NMR chemical shift reagents in structural determination of lipid derivatives: II. Methyl petroselinate and methyl oleate

Whentris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octaneodionato)europium (III)—Eu(fod)₃—forms a complex with a sufficiently basic functional group in a donor molecule, the change in the magnetic environment of protons near the coordination site causes their nuclear magnetic resonance (NMR) signals to shift to different positions. Consequently Eu(fod)₃ and other compounds that similarly affect NMR signals have been designated chemical shift reagents (csr). Because of their ability to shift proton signals, csr substantially increase the amount of structural information that can be obtained from NMR spectroscopy, frequently converting complicated splitting patterns into first-order spectra. Some generally useful experimental and interpretive csr techniques are described here using methyl petroselinate and methyl oleate as examples. Csr studies of methyl petroselinate reveal that the position of the double bond is at C-6, and that there is no chain substitution or branching before C-9. Csr studies of methyl oleate reveal that the position of the double bond is at or beyond C-9, and that there is no chain substitution or branching before C-6. Some suggestions are presented for expanding the amount of structural information that can be obtained by csr studies of unsaturated lipid derivatives. Presented in part at AOCS Meeting, Atlantic City, October, 1971.     

NMR chemical shift reagents in structural determination of lipid derivatives: IV. Methylcis- andtrans-9,10-epoxystearate and methylerythro- andthreo-9,10-dihydroxystearate

Chemical shift reagents were used to expand the amount of structural information obtainable from NMR studies of derivatives of methyl oleate and elaidate:methylcis-9,10-epoxystearate, methyltrans-9,10-epoxystearate, methyl erythro-9,10-dihydroxystearate, and methyl threo-9,10-dihydroxystearate. Chemical shift reagent studies of methyltrans-9,10-epoxystearate and methyl threo-9,10-dihydroxystearate afforded the most information. Chemical shift reagent studies of methylcis-9,10-epoxystearate and methyl erythro-9,10-dihydroxystearate were decidedly inferior. The series of complementary interpretive techniques previously developed during chemical shift reagent studies of monofunctional fatty esters and model polyfunctional fatty esters were found to be applicable in the current study. However, to avoid ambiguity in several proton assignments, supplementary spin decoupling experiments were necessary.     

Positional analysis of isovaleroyl triglycerides using proton magnetic resonance with Eu(fod)3 and Pr(fod)3 shift reagents: I. Model compounds

The proton magnetic resonance spectra of isomeric triglycerides of isovaleric and palmitic acids in the presence of the downfield and upfield chemical shift reagents Eu(fod)₃ and Pr(fod)₃ were studied. The resonance profiles of the γ-protons on the isovaleroyl chains are distinctive for each of the four possible triglyceride isomers at low shift reagent/triglyceride ratios. With either reagent, the well defined γ-methyl isovalerate doublets can be used to identify 2-isovaleroyl and 1,3-isovaleroyl structures and to analyze isomeric mixtures. This technique will be useful for positional analysis of natural cetacean triglycerides containing isovaleric acid.     

Application of lanthanide n.m.r. shift reagents for functional group studies of shale bitumen asphaltenes

Ytterbium (fod)₃ was used as a shift reagent in conjunction with solution ¹H n.m.r. studies of asphaltene isolated from Devonian shale bitumen. Upon addition of the reagent, bands attributed to protons on alkyl groups alpha to oxygen atoms were shifted and separated from that attributed to protons alpha to two aromatic systems. Similar experiments with Green River bitumen asphaltene did not show any observable shift. The presence and absence of the ether formations in shale asphaltenes can be substantiated by ¹³C n.m.r.     

Quantification of specific interactions between CO2 and the carbonyl group in polymers via ATR-FTIR measurements

We have used in situ ATR-FTIR measurements to provide estimates of the strength of specific interactions between carbon dioxide (CO₂) and carbonyl groups in polymers such as poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc), poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA). Polymer films were exposed to high pressure CO₂ and the carbonyl stretching vibration at 1700 cm⁻¹ and the CO₂ bending mode at 660 cm⁻¹ were studied. The observed shift in the carbonyl stretching band to higher wavenumber was attributed to dielectric effects according to the Kirkwood-Bauer-Magat (KBM) equation. On the other hand, the splitting of the CO₂ bending mode provided direct evidence of specific interactions between the polymer and CO₂. These interactions were quantified via an equilibrium constant for the association reaction between CO₂ and the carbonyl group.     

TWO-PHASE WITTIG REACTION OF SYNTHESIZING LIQUID CRYSTAL INTERMEDIATE BY ACTIVE QUATERNARY PHOSPHONIUM SALT

In this work, (4-methyl)methyl benzoatyltriphenylphosphonium bromide (BrPPh₃CH₂C₆H₄COOCH₃, MBPB), which was prepared from the reaction of (4-bromomethyl)methyl benzoate BrCH₂(C₆H₄)COOCH₃ and triphenyl phosphine (PPh₃) in a CH₂Cl₂/H₂O two-phase medium in the laboratory, acted as the active reagent to synthesize methyl {4-[4-(nonyloxy)-styryl]} benzoate in Z- and E-form (n-C₉H₁₉O(C₆H₄)CH=CH(C₆H₄)COOCH₃, MNSB). The product is a useful liquid crystal intermediate used in industries. Through the active reagent, MNSB is synthesized from the reaction of 4-nonyloxybenzoic aldehyde (n-C₉H₁₉O(C₆H₄)CHO, NAOD) in an alkaline solution of NaOH/organic solvent two-phase medium. The reaction is largely enhanced in the presence of MBPB compound as the active reagent in the Wittig reaction. Under most reaction conditions, this reaction is favorable for the production of E-form MNSB product rather than forming the Z-form MNSB product. A kinetic model was developed and a pseudo-first-order rate law was found to be sufficient to express the kinetic behaviors of the reaction. Effects of the reaction conditions, including the agitation speed, the temperature, the reactant concentration, the organic solvents, the sodium hydroxide concentration, and the 4-nonyloxybenzoic aldehyde concentration on the conversion of NAOD and the reaction rate were investigated in detail. Rational explanations to the observed results have been made.     

Radical copolymers of 2-vinyl pyridine with methyl acrylate and methacrylate. A study of microstructures by 1H n.m.r.

Radical copolymerization of 2-vinyl pyridine with methyl acrylate and methacrylate, respectively, has been carried out in benzene solution with low conversion. The reactivity ratios for the two systems, have been determined using the Fineman-Ross and Kelen-Tüdös methods. The values obtained satisfy the terminal model of copolymerization. The signals sensitive to sequence distribution and configuration in the ¹H n.m.r. spectra are αCH₃ and OCH₃ from methyl methacrylate, OCH₃ from methyl acrylate and the aromatic proton signal from 2-vinyl pyridine. The configurational model for the two types of copolymers is discussed using the information from the signals together with influence of the neighbouring and next-neighbour units on signal splitting.     

Effect of temperature on tacticity in thermal polymerization of p-methylstyrene by 13C NMR spectroscopy

Poly(p-methylstyrene) (Pp-MS) was synthesized at three different temperatures of 50, 150 and 250?°C via bulk thermal polymerization method. The assignment of all stereosequences at triad and pentad levels for two quaternary aromatic carbons and hexad level for methylene carbon was carried out by ¹³C liquid nuclear magnetic resonance spectroscopy (NMR) in deuterated chloroform at similar conditions. The probability of meso addition (P _m) was calculated from second quaternary aromatic carbon and used to predict the relative intensities of methylene and first quaternary aromatic carbon by Bernoullian and first-order Markov statistical models. The results were compared with experimental data. It is shown that the Bernoullian statistics fit better than first-order Markov model for all three samples. The results indicate that P _m increases by increasing polymerization temperature. The corresponding P _m values determined for synthesized Pp-MSs at 50, 150 and 250?°C were 0.383, 0.392 and 0.404, respectively. It was observed that higher resolutions and better splitting patterns were achievable by increasing the NMR acquisition temperature from 20 to 50?°C. When temperature increased during NMR acquisition, the resolution improved for the first and second quaternary aromatic carbons and methylene carbon, though there was no splitting pattern observed for methyl carbon atom at the para-position of the aromatic ring.     

The thermal Aromatization of Methyl-1,3-cyclohexadienes – an important argument against commonly accepted sigmatropic 1,7-H-shift reactions

It has been demonstrated that the methyl and ring C-atoms of methyl-1,3-cyclohexadienes interchange their positions intramolecularly during the thermal conversion to toluene at temperatures above 600°C in a quartz flow system. Gas phase pyrolysis of double ¹³C-labeled methyl-1,3-cyclohexadienes with ¹³C-labels for the primary and the tertiary C-atom gave definite ¹³C-distribution patterns in the aromatic ring systems of the formed toluene as well as benzene with far-reaching similarities. The NMR data of the [¹³C₂]toluene isotopomers definitely rule out that the observed integration of the methyl C-atom into the ring system proceeds via the hitherto well-established sequence: electrocyclic ring opening of the 5-methyl-1,3-cyclohexadiene to 1,3,5-heptatriene, its sigmatropic 1,7-H shift and ensuing recyclization of the 1,3,5-heptatriene to methyl-1,3-cyclohexadienes.     

The Fluorescent Quantum Efficiency of Copolymers Containing Coumarin-6 at the Side-chain

Coumarin-6 containing acrylates (CA) with different spacers were synthesized. Copolymers of CA with methyl methacrylate (MMA) in CA/MMA in the weight ratios of 1/20, 1/40 and 1/60 were prepared by using AIBN as initiator. The copolymer compositions were determined from uv-visible spectroscopic analyses, according to Beer’s law. UV absorption and photoluminescence (PL) spectra indicated a concentration quenching, which increased with increasing coumarin-6 concentration in the copolymer compositions and also increasing the spacer length from the copolymer to coumarin-6 moiety, leading to a decreased fluorescence efficiency (φ_s/φ_o) as well as a red shift of λ_max. Furthermore, as the spacer, n in –(CH₂)_n–, increases from n=2, 3 to 6, excimers formed due to overlap of chromophores, resulting in the splitting of the PL emission band and lowering the PL intensity. Experimental results revealed that when the ratio of CA/MMA=1/60 and the spacer n=2, the copolymer film showed an optimized fluorescent quantum efficiency.     

Lanthanide shift reagents as an aid in the NMR analysis of the normal alcohols C6 to C11

A method is described that substantially aids in the interpretation of the nuclear magnetic resonance (NMR) spectrum of a series of six fatty alcohols (C₆ to C₁₁). The lanthanide shift reagent tris (2,2,6,6-tetramethylheptanedionate)praseodymium-(III)[Pr(DPM)₃] is employed, and produces large shifts in the resonances of the various methylene groups in the chain depending on their position with respect to the hydroxy group. This paramagnetic shift for the first seven methylenes of these six alcohols is found to to be directly proportional to the amount of Pr(DPM)₃ added. Measurement of the coupling constants for the methylene groups in the chain are reported. The power of lanthanide shift reagents for both analytical and conformational information derived from their NMR spectra is demonstrated.     

Sunlight driven high photocatalytic activity of Sn doped N-TiO2 nanoparticles synthesized by a microwave assisted method

Environment-friendly photocatalysts under sunlight with wide spectral responses for wastewater treatment are currently an exciting area of research. Herein, we report the synthesis of Sn doped N-TiO₂ nanoparticles with different contents of Sn by a greener microwave assisted method. The phase purity, morphology, particle size, optical properties, and elemental composition were systematically analyzed by various sophisticated analytical techniques. The X-ray diffraction (XRD) patterns revealed Sn doped N-TiO₂ nanoparticles in the anatase phase. The shift of XRD peaks observed at lower angle and the XPS results indicate the successful doping of Sn⁴⁺ in the lattice of N-TiO₂. The optical absorption edges of Sn-doped N-TiO₂ showed an obvious red shift that plays a crucial role in the photocatalytic activity under abundant sunlight. We further explored Sn doped N-TiO₂ for photodegradation of methyl orange (MO) and Zopiclone (Z-class drug) under sunlight irradiation. A maximum of 95% and 91% of MO and Zopiclone were photodegraded over 0.25% Sn doped N-TiO₂ under sunlight within 80 and 120 min, respectively, which is ∼7-fold higher than bare N-TiO₂. The enhanced photocatalytic activity could be attributed to combined effects of reduced crystallite size, suppressed recombination rate of photogenerated electron-hole pairs, and increased optical absorption towards visible light that establish their impending use to treat polluted water. The possible mechanism for high photocatalytic activity of Sn doped N-TiO₂ has also been discussed.     

A study of the water–gas shift reaction in Ru-promoted Ir-catalysed methanol carbonylation utilising experimental design methodology

The water–gas shift reaction occurs competitively to the main reaction of the Ir-catalysed methanol carbonylation process. To study the effect of seven factors including temperature, pressure, iridium, ruthenium, methyl iodide, methyl acetate and water concentrations on the formation of hydrogen and carbon dioxide as a result of the water–gas shift reaction and other side reactions in the carbonylation of methanol to acetic acid, the experimental design method combined with response surface methodology (RSM) was utilised. Central composite design at five levels (with α=1.63) was used to design experiments. A quadratic model that included the main and interaction effects of variables for H₂ and CO₂ formation was developed. For two responses, R² was in reasonable agreement “Adj-R²”. Furthermore, statistical tests confirmed the accuracy and the precision of models developed in this research. For CO₂ formation, pressure, iridium and methyl iodide concentrations and for H₂ formation, water and iridium concentrations had the most pronounced effects. Optimum conditions to minimise H₂ and CO₂ and CH₄ formation were determined as follows: temperature of 189 °C, pressure of 32.0 bar, iridium content of 859 ppm, ruthenium concentration of 528 ppm, methyl iodide content of 8.68 wt%, methyl acetate concentration of 23.9 wt% and water content of 6.49 wt%. Ultimately, an experiment at optimum conditions revealed satisfactory agreement between the experimental and predicted data.     

Study on the Structure of Fe/MgO Catalysts for H2S Wet Oxidation

Mg-doped WO₃ with band gap energy of about 2.6 eV is a viable photocatalyst for visible light-induced water splitting in the presence of hole scavengers. The conduction band edge position of p-type Mg-doped WO₃ was -2.7 V versus SCE at pH 12. By doping Mg on WO₃, the conduction and valence band positions were shifted by 2.25 V negatively, leading to a conduction band edge position which was negative enough for H⁺ ions to be reduced thermodynamically, with little change in band gap energy. The negative shift in band position might be ascribed to lowering of the effective electron affinity of WO₃ by doping Mg with a very low electron affinity.     

Reactivity of O-methylated Illinois No. 6 coal towards alkyllithiums/methyl iodide

An O-methylated Illinois No. 6 vitrain was treated repeatedly with a series of C-H indicator bases of known pK_a and quenched with ^13,14C-methyl iodide. The extent of ¹⁴CH₃ incorporation depended strongly upon base strength, increasing in the order 9-phenylfluorenyllithium < fluorenyllithium < trityllithium. A significant number of methyl groups ($\text{0.7–1.2}\text{100}$ coal carbons) were introduced with fluorenyllithium and trityllithium as the base. Additional methyl groups were added upon a second and third treatment with base and alkylating agent. After three treatments, the number of added methyl groups had doubled. The extent of base reagent incorporation was established by parallel experiments using ¹⁴C-enriched bases. CP/MAS ¹³C n.m.r. of the first coal alkylation product using trityllithium and ¹³C-enriched methyl iodide was consistent with predominantly C-alkylation. From these results, a unified picture for coal structure emerges which contains a distribution of reactive C-H sites, distinguishable on the basis of their acid-base properties. Possible reactive sub-structures are considered.     

Synthesis of cis‐1,4‐polyisoprene with Al‐Ti catalysts modified by different electron donor reagent

The preparation of the high cis ?1,4‐polyisoprene by Ziegler‐Natta catalysis system was studied. The effect of Al‐Ti catalysts modified by ethers with different structures which are different electron donor reagent on polymerization of isoprene has been mainly investigated. By the measurement method of the monomer conversion, FTIR, and ¹H NMR spectroscopy, the influence of, respectively, added diphenyl ether, anisole, dibutyl ether, or methyl tert ‐butyl methyl ether as a third active component on the heterogeneous TiCl₄‐Al(i ‐Bu)₃‐ether catalyst activity and microstructure of synthetic polyisoprene was analyzed. By the adding of diphenyl ether or dibutyl ether, the process of prefabricated heterogeneous catalyst is quickly and catalyst particle quantity is large. The polymerization conversion is high and the microstructure cis ?1,4 content of the resulting polymer can reach 92%. But Al(i ‐Bu)₃ added anisole or methyl tert ‐butyl methyl ether hard to cooperate with TiCl₄. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 44357.     

Preparation and properties of poly(methyl methacrylate)/iron carbonate(p) nanocomposites

The mass transport of methanol mixed with ferric chloride hexahydrate (FeCl₃ · 6H₂O) in poly(methyl methacrylate) and poly(methyl methacrylate)/iron carbonate particulate_(p) nanocomposites is prepared by chemical vapor crystallization and the resulting materials, which are subjected to characterization to evaluate thermal and optical properties, have been investigated. Mass transport is an anomalous and endothermic process and satisfies the van't Hoff plot. We have prepared successfully poly(methyl methacrylate)(PMMA)/iron carbonate particulates nanocomposites using CO₂ gas slowly diffused into saturated solvent mixture‐treated poly(methyl methacrylate) for 48 h. After SEM observation, approximately 80 nm iron carbonate particulates were precipitated and evenly distributed in the poly(methyl methacrylate) matrix. In comparison with solvent mixture‐treated PMMA, the cut‐off wavelength of transmittance in nanocomposites shifts to the shorter wavelength side (red shift). The presence of nanoscale iron carbonate particulates increased the glass transition temperature of the nanocomposites as determined by differential scanning calorimeter, and the glass transition temperature increased with increasing content of nanoscale iron carbonate particulates. The FTIR spectra of solvent mixture‐treated poly(methyl methacrylate) and nanocomposites are also studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2329–2338, 2005     

Synthesis and characterization of colloidal TBA-silicalite-2

Colloidal TBA-silicalite-2 (MEL type) was hydrothermally synthesized in the reactant system TBAOH–TEOS–H₂O. The influences of reactant composition, reaction temperature, and crystallization period on particle size of the zeolite were investigated. The colloidal silicalite-2 was characterized by XRD, SEM, TEM, FT-IR, ²⁹Si MAS NMR, ¹³C CP MAS NMR, thermogravimetric analysis and N₂ adsorption. The as-synthesized colloidal zeolite with a particle size of 100 nm is an agglomerate composed of nano-sized crystals of about 20 nm, displaying unique structural characteristics such as high content of silanol defects in the framework, splitting of the double-ring vibration in FT-IR spectrum and an unusual signal for methyl groups of TBA in ¹³C CP MAS NMR spectrum.     

Conjugate Vaccines from Bacterial Antigens by Squaric Acid Chemistry: A Closer Look

By using O‐SP‐core (O‐SPcNH₂) polysaccharide, isolated from Vibrio cholera O1 lipopolysaccharide (LPS) and related synthetic substances, a detailed study of factors that affect conjugation of bacterial polysaccharides to protein carriers through squaric acid chemistry to form conjugate vaccines has been carried out. Several previously unrecognized processes that take place during the squarate labeling of the O‐SPcNH₂ and subsequent conjugation of the formed squarate (O‐SPcNH‐SqOMe) have been identified. The efficiency of conjugation at pH 8.5, 9.0, and 9.5 to bovine serum albumin (BSA) and to the recombinant tetanus toxin fragment C (rTT‐Hc) has been determined. The study led to a protocol for more efficient labeling of O‐SPcNH₂ antigen with the methyl squarate group, to yield a higher‐quality, more potent squarate conjugation reagent. Its use resulted in about twofold increases in conjugation efficiency (from 23–26 % on BSA to 51 % on BSA and 55 % on rTT‐Hc). The spent conjugation reagent could be recovered and regenerated by treatment with MeI in the absence of additional base. The immunological properties of the experimental vaccine made from the regenerated conjugation reagent were comparable with those of the immunogen made from the parent O‐SPcNH‐SqOMe.     

The mechanism of chain growth in the Fischer-Tropsch hydrocarbon synthesis

It is proposed that the slow step in chain growth during the Fischer-Tropsch hydrocarbon synthesis is the formation of an adsorbed ethylidene species from two adsorbed methylenes. Addition of a further methylene species gives a diadsorbed C₃H₆ entity, which leads to a singly attached carbonium ion. A 1,2 hydrogen shift then forms a methyl substituted ethylidene species, which is available for further polymerisation. Further hydrogen shift may occur, yielding an olefin and terminating the chain growth. The extent of chain branching is dictated by the relative stability of secondary and primary carbonium ions, as previously proposed by McCandlish, (J. Catalysis 83 (1983) 362).