Several copper corrole complexes were synthesized, and their catalytic activities for hydrogen (H 2 ) evolution were examined. Our results showed that substituents at the meso positions of corrole macrocycles played significant roles in regulating the redox and thus the catalytic properties of copper corrole complexes: strong electron-withdrawing substituents can improve the catalysis for hydrogen evolution, while electron-donating substituents are not favored in this system. Copper complex of 5,15-pentafluorophenyl-10-(4-nitrophenyl)corrole (1) was shown to have the best electrocatalytic performance among copper corroles examined. Complex 1 can electrocatalyze H 2 evolution using trifluoroacetic acid (TFA) as the proton source in acetonitrile. In cyclic voltammetry, the value of i cat /i p = 303 (i cat is the catalytic current, i p is the one-electron peak current of 1 in the absence of acid) at scan rate 100 mV s −1 and 20 °C is remarkable. Electrochemical and spectroscopic measurements revealed that 1 has the desired stability in concentrated TFA acid solution and is unchanged by functioning as an electrocatalyst. Stopped-flow, spectroelectrochemistry and theoretical studies provided valuable insights into the mechanism of hydrogen evolution mediated by 1. Doubly reduced 1 is the catalytic active species that reacts with a proton to give the hydride intermediate for subsequent generation of H 2 .

Simultaneous deep brain stimulation (DBS) and functional magnetic resonance imaging (fMRI) constitutes a powerful tool for elucidating brain functional connectivity, and exploring neuromodulatory mechanisms of DBS therapies. Previous DBS-fMRI studies could not provide full activation pattern maps due to poor MRI compatibility of the DBS electrodes, which caused obstruction of large brain areas on MRI scans. Here, we fabricate graphene fiber (GF) electrodes with high charge-injection-capacity and little-to-no MRI artifact at 9.4T. DBS-fMRI with GF electrodes at the subthalamic nucleus (STN) in Parkinsonian rats reveal robust blood-oxygenation-level-dependent responses along the basal ganglia-thalamocortical network in a frequency-dependent manner, with responses from some regions not previously detectable. This full map indicates that STN-DBS modulates both motor and non-motor pathways, possibly through orthodromic and antidromic signal propagation. With the capability for full, unbiased activation pattern mapping, DBS-fMRI using GF electrodes can provide important insights into DBS therapeutic mechanisms in various neurological disorders.

Soft and magnetic resonance imaging (MRI) compatible neural electrodes enable stable chronic electrophysiological measurements and anatomical or functional MRI studies of the entire brain without electrode interference with MRI images. These properties are important for many studies, ranging from a fundamental neurophysiological study of functional MRI signals to a chronic neuromodulatory effect investigation of therapeutic deep brain stimulation. Here we develop soft and MRI compatible neural electrodes using carbon nanotube (CNT) fibers with a diameter from 20 μm down to 5 μm. The CNT fiber electrodes demonstrate excellent interfacial electrochemical properties and greatly reduced MRI artifacts than PtIr electrodes under a 7.0 T MRI scanner. With a shuttle-assisted implantation strategy, we show that the soft CNT fiber electrodes can precisely target specific brain regions and record high-quality single-unit neural signals. Significantly, they are capable of continuously detecting and isolating single neuronal units from rats for up to 4−5 months without electrode repositioning, with greatly reduced brain inflammatory responses as compared to their stiff metal counterparts. In addition, we show that due to their high tensile strength, the CNT fiber electrodes can be retracted controllably postinsertion, which provides an effective and convenient way to do multidepth recording or potentially selecting cells with particular response properties. The chronic recording stability and MRI compatibility, together with their small size, provide the CNT fiber electrodes unique research capabilities for both basic and applied neuroscience studies.

Living radical polymerization (LRP) methods 1-14 can be divided into two broad categories currently referred to as reversible termination (RT) and degenerative transfer (DT). 15 Both RT and DT approaches for LRP use a dormant species (X-P) as a storage location for latent propagating radicals (P • ) and relatively fast exchange of freely diffusing radicals (P′ • ) from solution with the latent radicals in X-P as the means for obtaining low polydispersity (eq 1). The clear distinction between RT and DT pathways for LRP is the source and method for control of the propagating radicals and the features that give living character to the radical polymerization. The dormant complex (X-P) is the exclusive source of radicals (P • ) for all reversible termination (RT) processes which can occur by either homolytic dissociation (DC, 16 SFRP, 10 NMP, 12 OMRP 17 ) (eq 2) or atom transfer (ATRP) (eq 3). 1,4,5 Quasi-equilibria between freely diffusing radicals and a dormant complex described by eqs 2 and 3 provide a nearly constant low concentration of propagating radicals (P • ) in solution which slowly declines as radical termination occurs. Control of the radical concentration by the dormant complex contributes to the living character for reversible termination (RT) processes through the suppression of bimolecular radical termination relative to polymer propagation by the persistent radical effect (PRE). 3,18 Processes that are currently called degenerative transfer (DT) 15 such as iodide-mediated polymerization 19 and RAFT 13 utilize a continual influx of radicals (R • ) from an external radical source like AIBN to initiate polymerization of monomers and exchange with latent radicals in the dormant complex (X-P). The term degenerative transfer refers to the interchange of activity between active and dormant species. 15 Degenerative transfer in radical polymerization occurs when an active propagating radical in solution (P′ • ) interchanges roles with a latent radical (P • ) in a dormant complex (P-X). The degenerative transfer reaction is usually depicted as an associative process, 14,15 but the same exchange of active and latent radicals can be accomplished by a two-step dissociative process (Scheme 1). If the radicals P • and P′ • are polymeric radicals that differ only in the chain length, then the exchange process is nearly degenerate (∆G°≈ 0) and the equilibrium constant approaches unity. The concentration of radicals for a DT process is primarily determined by the concentration of the external radical source (AIBN, V-70) and the rate constants for radicals to enter solution (k i ) and terminate (k t ) ([R • ] ) (k i [I]/2k t ) 1/2 ). The concentration of radicals and rates of polymerization for DT processes approach the values for regular uncontrolled radical polymerization, and thus the persistent radical effect does not contribute living character to DT processes. This communication reports that organo-cobalt porphyrin complexes function as a dormant complex and latent source of radicals for living radical polymeriza...

Aqueous solutions of rhodium(III) tetra p-sulfonatophenyl porphyrin ((TSPP)Rh(III)) complexes react with dihydrogen to produce equilibrium distributions between six rhodium species including rhodium hydride, rhodium(I), and rhodium(II) dimer complexes. Equilibrium thermodynamic studies (298 K) for this system establish the quantitative relationships that define the distribution of species in aqueous solution as a function of the dihydrogen and hydrogen ion concentrations through direct measurement of five equilibrium constants along with dissociation energies of D(2)O and dihydrogen in water. The hydride complex ([(TSPP)Rh-D(D(2)O)](-4)) is a weak acid (K(a)(298 K) = (8.0 +/- 0.5) x 10(-8)). Equilibrium constants and free energy changes for a series of reactions that could not be directly determined including homolysis reactions of the Rh(II)-Rh(II) dimer with water (D(2)O) and dihydrogen (D(2)) are derived from the directly measured equilibria. The rhodium hydride (Rh-D)(aq) and rhodium hydroxide (Rh-OD)(aq) bond dissociation free energies for [(TSPP)Rh-D(D(2)O)](-4) and [(TSPP)Rh-OD(D(2)O)](-4) in water are nearly equal (Rh-D = 60 +/- 3 kcal mol(-1), Rh-OD = 62 +/- 3 kcal mol(-1)). Free energy changes in aqueous media are reported for reactions that substitute hydroxide (OD(-)) (-11.9 +/- 0.1 kcal mol(-1)), hydride (D(-)) (-54.9 kcal mol(-1)), and (TSPP)Rh(I): (-7.3 +/- 0.1 kcal mol(-1)) for a water in [(TSPP)Rh(III)(D(2)O)(2)](-3) and for the rhodium hydride [(TSPP)Rh-D(D(2)O)](-4) to dissociate to produce a proton (9.7 +/- 0.1 kcal mol(-1)), a hydrogen atom (approximately 60 +/- 3 kcal mol(-1)), and a hydride (D(-)) (54.9 kcal mol(-1)) in water.