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91.
Heavy‐Atom Tunneling in the Ring Opening of a Strained Cyclopropene at Very Low Temperatures 下载免费PDF全文
Melanie Ertelt Dr. David A. Hrovat Prof. Dr. Weston Thatcher Borden Prof. Dr. Wolfram Sander 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4713-4720
The highly strained 1H‐bicyclo[3.1.0]‐hexa‐3,5‐dien‐2‐one 1 is metastable, and rearranges to 4‐oxacyclohexa‐2,5‐dienylidene 2 in inert gas matrices (neon, argon, krypton, xenon, and nitrogen) at temperatures as low as 3 K. The kinetics for this rearrangement show pronounced matrix effects, but in a given matrix, the reaction rate is independent of temperature between 3 and 20 K. This temperature independence means that the activation energy is zero in this temperature range, indicating that the reaction proceeds through quantum mechanical tunneling from the lowest vibrational level of the reactant. At temperatures above 20 K, the rate increases, resulting in curved Arrhenius plots that are also indicative of thermally activated tunneling. These experimental findings are supported by calculations performed at the CASSCF and CASPT2 levels by using the small‐curvature tunneling (SCT) approximation. 相似文献
92.
Jonathan W. Dube Cameron M. E. Graham Prof. Charles L. B. Macdonald Dr. Zachary D. Brown Prof. Philip P. Power Prof. Paul J. Ragogna 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6739-6744
Two unique systems based on low‐coordinate main group elements that activate P4 are shown to quantitatively release the phosphorus cage upon short exposure to UV light. This reactivity marks the first reversible reactivity of P4, and the germanium system can be cycled 5 times without appreciable loss in activity. Theoretical calculations reveal that the LUMO is antibonding with respect to the main group element–phosphorus bonds and bonding with respect to reforming the P4 tetrahedron, providing a rationale for this unprecedented activity, and suggesting that the process is tunable based on the substituents. 相似文献
93.
Photoionization and Pyrolysis of a 1,4‐Azaborinine: Retro‐Hydroboration in the Cation and Identification of Novel Organoboron Ring Systems 下载免费PDF全文
Fabian Holzmeier Dipl.‐Chem. Melanie Lang Dr. Patrick Hemberger Dr. Andras Bodi Dipl.‐Chem. Marius Schäfer Dr. Rian D. Dewhurst Prof. Dr. Holger Braunschweig Prof. Dr. Ingo Fischer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9683-9692
The photoionization and dissociative photoionization of 1,4‐di‐tert‐butyl‐1,4‐azaborinine by means of synchrotron radiation and threshold photoelectron photoion coincidence spectroscopy is reported. The ionization energy of the compound was determined to be 7.89 eV. Several low‐lying electronically excited states in the cation were identified. The various pathways for dissociative photoionization were modeled by statistical theory, and appearance energies AE0K were obtained. The loss of isobutene in a retro‐hydroboration reaction is the dominant pathway, which proceeds with a reverse barrier. Pyrolysis of the parent compound in a chemical reactor leads to the generation of several yet unobserved boron compounds. The ionization energies of the C4H6BN isomers 1,2‐ and 1,4‐dihydro‐1,4‐azaborinine and the C3H6BN isomer 1,2‐dihydro‐1,3‐azaborole were determined from threshold photoelectron spectra. 相似文献
94.
Experimental and Computational Studies of a Multi‐Electron Donor–Acceptor Ligand Containing the Thiazolo[5,4‐d]thiazole Core and its Incorporation into a Metal–Organic Framework 下载免费PDF全文
Felix J. Rizzuto Dr. Thomas B. Faust Dr. Bun Chan Carol Hua Dr. Deanna M. D'Alessandro Prof. Cameron J. Kepert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(52):17597-17605
A ligand containing the thiazolo[5,4‐d]thiazole (TzTz) core (acceptor) with terminal triarylamine moieties (donors), N,N′‐(thiazolo[5,4‐d]thiazole‐2,5‐diylbis(4,1‐phenylene))bis(N‐(pyridine‐4‐yl)pyridin‐4‐amine ( 1 ), was designed as a donor–acceptor system for incorporation into electronically active metal–organic frameworks (MOFs). The capacity for the ligand to undergo multiple sequential oxidation and reduction processes was examined using UV/Vis‐near‐infrared spectroelectrochemistry (UV/Vis‐NIR SEC) in combination with DFT calculations. The delocalized nature of the highest occupied molecular orbital (HOMO) was found to inhibit charge‐transfer interactions between the terminal triarylamine moieties upon oxidation, whereas radical species localized on the TzTz core were formed upon reduction. Conversion of 1 to diamagnetic 2+ and 4+ species resulted in marked changes in the emission spectra. Incorporation of this highly delocalized multi‐electron donor–acceptor ligand into a new two‐dimensional MOF, [Zn(NO3)2( 1 )] ( 2 ), resulted in an inhibition of the oxidation processes, but retention of the reduction capability of 1 . Changes in the electrochemistry of 1 upon integration into 2 are broadly consistent with the geometric and electronic constraints enforced by ligation. 相似文献
95.
An Investigation of Photo‐ and Pressure‐Induced Effects in a Pair of Isostructural Two‐Dimensional Spin‐Crossover Framework Materials 下载免费PDF全文
Dr. Natasha F. Sciortino Dr. Suzanne M. Neville Dr. Cédric Desplanches Dr. Jean‐François Létard Dr. Victor Martinez Prof. José Antonio Real Dr. Boujemaa Moubaraki Prof. Keith S. Murray Prof. Cameron J. Kepert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7448-7457
Two new isostructural iron(II) spin‐crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)2(NCX)2] (dpms=4,4′‐dipyridylmethyl sulfide; X=S ( SCOF‐6(S) ), X=Se ( SCOF‐6(Se) )) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF‐6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high‐spin (HS) to low‐spin iron(II) sites over the temperature range 300–4 K (T1/2=75 K). In contrast, the NCSe? analogue, SCOF‐6(Se) , displays a complete SCO transition (T1/2=135 K). Photomagnetic characterizations reveal quantitative light‐ induced excited spin‐state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF‐6(S) and SCOF‐6(Se) , respectively. Variable‐pressure magnetic measurements were performed on SCOF‐6(S) , revealing that with increasing pressure both the T1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF‐6(S) at ambient pressure due to an interplay between close T1/2 and T(LIESST) values. 相似文献
96.
Chemical Probing of the Human Sirtuin 5 Active Site Reveals Its Substrate Acyl Specificity and Peptide‐Based Inhibitors 下载免费PDF全文
Claudia Roessler Theresa Nowak Martin Pannek Dr. Melanie Gertz Giang T. T. Nguyen Michael Scharfe Dr. Ilona Born Prof. Dr. Wolfgang Sippl Prof. Dr. Clemens Steegborn Prof. Dr. Mike Schutkowski 《Angewandte Chemie (International ed. in English)》2014,53(40):10728-10732
Sirtuins are NAD+‐dependent deacetylases acting as sensors in metabolic pathways and stress response. In mammals there are seven isoforms. The mitochondrial sirtuin 5 is a weak deacetylase but a very efficient demalonylase and desuccinylase; however, its substrate acyl specificity has not been systematically analyzed. Herein, we investigated a carbamoyl phosphate synthetase 1 derived peptide substrate and modified the lysine side chain systematically to determine the acyl specificity of Sirt5. From that point we designed six potent peptide‐based inhibitors that interact with the NAD+ binding pocket. To characterize the interaction details causing the different substrate and inhibition properties we report several X‐ray crystal structures of Sirt5 complexed with these peptides. Our results reveal the Sirt5 acyl selectivity and its molecular basis and enable the design of inhibitors for Sirt5. 相似文献
97.
Time‐Resolved Assembly of Cluster‐in‐Cluster {Ag12}‐in‐{W76} Polyoxometalates under Supramolecular Control 下载免费PDF全文
Caihong Zhan Jamie M. Cameron Jing Gao Jamie W. Purcell De‐Liang Long Leroy Cronin 《Angewandte Chemie (International ed. in English)》2014,53(39):10362-10366
We report the time‐resolved supramolecular assembly of a series of nanoscale polyoxometalate clusters (from the same one‐pot reaction) of the form: [H(10+m)Ag18Cl(Te3W38O134)2]n, where n=1 and m=0 for compound 1 (after 4 days), n=2 and m=3 for compound 2 (after 10 days), and n=∞ and m=5 for compound 3 (after 14 days). The reaction is based upon the self‐organization of two {Te3W38} units around a single chloride template and the formation of a {Ag12} cluster, giving a {Ag12}‐in‐{W76} cluster‐in‐cluster in compound 1 , which further aggregates to cluster compounds 2 and 3 by supramolecular Ag‐POM interactions. The proposed mechanism for the formation of the clusters has been studied by ESI‐MS. Further, control experiments demonstrate the crucial role that TeO32?, Cl?, and Ag+ play in the self‐assembly of compounds 1 – 3 . 相似文献
98.
Perturbation of Spin Crossover Behavior by Covalent Post‐Synthetic Modification of a Porous Metal–Organic Framework 下载免费PDF全文
John E. Clements Dr. Jason R. Price Dr. Suzanne M. Neville Prof. Cameron J. Kepert 《Angewandte Chemie (International ed. in English)》2014,53(38):10164-10168
Covalent post‐synthetic modification is a versatile method for gaining high‐level synthetic control over functionality within porous metal–organic frameworks and for generating new materials not accessible through one‐step framework syntheses. Here we apply this topotactic synthetic approach to a porous spin crossover framework and show through detailed comparison of the structures and properties of the as‐synthesised and covalently modified phases that the modification reaction proceeds quantitatively by a thermally activated single‐crystal‐to‐single‐crystal transformation to yield a material with lowered spin‐switching temperature, decreased lattice cooperativity, and altered color. Structure–function relationships to emerge from this comparison show that the approach provides a new route for tuning spin crossover through control over both outer‐sphere and steric interactions. 相似文献
99.
100.
Dr. Melanie M. Britton 《Chemphyschem》2014,15(9):1731-1736
The development of improved energy‐storage devices, as well as corrosion prevention and metal‐electrofinishing technologies, requires knowledge of local composition and transport behaviour in electrolytes near bulk metals, in situ and in real time. It remains a challenge to acquire such data and new analytical methods are required. Recent work shows that magnetic resonance imaging (MRI) is able to map concentration gradients and visualise electrochemical processes in electrochemical cells containing bulk metals. This recent work, along with the challenges, and solutions, associated with MRI of these electrochemical cells are reviewed. 相似文献