Oxidative Conversion of a Europium(II)‐Based T1 Agent into a Europium(III)‐Based paraCEST Agent that can be Detected In Vivo by Magnetic Resonance Imaging

The Eu^II complex of 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) tetra(glycinate) has a higher reduction potential than most Eu^II chelates reported to date. The reduced Eu^II form acts as an efficient water proton T₁ relaxation reagent, while the Eu^III form acts as a water‐based chemical exchange saturation transfer (CEST) agent. The complex has extremely fast water exchange rate. Oxidation to the corresponding Eu^III complex yields a well‐defined signal from the paraCEST agent. The time course of oxidation was studied in vitro and in vivo by T₁‐weighted and CEST imaging.     

Improved self‐assembly of poly(dimethylsiloxane‐b‐ethylene oxide) using a hydrogen‐bonding additive

Block copolymers with increased Flory–Huggins interaction parameters (χ) play an essential role in the production of sub‐10 nm nanopatterns in the growing field of directed self‐assembly for next generation lithographic applications. A library of PDMS‐b‐PEO block copolymers were synthesized by click chemistry and their interaction parameters (χ) determined. The highest χ measured in our samples was 0.21 at 150 °C, which resulted in phase‐separated domains with periods as small as 7.9 nm, suggesting that PDMS‐b‐PEO is a prime candidate for sub‐10 nm nanopatterning. To suppress PEO crystallization, PDMS‐b‐PEO was blended with (l )‐tartaric acid (LTA) which allows for tuning of the self‐assembled morphologies. Additionally, it was observed that the order‐disorder transition temperature (T_ODT) of PDMS‐b‐PEO increased dramatically as the amount of LTA in the blend increased, allowing for further control over self‐assembly. To understand the mechanism of this phenomenon, we present a novel field‐based supramolecular model, which describes the formation of copolymer‐additive complexes by reversible hydrogen bonding. The mean‐field phase separation behavior of the model was calculated using the random phase approximation (RPA). The RPA analysis reproduces behavior consistent with an increase of the effective χ in the PDMS‐b‐(PEO/LTA suprablock). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2200–2208     

Molecular structures and dynamics of the stepwise activation mechanism of a matrix metalloproteinase zymogen: challenging the cysteine switch dogma

Activation of matrix metalloproteinase zymogen (pro-MMP) is a vital homeostatic process, yet its molecular basis remains unresolved. Using stopped-flow X-ray spectroscopy of the active site zinc ion, we determined the temporal sequence of pro-MMP-9 activation catalyzed by tissue kallikrein protease in milliseconds to several minutes. The identity of three intermediates seen by X-ray spectroscopy was corroborated by molecular dynamics simulations and quantum mechanics/molecular mechanics calculations. The cysteine-zinc interaction that maintains enzyme latency is disrupted via active-site proton transfers that mediate transient metal-protein coordination events and eventual binding of water. Unexpectedly, these events ensue as a direct result of complexation of pro-MMP-9 and kallikrein and occur before proteolysis and eventual dissociation of the pro-peptide from the catalytic site. Here we demonstrate the synergism among long-range protein conformational transitions, local structural rearrangements, and fine atomic events in the process of zymogen activation.     

Mass spectrometric separation and quantitation of overlapping isotopologues. H2O/HOD/D2O and H2Se/HDSe/D2Se mixtures

Three conceptually different mathematical methods are presented for accurate mass spectrometric determination of H2O/HOD/D2O and H2Se/HDSe/D2Se concentrations from mixtures. These are alternating least-squares, weighted two-band target entropy minimization, and a statistical mass balance model. The otherwise nonmeasurable mass spectra of partially deuterated isotopologues (HOD and HDSe) are mathematically constructed. Any recorded isotopologue mixture mass spectra are then deconvoluted by least-squares into their components. This approach is used to study the H2O/D2O exchange reaction, and is externally validated gravimetrically. The H2O/D2O exchange equilibrium constant is also measured from the deconvoluted 70 eV electron impact GC/MS data (K = 3.85 +/- 0.03).     

Experimental strategy for characterization of essential dynamical variables in oscillatory systems: effect of double-layer capacitance on the stability of electrochemical oscillators

An experimentally accessible algorithm for changing the time scale associated with a dynamical variable is proposed. In general, a differential controller can be applied to (a) identify the essential species in oscillatory systems and (b) explore their role in the feedback loops. Here, we report on classifying electrochemical oscillators by changing the time scale over which the electrode potential varies; the type of different electrochemical oscillators is identified based on whether the controlled modification of pseudo-capacitance induces or suppresses current oscillations.     

Growth of uncapped, subnanometer size gold clusters prepared via electroporation of vesicles

Electric-field-induced transient pore formation (electroporation) in synthetic unilamellar vesicles is utilized for the preparation of subnanometer size uncapped gold quantum dots. With the precursor AuCl4(-) placed in the aqueous bulk solution and the reducing agent BH4(-) originally entrapped in the vesicles' compartments, the redox reaction--that occurs in the bulk--is initiated by the opening of transient pores in the vesicles' bilayers. The absence of caps permits (i) continued growth of the Au clusters formed, (ii) the assessment of their true absorption spectra unaltered by stabilizing ligands, and (iii) the previously inaccessible live observation of the growth of the clusters in the molecular size regime. The normally rapid self-aggregation of Au atoms is slowed to the time scales of hour and week by their adsorption at the exterior surface of the vesicles. The UV spectra exhibit novel, time-dependent, oscillating red and blue shifts of the characteristic absorption band, which can be attributed to the evolution of cluster size transiently halting at magic aggregation numbers corresponding to Au2, Au8, Au20, and Au34. Subsequent growth is associated with a monotonic red shift of the absorption band up to the characteristic surface plasmon absorption at 520 nm.     

On the benefits of ODT-based stochastic turbulence modeling

We summarize the group's progress in applying, analyzing, and improving ODT and ODT-based stochastic turbulence models like ODTLES. Compared to DNS these models span a wider range of scales while compared to RANS/LES (i) the molecular effects are retained and (ii) no assumption of scale separation is made. In this regard ODTLES has more properties of DNS than of standard LES. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Local Central Limit Theorem for Multi-group Curie–Weiss Models

Journal of Theoretical Probability - We study a multi-group version of the mean-field Ising model, also called Curie–Weiss model. It is known that, in the high-temperature regime of this...     

Hybrid computational aeroacoustics based on compressible flow data at low Mach numbers

In some practical applications (e.g. cavity with a lip), even at low Mach numbers, acoustic feedback mechanisms excite flow structures. The compressible flow simulation cannot distinguish between a pure fluid dynamic part and acoustic phenomena. With this in mind, we propose a workflow based on Helmholtz-Hodge decomposition, to extract pure source terms of the compressible flow simulation, to model the sound radiation. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)