Accurate solubility prediction with error bars for electrolytes: a machine learning approach

Accurate in silico models for predicting aqueous solubility are needed in drug design and discovery and many other areas of chemical research. We present a statistical modeling of aqueous solubility based on measured data, using a Gaussian Process nonlinear regression model (GPsol). We compare our results with those of 14 scientific studies and 6 commercial tools. This shows that the developed model achieves much higher accuracy than available commercial tools for the prediction of solubility of electrolytes. On top of the high accuracy, the proposed machine learning model also provides error bars for each individual prediction.     

Aryl calcium compounds: syntheses, structures, physical properties, and chemical behavior

Organocalcium chemistry is still in its infancy. The direct synthesis of activated calcium and (substituted) iodobenzenes allows for the large-scale and high-yield synthesis of aryl calcium iodides. The influence of the substitution patterns of the phenyl group, halogen atom, and solvent is discussed. Aryl calcium iodides show a Schlenk equilibrium that enables the isolation of diaryl calcium derivatives. Owing to the high reactivity of aryl calcium halides, low temperatures have to be maintained throughout the preparative procedures in order to avoid side reactions. A decrease of reactivity and, hence, an enhanced stability at higher temperatures can be achieved by shielding of the calcium atom by increasing the coordination number of the metal center or by substitution of the iodide anion by bulky groups.     

Phosphate recognition in structural biology

Drug-discovery research in the past decade has seen an increased selection of targets with phosphate recognition sites, such as protein kinases and phosphatases, in the past decade. This review attempts, with the help of database-mining tools, to give an overview of the most important principles in molecular recognition of phosphate groups by enzymes. A total of 3003 X-ray crystal structures from the RCSB Protein Data Bank with bound organophosphates has been analyzed individually, in particular for H-bonding interactions between proteins and ligands. The various known binding motifs for phosphate binding are reviewed, and similarities to phosphate complexation by synthetic receptors are highlighted. An analysis of the propensities of amino acids in various classes of phosphate-binding enzymes showed characteristic distributions of amino acids used for phosphate binding. This review demonstrates that structure-based lead development and optimization should carefully address the phosphate-binding-site environment and also proposes new alternatives for filling such sites.     

Photodissociation of uracil

We investigate the photochemistry and photodissociation dynamics of uracil by two-colour photofragment Doppler spectroscopy and by two-colour slice imaging at excitation wavelengths between 268 and 235 nm. We observe the loss of a hydrogen atom upon excitation into the pipi* state. The angular distribution indicates a statistical process, while the translational energy distribution agrees with a dissociation that takes place on the electronic ground state. The pipi* state most likely deactivates via the lower-lying npi* state. In addition there is evidence for a second pathway: direct decay of the pipi* state to the electronic ground state with subsequent dissociation. Experiments on uracil-1,3-D(2) show that there is no site selectivity in the dissociation process. No evidence was found for the direct dissociation via a pisigma* excited state that seems to be relevant in the photochemistry of adenine and many other heterocyclic molecules. Overall, the photochemistry of uracil is similar to that of thymine.     

On the Complexes of Bis(trifluoromethyl)ditellurium,Te2(CF3)2, with Halide Ions – A Crystallographic Study of the Pseudo‐trihalides [PNP][(TeCF3)2X] (PNP = Bis(triphenylphosphoranyliden)ammonium; X = Cl,Br, I)

The anions [(TeCF₃)₂X]^? (X = Cl, Br, I) resemble the trihalides [I₂X]^? in the solid state and show similar dynamic behaviour in solution. All three compounds crystallize iso‐structurally in the triclinic space group with Z = 2 and exhibit cell dimensions according to the sizes of the halogen atoms.     

New nickel(II) diimine complexes and the control of polyethylene microstructure by catalyst design

Starting from differently substituted boronic acids as versatile building block, new "ortho-aryl" alpha-diimine ligands a-h were synthesized in an easy, high-yielding route. Reaction of the complex precursor diacetylacetonato-nickel(II) with a trityl salt, like [CPh3] [B(C6F5)4] or [CPh3] [SbCl6], in the presence of the diimine ligands afford the monocationic, square planar complexes 2a-g in almost quantitative yields. Suitable crystals (2d',e,f,g) were submitted for X-ray diffraction analysis. A geometry model was developed to describe the orientation of ligand fragments around the nickel(II) center that influence the polymer microstructure. At elevated reaction temperature and pressure, and in the presence of hydrogen, 2a-e catalyze the homopolymerization of ethylene to give branched PE products ranging from HD- to LLD-PE grades. The polymerization results indicate the possibility of precise microstructure control depending on the particular complex substitution. Preliminary investigations on material density and mechanical behavior by uniaxial stretching until failure point toward new material properties that can result from the simple ethylene monomer by catalyst design.