Search

• Photoreactions of alkenyl- and thiolate-bridged diiron carbonyls with alkynes. • A series of thiolate-bridged diiron acyl complexes was synthesized. • Facile insertion of alkynes into the iron-alkenyl bond is followed by CO insertion. • Dynamic behavior of an alkenyl-thiolate ligand was investigated. The alkenyl- and thiolate-bridged diiron carbonyl complexes [Fe 2 (μ-SC 6 H 4 CR1CH)(CO) 6 ] (R1 = H or Me), which are derived from [Fe 3 (CO) 12 ] and benzothiophenes, reacted with alkynes (R2CCR3) under photoirradiation conditions to form the acyl complexes [Fe 2 {μ-SC 6 H 4 CR1CHCR2C(R3)CO}(CO) 5 ]. In this reaction, an alkyne and CO are inserted into the Fe–alkenyl bond, and the bulky substituents of alkynes, including a redox active ferrocenyl group, occupy the R3 position. To elucidate the reaction pathway, the reaction of the in situ generated acetonitrile complex [Fe 2 (μ-SC 6 H 4 CHCH)(CO) 5 (NCCH 3)] with ethynylbenzene was monitored by 1H NMR spectroscopy. The results demonstrated that the acetonitrile complex undergoes facile insertion of the alkyne, which is followed by CO insertion to give the corresponding acyl complex [Fe 2 {μ-SC 6 H 4 (CH) 3 C(Ph)CO}(CO) 5 ]. The reactivity of the bridging alkenyl moiety is related to the dynamic behavior of the alkenyl-thiolate ligand (SC 6 H 4 CHCH)2- as well as the entering alkyne. Temperature dependent 31P NMR measurements of the dmpm-bridged complex [Fe 2 (μ-SC 6 H 4 CHCH)(μ-dmpm)(CO) 4 ] (dmpm = bis(dimethylphosphino)methane) revealed that the activation parameters for the flip-flop motion of the alkenyl-thiolate ligand are Δ H ‡ = 46.7(7) kJ mol-1 and Δ S ‡ = −46(2) J mol-1 K-1. [Display omitted] [ABSTRACT FROM AUTHOR]

Clusters can be model systems for nanoparticles with regard to the chemistry of surface groups. Metal oxo clusters with carboxylato ligands are easily accessible and therefore well-suited for investigating the chemistry of cluster-bonded ligands. This review article gives an account on issues like ligand dynamics, post-synthesis ligand exchange, stability of the cluster core during ligand exchange, possible mechanisms of intra- and intermolecular ligand exchange or utilizing functional ligands. [ABSTRACT FROM AUTHOR]

A series of new chiral [(NHC)Au(I)Cl] are synthesized. The chiral NHC ligands feature pairs of ortho-biphenyl groups. The distal phenyl groups of the biphenyl substituents are varied from simple phenyl, 3,5-dimethylphenyl, to 3,5-di-t-butylphenyl. X-Ray structure analysis were performed for two such [(NHC)Au(I)Cl] complexes. High percent buried volumes were calculated for two novel chiral [(NHC)Au(I)Cl]complexes whose structure were solved by an X-ray analysis. The rotational motion in the biphenyl group is slow on the NMR time scale. Rotational barriers were determined using WINDNMR for two of the chiral gold complexes. [ABSTRACT FROM AUTHOR]

Background The nature of ligand motion in proteins is difficult to characterize directly usingexperiment. Specifically, it is unclear to what degree these motions are coupled. Methods All-atom simulations are used to sample ligand motion in truncated Hemoglobin N. A transition network analysis including ligand- and protein-degrees of freedom is used to analyze the microscopic dynamics. Results Clustering of two different subsets of MD trajectories highlights the importance of a diverse and exhaustive description to define the macrostates for a ligand-migration network. Monte Carlo simulations on the transition matrices from one particular clustering are able to faithfully capture the atomistic simulations. Contrary to clustering by ligand positions only, including a protein degree of freedom yields considerably improved coarse grained dynamics. Analysis with and without imposing detailed balance agree closely which suggests that the underlying atomistic simulations are converged with respect to sampling transitions between neighboring sites. Conclusions Protein and ligand dynamics are not independent from each other and ligand migration through globular proteins is not passive diffusion. General significance Transition network analysis is a powerful tool to analyze and characterize the microscopic dynamics in complex systems. This article is part of a Special Issue entitled Recent developments of molecular dynamics. [ABSTRACT FROM AUTHOR]

The catalytic site of heme–copper oxidases encompasses two close-lying ligand binding sites: the heme, where oxygen is bound and reduced and the Cu B atom, which acts as ligand entry and release port. Diatomic gaseous ligands with a dipole moment, such as the signaling molecules carbon monoxide (CO) and nitric oxide (NO), carry clear infrared spectroscopic signatures in the different states that allow characterization of the dynamics of ligand transfer within, into and out of the active site using time-resolved infrared spectroscopy. We review the nature and diversity of these processes that have in particular been characterized with CO as ligand and which take place on time scales ranging from femtoseconds to milliseconds. These studies have advanced our understanding of the functional ligand pathways and reactivity in enzymes and more globally represent intriguing model systems for mechanisms of ligand motion in a confined protein environment. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. [ABSTRACT FROM AUTHOR]

Abstract: Optical spectroscopy on ensembles and single CdSe/ZnS semiconductor quantum dots (QDs) demonstrates a competition of trap and near band edge photoluminescence (PL). This competition can be markedly influenced by a few surface attached pyridyl functionalized dye molecules (porphyrins or perylene diimides) forming nanoassemblies with well defined geometries. Temperature variation and related changes in absorption and emission reveal sharp changes of the ligand shell structure in a narrow temperature range for organic (TOPO and amine) surfactants (phase transition). The effects on QD PL at this transition become considerably pronounced upon attachment of only a few dye molecules to QD surface. Moreover, under ambient conditions amine capped QDs are photodegraded in the course of time. This process is enhanced by attached dye molecules both on the ensemble and single particle/dye level. This investigation elaborates the importance of (switchable) surface states for the characterization of the PL of QDs. [Copyright &y& Elsevier]

Abstract: The active site of nitric oxide reductase from Paracoccus denitrificans contains heme and non-heme iron and is evolutionarily related to heme-copper oxidases. The CO and NO dynamics in the active site were investigated using ultrafast transient absorption spectroscopy. We find that, upon photodissociation from the active site heme, 20% of the CO rebinds in 170 ps, suggesting that not all the CO transiently binds to the non-heme iron. The remaining 80% does not rebind within 4 ns and likely migrates out of the active site without transient binding to the non-heme iron. Rebinding of NO to ferrous heme takes place in ~13 ps. Our results reveal that heme-ligand recombination in this enzyme is considerably faster than in heme-copper oxidases and are consistent with a more confined configuration of the active site. [Copyright &y& Elsevier]