Crystal defects in highy luminescent colloidal nanocrystals (NCs) of CsPbX3 perovskites (X = Cl, Br, I) are investigated. Here, using X-ray total scattering techniques and the Debye scattering ...equation (DSE), we provide evidence that the local structure of these NCs always exhibits orthorhombic tilting of PbX6 octahedra within locally ordered subdomains. These subdomains are hinged through a two-/three-dimensional (2D/3D) network of twin boundaries through which the coherent arrangement of the Pb ions throughout the whole NC is preserved. The density of these twin boundaries determines the size of the subdomains and results in an apparent higher-symmetry structure on average in the high-temperature modification. Dynamic cooperative rotations of PbX6 octahedra are likely at work at the twin boundaries, causing the rearrangement of the 2D or 3D network, particularly effective in the pseudocubic phases. An orthorhombic, 3D γ-phase, isostructural to that of CsPbBr3 is found here in as-synthesized CsPbI3 NCs.
Interactions between proteins and surfactants are of relevance in many applications including food, washing powder formulations, and drug formulation. The anionic surfactant sodium dodecyl sulfate ...(SDS) is known to unfold globular proteins, while the non-ionic surfactant octaethyleneglycol monododecyl ether (C
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) can be used to refold proteins from their SDS-denatured state. While unfolding have been studied in detail at the protein level, a complete picture of the interplay between protein and surfactant in these processes is lacking. This gap in our knowledge is addressed in the current work, using the β-sheet-rich globular protein β-lactoglobulin (bLG). We combined stopped-flow time-resolved SAXS, fluorescence, and circular dichroism, respectively, to provide an unprecedented in-depth picture of the different steps involved in both protein unfolding and refolding in the presence of SDS and C
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. During unfolding, core-shell bLG-SDS complexes were formed within ∼10 ms. This involved an initial rapid process where protein and SDS formed aggregates, followed by two slower processes, where the complexes first disaggregated into single protein structures situated asymmetrically on the SDS micelles, followed by isotropic redistribution of the protein. Refolding kinetics (>100 s) were slower than unfolding (<30 s), and involved rearrangements within the mixing deadtime (∼5 ms) and transient accumulation of unfolded monomeric protein, differing in structure from the original bLG-SDS structure. Refolding of bLG involved two steps: extraction of most of the SDS from the complexes followed by protein refolding. These results reveal that surfactant-mediated unfolding and refolding of proteins are complex processes with rearrangements occurring on time scales from sub-milliseconds to minutes.
The time-resolved study reveals several transition states during SDS-induced unfolding of the protein, as well as under refolding of the protein by the nonionic surfactant C
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Despite over a century of modern surfactant science, the kinetic pathways of morphological transitions in micellar systems are still not well understood. This is mainly as a result of the lack of ...sufficiently fast methods that can capture the structural changes of such transitions. Herein, a simple surfactant system consisting of sodium dodecyl sulfate (SDS) in aqueous NaCl solutions is investigated. Combining synchrotron radiation small‐angle X‐ray scattering (SAXS) with fast stopped‐flow mixing schemes allows monitoring the process where polymer‐like micelles are formed from globular micelles when the salt concentration is suddenly increased. The results show that “worm‐like” micelles are formed by fusion of globular micelles and short cylinders in a fashion that bears similarities to a step‐like polymerization process.
Surfactants in action: The formation of “worm‐like” micelles by fusion of globular micelles and short cylinders composed of sodium dodecyl sulfate, which occurs when the salt concentration is suddenly increased, is followed using a combination of time‐resolved small‐angle X‐ray scattering and fast stopped‐flow experiments.
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•MSNs can be loaded with multiple antibiotics, such as polymyxin B and vancomycin.•MSNs surface chemistry affects the adsorption and release kinetics.•MSNs-loaded antibiotics had ...stronger synergy and higher antimicrobial effect.•Using MSNs as carrier for antibiotics decreased the cytotoxicity of antibiotics.
Treatment of polymicrobial infections requires combination therapy with drugs that have different antimicrobial spectra and possibly work in synergy. However, the different pharmacokinetics and adverse side effects challenge the simultaneous delivery of multiple drugs at the appropriate concentrations to the site of infection. Formulation of multiple drugs in nano-carrier systems may improve therapeutic efficacy by increasing the local concentration and lowering the systemic concentration, leading to fewer side effects. In this study, we loaded polymyxin B and vancomycin on bare and carboxyl-modified mesoporous silica nanoparticles (B-MSNs and C-MSNs, respectively) to achieve simulataneous local delivery of antibiotics against Gram-positive and –negative bacteria. Polymyxin B adsorbed preferentially to nanoparticles compared to vancomycin. The total antibiotic loading was 563 μg and 453 μg per mg B-MSNs or C-MSNs, respectively. Both B-MSNs and C-MSNs loaded with antibiotics were effective against Gram-negative and Gram-positive bacteria. The antibiotics had synergistic interactions against Gram-negative bacteria, and the antimicrobial efficacy was higher for antibiotic-loaded C-MSNs compared to free antibiotics at the same concentration even though the cytotoxicity was lower. Our study shows that formulations of existing antibiotics in nanocarrier systems can improve their therapeutic efficiency, indicating that combination therapy with drug-loaded silica nanoparticles may provide a better treatment outcome for infections that require high concentrations of multiple drugs.
CONTEXT The need for anticoagulation after surgical aortic valve replacement (AVR) with biological prostheses is not well examined. OBJECTIVE To perform a nationwide study of the association of ...warfarin treatment with the risk of thromboembolic complications, bleeding incidents, and cardiovascular deaths after bioprosthetic AVR surgery. DESIGN, SETTING, AND PARTICIPANTS Through a search in the Danish National Patient Registry, 4075 patients were identified who had bioprosthetic AVR surgery performed between January 1, 1997, and December 31, 2009. Concomitant comorbidity and medication were retrieved. Poisson regression models were used to determine risk. MAIN OUTCOME MEASURES Incidence rate ratios (IRRs) of strokes, thromboembolic events, cardiovascular deaths, and bleeding incidents by discontinuing warfarin as opposed to continued treatment 30 to 89 days, 90 to 179 days, 180 to 364 days, 365 to 729 days, and at least 730 days after surgery. RESULTS The median duration of follow-up was 6.57 person-years. Estimated rates of events per 100 person-years in patients not treated with warfarin compared with those treated with warfarin with comparative absolute risk were 7.00 (95% CI, 4.07-12.06) vs 2.69 (95% CI, 1.49-4.87; adjusted IRR, 2.46; 95% CI, 1.09-5.55) for strokes; 13.07 (95% CI, 8.76-19.50) vs 3.97 (95% CI, 2.43-6.48; adjusted IRR, 2.93; 95% CI, 1.54-5.55) for thromboembolic events; 11.86 (95% CI, 7.81-18.01) vs 5.37 (95% CI, 3.54-8.16; adjusted IRR, 2.32; 95% CI, 1.28-4.22) for bleeding incidents; and 31.74 (95% CI, 24.69-40.79) vs 3.83 (95% CI, 2.35-6.25; adjusted IRR, 7.61; 95% CI, 4.37-13.26) for cardiovascular deaths within 30 to 89 days after surgery; and 6.50 (95% CI, 4.67-9.06) vs 2.08 (95% CI, 0.99-4.36; adjusted IRR, 3.51; 95% CI, 1.54-8.03) for cardiovascular deaths within 90 to 179 days after surgery. CONCLUSION Discontinuation of warfarin treatment within 6 months after bioprosthetic AVR surgery was associated with increased cardiovascular death.
The kinetic pathways for coacervation and micelle formation are still not fully understood. Driven by electrostatic interactions and entropically driven counterion release, complexation of oppositely ...charged macromolecules leads to the formation of micellar nanostructures. Here we study the coacervation process, from initial formation and growth of stable micelles, on a nanometric length scale using time-resolved small-angle X-ray scattering (TR-SAXS). The micellar coacervates are formed through the complexation of anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSSS) and cationic block–copolymer poly(ethylene oxide)-block-poly((vinylbenzyl)trimethylammonium chloride) (PEO-b-PVBTA). Mixing the polyelectrolytes in a stoichiometric 1:1 charge ratio resulted in the formation of stable spherical core–shell micellar-like coacervates consisting of a central core of complexed PSSS and PVBTA with a PEO corona. By use of synchrotron SAXS coupled to a stopped-flow mixing apparatus, the whole formation kinetics of coacervates could be followed in situ from a few milliseconds. The results of a detailed data modeling reveal that the formation of these polyelectrolyte coacervates follows a two-step process: (i) first, metastable large-scale aggregates are formed upon a barrier-free complexation immediately after mixing; (ii) subsequently, the clusters undergo charge equilibration upon chain rearrangement and exchange processes yielding micellar-like aggregates with net neutral charge that are pinched off to yield the final stable micelle-like coacervates. While the initial cluster formation is very fast and completed within the dead time of mixing, the subsequent rearrangement becomes significantly slower with increasing molecular weight of the PVBTA block. Interestingly, the overall kinetic process was essentially concentration independent, indicating that the rearrangement process is mainly accomplished via noncooperative chain rearrangement and chain exchange processes.
Bovine α‐lactalbumin (aLA) and oleate (OA) form a complex that has been intensively studied for its tumoricidal activity. Small‐angle X‐ray scattering (SAXS) has revealed that this complex consists ...of a lipid core surrounded by partially unfolded protein. We call this type of complex a liprotide. Little is known of the molecular interactions between OA and aLA, and no technique has so far provided any high‐resolution structure of a liprotide. Here we have used coarse‐grained (CG) molecular dynamics (MD) simulations, isothermal titration calorimetry (ITC) and SAXS to investigate the interactions between aLA and OA during the process of liprotide formation. With ITC we found that the strongest enthalpic interactions occurred at a molar ratio of 12.0±1.4:1 OA/aLA. Liprotides formed between OA and aLA at several OA/aLA ratios in silico were stable both in CG and in all‐atom simulations. From the simulated structures we calculated SAXS spectra that show good agreement with experimentally measured patterns of matching liprotides. The simulations showed that aLA assumes a molten globular (MG) state, exposing several hydrophobic patches involved in interactions with OA. Initial binding of aLA to OA occurs in an area of aLA in which a high amount of positive charge is located, and only later do hydrophobic interactions become important. The results reveal how unfolding of aLA to expose hydrophobic residues is important for complex formation between aLA and OA. Our findings suggest a general mechanism for liprotide formation and might explain the ability of a large number of proteins to form liprotides with OA.
Complexes of proteins and fatty acids—termed liprotides—form structures based on a lipid core surrounded by partially disordered protein. Molecular dynamics simulation of these complexes can help in achieving better understanding of the protein–lipid interactions. Combining the in silico method with experimental measurements helped to validate the approach and provided further structural insight into liprotides.
Despite a successful application of solvent‐free liquid protein (biofluids) concept to a number of commercial enzymes, the technical advantages of enzyme biofluids as hyperthermal stable biocatalysts ...cannot be fully utilized as up to 90–99% of native activities are lost when enzymes were made into biofluids. With a two‐step strategy (site‐directed mutagenesis and synthesis of variant biofluids) on Bacillus subtilis lipase A (BsLA), we elucidated a strong dependency of structure and activity on the number and distribution of polymer surfactant binding sites on BsLA surface. Here, it is demonstrated that improved BsLA variants can be engineered via site‐mutagenesis by a rational design, either with enhanced activity in aqueous solution in native form, or with improved physical property and increased activity in solvent‐free system in the form of a protein liquid. This work answered some fundamental questions about the surface characteristics for construction of biofluids, useful for identifying new strategies for developing advantageous biocatalysts.
Schematic illustration showing cationization of B. subtilis lipase A (BsLA) and its mutants using N,N‐dimethyl‐1,3‐propanediamine (DMPA) followed by electrostatic coupling of anionic polymer‐surfactant to yield a charge neutral stoichiometric conjugate cBsLASs. Blue regions on the surface of the BsLA structures show the cationic binding sites and S molecules are represented using pink tubes.
The conformation of cylindrical brush polymers with a polymethacrylate main and polystyrene side chains (6 ≤ ≤ 33, with the number-average degree of polymerization of the side chains) were studied by ...combined light and small-angle neutron scattering experiments. The results reveal that the main chain stiffness expressed in terms of the Kuhn statistical segment length, l k, increases with side chain length but does not follow scaling predictions which most probably is due to the limited length of the side chains investigated experimentally. In this respect the present work addresses the transition regime from flexible coils to stiff cylindrical brushes as a function of side chain length. In detail, the increase of l k is stronger in toluene, a very good solvent for the side chains, than in the poor solvent cyclohexane and does not level off for the longest side chains investigated ( = 33). In contrast to earlier work, the cylinder length per main chain monomer is found to be independent of side chain length but to depend slightly on the solvent quality, i.e., l m = 0.241 nm in toluene and l m = 0.207 nm in cyclohexane. The value determined in toluene is close to the maximum value of l m = 0.25 nm expected for a fully stretched vinylic main chain, whereas the smaller value for l m in cyclohexane suggests a local coiling of the main chain, most probably caused by less repulsive interactions between the side chains. The discrepancy to some earlier scattering experiments could be resolved, but the origin of frequently reported much smaller cylinder lengths derived by atomic force microscopy remains unclear.
The complement system is an important antimicrobial and inflammation-generating component of the innate immune system. The classical pathway of complement is activated upon binding of the 774-kDa C1 ...complex, consisting of the recognitionmolecule C1q and the tetrameric protease complex C1r₂s₂, to a variety of activators presenting specific molecular patterns such as IgG- and IgM-containing immune complexes. A canonical model entails a C1r₂s₂ with its serine protease domains tightly packed together in the center of C1 and an intricate intramolecular reaction mechanism for activation of C1r and C1s, induced upon C1 binding to the activator. Here, we show that the serine protease domains of C1r and C1s are located at the periphery of the C1r₂s₂ tetramer both when alone or within the nonactivated C1 complex. Our structural studies indicate that the C1 complex adopts a conformation incompatible with intramolecular activation of C1, suggesting instead that intermolecular proteolytic activation between neighboring C1 complexes bound to a complement activating surface occurs. Our results rationalize how a multitude of structurally unrelated molecular patterns can activate C1 and suggests a conserved mechanism for complement activation through the classical and the related lectin pathway.
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