A 'meta effect' in the fragmentation reactions of ionised alkyl phenols and alkyl anisoles

The competition between benzylic cleavage (simple bond fission [SBF]) and retro-ene rearrangement (RER) from ionised ortho, meta and para RC(6) H(4) OH and RC(6) H(4) OCH(3) (R?=?n-C(3) H(7) , n-C(4) H(9) , n-C(5) H(11) , n-C(7) H(15) , n-C(9) H(19) , n-C(15) H(31) ) is examined. It is observed that the SBF/RER ratio is significantly influenced by the position of the substituent on the aromatic ring. As a rule, phenols and anisoles substituted by an alkyl group in meta position lead to more abundant methylene-2,4-cyclohexadiene cations (RER fragmentation) than their ortho and para homologues. This 'meta effect' is explained on the basis of energetic and kinetic of the two reaction channels. Quantum chemistry computations have been used to provide estimate of the thermochemistry associated with these two fragmentation routes. G3B3 calculation shows that a hydroxy or a methoxy group in the meta position destabilises the SBF and stabilises the RER product ions. Modelling of the SBF/RER intensities ratio has been performed assuming two single reaction rates for both fragmentation processes and computing them within the statistical RRKM formalism in the case of ortho, meta and para butyl phenols. It is clearly demonstrated that, combining thermochemistry and kinetics, the inequality (SBF/RER)(meta) 相似文献   

An efficient and facile nitration of phenols with nitric acid/zinc chloride under ultrasonic conditions

An efficient and facile nitration of phenols using nitric acid/zinc chloride under ultrasonic condition has exhibited significant chemo as well as regioselectivity. This study has been extended to other aromatic compounds like naphthalene and anthracene.     

Course of Uptake of Weed-Borne Nitrogen by Maize,Tested with 15N

Abstract

The course of uptake of weed-borne nitrogen by maize was tested with ¹⁵N in a pot experiment with silty loam after common growth of maize and Chenopodium album L., and mulching the weed in the 5-leaf stage of maize. Harvests 4,8 and 12 weeks after mulching show that the maize took up 35, 63 and 70% of the weed-borne nitrogen, resp., in consequence of a rapid and almost complete mineralization. The portion of weed-borne nitrogen in total N of the maize was 16% at all harvest dates. The differences in yield between weeded and unweeded maize were not significant neither at 5-leaf stage nor at corn maturity.     

Test for the shell-model-Weinberg treatment of the reaction15N(n,n′)15N* with a separable interaction

A modification of Weinberg's method in connection with the Born approximation was first employed by Ebenhöhet al. to describe the reaction¹⁵N(n, n′)¹⁵N^* using a delta-force as residual interaction. This method is now applied to the same reaction but using a surface-delta-interaction. For this separable interaction also the exact solution of the problem is presented. We were not interested in adjusting any parameters to obtain optimal agreement with experiment. Only the results of these two approaches are compared. The good agreement may give confidence in the application of the modified Weinberg method in connection with non-separable interactions.     

Mechanistic and conformational studies on the interaction of anti-inflammatory drugs, isoxicam and tenoxicam with bovine serum albumin

The mechanism of interaction of the non-steroidal anti-inflammatory drugs, isoxicam (IXM) and tenoxicam (TXM) with bovine serum albumin (BSA) has been studied using spectroscopic techniques, viz., spectrofluorescence, circular dichroism (CD), UV-visible absorption and FT-IR under simulative physiological conditions. Stern-Volmer analysis of fluorescence quenching data shows the presence of the static quenching mechanism. Thermodynamic parameters (negative ΔH⁰ and positive ΔS⁰ values obtained in the present study) revealed that the hydrophobic interactions played a major role in the interaction of these drugs with BSA. The distance, r between the donor (BSA) and acceptor (IXM/TXM) was calculated based on the Forster’s theory of non-radiation energy transfer and the values were observed to be 3.85 nm and 2.60 nm in IXM-BSA and TXM-BSA system, respectively. CD and FT-IR studies indicated that the binding of IXM/TXM to BSA induced conformational changes in BSA. The effect of common ions on the binding of IXM/TXM to BSA has been investigated.     

15N Distribution in Wheat and Chemical Fractionation of Root-Borne 15N in the Soil

Abstract

Spring wheat plants were grown in split-root containers and labelled with ¹⁵N by fertilizing one compartment of the container with ¹⁵NH₄ ¹⁵NO₃ (95 at.-% ¹⁵N exc.). After the harvest, approx. 90% of the ¹⁵N incorporated by the plants were found in the shoots and 3% in the roots; approx. 7% had been released into the soil of the unlabelled compartment. The ¹⁵N in the soil of the unlabelled compartment was extracted with KCl and hydrolysed with HCl. Approx. 60% of the ¹⁵N was found in the hydrolysable organic N pool of the soil and 9% in the fraction of the soluble and exchangeable inorganic nitrogen.     

15N(p,po)15N and the levels of 16O for Ex = 14.8–18.6 MeV

Angular distributions of cross section and analyzing power for elastic scattering of protons from ¹⁵N have been measured for E_p = 2.7–7.0 MeV. A phase-shift analysis of the data yields spin-parity assignments and level parameters for seventeen states of ¹⁶O in the excitation energy region 14.8–18.6MeV. Three of the resonances have not previously been identified, among them being a broad J^π = 2^? level at E_p = 6.1 MeV which is almost certainly the analog of the 2^? 1p1h state with configuration ($\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{,}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$) at E_x ∽ 5.0 MeV in ¹⁶N. The broad level previously reported near E_p = 5.0 MeV has been observed and its parameters determined. A resonance analysis of the phase shifts yielded values of E_r, Γ and Γ_p for all of the levels. The J^π assignments are in agreement with previously reported values. For resonances having J = l, the data can usually be fit with a resonant phase shift corresponding to either J = l + 1 or J = l ? 1, in addition to the phase shift for J = l. Which of the two spurious-J solutions occurs seems to depend on whether the partial wave through which the resonant state is formed is $\text{J = l +}\text{1}\text{2}\text{or}\text{J = l ?}\text{1}\text{2}$.     

Mechanism of the 12C(11B,15N)8Be reaction and 8Be + 15N optical-model potential

Angular distributions of the ¹²C( ¹¹B, ¹⁵N) ⁸Be reaction were measured at the energy E_lab(¹¹B) = 49 MeV for the transitions to the ground and 2.94 MeV (2⁺) excited state of ⁸Be and to the ground and 5.270 MeV (5/2⁺) + 5.299 MeV (1/2⁺), 6.324 MeV (3/2^-), 7.155 MeV (5/2⁺) + 7.301 MeV (3/2⁺), 7.567 MeV (7/2⁺) excited states of ¹⁵N. The data were analyzed by the coupled-reaction-channel method. The elastic, inelastic scattering and one- and two-step transfers were included in the coupling scheme. The data of the ¹²C( ¹¹B, ⁸Be) ¹⁵N reaction at E_cm = 9.4-17.8 MeV known from the literature, were also included in the analysis. The mechanism of the ¹²C( ¹¹B, ¹⁵N) ⁸Be reaction and the optical-model potential parameters for the ¹⁵N + ⁸Be channel were deduced. The energy dependence of the optical-model parameters for the ¹⁵N + ⁸Be channel was obtained.     

Estimation of N Absorption and Secretion by Digesta Exchange between 15N Labelled and Unlabelled Pigs

Abstract

Three female pigs (LW～30 kg) were fitted with re-entrant cannulas in the duodenum and the ileum and with bladder catheters. Animal No. 1 was labelled by continuous infusion of [¹⁵N]leucine via a catheter into the vena jugularis. After reaching a steady state in the level of endogenous N (4–5 d after beginning of the infusion) the digesta of the labelled animal No. 1 and the two unlabelled animals were exchanged in a 3 day experiment. During this time the course of transit rates of digesta, digesta N and ¹⁵N through duodenum and ileum as well as the proportion of endogenous N: exogenous N were estimated. Using these data it was possible to calculate the secretion and absorption rates of endogenous and exogenous N in the three segments of the digestive tract: mouth-duodenum, duodenum-ileum, ileum-anus and in addition the reabsorption (intestinal recycling) of the endogenous N during its passage through the gut could be computed.     

Ultrasonic and viscometric studies of molecular interactions in binary mixtures of formamide with ethanol, 1-propanol, 1,2-ethanediol and 1,2-propanediol at different temperatures

The ultrasonic speeds, u and viscosities, η of binary mixtures of formamide (FA) with ethanol, 1-propanol, 1,2-ethanediol, and 1,2-propanediol, including those of pure liquids, over the entire composition range were measured at 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15 K. From the experimental values of u and η, the deviations in isentropic compressibility, Δk_s, in ultrasonic speed, Δu, and in viscosity, Δη were calculated. The variation of these parameters with composition and temperature of the mixtures are discussed in terms of molecular interaction in these mixtures. The observed trends in Δk_s values indicate the presence of specific interactions between FA and alkanol molecules. The Δk_s values follow the order: ethanol < 1-propanol < 1,2-propanediol < 1,2-ethanediol. It is observed that the Δk_s values depend upon the number of hydroxyl groups and alkyl chain length in these alkanol molecules. Furthermore, the free energies, ΔG, enthalpies, ΔH and entropies, ΔS of activation of viscous flow have also been obtained by using Eyring viscosity equation and their dependence on composition of the mixtures have been discussed.     

Measurements of the 3ν 3 band of 14N15N16O and 15N14N16O using continuous-wave cavity ring-down spectroscopy

The absorption spectra of the 3ν₃ band of nitrous oxide isotopologues, ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O, have been measured using diode laser cavity ring-down spectroscopy in 6400–6463 and 6465–6532 cm^-1, respectively. Spectroscopic parameters and the rotational line intensities of the bands have been determined. We have applied this spectroscopic technique to the measurements of the absolute isotope ratio of those isotopologues using the absolute line intensities. PACS 32.10.Bi; 33.20.Vq; 33.70.-w; 42.55.Px; 42.62.Fi     

N.M.R. studies of cis-1,2-difluoroethylene and vinyl fluoride in a nematic solvent

Constrained anisotropic dipole oscillator strength techniques are used to obtain reliable values for a wide range of anisotropic and isotropic dipole properties of NO, including most anisotropic components of the dipole-dipole dispersion energy coefficients for the interaction of NO with NO, O₂, H₂, N₂, CO, He, Ne, Ar, Kr and Xe. Some of the anisotropic constraints required for our calculations are obtained via dipole sum rules from ab initio, multi-reference configuration interaction wavefunctions for NO. The individual dipole properties of NO considered include the dipole oscillator strength sums S_k , k = 2,1,0(? 1/2)? 2,? 3,? 4,..., the logarithmic dipole sums L_k and mean excitation energies I_k , k = 2(? 1)? 2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarizaiton ratio, and the Rayleigh scattering cross-section. Our constrained dipole oscillator strength results are often the only reliable, and often the only available, values for many of the properties and dispersion energies considered.     

Utilization by maize of phosphonitrilic hexamide labelled with 15N at cyclic and at amino positions

Abstract

The phosphonitrilic hexamides (PNH) [¹⁵N₆] hexamino-phosphatriazine and hexaminophospha-[¹⁵N₃] triazine were synthesized. Vegetation experiments showed that PNH has a favourable effect on the maize growth. Also the results demonstrated that the major part of PNH is mineralized during the following days. This process diminishes after 60 days. The total N-fertilizer uptake is about 46%, 29% of which came from amino-N and 17% from cyclic N, respectively. PNH behaved as a slow releasing N-fertilizer.     

An AES and ESCA study of GCr15 steel coated with Ti,Cr and bombarded by N+ and Ar+

GCr15 steel specimens coated with Ti, Cr and bombarded with N⁺, Ar⁺ were analyzed by AES and ESCA (PHI-550). The results show that (1) the specimens bombarded with N⁺ have improved surface mechanical properties compared to those bombarded with Ar⁺; (2) the changes in the surface properties are related to the composition of the surface layer, mainly to TiO₂, TiN, Cr₂O₃, and other compounds. Also, the presence of carbon is found to be advantageous in modifying GCr15 bearing steel.     

Plant delta(15)N associated with arbuscular mycorrhization, drought and nitrogen deficiency

It has long been evident that plant (15)N chiefly reflects the processes which fractionate (15)N/(14)N rather than the (15)N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant (15)N is the presence/absence, type or species of mycorrhiza, especially when interacting with nutrient deficiency. Ecto- and ericoid mycorrhizas are frequently associated with (15)N-depleted foliar (15)N, commonly as low as -12 per thousand. As shown by the present study, plants having no mycorrhiza, or those infected with various species of arbuscular mycorrhiza (AM)-forming fungi, interact with varying concentrations of soil nitrogen [N] and moisture to enrich plant (15)N by as much as 3.5 per thousand. Hence the lack of a mycorrhiza, or variation in the species of AM-forming fungal associations, can account for about 25% of the usually reported variations of foliar (15)N found in field situations and do so by (15)N enrichment rather than depletion. Copyright 1999 John Wiley & Sons, Ltd.     

Rapid, Sensitive and Highly Selective (15)N Analysis of (15)N Enriched Nitrite in Water Samples and Soil Extracts by Nitric Oxide Production and CF-QMS Measurement

Abstract Nitrite is a very important intermediate in many microbiological N transformations in soils and water. The stable isotope (15)N is often used to investigate these processes. The determination of (15)N in low concentrations of nitrite in the presence of large concentrations of nitrate is very difficult. Methods used so far for the isotope analysis of nitrite are unsatisfactory, because the nitrite must be calculated as the difference between nitrate plus nitrite and nitrate alone. More useful are mehods by which the nitrite is selectively converted into a chemical form that is suitable for (15)N analysis and that is free from interference from other N species, particularly nitrate. Using this principle in the present study we developed a method where the nitrite is reduced to nitric oxide by iodide in acid medium. This reaction is fast and quantitative, and the (15)N abundance of NO can be precisely measured by continuous flow mass spectrometry. This method is used for samples from tracer experiments with artificially enriched nitrogen 15. Therefore, the use of simple quadrupole mass spectrometers directly linked to the reaction unit is possible with sufficient precision (Reaction-Continuous Flow Quadrupole Mass Spektrometry-RCFQMS). Using the technique developed sample volumes up to 10ml containing at least 1.0 μg nitrite-N (0, 1 μg/ml) with a (15)N abundance of ? 0.42 at.% gave a precision of RSD ? ± 3%.     

One- and two-dimensional 15N exchange CP/MAS NMR studies of the structure and electronic properties of the intermolecular N-H...N hydrogen bond in imidazole crystal

The hydrogen bond of the type N-H...N in imidazole crystal has been studied by one and two-dimensional 15N exchange CP/MAS NMR measurements as well as the powder NMR spectrum. The chemical shift anisotropies for -N= and -N< were determined from the powder 1D spectrum. In 2D exchange CP/MAS NMR spectrum, the cross peaks between the 15N main resonance peaks for -N= and -N< were observed, implying that magnetization exchange between -N= and -N< takes place. The 1D exchange CP/MAS NMR measurements determined the exchange rate of magnetization at 289 K to be 1.3 and 1.5 s(-1) for -N= and -N<, respectively. The proton-driven spin-diffusion model interprets the experimental values, and the exchange rate depends strongly on the RF power of the proton decoupling field, suggesting that the magnetization transfer between -N= and -N< takes place by the 1H-driven spin-diffusion mechanism.     

Mass measurement and spectroscopy of57Cu with the58Ni(14N,15C)-reaction

The mass of⁵⁷Cu has been measured with the⁵⁸Ni(¹⁴N,¹⁵C)-reaction at 150 MeV incident energy with theQ 3D-spectrometer. The reaction has been selected after a careful inspection of the DWBA-expression for the cross section with respect to the highest weighting factors for spins andl-transfer. Cross sections of several μb/sr have been obtained. TheQ-value has been measured to beQ ₀=?19.90 (4) MeV and the⁵⁷Cu mass excess is ?47 340 (40) keV. Four lines of excited states have been observed up to 5.7 MeV. These states have a structure of single particle character, since⁵⁷Cu consists of a doubly closed core with N=Z=28 and a proton outside, and states up to the 2d 5-shell are observed.     

Magnetic resonance tensors in Uracil: Calculation of 13C, 15N, 17O NMR chemical shifts, 17O and 14N electric field gradients and measurement of 13C and 15N chemical shifts

The experimental ¹³C NMR chemical shift components of uracil in the solid state are reported for the first time (to our knowledge), as well as newer data for the ¹⁵N nuclei. These experimental values are supported by extensive calculated data of the ¹³C, ¹⁵N and ¹⁷O chemical shielding and ¹⁷O and ¹⁴N electric field gradient (EFG) tensors. In the crystal, uracil forms a number of strong and weak hydrogen bonds, and the effect of these on the ¹³C and ¹⁵N chemical shift tensors is studied. This powerful combination of the structural methods and theoretical calculations gives a very detailed view of the strong and weak hydrogen bond formation by this molecule. Good calculated results for the optimized cluster in most cases (except for the EFG values of the ¹⁴N3 and ¹⁷O4 nuclei) certify the accuracy of our optimized coordinates for the hydrogen nuclei. Our reported RMSD values for the calculated chemical shielding and EFG tensors are smaller than those reported previously. In the optimized cluster the 6-311+G** basis set is the optimal one in the chemical shielding and EFG calculations, except for the EFG calculations of the oxygen nuclei, in which the 6-31+G** basis set is the optimal one. The optimal method for the chemical shielding and EFG calculations of the oxygen and nitrogen nuclei is the PW91PW91 method, while for the chemical shielding calculations of the ¹³C nuclei the B3LYP method gives the best results.