Using the t-distribution to improve the absolute structure assignment with likelihood calculations

The previously described method for absolute structure determination [Hooft, Straver & Spek (2008). J. Appl. Cryst. 41, 96–103] assumes a Gaussian error distribution. The method is now extended to make it robust against poor data with large systematic errors with the introduction of the Student t-distribution. It is shown that this modification makes very little difference for good data but dramatically improves results for data with a non-Gaussian error distribution

Probability plots based on student’s t-distribution

The validity of the normal distribution as an error model is commonly tested with a (half) normal probability plot. Real data often contain outliers. The use of t-distributions in a probability plot to model such data more realistically is described. It is shown how a suitable value of the parameter of the t-distribution can be determined from the data. The results suggest that even data that seem to be modeled well using a normal distribution can be better modeled using a t-distribution

Determination of absolute structure using Bayesian statistics on Bijvoet differences

A new probabilistic approach is introduced for the determination of the absolute structure of a compound which is known to be enantiopure based on Bijvoet-pair intensity differences. The new method provides relative probabilities for different models of the chiral composition of the structure. The outcome of this type of analysis can also be cast in the form of a new value, along with associated standard uncertainty, that resembles the value of the well known Flack x parameter. The standard uncertainty we obtain is often about half of the standard uncertainty in the value of the Flack x parameter. The proposed formalism is suited in particular to absolute configuration determination from diffraction data of biologically active (pharmaceutical) compounds where the strongest resonant scattering signal often comes from oxygen. It is shown that a reliable absolute configuration assignment in such cases can be made on the basis of Cu Kα data, and in some cases even with carefully measured Mo Kα data

Crystal engineering of melamine - imide complexes: tuning the stoichiometry by steric hindrance of the imide carbonyl groups

A defined melamine–imide ratio in cocrystals can be selected by changing the steric hindrance around the hydrogen-bond acceptor sites of the imides. Crystalline 1:1, 1:2, and 1:3 complexes of melamine may thus be obtained with succinimide, glutarimide, and 1-N-propylthymine (see picture), respectively

Bioinformatics in the Netherlands: the value of a nationwide community

This review provides a historical overview of the inception and development of bioinformatics research in the Netherlands. Rooted in theoretical biology by foundational figures such as Paulien Hogeweg (at Utrecht University since the 1970s), the developments leading to organizational structures supporting a relatively large Dutch bioinformatics community will be reviewed. We will show that the most valuable resource that we have built over these years is the close-knit national expert community that is well engaged in basic and translational life science research programmes. The Dutch bioinformatics community is accustomed to facing the ever-changing landscape of data challenges and working towards solutions together. In addition, this community is the stable factor on the road towards sustainability, especially in times where existing funding models are challenged and change rapidly.Molecular Technology and Informatics for Personalised Medicine and Healt