Mark-Houwink-Kuhn-Sakurada Research Articles

Inter-laboratory analysis of cereal beta-glucan extracts of nutritional importance: An evaluation of different methods for determining weight-average molecular weight and molecular weight distribution

In an interlaboratory study we compare different methods to determine the weight-average molecular weight (Mw) and molecular weight distribution of six cereal beta-glucan isolates of nutritional importance. Size-exclusion chromatography (SEC) with multi-angle light scattering (MALS), capillary viscometry, sedimentation velocity analytical ultracentrifugation and one asymmetric flow field-flow fractionation (AF4)-MALS method all yielded similar Mw values for mostly individual chains of dissolved beta-glucan molecules. SEC with post-column calcofluor detection underestimated the Mw of beta-glucan >500 × 103 g/mol. The beta-glucan molecules analysed by these methods were primarily in a random coil conformation as evidenced from individual Mark-Houwink-Kuhn-Sakurada (MHKS) scaling coefficients between 0.5 and 0.6 and Wales-Van Holde ratios between 1.4 and 1.7. In contrast, a second AF4-MALS method yielded much larger Mw values for these same samples indicating the presence and detection of beta-glucan aggregates. Storage of the six beta-glucan solutions in the dark at 4 °C for 4 years revealed them to be stable. This suggests an absence of storage-induced irreversible aggregation phenomena or chain-scission. Shear forces in SEC and the viscometer capillary and hydrostatic pressure in analytical ultracentrifugation probably led to the reversable dissociation of beta-glucan aggregates into molecularly dissolved species. Thus, all these methods yield true weight-average molecular weight values not biased by the presence of aggregates as was the case in one of the AF4 based methods employed.

Conformation of the von Willebrand factor/factor VIII complex in quasi-static flow

Von Willebrand factor (VWF) is a plasma glycoprotein that circulates noncovalently bound to blood coagulation factor VIII (fVIII). VWF is a population of multimers composed of a variable number of ∼280 kDa monomers that is activated in shear flow to bind collagen and platelet glycoprotein Ibα. Electron microscopy, atomic force microscopy, small-angle neutron scattering, and theoretical studies have produced a model in which the conformation of VWF under static conditions is a compact, globular “ball-of-yarn,” implying strong, attractive forces between monomers. We performed sedimentation velocity (SV) analytical ultracentrifugation measurements on unfractionated VWF/fVIII complexes. There was a 20% per mg/ml decrease in the weight-average sedimentation coefficient, sw, in contrast to the ∼1% per mg/ml decrease observed for compact globular proteins. SV and dynamic light scattering measurements were performed on VWF/fVIII complexes fractionated by size-exclusion chromatography to obtain sw values and z-average diffusion coefficients, Dz. Molecular weights estimated using these values in the Svedberg equation ranged from 1.7 to 4.1 MDa. Frictional ratios calculated from Dz and molecular weights ranged from 2.9 to 3.4, in contrast to values of 1.1–1.3 observed for globular proteins. The Mark–Houwink–Kuhn–Sakurada scaling relationships between sw, Dz and molecular weight, and , yielded estimates of 0.51 and –0.49 for as and aD, respectively, consistent with a random coil, in contrast to the as value of 0.65 observed for globular proteins. These results indicate that interactions between monomers are weak or nonexistent and that activation of VWF is intramonomeric.

Characterization of Amphiphilic Cobaltocenium Copolymers via Size Exclusion Chromatography with Online Laser-Light Scattering and Viscometric Detectors

A sample of cobaltocenium copolymer (Copolym) obtained by a controlled polymerization method was characterized by a multi-detector size exclusion chromatography (MD-SEC) method eluted by various pure and mixed mobile phases. The value of number average molecular weight (), estimated by MD-SEC using the above elutes, was comparable with the ones obtained from the SEC standard calibration curve and estimation by the monomer conversion method. The solution properties of the Copolym were studied based on the Mark-Houwink-Kuhn-Sakurada (MH) relationship where the values of the MH exponent of the Copolym in the above solutions were within the values corresponding to a flexible random coil system. The unperturbed end-to-end dimensions of the Copolym were obtained based on the Stockmayer-Fixman extrapolation method. It was found that the degree of flexibility of the Copolym was higher than that of C-C backbone polymers such as atactic polypropylene, and in the range of poly(acrylic acid), which is suggested to be due to the short-range interference effect of the ionic side chains and solvent molecules on the degree of free rotation of the copolymer.

Hydrodynamic Compatibility of Hyaluronic Acid and Tamarind Seed Polysaccharide as Ocular Mucin Supplements.

Hyaluronic acid (HA) has been commonly used in eyedrop formulations due to its viscous lubricating properties even at low concentration, acting as a supplement for ocular mucin (principally MUC5AC) which diminishes with aging in a condition known as Keratoconjunctivitis sicca or “dry eye”. A difficulty has been its short residence time on ocular surfaces due to ocular clearance mechanisms which remove the polysaccharide almost immediately. To prolong its retention time, tamarind seed gum polysaccharide (TSP) is mixed as a helper biopolymer with HA. Here we look at the hydrodynamic characteristics of HA and TSP (weight average molar mass Mw and viscosity ) and then explore the compatibility of these polymers, including the possibility of potentially harmful aggregation effects. The research is based on a novel combination of three methods: sedimentation velocity in the analytical ultracentrifuge (SV-AUC), size-exclusion chromatography coupled to multiangle light scattering (SEC-MALS) and capillary viscometry. HA and TSP were found to have ) kg/mol and ) kg/mol respectively, and and ml/g, respectively. The structure of HA ranges from a rodlike molecule at lower molar masses changing to a random coil for Mw > 800 kg/mol, based on the Mark–Houwink–Kuhn–Sakurada (MHKS) coefficient. TSP, by contrast, is a random coil across the range of molar masses. For the mixed HA-TSP systems, SEC-MALS indicates a weak interaction. However, sedimentation coefficient (s) distributions obtained from SV-AUC measurements together with intrinsic viscosity demonstrated no evidence of any significant aggregation phenomenon, reassuring in terms of eye-drop formulation technology involving these substances.

Intrinsic viscosity of poly(N-vinylcaprolactam) with varying the architecture

Five CTA’s xanthate-type were synthesized and characterized and used in the controlled polymerization of N-vinylcaprolactam (NVCL) via reversible addition-fragmentation chain transfer (RAFT) polymerization. The CTA’s are linear (bifunctional), with three arms (from cholic acid or trimethylolpropane tris[poly(propylene glycol), amine terminated] ether), with six arms (from DPERT) and nine arms (from glycerol functionalized with cholic acid). Three of the synthesized CTA’s are reported for the first time. The intrinsic viscosity [η] and the Mark-Houwink-Kuhn-Sakurada (MHKS) constants were estimated in ethanol at 35 °C for each PNVCL polymer group. The η values for star-shaped polymers were lower compared with the linear analogues with similar molecular weights. Interestingly, the intrinsic viscosity values of two groups of polymers having three arms shown a noticeable difference, probably due to starting material used to prepare the CTA (rigid or flexible core). The MHKS exponents ranged from 0.68 to 0.82 indicates that all polymers behave as a flexible expanded conformation. The hydrodynamic diameter (Dh) of the polymers in ethanol solution was measured using DLS. The Dh values decreased significantly with the molecular weight (Mn) decreasing. The Dh values of linear polymers were higher compared with the stars one with similar molecular weights. Star-shaped PNVCL polymers containing cholane skeleton shown remarkable lower viscosity values.

Characterization of Recovered Polyvinylchloride by Size Exclusion Chromatography and Triple Detectors Technique

Polyvinyl chloride (PVC) is an indispensable compound that accounts for 66% of the water distribution infrastructure and 75% of sanitary sewer pipe applications in the U.S.A. In this study PVC resin was recovered by solvent extraction from a postconsumer PVC pipe. The recovered PVC (PVC-R) was characterized by a multi-detector size exclusion chromatography system eluted with tetrahydrofuran (THF) at 30 °C. The values of the Mark-Houwink-Kuhn-Sakurada (MH) parameters of the PVC-R were obtained by averaging three replicable experiments and the results were comparable with the reported values of pure PVC. The Stockmayer-Fixman plot of the PVC-R in THF had a curved shape which is due to the notorious tendency of the PVC molecules to remain partly associated in supermolecular aggregates even if the PVC is dissolved in a good solvent. As a results, the unperturbed molecular dimension, of the PVC-R was dependent on a function of the excluded volume, z, where the z2 coefficient was not zero. The obtained value of the of PVC-R, having a = 87 kDa and = 1.41, was 8.19 × 10−9 (cgs), comparable with the reported value for pure industrial PVCs in THF, 6.4 kDa < < 650 kDa at 25 °C, 8.17 × 10−9 (cgs) and in benzyl alcohol, an ideal solvent, at 155.4 °C, 40 kDa < < 350 kDa, 8.20 × 10−9 (cgs). The comparison of the results showed that the PVC-R had similar characteristics to the industrial PVC reported in the published literature, and hence can be reused as a resin for the manufacturing of PVC commodities.

Physicochemical Parameters for Brea Gum Exudate from Cercidium praecox Tree

Brea gum (BG) is a hydrocolloid obtained as an exudate from the Cercidium praecox tree. The physicochemical properties of brea gum are similar to those of the arabic gum and, in many cases, the former can replace the latter. The brea gum was incorporated in 2013 into the Argentine Food Code because of its ancestral background and its current food uses. Brea gum could be also used as additive or excipient for pharmacological formulations. This work reports intrinsic viscosity, coil overlap, and Mark–Houwink–Kuhn–Sakurada (MHKS) parameters of BG solutions. Partially hydrolyzed BG solution was analyzed using intrinsic viscosity measurements, dynamic light scattering and size-exclusion chromatography (SEC). The MHKS parameters, a and k, were determined for BG at 25 °C, with values of 0.4133 and 0.1347 cm3 g−1, respectively. The viscometric molecular weight of BG was 1890 kg mol−1. The hydrodynamic parameters of BG were indicative of a hyperbranched structure and spherical conformation. The knowledge obtained on the physicochemical properties of brea gum favors its use in food and pharmaceutical applications.

Investigating the propagation kinetics of a novel class of nitrogen-containing methacrylates via PLP-SEC

The Mark–Houwink–Kuhn–Sakurada parameters as well as Arrhenius parameters of the propagation rate coefficient for a new group of nitrogen-containing methacrylates were determined via triple detector SEC and pulsed laser polymerization–size exclusion chromatography, respectively.

Facile Synthesis of Well-Defined MDMO-PPV Containing (Tri)Block—Copolymers via Controlled Radical Polymerization and CuAAC Conjugation

A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene) (PPV) materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA) concentration and reaction temperature. For the chain transfer constant, a negative activation energy of −12.8 kJ·mol−1 was deduced. Good control over molecular weight is achieved for both the sulfinyl and the dithiocarbamate route (DTC). PPVs with molecular weights ranging from thousands to ten thousands g·mol−1 were obtained. To allow for a meaningful analysis of the CTA influence, Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were determined for conjugated MDMO-PPV ([2-methoxy-5-(3',7'-dimethyloctyloxy)]-1,4-phenylenevinylene) to α = 0.809 and k = 0.00002 mL·g−1. Further, high-endgroup fidelity of the CBr4-derived PPVs was proven via chain extension experiments. MDMO-PPV-Br was successfully used as macroinitiator in atom transfer radical polymerization (ATRP) with acrylates and styrene. A more polar PPV counterpart was chain extended by an acrylate in single-electron transfer living radical polymerization (SET-LRP). In a last step, copper-catalyzed azide alkyne cycloaddition (CuAAC) was used to synthesize block copolymer structures. Direct azidation followed by macromolecular conjugation showed only partial success, while the successive chain extension via ATRP followed by CuAAC afforded triblock copolymers of the poly(p-phenylene vinylene)-block-poly(tert-butyl acrylate)-block-poly(ethylene glycol) (PPV-b-PtBuA-b-PEG).

Hydrodynamic characterisation of chitosan and its interaction with two polyanions: DNA and xanthan.

Chitosan, a soluble polycationic derivative of insoluble chitin, has been widely considered for use in the food, cosmetic and pharmaceutical industries. 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%) were compared with regards to (i) weight-average molecular weight (Mw); (ii) sedimentation coefficient (s(o)(20,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. Polydisperse distributions were seen from sedimentation coefficient distributions and elution profiles from SEC-MALS. Mw values obtained for each sample by sedimentation equilibrium measurements 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. 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 then 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.

Thermal degradation and stability of sodium hyaluronate in solid state

The kinetics and mechanism of depolymerisation of solid sodium hyaluronate at elevated temperatures and various pH have been investigated. Depolymerisation was found to be governed by random chain scission. The activation energy at neutral pH was found to be 127kJ/mol. The solid polymer was most stable at neutral pH. Results suggest the depolymerisation mechanism in solid- and solution state to be the same. Correlation of log intrinsic viscosity to log weight-average molecular weight was investigated to ensure high quality data for polymer size. Based on more than sixty hyaluronate samples spanning from 0.4 to 2.3MDa, it was concluded that a second order polynomial regression gives a better fit than the linear regression offered by classical Mark–Houwink–Kuhn–Sakurada description. This finding was supported by literature data and could be expanded to other simple, well behaving linear polymers, such as polystyrene and polyethylene.

Dilute solution properties of carboxymethyl celluloses of various molecular weights and degrees of substitution

The intrinsic viscosities of six carboxymethyl celluloses (CMC) of different degrees of substitution, molecular weights, and molecular weight distributions (MWDs) were measured as a function of pH, ionic strength, and temperature. The molecular weights and MWDs were determined by analytical ultracentrifugation. It was demonstrated that the raw viscosity data could be represented by the Fedors equation allowing for accurate determination of the intrinsic viscosity. Ionic strength, rather than pH or temperature had the strongest effect on the conformation of CMC. An estimate of the Mark–Houwink–Kuhn–Sakurada exponent (α=0.83) and calculations of chain flexibility and expansion factors indicated that CMC has semi-flexible, randomly coiling chains in solution with persistence lengths on the order of 8.8–24.5nm in distilled water and 11.3–14.8nm in 0.01mol/L sodium chloride. It was also found that the lowest molecular weight CMC was most flexible among the tested samples.

An analytical ultracentrifugation based study on the conformation of lambda carrageenan in aqueous solution

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=340,000-870,000g/mol. The origin of the larger sedimentation coefficient component appearing at the higher concentrations is considered.

Mark–Houwink Parameters for the Universal Calibration of Acrylate, Methacrylate and Vinyl Acetate Polymers Determined by Online Size‐Exclusion Chromatography—Mass Spectrometry

AbstractSize exclusion chromatography coupled online to electrospray ionization mass spectrometry (SEC/ESI‐MS) is employed to establish universal calibration (UC) relationships for a number of linear poly(alkyl acrylates) and poly(alkyl methacrylates) as well as poly(vinyl acetate) synthesized via radical chain transfer polymerization. It is demonstrated that in the analyzed molecular weight range, Mark–Houwink–Kuhn–Sakurada (MHKS) coefficients can be successfully determined in relation to values of pMMA. The agreement between the UC model using mass spectrometry‐derived MHKS coefficients and the measured data was generally better than 10%. The MHKS values reported herein are expected to remain valid up to 20 kDa. A comparison with the outcome of UC using literature reported MHKS coefficients determined by intrinsic viscosity—molecular weight (IV‐MW) measurements is provided. Errors of more than 30% can result when these literature values are employed in the low molecular weight range ( &lt; 20 kDa). Use of MHKS coefficients derived from IV‐MW measurements in UC is, therefore, strongly discouraged at molecular weights below 20 kDa.magnified image

Macromolecular conformation of chitosan in dilute solution: A new global hydrodynamic approach

Chitosans of different molar masses were prepared by storing freshly prepared samples for up to 6 months at either 4, 25 or 40 °C. The weight-average molar masses, M w and intrinsic viscosities, [ η] were then measured using size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS) and a “rolling ball” viscometer, respectively. The solution conformation of chitosan was then estimated from: (a) the Mark–Houwink–Kuhn–Sakurada (MHKS) power law relationship [ η] = kM w a and (b) the persistence length, L p calculated from a new approach based on equivalent radii [Ortega, A., & Garcia de la Torre, J. (2007). Equivalent radii and ratios of radii from solution properties as indicators of macromolecular conformation, shape, and flexibility. Biomacromolecules, 8, 2464–2475]. Both the MHKS power law exponent ( a = 0.95 ± 0.01) and the persistence length ( L p = 16 ± 2 nm) are consistent with a semi-flexible rod type (or stiff coil) conformation for all 33 chitosans studied. A semi-flexible rod conformation was further supported by the Wales–van Holde ratio, the translational frictional ratio and sedimentation conformation zoning.

Depolymerization kinetics of di(4‐tert‐butyl cyclohexyl) itaconate and Mark‐Houwink‐Kuhn‐Sakurada parameters of di(4‐tert‐butyl cyclohexyl) itaconate and di‐n‐butyl itaconate

AbstractMultipulse pulsed laser polymerization coupled with size exclusion chromatography (MP‐PLP‐SEC) has been employed to study the depropagation kinetics of the sterically demanding 1,1‐disubstituted monomer di(4‐tert‐butylcyclohexyl) itaconate (DBCHI). The effective rate coefficient of propagation, k, was determined for a solution of monomer in anisole at concentrations, c, 0.72 and 0.88 mol L−1 in the temperature range 0 ≤ T ≤ 70 °C. The resulting Arrhenius plot (i.e., ln k vs. 1/RT) displayed a subtle curvature in the higher temperature regime and was analyzed in the linear part to yield the activation parameters of the forward reaction. In the temperature region where no depropagation was observed (0 ≤ T ≤ 50 °C), the following Arrhenius parameters for kp were obtained (DBCHI, Ep = 35.5 ± 1.2 kJ mol−1, ln Ap = 14.8 ± 0.5 L mol−1 s−1). In addition, the k data was analyzed in the depropagatation regime for DBCHI, resulting in estimates for the associated entropy (−ΔS = 150 J mol−1 K−1) of polymerization. With decreasing monomer concentration and increasing temperature, it is increasingly more difficult to obtain well structured molecular weight distributions. The Mark Houwink Kuhn Sakurada (MHKS) parameters for di‐n‐butyl itaconate (DBI) and DBCHI were determined using a triple detection GPC system incorporating online viscometry and multi‐angle laser light scattering in THF at 40 °C. The MHKS for poly‐DBI and poly‐DBCHI in the molecular weight range 35–256 kDa and 36.5–250 kDa, respectively, were determined to be KDBI = 24.9 (103 mL g−1), αDBI = 0.58, KDBCHI = 12.8 (103 mL g−1), and αDBCHI = 0.63. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1931–1943, 2007

A correlation of the limiting viscosity number, molecular mass and composition of statistical linear styrene–methyl methacrylate copolymers

Statistical copolymers of styrene and methyl methacrylate of different compositions were synthesized by the radical solution copolymerization in a batch isothermal reactor. Copolymers were characterized by the size exclusion chromatography (SEC), elemental analysis and dilute solution viscometry. Experimental limiting viscosity numbers were described by the Mark–Houwink–Kuhn–Sakurada correlation as the function of the molar mass and by the Mendelson correlation as the function of both the molar mass and copolymer composition. A new correlation of the intrinsic viscosity number, molar mass and composition was developed, based on semiempirical considerations. The correlation takes into consideration all the effects which affect the dimensions of random linear copolymer coils in solvents. The new equation was found to be superior to the Mendelson’s one in correlating the experimentally obtained intrinsic viscosities.

A physico-chemical comparative study on extracellular carbohydrate polymers from five desert algae

Hydrodynamic properties of five newly isolated algal extracellular polysaccharides with putative adhesive properties are described, using a combination of size exclusion chromatography, total or ‘multi-angle’ laser light scattering and analytical ultracentrifugation. The respective polysaccharides had been extracted from four filamentous cyanobacteria: Microcoleus vaginatus, Scytonema javanicum, Phormidium tenue and Nostoc sp. and a coccoid single-cell green algae Desmococcus olivaceus that had been separated from desert algal crusts of the Chinese Tegger Desert. SEC/MALLS experiments showed that the saccharides had diverse weight average molecular weights ranging from 4000 to 250,000 g/mol and all five showed either bi-modal or tri-modal molecular weight distribution profiles. Use of the Mark–Houwink–Kuhn–Sakurada (MHKS) scaling relationship between sedimentation coefficient and (weight average) molecular weight for the five samples, assuming a homologous conformation series revealed an MHKS b exponent of (0.33±0.04), suggesting a conformation between that of a stiff rod ( b∼0.18) and a random coil ( b∼0.4–0.5), i.e. a ‘ flexible rod’ or ‘stiff coil’.

Polystyrene-equivalent molecular weight versus true molecular weight in size-exclusion chromatography

The evaluation of the size-exclusion chromatography (SEC) concentration elution curves by means of a calibration dependence obtained in a given SEC set for a polymer different from the polymer to be analyzed results in an error in the determination of both molecular weight and molecular-weight distribution (MWD). The problem is analyzed assuming the validity of the universal-calibration concept. The differences between the true and apparent values of molecular weight, MWD and M w/ M n depend on and are expressed in terms of the parameters of the Mark–Houwink–Kuhn–Sakurada equation, describing the molecular-weight dependence of intrinsic viscosity, for the polymer to be analyzed and the polymer used for calibration. The differences in molecular weight and the M w/ M n ratio are typically tens of percent and, in extreme cases, can amount up to a factor of three for molecular weight and a factor of two for the M w/ M n ratio.

Treatments of intrinsic viscosity and glass transition temperature data of poly(2,6-dimethylphenylmethacrylate)

A useful relationship, ln( T g)=ln( T g,∞)− m[ η] − ν , between intrinsic viscosity and glass transition temperature for a series of homologous polymers was obtained by combining the Mark–Houwink–Kuhn–Sakurada (MHKS) relation for intrinsic viscosity and molecular mass, and the Fox–Flory equation for glass transition temperature and number-average molecular mass. This relationship was applied to poly(2,6-dimethylphenylmethacrylate) (PDMPh) in a variety of solvents (ideal to good) such as toluene, tetrahydrofuran/water, tetrahydrofuran, and chlorobenzene systems. The parameter α estimated by this procedure in toluene, tetrahydrofuran/water, tetrahydrofuran, and chlorobenzene systems are 0.50 6, 0.51 1, 0.56 7, and 0.67 3, respectively which are in agreement with those of Mark–Houwink–Kuhn–Sakurada values by less than 5% differences. The T g,∞ quantity estimated from this equation also is within the standard deviation of that obtained from the Fox–Flory method. The m quantity is increasing as the thermodynamic quality of the solvent improves, therefore, m may be considered as an indicator of coil conformations in a given solvent.