Ab initio calculations on large molecules using molecular fragments. Characterization of the zwitterion of glycine

The ab initio molecular fragment approach is applied to a characterization study of the ground state of the zwitterion of glycine. Included among the properties studied are the — conformational energy surface, the electronic structure, and the magnitude and direction of the dipole moment. The results of the present study are compared to the results of other theoretical and experimental studies.This work was supported in part by the National Science Foundation, the University of Kansas, and the Upjohn Company, Kalamazoo, Michigan 49001.NSF Trainee (1969-1972).Alfred P. Sloan Research Fellow (1971–1973).     

Prolonged bone marrow T1-relaxation in patients with polycythemia vera

In vitro as well as in vivo studies have shown prolonged T1 relaxation times in patients with acute leukemia. The mechanism behind this finding is not known. In order to evaluate if this was specific for leukemia we examined eight patients with polycythemia vera, representing a condition with a rather benign bone marrow neoplasia. In this group of patients we found prolonged T1 relaxation times but normal T2 relaxation times. This may indicate that the prolonged T1 relaxation time seen in leukemic bone marrow is not due to the malignant cell per se.     

Stereoelectronic properties of photosynthetic and related systems: Ab initio configuration interaction calculations on the ground and lower excited singlet and triplet states of magnesium chlorin and chlorin

Ab initio configuration interaction wavefunctions and energies are reported for the ground state and many low-lying singlet and triplet states of magnesium chlorin and chlorin, and are employed in an analysis of the electronic absorption spectra of these systems.In chlorin, the calculated visible spectrum consists of two ${}^1\text{(π, π}{}^1\text{)}$ states, the lower energy, y-polarized state exhibiting moderate absorption intensity in contrast to the very weak absorption of the higher energy x-polarized state. The configurational composition of both states is well described by the four-orbital model. Five ${}^1\text{(π, π}{}^1\text{)}$ states are responsible for the Soret band envelope. A moderately intense y-state lies under the low energy edge of the band envelope, while two x-polarized states of moderate and strong intensity, respectively, are responsible for the band maximum. The final two ${}^1\text{(π, π}{}^1\text{)}$ states lie at the high energy edge of the Soret band and introduce a measure of asymmetry into the band envelope. Two ${}^1\text{(n, π}{}^1\text{)}$ states of very weak oscillator strength are also found in this region of the spectrum. All the Soret states are of complex configurational composition, and several of the higher lying states contain contributions from doubly excited configurations.The calculated visible spectrum of magnesium chlorin also consists of two ${}^1\text{(π, π}{}^1\text{)}$ states, with the weakly absorbing x-polarized state lying approximately 200 cm^?1 lower in energy than the moderately intense y-polarized state. The configurational composition of both states is well described by the four-orbital model. Four ${}^1\text{(π, π}{}^1\text{)}$ states constitute the bulk of the intensity in the Soret band envelope. In distinction to chlorin, the moderately intense ${}^1\text{(π, π}{}^1\text{)}$ state at the low energy edge of the band envelope is x-polarized. Two intense ${}^1\text{(π, π}{}^1\text{)}$ states of y- and x-polarization, respectively, constitute the band maximum region, and a single x-polarized state of moderately strong intensity can be assigned to the high energy shoulder of the band envelope. Two other weakly absorbing ${}^1\text{(π, π}{}^1\text{)}$ states are also found in this region, along with another weakly absorbing state of mixed in-plane and out-of-plane polarization. No clearly defined ${}^1\text{(n, π}{}^1\text{)}$ states are observed. As was the case for chlorin, all the Soret states are of complex configurational composition, and some of the higher energy states contain significant contributions from doubly excited configurations.Chlorin and magnesium chlorin both possess three ${}^3\text{(π, π}{}^1\text{)}$ states which lie below S₁ and a single ${}^3\text{(π, π}{}^1\text{)}$ which lies slightly above S₂. All four of the low-lying ${}^3\text{(π, π}{}^1\text{)}$ states in each molecule are well described by the four-orbital model, with T₁ being essentially a single configuration in each case. The remainder of the ${}^3\text{(π, π}{}^1\text{)}$ states are clustered in the same energetic region as the comparable ${}^1\text{(π, π}{}^1\text{)}$ Soret states, with comparably complex configurational compositions.Dipole moments and charge distributions for low-lying singlet and triplet states are also reported, and are used to rationalize chemical reactivity characteristics.     

Overturning of tractors

Summary A simple rule for design of safety cabs and frames for tractors is presented. The rule guarantees that on overturning accident is not followed by continued rolling of the tractor. Violation of the design rule implies that the tractor will indeed begin jumping or rolling subsequent to the first impact.

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Umsturz von Traktoren

Übersicht Vorgestellt wird eine einfache Regel für den Entwurf von Sicherheits-Lenkhäusern und Rahmen von Traktoren. Diese Regel garantiert, daß ein Umsturz nicht von weiteren Überschlägen begleitet ist. Die Verletzung der Entwurfsregel bedeutet, daß der Traktor nach dem ersten Aufschlag zu springen oder zu rollen beginnt.

     

Rotational band contours in the 5000 Å 1 B 1g -1 Ag electronic system of p-benzoquinone

Using the technique of computer simulation of rotational band contours the 1–0 band in v ₇, band E, in the 5000 Å ¹ B _1g -¹ A_g system of p-benzoquinone has been rotationally analysed. It is a type A band and the excited state rotational constants are:

The excited state inertial defect determined from these constants is -0·8 ± 0·2 uÅ ². This value is almost certainly due not to non-planarity of the excited state but to a Coriolis interaction between v ₇ and perhaps the b _1u vibration v ₁₃. Such an interaction, if it were weak, would affect only the A′ rotational constant.

Previous assignments [2] of other type A bands and type B bands in the spectrum are reviewed where possible with the new evidence of the computed contours and the assignments remain largely unaltered.     

Identification of patients with hereditary haemochromatosis by magnetic resonance imaging and spectroscopic relaxation time measurements

A total of 4302 healthy blood donors were screened for elevated serum ferritin and transferrin saturation. Fifteen had increased serum ferritin at a follow-up examination. Five relatives of these donors also entered the study. Eleven patients had elevated liver iron concentrations, while five had normal liver iron concentrations. The R₂ relaxation rate in the liver was first measured with a conventional multi-spin-echo imaging sequence, and then by a volume-selective spectroscopic multi-spin-echo sequence, in order to achieve a minimum echo time of 4 msec. No correlation was found between the relaxation rate R₂ and the liver iron concentration, when R₂ was calculated from the imaging data. Multi-exponential transverse relaxation could be resolved when the spectroscopic sequence was used. A strong correlation between the initial slope of the relaxation curve and the liver iron concentration was found (r = 0.90, p < 0.001). Signal intensity ratios between liver and muscle were calculated from the first three echoes in the multi-echo imaging sequence, and from a gradient echo sequence. A strong correlation between the logarithm of the signal intensity ratios and the liver iron concentration was found. Although both spectroscopic T₂ relaxation time measurements and signal intensity ratios could be used to quantify liver iron concentration, the gradient echo imaging seemed to be the best choice. Gradient echo imaging could be performed during a single breath hold, so motion artifacts could be avoided. The accuracy of liver iron concentration estimates from signal intensity ratios in the gradient echo images was about 35%.     

A new method for the calculation of vibrational force constants. Application to H2

A new method for the quantum mechanical calculation of vibrational force constants is presented. This method is applied to the calculation of the vibrational force constant of H₂, using a completely optimized wavefunction constructed from a single gaussian orbital. The value of the force constant obtained using this method is k₀ = 0.422341088751 au (= 6.5754 × 10⁵ dyne/cm), compared to the value of k₀ = 0.42234079S380 au (= 6.5754 × 10⁵ dyne/cm) obtained using an analytic method, and the experimental value of k_e = 0.3692 au (= 5.748 × 10⁵ dyne/cm).     

Relativistic effects in aromatic molecules

Evaluation of the relativistic correction due to the orbit-orbit operator of the Breit Hamiltonian has been considered in general, including the presence of a magnetic field. For conjugated molecules, the change in energy due to this relativistic effect is shown to be expressible in terms of two types of integrals and their derivatives. The interaction results in an intermolecular contribution to the diamagnetic susceptibility which, for two parallel benzene rings, is found to be smaller than the molecular terms by a factor of ². Several molecular integrals not previously evaluated were encountered, and their evaluation as asymptotic expansions is discussed.

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Zusammenfassung Die Berechnung eines relativistischen Termes, nÄmlich des Bahn-Bahn-Anteiles des Breit'schen Hamilton-Operators, ist bei vorhandenem Magnetfeld in allgemeiner Form durchgeführt worden. Bei konjugierten Molekülen erscheinen im Ausdruck für die zugehörige EnergieÄnderung zwei Arten von Integralen und ihren Ableitungen. Die Wechselwirkung liefert einen intermolekularen Beitrag zur diamagnetischen SuszeptibilitÄt, der allerdings im Fall zweier paralleler Benzolringe um den Faktor ² kleiner als die innermolekularen Terme ist. In diesem Zusammenhang traten einige bisher nicht benötigte Integrale auf, deren asymptotische Entwicklung durchgeführt wurde.

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Résumé Nous avons étudié, en forme générale, la correction relativiste due a l'opérateur orbite-orbite de Breit en présence d'un champ magnétique. Pour les molécules conjuguées, l'effet énergétique de ce terme peut Être exprimé par deux types d'intégrales et leurs dérivées. La contribution intermoléculaire a la susceptibilité diamagnetique est trouvée, pour deux noyaux parallèles de benzène, d'Être d'un facteur ² plus petit que les termes moléculaires. Quelques intégrales moléculaires, incalculées jusque la, ont été évaluées par expansion asymptotique.

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This investigation was supported in part by Public Health Service Fellowship No. 1F2 GM-18, 898-01 from the Division of General Medical Sciences, National Institutes of Health, U.S.A.