Phosphorus Derivatives of Natural Lactones. Synthesis of New Grosshemin Dialkylphosphonates

New phosphorus-containing derivatives of grosshemin were synthesized in 68-70% yield by reacting this guaianolide with dialkylphosphites. Their structures were established by IR, PMR, ¹³C NMR, and ³¹P NMR spectroscopies and two-dimensional ¹H-¹H NMR spectroscopy (COSY). The reaction of grosshemin with dialkylphosphites was found to be highly stereoselective.     

Phosphate Derivatives of Natural Lactones. II. Synthesis of Novel Dialkylphosphonates of Arteannuin B

Novel dialkylphosphonates of arteannuin B were synthesized in 45-47% yields by reaction of this cadinanolide with dialkylphosphites. Their structures were established using IR, PMR, ¹³C and ³¹P NMR spectroscopy, and two-dimensional ¹H-¹H NMR (COSY) spectroscopy. The reaction of arteannuin B and dialkylphosphites is highly stereoselective.     

Fractionation and physico-chemical analysis of degraded lignins from the black liquor of Eucalyptus pellita KP-AQ pulping

The degraded Eucalyptus pellita kraft lignin from the black liquor of KP-AQ pulping was precipitated directly at pH ∼2.0 without further purifying, since the lignin obtained is more representative with a whole distribution of molecular weight. The precipitated lignin was fractionated into six fractions by successive extraction with organic solvents. A comparison study of the lignin heterogeneity between the fractions was made in terms of fractional yield, content of associated polysaccharides, alkaline nitrobenzene oxidation, molecular weight distribution, ¹H NMR and ¹³C NMR spectroscopy and thermal stability. It was found that the lignin fractions contained higher associated hemicelluloses and ratios of non-condensed syringyl/guaiacyl units which were extracted by organic solvents with higher Hildebrand solubility parameters. The results from GPC and TGA showed that the polydispersity and the thermal stability of the lignin fractions increased with increasing molecular weight. In the low molecular weight fraction, small amounts of β-aryl ether bond (β-O-4) surviving the KP-AQ pulping were detected by both ¹H and ¹³C NMR spectra.     

Host–guest Complex of a Water-soluble Cucurbit[6]uril Derivative with the Hydrochloride Salt of 3-amino-5-phenylpyrazole

Interaction between tetramethylcucurbit[6]uril and 3-amino-5-phenylpyrazole hydrochloride in aqueous solution has been investigated by using ¹H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy, as well as by a single crystal X-ray diffraction determination. The ¹H NMR spectra analysis established a basic interaction model in which an inclusion complex with a host:guest ratio of 1:1 forms, in which the host selectively binds the phenyl moiety of the guest. Absorption spectrophotometric and fluorescence spectroscopic analysis in aqueous solution defined the stability of the host–guest inclusion complexes quantitatively as 6.8 × 10⁵ mol^? 1 L at pH 2.6; the interaction is pH dependent, decreasing as pH rises. The single crystal X-ray structure of the isolated inclusion complex shows the phenyl moiety of the guest inserted into the host cavity, which supports particularly the ¹H NMR spectroscopic study in solution. In the crystal structure of the inclusion complex, the host–guest interaction involves both inter- and intra-complex hydrogen bonding, forming 2:2 dimers that stack in one dimension as supramolecular tubes.     

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.     

1H, 13C,and 14N NMR study of 3-methylfurazans with nitrogen-containing substituents at position 4

3-Methylfurazans with nitrogen-containing substituents at position 4 were studied by ¹H, ¹³C, and ¹⁴N NMR spectroscopy. A correlation between the chemical shifts in ¹³C NMR spectra of these furazans and monosubstituted benzenes with the same substituents was found. The increments for a number of furazan-containing substituents were determined for the first time.     

Characterization of degradation products of poly[(3,3,3-trifluoropropyl)methylsiloxane] by nuclear magnetic resonance spectroscopy, mass spectrometry and gas chromatography

Poly[(3,3,3-trifluoropropyl)methylsiloxane] (PTFPMS) was treated with the solvents acetone, ethyl acetate and methanol and its degradation products were analyzed with multiple techniques. ¹H, ²⁹Si and ¹⁹F nuclear magnetic resonance (NMR) spectroscopy were useful for the characterization of the intact polymers and for the determination of cyclosiloxanes. Cyclosiloxanes with a ring size of up to 23 were quantified by gas chromatography. The only degradation products found were TFPmethyl-cyclosiloxanes. 1,3,5,7-Tetrakis(TFPmethyl)-cyclotetrasiloxane was predominant, and (TFPmethyl)cyclotri-, penta- and hexasiloxane could be detected at lower concentrations. The identity of cyclic degradation products with a ring size of up to 6 was unambiguously confirmed by direct infusion mass spectrometry. The TFPmethyl-cyclosiloxanes were successfully ionized by electrospray ionization in the negative mode. None of the techniques applied gave hints to other degradation products such as short linear oligomers. Almost complete degradation of PTFPMS occurred in acetone and methanol, while degradation is distinctly reduced in ethyl acetate.     

The effect of silica nanoparticles on the morphology, mechanical properties and thermal degradation kinetics of PMMA

Silica-PMMA nanocomposites with different silica quantities were prepared by a melt compounding method. The effect of silica amount, in the range 1-5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics of PMMA was investigated by means of transmission electron microscopy (TEM), X-ray diffractometry (XRD), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), ¹³C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (¹³C{¹H} CP-MAS NMR) and measures of proton spin-lattice relaxation time in the rotating frame (T_1ρ(H)), in the laboratory frame (T₁(H)) and cross-polarization times (T_CH). Results showed that silica nanoparticles are well dispersed in the polymeric matrix whose structure remains amorphous. The degradation of the polymer occurs at higher temperature in the presence of silica because of the interaction between the two components.     

2H Chemical-shift resolution and dipolar2H-1H,2H-15N correlations in solid-state MAS NMR spectroscopy for structure determination and distance measurements in hydrogen-bonded systems

In solid-state NMR, deuteron (²H) spectroscopy can be performed in full analogy to¹H spectroscopy, including²H chemical-shift resolution and²H-X dipolar correlation schemes, when the NMR experiments are conducted in a “rotor-synchronized” fashion under fast magic-angle spinning. Here, 2H-X NMR experiments of this type, including²H-¹⁵N and²H-¹H chemical-shift correlations and distance measurements, are introduced and demonstrated on cytosine monohydrate, whose acidic protons can readily be replaced by deuterons by recrystallization from D₂O. In this way,²H NMR spectroscopy provides information complementary to¹H NMR data, which is particularly useful for studying hydrogen bonds in supra- or biomolecular systems. Electronic supplementary material Supplementary material is available in the online versionof this article atand is accessible for authorized users.     

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.     

Determination of the Chemical Structure of Poly-β (-)-pinene by NMR Spectroscopy

This paper is dedicated to the memory of our friend and colleague Annalaura Segre.

The chemical structure of a series of β (-)-pinene polymers (PBP) obtained by radiation-induced polymerization, free radical initiation, cationic polymerization over a Friedel-Craft catalyst and by coordinative polymerization over a Ziegler-Natta catalyst has been fully elucidated by ¹H and ¹³C-NMR spectroscopy. 2D NMR techniques have been applied in order to assign all the NMR resonances to the structures of the PBP investigated. The NMR spectra show that the most regular PBP structure is obtained by radiation-induced polymerization followed by the free radical initiated polymerization. The most defective structure has been observed in the case of PBP prepared by cationic mechanism over a Friedel-Crafts catalyst. The discussion accounts for different types of defects and cross-links present in the PBPs investigated whose fundamental structure is based on the p-menthene repeating unit.

NMR self-diffusion measurements have been performed to evaluate the molecular weight of all the PBP investigated. The highest molecular weight (2600 Dalton) was found in the case of PBP prepared by Ziegler-Natta catalyst, while the lowest molecular weight was found in the case of PBP prepared by radiation-induced polymerization (about 1000 Dalton).     

An NMR study of sequential intermediates and collateral products in the conversion of 1,3,6,8-tetraazatricyclo[4.4.1.1]dodecane (TATD) to 1,3,6,8-tetraazatricyclo[4.3.1.1]undecane (TATU)

In situ ¹H nuclear magnetic resonance spectroscopy was used to investigate the processes that occur during the synthesis of 1,3,6,8-tetraazatricyclo[4.3.1.1^3,8]undecane (TATU). NMR analysis showed a reaction mixture containing more than one compound. The production of these intermediates and collateral products was rationally supported by a careful ¹H NMR monitoring study. We characterized 1,3,5-triazabicyclo[3.2.1]octane (TABO, 4) and 3-(2-aminoethyl)-1,3,5-triazabicyclo[3.2.1]octane (AETABO, 7) by ¹H and ¹³C NMR in D₂O solution inside the NMR sample tube, as an intermediate and collateral product of the reaction, respectively. Further, a reaction of 1,3,6,8-tetraazatricyclo[4.4.1.1^3,8]dodecane (TATD) with ¹⁵N-labeled ammonium chloride was carried out. The ¹⁵N NMR and GC-MS experiments indicated that ¹⁵N was incorporated into TATU, TABO, and urotropine.     

Phosphate Derivatives of Natural Lactones. I. Synthesis of Novel Isoalantolactone Dialkylphosphonates

Novel isoalantolactone dialkylphosphonates were synthesized in 70-87% yields by reacting this eudesmanolide with dialkylphosphites. Their structures were proved by spectral analysis using IR, PMR, ¹³C and ³¹P NMR, and two-dimensional ¹H-¹H (COSY) spectroscopy. The reaction of isoalantolactone with dialkylphosphites is highly stereoselective.     

Detection and quantification of phenolic compounds in olive oil by high resolution H nuclear magnetic resonance spectroscopy

High resolution ¹H NMR spectroscopy has been employed as a versatile and rapid method to analyze the polar fraction of extra virgin olive oils containing various classes of phenolic compounds. The strategy for identification of phenolic compounds is based on the NMR chemical shifts of a large number of model compounds assigned by using two-dimensional (2D) NMR spectroscopy. Furthermore, 2D NMR was applied to phenolic extracts in an attempt to discover additional phenolic compounds. The ¹H NMR methodology was successful in detecting simple phenols, such as p-coumaric acid, vanillic acid, homovanillyl alcohol, vanillin, free tyrosol, and free hydroxytyrosol, the flavonols apigenin and luteolin, the lignans (+) pinoresinol, (+) 1-acetoxypinoresinol and syringaresinol, two isomers of the aldehydic form of oleuropein and ligstroside, the dialdehydic form of oleuropein and ligstroside lacking a carboxymethyl group, and finally total hydroxytyrosol and total tyrosol reflecting the total amounts of free and esterified hydroxytyrol and tyrosol, respectively. The absolute amount of each phenolic constituent was determined in the polar fraction by using anhydrous 1,3,5-triazine as an internal standard.     

NMR determination of enantiomeric composition of 1-substituted 3-amino-1,2-dicarba-closo-dodecaboranes using Eu(hfc)3

Experimental conditions for determination of enantiomeric composition of 1-substituted 3-aminocarboranes by ¹H and ¹³C NMR spectroscopy using chiral shift reagent Eu(hfc)₃ have been found.     

Combination of H nuclear magnetic resonance spectroscopy and mass spectrometry as tools for investigation of the thermolytic and solvolytic effects: Case of carbamates analysis

The carbamate pesticides are a well known thermo-sensible compound class. Under unfavourable conditions, these compounds are highly prone to degradation via fragmentation and/or rearrangement mechanisms. Their transformation processes are observed in consequence of two factors: structure with fragile bonds on the one hand and a stressing environment on the other hand leading to a difficult direct gas chromatography (GC) analysis, i.e. without derivatisation. In this paper, we investigated an original methodology based on the complementarity of analysis by proton nuclear magnetic resonance spectroscopy (¹H NMR) and those provided by GC hyphenated with ion-trap mass selective detection (GC–ITMS) to investigate combined effects of temperature and solvent nature affecting the behaviour of 16 carbamates. Among tested solvents, toluene and acetonitrile with 0.1% acetic acid were considered as the best solvents for storage and GC analysis respectively. Carbaryl, chlorpropham, carbofuran and N-sulfenylated compounds began to be thermodegraded with a loss equal to 1–5% even at 50 °C. An on-column injection validated as providing no degradation was used to analyse the identical solution that in ¹H NMR and it was emphasised that results of the measured degradation rates were identical at ±2%. It was highlighted that this methodology was extensible to study mechanisms and parameters with other (bio)molecules.     

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.     

Highly routinely reproducible alignment of H NMR spectral peaks of metabolites in huge sets of urines

A method to obtain high reproducibility of ¹H NMR chemical shift of peaks of biofluid metabolites, by simple acidification with HCl is evaluated. Biofluid ¹H NMR analysis is indeed spoiled by a strong chemical shift dependence of metabolite peaks on parameters such as ionic strength, concentration of some earth alkali cations and, mostly, on pH of samples. The resulting chemical shift variations, as large as 0.1 ppm, generate misalignments of homogeneous peaks, artifacts and misinterpretations.Reproducible alignment is essential in ¹H NMR based metabonomics, where peak misalignments prevent even very wide bins (i.e., 0.04 ppm, as elsewhere proposed) from being used to integrate spectral data for multivariate statistical analysis. Here is demonstrated that routine acidification with HCl to 1.2 ≤ pH ≤ 2.0 ensures highly reproducible peak alignment of urine ¹H NMR spectra. In this respect, simple inspection of citrate peaks in the urine can be used to measure pH, as it will be extensively discussed, in that at such low pH they show no dependency on other urine components as reported at higher pH. Under these conditions, in as many as 493 urine samples, in which concentrations of Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl⁻, phosphate, and creatinine and ionic strength measured by means of well standardized conventional procedures, showed very wide ranges, peaks align within a SD always lower than 0.002 ppm, thus allowing the use of integration bins at least five times narrower than 0.04 ppm.     

Experimental Analysis of Complex Formation of Niflumic Acid with β-Cyclodextrins

Complex formation of niflumic acid with β-, hydroxypropyl-β- and methyl-β-cyclodextrins in aqueous solution (pH 7.4) were studied by calorimetry of solution, ¹H NMR spectroscopy and solubility method. The enhancement of niflumic acid solubility in the presence of hydroxypropyl-β-cyclodextrin was detected. This effect is explained on the basis of ¹H NMR data confirming the inclusion of hydrophobic trifluoromethylphenyl residue of niflumic acid molecule into the macrocyclic cavity. The thermodynamic parameters of 1:1 binding were derived from the data of␣calorimetry and solubility measurements. It was obtained, that complex formation of niflumic acid with β-cyclodextrin and both its derivatives is enthalpy driven. Substitutes surrounding the macrocyclic cavity slightly influence the thermodynamics of complex formation resulting in decrease of stability of the complexes formed.     

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.