A quantum mechanics-molecular mechanics study of dissociative electron transfer : The methylchloride radical anion in aqueous solution

The dissociative electron transfer reaction CH3Cl+e−→CH3•+Cl− in aqueous solution is studied by using a QM/MM method. In this work the quantum subsystem (a methylchloride molecule plus an electron) is described using density functional theory while the solvent (300 water molecules) is described using the TIP3P classical potential. By means of molecular dynamics simulations and the thermodynamic integration technique we obtained the potential of mean force (PMF) for the carbon–chlorine bond dissociation of the neutral and radical anion species. Combining these two free energy curves we found a quadratic dependence of the activation free energy on the reaction free energy in agreement with Marcus’ relationship, originally developed for electron transfer processes not involving bond breaking. We also investigated dynamical aspects by means of 60 dissociative trajectories started with the addition of an extra electron to different configurations of a methylchloride molecule in solution. The PMF shows the existence of a very flat region, in which the system is trapped during some finite time if the quantum subsystem quickly losses its excess kinetic energy transferring it to the solvent molecules. One of the most important factors determining the effectiveness of this energy transfer seems to be the existence of close contacts (hydrogen bonds) between the solute and the [email protected] [email protected]

Molecular dynamics simulations of elementary chemical processes in liquid water using combined density functional and molecular mechanics potentials. I. Proton transfer in strongly H-bonded complexes

The first molecular dynamics (MD) simulation of a chemical process in solution with an ab initio description of the reactant species and a classical representation of the solvent is presented. We study the dynamics of proton (deuterium) transfer in strongly hydrogen-bonded systems characterized by an energy surface presenting a double well separated by a low activation barrier. We have chosen the hydroxyl-water complex in liquid water to analyze the coupling between the reactive system and the environment. The proton is transferred from one well to the other with a frequency close to 1 ps−1 which is comparable to the low-frequency band associated to hindered translations, diffusional translation and reorientation of water molecules in water. The proton transfer takes place in 20–30 fs whereas the solvent response is delayed by about 50 fs. Therefore, the reaction occurs in an essentially frozen-solvent configuration. In principle, this would produce a barrier increase with respect to the equilibrium reaction path. However, solvent fluctuations play a substantial role by catalyzing the proton transfer. The solvent relaxation time after proton transfer has been evaluated. Since it falls in the same time scale than the reactive events (0.6 ps) it substantially influences the proton dynamics. The present study is intended to model charge transfer processes in polar media having a low activation barrier for which many reactive events may be predicted in a MD simulation. The case of reactions with large activation barriers would require the use of special techniques to simulate rare events. But still in that case, hybrid QM/MM simulations represent a suitable tool to analyze reaction dynamics and non-equilibrium solvent effects in solution [email protected]

Dietary and fluid adherence among haemodialysis patients attending public sector hospitals in the Western Cape

Objective There has been considerable debate about the extent to which social cognitive models of health behaviour apply in developing countries. The purpose of this paper was to determine the applicability of the Theory of Planned Behaviour (TPB) in predicting dietary and fluid adherence among a sample of haemodialysis patients attending public sector hospitals in the Western Cape. Design and methods A sample of 62 historically disadvantaged patients undergoing haemodialysis completed a battery of psychometric instruments measuring attitudes, subjective norms, perceived behavioural control regarding dietary and fluid adherence, health literacy, perceived social support, and self-reported dietary and fluid adherence. Interdialytic weight gain (IDWG), predialytic serum potassium levels, and predialytic serum phosphate levels served as biochemical indicators of dietary and fluid adherence. Results Regression analyses indicated that the linear combination of attitudes and perceived behavioural control significantly accounted for 15.5% of the variance in self-reported adherence (a medium-effect size) and 11.4% of the variance in IDWG (a modest-effect size). No significant predictors were identified for predialytic serum potassium and predialytic serum phosphate levels. Interpretation and conclusions The results indicate that, while the TPB may not function in the same manner as it does in Western samples, it may have some nuanced applicability among haemodialysis patients attending public sector hospitals in the Western Cape. SAJCN Vol. 21 (2) 2008: pp. 7-1

Screening for HIV-related PTSD: Sensitivity and specificity of the 17-item Posttraumatic Stress Diagnostic Scale (PDS) in identifying HIV-related PTSD among a South African sample

Objectives: The identification of HIV-positive patients who exhibit criteria for Post traumatic Stress Disorder (PTSD) and related trauma symptomatology is of clinical importance in the maintenance of their overall wellbeing. This study assessed the sensitivity and specificity of the 17-item Post traumatic Stress Diagnostic Scale (PDS), a self-report instrument, in the detection of HIVrelated PTSD. An adapted version of the PTSD module of the Composite International Diagnostic Interview (CIDI) served as the gold standard. Method: 85 HIV-positive patients diagnosed with HIV within the year preceding data collection were recruited by means of convenience sampling from three HIV clinics within primary health care facilities in the Boland region of South Africa. Results: A significant association was found between the 17-item PDS and the adapted PTSD module of the CIDI. A ROC curve analysis indicated that the 17-item PDS correctly discriminated between PTSD caseness and non-caseness 74.9% of the time. Moreover, a PDS cut-off point of ≥ 15 yielded adequate sensitivity (68%) and 1-specificity (65%). The 17-item PDS demonstrated a PPV of 76.0% and a NPV of 56.7%. Conclusion: The 17-item PDS can be used as a brief screening measure for the detection of HIV-related PTSD among HIV-positive patients in South Africa.Key Words: ROC analysis; Posttraumatic Stress Diagnostic Scale (PDS); Composite International Diagnostic Interview (CIDI); South Afric

Anxiety, depression, traumatic stress and quality of life in colorectal cancer after different treatments: A study with Portuguese patients and their partners

Purpose: This study examines the impact of different modes of treatment on depression, anxiety, traumatic stress and quality of life in colorectal cancer patients and their partners. Methods: The sample was comprised of 114 oncology patients and 67 partners. All patients were diagnosed with colorectal cancer. Participants were recruited from an Oncology Hospital in the North of Portugal and had been submitted to three modes of treatment: surgery, surgery plus chemotherapy or surgery followed by radiotherapy. Results: The results showed that patients who received only surgery, as treatment, had lower levels of depression, anxiety and traumatic stress symptoms when compared with patients who received surgery and chemotherapy or surgery plus radiotherapy. Partners of surgical patients presented lower levels of state anxiety and traumatic stress symptoms when compared with the other two groups. Patients with more depression had partners also more depressed. No relationship was found between anxiety and traumatic stress symptoms in patients and partners. Patients who received a diagnosis longer than 12 months had more traumatic stress, intrusion and hypervigilance. Patients with illness recurrence showed more traumatic symptoms. Anxiety and depression were the main predictors of patient’s quality of life. Traumatic stress was a predictor of symptom distress - pain/bowel pattern. Conclusion: This study highlights the importance of providing psychological interventions for cancer patients and their partners. Chemotherapy patients and those diagnosed over a year, as well as their partners, are more at risk

Forgiveness, forbearance, and time: The temporal unfolding of transgression-related interpersonal motivations.

The investigators proposed that transgression-related interpersonal motivations result from 3 psycholog-ical parameters: forbearance (abstinence from avoidance and revenge motivations, and maintenance of benevolence), trend forgiveness (reductions in avoidance and revenge, and increases in benevolence), and temporary forgiveness (transient reductions in avoidance and revenge, and transient increases in benev-olence). In 2 studies, the investigators examined this 3-parameter model. Initial ratings of transgression severity and empathy were directly related to forbearance but not trend forgiveness. Initial responsibility attributions were inversely related to forbearance but directly related to trend forgiveness. When people experienced high empathy and low responsibility attributions, they also tended to experience temporary forgiveness. The distinctiveness of each of these 3 parameters underscores the importance of studying forgiveness temporally. The concept of forgiveness has long been a focus of the world’s religions (McCullough & Worthington, 1999; Rye et al., 2000), but only during the last decade did psychologists develop a sus-tained interest in the topic. Recent work has shed light on the social–psychological precursors to forgiveness (Exline &amp

Feeling Tired?: How Sharing Positive Experiences Can Boost Vitality

Three studies indicated how sharing positive experiences can boost vitality

Molecular dynamics simulations of elementary chemical processes in liquid water using combined density functional and molecular mechanics potentials. II. Charge separation processes

A new approach to carry out molecular dynamics simulations of chemical reactions in solution using combined density functional theory/molecular mechanics potentials is presented. We focus our attention on the analysis of reactive trajectories, dynamic solvent effects and transmission coefficient rather than on the evaluation of free energy which is another important topic that will be examined elsewhere. In a previous paper we have described the generalities of this hybrid molecular dynamics method and it has been employed to investigate low energy barrier proton transfer process in water. The study of processes with activation energies larger than a few kT requires the use of specific techniques adapted to “rare events” simulations. We describe here a method that consists in the simulation of short trajectories starting from an equilibrated transition state in solution, the structure of which has been approximately established. This calculation is particularly efficient when carried out with parallel computers since the study of a reactive process is decomposed in a set of short time trajectories that are completely independent. The procedure is close to that used by other authors in the context of classical molecular dynamics but present the advantage of describing the chemical system with rigorous quantum mechanical calculations. It is illustrated through the study of the first reaction step in electrophilic bromination of ethylene in water. This elementary process is representative of many charge separation reactions for which static and dynamic solvent effects play a fundamental [email protected]

Psychological perspectives on divine forgiveness: 3. Trait self-control is associated with well-being through seeking divine forgiveness

IntroductionAlthough a majority of the world’s population believes in a Higher Power and subscribes to a religion in which divine forgiveness is emphasized, little work has been done to understand individual differences associated with seeking divine forgiveness.MethodsBuilding on work that suggests trait self-control facilitates well-being, the current study (N = 439, undergraduate students) applies structural equation modeling (SEM) to test whether believers higher (vs. lower) in trait self-control are more likely to seek divine forgiveness, and, in turn, have better psychological health.Results and discussionWe find that people higher in self-control engage in more divine forgiveness seeking (b = 0.16), and seeking divine forgiveness represents one of the pathways associated with psychological health (i.e., seeking is associated with higher well-being, b = 0.21, and lower distress, b = −0.07). Crucially, we operationalize both positive (well-being and flourishing) and negative (depression, anxiety, stress) aspects of psychological health and control for religiosity. These results suggest that for those who believe in God, seeking divine forgiveness may be one mechanism that links individuals’ self-control to good psychological health, and this is not merely an artifact of higher levels of religiosity. Limitations and future directions are discussed