19 research outputs found

    Polymorphism in p-Aminobenzoic Acid

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    We review the polymorphism of p-aminobenzoic acid (pABA), a model drugcompound whose crystallisation and polymorphic behaviour has been extensively studied in recent years. Beyond the well-known and characterised α and ÎČ forms, pABA also crystallises as a Îł polymorph, which is structurally similar to the α form. In addition we also compare the newly reported ÎŽ form, obtained by high pressure crystallisation and through compression of the α-form. A structural analysis and comparison of all of the forms is presented, the conditions by which each of them is obtained summarised. Crystal structure prediction calculations have also been carried out in order to probe the solid form energy landscape of this compound. The overall picture of the polymorphism of pABA, reveals, surprisingly, the rarity of the ÎČ form

    Rationalising the difference in crystallisability of two sulflowers using efficient in silico methods

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    The molecular structures of the first and second generation sulflowers, sulflower and persulfurated coronene (PSC), are remarkably similar: carbon ring structures decorated with sulfur atoms, without any additional moiety

    Full Agreement and the Provision of Threshold Public Goods

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    The experimental evidence suggests that groups are inefficient at providing threshold public goods. This inefficiency appears to reflect an inability to coordinate over how to distribute the cost of providing the good. So, why do groups not just split the cost equally? We offer an answer to this question by demonstrating that in a standard threshold public good game there is no collectively rational recommendation. We also demonstrate that if full agreement is required in order to provide the public good then there is a collectively rational recommendation, namely, to split the cost equally. Requiring full agreement may, therefore, increase efficiency in providing threshold public goods. We test this hypothesis experimentally and find support for it

    Report on the sixth blind test of organic crystal-structure prediction methods

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    The sixth blind test of organic crystal-structure prediction (CSP) methods has been held, with five target systems: a small nearly rigid molecule, a polymorphic former drug candidate, a chloride salt hydrate, a co-crystal, and a bulky flexible molecule. This blind test has seen substantial growth in the number of submissions, with the broad range of prediction methods giving a unique insight into the state of the art in the field. Significant progress has been seen in treating flexible molecules, usage of hierarchical approaches to ranking structures, the application of density-functional approximations, and the establishment of new workflows and "best practices" for performing CSP calculations. All of the targets, apart from a single potentially disordered Z` = 2 polymorph of the drug candidate, were predicted by at least one submission. Despite many remaining challenges, it is clear that CSP methods are becoming more applicable to a wider range of real systems, including salts, hydrates and larger flexible molecules. The results also highlight the potential for CSP calculations to complement and augment experimental studies of organic solid forms

    INCOME INEQUALITY, RECIPROCITY AND PUBLIC GOOD PROVISION: AN EXPERIMENTAL ANALYSIS

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    This paper analyses the impact of income inequality on public good provision in an experimental setting. A sample of secondary school students were recruited to participate in a simple linear public goods game where income heterogeneity was introduced by providing participants with unequal token endowments. The results show that endowment heterogeneity does not have any significant impact on contributions to the public good, and that consistent with models of reciprocity, low and high endowment players contribute the same fraction of their endowment to the public pool. Moreover, individuals appear to adjust their contributions in order to maintain a fair share rule. Copyright (c) 2007 The Authors; Journal compilation (c) 2007 Economic Society of South Africa.
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