Semiquantitative analysis of thiophenic compounds in light cycle oil (LCO) using C NMR spectroscopy

S-methyltetrafluoroborate salts of the thiophenic compounds (CH₃-S⁺:BF₄⁻) present in LCO petroleum fractions were obtained and analyzed by ¹H and ¹³C NMR spectroscopy. The methylation of the samples was carried out using 99.5% ¹³C enriched methyl iodine, to improve the sensitivity of the technique. The amount of the methylated derivatives was determined by the internal standard method; using dioxane as a reference, 37 sulphur compounds were detected. Among them, benzo[b]thiophene, dibenzo[b,d]thiophene, and several isomers of methyl, dimethyl and trimethyl[b]benzothiophenes were the most abundant. With this research, it was demonstrated that NMR spectroscopy can be used to analyze thiophenic compounds from petroleum medium fractions.     

Synthesis of dimer and oligomers from (R)-methyl hydnocarpate

We report synthesis and characterization of dimer and oligomer acids from chaulmoogra oil. (R)-Methyl hydnocarpate (methyl ester of the major fatty acid component of chaulmoogra oil) was brominated to give threo-2,3-dibromocyclopentane-1-methyl undecanoate. Formation of two diastereoisomers, viz., threo-2(R),3(R)-dibromocyclopentane-1(R)-methyl undecanoate and threo-2(S),3(S)-dibromocyclopentane-(R)-1-methyl undecanoate, was observed. Dehydrobromination of bromo derivatives using alcoholic KOH gave a cyclopentadiene derivative as intermediate, which underwent Diels-Alder reaction to give dimer and oligomer fatty acids. The products were characterized by ultraviolet, direct exposure probe-mass spectroscopy, ¹H nuclear magnetic resonance (NMR), and ¹³C NMR spectroscopic techniques.     

Diffusional behavior of amino acids in solid-phase reaction field as studied by H pulsed-field-gradient spin-echo NMR method

The diffusion coefficients (D) of tert-butyloxycarbonyl-l-phenylalanine (Boc-Phe) in Merrifield network polystyrene gels, used as a solid-phase reaction field have been determined as a function of the amino acid concentration over the temperature range from 30 to 50 °C by means of the ¹H pulsed-field-gradient spin-echo NMR method. From these experimental results, it was found that the D value of Boc-Phe in DMF-d₇ solution, in DVB 1 and 2% cross-linked network polystyrene gels depends on the amino acid concentration. The D value of Boc-Phe·Cs(tert-butyloxycarbonyl-l-phenylalanine cesium) salt in the solid-phase reaction field under chemical reaction was determined at 50 °C. Further, it was found that the D value depends on the NMR observation time, that is the applied two field-gradient pulse interval. Details of its analysis were discussed.     

Thiacalixarenes with Sulfur Functionalities at Lower Rim: Heavy Metal Ion Binding in Solution and 2D-Confined Space

Sulfur-containing groups preorganized on macrocyclic scaffolds are well suited for liquid-phase complexation of soft metal ions; however, their binding potential was not extensively studied at the air–water interface, and the effect of thioether topology on metal ion binding mechanisms under various conditions was not considered. Herein, we report the interface receptor characteristics of topologically varied thiacalixarene thioethers (linear bis-(methylthio)ethoxy derivative L², O₂S₂-thiacrown-ether L³, and O₂S₂-bridged thiacalixtube L⁴). The study was conducted in bulk liquid phase and Langmuir monolayers. For all compounds, the highest liquid-phase extraction selectivity was revealed for Ag⁺ and Hg²⁺ ions vs. other soft metal ions. In thioether L² and thiacalixtube L⁴, metal ion binding was evidenced by a blue shift of the band at 303 nm (for Ag⁺ species) and the appearance of ligand-to-metal charge transfer bands at 330–340 nm (for Hg²⁺ species). Theoretical calculations for thioether L² and its Ag and Hg complexes are consistent with experimental data of UV/Vis, nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffractometry of Ag–thioether L² complexes and Hg–thiacalixtube L⁴ complex for the case of coordination around the metal center involving two alkyl sulfide groups (Hg²⁺) or sulfur atoms on the lower rim and bridging unit (Ag⁺). In thiacrown L³, Ag and Hg binding by alkyl sulfide groups was suggested from changes in NMR spectra upon the addition of corresponding salts. In spite of the low ability of the thioethers to form stable Langmuir monolayers on deionized water, one might argue that the monolayers significantly expand in the presence of Hg salts in the water subphase. Hg²⁺ ion uptake by the Langmuir–Blodgett (LB) films of ligand L³ was proved by X-ray photoelectron spectroscopy (XPS). Together, these results demonstrate the potential of sulfide groups on the calixarene platform as receptor unit towards Hg²⁺ ions, which could be useful in the development of Hg²⁺-selective water purification systems or thin-film sensor devices.     

Change in the structure of poly(tetramethylene succinate) under tensile stress monitored with solid state C NMR

A new solid-state NMR experimental equipment was developed to monitor the structural change of polymer and protein fibers under active uniaxial deformation. The equipment was applied to monitoring change in the structure of a biodegradable aliphatic polyester fiber, poly(tetramethylene succinate) (PTMS; [-O(CH₂)₄OCO-(CH₂)₂CO-]_n), as a function of tensile stress. The crystal transition from α to β forms for PTMS was induced by stress and monitored by the change of the methylene region in the ¹³C NMR spectra. The ¹³C chemical shielding constant for the model compound of poly(tetramethylene succinate) was calculated using the GIAO-CHF (gauge invariant atomic orbitals-coupled Hartree-Fock) with ab initio 6-311G^∗∗ basis set. This calculation acceptably explains the experimental results.     

Strain-induced crystallization of natural rubber as studied by high-resolution solid-state C NMR spectroscopy

A series of high-resolution solid-state ¹³C NMR experiments were performed on both unstretched and in situ stretched natural rubber samples. From the ¹³C CP/MAS spectra, it was found that natural rubber does form small crystals at room temperature though the degree of crystallinity is very small. Furthermore, from the ¹³C DD/MAS spectra, the crystalline signals were found to increase with the increase of draw ratio. ¹³C spin-lattice relaxation time (T₁) and ¹H spin-spin relaxation time (T₂) of in situ stretched natural rubber were measured for the first time, which provided further evidences for the conclusion that there exist crystals in both stretched and unstretched natural rubber samples. Quantitative ¹³C NMR measurements indicated that strain-induced crystallization occurs when the draw ratio reaches about 2.0 and the maximum crystallinity of our natural rubber samples can be as high as 19.3% upon stretching.     

13C solid state NMR evidence for the existence of isobutyl carbenium ion in the reaction of isobutyl alcohol dehydration in H-ZSM-5 zeolite

Using two-dimensionalJ-resolved and CP/MAS¹³C NMR, the pathway for the transfer of the¹³C label from the CH₂ group of isobutyl alcohol into the hydrocarbon skeleton of butene oligomers has been elucidated in the course of isobutyl alcohol dehydration inside H-ZSM-5 zeolite. First, the label is transferred selectively into the CH₂ group of the isobutyl silyl ether reaction intermediate (IBSE), and then into the CH and CH₃ groups of the isobutyl fragment (-CH₂CH(CH₃)₂) of IBSE and/or butene oligomers. Finally, it is scrambled over the carbon skeleton of the oligomers. The obtained data suggest that isobutyl carbenium ion is formed as a reaction intermediate or transition state during the transformation of isobutyl silyl ether into butene oligomers.     

A polymer based fluorescent sensor for Zn detection and its application for constructing logic gates

A polymer-based fluorescent sensor was synthesized by polymerization of (S)-6,6′-dibutyl-3,3′-(di-5-salicylde-ethynyl)-2,2′-binaphthol (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic addition-elimination reaction. The responsive optical properties of the polymer on transition metal ions were investigated by fluorescence and UV-vis spectra. The polymer (1.0 × 10⁻⁵ mol/L in THF) could emit fluorescence at 550 nm and exhibit high selectivity for sensing Zn²⁺ with 36.1-fold fluorescence enhancement. Three logic gates were designed according to the different fluorescence responses of this polymer sensor to Zn²⁺ and Cu²⁺.     

Fully quantitative carbon-13 NMR characterization of resol phenol-formaldehyde prepolymer resins

Different resol phenol-formaldehyde prepolymer resins have been synthesized with different Formaldehyde/Phenol (F/P) ratios or different catalysts and characterized by ¹³C NMR spectroscopy in solution. A fast quantitative measuring protocol is proposed based on the use of chromium(III)acetylacetonate as a relaxation agent. APT (attached proton test) and DEPT (distortionless enhancement by polarisation transfer) spectra were acquired to enable proper resonance assignments, especially in the regions with severe signal overlap. Equations are presented in which the methylene bridges (MB), the methylol groups (MG) and the dimethylene ether bridges (DMEB) of resol resins are quantitatively taken into account. Important structural factors determined quantitatively for resol prepolymer resins are the F/P ratio after reaction, the degree of polymerization (n), the number average molecular weight (M_n) and the content of free ortho and para positions.     

Configurational purity of lesquerolic acid

Conversion of the methyl ester of lesquerolic acid, (R)-14-hydroxy-Z-11-eicosenoic acid, to a carbamate with (S)-1-(1′-naphthyl)ethylisocyanate gave a single diastereomer. Comparisons of elution orders of the relevant diastereomers obtained from the racemic ester and from a sample of lesquerolic acid synthesized from ricinoleic acid, (R)-12-hydroxy-Z-9-octadecenoic acid, were consistent with the original assignment of (R)-configuration for the longer-chain acid. Although the configuration had not been in doubt, this work demonstrates the configurational purity of the lesquerolic acid.     

Network structures and dynamics of dry and swollen poly(acrylate)s. Characterization of high- and low-frequency motions as revealed by suppressed or recovered intensities (SRI) analysis of C NMR

We recorded temperature-dependent high-resolution ¹³C NMR spectra of dry and swollen poly(acrylate)s [poly(2-methoxyethyl acrylate) (PMEA), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(tetrahydrofurfuryl acrylate) (PTHFA)] by dipolar decoupled-magic angle spinning (DD-MAS) and cross-polarization-magic angle spinning (CP-MAS) methods, to gain insight into their network structures and dynamics. Suppressed or recovered intensities (SRI) analysis of ¹³C CP-MAS and DD-MAS NMR was successfully utilized, to reveal portions of dry and swollen polymers which undergo fast and slow motions with fluctuation frequencies in the order of 10⁸ Hz and 10⁴-10⁵ Hz, respectively. Fast isotropic motions with frequency higher than 10⁸ Hz at ambient temperature were located to the portions in which ¹³C CP-MAS NMR signals of swollen PMEA were selectively suppressed. In contrast, low-frequency motion was identified to the portions in which ¹³C DD-MAS (and CP-MAS) signals are most suppressed at the characteristic suppression temperature(s) T_s. Network of PMEA gels (containing 7 wt% of water) turns out to be formed by partial association of backbones only, as manifested from their T_s gradient at lowered temperature, whereas networks of PHEMA (containing 40 wt% of water) and PTHFA (9 wt% of water) gels are tightly formed through mutual inter-chain associations of both backbones and side-chains, as viewed from the raised T_s values for both near at ambient temperature. It is also interesting to note that flexibility of gel network (PMEA > PTHFA > PHEMA) characterized by the suppression temperature T_s (PMEA < PTHFA < PHEMA) is well related with a characteristic parameter for biocompatibility such as the production of TAT (thrombin-antithrombin III complex) as a marker of activation of the coagulation system.     

Molecular Rearrangement of Pyrazino[2,3-c]quinolin-5(6H)-ones during Their Reaction with Isocyanic Acid

New tetrahydropyrazino[2,3-c]quinolin-5(6H)-ones were prepared from 3-chloroquinoline-2,4(1H,3H)-diones and ethylene diamine. In their reaction with HNCO, an unprecedented molecular rearrangement produced new types of hydantoin derivatives. All prepared compounds were characterized on the basis of their ¹H, ¹³C, and ¹⁵N NMR and ESI mass spectra and some were authenticated by X-ray analysis of single crystalline material. A proposed mechanism for rearrangement is discussed in this essay. The CDK and ABL inhibition activity as well as in vitro cytotoxicity of the prepared compounds was also tested.     

NMR determination of crystallinity for poly(?-l-lysine)

Crystallinity of poly(?-l-lysine) (?-PL) was discussed by analyzing the differences in the ¹H spin-spin relaxation times (T₂^H), the ¹³C spin-lattice relaxation times (T₁^C), and the ¹³C NMR signal shapes between the crystalline and the non-crystalline phases. The observed ¹H relaxation curve (free induction decay followed by solid-echo method) showed the sum of Gaussian and exponential decays. Similarly, the observed ¹³C relaxation curves obtained from the Torchia method were double-exponential. The ¹³C NMR spectrum of ?-PL was divided into the narrow and the broad lines by utilizing the intrinsic differences in the ¹H spin-lattice relaxation times in the rotating-frame between them, which are attributed to the crystalline and the non-crystalline phases, respectively. Even though the crystallinity is obtained from the identical NMR measurements, the estimated values are different with each other. The crystallinity estimated from the T₂^H differences was 75.8 ± 0.1% at 333 K and 60.7 ± 0.4% at 353 K. From the T₁^C differences, the value was estimated to be 62 ± 11%. Furthermore, the value estimated from the NMR signal separation was 54 ± 5%. In this study we have explained these discrepancies by the difference in susceptibility among the experiments for the inter-phase, which exists in-between the crystalline and the amorphous phases. Furthermore, the estimated crystallinity was ascertained by the X-ray diffraction experiment.     

Lower temperature limit of NBS (DIN) pH standard buffer solution potassium tetroxalate

NBS pH standard buffer solution 0.05 m potassium tetroxalate with assigned pH(S) between 0 and 95°C is saturated at 5°C. The temperature dependence of pH of the saturated solution differs noticeably from that of pH(S). Similarly, 0.1 m tetroxalate with assigned pH(S) between 15 and 60°C is saturated at 22°C. Additional experiments indicate that the extrapolation method of determining pH(S) allowed to obtain pH(S) values below the saturating temperatures although the pure supersaturated solutions cannot be obtained.     

(3R*,5S*,6R*)-3,5-dimethyl-6-(methylethyl)-3,4,5,6-tetrahydropyran-2-one,a third sex pheromone component forMacrocentrus grandii (goidanich) (Hymenoptera: Braconidae) and evidence for its utility at eclosion

The compound (3R^*,5S^*,6R^*)-3,5-dimethyl-6-(methylethyl)-3, 4,5,6-tetrahydropyran-2-one was identified as a sex pheromone component ofM. grandii. Laboratory and field bioassays demonstrated that it elicits flight initiation, upwind anemotaxis, and casting in male wasps. The compound acts synergistically with (Z)-4-tridecenal, a previously identified sex pheromone component of femaleM. grandii, to increase male response to the aldehyde component. The source of the lactone was determined to be the mandibular glands of male and female wasps. At eclosion a majority of male-female and female-only cocoon masses released the lactone and attracted male wasps. Male-only cocoon masses were not attractive at eclosion and the lactone component was either not released or released at below-threshold concentration. Mating was observed to occur following eclosion in laboratory and field studies.     

Characterization of siloxane copolymers by solution O NMR spectroscopy

Solution ¹⁷O NMR spectroscopy was used for structure elucidation of siloxane copolymers with the natural abundance of ¹⁷O, i.e. without any enrichment prior to spectroscopy. Homo, co, and terpolymers, as well as linear chains, cyclic oligomers, and graft polymers were investigated. All relevant chemical shifts and corresponding linewidths were reported for siloxane polymers substituted with methyl, phenyl, 3-cyanopropyl, 2-cyanoethyl, 3,3,3-trifluoropropyl, and polyethylene glycol ligands and with the backbone stiffening groups tetramethyl-p-silphenylene, tetramethyl-p,p′-sildiphenylene ether, and m-carborane. An increment system was extended to predict the chemical shifts of substituted siloxane copolymers. ¹⁷O NMR spectroscopy of polysiloxanes provided information concerning their chemical composition, average molecular weight, and microstructure.     

Grain boundaries and the influence of the ionophilic-ionophobic balance on Li and F NMR and conductivity in low-dimensional polymer electrolytes with lithium tetrafluoroborate

⁷Li and ¹⁹F NMR linewidths and impedance spectra are reported for low-dimensional CmOn (I):LiBF₄ mixtures. Data for the ionophilic polymer C18O5 is compared with that for the ionophobic C18O1 and the block copolymer C16O1O5(21%) (21 mol% of C16O5). In C18O5:LiBF₄ (1:1) narrow ⁷Li linewidths, which were observed in the liquid crystal phase above the side chain melting temperature (∼50 °C), persist in the crystal down to ca. 0 °C and broaden below −20 °C. However, in C18O1:LiBF₄ (1:0.6) narrow ⁷Li linewidths were also observed down to −20 °C suggesting highly mobile neutral aggregates of salt since this system is non-conductive. In the copolymer C16O1O5(21%):LiBF₄ (1:0.7) the linewidths were even narrower down to −70 °C with weak temperature dependence. In all systems ¹⁹F linewidths were significantly broader than ⁷Li linewidths. The complex plane plots obtained by impedance spectroscopy exhibit characteristic minima identified with ‘grain boundary’ resistance and, following heat treatment, minima with weak temperature dependence identified with ‘internal crystal’ resistance, R_i, and conductivities, σ_i ≥ 10⁻⁴ S cm⁻¹. Four-component mixtures of copolymers CmO1O5 and CmO1O4 with LiBF₄ and ‘salt-bridge’ poly(tetramethylene oxide)-dodecamethylene copolymers gave conductivities of ca. 4 × 10⁻⁴ S cm⁻¹ at 20 °C with weak temperature dependence. A novel carrier-hopping mechanism of lithium transport decoupled from side chain melting in the crystalline state is postulated.      

Influence of short distance sequence regularity on preparation of poly(p-oxybenzoyl-co-p-mercaptobenzoyl) whisker

Preparation of the poly(p-oxybenzoyl-co-p-mercaptobenzoyl) whiskers was examined by means of the crystallization of oligomers during solution polymerization. Polymerizations were carried out in liquid paraffin at the concentration of 1.0% and 300 °C for 6 h. Copolymerization of 4-acetoxybenzoic acid and S-acetyl-4-mercaptobenzoic acid did not yield the whiskers. This was attributed to tendency that the copolymerization reduced the crystallizability of oligomers and induced the liquid-liquid phase separation of oligomers due to the lower freezing point. In order to induce short distance sequence regularity into oligomers, copolymerizations of two among four monomers were conducted, which were 4-(4-acetoxybenzoyl)oxybenzoic acid, S-(4-acetoxybenzoyl)-4-mercaptobenzoic acid, 4-(S-acetyl-4-mercaptobenzoyl)oxybenzoic acid and S-(S-acetyl-4-mercaptobenzoyl)-4-mercaptobenzoic acid. The copolymerizations of two of these monomers yielded the whiskers but for that of 4-(4-acetoxybenzoyl)oxybenzoic acid and S-(S-acetyl-4-mercaptobenzoyl)-4-mercaptobenzoic acid. The short distance sequence regularity of oligomers brought about the crystallization of oligomers, leading to the formation of whiskers.     

Structural characterization of maleic anhydride grafted polyethylene by C NMR spectroscopy

Maleic anhydride grafted polyethylene, [2,3-¹³C₂] MA-g-PE, which was synthesized with ¹³C labeled maleic anhydride [2,3-¹³C₂] MA in solution, was characterized by ¹³C NMR spectroscopy in order to make clear the structure of graft groups. The results reveal that [2,3-¹³C₂] MA-g-PE has succinic anhydride oligomeric grafts with a terminal unsaturated MA ring in addition to well-known saturated succinic anhydride oligomeric grafts and that the former grafts are longer but fewer than the latter.     

Two New Quinochalcone C-Glycosides from the Florets of Carthamus tinctorius

Two new quinochalcone C-glycosides, named hydroxysafflor yellow B (1) and hydroxysafflor yellow C (2), along with two known quinochalcone C-glycosides, safflomin C (3) and saffloquinoside C (4), and one known flavanone, (2R)-4'',5-dihydroxyl-6,7-di-O-β-d-glucopyranosyl flavanone (5), were isolated from the florets of Carthamus tinctorius. Their structures were determined by extensive spectroscopic (UV, IR, HR-ESI-MS, 1D and 2D NMR) analyses. In addition, these quinochalcone C-glycosides together with hydroxysafflor yellow A and anhydrosafflor yellow B were evaluated for their anti-oxidative effects against H₂O₂-induced cytotoxicity in cultured H9c2 cells. Among them, compound 2 exhibited significant anti-oxidative effects.