Observation of Te···π and X···X Bonding in para-Substituted Diphenyltellurium Dihalides, (p-Me2NC6H4)(p-YC6H4)TeX2(X=Cl, Br, I; Y=H, EtO, Me2N)-

The supramolecular association of the previously described para-dimethylaminophenyl-substituted diorganotellurium dihalides (p-Me₂NC₆H₄)₂TeX₂ (X = Cl (1), Br (2), I (3)) and (p-Me₂NC₆H₄)RTeCl₂ (R = Ph (4), p-EtOC₆H₄ (5)), was investigated by X-ray crystallography. Unlike almost all other structurally characterized diorganotellurium dihalides, (p-Me₂NC₆H₄)₂TeX₂ (X = Cl (1), Br (2), I (3)) reveal no secondary Te∙∙∙X interactions, but X∙∙∙X interactions. The structure of (p-Me₂NC₆H₄)PhTeCl₂ (4) resembles that of Ph₂TeCl₂ and shows one secondary Te∙∙∙Cl contact, whereas (p-Me₂NC₆H₄)(p-EtOC₆H₄)TeCl₂ (5) exhibits neither secondary Te∙∙∙Cl nor Cl∙∙∙Cl interactions. The unusual structural characteristics of 1–5 are attributed to the occurrence of intermolecular Te∙∙∙π and π∙∙∙π contacts associated with quinoid π-electron delocalization across the para-dimethylaminophenyl (1–5) and para-ethoxyphenyl (5) groups.

The interplay of secondary Te···N, Te···O, Te···I and I···I interactions, Te···π contacts and π-stacking in the supramolecular structures of [{2-(4-nitrobenzylideneamino)-5-methyl}phenyl](4-methoxyphenyl)tellurium dihalides

The unsymmetrical1y substituted diorganotellurium dihalides [2-(4,4'-N0₂C₆H₄CHNC₆H₃Me]RTeX₂ (R = 4-MeOC₆H₄, X = Cl,
1a; Br, 1b; I, 1c; R =4-MeC₆H₄ ; X = Cl, 2; R =C₆H₅, X = Cl, 3) were prepared in good yields and characterized by solution and solid-state ¹²⁵Te NMR spectroscopy, IR spectroscopy and X-ray crystallography. In the solid-state, molecular structures of 1a and 1c possess scarcely observed 1,4-type intramolecular Te···N secondary interaction. Crystal packing of these compounds show an unusually rich diversity of intermolecular secondary, Te·· ·0, Te· .. \ and 1···1 interactions, Te·· ·π contacts as well as extensive
π-stacking of the organic substituents.

Selective hydrogen bonding and hierarchical nanostructures in poly(hydroxyether of bisphenol A)/poly(ε-caprolactone)-block-poly(2-vinyl pyridine) blends

The phase behavior, hydrogen bonding interactions and morphology of poly(hydroxyether of bisphenol A) (phenoxy) and poly(var epsilon-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP) were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy and atomic force microscopy (AFM). In this A-b-B/C type block copolymer/homopolymer system, both P2VP and PCL blocks have favorable intermolecular interaction towards phenoxy via hydrogen bonding. However, the hydrogen bonding between P2VP and phenoxy is significantly stronger than that between PCL and phenoxy. Selective hydrogen bonding between phenoxy/P2VP pair at lower phenoxy contents and co-existence of two competitive hydrogen bonding interactions between phenoxy/P2VP and phenoxy/PCL pairs at higher phenoxy contents were observed in the blends. This leads to the formation of a variety of composition dependent nanostructures including wormlike, hierarchical and core–shell morphologies. The blends became homogeneous at 95 wt% phenoxy where both blocks of the PCL-b-P2VP were miscible with phenoxy due to hydrogen bonding. In the end, a model was proposed to explain the microphase morphology of blends based on the experimental results obtained. The swelling of the PCL-b-P2VP block copolymer by phenoxy due to selective hydrogen bonding causes formation of different microphases

Self-assembled complexes of poly(4-vinylphenol) and poly(ε-caprolactone)-block-poly(2-vinylpyridine) via competitive hydrogen bonding

Nanostructured complexes were prepared from poly(ε-caprolactone)-block-poly(2-vinylpyridine) (PCL-b-P2VP) and poly(4-vinylphenol) (PVPh) in tetrahydrofuran (THF). The phase behavior, specific interactions, and morphology were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). In this A-b-B/C type block copolymer/homopolymer system, both blocks of the PCL-b-P2VP block copolymer have favorable intermolecular interaction toward PVPh via hydrogen bonding, but the interaction between P2VP block and PVPh is significantly stronger than that between PCL block and PVPh. It was found that the disparity in competitive intermolecular interactions, specifically PVPh and P2VP block interact strongly whereas PVPh and PCL block interact weakly, leads to the formation of a variety of nanostructures depending on PVPh concentration. Spherical micelles of 30−40 nm in diameter were obtained in the complex with 10 wt % PVPh, followed by wormlike micelles with size in the order of 40−50 nm in the complexes with 30−60 wt % PVPh. At low PVPh concentrations, PCL interacts weakly with PVPh, whereas in the complexes containing more than 20 wt % PVPh, the PCL block began to interact considerably with PVPh, leading to the formation of composition-dependent nanostructures. The complex becomes homogeneous with PVPh content beyond 60 wt %, since a sufficient amount of PVPh is available to form hydrogen bonds with both PCL and P2VP. Finally, a model was proposed to explain the self-assembly and microphase morphology of these complexes based on the experimental results obtained. The competitive hydrogen-bonding interactions cause the self-assembly and formation of different microphase morphologies.

Competitive hydrogen bonding and self-assembly in Poly(2-vinyl pyridine)-block-Poly(methyl methacrylate)/ Poly(hydroxyether of bisphenol A) blends

Blends of poly(2-vinyl pyridine)-block-poly(methyl methacrylate) (P2VP-b-PMMA) and poly(hydroxyether of bisphenol A) (phenoxy) were prepared by solvent casting from chloroform solution. The specific interactions, phase behavior and nanostructure morphologies of these blends were investigated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this block copolymer/homopolymer blend system, it is established that competitive hydrogen bonding exists as both blocks of the P2VP-b-PMMA are capable of forming intermolecular hydrogen bonds with phenoxy. It was observed that the interaction between phenoxy and P2VP is stronger than that between phenoxy and PMMA. This imbalance in the intermolecular interactions and the repulsions between the two blocks of the diblock copolymer lead to a variety of phase morphologies. At low phenoxy concentration, spherical micelles are observed. As the concentration increases, PMMA begins to interact with phenoxy, leading to the changes of morphology from spherical to wormlike micelles and finally forms a homogenous system. A model is proposed to describe the self-assembled nanostructures of the P2VP-b-PMMA/phenoxy blends, and the competitive hydrogen bonding is responsible for the morphological changes.

Self-assembly and morphology in double crystalline diblock copolymer/homopolymer blends with competitive hydrogen bonding

Block copolymers are of particular interest due to their ability to form a rich variety of nanostructures via self-assembly [1]. The self-assembly via competitive hydrogen bonding is a novel concept which is based on the competition between different blocks of the block copolymer to form more than one kind of intermolecular interaction with the complimentary polymer in the system. Recently, Guo and co-workers have proven that careful selection of the polymers specifically the block copolymer, and the experimental conditions can lead to self-assembled structures in blends and complexes exhibiting competitive hydrogen bonding [2-5].

Profiling of secondary metabolites in blue lupin inoculated with Phytophthora cinnamomi following phosphite treatment

In order to discover phytochemicals that are potentially bioactive against Phytophthora cinnamomi, (a soil-borne plant pathogen) a metabolite profiling protocol for investigation of metabolic changes in Lupinus angustifolius L. plant roots in response to pathogen challenge has been established. Analysis of the metabolic profiles from healthy and P. cinnamomi-inoculated root tissue with high resolution mass spectrometry and nuclear magnetic resonance spectroscopy confirmed that although susceptible, L. angustifolius upregulated a defence associated genistein and 2′-hydroxygenistein-based isoflavonoid and a soyasapogenol saponin at 12h post inoculation which increased in concentration at 72h post inoculation. In contrast to the typical susceptible interaction, the application of a phosphorous-based treatment to L. angustifolius foliage 48h before P. cinnamomi challenge negated the ability of the pathogen to colonise the root tissue and cause disease. Importantly, although the root profiles of water-treated and phosphite-treated plants post pathogen inoculation contained the same secondary metabolites, concentration variations were observed. Accumulation of secondary metabolites within the P. cinnamomi-inoculated plants confirms that pathogen ingress of the root interstitially occurs in phosphite-treated plants, confirming a direct mode of action against the pathogen upon breaching the root cells.

Changing from primary to secondary school highlights opportunities for school environment interventions aiming to increase physical activity and reduce sedentary behaviour: a longitudinal cohort study.

BACKGROUND: There is little empirical evidence of the impact of transition from primary to secondary school on obesity-related risk behaviour. The purpose of this study was to examine the effect of a change of school system on physical activity (PA) and sedentary behaviour in pre-early adolescents. METHODS: Fifteen schools in Victoria, Australia were recruited at random from the bottom two strata of a five level socio-economic scale. In nine schools, students in year 6 primary school transitioned to a different school for year 7 secondary school, while in six schools (combined primary-secondary), students remained in the same school environment from year 6 to year 7. Time 1 (T1) measures were collected from students (N=245) in year 6 (age 11-13). Time 2 (T2) data were collected from 243 (99%) of the original student cohort when in year 7. PA and sedentary behaviour data were collected objectively (via ActiGraph accelerometer) and subjectively (via child self-report recall questionnaire). School environment data were collected via school staff survey. Change of behaviour analyses were conducted longitudinally i) for all students and ii) by change/no change of school. Mixed model regression analysis tested for behavioural interaction effects of changing/not changing school. RESULTS: Sixty-three percent (N=152) changed schools from T1 to T2. Across all students we observed declines in average daily moderate to vigorous physical activity (MVPA) (-4 min) and light PA (-23 min), and increases in average daily sedentary behaviour (16 min), weekday leisure screen time (17 min) and weekday homework screen time (25 min), all P<0.05. Compared to students who remained in the same school environment, students who changed school reported a greater reduction in PA intensity at recess and lunch, less likelihood to cycle to/from school, greater increase in weekday (41 mins) and weekend (45 mins) leisure screen time (P<0.05) and greater encouragement to participate in sport. School staff surveys identified that sport participation encouragement was greater in primary and combined primary-secondary than secondary schools (P<0.05). CONCLUSION: Transitioning from primary to secondary school negatively impacts on children's PA and sedentary behaviour, and has further compounding effects on behaviour type by changing school environments.

Co-cultivation of plant cells as a technique for the elicitation of secondary metabolite production

Cells of Mikania glomerata, Cephaelis ipecacuanha and Maytenus aquifolia were co-cultured in a two-phase system using filter paper as a solid support. The species were co-cultured in all possible paired combinations. Interaction between Mikania and Maytenus cells resulted in increased biomass production of Maytenus cells, but the friedelin content was reduced. Co-cultivation of Cephaelis and Mikania cells enhanced coumarin content, but inhibited the growth of Mikania cells. However, yield of emetine as well as Cephaelis biomass accumulation were positively stimulated by the co-cultivation. Results indicate a possible occurrence of allelopathy in such a system.

Investigation of the interaction between Tc85-11 protein and antibody anti-T cruzi by AFM and amperometric measurements

This present work reports on development of an amperometric immunosensor for the diagnosis of Chagas' disease using a specific glycoprotein of the trypomastigote surface, which belongs to the Tc85-11 protein family of Trypanosoma cruzi (T cruzi). An atomically flat gold surface on a silicon substrate and gold screen-printed electrodes were functionalized with cystatrine and later activated with glutaraldehyde (GA), which was used to form covalent bonds with the purified recombinant antigen (Tc85-11). The antigen reacts with the antibody from the serum, and the affinity reaction was monitored directly using atomic force microscopy or amperometry through a secondary antibody tagged to peroxidase (HRP). Surface imaging allowed to us to differentiate the modification steps and antigen-antibody interaction allowed to distinguish the affinity reactions. In the amperometric immunosensor, peroxidase catalyses the L-2 formation in the presence of hydrogen peroxide and potassium iodide, and the reduction current intensity was measured at a given potential with screen-printed electrodes. The immunosensor was applied to sera of chagasic patients and patients having different systemic diseases. (c) 2006 Elsevier Ltd. All rights reserved.

The influence of time interval between bleaching and enamel bonding

Objectives: the purpose of this study was to investigate the penetration of a conventional adhesive material into enamel bleached with 16% carbamide peroxide and 38% hydrogen peroxide using optical light microscopy.Methods: Extracted human teeth were randomly divided into eight experimental groups with six specimens each, according to the bleaching material and time interval after bleaching and before the bonding procedure. Groups were designated as follows: control group, restorations in unbleached teeth; restorations performed immediately after bleaching; restorations performed 7 days after bleaching; restorations performed 14 days after bleaching; and restorations performed 30 days after bleaching. The length of resin tags was measured with an Axiophot photomicroscope at 400x magnification for the calculation of the proportion of tags of study groups compared to the respective control groups. Analysis of variance was applied for comparison between groups; data were transformed into arcsine (p < 0.05).Results: the specimens of experimental groups, in which restorations were performed 7, 14, and 30 days after bleaching, showed better penetration of adhesive material into enamel than specimens restored immediately after bleaching. There was no statistically significant difference between the bleaching materials employed or in the interaction between bleaching agent and time interval.Conclusions: This suggests that a time interval of at least 7 days should be allowed between enamel bleaching and placement of adhesive bonding agents for accomplishment of composite resin restorations.

EFFECT of DIFFERENT AIRBORNE-PARTICLE ABRASION/BONDING AGENT COMBINATIONS on THE BOND STRENGTH of A RESIN CEMENT TO A BASE METAL ALLOY

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Identification of continuous interaction sites in PLA(2)-based protein complexes by peptide arrays

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effects of mechanical cycling on the bonding of zirconia and fiber posts to human root dentin

Purpose: To evaluate the effect of cyclical mechanical loading on the bond strength of a fiber and a zirconia post bonded to root dentin.Materials and Methods: Forty single-rooted human teeth (maxillary incisors and canines) were sectioned, and the root canals were prepared at 12 mm. Twenty randomly seleced specimens received a quartz fiber post (FRC) (D.T. Light-Post) and 20 others received a zirconia post (ZR) (Cosmopost). The posts were resin luted (All Bond 2 + resin cement Duo-link) and each specimen was embedded in epoxy resin inside a PVC cylinder. Ten specimens with FRC post and 10 specimens with ZR post were submitted to fatigue testing (2,000,000 cycles; load: 50 N; angle of 45 degrees; frequency: 8 Hz), while the other 20 specimens were not fatigued. Thus, 4 groups were formed: G1: FRC+O cycles; G2: FRC+2,000,000 cycles; G3: ZR+O cycles; G4: ZR+2,000,000 cycles. Later, the specimens were cut perpendicular to their long axis to form 2-mm-thick disk-shaped samples (4 sections/specimen), which were submitted to the push-out test (1 mm/min). The mean bond strength values (MPa) were calculated for each tooth (n = 10) and data were submitted to statistical analysis (alpha = 0.05).Results: Two-way ANOVA revealed that the bond strength was significantly affected by mechanical cycling (p = 0.0014) and root post (p = 0.0325). The interaction was also statistically significant (p = 0.0010). Tukey's test showed that the mechanical cycling did not affect the bonding of FRC to root dentin, while fatigue impaired the bonding of zirconium to root dentin.Conclusion: (1) the bond strength of the FRC post to root dentin was not reduced after fatigue testing, whereas the bonding of the zirconia post was significantly affected by the fatigue. (2) Cyclical mechanical loading appears to damage the bond strength of the rigid post only.

Measurement of B(B)over-bar angular correlations based on secondary vertex reconstruction at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)