16O Nuclei Research Articles

Theory of Electronic Structure and Nuclear Quadrupole Interactions in Heroin

A first principle investigation has been carried out for the electric field gradient tensor at the 14N nucleus in heroin (C21H23NO5) using the Hartree−Fock−Roothaan procedure for determination of the electronic structure employing atomic coordinates based on available X-ray diffraction data. The hydrogen positions were not available from experiment and were determined by energy optimization in our investigations. Our calculated quadrupole coupling constant e2qQ for 14N was found to be −4.906 MHz, the magnitude being in good agreement with the corresponding recently available magnitude of 5.3163 MHz from nuclear quadrupole resonance measurements. The value of the asymmetry parameter η was found to be 0.054, the smallness of its size being in agreement with that of the experimental value of 0.028. Possible sources that could further improve the quantitative agreement between theory and experiment are discussed. The quadrupole interaction parameters for the 17O and 2H nuclei are presented with the hope that ...

Gamma-Ray Line Spectroscopy Results from COMPTEL

Comptel aboard NASA's Compton Observatory has led to a major progress in the field of astronomical gamma-ray line spectroscopy. Highlights are the all-sky map of the 1.8 MeV line from radioactive 26Al, the first detection of the 1.156 MeV line from radioactive 44Ti from a Supernova remnant (Cas A), and the detection of excessive MeV emission from the Orion complex that may be ascribed to excitation of 12C and 16O nuclei.

Structure of peptides and polypeptides in the solid state as elucidated by NMR chemical shift

It is reviewed that through the observation of solid-state 13C NMR chemical shift, the main-chain conformation and hydrogen-bonded structure of peptides, polypeptides and proteins in the solid state have been successfully elucidated, and the combination of solid state 13C NMR and chemical shift calculation by quantum chemistry is a powerful means for the structural characterization. Furthermore, it is briefly introduced that solid state NMR of 15N and 17O nuclei is very useful for obtaining information about hydrogen-bonded structure. This review article is communicated on the basis of our recent works on structural characterization of peptides and polypeptides including proteins in the solid state by high-resolution solid-state NMR spectroscopy and its combination with quantum chemical calculation.

Theory and calculations of electric field effects on hyperfine interactions

A recently published theory of electric field effects on electron spin resonance hyperfine couplings [Phys. Ref. Lett. 79, 379, (1997)] is extended to nuclear quadrupole coupling. With the use of the ab initio coupled Hartree–Fock approach and augmented Sadlej basis set, results are obtained for the first-order corrections to the isotropic and anisotropic parts of hyperfine coupling tensor and the electronic part of the electric field gradient tensor for 17O and 2H nuclei in OH radical. The first-order coefficients exhibit a number of interesting features. The calculated results, in general, appear to be insensitive to the bond-centered polarization functions used in the calculation. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 771–778, 1998

Correlations and the cross section of exclusive ( e, e′ p) reactions for 16O

The reduced cross section for exclusive ( e, e′ p) reactions has been studied in DWIA for the example of the nucleus 16O using a spectral function containing effects of correlations. The spectral function is evaluated directly for the finite nucleus starting from a realistic nucleon-nucleon interaction within the framework of the Green's function approach. The emphasis is focused on the correlations induced by excitation modes at low energies described within a model-space of shell-model configurations including states up to the sdg shell. Cross sections for the p-wave quasi-hole transitions at low missing energies are presented and compared with the most recent experimental data. In the case of the so-called perpendicular kinematics the reduced cross section derived in DWIA shows an enhancement at high missing momenta as compared to the PWIA result. Furthermore the cross sections for the s- and d-wave quasi-hole transitions are presented and compared to available data at low missing momenta. Also in these cases, which cannot be described in a model without correlations, a good agreement with the experiment is obtained.

Imaging H2(17)O distribution in a phantom and measurement of metabolically produced H2(17)O in live mice by proton NMR.

Previously we suggested a method for indirect detection of H2(17)O via a combination of 1H spin-echo sequence and 17O decoupling. The method is based on the shortening of the water proton T2 due to the residual spin-spin coupling with the 17O nucleus, and on our finding that this shortening is abolished by applying an radio frequency field at the 17O resonance frequency. In the present work we demonstrate how the method can be used for imaging low concentrations of H2(17)O, and report for the first time an application of this method to in vivo detection of H2(17)O in live newborn mice, where the H2(17)O was introduced either directly i.p. or by inhalation of 17O2 where it was formed by oxidative metabolic activity.

Electroinduced two-nucleon knockout and correlations in nuclei

A model to calculate cross sections for electroinduced two-nucleon emission from finite nuclei is presented. Short-range correlations in the wave functions and meson-exchange contributions to the photoabsorption process are implemented. Effects of the short-range correlations are studied with the aid of a perturbation expansion method with various choices of the Jastrow correlation function. The model is used to investigate the relative importance of the different reaction mechanisms contributing to the A(e,e′pn) and A(e,e′pp) process. Representative examples for the target nuclei 12C and 16O and for kinematical conditions accessible with contemporary high-duty cycle electron accelerators are presented. A procedure is outlined to calculate the two-nucleon knockout contribution to the semi-exclusive (e,e′p) cross section. Using this technique we investigate to what extent far semi-exclusive (e,e′p) reactions can be used to detect high-momentum components in the nuclear spectral function.

Multicluster models for reactions of astrophysical interest

We use the Generator Coordinate Method to investigate some nuclei between A=12 and A=16, in a multicluster model. The microscopic wave functions are defined from cluster wave functions, involving three α particles and any s-shell nucleus. The α clusters are located at the apexes of an equilateral triangle, and form the basis of a tetrahedral structure, with the additional s cluster at the top of its height. Optimal configurations are determined for the 12C, 13C, 14C, 15N and 16O nuclei. We show that, with respect to the more usual shell-model approach, the multicluster description significantly improves the binding energy and the spectroscopic properties. Future applications to reactions of astrophysical interest are discussed.

Long-range correlations in finite nuclei: comparison of two self-consistent treatments

Long-range correlations, which are partially responsible for the observed fragmentation and depletion of low-lying single-particle strength, are studied in the Green's function formalism. The self-energy is expanded up to second order in the residual interaction. We compare two methods of implementing self-consistency in the solution of the Dyson equation beyond Hartree-Fock, for the case of the 16O nucleus. It is found that the energy-bin method and the BAGEL method lead to globally equivalent results. In both methods the final single-particle strength functions are characterized by exponential tails at energies far from the Fermi level.

Analysis of the interaction of water with the manganese cluster of photosystem II using isotopically labeled water.

The association of water with the Mn of the water oxidizing complex was investigated using H2(17)O- and 2H2O-reconstituted lyophilized photosystem II particles. The pulsed electron paramagnetic resonance (EPR) technique of electron spin echo envelope modulation (ESEEM) was used to investigate the interaction of the magnetic 2H and 17O nuclei with the paramagnetic S2 state of the Mn complex and other photosystem II components. ESEEM offers a much more specific and sensitive detection of this type of interaction than continuous wave (CW) EPR. Unlike earlier reports using CW EPR, these experiments did not detect any interaction of water with the multiline EPR signal from the S2 state of the Mn complex. No signals indicating specific interaction of either H or O with the multiline signal were detected. Signals due to 2H and 17O were detected only at the Larmour frequency, indicating nonspecific "distant ENDOR" effects. A weak interaction with 17O was detected both in S1, when the Mn is EPR silent, and in S2, but only on the high-field side of g = 2. This interaction may be with the Rieske iron-sulfur center in the cytochrome b6f complex. The results were the same whether the multiline signal was generated by 200 K illumination of dark-frozen samples, or by room temperature illumination in the presence of the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Illumination at room temperature in the presence of an electron acceptor to allow multiple turnovers of the system with cycling of the S states did not result in the appearance of any new interactions. These results appear to exclude close (less than 6 A) binding of water to the Mn center giving rise to the multiline signal, and also to exclude mechanisms in which water oxidation involves the breaking and re-formation of the mu-oxo bridges of the Mn complex. They cannot, however, exclude models in which water binding to the manganese complex and direct oxidation by the manganese complex occur in the higher S states, or are catalyzed by one bis(mu-oxo) Mn dimer while oxidizing equivalents are accumulated in the S2 state by a second bis(mu-oxo) Mn dimer.

Triaxial deformation of unstable nuclei in the relativistic mean-field theory

We study the properties of unstable nuclei including the possibility of triaxial deformation in the relativistic mean-field theory. We calculate the energy surfaces of various light mass nuclei: 16O, 40Ca, 20Ne, 24Ne and 24Mg and a series of even mass sulfur isotopes, in the βγ plane. We find the well-known spherical solution for the 16O and 40Ca nuclei strong prolate solutions for 20Ne, 24Ne and 24Mg, which are in agreement with the experimental data and the non-relativistic density-dependent Hartree-Fock results. For the sulfur isotopes, we find that the energy minimum moves from a prolate shape below 46S through triaxial shapes for 48–52S to an oblate shape above 54S.

A Study of Solvation-Shell Symmetry in Electrolyte Solutions Using Quadrupolar NMR Relaxation of the Nuclei of Monoatomic Ions

The spin-lattice relaxation rates of 7Li, 23Na, 27Al, 71Ga, and 139La nuclei in electrolyte solutions have been investigated as functions of the isotopic composition of the solvent. The results show that quadrupolar relaxation of the nuclei of monoatomic ions is extremely sensitive to the symmetry of the solvation shells. The data are compared to the results for the 2H and 17O nuclei of the solvent molecules and the 14N nucleus of the nitrate anion. A semiquantitative description of the observed effects is given.

Multicluster description of p-shell nuclei in a microscopic model

Abstract We use the Generator Coordinate Method to investigate some nuclei between A = 12 and A = 16 in a multicluster model. The microscopic wave functions are defined from clluster wave functions, involving three α particles and any s-shell nucleus. The α clusters are located at the apexes of an equilateral triangle, and form the basis of a tetrahedral structure, with the additional s cluster at the top of its height. Optimal configurations are determined for the 12C, 13C, 14C, 15N and 16O nuclei. We show that, with respect to the more usual shell-model approach, this multicluster description significantly improves the binding energy and the spectroscopic properties.

NMR Studies on Dynamic Structure of Hydrated Water Molecules in Alcohol-D 2 O Solutions

The spin-lattice relaxation times (T 1) of D and 17O nuclei of coordinated D 2O molecules in n-ROH (R= Me, Et, Pr and Bu) dilute aqueous solutions in the concentration range of 0.2 and 1.0 mol kg −1( 0.004 - 0.02 molar fraction ) at 25°C were measured by NMR spectroscopy. The relaxation rates (R 1=1/T 1) of D and 17O nuclei increased linearly with the concentration. B 1(i=D or 17O) is defined by R 1=R 1 0(1 + B 1 m), where R 1 and R 1 0 are spin-lattice relaxation rates of the D 2O molecule at concentration m (mol kg −1) and that of pure D 2O. B 1 increases with the size of the alkyl group of n-ROH. T 1 in alcohol/water solutions were interpreted with bulk and coordinated water. Positive and molecular size dependent B 1, values are caused by the hydrophobic hydration of the alkyl group. The dynamic hydration number of alcohol solution had good correlation with partial molar volume quantitatively through solute-solvent interactions.

Model calculations of doubly closed shell nuclei in CBF theory III. jj coupling and isospin dependence

Correlated Basis Function theory and Fermi Hypernetted Chain technique are extended to study medium-heavy, doubly closed shell nuclei in j-j coupling scheme, with different single particle wave functions for protons and neutrons and isospin dependent two-body correlations. Central semirealistic interactions are used. Ground state energies, one-body densities, distribution functions and momentum distributions are calculated for 12C, 16O, 40Ca, 48Ca and 208Pb nuclei. The values of the ground state energies provided by isospin dependent correlations are lower than those obtained with isospin independent correlations. In finite nuclear systems, the two--body Euler equations provide correlation functions variationally more effective than those obtained with the same technique in infinite nuclear matter.

17O Nuclear Quadrupole Coupling in Molecular and Lattice Systems by ab initio Calculation of Electric Field Gradients

Abstract We present ab initio Hartree-Fock calculations of electric field gradients, which are related to experimental determinations of nuclear quadrupole coupling constants. The nucleus of special interest is 17O but other nuclei in the molecules, especially 14N, 2H and 33S are included. The calculations were performed (a) as single molecules either at the SCF and MP2 correlated levels, (b) as clusters of molecules about a test site, or (c) as lattice calculations computed in the unit cell environment. The basis sets are triple zeta valence plus polarisation in (a). Because of limitations in exponent range in (c), the bases in both (b) and (c), where comparison was sought, are DZ at the SCF level.

Study of locally dense and locally saturated basis sets in localized molecular orbital calculations of nuclear shielding: Ab initio LORG calculations for13C and17O in norbornenone

This study demonstrates the use of uneven atomic basis sets for ab initio calculations of NMR shielding in the localized orbital/local origin (LORG) approach with norbornenone as the test case. We distinguish between locally dense sets (extended basis on target atom only) and locally saturated sets (extended bases on target atom and atoms in its first bonding sphere), using 6-311G** and 6-31G sets to describe the high and low level of function sets. It is shown that the use of these uneven sets can simulate high basis set level calculations of shieldings for 1H and for all the 13C nuclei in this molecule and, hence, allows quite accurate ab initio calculations of shielding properties of these nuclei in large molecules using relatively modest computational facilities. The shielding of the double-bonded 17O nucleus is apparently sensitive to basis-set quality beyond the first bonding sphere. © 1996 John Wiley & Sons, Inc.

Rotational spectrum of the isotopically substituted van der Waals complex Ar–CO2investigated with a molecular beam Fourier transform microwave spectrometer

Pure rotational spectra of the isotopomers Ar–16O 13C16O, Ar–17O12C16O and Ar–18O12C16O of Ar–CO2 have been investigated using a molecular beam Fourier-transform microwave spectrometer. The analyses of the experimental data yielded rotational and centrifugal distortion constants. These data were included in a force field analysis which has resulted in values for van der Waals stretching and bending force constants and harmonic vibration frequencies. In the case of Ar–17O12C16O, hyperfine structure of rotational transitions due to the quadrupolar 17O nucleus was observed and the corresponding nuclear quadrupole coupling constant could be determined. The obtained data are discussed in terms of structural and dynamical parameters.

TEMPERATURE EFFECTS ON THE ROTATIONAL MOTION OF THE COORDINATED D2O MOLECULES IN NaBr AND KBr AQUEOUS SOLUTIONS STUDIED BY NMR SPECTROSCOPY

The spin-lattice relaxation times (T1) of D and 17O nuclei of coordinated heavy water (D2O) molecules for Na+ and K+ in sodium bromide and potassium bromide dilute aqueous solutions were measured in the range of 5-50°C by means of NMR. The spin-lattice relaxation rates (R1=1/T1) varied linearly with the concentration up to 1mol/kg at a given temperature. The parallel (D) and the perpendicular (17O) rotational correlation times of coordinated D2O molecules for Na+ and K+ were determined. The ratio τ(D)/τ(17O) of the rotational correlation times of the coordinated D2O molecules was larger and smaller than unity for Na+ and K+, respectively, and was practically independent of temperature, which indicated that the rotational anisotropies of the coordinated D2O molecules was almost temperature independent.

Y-SCALING QUANTITIES AND NUCLEON CORRELATION EFFECTS IN NUCLEI

The asymptotic scaling function F(y) and the binding correction B(y), the mean kinetic 〈T〉 and removal 〈E〉 energies, as well as the occupation probabilities Sgr and Sex are calculated in the cases of the 4He, 12C, 16O and 40Ca nuclei using the nucleon momentum distributions obtained within the Jastrow correlation method and the phenomenological model which takes into account short-range and tensor nucleon-nucleon correlations. It is shown that the scaling functions F(y) differ from those obtained in the mean-field approximation but qualitatively agree with the available experimental data. The binding correction B(y) is explicitly evaluated using a model nuclear spectral function. The nucleon-nucleon correlation effects increase the values of the mean kinetic 〈T〉 and mean removal 〈E〉 energies in comparison with their values in the mean-field approximation.