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A research on the ways by which copper phenanthroline bind to beta-form DNA involved the varying of the composition of the DNA, and the use of poly (dG-dC).poly (dG-dC), M. lysodeikticus DNA, salmon testes DNA and poly (dA-dT).poly (dA-dT) as hosts. The dmp complex bound externally in a solvent accessible site was discovered. The presence of DNA causes Cu(bcp)2+ to be emissive. Hence, the metal center is accessible to the solvent.

13C NMR coupled relaxation techniques were used to measure the relaxation of different magnetization modes in the synthesized isotopic decanols 13C labeled at 1, 5 and 9 positons. Comparison of the correlation times for the 13CH2 group at varying positions and solvents revealed that the formation of a hydrogen bond between 1-decanol and the solvents influences the movement of neighboring chain segments. Stochastic dynamic studies support the use of ordinary Langevin equations for the description of the solute relaxationwithout relaxation modes with the ability to bind with the solute chain.

We have investigated the gas-phase production of isoquinoline by performing collisional activation on benzalaminoacetal, the first intermediate in the classic solution-phase Pomeranz--Fritsch synthesis of isoquinoline. We have elucidated the reaction pathways in the gas phase using tandem mass spectrometry. Unlike the corresponding condensed-phase reaction, where catalytic proton exchange between intermediate(s) and solvent (Brønsted--Lowry base) is known to drive the reaction, the gas-phase reaction follows the "mobile proton model" to form the products via a number of intermediates, some the same as in their condensed-phase counterparts. Energy-resolved mass spectrometry, deuterium labeling experiments, and theoretical calculations (B3LYP/6-31G**) identified 27 different reaction routes in the gas phase, forming a complex interlinked reaction network. The experimental measurements and theoretical calculations confirm the proton hopping onto different basic sites of the precursors and intermediates to transform them ultimately into isoquinoline. [ABSTRACT FROM AUTHOR]

Nature synthesizes many strained natural products that have diverse biological activities. Uncovering these biosynthetic pathways may lead to biomimetic strategies for organic synthesis of such compounds. In this work, we elucidated the concise biosynthetic pathway of herquline A, a highly strained and reduced fungal piperazine alkaloid. The pathway builds on a nonribosomal peptide synthetase derived dityrosine piperazine intermediate. Following enzymatic reduction of the P450-cross-linked dicyclohexadienone, N-methylation of the piperazine serves as a trigger that leads to a cascade of stereoselective and nonenzymatic transformations. Computational analysis of key steps in the pathway rationalizes the observed reactivities. [ABSTRACT FROM AUTHOR]

The Diels-Alder reactions of seven 1,2,4,5-tetrazines with unstrained and strained alkenes and alkynes were studied with quantum mechanical calculations (M06-2X density functional theory) and analyzed with the distortion/interaction model. The higher reactivities of alkenes compared to alkynes in the Diels-Alder reactions with tetrazines arise from the differences in both interaction and distortion energies. Alkenes have HOMO energies higher than those of alkynes and therefore stronger interaction energies in inverse-electron-demand Diels-Alder reactions with tetrazines. We have also found that the energies to distort alkenes into the Diels-Alder transition-state geometries are smaller than for alkynes in these reactions. The strained dienophiles, trans-cyclooctene and cyclooctyne, are much more reactive than unstrained trans-2-butene and 2-butyne, because they are predistorted toward the Diels-Alder transition structures. The reactivities of substituted tetrazines correlate with the electron-withdrawing abilities of the substituents. Electron-withdrawing groups lower the LUMO+1 of tetrazines, resulting in stronger interactions with the HOMO of dienophiles. Moreover, electron-withdrawing substituents destabilize the tetrazines, and this leads to smaller distortion energies in the Diels-Alder transition states. [ABSTRACT FROM AUTHOR]

The Diels-Alder reactions of the cycloalkenes, cyclohexene through cyclopropene, with a series of dienes?1,3-dimethoxybutadiene, cyclopentadiene, 3,6-dimethyltetrazine, and 3,6-bis(trifluoromethyl)- tetrazine?were studied with quantum mechanical calculations and compared with experimental values when available. The reactivities of cycloalkenes as dienophiles were found by a distortion/interaction analysis to be distortion controlled. The energies required for cycloalkenes to be distorted into the Diels-Alder transition states increase as the ring size of cycloalkenes increases from cyclopropene to cyclohexene, resulting in an increase in activation barriers. The reactivities of the dienes are controlled by both distortion and interaction energies. In normal Diels-Alder reactions with cycloalkenes, the electron-rich 1,3-dimethoxybutadiene exhibits stronger interaction energies than cyclopentadiene, but the high distortion energies required for 1,3-dimethoxybutadiene to achieve transition-state geometries overtake the favorable interaction, resulting in higher activation barriers. In inverse-electrondemand Diels-Alder reactions of 3,6-dimethyltetrazine and 3,6-bis(trifluoromethyl)tetrazine, the reactivities are mainly controlled by interaction energies. [ABSTRACT FROM AUTHOR]

Ozonolysis of alkenes in the troposphere produces Criegee intermediates, which have eluded detection in the gas phase until very recently. This laboratory has synthesized the simplest Criegee intermediate within a quartz capillary tube affixed to a pulsed valve to cool and isolate CH2OO in a supersonic expansion. UV excitation resonant with the B 1A' 2 X 1A' transition depletes the ground-state population of CH2OO, which is detected by single-photon ionization at 118 nm. The large UV-induced depletion (approaching 100%) near the peak of the profile at 335 nm is indicative of rapid dissociation, consistent with the repulsive B 1A' potential along the O-O coordinate computed theoretically. The experimental spectrum is in very good accord with the absorption spectrum calculated using the one-dimensional reflection principle. The B ← X spectrum is combined with the solar actinic flux to estimate an atmospheric lifetime for CH2OO at midday on the order of 1 s with respect to photodissociation. [ABSTRACT FROM AUTHOR]

Examines photochemical reactivity in a self-assembled monolayer on a colloidal gold cluster. Characterization of surface-modified nanoparticles; Effect of surface-bound reagents on structure-property relationships; Wavelength selectivity of photoisomerization and photocleavage.