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At least 307 records · Page 17Linked to original sources
PubMed2005

Reactivity and stability of organocopper(I), silver(I), and gold(I) ate compounds and their trivalent derivatives.

Organocuprate (R(2)Cu(-)) reagents react with a carbon electrophile to form a new C-C bond, yet their silver and gold counterparts seldom serve for such purposes. The origin of this striking difference is discussed with the aid of the quantum mechanical calculations using hybrid density functional method. The copper reaction takes place through two steps, the nucleophilic reaction of the ate complex R(2)Cu(I)(-) with an electrophile E(+) and the decomposition of the resulting R(2)(E)Cu(III) intermediate. These two steps were examined for Cu, Ag, and Au to find the reasons for the superiority of organocopper compounds to the silver and the gold counterparts. The first reaction is favored because of the higher-lying d-orbitals that directly participate in the nucleophilic reaction. The second reaction is faster with copper because of the intrinsic instability of the high valent copper species.

Journal Article↗
PubMed1996

Fluoride release profiles of restorative glass ionomer formulations.

OBJECTIVES: The amounts of fluoride released by different glass ionomer formulations were compared on the basis of individual fluoride release profiles in order to derive the effect of the physical and chemical formulation on the fluoride release process. METHODS: The fluoride release profiles of each of five specimens of ten glass ionomer cements setting by an acid-base reaction were investigated. The profiles were obtained by determining the amount of fluoride released [F] after equilibrating the samples at 37 degrees C in distilled water for 140 d. The [[F],t]-profiles were compared with a Multivariate Data Analysis on the basis of a Principal Component Analysis. RESULTS: The Multivariate Data Analysis reveals that eight of the ten glass ionomers can be classified into four distinct groups. When the cumulative amount of fluoride released by each sample, [F]c, is calculated and fitted as a function of time, a regression analysis (r > 0.99) reveals that [F]c for all samples is most adequately represented by [F]c = ([F]l x t)/(t + t1/2) + beta x square root of t, indicating that two kinetic processes are responsible for the fluoride release profiles. SIGNIFICANCE: A comparison of the parameters of this equation shows that the physicochemical rationale for the classification of the glass ionomers conforms to differences in the kinetics of these processes which are determined by the qualitative and quantitative chemical composition as well as by the presentation (hand-mixed vs. capsules) of the glass ionomer. From the classification, it becomes apparent that different formulations can result in the same fluoride release profiles.

Analysis of Variance↗
PubMed2004

Improved planar amperometric nitric oxide sensor based on platinized platinum anode. 1. Experimental results and theory when applied for monitoring NO release from diazeniumdiolate-doped polymeric films.

An improved miniature amperometric nitric oxide sensor design with a planar sensing tip (ranging from 150 microm to 2 mm in diameter) is reported. The sensor is fabricated using a platinized platinum anode and a Ag/AgCl cathode housed behind a microporous poly(tetrafluoroethylene) (PTFE; Gore-tex) gas-permeable membrane. Platinization of the working platinum electrode surface dramatically improves the analytical performance of the sensor by providing approximately 10-fold higher sensitivity (0.8-1.3 pA/nM), approximately 10-fold lower detection limit (< or =1 nM), and extended (at least 3-fold) stability (>3 d) compared to sensors prepared with bare Pt electrodes. These improvements in performance arise from increasing the kinetics and lowering the required potential for the 3-electron oxidation of NO to nitrate, relative to that observed using a nonplatinized working electrode. The outer porous PTFE membrane provides complete selectivity for NO over nitrite ions (up to 10 mM nitrite). The new sensor is applied for surface measurements of NO released from diazeniumdiolate-loaded silicone rubber films (SR-DACA-6/N(2)O(2)). The effects of sensor size (for sensor dimensions of 0.15-, 1-, and 2-mm o.d.) and the distance of the sensor from the surface of the NO-emitting polymer film are investigated via experiments as well as theoretical calculations. A significant analyte trapping effect is demonstrated, the degree of which depends on the sensor size and its distance from the surface. It is further demonstrated that surface NO concentrations for fresh SR-DACA-6/N(2)O(2) loaded films are also influenced by the polymer film thickness, with thicker films generating higher surface concentrations of NO.

Azo Compounds↗
PubMed1994

Pin tract infections: silver vs uncoated pins.

To test the hypothesis that coating external fixation pins with a silver-containing compound (Spi-Argent, Spire Corp, Bedford, Mass) will reduce bacterial colonization and/or pin tract infection, 36 silver-coated and 12 conventional stainless steel pins were placed in the iliac crest of six sheep and inoculated with Staphylococcus aureus. After 2 1/2 weeks the pin sites were examined for motion and inflammation, and the pin tips were quantitatively cultured and examined with scanning electron microscopy (SEM). We found that 84% of the uncoated pins were infected, while 62% of the silver-coated pins were infected. Silver-coated pins were less frequently infected than uncoated pins (confidence interval [CI] > 85%). Also, silver-coated pins were loose less frequently than uncoated pins. Pin motion was closely correlated with infection: 28 of 32 infected pins (88%) had motion, while only 9 of 16 uninfected pins (56%) had motion (CI > 80%). SEM study of the pin tips showed a decreased level of glycocalyx-protected colonization on the surface of the silver-coated pins. Clinically, these results suggest that silver-coated pins will result in less infection and motion at the pin site, the most significant problems in external fixation.

Animals↗
PubMed2006

Topical antimicrobials in the control of wound bioburden.

Bacterial colonization and infection are important factors in compromised wound healing, particularly in chronic wounds. Although "best practice" for controlling these factors currently is not defined, systemic antibiotics are generally accepted as the preferred choice for treating infection, provided ischemia does not reduce their bioavailability. However, widespread use of systemic and topical antibiotics is associated with the emergence of resistant bacterial strains such as methicillin-resistant Staphylococcus aureus. Colonization of wounds presents a double problem--potentially delayed healing and a potential source for cross-contamination. The judicious use of dressings, notably those containing certain antiseptic agents, can be a valuable option to control infection and promote healing. A review of the literature underscores the importance of considering the antiseptic route as part of a concerted approach to wound management and infection control.

Acute Disease↗
PubMed1992

A comparison between low background silver diammine and silver nitrate protein stains.

Several methods of silver staining of proteins after sodium dodecyl sulfate-electrophoresis in polyacrylamide gels were compared. The most rapid methods were found to be less sensitive than more time-consuming methods. Among the long methods, those using glutaraldehyde treatment of the gel and silver diammine complex as the silvering agent were found to be the most sensitive, at the expense of the use of a modified polyacrylamide matrix and higher silver concentrations.

Ammonia↗
PubMed2007

Desorption/ionization on porous silicon mass spectrometry (DIOS) of model cationized fatty acids.

Desorption/ionization on porous silicon (DIOS) is a very useful technique in the case of small molecular weight compounds, compared to the matrix-assisted laser desorption ionization (MALDI). This is because MALDI generates matrix-related ions that overlap with the mass range of interest. The aim of our work was to investigate the suitability of the DIOS technique in the case of fatty acids in negative ion mode. The analysis of the chosen fatty acid models, nonadecanoic acid (C(19)H(38)O(2)) and heneicosanoic acid (C(21)H(42)O(2)), gave rise to the observation of the deprotonated monomeric species and selective cationized multimeric species. This cation selectivity was further elucidated by complementary studies based on the addition of various metals such as Ag(I), Zn(II), Fe(II), and also Cu(II). Specific behavior, depending upon the introduced metal, was highlighted by different redox reaction processes and also metastable decompositions (in PSD mode).

Acetates↗
PubMed2003

Complexation of silver and co-recovered metals with novel aza-crown ether macrocycles by electrospray ionization mass spectrometry.

Electrospray ionization mass spectrometry (ESI-MS) is used to evaluate the metal binding selectivities of an array of novel caged macrocycles for silver, gold, copper, nickel, zinc, iron, lead, manganese and alkali metal ions. It is found that five of the new compounds display silver selectivity, and their relative affinities for various metals depend on the type, number, and arrangement of heteroatoms (N, O), the cavity size, and the presence of aromatic substituents. Alkali metal cation binding studies are used to evaluate the size-selectivities of the cavities of the macrocycles. Electronic structure calculation by B3LYP density function theory methods were used to model the metal complexes. The presence of nitrogen atoms in the macrocyclic ring is essential for silver selectivity over other transition metals and alkali metal ions, and the presence of aromatic groups also enhances silver avidity. Macrocycle 3, a triaza-18-crown-6 analog modified with two phenyl groups and a cage group, is capable of selective extraction of Ag+ from aqueous solutions in the presence of other transition metal ions and the most common alkali and alkaline earth metal ions.

Crown Ethers↗