No abstract

No abstract

No abstract

No abstract

The ruthenium(II) polypyridyl complexes (RPCs), [(phen)2Ru(tatpp)]Cl2 (3Cl2) and [(phen)2Ru (tatpp)Ru(phen)2]Cl4 (4Cl4), containing the large planar and redox‐active tetraazatetrapyrido‐pentacene (tatpp) ligand, cleave DNA in the presence of reducing agents in cell‐free assays and show significant tumor regression in mouse tumor models with human non‐small cell lung carcinoma xenografts. ITC, CD, and ESI‐MS techniques were used to study the thermodynamics of RPC·DNA complex formation and the complex structure for binding three different RPCs to duplex DNA. The specific RPCs were [Ru(phen)3]2+ (12+), [Ru(phen)2(dppz)]2+ (22+), and [Ru(phen)2(tatpp)]2+ (32+). We examined the enatiomerically pure Δ‐RPC and Λ‐RPC isomers as well as the racemic mixture in terms of their binding to B‐DNA. B‐DNA binding of the three RPCs is characterized by a combination of groove binding (including electrostatic effects) and intercalation, with the thermodynamics being very similar for binding both the enantiomerically pure compounds and the racemic mixture. 12+ is the weakest DNA binder, exhibiting a Ka = 1.3 × 104 m–1 while 22+ binds with significantly higher affinity, Ka,1 = 1.4 × 106 m–1, and 32+ exhibits the tightest binding, Ka = 4.7 × 106 m–1. The trend is to increase the affinity as longer bridging ligands engage in additional π‐bonding with the DNA base pairs via an intercalative binding mode. A second binding mode, two orders of magnitude weaker was also seen for 22+. The ITC values for binding the racemic mixtures exhibit ΔGs ranging from –5.6 to –9.1 kcal mol–1 (12+·DNA and 32+·DNA respectively), while the ITC values for ΔH range from +4.9 to –5.0 kcal mol–1 (32+·DNA and mode 2 binding for 22+·DNA respectively). All of the primary complexes exhibit very negative values for –TΔS ranging from –7.3 to –14.0 kcal mol–1 (mode 1 binding for 22+·DNA and 32+·DNA respectively). To further understand the intercalation vs. groove binding contributions to the overall binding energy we compared the thermodynamics for formation of the 12+·DNA, 22+·DNA, and 32+·DNA complexes to the thermodynamics for formation of the 44+·DNA complex. The RPC binding affinities to duplex DNA follow the trend: 12+ < 44+ < 22+ < 32+. Differences in the affinity for binding 12+ vs. 22+ or 32+ are almost entirely due to the size of the intercalating moiety, e.g. phen which can only be partially intercalated in comparison to dppz and tatpp which can be completely intercalated. The lower affinity for the dinuclear ruthenium 44+ is due to the solvation penalty for the second Ru core complex that extends out from the major groove. Comparing these results, we have begun to develop the structure function relationships for the interaction of RPCs with B‐DNA.

No abstract

Soil microbial respiration is one of the largest sources of carbon (C) emissions to the atmosphere in terrestrial ecosystems, which is strongly dependent on multiple environmental variables including soil moisture. Soil moisture content is strongly dependent on soil texture, and the combined effects of texture and moisture on microbial respiration are complex and less explored. Therefore, this study examines the effects of soil moisture on the mineralization of soil organic C Soil organic carbon in three different soils, Ultisol, Alfisol and Vertisol, collected from mixed forests of Georgia, Missouri, and Texas, United States , respectively. A laboratory microcosm experiment was conducted for 90 days under different moisture regimes. Soil respiration was measured weekly, and destructive harvests were conducted at 1, 15, 60, and 90 days after incubation to determine extractable organic C (EOC), phospholipid fatty acid based microbial community, and C-acquiring hydrolytic extracellular enzyme activities (EEA). The highest cumulative respiration in Ultisol was observed at 50% water holding capacity (WHC), in Alfisol at 100% water holding capacity, and in Vertisol at 175% WHC. The trends in Extractable Organic Carbon were opposite to that of cumulative microbial respiration as the moisture levels showing the highest respiration showed the lowest EOC concentration in all soil types. Also, extracellular enzyme activities increased with increase in soil moisture in all soils, however, respiration and EEA showed a decoupled relationship in Ultisol and Alfisol soils. Soil moisture differences did not influence microbial community composition.

The cover picture shows Ru(phen)2(tatpp)]2+ binding to DNA through an intercalative mechanism. In the hypoxic environment of a lung cancer tumor, the ruthenium(II) polypyridyl complex (RPC) reacts with oxygen to produce H2O2 as opposed to superoxide and oxidizes DNA, resulting in the cleavage of phosphodiester backbone bonds in both strands. This cleavage is shown at the center of the image. The RPCs used in this study have shown some potential as anticancer compounds, particularly for the treatment of lung cancer, so we have displayed a background of carcinoma cells from a tumor that is stained blue and surrounded by purple‐stained normal lung tissue (background reproduced with permission from the Experimental Histopathology Core at the Fred Hutchinson Cancer Research Center; copyright 2014). Details are discussed in the article by F. M. MacDonnell, E. A. Lewis et al. on page 3604 ff (https://doi.org/10.1002/ejic.201700462). For more on the story behind the cover research, see the Cover Profile (https://doi.org/10.1002/ejic.201700778).