Prediction of protein solubility in Escherichia coli using logistic regression.

In this article we present a new and more accurate model for the prediction of the solubility of proteins overexpressed in the bacterium Escherichia coli. The model uses the statistical technique of logistic regression. To build this model, 32 parameters that could potentially correlate well with solubility were used. In addition, the protein database was expanded compared to those used previously. We tested several different implementations of logistic regression with varied results. The best implementation, which is the one we report, exhibits excellent overall prediction accuracies: 94% for the model and 87% by cross-validation. For comparison, we also tested discriminant analysis using the same parameters, and we obtained a less accurate prediction (69% cross-validation accuracy for the stepwise forward plus interactions model).

Size matters: room temperature P-C bond formation through C-H activation in m-terphenyldiiodophosphines.

m-Terphenyl- and biphenyl-2-diiodophosphines, TerphPI 2 and BiphPI 2, have been obtained by halide exchange from the chloro derivatives TerphPCl 2 and BiphPCl 2 and excess LiI in a benzene solution at room temperature. Whereas BiphPI 2 compounds are stable, the TerphPI 2 species undergo intramolecular C-H activation at room temperature and cyclize to form unsymmetrical 9-iodo-9-phosphafluorenes 1-(3,5-dimethylphenyl)-6,8-dimethyl-9-iodo-9-phosphafluorene, 4; 1-(4-t-butylphenyl)-7-t-butyl-9-iodo-9-phosphafluorene, 5; and 1-(2-methylphenyl)-5-methyl-9-iodo-9-phosphafluorene, 6, albeit the latter reaction is rather slow due to unfavorable steric interactions. Cyclization of the alkyl-substituted 4,4'-di- tert-butyl-biphenyl-2-diiodophosphine, 11, is slow in refluxing benzene solution, but faster than that for the parent biphenyl-2-diiodophosphine. Ab initio and density functional theory calculations are in agreement with an electrophilic aromatic substitution mechanism that is facilitated by steric strains in the terphenyl compounds 2,6-(3,5-Me2C6H3)2C6H3PI2, 1; 2,6-(4-t-BuC6H4)2C6H3PI 2, 2; and 2,6-(2-MeC6H4)2C6H3PI 2, 3. All new compounds have been characterized by multinuclear NMR spectroscopy and direct analysis in real time mass spectrometry. 9-Iodo-9-phosphafluorene, 12, was also analyzed by X-ray diffraction.

Facile synthesis of unsymmetrical 9-phospha- and 9-arsafluorenes.

Unsymmetrical 9-chloro-9-phosphafluorenes (dibenzophospholes) and 9-chloro-9-arsafluorenes (dibenzoarsoles) have been obtained by simple thermolysis of m-terphenyldichlorophosphines and -arsines in close to quantitative yields. The reaction temperatures are about 200 degrees C for the phosphines and 140 degrees C for the arsine, and the reactions are complete within 5 min. Alternatively, these compounds can be synthesized through an AlCl3-catalyzed Friedel-Crafts type ring-closure reaction at low temperatures, but this method suffers from difficult workup procedures. The P(As)-Cl functionality is readily alkylated. Methylation of m-xylyl derivative 4 afforded 1-(3,5-dimethylphenyl)-6,8,9-trimethyl-9-phosphafluorene, 11. The latter compound formed the complexes 11 x Fe(CO)4, 12, and 11 x RuCl2(eta(6)-p-cymene), 13, indicating its good donor properties. The new compounds have been characterized by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy; mass spectrometry; and single-crystal X-ray crystallography in the case of 11, 12, and 13.