Hydrothermal-induced assembly of colloidal silver spheres into various nanoparticles on the basis of HTAB-modified silver mirror reaction

Small colloidal silver spheres (diameter < 10 nm) were found to assemble into various silver nanoparticles including cubes, triangles, wires, and rods in water in the presence of HTAB (n-hexadecyltrimethylammonium bromide) at 120 degrees C, while the colloids were generated in situ on the basis of a HTAB-modified silver mirror reaction during the synthesis process. Adjustment of the synthesis parameters, in particular the concentrations of HTAB and [Ag(NH3)2]+, led to an obvious shape evolution of silver nanoparticles, thus resulting in the shape-selective formation of the silver nanoparticles. The monodisperse nanocubes with a well-defined crystallographical structure (a single crystal bounded by six {200} facets) have a strong tendency to assemble into two-dimensional arrays on substrates. The nanowires with uniform diameter usually existed in the form of two-dimensional alignments. The findings suggested that hydrothermal-induced assembly of small silver colloidal particles should be a convenient and effective approach to the preparation of various silver nanoparticles.     

Interactions between colloidal silver and photosynthetic pigments located in cyanobacteria fragments and in solution

Changes in the yield of the fluorescence emitted by pigments of photosynthetic organisms could be used for the establishment of the presence of some toxic substances. The presence of colloidal metals can be indicated by enhancement of pigments' emission as a result of plasmons generation. The spectra of the pigments of cyanobacterium Synechocystis located in the bacterium fragments and in solutions with and without colloidal silver additions have been measured. The quantum yield of the pigments' fluorescence in solution has been observed to increase at some wavelength of excitation, while the fluorescence of the pigments in the bacteria fragments has been only quenched as a consequence of interactions with colloidal silver particles. Close contact between pigment molecules located in bacteria fragments and silver particles is probably not possible. We plan in future to investigate the influence of other, more typical metal pollutants of water, using similar spectral methods and several other photosynthetic bacteria pigments, in solution, in cell fragments and in the whole bacteria organisms.     

Effect of the oligodimethylsiloxane chain length and concentration of carboxyl groups on the colloidal chemical properties and characteristics of polymethyl methacrylate suspensions

Russian Chemical Bulletin - The elongation of the oligodimethylsiloxane chain in a wide range of values (from 10 to 136 units) and, correspondingly, an increase in the concentration of carboxyl...     

Synthesis of C-terminal fragments of bombesin and their analogues

With the aim of structural-functional studies in the bombesin series, a number of bombesin fragments and analogues have been synthesized. The synthesis was performed by the carbodiimide method and by the activated-ester method. Fragments with the sequences 7–14, 8–14, and 9–14 were obtained by 4+4, 3+4, and 2+4 schemes and a pentapeptide with the sequence 9–13 by a 3 + 2 scheme. Acetylation of the octapeptide BN(7–14) was carried out by the action of acetic anhydride in pyridine. Analogues of the C-terminal nonapeptide of bombesin [DPhe⁷]BN(6–14) and [Pro⁶, Gly⁷, DAla¹¹]BN(6–14) were synthesized by fragment condensation using the 5 + 4 scheme. The individuality of the compounds obtained was confirmed by their chromatographic behavior on plates coated with silica gel, and by the results of amino acid analysis, high-voltage electrophoresis, and high-performance liquid chromatography, and their structures were confirmed by the results of high-resolution¹H NMR spectroscopy (360 MHz). In experiments on rabbits, in a dose of 1 µg with central administration the full hypothermic effect of bombesin was shown by the preparation [AcGln⁷]BN(7–14), while the preparation [DPhe⁷]BN(6–14) and [Pro⁶,Gly⁷,DAla¹¹]BN(6–14) possessed only a slight effect (1% of the activity of bombesin).Leningrad State University. Institute of Organic Synthesis, Latvian SSR Academy of Sciences, Riga. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 554–564, July–August, 1989.     

Synthesis of C-terminal fragments of bombesin and their analogues

With the aim of structural-functional studies in the bombesin series, a number of bombesin fragments and analogues have been synthesized. The synthesis was performed by the carbodiimide method and by the activated-ester method. Fragments with the sequences 7–14, 8–14, and 9–14 were obtained by 4+4, 3+4, and 2+4 schemes and a pentapeptide with the sequence 9–13 by a 3 + 2 scheme. Acetylation of the octapeptide BN(7–14) was carried out by the action of acetic anhydride in pyridine. Analogues of the C-terminal nonapeptide of bombesin [DPhe⁷]BN(6–14) and [Pro⁶, Gly⁷, DAla¹¹]BN(6–14) were synthesized by fragment condensation using the 5 + 4 scheme. The individuality of the compounds obtained was confirmed by their chromatographic behavior on plates coated with silica gel, and by the results of amino acid analysis, high-voltage electrophoresis, and high-performance liquid chromatography, and their structures were confirmed by the results of high-resolution¹H NMR spectroscopy (360 MHz). In experiments on rabbits, in a dose of 1 µg with central administration the full hypothermic effect of bombesin was shown by the preparation [AcGln⁷]BN(7–14), while the preparation [DPhe⁷]BN(6–14) and [Pro⁶,Gly⁷,DAla¹¹]BN(6–14) possessed only a slight effect (～1% of the activity of bombesin).     

Surface-enhanced resonance Raman scattering and density functional calculations of hemicyanine adsorbed on colloidal silver surface

Resonance Raman (RR) and surface-enhanced resonance Raman scattering (SERRS) of 4'-(N,N'-dimethylaminostyryl)-4-propylpyridinium bromide (hemicyanine, HC dye) in acetonitrile solution and on a colloidal silver surface have been investigated. The structure of the dye in the ground (S0) and excited (S1) electronic states was optimized using density functional calculations along with the B3LYP and the configuration interaction with the singlet excitation (CIS) methods, respectively, using the 6-31G basis set. The vibrational frequencies of the molecule were computed at the optimized geometry and compared with the observed Raman bands. A complete normal-mode analysis has been carried out because it is essential for the accurate assignment of the vibrational spectra. From the observed enhancement along various in-plane and out-of-plane vibrations in the SERRS spectrum and from theoretical calculations, it has been inferred that the interaction with the silver surface occurs via the nitrogen lone pair of the pyridyl or the dimethylamino group of the molecule with a tilted orientation. The observed red-shifts in the SERRS spectrum along various vibrations indicate strong interaction (chemisorption) of the HC dye with the silver surface. This is also supported by the presence of a Ag-N stretching vibration at 241 cm(-1). The effect of the dye concentration on the orientation of the molecule is also discussed.     

Synthesis of core-shell silver colloidal particles by surface immobilization of an azo-initiator

Silver nanoparticles, with the diameter of approximately 100 nm, were coated with a 5–10 nm layer of poly(styrene-co-4-styrenesulfonic acid sodium salt). Polymerization was initiated on the particles by a surface adsorbed 4,4-azobis(4-cyanovaleric acid) initiator. FTIR, electron microscopy, dynamic light scattering, and optical spectroscopy were employed to differentiate between the original and coated particles.     

Hydrogen bonding of carboxyl and amide groups to nucleosides

Carboxylic acid-nucleoside systems are studied by infrared spectroscopy. Intermolecular interactions of these systems in aqueous solution are investigated as a function of the degree of hydration and ΔpK_a. On the other hand, thermodynamic parameters for the association of N-methyl-acetamide with lactams in organic solvents have been determined by infrared spectroscopy. The low enthalpy values suggest open dimers formation.     

Effect of surface modification with various thiol compounds on colloidal stability of gold nanoparticles

Gold nanoparticles (AuNPs) are attractive materials due to their special optical and electronic properties. However, they tend to aggregate particularly in the presence of thiol‐containing compounds. In this study, to investigate the effect of surface conjugation with thiol‐containing compounds on colloidal stability, thiol compounds with various structures as modifying agents were used. To this end, AuNPs were synthesized and stabilized by trisodium citrate in aqueous solution, and then modified with thiol‐containing compounds, namely cysteamine hydrochloride (MEA, containing primary amine groups), 2‐mercaptoethanol (BME, containing hydroxyl groups), 1‐dodecanthiol (LCA, containing long‐chain alkyl groups) and thioglycolic acid (TGA, containing carboxylic acid groups). We studied the effect of thiol ligands on solution stability of colloidal AuNPs and on the formation of aggregates originating from the modification process using UV–visible spectroscopy, dynamic light scattering, field emission scanning electron microscopy and transmission electron microscopy. Results showed that surface modification with MEA, BME and LCA led to the formation of aggregates. However, conjugation with TGA showed a concentration‐dependent behaviour: surface modification with low concentration resulted in the formation of aggregates whereas that with high concentration of TGA did not disturb the colloidal stability of AuNPs. Finally, the effect of surface modification on temperature increase of solutions originating from infrared light irradiation was studied, where the temperature increase depends on the surface‐modifying compound.     

Size controlled formation of silver nanoparticles by direct bonding of ruthenium complexes bearing a terminal mono- or bi-pyridyl group

Two polypyridyl ruthenium complexes containing either a terminal pyridine or phenanthroline group have been used to coat silver nanoparticles and control their size depending on the Ag/[RuII] ratio.     

Adsorption of the fluoride ion on the surface of various faces of a single crystal of silver: a quantum-chemical study

The fluoride ion adsorption from a gas phase on various faces of a single crystal of silver is studied by a density functional method within a cluster model for metal. The adsorption bond energy is found to increase in the series Ag(100) < Ag(111) < Ag(311) < Ag(110). A substantial structural and energetic heterogeneity of various adsorption sites is revealed. The results are utilized to simulate the electrochemical interface between individual faces of a single crystal of silver and aqueous solutions containing the fluoride ion. It is assumed that the adsorption potential may be represented as the sum of two contributions, one of which describes the metal–ion interaction and the other, the ion solvation energy. The plotted adsorption terms take into account partial degradation of the fluoride ion when adsorbed from an aqueous solution. Estimates of discreteness of the electrical double layer are presented. A conclusion on the maximum manifestation of specific adsorption of the fluoride ion for the Ag(100) face is made.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 232–238.Original Russian Text Copyright © 2005 by Nazmutdinov, Zinkicheva.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Molecular orientation of phthalimide adsorbed on colloidal silver

Surface Enhanced Raman Scattering (SERS) obtained for phthalimide (PIMH) and potassium phthalimide (PIMK) are identified with the phthalimide anion adsorbed on the surface of colloidal silver. The molecular orientation on the surface is discussed in terms of the relative intensities of vibrational modes assigned to irreducible representations of the _C2ν point group.     

Surface-enhanced Raman spectrometry of amiloride on colloidal silver

Surface-enhanced Raman spectrometry (SERS) of the diuretic drug amiloride is discussed. The SERS-active substrate used is colloidal silver, which is prepared at room temperature by simple tetrahydroborate reduction of an aqueous solution of silver nitrate. SERS detection of amiloride in human urine is illustrated. The reproducibility of quantitative SERS data is supported by the simultaneous measurement of the scattering signal and transmitted light. Relative standard deviations at the 5% level are compatible with many practical analytical situations.     

Experimental and theoretical surface enhanced Raman scattering study of 2-amino-4-methylbenzothiazole adsorbed on colloidal silver particles

The adsorption of 2-amino-4-methylbenzothiazole (2-AMBT) on colloidal silver particles has been investigated by a surface enhanced Raman scattering (SERS) study. The SERS spectra of the 2-AMBT molecule at varied adsorbate concentrations recorded in different time domains are compared with its Fourier transform infrared (FTIR) spectrum and normal Raman spectrum (NRS) in the bulk and in solution. The experimentally observed SERS spectra are compared with the theoretically modeled surface complexes using ab initio restricted Hatree-Fock (RHF) and density functional theory (DFT) calculations. The most favorable adsorptive sites of the 2-AMBT molecule have been estimated by natural population analysis (NPA) using the above-mentioned high level of theories. The enhancement of the in-plane modes together with the appearance of Ag-N stretching frequency at 215 cm(-1) indicates that the 2-AMBT molecule is adsorbed on the silver surface through the lone pair electrons of both nitrogen atoms with the molecular plane nearly vertical to the surface.     

Synthesis and characterization of colloidal fluorescent silver nanoclusters

Ultrasmall water-soluble silver nanoclusters are synthesized, and their properties are investigated. The silver nanoclusters have high colloidal stability and show fluorescence in the red. This demonstrates that like gold nanoclusters also silver nanoclusters can be fluorescent.     

Sers excitation profile investigation of a cyanine dye adsorbed on silver colloidal particles

An excitation profile investigation of 3,3′-diethyl-2,2′-benzthiatrimethinecyanine adsorbed on silver sol shows, for the pure surface enhancement, a relative minimum near the dye absorption (about 550 nm) and a strong increase for yellow-red wavelengths, which is explained qualitatively in terms of an “electromagnetic” model.     

Cluster calculation on the interaction and discharge of ions on a silver surface

The interaction of halogen and alkali ions with the (100) surface of silver was studied at very short distances. Calculations were performed by the iterative extended Hückel method (IEHT) for (Ag_nX)^± clusters with n=9 and n=37 and X=F, Cl for the negative and X=Na, K for the positive clusters. A careful analysis of the parameters used in the IEHT was performed and the main results obtained are: Cl⁻ ions lose more of their negative charge than F⁻ ions on approaching the (100) silver surface, and the electronic charge thus transferred to the silver cluster is distributed as far as possible from the adsorbed species. Both halogens form localized bonds with the nearest Ag atoms, which are very similar to those for the neutral adsorbed species. The interaction of the alkali ions with silver is very small and it decreases as the size of the cluster increases, supporting the idea that the alkali ions interact only via a solvation shell.     

Ion-specific forces between a colloidal nanoprobe and a charged surface

We investigate the effect of ion-specific potentials on the force between a nanoprobe attached to a cantilever tip, and a charged surface. The probe is treated as a spherical nanoparticle with constant charge. A modified Poisson-Boltzmann equation in bispherical coordinates is used to address this problem in a more quantitative way. We predict that the ion-specific series of measured forces depend on the sign and magnitude of surface charge densities.