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Biomedical subjects

L Pauling

Publications and source records attributed to L Pauling.

At least 55 records · Page 3Linked to original sources
PubMed1987

Crystal structure of hexagonal MnAl(4).

A structure is proposed for the hexagonal form of MnAl(4), with a(H) = 28.4 A and c(H) = 12.43 A, on the basis of a high-resolution electron micrograph and comparison with crystals of known structures. The proposed structure involves seven 104-atom complexes of 20 Friauf polyhedra, sharing some atoms with one another. It is closely related to the 23.36-A cubic structure of MnAl(4) and to the 14.19-A cubic structure of Mg(32)(Al,Zn)(49).

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PubMed1987

Evidence from x-ray and neutron powder diffraction patterns that the so-called icosahedral and decagonal quasicrystals of MnAl(6) and other alloys are twinned cubic crystals.

It is shown that the x-ray powder diffraction patterns of rapidly quenched MnAl(6) and Mg(32)(Al,Zn)(49) and the neutron powder diffraction pattern of MnAl(6) are compatible with the proposed 820-atom primitive cubic structure [Pauling, L. (1987) Phys. Rev. Lett. 58, 365-368]. The values found for the edge of the unit cube are 23.365 A (x-ray) and 23.416 A (neutron) for MnAl(6) and 24.313 A (x-ray) for Mg(32)(Al,Zn)(49).

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PubMed1987

Factors determining the average atomic volumes in intermetallic compounds.

In formation of an intermetallic compound from the elementary metals there is usually a contraction in volume. Electron transfer leading to the charge states M(+) and M(-) with increase in valence and decrease in volume explains the more than 2-fold range in contraction for different compounds in the same binary system. In a more thorough analysis, the better packing of atoms of different sizes also needs to be considered.

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PubMed1986

A revised set of values of single-bond radii derived from the observed interatomic distances in metals by correction for bond number and resonance energy.

An earlier discussion [Pauling, L. (1947) J. Am. Chem. Soc. 69, 542] of observed bond lengths in elemental metals with correction for bond number and resonance energy led to a set of single-bond metallic radii with values usually somewhat less than the corresponding values obtained from molecules and complex ions. A theory of resonating covalent bonds has now been developed that permits calculation of the number of resonance structures per atom and of the effective resonance energy per bond. With this refined method of correcting the observed bond lengths for the effect of resonance energy, a new set of single-bond covalent radii, in better agreement with values from molecules and complex ions, has been constructed.

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PubMed1985

Effect of dietary ascorbic acid on the incidence of spontaneous mammary tumors in RIII mice.

A study of the effect of different amounts of L-ascorbic acid (vitamin C), between 0.076% and 8.3%, contained in the food has been carried out with ten groups of RIII mice (seven ascorbic acid and three control groups), with 50 mice in each group. With an increase in the amount of ascorbic acid there is a highly significant decrease in the first-order rate constant for appearance of the first spontaneous mammary tumor after the lag time to detection by palpation. There is also an increase in the lag time. The mean body weight and mean food intake were not significantly different for the seven ascorbic acid groups. Striking differences were observed between the 0.076% ascorbic acid and the control groups (which synthesize the vitamin): smaller food intake, decreased lag time, and increased rate constant of appearance of the first mammary tumor. This comparison cannot be made experimentally for guinea pigs and primates because the control groups would develop scurvy.

Animals↗
PubMed1985

Comparison of theoretical and experimental values of the number of metallic orbitals per atom in hypoelectronic and hyperelectronic metals.

The statistical resonating-valence-bond theory of metals is applied in the purely theoretical calculation of the composition of the Ni-Cu alloy at the foot of the curve of saturation ferromagnetic moment, which marks the boundary between hypoelectronic and hyperelectronic metals and determines the value of the number of metallic orbitals per atom. The results, Ni(44)Cu(56) and 0.722 metallic orbitals, agree with the observed values. This agreement provides strong support of the theory.

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PubMed1984

Structure of the Hf nucleus in high rotational states.

The values of the moment of inertia of the ground-state band of (168)Hf from J = 0(+) to 22(+) are interpreted as involving a revolving cluster with composition increasing steadily from p(10.5)n(14) to p(20.5)n(24), with radius of revolution 6.390 fm. The excited bands from 14(+) to 34(+), 21(-) to 33(-), and 18(-) to 30(-) have nearly the same very large moment of inertia. It is interpreted as involving two caps, each consisting of 11 tritons, on opposite sides of the nearly doubly magic sphere p(50)n(52), the value of the radius of revolution being 6.445 fm.

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PubMed1984

Evidence from bond lengths and bond angles for enneacovalence of cobalt, rhodium, iridium, iron, ruthenium, and osmium in compounds with elements of medium electronegativity.

Enneacovalence of neutral atoms can be achieved for Co, Rh, and Ir by promoting some electrons from the nd orbital to the (n + 1)s and (n + 1)p orbitals and for Fe, Ru, and Os by a similar promotion together with the addition of an electron, which may be provided by an electron pair from a singly bonded carbonyl group or other group. The bond lengths and bond angles are predicted by the theory of enneacovalence to be significantly different for the different transition metals. Recently reported experimental values are shown to be in good agreement with the predicted values, providing support for the theory of enneacovalence and the theory of hybrid sp(3)d(5) bond orbitals.

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PubMed1983

Resonance of an unshared electron pair between two atoms connected by a single bond.

The reported structure of the dimer of a compound of bicovalent tin indicates that the tin-tin bond is of a new type. It can be described as involving resonance between two structures in which there is transfer of an electron pair from one tin atom to the other. The tin atoms are connected by a single covalent bond (each also forms two covalent bonds with carbon atoms), and an unshared electron pair resonates between the fourth sp(3) orbitals of the two atoms. Similar structures probably occur in digermene and distannene.

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PubMed1983

Enhancement of antitumor activity of ascorbate against Ehrlich ascites tumor cells by the copper:glycylglycylhistidine complex.

Ascorbate in an aqueous solution is easily oxidized by molecular oxygen in the presence of cupric ion, thus producing reactive oxygen species and exhibiting cytotoxicity. In order to increase the antitumor activity of ascorbate, we used the innocuous form of cupric ion complexed with glycylglycylhistidine, a tripeptide designed to mimic the specific Cu(II) transport site of albumin molecule. Although this square planar copper:glycylglycylhistidine complex did not significantly oxidize ascorbate at pH 7.4, it killed Ehrlich ascites tumor cells in vitro in a high concentration of ascorbate. The injections of large doses of ascorbate together with copper: glycylglycylhistidine prolonged the life span of mice inoculated i.p. with Ehrlich tumor cells. The target specificity against tumor cells was primarily attributable to their high peptide-cleaving activity.

Animals↗