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161.
Albrecht M Wessel C de Groot M Rissanen K Lüchow A 《Journal of the American Chemical Society》2008,130(14):4600-4601
A series of pentafluorophenyl substituted ammonium, iminium, amidinium, and phosphonium halides are presented which show extensive anion-pi interactions. Hereby, the well-known anion-donor-pi-acceptor as well as "eta6" anion-pi-complex type interactions are observed. The latter is supported by fixation of the anion on top of the aromatic system through hydrogen bonding. This arrangement was investigated by theoretical methods showing a highly attractive anion-pi interaction. In addition an eta2-type coordination of the anions to only two C-atoms of the electron-deficient ring system is described. 相似文献
162.
Pederson K Meints GA Shajani Z Miller PA Drobny GP 《Journal of the American Chemical Society》2008,130(28):9072-9079
The dynamics of the phosphodiester backbone in the [5'-GCGC-3'] 2 moiety of the DNA oligomer [d(G 1A 2T 3A 4 G 5 C 6 G 7 C 8T 9A 10T 11C 12)] 2 are studied using deuterium solid-state NMR (SSNMR). SSNMR spectra obtained from DNAs nonstereospecifically deuterated on the 5' methylene group of nucleotides within the [5'-GCGC-3'] 2 moiety indicated that all of these positions are structurally flexible. Previous work has shown that methylation reduces the amplitude of motion in the phosphodiester backbone and furanose ring of the same DNA, and our observations indicate that methylation perturbs backbone dynamics through not only a loss of mobility but also a change of direction of motion. These NMR data indicate that the [5'-GCGC-3'] 2 moiety is dynamic, with the largest amplitude motions occurring nearest the methylation site. The change of orientation of this moiety in DNA upon methylation may make the molecule less amenable to binding to the HhaI endonuclease. 相似文献
163.
Raatikainen K Huuskonen J Kolehmainen E Rissanen K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(11):3297-3305
Reaction of piperazine and 1,3-bis(bromomethyl)-2-nitrobenzene under high-dilution conditions yields cyclic trimeric trinitro, tetrameric tetranitro, and pentameric pentanitro piperazine cyclophanes. Reduction of the nitro groups with SnCl(2) under acidic conditions produces the corresponding triamino and tetraamino piperazine cyclophanes. The solution studies of both nitro and amino piperazine cyclophanes at 30 degrees C by (1)H NMR spectroscopy shows symmetrical structures owing to the fast conformational exchange, whereas the low temperature studies of the tetraamino piperazine cyclophane reveals interesting dynamic behavior that indicates additional intramolecular interactions. Careful crystallizations of the trimeric trinitro and triamino and the tetrameric tetraamino cyclophanes resulted in crystals suitable for X-ray diffraction studies. In the crystalline state the amino-functionalized cyclophanes manifest an extraordinary circular intramolecular hydrogen-bonding network that leads to a fixed 3D structure. Hydrogen bonding in the triamino trimer leads to orientation of all three of the amino groups on the same side of the macrocycle, namely, the rcc conformation, whereas the tetraamino tetramer folds into a more compact shell-like conformation. During the crystallization process one acetonitrile guest is enclosed into the cavity of the tetraamino cyclophane, which gives a crystalline inclusion complex with remarkable resemblance to the famous Pacman motif. The folding, which mimics the behavior of some cyclic peptides and pyrroles, is induced by intramolecular hydrogen bonding from the amino groups to the tertiary amine groups of the piperazines. The cavity of the tetraamino tetramer is markedly smaller than in the corresponding, but nonfolded, tetranitro tetramer and the guest/host volume ratio (packing coefficient) for the acetonitrile and the cavity is approximately 50 %, which indicates a good size match for acetonitrile inclusion. 相似文献
164.
Density functional studies of the hydrolysis of aluminum (chloro)hydroxide in water with CPMD and COSMO 总被引:1,自引:0,他引:1
Car-Parrinello molecular dynamics (CPMD) and the static density functional method (DFT) with a conductor-like screening model (COSMO) were used to investigate the chemistry of aluminum (chloro)hydroxide in water. With these methods, the stability, reactivity, and acidic nature of the chosen chlorohydrate were able to be determined. Constrained molecular dynamics simulations were used to investigate the binding of chlorine in an aquatic environment. According to the results, aluminum preferred to be 5-fold-coordinated. In addition, the activation energy barriers for the dissociation of chlorine atoms from the original chlorohydrate structure were able to be determined. The actual values for the barriers were 14 +/- 3 and 40 +/- 5 kJ mol (-1). The results also revealed the acidity of the original cationic dimer. DFT with COSMO was used to determine free energy differences for the reactions detected in the molecular dynamic simulations. In conclusion, new results and insight into the aquatic chemistry of the aluminum (chloro)hydroxides are provided. 相似文献
165.
166.
Copeland KL Anderson JA Farley AR Cox JR Tschumper GS 《The journal of physical chemistry. B》2008,112(45):14291-14295
To examine the effects of pi-stacking interactions between aromatic amino acid side chains and adenine bearing ligands in crystalline protein structures, 26 toluene/(N9-methyl)adenine model configurations have been constructed from protein/ligand crystal structures. Full geometry optimizations with the MP2 method cause the 26 crystal structures to collapse to six unique structures. The complete basis set (CBS) limit of the CCSD(T) interaction energies has been determined for all 32 structures by combining explicitly correlated MP2-R12 computations with a correction for higher-order correlation effects from CCSD(T) calculations. The CCSD(T) CBS limit interaction energies of the 26 crystal structures range from -3.19 to -6.77 kcal mol (-1) and average -5.01 kcal mol (-1). The CCSD(T) CBS limit interaction energies of the optimized complexes increase by roughly 1.5 kcal mol (-1) on average to -6.54 kcal mol (-1) (ranging from -5.93 to -7.05 kcal mol (-1)). Corrections for higher-order correlation effects are extremely important for both sets of structures and are responsible for the modest increase in the interaction energy after optimization. The MP2 method overbinds the crystal structures by 2.31 kcal mol (-1) on average compared to 4.50 kcal mol (-1) for the optimized structures. 相似文献
167.
Pappenfus TM Hermanson BJ Helland TJ Lee GG Drew SM Mann KR McGee KA Rasmussen SC 《Organic letters》2008,10(8):1553-1556
Direct addition of tetracyanoethylene to N-(p-hexylphenyl)dithieno[3,2-b:2',3'-d]pyrrole yields not only the aromatic mono- and bis-tricyanovinyl-substituted products but also a quinoidal product with dicyanomethylene groups. The analogous reaction with dithieno[3,2-b:2',3'-d]thiophene yields exclusively the aromatic mono-tricyanovinyl product. The aromatic and quinoidal products possess red-shifted absorptions, increased electron affinities, and favorable pi-stacking motifs in comparison to the unsubstituted oligomers. 相似文献
168.
Christina Jäger Dr. Martin Nieger Prof. Kari Rissanen Prof. Dr. Jan Deska 《European journal of organic chemistry》2023,26(39):e202300288
The assembly of enzymatic cascades and multi-step reaction sequences represents an attractive alternative to traditional synthetic-organic approaches. The biocatalytic reaction mediators offer not only mild conditions and permit the use of environmentally benign reagents, but the high compatibility of different enzymes promises more streamlined reaction setups. In this study, a triple-enzymatic strategy was developed that enables the direct conversion of γ,δ-unsaturated esters to N-hydroxy-γ-lactam building blocks. Hereby, a lipase-catalyzed hydroxylaminolysis generates hydroxamic acid intermediates that are subsequently aerobically activated by horseradish peroxidase and glucose oxidase to cyclize in an intramolecular nitroso ene reaction. Utilizing the hydroxylaminolysis/ene-cyclization sequence for the preparation of an aza-spirocyclic lactam, the multi-enzymatic methodology was successfully employed in the synthesis of key intermediates en route to alkaloids of the Cephalotaxus family. 相似文献
169.
For the efficient self-assembly of metallo-supramolecular complexes, not only reversibility is required but also two other properties have to be controlled as well: (i) The right binding sites need to be programmed into the building blocks at the appropriate positions. (ii) The building blocks must be rigid enough to support the geometrical arrangement and to avoid the unfavorable entropy effects connected with the conformational fixation of flexible molecules. A series of different bis-pyridyl ligands is reported which self-assemble with (dppp)M(OTf) 2 complexes (dppp = 1,3-bis-(diphenylphosphino)propane; M = Pd (II), Pt (II)) to yield squares and/or triangles as the products. Enthalpic contributions (higher strain in the triangle) and entropic contributions (higher number of triangles from the same building blocks) determine the equilibrium. The effects of concentration, temperature, and solvent properties on the equilibrium have been studied. To characterize the complexes under study, a combination of (1)H, (31)P, and diffusion-ordered NMR spectroscopy, electrospray-ionization Fourier-transform ion-cyclotron-resonance mass spectrometry, and X-ray crystallography is needed. Variable-temperature NMR spectroscopy provides evidence for fast ligand-exchange processes occurring for the Pd complexes, while the Pt complexes exchange ligands much more slowly. 相似文献
170.
Coordinatively Unsaturated Lanthanide(III) Helicates: Luminescence Sensors for Adenosine Monophosphate in Aqueous Media
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Jashobanta Sahoo Rajendran Arunachalam Dr. Palani S. Subramanian Dr. Eringathodi Suresh Dr. Arto Valkonen Prof. Dr. Kari Rissanen Prof. Dr. Markus Albrecht 《Angewandte Chemie (International ed. in English)》2016,55(33):9625-9629
Coordinatively unsaturated double‐stranded helicates [(H2L)2Eu2(NO3)2(H2O)4](NO3)4, [(H2L)2Tb2(H2O)6](NO3)6, and [(H2L)2Tb2(H2O)6]Cl6 (H2L=butanedioicacid‐1,4‐bis[2‐(2‐pyridinylmethylene)hydrazide]) are easily obtained by self‐assembly from the ligand and the corresponding lanthanide(III) salts. The complexes are characterized by X‐ray crystallography showing the helical arrangement of the ligands. Co‐ligands at the metal ions can be easily substituted by appropriate anions. A specific luminescence response of AMP in presence of ADP, ATP, and other anions is observed. Specificity is assigned to the perfect size match of AMP to bridge the two metal centers and to replace quenching co‐ligands in the coordination sphere. 相似文献