Search results for "xi"

Mechanism of activated chemiluminescence of cyclic peroxides: 1,2-dioxetanes and 1,2-dioxetanones

2017

Almost all chemiluminescent and bioluminescent reactions involve cyclic peroxides. The structure of the peroxide and reaction conditions determine the quantum efficiency of light emission. Oxidizable fluorophores, the so-called activators, react with 1,2-dioxetanones promoting the former to their first singlet excited state. This transformation is inefficient and does not occur with 1,2-dioxetanes; however, they have been used as models for the efficient firefly bioluminescence. In this work, we use the SA-CASSCF/CASPT2 method to investigate the activated chemiexcitation of the parent 1,2-dioxetane and 1,2-dioxetanone. Our findings suggest that ground state decomposition of the peroxide com…

Electrostatic complementarity in pseudoreceptor modeling based on drug molecule crystal structures: the case of loxistatin acid (E64c)

2015

After a long history of use as a prototype cysteine protease inhibitor, the crystal structure of loxistatin acid (E64c) is finally determined experimentally using intense synchrotron radiation, providing insight into how the inherent electronic nature of this protease inhibitor molecule determines its biochemical activity. Based on the striking similarity of its intermolecular interactions with those observed in a biological environment, the electrostatic potential of crystalline E64c is used to map the characteristics of a pseudo-enzyme pocket.

NMR T1-Relaxation Measurements on Paramagnetic Organolanthanides: An Alternative Tool for Structure Determination in Solution

2005

1H NMR investigations were conducted on four paramagnetic organolanthanides, all bearing the tetraisopropylcyclopentadienyl ligand Cp4i (HC5iPr4) in order to verify whether or not interactions observed in the solid state are maintained in solution. In some cases variable-temperature experiments were necessary to enhance the resolution and determine the best conditions for the study. The 1D NMR spectrum could be interpreted in every case. Complementary 2D COSY experiments allowed the full attribution of the signals. T1 (1H) relaxation values were determined for all the paramagnetic complexes at the most suitable temperature, and compared with those of the diamagnetic KCp4i. The same tendency…

2021

A nickel complex incorporating an N2 O ligand with a rare η2 -N,N'-coordination mode was isolated and characterized by X-ray crystallography, as well as by IR and solid-state NMR spectroscopy augmented by 15 N-labeling experiments. The isoelectronic nickel CO2 complex reported for comparison features a very similar solid-state structure. Computational studies revealed that η2 -N2 O binds to nickel slightly stronger than η2 -CO2 in this case, and comparably to or slightly stronger than η2 -CO2 to transition metals in general. Comparable transition-state energies for the formation of isomeric η2 -N,N'- and η2 -N,O-complexes, and a negligible activation barrier for the decomposition of the lat…

Advances in photochemical and electrochemical incorporation of sulfur dioxide for the synthesis of value-added compounds.

2021

Organic photochemistry and electrochemistry currently receive tremendous attention in organic synthesis as both techniques enable the reagent-less activation of organic molecules without using expensive and hazardous redox reagents. The incorporation of SO2 into organic molecules is a relatively modern research topic, which likewise gains immense popularity since the discovery of the SO2 surrogate DABSO. Sulfur-containing organic molecules are omnipresent in pharmaceuticals and agrochemicals. This review covers the recent progress in electrochemical and photochemical methodologies for the incorporation and uses of SO2 in the synthesis of value-added compounds. Additionally, different work t…

Structure effects induced by high mechanical compaction of STAM-17-OEt MOF powders

2021

Financial support by PJ-RIC-FFABR_2017 and the EPSRC grant EPSRC industrial CASE award (grant EP/N50936X/1) are acknowledged. The research programme Nanoporous materials (P1-0021) financially supported by Slovenian Research Agency (ARRS) is acknowledged as well. Metal-organic frameworks (MOFs) are promising materials for many potential applications, spacing from gas storage to catalysis. However, the powder form of which they are generally made is not suitable, mainly because of the low packing density. Powder compaction is therefore necessary, but also challenging because of their typical mechanical fragility. Indeed, generally, they undergo irreversibly damages upon densification processe…

Selective Formation of 4,4'-Biphenols by Anodic Dehydrogenative Cross- and Homo-Coupling Reaction.

2019

A simple and selective electrochemical synthesis by dehydrogenative coupling of unprotected 2,6- or 2,5-substituted phenols to the desired 4,4'-biphenols is reported. Using electricity as the oxidizing reagent avoids pre-functionalization of the starting materials, since a selective activation of the substrates takes place. Without the necessity for metal-catalysts or the use of stoichiometric reagents it is an economic and environmentally friendly transformation. The elaborated electrochemical protocol leads to a broad variety of the desired 4,4'-biphenols in a very simplified manner compared to classical approaches. This is particular the case for the cross-coupled products.

Mild, Fast, and Easy To Conduct MoCl5-Mediated Dehydrogenative Coupling Reactions in Flow

2018

A convenient and straightforward approach to performing oxidative coupling reactions in flow is presented. A collection of electron-rich benzene derivatives was subjected to this protocol, and the distinct utility of molybdenum pentachloride (MoCl5) is established. Using this unexplored protocol, biphenyls could be obtained in 21–91% isolated yield. This simple protocol opens a new chapter in reagent-mediated dehydrogenative coupling reactions, and yields are compared to classical approaches.

Organotin(IV) derivatives containing heteroditopic pyridyl-quinolin-8-olate ligands: Synthesis and structures

2021

Abstract Six novel neutral organotin(IV) complexes, viz. [n-Bu2Sn(L4-PyAQ)2] 1, [Bz2Sn(L4-PyAQ)2] 2, [Ph2Sn(L4-PyAQ)2] 3, [Ph2Sn(L3-PyAQ)2] 4, [Bz3Sn(L4-PyAQ)] 5 and [Ph3Sn(L4-PyAQ)] 6 have been synthesized via reactions of 3/4-pyridyl-quinolin-8-ol pro-ligands, with appropriate diorganotin oxide and triorganotin hydroxide precursors, respectively. The compounds 1-6 were characterized in solution by means of NMR spectroscopy while the solid-state structures of 1, 6, and of the solvates 2·1.5C6H6, 3·0.25C6H6, 2·4·C6H6, and 5·0.5H2O were authenticated by single crystal X-ray diffraction analysis. In the solid-state, the tin centers in 1-2·4·C6H6 are hexacoordinated and reveal a distorted cis-…

A Strongly Luminescent Chromium(III) Complex Acid

2018

The synthesis, structure, reactivity, and photophysical properties of a novel acidic, luminescent chromium(III) complex [Cr(H2 tpda)2 ]3+ (23+ ) bearing the tridentate H2 tpda (2,6-bis(2-pyridylamino)pyridine) ligand are presented. Excitation of 23+ at 442 nm results in strong, long-lived NIR luminescence at 782 nm in water and in acetonitrile. X-ray diffraction analysis and IR spectroscopy reveal hydrogen-bonding interactions of the counter ions to the NH groups of 23+ in the solid state. Deprotonation of the NH groups of 23+ by using a non-nucleophilic Schwesinger base in CH3 CN switches off the luminescence. Re-protonation by using HClO4 restores the emission. In water, the pKa value of …