Development of metal-resin composite restorative material. Part 5: Evaluation of the bonding between Ag-Sn particle and 4-META coupling agent of the metal-resin composite

This study evaluated the oxide characteristics on a Ag-Sn particle surface modified by acid and heat in order to understand the bonding mechanism. Nine different Ag-Sn particles including standard Sn, SnO and SnO2 were evaluated by X-ray Photoelectron Spectroscopy (XPS). The particles were also used for preparing the composite to test the flexural properties following the ISO 4049. A high correlation between flexural strength of the composites and Sn3d binding energy of their filler particles was found. Different oxide forms (SnO and SnO2) showed different adhesive abilities to bond with 4-META, regarding the difference in flexural strength of the composite. The highest flexural strength composite showed Sn3d binding energy of its filler at 486.4 eV, which was the SnO binding area. This implies that SnO was responsible for a good bond between particle surface and 4-META coupling agent.

Transmission electron microscopic investigation of a Pd-Ag-In-Sn dental alloy

With the price volatility of palladium, there has been renewed interest in palladium-silver alloys for metal-ceramic restorations in dentistry. The microstructures of a popular Pd-Ag dental alloy were investigated in the as-cast and simulated porcelain-firing heat-treated conditions, using transmission electron microscopy. In the as-cast condition, the microstructure was strongly influenced by microsegregation, and contained the face-centered cubic Pd solid solution matrix, a eutectic structure with lattice parameters that varied for the two phases, and a face-centered tetragonal (fct) precipitate. After heat treatment, the lattice parameters for the two phases in the eutectic structure were uniform, and discontinuous precipitates with [011](matrix) habit planes and dislocations appeared in the matrix. An unusual nanostructured constituent was found in the fct set of eutectic lamellae in the heat-treated alloys.

Room-temperature Stille cross-couplings of alkenyltin reagents and functionalized alkyl bromides that possess beta hydrogens

This communication describes a significant expansion in the scope of Stille reactions of Csp3-X electrophiles, specifically, that Pd/P(t-Bu)2Me catalyzes the room-temperature cross-coupling of a variety of functionalized, beta-hydrogen-containing alkyl bromides with an array of alkenyltin reagents. The structure of the phosphine (P(t-Bu)2Me) is well suited for facilitating oxidative addition and avoiding beta-hydride elimination, while the fluoride serves to activate the tin reagent for efficient transmetalation.

Stereoselective synthesis of 1'-C-branched arabinofuranosyl nucleosides via anomeric radicals generated by 1,2-acyloxy migration

Stereoselective C-C bond formation at the anomeric position of uracil and adenine nucleoside has been accomplished through reaction of the anomeric radical, generated by 1,2-acyloxy migration, with a radical acceptor. The present method consists of the following steps: (1) electrophilic addition (bromo-pivaloyloxylation) to 3',5'-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)-protected 1',2'-unsaturated nucleoside, (2) tin radical-mediated reaction of the resulting adduct with a radical acceptor. The use of allyl(tributyl)tin gave the 1'-C-allylated uracil nucleoside 14 in 66% yield together with the unrearranged 2'-C-allylated product 15 (6%). Radical acceptors such as styryl(tributyl)tin and 3-bromo-2-methylacrylonitrile can also be used in the reaction of 5, giving 16 (70%) and 17 (76%) without the formation of unrearranged product. The radical-mediated C-C bond formation of the adenine counterpart 12 was also investigated.

[Di-n-butytin tridentate acylhydrazone Schiff base complexes: synthesis and studies by infrared spectroscopy]

Four tridentate acylhydrazone schiff base ligands H2L [H2L1:C6H5C(O)NHN = CHC6H4OH-2, H2L2:C6H5C(O)NHN = CHC6H3(OH)(2)-2,4, H2L3:NC5H4C(O)NHN = CHC6H4OH-2, H2L4:NC5H4C(O)NHN = CHC6H3(OH)(2)-2,4] were synthesized and use to form four novel di-n-Butytin complexes of the type (n-Bu)2SnL with di-n-Butytin oxide [(n-Bu)2SnO]. All these ligands and complexes were characterized by elemental analysis and infrared spectroscopy. Their principal infrared spectral absorption peaks were assigned and discussed for the region of 4,000-400 cm-1. A comparison of the infrared spectra of the ligands with those of the corresponding complexes reveals that the disappearance of the bands assigned to carbonyl unambiguously confirms that the ligands coordinate with tin in the enol form. The coordination manner for tridentate acylhydrazone schiff base ligands with tin atom in the complexes was determined. The results indicated that the Sn atom in these complexes is five-coordinated.

Reactions between M+ (M = Si, Ge, Sn and Pb) and benzene in the gas phase

Using a laser ablation/inert buffer gas ion source coupled with a reflectron time-of-flight mass spectrometer, the gas-phase reactions between the IVA group element ions M(+) (M = Si, Ge, Sn and Pb) and benzene seeded in argon gas were studied. In addition to the association reaction pathway (forming [M(C(6)H(6))(x)](+), x = 1, 2, etc.), benzene was dissociated to form complex ions [M(C(5)H(5))](+), [M(C(7)H(5))](+) and [M(C(9)H(x))](+) (x = 5, 7 and 9), etc. DFT theoretical calculations indicated that, in the association products [M(C(6)H(6))](+), the M atom is close to one carbon atom of benzene, while in most of the dissociation complexes, pentagonal structures (M/cyclopentadienyl derivatives) were formed, with the M atom situated near the fivefold axis of the five-membered ring. The bond patterns in these complexes are discussed.

Selective lethal photosensitization of methicillin-resistant Staphylococcus aureus using an IgG-tin (IV) chlorin e6 conjugate

OBJECTIVES

The growing resistance of methicillin-resistant Staphylococcus aureus (MRSA) to conventional antimicrobial agents necessitates the development of alternative approaches to preventing and treating infections. One such approach is photodynamic therapy, whereby target cells are treated with light-activated drugs (photosensitizers). This investigation aimed to determine whether the ability of MRSA to express the IgG-binding protein, protein A, could be exploited to enable selective lethal photosensitization of the organism with a photosensitizer [tin (IV) chlorin e6; SnCe6] linked to IgG.

METHODS

Various strains of MRSA were exposed to light from a helium/neon laser in the presence of an IgG-SnCe6 conjugate and the survivors enumerated by viable counting. Controls consisted of suspensions irradiated in the presence or absence of the conjugate and suspensions kept in the dark in the presence of the conjugate. Similar experiments were also carried out using the unconjugated photosensitizer. The experiments were repeated using a suspension consisting of both EMRSA-16 and Streptococcus sanguis.

RESULTS

EMRSA-16 was killed by IgG-SnCe6 and SnCe6 in a light-dose- and photosensitizer-dependent manner. Greater kills were achieved with the IgG-SnCe6 than with the unconjugated SnCe6 using the same light energy dose and photosensitizer concentration. Furthermore, the IgG-SnCe6 conjugate, but not SnCe6, was able to kill EMRSA-16 selectively in a suspension that also contained S. sanguis without any reduction in the viable count of the latter.

CONCLUSION

These results demonstrate that selective lethal photosensitization of MRSA can be achieved using an IgG-tin (IV) chlorin e6 conjugate. The effectiveness of killing was dependent, in part, on the particular MRSA strain used, with the clinically important EMRSA-16 strain being the most susceptible.

Tin-free radical sequences under acidic conditions. Convergent access to azole-containing structures

[reaction: see text] Various xanthates add efficiently to olefins bearing [1,2,4]triazole, imidazole, or benzimidazole moieties in the presence of camphorsulfonic acid via a radical chain reaction initiated by a small amount of lauroyl peroxide. The adducts may be transformed to more complex molecules by implementing a further radical cyclization.

5-Substituted-1H-tetrazoles as carboxylic acid isosteres: medicinal chemistry and synthetic methods

5-Substituted-1H-tetrazoles (RCN4H) are often used as metabolism-resistant isosteric replacements for carboxylic acids (RCO2H) in SAR-driven medicinal chemistry analogue syntheses. This review provides a brief summary of the medicinal chemistry of tetrazolic acids and highlights some examples of tetrazole-containing drug substances in the current literature. A survey of representative literature procedures for the preparation of 5-substituted-1H-tetrazoles, focusing on preparations from aryl and alkyl nitriles, is presented in sections by generalized synthetic methods.

Second-generation synthesis of the polypropionate subunit of callystatin A based on regioselective internal alkyne hydrostannation

[formula: see text] An improved route to the polypropionate segment of callystatin A is described in which the efficient directed hydrostannation of an internal alkyne and subsequent iodinolysis provides a key vinylic iodide intermediate.

Mechanical properties and radiopacity of experimental glass-silica-metal hybrid composites

OBJECTIVES

Experimental glass-silica-metal hybrid composites (polycomposites) were developed and tested mechanically and radiographically in this fundamental pilot study. To determine whether mechanical properties of a glass-silica filled two-paste dental composite based on a Bis-GMA/polyglycol dimethacrylate blend could be improved through the incorporation of titanium (Ti) particles (particle size ranging from 1 to 3 microm) or silver-tin-copper (Ag-Sn-Cu) particles (particle size ranging from 1 to 50 microm) we measured the diametral tensile strength, fracture toughness and radiopacity of five composites.

METHODS

The five materials were: I, the original unmodified composite (control group); II, as group I but containing 5% (wt/wt) of Ti particles; III, as group II but with Ti particles treated with 4-methacryloyloxyethyl trimellitate anhydride (4-META) to promote Ti-resin bonding; IV, as group I but containing 5% (wt/wt) of Ag-Sn-Cu particles; and V, as group IV but with the metal particles treated with 4-META. Ten specimens of each group were tested in a standard diametral tensile strength test and a fracture toughness test using a single-edge notched sample design and five specimens of each group were tested using a radiopacity test.

RESULTS

The diametral tensile strength increased statistically significantly after incorporation of Ti treated with 4-META, as tested by ANOVA (P=0.004) and Fisher's LSD test. A statistically significant increase of fracture toughness was observed between the control group and groups II, III and V as tested by ANOVA (P=0.003) and Fisher's LSD test. All other groups showed no statistically significant increase in diametral tensile strength and fracture toughness respectively when compared to their control groups. No statistically significant increase in radiopacity was found between the control group and the Ti filled composite, whereas a statistically significant increase in radiopacity was found between the control group and the Ag-Sn-Cu filled composite as tested by ANOVA (P=0.000) and Fisher's LSD procedure.

SIGNIFICANCE

The introduction of titanium and silver-tin-copper fillers has potential as added components in composites to provide increased mechanical strength and radiopacity, for example for use in core materials.

Enhancement of contrast sensitivity and losses of chromatic discrimination with tinted lenses

PURPOSE

Tinted lenses for everyday use should not impair visual acuity and contrast sensitivity or cause radical changes in color perception. The main aim of this study was to compare the performance in contrast detection and color discrimination tasks of a set of tinted lenses with that of gray filters of equal luminance under D65.

METHODS

The contrast sensitivity functions of 10 observers were measured using sinusoidal gratings of mean luminance of 13 cd/m2 by the adjustment method. Color discrimination thresholds from white (x = 0.313, y = 0.330), green (x = 0.346, y = 0.407), and blue (x = 0.280, y = 0.253) were measured along 12 directions in the CIE-1931 xy diagram with and without lenses.

RESULTS

Green, brown, and blue filters did not cause significant changes in contrast sensitivity compared with a gray filter of equal luminance, although chromatic discrimination was disturbed. Yellow and orange filters improved achromatic contrast at certain spatial frequencies, but impaired chromatic discrimination.

CONCLUSIONS

Compared with gray filters of the same luminance, yellow filters may be useful when enhancement of low achromatic contrasts is desirable, although overall brightness decrements may occur. Nevertheless, these lenses cause tritan-like defects with discrimination losses increasing with the cutoff wavelength.

Polylactones. 59. Biodegradable networks via ring-expansion polymerization of lactones and lactides with a spirocyclic tin initiator

Spirocyclic tin initiators were prepared by condensation of commercial hydroxyethylated pentaerythritol with Bu(2)Sn(OMe)(2). These tin-containing spirocycles served as initiators for the ring-expansion polymerization of epsilon-caprolactone, beta-D,L-butyrolactone or D,L-lactide. The in situ polycondensation of these expanded spirocycles with terephthaloyl chloride or sebacoyl chloride yielded the desired biodegradable networks with elimination of the Bu(2)Sn group. The segment length (pore size) could be controlled via the monomer-initiator ratio (M/I) of the ring-expansion polymerization. Biodegradable networks were also obtained when Sn-containing spirocyclic polylactones were polycondensed with diphenyl dichlorosilane, benzene phosphonic dichloride, and phenyl phosphoric dichloride.

Controlled synthesis of star-shaped L-lactide polymers using new spirocyclic tin initiators

The reaction between pentaerythritol ethoxylate compounds and dibutyltin oxide was developed as a route to synthesize two new spirocyclic tin initiators. The initiators were successfully synthesized and they were characterized by (1)H NMR and differential scanning calorimetry (DSC). The (1)H NMR spectra showed the characteristic signals for the methylene protons in the ether chains. Furthermore, the usefulness of the new initiators was examined in ring-opening polymerizations of L-lactide in chloroform at 60 degrees C. L-Lactide was polymerized at monomer-to-initiator ([M]/[I]) ratios between 20 and 500. The results indicated that the initiation was instantaneous and that the molecular weight distribution was very narrow, <1.13. The number average molecular weight could be controlled by the [M]/[I] ratio, and the yield was very high. (1)H NMR, size exclusion chromatography, and DSC were used to clarify the architecture. The expected results were obtained. The star-shaped polymers had a smaller hydrodynamic volume, and the melting point was lower than that obtained for the corresponding linear poly(L-lactide).

Effect of small additions of Ir on properties of a binary Au-Ti alloy

OBJECTIVES

Previous investigations in the binary system Au-Ti have shown that a Au based alloy with 1.7 wt% Ti reveals properties, which are appropriate to dental applications. Aim of this investigation was to refine the coarse grained dendritic microstructure of the alloy. Derived from experience with traditional high gold alloys and based on theoretical considerations, Ir was chosen as potential grain refiner and its influence on grain size, hardness, and thermal distortion was investigated.

METHOD

Seven different Au-Ti alloys with Ir contents of 0-0.5 wt% were prepared in an arc furnace and test pieces cast by the dental casting technique. Microstructures of the alloys were documented by light microscopy. Grain size was assessed by a comparison procedure, hardness was measured by the indentation test, and thermal distortion by a three point bending test in a modified dilatometer.

RESULTS

It revealed that Ir has a grain refining effect on the alloy with smallest grain sizes at a concentration of at least 0.3 wt%. It seems that the alloy with 0.5 wt% Ir shows slight grain growth during firing. Little homogenization was observed after firing. The influence of Ir on hardness was negligible. Thermal distortion is minimized with a concentration of 0.1 wt% Ir. In order to profit by the high thermal distortion resistance, the alloy Au(98.2)Ti(1.7)Ir(0.1) (wt) was chosen as definite composition, although 0.1 wt% Ir does not satisfactorily refine the alloy.

SIGNIFICANCE

The alloy Au(98.2)Ti(1.7)Ir(0.1) (wt) revealed properties appropriate for the crown and bridge technique.

[The analysis of UV absorption spectrum and X-ray diffraction spectrum of Sn-doped C60 thin films]

In this article, We report our measured results of UV-Vis absorption, X-ray diffraction and scanning electron microscope for Sn-doped C60 thin film. The results show the two absorption peaks in respective short wave range of UV absorption have an apparent decline after doping Sn, and the position of three absorption peaks have a slightly shift respectively to red wave direction. The electron absorption transition of Sn-C60 film is indirect transition, and there are impurity levels in the energy band; X-ray diffraction shows that the crystal structure of Sn-C60 film is f. c. c. The film is in the form of tiny drops in nano magnitude.

Development of metal-resin composite restorative material. Part 4. Flexural strength and flexural modulus of metal-resin composite using Ag-In alloy particles as filler

The flexural strength and flexural modulus of an experimental metal-resin composite, which used Ag-In alloy particle as the filler, were evaluated. The effect of acid treatment and heat treatment on the Ag-In alloy particle was investigated. The flexural strength of the experimental metal-resin composites ranged from 65.5 MPa to 91.0 MPa. The flexural strength of the metal-resin composite increased with the temperature of the heat treatment until 350 degrees C, but its effect varied with the concentrations of HCl of the acid treatment. A metal-resin composite, which used acid-treated and 350 degrees C heat-treated Ag-In alloy fillers, matched the requirement of strength of ISO 4049. The average of flexural modulus of the experimental metal-resin composite was 9.1 GPa. The flexural modulus of the metal-resin composite did not vary with the treatment conditions of the metal filler. The flexural modulus of a metal-resin composite, which used Ag-In alloy particle as the filler, was lower than that of Ag-Sn alloy metal-resin composite, which was reported previously. However, the flexural strength of the Ag-In alloy metal-resin composite was similar to that of Ag-Sn alloy metal-resin composite. We can control a flexural modulus of a metal-resin composite without decreasing flexural strength by choosing filler materials.

Total synthesis of (-)-(6S,7S,8S,9R,10S,2'S)-membrenone-A and (-)-(6S,7S,8S,9R,10S)- membrenone-B and structural assignment of membrenone-C

[reaction: see text] (-)-(6S,7S,8S,9R,10S,2'S)-Membrenone-A and (-)-(6S,7S,8S,9R,10S)-membrenone-B were prepared in 11 steps (3% and 2.4% overall yield, respectively). Key steps included a tin(II)-mediated aldol followed by a syn selective reduction, giving the C7-C9 stereocenters, a second chain extending aldol coupling, and a p-TsOH-promoted cyclization/dehydration giving the common gamma-dihydropyrone precursor. We have thus established that synthetic (-)-(6S,7S,8S,9R,10S,2'S)-membrenone-A, (-)-(6S,7S,8S,9R,10S)-membrenone-B, and (-)-(6S,7S,8S,9R,10S)-membrenone-C are the enantiomers of the natural products.

Application of tin and nanometer tin in allylation of carbonyl compounds in tap water

[reaction: see text] Nanometer tin-mediated allylation of aldehydes or ketones in distilled or tap water gave rise to corresponding homoallyl alcohol in high yield without any other assistance such as heat or supersonic or acidic media.

Studies toward the synthesis of alpha-fluorinated phosphonates via tin-mediated cleavage of alpha-fluoro-alpha-(pyrimidin-2-ylsulfonyl)alkylphosphonates. Intramolecular cyclization of the alpha-phosphonyl radicals

Treatment of the alpha carbanions generated from several alpha-(pyrimidin-2-ylsulfonyl)alkylphosphonates with Selectfluor gave high yields of the alpha-fluoro-alpha-(pyrimidin-2-ylsulfonyl)alkylphoshonates, which were desulfonylated [Bu(3)SnH/2,2'-azobisisobutyronitrile (AIBN)/benzene or toluene/Delta] to give alpha-fluoroalkylphosphonates. "Catalytic" tin hydride, generated from tributyltin chloride and excess polymethylhydrosiloxane in the presence of potassium fluoride, also effected removal of the pi-deficient alpha-(pyrimidin-2-ylsulfonyl) group from the phosphonate esters. Substitution of Bu(3)SnD for Bu(3)SnH gave access to alpha-deuterium-labeled phosphonates. Prolonged treatment of alpha-(pyridin-2-ylsulfonyl)alkylphosphonate with excess Bu(3)SnH/AIBN or catalytic tin hydride also effected desulfonylation but in moderate yields. This represents a mild new methodology for removal of the synthetically useful pi-deficient heterocyclic sulfone moiety and an alternative route for the preparation of alpha-fluorinated phosphonates. Desulfonylation is suggested to proceed via attack of tin radical at an oxygen (or sulfur) atom of the sulfonyl group to give a stabilized alpha-phosphonyl radical intermediate. The latter was found to undergo 5-exo-trig ring closure to give the corresponding 2-methylcyclopentylphosphonates. Treatment of diethyl 1-bromohex-6-enylphosphonate with Bu(3)SnH/AIBN produced an analogous mixture of ring-closure products. Treatment of [(2-bromo-5- methoxyphenyl)(fluoro)(pyrimidin-2-ylsulfonyl)]methylphosphonate with Bu(3)SnH resulted in an intramolecular radical [1,5]-ipso substitution reaction and migration of the pyrimidinyl ring to give fluoro[5-methoxy-2-(pyrimidin-2-yl)phenyl]methylphosphonate.

Accuracy of check-bite registration and centric condylar position

In a dentate subject a jaw relation can either be determined in maximum intercuspation and is as such given by the occlusal morphology, or the mandibular position can be allocated according to the centric position of the condyles. For comprehensive restorative treatment or analytic measures of the occlusion it is important to record the centric condylar position. Various registration methods have been described in the literature, but there is no consensus on which is the 'best'. The aim of the present study was therefore to assess the accuracy of various registration methods and evaluate a possible influence of the used materials. Four dentists were involved in the clinical part of the study, another was responsible for the measurements. Impressions were taken from 81 fully dentate volunteers. The casts were mounted by face-bow transfer and central-bearing-point (CBP) registration into Dentatus articulators. Subsequently the centric condylar position was determined with six different methods and materials, respectively. Each method was reproduced twice so that a total of 18 registrations was performed per patient. The mandibular positions which resulted from the individual registrations were then repeatedly compared in the condylar area using a computer supported specially modified measuring articulator. The accuracy was found best for the unrefined wax wafer registration (x=0.33 mm) and with an average of 0.44 mm worst when using acrylic wafers. The CBP and frontal jig methods as well as tin-foil and refined wax wafers showed an accuracy in-between these boundaries. The biggest measured mandibular displacement between any two registrations were considerably 2.0 mm. However, the described differences in accuracy between the various methods and materials proved statistically not significant. All investigated jaw registrations showed an accuracy of about 20 times the tactile fine sensibility of natural teeth which has to be taken into account when inserting fixed prosthetic restorations in centric condylar position. Despite meticulous clinical and technical procedures small occlusal adjustments are therefore almost unavoidable.

New entry of coupling reaction of phenacylamine derivatives with silylstannane

The new coupling reaction of phenacylamines with silylstannane and lithium diisopropylamide (LDA) is reported. The treatment of a phenacylamine iodide 1 with (trimethylsilyl)tributylstannane (Me3SiSnBu3) and cesium fluoride (CsF) gave a dimerization product 2 having no iodine atom. Reaction of 1 with LDA afforded a dimerization product 3 with an iodine atom. The products 2 and 3 were separated to the meso and racemic isomers, respectively.

Synthesis and characterization of PtSn/carbon and Pt3Sn/carbon nanocomposites as methanol electrooxidation catalysts

Two Pt-Sn/vulcan carbon nanocomposites containing nanoclusters of PtSn (niggliite) and Pt3Sn highly dispersed on a carbon powder support have been prepared using Pt(SnPh2Cl)(PPh3)2(Ph) or [Pt3[mu-(PPh2)2CH2]3(mu 3-SnF3) (mu 3-CO)][PF6] as single-source precursors of metal alloy. PtP2 or Pt metal is also present as a secondary phase. Bimetallic Pt-Sn nanoclusters with an average diameter of 5-8 nm are formed at a total metal loading of ca. 15 wt%. Evaluation of both Pt-Sn/C nanocomposites as electrooxidation catalysts in a direct methanol fuel cell gives fuel cell performances comparable to that expected for Pt-Sn catalysts prepared by more conventional methods.

Regioselectivity in the palladium-catalyzed addition of carbon nucleophiles to carbocyclic derivatives

The regioselectivity of Pd-catalyzed malonate additions and arylations to cycloalkenyl esters can be predicted by completing a stereochemical analysis of the Pd-pi-allyl complex. The Pd-catalyzed malonate additions which have the greatest degree of regioselectivity are in which substituents have a steric influence in blocking the incoming nucleophile. Cyclopentenyl substrates displayed lower regioselectivity than the cyclohexyl counterparts presumably due to increased planarity of the system. Arylations using tin and hypervalent silicon reagents were compared.