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.

     

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.     

Solid State NMR of Drugs: Soluble Aspirin

Abstract

Natural abundance ¹³C NMR spectra of a soluble aspirin and model mixtures of acetylsalicylic acid with buffering components have been recorded in the solid state by using the combined techniques of cross polarization, high-power decoupling and magic-angle spinning. The solid-state spectrum of the soluble aspirin tablet showed more resonances than the solution spectrum. These multiplicities were originated in the buffer mixture containing citric and tartaric acid, as well as their salts. Solid-state ¹³C NMR was therefore found to provide information that is lost in the solution spectrum due to the fast proton exchange between the organic acids and their conjugated salts.     

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.     

Interaction and Scale of Mixing in Cellulose Acetate/Poly(<Emphasis Type="Italic">N</Emphasis>-vinyl Pyrrolidone-co-vinyl Acetate) Blends

Binary blends and pseudo complexes of cellulose acetate (CA) with vinyl polymers containing N-vinyl pyrrolidone (VP) units, poly(N-vinyl pyrrolidone) (PVP) and poly(N-vinyl pyrrolidone-co-vinyl acetate) [P(VP-co-VAc)], were prepared, respectively, by casting from mixed polymer solutions in N,N-dimethylformamide as good solvent and by spontaneous co-precipitation from solutions in tetrahydrofuran as comparatively poor solvent. The scale of miscibility and intermolecular interaction were examined for the blends and complexes by solid-state ¹³C-NMR spectroscopy. It was revealed that the formation of complexes was due to a higher frequency of hydrogen-bonding interactions between the residual hydroxyl groups of CA and the carbonyl groups of VP residues in the vinyl polymer component. From measurements of CP/MAS spectra and proton spin-lattice relaxation times (T_1ρ^H) in the NMR study, the existence of the hydrogen-bonding interaction was also confirmed for the miscible blends and the homogeneity of the mixing was estimated to be substantially on a scale within a few nanometers.     

Solid-state Na and C NMR characterization of Na3C60

Two separate samples of Na₃C₆₀ were prepared by direct reaction of C₆₀ with sodium metal vapor, and subjected to different annealing times of 10 days and 16 days. Solid-state ¹³C and ²³Na NMR, along with elemental analysis, powder X-ray diffraction (XRD) and Raman spectroscopy, were used to characterize both samples. The Raman spectra of both materials have a single peak at 1447 cm⁻¹ which correspond to the A_g peak of C₆₀³⁻, consistent with the stoichiometry of Na_xC₆₀ with x=3. The powder XRD patterns are also virtually identical for both samples. However, solid-state ²³Na and ¹³C NMR spectra of the two samples are significantly different, suggesting a relationship between annealing times and the final structure of the alkali fulleride. Variable-temperature ²³Na magic-angle spinning (MAS) NMR experiments reveal the existence of two or three distinct sodium species and reversible temperature-dependent diffusion of sodium ions between octahedral and tetrahedral interstitial sites. ¹³C MAS NMR experiments are used to identify resonances corresponding to free C₆₀ and fulleride species, implying that the samples are segregated-phase materials composed of C₆₀ and non-stoichiometric Na₃C₆₀. Variable-temperature ¹³C MAS NMR experiments reveal temperature-dependent motion of the fullerides.     

Designing nickel phthalocyanine periphery by alkyl chain via [1,3,4]-oxadiazole

Nickel phthalocyanine (NiPc, 1) periphery has been decorated by alkyl chains of varying chain length via [1,3,4]-oxadiazole moiety (NiPcs 3a–3f). All the newly synthesized compounds NiPcs 3a–3d have been completely characterized by elemental analysis, FT-IR, solid-state UV-Vis, and solid-state ¹³C NMR spectroscopy, in addition to X-ray diffraction, scanning electron microscopy, and thermal analysis. The effect of chain length in the NiPc periphery on electronic absorption and DC electrical conductivity has been investigated.     

Structural and spectroscopic analysis of dipeptide <Emphasis Type="SmallCaps">l</Emphasis>-methionyl-glycine and its hydrochloride

Dipeptide l-methionyl-glycine (Met-Gly) hydrochloride was characterized structurally by means of solid-state linear polarized IR (IR-LD) spectroscopy of oriented samples as colloidal suspension in nematic liquid crystal. Quantum chemical ab initio calculations and vibrational analysis support the experimental data. ¹H and ¹³C nuclear magnetic resonance (NMR) data, mass spectrometry (ESI-MS and FAB-MS) techniques, thermogravimetry (TGV), and differential scanning calorimetry (DSC) method were employed as well. The experimental and theoretical data of hydrochloride salt were compared with analogous data of the neutral dipeptide with the aim to explain the role of intermolecular hydrogen bonding on the conformational behavior and spectroscopic properties of the compound studied.     

Influence of chain length of prepolymers in permanent memory effect of PDLC assessed by solid-state NMR

ABSTRACT

The relationship between linear chain (ethylene oxide units) length of polymerisable monomers with morphology, electro-optical properties and ¹³C nuclear magnetic resonance (NMR) spectroscopy of the corresponding polymer-dispersed liquid crystal (PDLC) films was investigated. The preferred liquid crystal molecule alignment and permanent memory effect of PDLC were greatly influenced by the length of the molecular chain of prepolymers to be incorporated as a polymer matrix. By increasing the number of ethylene oxide in prepolymer chain and maintaining the number of functionalities (polymerisable groups in each monomer molecule), the permanent memory effect of PDLC increased, as proved by solid-state ¹³C NMR spectroscopy.     

Characterization of Functional Groups in Estuarine Dissolved Organic Matter by DNP-enhanced 15N and 13C Solid-State NMR

Estuaries are key ecosystems with unique biodiversity and are of high economic importance. Along the estuaries, variations in environmental parameters, such as salinity and light penetration, can modify the characteristics of dissolved organic matter (DOM). Nevertheless, there is still limited information about the atomic-level transformations of DOM in this ecosystem. Solid-state NMR spectroscopy provides unique insights into the nature of functional groups in DOM. A major limitation of this technique is its lack of sensivity, which results in experimental time of tens of hours for the acquisition of ¹³C NMR spectra and generally precludes the observation of ¹⁵N nuclei for DOM. We show here how the sensitivity of solid-state NMR experiments on DOM of Seine estuary can be enhanced using dynamic nuclear polarization (DNP) under magic-angle spinning. This technique allows the acquisition of ¹³C NMR spectra of these samples in few minutes, instead of hours for conventional solid-state NMR. Both conventional and DNP-enhanced ¹³C NMR spectra indicate that the ¹³C local environments in DOM are not strongly modified along the Seine estuary. Furthermore, the sensitivity gain provided by the DNP allows the detection of ¹⁵N NMR signal of DOM, in spite of the low nitrogen content. These spectra reveal that the majority of nitrogen is in the amide form in these DOM samples and show an increased disorder around these amide groups near the mouth of the Seine.     

Encapsulation of Indomethacin in PVP: Solid-State NMR Studies

Summary: ¹³C solid-state NMR and ¹H relaxation time measurements have been used to determine the structure of the crystalline and amorphous forms of the pharmaceutical drug indomethacin. Cross-polarization dynamics parameters were calculated for individual NMR resonances providing an insight into the mobility of functional groups in two forms of indomethacin. The changes of mobility in indomethacin/polyvinylpyrrolidone (PVP) formulation have been investigated via¹H-¹³C solid-state NMR methods. Differences between the amorphous material and its crystalline counterpart have been observed. The γ-amorphous indomethacin rapidly crystallizes with time. It has been shown that encapsulation in the PVP stabilizes the amorphous form of the drug by preventing crystallization due to reduced mobility of the guest in the formulation.     

An Au(III) complex of glycyl- S -serine: a linear polarized IR and 1H- and 13C-NMR investigation

The structure of a mononuclear Au(III) complex of the dipeptide glycyl-S-serine (Gly-Ser) has been predicted using solid-state linear dichroic IR (IR-LD) spectroscopy, based on an orientation technique in a nematic liquid crystal suspension. Results are compared with data from ¹H- and ¹³C-NMR, MS, elemental analysis, thermogravimetry and differential scanning calorimetry. The metal ion is coordinated as a tridentate through NH₂, N (from deprotonated amide) and O (COO^?) groups to form [Au(C₅H₉N₂O₄)Cl], with the fourth position of the square-planar coordination sphere being completed by a Cl^? ion.     

Stereochemicai study of 7-aryl-1,7,8,8a-tetrahydro-3(2H)indolizinones by1H and13C NMR

Stereochemistry of 7-aryl-1,7,8,8a-tetrahydro-3(2H)-indolizinones was studied by¹H and¹³C NMR. Complete assignment of¹H NMR signals and analysis of¹H-¹H coupling constants were performed using the iterative PANIC program. Values of³ J _6,7,³ J _7,8endo, and⁴ J _5,7 allow one to unambiguously identify the correspondingexo- andendo-stereoisomers. For stereoisomers with exo-orientation of H(7), complete assignment of¹³C NMR signals was performed on the basis of analysis of the¹³C-¹H coupling constants using two dimensional heteronuclear shift-correlating spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 591–593, March, 1996.     

Tin(IV) Chloride Complexes of β-Chlorovinyl Aldehydes: A Multinuclear Nmr Characterization in Solution

Abstract

The reaction of SnCl₄ with β-chlorovinyl aldehydes in anhydrous dichloromethane gave a series of octahedral complexes of the general formula SnCl₄·2L (L = aldehyde). The adducts have been characterized in solution using multinuclear (¹H, ¹³C, and ¹¹⁹Sn) NMR and IR spectroscopy. Solution NMR studies show that the complexes undergo rapid ligand dissociation at ambient temperature. Ligand exchange is slowed significantly at low temperature, such that, in most of the complexes, it is possible to identify both the cis and trans isomers with predominance of the cis form. The magnitude of the metal-ligand interaction was estimated on the basis of ¹¹⁹Sn NMR chemical shifts and used to classify the aldehydes studied according to their Lewis basicity.     

NMR study of mono- and dilithium derivatives of alkyl and arylstannanes

Element-centered mono- and dianions of alkyl- and arylstannanes were studied by NMR spectroscopy. The ¹³C and ¹¹⁹Sn NMR chemical shifts for the dianions R₂SnLi₂ (R = Ph, Et) were measured for the first time.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2229–2231, October, 2004.     

A set of triple-resonance nuclear magnetic resonance experiments for structural characterization of organophosphorus compounds in mixture samples

The ¹H, ¹³C correlation NMR spectroscopy utilizes J_CH couplings in molecules, and provides important structural information from small organic molecules in the form of carbon chemical shifts and carbon-proton connectivities. The full potential of the ¹H, ¹³C correlation NMR spectroscopy has not been realized in the Chemical Weapons Convention (CWC) related verification analyses due to the sample matrix, which usually contains a high amount of non-related compounds obscuring the correlations of the relevant compounds. Here, the results of the application of ¹H, ¹³C, ³¹P triple-resonance NMR spectroscopy in characterization of OP compounds related to the CWC are presented. With a set of two-dimensional triple-resonance experiments the J_HP, J_CH and J_PC couplings are utilized to map the connectivities of the atoms in OP compounds and to extract the carbon chemical shift information. With the use of the proposed pulse sequences the correlations from the OP compounds can be recorded without significant artifacts from the non-OP compound impurities in the sample. Further selectivity of the observed correlations is achieved with the application of phosphorus band-selective pulse in the pulse sequences to assist the analysis of multiple OP compounds in mixture samples. The use of the triple-resonance experiments in the analysis of a complex sample is shown with a test mixture containing typical scheduled OP compounds, including the characteristic degradation products of nerve agents sarin, soman, and VX. The viability of the approach in verification analysis is demonstrated in the analysis of the 30th OPCW Proficiency Test sample.     

Study of Ion-Exchanged Microporous Lithosilicate Na-RUB-29 Using Synchrotron X-Ray Single-Crystal Diffraction and Li MAS NMR Spectroscopy

Synchrotron X-ray single-crystal diffraction analyses revealed that as-synthesized and Na-exchanged RUB-29 (Cs_1−x, Na_x)₁₄Li₂₄[Si₇₂Li₁₈O₁₇₂]·yH₂O (x=0, 0.9) displays the lattice symmetry I222. With increasing ion-exchange time, the Na cations preferentially replace Cs in the larger sites located at the intersections of the 10MR/10MR/8MR channels. The smaller Cs sites are then replaced. While Na cations are easily incorporated on the Cs sites, most of non-framework Li cations remain in the channel system. Relocation of Li cations onto new sites within the channels was observed only after 13 days of ion exchange. Using high-field (14.1 T) NMR spectroscopy, at least six separate ⁶Li resonances could be resolved for the first time by solid-state ⁶Li MAS NMR spectroscopy and assigned to Li in the framework and non-framework sites of the microporous lithosilicate materials. The fate of Li in both framework and extra-framework sites during exchange was also followed by ⁶Li MAS NMR spectroscopy with an Na-exchanged RUB-29 powder sample.     

Correlation NMR spectroscopy of 1,1-dichloro-2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-diene

Assignment of all of the signals in the¹H and¹³C NMR spectra of 1,1-dichloro-2,3,4,5-tetraphenyl-l-germacyclopenta-2,4-diene has been carried out using two-dimensional NMR spectroscopy. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 3, pp. 623–625, March, 1997.     

Synthesis of alkyl-substituted phosphorus phthalocyanines and triazatetrabenzocorroles

New alkyl-substituted phosphorus phthalocyanines and triazatetrabenzocorroles were synthesized. The structures of these complexes were confirmed by ¹H, ¹³C, and ³¹P NMR spectroscopy, mass spectrometry, and electronic absorption spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1403–1407, July, 2007.     

X-ray photoelectron spectra and structure of 2-(2-phenylhydrazono) acetoacetanilide

2-(2-Phenylhydrazono)acetoacetanilide, itsN-methyl derivatives, and model compounds were studied by X-ray photoelectron spectroscopy. The chemical shifts were obtained from the¹³C NMR spectra. A correlation between the calculated charges, the binding energies on N atoms, and the¹³C NMR chemical shifts was found. The analysis of the XPS data and the¹³C NMR chemical shifts led to the conclusion that crystalline 2-(2-phenylhydrazono)acetoacetanilide exists mainly in the oxo hydrazone form. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 488–491, March, 1999.