A one-pot reduction route to bimetallic manganese 1,8-naphthyridine complexes.

Reaction of the dinucleating ligand 2,7-bis(6-methyl-2-pyridyl)-1,8-naphthyridine (MeL) with the MnI and MnII precursors MnBr(CO)5 and MnCl2 resulted in the formation of the monometallic complexes [MnBr(CO)3(MeL)] (1) and [MnCl2(MeL)] (3). In both cases, formation of bimetallic manganese complexes could be achieved by reduction with KC8, yielding the carbonyl-bridged complex [Mn2(CO)6(MeL)] (2) and the helicate complex [Mn2(MeL)2] (4), respectively. EPR results demonstrate that 4 represents a novel, weakly antiferromagnetically coupled homovalent dimer (J = -0.85 cm-1). The two formally Mn0 ions are both high spin (S = 3/2) and exhibit a zero-field splitting of ≈1 cm-1, suggesting reduction of the complex is substantially ligand centered, and may be better described as a MnII complex coupled to two open shell singlet ligands [MnII2(MeL2-)2]. X-ray crystallography, UV-Vis spectroscopy and DFT analysis support this finding.

Copper and Zinc Complexes of 2,7-Bis(6-methyl-2-pyridyl)-1,8-naphthyridine─A Redox-Active, Dinucleating Bis(bipyridine) Ligand.

The ligand 2,7-bis(6-methyl-2-pyridyl)-1,8-naphthyridine (MeL) acts as a dinucleating analogue of ubiquitous 2,2'-bipyridine ligands. Coordination of MeL to [Cu(NCMe)4]PF6 and Zn(OAc)2 led to isolation of monometallic [Zn(OAc)2(MeL)], homobimetallic [Cu2(MeL)2][PF6]2, and heterobimetallic [CuZn(µ-OAc)2(MeL)]PF6 complexes. The redox-active nature of the ligand enables access to four redox states of the complex [Cu2(MeL)2][PF6]2. DFT studies indicate that these comprise a metal-centered oxidative and ligand-centered reductive processes.

Cooperative approaches in catalytic hydrogenation and dehydrogenation.

Metal-ligand cooperativity (MLC) is an established strategy for developing effective hydrogenation and dehydrogenation catalysts. Metal-metal cooperativity (MMC) in bimetallic complexes is not as well understood, and to date has had limited implementation in (de)hydrogenation. Herein we use (de)hydrogenation processes as a platform to examine modes of cooperativity, with a particular focus on catalytic mechanisms. We investigate how lessons learnt from the extensive development of metal-ligand cooperative catalysts can aid the ongoing development of metal-metal cooperative catalysts.

Contrasting Synergistic Heterobimetallic (Na-Mg) and Homometallic (Na or Mg) Bases in Metallation Reactions of Dialkylphenylphosphines and Dialkylanilines: Lateral versus Ring Selectivities.

A series of dialkylphenylphosphines and their analogous aniline substrates have been metallated with the synergistic mixed-metal base [(TMEDA)Na(TMP)(CH2 SiMe3 )Mg(TMP)] 1. Different metallation regioselectivities for the substrates were observed, with predominately lateral or meta-magnesiated products isolated from solution. Three novel heterobimetallic complexes [(TMEDA)Na(TMP)(CH2 PCH3 Ph)Mg(TMP)] 2, [(TMEDA)Na(TMP)(m-C6 H4 PiPr2 )Mg(TMP)] 3 and [(TMEDA)Na(TMP)(m-C6 H4 NEt2 )Mg(TMP)]  4 and two homometallic complexes [{(TMEDA)Na(EtNC6 H5 )}2 ] 5 and [(TMEDA)Na2 (TMP)(C6 H5 PEt)]2  6 derived from homometallic metallation have been crystallographically characterised. Complex 6 is an unprecedented sodium-amide, sodium-phosphide hybrid with a rare (NaNNaP)2 ladder motif. These products reveal contrasting heterobimetallic deprotonation with homometallic induced ethene elimination reactivity. Solution studies of metallation mixtures and electrophilic iodine quenching reactions confirmed the metallation sites. In an attempt to rationalise the regioselectivity of the magnesiation reactions the C-H acidities of the six substrates were determined in THF solution using DFT calculations employing the M06-2X functional and cc-pVTZ Dunning's basis set.

Influences of unconscious priming on voluntary actions: Role of the rostral cingulate zone.

The ability to make voluntary, free choices is fundamental to what it means to be human. A key brain region that is involved in free choices is the rostral cingulate zone (RCZ), which is part of the medial frontal cortex. Previous research has shown that activity in this brain region can be modulated by bottom-up information while making free choices. The current study extends those findings, and shows, for the first time, that activation in the RCZ can also be modulated by subliminal information. We used a subliminal response priming paradigm to bias free and cued choices. We observed more activation in the RCZ when participants made a choice that went against the prime's suggestion, compared to when they chose according to the prime. This shows that the RCZ plays an important role in overcoming externally-triggered conflict between different response options, even when the stimuli triggering this conflict are not consciously perceived. Our results suggest that an important mechanism of endogenous action in the RCZ may therefore involve exerting an internally-generated action choice against conflicting influences, such as external sensory evidence. We further found that subliminal information also modulated activity in the anterior insula and the supramarginal gyrus.

The histone chaperone Vps75 forms multiple oligomeric assemblies capable of mediating exchange between histone H3-H4 tetramers and Asf1-H3-H4 complexes.

Vps75 is a histone chaperone that has been historically characterized as homodimer by X-ray crystallography. In this study, we present a crystal structure containing two related tetrameric forms of Vps75 within the crystal lattice. We show Vps75 associates with histones in multiple oligomers. In the presence of equimolar H3-H4 and Vps75, the major species is a reconfigured Vps75 tetramer bound to a histone H3-H4 tetramer. However, in the presence of excess histones, a Vps75 dimer bound to a histone H3-H4 tetramer predominates. We show the Vps75-H3-H4 interaction is compatible with the histone chaperone Asf1 and deduce a structural model of the Vps75-Asf1-H3-H4 (VAH) co-chaperone complex using the Pulsed Electron-electron Double Resonance (PELDOR) technique and cross-linking MS/MS distance restraints. The model provides a molecular basis for the involvement of both Vps75 and Asf1 in Rtt109 catalysed histone H3 K9 acetylation. In the absence of Asf1 this model can be used to generate a complex consisting of a reconfigured Vps75 tetramer bound to a H3-H4 tetramer. This provides a structural explanation for many of the complexes detected biochemically and illustrates the ability of Vps75 to interact with dimeric or tetrameric H3-H4 using the same interaction surface.

Interhemispheric communication influences reading behavior.

We can read words at an amazing speed, with the left hemisphere taking the burden of the processing in most readers (i.e., over 95% of right-handers and about 75% of left-handers). Yet, it is a long-standing question whether word reading in central vision is possible without information transfer between the left and right hemispheres (LH/RH). Here we show that such communication is required by comparing word naming latencies and eye movement data of people with LH language dominance and a unique sample of healthy RH dominant people. The results reveal that individuals with LH speech dominance name words faster when they are allowed to fixate at the word beginning, whereas RH dominants are faster for fixations toward the end. In text reading, the eyes of LH dominants land more to the left than the eyes of RH dominants, making more information directly available to the dominant hemisphere. We conclude that the traditional view of bilateral projections in central vision is incorrect. In contrast, interhemispheric communication is needed in central vision, and eye movements are adjusted to optimize information uptake. Our findings therefore call into question the explanation of macular sparing in hemianopia based on a bilaterally projecting fovea. In addition, these results are in line with the increase of white matter in the splenium of the corpus callosum when people learn to read.

Theta burst stimulation dissociates attention and action updating in human inferior frontal cortex.

Everyday circumstances require efficient updating of behavior. Brain systems in the right inferior frontal cortex have been identified as critical for some aspects of behavioral updating, such as stopping actions. However, the precise role of these neural systems is controversial. Here we examined how the inferior frontal cortex updates behavior by combining reversible cortical interference (transcranial magnetic stimulation) with an experimental task that measures different types of updating. We found that the right inferior frontal cortex can be functionally segregated into two subregions: a dorsal region, which is critical for visual detection of changes in the environment, and a ventral region, which updates the corresponding action plan. This dissociation reconciles competing accounts of prefrontal organization and casts light on the neural architecture of human cognitive control.

STOP-IT: Windows executable software for the stop-signal paradigm.

The stop-signal paradigm is a useful tool for the investigation of response inhibition. In this paradigm, subjects are instructed to respond as fast as possible to a stimulus unless a stop signal is presented after a variable delay. However, programming the stop-signal task is typically considered to be difficult. To overcome this issue, we present software called STOP-IT, for running the stop-signal task, as well as an additional analyzing program called ANALYZE-IT. The main advantage of both programs is that they are a precompiled executable, and for basic use there is no need for additional programming. STOP-IT and ANALYZE-IT are completely based on free software, are distributed under the GNU General Public License, and are available at the personal Web sites of the first two authors or at expsy.ugent.be/tscope/stop.html.