The case for programmed mammal aging

Are the deteriorative processes associated with mammal aging purposely and actively programmed by the organism’s design or are they merely a passive result of the organism’s inability to better resist damage from fundamental deteriorative processes? This question has now persisted for 150 years. Historically, observational evidence generally favors active aging. However, the nature of the evolution process has been thought to preclude evolution and retention of organism design features that purposely cause deterioration or otherwise actively limit life span. More recently, discoveries such as aging genes have increased the weight of empirical evidence for programmed aging and our increasing knowledge regarding the nature of the mammal inheritance process has added to questions regarding the validity of traditional evolutionary mechanics concepts. Alternatives to traditional mechanics concepts have subsequently appeared, most of which support active aging, and theories of biological aging based on the alternative evolutionary mechanics theories have been produced.This article compares active and passive aging concepts in light of various observations, provides an overview of the historical interaction between aging theory and evolution theory, and outlines major issues that currently exist regarding the mechanics of evolution. A specific candidate structure for an active mammal aging mechanism is presented and a specific evolutionary rationale, an evolvability theory of aging, which allows for the evolution of that mechanism, is suggested.This issue has substantial public health implications because understanding of massively age-dependent conditions such as cancer demands understanding of the aging process. Also, active theories suggest significant additional possibilities for treatment of age-related conditions.     

Radiation chemistry of polybutadiene and butadiene-styrene block copolymers. II. Kinetics and mechanisms of free-radical decay reactions

The decay of free radicals produced in polybutadiene, polystyrene, and block copolymers of butadiene and styrene by γ irradiation at 77 K has been studied at ?110°C in the case of polybutadiene and at ?95°C for the other samples. The free-radical decay rate is best interpreted in terms of an equation based on a second-order decay mechanism of a fraction of the free radicals decaying in the presence of other nondecaying free radicals. Hydrogen gas accelerates the free-radical decay. Increase of radiation dose increases the fraction of the radicals that decay, while increase of the fraction of styrene segments decreases the decaying fraction. In pure polybutadiene the higher the cis content, the greater fraction of decaying free radicals, but the second-order decay constant is less in the high-cis-content polybutadiene and is also less at the higher dose, probably owing to the hindrance of the radiation-produced crosslinks on the free-radical decay. The decrease of the second-order constant with increase of dose is also true for all the block copolymers studied.     

Mechanism of propagation and degenerate chain branching in the oxidation of polypropylene and polyethylene

Samples of polypropylene with adjacent and isolated hydroperoxide groups have been prepared. The rate constants of free-radical formation from solid hydroperoxides were measured by the inhibitor method. It was found that the free radicals yielded by adjacent hydroperoxide groups are formed more rapidly. The main reaction of free-radical formation in oxidized polypropylene is of the type: ROOH + ROOH → RO + H₂O + RO₂^˙. The average yield of free radicals from polypropylene hydroperoxide is 2–4%. Oxygen has no effect on the yield of free radicals. However, the pressure of oxygen Po₂ affects the rate of degenerate chain branching in polypropylene. The number of adjacent hydroperoxide groups and the rate of initiation increase with Po₂. Consequently, a reaction of the type, R^˙, + RH → RH + R^˙, plays an important part in transport of free valence through solid polymer. This reaction is very fast in polyethylene, and no adjacent hydroperoxide groups are formed. The free radicals from polyethylene hydroperoxide are found to form by a reaction of the type: ROOH → RO^˙ + HO^˙.     

Graft and modified polymers from rubber network. I. Method of obtaining graft and modified polymers from sulfur vulcanizates with dehydrogenated Raney nickel and Raney cobalt

The present paper reports on an investigation of eliminating sulfur from sulfur vulcanizates by using dehydrogenated Raney Ni (Raney Co). The dehydrogenated Raney metal eliminates the sulfur by forming free radicals which recombine with each other. The result is a heavily crosslinked product containing traces of sulfur. When applying dehydrogenated Raney metal in the presence of substances readily producing free radicals or monomers polymerizing by way of a free-radical mechanism, one obtains a modified or a grafted high molecular product.     

FSDB: a frameshift signal database

Programmed frameshifting is a recoding event in which a ribosome shifts reading frame by one or more nucleotides at a specific mRNA signal between overlapping genes. Programmed frameshifting is involved in the expression of many genes in a wide range of organisms, especially in viruses and bacteria. The mechanism of programmed frameshifting is not fully understood despite many studies, and there are few databases available for detailed information on programmed frameshifting. We have developed a database called FSDB (Frameshift Signal Database), which is a comprehensive compilation of experimentally known or computationally predicted data about programmed ribosomal frameshifting. FSDB provides a graphical view of frameshift signals and the genes using programmed frameshifting for their expression. It also allows the user himself/herself to find programmed frameshift sites in genomic sequences using a program called FSFinder (http://wilab.inha.ac.kr/fsfinder2). We believe FSDB will be a valuable resource for scientists studying programmed ribosomal frameshifting. FSDB is freely accessible at http://wilab.inha.ac.kr/fsdb/.     

A study on the free-radical evolution and its correlation with the optical degradation of 170 keV proton-irradiated polyimide

In this paper, the damage process was investigated on the 170 keV proton-irradiated polyimide, based on the evolution of free radical and its correlation with degradation of the optical transmittance using electron paramagnetic resonance (EPR) and optical-transmittance measurements. The results indicate that the g value of irradiated free radicals keeps at a constant of 2.0025 but the spectral intensity of the free radicals increased with the increasing proton fluence. It is found that during the post-storage after irradiation, the concentration of free radical decreased in an exponential rule with the post-storage time and the free-radical stability can be defined by the corresponding time constant at around 2.3 h. It is interested that the recovery of optical-transmittance follows the same mode as that of free radicals. The mechanisms on the free-radical evolution and the correlation between free radical and optical property are discussed in the paper.     

Diffusion theory of the post-irradiation oxidation of polyethylene

The primary reaction of oxygen with irradiated polyethylene has been followed by observing the rapid disappearance of the ultraviolet absorption bands at 258 and 285 mμ, bands attributed to the allyl and dienyl free radicals. A mathematical theory based on diffusion equations has been developed by means of which a quantitative estimate of the total initial free-radical concentration can be made. From the shape of the free-radical decay curve it can be concluded that the initial oxygen–free-radical reactions occur about three times as frequently in the amorphous regions as in the crystalline.     

Studies on the photooxidation mechanism of polymers. IV. Effect of ultraviolet light (2537 Å) on solid PVC particles suspended in different liquids

The photolysis of virgin PVC powder suspended in water, methanol, n-hexane, aqueous NH₄OH (30 wt-%), and 0.1 wt-% iodine in methanol and also as dry powder was studied. The mechanism of photolysis of PVC powder has been investigated by using ESR spectroscopy, conductivity titration, gel-permeation chromatography (GPC), and absorption spectroscopy. Photolysis of PVC has been found to occur by a free-radical mechanism. ESR spectroscopy permits a partial identification of several different types of free radicals in PVC such as alkyl, polyenyl, and peroxy radicals. An interpretation is proposed of the mechanism of formation of conjugated polyene structures, and also a new explanation of the crosslinking mechanism, in which transfer of unpaired electrons to double bonds occurs, is suggested. It has also been found that conjugated double bonds can photosensitize free-radical formation as a result of increased ultraviolet absorption due to polyene structures.     

Kinetics of emulsion polymerization

The quantitative theory of the free-radical mechanism in emulsion polymerization is reexamined. A mechanism involving desorption and reabsorption of radicals is discussed. The average number of radicals per particle has been calculated as a function of three parameters. A simplified, approximate solution for the average number of radicals per particle is given for cases where this number is low.     

Radiation chemistry of linear low-density polyethylene. II. Kinetics of alkyl and allyl free-radical decay reactions

Quenched and annealed samples of linear low-density polyethylene (LLDPE) were γ irradiated in vacuo at 77 K; the kinetics of the alkyl free-radical decay reactions were studied at room temperature, and of the allyl free-radical reactions at 60, 70, and 80°C. The ESR signals saturate at a slightly higher microwave power in the LLDPE than in high-density polyethylene (HDPE), and the alkyl radicals start decaying at a lower temperature in the LLDPE than in the HDPE. As in the HDPE the decay of the alkyl free radicals at room temperature in the LLDPE follows the kinetic equation for two simultaneous first-order reactions with the fraction of the faster-decaying component being slightly greater in the quenched than in the annealed samples. In the case of the allyl free radicals the decay at 60°C follows the equation based on one fraction of the radicals decaying according to second-order kinetics in the presence of other nondecaying radicals. At higher temperatures the data are best understood in terms of a second-order rate equation with a continuously variable time-dependent rate constant as suggested by Hamill and Funabashi.     

LIGHT-INDUCED FREE RADICALS IN ORIENTED DNA-PROFLAVINE COMPLEXES

Abstract— Oriented wet DNA-proflavine complexes were illuminated with visible light, Λ > 395 nm, at 77 K, in the presence or absence of oxygen. The electron paramagnetic resonance spectra at 77 K and low microwave power (3 μ W) indicated formation of anionic free radicals in thymine and cationic free radicals, probably in guanine, identical to those induced by y rays at 77 K in similar samples of pure DNA.
The free-radical formation rate showed a quadratic dependence on light intensity, indicating a biphotonic mechanism. The proflavine triplet spectrum was observed during illumination. If the exciting light includes wavelengths below 390 nm, significant amounts of hydrogen addition radicals in thymine are found.     

How to cancel the program of body aging?

This issue is devoted to biochemical aspects of studies on aging of living organisms. During last several years, new evidence was published to show that aging is programmed by the genome. If this is really the case, there is a chance to prevent aging just as the programmed cell death (apoptosis) can be prevented by inhibitors arresting some steps of this process. That is why the main problem discussed by the majority of the authors contributing to this issue consists in an attempt to answer the question whether aging is programmed or not. At present it is hardly possible to solve this problem. However, we already can assume that at least there are no facts allowing to exclude existence of the aging program in humans. Thus, there is a perspective to invent a chemical agent competent in transferring humans from aging to non-aging creatures, which is exemplified by the naked mole rat whose death rate is independent of age.     

Radiolysis of poly(vinyl chloride)

Allyl free-radical intermediates are detected by ultraviolet absorption at 255 mu in poly(vinyl chloride) irradiated at ?196°C and stored at 25°C. In vacuum at 25°C, allyl radicals are converted into polyenyl free radicals and polyenes. From the nature of allyl radical decay in vacuum, radical chain transfer between polyenyl radicals and poly(vinyl chloride) is inferred. Allyl and polyenyl free radicals are scavenged by oxygen on post-irradiation storage in air.     

Study of protein coatings cross-linked via the free-radical mechanism on magnetic nanoparticles by the method of spectral and fluorescent probes

Magnetite nanoparticles have been obtained with stable coatings formed from bovine and human serum albumins. The coatings are fixed by free-radical cross-linking of the proteins with the use of their ability to form interchain covalent bonds under the action of free radicals, which are generated with participation of transition metals present on nanoparticle surface. The method of spectral and fluorescent probes has been employed for the first time to describe the properties of coatings with the use of various dyes. It has been shown that, when studying the adsorption and free-radical cross-linking of proteins on nanoparticles, it is reasonable to use polymethine and squarylium dyes for estimating the functional properties of the proteins forming the coatings. It has been found that as many as 50% of molecules forming an albumin coating crosslinked via the free-radical mechanism retain their capability of bonding to a fluorescent dye. It has been concluded that the proteins occurring in the structure of the coatings retain their functional properties.     

Formation of CC Bonds by Addition of Free Radicals to Alkenes

There are many reactions in which CC bonds are formed by addition of free radicals to alkenes. Information about the mechanism is important for the synthesis of specific target molecules. The rate of addition of alkyl radicals to alkenes is controlled by steric and polar effects. The stabilities of the educts and products are of only limited importance, since the transition states for these exothermic reactions occur very early on the reaction coordinate. Variations in reactivity and selectivity can be described using frontier orbital theory: for nucleophilic radicals the dominant interactions are those between SOMO's and LUMO's, and for electrophilic radicals those between SOMO's and HOMO's. The large differences in the steric effects of α - and β- substituents of alkenes can be explained by postulating an unsymmetrical transition state— the radical approaches one of the C atoms preferentially. Regioand stereoselectivities can be predicted and are determined, in general, by steric effects.     

Development of free radicals in sulfonated polystyrene ion-exchange resins upon drying

On exhaustive drying of sulfonated polystyrene-based ion-exchange resins, it is shown that free-radical centers develop. These have been examined by electron-spin resonance spectroscopy. The formation of the free radicals is largely reversible with respect to desorption and sorption of water which was measured by means of a quartz spiral microbalance. The spin-concentration isotherm as a function of sorbed water concentration is obtained. The presence of free radicals, dependent on water content in the resins, interferes with proton magnetic relaxation studies of hydration of ionized resins by providing a faster electron-spin coupled nuclear magnetic relaxation mechanism.     

Kinetics and mechanism of hydrogen peroxide decomposition in the presence of the tetraaquapalladium(<Emphasis Type="SmallCaps">II</Emphasis>) complex

Kinetics of hydrogen peroxide decomposition in the presence of the tetraaquapalladium(II) complex in an aqueous solution at 40–70 °C was studied. The reaction rate is the first order with respect to the concentration of both Pd^II and H₂O₂ and the negative first order with respect to perchloric acid. Using free radicals traps, the reaction mechanism was found to differ from the traditional free-radical mechanism known for d-metal aqua ions and proceeds without generation of hydroxyl radicals. The kinetic data obtained suggest a mechanism involving the formation of an intermediate palladium complex with oxygen. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1077–1082, May, 2005.     

Evaluation of potential reaction mechanisms leading to the formation of coniferyl alcohol α-linkages in lignin: a density functional theory study

Five potential reaction mechanisms, each leading to the formation of an α-O-4-linked coniferyl alcohol dimer, and one scheme leading to the formation of a recently proposed free-radical coniferyl alcohol trimer were assessed using density functional theory (DFT) calculations. These potential reaction mechanisms were evaluated using both the calculated Gibbs free energies, to predict the spontaneity of the constituent reactions, and the electron-density mapped Fukui function, to determine the most reactive sites of each intermediate species. The results indicate that each reaction in one of the six mechanisms is thermodynamically favorable to those in the other mechanisms; what is more, the Fukui function for each free radical intermediate corroborates with the thermochemical results for this mechanism. This mechanism proceeds via the formation of two distinct free-radical intermediates, which then react to produce the four α-O-4 stereoisomers.     

Spin-symmetry forbidden properties of free-radical cycloadditions

Stabilities of free radicals with linear, Hückel and Möbius Hückel conformations are investigated on the basis of the stability conditions of the RHF solutions. The spin-symmetry forbidden properties of free-radical cycloadditions are discussed in terms of the above stability analyses.     

Kinetics and mechanism of the initiated oxidation of a number of 1,3-dioxacyclanes

The initiated oxidation of a number of cyclic acetals at 50–95°C was studied by kinetic methods. It was found that the examined 1,3-dioxacyclanes are oxidized via a free-radical mechanism with quadratic termination of the chains in the peroxide radicals. The strengths of the carbon-hydrogen bonds undergoing attack by the peroxide radicals range from 80 to 90 kcal/mole.