Diels-alder adducts of 3,6-dibromophencyclone with symmetrical 1,4-disubstituted-cis-2-butenes: comparisons with the adduct of phencyclone and N-benzylmaleimide, and one-dimensional and two-dimensional nuclear magnetic resonance studies and ab initio structure calculations

Hindered Diels-Alder adducts have been prepared from 3,6-dibromophencyclone, 2, with cis-1,4-diacetoxy-2-butene, 3; cis-2-butene-1,4-diol, 4; and N-benzylmaleimide, 5. The adduct from the parent phencyclone, 1, with N-benzylmaleimide was prepared for comparison. One- and two-dimensional (1D and 2D) proton and carbon-13 NMR studies (at 7.05 tesla, ambient temperatures), including high-resolution COSY45 and HETCOR (XHCORR) chemical shift correlation spectra, were performed, allowing extensive rigorous assignments for protons and protonated carbons. Substantial anisotropic shielding was seen for the ortho protons of the N-benzyl group in the adducts of 5 with 1 or 2, with these aryl protons resonating at 6.25 ppm (CDCl3) for each adduct. The unsubstituted bridgehead phenyls of all four adducts showed slow exchange limit (SEL) 1H and 13C spectra. Greater shift dispersions for the bridge-head phenyl protons in the adducts from 5 relative to those from 3 or 4 suggested the role of the imide carbonyls for anisotropic contributions or for influences on adduct geometry. Ab initio geometry optimizations were performed at the Hartree-Fock level with the 6-31G* basis set (or the LACVP* basis set for the bromine-containing compounds) for each of the adducts. For the two adducts from benzylmaleimide, separate minima were located corresponding to conformers in which the benzyl group was directed into the adduct cavity (syn) or out of the adduct cavity (anti). Calculated energies and geometric parameters for the adducts are presented, and these suggested a significantly different structure for the dibromo diacetate adduct, in terms of general symmetry and bridgehead phenyl geometries, compared to the other adducts.     

1H and 13C nuclear magnetic resonance studies of the hindered phencyclone adducts of some smaller branched N-alkyl maleimides: rigorous aryl proton assignments with high-resolution two-dimensional (COSY45) spectroscopy, and anisotropic shielding effects and ab initio geometry optimizations

Phencyclone, 1, a potent Diels-Alder diene, reacts with a series of N-alkylmaleimides, 2, to form hindered adducts, 3. The 300 MHz 1H and 75 MHz 13C NMR studies of these adducts at ambient temperatures have demonstrated slow rotations on the nuclear magnetic resonance (NMR) timescales for the unsubstituted bridgehead phenyl groups, and have revealed substantial magnetic anisotropic shielding effects in the 1H spectra of the N-alkyl groups of the adducts. The selected N-alkyl groups for the target compounds emphasized smaller branched alkyls, including C3 (isopropyl, a); C4 (isobutyl, b; and t-butyl, c); C5 (n-pentyl, d; isopentyl [isoamyl], e; 1-ethylpropyl, f; t-amyl, g;) and a related C8 isomer (1,1,3,3-tetramethylbutyl ["t-octyl"], h). The straight-chain n-pentyl analog was included as a reference. This present work on the branched N-alkylmaleimide adducts appreciably extends our earlier compilation on the N-n-alkylmaleimide adducts. Key methods for proton assignments included "high-resolution" 1H-1H chemical shift correlation spectroscopy, COSY45. 13C NMR of the adducts, 3, verified the expected number of aryl carbons for slow exchange limit (SEL) spectra of the bridgehead phenyl groups. The synthetic routes involved reaction of the corresponding amines, 4, with maleic anhydride to give the N-alkylmaleamic acids, 5, which underwent cyclodehydration to form the maleimides, 2. Magnetic anisotropic shielding magnitudes for alkyl group protons in the adducts were calculated relative to corresponding proton chemical shifts in the maleimides. Geometry optimizations for the above adducts (and for the N-n-butylmaleimide adduct) were performed at the Hartree-Fock level with the 6-31G* basis set. The existence of different contributing conformers for the adducts is discussed with respect to their calculated energies and implications regarding experimentally observed anisotropic shielding magnitudes.     

A computer-assisted structure elucidation scheme based upon the pattern of assembly of peaks in carbon-13/ proton NMR spectra

Hashimoto, M.S., Tanaka, Y., Sasabuchi, H. and Hattori, C.F., 1989. A computer-assisted structure elucidation scheme based upon the pattern of assembly of peaks in carbon-13/proton NMR spectra. Chemometrics and Intelligent Laboratory Systems, 6: 143–155.The basic idea reported previously in the qualitative analysis of carbon-13 NMR spectra by a computer-assisted structure elucidation scheme was extended so that it is now applicable to proton NMR spectra.Peaks in proton NMR spectra were grouped into several multiple bands with an evaluation of whether the peaks are close to each other within ± σ ppm, or not. The multiple bands were further patterned to rectangles, of which the widths and lengths correspond to the patterned multiplicities and the intensities of the maximum peaks in the groups.The patterned spectra of unknown compounds were compared with those of reference spectra by evaluating the quantities proportional to the reciprocal of the difference of chemical shifts, that of the multiplicities and that of the intensities of the unknown and the reference spectra.The applicability of this method was examined for steroid compounds and it was shown that the method can be used for structure elucidation problems.     

Low frequency magnetic shielding of YBa2Cu3O7-δ: Agx high temperature superconductors

Two measurement systems were used to investigate the low frequency magnetic shielding behavior of pure YBa₂Cu₃O_7−δ, silver doped YBa₂Cu₃O_7−δ, a packed powder, a laser ablated thin film and copper. It was found that factors which influence low frequency magnetic shielding include material composition, microstructure and properties, external a.c. and d.c. fields and sample dimensions. Among the experimental materials, only bulk ceramics showed good shielding factors which were constant with frequency in the range 10–3000 Hz. A macroscopic shielding current was necessary for a good shield. The thickness of the ceramic played a crucial role in shielding. Flux breakthrough occurred when the external field exceeded a certain value. The breakthrough field increased with sample thickness. The influence of d.c. fields on the shielding behaviour depended on the history and magnitudes of the fields. Magnetic shielding hysteresis was observed and its potential application is discussed.     

C70 Fullerene charge-transfer interaction with alkylnaphthalenes,pinenes, and a diene

Alkylnaphthalenes are not able to form Diels-Alder adducts with C₇₀ fullerene but selected alkylnaphthalenes are able to yield weak charge-transfer complexes (CTC) with C₇₀. More in detail, 1-methylnaphthalene, 2-ethylnaphthalene, and pure naphthalene are not able to produce neither Diels-Alder adducts with C₇₀ fullerene nor CTC. Instead, 1,4-dimethylnaphthalene, 2,6-diethylnaphthalene yield weak 1:1 CTC with C₇₀ fullerene. These CTC are decomposed above ambient temperature. The conjugated diene 2,4-dimethyl-1,3-pentadiene initially forms a weak 1:1 CTC with C₇₀ and evolves into a Diels-Alder multiple adduct where C₇₀ acts as a multisite dienophile.     

Carbon-13 cross-polarization magic-angle-spinning nuclear magnetic resonance investigation of the interactions between maleic anhydride grafted polypropylene and wood polymers

The chemical interactions between maleic anhydride grafted polypropylene (MAPP) and wood were studied with solid-state carbon-13 cross-polarization magic-angle-spinning nuclear magnetic resonance ((13)C CPMAS NMR) spectroscopy. MAPP was synthesized with 100% (13)C enrichment at the C(1) and C(4) carbons to allow detection of the [1,4-(13)C(2)]MAPP functional groups and was melt blended with cellulose, lignin, and maple wood. In the cellulose/MAPP blend, changes in (13)C CPMAS NMR corrected signal intensities for the anhydride and dicarboxylic maleic acid functionalities suggested that esterification may have occurred predominantly from the more numerous diacid carbons. A single proton longitudinal relaxation in the rotating frame, (H)T(1rho), for the MAPP and the cellulose carbons in the blend suggested that they were spin coupled, i.e., homogeneous on a 10-200 Angstrom scale. Esterification was also suggested in the lignin/MAPP blend. Furthermore, the more significant changes in the intensities of the carbonyl signals and (H)T(1rho) values suggested that lignin may be more reactive to MAPP than cellulose. Finally, when maple was melt blended with MAPP, the same trends in the (13)C CP-MAS NMR spectra and (H)T(1rho) behavior were observed as when MAPP was blended with cellulose or lignin. This study therefore clarifies that during melt compounding of wood with MAPP, esterification occurs with wood polymers, preferentially with lignin. Understanding the interactions of MAPP with wood is of significance for the development of natural-fiber-reinforced thermoplastic composites.     

Analytical shielding calculations for a proton therapy facility

The University of Pennsylvania is building a proton therapy facility in collaboration with Walter Reed Army Medical Center. The proposed facility has four gantry rooms, a fixed beam room and a research room, and will use a cyclotron as the source of protons. In this study, neutron shielding considerations for the proposed proton therapy facility were investigated using analytical techniques and Monte Carlo simulated neutron spectra. Neutron spectra calculations were done using the GEANT4 (v6.2) simulation code for various materials: water, carbon, iron, nickel and tantalum to estimate the neutron production at proton beam energies of 100, 175 and 250 MeV. Dose equivalent calculations were performed using analytical methods at various critical points within the facility, by folding the GEANT4 produced neutron spectra with dose equivalent rate data from the National Council on Radiation Protection and Measurements (NCRP) Report #144.     

Ab initio molecular orbital calculations of the NMR chemical shieldings for mannose and mannobiose

The ¹³C and ¹H NMR shielding constants for -methylmannose and -methylmannobiose have been calculated using the ab initio gauge-including atomic orbital (GIAO) method to study the conformational dependencies of the NMR chemical shifts of the sugars. The molecular structures were fully optimized using B3LYP/6-31G^* and the NMR shielding constants were calculated at both Hartree–Fock (HF) and density functional (DF) levels of theory with various kinds of basis sets. The values determined using the B3LYP hybrid functional were a little closer to those obtained experimentally than those determined at the HF level. Both, HF and B3LYP with the 6-311+G(2d,p) basis were found to give a very good correlation between the experimental and calculated shielding constants, especially for ¹³C.     

Effects of mobile-phase additives, solution pH, ionization constant, and analyte concentration on the sensitivities and electrospray ionization mass spectra of nucleoside antiviral agents

The effects of various mobile-phase additives, solution pH, pKa, and analyte concentration on electrospray ionization mass spectra of a series of purine and pyrimidine nucleoside antiviral agents were studied in both positive and negative ion models. The use of 1% acetic acid resulted in good HPLC separation and the greatest sensitivity for [M + H]+ ions. In the negative ion mode, 50 mM ammonium hydroxide gave the greatest sensitivity for [M - H]- ions. The sensitivities as [M + H]+ ions were significantly larger than the sensitivities as [M - H]- ions for purine antiviral agents. Vidarabine monophosphate and pyrimidine antiviral agents, however, showed comparable or greater sensitivities as [M - H]- ions. The sensitivity as [M + H]+ showed no systematic variation with pH; however, the sensitivity as [M - H]- did increase with increasing pH. At constant pH, the ion intensity of the protonated species increased with increasing pKa. At higher analyte concentrations, dimer (M2H+) and trimer (M3H+) ions were observed. [M + Na]+ adducts were the dominant ions with 0.5 mM sodium salts for these compounds. The spectra of the more basic purine antiviral agents showed no [M + NH4]+ adduct ions, but [M + NH4]+ ions were the major peaks in the spectra of the less basic pyrimidine antiviral agents with ammonium salts. The ammonium adduct ion was formed preferentially when the proton affinity of the analyte was close to that of NH3. Abundant [M + OAc]- ions were observed for all of the antiviral agents except vidarabine monophosphate from solutions with added HOAc, NaOAc, and NH4OAc. The utility of mobile phases containing 1% HOAc or 50 mM NH4OH was demonstrated for chromatographic separations.     

盐酸普罗帕酮的核磁共振谱分析

该文利用核磁共振实验技术详细研究了抗心律失常药物盐酸普罗帕酮的化学结构特征，并借助二维核磁共振实验技术对盐酸普罗帕酮的氢谱和碳谱进行了完全归属，为该类化合物的结构解析提供了有益的分析依据。     

Characterization of hydrogenated amorphous carbon films by nuclear magnetic resonance techniques

Different nuclear magnetic resonance (NMR) methods have been used to investigate the structure of hydrogenated amorphous carbon films. Besides measuring the sp²-to-sp³ ratio by means of ¹³C cross-polarization magic-angle spinning total suppression of spinning sidebands NMR we studied the distribution of covalently bound hydrogen over sp²- and sp³-type carbon atoms using dipolar dephasing techniques. The reliability of the dipolar dephasing measurements is discussed and the results are compared with the data derived from a simple statistical model. Moreover they are compared with previous IR spectroscopy measurements. ¹H combined rotation-and-multipulse NMR spectra are presented which do not show resolved proton resonances in the case of as-deposited films but correspond in their line shape to the proton distribution measured with dipolar dephasing. Finally a few considerations concerning a refined structural model are presented.     

Hyphenation of solid-phase extraction with liquid chromatography and nuclear magnetic resonance: application of HPLC-DAD-SPE-NMR to identification of constituents of Kanahia laniflora

The introduction of on-line solid-phase extraction (SPE) in HPLC-NMR has dramatically enhanced the sensitivity of this technique by concentration of the analytes in a small-volume NMR flow cell and by increasing the amount of the analyte by multiple peak trapping. In this study, the potential of HPLC-DAD-SPE-NMR hyphenation was demonstrated by structure determination of complex constituents of flower, leaf, root, and stem extracts of an African medicinal plant Kanahia laniflora. The technique was shown to allow acquisition of high-quality homo- and heteronuclear 2D NMR data following analytical-scale HPLC separation of extract constituents. Four flavonol glycosides [kaempferol 3-O-(6-O-alpha-l-rhamnopyranosyl)-beta-d-glucopyranoside; kaempferol 3-O-(2,6-di-O-alpha-l-rhamnopyranosyl)-beta-d-glucopyranoside; quercetin 3-O-(2,6-di-O-alpha-l-rhamnopyranosyl)-beta-d-glucopyranoside (rutin); and isorhamnetin, 3-O-(6-O-alpha-l-rhamnopyranosyl)-beta-d-glucopyranoside] and three 5alpha-cardenolides [coroglaucigenin 3-O-6-deoxy-beta-d-allopyranoside; coroglaucigenin 3-O-(4-O-beta-d-glucopyranosyl)-6-deoxy-beta-d-glucopyranoside; 3'-O-acetyl-3'-epiafroside] were identified, with complete assignments of 1H and 13C resonances based on HSQC and HMBC spectra whenever required. Confirmation of the structures was provided by HPLC-MS data. The HPLC-DAD-SPE-NMR technique therefore speeds up the dereplication of complex mixtures of natural origin significantly, by characterization of individual extract components prior to preparative isolation work.     

INTERACTION OF MAGNESIUM AND LITHIUM IONS WITH [60]FULLERENE DERIVATIVES BEARING A PHOSPHORUS YLIDE GROUP

[60]Fullerene derivative 1 containing of an α-ylide group exists as a mixture of E and Z isomers. Treatment of 1 with MgBr₂ or LiI in CDCl₃ under ultrasonic agitation gave an adduct in which the carbonyl oxygen of α-ylide ester moiety in 1 is coordinated to the metal ion. The NMR spectra show that the adducts exist as a single isomeric form. After ultrasonic agitation, the adducts gradually revert to the original E,Z-mixture owing to slow absorption of moisture. Further ultrasonic treatment of the mixture resumes the complexation as long as enough anhydrous metal halides are still present.     

含穴醚N_8O_3配体的金属大环化合物的NMR研究(Ⅱ)

含有穴醚N_8O_3配体(H_3L)的金属大环化合物[M(H_3L)(CIO_4)]在溶液中,室温下,作了~1H NMR谱的测定.在化合物(6)—DMSO—d6溶液中还作~1H—~1H COSY(氢—氢相关二维谱)NMR谱的测定,归属了所有的~1H谱线,对其配位行为通过~1HNMR试验作了简单的讨论。     

Multiple solenoidal microcoil probes for high-sensitivity, high-throughput nuclear magnetic resonance spectroscopy

Two designs for incorporating multiple solenoidal microcoils into a single probe head are presented to increase the throughput of high-resolution NMR. Through a combination of radio frequency switches and low-noise amplifiers, multiple NMR spectra can be acquired in the same time as a single spectrum from a conventional probe consisting of one coil. Since this method does not compromise sensitivity with regard to the individual microcoils, throughput increases linearly with the number of coils. Only one receiver is needed, and data acquisition parameters can be optimized for each sample. Specifically, a four-coil system has been implemented for proton NMR at 250 MHz using a wide-bore magnet, with an observe volume of 28 nL for each microcoil. Signal cross-contamination was approximately 0.2% between individual coils, and simultaneous one- and two-dimensional spectra have been obtained from samples of fructose, galactose, adenosine triphosphate, and chloroquine (7 nmol of each compound). A more compact two-coil configuration has also been designed for operation at 500 MHz, with observe volumes of 5 and 31 nL for the two coils. One- and two-dimensional spectra were acquired from samples of 1-butanol (55 nmol) and ethylbenzene (250 nmol).     

Negative-mode MALDI-TOF/TOF-MS of oligosaccharides labeled with 2-aminobenzamide

MALDI-TOF-MS of 2-aminobenzamide-labeled N-glycans was shown to allow the analysis of sodium adducts and proton adducts in the positive-ion mode as well as deprotonated species in the negative-ion mode from a single preparation spot, using N-glycans of adult worms of the human parasite Schistosoma mansoni as model substances. Fragment ion analysis of these species was performed by MALDI-TOF/TOF-MS. With laser-induced dissociation, sodium adducts and proton adducts mainly showed cleavage of glycosidic linkages. High-energy collision-induced dissociation of sodium adducts resulted in extensive cross-ring cleavages and provided information on linkage positions. Of particular value were the negative-mode MALDI-TOF/TOF-MS analyses of the deprotonated N-glycans, which featured (1) various ring fragmentations giving linkage information, (2) extensive (1,3)A cross-ring cleavage of mannoses carrying an antenna readily revealing the composition of the antenna, (3) D as well as [D-18]- ions providing specifically the composition of the 6-antenna, and (4) pronounced stability of fucose linkages resulting in detailed information on fucosylation positions. The outlined approach thus allows the acquisition of both heCID MS/MS spectra of sodium adducts and LID MS/MS spectra of deprotonated species from a 2-aminobenzamide-labeled N-glycan prepared in 6-aza-2-thiothymine, resulting in a wealth of structural information.     

Multivariate curve resolution applied to the analysis and resolution of two-dimensional [1H,15N] NMR reaction spectra

Multivariate curve resolution is proposed for the study of complex chemical reactions monitored by two-dimensional (2D) NMR spectroscopy. In particular, in this work, multivariate curve resolution is applied to the study of the reaction between (15)N-labeled cisplatin and the amino acid-nucleotide hybrid (Phac-Met-linker-p(5')dG). At several stages of the reaction, 2D [(1)H,(15)N] HSQC NMR spectra were acquired and stored in data matrices. In a first step, multivariate curve resolution was applied to analyze individually each one of these 2D spectra, allowing the resolution of the corresponding (1)H and (15)N one-dimensional correlation spectra. In a second step, the whole set of 2D spectra recorded along the reaction were simultaneously analyzed by multivariate curve resolution, allowing the resolution of the kinetic concentration profiles and of the pure 2D NMR spectra of each of the species detected along the reaction. Results finally obtained confirmed previously postulated reaction mechanisms involving the existence of two monofunctional adducts and of two bifunctional adducts, with the structure of one of them not completely resolved.     

Effect of proton irradiation on the magnetic properties of manganese ferrite

Cubic-spinel MnFe2O4 magnetic nanoparticles (NPs) were prepared, with an average particle size of about 4 nm determined from a high-resolution transmission electron microscope. When the NPs were proton-irradiated, the lattice constants decreased with increasing proton irradiation. Before the proton irradiation, the NPs exhibited 36.2 +/- 0.1 emu/g magnetization (M(S)) and 11.1 +/- 0.1 Oe coercivity (H(C)). After the irradiation of the samples with 5 and 10 pC/microm2 doses, the M(S) changed to 35.6 and 35.1 +/- 0.1 emu/g, and the H(C) to 11.3 and 12.9 +/- 0.1 Oe, respectively. The room-temperature M?ssbauer spectra of the NPs showed superparamagnetic characteristics, with the single-absorption line of two sites and a large relaxation frequency. During the proton irradiation, the relaxation frequency decreased to 156.02 and 134.29 +/- 0.01 Gamma/? from the unirradiated sample's 164.02 +/- 0.01 Gamma/?. It is suggested that the proton irradiation induced the increase in the anisotropy energy of the MnFe2O4 NPs. Moreover, from the external-field-induced M?ssbauer spectra at 4.2 K, an increase in the canted angle of the hyperfine field between sites A (tetrahedral) and B (octahedral) was observed with proton irradiation.     

Separation and identification of DNA-carcinogen adduct conformers by polyacrylamide gel electrophoresis with laser-induced fluorescence detection.

We have developed a separation protocol utilizing high-resolution polyacrylamide gel electrophoresis (PAGE) to isolate stable anti-benzo[a]pyrene diol epoxide adducts of oligodeoxynucleotides. Both enantiomers produced multiple adduct species. The distribution of adduct types could be quantitated by densitometry of autoradiograms or Cerenkov counting of eluted oligomers modified by anti-BPDE isomers. Laser-induced fluorescence (LIF) spectra of eluted adducts at 4.2 K (fluorescence line-narrowing spectroscopy) and 77 K revealed that bands corresponded to pure conformers of pyrene chromophore. Carcinogen-modified oligodeoxynucleotides were single-stranded, but there were often considerable stacking interactions between the pyrenyl residues and the oligonucleotide bases, indicating that electrophoresed oligomers were single-stranded but in a native, versus random coil, conformation. The ability to identify and quantitate adducts by PAGE-LIF, coupled with the high resolution and sensitivity of both techniques, makes PAGE and LIF in tandem a potentially powerful tool in the study of chemical carcinogenesis or other ligand-DNA interactions.     

NMR Parameters of Aza-Fullerene and its Derivatives

The quantum mechanical investigations of the one isomer of aza-fullerene molecules have been performed. The investigation of the NMR spectra indicate that adducts and presence of PyO and HCl molecule leads to separation of NMR spectra.