Quantum-chemical simulation and experimental study of some magnetic nanoparticles stabilized in fluid suspensions by using organic coating

Abstract

The biomedical applications of magnetic nanoparticles require the surface modification with organic, hydrophilic molecules, able to ensure the stability of the resulted colloidal suspensions. We present the quantum mechanical approach of two molecules developing stable interfaces with magnetic Co_0.5Fe_2.5O₄ nanoparticles. Sodium oleate, and citric acid, ensuring steric and respectively electrostatic stabilization are comparatively analyzed. The roles of dipole moment and frontier orbitals energies were emphasized to better understanding of some interface phenomena for the optimization of magnetic nanoparticle suspension preparation. Further, practical yielding of colloidal Co_0.5Fe_2.5O₄ nanoparticles by coating with sodium oleate and respectively with citric acid is discussed.     

A Water Rich Crystalline Hydrate Formed by 1,4,7,10-Tetraazacyclododecane, Siliconhydrofluoric Acid and Water: Structure and Properties

Novel complementary associations have been found in a crystalline ternarycomplex of the macrocyclic tetramine, [12]aneN₄ (e.g. =1,4,7,10-tetraazacyclododecane, cyclen, L), hexafluorosilicate ions andwater (I). The final compound belongs to the host—guest type with themacrocycle as the host (H), the inorganic entity as a guest (G) and watermolecules. It was characterized by X-ray techniques, IR spectroscopy andthermogravimetric study. X-ray crystal analysis revealed that the structureis built of the charged entities, with a 3D-network uniting thequadriprotonated form of the macrocycle, hexafluorosilicate as counterionsand lattice water molecules viaN—H⁺...F^-,N—H⁺...O(w),OH...F^- and O—-H(w)...O(w)hydrogen bonds. The overall complex stoichiometry comprises fourSiF₆ ^2- anions and seven water molecules per two[LH₄]⁴⁺ cations. Crystals of (I) are monoclinic,space group P2₁/n with a = 14.585(3), b = 16.384(2), c =16.500(3) Å, = 92.84(3)°, V = 3938(1)ų and Z = 8 forC₈H₃₁F₁₂N₄O_3.5Si₂.     

Effect of reactor wall material on the nucleation of methane hydrate in water-in-oil emulsions

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Synthesis of tetrahydro-4H-thiopyran-4-ones (microreview)

Chemistry of Heterocyclic Compounds - In this microreview, we consider the methods used for the synthesis of tetrahydro-4H-thiopyran-4-ones over the last 7 years.     

Mechanisms of Methylenecyclobutane Hydrogenation over Supported Metal Catalysts Studied by Parahydrogen-Induced Polarization Technique

In this work the mechanism of methylenecyclobutane hydrogenation over titania-supported Rh, Pt and Pd catalysts was investigated using parahydrogen-induced polarization (PHIP) technique. It was found that methylenecyclobutane hydrogenation leads to formation of a mixture of reaction products including cyclic (1-methylcyclobutene, methylcyclobutane), linear (1-pentene, cis-2-pentene, trans-2-pentene, pentane) and branched (isoprene, 2-methyl-1-butene, 2-methyl-2-butene, isopentane) compounds. Generally, at lower temperatures (150–350 °C) the major reaction product was methylcyclobutane while higher temperature of 450 °C favors the formation of branched products isoprene, 2-methyl-1-butene and 2-methyl-2-butene. PHIP effects were detected for all reaction products except methylenecyclobutane isomers 1-methylcyclobutene and isoprene implying that the corresponding compounds can incorporate two atoms from the same parahydrogen molecule in a pairwise manner in the course of the reaction in particular positions. The mechanisms were proposed for the formation of these products based on PHIP results.     

Tetrahydropyridine (THP) ring expansion under the action of activated terminal alkynes. The first synthesis and X-ray crystal structure of tetrahydropyrimido[4,5-d]azocines

Tetrahydropyridopyrimidines (THPPm) 1-3 underwent tandem cleavage-cyclization piperidine ring enlargement under the action of terminal activated alkynes to produce tetrahydropyrimido[4,5-d]azocines 4-7 in good preparative yields. The latter compounds are representatives of a new heterocyclic system.     

Tandem enlargement of the tetrahydropyridine ring in 1-aryl-tetrahydroisoquinolines using activated alkynes—a new and effective synthesis of benzoazocines

Tetrahydroisoquinolines 3a-e underwent piperidine ring enlargement under the action of activated alkynes, giving benzoazocines 4, 5 and 7-11 in high yields.     

Defect evolution in block copolymer thin films via temporal phase transitions

We study the details of the defect dynamics in thin films of a cylinder-forming polystyrene-block-polybutadiene (SB) diblock copolymer melt. The high temporal resolution of in-situ scanning force microscopy (SFM) uncovers elementary dynamic processes of structural rearrangements on time scales not accessible so far. Short-term interfacial undulations and the formation of transient phases (spheres, perforated lamellae, and lamellae) are observed. We demonstrate that the well-known structural defects are annihilated by short-term phase transitions into what may be considered excited states. These temporary phase transitions are reproduced in simulations based on dynamic self-consistent field theory. We discuss the role of the observed structural evolution in the context of the equilibrium phase behavior in SB thin films.     

Evolutionary patterns of retinal-binding pockets of type I rhodopsins and their functions

Genome sequencing projects resulted in the identification of a large number of new sequence homologs of archaeal rhodopsins in marine bacteria, fungi, and unicellular algae. It is an important task to unambiguously predict the functions of these new rhodopsins, as it is difficult to perform individual experiments on every newly discovered sequence. The transmembrane segments of rhodopsins have similar three-dimensional structures where the seven transmembrane helices form a tightly packed scaffold to accommodate a covalently bound retinal. We use geometric computations to accurately define the retinal-binding pockets in high-resolution structures of rhodopsins and to extract residues forming the wall of the retinal-binding pocket. We then obtain a tree defining the functional relationship of rhodopsins based on the short sequences of residues forming the wall of the retinal-binding pocket concatenated from the primary sequence, and show that these sequence fragments are often sufficient to discriminate phototactic vs transporting function of the bacterial and unicellular algal rhodopsins. We further study the evolutionary history of retinal-binding pockets by estimating the pocket residue substitution rates using a Bayesian Monte Carlo method. Our findings indicate that every functional class of rhodopsins has a specific allowed set of fast-rate amino acid substitutions in the retinal-binding pocket that may contribute to spectral tuning or photocycle modulation. The substitution rates of the amino acid residues in a putative retinal-binding pocket of marine proteorhodopsins together with the clustering of pocket sequences indicate that green-absorbing and blue-absorbing proteorhodopsins have similar function. Our results demonstrate that the evolutionary patterns of the retinal-binding pockets reflect the functional specificity of the rhodopsins. The approach we describe in this paper may be useful for large-scale functional prediction of rhodopsins.