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Full-Text Articles in Chemistry
Excited-State Equilibration Over 30 Angstrom In A Platinum(Ii) Quinolinolate-Bridge-Platinum(Ii) Porphyrin Complex, Victor A. Montes, Michael A. J. Rodgers, Pavel Anzenbacher Jr.
Excited-State Equilibration Over 30 Angstrom In A Platinum(Ii) Quinolinolate-Bridge-Platinum(Ii) Porphyrin Complex, Victor A. Montes, Michael A. J. Rodgers, Pavel Anzenbacher Jr.
Chemistry Faculty Publications
Long-range triplet excited-state equilibration occurs over a nanometric distance between platinum(II) 8-quinolinolate ((3)Ptq(2) = 1.87 eV) and platinum(II) tetraphenylporphyrin ((PtTPP)-Pt-3 = 1.89 eV). The equilibrium is mediated by a fluorene-thiophene-fluorene bridge ((FTF)-F-3 = 1.92 eV) and is characterized by a double-exponential decay (tau(1) = 39 +/- 4 ps; tau(2) = 351 +/- 15 ps) that suggests the participation of three separate excited states : (3)Ptq(2), (FTF)-F-3, and 3PtTPP, respectively. Numerical simulation of the dual equilibrium allowed for estimation of the individual rate constants for each of the reversible steps (k(ET) = 3.9 x 10(9)-4.1 x 10(10) s(-1)). As a result …
Formation Of Peptide Nanospheres And Nanofibrils By Metal Coordination, Mikhail V. Tsurkan, Michael Y. Ogawa
Formation Of Peptide Nanospheres And Nanofibrils By Metal Coordination, Mikhail V. Tsurkan, Michael Y. Ogawa
Chemistry Faculty Publications
Two amphipathic polypeptides were coordinated to the cis positions of a square planar Pt(II) complex in order to provide the metal center with two noncovalent oligomerization domains. This resulted in the formation of new metal-peptide nanoassemblies which are shown to exist as nanometer-sized spheres and fibrils. Construction of these assemblies was based on the 30-residue polypeptide AQ-Pal14 which was designed for its ability to self-assemble into the common protein oligomerization motif of a noncovalent coiled-coil, and modified to contain a metal-binding 4-pyridylalanine residue at its surface. When AQ-Pal14 was reacted with Pt(en)(NO3)(2), a new metal-peptide complex was formed in which …
Reactivity Of Iso-Diiodomethane And Iso-Iodoform, Isomers Of Ch2i2 And Chi3, Toward The Double Bond Of A Variety Of Cycloalkenes, Alexander N. Tarnovsky, Irmin Pascher, Torbjorn Pascher
Reactivity Of Iso-Diiodomethane And Iso-Iodoform, Isomers Of Ch2i2 And Chi3, Toward The Double Bond Of A Variety Of Cycloalkenes, Alexander N. Tarnovsky, Irmin Pascher, Torbjorn Pascher
Chemistry Faculty Publications
The metastable CH2I-I and CHI2-I isomers formed by UV photolysis of CH2I2, and CHI3 transfer methylene and iodomethylene groups, respectively, to a variety of cycloalkenes, leading to their cyclopropanation. More than a 100-fold increase of the reaction rate with increasing solvent polarity suggests a dipolar transition state. The fastest second-order rates observed were in CH3CN. However, CH2Cl2 will be the more appropriate reaction medium because the isomer thermal stability is greater in CH2Cl2 than in the more polar CH3CN.
Luminescent Charge-Transfer Platinum(Ii) Metallacycle, Fei Hua, Solen Kinayyigit, Aaron A. Rachford, Elena A. Shikhova, Sebastien Goeb, John R. Cable, Christopher J. Adams, Kristin Kirschbaum, A. Alan Pinkerton, Felix N. Castellano
Luminescent Charge-Transfer Platinum(Ii) Metallacycle, Fei Hua, Solen Kinayyigit, Aaron A. Rachford, Elena A. Shikhova, Sebastien Goeb, John R. Cable, Christopher J. Adams, Kristin Kirschbaum, A. Alan Pinkerton, Felix N. Castellano
Chemistry Faculty Publications
The photophysical and electrochemical properties of a platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2'-diacetylide (tda), Pt(dbbpy)(tda) [dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine] (1), are compared with two reference compounds, Pt(dbbpy)(C CPh)(2) (2) and Pt(dppp)tda [dppp = 1,3-bis(diphenylphosphino)propane] (3), respectively, The X-ray crystal structure of 1 is reported, which illustrates the nearly perfect square planarity exhibited by this metallacycle. Chromophore 2 possesses low-lying charge-transfer excited states analogous to 1, whereas structure 3 lacks such excited states but features a low-lying platinum-perturbed tda intraligand triplet manifold. In CH2Cl2, 1 exhibits a broad emission centered at 562 nm at ambient temperature, similar to 2, …
Ultrafast Dynamics Of Triplet Excitons In Alq(3)-Bridge-Pt(Ii)Porphyrin Electroluminescent Materials, Victor A. Montes, Cesar Perez-Bolivar, Leandro A. Estrada, Joseph Shinar, Pavel Anzenbacher Jr.
Ultrafast Dynamics Of Triplet Excitons In Alq(3)-Bridge-Pt(Ii)Porphyrin Electroluminescent Materials, Victor A. Montes, Cesar Perez-Bolivar, Leandro A. Estrada, Joseph Shinar, Pavel Anzenbacher Jr.
Chemistry Faculty Publications
Excited-state dynamics are crucial for maximizing the performance of organic light-emitting diodes (OLEDs). Because electron-hole recombination yields singlet and triplet excited states in a 3:1 ratio, it is important to harvest the energy of triplets in light-emitting processes. Self-assembled multichromophore electroluminescent materials consisting of a trisquinolinolate aluminum(III) (Alq(3)) donor, fluorene-based conjugated oligomers; as a bridge, and Pt(II)tetraphenylporphyrin as an acceptor and phosphorescent emitter are described. In these materials, the energy of singlet as well as triplet states is harvested and emitted as red phosphorescence from the porphyrin acceptor. Attention was devoted to the triplet exciton dynamics, which was investigated by …
Metal-Mediated Peptide Assembly: Use Of Metal Coordination To Change The Oligornerization State Of An Alpha-Helical Coiled-Coil, Mikhail V. Tsurkan, Michael Y. Ogawa
Metal-Mediated Peptide Assembly: Use Of Metal Coordination To Change The Oligornerization State Of An Alpha-Helical Coiled-Coil, Mikhail V. Tsurkan, Michael Y. Ogawa
Chemistry Faculty Publications
Metal coordination is used to alter the oligomerization state of a designed peptide structure. The 30-residue polypeptide AQ-Pal21 4Pal21 contains two metal-binding 4-pyridylalanine (Pal) residues on its solvent-exposed surface and exists as a very stable two-stranded a-helical coiled-coil. Upon the addition of Pt(en)(NO3)(2), a significant conformational change to a metal-bridged, four-helix bundle is seen.
Fluctuating Two-State Light Harvesting In A Photosynthetic Membrane, Duohai Pan, Dehong Hu, Ruchuan Liu, Xiaohua Zeng, Samuel Kaplan, H. Peter Lu
Fluctuating Two-State Light Harvesting In A Photosynthetic Membrane, Duohai Pan, Dehong Hu, Ruchuan Liu, Xiaohua Zeng, Samuel Kaplan, H. Peter Lu
Chemistry Faculty Publications
The mechanism by which light is converted into chemical energy in a natural photosynthetic system has drawn considerable research interest. Using fluorescence spectroscopy and microscopic imaging, we have observed fluctuating intermolecular protein fluorescence resonant energy transfers (FRET) among light-harvesting proteins I and II (LH1 and LH2) in bacterial photosynthetic membranes. Using two-channel, FRET, photon-counting detection and a novel, two-dimensional cross-correlation function amplitude-mapping analysis, we revealed fluorescence intensity and spectral fluctuations of donor (LH2) and acceptor (LH1) fluorescence involving FRET. Our results suggest that there are dynamic coupled and noncoupled states of the light-harvesting protein assemblies in photosynthetic membranes. The light-harvesting …
Supramolecular Chemistry Approach To The Design Of A High-Resolution Sensor Array For Multianion Detection In Water, Manuel A. Palacios, Ryuhei Nishiyabu, Manuel Marquez, Pavel Anzenbacher Jr.
Supramolecular Chemistry Approach To The Design Of A High-Resolution Sensor Array For Multianion Detection In Water, Manuel A. Palacios, Ryuhei Nishiyabu, Manuel Marquez, Pavel Anzenbacher Jr.
Chemistry Faculty Publications
Reliable sensing of structurally similar anions in water is a difficult problem, and analytical tests and sensor devices for reliable sensing of multiple anions are very rare. This study describes a method for fabrication of simple colorimetric array-based assays for aqueous anion solutions, including complex analytes encountered in real-life applications. On the fundamental level, this method shows how the discriminatory capacity of sensor arrays utilizing pattern recognition operating in multianalyte environments may be dramatically improved by employing two key features. The synergy between the sensor and hydrogel host resembles the cooperative effects of an apoenzyme and cofactor: the host hydrogel …
Triplet Energy Studies Of Thiophene And Para-Phenylene Based Oligomers, Leandro A. Estrada, Victor A. Montes, Grigory Zyryanov, Pavel Anzenbacher Jr.
Triplet Energy Studies Of Thiophene And Para-Phenylene Based Oligomers, Leandro A. Estrada, Victor A. Montes, Grigory Zyryanov, Pavel Anzenbacher Jr.
Chemistry Faculty Publications
A series of conjugated materials based on oligomers of the para-phenylene type and oligothiophenes was prepared, and their phosphorescence spectra were recorded at 77 K using a pulsed flash-lamp as a light source and gated detection. The triplet energies of the oligomers were estimated and correlated with their chemical structure. It was found that simple changes in the building block sequence in the thiophene-containing oligomers allowed for tuning the triplet energy from 1.86 to 2.35 eV (530-670 nm). Hypsochromic shifts and little variation of the triplet energy were obtained with increasing length of the pi-system for thiophene end-capped oligomers, contrary …
Watching Ultrafast Barrierless Excited-State Isomerization Of Pseudocyanine In Real Time, Benjamin Dietzek, Arkady Yartsev, Alexander N. Tarnovsky
Watching Ultrafast Barrierless Excited-State Isomerization Of Pseudocyanine In Real Time, Benjamin Dietzek, Arkady Yartsev, Alexander N. Tarnovsky
Chemistry Faculty Publications
The photoinduced excited-state processes in 1,1'-diethyl-2,2'-cyanine iodine are investigated using femtosecond time-resolved pump-probe spectroscopy. Using a broad range of probe wavelengths, the relaxation of the initially prepared excited-state wavepacket can be followed down to the sink region. The data directly visualize the directed downhill motion along the torsional reaction coordinate and suggest a barrierless excited-state isomerization in the short chain cyanine dye. Additionally, ultrafast ground-state hole and excited-state hole replica broadening is observed. While the narrow excited-state wavepacket broadens during pump-probe overlap, the ground-state hole burning dynamics takes place on a significantly longer time-scale. The experiment reported can be considered …
The Role Of The Intersection Space In The Photochemistry Of Tricyclo[3.3.0.0(2,6)]Octa-3,7-Diene, Luis Manuel Frutos, Unai Sancho, Marco Garavelli, Massimo Olivucci, Obis Castano
The Role Of The Intersection Space In The Photochemistry Of Tricyclo[3.3.0.0(2,6)]Octa-3,7-Diene, Luis Manuel Frutos, Unai Sancho, Marco Garavelli, Massimo Olivucci, Obis Castano
Chemistry Faculty Publications
CASSCF and CASPT2 methods were used to study the photochemistry of tricyclo[3.3.0.0(2,6)]octa-3,7-diene (TOD). The analysis of different S-1 reaction paths as well as the topology of the S-1/S-0 intersection space allows us to establish two novel properties associated with the photochemical behavior of this compound: (i) simple low-lying intersection space domains can mediate different photoproducts, and (ii) TOD photochemistry is probably mediated by two disconnected intersection space domains, related to the formation of cyclooctatetraene and semibulvalene in different time-scales. It is shown that these domains are chemically distinct since the first, leading to COT, mediates barrierless pericyclic reactions while the …
Exploring The Mechanism Of Flexible Biomolecular Recognition With Single Molecule Dynamics, H. Peter Lu, Qiang Lu, Jin Wang
Exploring The Mechanism Of Flexible Biomolecular Recognition With Single Molecule Dynamics, H. Peter Lu, Qiang Lu, Jin Wang
Chemistry Faculty Publications
Combining a single-molecule study of protein binding with a coarse grained molecular dynamics model including solvent (water molecules) effects, we find that biomolecular recognition is determined by flexibilities in addition to structures. Our single-molecule study shows that binding of CBD (a fragment of Wiskott-Aldrich syndrome protein) to Cdc42 involves bound and loosely bound states, which can be quantitatively explained in our model as a result of binding with large conformational changes. Our model identified certain key residues for binding consistent with mutational experiments. Our study reveals the role of flexibility and a new scenario of dimeric binding between the monomers: …