A molecular mechanics and semiempirical conformational analysis of the herbicide diuron inhibitor of photosystem II

The potential energy surface (PES) for the herbicide diuron (DCMU), a photosystem II inhibitor, has been extensively investigated using the quantum-mechanical semiempirical molecular orbital methods AM1 and PM3 and molecular mechanics method. A detailed conformational search has been carried out which revealed the occurrence of four genuine minimum energy structures. The relative stability of the conformers and rotational barriers to conformational interconversion were evaluated using distinct theoretical approaches. The results showed that thetrans form of the diuron molecule is more stable than thecis form in all methods, and so it may possibly be the biologically active isomer.     

Synthesis of 3-nitro- and 3-aminoquinoline-2,4-diones. An unexpected route to 3-hydroxyquinoline-2,4-diones

Nitration of 3-substituted-4-hydroxy-2(1H)-quinolones 1 with nitric acid leads either to 3-nitro- 2 or 3-hydroxyquinolinediones 3 , depending on the reaction conditions. 3-Substituted-3-hydroxyquinolinediones 3 are also obtained by oxidative hydroxylation with peracetic acid. Amination of 3-substituted-3-chloroquinolinediones 4 with ammonium hydroxide predominantly leads again to 3-substituted-3-hydroxyquinolinediones 3 , only in one case the 3-aminoquinolinedione 5 could be isolated. With morpholine or pyridine as amines the expected 3-aminoquinolinediones 6 and 7 were obtained.     

Nucleophile Ringöffnung von α-Nitrocyclopropancarbonsäure-arylestern mit sterisch geschützter,aber elektronisch wirksamer Carbonyl- und Nitro-Gruppe. Ein neues Prinzip der α-Aminosäure-Synthese (2-Aminobutansäure-a4-Synthon)

Nucleophilic Ring Opening of Aryl α-Nitrocyclopropanecarboxylates with Sterically Protected but Electronically Effective Carbonyl and Nitro Group. A New Principle of α-Amino Acid Synthesis (2-Aminobutanoic Acid a⁴-Synthon) The readily available 2,4,6-tri(tert-butyl)-and 2,6-di(tert-butyl)-4-methoxypahenol esters 2 of α-nitrocyclo-propanecarboxaylic acid ring opening with C-, N-, O-, and S-nucleophiles (cyanide, malonate, azide, anilines, alkoxides, phenoxides, thiolates) in DMF or alcohol solvents (80–95% yield). The products 6 – 14 are 2-nitrobutanoates with the newly introduced substituent in the 4-position. Reduction of the NO₂ group with Zn/AcOH/Ac₂O gives N-acetyl-α-amino acid esters 16 – 22 (40–90% yield). Subsequent oxidative cleavage (H₂O₂/HCOOH) of The p-methoxy-phenyl esters 18 and 20 produces free amino acids (65% 23 and 67% 24 , respectively). Thus, the nitro ester 2 corresponds to a 2-aminobutanoic-acid a⁴-synthon, it is a ‘homo-Michael acceptor’ producing γ-substituted α-amino acids.     

Substitution, cage functionalization, and oxidation of the charge-compensated triruthenium monocarbollide cluster complex [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)6}-closo-2,1-RuCB10H8

The compound [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)6}-closo-2,1-RuCB10H8] 1a reacts with PMe3 or PCy3(Cy = cyclo-C6H11) to give the structurally different species [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)5(PMe3)}-closo-2,1-RuCB10H8] 4 and [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(CO)5(PCy3)}-closo-2,1-RuCB10H8]5, respectively. A symmetrically disubstituted product [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)4(PMe3)2}-closo-2,1-RuCB10H8] 6 is obtained using an excess of PMe3. In contrast, the chelating diphosphines 1,1'-(PPh2)2-Fe(eta-C5H4)2 and 1,2-(PPh2)2-closo-1,2-C2B10H10 react with 1a to yield oxidative-insertion species [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(micro-[1',1'-(PPh2)2-Fe(eta-C5H4)2])(CO)4}-closo-2,1-RuCB10H8] 7 and [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(CO)4(1',2'-(PPh2)2-closo-1',2'-C2B10H10)}-closo-2,1-RuCB10H8] 8, respectively. In toluene at reflux temperatures, 1a with Bu(t)SSBu(t) gives [1-SMe2-2,2-(CO)2-7-(mu-SBu(t))-11-(mu-H)-2,7,11-{Ru2(mu-H)(mu-SBu(t))(CO)4}-closo-2,1-RuCB10H8] 9, and with Bu(t)C [triple bond] CH gives [1-SMe2-2,2-(CO)2-7-{mu:eta2-(E)-CH=C(H)Bu(t)}-11-{mu:eta2-(E)-CH=C(H)Bu(t)}-2,7,11-{Ru2(CO)5}-closo-2,1-RuCB10H8] 10. In the latter, two alkyne groups have inserted into cage B-H groups, with one of the resulting B-vinyl moieties involved in a C-H...Ru agostic bond. Oxidation of 1a with I2 or HgCl2 affords the mononuclear ruthenium complex [1-SMe2-2,2,2-(CO)3-closo-2,1-RuCB10H10] 11.     

Mechanism of homogeneously and heterogeneously catalysed Meerwein-Ponndorf-Verley-Oppenauer reactions for the racemisation of secondary alcohols

The mechanism of hydrogen transfer from alcohols to ketones, catalysed by lanthanide(III) isopropoxides or zeolite Beta has been studied. For the lanthanide catalysed reactions, (S)-1-phenyl-(1-(2)H(1))ethanol and acetophenone were used as case studies to determine the reaction pathway for the hydrogen transfer. Upon complete racemisation all deuterium was present at the 1-position, indicating that the reaction exclusively takes place via a carbon-to-carbon hydrogen transfer. Zeolite Beta with different Si/Al ratios was applied in the racemisation of (S)-1-phenylethanol. In this case the racemisation does not proceed via an oxidation/reduction pathway but via elimination of the hydroxy group and its re-addition. This mechanism, however, is not characteristic for all racemisation reactions with zeolite Beta. When 4-tert-butyl cyclohexanone is reduced with this catalyst, a classical MPV reaction takes place exclusively. This demonstrates that zeolite Beta has a substrate dependent reaction pathway.     

Direct iodination of alkanes

[reaction: see text] A cheap and efficient iodination of hydrocarbons can be achieved by generating tert-butyl hypoiodite from iodine and sodium tert-butoxide. The alkane is reactant and solvent, and this metal-free process provides a clean solution for their direct iodination.     

Resonance Raman studies of beta-substituted porphyrin systems with unusual electronic absorption properties.

Zn(II) and Cu(II) porphyrins with beta-conjugated barbiturate functional groups have low-energy electronic transitions which are unusual in that there are two strong bands in the Soret region. Resonance excitation of the two bands shows that each has features characteristic of both the porphyrin and barbiturate groups, with some perturbation to these features caused by the interaction of the two chromophores. The resonance Raman (RR) spectrum (lambda(exc)=413.1 nm) of the 412 nm band shows two bands at 1722 and 1743 cm(-1) attributable to C==O stretches in the substituent. Changes in frequency of porphyrin core modes due to the differing metal centres are reproduced by density functional theory calculations. The Q band RR spectra show modes with anomalous polarization which may be attributed to A(2g) modes, however no overtone or combination bands are observed.     

Das Reaktionsverhalten von Cp2NbCl2 gegenüber WF6—Struktur von [Cp2NbCl2]4[WF6]2[WCl6]

The oxidation of Cp₂NbCl₂ with pure WF₆ in SO₂ solution yielded the cationic metallocene species [Cp₂NbCl₂]⁺[WF₆]⁻ essentially in quantitative yield. The same reaction carried out in the presence of either equimolar amounts or a two-fold excess of HCN led to the preparation of the new niobocenium salt [Cp₂NbCl₂]₄⁺[WF₆]²⁻ which was studied by single crystal X-ray diffraction. This compound represents the first example of a structurally characterized metallocene-WF₆⁻ complex, and crystallizes in the tetragonal system: space group, P4₁2₁2(No. 92), a = 11.083(8) Å, c = 48.285 (9) Å; Z = 8; R = 0.0759, R_W = 0.0841. ab]Die Oxidation von Cp₂NbCl₂ mit reinem WF₆ führt in SO₂-Lösung zur Synthese von [Cp₂NbCl₂ ]⁺[WF₆]⁻ in nahezu quantitativer Ausbeute. Die analoge Reaktion führt unter Anwesenheit der äquimolaren Menge oder eines zweifachen Überschusses an HCN zur Ausbildung des Niobocenium-Komplexsalzes [Cp₂NbCl₂]₄⁺ [WF₆]₂⁻[WCl₆]²⁻, von dem eine Röntgenstrukturanalyse angefertigt wurde. Diese Verbindung repräsentiert den ersten structurell charakterisierten Vertreter eines Metallocen-WF₆⁻-Komplexes und kristallisiert im tetragonalen System: Raumgruppe P4₁2₁2 (Nr. 92), a = 11.083(8) Å, c = 48.285(9) Å; Z = 8; R = 0.0759, R_W = 0.0841. kw]Niobium; X-ray diffraction; Oxidation; Metallocenes     

Highly efficient electrocatalytic hydrogen evolution promoted by O–Mo–C interfaces of ultrafine β-Mo2C nanostructures

Optimizing interfacial contacts and thus electron transfer phenomena in heterogeneous electrocatalysts is an effective approach for enhancing electrocatalytic performance. Herein, we successfully synthesized ultrafine β-Mo₂C nanoparticles confined within hollow capsules of nitrogen-doped porous carbon (β-Mo₂C@NPCC) and found that the surface layer of molybdenum atoms was further oxidized to a single Mo–O surface layer, thus producing intimate O–Mo–C interfaces. An arsenal of complementary technologies, including XPS, atomic-resolution HAADF-STEM, and XAS analysis clearly reveals the existence of O–Mo–C interfaces for these surface-engineered ultrafine nanostructures. The β-Mo₂C@NPCC electrocatalyst exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) in water. Theoretical studies indicate that the highly accessible ultrathin O–Mo–C interfaces serving as the active sites are crucial to the HER performance and underpinned the outstanding electrocatalytic performance of β-Mo₂C@NPCC. This proof-of-concept study opens a new avenue for the fabrication of highly efficient catalysts for HER and other applications, whilst further demonstrating the importance of exposed interfaces and interfacial contacts in efficient electrocatalysis.

Ultrafine β-Mo₂C nanostructures encapsulated in N-doped carbon capsules featuring O–Mo–C interfaces as the active sites for HER have been unveiled.