X-Ray crystallographic and EPR spectroscopic characterization of a pyrrolidine adduct of Y3N@C80

Crystallographic data for the pyrrolidine adduct Y3N@C80C4H9N x 2.5CS2 reveals a slightly pyramidalized Y3N unit with idealized mirror symmetry that straddles the site of addition but does not directly interact with the addend.     

The developmental pattern of stimulus and response interference in a color-object Stroop task: an ERP study

Background

Several studies have shown that Stroop interference is stronger in children than in adults. However, in a standard Stroop paradigm, stimulus interference and response interference are confounded. The purpose of the present study was to determine whether interference at the stimulus level and the response level are subject to distinct maturational patterns across childhood. Three groups of children (6–7 year-olds, 8–9 year-olds, and 10–12 year-olds) and a group of adults performed a manual Color-Object Stroop designed to disentangle stimulus interference and response interference. This was accomplished by comparing three trial types. In congruent (C) trials there was no interference. In stimulus incongruent (SI) trials there was only stimulus interference. In response incongruent (RI) trials there was stimulus interference and response interference. Stimulus interference and response interference were measured by a comparison of SI with C, and RI with SI trials, respectively. Event-related potentials (ERPs) were measured to study the temporal dynamics of these processes of interference.

Results

There was no behavioral evidence for stimulus interference in any of the groups, but in 6–7 year-old children ERPs in the SI condition in comparison with the C condition showed an occipital P1-reduction (80–140 ms) and a widely distributed amplitude enhancement of a negative component followed by an amplitude reduction of a positive component (400–560 ms). For response interference, all groups showed a comparable reaction time (RT) delay, but children made more errors than adults. ERPs in the RI condition in comparison with the SI condition showed an amplitude reduction of a positive component over lateral parietal (-occipital) sites in 10–12 year-olds and adults (300–540 ms), and a widely distributed amplitude enhancement of a positive component in all age groups (680–960 ms). The size of the enhancement correlated positively with the RT response interference effect.

Conclusion

Although processes of stimulus interference control as measured with the color-object Stroop task seem to reach mature levels relatively early in childhood (6–7 years), development of response interference control appears to continue into late adolescence as 10–12 year-olds were still more susceptible to errors of response interference than adults.     

Colorless, non-luminescent; colorless, luminescent; and yellow, luminescent crystals of the cation [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](+). The roles of anions and hydrogen bonding in determining the aggregation of two-coordinate gold(I) cations

Crystallographic and luminescence studies on salts of the two-coordinate carbene cation, [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](+), demonstrate the ability of the cation to exist in three different states of aggregation. In colorless, non-luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]Cl the cation crystallizes as a monomer with the nearest gold(i) center 6.7890(11) A away. Colorless, luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]AsF(6) forms dimers with an AuAu separation of 3.1288(4) A. These dimers form weakly associated extended chains of cations with additional AuAu separations of 3.6625(5) A. [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]PF(6) is isostructural. Yellow, luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](3)(AsF(6))(2)Cl.0.5(H(2)O)(2) and [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](3)(PF(6))(2)Cl.0.5(H(2)O)(2) form trimers that further aggregate into extended chains with rather short AuAu separations of 3.1301(14) A, 3.1569(14) A and 3.1415(14) A. Absorption, emission and excitation spectra are reported for these salts. The excitation and emission results from the interactions between the gold centers and involves transitions between the filled d(z)((2)) band and the empty p(z) bands with the z axis pointing along the chain of cations.     

[U(bipy)4]: A Mistaken Case of U0?

After more than 50 years, the synthesis and electronic structure of the first and only reported “U⁰ complex” [U(bipy)₄] ( 1 ) has been reinvestigated. Additionally, its one‐electron reduced product [Na(THF)₆][U(bipy)₄] ( 2 ) has been newly discovered. High resolution crystallographic analyses combined with magnetic and computational data show that 1 and its derivative 2 are best described as highly reduced species containing mid‐to‐high‐valent uranium ligated by redox non‐innocent ligands.     

Boronic acid-based bipyridinium salts as tunable receptors for monosaccharides and alpha-hydroxycarboxylates

Several novel diboronic acid-substituted bipyridinium salts were prepared and, using a fluorescent reporter dye, were tested for their ability to selectively bind various monosaccharides and alpha-hydroxycarboxylates in an aqueous medium. The fluorescence sensing mechanism relies on the formation of a ground-state charge-transfer complex between the dye and bipyridinium. An X-ray crystal structure of this complex is described herein. Glucose selectivity over fructose and galactose was achieved by designing the bipyridinium-based receptors to be capable of attaining a 1:1 receptor/substrate stoichiometry via cooperative diboronic acid binding.     

A study of piperidinium structure-directing agents in the synthesis of silica molecular sieves under fluoride-based conditions

This study is a continuation of our efforts to understand the interplay in the self-assembly chemistry for formation of molecular sieves from guest organocations and inorganic silicon oxide. In this particular study we focus on the competitive interplay of the organocations and the synthesis cofactor fluoride anion. The anions play a key role in structure determination, as a function of net solution concentration. They compete with the role for the space-filling organocation in determining which molecular sieve host structure will be specified. In this study we look at this competition in the synthesis for a series of 33 different organocations derived from the piperidine ring system. Derivatives were prepared which both fixed substituents on the carbon and nitrogen centers on the ring. Results were discussed in terms of product selectivity from synthesis as a function of solution concentration for the reactants. A total of 17 different host topologies were found in this series, and a correlation was seen for (a) open-framework lattices (low framework densities) under the most concentrated reaction conditions and then (b) high framework density products once the conditions were more dilute. Some surprising synthesis differences are seen in comparing the performance of these structure directing agents (SDAs) in fluoride media vs hydroxide media (the more conventional environment for zeolite/molecular sieve syntheses involving silicate chemistry). Finally molecular modeling was used to understand some of the trends in product selectivity for closely related guest (SDA) candidates.     

Synthesis and structural characterization of cross-linked histidine-phenol Cu(ii) complexes as cytochrome c oxidase active site models

Tridentate cross-linked histidine-phenol Cu(ii) ether and ester complexes, chemical analogs of the active site of several heme-copper oxidases, have been synthesized and crystallized.