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A new method is proposed for the fabrication of a well-defined size and shape distribution of silver nanoparticles in solution; the method employs direct laser irradiation of an aqueous solution containing a silver salt and a surfactant in the absence of reducing agents.
We report the results of a detailed examination of the occlusion of silver nitrate in silver zeolite A (AgA). The superlattice reported to occur in (AgNO3)9-AgA was found to melt at between 80 and 100 degrees C on heating and reappear when the sample was cooled down to 80 degrees C. Annealing in this temperature range and rigorous exclusion of water produced an enhancement of the superlattice peaks, which results from ordering of the contents of the zeolite cages. Peaks assigned to the superlattice were indexed with the tetragonal lattice parameters a = 17.440(5) and c = 12.398(4) A and proposed space group P4/nmm. The sharp peaks representing the lattice of the framework (a = 12.3711(5) A, Pm3m) remained largely unaffected by the guest in this compound, which was found to exhibit strong negative thermal expansion. The host and guest lattices are incommensurate with the tetragonal guest lattice being slightly larger than the cubic host in the c-direction and slightly smaller in the a- and b-directions.
The crystal structures of two new diphosphates, sodium silver tricobalt bis(diphosphate), (Na(1.42)Ag(0.58))Co(3)(P(2)O(7))(2), and sodium silver copper(II) diphosphate, (Na(1.12)Ag(0.88))CuP(2)O(7), provide examples of the effect of mixing Na and Ag in the same site of known host phosphate compounds. The small differences in ionic radii of the two monocations do not lead to significant differences in the structural details. In the latter compound, the Cu atom lies on an inversion center.
In catena-poly[[(di-2-pyridylamine-kappa(2)N,N')silver(I)]-mu-nicotinato-kappa(2)N:O], [Ag(C(6)H(4)NO(2))(C(10)H(9)N(3))](n), the Ag(I) atom is tetracoordinated by two N atoms from the di-2-pyridylamine (BPA) ligand [Ag-N = 2.3785 (18) and 2.3298 (18) angstroms] and by one N atom and one carboxylate O atom from nicotinate ligands [Ag-N = 2.2827 (15) angstroms and Ag-O = 2.3636 (14) angstroms]. Bridging by nicotinate N and O atoms generates a polymeric chain structure, which extends along [100]. The carboxyl O atom not bonded to the Ag atom takes part in an intrachain C-H...O hydrogen bond, further stabilizing the chain. Pairs of chains are linked by N-H...O hydrogen bonds to generate ribbons. There are no pi-pi interactions in this complex. In catena-poly[[(di-2-pyridylamine-kappa(2)N,N')silver(I)]-mu-2,6-dihydroxybenzoato-kappa(2)O(1):O(2)], [Ag(C(7)H(5)O(4))(C(10)H(9)N(3))](n), the Ag(I) atom has a distorted tetrahedral coordination, with three strong bonds to two pyridine N atoms from the BPA ligand [Ag-N = 2.286 (5) and 2.320 (5) angstroms] and to one carboxylate O atom from the 2,6-dihydroxybenzoate ligand [Ag-O = 2.222 (4) angstroms]; the fourth, weaker, Ag-atom coordination is to one of the phenol O atoms [Ag...O = 2.703 (4) angstroms] of an adjacent moiety, and this interaction generates a polymeric chain along [100]. Pairs of chains are linked about inversion centers by N-H...O hydrogen bonds to form ribbons, within which there are pi-pi interactions. The ribbons are linked about inversion centers by pairs of C-H...O hydrogen bonds and additional pi-pi interactions between inversion-related pairs of 2,6-dihydroxybenzoate ligands to generate a three-dimensional network.
A coated-wire ion-selective electrode (ISE) based on cyclam (1,4,8,11-tetraazacyclotetradecane) as a neutral carrier in a polyvinyl chloride (PVC) matrix was fabricated for the determination of Ag(I) ions. The coated-wire ISE exhibited a linear Nernstian response over the range 1 x 10(-1) to 1 x 10(-7) M with a slope of 59 +/- 2 mV per decade change and a detection limit of 5 x 10(-8) M. The ISE shows a greater preference for Ag over other cations with good precision. The electrode was selective towards Ag(I) ions in the presence of 13 different metal ions tested. The selectivity coefficients (K(ij)) were determined for Na(I), K(I), Mg(II), Ca(II), Ba(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II). The selectivity coefficients of these cations are in the range of 10(-4) to 10(-2). This ISE was used for the determination of free silver and total silver in electroplating bath solutions, additives and brighteners.
A new wire-coated silver ion-selective electrode with a wider concentration range (10(-7) M - 10(-1) M) was developed using 2-mercaptobenzothiazole (MBT) as a neutral ionophore. An optimum mixture of PVC, ionophore, dioctylphtalate (DOP) as a plasticizer and sodium tetraphenylborate (NaTPB) as an ion-pairing agent was used in preparing the coatings. The effect of various parameters, such as the electrode bed nature, coating composition and solution pH, on the efficiency of the electrode is described. It has been shown that platinum acts as a more suitable bed for electrode preparation, and exhibits a slope of 59.5 +/- 1 mV over the whole range of studied concentrations. The selectivity coefficient of the electrode towards various interfering cations as well as its reproducibility, response time and lifetime of the electrode were estimated. The developed electrode was successfully used for the determination of trace amounts of silver in human hair and photographic waste as real samples and in the potentiometric titration of halides as an indicator electrode.
Conjugated linoleic acids (CLA) are octadecadienoic acids (18:2) that have a conjugated double-bond system. Interest in these compounds has expanded since CLA were found to be associated with a number of physiological and pathological responses such as cancer, metastases, atherosclerosis, diabetes, immunity, and body fat/protein composition. The main sources of these conjugated fatty acids are dairy fats. Rumen bacteria convert polyunsaturated fatty acids, especially linoleic and linolenic acids, to CLA and numerous trans- containing mono- and diunsaturated fatty acids. It has been established that an additional route of CLA synthesis in ruminants and monogastric animals, including humans, occurs via delta9 desaturation of the trans-18:1 isomers. To date, a total of 6 positional CLA isomers have been found in dairy fats, each occurring in 4 geometric forms (cis,trans; trans,cis; cis,cis; and trans,trans) for a total of 24. All of these CLA isomers can be resolved only by a combination of gas chromatography (GC), using 100 m highly polar capillary columns, and silver-ion liquid chromatography, using 3 of these 25 cm columns in series. Complete analysis of all the trans-18:1 isomers requires prior isolation of trans monoenes by silver-ion thin-layer chromatography (TLC), followed by GC analysis using the same 100 m capillary columns operated at low temperatures starting from 120 degrees C. These analytical techniques are required to assess the purity of commercial CLA preparations, because their purity will affect the interpretation of any physiological and/or biochemical response obtained. Prior assessment of CLA preparations by TLC is also recommended to determine the presence of any other impurities. The availability of pure CLA isomers will permit the evaluation and analysis of individual CLA isomers for their nutritional and biological activity in model systems, animals, and humans. These techniques are also essential to evaluate dairy fats for their content of specific CLA isomers and to help design experimental diets to increase the level of the desired CLA isomers in dairy fats. These improved techniques are further required to evaluate the CLA profile in monogastric animals fed commercial CLA preparations for CLA enrichment of animal products. This is particularly important because absorption and metabolism will alter the ingested-CLA profile in the animal fed.
Microbiologically it was demonstrated that amino acids, e.g. cysteine (CySH), and other compounds, e.g. sodium thioglycollate, containing thiol groups neutralized the activity of silver nitrate against Pseudomonas aeruginosa PAO1. Amino acids with disulphide bonds were inactive, with the exception of L-cystine dimethyl ester, as were all amino acids with no sulphur groups. Iodoacetamide reacted with CySH to produce a CyS-acetamide complex that was unable to quench the activity of Ag+. Chemical analyses using cyclic voltammetry demonstrated that high coordination numbers (3.1) were obtained with thiol-containing amino acids and low numbers (0.28-0.4) with other amino acids. Both microbiologically and chemically, the results imply that interaction of Ag+ with thiol groups plays an essential role in bacterial inactivation.
A plunge electrode is made from a hypodermic needle with one side cut open and multiple electrodes exposed from tip to base. A method for constructing chlorided silver electrode plunge needles is explained as well as problems associated with electrode chloriding. The small surface area of these electrodes makes empirical methods of chloriding difficult to use. A monitor was constructed for the testing and chloriding of a twelve-electrode plunge needle. This system continuously measures the impedance of the electrodes during chloriding.
Sixty patients with moderate and severe burns were randomly assigned to receive topical silver sulfadiazine (SSD) alone (n=30) or SSD combined with cerium nitrate (SSD-CN) (n=30). There were four deaths in the SSD group and one in the SSD-CN group; more patients with higher risk severity survived in the SSD-CN group. Wound infection did not differ significantly between the groups. The rate of re-epithelialization of partial thickness burns was faster by 8 days in the SSD-CN group. The relatively dry shell-like eschar of the SSD-CN-treated burn allowed planned excisions with immediate autologous grafting and the tissue beneath was ready to accept grafting 11 days earlier than in the SSD group (p=0.03). This resulted in a significantly shorter hospital stay for those in the SSD-CN group than in the SSD group (23.3 vs. 30.7 days; p=0.03) with consequent cost savings. A higher incidence of transient stinging pain was reported with application of SSD-CN, but this was effectively managed with analgesics where necessary. The results of this study confirm the greater efficacy of SSD-CN in the treatment of burns patients.
Three competing ligand methods were compared to determine characteristics of Ag(I) complexation by dissolved and colloidal ligands present in three rivers and one sewage treatment plant effluent. Iminodiacetate groups on Chelex-100 resin (used in batch and column experiments) and diethyldithiocarbamate (DDC) were used as competing ligands. Results of batch Chelex and DDC competition experiments show good agreement with regard to relative extent of Ag binding by natural ligands among the three river systems. Results of both methods also show a possible correlation between extent of Ag(I) complexation and organic matter concentration and/or Fe concentration. Fraction of Ag(I) associated with Chelex in both batch and column Chelex experiments was similar in each of the four systems tested, indicating that lability of Ag complexes does not change significantly on time scales ranging from seconds to 24 h. Results of Chelex and DDC competition were compared using a model based on a hypothetical single natural ligand. Under the experimental conditions used, this model quantified Ag(I) complexes with log Kcond values from approximately 12 to 14. For the three rivers studied, ligands with silver-association characteristics similar to those of reduced sulfur groups (log K = 14-16) present at subnanomolar concentrations likely dominate Ag(I) speciation in these systems. A weaker ligand (e.g., log Kcond < 12) at concentrations > 0.7 nM dominated Ag(I) speciation in the treatment plant effluent. This may result from elevated concentration of metals that compete for reduced sulfur groups rather than from a lower total concentration of these groups.
Crystal structures of four lanthanide complexes of La[Au(CN)2](3).3H2O, La[Ag(CN)2](3).3H2O, La[Ag(0.83)Au(0.17)(CN)2](3).3H2O, and La[Ag(0.39)Au(0.61)(CN)2](3).3H2O are reported. Studies reveal that all the structures reported are isostructural. All systems were found to be in the hexagonal crystal system, space group P6(3)/mcm. The metal-metal distance for the pure gold system is 3.332 (1) A versus 3.359(1) A for the pure silver system. The mixed-metal systems have shown no distinct differences in the location of the metal atoms, with the La[Ag(0.83)Au(0.17)(CN)2](3).3H2O complex having a metal-metal Ag-Au separation of 3.346(1) A, and 3.344(1) A for the La[Ag(0.39)Au(0.61)(CN)2](3).3H2O complex. The crystal structures of the pure and mixed La complexes have been solved to provide evidence of Ag-Au heterometallic interactions and as a basis for understanding the interesting optical properties of the systems.
The purpose of the study was to carry out a further investigation of the efficacy of topical antimicrobial treatment of Ag-NFL in comparison with that of the most commonly used topical agent Ag-SD. An experimental model of rats with 20% TBSA full thickness burns seeded with 109 CFU of Pseudomonas aeruginosa ATCC-27853 was used. At 24, 48 and 72h after the seeding bacteriologic examination showed that the subeschar bacterial counts exceeded 10(6) CFU per gram of tissue. Subeschar bacterial counts were zero in the group in which Ag-NFL was used, while those in the group using Ag-SD were almost the same as the control. The amount of silver accumulated in the eschar of Ag-NFL, treated rats was significantly higher than that of Ag-SD treated rats. In conclusion, Ag-NFL was proved valuable in the treatment of burn wound infection caused by invading organisms, particularly by the Ag-SD resistant strain of Pseudomonas.
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The motion of silver ions in (AgI)x-(Ag2O-B2O3)1-x glasses with AgI concentrations of x=0.5 and 0.7 was studied using 109Ag-NMR. The NMR spectra were analyzed in terms of a superposition of two different contributions. These are associated with Ag ions, which hop on vastly different time scales. The existence of dynamic heterogeneity, i.e. the existence of slow and of fast contributions to the hopping dynamics was directly demonstrated using a four-time stimulated-echo experiment. The results are compatible with an intrinsically exponential response. From measurements of the spectra and of two-time correlation functions a Gaussian distribution of energy barriers, hindering the ionic motion, could be mapped out.
A disk-shaped tridentate ligand 1 arranges silver(I) ions in a two-dimensional triangular and a three-dimensional tetrahedral fashion in the metal-ligand ratios, 3:2 and 1:1, respectively. The resulting sandwich-type (Ag312) and tetrahedral (Ag414) architectures are in a dynamic equilibrium in solution.
Unprecedented eta 3 pi-donor behavior of the benzyltrimethy-lammonium ion is observed in the polymeric silver(I) complex [(PhCH2NMe3)Ag7(C2)(CF3CO2)6]n that comprises a columnar backbone constructed from the fusion of Ag8 square antiprisms each enclosing an acetylide dianion.