Bystanders

Another view of the Si(lOO) etching mechanism has been proposed recently [28], Calculations have revealed that the most important step may actually be the escape of the bystander silicon atom, rather than SiBr2 desorption. In this way, the SiBr2 becomes trapped in a state that otherwise has a very short lifetime, pennitting many more desorption attempts. Prelimmary results suggest that indeed this vacancy-assisted desorption is the key step to etching Si(lOO) with Br2. 

On May 30, 1970, a tank truck partially filled with liquefied oxygen exploded after making a delivery in a hospital in Brooklyn, New York. The force of the explosion and subsequent fires caused the deaths of the driver and bystander. Thirty other people were injured and substantial property damage resulted. 

The driver and a bystander were fatally injured by the fire and explosion. Thirty other persons sustained minor injuries, including twenty-four who sustained injuries... 

Simpson (1988) reviewed studies which considered individual differences in risk perception and the effects of these differences on behavior. A study by Verhaegen et al. (1985) looked at three groups of workers in wire mills. The first group comprised those who had been directly involved in events which led to the accident (the "active" group). The second group ("passive") were those who had only been involved indirectly ("innocent bystanders") and the third group were a control group who had not been involved in accidents at all. 

Secure the scene get medical attention to tlie injured. Move bystanders aw ay to a safe distance. Inform print and electronic media. Protect people and property as necessary. Be aware tliat explosive materials and toxic vapors can do damage at a great distance... 

Rumford decided to try a more controlled experiment. He placed a brass gun barrel in a wooden box containing about nineteen pounds of cold water, and used a team of horses to rotate a blunt steel borer inside the barrel. After 2.5 hours, the water boiled As Rumford described it, It would be difficult to describe the surprise and astonishment expressed on the countenances of the bystanders on seeing so large a quantity of cold water heated, and actually made to boil, without any fire. ... 

Degrfeve B, De Clercq E, Balzarini J (1999) Bystander effect of purine nucleoside analogues in HSV-1 tk suicide gene therapy is superior to that of pyrimidine nucleoside analogues. Gene Ther 6 162-170... 

Antiviral Gene Products with a Bystander Effect.283... 

Allie R, Hu L, MuUen KM, Dhib-Jalbut S, Calabresi PA (2005) Bystander modulation of chemokine receptor expression on peripheral blood T lymphocytes mediated by glatiramer therapy. Arch Neurol 62 889-894... 

Winship IR, Plaa N, Murphy TH (2007) Rapid astrocyte calcium signals correlate with neuronal activity and onset of the hemodynamic response in vivo. J Neurosci 27 6268-6272 Wu MM, Buchanan J, Luik RM, Lewis RS (2006) Ca store depletion causes STIMl to accumulate in ER regions closely associated with the plasma membrane. J Cell Biol 174 803-813 Wyss-Coray T (2006) Inflammation in Alzheimer disease driving force, bystander or beneficial response Nat Med 12 1005-1015... 

HIV-1 protein virotoxins (Nath 2002), released from infected cells, have direct bystander effects on neighboring gUa and neurons and cause many of the deleterious consequences of HIV-1. Residual viral proteins, including Tat, gpl20 and Vpr,... 

HIV proteins can also disrupt ion homeostasis in astrocytes, which compromises neuronal function (Pulliam et al. 1993 Benos et al. 1994a, b Holden et al. 1999). Intact HIV-1 virions or gpl20 also markedly inhibit glutamate uptake by astrocytes and cause reductions in excitatory amino acid transporter-2 (EAAT2) mRNA and protein levels (Wang et al. 2003). The inability of astrocytes to buffer extracellular glutamate is likely to decrease the excitotoxic threshold of bystander neurons. 

In some studies it has been shown that ITCs can cause increases in the pro-apoptotic caspase enzymes, caspase 3, caspase 8 or caspase However, in other work, specific caspase inhibitors failed to block cell death or cell detachment from the substratum . This suggests that caspase-activation may only be a bystander event, or may only occur after the initiating event of a block in the cell cycle. Indeed, although expression of c-Jun amino-terminal kinase (INK) in response to ITCs has been linked to the pro-apoptotic process, it remains entirely possible that this is a parallel signalling pathway, more closely related to the induction of Phase 1 or Phase 2 enzymes than to the... 

The iji vitro experiments, using the S-9 fraction from livers of uninduced Fisher 344 rats, was complicated by the fact that it became apparent that formaldehyde production was a poor measure of the extent of metabolism. The reason for that was that the S-9 fraction apparently catalyzed the oxidation of formaldehyde to formate. Consequently, determination of formaldehyde in an S-9 catalyzed reaction consistently gave low values of nitrosamine metabolism. Many workers use semicarbazide to suppress formaldehyde loss. We found, however, that semicarbazide is not a neutral bystander. 

Methods to determine the a.i., and/or relevant metabolites in air during or shortly after the application must be submitted unless it can be justified that exposure of operators, workers, or bystanders does not occur. In SANCO/825/00 it is stated that spray drift and particle-associated as well as gaseous substances have to be taken into consideration because both can cause relevant exposure of operators, workers, or bystanders. Therefore, an analytical method must also be submitted for relevant substances with a low vapor pressure (< 10-5 Pa). 

The method must be capable of determining all components (a.i. and relevant/major metabolites) that are included in the residue definitions used in the assessment of risk to nontarget organisms. For ground (drinking) water and air, the risk to con-sumers/operators or bystanders must also be considered. 

The matrices to be validated depend on the target/purpose of the study, e.g., blood, urine, muscle, or liver. The latter two may be covered by methods developed for food of animal origin. The method must take into account all relevant compounds used in the assessment of risk to consumers/operators or bystanders. The required LOQ... 

Grandjean P, Bach E. 1986. Indirect exposures The significance of bystanders at work and at home. Am Ind Hyg Assoc J 47 819-824. 

Arab, L., S. Steck-Scott, and P. Bowen. 2001. Participation of lycopene and beta-carotene in carcinogenesis Defenders, aggressors, or passive bystanders Epidemiol Rev 23(2) 211-230. 

Information on which parasite products might regulate infected muscle cell characteristics is unresolved. Parasite proteins will be the focus of this discussion. This focus results in part from general lack of information on other secreted products/metabolic wastes and their potential influences on the host cell. In addition, arguments for cell-permeable parasite products are less compelling, and no clear evidence exists for a bystander effect in which bona fide infected cell characteristics become established in neighbouring, uninfected host muscle cells. 

Metal alkoxides undergo alkoxide exchange with alcoholic compounds such as alcohols, hydro-xamic acids, and alkyl hydroperoxides. Alkyl hydroperoxides themselves do not epoxidize olefins. However, hydroperoxides coordinated to a metal ion are activated by coordination of the distal oxygen (O2) and undergo epoxidation (Scheme 1). When the olefin is an allylic alcohol, both hydroperoxide and olefin are coordinated to the metal ion and the epoxidation occurs swiftly in an intramolecular manner.22 Thus, the epoxidation of an allylic alcohol proceeds selectively in the presence of an isolated olefin.23,24 In this metal-mediated epoxidation of allylic alcohols, some alkoxide(s) (—OR) do not participate in the epoxidation. Therefore, if such bystander alkoxide(s) are replaced with optically active ones, the epoxidation is expected to be enantioselective. Indeed, Yamada et al.25 and Sharp less et al.26 independently reported the epoxidation of allylic alcohols using Mo02(acac)2 modified with V-methyl-ephedrine and VO (acac)2 modified with an optically active hydroxamic acid as the catalyst, respectively, albeit with modest enantioselectivity. 

Ishii Morita, H., Agbaria, R., Mullan, C.A., Hirano, H., Koeplin, D.A., Ram, Z., Oldfield, E.H., lohns, D.G., and Blaese, R.M., Mechanism of bystander effect killing in the herpes simplex thymidine kinase gene therapy model of cancer treatment, Gene Therapy, 1997, 4, 244—251. 

We have seen that 1,2-H migrations in singlet carbenes may be affected by (e.g.) the participation of carbene precursor excited states, QMT, stabilization of the hydride shift transition state by polar solvents, and temperature. Here, we consider our third principal theme, the effect of substituents on the kinetics of carbenic rearrangements. We first examine the influence of bystander and spectator substituents (as defined in Eq. 22) on 1,2-H rearrangements of alkyl, alkylchloro, and alkylacetoxycarbenes. 

Using literature data, bystander assistance factors, B[Y], could be calculated for a number of substituents. For example, the thermolysis of certain ketone tosylhydrazone salts afforded dialkylcarbenes which gave competitive 1,2-H shifts, Eq. 23, where either Ha or Hb migrated. 

The product ratio a /b (statistically corrected for the number of competing H migrants), gives the relative migration rate of Ha vs. Hb, or k /kub- The rate constant for the migration of Ha corresponds to the intrinsic migratory aptitude of Ha (M[H]) multiplied by the bystander assistance factor for Y, B[Y], The carbon atom that bears Hb has no bystander substituent, so that km, is simply A/[H], We thus obtain Eq. 24. 

Both Af[H]s cancel, so that the bystander assistance factor, B[Y], for any substituent, Y, is simply the corrected product ratio a /b. 8 In Eqs. 23 and 24, bystanders Y were found to enhance H-shifts in the order MeO > alkyl > Ph quantitative data appear in Table 3.8... 

The bystander substituent (Y) exerts a direct influence on the migrant group (M) at the migration origin. In contrast, a spectator substituent (X in Eq. 22)... 

Table 3. Bystander Assistance Factors for Hydrogen Migration in Dialkylcarbenes°...

A more detailed analysis of bystander substituent effects considers rearrangements in cyclic systems e.g., cyclohexylidene, 56.8... 

The effectiveness of equatorial vs. axial bystanders at promoting the 1,2-H shift (MeO > Me > Ph) may be related to their ability to stabilize the partial positive charge that arises at the migration origin during the 1,2-H shift. In this scenario, the lone pairs of the MeO group are superior to the hyperconjugative and inductive properties of Me, whereas the conformationally dependent h-electron release of Ph is the least effective. 

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