Elucidating Factors Manipulated the Formation of Multiply Charged Protein Homomultimeric Complexes by Electrospray Ionization

Native non‐covalently bonded protein‐protein and protein‐substrate complexes are of great interest and have been extensively studied by electrospray ionization mass spectrometry (ESI‐MS). Multiply charged protein homomultimeric complexes are shown to form by ESI‐MS. This study addresses factors that can artificially induce the formation of multiply charged protein homomultimeric complexes. Cytochrome c (Cyt c) and ubiquitin, which are monomers in solution, were found to generate (Cyt c)_mⁿ⁺ by electrospray ionization (ESI). The homomultimeric complexes were not limited to dimeric complexes but include also multiply charged trimers, tetramers, and pentamers. The observation of these homomultimeric complexes has never been revealed from a Cyt c solution at the concentration as low as 10 μM. Increasing the concentration of Cyt c enhanced the formation of (Cyt c)_mⁿ⁺ as expected; however, the protein concentration does not affect the relative intensities of monomeric and dimeric complexes. Additionally the enrichment of NH₄OH also promotes the formation of (Cyt c)_mⁿ⁺. Notably, source collision‐induced dissociations (source‐CID) of (Cyt c)_mⁿ⁺ alter the charge state distribution (CSD) and may lead to an incorrect interpretation of Cyt c conformations. Hence, extra care should be taken when using CSD to interpret the conformation of a protein derived from ESI‐MS.     

Theoretical and experimental investigation of the effect of proton transfer on the (27)al MAS NMR line shapes of zeolite-adsorbate complexes: an independent measure of solid Acid strength

Assessing the degree of proton transfer from a Br?nsted acid site to one or more adsorbed bases is central to arguments regarding the strength of zeolites and other solid acids. In this regard certain solid-state NMR measurements have been fruitful; for example, some (13)C, (15)N, or (31)P resonances of adsorbed bases are sensitive to protonation, and the (1)H chemical shift of the Br?nsted site itself reflects hydrogen bonding. We modeled theoretically the structures of adsorption complexes of several bases on zeolite HZSM-5, calculated the quadrupole coupling constants (Q(cc)) and asymmetry parameters (eta) for aluminum in these complexes and then in turn simulated the central transitions of their (27)Al MAS NMR spectra. The theoretical line width decreased monotonically with the degree of proton transfer, reflecting structural relaxation around aluminum as the proton was transferred to a base. We verified this experimentally for a series of adsorbed bases by way of single-pulse MAS and triple quantum MQMAS (27)Al NMR. The combined theoretical and experimental approach described here provides a strategy by which (27)Al data can be applied to resolve disputed interpretations of proton transfer based on other evidence.     

Synthesis and Cytotoxicity Evaluation of Metal‐Chelator‐Bearing Flavone,Carbazole, Dibenzofuran,Xanthone, and Anthraquinone

2‐(Aryloxymethyl)‐5‐benzyloxy‐1‐methyl‐1H‐pyridin‐4‐ones 8a – 8g , 2‐(aryloxymethyl)‐5‐hydroxy‐4H‐pyran‐4‐ones 9a – 9g , and 2‐(aryloxymethyl)‐5‐hydroxy‐1‐methyl‐1H‐pyridin‐4‐ones 10a – 10g were prepared from the known 5‐benzyloxy‐2‐(hydroxymethyl)pyran‐4‐one ( 3 ) in a good overall yield. These compounds were evaluated in vitro against a three‐cell lines panel consisting of MCF7 (breast), NCI‐H460 (lung), and SF‐268 (CNS), and the active compounds passed on for evaluation in the full panel of 60 human tumor cell lines derived from nine cancer cell types. The results indicated that 5‐hydroxy derivatives are more favorable than their corresponding 5‐benzyloxy precursors ( 10a – 10g vs. 8a – 8g ), and 1‐methyl‐1H‐pyridin‐4‐ones are more favorable than their corresponding pyran‐4(1H)‐ones ( 10a – 10g vs. 9a – 9g ). Among these three types of compounds, 2‐(aryloxymethyl)‐5‐hydroxy‐1‐methyl‐1H‐pyridin‐4‐ones 10a – 10g were the most cytotoxic; they inhibited the growth of almost all the cancer cells tested. On the contrary, compound 8a (a mean GI₅₀=27.8 μM ), 8b (38.5), 8d (11.0), and 8e (30.5) are especially active against the growth of SK‐MEL‐5 (a melanoma cancer cell) with a GI₅₀ of <0.01, 5.65, 0.55, and 0.03 μM , respectively (cf. Table 2).     

Expanding the Synthesis Field of High-Silica Zeolites

Aluminosilicate zeolites are synthesized under hydrothermal conditions in a basic/alkaline medium in the pH range between 9 and 14. The synthesis of MFI-type zeolite in an acidic medium is presented. The critical parameter determining the zeolite formation in an acidic medium was found to be the isoelectric point (IEP) of gel particles. MFI-type zeolite was synthesized above the isoelectric point of the employed silica source, where the silica species exhibit a negative charge and the paradigm of zeolite formation based on the electrostatic interaction with the positively charged template is retained. No zeolite formation is observed below the isoelectric point of silica. The impact of aluminum on the zeolite formation is also studied. The results of this study will serve to extend the synthesis field of high silica zeolites to the acidic medium and thus open new opportunities to control the zeolite properties.     

Jamming, two-fluid behavior, and "self-filtration" in concentrated particulate suspensions

We study the flow of model hard-sphere colloidal suspensions at high volume fraction Phi driven through a constriction by a pressure gradient. Above a particle-size dependent limit Phi(0), direct microscopic observations demonstrate jamming and unjamming-conversion of fluid to solid and vice versa-during flow. We show that such a jamming flow produces a reduction in colloid concentration Phi(x) downstream of the constriction. We propose that this "self-filtration" effect is due to a combination of jamming of the particulate part of the system and continuing flow of the liquid part, i.e., the solvent, through the pores of the jammed solid. Thus we link jamming in colloidal and granular media with a "two-fluid-like" picture of the flow of concentrated suspensions. Results are also discussed in the light of the original experiments of Reynolds on dilation in granular materials.     

Study of the decay B0(B- 0)-->rho+rho-, and constraints on the Cabibbo-Kobayashi-Maskawa angle alpha

Using a data sample of 89 x 10(6) Upsilon(4S)-->BB decays collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC, we measure the B0(B (0))-->rho(+)rho(-) branching fraction as [30+/-4(stat)+/-5(syst)]x10(-6) and a longitudinal polarization fraction of f(L)=0.99+/-0.03(stat)+0.04-0.03(syst). We measure the time-dependent-asymmetry parameters of the longitudinally polarized component of this decay as C(L)=-0.17+/-0.27(stat)+/-0.14(syst) and S(L)=-0.42+/-0.42(stat)+/-0.14(syst). We exclude values of alpha between 19 degrees and 71 degrees (90% C.L.).     

Measurement of the B-->Xsl+l- branching fraction with a sum over exclusive modes

We measure the branching fraction for the flavor-changing neutral-current process B-->X(s)l(+)l(-) with a sample of 89x10(6) Upsilon(4S)-->BBmacr; events recorded with the BABAR detector at the PEP-II e(+)e(-) storage ring. The final state is reconstructed from e(+)e(-) or micro(+)micro(-) pairs and a hadronic system X(s) consisting of one K+/- or K(0)(S) and up to two pions, with at most one pi(0). We observe a signal of 40+/-10(stat)+/-2(syst) events and extract the inclusive branching fraction B(B-->X(s)l(+)l(-))=(5.6+/-1.5(stat)+/-0.6(exp syst)+/-1.1(model syst))x10(-6) for ml(+)(l(-))>0.2 GeV/c(2).     

A dynamical systems model of unorganized segregation

We consider Schelling’s bounded neighborhood model (BNM) of unorganized segregation, from the perspective of modern dynamical systems theory. We carry out a complete quantitative analysis of the system for linear tolerance schedules. We derive a fully predictive model and associate each term with a social meaning. We recover and generalize Schelling’s qualitative results.

For the case of unlimited population movement, we derive exact formulae for regions in parameter space where stable integrated population mixes can occur, and show how neighborhood tipping can be explained in terms of basins of attraction.

When population movement is limited, we derive exact criteria for the occurrence of new population mixes.

For nonlinear tolerance schedules, we illustrate our approach with numerical simulations.