Buffer-Induced Electrocatalytic Nitrite Reduction: Impact on Catalytic Rate and Product Selectivity

The complex [Co(CR)Br2]+, where CR is the redox-active macrocycle 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene, is known as an electrocatalyst for the reduction of aqueous nitrite (NO2–). Here, we report that buffer induces a catalytic wave for NO2– reduction at a significantly more anodic potential than under unbuffered conditions. In addition, buffer increases the rate of electrocatalysis. This enhanced electrocatalytic activity is enabled by a number of buffering agents, with 3-(N-morpholino)propanesulfonic acid showing the largest catalytic current. In addition to the greater catalytic activity, buffering agents influence the selectivity of the reduction products, as well as catalyst longevity

Wind-speed thresholds for predicted fire types (km/hr), where canopy fuel moisture is constant.

<p>Wind speeds (km/hr) at which four fire types are expected for the four MPB stages: Green, Red, Grey and Old-MPB under three moisture scenarios: extreme drought (XD), very dry (VD) and moderately dry (D) moisture scenarios, where available canopy fuel moisture is held constant across MPB stage at that of the Green stage. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030002#pone-0030002-t002" target="_blank">Table 2</a> for description of fire types.</p

Low-Valent Iron Carbonyl Complexes with a Tripodal Carbene Ligand

A bulky tris­(carbene)­borate ligand allows several low-valent iron carbonyl complexes to be isolated. One-electron reduction of the cationic iron­(II) complex [PhB­(MesIm)₃Fe­(CO)₃]­[B­(C₆F₅)₄] (<b>1</b>) ([PhB­(MesIm₃)]⁻ = phenyltris­(1-mesitylimidazol-2-ylidene)­borate) yields the low-spin (<i>S</i> = 1/2) iron­(I) complex PhB­(MesIm)₃Fe­(CO)₂ (<b>2</b>), as determined by structural and spectroscopic methods. This complex can in turn be reduced to provide the anionic dicarbonyl complex [K]­[PhB­(MesIm)₃Fe­(CO)₂] (<b>3</b>), which crystallizes as a dimer in which the potassium cation coordinates in a side-on fashion to one CO ligand. Protonation of <b>3</b> yields the weakly acidic iron hydride PhB­(MesIm)₃Fe­(CO)₂H (<b>4</b>), which can also be isolated by treating the κ³-coordinated alkylborohydrido complex PhB­(MesIm)₃­Fe­(κ³-BH­(CH₂CH₃)₃) (<b>5</b>) with CO. The strong donor ability of the tris­(carbene)­borate ligand results in significant reduction of the CO bonds, as measured by IR spectroscopy

Idealized progression of four stages of MPB attack.

<p>Graphic characterizing an idealized sequence of Green unattacked stands, compared to the three stages subsequent to MPB attack. In this chronosequence, 40% of the trees were killed by MPB in the Red stand. In the Grey stand needles fall from the MPB-attacked trees with some attacked trees fallen, opening up the canopy and allowing for higher wind speeds. In the Old-MPB stand most of the MPB-attacked trees have fallen to the ground contributing to high 1000-hr surface fuel load and slightly diminished wind speeds compared to the Grey stand.</p

Wind-speed thresholds for predicted fire types (km/hr), where canopy fuel moisture varies.

<p>Wind speeds (km/hr) at which four fire types are expected for the four MPB stages: Green, Red, Grey and Old-MPB under three moisture scenarios: extreme drought (XD), very dry (VD) and moderately dry (D) moisture scenarios, where available canopy fuel moisture reflects the proportion of red and green needles in each stage as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030002#pone-0030002-t001" target="_blank">Table 1C</a>. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030002#pone-0030002-t002" target="_blank">Table 2</a> for description of fire types.</p

Canopy fuels in four stages of MPB attack.

<p>Total and proportion of total basal area of green, red/fading, and grey trees among four stages of MPB attack (Green, Red, Grey, Old-MPB; see text for description of MPB stages), and comparison of average canopy fuel loads among the four MPB stages of MPB attack with bars representing standard errors. P-values from ANOVAs in upper right of each graph, with letters indicating significant difference based on Tukey's pairwise comparison of means.</p

Boolean logic for predicting fire types.

<p>Predicted fire types based on the wind speed at which the Transition Ratio and Active Ratio are <1 (NO) and/or >1(YES). If the Transition Ratio is ≥1 for a given wind speed, Surface Fireline Intensity is sufficient for transition to crown fire at that wind speed or greater. If the active ratio is ≥1 for a given wind speed, the fire is predicted to be an active crown fire at that wind speed or greater. Fire types are: 1) Surface (understory fire that does not reach the crowns), 2) Torching (also known as Passive Crown Fire; surface fire with occasional torching of individual trees), 3) Conditional Crown (active crown fire possible, if the fire transitions to the overstory, but such crown transition is not predicted in the current stand for the given wind conditions), and 4) Active Crown Fire (fire spreads from crown to crown).</p

Dead surface fuels in four stages of MPB attack.

<p>Comparison of average dead surface fuel loads among four stages of MPB attack (Green, Red, Grey, Old-MPB; see text for description of MPB stages), with bars representing standard errors. P-values from ANOVAs in upper right of each graph, with letters indicating significant difference based on Tukey's pairwise comparison of means.</p

Photoinduced Single-Molecule Magnet Properties in a Four-Coordinate Iron(II) Spin Crossover Complex

The four-coordinate Fe­(II) complex, PhB­(MesIm)₃Fe-NPPh₃ (<b>1</b>) has been previously reported to undergo a thermal spin-crossover (SCO) between high-spin (HS, <i>S</i> = 2) and low-spin (LS, <i>S</i> = 0) states. This complex is photoactive below 20 K, undergoing a photoinduced LS to HS spin state change, as determined by optical reflectivity and photomagnetic measurements. With continuous white light irradiation, <b>1</b> displays slow relaxation of the magnetization, i.e. single-molecule magnet (SMM) properties, at temperatures below 5 K. This complex provides a structural template for the design of new photoinduced mononuclear SMMs based on the SCO phenomenon

A Tripodal Ligand Constructed from Mesoionic Carbene Donors

A tripodal ligand constructed solely from mesoionic carbene donors is reported. The donor strength of this ligand is lower than most imidazol-2-ylidene-based tris­(carbene)­borate ligands, as measured by IR spectroscopy of {NiNO}¹⁰ and {Mn­(CO)₃}⁺ derivatives. The attenuated donor strength is proposed to be due to the collective electron-withdrawing effect of the ligand’s aryl substituents