACMs) on the interface of two media (i.e., Z-PCMI) with a large refractive index difference. The maximum reflection CDR from the complex system can reach about 0.840 when the refractive index is set as ntop = 4.0 and nbottom = 1.49, which is approximately three times larger than that of placing the Z-shaped PACMs directly on the substrate (i.e., Z-PCMS). While the minimum reflection CDR is 0.157 when the refractive index is set as nbottom = 1.49. So we can get a large available range of reflection CDR from –0.840 to –0.157. Meanwhile, the transmission CDT remains unchanged with the refractive index ntop increment. Our in-depth research indicates that the large reflection CDR is derived from the difference of non-conversion components of the planar anisotropic chiral metamaterials’ reflection matrices. In short, we provide a simple and practical method to enhance the chiroptical effect by changing the refractive index difference between two media without having to design a complex chiral structure.

A possible optical gauge for supervising particle size in nanofluids

We examine theoretically using the ratio between the real and imaginary parts of the effective refractive increment in metallic nanofluids as a particle size monitor. We refer to this ratio as X and show it can be a sensitive gauge of the particles’ size once these are larger than a few nanometers in radius. The parameter X is independent of the particles’ concentration as long as measurements are performed within the independent-scattering regime and it could be a viable candidate for monitoring in real time the growth and generation of nanoparticles during the fabrication processes of nanofluids. We present graphs of X as a function of wavelength for gold, silver and copper nanofluids made of spherical nanoparticles of different radii and suspended in water. We identify the range in wavelengths for which the proposed effective parameter is sensitive to the particle size and analyze whether it is measurable with current instrumentation. We also study the limits in particles’ concentration due to dependent-scattering effects. Effects of particles shape are briefly discussed.

Incorporating Pendent Fullerenes with High Refractive Index Backbones: A Conjunction Effect Method for High Refractive Index Polymers

To achieve high refractive index polymers (HRIPs), we report here the design and synthesis of four fullerene polyesters (P1–P4), based on the conjunction effect from the high refractive index polyester backbones and pendent fullerene side chains. At sodium D line (589 nm), the refractive indices of the fullerene polyesters are all higher than 1.80, the used believed upper limitation of intrinsic organic polymers. To achieve precise pendent fullerene structure, these polyesters were synthesized via condensation polymerization by a fullerene diol with different aromatic diacyl chlorides, where the diacyl chlorides with high molar refraction increment value moiety were selected by molecular tailoring according to Lorentz–Lorenz equation. The fullerene polyesters are characterized by gel permeation chromatography (GPC), ultraviolet–visible (UV–vis) spectroscopy, and the molecular weights are obtained by a quantitative NMR technique with end-group estimation. The formation of fullerene polyesters is also prove...

Primary sequence contribution to the optical function of the eye lens.

The crystallins have relatively high refractive increments compared to other proteins. The Greek key motif in βγ-crystallins was compared with that in other proteins, using predictive analysis from a protein database, to see whether this may be related to the refractive increment. Crystallins with Greek keys motifs have significantly higher refractive increments and more salt bridges than other proteins with Greek key domains. Specific amino acid substitutions: lysine and glutamic acid residues are replaced by arginine and aspartic acid, respectively as refractive increment increases. These trends are also seen in S-crystallins suggesting that the primary sequence of crystallins may be specifically enriched with amino acids with appropriate values of refractive increment to meet optical requirements. Comparison of crystallins from five species: two aquatic and three terrestrial shows that the lysine/arginine correlation with refractive increment occurs in all species investigated. This may be linked with formation and maintenance of salt bridges.

The refractive index of human hemoglobin in the visible range

Because the refractive index of hemoglobin in the visible range is sensitive to the hemoglobin concentration, optical investigations of hemoglobin are important for medical diagnostics and treatment. Direct measurements of the refractive index are, however, challenging; few such measurements have previously been reported, especially in a wide wavelength range. We directly measured the refractive index of human deoxygenated and oxygenated hemoglobin for nine wavelengths between 400 and 700 nm for the hemoglobin concentrations up to 140 g l−1. This paper analyzes the results and suggests a set of model functions to calculate the refractive index depending on the concentration. At all wavelengths, the measured values of the refractive index depended on the concentration linearly. Analyzing the slope of the lines, we determined the specific refraction increments, derived a set of model functions for the refractive index depending on the concentration, and compared our results with those available in the literature. Based on the model functions, we further calculated the refractive index at the physiological concentration within the erythrocytes of 320 g l−1. The results can be used to calculate the refractive index in the visible range for arbitrary concentrations provided that the refractive indices depend on the concentration linearly.

Evaluation of charges on sulfur atom from refraction

Approximate dependence of the refraction of sulfur atom (R D) on its charge (q S) is determined. On its basis R D S values in different sulfur compounds were calculated. Refraction of the unshared electron pair on sulfur atom was found to be equal to 0.96. Refraction increments (Δ = MR Dfound − MR Dcalc) of sulfur-containing saturated heterocycles were calculated (thietanes Δ = −0.28, thiolanes Δ = −0.28, thianes Δ = −0.24) as well as the refraction of deuterium atom bound with carbon (1.10). The values of q S and R D S in sulfoxides (−0.1 and 6.5 respectively), in sulfones (0.72 and 3.73 respectively), q S in dialkyl sulfides (−0.25), and also R D of S4+ ion (0.77) were refined.

Optical Properties of Poly(vinyl-g-dimethylsiloxane) Copolymers

Refractive index is a key criterion in the evaluation of optical polymers. The continuous development of new materials for biomedical applications such as optical fibers or lenses raises questions on the fundamental physical limits of this class of materials. Using the Lorenz-Lorentz equations, we have investigated the theoretical refractive index and specific refractive index increments of some copolymers obtained by radical copolymerization of methyl methacrylate or styrene with allyl methacrylate, followed by the hydrosilation of the resulting copolymers with mono hydro-terminated polydimethylsiloxanes, starting from the refractive increments of the functional groups.

Modeling of the anticancer action for radical derivatives of nitroazoles: quantitative structure-activity relationship (QSAR) study.

A QSAR analysis of the anti-tumor, anti-metastasis and anti-colony formation (for metastatic colonies) activities of eighteen nitroazoles (including metronidazole and hypoxic radiosensitizers RP-170, KU-2285 and sanazole (drug AK-2123)) and their nitro and nitroso anion radical derivatives against melanoma B16 in mice has been performed. The QSAR models were built with the use of the frontal polygon method. This approach has features of different 3D QSAR methodologies and belongs to the group of "indirect" methods. The procedure allows to build robust models with high predictive ability even in series of diverse and conformationally flexible compounds. Key atomic characteristics accompany the geometrical requirements in the analysis of local 3D molecular similarity. By variation of weight coefficients for hydrophobicity, refraction increments, and partial charge it is possible to achieve better quality of QSAR and evaluate the importance of each characteristic for biological activity under consideration. It was found that hydrophobicity, molar refraction and charge characteristics of nitro anion radical derivatives are more significant for interaction with molecular targets than those of the parent compounds and of the nitroso anion radical derivatives. Size and hydrophobic properties of substituents in nitro anion radicals play significant role for ligand-target interaction in the processes of inhibition of metastatic spreading and growth of metastatic colonies by nitroazoles. A scheme of competitive interaction of parent nitroazoles and their anion radicals with a target in organism is suggested. It can be concluded that the step of one-electron reduction of nitroazoles can be important for anticancer activity of these drugs.

Dynamo-optical properties of methylcellulose solutions and the optical anisotropy of glucopyranose ring

Dynamic flow birefringence of methylcellulose (MC) solutions with the degree of substitution 1.68 was studied in water and dimethylsulphoxide in the molecular weight range 20< M×10 −3<400. The comparison of values of reduced birefringence in water in which the refractive increment is high, and in dimethylsulphoxide, in which it is low, gave a quantitative evaluation of the intrinsic optical anisotropy of a statistical segment of MC macromolecules equal to ( α 1− α 2)=+22×10 −24 cm 3, and the anisotropy of unit length equal to β=1.41×10 −17 cm 2. The value of ( α 1− α 2) is discussed and compared with those values obtained previously for other polysaccharides and cellulose derivatives.

Protein standardization II: Dry mass determination procedure for the determination of the dry mass of a pure protein preparation.

A procedure has been developed for the determination of the dry mass of a pure protein preparation dissolved in one electrolyte. The procedure not only renders the concentration (in g/l), but additionally gives the partial specific volume of the protein (in ml/g). The latter is an important parameter for the characterization of a specific protein. Furthermore, the importance of extensive dialysis against one electrolyte is discussed. For the drying of human serum proteins it is clearly shown that KCl is preferred to NaCl due to its stable temperature curve. By observing the parallel fluctuations in the weight of the empty vials during drying, an average correction factor is introduced, which greatly minimizes these changes. The assay principle is discussed from a mathematical as well as from a practical point of view. A detailed procedure is described and the final results for three primary pure proteins (prealbumin, orosomucoid and transferrin) are presented. Finally, important parameters such as the wavelength of maximum absorbance, the absorption coefficient and the specific refractive increment are discussed and values for the three proteins are presented. When these parameters have been established the future determination of concentration and the characterization of pure protein solutions are greatly facilitated. These procedures were important tools for ascribing mass values for prealbumin, orosomucoid and transferrin to the international reference preparation CRM 470.

Optical selection of the preferred solvent of a standard polymer for laser light scattering phenomena investigations

As an application of the interferometric technique we used a Mach–Zehnder interferometer (MZI) to determine both refractive indices (RIs) and RI's increments (dn dc) for a polymer material (standard polystyrene) in different solvents. The solvents we used are benzene, methyl ethyl ketone (MEK) and dimethylformamide (DMF). The polystyrene is solved in each solvent with different concentrations. The light source we have used is the Argon-ion laser (all lines). This work is a step for the determination of the weight average of molecular weight (WAMW) of standard polystyrene and other related scattering parameters.

Molecular weight determination from light scattering and refraction in solutions. A new and coherent theoretical equation

The classical theoretical equation allowing for the determination of the solute's molecular weight ( M 2) from light scattering (LS) and refractive measurements in diluted solutions is reexamined. Serious theoretical and practical defects in its derivation and application are pointed out, especially about the refraction increment dn dc . A new theoretical equation is deduced from a more consistent application of the basic molecular orientation formulae to binary liquid mixtures. More adequate additive molecular properties, the specific mean polarizability \\ ̄ ga M and the specific square of the mean polarizability ( \\ ̄ ga) 2 M instead of \\ ̄ ga and ( \\ ̄ ga) 2 , are considered with respect to refraction and LS, respectively. Inadequate approximations are avoided and a corrected LS intensity expression is used. The new equation is tested upon several typical mixtures of small molecules from measurements either performed in this work or collected in the literature (for LS perpendicular to the incident beam) to ensure objectivity. Examples of measurements in macromolecule solutions from other authors are also analysed. The new equation is suitable for practical applications, because it is based upon easy relative measurements only, and allows for a reliable determination of the M 2 values in macromolecules. The reasons for which the classic equation leads to realistic values, in spite of its theoretical inconsistency, are also explained.

Molecular weight determination from light scattering and refraction in solutions. A new and coherent theoretical equation

The classical theoretical equation allowing for the determination of the solute's molecular weight ( M 2) from light scattering (LS) and refractive measurements in diluted solutions is reexamined. Serious theoretical and practical defects in its derivation and application are pointed out, especially about the refraction increment dn dc . A new theoretical equation is deduced from a more consistent application of the basic molecular orientation formulae to binary liquid mixtures. More adequate additive molecular properties, the specific mean polarizability (ᾱ/ M and the specific square of the mean polarizability ( α ̄ ) 2/M instead of ᾱ and ( α ̄ ) 2 , are considered with respect to refraction and LS, respectively. Inadequate approximations are avoided and a corrected LS intensity expression is used. The new equation is tested upon several typical mixtures of small molecules from measurements either performed in this work or collected in the literature (for LS perpendicular to the incident beam) to ensure objectivity. Examples of measurements in macromolecule solutions from other authors are also analysed. The new equation is suitable for practical applications, because it is based upon easy relative measurements only, and allows for a reliable determination of the M 2 values in macromolecules. The reasons for which the classic equation leads to realistic values, in spite of its theoretical inconsistency, are also explained.

96/00200 Study of hydrogen-donor solvent in the NEDOL process

The refractive indices of orthorhombic and monoclinic crystals of β-lactoglobulin have been measured by microscope interferometry and found to be 1.4536 ± 0.0015 and 1.4765 ± 0.0015 respectively, these values being for a particular orientation of the light electric vector relative to the crystal axes. Combining these values with data4 on the dry weight of protein per unit volume of crystals, the specific refraction increments of orthorhombic and monoclinic crystals are calculated to be 0.00196 ± 0.00003 and 0.00191 ± 0.00002 respectively. The values are in fairly good agreement with that of 0.00182 found8 for dilute solutions of β-lactoglobulin. This conclusion is not altered when the birefringence of the crystals, which has also been measured, is taken into account. Both types of crystal approximate in behaviour to uniaxial crystals with birefringence values of 0.00086 ± 0.00003 and about 0.0036 for orthorhombic and monoclinic crystals respectively.

96/00195 RTDS: A continuous, rapid, thermal synthesis method

The refractive indices of orthorhombic and monoclinic crystals of β-lactoglobulin have been measured by microscope interferometry and found to be 1.4536 ± 0.0015 and 1.4765 ± 0.0015 respectively, these values being for a particular orientation of the light electric vector relative to the crystal axes. Combining these values with data4 on the dry weight of protein per unit volume of crystals, the specific refraction increments of orthorhombic and monoclinic crystals are calculated to be 0.00196 ± 0.00003 and 0.00191 ± 0.00002 respectively. The values are in fairly good agreement with that of 0.00182 found8 for dilute solutions of β-lactoglobulin. This conclusion is not altered when the birefringence of the crystals, which has also been measured, is taken into account. Both types of crystal approximate in behaviour to uniaxial crystals with birefringence values of 0.00086 ± 0.00003 and about 0.0036 for orthorhombic and monoclinic crystals respectively.

95/00197 How to manage the oil price risk

The refractive indices of isoionic crystals of a α-chymotrypsinogen have been measured by microscope interferometry employing two procedures. In principle, the index-values are deduced from measurement of optical path of crystal relative to mother liquor by combining this value with measurements first on an air-bubble3,4 squeezed to the same thickness as the crystal, and second, on the crystal located inside an airbubble. The two principle refractive indices are 1.483 ± 0.003 and 1.486 ± 0.001 by method 1, and 1.480 ± 0.001 and 1.482 ± 0.001 by method 2. Separate measurements of birefringence by the polarizing microscope gave a value of 0.0039 ± 0.00005. The crystals are orthorhombic; it was not possible to measure the third refractive index. Combining these values with data5 on the dry weight of protein per unit volume of crystal, the principal specific refraction increments are on average 0.00192 and 0.00195. These values are in fairly good agreement with the value of 0.00185 for dilute solutions of α-chymotrypsinogen.