Galvanic exchange platinization reveals laser-inscribed pattern in 3D-LAM-printed steel

Galvanic exchange involving dissolution of iron and the simultaneous growth of platinum onto 316 L stainless steel was investigated for specimens manufactured by 3D-printing, and the behavior was compared to conventional stainless steel. Novel phenomena associated with the 3D-printed steel, but not conventional steel, reacting in three distinct phases were observed: first, with low platinum loading, a bright etching pattern linked to the laser-manufacturing process is revealed at the steel surface; second, a nanostructured pore pattern with platinum nano-deposits forms; and third, a darker platinum film coating of typically 500-nm thickness forms and then peels off the steel surface with further platinum growth underneath. Unlike the conventional steel (and mainly due to residual porosity), 3D-printed steel supports well-adhered platinum films for potential application in electrocatalysis, as demonstrated for alkaline methanol oxidation.

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Replacing the cholesterol hydroxyl group with the ketone group facilitates sterol flip-flop and promotes membrane fluidity

The 3alpha-hydroxyl group is a characteristic structural element of all membrane sterol molecules, while the 3-ketone group is more typically found in steroid hormones. In this work, we investigate the effect of substituting the hydroxyl group in cholesterol with the ketone group to produce ketosterone. Extensive atomistic molecular dynamics simulations of saturated lipid membranes with either cholesterol or ketosterone show that, like cholesterol, ketosterone increases membrane order and induces condensation. However, the effect of ketosterone on membrane properties is considerably weaker than that of cholesterol. This is largely due to the unstable positioning of ketosterone at the membrane-water interface, which gives rise to a small but significant number of flip-flop transitions, where ketosterone is exchanged between membrane leaflets. This is remarkable, as flip-flop motions of sterol molecules have not been previously reported in analogous lipid bilayer simulations. In the same context, ketosterone is found to be more tilted with respect to the membrane normal than cholesterol. The atomic level mechanism responsible for the increase of the steroid tilt and the promotion of flip-flops is the decrease in polar interactions at the membrane-water interface. Interactions between lipids or water and the ketone group are found to be weaker than in the case of the hydroxyl group, which allows ketosterone to penetrate through the hydrocarbon region of a membrane.     

Icosahedral Au(72): a predicted chiral and spherically aromatic golden fullerene

Quantum chemical calculations demonstrate the spherical aromaticity and high thermodynamic stability of Au(72), a predicted I-symmetric golden fullerene.     

Bisphosphonate derivatives of nucleoside antimetabolites: hydrolytic stability and hydroxyapatite adsorption of 5'-beta,gamma-methylene and 5'-beta,gamma-(1-hydroxyethylidene) triphosphates of 5-fluorouridine and ara-cytidine

Kinetics of the hydrolytic reactions of four bisphosphonate derivatives of nucleoside antimetabolites, viz., 5-fluorouridine 5'-beta,gamma-(1-hydroxyethylidene) triphosphate ( 4), 5-fluorouridine 5'-beta,gamma-methylene triphosphate ( 5), ara-cytidine 5'-beta,gamma-(1-hydroxyethylidene) triphosphate ( 6), and ara-cytidine 5'-beta,gamma-methylene triphosphate ( 7), have been studied over a wide pH range (pH 1.0-8.5) at 90 degrees C. With each compound, the disappearance of the starting material was accompanied by formation of the corresponding nucleoside 5'-monophosphate, the reaction being up to 2 orders of magnitude faster with the beta,gamma-(1-hydroxyethylidene) derivatives ( 4, 6) than with their beta,gamma-methylene counterparts ( 5, 7). With compound 7, deamination of the cytosine base competed with the phosphate hydrolysis at pH 3-6. The measurements at 37 degrees C (pH 7.4) in the absence and presence of divalent alkaline earth metal ions (Mg (2+) and Ca (2+)) showed no sign of metal ion catalysis. Under these conditions, the initial product, nucleoside 5'-monophosphate, underwent rapid dephosphorylation to the corresponding nucleoside. Hydrolysis of the beta,gamma-methylene derivatives ( 5, 7) to the corresponding nucleoside 5'-monophosphates was markedly faster in mouse serum than in aqueous buffer (pH 7.4), the rate-acceleration being 5600- and 3150-fold with 5 and 7, respectively. In human serum, the accelerations were 800- and 450-fold compared to buffer. In striking contrast, the beta,gamma-(1-hydroxyethylidene) derivatives did not experience a similar decrease in hydrolytic stability. The stability in human serum was comparable to that in aqueous buffer (tau 1/2 = 17 and 33 h with 4 and 6, respectively), and on going to mouse serum, a 2- to 4-fold acceleration was observed. To elucidate the mineral-binding properties of 4- 7, their retention on a hydroxyapatite column was studied and compared to that of zoledronate ( 1a) and nucleoside mono-, di-, and triphosphates.     

High-affinity small molecule-phospholipid complex formation: binding of siramesine to phosphatidic acid

Siramesine (SRM) is a sigma-2 receptor agonist which has been recently shown to inhibit growth of cancer cells. Fluorescence spectroscopy experiments revealed two distinct binding sites for this drug in phospholipid membranes. More specifically, acidic phospholipids retain siramesine on the bilayer surface due to a high-affinity interaction, reaching saturation at an apparent 1:1 drug-acidic phospholipid stoichiometry, where after the drug penetrates into the hydrocarbon core of the membrane. This behavior was confirmed using Langmuir films. Of the anionic phospholipids, the highest affinity, comparable to the affinities for the binding of small molecule ligands to proteins, was measured for phosphatidic acid (PA, mole fraction of X(PA) = 0.2 in phosphatidylcholine vesicles), yielding a molecular partition coefficient of 240 +/- 80 x 10(6). An MD simulation on the siramesine:PA interaction was in agreement with the above data. Taking into account the key role of PA as a signaling molecule promoting cell growth our results suggest a new paradigm for the development of anticancer drugs, viz. design of small molecules specifically scavenging phospholipids involved in the signaling cascades controlling cell behavior.     

Redox Properties and in Vivo Magnetic Resonance Imaging of Cyclodextrin-Polynitroxides Contrast Agents

This paper reports the synthesis, characterization and in vivo application of water-soluble supramolecular contrast agents (Mw: 5–5.6 kDa) for MRI obtained from β-cyclodextrin functionalized with different kinds of nitroxide radicals, both with piperidine structure ( CD2 and CD3 ) and with pyrrolidine structure ( CD4 and CD5 ). As to the stability of the radicals in presence of ascorbic acid, CD4 and CD5 have low second order kinetic constants (≤0.05 M⁻¹ s⁻¹) compared to CD2 (3.5 M⁻¹ s⁻¹) and CD3 (0.73 M⁻¹ s⁻¹). Relaxivity (r₁) measurements on compounds CD3 - CD5 were carried out at different magnetic field strength (0.7, 3, 7 and 9.4 T). At 0.7 T, r₁ values comprised between 1.5 mM⁻¹ s⁻¹ and 1.9 mM⁻¹ s⁻¹ were found while a significant reduction was observed at higher fields (r₁≈0.6-0.9 mM⁻¹ s⁻¹ at 9.4 T). Tests in vitro on HEK293 human embryonic kidney cells, L929 mouse fibroblasts and U87 glioblastoma cells indicated that all compounds were non-cytotoxic at concentrations below 1 μmol mL⁻¹. MRI in vivo was carried out at 9.4 T on glioma-bearing rats using the compounds CD3 - CD5 . The experiments showed a good lowering of T₁ relaxation in tumor with a retention of the contrast for at least 60 mins confirming improved stability also in vivo conditions.     

Cages versus Sheets: A Critical Comparison in the Size Range Expected for Methylaluminoxane (MAO)

New cage models (MeAlO)_n(Me₃Al)_m (n=16, m=6 or 7) isomeric with previously reported sheet models for the principle activator found in hydrolytic MAO (h-MAO) are compared at M06-2X and MN15 levels of theory using density functional theory with respect to their thermodynamic stability. Reactivity of the neutrals or corresponding anions with formula [(MeAlO)₁₆(Me₃Al)₆Me]⁻ towards chlorination, and loss of Me₃Al is explored while reactivity of the neutrals towards formation of contact- and outer-sphere ion pairs from Cp₂ZrMe₂ and Cp₂ZrMeCl is examined. The results suggest on balance that a cage model for this activator is less consistent with experiment than an isomeric sheet model, although the latter are more stable based on free energy.