Multidimensional solid‐state NMR studies of the structure and dynamics of pectic polysaccharides in uniformly 13C‐labeled Arabidopsis primary cell walls

Plant cell wall (CW) polysaccharides are responsible for the mechanical strength and growth of plant cells; however, the high‐resolution structure and dynamics of the CW polysaccharides are still poorly understood because of the insoluble nature of these molecules. Here, we use 2D and 3D magic‐angle‐spinning (MAS) solid‐state NMR (SSNMR) to investigate the structural role of pectins in the plant CW. Intact and partially depectinated primary CWs of Arabidopsis thaliana were uniformly labeled with ¹³C and their NMR spectra were compared. Recent ¹³C resonance assignment of the major polysaccharides in Arabidopsis thaliana CWs allowed us to determine the effects of depectination on the intermolecular packing and dynamics of the remaining wall polysaccharides. 2D and 3D correlation spectra show the suppression of pectin signals, confirming partial pectin removal by chelating agents and sodium carbonate. Importantly, higher cross peaks are observed in 2D and 3D ¹³C spectra of the depectinated CW, suggesting higher rigidity and denser packing of the remaining wall polysaccharides compared with the intact CW. ¹³C spin–lattice relaxation times and ¹H rotating‐frame spin–lattice relaxation times indicate that the polysaccharides are more rigid on both the nanosecond and microsecond timescales in the depectinated CW. Taken together, these results indicate that pectic polysaccharides are highly dynamic and endow the polysaccharide network of the primary CW with mobility and flexibility, which may be important for pectin functions. This study demonstrates the capability of multidimensional SSNMR to determine the intermolecular interactions and dynamic structures of complex plant materials under near‐native conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural characterization of native high-methoxylated pectin using nuclear magnetic resonance spectroscopy and ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Comparative use of 2,5-dihydroxybenzoic acid and nor-harmane as UV-MALDI matrices

The successful analysis by ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS) of native and hydrolyzed high-methoxylated pectin samples is described. In order to find the optimal conditions for UV-MALDI-TOF MS analysis several experimental variables were studied such as: different UV-MALDI matrices (nor-harmane, 2,5-dihydroxybenzoic acid), sample preparation methods (mixture, sandwich), inorganic salt addition (doping salts, NaCl, KCl, NH(4)Cl), ion mode (positive, negative), linear and reflectron mode, etc. nor-Harmane has never been used as a UV-MALDI matrix for the analysis of pectins but its use avoids pre-treatment of the sample, such as an enzymatic digestion or an acid hydrolysis, and there is no need to add salts, making the analysis easier and faster. This study suggested an alternative way of analyzing native high-methoxylated pectins, with UV-MALDI-TOF MS, by using nor-harmane as the matrix in negative ion mode. The analysis by (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy of the native and hydrolyzed pectin is also briefly described.     

Stereochemistry of the free‐radical polymerization of zinc methacrylates coordinated with a bidentate ligand

The polymerization of zinc methacrylates coordinated with a bidentate ligand ( 1 – 4 ) was carried out in chloroform at 60°C. The polymerization of these monomers gave chloroform‐insoluble polymers. Stereoregularity of the polymers was estimated from ¹H NMR spectra of poly(methyl methacrylate)s (PMMAs) derived from the original polymers. Monomers 1 and 2 gave slightly different polymers compared with conventional ones obtained by polymerization of methacrylic acid, while 3 afforded higher amounts of isotactic polymers than 1 and 2 . Conversely, 4 gave a polymer of high syndiotacticity. Furthermore, the relationship between triad tacticity and monomer concentration in the feed was studied. Consequently, it was demonstrated that the structure of bidentate ligands coordinated with zinc ion influences the stereoregularity of the resulting polymers.     

Sequence distribution of PMMA/iBuA copolymer by incremental calculation of 13C NMR spectra

An incremental method for characterizing triad and pentad distribution by ¹³C NMR spectroscopy was applied to the poly(methyl methacrylate-co-isobutyl acrylate) copolymer. Calculation of the intensity of individual lines was performed applying Bernoulli statistics, while the chemical shifts for each sequence were calculated by an incremental method. Based on these data, the carbonyl signal was simulated yielding good agreement at the triad and pentad level.     

Synthesis of Poly(methyl methacrylate) Labeled with Fluorescein Moieties via Atom Transfer Radical Polymerization

Fluorescein chromophore‐labeled poly(methyl methacrylate) (PMMA) was prepared via atom transfer radical polymerization (ATRP) with two novel bromine‐containing fluorescein derivatives, 3,6‐bi(2′‐bromo‐2′‐methyl‐propionic acid) fluorescein ester (Fla‐Br) and 3‐(2′‐bromo‐2′‐methyl‐propionic acid) fluorescein ester (Flb‐Br), as the functional initiators, and CuBr/PMDETA as the catalyst, respectively. The above mentioned fluorescein containing bromine were synthesized in our lab. The ATRP of PMMA was proved in a controlled fashion. The resultant PMMA with narrow molecular weight distribution was endowed with the fluorescein chromophore incorporated into the polymer backbone. The presence of the fluorescein labeling of the polymers was confirmed by ¹H‐NMR and GPC trace under UV detector. The UV spectroscopy and fluorescence measurements of the resultant polymer gave further evidence of the functionality of the fluorescein labeling.     

Microstructural characterization of terpolymers of leucine, β‐benzyl aspartate,and valine

Three different characterization methods—¹³C NMR spectroscopy, a terminal terpolymerization model, and a probability analysis based on the Poisson distribution—were used to determine the microstructure of random terpolymers. The methods were used to determine the amino acid sequence distribution of random terpolymers prepared from the polymerization of N‐carboxyanhydrides that contained L ‐leucine, β‐benzyl‐L ‐aspartate, and L ‐valine. Poly(L ‐leucine‐L ‐aspartic acid‐L ‐valine) [poly(LDV)] was designed as a target specific substrate for the α₄β₁ integrin that recognizes the tripeptide sequence leucine‐aspartic acid‐valine (LDV). The presence of the tripeptide sequence LDV within the polymer was determined to be eight LDV triad sequences on average in terpolymers of approximately 100 kDa. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4328–4337, 2006     

Hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s: Synthesis,characterization, end‐group modification,and optical properties

Novel AB₂‐type monomers such as 3,5‐bis(4‐methylolphenoxy)benzoic acid ( monomer 1 ), methyl 3,5‐bis(4‐methylolphenoxy) benzoate ( monomer 2 ), and 3,5‐bis(4‐methylolphenoxy)benzoyl chloride ( monomer 3 ) were synthesized. Solution polymerization and melt self‐polycondensation of these monomers yielded hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s. The structure of these polymers was established using FTIR and ¹H NMR spectroscopy. The molecular weights (M_w) of the polymers were found to vary from 2.0 × 10³ to 1.49 × 10⁴ depending on the polymerization techniques and the experimental conditions used. Suitable model compounds that mimic exactly the dendritic, linear, and terminal units present in the hyperbranched polymer were synthesized for the calculation of degree of branching (DB) and the values ranged from 52 to 93%. The thermal stability of the polymers was evaluated by thermogravimetric analysis, which showed no virtual weight loss up to 200 °C. The inherent viscosities of the polymers in DMF ranged from 0.010 to 0.120 dL/g. End‐group modification of the hyperbranched polymer was carried out with phenyl isocyanate, 4‐(decyloxy)benzoic acid and methyl red dye. The end‐capping groups were found to change the thermal properties of the polymers such as T_g. The optical properties of hyperbranched polymer and the dye‐capped hyperbranched polymer were investigated using ultraviolet‐absorption and fluorescence spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5414–5430, 2008     

300 MHz 1H-NMR study of poly(propylene sulfide)

An ¹H 300-MHz NMR spectroscopic study of deuterated poly(propylene sulfide) shows that methylene protons are sensitive to triad effects. It was possible to distinguish i, h_i, s, and h_s triads. Experimental values found for different polymers are in good agreement with theoretical amounts obtained from statistical probability calculation. The methyl groups are also slightly stereosensitive. By using optically active deuterated monomers with different R/S ratios it was possible to confirm the assignment of peaks and the tacticity. Nondeuterated polymers give very complicated spectra, and only the highly stereoregular polymer could be analyzed through its ABCX₃ spin system.     

Carbon-13 NMR spectra of some pentacyclic triterpenoids with the olean-12-ene and 18α-olean-12-ene skeleton

The ¹³C NMR spectra of some pentacyclic triterpenoids, 3β-acetoxy-11-oxo-olean-12-ene-30-oic acid methyl ester, 3β-acetoxy-11-oxo-olean-12-ene-29-oic acid methyl ester, the corresponding 11-desoxo methyl esters, 3β-acetoxy-11-oxo-18α-olean-12-en-30-oic acid methyl ester and 3β-acetoxy-11-oxo-18α-olean-12-en-29-oic acid methyl ester are discussed. The shielding data are interpreted in term of the different orientation of the carbomethoxy group and of the change in configuration at the D/E ring junction and are diagnostically valuable for the differentiation of the mentioned compounds.     

Pd(II)‐catalyzed polymerization of optically active norbornene carboxylic acid esters

(?)‐(1S,2R)‐Norbornene‐2‐carboxylic acid alkyl esters (alkyl = Me, Bz, L ‐menthyl, or D ‐menthyl) were successfully prepared by the Diels–Alder reaction of cyclopentadiene with (R)‐(?)‐pantolactone‐O‐yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)‐based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [α]_D = ?24.7, polymer [α]_D = ?98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in ¹³C NMR spectra. No crystallinity was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1263–1270, 2006     

Molecular design of diene monomers containing an ester functional group for the synthesis of poly(diene sulfone)s by radical alternating copolymerization with sulfur dioxide

Functional poly(diene sulfone)s are prepared by the radical alternating copolymerization of 1,3‐diene monomers containing an ester substituent with sulfur dioxide. Methyl 3,5‐hexadienoate (MH) and methyl 5,7‐octadienoate (MO) with both an alkylene spacer and a terminal diene structure are suitable to produce a high‐molecular‐weight copolymer in a high yield, while the copolymerization of 5,7‐nonadienoic acid, ethyl 2,4‐pentadienoate, and ethyl 4‐methyl‐2,4‐pentadienoate including either an alkylene spacer or a terminal diene structure lead to unsuccessful results. The ¹³C NMR chemical shift values of MH and MO suggest a high electron density at their reacting α‐carbon for exhibiting a high copolymerization reactivity. Fluorene‐containing diene monomers, 9‐fluorenyl 3,5‐hexadienoate (FH) and 9‐fluorenyl 5,7‐octadienoate (FO), are also prepared and copolymerized with sulfur dioxide. The thermal and optical properties of the poly(diene sulfone)s containing the methyl and fluorenyl ester substituents in the side chain are investigated. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1000–1009     

Influence of mechanical properties of pectin films on charge density and charge density distribution in pectin macromolecule

The hydration and mechanical properties of citrus pectin films were examined in conditions relevant to those in the plant cell wall. The pectins used for this study varied in the degree of esterification (DE) (high or low) and charge distribution on the backbone (random or block). The hydration of the films was controlled in an osmotic pressure experiment using polyethylene glycol solutions (PEG 20000). Hysteresis tests at constant deformation rate (stress vs deformation) were used for investigating the mechanical behaviour of films. Mechanical and hydration properties of pectin films were examined as a function of charge density, charge density distribution and counterion environment—K⁺, Ca²⁺, Mg²⁺. Swelling decreased with increasing counterion concentration. The effect is stronger in the case of Ca²⁺ and Mg²⁺ for low esterified pectins and therefore crosslinks from divalent ions could be assumed. The crosslink effect is confirmed in mechanical experiments where an increase in the film tensile modulus is observed with increasing counterion concentration. It is shown for the first time that in case of highly concentrated pectin solutions Mg²⁺ cations also act as a crosslinker for pectin macromolecules.     

Stereochemistry of alternating methacryloyl-L-valine methyl ester–maleic anhydride copolymer

The stereochemical composition of an alternating methacryloyl-L -valine methyl estermaleic anhydride (L-MAVM/MAn) copolymer which was prepared by the photocopolymerization of L-MAVM and MAn in dioxane at 25°C without initiator was investigated by proton magnetic resonance spectroscopy. The resonance of the ester methyl protons of the L-MAVM unit appeared as three split peaks at 3.65, 3.76, and 3.82 ppm, which could be assigned to those of the coisotactic (di-threo-tri-isotactic), coheterotactic and cosyndiotactic triads, respectively. The triad cotacticity determined according to these assignments indicated that the copolymer was composed predominantly of di-threo-tri-isotactic triad. Similarly PMR spectroscopic investigation of the acryloyl-L -valine methyl ester–maleic anhydride (L-AVM/MAn) copolymer with a 1:1 molar ratio of the monomers showed that the main tactic fraction of the copolymer was also di-threo-tri-isotactic one. Nevertheless, the circular dichroic investigation of the L-AVM/MAn copolymer before and after hydrolysis denied asymmetric induction into the polymer main chain. These results suggest that the propagation step in the photocopolymerization of L-MAVM or L-AVM with MAn proceeds by the trans-trans opening of the complexmer composed of a 1:1 molar ratio of L-MAVM or L-AVM and MAn.     

4-Vinylbenzenesulfonic acid adduct of epoxidized soybean oil: Synthesis, free radical and ADMET polymerizations

In this work new radically polymerizable triglyceride based monomers were synthesized by the reaction of epoxidized methyl oleate (EMO) and epoxidized soybean oil (ESO) with 4-vinyl benzene sulfonic acid (4VBSA). The products are 1-(4-vinylbenzene sulfonyl)oxy-2-alkonols of epoxidized soybean oil (SESO) and 1-(4-vinylbenzene sulfonyl)oxy-2-alkonols of epoxidized methyl oleate (SEMO). These adducts were characterized by ¹H NMR, ¹³C NMR, IR and CHNS elemental analysis. SESO was found to contain, on the average, 2.47 4VBSA units per triglyceride. SESO was free radically polymerized and co-polymerized with styrene and the mechanical and thermal properties of the resulting thermosets were determined by DMA, DSC and TGA. SEMO was used as a model compound to determine the efficiency of metathesis catalysts for these fatty acid derivatives. The second generation Hoveyda–Grubbs catalyst was found to give best yields. ADMET polymerization of SESO with this catalyst with and without solvent gave ∼80% yield of a thermoset polymer. Polymers obtained by free radical route swelled in water at room temperature, and hydrolyzed in water at 60 °C.     

Polysaccharides ofEremurus. XV. Structure of the glucomannan ofEremurus lactiflorus

Ten oligosaccharides have been isolated from the products of the partial hydrolysis of a native acetylated glucomannan obtained fromEremurus lactiflorus O. Fedtsch. Their structures have been studied with the aid of acid hydrolysis before and after reduction with NaBH₄, by the GLC method, and also by chromatography with markers. The compositions and sequence of the monomers in tetra- and heptaoligo-saccharides have been determined by the¹³C NMR method. The glucommannan ofE. lactiflorus differs from theEremurus glucomannans studied previously by the ratio of monosaccharides, the presence of 0-Ac groups, the degree of polymerization, and the presence of a cellobiose unit (Glcp-Glcp) in the polymer chain. The repeating unit consists of 14 hexose residues.     

Synthesis and chiral recognition properties of two novel chiral calix[4]arene tartaric ester derivatives

Two new chiral calix[4]arene derivatives containing tartaric acid ester moieties were synthesized. The chiral calix[4]arenes are in a ‘cone’ conformation according to NMR spectroscopy. The chiral recognition capabilities of 1–4 toward the guests, 1,2-propanediol and serine methyl ester hydrochloride (SerOMe), were investigated (¹H NMR spectroscopy). The extraction properties of compounds 1 and 2 toward selected α-amino acid methyl esters were also studied.     

Synthesis and characterization of new low bandgap polyfluorene copolymers for bulk heterojunction solar cells

Two new low bandgap alternating polyfluorene copolymers based on dioctylfluorene and donor‐acceptor‐donor monomers have been synthesized via a Suzuki polymerization reaction. The resulting copolymers have low optical bandgaps at 1.99–1.98 eV. The bulk heterojunction polymer solar cells were fabricated with the conjugated polymers as the electron donor and 6.6‐phenyl C₆₁‐butyric acid methyl ester as the electron acceptor. The power conversion efficiencies of the solar cells based on copolymers 1 and 2 are 0.37 and 0.42%, respectively, under the illumination of AM 1.5, 100 mW/cm². The results indicate that the two copolymers are promising conjugated polymers for polymer solar cells. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5336–5343, 2009     

Isolation,Chemical Characterization and Antioxidant Activity of Pectic Polysaccharides of Fireweed (Epilobium angustifolium L.)

The aim of this study was to isolate pectins with antioxidant activity from the leaves of Epilobium angustifolium L. Two pectins, EA-4.0 and EA-0.8, with galacturonic acid contents of 88 and 91% were isolated from the leaves of E. angustifolium L. by the treatment of plant raw materials with aqueous hydrochloric acid at pH 4.0 and 0.8, respectively. EA-4.0 and EA-0.8 were found to scavenge the DPPH radical in a concentration-dependent manner at 17–133 μg/mL, whereas commercial apple pectin scavenged at 0.5–2 mg/mL. The antioxidant activity of EA-4.0 was the highest and exceeded the activity of EA-0.8 and a commercial apple pectin by 2 and 39 times (IC₅₀—0.050, 0.109 and 1.961 mg/mL), respectively. Pectins EA-4.0 and EA-0.8 were found to possess superoxide radical scavenging activity, with IC₅₀s equal to 0.27 and 0.97 mg/mL, respectively. Correlation analysis of the composition and activity of 32 polysaccharide fractions obtained by enzyme hydrolysis and anionic exchange chromatography revealed that the antioxidant capacity of fireweed pectins is mainly due to phenolics and is partially associated with xylogalacturonan chains. The data obtained demonstrate that pectic polysaccharides appeared to be bioactive components of fireweed leaves with high antioxidant activity, which depend on pH at their extraction.     

Calculation of Reactivity Ratios and Sequence Distributions in Copolymers from Monomers 13C-NMR Data

A screening procedure has been developed to predict the average sequence distribution in vinyl copolymers from monomer ¹³C-NMR data. The ¹³C-NMR absorption frequencies of the carbon atoms of the polymerizable double bond are used to calculate the Alfrey-Price Q and e values as previously described by Borchardt and Dalrymple. These, in turn, are used to calculate the monomer reactivity ratios. Reactivity ratios for 54 copolymerizations were calculated by this procedure and compared to literature values. The copolymer sequence distribution may then be determined by means of a computer program written by Harwood. The sequence distribution in copolymers of methacrylic acid and dimethyl-aminoethyl methacrylate, acrylonitrile and methyl methacrylate, 1,1-dichloroethylene and methacrylonitrile, ethyl acrylate and n-butyl methacrylate, and acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate were calculated from reactivity ratios derived from ¹³C-NMR data and compared to literature values. This procedure may be used to calculate the reactivity ratios from ¹³C-NMR spectra of monomers for which no Q and e values are known. By this method the average sequence distribution of such monomers in copolymers may be predicted, significantly reducing the number of copolymers to be synthesized and tested for use in various applications.     

Nouvelle Synthese de L'Acide 3-Desoxy-D-Erythro-2-Hexulosonique (KDG). A Partir De La D-Glucono-1,5-Lactone Synthese Et Etude De RMN De Derives O-Methyles Du KDG

ABSTRACT

3-Deoxy-D-erythro-2-hexulosonic acid (KDG), an important metabolite of bacterial polysaccharide degradation, was prepared from D-glucono-1,5-lactone through a six-step sequence, with a 45% overall yield. Using suitable intermediates. KDG methyl ester and its 5- and 6-O-methylated derivatives were also synthesized. ¹H and ¹³C NMR studies of 5- and 6-O-methylated derivatives (pyranoid and furanoid forms respectively) compared to those of KDG and its methyl ester allowed us to conclude that these two latter compounds exist in equilibrium as forms whose percentages were determined.