Transition-state-theory calculations for reactions of O(3P) with halogenated olefins

The potential energy surfaces for the reactions of atomic oxygen in its ground electronic state, O(P-3), with the olefins: CF2=CCl2 and CF2=CF - CF3, have been characterized using ab initio molecular orbital calculations. Geometry optimization and vibrational frequency calculations were performed for reactants, transition states and products at the MP2 and QCISD levels of theory using the 6-31G(d) basis set. This database was then used to calculate the rate constants by means of Transition-State-Theory. To obtain a better reference and to test the reliability of the activation barriers we have also carried out computations using the CCSD(T)(fc)/6-311Gdagger, MP4(SDQ)(fc)/CBSB4 and MP2(fc)/CBSB3 single point energy calculations at both of the above levels of theory, as well as with the composite CBS-RAD procedure ( P. M. Mayer, C. J. Parkinson, D. M. Smith and L. Radom, J. Chem. Phys., 1998, 108, 604) and a modi. cation of this approach, called: CBS-RAD( MP2, MP2). It was found that the kinetic parameters obtained in this work particularly with the CBS-RAD ( MP2, MP2) procedure are in reasonable agreement with the experimental values. For both reactions it is found that the channels leading to the olefin double-bond addition predominates with respect to any other reaction pathway. However, on account of the different substituents in the alkenes we have located, at all levels of theory, two transition states for each reaction. Moreover, we have found that, for the reactions studied, a correlation exists between the activation energies and the electronic structure of the transition states which can explain the influence of the substituent effect on the reactivity of the halo-olefins.

Competitive sorption reactions between phosphorus and organic matter in soil: a review

The incorporation of organic matter ( OM) in soils that are able to rapidly sorb applied phosphorus ( P) fertiliser reportedly increases P availability to plants. This effect has commonly been ascribed to competition between the decomposition products of OM and P for soil sorption sites resulting in increased soil solution P concentrations. The evidence for competitive inhibition of P sorption by dissolved organic carbon compounds, derived from the breakdown of OM, includes studies on the competition between P and (i) low molecular weight organic acids (LOAs), (ii) humic and fulvic acids, and (iii) OM leachates in soils with a high P sorption capacity. These studies, however, have often used LOAs at 1 - 100 mM, concentrations much higher than those in soils ( generally < 0.05 mM). The transience of LOAs in biologically active soils further suggests that neither their concentration nor their persistence would have a practical benefit in increasing P phytoavailability. Higher molecular weight compounds such as humic and fulvic acids also competitively inhibit P sorption; however, little consideration has been given to the potential of these compounds to increase the amount of P sorbed through metal - chelate linkages. We suggest that the magnitude of the inhibition of P sorption by the decomposition products of OM leachate is negligible at rates equivalent to those of OM applied in the field. Incubation of OM in soil has also commonly been reported as reducing P sorption in soil. However, we consider that the reported decreases in P sorption ( as measured by P in the soil solution) are not related to competition from the decomposition products of OM breakdown, but are the result of P release from the OM that was not accounted for when calculating the reduction in P sorption.

Intra- vs intermolecular photoinduced electron transfer reactions of a macrocyclic donor-acceptor dyad

The synthesis, structural characterization, and photophysical behavior of a 14-membered tetraazamacrocycle with pendant 4-dimethylaminobenzyl (DMAB) and 9-anthracenylmethyl groups is reported (L-3, 6-((9-anthracenylmethyl)amino)-trans-6,13-dimethyl-13-((4-dimethylaminobenzyl)amino)-1,4,8,11-tetraaza-cyclotetradecane). In its free base form, this compound displays rapid intramolecular photoinduced electron transfer (PET) quenching of the anthracene emission, with both the secondary amines and the DMAB group capable of acting as electron donors. When complexed with Zn(II), the characteristic fluorescence of the anthracene chromophore is restored as the former of these pathways is deactivated by coordination. Importantly, it is shown that the DMAB group, which remains uncoordinated and PET active, acts only very weakly to quench emission, by comparison to the behavior of a model Zn complex lacking the pendant DMAB group, [ZnL2](2+) (Chart 1). By contrast, Stern-Volmer analysis of intermolecular quenching of [ZnL2](2+) by N,N-dimethylaniline (DMA) has shown that this reaction is diffusion limited. Hence, the pivotal role of the bridge in influencing intramolecular PET is highlighted.

Are insect immune suppressors driving cellular uptake reactions?

Many insect parasitoids that deposit their eggs inside immature stages of other insect species inactivate the cellular host defence to protect the growing embryo from encapsulation. Suppression of encapsulation by polydnavirus-encoded immune-suppressors correlates with specific alterations in hemocytes, mainly cytoskeletal rearrangements and actin-cytoskeleton breakdown. We have previously shown that the Cotesia rubecula polydnavirus gene product CrV1 causes immune suppression when injected into the host hemocoel. CrV1 is taken up by hemocytes although no receptors have been found to bind the protein. Instead CrV1 uptake depends on dimer formation, which is required for interacting with lipophorin, suggesting a CrV1-lipophorin complex internalisation by hemocytes. Since treatment of hemocytes with oligomeric lectins and cytochalasin D can mimic the effects of CrV1, we propose that some dimeric and oligomeric adhesion molecules are able to cross-link receptors on the cell surface and depolymerise actin by leverage-mediated clearance reactions in the hemolymph.

The role of leader-member exchanges in mediating the relationship between locus of control and work reactions

The relationship between locus of control, the quality of exchanges between subordinates and leaders (LMX), and a variety of work-related reactions (intrinsic/extrinsic job satisfaction, work-related well-being, and organizational commitment) are examined. It was predicted that people with an internal locus of control develop better quality relations with their manager and this, in turn, results in more favourable work-related reactions. Results from two different samples (N = 404, and N = 51) supported this prediction, and also showed that LMX either fully, or partially, mediated the relationship between locus of control and all the work-related reactions.

A gradient descent algorithm for minimizing amino acid coupling reactions when synthesizing cyclic-peptide libraries

Combinatorial chemistry has become an invaluable tool in medicinal chemistry for the identification of new drug leads. For example, libraries of predetermined sequences and head-to-tail cyclized peptides are routinely synthesized in our laboratory using the IRORI approach. Such libraries are used as molecular toolkits that enable the development of pharmacophores that define activity and specificity at receptor targets. These libraries can be quite large and difficult to handle, due to physical and chemical constraints imposed by their size. Therefore, smaller sub-libraries are often targeted for synthesis. The number of coupling reactions required can be greatly reduced if the peptides having common amino acids are grouped into the same sub-library (batching). This paper describes a schedule optimizer to minimize the number of coupling reactions by rotating and aligning sequences while simultaneously batching. The gradient descent method thereby reduces the number of coupling reactions required for synthesizing cyclic peptide libraries. We show that the algorithm results in a 75% reduction in the number of coupling reactions for a typical cyclic peptide library.

Adolescents' reactions to universal and indicated prevention programs for depression: Perceived stigma and consumer satisfaction

There is a common view that one of the major considerations in selecting between universal and indicated interventions is the marked stigma produced by the latter. However, to date there has been no empirical examination of this assumption. The current study examined reported stigma and program satisfaction following two school-based interventions aimed at preventing depression in 532 middle adolescents. The interventions were conducted either across entire classes by classroom teachers (universal delivery) or in small high risk groups by mental health professionals (indicated delivery). The indicated delivery was associated with significantly greater levels of perceived stigma, but effect sizes were small and neither program was associated with marked stigma in absolute terms. Perceived stigma was more strongly associated with aspects of the individual including being male and showing greater externalizing symptomatology. In contrast, the indicated program was evaluated more positively by both participants and program leaders and effect sizes for these measures of satisfaction were moderate to large. The results point to the need for further empirical evaluation of both perceived stigma and program satisfaction in providing balanced considerations of the value of indicated and universal programs.

Cognitive asymmetry in employee emotional reactions to leadership behaviors

This article is predicated on the idea that leaders shape workplace affective events. Based on Affective Events Theory (AET), I argue that leaders are sources of employee positive and negative emotions at work. Certain leader behaviors displayed during interactions with their employees are the sources of these affective events. The second theoretical underpinning of the article is the Asymmetry Effect of emotion. Consistent with this theory, employees are more likely to recall negative incidents than positive incidents. In a qualitative study, evidence that these processes exist in the workplace was found. Leader behaviors were sources of positive or negative emotional responses in employees; employees recalled more negative incidents than positive incidents, and they recalled them more intensely and in more detail than positive incidents. Consequently, leaders may need to exercise their emotional intelligence to generate emotional uplifts to overcome the hassles in the workplace that employees seem to remember so vividly. (c) 2006 Elsevier Inc. All rights reserved.

Direct access to functionalized cyclic enones using Mannich, Morita-Baylis-Hillman and elimination reactions

A series of highly functionalized cyclic enones were obtained from Mannich, Morita-Baylis-Hiliman and elimination reaction with cyclic enones.

Introduction of routine outcome measures: staff reactions and issues for consideration

The aim of this study was to explore clinician reactions to (i) the introduction of routine outcome measures and (ii) the utility of outcomes data in clinical practice. Focus group discussions (n = 34) were conducted with mental health staff (n = 324) at approximately 8 months post implementation of routine outcome measures. A semi-structured interview schedule was used to collect data on two key issues; reactions to the introduction of outcome measures and factors influencing the utility of outcomes data in clinical practice. Data from the discussion groups were analysed using content analysis to isolate emerging themes. While the majority of participants endorsed the collection and utilization of outcomes data, many raised questions about the merits of the initiative. Ambivalence, competing work demands, lack of support from senior medical staff, questionable evidence to support the use of outcome measures, and fear of how outcomes data might be used emerged as key issues. At 8 months post implementation a significant number of clinical staff remained ambivalent about the benefits of outcome measurement and had not engaged in the process. The shift to a service model driven by outcomes and case-mix data will take time and resources to achieve. Implications for nursing staff are discussed.

Reactions to positive deviance: Social identity and attribution dimensions

This research examines whether evaluations of positive deviates (i.e. high achieving group members) are influenced by the attributions they make for their performance. We argue that ingroup positive deviates who make group attributions help enhance the ingroup's image and thus attract favorable evaluations. In Experiment 1, ingroup positive deviates who made group attributions were generally evaluated more favorably than ingroup positive deviates who made individual attributions. There was also evidence that the positive deviates' attribution style influenced group and self-evaluations. Evaluations of outgroup positive deviates were not influenced by their attribution style. In Experiment 2, an ingroup positive deviate who was successful and attributed that success to the group was upgraded relative to an ingroup positive deviate who made individual attributions. Group evaluations were also higher when the positive deviate made group attributions. This pattern did not emerge when the positive deviate failed. The results are discussed from a social identity perspective.

Comparative studies of hyperhomodesmotic reactions for the calculation of standard heats of formation of fullerenes

How can the accuracy of the calculated standard heats of formation Delta H-f(0) of fullerenes be improved? How reliable are the values of Delta H-f(0) calculated from hyperhomodesmotic reactions? This work is the first to address these questions. By comparing the results obtained from three hyperhomodesmotic reactions containing only fullerenes, it is illustrated that both the resonance contribution and the strain energy contribution should be considered in the construction of hyperhomodesmotic reactions. An attempt to construct such hyperhomodesmotic reactions for fullerenes has been carried out, and several new insights are indicated.