Localization of a multiblock copolymer at a selective interface: scaling predictions and Monte Carlo verification

We investigate the localization of a hydrophobic-polar regular copolymer at a selective solvent-solvent interface with emphasis on the impact of block length M on the copolymer behavior. The considerations are based on simple scaling arguments and use the mapping of the problem onto a homopolymer adsorption problem. The resulting scaling relations treat the gyration radius of the copolymer chain perpendicular and parallel to the interface in terms of chain length N and block size M, as well as the selectivity parameter chi. The scaling relations differ for the case of weak and strong localization. In the strong localization limit a scaling relation for the lateral diffusion coefficient D( parallel) is also derived. We implement a dynamic off-lattice Monte Carlo model to verify these scaling predictions. For chain lengths in a wide range (32相似文献   

Relaxivity and water exchange studies of a cationic macrocyclic gadolinium(III) complex

We conducted relaxometric and water exchange studies of the cationic [Gd((S,S,S,S)-THP)(H2O)]3+ complex (THP 1,4,7,10-tetrakis(2-hydroxy-propyl)-1,4,7,10-tetraazacyclododecane). While the NMRD profiles obtained are typical for DOTA-like complexes (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), variable-temperature 7O NMR investigations revealed a relatively high water exchange rate (k(298)(ex) = 1.89 x 10(7) s(-1)). These results differ from those reported for other cationic tetraamide macrocyclic Gd(III) complexes, which exhibit characteristically low exchange rates. Since the low exchange rates are attributed partially to the geometry of the M isomer (square antiprismatic) in the tetraamide derivatives, the atypical water exchange rate observed in [Gd((S,S,S,S)-THP-(H2O)]3+ may result from a twisted square antiprismatic structure in this complex and from the relatively high steric strain at the water coordination site as a result of the presence of methyl groups at the alpha-position with respect to the Gd(III)-bound O atoms of THP.     

Oscillator Synchronisation under Arbitrary Quasi-periodic Forcing

We study the problem of existence of response solutions for a real-analytic one-dimensional system, consisting of a rotator subject to a small quasi-periodic forcing with Bryuno frequency vector. We prove that at least one response solution always exists, without any assumption on the forcing besides smallness and analyticity. This strengthens the results available in the literature, where generic non-degeneracy conditions are assumed. The proof is based on a diagrammatic formalism and relies on renormalisation group techniques, which exploit the formal analogy with problems of quantum field theory; a crucial role is played by remarkable identities between classes of diagrams.     

Phase-locked, time-delayed harmonic pulses for high spectral resolution in the extreme ultraviolet

We present experiments in the time and frequency domains aimed at confirming the measured mutual phase coherence of time-delayed, collinear harmonic pulses. We show that pairs of phase-locked harmonic pulses of medium order can be generated for peak intensities up to ~1.5 10(14)W/cm(2) in xenon, demonstrating the possibility of performing high-resolution spectroscopy in the extreme ultraviolet with Ramsey-like techniques.     

Pressure broadening and shift of transitions of the first overtone of HCl

High-resolution spectroscopic measurements were made using distributed feedback diode lasers. We measured line strength and pressure-induced broadening and shift for two lines, R(3) and P(4), of the first overtone (2?0) ro-vibrational band, for the two isotopomers H³⁵Cl and H³⁷Cl, according to their natural abundances; measurements were also made in the presence of foreign gases. Comparison was made with available data when possible. Received: 29 February 2000 / Published online: 8 November 2000     

A convergent approach toward phoslactomycins and leustroducsins

Synthetic studies devoted to the development of a convergent approach toward phoslactomycins and leustroducsins, a family of natural products inhibitors of serine/threonine phosphatase 2A, are reported. A formal synthesis of phoslactomycin B was achieved in which the key steps are a [2,3]-Wittig rearrangement to control the C4 and C5 stereocenters, a diastereoselective addition of an acetylenic Grignard reagent to an α-alkoxy ketone to create the C8 tertiary alcohol, and a relay ring-closing metathesis to construct the α,β-unsaturated δ-lactone. In this approach, all the stereocenters originate, either directly or indirectly, from catalytic enantioselective reductions of acetylenic ketones.     

High-resolution investigation of the weak ν1+3ν21-ν21+ν3 band of CO2 around 2 μm

Fundamental spectroscopical parameters of the weak ν₁+3ν₂ ¹-ν₂ ¹+ν₃ band of CO₂ are reported using a high-resolution, direct-absorption spectrometer, based on a distributed feed-back diode laser emitting at 2 μm. Line intensities and self-broadening coefficients have been measured for the first time with high accuracy, for nine lines of the R branch, from R(44) up to R(59). Comparison with available data has been made, and a generally good agreement has been found. Received: 30 August 1999 / Published online: 24 March 2000     

Site-specific conjugation of ScFvs antibodies to nanoparticles by bioorthogonal strain-promoted alkyne-nitrone cycloaddition

Particularly suitable: An N-terminal serine mutant of anti-HER2 scFv antibody was conjugated to polymer-coated magnetofluorescent nanoparticles by strain-promoted alkyne-nitrone cycloaddition. The resulting nanoparticles (see scheme) proved effective in targeting and labeling HER2-positive breast cancer cells.     

X-ray fluorescence from the element with atomic number Z=120

An atomic clock based on x-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6 MeV/A. Inner shell vacancies are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by a x-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the x-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K x rays from the element with Z=120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time τ(f)=2.5×10(-18) s has been deduced for Z=120 from the measured x-ray multiplicity.