Diffusion of water and ethanol in ion-exchange membranes: limits of the geometric approach

Diffusion coefficients of water as a solvent and ethanol as a tracer in sulphonated polyethylene (SPE) were measured by the pulsed-gradient spin-echo NMR method. Comparison with the data available for a number of ionic and non-ionic polymers and solvents shows that, except for Nafion, all the materials exhibit a fairly universal dependence of diffusivity on the volume fraction of the solvent. This result is explained on the basis of the geometric obstruction approach and general conditions are formulated for the observed universal dependence. Explanations are proposed for the peculiar behaviour of Nafion and for the low diffusivity of ethanol within the same framework.     

Structural Assignment of Side Chain Liquid Crystalline Monomer and Polymer by 1-D and 2-D Solution NMR Studies

In the present study, the synthesis and characterization of a methacrylic-based side chain liquid crystalline monomer and its polymer were investigated with the aid of both 1-D and 2-D nuclear magnetic resonance (NMR) techniques. The mesophase characteristics of the monomer and polymer were determined by hot-stage optical polarized microscopy (HOPM). The nematic and smectic phases were observed for the monomer and polymer. Furthermore, ¹³C spin-lattice relaxation time measurements were performed on the above systems in order to monitor molecular dynamics. The present study provides an opportunity to carry out a systematic comparison of the evolution of structural as well as dynamical changes of the monomer and the polymer.     

Pseudo cyclic ionophores: ‘Binary-effect’ of quinolinyloxy groups at both ends of oligoethylene glycols on the conformational stabilization of their complexes with alkali metal salts

A series of noncyclic neutral ionophores has been synthesized by the reaction of oligoethylene glycol dihalides with 8-quinolinol. Complexation properties for alkali metal picrates were evaluated from solvent extraction and bulk liquid membrane transport experiments. Complexation profiles of the newly synthesized ionophores with a hexyl chain were similar to those of their homologues without the hexyl chain in the extraction experiments. Among them, the pentaethylene glycol derivatives showed the highest extraction efficiency and selectivity towards potassium ion. From the¹H NMR spectra (400 MHz), the change in chemical shifts of the aromatic protons upon the addition of alkali metal thiocyanates suggested the existence of a stabilization effect which is caused by intramolecular stacking conformations between the quinoline rings during complexation. Aryl stacking interactions depend on the size of the cations and on the chain length of the oligoethylene glycol. The relationship between transport ability towards alkali metal cations and lipophilicity of these ionophores is also discussed.     

Na-nitroprusside and HgCl2 modify the water permeability and volume of human erythrocytes

The passage of water through the aquaporin-1 (AQP1) transmembrane channel protein of the human erythrocyte is known to be inhibited by organic mercurials such as p-chloromercuribenzoate (pCMB), which react with the free SH-group of the critical cysteine (Cys189) located near the constriction of the AQP1 water-specific channel. Sodium nitroprusside (SNP), which is known as a nitric oxide (NO) donor in interactions with SH-containing molecules, is shown here to suppress the diffusional water permeability (P(d)) of the erythrocyte membrane, presumably as a result of reaction with the Cys189 of the human erythrocyte AQP1 water channels. Further, treatment of erythrocytes with HgCl(2) is found to result in a cell volume decrease that can be related to activation of membrane K(+)-selective Gárdos channels and subsequent loss of intracellular K(+) and cell shrinkage. The variations in P(d) and volume of the erythrocyte were deduced from induced variations in the measured proton ((1)H) nuclear magnetic resonance (NMR) transverse (T(2)) relaxation functions of water exchanging between diamagnetic intracellular and paramagnetic extracellular compartments of the 20-25% hematocrit samples. The extracellular solvent contained 10 mM membrane-impermeable paramagnetic Mn(2+) ions. The (1)H-T(2) NMR technique allows determination of the time constant tau(exch) (for exchange of the erythrocyte intracellular water) that is inversely proportional to the permeability coefficient P(d) when the intracellular water volume is left unmodified, as in the case of SNP-treated erythrocytes. However, for HgCl(2)-treated erythrocytes, this technique showed simultaneous variation of both tau(exch) and the volume ratio V(in)/V(out) of intracellular and extracellular water in proportions suggesting that P(d) was left unmodified. The HgCl(2) effect has been found to be partly reversible by the reducing activity of added mercaptoethanol.     

Structure of red and orange fluorescein

The structures of colorless, red, and yellow-orange fluorescein have been investigated by a combination of solution and solid state¹³C NMR. It is demonstrated that the three forms have lactonic, zwitterionic, and quinoid structures, respectively. Conflicting X-ray, NMR, and IR structural evidence is discussed for samples of red fluorescein which cannot readily be obtained in definite crystalline form. It is concluded that solid-state¹³C NMR spectroscopy is superior by revealing primarily the molecular structure but being fairly insensitive toward lattice variations.The Editors regret the long delay in having this paper printed due to an unfortunate administrative error.     

Structural elucidation of the oxidation product of aminoethylcysteine ketimine decarboxylated dimer by peroxynitrite

Aminoethylcysteine ketimine decarboxylated dimer (2) is a natural sulfur compound with antioxidant properties. 2 Inhibits some reactions mediated by peroxynitrite, a strong oxidizing and nitrating agent that reacts with several biomolecules. This work aims to elucidate the structure of the product resulting from the interaction of 2 with peroxynitrite using 1D and 2D NMR experiments and ion trap mass spectrometry. This product is a dimerized form of 2 and is hereafter referred to as 3. During the reactions leading to 2 and during the formation of 3, no chiral selection is operated; all optical isomers are present in D₂O and have been evidenced by ¹H NMR methods in D₂O plus β- or γ-cyclodextrin.     

Determination of components of the order parameter tensor of cholesteryl myristate by1H NMR data

The order parameter and orientation of the long axis of a cholesteryl myristate molecule have been determined by the second, fourth, and sixth moments of the¹H NMR line of a polycrystalline sample in the smectic phase. The effects of molecular diffusion in the cholesteric phase are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1269–1272, July, 1995.     

Quality assessment of Radix Codonopsis by quantitative nuclear magnetic resonance

Radix Codonopsis (Dangshen) is a famous traditional Chinese medicine and has long been used for replenishing energy deficiency, strengthening the immune system, lowering blood pressure and improving appetite in China, Japan and Korea. A highly specific quantification method using ¹H NMR has been developed for the simultaneous determination of novel quaternary ammonium alkaloids codotubulosine A and B, adenosine and 5-(hydroxymethyl)furfural in Radix Codonopsis materials Codonopsis pilosula, C. pilosula var. modesta, C. tangshen, C. tubulosa, C. subglobosa, C. clematidea, C. lanceolota and Campanumoea javanica collected from different regions of China and Taiwan. A solid-phase extraction with C-18 cartridge followed by elution with water can easily remove sugars the major components that may affect the determination of target constituents. In the ¹H NMR spectrum, the signals of N-CH₃ of codotubulosine A (δ 2.75) and B (δ 2.83), H-8 of adenosine (δ 8.15), and CHO signal of 5-(hydroxymethyl)furfural (δ 9.49) are well separated from other signals in [²H₄]methanol. The quantity of the compounds was calculated by the relative ratio of the integral values of the target peaks of each compound to the known amount of internal standard pyrazine. The described NMR method is found to be relatively simple, specific, precise and accurate for the quality control of Radix Codonopsis herbs and no reference compounds are required for calibration curves, in comparison to conventional HPLC methods, for instance.     

Evidences of a hydrolysis process in the synthesis of N-vinylcaprolactam-based microgels

The hydrolysis process suffered by vinylcaprolactam (VCL) monomer during polymerization and the way of avoiding it is a matter of considerable interest when the final material is used in biomedical applications. In this work, in order to study the hydrolysis process in the synthesis of VCL-based microgels, VCL was polymerized by emulsion polymerization in batch and semi-batch reactors by using N,N′-methylenebisacrylamide (BA) as cross-linker and potassium persulfate (KPS) as initiator. Moreover, the partial conversion evolutions of VCL and BA were analyzed by ¹H NMR. The colloidal characterization was carried out by measuring the final average diameters as a function of temperature. The results showed that there were two competitive reactions (hydrolysis and propagation) in the polymerizations carried out in the absence of a buffer. However, VCL did not suffer hydrolysis by adding a buffer in the recipes. A new reliable method for the determination of the partial conversions was developed using the quantitative NMR method. The final cross-linked colloidal particles (microgel particles) obtained in the buffered reaction presented the conventional swelling de-swelling behavior corresponding to temperature sensitive microgels.     

Structural characterization of C-S-H and C-A-S-H samples—Part II: Local environment investigated by spectroscopic analyses

Spectroscopic studies (¹H, ²³Na and ²⁷Al MAS NMR and Raman spectroscopy) have been used to characterize three series of C-S-H samples (0.8<Ca/Si<1.7): one C-S-H series, one aluminum inserted C-S-H series (named C-A-S-H series), and one sodium and aluminum inserted C-S-H series (named C-N-A-S-H series). Previous Rietveld analyses have been performed on the two first series and have clearly shown that (1) a unique ‘tobermorite M defect’ structural model allows to describe the C-S-H structure whatever the Ca/Si ratio and (2) the insertion of aluminum into the C-S-H structure led to the degradation of the crystallinity and to a systematic increase of the basal spacing of about 2 Å regardless the Ca/(Si+Al) ratio (at a constant Al/Si ratio of 0.1). Spectroscopic investigations indicate that the main part of the Al atoms is readily incorporated into the interlayer region of the C-S-H structure. Al atoms are mainly inserted as four-fold coordinated aluminates in the dreierketten silicate chain (either in bridging or paired tetrahedra) at low Ca/Si ratio. Four-fold aluminates are progressively replaced by six-fold coordinated aluminates located into the interlayer region of the C-S-H structure and bonded to silicate chains. Investigation of the hydrogen bonding in C-S-H indicates that the main part of the hydrogen bonds is intra-main layer, and thus explains the low stacking cohesion of the C-S-H structure leading to its nanometric crystal size and the OD character of the tobermorite like structures.     

A comparative study of NMR chemical shifts of sparteine thiolactams and lactams

The ¹³C and ¹H NMR spectra of the four possible thiolactams of sparteine (1) were recorded and the thiolactam group effects were determined. Most of the effects are greater than those of the lactam group in the oxo analogs. A good linear correlation between the ¹³C chemical shifts of CS and those of CO was found. The effects could help in assignment of the spectra and determination of conformation of thiolactams and related thiocarbonyl compounds.     

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.     

N-Acyl andN-sulfonyl derivatives of thiazolidines

The major reaction center in the reaction of 4,4-dialkyl-5-methylene-2-phenyliminothiazolidines with acid chlorides or anhydrides and with arenesulfonyl chlorides is the nitrogen atom at position 3 of the ring.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2968–2970, December, 1996.     

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.     

[1,3]Dioxolo[5,6][1]benzothieno[2,3-c]-quinolin-6(5H)-ones

Summary The reaction of 3,4-methylenedioxycinnamic acid (1) with thionyl chloride resulted in the formation of 7-chlorothieno[2,3-f]-1,3-benzodioxole-6-carbonyl chloride (2) and cinnamoyl chloride (3). Subsequent reaction of the former withp-substituted anilines led to the formation of 7-chloro-N-(p-substituted phenyl)-thieno[2,3-f]-1,3-benzodioxole-6-carboxamides (4a–c) which on photocyclization afforded 2-substituted [1,3]dioxolo[5,6][1]benzothieno[2,3-c]quinolin-6(5H)-ones (5a–c) in fairly good yields and high purity. The structures have been confirmed by IR,¹H NMR, and analytical methods.Accepted for presentation at the Hong Kong International Symposium on Heterocyclic Chemistry (August 13–16, 1995)     

Identification and quantification of the main organic components of vinegars by high resolution 1H NMR spectroscopy

A detailed analysis of the proton high-field NMR spectra of vinegars (in particular of Italian balsamic vinegars) is reported. A large number of organic substances belonging to different classes, such as carbohydrates, alcohols, organic acids, volatile compounds and amino acids, were assigned. The possibility of quantification of the substances identified in the whole vinegar sample, without extraction or pre-concentration steps, was also tested. The data validity was demonstrated in terms of precision, accuracy, repeatability and inter-day reproducibility. The effects of the most critical experimental parameters (sample concentration, water suppression and relaxation time) on the analysis response were also discussed. ¹H NMR results were compared with those obtained by traditional techniques (GC-MS, titrations), and good correlations were obtained. The results showed that ¹H NMR with water suppression allows a rapid, simultaneous determination of carbohydrates (glucose and fructose), organic acids (acetic, formic, lactic, malic, citric, succinic and tartaric acids), alcohols and polyols (ethanol, acetoin, 2,3-butanediol, hydroxymethylfurfural), and volatile substances (ethyl acetate) in vinegar samples. On the contrary, the amino acid determination without sample pre-concentration was critical. The ¹H NMR method proposed was applied to different samples of vinegars, allowing, in particular, the discrimination of vinegars and balsamic vinegars.     

Diels-Alder reaction of 2-phosphaindolizines catalysed by organoaluminium reagent: theoretical and experimental results

Theoretical calculations at the DFT (B3LYP/6-31+G^**) level of the model Diels-Alder (DA) reactions of 1-methyl-3-(methoxycarbonyl)-2-phosphaindolizine with 1,3-butadiene in the presence of methylaluminium dichloride reveal that the co-ordination of organoaluminium reagent to the carbonyl oxygen increases the activation barrier compared to that for the uncomplexed 2-phosphaindolizine. On the other hand, co-ordination of the organoaluminium reagent to the σ², λ³ P atom lowers the activation barrier by ∼6 kcal mol⁻¹. 1-Methyl-2-phosphaindolizines having an electron-withdrawing group at the 3-position only undergo DA reaction with 2,3-dimethylbutadiene in the presence of the ethylaluminium dichloride catalyst in methylene chloride at a low temperature to afford [2+4] cycloadducts. The formation of an intermediate having the ethylaluminium reagent co-ordinated to σ², λ³ P atom has been detected by ³¹P NMR. The products have been characterized by ³¹P and ¹H NMR studies.     

Quaternary ammonium compounds in roots and leaves of Capparis spinosa L. from Saudi Arabia and Italy: investigation by HPLC-MS and 1H NMR

Capparis spinosa L. is a perennial plant typical of the Mediterranean flora and a multipurpose plant used for curing various human ailments. Quaternary ammonium compounds (QACs), as constituents of Capparaceae, play important roles in protecting against abiotic stress. Aim of this work was to determine QACs in root and leaves of caper from two proveniences. The presence of stachydrine, choline, glycine betaine and homo-stachydrine has been confirmed by high resolution MS, while ¹H NMR was applied to quantify the main QACs in the aqueous extracts. Stachydrine was quantified at 20.2 mg/g and 32.3 mg/g on dry leaves from South of Italy and Saudi Arabia, respectively, while a minor content was in dry roots (from 10.4 to 12.5 mg/g). Choline was considerably lower both in leaves and roots (from 0.3 to 1.2 mg/g). To our knowledge, this is the first report on the determination of QACs both in root and leaves of C. spinosa.     

Refinement of NMR data on the structure of bound water in collagen using scanning calorimetry

In disordered regions of the structure of collagen protein, water has a tectohydrate type of structure with a continuous three-dimensional framework of tetrahedrally coordinated water molecules characteristic of ice and clathrate hydrates.     

Structural Refinement of Carbimazole by NMR Crystallography

The characterization of the three-dimensional structure of solids is of major importance, especially in the pharmaceutical field. In the present work, NMR crystallography methods are applied with the aim to refine the crystal structure of carbimazole, an active pharmaceutical ingredient used for the treatment of hyperthyroidism and Grave’s disease. Starting from previously reported X-ray diffraction data, two refined structures were obtained by geometry optimization methods. Experimental ¹H and ¹³C isotropic chemical shift measured by the suitable ¹H and ¹³C high-resolution solid state NMR techniques were compared with DFT-GIPAW calculated values, allowing the quality of the obtained structure to be experimentally checked. The refined structure was further validated through the analysis of ¹H-¹H and ¹H-¹³C 2D NMR correlation experiments. The final structure differs from that previously obtained from X-ray diffraction data mostly for the position of hydrogen atoms.