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The aqueous reaction of acidic Cl2 with excess SCN- rapidly generates a UV-absorbing intermediate identified as an equilibrium mixture of thiocyanogen, (SCN)2, and trithiocyanate, (SCN)3(-). The decomposition of this mixture can be described as 3(SCN)2 + 4H2O --> 5HSCN + H2SO4 + HCN. Under our conditions the decomposition is sufficiently slow that its kinetics can be studied using standard stopped-flow methodology. Over the pH range 0-2 the decomposition rate law is -d[(SCN)2]/dt = (3/2)[k(disp)K(hyd)2[(SCN)2]2/([SCN-]2[H+]2 + K(SCN)3-[SCN-]3[H+]2 + K(hyd)[SCN-][H+])] with K(SCN)3(-) = 0.43 +/- 0.29 M(-1), K(hyd) = (5.66 +/- 0.77) x 10(-4) M2, and k(disp) = (6.86 +/- 0.95) x 10(4) M(-1) s(-1) at 25 degrees C and micro = 1 M. The K(SCN)3(-) and K(hyd) terms are significant enhancements relative to one of the rate laws conventionally cited. In the proposed mechanism, K(SCN)3(-) refers to the formation of (SCN)3(-) by association of SCN- with (SCN)2, K(hyd) refers to the hydrolysis of (SCN)2 to form HOSCN, and k(disp) is the rate constant for the bimolecular irreversible disproportionation of HOSCN, which leads ultimately to SO4(2-) and HCN. Ab initio calculations support the values of K(SCN)3(-) and K(hyd) reported herein. The high value for k(disp) indicates that HOSCN is a short-lived transient, while the magnitude of K(hyd) provides information on its thermodynamic stability. These results bear on the physiological role of enzymes that catalyze the oxidation of SCN- such as salivary peroxidase and myeloperoxidase. 相似文献
4.
Arisaka K Auerbach LB Axelrod S Belz J Biery KA Buchholz P Chapman MD Cousins RD Diwan MV Eckhause M Ginkel JF Guss C Hancock AD Heinson AP Highland VL Hoffmann GW Horvath J Irwin GM Joyce D Kaarsberg T Kane JR Kenney CJ Kettell SH Kinnison WW Knibbe P Konigsberg J Kuang Y Lang K Lee DM Margulies J Mathiazhagan C McFarlane WK McKee RJ Melese P Milner EC Molzon WR Ouimette DA Riley PJ Ritchie JL Rubin P Sanders GH Schwartz AJ Sivertz M Slater WE Urheim J Vulcan WF Wagner DL Welsh RE Whyley RJ 《Physical review letters》1993,71(24):3910-3913
5.
McKee ML 《Inorganic chemistry》2000,39(19):4206-4210
A comprehensive survey of the (CH)2(BH)2 potential energy surface was carried out at the [MP4/6-311 + G(d,p)]//MP2/6-31G(d) level. Many of the classical and nonclassical isomers of the carborane surface are separated by high activation barriers, which explains why derivatives of most isomers could be prepared as stable compounds at room temperature. The transition states are grouped into two types, hydrogen migration (terminal-to-bridge and bridge-to-terminal) and group migration (BH, CH, and CH2). The rearrangement of 1,3-diamino-1,3-diboretene (1-NH2) to 1,2-diamino-1,2-diboretene (2-NH2) was computed and compared to the rearrangement in the parent (1-->2). The effect of the amino group is to substantially increase the barrier height and stabilize the product, 2-NH2. 相似文献
6.
Density functional theory (BPW91/TZ2P) is used to explore the nature of cation-cation interactions (CCIs) that exist between two actinyl cations in solution. Solvation, which is modeled using COSMO, favors the complexes (ONpO-ONpO)2+ and (ONpO-OUO)3+ over separated NpO2+(aq) and UO2(2+)(aq) cations because of the quadratic dependence of solvation on charge. For (OUO-OUO)4+, solvation effects, even though very large, are unable to overcome intrinsic electrostatic repulsion between the units. The actinyl-actinyl complexes are T-shaped, with the oxygen of one unit coordinated to the actinide metal of the other unit. The association free energies of (ONpO-ONpO)2+ and (ONpO-OUO)3+ are calculated as -42.1 and -29.2 kcal/mol. Explicit consideration of the first solvation shell at the B3LYP/LANL2DZ level suggests that the free energies of binding may be overestimated. The Hg2(2+) dication, though not considered a "traditional" CCI, is very similar to the actinyl-actinyl interaction. The binding free energy of Hg2(2+) in solution is calculated as -16.0 kcal/mol. 相似文献
7.
The cyclotides are a recently discovered, structurally unique family of bioactive plant peptides. Their discovery spawned a series of structural analyses, synthetic efforts, and studies to define the biosynthesis and biological properties of these novel peptide metabolites. Cyclotides have a head-to-tail cyclized amino acid backbone and a conserved cystine knot motif that provides an extremely stable structural framework. They all share a common global fold and are highly resistant to denaturation and to cleavage by proteolytic enzymes. However, these macrocyclic peptides are quite permissive to amino acid substitutions or additions in several peripheral loop regions, since changes in these loops do not alter the core cyclotide structure. These features make cyclotides attractive templates for incorporating desired amino acid sequences and then delivering these peptide sequences in a well defined, highly stable framework. Cyclotides likely function in a defensive role in the source plants since they exhibit a broad spectrum of antimicrobial activity and are detrimental to the growth and survival of herbivorous insects. Cyclotides are gene-encoded polypeptides that are cleaved from larger precursor proteins and then cyclized. This review summarizes research done on a subset of cyclotides that were discovered due to their HIV inhibitory properties. It details the isolation and characterization of these compounds and describes this work in the context of our current state of knowledge of the entire cyclotide family. 相似文献
8.
McKee ML 《Inorganic chemistry》2001,40(22):5612-5619
Two pathways have been considered in the fluorination of CB(5)H(6)(-) and CB(9)H(10)(-) by HF. In the ionic HF fluorination pathway, the monocarborane anion cage is first protonated in a BBB face followed by H(2) elimination and fluoride anion addition. In the covalent HF fluorination pathway, HF is first coordinated through hydrogen to the BBB face. Next, the fluorine can add to either an axial or equatorial boron atom which opens the cage to a nido structure with an endo fluoride substituent. Endo to exo rearrangement occurs with a small activation barrier followed by H(2) elimination. In both pathways, fluorination at the equatorial boron position is predicted to have smaller activation barriers even though substitution at the axial position leads to the more stable products. 相似文献
9.
N. Barnes P. Healey P. McKee A. W. O'Neill M. A. Z. Rejman-Greene E. G. Scott R. P. Webb B. R. White D. Wood 《Optical and Quantum Electronics》1992,24(4):S505-S516
An experimental 16-channel parallel interconnection system able to support 100 Mbits–1 per channel and an opto-electronic neural network operating at up to 50 Mbits–1 have been constructed to demonstrate the potential of optics in processing systems. Both experiments operate at a wavelength of 1.5m. Components developed for these systems include arrays of InGaAs/InP MQW surface modulators for low-power electrical-to-optical conversion; InGaAs/InP for detector arrays, which are hybrid integrated with GaAs amplifier arrays; and computer-generated holograms for efficient beam splitting and to encode weights in the optical beam intensities. Each of these demonstrations has considerable scope for increasing the degree of parallelism and the operating speed. Recent modifications to the neural network enable the weights to be varied and training has been demonstrated with a novel algorithm that uses the high operating speed to advantage. 相似文献
10.
Dr. Nicoló Zuin Fantoni Dr. Zara Molphy Sinéad O'Carroll Dr. Georgia Menounou Dr. George Mitrikas Dr. Marios G. Krokidis Dr. Chryssostomos Chatgilialoglu Dr. John Colleran Dr. Anna Banasiak Prof. Martin Clynes Dr. Sandra Roche Suainibhe Kelly Prof. Vickie McKee Prof. Andrew Kellett 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):971-983
We report a series of copper(II) artificial metallo-nucleases (AMNs) and demonstrate their DNA damaging properties and in-vitro cytotoxicity against human-derived pancreatic cancer cells. The compounds combine a tris-chelating polypyridyl ligand, di-(2-pycolyl)amine (DPA), and a DNA intercalating phenanthrene unit. Their general formula is Cu-DPA-N,N' (where N,N'=1,10-phenanthroline (Phen), dipyridoquinoxaline (DPQ) or dipyridophenazine (DPPZ)). Characterisation was achieved by X-ray crystallography and continuous-wave EPR (cw-EPR), hyperfine sublevel correlation (HYSCORE) and Davies electron-nuclear double resonance (ENDOR) spectroscopies. The presence of the DPA ligand enhances solution stability and facilitates enhanced DNA recognition with apparent binding constants (Kapp) rising from 105 to 107 m −1 with increasing extent of planar phenanthrene. Cu-DPA-DPPZ, the complex with greatest DNA binding and intercalation effects, recognises the minor groove of guanine–cytosine (G-C) rich sequences. Oxidative DNA damage also occurs in the minor groove and can be inhibited by superoxide and hydroxyl radical trapping agents. The complexes, particularly Cu-DPA-DPPZ, display promising anticancer activity against human pancreatic tumour cells with in-vitro results surpassing the clinical platinum(II) drug oxaliplatin. 相似文献