Hypokinesia in adolescents

Title: Hypokinesia in adolescents Objectives: The main target is, to find out how frequent and extensive the hypokinesis appears in terms of the exploratory subject. We mainly search for the relationship of high school adolescents to the physical activities, how often it's being practicised and in which kind of environment. Methods: In order to prove my thesis, we decided to use a long version of international standardized IPAQ questionnaire translated to the czech language. The exploratory sample consisted of 46 high school adolescent students. The results were afterwards analysed according to the basic statistic principles. Subsequently we compared the quantity of physical activity between boys and girls during seven days of the research. Results: The results of research apparently meet the criteria of the sufficient count of teenager activities. In the average the sample was evaluated as moderately active individuals in both gender types. Despite the negative public image in terms of quantity of youth physical activities, the actual rate meets general requirements. Boys reached the rate of 1333,8 MET- min/week, girls reached the count of 2013,9 MET-min/week. Keywords: adolescence, physical activity, lack of exercise, lifestyl

Closely-Related Zn^II₂Ln^III₂ Complexes (Ln^III = Gd, Yb) with Either Magnetic Refrigerant or Luminescent Single-Molecule Magnet Properties

The reaction of the compartmental ligand <i>N</i>,<i>N</i>′,<i>N</i>″-trimethyl-<i>N</i>,<i>N</i>″-bis­(2-hydroxy-3-methoxy-5-methylbenzyl)­diethylenetriamine (H₂L) with Zn­(NO₃)₂·6H₂O and subsequently with Ln­(NO₃)₃·5H₂O (Ln^III = Gd and Yb) and triethylamine in MeOH using a 1:1:1:1 molar ratio leads to the formation of the tetranuclear complexes {(μ₃-CO₃)₂[Zn­(μ-L)­Gd­(NO₃)]₂}·4CH₃OH (<b>1</b>) and­{(μ₃-CO₃)₂[Zn­(μ-L)­Yb­(H₂O)]₂}­(NO₃)₂·4CH₃OH (<b>2</b>). When the reaction was performed in the absence of triethylamine, the dinuclear compound [Zn­(μ-L)­(μ-NO₃)­Yb­(NO₃)₂] (<b>3</b>) is obtained. The structures of <b>1</b> and <b>2</b> consist of two diphenoxo-bridged Zn^II–Ln^III units connected by two carbonate bridging ligands. Within the dinuclear units, Zn^II and Ln^III ions occupy the N₃O₂ inner and the O₄ outer sites of the compartmental ligand, respectively. The remaining positions on the Ln^III ions are occupied by oxygen atoms belonging to the carbonate bridging groups, by a bidentate nitrate ion in <b>1</b>, and by a coordinated water molecule in <b>2</b>, leading to rather asymmetric GdO₉ and trigonal dodecahedron YbO₈ coordination spheres, respectively. Complex <b>3</b> is made of acetate–diphenoxo triply bridged Zn^IIYb^III dinuclear units, where the Yb^III exhibits a YbO₉ coordination environment. Variable-temperature magnetization measurements and heat capacity data demonstrate that <b>1</b> has a significant magneto–caloric effect, with a maximum value of −Δ<i>S</i>_m = 18.5 J kg^–1 K^–1 at <i>T</i> = 1.9 K and <b>B</b> = 7 T. Complexes <b>2</b> and <b>3</b> show slow relaxation of the magnetization and single-molecule magnet (SMM) behavior under an applied direct-current field of 1000 Oe. The fit of the high-temperature data to the Arrhenius equation affords an effective energy barrier for the reversal of the magnetization of 19.4(7) K with τ_o = 3.1 × 10^–6 s and 27.0(9) K with τ_o = 8.8 × 10^–7 s for <b>2</b> and <b>3</b>, respectively. However, the fit of the full range of temperature data indicates that the relaxation process could take place through a Raman-like process rather than through an activated Orbach process. The chromophoric L^2– ligand is able to act as an “antenna” group, sensitizing the near-infrared (NIR) Yb^III-based luminescence in complexes <b>2</b> and <b>3</b> through an intramolecular energy transfer to the excited states of the accepting Yb^III ion. These complexes show several bands in the 945–1050 nm region, corresponding to ²F_5/2→²F_7/2 transitions arising from the ligand field splitting of both multiplets. The observed luminescence lifetimes τ_obs are 0.515 and 10 μs for <b>2</b> and <b>3</b>, respectively. The shorter lifetime for <b>2</b> is due to the presence of one coordinated water molecule on the Yb^III center (and to a lesser extent noncoordinated water molecules), facilitating vibrational quenching via O–H oscillators. Therefore, complexes <b>2</b> and <b>3</b>, combining field-induced SMM behavior and NIR luminescence, can be considered to be dual magneto–luminescent materials

Synthesis, Structure, and Magnetism of a Family of Heterometallic {Cu₂Ln₇} and {Cu₄Ln₁₂} (Ln = Gd, Tb, and Dy) Complexes: The Gd Analogues Exhibiting a Large Magnetocaloric Effect

The syntheses, structures, and magnetic properties of two heterometallic Cu^II–Ln^III (Ln^III = Gd, Tb, and Dy) families, utilizing triethanolamine and carboxylate ligands, are reported. The first structural motif displays a nonanuclear {Cu^II₂Ln^III₇} metallic core, while the second reveals a hexadecanuclear {Cu^II₄Ln^III₁₂} core. The differing nuclearities of the two families stem from the choice of carboxylic acid used in the synthesis. Magnetic studies show that the most impressive features are displayed by the {Cu^II₂Gd^III₇} and {Cu^II₄Gd^III₁₂} complexes, which display a large magnetocaloric effect, with entropy changes −Δ<i>S</i>_m = 34.6 and 33.0 J kg^–1 K^–1 at <i>T</i> = 2.7 and 2.9 K, respectively, for a 9 T applied field change. It is also found that the {Cu^II₄Dy^III₁₂} complex displays single-molecule magnet behavior, with an anisotropy barrier to magnetization reversal of 10.1 K

Thiocyanate Complexes of Uranium in Multiple Oxidation States: A Combined Structural, Magnetic, Spectroscopic, Spectroelectrochemical, and Theoretical Study

A comprehensive study of the complexes A₄[U­(NCS)₈] (A = Cs, Et₄N, ⁿBu₄N) and A₃[UO₂(NCS)₅] (A = Cs, Et₄N) is described, with the crystal structures of [ⁿBu₄N]₄[U­(NCS)₈]·2MeCN and Cs₃[UO₂(NCS)₅]·O_0.5 reported. The magnetic properties of square antiprismatic Cs₄[U­(NCS)₈] and cubic [Et₄N]₄[U­(NCS)₈] have been probed by SQUID magnetometry. The geometry has an important impact on the low-temperature magnetic moments: at 2 K, μ_eff = 1.21 μ_B and 0.53 μ_B, respectively. Electronic absorption and photoluminescence spectra of the uranium­(IV) compounds have been measured. The redox chemistry of [Et₄N]₄[U­(NCS)₈] has been explored using IR and UV–vis spectroelectrochemical methods. Reversible 1-electron oxidation of one of the coordinated thiocyanate ligands occurs at +0.22 V vs Fc/Fc⁺, followed by an irreversible oxidation to form dithiocyanogen (NCS)₂ which upon back reduction regenerates thiocyanate anions coordinating to UO₂²⁺. NBO calculations agree with the experimental spectra, suggesting that the initial electron loss of [U­(NCS)₈]^4– is delocalized over all NCS^– ligands. Reduction of the uranyl­(VI) complex [Et₄N]₃[UO₂(NCS)₅] to uranyl­(V) is accompanied by immediate disproportionation and has only been studied by DFT methods. The bonding in [An­(NCS)₈]^4– (An = Th, U) and [UO₂(NCS)₅]^3– has been explored by a combination of DFT and QTAIM analysis, and the U–N bonds are predominantly ionic, with the uranyl­(V) species more ionic that the uranyl­(VI) ion. Additionally, the U­(IV)–NCS ion is more ionic than what was found for U­(IV)–Cl complexes

New Dioximes as Bridging Ligands in 3d/4f-Metal Cluster Chemistry: One-Dimensional Chains of Ferromagnetically Coupled {Cu₆Ln₂} Clusters Bearing Acenaphthenequinone Dioxime and Exhibiting Magnetocaloric Properties

The employment of the tetradentate ligand acenaphthenequinone dioxime (acndH₂) for a first time in heterometallic Cu^II/Ln^III (Ln = Gd and Dy) chemistry has afforded the one-dimensional coordination polymers [Cu₆Gd₂(acnd)₆­(acndH)₆­(MeOH)₆]_<i>n</i> (<b>1</b>) and [Cu₆Dy₂(acnd)₆­(acndH)₆­(MeOH)₂]_<i>n</i> (<b>2</b>), which consist of repeating {Cu₆Ln₂} clusters that are intermolecularly linked to each other through the oximate groups of two η²:η¹:η¹:μ₃ acnd^2– ligands. The [Cu₆Ln₂­(μ₃-NO)₆­(μ-NO)₈]⁴⁺ core is unprecedented in heterometallic cluster chemistry and comprises two symmetry-related {Cu₃Ln} subunits, each with a distorted trigonal pyramidal topology. Magnetic susceptibility studies revealed the presence of predominant ferromagnetic exchange interactions within the {Cu₃Ln} subunits and weak antiferromagnetic interactions between them. As a result, the magnetic and magnetocaloric properties of the {Cu₆Gd₂}_<i>n</i> compound could be rationalized in terms of two weakly coupled <i>S</i> = 5 spins that yield a magnetic entropy change of −Δ<i>S</i>_m = 11.8 J kg^–1 K^–1 at <i>T</i> = 1.6 K for μ₀Δ<i>H</i> = 7 T

Theoretical Studies on Polynuclear {Cu^II₅Gd^III_<i>n</i>} Clusters (<i>n</i> = 4, 2): Towards Understanding Their Large Magnetocaloric Effect

Density functional theory (DFT) studies on two polynuclear clusters, [Cu^II₅Gd^III₄O₂­(OMe)₄­(teaH)₄­(O₂CC­(CH₃)₃)₂(NO₃)₄] (<b>1</b>) and [Cu₅Gd₂­(OH)₄­(Br)₂-(H₂L)₂­(H₃L)₂­(NO₃)₂­(OH₂)₄] (<b>2</b>), have been carried out to probe the origin of the large magnetocaloric effect (MCE). The magnetic exchange interactions for <b>1</b> and <b>2</b> via multiple pathways are estimated using DFT calculations. While the calculated exchange parameters deviate from previous experimental estimates obtained by fitting the magnetic data, the DFT parameter set is found to offer a striking match to the magnetic data for both complexes, highlighting the problem of overparameterization. Magnetostructural correlations for {Cu–Gd} pairs have been developed where both the Cu–O–Gd angles and Cu–O–Gd–O dihedral angles are found to significantly influence the magnitude and sign of the exchange constants. The magnitude of the MCE has been examined as a function of the exchange interactions, and clues on how the effect can be enhanced are discussed

Molecular Nanoscale Magnetic Refrigerants: A Ferrimagnetic {Cu^II₁₅Gd^III₇} Cagelike Cluster from the Use of Pyridine-2,6-dimethanol

The employment of pyridine-2,6-dimethanol in 3d/4f metal cluster chemistry has afforded a new {Cu^II₁₅Gd^III₇} cagelike molecule with a beautiful structure built by fused triangular subunits; the compound exhibits an overall ferrimagnetic behavior with an appreciable ground-state spin value and shows promise as a low-temperature magnetic refrigerant

Single-Molecule Magnet Behavior and Magnetocaloric Effect in Ferromagnetically Coupled Ln^III-Ni^II-Ni^II-Ln^III (Ln^III = Dy^III and Gd^III) Linear Complexes

New types of linear tetranuclear Ln^III-Ni^II-Ni^II-Ln^III (Ln^III = Dy (<b>1</b>), Gd (<b>2</b>)) complexes have been prepared using the multidentate ligand <i>N</i>,<i>N</i>′-bis­(3-methoxysalicylidene)-1,3-diaminobenzene, which has two sets of NO and OO′ coordination pockets that are able to selectively accommodate Ni^II and Ln^III ions, respectively. The X-ray structure analysis reveals that the Ni^II ions are bridged by phenylenediimine groups forming a 12-membered metallacycle in the central body of the complex, whereas the Ln^III ions are located at both sides of the metallacycle and linked to the Ni^II ions by diphenoxo bridging groups. Phenylenediimine and diphenoxo bridging groups transmit ferromagnetic exchange interactions between the two Ni^II ions and between the Ni^II and the Ln^III ions, respectively. Complex <b>1</b> shows slow relaxation of the magnetization at zero field and a thermal energy barrier <i>U</i>_eff = 7.4 K with <i>H</i>_DC = 1000 Oe, whereas complex <b>2</b> exhibits an S = 9 ground state and significant magnetocaloric effect (−Δ<i>S</i>_m = 18.5 J kg^–1 K^–1 at <i>T</i> = 3 K and Δ<i>B</i> = 5 T)

Asymmetric [2+2+1] cyclopentannulation of olefins. Ring expansion of 2-N-methyl-N-tosyl-cyclobutanone

alpha-N-Methyl-N-tosyl cyclobutanones 2 which had been previously prepared in good yields and high enantiomeric excesses from olefins and chiral keteniminium salts have been converted into the corresponding oxiranes 3 by reaction with dimethylsulfonium methylid. The stereochemistry of this reaction was found to be dependent on several factors which have been analyzed. Treatment of these oxiranes with a stoichiometric amount of lithium iodide in refluxing tetrahydrofuran gave excellent yields of monocyclic or fused cyclopentenones 4 resulting from a P-elimination of N-methyl-N-tosylamide from a primarily formed cyclopentanone. The ring-expansion was totally selective but for oxiranes attached to a bicyclo[4.2.0]octanone system. In all cases, the enantiomeric purities of the starting cyclobutanones were preserved throughout the sequence which thus represents a useful [2+2+1] strategy for the cyclopentannulation of olefins. (C) 2002 Elsevier Science Ltd. All rights reserved

Fluoride Bridges as Structure-Directing Motifs in 3d-4f Cluster Chemistry

The use of kinetically robust chromium­(III) fluorido complexes as synthons for mixed 3d-4f clusters is reported. The tendency toward linear {Cr^III–F–Ln^III} units dictates the cluster topology. Specifically, we show that reaction of <i>cis</i>-[Cr^IIIF₂(NN)₂]­NO₃ (NN = 1,10-phenanthroline (“phen”) or 2,2′-bipyridine (“bpy”)) with Ln­(NO₃)₃·<i>x</i>H₂O produces isostructural series of molecular {Ln₂Cr₂} squares (<b>1</b>–<b>9</b>) with linear fluoride bridges. In a parallel fashion, <i>fac</i>-[Cr^IIIF₃L], where L = <i>N</i>,<i>N′</i>,<i>N</i>″-trimethyl-1,4,7-triazacyclononane (“Me₃tacn”), reacts with Nd­(NO₃)₃·6H₂O to form a fluoride-centered penta-nuclear complex and <i>fac</i>-[Cr^IIIF₃L′], with L′ = 1,1,1-tris-((methylamino)­methylethane) (“Me₃tame”), reacts with [Ln­(hfac)₃(H₂O)₂] (hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone) to yield an isostructural series of {Ln₃Cr₂} (<b>10</b>–<b>14</b>) trigonal bipyramids with no central ligand. The formation of the latter is accompanied by a partial solvolysis of the Cr­(III) precursor but without formation of insoluble LnF₃. The magnetic properties of the gadolinium containing clusters allow quantification of fluoride-mediated, antiferromagnetic Gd–Cr exchange interactions of magnitude between 0.14 cm^–1 and 0.71 cm^–1 (<i>Ĥ</i> = <i>J</i>₁₂<b>Ŝ</b>₁·<b>Ŝ</b>₂ formalism) and vanishingly small <i>J</i>_Gd–Gd of 0.06(0) cm^–1. The large spin and small anisotropy together with weak exchange interactions in the {Gd₃Cr₂} (<b>11</b>) cluster give rise to a very large magneto-caloric effect of −Δ<i>S</i>_m = 28.7 J kg^–1 K^–1 (μ₀<i>H</i> = 90 to 0 kOe)