Synthesis and reactivity of cyclam-based enediynes

Cyclam-based enediynes 1-3 have been synthesized for the first time either by direct bis- or tetra-alkylation of the cyclam or via double alkylation of the 1,8-bis-sulfonyl derivative. The enediyne 1 readily forms a complex with Ni(II), which also lowered the onset temperature for Bergman cyclization of the parent enediyne by 60 °C. In the presence of a co-oxidant, MMPP, the Ni-complex can cleave ds-DNA into the nicked relaxed form at micromolar concentrations.     

Complex series [Ru(tpy)(dpk)(X)]n+ (tpy = 2,2':6',2''-terpyridine; dpk = 2,2'-dipyridyl ketone; X = Cl-, CH3CN, NO2(-), NO+, NO*, NO-): substitution and electron transfer, structure, and spectroscopy

The complex framework [Ru(tpy)(dpk)]2+ has been used to study the generation and reactivity of the nitrosyl complex [Ru(tpy)(dpk)(NO)]3+ ([4]3+). Stepwise conversion of the chloro complex [Ru(tpy)(dpk)(Cl)]+ ([1]+) via [Ru(tpy)(dpk)(CH3CN)]2+ ([2]2+) and the nitro compound [Ru(tpy)(dpk)(NO2)]+ ([3]+) yielded [4]3+; all four complexes were structurally characterized as perchlorates. Electrochemical oxidation and reduction was investigated as a function of the monodentate ligand as was the IR and UV-vis spectroscopic response (absorption/emission). The kinetics of the conversion [4]3+/[3]+ in aqueous environment were also studied. Two-step reduction of [4]3+ was monitored via EPR, UV-vis, and IR (nu(NO), nu(CO)) spectroelectrochemistry to confirm the {RuNO}7 configuration of [4]2+ and to exhibit a relatively intense band at 505 nm for [4]+, attributed to a ligand-to-ligand transition originating from bound NO-.     

Effect of electrode membrane surface ratio and thickness on lead electrode potential

Summary The lead ion selective electrode (ISE) consisting of PbS-Ag₂S is normally used with a membrane surface of outer layer areaA _o) and inner layer area (A _i) at unity (A _o=A _i). Partial covering of one surface area with an insulating material and keeping the other surface layer intact resulted in different ratios of membrane surface areas exposed to lead solutions. The potential linearly increased with increasing theA _o/A _i ratio and decreased with decreasing theA _o/A _i ratio. The lead ISE potential increased linearly with increasing the membrane thickness, but which required much longer time for a stable potential.

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Wirkung von Oberflächenverhältnis und Dicke der Elektrodenmembran auf das Potential einer Bleielektrode

Zusammenfassung Die aus PbS-Ag₂S bestehende spezifische Bleiionen-Elektrode wird üblicherweise mit einem Oberflächenverhältnis der Außenfläche (A _o) und der Innenfläche (A _i) mitA _o=A _i verwendet. Durch teilweise Abdeckung einer Oberfläche mit isolierendem Material, ohne daß die andere Oberfläche verändert wird, ergaben sich verschiedene Verhältnisse der mit der Bleilösung in Berührung stehenden Oberflächen. Mit dem VerhältnisA _o/A _i stieg das Potential linear an bzw. es fiel mit diesem Verhältnis ab. Das Potential der spezifischen Bleielektrode stieg mit der Dicke der Membran, stabilisierte sich aber wesentlich langsamer.

     

Elevated Catalytic Activity of Ruthenium(II)–Porphyrin‐Catalyzed Carbene/Nitrene Transfer and Insertion Reactions with N‐Heterocyclic Carbene Ligands

Bis(NHC)ruthenium(II)–porphyrin complexes were designed, synthesized, and characterized. Owing to the strong donor strength of axial NHC ligands in stabilizing the trans M?CRR′/M?NR moiety, these complexes showed unprecedently high catalytic activity towards alkene cyclopropanation, carbene C? H, N? H, S? H, and O? H insertion, alkene aziridination, and nitrene C? H insertion with turnover frequencies up to 1950 min^?1. The use of chiral [Ru(D₄‐Por)(BIMe)₂] ( 1 g ) as a catalyst led to highly enantioselective carbene/nitrene transfer and insertion reactions with up to 98 % ee. Carbene modification of the N terminus of peptides at 37 °C was possible. DFT calculations revealed that the trans axial NHC ligand facilitates the decomposition of diazo compounds by stabilizing the metal–carbene reaction intermediate.     

Radioactive tracer study of adsorption and exchange reaction of lead ion selective electrode membrane

Summary The amount of adsorption and exchange of lead on the electrode membrane as a function of time was correlated to the potential measurement stability. The adsorption and exchange of lead in various organic solvents tend to be increased relating to the increase in the dielectric constant of solvents. Removal of O₂ and CO₂ and addition of methanol and formaldehyde are very effective means to improve the potential stability. The behavior of lead ISE exposed to solutions containing lead and other interfering ions was also studied.

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Radiochemische Untersuchung der Adsorptions- und Austauschreaktionen bleiionenspezifischer Elektroden

Zusammenfassung Adsorption und Austausch von Blei an der Elektrodenmembran als Funktion der Zeit wurden zur Stabilität der Potentialmessung in Beziehung gesetzt. In verschiedenen organischen Lösungsmitteln steigen Adsorption und Austausch mit der Dielektrizitätskonstante an. Die Entfernung von O₂ und CO₂ sowie der Zusatz von Methanol und Formaldehyd verbessern die Stabilität des Potentials. Das Verhalten von bleiionenspezifischen Elektroden gegenüber Lösungen, die Blei und andere störende Ionen enthalten, wurde untersucht.

     

Unusual monodentate binding mode of 2,2'-dipyridylamine (L) in isomeric trans-(acac)2RuII(L)2, trans-[(acac)2RuIII(L)2]ClO4, and cis-(acac)2RuII(L)2 (acac = acetylacetonate). synthesis, structures, and spectroscopic, electrochemical, and magnetic aspects

The reaction of cis-Ru(acac)2(CH3CN)2 (acac = acetylacetonate) with 2,2'-dipyridylamine (L) in ethanolic medium resulted in facile one-pot synthesis of stable [(acac)2RuIII(L)]ClO4 ([1]ClO4), trans-[(acac)2RuII(L)2] (2), trans-[(acac)2RuIII)L)2]ClO4 ([2]ClO4), and cis-[(acac)2RuII(L)2] (3). The bivalent congener 1 was generated via electrochemical reduction of [1]ClO4. Although in [1]+ the dipyridylamine ligand (L) is bonded to the metal ion in usual bidentate fashion, in 2/[2]+ and 3, the unusual monodentate binding mode of L has been preferentially stabilized. Moreover, in 2/[2]+ and 3, two such monodentate L's have been oriented in the trans- and cis-configurations, respectively. The binding mode of L and the isomeric geometries of the complexes were established by their single-crystal X-ray structures. The redox stability of the Ru(II) state follows the order 1 < 2 < 3. In contrast to the magnetic moment obtained for [1]ClO4, mu = 1.84 muB at 298 K, typical for low-spin Ru(III) species, the compound [2]ClO4 exhibited an anomalous magnetic moment of 2.71 muB at 300 K in the solid state. The variable-temperature magnetic measurements showed a pronounced decrease of the magnetic moment with the temperature, and that dropped to 1.59 muB at 3 K. The experimental data can be fitted satisfactorily using eq 2 that considered nonquenched spin-orbit coupling and Weiss constant in addition to the temperature-independent paramagnetism. [1]ClO4 and [2]ClO4 displayed rhombic and axial EPR spectra, respectively, in both the solid and the solution states at 77 K.     

Oxomolybdenum(VI) and (IV) complexes of pyrazole derived ONO donor ligands – synthesis,crystal structure studies and spectroelectrochemical correlation

Four cis-dioxomolybdenum complexes of general formula [MoO₂(Lⁿ)EtOH] (n = 1–4) and one oxomolybdenum(IV) complex [MoO(L⁴)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh₃. The complexes are characterized by elemental analysis, electronic spectra, IR, ¹H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole –N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO₅ donor environment.     

New phenylethanoid glycosides from Bacopa monniera

Three new phenylethanoid glycosides, viz. monnierasides I-III (1-3) along with the known analogue plantainoside B were isolated from the glycosidic fraction of Bacopa monniera. Their structures were elucidated mainly on the basis of two dimensional (2D) NMR spectral analyses.     

Concise total synthesis of (+)-crocacin C

The cytotoxic natural product (+)-crocacin C ( 1) has been synthesized in 10 linear steps from commercially available Evans' chiral propionimide in 5% overall yield (8 steps from Evans' chiral dipropionate synthon). No protecting groups were utilized.