Enantioselective DNA threading dynamics by phenazine-linked.

The interactions between the stereoisomers of the chiral bis-intercalator [mu-C4(cpdppz)(2)-(phen)(4)Ru(2)](4+) and DNA reveal interesting dynamic discrimination properties. The two enantiomers Delta-Delta and Lambda-Lambda both form very strong complexes with calf thymus DNA with similar thermodynamic affinities. By contrast, they display considerable variations in their binding kinetics. The Delta-Delta enantiomer has higher affinity for calf thymus DNA than for [poly(dA-dT)](2), and the association kinetics of the dimer to DNA, as well as to polynucleotides, requires a multiexponential fitting function. The dissociation reaction, on the other hand, could be described by a single exponential for [poly(dA-dT)](2), whereas two exponentials were required for mixed-sequence DNA. To understand the key mechanistic steps of the reaction, the kinetics was studied at varied salt concentration for different choices of DNA and chirality of the threading complex. The enantiomers were found to have markedly different dissociation rates, the Lambda-Lambda enantiomer dissociating about an order of magnitude faster than the Delta-Delta enantiomer. Also, the salt dependence of the dissociation rate constants differed between the enantiomers, being stronger for the Lambda-Lambda enantiomer than for the Delta-Delta enantiomer. Since the dissociation reaction requires unthreading of bulky parts of the bis-intercalator through the DNA helix, a considerable conformational change of the DNA must be involved, possibly defining the rate-limiting step.     

The Intermetalloid Cluster [(Cp*AlCu)6H4], Embedding a Cu6 Core Inside an Octahedral Al6 Shell: Molecular Models of Hume–Rothery Nanophases

Defined molecular models for the surface chemistry of Hume–Rothery nanophases related to catalysis are very rare. The Al‐Cu intermetalloid cluster [(Cp*AlCu)₆H₄] was selectively obtained from the clean reaction of [(Cp*Al)₄] and [(Ph₃PCuH)₆]. The stronger affinity of Cp*Al towards Cu sweeps the phosphine ligands from the copper hydride precursor and furnishes an octahedral Al₆ cage to encapsulate the Cu₆ core. The resulting hydrido cluster M₁₂H₄ reacts with benzonitrile to give the stoichiometric hydrometalation product [(Cp*AlCu)₆H₃(N=CHPh)].     

Reactivity and Operational Stability of N‐Tailed TAMLs through Kinetic Studies of the Catalyzed Oxidation of Orange II by H2O2: Synthesis and X‐ray Structure of an N‐Phenyl TAML

The catalytic activity of the N‐tailed (“biuret”) TAML (tetraamido macrocyclic ligand) activators [Fe{4‐XC₆H₃‐1,2‐( N COCMe₂ N CO)₂NR}Cl]^2? ( 3 ; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me ( a ); NO₂, Me ( b ); H, Ph ( c )] in the oxidative bleaching of Orange II dye by H₂O₂ in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4‐XC₆H₃‐1,2‐( N COCMe₂ N CO)₂CMe₂}OH₂]^? ( 1 ) and the more aggressive analogue [Fe(Me₂C{CON(1,2‐C₆H₃‐4‐X) N CO}₂)OH₂]^? ( 2 ). Catalysis by 3 of the reaction between H₂O₂ and Orange II (S) occurs according to the rate law found generally for TAML activators (v=k_Ik_II[Fe^III][S][H₂O₂]/(k_I[H₂O₂]+k_II[S]) and the rate constants k_I and k_II at pH 7 both decrease within the series 3 b > 3 a > 3 c . The pH dependency of k_I and k_II was investigated for 3 a . As with all TAML activators studied to‐date, bell‐shaped profiles were found for both rate constants. For k_I, the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a . For k_II, the broad bell pH profile exhibits a maximum at pH about 10.5. The condition k_I?k_II holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants k_i for suicidal inactivation of the active forms of complexes 3 a – c were calculated using the general formula ln([S₀]/[S_∞])=(k_II/k_i)[Fe^III]; here [Fe^III], [S₀], and [S_∞] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X‐ray characterization of 3 c are also described.     

Synthesis of Fructooligosaccharides from Aspergillus niger Commercial Inulinase Immobilized in Montmorillonite Pretreated in Pressurized Propane and LPG

Commercial inulinase from Aspergillus niger was immobilized in montmorillonite and then treated in pressurized propane and liquefied petroleum gas (LPG). Firstly, the effects of system pressure, exposure time, and depressurization rate, using propane and LPG, on enzymatic activity were evaluated through central composite design 2³. Residual activities of 145.1 and 148.5 % were observed for LPG (30 bar, 6 h, and depressurization rate of 20 bar?min^?1) and propane (270 bar, 1 h, and depressurization rate of 100 bar?min^?1), respectively. The catalysts treated at these conditions in both fluids were then used for the production of fructooligosaccharides (FOS) using sucrose and inulin as substrates in aqueous and organic systems. The main objective of this step was to evaluate the yield and productivity in FOS, using alternatives for enhancing enzyme activity by means of pressurized fluids and also using low-cost supports for enzyme immobilization, aiming at obtaining a stable biocatalyst to be used for synthesis reactions. Yields of 18 % were achieved using sucrose as substrate in aqueous medium, showing the potential of this procedure, hence suggesting a further optimization step to increase the process yield.     

Chaotic spin-wave solitons in magnetic film feedback rings

Chaotic spin-wave solitons in magnetic film active feedback rings were observed for the first time. At some ring gain level, one observes the self-generation of a single spin-wave soliton pulse in the ring. When the pulse circulates in the ring, its amplitude varies chaotically with time. Numerical simulations based on a gain-loss nonlinear Schr?dinger equation reproduce the observed responses.     

Observation of the h(c)(1P) Using e+ e- collisions above the DD threshold

Using 586 pb(-1) of e+ e- collision data at E(c.m.) = 4170 MeV, produced at the Cornell Electron Storage Ring collider and collected with the CLEO-c detector, we observe the process e+ e- → π+ π- h(c)(1P). We measure its cross section to be 15.6±2.3±1.9±3.0 pb, where the third error is due to the external uncertainty on the branching fraction of ψ(2S) → π0 h(c)(1P), which we use for normalization. We also find evidence for e+ e- → ηh(c)(1P) at 4170 MeV at the 3σ level and see hints of a rise in the e+ e- → π+ π- h(c)(1P) cross section at 4260 MeV.     

Health-Promoting Compounds in Stevia: The Effect of Mycorrhizal Symbiosis,Phosphorus Supply and Harvest Time

This work aimed to establish the synergic role of arbuscular mycorrhizal fungi (AMF) symbiosis, phosphorus (P) fertilization and harvest time on the contents of stevia secondary metabolites. Consequently, steviol glycosides (SVglys) concentration and profile, total phenols and flavonoids as well as antioxidant assays, have been assessed in inoculated and no-inoculated plants, grown with or without P supply and collected at different growth stages(69, 89 and 123 days after transplanting).The obtained results suggest that the synthesis of stevia secondary metabolites is induced and/or modulated by all the investigated variability factors. In particular, AMF symbiosis promoted total SVglys content and positively influenced the concentration of some minor compounds (steviolbioside, dulcoside A and rebaudioside B), indicating a clear effect of mycorrhizal inoculation on SVglys biosynthetic pathway. Interestingly, only the mycorrhizal plants were able to synthesize rebaudioside B. In addition, P supply provided the highest levels of total phenols and flavonoids at leaf level, together with the maximum in vitro antioxidant activities (FRAP and ORAC). Finally, the harvest time carried out during the full vegetative phase enhanced the entire composition of the phytocomplex (steviolbioside, dulcoside A, stevioside, rebaudioside A, B, C. total phenols and flavonoids). Moreover, polyphenols and SVglys appeared to be the main contributors to the in vitro antioxidant capacity, while only total phenols mostly contributed to the cellular antioxidant activity (CAA). These findings provide original information about the role played by AMF in association with P supply, in modulating the accumulation of bioactive compounds during stevia growth. At the cultivation level, the control of these preharvest factors, together with the most appropriate harvest time, can be used as tools for improving the nutraceutical value of raw material, with particular attention to its exploitation as functional ingredient for food and dietary supplements and cosmetics.     

Thread Insertion of a Bis(dipyridophenazine) Diruthenium Complex into the DNA Double Helix by the Extrusion of AT Base Pairs and Cross‐Linking of DNA Duplexes

The crystal structure of the Δ,Δ enantiomer of the binuclear “light‐switch” ruthenium complex [μ‐(11,11′‐bidppz)(1,10‐phenanthroline)₄ Ru₂]⁴⁺ bound to the oligonucleotide d(CGTACG) shows that one dppz moiety of the dumbbell‐like compound inserts into the DNA stack through the extrusion of an AT base pair. The second dppz moiety recruits a neighboring DNA molecule, and the complex thus cross‐links two adjacent duplexes by bridging their major grooves.