Different binding thermodynamics of Ni2+, Cu2+, and Zn2+ to bacitracin A1 determined by capillary electrophoresis

Thermodynamics of the binding of Ni(2+), Cu(2+) and Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis measuring the peptide effective mobility at different pH in the presence of increasing concentration of the three ligands. The affinity follows the order Ni(2+) > Cu(2+) > Zn(2+), with association constant values of (2.3 +/- 0.1)x10(4), (4.9 +/- 0.2)x10(3), and (1.5 +/- 0.1)x10(3) M(-1), respectively. The only model able to rationalize mobility data implies that metal ion binds to the P(0) peptide form. Moreover, mobility values indicated a change of bacitracin A(1) acidic properties on Ni(2+) and Cu(2+) binding, with a shift of the pK(a) of N-terminal Ile-1 from 7.6 to about 5 and of the pK(a) of the delta-amino group of D-Orn-7 from 9.7 to about 7. Even though on Zn(2+) binding a shift of the N-terminal Ile-1 pK(a) was observed, restrictions in the pH range suitable for investigation, due to precipitation phenomena, did not allow establish if the shift of D-Orn-7 lateral chain pK(a) also occurred. Nonetheless, if present, the shift should be limited to the 7.8-9.7 range. Mobility data indicated that the Stokes radius of the complexes is ca. 3 A lower than that of the free peptide. The present results indicate that metal-ion binding to bacitracin A(1) is more complex than previously assumed.     

MODULATION AND DYNAMICS OF PHASE PROPERTIES IN PHOSPHOLIPID MIXTURES DETECTED BY LAURDAN FLUORESCENCE*

Steady-state and dynamic fluorescence properties of 6-lauroyl-2-dimethylaminonaphthalene (Laurdan) have been used to ascertain the coexistence of separate phase domains and their dynamic properties in phospholipid vesicles composed of different mole ratios of dilauroyl- and dipalmitoyl-phosphatidylcholine (DLPC and DPPC, respectively). The recently introduced generalized polarization together with time-resolved emission spectra have been utilized for detecting changes. The results indicate the coexistence of phospholipid phase domains in vesicle compositions in the range between 30 mol% and 70 mol% DPPC in DLPC. Below and above these concentrations a homogeneous phase is observed, with averaged properties. In the case of coexisting phase domains, the properties of each individual phase are largely influenced by the presence of the other phase. Implications on fluctuations between the coexisting phases and on the size and shape of domains are discussed.     

Facts and artifacts in proteomics of body fluids. What proteomics of saliva is telling us?

This review briefly depicts several salient points of the current status of knowledge on salivary peptidoma. It outlines the intrinsic difficulties in its characterization connected to different factors of variability, such as: i) the high genetic polymorphisms, complicated by individual insertions/deletions and alternative splicing; ii) complex post-translational maturations comprehending different proteolytic cleavages, glycosylation, phosphorylation and sulfation processes; iii) physiological variations and different contributions to the whole. Moreover, several technological and analytical problems and pitfalls that had to be surmounted during our studies focussed on the extensive qualitative and quantitative characterization of salivary peptidoma and mainly based on LC-MS analyses of intact naturally occurring peptides are here described. The hope is that the information provided might be helpful to other groups engaged on the analysis of saliva or other body fluids for clinical applications.     

Impulsive semilinear differential inclusions: Topological structure of the solution set and solutions on non-compact domains

This paper deals with an impulsive Cauchy problem governed by the semilinear evolution differential inclusion x^′(t)∈A(t)x(t)+F(t,x(t))$x^{\prime }\left(t\right)\in A\left(t\right)x\left(t\right)+F(t,x\left(t\right))$, where _{{A(t)}t∈[0,b]}${\left\{A\left(t\right)\right\}}_{t\in [0,b]}$ is a family of linear operators (not necessarily bounded) in a Banach space E$E$ generating an evolution operator and F$F$ is a Carathéodory type multifunction. First a theorem on the compactness of the set of all mild solutions for the problem is given. Then this result is applied to obtain the existence of mild solutions for the impulsive Cauchy problem defined on non-compact domains.     

Secondary metabolites from Paronychia argentea

Two new oleanane saponins (1 and 2) and one new flavonol glycoside (3) together with six known flavonoids, were isolated from the aerial parts of Paronychia argentea. Their structures were elucidated by 1D and 2D NMR experiments including 1D-TOCSY, DQF-COSY, NOESY, HSQC, and HMBC spectroscopy, as well as ESI-MS analysis.     

Spider-like oligothiophenes

Careful analysis and comparison of optical and electrochemical data available in recent literature for multi-thiophene molecular assemblies suggested a few basic rules for the design of structurally simple and easily accessible oligothiophenes endowed with properties not far from those exhibited by much more complex and synthetically demanding architectures. The synthesis and computational investigation of three examples of a class of oligothiophenes (spider-like) tailored according to these indications are reported together with their exhaustive optical and electrochemical characterization. The new compounds (T9 5, T14 6, T19 7) are characterized by a thiophene, a 2,2'-bithiophene and a 2,2',5',2'-terthiophene unit (the spider body) fully substituted with 5-(2,2'-bithiophen)yl pendants (the spider legs). Absorption and electrochemical data are in good agreement and point to a high pi-conjugation level, comparable to those displayed by much larger assemblies. Electrode potential cycling in proximity of the first oxidation peak affords fast and reproducible formation of conducting, highly stable [TXn]m films, mainly consisting of dimers (m=2). Electrooxidation kinetic experiments on deuterium-labelled T9 5, coupled to laser-desorption-ionization mass spectroscopy on the resulting dimer demonstrated that the coupling process is extremely regioselective in the alpha positions of the more conjugated pentathiophene chain. The optical and the electrochemical properties of the films are reported and discussed. A peculiar feature is their impressive charge-trapping ability. Spider-like oligothiophenes are promising materials for applications as active layers in multifunctional organic devices.     

Photosensitized oxidation of alkyl phenyl sulfoxides. C-S bond cleavage in alkyl phenyl sulfoxide radical cations

The 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)ClO4(-))-photosensitized oxidation of phenyl alkyl sulfoxides (PhSOCR1R2R3, 1, R1 = R2 = H, R3 = Ph; 2, R1 = H, R2 = Me, R3 = Ph; 3, R1 = R2 = Ph, R3 = H; 4, R1 = R2 = Me, R3 = Ph; 5, R1 = R2 = R3 = Me) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Steady-state photolysis showed the formation of products deriving from the heterolytic C-S bond cleavage in the sulfoxide radical cations (alcohols, R1R2R3COH, and acetamides, R1R2R3CNHCOCH3) accompanied by sulfur-containing products (phenyl benzenethiosulfinate, diphenyl disulfide, and phenyl benzenethiosulfonate). By laser irradiation, the formation of 3-CN-NMQ(*) (lambda(max) = 390 nm) and sulfoxide radical cations 1(*+) , 2(*+), and 5(*+) (lambda(max) = 550 nm) was observed within the laser pulse. The radical cations decayed by first-order kinetics with a process attributable to the heterolytic C-S bond cleavage leading to the sulfinyl radical and an alkyl carbocation. The radical cations 3(*+) and 4(*+) fragment too rapidly, decaying within the laser pulse. The absorption band of the cation Ph2CH(+) (lambda(max) = 440 nm) was observed with 3 while the absorption bands of 3-CN-NMQ(*) and PhSO(*) (lambda(max) = 460 nm) were observed just after the laser pulse in the LFP experiment with 4. No competitive beta-C-H bond cleavage has been observed in the radical cations from 1-3. The C-S bond cleavage rates were measured for 1(*+), 2(*+), and 5(*+). For 3(*+) and 4(*+), only a lower limit (ca. >3 x 10(7) s(-1)) could be given. Quantum yields (Phi) and fragmentation first-order rate constants (k) appear to depend on the structure of the alkyl group and on the bond dissociation free energy (BDFE) of the C-S bond of the radical cations determined by a thermochemical cycle using the C-S BDEs for the neutral sulfoxides 1-5 obtained by DFT calculations. Namely, Phi and k increase as the C-S BDFE becomes more negative, that is in the order 1 < 5 < 2 < 3, 4, which is also the stability order of the alkyl carbocations formed in the cleavage. An estimate of the difference in the C-S bond cleavage rate between sulfoxide and sulfide radical cations was possible by comparing the fragmentation rate of 5(*+) (1.4 x 10(6) s(-1)) with the upper limit (10(4) s(-1)) given for tert-butyl phenyl sulfide radical cation (Baciocchi, E.; Del Giacco, T.; Gerini, M. F.; Lanzalunga, O. Org. Lett. 2006, 8, 641-644). It turns out that sulfoxide radical cations undergo C-S bond breaking at a rate at least 2 orders of magnitude faster than that of corresponding sulfide radical cations.     

2,5-Dimethyl-3,4-bis[(2R,5R)-2,5-dimethylphospholano]thiophene: first member of the hetero-DuPHOS family

[reaction: see text] The 2,5-dimethyl-3,4-bis[(2R,5R)-2,5-dimethylphospholano]thiophene (UlluPHOS), a new thiophene-based analogue of (R,R)-1,2-bis(phospholano)benzene (Me-DuPHOS), was synthesized, geometrically and electronically characterized, and employed as ligand of Rh and Ru in some standard hydrogenation reactions of prostereogenic functionalized carbon-carbon and carbon-oxygen double bonds. The synthesis of UlluPHOS is much easier than that provided for Me-DuPHOS. UlluPHOS and Me-DuPHOS display very similar geometries, while the electronic availability of the former is higher than that exhibited by the latter. The Rh and Ru complexes of UlluPHOS produced excellent enantiomeric excesses (98.9-99.5%) in the hydrogenation of N-acetyl-alpha-enamino acids and reaction rates higher than those found when employing the analogous complexes of Me-DuPHOS.     

Thermally stimulated current investigation of copper octaethylporphyrin dimer Langmuir-Blodgett films

Langmuir-Blodgett films containing meso,meso'-buta-1,3-diyne-bridge Cu(II) octaethylporphyrin dimer have been deposited with the aim of carrying out a thermally stimulated current (TSC) investigation. This characterization was obtained upon cooling samples irradiated by light and others without irradiation: in this way TSC curves have been registered in the temperature range of 100-300 K. Analysis of experimental data has been performed through the application of three different approaches: the initial rate, the heating rate, and Chen's methods. In particular, a trap center at about 0.38 eV has been evidenced and the three different methods have given results in close accordance.