Mechanistic Investigation of Dirhodium-Catalyzed Intramolecular Allylic C–H Amination versus Alkene Aziridination

The reaction mechanisms and chemoselectivity on the intramolecular allylic C–H amination versus alkene aziridination of 4-pentenylsulfamate promoted by four elaborately selected dirhodium paddlewheel complexes are investigated by a DFT approach. A predominant singlet concerted, highly asynchronous pathway and an alternative triplet stepwise pathway are obtained in either C–H amination or alkene aziridination reactions when mediated by weak electron-donating catalysts. A singlet stepwise C–H amination pathway is obtained under strongly donating catalysts. The rate-determining step in the C–H amination is the H-abstraction process. The subsequent diradical-rebound C–N formation in the triplet pathway or the combination of the allylic carbocation and the negative changed N center in the singlet pathway require an identical energy barrier. A mixed singlet–triplet pathway is preferred in either the C–H insertion or alkene aziridination in the Rh₂(NCH₃CHO)₄ entry that the triplet pathway is initially favorable in the rate-determining steps, and the resultant triplet intermediates would convert to a singlet reaction coordinate. The nature of C–H amination or alkene aziridination is estimated to be a stepwise process. The theoretical observations presented in the paper are consistent with the experimental results and, more importantly, provide a thorough understanding of the nature of the reaction mechanisms and the minimum-energy crossing points

Mechanistic Insights Into the Factors That Influence the DNA Nuclease Activity of Mononuclear Facial Copper Complexes Containing Hetero-Substituted Cyclens

The factors that influence the DNA nuclease activity of mononuclear facial copper complexes containing heterosubstituted cyclens were systematically investigated in this work using density functional theory (DFT) calculations. The heterosubstitution of cyclens were found to significantly affect the dimerization tendency of the mononuclear Cu­(II) complexes examined and their respective p<i>K</i>_a values of the metal-bonded water molecules. The Cu­(II)–oxacyclen complex was found to be more favorable for the hydrolytic cleavage of the DNA dinucleotide analogue BNPP^–(bis (<i>p</i>-nitrophenyl) phosphate). This was due to this species having a higher dimerization resistance to give rise to a higher concentration of the active catalyst and a lower p<i>K</i>_a value of the Cu­(II)-coordinated water molecule to facilitate an easier generation of the better nucleophile hydroxyl ion, which gave a lower reaction barrier. The dimerization of the Cu­(I) complexes studied and their corresponding redox potentials were determined, and a remarkable reaction barrier was observed for the generation of a superoxide ROS (reactive oxygen species) mediated by the Cu­(I)–oxacyclen complex. This behavior was attributed to the higher electronegativity of the O heteroatom, which facilitates the nucleophilic attack of the oxygen molecule and the Cu–O­(OH₂) bond fission via an enhancement of the Lewis acidity of the metal center and the formation of a significant hydrogen bond between the heterocyclic oxygen and the metal-bonded water molecule. The theoretical results reported here are in good agreement with the literature experimental observations and more importantly help to systematically elucidate the factors that influence the DNA nuclease activity of mononuclear facial copper complexes containing heterosubstituted cyclens in detail

General Design Strategy for Aromatic Ketone-Based Single-Component Dual-Emissive Materials

Materials with both fluorescence and room-temperature phosphorescence (RTP) can be useful in the field of optoelectronics. Here we present a general strategy, taking advantage of carbonyl compounds, which have been known to possess efficient intersystem crossing with high triplet state yield, as well as a strongly fluorescent intramolecular charge-transfer (ICT) state, to produce materials with both fluorescence and RTP at the same time, or dual-emission. In the presented model systems, in order to generate a suitable ICT state, Lewis acid binding to aromatic ketone derivatives has been proved to be a viable method. We have selected AlCl₃, BCl₃, BF₃, and GdCl₃ as binding Lewis acids, in that they exhibit sufficiently strong binding affinity toward the aromatic ketone derivatives to afford stable complexes and yet do not possess low-lying electronic transitions vs the ligands. We have successfully observed dual-emission from these designed complexes in polymers, which act to suppress competitive thermal decay at room temperature. One of the complexes is particularly interesting as it is dual-emissive in the crystalline state. Single-crystal XRD reveals that the molecule forms multiple hydrogen bonds with its neighbors in crystals, which may significantly enhance the rigidity of the environment

Two-Dimensional Charge-Separated Metal–Organic Framework for Hysteretic and Modulated Sorption

A charge-separated metal–organic framework (MOF) has been successfully synthesized from an imidazolium tricarboxylate ligand, <i>N</i>-(3,5-dicarboxylphenyl)-<i>N</i>′-(4-carboxylbenzyl)­imidazolium chloride (DCPCBImH₃Cl), and a zinc­(II) dimeric secondary building unit, namely, <b>DCPCBim-MOF-Zn</b>, which shows an unprecedented 3,6-connected two-dimensional net topology with the point (Schläfli) symbol (4².6)₂(4⁴.6⁹.8²). The framework contains one-dimensional highly polar channels, and density functional theory calculations show that positive charges are located on the imidazolium/phenyl rings and negative charges on the carboxylate moieties. The charge-separated nature of the pore surface has a profound effect in their adsorption behavior, resulting in remarkable hysteretic sorption of various gases and vapors. For CO₂, the hysteretic sorption was observed to occur even up to 298 K. Additionally, trace chloride anions present in the pore channels are able to modulate the gas-sorption behavior

Two-Dimensional Charge-Separated Metal–Organic Framework for Hysteretic and Modulated Sorption

A charge-separated metal–organic framework (MOF) has been successfully synthesized from an imidazolium tricarboxylate ligand, <i>N</i>-(3,5-dicarboxylphenyl)-<i>N</i>′-(4-carboxylbenzyl)­imidazolium chloride (DCPCBImH₃Cl), and a zinc­(II) dimeric secondary building unit, namely, <b>DCPCBim-MOF-Zn</b>, which shows an unprecedented 3,6-connected two-dimensional net topology with the point (Schläfli) symbol (4².6)₂(4⁴.6⁹.8²). The framework contains one-dimensional highly polar channels, and density functional theory calculations show that positive charges are located on the imidazolium/phenyl rings and negative charges on the carboxylate moieties. The charge-separated nature of the pore surface has a profound effect in their adsorption behavior, resulting in remarkable hysteretic sorption of various gases and vapors. For CO₂, the hysteretic sorption was observed to occur even up to 298 K. Additionally, trace chloride anions present in the pore channels are able to modulate the gas-sorption behavior

Mechanistic Implications in the Phosphatase Activity of Mannich-Based Dinuclear Zinc Complexes with Theoretical Modeling

An “end-off” compartmental ligand has been synthesized by an abnormal Mannich reaction, namely, 2-[bis­(2-methoxyethyl)­aminomethyl]-4-isopropylphenol yielding three centrosymmetric binuclear μ-phenoxozinc­(II) complexes having the molecular formula [Zn₂(L)₂X₂] (<b>Zn-1</b>, <b>Zn-2</b>, and <b>Zn-3</b>), where X = Cl^–, Br ^–, and I ^–, respectively. X-ray crystallographic analysis shows that the ZnO₃NX chromophores in each molecule form a slightly distorted trigonal-bipyramidal geometry (τ = 0.55–0.68) with an intermetallic distance of 3.068, 3.101, and 3.083 Å (<b>1</b>–<b>3</b>, respectively). The spectrophotometrical investigation on their phosphatase activity established that all three of them possess significant hydrolytic efficiency. Michaelis–Menten-derived kinetic parameters indicate that the competitiveness of the rate of P–O bond fission employing the phosphomonoester (4-nitrophenyl)­phosphate in 97.5% <i>N</i>,<i>N</i>-dimethylformamide is <b>3</b> > <b>1</b> > <b>2</b> and the <i>k</i>_cat value lies in the range 9.47–11.62 s^–1 at 298 K. Theoretical calculations involving three major active catalyst forms, such as the dimer-cis form (D-Cis), the dimer-trans form (D-Trans), and the monoform (M-1 and M-2), systematically interpret the reaction mechanism wherein the dimer-cis form with the binuclear-bridged hydroxide ion acting as the nucleophile and one water molecule playing a role in stabilizing the leaving group competes as the most favored pathway

Increased chemotactic migration and growth in heparanase-overexpressing human U251n glioma cells-4

-GSK3. β1 integrin, phospho-FAK and phospho-ERK levels were not significantly changed.<p><b>Copyright information:</b></p><p>Taken from "Increased chemotactic migration and growth in heparanase-overexpressing human U251n glioma cells"</p><p>http://www.jeccr.com/content/27/1/23</p><p>Journal of Experimental & Clinical Cancer Research : CR 2008;27(1):23-23.</p><p>Published online 22 Jul 2008</p><p>PMCID:PMC2499998.</p><p></p

Increased chemotactic migration and growth in heparanase-overexpressing human U251n glioma cells-0

By Western blot. Both U251n and U87 exhibited baseline level of heparanase expression. Latent form of heparanase was detected in HF2303 cells. Increased heparanase expression, both the latent (65 kDa) and active (50 kDa) forms, was observed in cell lysate derived from U251n-hpa cells, as compared to U251n-pc control cells. (B) U251n-hpa cells expressed about 100 times more mRNA than U251n-pc cells. (C) Increased heparanase activity was detected in U251n-hpa cells.<p><b>Copyright information:</b></p><p>Taken from "Increased chemotactic migration and growth in heparanase-overexpressing human U251n glioma cells"</p><p>http://www.jeccr.com/content/27/1/23</p><p>Journal of Experimental & Clinical Cancer Research : CR 2008;27(1):23-23.</p><p>Published online 22 Jul 2008</p><p>PMCID:PMC2499998.</p><p></p

Increased chemotactic migration and growth in heparanase-overexpressing human U251n glioma cells-2

T manner (5% and 10% FBS), and increased migration was significantly blocked by 40 μg/ml heparin. **, < 0.01, compared with the same treatment of U251n-pc cells. $, < 0.01, compared with 5% FBS group of U251n-hpa. #, P < 0.01, compared with 10% FBS group of U251n-hpa. (B) SDF-1 significantly increased cell chomatactic migration in the presence of 10% FBS medium. Increased migration was not observed when SDF-1 was added in serum free medium. **, < 0.01, compared with the same treatment of U251n-pc cells. #, < 0.01, compared with 10%FBS group of each cell line.<p><b>Copyright information:</b></p><p>Taken from "Increased chemotactic migration and growth in heparanase-overexpressing human U251n glioma cells"</p><p>http://www.jeccr.com/content/27/1/23</p><p>Journal of Experimental & Clinical Cancer Research : CR 2008;27(1):23-23.</p><p>Published online 22 Jul 2008</p><p>PMCID:PMC2499998.</p><p></p

Increased chemotactic migration and growth in heparanase-overexpressing human U251n glioma cells-1

D by BD invasion assay. Increased cell invasion was greatly inhibited by 40 μg/ml heparin. **, < 0.01, compared with U251n-pc cells. #, < 0.01, compared with U251n-hpa group of no heparin treatment. (B) mRNA levels of MMP-2 and MMP-9 showed no significant difference between U251n-pc and U251n-hpa cells. (C) No significant differences were detected in MMP-2 and MMP-9 activity between U251n-hpa cells and U251n-pc cells as measured by zymography assay.<p><b>Copyright information:</b></p><p>Taken from "Increased chemotactic migration and growth in heparanase-overexpressing human U251n glioma cells"</p><p>http://www.jeccr.com/content/27/1/23</p><p>Journal of Experimental & Clinical Cancer Research : CR 2008;27(1):23-23.</p><p>Published online 22 Jul 2008</p><p>PMCID:PMC2499998.</p><p></p