Mapping the macaque superior temporal sulcus: functional delineation of vergence and version eye-movement-related activity.

It is currently thought that the primate oculomotor system has evolved distinct but interrelated subsystems to generate different types of visually guided eye movements (e.g., saccades/smooth pursuit/vergence). Although progress has been made in elucidating the neural basis of these movement types, no study to date has investigated all three movement types on a large scale and within the same animals. Here, we used fMRI in rhesus macaque monkeys to map the superior temporal sulcus (STS) for BOLD modulation associated with visually guided eye movements. Further, we ascertained whether modulation in a given area was movement type specific and, if not, the modulation each movement type elicited relative to the others (i.e., dominance). Our results show that multiple areas within STS modulate during all movement types studied, including the middle temporal, medial superior temporal, fundus of the superior temporal, lower superior temporal, and dorsal posterior inferotemporal areas. Our results also reveal an area in dorsomedial STS that is modulated almost exclusively by vergence movements. In contrast, we found that ventrolateral STS is driven preferentially during versional movements. These results illuminate an STS network involved in processes associated with multiple eye movement types, illustrate unique patterns of modulation within said network as a function of movement type, and provide evidence for a vergence-specific area within dorsomedial STS. We conclude that producing categorically different eye movement types requires access to a common STS network and that individual network nodes are recruited differentially based upon the type of movement generated.

Electron transfer within charge-localized arylhydrazine-centered mixed valence radical cations having larger bridges.

Kinetics for intramolecular charge transfer between two diarylhydrazine units, measured by ESR, are reported for six charge-localized mixed valence compounds having 9, 11, 13, and 16 bonds between the nitrogen atoms. A 17-bond bridged compound had too slow electron transfer to measure the rate constant by ESR. The optical spectra of these radical cations are compared with tert-butyl,aryl-substituted hydrazines, and rate constants calculated using parameters derived from the optical spectra are compared with the experimental values where possible. The charge-transfer band overlapped too badly with bridge-centered absorption for the 16-bond bridged compound to allow the comparison to be made. The 13-bond bridged compound gave worse agreement than the other compounds. Its optical rate constant was about 5.4 times the ESR rate constant at a temperature between the ranges in which the data were collected.

Charge distribution in arylhydrazine-centered mixed valence compounds with smaller bridges (five to nine bonds between closest nitrogens).

Charge distribution in six aromatic-bridged, aryldialkylhydrazine-centered mixed valence radical cations is discussed through consideration of their optical spectra. The compounds considered have two 2-phenyl-2,3-diazabicyclo-[2.2.2]octane-3-yl (HyPh) charge-bearing units linked by a 1,4-phenylene bridge and its p-methoxyphenyl (HyAn) analogue, as well as the (HyPh)(2)-substituted 1,4-naphthalene, 2,6-naphthalene, 9,10-anthracene, and 4,4'-biphenyl compounds in methylene chloride and acetonitrile. Consideration of band shape and position leads us to assign the 1,4-phenylene- and 2,6-naphthalene-bridged compounds as charge-delocalized (class III) in both solvents, but the 1,4-naphthalene-bridged one lies closer to the borderline, and appears to be charge-localized (class II) in acetonitrile. The 4,4'-biphenyl-bridged compound is clearly class II in acetonitrile, and possibly also in methylene chloride. The lowest energy absorption band for the 9,10-anthracene-bridged compound is assigned as a bridge-to-HyPh band, and its charge distribution is not clear. Problems with the often-used relationship that the electronic coupling is half the transition energy for the lowest energy band of class III mixed valence compounds are discussed, as is interpretation of the vertical reorganization energy near the class II, class III borderline.

Interpretation of mixed-valence compound optical spectra near the class II/III border: dinitrobiphenyl and dinitrophenanthrene radical anions.

The optical spectra of 4,4'-dinitrobiphenyl and other similar 9-bond bridged radical anions show that these mixed-valence compounds are predominantly charge-localized in the high lambda(S) solvent MeCN, charge-delocalized in the low lambda(S) solvent HMPA, and show intermediate behavior in DMF. Hush analysis of the localized charge-transfer band in MeCN allowed the calculation of the electronic coupling between nitro groups (Hab). Hab changes with bridge structure, depending mainly on the twist angle between the two aromatic rings: Hab is higher for the planar 9,9-dimethyl-2,7-dinitrofluorene radical anion (1100 cm(-1)) and about one-half of this value for the more twisted 2,2'-dimethyl-4,4'-dinitrobiphenyl radical anion (540 cm(-1)). The reorganization energy lambda decreases as Hab increases. We suggest that this is due to a decrease of the internal reorganization energy lambda(v) as the Class II/Class III borderline is approached, and that lambda(v) should be zero at the borderline. Subtracting from the experimental spectra the fraction corresponding to the delocalized part (taken as the spectrum in HMPA or THF), we get localized charge-transfer bands that show a significant cutoff effect at the low energy side, as predicted by classical Marcus-Hush theory.

Alkylated trimethylene-bridged bis(p-phenylenediamines).

One and two electron oxidation of N,N',N'',N'''-tetramethyl-1,5,12,16-tetraaza[5,5]paracyclophane (Me3C), a bis-trimethylene bridged bis-p-phenylene diamine (PD), and its ethyl and isopropyl analogues are discussed. The monocation and dication are both stable, as demonstrated by optical studies that show they are in equilibrium in solution, with an especially small difference in first and second oxidation potentials for Me3C in MeCN (+23 to -20 mV, measured by simulation of the optical spectrum and of the cyclic voltammogram, respectively). The monocations have charge localized in one PD unit and show a Hush-type mixed valence transition between their PD0 and PD.+ groups. The dications Me3C2+ and Et3C2+ have optical spectra that appear to show large splittings between their PD.+ groups and have a weak ESR spectrum, and 1H NMR data show that the former is a ground-state singlet. iPr3C2+ has a very different optical spectrum and exhibits a triplet ESR spectrum at 120 K. X-ray crystal structures show that for Me3C0 the N(CH2)3N units on each side are in doubly anti (aa) conformations that put the aryl rings as far apart as possible, but Me3C2+ has doubly gg N(CH2)3N trimethylene bridges and both N,N and C,C distances between the PD.+ groups that are significantly below van der Walls contact. In contrast, iPr3C0 is in a doubly ag conformation, and its diradical dication is suggested to be a triplet because it does not attain the doubly gg conformation.

Mixed valence compounds as probes to determine the polarity of 1-butyl-3-methylimadazolium ionic liquids.

Radical cations and dications of three bishydrazines belonging to the Class II mixed valence compounds have been generated, either spontaneously or by oxidation with AgSbF6, in two 1-butyl-3-methylimidazolium (4+) ionic liquids having BF4(-) and PF6(-) as counterions. The optical spectra of these intermediates have allowed evaluation of Marcus' reorganization energy lambda(s), a parameter that is directly proportional to the solvent polarity. Remarkable differences in lambda(s), as large as 600 cm(-1), have been observed as a function of the counterion, with these data providing support for the observed differences between both ionic liquids (4(+)BF4(-) and 4(+)PF6(-)) in catalysis. However, in terms of polarity, the lambda(s) values rank the hydrophilic 4(+)BF4(-) as being similar to dimethyl sulfoxide and dimethylformamide, while the polarity of hydrophobic 4(+)PF6(-) is analogous to acetonitrile. Overall, our results indicate that ionic liquids are not exceptional liquids in terms of polarity.

Structure of gas phase radical cation of 1,3,6,8-tetraazatricyclo[4.4.1.1(3,8)] dodecane determined from zero kinetic energy photoelectron spectroscopy.

We report gas-phase vibrational spectroscopy of the ground-state cation of 1,3,6,8-tetraazatricyclo[4.4.1.1(3,8)]dodecane (TTD) using two-color two-photon zero kinetic energy photoelectron spectroscopy. From the distribution of active vibrational modes and comparisons between the experiment and theoretical simulation, we offer proof that the cationic state and the first electronically excited state have the same D(2d) symmetry.