Determination of trace elements in biological standard kale by neutron activation analysis

Fifteen elements at trace levels have been determined by neutron activation analysis in the biological standard kale distributed byBowen. La, Br, As, Se, Sc, Ag, Zn, Co, Cr, Sb, Eu, Fe, and Zr have been determined by a nondestructive technique using a high-resolution Ge(Li) detector. Two more elements, Au and Hg, have been determined after radiochemical separation. The nondestructive procedure is shown to yield data in generally good agreement with those obtained by destructive techniques. Potential sources of error in the nondestructive technique are discussed.     

THE EFFECT OF 1,4-DIAZABICYCLO[2.2.2]OCTANE ON THE RADIOSENSITIVITY OF BACTERIA

Abstract— Hydroxyl radicals ('OH) are scavenged by 1,4-diazabicyclo[2.2.2]octane (DABCO) at a diffusion-controlled rate of 1.25 ± 0.1 × 10⁹ M ^-1s^-1. Unlike other efficient 'OH scavengers which exhibit protection of bacteria against irradiation both in oxic and hypoxic conditions, DABCO has been shown to protect Serratia marcescens and various strains of Escherichia coli only in oxic conditions.
DABCO appears to eliminate a component of the sensitization afforded by oxygen in all strains of E. coli tested. The level of this protection increases from ∼15% in the wild type AB 1157 to ∼100% in the recA uvrA mutant AB 2480. It is suggested that DABCO protects against lethal events that can occur on macromolecules other than DNA such as the cell membrane.
Results with added glycerol, as well as work in D₂O solution, indicate that DABCO is more likely to be acting by scavenging radicals rather than by quenching ¹O₂. If ¹O₂ is a component of the sensitization afforded by oxygen, then it is unlikely to be formed in a hydrophilic environment in the cell.     

1,2,4-Triazoles—XXXIII: Photodimerization of some sym-di(3-s-triazolo-[4,3-a]pyridyl)-alkanes and related derivatives

Irradiation of 3,3'-[ethane-1,2-diyl]bis-[1,2,4-triazolo-[4,3-a]pyridine] at 300 nm gave the cisoid-fused cyclobutane dimer 5aα,5bα-10bα,10cα-tetrahydro-1,10-ethano-2,3,8,9,10a,10d-hexaazadicyclopenta[a,i]biphenylene. Under the same conditions 3,3'-[propane-1,3-diyl]bis-[1,2,4-triazolo[4,3-a]pyridine] gave the corresponding cyclobutane dimer, 5aα,5bα,10bα,10cα-tetrahydro-1,10-propano-2,3,8,9,10a,10d-hexaazadicyclopenta[a,i]biphenylene whereas at 254 nm the photoproduct obtained had the “cage-like” structure 3b,3c,3d,3e,6b,6c,6d,6e-octahydro-3, 4-propano-1,2,3a,3f,5,6-hexaazadicyclobuta[def,jkl]dicyclopenta[b,h]biphenylene. Replacement of the hydrocarbon linkage with the oxybis(methylene) or a thiobis(methylene) unit and irradiation at 300 nm gave the corresponding cisoid-fused, cyclobutane dimers only. The effect of methyl substituents in the pyridine ring of the bicyclic system on the dimerization process was also studied.     

Röntgenkleinwinkeluntersuchungen an Lösungen von Schweineserum-Albumin bei verschiedenen pH-Werten

Zusammenfassung Schweineserum-Albumin wurde nach sorgfältiger Reinigung bei den pH-Werten 7,0, 5,1 und 3,7 mit Hilfe der Röntgenkleinwinkelstreuung untersucht. Es wurde bei allen Messungen praktisch dasselbe Molekulargewicht gefunden: der Mittelwert liegt bei 70 300±2 500. Die Ermittlung der Streumassenradien ergab bei pH 7,0 und pH 5,1 ähnliche Werte (33,0 Å bzw. 31,1 Å), bei pH 3,7 dagegen einen Wert von 37,8 Å. Die Formbestimmung ergab bei pH 7,0 und pH 5,1 identische Achsenverhältnisse (0,75 : 1 : 2), während bei pH 3,7 ein solches von 0,2 : 1 : 1 gefunden wurde.

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X-ray small-angle scattering investigations on solutions of porcine serum albumin at differentpH-values

Higly purified samples of porcine serum albumin were measured by the X-ray small-angle scattering method at pH 7.0, 5.1, and 3.7. The molecular weight is found to be the same in all three cases: the mean value is 70 300±2 500. The radius of gyration is 31.1 Å and 33.0 Å at pH 5.1 and 7.0 resp., whereas at pH 3.7 a value of 37.8 Å is found. The determination of the molecular conformation yields a similar axial ratio at pH 5.1 and pH 7.0 of 0.75 : 1 : 2; at pH 3,7 we find an axial ratio of 0.2 : 1 : 1 to be consistent with the scattering curves.

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Herrn Prof. Dr.H. Nowotny gewidmet.     

The correlation of NMR chemical shifts with EHT calculated electron densities for 3-pyridinols

The NMR spectra of a series of five 3-pyridinols in dioxane and dimethyl sulfoxide have been correlated with electron densities calculated by the Extended Hückel MO method. The data were found to fit a straight line of the form y=ax+b. The effects of hydrogen-bonding between pyridinol molecules on the correlation have been considered, and they have been estimated quantitatively for 6-methyl-3-pyridinol via Extended Hückel Calculations on a hydrogen-bonded model.

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Zusammenfassung Die Kernresonanzspektren von fünf 3-Pyridinolen in Dioxan und Dimethylsulfoxyd wurden mit den Elektronendichten aus dem erweiterten Hückelverfahren korreliert, und zwar ergibt sich eine lineare Beziehung. Der Einfluß von intermolekularen Wasserstoffbrücken ist für einen Fall (die 6-Methyl-Verbindung) durch EHT-Rechnungen festgestellt und in den übrigen Fällen geschätzt worden.

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Résumé Les spectres NMR d'une série de cinq 3-pyridinols dans le dioxane et le diméthyle-sulfoxyde ont été corrélés avec les densités électroniques calculées par la méthode de Hückel Etendue. Les données se placent correctement sur une droite y=ax+b. Les effets de la liaison hydrogène entre les molécules de pyridinol ont été envisagés et estimés quantitativement pour le 6-méthyl-3-pyridinol par des calculs EHT sur un modèle à liaison hydrogène.

     

Comparison of cartesian and lobe function Gaussian basis sets

The lobe function and cartesian (spherical harmonic) gaussian are compared with reference to calculations for second-row atoms. Single and grouped gaussian basis sets which have been reported for cartesian functions are taken over directly to construct corresponding lobe function bases with identical sets of exponents and with lobe separations chosen by a scaling procedure. Total and orbital energies and SCF coefficients resulting from calculations on the second-row atoms using the two types of functions for both primitive and grouped gaussian basis sets are seen to be in excellent agreement, thereby emphasizing the essential equivalence of lobe functions and cartesian gaussians, at the very least with respect to calculation of energy surfaces.

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Zusammenfassung Die Lobe-Funktionen und kartesischen (Kugelfunktions-) Gaußfunktionen werden in Berechnungen von Atomen der zweiten Reihe des periodischen Systems verglichen. Schon bekannte einfache und gruppierte Gaußfunktionsbasissätze für kartesische Funktionen werden direkt übernommen, um entsprechende Lobe-Funktionsbasen mit identischen Exponenten zu konstruieren, wobei die zugehörigen Lobe-Abstände nach einer Koordinatenstreckungs-(scaling) Methode berechnet werden. Gesamt- und Orbitalenergien sowie SCF-Koeffizienten für die Atome der zweiten Reihe stimmen bei Benutzung der beiden verschiedenen Funktionstypen, sowohl bei einfacher als auch bei gruppierter Gaußfunktionsbasis, außerordentlich gut überein, wodurch die wesentliche Gleichwertigkeit von Lobe-Funktionen und kartesischen Gaußfunktionen betont wird, zum allermindesten hinsichtlich der Berechnung von Energieflächen.

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Résumé La fonction de lobe et la gaussienne cartésienne (harmonique sphérique) sont comparées sur des calculs d'atomes de la seconde ligne. Des bases de gaussiennes simples et groupées utilisées pour les fonctions cartésiennes sont directement employées pour construire les bases correspondantes de fonctions à lobes avec des ensembles d'exposants identiques et des séparations de lobes choisis par calibrage. L'emploi de ces deux types de fonctions donne des résultats concordants pour l'énergie totale, les énergies orbitales et les coefficients SCF, mettant l'accent sur l'équivalence essentielle des fonctions à lobe et des gaussiennes cartésiennes, tout au moins pour le calcul des surfaces d'énergie.

     

The electronic structure of molecules by a many-body approach : II. Ionization potentials one-electron properties of pyridine and phosphoridine

The valence ionization potential (IPs) of pyridine and phosphoridine are studied by an ab initio many-body approach which includes the effects of electron correlation and reorganization beyond the Hartree-Fock approximation. For pyridine the order of the first three IPs is a₂(π), a₁(n), b₁(π), but the IPs of the a₂ and a₁ orbitals are so close together that they have to be regarded as identical in binding energy, which is also concluded from experiment. Whereas for pyridine the ordering of the IPs calculated in the HF approximation is incorrect, it is correct for phosphoridine. For this latter molecule the first three ionization potentials are due to ionization from the b₁(π), a₂(π), and a₁(n) orbitals. Several one-electron properties are calculated and compared with experimental and other theoretical data. The localized molecular orbitals are discussed as well.     

Theoretical study of the electronic spectrum of diimide by AB initio methods

A series of ab initio calculations is reported for the ground and low-lying valence and Rydberg states of diimide N₂H₂. Symmetric bending potential curves for both the cis and trans forms of this system have been obtained at the SCF level of treatment. In addition Cl calculations have been carried out for the trans-diimide ground state equilibrium nuclear conformation, using a configuration selection procedure described elsewhere; an associated energy extrapolation scheme is also employed which enables the effective solution of secular equations with orders of up to 40000. The ensuing Cl wavefunctions are interpreted in the discussion and the corresponding calculated energy differences between the various electronic states are compared with experimental transition energy results for both diimide and for related systems such as trans-azomethane. A more detailed analysis of the observed absorption bands in the ¹B_g-X¹A_g transition in N₂H₂ is also given, making use of calculated potential curve data as well as the pertinent Cl vertical energy difference. The dipole-forbiddenness of the excitation process is thereupon concluded to result in a distinct non-verticality for this electronic band system, causing its absorption maximum to occur at a position some 0.6 eV to the blue of the so-called vertical transition, i.e., that for which maximum vibrational overlap is obtained.     

Long-range interaction between 1s and 2s or 2p hydrogen atoms

Long-range interaction energy between two hydrogen atoms has been computed in the second order of the perturbation theory. All states of the system arising when one of the atoms is in the 1s and the other in the 2s or 2p state have been considered. The energy represented by a series expansion in inverse powers of the internuclear distance, R, has been computed up to the terms in R^?8. The results are believed to give reliable interaction energies for R > 15 a.u. Accurate interaction energy for two ground-state hydrogen atoms has also been obtained up to the terms in R^?10. Results for the B′ ¹∑ state are employed to discuss the experimental ground-state dissociation energy of H₂, D₂, and HD. For H₂ all values of the dissociation energy obtained from various experimental absorption limits, by using the computed potential energy curve to separate off the effect of rotation, are shown to be satisfactorily consistent. The resulting total energy of H₂ is, however, higher than the most accurate theoretical value.