Shear Bond Strength and Ultrastructural Interface Analysis of Different Adhesive Systems to Bleached Dentin

Background: It remains unclear as to whether or not dental bleaching affects the bond strength of dentin/resin restoration. Purpose: To evaluated the bond strength of adhesive systems to dentin submitted to bleaching with 38% hydrogen peroxide (HP) activated by LED-laser and to assess the adhesive/dentin interfaces by means of SEM. Study design: Sixty fragments of dentin (25 mm(2)) were included and divided into two groups: bleached and unbleached. HP was applied for 20 s and photoactivated for 45 s. Groups were subdivided according to the adhesive systems (n = 10): (1) two-steps conventional system (Adper Single Bond), (2) two-steps self-etching system (Clearfil standard error (SE) Bond), and (3) one-step self-etching system (Prompt L-Pop). The specimens received the Z250 resin and, after 24 h, were submitted to the bond strength test. Additional 30 dentin fragments (n = 5) received the same surface treatments and were prepared for SEM. Data were analyzed by ANOVA and Tukey`s test (alpha = 0.05). Results: There was significant strength reduction in bleached group when compared to unbleached group (P < 0.05). Higher bond strength was observed for Prompt. Single Bond and Clearfil presented the smallest values when used in bleached dentin. SEM analysis of the unbleached specimens revealed long tags and uniform hybrid layer for all adhesives. In bleached dentin, Single Bond provided open tubules and with few tags, Clearfil determined the absence of tags and hybrid layer, and Prompt promoted a regular hybrid layer with some tags. Conclusions: Prompt promoted higher shear bond strength, regardless of the bleaching treatment and allowed the formation of a regular and fine hybrid layer with less deep tags, when compared to Single Bond and Clearfil. Microsc. Res. Tech. 74:244-250, 2011. (C) 2010 Wiley-Liss, Inc.

Effect of methyl methacrylate monomer on bond strength of denture base resin to acrylic teeth

Bond failures at the acrylic teeth and denture base resin interface are still a common clinical problem in prosthodontics. The effect of methyl methacrylate (MMA) monomer on the bond strength of three types of denture base resins (Acron MC, Lucitone 550 and QC-20) to two types of acrylic teeth (Biotone and Trilux) was evaluated. Twenty specimens were produced for each denture base resin/acrylic tooth combination and were randomly divided into control (acrylic teeth received no surface treatment) and experimental groups (MMA was applied to the surface of the acrylic teeth for 180 s) and were submitted to shear tests (1 mm/mm). Data (MPa) were analyzed using three-way ANOVA/Student`s test (alpha = 0.05). MMA increased the bond strength of Lucitone denture base resins and decreased the bond strength of QC-20. No difference was detected for the bond strength of Acron MC base resin after treatment with MMA. (C) 2008 Elsevier Ltd. All rights reserved.

NMR structure and backbone dynamics of a concatemer of epidermal growth factor homology modules of the human low-density lipoprotein receptor

The ligand-binding region of the low-density lipoprotein (LDL) receptor is formed by seven N-terminal, imperfect, cysteine-rich (LB) modules. This segment is followed by an epidermal growth factor precursor homology domain with two N-terminal, tandem, EGF-like modules that are thought to participate in LDL binding and recycling of the endocytosed receptor to the cell surface. EGF-A and the concatemer, EGF-AB, of these modules were expressed in Escherichia coli. Correct protein folding of EGF-A and the concatemer EGF-AB was achieved in the presence or absence of calcium ions, in contrast to the LB modules, which require them for correct folding. Homonuclear and heteronuclear H-1-N-15 NMR spectroscopy at 17.6 T was used to determine the three-dimensional structure of the concatemer. Both modules are formed by two pairs of short, anti-parallel beta -strands. In the concatemer, these modules have a fixed relative orientation, stabilized by calcium ion-binding and hydrophobic interactions at the interface. N-15 longitudinal and transverse relaxation rates, and {H-1}-N-15 heteronuclear NOEs were used to derive a model-free description of the backbone dynamics of the molecule. The concatemer appears relatively rigid, particularly near the calcium ion-binding site at the module interface, with an average generalized order parameter of 0.85 +/- 0.11. Some mutations causing familial hypercholesterolemia may now be rationalized. Mutations of D41, D43 and E44 in the EGF-B calcium ion-binding region may affect the stability of the linker and thus the orientation of the tandem modules. The diminutive core also provides little structural stabilization, necessitating the presence of disulfide bonds. The structure and dynamics of EGF-AB contrast with the N-terminal LB modules, which require calcium ions both for folding to form the correct disulfide connectivities and for maintenance of the folded structure, and are connected by highly mobile linking peptides. (C) 2001 Academic Press.

X-ray scattering studies of mixed langmuir monolayers and Langmuir-Blodgett films of a noncentrosymmetric porphyrin with cadmium arachidate

The structures of mixed Langmuir (floating) monolayers and Langmuir-Blodgett (LB) films of a phenanthroline-porphyrin with cadmium arachidate (PhenPor + CdAr) have been investigated by synchrotron X-ray grazing incidence diffraction (GIXD) and specular X-ray reflectivity (SXR). GIXD measurements of the floating monolayers showed only one peak, arising from the CdAr domains in the films, at a scattering angle of 21.5 degrees. This is consistent with a hexagonal structure (alpha = 4.77 Angstrom). The correlation length in these domains is 250 Angstrom. GMD measurements of the LB films, however, show two sets of diffraction features: one arises from CdAr domains with a rectangular in-plane structure (alpha = 7.44 Angstrom and b = 4.90 Angstrom) and a correlation length of 85 Angstrom; the other is from porphyrin domains with an oblique in-plane structure (alpha (p) 15.2 Angstrom, b(p) = 8.86 Angstrom, and gamma (p) = 80 degrees) and a correlation length of 105 Angstrom. These dimensions are consistent with the surface pressure-area isotherm measurements and indicate that the two components are immiscible. The thickness of the bilayer is 57 Angstrom, and there is no correlation between the bilayers. Introduction of a trigger compound does not alter the structure of the films but slightly increases the bilayer thickness. The SXR measurements of the floating monolayers also support the suggested immiscibility of the two components in the films.

Structural effects of lipophilic methotrexate conjugates on model phospholipid biomembranes

Lipophilic conjugates of the antitumor drug methotrexate (MTX) with lipoamino acids (LAAs) have been previously described as a tool to enhance MTX passive entrance into cells, overcoming a form of transport resistance which makes tumour cells insensitive to the antimetabolite. A knowledge of the mechanisms of interaction of such lipophilic derivatives with cell membranes could be useful for planning further lipophilic MTX derivatives with an optimal antitumour activity. To this aim, a calorimetric study was undertaken using a biomembrane model made from synthetic 1,2-dipalmitoyl-glycero-3-phosphocholine (DPPC) multilamellar liposomes. The effects of MTX and conjugates on the phase transition of liposomes were investigated using differential scanning calorimetry. The interaction of pure MTX with the liposomes was limited to the outer part of the phospholipid bilayers, due to the polar nature of the drug. Conversely, its lipophilic conjugates showed a hydrophobic kind of interaction, perturbing the packing order of DPPC bilayers. In particular, a reduction of the enthalpy of transition from the gel to the liquid crystal phase of DPPC membranes was observed. Such an effect was related to the structure and mole fraction of the conjugates in the liposomes. The antitumour activity of MTX conjugates was evaluated against cultures of a CCRF-CEM human leukemic T-cell line and a related MTX resistant sub-line. The in vitro cell growth inhibitory activity was higher for bis(tetradecyl) conjugates than for both the other shorter- and longer-chain derivatives. The biological effectiveness of the various MTX derivatives correlated very well with the thermotropic effects observed on the phase transition of DPPC biomembranes. (C), 2001 Elsevier Science B.V All rights reserved.

Schistosoma japonicum cathepsin D aspartic protease cleaves human IgG and other serum components

Recombinant cathepsin D aspartic protease of Schistosoma japonicum cleaved human IgG in vitro in a time and dose-dependent manner. Optimal cleavage was seen at pH 3.6-4.5; modest cleavage remained at pH 5.0, and no cleavage was detected above pH 5.0. Amino terminal sequencing of the major cleavage fragments of human IgG identified a Fab fragment from the VH1 domain, and 2 cleavage sites in the CH2 domain below the hinge region. The P1 and P1' residues at the 2 CH2 cleavage sites were Phe254-Leu255 and Leu325-Thr326, indicating a preference by the schistosome protease for bulky hydrophobic residues flanking the scissile bond. No cleavage of the immunoglobulin light chain was detected. In addition, the recombinant schistosome protease indiscriminately degraded the human serum proteins complement C3 and serum albumin into numerous small fragments. These results demonstrate specific cleavage of human IgG by the recombinant schistosome aspartic protease, and highlight the broad range digestive specificity of the enzyme which may play a role in the degradation of host serum proteins ingested as part of the schistosome bloodmeal.

Solution structure of BSTI: A new trypsin inhibitor from skin secretions of Bombina bombina

The three-dimensional solution structure of BSTI, a trypsin inhibitor from the European frog Bombina bombina, has been solved using H-1 NMR spectroscopy. The 60 amino acid protein contains five disulfide bonds, which were unambiguously determined to be Cvs (4-38), Cys (13-34), Cys (17-30), Cys (21-60), and Cys (40-54) by experimental restraints and subsequent structure calculations. The main elements of secondary structure are four beta -strands, arranged as two small antiparallel beta -sheets, The overall fold of BSTI is disk shaped and is characterized by the lack of a hydrophobic core. The presumed active site is located on a loop comprising residues 21-34, which is a relatively disordered region similar to that seen in many other protease inhibitors. However, the overall fold is different to other known protease inhibitors with the exception of a small family of inhibitors isolated from nematodes of the family Ascaris and recently also from the haemolymph of Apis mellifera. BSTI may thus be classified as a new member of this recently discovered family of protease inhibitors.

Organophilicity of MCM-41 adsorbents studied by adsorption and temperature-programmed desorption

In this paper, the organophilic property of MCM-41 was studied and compared with hydrophobic silicalite-l using adsorption and temperature-programmed desorption (TPD) methods. The surface heterogeneity of MCM-41 was evaluated in terms of activation energy for desorption (E-d) and isosteric heat of adsorption (q(st)). Results show that MCM-41 has a higher affinity to polar organic compounds than to non-polar organics while silicalite-l has a higher affinity to non-polar organic compounds than to polar organics. This organophilic behaviour of MCM-41 is attributed to its surface heterogeneity. (C) 2001 Elsevier Science B.V. All rights reserved.

Engineering the structures of nanoporous clays with micelles of alkyl polyether surfactants

Composite clay nanostructures (CCNs) were observed in intercalating Laponite clay with alumina in the presence of alkyl polyether surfactants which contain hydrophobic alkyl chains and ether groups. Such nanostructured clays are highly porous solids consisting of randomly orientated clay platelets intercalated with alumina nanoparticles. The pores in the product solids are larger than the dimension of the surfactant molecules, ranging from 2 to 10 nm. This suggests that the micelles of the surfactant molecules, rather than the molecules, act as templates in the synthesis. Interestingly, it is found that the size of the framework pores was directly proportional to the amount of the surfactants in terms of moles, but shows no evident dependence on the size of the surfactant molecules. Broad pore size distributions were observed for the product CCNs. This study demonstrates that introducing surfactants in the pillaring process of clays is a powerful strategy for tailoring the pore structures of nanoporous clays. With this new technique, it is possible to design and engineer such composite clay nanostructures with desired pore and surface properties by the proper choice of surfactant amounts and preparation conditions.

Hydrophobicity of Templated Silica Xerogels for Molecular Sieving Applications

Silica xerogels were prepared by a sol-gel process catalyzed by acid with tetraethylorthosilicate, and using an organic covalent ligand template (methyltriethoxysilane) or a noncovalent template C6 surfactant (triethylhexylammonium bromide). The influence of hydrotreatment on the structure of templated xerogels is examined in terms of surface area, micropore volume, average pore size, and pore size distribution, and compared against a blank xerogel (nontemplated). The role of surface functional groups was evaluated using Si-29 nuclear magnetic resonance. The structural integrity of the xerogel was maintained to a large extent in samples that had a high contribution of Q(4) species (siloxane groups). Xerogel matrix densification occurred when there was a large concentration of Q(3) and Q(2) species (silanol groups), which also were responsible for increased hydrophilicity. The templated xerogels resulted in up to a 25% concentration of methyl functional groups (T-3 and T-2 species), leading to hydrophobic xerogels. The best results in terms of structural integrity and hydrophobicity were obtained with templated xerogels prepared with the C6 surfactant. The results in this study suggest that surfactant-enhanced condensation reactions lead to structures with a high contribution of Q(4) groups, which are not susceptible to water attack, but are strong enough to oppose matrix densification during rehydration.

Myelin proteolipid protein - the first 50 years

Myelin proteolipid protein (PLP), the most abundant protein of central nervous system (CNS) myelin, is a hydrophobic integral membrane protein. Because of its physical properties, which make it difficult to work with, progress towards determining the exact function(s) and disease associations of myelin PLP has been slow. However, recent molecular biology advances have given new life to investigations of PLP, and suggest that it has multiple functions within myelin and is of importance in several neurological disorders. (C) 2002 Elsevier Science Ltd. All rights reserved.

Preliminary characterisation and extraction of anterior adhesive secretion in monogenean (platyhelminth) parasites

Secreted anterior adhesives, used for temporary attachment to epithelial surfaces of fishes (skin and gills) by some monogenean (platyhelminth) parasites have been partially characterised. Adhesive is composed of protein. Amino acid composition has been determined for seven monopisthocotylean monogeneans. Six of these belong to the Monocotylidae and one species, Entobdella soleae (van Beneden et Hesse, 1864) Johnston, 1929, is a member of the Capsalidae. Histochemistry shows that the adhesive does not contain polysaccharides, including acid mucins, or lipids. The adhesive before secretion and in its secreted form contains no dihydroxyphenylalanine (dopa). Secreted adhesive is highly insoluble, but has a soft consistency and is mechanically removable from glass surfaces. Generally there are high levels of glycine and alanine, low levels of tyrosine and methionine, and histidine is often absent. However, amino acid content varies between species, the biggest differences evident when the monocotylid monogeneans were compared with E. soleae. Monogenean adhesive shows similarity in amino acid profile with adhesives from starfish, limpets and barnacles. However, there are some differences in individual amino acids in the temporary adhesive secretions of, on the one hand, the monogeneans and, on the other hand, the starfish and limpets. These differences may reflect the fact that monogeneans, unlike starfish and barnacles, attach to living tissue (tissue adhesion). A method of extracting unsecreted adhesive was investigated for use in further characterisation studies on monogenean glues.

Characterization of the retinoid orphan-related receptor-alpha coactivator binding interface: A structural basis for ligand-independent transcription

The retinoid orphan-related receptor-alpha (RORalpha) is a member of the ROR subfamily of orphan receptors and acts as a constitutive activator of transcription in the absence of exogenous ligands. To understand the basis of this activity, we constructed a homology model of Rill using the closely related TRbeta as a template. Molecular modeling suggested that bulky hydrophobic side chains occupy the RORa ligand cavity leaving a small but distinct cavity that may be involved in receptor stabilization. This model was subject to docking simulation with a receptor-interacting peptide from the steroid receptor coactivator, GR-interacting protein-1, which delineated a coactivator binding surface consisting of the signature motif spanning helices 3-5 and helix 12 [activation function 2 (AF2)]. Probing this surface with scanning alanine mutagenesis showed structural and functional equivalence between homologous residues of RORalpha and TRbeta. This was surprising (given that Rill is a ligand-independent activator, whereas TRbeta has an absolute requirement for ligand) and prompted us to use molecular modeling to identify differences between Rill and TRbeta in the way that the All helix interacts with the rest of the receptor. Modeling highlighted a nonconserved amino acid in helix 11 of RORa (Phe491) and a short-length of 3.10 helix at the N terminus of AF2 which we suggest i) ensures that AF2 is locked permanently in the holoconformation described for other liganded receptors and thus 2) enables ligand-independent recruitment of coactivators. Consistent with this, mutation of RORa Phe491 to either methionine or alanine (methionine is the homologous residue in TRbeta), reduced and ablated transcriptional activation and recruitment of coactivators, respectively. Furthermore, we were able to reconstitute transcriptional activity for both a deletion mutant of Ill lacking All and Phe491 Met, by overexpression of a GAL-AF2 fusion protein, demonstrating ligand-independent recruitment of AF2 and a role for Phe491 in recruiting AF2.

Effects of surface chemistry on aromatic compound adsorption from dilute aqueous solutions by activated carbon

Adsorption of one nondissociating and four dissociating aromatic compounds onto three untreated activated carbons from dilute aqueous solutions were investigated. All adsorption experiments were preformed in pH-controlled solutions. The experimental isotherms were analyzed using the homogeneous Langmuir model. The surface chemical properties of the activated carbons were characterized using a combination of water adsorption, X-ray photoemission spectroscopy, and mass titration. These data give rise to a new insight into the adsorption mechanism of aromatic solutes, in their molecular and ionic forms, onto untreated activated carbons. It was found that, for the hydrophilic activated carbons, the dominant adsorption forces were observed to be dipolar interactions when the solutes were in their molecular form whereas dispersive forces, such as pi-pi interactions, were most likely dominant in the case of the basic hydrophobic carbons. However, when the solutes were in their ionic form adsorption occurs in all cases through dispersive forces.

The structural and functional diversity of naturally occurring antimicrobial peptides

Antimicrobial peptides occur in a diverse range of organisms from microorganisms to insects, plants and animals. Although they all have the common function of inhibiting or killing invading microorganisms they achieve this function using an extremely diverse range of structural motifs. Their sizes range from approximately 10-90 amino acids. Most carry an overall positive charge, reflecting a preferred mode of electrostatic interaction with negatively charged microbial membranes. This article describes the structural diversity of a representative set of antimicrobial peptides divided into five structural classes: those with agr-helical structure, those with bgr-sheet structure, those with mixed helical / bgr- sheet structure, those with irregular structure, and those incorporating a macrocyclic structure. There is a significant diversity in both the size and charge of molecules within each of these classes and between the classes. The common feature of their three-dimensional structures is, however, that they have a degree of amphipathic character in which there is separate localisation of hydrophobic regions and positively charged regions. An emerging trend amongst antimicrobial proteins is the discovery of more macrocyclic analogues. Cyclisation appears to impart an additional degree of stability on these molecules and minimizes proteolytic cleavage. In conclusion, there appear to be a number of promising opportunities for the development of novel clinically useful antimicrobial peptides based on knowledge of the structures of naturally occurring antimicrobial molecules.