Free COOH Groups Research Articles

Specific Structural-Functional Role of the Pronounced Negative Molecular Charge of the Sturgeon Gonadotropin β-Subunit

Free negatively charged carboxyl groups (COOH) were selectively modified (neutralised) in sturgeon (Acipenser güldenstädti Br) gonadotropic hormone (GTH) β-subunit (βGTH). Eight COOH groups were neutralised by reaction with glycine ethyl ester. Investigation of modified βGTH showed that specific immunoactivity with antiserum raised against standard βGTH was completely lost. Analysis of CD spectra and the content of secondary structure elements of standard and modified βGTH did not indicate any considerable differences. Investigation of reassociated α-β dimer comprising standard αGTH and modified βGTH showed that hormonal activity was completely lost while immunoreactivity was lowered by about 30% in comparison with that of the standard subunit α-β dimer. It was concluded that eight free COOH groups located on the surface of βGTH are the main structural components of the species-specific antigenic determinant groups of the subunit, but are not directly involved in either maintaining the conformation of the subunit nor in its ability to interact with the native counterpart subunit. COOH groups, as bearers of the negative charge located on the surface of βGTH, play a decisive role in the specific hormonal activity of GTH determined by oocyte maturation tests. Free COOH groups are included in the effector zones (active sites) of GTH dimer molecule responsible for the stereospecific interaction with the test-oocyte membrane hormone-sensitive binding (receptor) sites to induce the biological effects.

Synthesis of mesogenic phthalocyanine-C60 donor–acceptor dyads designed for molecular heterojunction photovoltaic devices

A series of phthalocyanine-C60 dyads 2a–d was synthesized. Key steps in their synthesis are preparation of the low symmetry phthalocyanine intermediate by the statistical condensation of two phthalonitriles, and the final esterification of the fullerene derivative bearing a free COOH group. Structural characterization of the molecules in solution was performed by NMR spectroscopy, UV–vis spectroscopy and cyclic voltammetry. Preliminary studies suggest formation of liquid crystalline (LC) mesophases for some of the prepared dyads. To the best of our knowledge, this is the first example of LC phthalocyanine-C60 dyads.

Cycloartane Triterpenes from Dikamali, the Gum Resin of Gardenia gummifera and Gardenia lucida

We report on the chemical investigation of dikamali gum, which is the resin of Gardenia gummifera and G. lucida (Rubiaceae). Six new cycloartane triterpenes, dikamaliartanes A-F (1-6, resp.), together with a known flavonoid (7), were isolated and identified by NMR spectroscopy. All six cycloartanes are characterized by an open A-ring with a free COOH group at C(3). In four of them, the C-atoms C(23)-C(27) form a 4-methylfuran-2-yl moiety. Bacterial assays using Staphylococcus aureus, Candida albicans, and Mycobacteria have been carried out but did not reveal significant activity.

Stabilization of Neutral NH2-R-COOH Form of the Antihypertensive Peptides L-Valyl-L-Prolyl-L-Proline and L-Isoleucyl-L-Prolyl-L-Proline

Spectroscopic and structural elucidation of the peptides L-Valyl-L-Prolyl-L-Proline (1) and L-Isoleucyl-L-Prolyl-L-Proline (2) are reported on the basis of experimental linear-polarized IR-spectroscopy in solid-state, 1H-NMR data and DFT. Curiously, the experimental data shown that both peptides stabilized in solution and in solid-state neutral H2N-R-COOH form. Conformational analysis made, shown two strong intramolecular NH2-O=C-N(Amide) and O=C-OH-NH2 hydrogen bonds with lengths of 2.979 A and 2.475 A in (1) and 2.599 A and 2.507 A in (2) respectively. The presence of the Pro-Pro fold resulted to strong steric effect leading to the stabilization of free COOH and NH2 groups. The Erel values of zwitterion form are significant higher than the neutral forms with a difference of 1.2 and 0.9 kJ/mol. The manner of interaction of the peptides with angiotensin-I converting enzyme is proposed.

Role of Carboxyl Groups in the Secondary Structure and Function of Sturgeon Gonadotropin

Role of Carboxyl Groups in the Secondary Structure and Function of Sturgeon Gonadotropin Free negatively charged carboxyl groups were selectively modified (neutralised) in sturgeon (Acipenser güldenstädti Br.) gonadotropic hormone (GTH) α and β subunits. Eleven free carboxyl groups, three in the α and eight in the β subunit, were neutralised by reaction with glycine ethyl ester. Investigation of reassociated α-β dimers (recombinants) comprising one or both modified subunits showed that specific hormonal activity was completely lost while immunoreactivity was lowered in comparison with that of the standard α-β dimer. CD-spectroscopy of the modified subunits did not indicate any considerable changes in their spatial structure. A conclusion was made that free COOH groups of GTH were important as bearers of the negative charge necessary for the hormone activity on the level of the hormone-specific membrane receptors.

Various Types of Hydrogen Bonds, Their Temperature Dependence and Water−Polymer Interaction in Hydrated Poly(Acrylic Acid) as Revealed by 1H Solid-State NMR Spectroscopy

Various types of hydrogen bonds, their temperature dependence and water−polymer interaction in hydrated poly(acrylic acid) (PAA) were systematically investigated using 1H CRAMPS solid-state NMR techniques in the temperature range from 25 to 110 °C. The 1H CRAMPS NMR methods are based on a recently developed continuous phase modulation technique for 1H−1H homonuclear dipolar decoupling. The 1H CRAMPS experiments revealed four types of protons in hydrated PAA which are assigned to protons from the mutually hydrogen-bonded COOH groups (1), from the free COOH groups (2), from the COOH groups bounded with water or from water bounded with COOH groups which are undergoing fast chemical exchange mutually (3), and from main chain groups (4), respectively. Furthermore, we proposed double-quantum filtered and dipolar filtered 1H CRAMPS experiments to further assign the protons according to their dipolar coupling strength. In addition, high-resolution spin echo 1H CRAMPS experiments were further employed to accurately determine the chemical shift of these protons. These NMR techniques were also used to elucidate the molecular mobility of the different groups. It was found that dehydration in PAA promotes the formation of hydrogen bonds between COOH groups. Variable-temperature 1H CRAMPS experiments demonstrated that the dissociation of the hydrogen bonds between COOH groups occurs dramatically at lower temperature in hydrated PAA and slowly over a wide range of temperature in dehydrated PAA. It was also found that the dehydration of water bounded with COOH groups in hydrated PAA occurs significantly at high temperature. The NMR results were compared with previous work using DSC and other techniques. Besides undergoing fast chemical exchange, the adsorbed water was also demonstrated in proximity with the free COOH groups and far from the hydrogen bonds between COOH groups by using two-dimensional 1H−1H spin-exchange NMR experiments.

Synthesis and characterization of functional elastomeric poly(ester amide) co-polymers

A new family of random co-poly(ester amides)s (co-PEAs) having reactive pendant functional carboxylic acid groups were synthesized by co-polycondensation of di-p-toluenesulfonic acid salts of bis-(L-α-amino acid (L-leucine and/or L-phenylalanine)) α,ω-alkylene diesters with active diesters of dicarboxylic acids using di-p-toluenesulfonic acid salt of L-lysine benzyl ester as a co-monomer. The lateral benzyl ester groups in the L-lysine segment of co-PEAs were subsequently transformed into free COOH groups by catalytic hydrogenolysis using Pd black as a catalyst. The co-PEA-based polyacids obtained, as well as the original co-PEA having lateral benzyl ester groups were characterized by standard methods. In vitro biodegradation studies in the presence of hydrolases like α-chymotrypsin and lipase showed significant enzymatic-catalyzed biodegradation of these co-PEAs. These co-PEA-based polyacids were used for covalent attachment of iminoxyl radicals (4-amino-TEMPO) and in vitro biodegradation of 4-aminoTEMPO attached polymer was studied along with releasing kinetic of iminoxyl radical.

Separation of phenylalanine by ultrafiltration using D-Phe imprinted polyacrylonitrile-poly(acrylic acid)-poly(acryl amide) terpolymer membrane

A D-phenylalanine (D-Phe) imprinted terpolymer P(AN-AA-AAm) membrane was prepared by the wet phase inversion method. Acrylamide (AAm) and acrylic acid (AA) were used as the functional monomer and acry- lonitrile (AN) was used as a physical cross linker. The te mplate molecules were removed from the terpolymer matrix by washing with a 5 percent acetic acid solution. The removal of template molecules from the membrane matrix increased the population of free COOH groups and reduced that of dimerized COOH groups in the membrane matrix, which is an indirect evidence of the formation of recognition sites. The adsorption selectivity of the D-Phe imprinted terpolymer membrane prepared by in-situ implanting method was 0.37 at pH 2 after 3 h batch adsorption using 100 mg Phe/ l racemate solution and reached nearly 1 after 24 h. In the ultrafiltration process, the permselectivity was 0.38 at pH 2 after 2.5 min. Separation of D-Phe from the racemate solution was demonstrated by a repeated ultrafiltration batch work.

Two-dimensional infrared spectroscopy study on phase transition and structural variations of a hydrogen-bonded liquid crystal

Infrared (IR) spectra have been measured for a liquid crystal (LC) consisting of one trans-butene diacid (BD) molecule as a proton donor and two 4-(2,3,4-tridecyloxybenzoyloxy)-4′-stilbazoles (DBS) molecules as a proton acceptor (DBS:BD:DBS) linked together with each other by inter-molecular hydrogen bonds over a temperature range from 20 to 120 °C to explore its phase transition and heat-induced structural variations. The temperature-dependent IR spectra have shown that the inter-molecular hydrogen bonds are stable in the liquid crystalline phase but become slightly decoupled with temperature increasing. Two kinds of two-dimensional (2D) correlation spectroscopy, variable–variable (VV) and sample–sample (SS) 2D spectroscopy, have been employed to analyze the observed temperature-dependent spectral variations more efficiently. The SS 2D correlation analysis in the spectral range of 2700–1800 cm −1 has demonstrated that a change in hydrogen bonds in the LC starts from 40 °C, which is not clarified by differential scanning calorimetry (DSC) and conventional IR and Raman spectroscopic analyses. On the other hand, the phase transition of LC revealed by SS 2D spectroscopy in the specific spectral regions of 1750–1650 and 3000–2700 cm −1 is in a good agreement with that revealed by DSC for the heating process. The VV 2D correlation spectroscopy analysis has provided information about the structural variations of inter-molecular hydrogen bonds. The different species of hydrogen-bonded and free COOH and COO groups in the LC have been clarified by the VV 2D correlation analysis. It has also elucidated the specific order of the temperature-induced structural changes in the intra- and inter-molecular hydrogen bonds concerning with the COOH and/or COO groups in the LC.

Derivatives of Coenzyme F430 with a Covalently Attached α‐Axial Ligand. Part II

AbstractCoenzyme F430 pentamethyl ester 2 was partially hydrolyzed to a mixture of the five F430 tetramethyl esters 7–11, which were separated by HPLC and identified by means of a full NMR characterization. The tetramethyl ester with a free COOH group at the side chain at C(3) of F430 was coupled to the N‐terminus of the peptidic spacerligand construct 12 selected and studied as described before. The UV/VIS and NMR spectra in CH2Cl2/3,3,3‐trifluoroethanol 6 : 1 show that the new derivative, the NiII(33‐dehydroxy‐83,122,133,182‐tetra‐O‐methyl‐F430‐33‐yl)‐L‐prolyl‐L‐prolyl‐Nπ‐methyl‐L‐histidine methyl ester (13), is an intramolecular, pentacoordinate, paramagnetic complex. In the same solvent system, the parent 33,83,122,133,182‐penta‐O‐methyl‐F430 (2) is four coordinate and diamagnetic even in the presence of equimolar 1H‐imidazole. Protonation of the axially coordinating histidine residue of 13 gave the diamagnetic tetracoordinate base‐off form, which allowed us to establish the constitution of 13 by NMR.

Structural Studies of a New Low Molecular Mass Organic Gelator for Organic Liquids Based on Simple Salt

A series of easy to prepare organic salt based on imidazole derivatives and cyclobutane-1,1-dicarboxylic acid have been studied for their gelation behavior after it was found that imidazolium hydrogen cyclobutane-1,1-dicarboxylate (1) can harden few organic liquids. 1 forms remarkably stable gel (remains intact for several months in an open container, gel dissociation temp TGel = 66 °C) with nitrobenzene at a very low concentration of 0.137 wt %, whereas bis-imidazolium cyclobutane-1,1-dicarboxylate (2) resulted in a weak and unstable gel with nitrobenzene, indicating the importance of the free COOH group in 1 in gel formation. Molecular packing in the primary assembly unit (fibers) of xerogel of 1/nitrobenzene is successfully established based on single-crystal X-ray and X-ray powder diffraction data. The morph responsible for gel formation of 1 with nitrobenzene is found to be different from that of its xerogel. Substitution on the imidazole moiety results in nongelators.

Characteristics of phenylalanine imprinted membrane prepared by the wet phase inversion method

A phenylalanine imprinted membrane without a sponge layer containing macrovoids was prepared by the wet phase inversion method. The structure of the phenylalanine imprinted membrane prepared by an in-situ implanting procedure was denser than that of the membrane prepared by post implanting. Consecutive washings with distilled water and acetic acid solution removed nearly all of the template molecules from the membrane prepared by the post implanting procedure, although much of the template molecules remained in the membrane prepared by in-situ implanting. The removal of the template molecules from the membrane increased the population of the free COOH groups but reduced that of the dimerized COOH groups in the membrane. A D-Phenylalanine imprinted membrane prepared by post implanting selectively adsorbed D-phenylalanine from a racemate solution, where the adsorption selectivity reached 4.79. A D-phenylalanine imprinted membrane prepared by in-situ implanting exhibited an inverse adsorption affinity.

Quantification of Holo-Transcobalamin, a Marker of Vitamin B12 Deficiency

We report a new method for measurement of holo-transcobalamin (holoTC), in which magnetic beads coated with vitamin B12 (cobalamins) precipitate apo-transcobalamin (apoTC) and the holoTC present in the supernatant is measured by ELISA. Serum holoTC denotes the part of vitamin B12 accessible for the cells of the body and is considered to be a sensitive marker of vitamin B12 deficiency (1)(2)(3). Serum holoTC is not easily measured because it accounts for only approximately one-third of the circulating vitamin B12 and because the major part of TC circulates unsaturated with vitamin B12 (apoTC) (1)(2)(3). In the few published attempts to measure holoTC, TC is separated from the other vitamin B12-binding protein, haptocorrin, before quantification of vitamin B12. This allows a direct measurement of the cobalamins attached to TC (4)(5)(6) or an indirect calculation of holoTC from measurement of total plasma cobalamins and the plasma cobalamins not attached to TC (7)(8)(9). We have chosen another path. We produced B12 beads and removed apoTC before ELISA quantification (10) of the protein moiety of holoTC. Vitamin B12 (400 mg; Fluka) was modified by acid treatment (11) to produce derivatives with a free COOH group. Magnetic beads (DB M-270 amine; DYNAL) from 10 mL of the original suspension were incubated overnight at room temperature with 10 mL of 2 mmol/L derivatives in 0.1 mol/L 2-morpholinoethane sulfonic acid, pH 5.5, in the presence of 10 mmol/L 1-ethyl-3-(dimethylaminopropyl)carbodiimide (Sigma). The beads were then washed twice with 50 mL of 1 mol/L Tris, pH 7.5, twice with 50 mL of 1 mol/L ammonium acetate, pH 4.6, and 10 times with 50 mL of 0.1 mol/L Tris–0.5 mol/L NaCl, …

Two-Dimensional/Attenuated Total Reflection Infrared Correlation Spectroscopy Studies on Secondary Structural Changes in Human Serum Albumin in Aqueous Solutions: pH-Dependent Structural Changes in the Secondary Structures and in the Hydrogen Bondings of Side Chains

Attenuated total reflection (ATR)/infrared (IR) spectra were measured for human serum albumin (HSA) in aqueous solutions over a pH range of 5.0−3.2. Generalized two-dimensional (2D) correlation analysis was applied to the amide I region of the spectra to investigate pH-dependent changes in secondary structures and in hydrogen bondings of side chains of HSA. The synchronous and asynchronous 2D spectra were generated from the pH-dependent spectral variations for the three states of HSA, the N isomeric form (pH 5.0−4.4), the N−F transition (pH 4.6−3.8), and the F isomeric form (pH 3.8−3.0). The most interesting finding in the 2D spectra is identification of four bands at 1740, 1715, 1705, and 1696 cm-1 due to a CO stretching mode of free and hydrogen bonded (weak, medium, and strong) COOH groups of HSA. The 2D correlation analysis provides unambiguous evidence for the existence at least the four CO bands, demonstrating its powerful deconvolution ability. The asynchronous spectrum of the N form is characterized by a rather broad cross-peak centered at (1715, 1654) cm-1. The sign of the cross-peak indicates that protonation of COO- groups of glutamic (Glu) and aspartic (Asp) acid residues occurs at pH's higher than those of structural changes in the α-helices. In the N−F transition, it seems that the formation of free COOH groups and those with the hydrogen bonds of the medium strength occurs is linked with changes in secondary structures of HSA. The asynchronous spectrum indicates that the formation of the strongly hydrogen-bonded COOH groups upon the protonation of COO- groups plays a key role in the initiation of the N−F transition, where mainly α-helices undergo the conformational changes. The synchronous and asynchronous spectra of the F form show that β-strands and β-turns of HSA change significantly in this pH region.

The competing effects of π–π packing and hydrogen bonding in a hexabenzocoronene carboxylic acid derivative: A 1H solid-state MAS NMR investigation

1 H solid-state NMR methods employing fast (νR=30 kHz) magic-angle spinning (MAS) are applied to the investigation of both the solid and columnar liquid-crystalline (LC) phases of HBC-C10COOH, a discotic molecule consisting of a hexa-peri-hexabenzocoronene core with six symmetrically attached alkyl chains, each chain being capped by a COOH group. In the solid phase at T=320 K, the presence of hydrogen-bonded COOH dimers is demonstrated by the observation of an auto COOH peak in the 1H double-quantum (DQ) MAS NMR two-dimensional spectrum, with the interproton distance being determined to be 0.279±0.09 nm. Considering the COOH peak in the one-dimensional 1H MAS spectra, both a shift to high field of the peak position as well as an initial increase followed by a subsequent decrease in the linewidth are observed upon heating. These observations are interpreted in terms of a chemical exchange process involving the making and breaking of hydrogen bonds, with the coalescence point corresponding to T=362 K. The equilibrium constant at a given temperature is calculated from the observed chemical shift, and a thermodynamic analysis yields for the opening of the hydrogen-bonded dimers: ΔH=45±4 kJ mol−1 and ΔS=113±11 J K−1 mol−1. In 1H DQ-filtered (DQF) MAS spectra, the intensity of the COOH peak is observed, upon heating, to reduce faster than expected from thermodynamic factors alone, and above T=380 K, no signal is detected. Using the fact that the observation of a DQ signal relies on the existence of a DQ coherence for the duration of the experiment, the kinetics of dimer opening are determined: the extracted activation energy and Arrhenius parameter equal 89±10 kJ mol−1 and 4.2×1016 s−1, respectively. On the transition to the LC phase, a marked narrowing of all resonances is observed, with the COOH chemical shift initially having a very high-field value, 9.0 ppm, which is indicative of free COOH groups. An analysis of DQ MAS spinning-sideband patterns shows that the dipolar coupling in the LC phase is reduced by a factor of 0.43±0.04.

Insoluble ionic complexes of polyacrylic acid with a cationic drug for use as a mucoadhesive, ophthalmic drug delivery system

We have developed a new mucoadhesive drug delivery formulation based on an ionic complex of partially neutralized poly(acrylic acid) (PAA) and a highly potent beta blocker drug, levobetaxolol · hydrochloride (LB · HCl), for use in the treatment of glaucoma. PAA was neutralized with sodium hydroxide to varying degrees of neutralization. Aqueous solutions containing concentrations of LB · HCl equivalent to the degree of PAA neutralization were added to the PAA solutions and formed insoluble complexes, which were isolated. The complex formation was followed by turbidimetric titration, and the complexes were characterized by IR and 1H NMR spectroscopy. Complexes were prepared with varying degrees of drug loading, such that the same PAA chain would have free COOH groups for mucoadhesion along with ionic complexes of LB · H+ with COO- groups. Thin films of the complexes dissociated to release the drug by ion exchange with synthetic tear fluid. The films shrunk continuously during release of the drug and dissolved completely in 1 h. Solid inserts of these films could be useful as a mucoadhesive ophthalmic drug delivery system.

Analysis of the hydrogen bonding in (2‐hydroxypropyl)cellulose‐poly(acrylic acid) composites by Raman spectroscopy

AbstractNovel anisotropic polymer composites obtained by the photopolymerisation of acrylic acid (AA) in lyotropic solutions of (2‐hydroxypropyl)cellulose (HPC) were investigated. Raman spectroscopy was used in the study of hydrogen bonding formed by carboxylic groups of poly(acrylic acid) (pAA) between themselves and with the hydroxyl groups of HPC macromolecules. These investigations show that the supramolecular structure of pAA obtained by photopolymerisation contains mainly inner oligomeric forms and cyclic dimer forms, as a consequence of the “matrix polymerisation” of AA. The presence of HPC affects the process of the photopolymerisation of AA, by a redistribution of hydrogen bonding within the system, leading to a different supramolecular structure of pAA. With increasing amounts of HPC the inner oligomeric forms characteristic of bulk pAA disappear. In the composites, the pAA chains probably form the terminal oligomeric structure, with some free COOH groups, as well as hydrogen bonds with HPC.

Functional group interactions in the fragmentation of protonated and methylated succinic acid derivatives

The methane chemical ionization (CI) mass spectra of succinic acid monoamide and monomethyl succinate have been determined. In addition, the unimolecular metastable ion fragmentation reactions and low-energy collision-induced dissociation reactions of the MH + and M.CH 3 + ions of these compounds have been determined. In the CH 4 CI mass spectra extensive fragmentation of the MH + ions is observed, indicative of functional group interactions. An important fragmentation reaction for the protonated monoamide involves formation of NH 4 + and it is suggested that this occurs through the intermediacy of a protonated succinic anhydride/ammonia ion-neutral complex. The [MH–H 2O] + and [MH–CH 3OH] + fragment ions formed in the CH 4 CI of monomethyl succinate give collision-induced dissociation (CID) spectra which are in agreement with the spectra obtained for methylated and protonated succinic anhydride, respectively; these results strongly support the suggestions that the formation of stable cationated cyclic anhydride structures are one of the factors which result in extensive fragmentation of protonated and cationated dicarboxylic acid derivatives. The M.CH 3 + adduct of succinic acid monoamide gives a CID spectrum which is distinctly different from that obtained for the protonated monomethyl ester of succinic acid monoamide. This result indicates that little addition of CH 3 + to the free COOH group of the monoamide occurs. The CID spectrum of the M.CH 3 + adduct of monomethyl succinate also shows substantial differences from the CID mass spectrum of protonated dimethyl succinate.

Infrared, Raman, and Near-Infrared Spectroscopic Evidence for the Coexistence of Various Hydrogen-Bond Forms in Poly(acrylic acid)

Fourier-transform infrared (FT-IR), near-infrared (NIR)-excited FT-Raman, and FT-NIR spectra have been measured for poly(acrylic acid) (PAA) in a cast film over a temperature range of 40−140 °C, to investigate structures of hydrogen bonds and their dissociation. The CO stretching bands in the FT-IR spectra are unraveled by a prevalent multiple species model for small aliphatic acids with various kinds of associated forms of carboxylic acid groups, namely cyclic dimer, linearly associated oligomers of COOH, and free COOH groups. These different structures of hydrogen bond persist even when the temperature rises well above the glass transition temperature. The FT-Raman spectra confirm the existence of such COOH groups. Temperature-dependent intensity changes in the first overtone of an OH stretching mode of PAA reveal that the COOH groups dissociate significantly at high temperatures. We propose that the coexistence of various possible hydrogen-bond forms analogous to those in small aliphatic acids best int...

Mechanical and dynamic mechanical properties of miscible blends of epoxidized natural rubber and poly(ethylene- co-acrylic acid)

The mechanical and dynamic mechanical properties of blends of poly(ethylene- co-acrylic acid) (PEA) and epoxidized natural rubber (ENR-50) have been studied after reactive blending in various proportions in a Brabender Plasticorder. The miscibility of the blends has been studied by using a computer simulation method and experimentally confirmed by dynamic mechanical analysis. The dynamic properties of the blends exhibit single glass transition temperature ( T g) values, thus conforming to the law of miscibility. A positive deviation from the Fox equation (theoretical T g) is a clear indication of miscibility via chemical interaction. A new β-transition peak in the blends appeared, and this is assumed to be due to the side-chain ester group vibration, confirming a chemical reaction between the in situ generated OH groups of the ENR and free COOH groups of the PEA. This leads to miscibility between the constituents forming the grafted structure, i.e. PEA- g-ENR. The mechanical properties exhibit a synergism above that calculated via the additivity rule. The chemical interactions have been further confirmed by swelling studies in a common solvent.