16 research outputs found
The Portrayal of Indonesian Image in 2007 Kompas Selected Short Stories: Social Problems, Criticisms and Hopes
Article aimed at exploring social problems reflected in 15 selected short stories printed in Kompas during 2007 both explicitly and implicitly. Specifically, this research is focused on the mapping of dominant social problems raised by the short stories, the social criticisms strongly voiced by the authors and the hopes of a better situation implicitly reflected in these interesting short stories. This study applies the Defamiliarization Effect promoted by Bertolt Brecht and Negative Dialectics or Negative Knowledge by Theodor Adorno, specifically in analyzing the literary works as a criticism tool. The result of the research shows that phenomena of social problems current lately in Indonesian context like identity, poverty, corruption, religious tensions, moral degradation, politics dirtiness, minority group problems, social security, natural disasters and the like are clearly seen and teased in these writings
Substituent Effects at the β‑Positions of the Nonfused Pyrroles in a Quadruply Fused Porphyrin on the Structure and Optical and Electrochemical Properties
We
have synthesized <b>2</b>, a derivative of zincÂ(II) quadruply
fused porphyrinato (Zn<sup>II</sup>QFP) that is tetrabrominated at
the β-positions of the two nonfused pyrroles, by treatment of
Zn<sup>II</sup>QFP with <i>N</i>-bromosuccinimide. X-ray
diffraction analysis of a single crystal obtained from a THF solution
of <b>2</b> by vapor diffusion of ethanol (EtOH) revealed that <b>2</b> formed an unprecedented dimeric structure, (<b>2</b>)<sub>2</sub>-L (L = EtOH), in which one of the brominated QFP ligands
acts as a bridging ligand in an unprecedented μ-η<sup>3</sup>:η<sup>1</sup> coordination mode. In the dimeric structure,
the two QFP ligands showed a unique η<sup>3</sup> coordination
mode for both Zn<sup>II</sup> centers. In (<b>2</b>)<sub>2</sub>-EtOH, one of the pyrrolic nitrogen atoms of the two nonfused pyrroles
dissociates from the Zn<sup>II</sup> center, and the dissociated pyrrolic
nitrogen atom coordinates to the Zn<sup>II</sup> center of the other
molecule in the dimer. The Zn<sup>II</sup> center having the μ-η<sup>3</sup>:η<sup>1</sup>-QFP ligand is coordinated by an EtOH
molecule, and the other Zn<sup>II</sup> center is coordinated by the
η<sup>3</sup>-QFP ligand and one nitrogen atom of the bridging
QFP ligand. The dimeric structure is stable and maintained even in
a solution of noncoordinating solvents such as dichloromethane. The
bromo groups of <b>2</b> can be substituted with phenyl groups
under Suzuki coupling conditions to afford the tetraphenyl derivative, <b>3</b>. Furthermore, the effects of the substituents at the β-positions
on the optical and electrochemical properties and Lewis acidity of
the Zn<sup>II</sup> centers have been investigated. The redox potentials
were positively shifted by introduction of electron-withdrawing groups
at the β-positions, and the shift widths exhibited a linear
correlation to the Hammett parameters of the substituents
Heteronuclear Ru<sup>II</sup>Ag<sup>I</sup> Complexes Having a Pyrroloquinolinequinone Derivative as a Bridging Ligand
Herein, we report the synthesis of
a novel heterohexanuclear complex (<b>1</b>) of a heteroaromatic
cofactor, pyrroloquinolinequinone (PQQ). The crystal structure of <b>1</b> was determined to reveal that two PQQ-bridged Ru<sup>II</sup>Ag<sup>I</sup> units were linked by two [Ag<sup>I</sup>(OTf)<sub>2</sub>]<sup>−</sup> units (OTf = CF<sub>3</sub>SO<sub>3</sub><sup>–</sup>). A solvent-bound Ru<sup>II</sup>Ag<sup>I</sup> heterodinuclear complex (<b>2</b>) was formed from <b>1</b> in a coordinating solvent such as acetone to show an intense metal-to-ligand
charge-transfer band at 709 nm
Acid–Base Properties of a Freebase Form of a Quadruply Ring-Fused PorphyrinStepwise Protonation Induced by Rigid Ring-Fused Structure
We report herein
unique stepwise protonation at inner imino-nitrogen
atoms of a freebase derivative of a quadruply fused porphyrin (H<sub>2</sub>QFP), which has been newly synthesized. H<sub>2</sub>QFP has
been revealed to have the two inner NH protons on the two nonfused
pyrroles by X-ray diffraction analysis and <sup>1</sup>H NMR spectroscopy.
The first protonation at one of the two imino-nitrogen atoms of the
fused pyrroles smoothly proceeds with trifluoroacetic acid (TFA) in
CH<sub>2</sub>Cl<sub>2</sub> and the equilibrium constant (<i>K</i><sub>1</sub>) of the protonation has been determined to
be (1.3 ± 0.1) × 10<sup>5</sup> M<sup>–1</sup>. In
contrast, the second protonation at the other imino-nitrogen atom
is hard to occur unless a large excess amount of TFA is used, as reflected
on a much smaller equilibrium constant, <i>K</i><sub>2</sub> = 7.3 ± 0.3 M<sup>–1</sup>. The stepwise protonation
is ascribed to the structural rigidity caused by the ring fusion and
the resultant steric repulsion among inner NH atoms of the diprotonated
form. Electrochemical studies have revealed that protonation at the
pyrrole nitrogen atoms caused positive shifts of the reduction potentials
of the QFP derivatives. In addition, the ESR spectrum of the electrochemically
one-electron-reduced monoprotonated QFP derivative showed well-resolved
hyperfine splitting to represent its unsymmetrical electronic structure
due to the monoprotonation
Heteronuclear Ru<sup>II</sup>Ag<sup>I</sup> Complexes Having a Pyrroloquinolinequinone Derivative as a Bridging Ligand
Herein, we report the synthesis of
a novel heterohexanuclear complex (<b>1</b>) of a heteroaromatic
cofactor, pyrroloquinolinequinone (PQQ). The crystal structure of <b>1</b> was determined to reveal that two PQQ-bridged Ru<sup>II</sup>Ag<sup>I</sup> units were linked by two [Ag<sup>I</sup>(OTf)<sub>2</sub>]<sup>−</sup> units (OTf = CF<sub>3</sub>SO<sub>3</sub><sup>–</sup>). A solvent-bound Ru<sup>II</sup>Ag<sup>I</sup> heterodinuclear complex (<b>2</b>) was formed from <b>1</b> in a coordinating solvent such as acetone to show an intense metal-to-ligand
charge-transfer band at 709 nm
Mechanistic Insights into C–H Oxidations by Ruthenium(III)-Pterin Complexes: Impact of Basicity of the Pterin Ligand and Electron Acceptability of the Metal Center on the Transition States
A rutheniumÂ(II) complex,
[RuÂ(dmdmp)ÂClÂ(MeBPA)] (<b>2</b>)
(Hdmdmp = <i>N</i>,<i>N</i>-dimethyl-6,7-dimethylpterin,
MeBPA = <i>N</i>-methyl-<i>N</i>,<i>N</i>-bisÂ(pyridylmethyl)Âamine), having a pterin derivative as a proton-accepting
ligand, was synthesized and characterized. Complex <b>2</b> shows
higher basicity than that of a previously reported Ru<sup>II</sup>-pterin complex, [RuÂ(dmdmp) (TPA)]<sup>+</sup> (<b>1</b>) (TPA
= trisÂ(2-pyridylmethyl)Âamine). On the other hand, 1e<sup>–</sup>-oxidized species of <b>1</b> (<b>1</b><sub>OX</sub>)
exhibits higher electron-acceptability than that of 1e<sup>–</sup>-oxidized <b>2</b> (<b>2</b><sub>OX</sub>). Bond dissociation
enthalpies (BDE) of the two Ru<sup>II</sup> complexes having Hdmdmp
as a ligand in proton-coupled electron transfer (PCET) to generate <b>1</b><sub>OX</sub> and <b>2</b><sub>OX</sub> were calculated
to be 85 kcal mol<sup>–1</sup> for <b>1</b><sub>OX</sub> and 78 kcal mol<sup>–1</sup> for <b>2</b><sub>OX</sub>. The BDE values are large enough to perform H atom transfer from
C–H bonds of organic molecules to the 1e<sup>–</sup>-oxidized complexes through PCET. The second-order rate constants
(<i>k</i>) of PCET oxidation reactions were determined for <b>1</b><sub>OX</sub> and <b>2</b><sub>OX</sub>. The logarithms
of normalized <i>k</i> values were proportional to the BDE
values of C–H bonds of the substrates with slopes of −0.27
for <b>1</b><sub>OX</sub> and −0.44 for <b>2</b><sub>OX</sub>. The difference between <b>1</b><sub>OX</sub> and <b>2</b><sub>OX</sub> in the slopes suggests that the
transition states in PCET oxidations of substrates by the two complexes
bear different polarization, as reflection of difference in the electron
acceptability and basicity of <b>1</b><sub>OX</sub> and <b>2</b><sub>OX</sub>. The more basic <b>2</b><sub>OX</sub> attracts a proton from a C–H bond via a more polarized transition
state than that of <b>1</b><sub>OX</sub>; on the contrary, the
more electron-deficient <b>1</b><sub>OX</sub> forms less polarized
transition states in PCET oxidation reactions of C–H bonds
Redox-Noninnocent Behavior of Tris(2-pyridylmethyl)amine Bound to a Lewis Acidic Rh(III) Ion Induced by C–H Deprotonation
RhÂ(III)
complexes having trisÂ(2-pyridylmethyl)Âamine (TPA) and its derivative
as tetradentate ligands showed reversible deprotonation at a methylene
moiety of the TPA ligands upon addition of a strong base as confirmed
by spectroscopic measurements and X-ray crystallography. Deprotonation
selectively occurred at the axial methylene moiety rather than equatorial
counterparts because of the thermodynamic stability of corresponding
deprotonated complexes. One-electron oxidation of the deprotonated
RhÂ(III)–TPA complex afforded a unique TPA radical bound to
the RhÂ(III) center by a ligand-centered oxidation. This is the first
example to demonstrate emergence of the redox-noninnocent character
of the TPA ligand
Tetranuclear Ruthenium(II) Complex with a Dinucleating Ligand Forming Multi-Mixed-Valence States
A square-shaped
tetranuclear rutheniumÂ(II) complex, [Ru<sup>II</sup><sub>4</sub>Cl<sub>5</sub>(bpmpm)<sub>2</sub>]<sup>3+</sup> [<b>1</b>; bpmpm =
4,6-bisÂ[[<i>N</i>,<i>N</i>-bisÂ(2′-pyridylmethyl)Âamino]Âmethyl]Âpyrimidine],
exhibited four reversible and stepwise one-electron-oxidation processes:
chemical oxidation of <b>1</b> formed three different mixed-valence
states, in one of which the charge is partially delocalized on the
two Ru centers, to be evidenced by observation of an intervalence
charge-transfer absorption band, categorized into the Robin–Day
class II