Characterizing vibrational motion beyond internal coordinates

We present a procedure for the decomposition of the normal modes of a composite system, including its rotations and translations, into those of fragments. The method permits—by the cross-contraction of dyads of mass-weighted displacement vectors, without recourse to valence coordinates—the direct comparison of nuclear motions of structurally similar but otherwise arbitrary fragments of molecules, and it leads to a quantitative definition of the similarity and the overlap of nuclear motions. We illustrate its usefulness by the quantification of the mixing of the normal modes of formic acid monomers upon the formation of a dimer, by the comparison of the overlap of the intermolecular normal vibrations of the water dimer computed with different ab initio schemes, and by the comparison of similarity and overlap of vibrations of (4S,7R)-galaxolide and (4S)-4-methylisochromane. The approach is expected to become a standard tool in vibrational analysis.     

Hydration of ionic species studied by the reference interaction site model with a repulsive bridge correction

We have tested the reference interaction site model (RISM) for the case of the hypernetted chain (HNC) and the partially linearized hypernetted chain (PLHNC) closures improved by a repulsive bridge correction (RBC) for ionic hydrated species. We have analyzed the efficiency of the RISM/HNC+RBC and RISM/PLHNC+RBC techniques for decomposition of the electrostatic and the nonpolar hydration energies on the energetic and the enthalpic parts for polyatomic ions when the repulsive bridge correction is treated as a thermodynamic perturbation, and investigate the repulsive bridge effect on the electrostatic potential induced by solvent on solute atoms. For a number of univalent and bivalent atomic ions, molecular cations, and anions, the method provides hydration energies deviating only by several percents from the experimental data. In most cases, the enthalpic contributions to the free energies are also close to the experimental results. The above models are able to satisfactory predict the hydration energies as well as the electrostatic potential around the ionic species. For univalent atomic ions, they also provide qualitative estimates of the Samoilov activation energies.     

Theory of three-dimensional alignment by intense laser pulses

We introduce a theoretical framework for study of three-dimensional alignment by moderately intense laser pulses and discuss it at an elementary level. Several features of formal interest are noted and clarified. Our approach is nonperturbative, treating the laser field within classical and the material system within quantum mechanics. The theory is implemented numerically using a basis set of rotational eigenstates, transforming the time-dependent Schrodinger equation to a set of coupled differential equations where all matrix elements are analytically soluble. The approach was applied over the past few years to explore different adiabatic and nonadiabatic three-dimensional alignment approaches in conjunction with experiments, but its formal details and numerical implementation were not reported in previous studies. Although we provide simple numerical examples to illustrate the content of the equations, our main goal is to complement previous reports through an introductory discussion of the underlying theory.     

Growth kinetics for AgI nanoparticles in AOT reverse micelles: effect of molecular length of hydrocarbon solvents

The growth kinetics for AgI nanoparticles formed in the solutions of water/AOT reverse micelles in n-hexane, n-octane, n-decane, and n-dodecane were investigated. In small micelles, the rate of nanoparticles growth was found to be independent of the type of solvent, while in large micelles the growth rate grew with increasing length of solvent molecules. The effect was explained by a different amount of free water in the micelle pools of the same size.     

1-Methylimidazolin-2-yl functionalized cyclopentadienyl complexes of titanium and zirconium. Crystal structure of {[η:η-κN-C5H4CPh2CH2-(1-Me-C3H4N2)]ZrCl2}2(μ-Cl)2

The novel bidentate ligand, C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3), has been prepared and characterized as its lithium salt LiC₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3-Li). Cyclopentadiene HC₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3-H) has been obtained from 6,6-diphenylfulvene and 1,2-dimethylimidazoline (1). In THF-d₈ solution in the presence of 1, (1-methylimidazoline-2-yl)methyllithium (2) has been proved to undergo gradual conversion into a dilithium derivative of N¹-methyl-N²-[(1E,2E)-1-methyl-2-(1-methylimidazolidine-2-idene)ethylidene]ethane-1,2-diamine (2a). In a solution, cyclopentadiene 3-H has been shown to undergo isomerization into 3-{N-[2-(N-methylamino)ethyl]amino}-1,1-diphenyl-1,2-dihydropentalene (4) and, further, into a mixture of 4 and two rotameric 3-[N-(2-aminoethyl)-N-methylamino]-1,1-diphenyl-1,2-dihydropentalenes (5a) and (5b). Treatment of the lithium salt 3-Li with Me₃SiCl has lead to 3-{N-[2-(N-trimethylsilylamino)ethyl]amino}-1,1-diphenyl-1,2-dihydropentalene (6) as the dominant component in the reaction mixture. In the latter case the expected Me₃Si-C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3-Si) was not observed. Stannylation of 3-Li with 1 equiv. of Me₃SnCl has resulted in formation of a mixture of Me₃Sn-C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3-Sn), (Me₃Sn)₂-C₅H₃CPh₂CH₂-(1-Me-C₃H₄N₂) (3-Sn₂), and cyclopentadiene 3-H in a ca. 2:1:1 molar ratio. Monocyclopentadienyl complexes {[η⁵:η¹-κN-C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂)]MCl₃ (M = Ti (7), Zr (8)) have been prepared starting from the organotin and organolithium compounds 3-Sn and 3-Li, respectively. The dynamic behavior of complexes 7 and 8 has been investigated by means of variable-temperature NMR spectroscopy in solutions. The molecular structures of the dihydropentalene 4, binuclear complex {[η⁵:η¹-κN-C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂)]ZrCl₂}₂(μ-Cl)₂8, and a coordination dimer of the dilithium salt 2a have been established by X-ray diffraction analysis. In the crystal structure of the 2a-dimer, the shortest known Li-Li contact has been found.     

Practical synthesis of 1,4-dioxane derivative of the closo-dodecaborate anion and its ring opening with acetylenic alkoxides

Practical method of synthesis of the 1,4-dioxane derivative of the closo-dodecaborate anion was developed. The cleavage of the dioxonium ring in [B₁₂H₁₁O(CH₂CH₂)₂O]⁻ with acetylenic alcohols gave rise to the preparation of closo-dodecaborate derivatives with terminal acetylene group. These compounds can be introduced into click reactions with phenylazide leading to the corresponding triazoles. The structures of (Bu₄N)[B₁₂H₁₁O(CH₂CH₂)₂O] and (Bu₄N)₂[B₁₂H₁₁(OCH₂CH₂)₂OCH₂CCH] · 0.5HOCH₂CCH were determined by single-crystal X-ray diffraction.     

Synthesis of cyclic peroxides containing the Si-gem-bisperoxide fragment. 1,2,4,5,7,8-Hexaoxa-3-silonanes as a new class of peroxides

A method was developed for the synthesis of the previously unknown class of organic peroxides, 1,2,4,5,7,8-hexaoxa-3-silonanes, based on the reaction of dialkyldichlorosilanes with 1,1'-dihydroperoxyperoxides. 1,2,4,5,7,8-Hexaoxa-3-silonanes are rather stable under ambient conditions and were characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. Their yields are in a range of 59-96%. The attempts were made to prepare 1,2,4,5-tetraoxa-3-silinanes by the reaction of dialkyldichlorosilanes with gem-bishydroperoxides. 1,2,4,5-Tetraoxa-3-silinanes were detected by NMR spectroscopy; these compounds rapidly decompose upon isolation.     

Cosmetic Formulations with Melaleuca alternifolia Essential Oil for the Improvement of Photoaged Skin: A Double-Blind,Randomized, Placebo-Controlled Clinical Study

This aim of this study was to evaluate the penetration depth, antioxidant capacity and the clinical efficacy of Melaleuca alternifolia pure essential oil and in a nanoemulsion to prevent skin photoaging. For this, 2% of pure essential oil or 2% of this essential oil in a nanoemulsion were vehiculated in a formulation. The skin penetration was evaluated using confocal Raman microspectroscopy. The radical protection factor was evaluated using electron paramagnetic resonance spectroscopy. For a clinical study, 40 male participants, aged 18–28 years, were enrolled, being divided into three groups: vehicle formulation, M. alternifolia pure essential oil and M. alternifolia Nanoemulsion. All the participants also received a sunscreen SPF 50 to use during the day. Before and after 90 days of study, skin hydrolipidics and morphological characteristics were performed by skin imaging and biophysical techniques. The nanoemulsion presented a lower antioxidant capacity and a higher penetration through the stratum corneum, reaching the viable epidermis, improving the stratum granulosum morphology. The groups presented an increase in the papillary depth, improving in the dermis echogenicity and the collagen fibers. Melaleuca alternifolia essential provides the potential to improve photoaged skin, being the application of nanoemulsion able to reach deeper skin layers.