The binding of free oligopeptides to cyclodextrins: The role of the tyrosine group

The formation of-cyclodextrin (-CD) and,-cyclodextrin (-CD) inclusion complexes with free tyrosine and the tyrosine residues within two free oligopeptides were investigated using steady-state fluorescence spectroscopy. The oligopeptides consist of five amino acids (pentapeptide) and the tyrosine residues are located at then-termini. The two peptides used in this study have well-known biological functions and are known to bind selectively to specific cell receptors. Cyclodextrins were used to model this receptor-peptide (protein-ligand) interaction. Equilibrium binding constants and the enthalpy and entropy of binding were recovered. Molecular size of the tyrosine-containing species and pH (7.0 vs. 10.0) were found to have little affect on-CD binding. However, tyrosine binding to-CD was dependent on the size (free tyrosine vs. peptide), structure, and pentapeptide conformation.     

Chemical Swarming: Depending on Concentration,an Amphiphilic Ruthenium Polypyridyl Complex Induces Cell Death via Two Different Mechanisms

The crystal structure and in vitro cytotoxicity of the amphiphilic ruthenium complex [ 3 ](PF₆)₂ are reported. Complex [ 3 ](PF₆)₂ contains a Ru?S bond that is stable in the dark in cell‐growing medium, but is photosensitive. Upon blue‐light irradiation, complex [ 3 ](PF₆)₂ releases the cholesterol–thioether ligand 2 and an aqua ruthenium complex [ 1 ](PF₆)₂. Although ligand 2 and complex [ 1 ](PF₆)₂ are by themselves not cytotoxic, complex [ 3 ](PF₆)₂ was unexpectedly found to be as cytotoxic as cisplatin in the dark, that is, with micromolar effective concentrations (EC₅₀), against six human cancer cell lines (A375, A431, A549, MCF‐7, MDA‐MB‐231, and U87MG). Blue‐light irradiation (λ=450 nm, 6.3 J cm^?2) had little influence on the cytotoxicity of [ 3 ](PF₆)₂ after 6 h of incubation time, but it increased the cytotoxicity of the complex by a factor 2 after longer (24 h) incubation. Exploring the unexpected biological activity of [ 3 ](PF₆)₂ in the dark elucidated an as‐yet unknown bifaceted mode of action that depended on concentration, and thus, on the aggregation state of the compound. At low concentration, it acts as a monomer, inserts into the membrane, and can deliver [ 1 ]²⁺ inside the cell upon blue‐light activation. At higher concentrations (>3–5 μm ), complex [ 3 ](PF₆)₂ forms supramolecular aggregates that induce non‐apoptotic cell death by permeabilizing cell membranes and extracting lipids and membrane proteins.     

Toward Tailored Xerogel Composites: Local Dipolarity and Nanosecond Dynamics within Binary Composites Derived from Tetraethylorthosilane and ORMOSILs,Oligomers or Surfactants

We explore the potential of xerogel composites to tailor the behavior of active dopants that are sequestered within the xerogel. Toward this end, we report on the local dipolarity and dynamics of two fluorescent probes (pyrene and rhodamine 6G, R6G) each co-doped at low concentration directly into a series of binary xerogel composites. The composites that we have investigated are composed of tetraethylorthosilicate (Si(OCH₂CH₃)₄,TEOS) plus one of several organically-modified silanes (ORMOSILs), organic oligomers, or a common surfactant. For convenience we divide these xerogel composites into two classes: (1) xerogels wherein the organic character arises from the addition of an ORMOSIL co-monomer, possessing a non-hydrolyzable organic functional group, that becomes covalently incorporated with in the xerogel and (2) xerogels wherein the organic content is adjusted by adding organic oligomers or a surfactant. Six organically-modified silylalkoxides of the form R _n Si(OR)_4–n were investigated as ORMOSILs. Poly(ethylene glycol), Nafion, and Ionene 6,2 were tested as oligomers. Triton X-100 was used as the surfactant. To estimate the local dipolarity within these composites we used the static fluorescence from pyrene molecules that were sequestered within the composites. These experiments showed that the local dipolarity surrounding the average pyrene molecule can be tuned significantly, but this depends on the actual organic species that one uses to prepare the xerogel composite. Time-resolved fluorescence anisotropy measurements were used to quantify the R6G mobility within the same composites. These results demonstrate that certain organic additive scan be used to adjust the R6G mobility within the xerogel composite.     

A new ion sensor based on fiber optics

A fluorimetric ion sensor based on fiber optics has been developed that employs Rhodamine 6G hydrophobically and electrostatically "trapped" on a Nafion film. The sensor is based on the measurement of quenching or enhancement of the Rhodamine 6G fluorescence by various ions. It was found that ions such as Co(2+), Cr(3+), Fe(2+), Fe(3+), Cu(2+), Ni(2+) and NH(+)(4) rapidly quench the Rhodamine 6G fluorescence at an initial rate that depends on the concentration of the ion. This quenching is then readily reversed by the addition of "reverser" ions such as H(+), Li(+), Na(+), K(+), Ba(2+), Ca(2+), Mn(2+), Zn(2+) and Mg(2+). Again, the initial rate for the attainment of the original fluorescence was found to depend on the concentration of the reverser ion. Therefore, by monitoring the quenching directly the concentration of quencher ions can be determined. In addition, by loading the film with quencher and monitoring the initial rate of return towards the original baseline signal, it is possible to determine non-quenching ions.     

Synthese und Kristallstrukturen der Thiochloroantimonate(III) PPh4[Sb2SCl5] und (PPh4)2[Sb2SCl6] · CH3CN

Syntheses and Crystal Structures of the Thiochloroantimonates(III) PPh₄[Sb₂SCl₅] and (PPh₄)₂[Sb₂SCl₆]. CH₃CN (PPh₄)₂Sb₃Cl₁₁, obtained from Sb₂S₃, PPh₄Cl and HCl, reacts with Na₂S₄ in acetonitrile forming PPh₄[Sb₂SCl₅]. From this and Na₂S₄ or from (PPh₄)₂[Sb₂Cl₈] and Na₂S₄ or K₂S₅ in acetonitrile (PPh₄)₂[Sb₂SCl₆] · CH₃CN is obtained. Data obtained from the X-ray crystal structure determinations are: PPh₄[Sb₂SCl₅], monoclinic, space group P2₁/c, a = 1002.9(3), b = 1705.6(5), c = 1653.7(5) pm, β = 99.12(2)°, Z = 4, R = 0.068 for 1283 reflextions; (PPh₄)₂[Sb₂SCl₆] · CH₃CN, triclinic, space group P1 , a = 1287.8(7), b = 1343.6(9), c = 1696.5(9) pm, α = 69.82(5), β = 85.08(4), γ = 71.54(6)°, Z = 2, R = 0.059 for 6409 reflexions. In every anion two Sb atoms are linked via one sulfur and one ore two chloro atoms, respectively. Paris of [SbSCl₅]^? ions are associated via Sb …? S and Sb …? Cl contacts forming dimer units. In both compounds every Sb atom has a distorted octahedral coordination when the lone electron pair is included in the counting.     

Linkage and redox isomerism in ruthenium complexes of catecholate, semiquinone, and o-acylphenolate ligands derived from 1,2-dihydroxy-9,10-anthracenedione (alizarin) and related species: syntheses, characterizations, and photophysics

The complexes Ru(CO)2L2(AL-2H) (AL = alizarin; L = PPh3, PCyc3, PBu3, P(m-NaSO3C6H4)3), Ru(CO)(dppe)(PBu3)(AL-2H), and RuH(CO)L2(AL-H) (L = PPh3, PCyc3), and Ru(CO)2L2(AR-2H) (AR = anthrarobin; L = PBu3) were prepared by reactions of Ru3(CO)12, L, and AL, and the complexes RuH(CO)(PPh3)2(AL-H), RuH(CO)(PPh3)2(QN-H) (QN = quinizarin), and RuH(CO)(PPh3)2(LQN-H) (LQN = leucoquinizarin) are prepared by reactions of RuH2(CO)(PPh3)3 with AL or QN. The AL-2H and AR-2H ligands act as 1,2-catecholates, whereas the AL-H, QN-H, LQN-H ligands are 1,9-o-acylphenolate ligands. RuH(CO)(PPh3)2(AL-H) is characterized by X-ray crystallography. The electrochemistry of these complexes is examined, and the semiquinone complexes [Ru(CO)2L2(AL-2H)]+ (L = PPh3, PCyc3, PBu3) and [Ru(CO)(dppe)(PBu3)(AL-2H)]+ are generated by chemical oxidation and were characterized by EPR and IR spectroscopy. The photophysical properties are also reported.     

On the dispersion function in particle transport theory

Elementary considerations are used to show in regard to particle transport theory that the dispersion function relevant to each of the Fourier-component problems resulting from a finite Legendre expansion of the scattering law cannot have a zero forv (–1, 1), and a condition for the endpoints ±1 to be zeros is reported. It is also shown that the dispersion function and the characteristic function cannot, for a given Fourier-component problem, vanish simultaneously for any value ofz [–1, 1].

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Zusammenfassung Mit elementaren Betrachtungen der Teilchentransport-Theorie wird gezeigt, daß die Dispersionsfunktion für jedes Fourier-Komponentenproblem, welches durch eine endliche Legendre-Entwicklung des Streuungsproblems entsteht, keine Nullstellen fürv (–1, 1) hat; eine Bedingung für Nullstellen an den Endpunkten ±1 wird angegeben. Es wird gezeigt, daß die Dispersionsfunktion und die charakteristische Funktion für ein gegebenes Fourier-Komponenten-Problem nicht gleichzeitig verschwinden können für Wertez [–1, 1].