Change In Optical Rotation Research Articles

On the origin of optical rotation changes during the κ-carrageenan disorder-to-order transition

It is well established that solutions of both polymeric and oligomeric κ-carrageenan exhibit a clear change in optical rotation (OR), in concert with gel-formation for polymeric samples, as the solution is cooled in the presence of certain ions. The canonical interpretation – that this OR change reflects a ‘coil-to-helix transition’ in single chains – has seemed unambiguous; the solution- or ‘disordered’-state structure has ubiquitously been assumed to be a ‘random coil’, and the helical nature of carrageenan in the solid-state was settled in the 1970s. However, recent work has found that κ-carrageenan contains substantial helical secondary structure elements in the disordered-state, raising doubts over the validity of this interpretation. To investigate the origins of the OR, density-functional theory calculations were conducted using atomic models of κ-carrageenan oligomers. Changes were found to occur in the predicted OR owing purely to dimerization of chains, and - together with the additional effects of slight changes in conformation that occur when separated helical chains form double-helices - the predicted OR changes are qualitatively consistent with experimental results. These findings contribute to a growing body of evidence that the carrageenan ‘disorder-to-order’ transition is a cooperative process, and have further implications for the interpretation of OR changes demonstrated by macromolecules in general.

Chiral Charge Carriers Chiralions for Polyaniline Examined with Optical Rotation Spectroelectrochemistry

In this study, the optical active polyaniline film was examined with optical rotatory dispersion (ORD) through change in potential with spectroelectrochemical method. Polyaniline is one of the representative conducting polymers. Preparation of polyaniline is convenient because synthesis of polyaniline can perform in water medium. Conducting polymers shows electrochromism via change in the electronic state upon electrochemical redox process. Polyaniline forms various electronic states such as emeraldine base, emeraldine salt, and pernigraniline. This change allows to color tuning through electrochemical method. Further, optically active polyanilines have been synthesized in the presence of (+) or (-)-camphorsulfonic acid (CSA) by electrochemical polymerization or chemical polymerization with ammonium persulfate (oxidizing agent). Both electrochemical method and chemical method produce polyaniline through radical polymerization process. Polyaniline emeraldine salt as prepared form of polyaniline is doped with CSA, showing optical activity in the circular dichroism. In this research, we carried out to synthesis of polyaniline in the presence of optically active CSA, according to previously reported method (by Wallace et al). Here, we have found that the polyaniline thus prepared showed optically active electrochromism via electrochemical redox process in circular dichroism spectroscopy measurements. In our previous study, we calculated the ORD spectra for the polymer by Kramars - Kronich (K-K) conversion from circular dichromism. In the present research, we successfully obtained experimental data of optical rotation-spectroelectrochemical result, as a first example of optical rotation control of natural optical activity for conjugated polymers based on electrochemical method. In the case of low potential for the polymer in the electrochemical redox process, the polymer shows intense optical rotation at visible wavelength range. On the other hands, higher potential at around 1 V affords to give doping process for the polymer, resulting generation of polaron as charge carrier, which shows optical activity at near infrared region. We referred this optical charge carrier as “chiral charge carrier chiralions”. The electrochemical oxidation equivalents to electrochemical doping from the polymer. In other words, electrochemical oxidation gives electrochemical doping which results change in degree of optical rotation for the polymer. The control of optical ration for materials can be driven by magnetic field (Faraday rotation), and electric field (Kerr rotation). We propose a new phenomenon as ‘‘electrochemical optical rotation’’. The electro-conductivity of the polymer is measured with four-probe method. The polymer which is electronic doped state with (+)-CSA as electric dopant for production of radical cation (polarons) or dication (bipolarons) as charge carriers and chiral inducer for twisting main-chain. The polymer film was synthesized as followed. First, electrochemical polymerization of aniline as a monomer was carried out in excessive optically active (+)-CSA with three electrode system consisting of working electrode (indium-tin oxide coated glass), counter electrode (platinum wire), and reference electrode (SCE) in water. The polymerization reaction is rapidly progressed with formation of polymer thin film onto the counter electrode. The polymer was washed with excess amount of water, acetone. The electroactive polymer film was thus deposited on the electrode was used for optical activity measurements. Cyclic voltammetry (CV) measurements were carried out for the resultant polymer (monomer free) deposited on to the ITO coated glass electrode. The CV results with change in scan rate from 10-100 mV/s indicates electroactive. Increase of scan rate increases current density for the polymer due to increase of diffusion of ion in the electrolyte solution. Oxidation signals of the polymer are observed due to change in electronic state of the polymer. Corresponding reduction signals against oxidation process are observed, indicating reversible redox activity for the polymer. ORD measurement reveled that the polymer film thus obtained is optically active. The polyaniline can be formed helical structure due to doping of optically active CSA. We carried out in-situ ORD measurement with potential change, evaluating electrochemical driven change in optical rotation. Chemical structure of the double layer polymer is examined with Fourie transform infrared optical absorption spectroscopy measurements which reveled this polymer is polyaniline, and CSA as a dopant. Ultra-violet optical absorption measurements for the polymer film indicates intense and wide range absorptions from invisible to infrared range as charge carriers the delocalized along the main-chain, indicating the polymers are conductive materials. The advantages of the polymer film are formation of self-standing redox activity, tuning of optical activity and color coordination. This paper reports novel function of control optical rotation with electrochemical method examined with spectroelectrochemistry. This concept can be a first example as optical rotation effect of electro-optically active conducting polymers. This paper reports the charge carries of helical polyaniline as chiralions can tune via electrochemical method.

Optical Activity of Triton X-100 Micelles in Aqueous Solutions

Polarimetry is used to study the optical activity of colloidal aqueous solutions of nonionic surfactant (NS) Triton X-100. It is found that these solutions rotate the plane of polarization to the right. It is shown that a change in the concentration of nonionic surfactants alters the structure of micelles. It is found that the transition to a continuous hexagonal mesophase is accompanied by a stepwise change in optical rotation.

Electro-Optically Active Polyaniline-Polypyrrole Double Layer Polymer Semiconducting Composite

Optically active polyanilines have been synthesized in the presence of chiral camphorsulfonic acid (CSA) by electrochemical polymerization in water medium. Polyaniline forms various electronic states such as emeraldine base, emeraldine salt, and pernigraniline. As prepared polyaniline in the presence of (+)-CSA is called as emeraldine salt. In this case, (+)-CSA shows two functions as 1) electro-dopant and 2) chiral inducer for the polyaniline, producing radical cation (polarons) and diction (bipolarons) as charge carriers and one-handed helically twist for the main chain. In the present research, we succeeded to obtain double layer conductive polymer film consisting of polyaniline and polypyrrole with electrochemical method. Fig. 1 shows the structure of the double layer polymer film. The optical activity of the polymer film was examined with optical rotatory dispersion (ORD). The double layer supports strength of the polymer film form. Electrical conductivity of the polymer film is ca. 0.25 S/cm evaluated with four-probe method. We carried out synthesis of a single layer polyaniline with (+)-CSA with potentiostat with three electrode system, Pt counter electrode saturated calomel electrode (SCE) as reference, and the polymer as working electrode. Fig.2 shows the results. Five scans afford to produce green polymer film deposited on the indium-tin oxide (ITO) coated grass electrode. The polymer shows redox activity conformed with cyclic voltammetry (CV). Increase of scan rate provides increase of current density in the electrochemical measurement because of increase of diffusion of ionic species in the electrolyte solution. The single layer polyaniline film displays electrochemical driven change in optical rotation evaluated with in-situ ORD/CV. The double layer polymer film was synthesized as followed. First, electrochemical polymerization of aniline as a monomer was carried out in concentrated optically active (+)-CSA with two electrode system. An application of electric filed (3.0 V) between electrodes in the electrolyte solution was carried out. The electrochemical polymerization reaction is rapidly progressed for formation of polymer thin film onto the anode side. Continuously, pyrrole as another kind of monomer was added to the electrolyte solution. The sequential electrochemical polymerization process affords to yield polypyrrole layer deposited onto the polyaniline layer. ORD measurement revealed that the double layer polymer film thus obtained is optically active. The bottom layer of polyaniline can be formed helical structure due to combination with optically active (+)-CSA. The top layer of polypyrrole may also form helical structure with aid of (+)-CSA as chiral doping agent. Chemical structure of the double layer polymer (composite) is examined with Fourie transform infrared optical absorption spectroscopy measurements. This result indicates that the polymer composite consists of polyaniline, polypyrrole, and CSA. The composite shows intense and wide range optical absorptions from invisible to infrared range due to delocalized charge carriers along the main-chain. The advantages of double conductive polymer film are redox activity, tunable optical activity, and color coordination. Top layer of polypyrrole is black in color with no polish and good redox character, and polyaniline as the bottom layer displays electro-optical activity. This paper reports convenient method for preparation of double layer system with electrochemical method. Further variation can be expected using different type of monomers for construction of multi-layer conductive polymer composite. This concept can be a first example as an electro-optically active conducting polymer composite. Figure 1

Electro-Optically Active Polyaniline-Polypyrrole Double Layer Polymer Semiconducting Composite

Double layer conducting polymer composite consisting of polyaniline and polypyrrole was prepared with electrochemical polymerization in water medium. Prior to synthesize of double layer polymer film, preparation of monolayer of polyaniline doped with optically active camphor sulfonic acid was carried out to examine optical property of the mono-layer polyaniline. The polymer shows electrochemical driven change in optical rotation. Cyclic voltammetry measurements revealed that electro-activity of the polymer. These results demonstrated that the polymer thus obtained has electro-optically active. Next, sequential double step polymerization of aniline and pyrrole successfully prepared electro-optically active conductive polymer composite. Infrared absorption spectroscopy measurements evaluated that the chemical structure of the double layer composite. The composite shows optical rotation.

Oxidative and non‐oxidative degradation pathways of L‐ascorbic acid

SummaryL‐Ascorbic acid (AA) is an essential component for organisms and is responsible for various functions in the human body. Its structure is in a way that suffering significant structural changes during storage. Herein, the stability of L‐ascorbic acid aqueous solution at various thermal (25 and 90 °C ± 2) and atmospheric oxygen or argon was monitored by optical rotation changes as a function of time intervals. Under oxygen, specific optical rotation [α] of the solution was decreased from + 22.0 to + 2.0 after 32 days and under argon + 11.5 after 9 months at 25 °C. The loss of [α] increased at 90 °C under both oxygen and argon atmospheres. Subsequently, the obtained reaction mixtures were evaporated to dryness and analysed by FT‐IR, 1H‐NMR and GC‐MS techniques. Results of these analyses indicate that AA was decomposed to a complex mixture of reaction products.

Anomalously rotary polarization discovered in homochiral organic ferroelectrics.

Molecular ferroelectrics are currently an active research topic in the field of ferroelectric materials. As complements or alternatives of conventional inorganic ferroelectrics, they have been designed to realize various novel properties, ranging from multiferroicity and semiconductive ferroelectricity to ferroelectric photovoltaics and ferroelectric luminescence. The stabilizing of ferroelectricity in various systems is owing to the flexible tailorability of the organic components. Here we describe the construction of optically active molecular ferroelectrics by introducing homochiral molecules as polar groups. We find that the ferroelectricity in (R)-(−)-3-hydroxlyquinuclidinium halides is due to the alignment of the homochiral molecules. We observe that both the specific optical rotation and rotatory direction change upon paraelectric-ferroelectric phase transitions, due to the existence of two origins from the molecular chirality and spatial arrangement, whose contributions vary upon the transitions. The optical rotation switching effect may find applications in electro-optical elements.

FORMULATION AND DEVELOPMENT OF S-(-)-AMLODIPINE BESYLATE TABLETS TO IMPROVE THE DISSOLUTION PROFILE

The object ive of the present study was to develop a tablet formulat ion of S- ( - ) - amlodipine besylate chiral separation drug, L-Type Calcium channel blocker for better management of hypertension and also suitable in the treatment diabetic hypertension patients, while reducing or avoiding undesirable adverse effects, such as headache and edema, dizziness, flushing, palpitation, fatigue, nausea, abdominal pain and somnolence which are often associated with administration of a racemic mixture of amlodipine. The R (+) enantiomer lacks or has a lower level of antihypertensive activity. I n the present study S- ( - ) - amlodipine besylate 5.0 mg tablets have been formulated and developed using wet granulation and direct compression techniques respectively, to provide a safe, highly effective method for treating severe hypertension while reducing undesirable adverse effects. Pre and post formulation parameters were studied for the formulated batches. The study was also carried out to design a suitable dissolution medium for S-(-)- amlodipine besylate. S-(-)- amlodipine besylate had maximum solubility in pH 1.2 and thus the most suitable media for S-(-)- amlodipine besylate dissolution studies. The dissolution profile of the formulated formulation was compared with the marketed preparation. The results indicated improved dissolution profile of formulation (WMS3). The RSD below 2% indicated insignificant batch-to-batch variation. The accelerated stability study of the optimized formulation was performed as per the ICH guidelines. The results indicated no change in optical rotation of S-(-)- amlodipine besylate.

Detection of Thermal Denaturation and Renaturation of Collagen: Optical Characteristics Using Angular Displacement-Enhanced Heterodyne Polarimeter

An angular displacement-enhanced heterodyne polarimeter has been employed to investigate the optical properties and thermal denaturation of collagen. In the angular measurement, the phase change of the collagen at different temperatures can be enhanced using a null-detection technique with a retardation-tunable wave-plate and analyzer into our common-path heterodyne polarimeter. Also, the environmental noise can be reduced by the interference of transverse magnetic (TM) and transverse electric (TE) waves from the optical common-path setup. We first measured the optical rotation of deionized water, glucose solution (dextrorotatory), and bovine serum albumin (BSA, levorotatory) to ensure the accuracy and high signal-to-noise ratio (SNR) of the experimental setup. It was found that the optical rotation from the measured phase difference can be enhanced up to 40-fold amplification with a soleil babinet compensator (SBC). Moreover, we have investigated the thermal denaturation from the denaturation temperature defined by the change of optical rotation, and the thermal renaturation of collagen has been studied by heating the samples to 55°C followed by cooling down to 25°C and then heating back to 55°C. The results reveal that 63% triple helices in the collagen structure have been refolded during the renaturation stage. This approach successfully provides with a real-time, noninvasive, and high resolution detection for thermal denaturation and renaturation of collagen.

Preparation and characterization of carboxymethyl derivatives of yeast mannans in aqueous solutions

Novel carboxymethyl derivatives of yeast mannans of different degrees of substitution (DS) were prepared by optimized reaction of concentrated polysaccharides in alkaline aqueous solution. Mannans from various yeasts differing in size and degree of branching show similar reactivity. Strong alkaline conditions during carboxymethylation caused degradation of the polysaccharides. The degree of substitution (DS) of Candida albicans mannan and dextran were proportional to the amount of monochloroacetate added. However, degrees of carboxymethylation of Candida albicans mannan (0.30, 0.41, 0.73) were lower than those of dextran (DS=0.33, 0.6, 1.1) using the same amounts of monochloroacetate. Evidently the resulted polyanionic derivatives have higher hydrodynamic sizes than the original polysaccharides. Non-uniform, variable position of substitutions results to non-proportional change of optical rotation and increase of complexity of NMR spectra. Basic physico-chemical characteristics of novel carboxymethyl mannans obtained by potentiometric titration, FT-IR, UV, HPLC, 1H NMR and optical rotation measurements are presented here.

Long range chirality transfer in free radical polymerization of vinylterphenyl monomers bearing chiral alkoxy groups

ABSTRACTTwo series of chiral bulky vinyl aromatics, 2‐(4'‐alkoxyphenyl)‐5‐(4'‐hexyloxyphenyl)styrene (S‐Am (m = 0, 1, 2, 3)/R‐A0) and 2‐(4'‐hexyloxyphenyl)‐5‐(4'‐alkoxyphenyl)styrene (S‐Bm (m = 0, 1, 2, 3)/R‐B0), were synthesized and radically polymerized (where m denotes the carbon number between stereogenic center and ether oxygen atom). The generation and stereomutation of helical structures as well as chirality transfer from the stereogenic center of the side‐group to the polymer backbone during polymerization were investigated by a combination of 1H‐ and 13C‐NMR, polarimetry, circular dichroism spectroscopy, liquid crystal induced circular dichroism, and computer simulation. All the polymers, except S‐B3, display optical rotations and Cotton effects in the UV‐Vis absorption region of terphenyl pendant, which are quite different from the corresponding model compounds and monomers, suggesting the formation of chiral secondary structures, that is, skewed packing of side‐groups and twisting of polymer backbones with a dominant screw sense. The sign of optical rotation changes alternatively and the strength diminishes when m increases from 1 to 3. However, although the stereogenic centers in S‐A0 and S‐B0 are closer to the vinyl group than those in S‐A1 and S‐B1, separately, a weaker chiral induction power is observed. Moreover, optical rotations of polymers derived from S‐A0/R‐A0 and S‐B0/R‐B0 are opposite in sign and increase with annealing time in tetrahydrofuran. These results are in a sharp contrast with our previous findings in similar vinylterphenyl compounds, where ‐COO‐ rather than ‐O‐ links the chiral alkyl tail to the terphenyl group, manifesting a remarkable effect of small structural variation of side‐group on polymer chiroptical properties and complexity of chirality transfer in helix‐sense‐selective polymerization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3674–3687

Exploring Light and Life

Exploring Light and Life

Study on gamma and electron beam sterilization of third generation cephalosporins cefdinir and cefixime in solid state

The effect of gamma radiation from 60Co source and 2 MeV e-beam was studied on two thermolabile cephalosporin antibiotics viz cefdinir and cefixime in solid state. The parameters studied to assess radiolytic degradation were loss of chemical and microbiological potency, change in optical rotation, electronic and vibrational absorption characteristics, thermal behavior and color modification. ESR spectroscopic study, HPLC related impurity profile, thermogram and Raman spectrum are applied in deducing the nature of radiolytic impurities and their formation hypotheses. Cefixime is radiation sensitive, whereas cefdinir has acceptable radiation resistance at 25 kGy dose. The nature of radiolytic related impurities and their concentrations indicates that the lactam ring is not highly susceptible to direct radiation attack, which otherwise is considered very sensitive to stress (thermal, chemical and photochemical).

A New, More Versatile, Optical Switching Helical Polycarbodiimide Capable of Thermally Tuning Polarizations ±359°

An in depth study of newly synthesized polycarbodiimides containing asymmetric aryl pendant groups has been performed. The focus of this study was to create new polymers capable of the low-energy, reversible, solvo-, and thermocontrollable conformational switching phenomenon previously discovered. Of the polymers synthesized, one polymer, N-(1-naphthyl)-N′-(n-octadecyl) polycarbodiimide, Poly-5, has been found to undergo reversible optical switching in various solvents, each of which alter the temperature at which the switching is observed. The switching is not due to helical inversions, but instead due to synchronous rearrangement of polyarene pendant groups around the helical backbone. This is further shown by anisotropic changes of the aromatic chemical shifts using variable temperature 1H NMR through the observed thermal switching range in THF-d8. The net change in specific optical rotation reaches a remarkable 1700° and changes in the direction of rotation. The polymer system is tunable and capable of holding the polarization output constant at constant temperature anywhere within the switching profile. Polarimetry and electronic circular dichroism (ECD) studies were performed to observe these conformational changes. Additionally reported are new polycarbodiimides that probe the effects of size and geometry of various arene pendant groups on the switching behavior of these polymer systems.

An insight into optical rotation of amino-acids

Optical specific rotation of naturally occurring L-amino-acids depend upon physico-chemical properties of amino-acids, solvent used for their preparation and incident radiation. The most important parameters like total polarization, dielectric constant, dipole moment, density and molecular weights of the amino-acids are connected to optical specific rotation by mathematical equations. The present paper elucidates the variation in specific optical rotation of amino-acids with a few physico-chemical properties namely total unbound electronic charge, molecular weight, furthest distance of substituent group from asymmetric carbon atom, surface area, charge density, molecular volume, solubility and pI values. Probable reasons for these observations have been offered. Intrinsic conformations of amino-acids and the total polarization with incident low ionizing radiation for amino-acids should lead to measurable changes in specific optical rotation as compared to un-irradiated amino-acids. So long the bonds between asymmetric carbon atom and functional groups do not disrupt upon impingement of low ionizing radiation the variation in optical rotation compared to un-irradiated amino-acid should be obtained. The potential uses of this study in dosimetry and radioprotection are bright.

Electrically and thermally modulated optical properties of polymer dispersed chiral liquid crystal

The polymer dispersed chiral liquid crystals (PDCLCs) film was fabricated by photopolymerization induced phase separation (PIPS) of chiral liquid crystal (CLC)/polymerizable monomers/photoinitiator composites. The effects of the electrical and thermal modulation on optical rotation properties of PDCLCs film were investigated. The microsized liquid crystal droplets were resulted from the rapid polymerization of trifunctional monomers. The effects of the electrically and thermally modulated on realignment of liquid crystal director were investigated. It was found that the intensity of electric and thermal field influenced the alignment of liquid crystal droplets' director on PDCLCs film, and the electro-optical properties of the composites were affected accordingly. The principle of free energy minimum was used for explaining the change of optical rotation and transmittance of PDCLCs film with applying the voltage to the film. The dispersion and sizes of liquid crystal droplets were described by polarizing optical microscope (POM). POLYM. COMPOS., 31:1535–1540, 2010. © 2009 Society of Plastics Engineers

Conformational ordering and gelation of gelatin in mixtures with soluble polysaccharides

Previous studies have shown that conformationally disordered, soluble biopolymers cause large enhancements in self-association of calcium pectinate, thermally denatured whey protein and gelling maltodextrin under conditions where the pre-gel solutions remained as a single phase. The purpose of the present work was to screen for similar enhancements in gel strength and rate of conformational ordering of gelatin on incorporation of soluble, disordered polysaccharides. Type B gelatin was used at a fixed concentration of 5.0 wt%, at a pH well above its isoelectric point of ∼4.5. Mixtures were prepared at 45 °C, where the gelatin is in the disordered coil form. Gel strength was characterised as Young's modulus ( E), derived from the initial slope of compression curves for gels formed by holding for 16 h at 5 °C. Rate of conformational ordering of gelatin (triple-helix formation) was monitored by changes in optical rotation during and after rapid quenching from 45 to 5 °C. The polysaccharides studied were carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), guar gum, gum arabic, dextran and inulin, all of which were used in compression testing. Combinations of gelatin with HPMC and guar gum became immediately turbid on mixing and could not, therefore, be included in the samples characterised by optical rotation. The other mixtures remained homogeneous (i.e. single-phase) on holding at 45 °C. The results obtained were entirely negative. Incorporation of the soluble polysaccharides caused no significant changes in Young's modulus, and optical rotation values remained within ∼10% of those for gelatin alone. It is suggested that the enthalpic advantage of segregation is sufficient to overcome the small reduction in entropy from association of conformationally immobile subunits in gelation of calcium pectinate, whey protein and maltodextrin, but not sufficient to overcome the much greater loss of entropy from conversion of flexible gelatin coils to rigid triple helices.

Specific Anion Effects on the Optical Rotation of α-Amino Acids

Changes in optical rotation of some alpha-amino acids are induced by electrolytes. Such effects on l- and d-enantiomers of a range of amino acids are explored for sodium salts with varying anion. The amino acids studied were alanine, aspartic acid, glutamic acid, glutamine, proline, threonine, and tryptophan. The anion's polarizability in solution accounts for the change in [alpha] only for the halides. Self-association of amino acids in solution and pH changes due to the presence of the electrolytes do not account for the observed variations in optical activity. Specific interactions of anions with the chiral amino acids (Hofmeister effects) and salt-induced perturbations of the amino acid hydration shell appear to be responsible for the effects, and conformational changes in the chiral solutes due to the presence of ionic species are discussed.

Chiral Helicenoid Diarylethene with Large Change in Specific Optical Rotation by Photochromism1,2

A diarylethene possessing one [4]thiaheterohelicene and one benzothiophene, the latter with a chiral methoxymethoxyethyl group on its C-3 position, was proved to work as a switch of specific optical rotation at a wavelength at which both colored and colorless forms have no absorption in solution. The difference of the specific optical rotation was 1300 degrees between the open form and the photostationary state. The specific optical rotation of one of the isolated optically active major colored forms was -4680 degrees. The conversion to the colored form was 64%, and the diastereomeric excess of photocyclization was 47%.

Segregative interactions between gelatin and polymerised whey protein

Polymerisation of whey proteins increases their potential use as food ingredients. In this investigation, mixtures of 6 wt% whey protein isolate (WPI) with 1–4 wt% type B (alkaline extract) gelatin, before and after polymerisation of WPI (heating to 85 °C and quenching to 5 °C), were characterised by measurements of solution viscosity at 45 °C (above the gelation temperature of gelatin) and by changes in optical rotation and turbidity (measured as optical density at 600 nm) over the temperature range 45–5 °C. Viscosities for mixtures of gelatin with un-polymerised WPI were only slightly higher than for gelatin alone, but after polymerisation they rose steeply above those of the individual components as the gelatin concentration was increased, giving values of 1.84 mPa s for 6 wt% polymerised WPI, 4.07 mPa s for 4 wt% gelatin, and 36.5 mPa s for the mixture of these. The large enhancements in viscosity are attributed to self-association of polymerised WPI in response to segregative interactions with gelatin. On cooling to 5 °C to gel the gelatin component, the unheated mixtures containing un-polymerised WPI showed only slight increases in turbidity, similar to those observed for WPI alone (polymerised or un-polymerised). Cooled mixtures of gelatin and polymerised WPI, however, gave very large increases in turbidity, which were fully reversible on re-heating to 45 °C. Optical rotation measurements showed no indication of direct association between gelatin and polymerised WPI at any temperature in the range studied (45–5 °C). It is suggested that association of gelatin molecules in the early stages of gelation triggers phase separation, giving a continuous matrix of gelatin gel with the polymerised whey protein dispersed through it in small droplets (which increase turbidity by scattering light).