MECHANISMS OF RADIOPROTECTION—A REVIEW

Abstract— Theories of radiation protection can be considered at both the molecular and biochemical-physiological levels. Four molecular level protection hypotheses, radical scavenging, hydrogen transfer reactions, the mixed disulfide hypothesis and the endogenous nonprotein sulhydryl hypothesis, probably describe different aspects of the actual protection mechanism, although each has inconsistencies. At the biochemical-physiological level, hypothermia induction, hypoxia induction and biochemical shock may be involved in protection of the organism against radiation induced damage and death. It is most likely that no single mechanism can account for the protection offered by a radioprotective drug. Certain compounds may operate primarily by means of physiological effects resulting in hypoxia or hypothermia in critical tissues. Others may operate primarily by influencing the intrinsic radiosensitivity of target molecules by causing localized radical scavenging or by donating a hydrogen atom. Metabolic effects such as biochemical shock, release of endogenous nonprotein sulfhydryls, induction of structural changes in target molecules or delay in DNA synthesis and cell division are also possible mechanisms for radioprotection.     

Unrestricted CNDO-MO calculations. II. MnO 4 2− and CrO 4 3−

The electronic structures of the tetrahedral molecule ions MnO ₄ ^2– and CrO ₄ ^3– have been investigated within an unrestricted CNDO-MO approximation [Theoret. Chim. Acta (Berl.)20, 317 (1971)]. Calculations assuming the unpaired electron occupies the 3a ₁, 2e, and 4t2 molecular orbitals indicate that the 3a ₁ and2e orbitals have similar orbital energies and that the 4t ₂ orbital is at a higher energy. The experimentally indicated2e orbital for the unpaired electron is obtained with expanded O^1– type atomic orbitals for oxygen and valence metal orbitals of the expanded 3d and plus one ion 4p types. The metal 4s orbitals must be held to the neutral atom type. The optimum valence orbitals above with a slightly contracted 4s type metal orbitals yield the minimum total energy and places the unpaired electron in the 3a ₁ orbital. Since the contracted 4s metal orbital produces results that are not in agreement with experimental data, the method used apparently does not adequately take into account the increased electron-electron repulsions that contracted 4s orbitals produce.     

In silico targeting PAD4 for the treatment of rheumatoid arthritis

Structural Chemistry - Rheumatoid arthritis (RA) is an autoimmune disorder that causes chronic inflammation with periodic bursts of activity in multiple synovial joints which lead to irreversible...     

Nuclear orbiting and anomalies in nuclear reactions

In this paper, we report our measurements of back-angle oxygen and carbon particle yields from ¹⁶O+⁸⁹Y, ¹²C+⁹³Nb reactions forming the same compound nucleus ¹⁰⁵Ag at the same excitation energy and spin distribution. We find anomalously large oxygen yield and entrance channel dependence at high excitation energies from ¹⁶O+⁸⁹Y reaction implying formation of a dinuclear orbiting complex. Possible connection between nuclear orbiting and fast fission is also discussed.     

Projective dimension and Brown-Peterson homology

$\text{BP}{}_1\text{(X)}$ is the reduced Brown-Peterson homology of a finite complex X for a fixed prime p. We study a sequence of homology theories $\text{BP}{}_1\text{(X)→?→BP〈n+1〉}{}_1\text{(X)}\text{→}\text{p(n,n + 1)}\text{BP〈n〉}{}_1\text{(X)}\text{→}\text{p(n - 1,n)}\text{BP〈n–1〉}{}_1\text{(X) →?→BP〈0〉}{}_1\text{(X)}\text{→}\text{p( - 1,0)}\text{BP〈–1〉}{}_1\text{(X)}$. Our main result states that there is an n such that ?, ?(n,n + 1), ?(n– 1, n) are all epimorphisms; each of the remaining homomorphism fails to be onto; and n is the projective dimension of $\text{BP}{}_1\text{(X)}$ as a module over the coefficient ring $\text{BP}{}_1$.The first two sections are introductory in nature while the third contains the core results. The reader should be pleased to know that 44–6 are independent of each other.     

Sulfenylation of some pyrroles and indoles

Methylsulfenylation of 1-substituted pyrroles and indoles was observed using 1-(methylthio)morpholine and an acid catalyst or with methylsulfenyl chloride and excess pyridine. 1-Substituents which are activating or weakly deactivating towards electrophilic substitution such as alkyl, 2-cyanoethyl, dimethylamino, trialkylsilyl, 2-chloroethyl and 2-phenylsulfonylethyl were used. The 2-chloroethyl and 2-phenylsulfonylethyl groups which can be removed with a strong base can be used to obtain 1H-methylthiopyrroles and indoles. 1-Phenylsulfonyl and 1-acetyl substituents are too strongly deactivating for these sulfenylations to be successful. Mono and disubstituted pyrroles and monosubstituted indoles can be isolated from these reactions, however, because the methylthio group is activating towards electrophilic substitution the main advantage of these reactions is the synthesis of tri and tetrasubstituted pyrroles and disubstituted indoles. 1-Methyl-2,3,4,5-tetra-methylthiopyrrole and 1-methyl-2,3-dimethylthioindole are oxidized to the corresponding 3,4-disulfoxide and 3-sulfoxide and with excess oxidizing agent to the tetrasulfone and disulfone, respectively.     

Scanning probe studies of water nucleation on aluminum oxide and gold surfaces

The nucleation of nanoscale water at surfaces in humid environments is sensitive to several factors, including the details of the surface morphology, ability of the surface to hydrate and the presence of contaminants. Tapping mode atomic force microscopy was used to investigate the nucleation process as a function of relative humidity (RH) on passive aluminum and gold thin films. Films exposed to the ambient environment prior to RH exposure showed discrete structures with lateral sizes ranging from 10 to 100 nm only at RH > 70%. These structures formed preferentially at grain boundaries, triple points and regions with significant topography such as protruding grains. The morphology of the passive aluminum surface is permanently altered at the sites where discrete structures were observed; nodules with heights ranging from 0.5 to 2 nm persist even after reducing the RH to <2%. The gold surface does not show such a permanent change in morphology after reducing the RH. Passive aluminum films exposed to high RH immediately after growth (e.g. no ambient exposure) do not show discrete structures even at the highest RH exposures of 90%, suggesting a hydrophilic surface and the importance of surface hydrocarbon contaminants in affecting the distribution of the water layer.