Reactive processing of polymers: Structural characterisation of products by H and C NMR spectroscopy for glycidyl methacrylate grafting onto EPR in the absence and presence of a reactive comonomer

Grafted GMA on EPR samples were prepared in a Thermo-Haake internal mixer by free radical melt grafting reactions in the absence (conventional system; EPR-g-GMA_CONV) and presence of the reactive comonomer divinyl benzene, DVB (EPR-g-GMA_DVB). The GMA-homopolymer (poly-GMA), a major side reaction product in the conventional system, was almost completely absent in the DVB-containing system, the latter also resulted in a much higher level of GMA grafting. A comprehensive microstructure analysis of the formed poly-GMA was performed based on one-dimensional ¹H and ¹³C NMR spectroscopy and the complete spectral assignments were supported by two-dimensional NMR techniques based on long range two and three bond order carbon-proton couplings from HMBC (Heteronuclear Multiple Bond Coherence) and that of one bond carbon-proton couplings from HSQC (Heteronuclear Single Quantum Coherence), as well as the use of Distortionless Enhancement by Polarization Transfer (DEPT) NMR spectroscopy. The unambiguous analysis of the stereochemical configuration of poly-GMA was further used to help understand the microstructures of the GMA-grafts obtained in the two different free radical melt grafting reactions, the conventional and comonomer-containing systems. In the grafted GMA, in the conventional system (EPR-g-GMA_CONV), the methylene protons of the GMA were found to be sensitive to tetrad configurational sequences and the results showed that 56% of the GMA sequence in the graft is in atactic configuration and 42% is in syndiotactic configuration whereas the poly-GMA was predominantly syndiotactic. The differences in the microstructures of the graft in the conventional EPR-g-GMA_CONV and the DVB-containing (EPR-g-GMA_DVB) systems is also reported     

Studies of end-groups in polystyrene using H NMR

Studies have been made by 400 MHz ¹H NMR of initiator fragments in polystyrene made by radical polymerization in solution at 60 °C. Azoisobutyronitrile, benzoyl peroxide and lauroyl peroxide have been used as initiators. The peaks arising from hydrogens in the end-groups have been recognized. They cause alterations in the ratio of “aromatic hydrogens” to “aliphatic hydrogens” for polystyrene.     

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.     

Conformational study of a strained tolanophane by dynamic 1H NMR spectroscopy and computational methods

The existence of a short C–H ⋯ π (alkyl–alkyne) interaction in the structure of a strained and relatively rigid tolanophane is expected to hinder the rotation about the C–C sp³ single bond. Variable-temperature NMR experiments (performed in three solvents, CDCl₃, THF-d₈, and acetone-d₆) and ab initio density functional calculations were carried out to investigate its dynamic nature. An energy barrier of 48.6 kJ/mol is determined at coalescence (210 K) with acetone-d₆ which is in good agreement with calculation result (54 kJ/mol). Correspondence: Hossein Reza Darabi, Chemistry and Chemical Engineering Research Center of Iran, Pajoohesh Blvd., km 17, Karaj Hwy, 14968-13151 Tehran, Iran.     

Dynamic H NMR study of 4-methylphenoxyimidoyl azides: conformational or configurational isomerisation?

Dynamic ¹H NMR (500 MHz) investigation of 4-methylphenoxyimidoyl azides (4-CH₃-C₆H₄-O-CN-Y)-N₃, Y=4-CH₃-C₆H₄-SO₂-, 4-Br-C₆H₄-SO₂-, C₆H₅SO₂-, CH₃-SO₂-, -CN in acetone-d₆ at temperature range of 195-280 K is reported. The observed free energy barrier (almost 12 kcal mol⁻¹) is attributed to conformational isomerisation about the N-S bond for Y=4-CH₃-C₆H₄-SO₂-, 4-Br-C₆H₄-SO₂-, C₆H₅SO₂-, CH₃-SO₂- and (almost 14 kcal mol⁻¹) to configurational isomerisation (E/Z) about CN bond for Y=-CN.     

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.     

Strategies for organic impurity quantification by H NMR spectroscopy: Constrained total-line-shape fitting

A constrained total-line-shape (CTLS) fitting strategy for organic impurity analysis from ¹H NMR spectra was developed and assessed by studying two examples. In general, total-line-shape fitting allows integration of overlapping lines without suffering from baseline artifacts as much as traditional integration methods. It is shown here that the constrained total-line-shape fitting, where the spectral structures of the multiplets to be fitted are taken into account in form of constraints, allows quantification of seriously overlapping lines and when the signals are close to the root of major signals. Also, a method for removal of ¹³C satellite signals is described. The results indicate that our approach significantly improves the usefulness of qNMR in impurity analysis and that impurity levels of 0.1 mol%, which in some cases means down to 0.01 wt%, can be easily determined with relative standard error smaller than 10%.     

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.     

A 1H NMR study of 1,4-bis(N-hexadecyl-N, N-dimethylammonium)butane dibromide/sodium anthranilate system: spherical to rod-shaped transition

The effect of addition of sodium anthranilate to 5 mM micellar solutions of gemini surfactant 1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide is investigated by ¹H NMR. The solubilization site of anthranilate anion near the micellar surface is inferred. In the micelles, the An⁻ ions intercalate among the surfactant headgroups producing morphological changes.     

“NMR invisible” aluminum species in dealuminated mordenite zeolite: a1H/27 AI TRAPDOR NMR study

Various kinds of aluminum species in dealuminated mordenite were investigated in detail, and the quadrupole coupling constants (QCCs) for aluminum atoms associated with these species were obtained by means of the newly introduced¹H/²⁷ AI TRAPWR method as well as²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). QCC values of 11.3, 15.3, 13.3 and (14.0± 0.6) MHz were determined from the TRAPDOR profiles for Lewis acid sites, Bronsted acid sites (SiOHAl) and two kinds of non-framework aluminum species Al(OH) _n , respectively. The source of the “invisible Al” is discussed on the basis of the NMR experimental results.     

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.     

1H NMR spectroscopic study of theert-butyl chloride—aluminum bromide cationic initiating system

The interaction oftert-butyl chloride with aluminum bromide in methylene dibromide at −30°C leads to the formation of two types of adducts, which give signals with δ 2.4 and 3.2 in the¹H NMR spectra in addition to that of free alkyl halide. these signals are attributed to a polarized complex (PC) and ion pair (IP), respectively. An excess of AlBr₃ shifts the equilibria toward IP. The latter contains more AlBr₃ than the polarized complex. Based on the spectral data, we calculated the limiting values of some equilibrium constants. The ability of AlBr₃ to solvate counterions is consistent with the results of isobutylene polymerization under the action of the initiating Bu^tCl−AlBr₃ system at different ratios of the starting concentrations [AlBr₃]₀/[Bu^tCl]₀. An increase in this ratio results in both the acceleration of polymerization and an increase in the relative role of chain transfer reactions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2217–2222, November, 1998.     

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.     

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.     

Determination of Metabolites from Scutellaria baicalensis by GC/MS and 1H NMR

The quality of medicinal herbs and their products is steadily becoming important in tandem with growing interest in complementary alternative medicine for treatment of diseases. Chemical assays with bioactive secondary compounds are usually used for chemical standardization in herbs for quality control purpose. In this study, an analytical platform comprising of a GC-MS technique with an unsupervised multivariate analysis and a complementary one-dimensional ¹H NMR technique was used to obtain the primary metabolite profiling of Scutellaria baicalensis obtained from different medical halls in Singapore. The key primary metabolites such as sucrose, proline, phenylalanine, fructose, and butanedioic acid for the biosynthesis of bioactive secondary metabolites in this medicinal herb were successfully characterized by the combination of the chromatography and spectroscopy techniques. Their results suggested that these compounds could serve as markers for quality control of the herb. The principal component analyses of the GC-MS data reliably discriminated between the various Scutellaria samples indicating that the developed platform was comprehensive and was applicable to assess the quality of other medicinal herbs.     

Halide ion effect on the chloroform chemical shift in supramolecular complexation studies with tetra-n-butylammonium salts: a 1H NMR and X-ray study

A ¹H NMR spectroscopic study of tetra-n-butylammonium halides (TBAX: X = Cl^? , Br^?  or I^? ) in CDCl₃ solutions was conducted. Complexation studies of TBAX salts with different host molecules using ¹H NMR in CDCl₃ have previously revealed that the reference residual CHCl₃ proton signal had been shifted downfield. The aim of the study was to quantify the extent of these chemical shift changes with TBAX salts. Linear concentration–chemical shift relationships in each case were obtained from the resulting titration plots obtained from the addition of the TBAX salts alone to CDCl₃. Interactions in the solid state as determined by X-ray crystallography support the solution-state investigations indicating halide ion–chloroform proton interactions.     

H NMR studies on the reductively triggered release of heterocyclic and steroid drugs from 4,7-dioxoindole-3-methyl prodrugs

Hypoxia is a feature of several disease states, including cancer and rheumatoid arthritis. Prodrug systems which, after bioreduction, selectively release active drugs in these tissues may be important in therapy. An improved preparation of 1,2-dimethyl-3-hydroxymethyl-5-methoxyindole-4,7-dione was developed. Mitsunobu coupling with (5-substituted) isoquinolin-1-ones (potent inhibitors of poly(ADP-ribose)polymerase) gave 1-(1,2-dimethyl-4,7-dioxo-5-methoxyindol-3-ylmethoxy)isoquinolines and N-(1,2-dimethyl-4,7-dioxo-5-methoxyindol-3-ylmethyl)isoquinolin-1-ones. Similar coupling with the anticancer drug pentamethylmelamine gave its potential prodrug 1,2-dimethyl-3-(N-(4,6-bis(dimethylamino)-1,3,5-triazin-2-yl)-N-methylaminomethyl)-5-methoxyindole-4,7-dione. Treatment of sodium prednisolone hemisuccinate with 3-chloromethyl-1,2-dimethyl-5-methoxyindole-4,7-dione gave an analogous candidate prodrug of the anti-inflammatory drug prednisolone. In a chemical model system for bioreduction, SnCl₂ in CDCl₃/CD₃OD triggered rapid stoichiometric release of isoquinolin-1-ones from the O-linked prodrugs but not from the N-linked analogues. Use of this system allowed the release process to be monitored in situ by ¹H NMR spectroscopy. Diethyl hydrazine-1,2-dicarboxylate was found to reduce Sn^IV to Sn^II, making the overall reductive release catalytic in tin. The reduced (hydroquinone) prodrug may have a short lifetime under these reductive conditions, meaning that only good leaving groups are expelled. Thus 1-(1,2-dimethyl-4,7-dioxo-5-methoxyindol-3-ylmethoxy)isoquinolines and analogues may be useful as reductively triggered prodrugs.     

A multinuclear NMR study in the solid state and in solution of thallium(I) tris-(pyrazol-1-yl)borates (thallium scorpionates)

The ¹H, ¹³C and ¹⁵N NMR spectroscopic properties of six thallium tris-(pyrazol-1-yl)borates, including a tetrakis derivative, were determined. The results in solution were necessary to understand those, more complicated, in the solid state. A collection of ²⁰⁵Tl-¹⁵N and ²⁰⁵Tl-¹³C couplings was measured in the latter state. Among those, a very large coupling constant (between 194 and 282 Hz) has been measured on the carbon at the position 4 of the pyrazole ring in several compounds and particularly for the cyclobutyl derivative [Tl(Tp^Cbu)]. It has been assigned to a direct interaction of the 4-C-H ? Tl type and related to the X-ray structures, when available.     

13C and1H NMR spectra of substituted dihydropyrroles prepared by the reaction of 2-aminooxazoles and maleimide

Substituted dihydropyrroles were characterized by¹³C and¹H NMR spectra. The spectral patterns of these compounds and reversible hydrogen—deuterium exchange are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 697–700, April, 2000.     

1H NMR and spectrophotometric study of alkaline metal ion complexes with N-dansyl aza-18-crown-6

Formation of complexes of A18C6-Dns and metal cations (Ca²⁺, Sr²⁺, Ba²⁺ and Mg²⁺) in acetonitrile has been studied by NMR, absorption and fluorescence spectroscopy and PM5 semi-empirical methods. A18C6-Dns forms stable complexes with Ca²⁺, Sr²⁺ and Ba²⁺ cations. The stability constants of various complexes are determined by different methods and their structures are visualised by the PM5 semi-empirical calculations.