New Strategies for Direct Methane-to-Methanol Conversion from Active Learning Exploration of 16 Million Catalysts

Despite decades of effort, no earth-abundant homogeneous catalysts have been discovered that can selectively oxidize methane to methanol. We exploit active learning to simultaneously optimize methane activation and methanol release calculated with machine learning-accelerated density functional theory in a space of 16 M candidate catalysts including novel macrocycles. By constructing macrocycles from fragments inspired by synthesized compounds, we ensure synthetic realism in our computational search. Our large-scale search reveals that low-spin Fe(II) compounds paired with strong-field (e.g., P or S-coordinating) ligands have among the best energetic tradeoffs between hydrogen atom transfer (HAT) and methanol release. This observation contrasts with prior efforts that have focused on high-spin Fe(II) with weak-field ligands. By decoupling equatorial and axial ligand effects, we determine that negatively charged axial ligands are critical for more rapid release of methanol and that higher-valency metals [i.e., M(III) vs M(II)] are likely to be rate-limited by slow methanol release. With full characterization of barrier heights, we confirm that optimizing for HAT does not lead to large oxo formation barriers. Energetic span analysis reveals designs for an intermediate-spin Mn(II) catalyst and a low-spin Fe(II) catalyst that are predicted to have good turnover frequencies. Our active learning approach to optimize two distinct reaction energies with efficient global optimization is expected to be beneficial for the search of large catalyst spaces where no prior designs have been identified and where linear scaling relationships between reaction energies or barriers may be limited or unknown.

High frequency of cytolytic T lymphocytes directed against a tumor-specific mutated antigen detectable with HLA tetramers in the blood of a lung carcinoma patient with long survival

We have identified an antigen recognized by autologous CTL on the lung carcinoma cells of a patient who enjoyed a favorable clinical evolution, being alive 10 years after partial resection of the primary tumor. The antigenic peptide is presented by HLA-A2 molecules and encoded by a mutated sequence in the gene coding for malic enzyme, an essential enzyme that converts malate to pyruvate. In the tumor cell line derived from the patient, only the mutated malic enzyme allele is expressed, because of a loss of heterozygosity in the region of chromosome 6 that contains this locus. Tetramers of soluble HLA-A2 molecules loaded with the antigenic peptide stained approximately 0.4% of the patient's blood CD8 T cells. When these cells were stimulated in clonal conditions, 25% of them proliferated, and the resulting clones were lytic and specific for the mutated malic enzyme peptide. T-cell receptor analysis indicated that almost all of these antimalic CTLs shared the same receptor. Antimalic T cells were consistently found in blood samples collected from the patient between 1990 and 1999, at frequencies ranging from 0.1 to 0.4% of the CD8 cells. Their frequency appeared to double within 2 weeks after intradermal inoculation of lethally irradiated autologous tumor cells. These results indicate that nonmelanoma cancer patients may also have a high frequency of blood CTLs directed against a tumor-specific antigen.

[Arterial hypertension from secretion of catecholamines in an infant with a ganglioneuroblastoma]

The case of a 16 month old infant presenting with an abdominal tumour and systemic hypertension is reported. The profile of urinary plasma and tumour catecholamine levels corresponded with that of a pheochromocitoma. The combination of alphablockers and betablockers was the only effective treatment of the peaks of preoperative hypetension. The tumour was completely excised and was found to be a ganglioneuroblastoma. No recurrence has been observed after 3 years post-operative follow-up. The incidence and mechanisms of hypertension in neuroblastoma are reviewed. Only these histological forms of ganglioblastoma have the enzymatic set up for the synthesis and release of pressor amines.