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Journal of Dentistry (Tehran, Iran) Jan 2014The aim of this study was to assess the effect of bleaching on elution of monomers from nanofilled and microhybrid composites.
OBJECTIVE
The aim of this study was to assess the effect of bleaching on elution of monomers from nanofilled and microhybrid composites.
MATERIALS AND METHODS
80 samples (5mm diameter and 3mm thickness) of each composite were prepared. After curing, half of them were randomly polished. Each group was divided into 8 subgroups and immersed in water or 10%, 20% and 30% H2O2 for 3 or 8 hours. Eluted Bis-GMA (Bis-phenol A Glycidyl Dimethacrylate), TEGDMA (Triethyleneglycol Dimethacrylate), UDMA (Urethane Dimethacrylate) and BisEMA (Bis-phenol A ethoxylate Dimethacrylate) were quantified by high performance liquid chromatography and the results were analyzed by univariate ANOVA and t-test (P<0.05).
RESULTS
Bleach significantly increased the overall release of monomers (P<0.001); TEGDMA was released more than Bis-GMA (P<0.001). Supreme released more TEGDMA compared to Z250 (P<0.001). Bleaching increased the release of this monomer (P<0.001). Increasing both the concentration of H2O2, and the immersion time, increased the release of TEGDMA (P<0.001). Polishing had no effect on release of this monomer (P=0.952). Supreme released more Bis-GMA than Z250 (P=0.000). The more concentrated H2O2 caused more elution of Bis-GMA (P= 0.003); while the effect of immersion time was not significant (P=0.824). Polishing increased the release of Bis-GMA (P=0.001). Neither the type of composite nor Bleaching had any effect on release of UDMA (P=0.972) and (P=0.811) respectively. Immersion duration increased the release of UDMA (P=0.002), as well as polishing (P=0.024).
CONCLUSION
Bleaching increased the release of monomers. Nanofilled composites released more monomer than the microfilled.
PubMed: 24910677
DOI: No ID Found -
The Journal of Biological Chemistry Sep 1997Mammalian alkaline phosphatases (APs) are zinc-containing metalloenzymes encoded by a multigene family and functional as dimeric molecules. Using human placental AP...
Mammalian alkaline phosphatases (APs) are zinc-containing metalloenzymes encoded by a multigene family and functional as dimeric molecules. Using human placental AP (PLAP) as a paradigm, we have investigated whether the monomers in a given PLAP dimer are subject to cooperativity during catalysis following an allosteric model or act via a half-of-sites model, in which at any time only one single monomer is operative. Wild type and mutant PLAP homodimers and heterodimers were produced by stably transfecting Chinese hamster ovary cells with mutagenized PLAP cDNAs followed by enzyme extraction, purification, and characterization. [Gly429]PLAP manifested negative cooperativity when partially metalated as a consequence of the reduced affinity of the incompletely metalated AP monomers for the substrate. Upon full metalation with Zn2+, however, the negative cooperativity disappeared. To distinguish between an allosteric and a half-of-sites model, a [Gly429]PLAP-[Ser84]PLAP heterodimer was produced by combining monomers displaying high and low sensitivity to the uncompetitive inhibitor L-Leu as well as a [Gly429]PLAP-[Ala92]PLAP heterodimer combining a catalytically active and inactive monomer, respectively. The L-Leu inhibition profile of the [Gly429]PLAP-[Ser84]PLAP heterodimer was intermediate to that for each homodimer as predicted by the allosteric model. Likewise, the [Gly429]PLAP-[Ala92]PLAP heterodimer was catalytically active, confirming that AP monomers act independently of each other. Although heterodimers are structurally asymmetrical, they migrate in starch gels with a smaller than expected weighted electrophoretic mobility, are more stable to heat denaturation than expected, and are more sensitive to L-Leu inhibition than predicted by a strict noncooperative model. We conclude that fully metalated mammalian APs are noncooperative allosteric enzymes but that the stability and catalytic properties of each monomer are controlled by the conformation of the second AP subunit.
Topics: Alkaline Phosphatase; Allosteric Regulation; Animals; Binding Sites; CHO Cells; Cricetinae; Dimerization; Humans; Kinetics; Mutagenesis, Site-Directed; Protein Conformation; Zinc
PubMed: 9278439
DOI: 10.1074/jbc.272.36.22781 -
Polymers Feb 2019Covalently crosslinked nanogels are widely explored as drug delivery systems and sensors. Radical polymerization provides a simple, inexpensive, and broadly applicable...
Covalently crosslinked nanogels are widely explored as drug delivery systems and sensors. Radical polymerization provides a simple, inexpensive, and broadly applicable approach for their preparation, although the random nature of the reaction requires careful study of the final chemical composition. We demonstrate how the different reactivities of the monomers influence the total degree of incorporation into the polymer matrix and the role played by the experimental parameters in maximizing polymerization efficiency. Nanogels based on -isopropylacrylamide, --propylacrylamide, and acrylamide crosslinked with -methylenebisacrylamide were included in this study, in combination with functional monomers -acryloyl-l-proline, 2-acrylamido-2-methyl-1-propanesulfonic acid, and 4-vinyl-1-imidazole. Total monomer concentration and initiator quantities are determining parameters for maximizing monomer conversions and chemical yields. The results show that the introduction of functional monomers, changes in the chemical structure of the polymerizable unit, and the addition of templating molecules can all have an effect on the polymerization kinetics. This can significantly impact the final composition of the matrices and their chemical structure, which in turn influence the morphology and properties of the nanogels.
PubMed: 30960337
DOI: 10.3390/polym11020353 -
Nature Communications Nov 2020Crystallization is a ubiquitous means of self-assembly that can organize matter over length scales orders of magnitude larger than those of the monomer units. Yet...
Crystallization is a ubiquitous means of self-assembly that can organize matter over length scales orders of magnitude larger than those of the monomer units. Yet crystallization is notoriously difficult to control because it is exquisitely sensitive to monomer concentration, which changes as monomers are depleted during growth. Living cells control crystallization using chemical reaction networks that offset depletion by synthesizing or activating monomers to regulate monomer concentration, stabilizing growth conditions even as depletion rates change, and thus reliably yielding desired products. Using DNA nanotubes as a model system, here we show that coupling a generic reversible bimolecular monomer buffering reaction to a crystallization process leads to reliable growth of large, uniformly sized crystals even when crystal growth rates change over time. Buffering could be applied broadly as a simple means to regulate and sustain batch crystallization and could facilitate the self-assembly of complex, hierarchical synthetic structures.
Topics: Buffers; Computer Simulation; Crystallization; DNA; Feedback; Fluorescence; Kinetics; Nanotubes; Time Factors
PubMed: 33247122
DOI: 10.1038/s41467-020-19882-8 -
Protein Science : a Publication of the... Jan 2015Chemokine CXCL8 and its receptor CXCR1 are key mediators in combating infection and have also been implicated in the pathophysiology of various diseases including...
Chemokine CXCL8 and its receptor CXCR1 are key mediators in combating infection and have also been implicated in the pathophysiology of various diseases including chronic obstructive pulmonary disease (COPD) and cancer. CXCL8 exists as monomers and dimers but monomer alone binds CXCR1 with high affinity. CXCL8 function involves binding two distinct CXCR1 sites - the N-terminal domain (Site-I) and the extracellular/transmembrane domain (Site-II). Therefore, higher monomer affinity could be due to stronger binding at Site-I or Site-II or both. We have now characterized the binding of a human CXCR1 N-terminal domain peptide (hCXCR1Ndp) to WT CXCL8 under conditions where it exists as both monomers and dimers. We show that the WT monomer binds the CXCR1 N-domain with much higher affinity and that binding is coupled to dimer dissociation. We also characterized the binding of two CXCL8 monomer variants and a trapped dimer to two different hCXCR1Ndp constructs, and observe that the monomer binds with ∼10- to 100-fold higher affinity than the dimer. Our studies also show that the binding constants of monomer and dimer to the receptor peptides, and the dimer dissociation constant, can vary significantly as a function of pH and buffer, and so the ability to observe WT monomer peaks is critically dependent on NMR experimental conditions. We conclude that the monomer is the high affinity CXCR1 agonist, that Site-I interactions play a dominant role in determining monomer vs. dimer affinity, and that the dimer plays an indirect role in regulating monomer function.
Topics: Amino Acid Sequence; Binding Sites; Humans; Interleukin-8; Models, Molecular; Molecular Sequence Data; Nuclear Magnetic Resonance, Biomolecular; Protein Binding; Protein Multimerization; Protein Structure, Tertiary; Receptors, Interleukin-8A
PubMed: 25327289
DOI: 10.1002/pro.2590 -
Frontiers in Bioengineering and... 2022Lignin structural analysis is important for the comprehensive utilization of lignin as well as delignification and bleaching during pulping while it is difficult to...
Lignin structural analysis is important for the comprehensive utilization of lignin as well as delignification and bleaching during pulping while it is difficult to completely elucidate lignin structure due to its structural complexity and heterogeneity. Depolymerization of lignin into simple monomers via alkaline cupric oxide oxidation (Ox) followed by chromatographic analysis of the monomers is an effective method for lignin structural analysis. Here we revisited the Ox of lignin model compounds (monomers and dimers) and three representative lignocelluloses (i.e., Eucalyptus, Masson pine, and corn stover) to understand the effects of reaction conditions and lignin sub-structures on oxidation product yields and distributions. The improved Ox was found to be effective in oxidatively breaking the robust interunit C-C bonds in the β-β' and β-5' moieties of lignin other than β-O-4' linkages at an elevated temperature (210°C). Further degradation of the monomeric oxidation products could also occur to reduce the monomer yields under a severe condition (i.e., high temperature and long reaction time). In addition, O inputs could reduce the monomer yields via nonselective overoxidation, thus having negative effects on accurate structural analysis of lignin. The O removal via ultrasonication combined with N flushing prior to the oxidation reaction could improve the monomer yield about 1.2 times (compared to that without O removal) at a low biomass loading of 5 wt%. By using the improved method of Ox, a monomer yield of 71.9% could be achieved from Eucalyptus (hardwood) lignin, which was much higher than conventional nitrobenzene oxidation (59.8%) and reductive depolymerization (51.9%). Considering the low cost, high availability, and low toxicity of CuO, the improved Ox could be a convenient and economic method for more accurate lignin structural analysis.
PubMed: 36159682
DOI: 10.3389/fbioe.2022.1002145 -
Dental Materials Journal 2012According to the 'Adhesion-Decalcification' concept, specific functional monomers within dental adhesives can ionically interact with hydroxyapatite (HAp). Some specific...
According to the 'Adhesion-Decalcification' concept, specific functional monomers within dental adhesives can ionically interact with hydroxyapatite (HAp). Some specific functional monomers form monomer-Ca salts due to chemical interactions. The chemical stability of the monomer-Ca salts was thought to contribute to bond durability. In the present study, we analyzed the chemical interaction between an acidic three-dimensional self-reinforcing monomer (3D-SR) of Bond Force and enamel, dentin and HAp, and assessed its chemical stability by thin-fi lm X-ray diffraction (TF-XRD). 3D-SR forms a hydrolysis-resistant Ca-salt on the dentin in a clinical application time period and on enamel and HAp in a longer time period. This suggests that the functional monomer 3D-SR is able to contribute to bond durability.
Topics: Adhesiveness; Animals; Calcium; Cattle; Crystallography, X-Ray; Dental Bonding; Dentin; Dentin-Bonding Agents; Durapatite; Resin Cements; Surface Properties; Tooth
PubMed: 22864227
DOI: 10.4012/dmj.2012-074 -
Dental Materials Journal Mar 2010This paper reviews the development of dental adhesives by collating information of related studies from original scientific papers, reviews, and patent literatures.... (Review)
Review
This paper reviews the development of dental adhesives by collating information of related studies from original scientific papers, reviews, and patent literatures. Through our development, novel radical polymerization initiators, adhesive monomers, and microcapsules were synthesized, and their effects on adhesion were investigated. It was found that 5-monosubstituted barbituric acid (5-MSBA)-containing ternary initiators in conjunction with adhesive monomers contributed to effective adhesion with good polymerization reactivity. Several kinds of novel adhesive monomers bearing carboxyl group, phosphonic acid group or sulfur-containing group were synthesized, and investigated their multi-purpose bonding functions. It was suggested that the flexible methylene chain in the structure of adhesive monomers played a pivotal role in their enhanced bonding durability. It was found that the combination of acidic monomers with sulfur-containing monomer markedly improved adhesion to enamel, dentin, porcelain, alumina, zirconia, non-precious metals and precious metals. A new poly(methyl methacrylate) (PMMA)-type adhesive resin comprising microencapsulated polymerization initiators was also found to exhibit both good formulation stability and excellent adhesive property.
Topics: Adhesives; Barbiturates; Carbon Dioxide; Dental Bonding; Dental Cements; Free Radicals; Humans; Organophosphonates; Polymers; Polymethyl Methacrylate; Sulfur
PubMed: 20379020
DOI: 10.4012/dmj.2009-057 -
The Journal of Biological Chemistry Dec 1976The formation of deoxyhemoglobin was examined by measuring the heme spectral change that accompanies the aggregation of isolated alpha and beta chains. At low...
The formation of deoxyhemoglobin was examined by measuring the heme spectral change that accompanies the aggregation of isolated alpha and beta chains. At low hemeconcentrations (less than 10(-5) M), tetramer formation can be described by two consecutive, second order reactions representing the aggregation of monomers followed by the association of alphabeta dimers. At neutral pH, the rates of monomer and dimer aggregation are roughly the same, approximately 5 X 10(5) M(-1) X(-1) at 20 degrees. Raising or lowering the pH results in a uniform decrease of both aggregation rates due presumably to repulsion of positively charged subunits at acid pH and repulsion of negatively charged subunits at alkaline pH. Addition of p-hydroxymercuribenzoate to alpha chains lowers the rate of monomer aggregation whereas addition of mercurials to the beta subunits appears to lower both the rate of monomer and the rate of dimer aggregation. At high heme concentrations (greater than 10(-5) M) or in the presence of organic phosphates, the rate of chain aggregation becomes limited, in part, by the slow dissociation of beta chain tetramers. In the case of inositol hexaphosphate, the rate of hemoglobin formation exhibits a bell-shaped dependence on phosphate concentration. When intermediate concentrations of inositol hexaphosphate (approximately 10(-4 M) are preincubated with beta subunits, a slow first order time course is observed and exhibits a half-time of about 8 min. As more inositol hexaphosphate is added, the chain aggregation reaction begins to occur more rapidly. Eventually at about 10(-2) M inositol hexaphospate, the time course becomes almost identical to that observed in the absence of phosphates. The increase in the velocity of the chain aggregation reaction at high phosphate concentrations suggests strongly that inositol hexaphosphate binds to beta monomers and, if added in sufficiently large amounts, promotes beta4 dissociation. A quantitative analysis of these results showed that the affinity of beta monomers for inositol hexaphosphate is the same as that of alphabeta dimers. Only when tetramers are formed, either alpha2beta2 or beta4, is a marked increase in affinity for inositol hexaphosphate observed.
Topics: Calorimetry; Diphosphoglyceric Acids; Heme; Hemoglobins; Humans; Hydrogen-Ion Concentration; Kinetics; Macromolecular Substances; Phytic Acid; Protein Binding; Spectrophotometry; Thermodynamics
PubMed: 12181
DOI: No ID Found -
ACS Sustainable Chemistry & Engineering Jul 2023The chemical complexity of lignin remains a major challenge for lignin valorization into commodity and fine chemicals. A knowledge of the lignin features that favor its...
The chemical complexity of lignin remains a major challenge for lignin valorization into commodity and fine chemicals. A knowledge of the lignin features that favor its valorization and which plants produce such lignins can be used in plant selection or to engineer them to produce lignins that are more ideally suited for conversion. Sixteen biomass samples were compositionally surveyed by NMR and analytical degradative methods, and the yields of phenolic monomers following hydrogenolytic depolymerization were assessed to elucidate the key determinants controlling the depolymerization. Hardwoods, including those incorporating monolignol -hydroxybenzoates into their syringyl/guaiacyl copolymeric lignins, produced high monomer yields by hydrogenolysis, whereas grasses incorporating monolignol -coumarates and ferulates gave lower yields, on a lignin basis. Softwoods, with their more condensed guaiacyl lignins, gave the lowest yields. Lignins with a high syringyl unit content released elevated monomer levels, with a high-syringyl polar transgenic being particularly striking. Herein, we distinguish phenolic monomers resulting from the core lignin vs those from pendent phenolate esters associated with the biomass cell wall, acylating either polysaccharides or lignins. The basis for these observations is rationalized as a means to select or engineer biomass for optimal conversion to worthy phenolic monomers.
PubMed: 37448721
DOI: 10.1021/acssuschemeng.3c01320