ENZYMATICALLY SYNTHESIZED POLYANILINE IN THE PRESENCE OF A TEMPLATE POLY(VINYLPHOSPHONIC ACID): A SOLID STATE NMR STUDY

Template guided enzymatic synthesis of conducting polyaniline (PANI) is a one-step reaction and more importantly, it is an environmentally friendly process. Understanding of the reaction and coupling mechanism at the molecular level is of paramount significance to improve its processability and conductivity. Solid-state NMR techniques are useful to investigate molecular structures of enzymatically synthesized polyaniline (PANI). The PANI sample in three different forms i.e., (a) as-synthesized, self-doped conducting form; (b) dedoped, base form and; (c) redoped, conducting form, are investigated by solid-state ¹³C and ¹⁵N CP/MAS NMR techniques. Solid-state NMR data analysis shows that the structural features of enzymatically synthesized PANI are similar to that of chemically synthesized PANI. The solid-state ¹³C CP/MAS NMR spectrum of the base form of PANI confirmed that benzenoid-quinoid repeating units are present in the backbone of the PANI polymer chain. The poly(vinylphosphonic acid) (PVP) template provides charge compensation during the chain growth of linear polyaniline. After the completion of template-guided synthesis of PANI, it is now possible that the PVP template can be completely removed from the complex by dedoping with aqueous NH₄OH. The detached PANI from the PANI-PVP complex can then be redoped to conducting form without the presence of the template. The conductivity of the PANI and PANI-PVP complex are of the same order of magnitude. The solid-state ¹⁵N CP/MAS NMR chemical shifts are sensitive to charge distribution on the nitrogens in the backbone. The solid-state ¹⁵N CP/MAS NMR spectrum of the base form of the enzymatically derived PANI sample showed the clear signature for benzenoid-quinoid repeating units in the polymer backbone.

     

Enzymatically Synthesized Conducting Polyaniline Nanocomposites: A Solid‐State NMR Study

Abstract

The chiral conducting polyaniline (PANI) nanocomposites [polyacrylic acid/polyaniline/(?) camphorsulphonic acid (CSA)] were synthesized using enzyme, horseradish peroxidase (HRP) in the aqueous buffer solution at pH 4.3. It appears that the enzyme HRP apart being a biocatalyst, plays an important role during the polymerization, which allows PANI to prefer a specific helical conformation whether the induced chirality in the monomer‐CSA complex is either by (+)CSA or (?)CSA. In this paper, we report, the structural characterization of these nanocomposites by solid‐state ¹³C cross‐polarization with magic angle spinning (CP/MAS) NMR techniques. The structural features of PANI in the conducting form of nanocomposite (as‐synthesized) are similar to that of enzymatically and chemically synthesized PANI. Preliminary data also suggest that some portion of nanocomposite samples are not completely doped. Dedoping of as‐synthesized PANI nanocomposite with aqueous NH₄OH shows the spectral features that of the emeraldine base form. Solid‐state ¹³C NMR data suggest that it is possible to detach PAA and CSA from PANI in the nanocomposite material.     

Hydrogen Transfer Polymerization Mechanism of Acrylamide Induced by Propagating Polyacrolein Anion

In order to investigate the interaction between acrolein (AL) and acrylamide (AAm) on anionic copolymerization, the homopolymer-izabilities of AL in the presence of several p-substituted phenyl-acetamides such as p-nitroacetanilide, p-chloroacetanilide, acet-anilide, and p-methylacetanilide were investigated in tetrahydro-furan at 0°C using imidazole as an anionic catalyst. A linear co-relation was obtained by Hammett′ s equation as described by log R /R = 0.28σ. This result suggests that the homopolymeriz- P Po ability of AL is influenced by the structure of the amide compound. An increase of the additive propionamide (PAm) on the homopolym-erization of AL induced by the pyridine-water initiation system increased the polymerization rate R; however, it decreased the intrinsic viscosity [η] of poly-AL. From the measurement of infrared spectroscopy and elementary analysis, the presence of a chain transfer reaction between the poly-AL anion and PAm was found. These results support the presence of interaction between AL and AAm derivatives in the copolymerization system.     

Spectral assignments for 1H, 13C and 15N solution and solid-state NMR spectra of s-tetrazine and dihydro-s-tetrazine derivatives

Tetrazine-based organic species are interesting intermediates for organic synthesis and represent a source of new materials bearing specific properties with potential applications in biology and material science. 1H, 13C, 15N NMR measurements carried out in solution and in the solid-state have been used to characterize a series of 3,6-disubstituted 1,2,4,5-tetrazine/dihydrotetrazine new derivatives. Experimental results presented here provide data for the assignment of 15N chemical shifts including new organic small molecules; two polymers having the tetrazine ring in the main chain and several previously published compounds. We report apparently for the first time 15N experimental chemical shift data for tetrazine systems in the solid state.     

A 1H, 13C and 15N NMR study in solution and in the solid state of six N-substituted pyrazoles and indazoles

Three N-substituted pyrazoles and three N-substituted indazoles [1-(4-nitrophenyl)-3,5-dimethylpyrazole (1), 1-(2,4-dinitrophenyl)-3,5-dimethylpyrazole (2), 1-tosyl-pyrazole (3), 1-p-chlorobenzoylindazole (4), 1-tosylinda-zole (5) and 2-(2-hydroxy-2-phenylethyl)-indazole (6)] have been studied by NMR spectroscopy in solution (1H, 13C, 15N) and in the solid state (13C, 15N). The chemical shifts have been compared with GIAO/DFT calculated absolute shieldings. Some discrepancies have been analyzed.     

Solid state N and C NMR study of dioxomolybdenum (VI) complexes of Schiff bases derived from trans-1,2-cyclohexanediamine

The ¹³C, ¹⁵N CP MAS NMR and FT-IR spectra of dioxomolybdenum (VI) complexes of trans-N,N′-bis-(R-salicylidene)-1,2-cyclohexanediamine (R=H, R=3,5-diCl, R=3,5-diBr, R=4,6-diOCH₃), trans-N,N′-bis-(2-OH-naphthylidene)-1,2-cyclohexanediamine and trans-N-(salicylidene)-N′-(2-OH-naphthylidene)-1,2-cyclohexanediamine have been measured. Comparative analysis of the NMR and IR spectra of the complexes with those of the corresponding ligands has shown that the complexation of the di-Schiff bases leads to changes in the conformation of the ligands and the charge redistribution. The asymmetric structure and non-planar structure of the complexes have been suggested.     

The use of chemical shifts <Emphasis Type="Italic">vs.</Emphasis> coupling constants for studying tautomerism: a combined experimental and theoretical approach

When observing average NMR signals originated from a rapid equilibrium, the procedure to estimate the composition of the mixture is to use interpolation. To illustrate the difficulties of this approach, the much-studied case of the NH and OH tautomers of pyrazolinones will be reexamined. Calculated absolute shieldings and coupling constants were compared with experimental data. Although the large predominance of the OH tautomer in DMSO was confirmed, the result is a little disappointing because no consistency in the percentages was achieved using chemical shifts and coupling constants.     

Effects of polymorphic differences for sulfanilamide, as seen through 13C and 15N solid-state NMR, together with shielding calculations

We recorded both carbon-13 and nitrogen-15 NMR spectra of the three solid forms of sulfanilamide most commonly known. This study led to an interpretation of the solid-state effects seen in cross-polarization magic angle spinning spectra. Relaxation times for the different forms were measured. These show different behaviour for the three forms, arising from mobility variations. To obtain information on local environments, static spectra and spinning sideband manifolds were recorded and analysed for the 15N resonances, using isotopically enriched samples. Shielding asymmetries and anisotropies for the two nitrogen nuclei were obtained, showing very different behaviour for the two sites. Shielding calculations were carried out for both 13C and 15N nuclei, and the results are discussed in relation to the experimental values.     

13C and 15N CP/MAS, 1H–15N SCT CP/MAS and FTIR spectroscopy as tools for qualitative detection of the presence of zwitterionic and non‐ionic forms of ansa‐macrolide 3‐formylrifamycin SV and its derivatives in solid state

¹³C, ¹⁵N CP/MAS, including ¹H–¹³C and ¹H–¹⁵N short contact time CP/MAS experiments, and FTIR methods were applied for detailed structural characterization of ansa‐macrolides as 3‐formylrifamycin SV (1) and its derivatives (2–6) in crystal and in powder forms. Although HPLC chromatograms for 2/CH₃OH and 2/CH₃CCl₃ were the same for rifampicin crystals dissolved in respective solvents, the UV–vis data recorded for them were different in 300–375 nm region. Detailed solid state ¹³C and ¹⁵N CP/MAS NMR and FTIR studies revealed that rifampicin (2), in contrast to 3‐formylrifamycin SV (1) and its amino derivatives (3–6), can occur in pure non‐ionic or zwitterionic forms in crystal and in pure these forms or a mixture of them in a powder. Multinuclear CP/MAS and FTIR studies demonstrated also that 3–6 derivatives were present exclusively in pure zwitterionic forms, both in powder and in crystal. On the basis of the solid state NMR and FTIR studies, two conformers of 3‐formylrifamycin SV were detected in powder form due to the different orientations of carbonyl group of amide moiety. The PM6 molecular modeling at the semi‐empirical level of theory, allowed visualization the most energetically favorable non‐ionic and zwitterionic forms of 1–6 antibiotics, strongly stabilized via intramolecular H‐bonds. FTIR studies indicated that the originally adopted forms of these type antibiotics in crystal or in powder are stable in standard laboratory conditions in time. The results presented point to the fact that because of a possible presence of two forms of rifampicin (compound 2), quantification of the content of this antibiotic in relevant pharmaceuticals needs caution. Copyright © 2013 John Wiley & Sons, Ltd.     

Solid-state C NMR and molecular modeling studies of acetyl aleuritolic acid obtained from Croton cajucara Benth

Solid-state ¹³C nuclear magnetic resonance (¹³C NMR) with magic-angle spinning (MAS) and with cross-polarization and magic-angle spinning (CP/MAS) spectra, and differential scanning calorimetry (DSC) techniques were used to obtain structural data from a sample of acetyl aleuritolic acid (AAA) extracted from the stem bark of Croton cajucara Benth. (Euphorbiaceae) and recrystallized from acetone. Since solid-state ¹³C NMR results suggested the presence of more than one molecule in the unitary cell for the AAA, DSC analysis and molecular modeling calculations were used to access this possibility. The absence of phase transition peaks in the DSC spectra and the dimeric models of AAA simulated using the semi-empirical PM3 method are in agreement with that proposal.     

Secondary structure of peptides 16th. Characterization of proteins by means of13C NMR CP/MAS spectroscopy

50.3 or 75.4 MHz¹³C NMR cross-polarization/magic angle spinning spectra of human hair, horse hair, horse hoof, parrot feather, sperm whale myoglobin, and horse heart cytochrome C were measured. The spectra of human hair and horse hair indicate nearly equal mole fractions of-sheets and-helices and a low percentage of amorphous regions, whereas horse hoof contains a higher fraction of amorphous proteins. The parrot feathers contain a small-helix fraction (ca. 10±5 %) in additon to a large-sheet fraction whereas cytochrome C contains 70–90%-helices. The spectrum of myoglobin could not interpreted in terms of defined secondary structures. The usefulness of the¹³C NMR CP/MAS spectroscopy for the characterization of proteins is compared with that of IR spectroscopy and X-ray diffraction.     

A 13C, 15N and 77Se NMR Study of Some Diseleno Sulfonamides

¹³C, ¹⁵N and ⁷⁷Se NMR data are reported for ten title compounds. Some linear correlations of selenium, nitrogen and carbon chemical shifts values are described. A number of one- and two- bond ⁷⁷Se-¹³C coupling constants values are also given.     

Solid-state NMR studies of pharmaceutical solids in polymer matrices

Biodegradable drug-delivery systems can be formulated to release drug for hours to years and have been used for the controlled release of medications in animals and humans. An important consideration in developing a drug-delivery matrix is knowledge of the long-term stability of the form of the drug and matrix after formulation and any changes that might occur to the drug throughout the delivery process. Solid-state NMR spectroscopy is an effective technique for studying the state of both the drug and the matrix. Two systems that have been studied using solid-state NMR spectroscopy are presented. The first system studied involved bupivacaine, a local anesthetic compound, which was incorporated into microspheres composed of tristearin and encapsulated using a solid protein matrix. Solid-state ¹³C NMR spectroscopy was used to investigate the solid forms of bupivacaine in their bulk form or as incorporated into the tristearin/protein matrix. Bupivacaine free base and bupivacaine-HCl have very different solid-state NMR spectra, indicating that the molecules of these compounds pack in different crystal forms. In the tristearin matrix, the drug form could be determined at levels as low as 1:100 (w/w), and the form of bupivacaine was identified upon loading into the tristearin/protein matrix. In the second case, the possibility of using solid-state ¹³C NMR spectroscopy to characterize biomolecules lyophilized within polymer matrices is evaluated by studying uniformly ¹³C-labeled asparagine (Asn) in 1:250 (w/w) formulations with poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) (PVA). This work shows the capability of solid-state NMR spectroscopy to study interactions between the amino acid and the polymer matrix for synthetic peptides and peptidomimetics containing selective ¹³C labeling at the Asn residue.     

Reaction of o-phenylenediamine with diacetyl monoxime: characterisation of the product by solid-state 13C and 15N MAS NMR

2,3-dimethylquinoxaline (DMQ) and dimethylglyoxime (DMGH2) form a 1:1 hydrogen-bonded complex in the solid state, which is completely dissociated in methanol solution. There are small differences in solid-state 13C shifts between the separated components DMQ and DMGH2 and the complex. The changes in 15N solid-state chemical shifts are more significant: the hydrogen bond imparting a low frequency shift of ca 19 ppm. The effect of direct protonation on the DMQ solid-state 15N shifts was measured, and the experimental 15N data correlated with those from GIAO molecular orbital (MO) calculations.     

Invertomers at nitrogen in aziridine carboxylates by mltltinuclear (1H,13C,17O,and15N) NMR study

A confrgurational and conformational study of NH, N-acetyl- and N-sulfonylaziridine carboxylates is performed by¹H ,¹³C,¹⁷O, and¹⁵N NMR spectroscopy. The presence of acetyl and su fonyl groups on the ring nitrogen atom seems to reduce greatly the configurational stability at nitrogen.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1226–1234, September, 1995.     

Mercury(II) cyanide complexes with alkyldiamines: solid-state/solution NMR,computational, and antimicrobial studies

Mercury cyanide complexes of alkyldiamines (1–6), [Hg(L)(CN)₂] (where L?=?en (1,2-diaminoethane), pn (1,3-diaminopropane), N-Me-en, N, N′-Me₂-en, N, N′-Et₂-en, and N, N′-ipr₂-en), have been synthesized and characterized by elemental analysis, IR, ¹³C, and ¹⁵N solution NMR in DMSO-d₆, as well as ¹³C, ¹⁵N, and ¹⁹⁹Hg solid-state NMR spectroscopy. Complexes 1 and 2 have been studied computationally, built and optimized by GAUSSIAN03 using DFT at B3LYP level with LanL2DZ basis set. Binding modes of en and bn (where bn?=?1,4-diaminobutane) toward Hg(CN)₂ are completely different. Complexes with en and pn show chelating binding to Hg(II), while bn behaves as a bridging ligand to form a polymeric structure, [Hg(CN)₂-bn]_∞ [B.A. Al-Maythalony, M. Fettouhi, M.I.M. Wazeer, A.A. Isab. Inorg. Chem. Commun., 12, 540 (2009).]. The solution ¹³C NMR of the complexes demonstrates a slight shift of the ?C≡N (0.9 to 2?ppm) and ?C–NH₂ (0.25 to 6?ppm) carbon resonances, while the other resonances are relatively unaffected. ¹⁵N labeling studies have shown involvement of alkyldiamine ligands in coordination to the metal. The principal components of the ¹³C, ¹⁵N, and ¹⁹⁹Hg shielding tensors have been determined from solid-state NMR data. Antimicrobial activity studies show that the complexes exhibit higher antibacterial activities toward various microorganisms than Hg(CN)₂.     

Investigation of the chemical modifications of beech wood lignin during heat treatment

Holocellulose, Klason lignin and milled wood lignin (MWL) of beech wood were extracted before and after heat treatment and analysed using CP MAS ¹³C NMR, ¹³C NMR, ³¹P NMR and size exclusion chromatography (SEC). Experimental results showed that the thermal treatment degrades hemicelluloses and affects lignin polymer through depolymerisation due mainly to cleavage of β-aryl-ether linkages and recondensation reactions. The spectroscopic analysis of MWL demonstrated that these recondensation reactions involved mainly guaiacyl units through formation of 5,5′-biphenolic and diarylmethane structures.Analysis of molecular weight distribution of MWL by SEC indicated that average molecular weights of heat treated milled wood lignin were lower than those of native milled wood lignin.     

A C and N experimental NMR and theoretical study of the structure of linear primary aliphatic amines and ammonium salts: from C1 to C18

Eighteen aliphatic linear amines, from methylamine to stearylamine, have been experimentally studied by NMR and theoretically calculated at the GIAO/B3LYP/6-311++G(d,p) level. A partial exploration of their conformation has been carried out, mainly to determine the effect on the chemical shifts. In solution and for neutral amines, ¹⁵N chemical shifts indicate a mixture of two conformations. In the solid state (CPMAS NMR) only the subset of solid amines has been studied (from C14 to C18). The ¹⁵N signals of the corresponding ammonium salts in the solid state depend on the counteranions, Cl⁻ and CF₃CO₂⁻, a result that is theoretically proven.     

On the accessibility and structure of xylan in birch kraft pulp

The structure of -(14)-xylan, both in isolated form and as a component of bleached birch kraft pulp, was studied employing CP/MAS ¹³C NMR spectroscopy. Bleached birch kraft pulp was treated with xylanases or alkali in order to distinguish between accessible and inaccessible xylan. In xylan which was alkali-extracted from bleached birch kraft pulp, the relative contents of xylose and 4-O-methylglucuronic acid were 99.4 and 0.6 weight %, respectively, and the degree of polymerization was 70. The supermolecular structure of xylan is very sensitive to the surrounding environment. All extracted xylan chains were accessible to water and methanol and the solvent molecules easily exchanged. In bleached birch kraft pulp, cellulose fibrils interact with xylan chains, causing these to adopt a conformation similar to one of the configurations observed for dry xylan. In birch pulp, about 1/3 of the xylan was found to be accessible to digestion by xylanases or extraction with 5% w/w potassium hydroxide (aq). A signal at 81.7ppm in the C-4 region of the CP/MAS ¹³C NMR spectrum of bleached birch kraft pulp originated from xylan at the accessible fibril surfaces. A portion of a broad signal at 83.5ppm reflected inaccessible xylan, which is probably present as co-aggregates with cellulose fibril aggregates.     

Molecular structure of the unusual complex of 1-piperidineacetic acid with 2,4,6-trinitrophenol studied by X-ray, FTIR and H, C and C CP MAS NMR

Crystals containing three kinds of molecules 1-piperidiniumacetate (II), 1-piperidiniumacetic acid (III) and 2,4,6-trinitrophenolate (picrate, TNP⁻), belong to the monoclinic system, space group P2₁/c and Z=4, a=12.831(3), b=26.093(5), c=7.157(1) Å, β=101.18(3)°, R=0.0758. The zwitterion molecule (II) is a double acceptor of protons from two molecules of 1-piperidiniumacetic acid (III) (N–HO, 2.735(5) Å and O–HO, 2.472(5) Å), and a donor of proton to the picrate molecule (N–HO, 2.747(5) Å). These three molecules, which have three donor centers and several acceptor groups, form hydrogen-bonded chains parallel to the z axis. The oxygen atoms inactive in these hydrogen bonds, are engaged in the C–HO short contacts, which can be treated as weak hydrogen bonds, and join the chains into a three-dimensional network. The presence of protonated 1-piperidineacetic acid (III) and its zwitterion (II) in the crystal has been confirmed by ¹³C CP MAS NMR and solid state FTIR spectra.