Reduction and aggregation of silver ions in <Emphasis Type="Italic">tert</Emphasis>-butanol

Silver ions undergo reduction reactions induced by radiolytically produced products of tert-butanol, a commonly used solvent and scavenger for hydroxyl radicals. Radiolytic reduction of silver ions and the subsequent formation of their clusters are compared with the corresponding processes in aqueous solution. The surface plasmon UV-Vis absorption band of silver nanocrystallites obtained by bombardment of tert-butanol solutions of silver salts with electron pulses showed an absorption maximum at 400 nm. Formation of different sizes of silver nanoparticles was found to be dependent on the dose rate. The nanocrystallites were found to have an average size of 20 nm.     

Glucosamine-functionalized silver glyconanoparticles: characterization and antibacterial activity

We report the analytical and in vitro antibacterial activity of glucosamine-functionalized silver glyconanoparticles. Morphological characterization ensured the surface topography and particle size distribution of both silver and glucosamine–silver nanoparticles. Surface plasmon resonance of both types of nanoparticle was determined from UV–visible spectroscopy using four different sample concentrations (10–40 μL). The resulting functionalized glyconanoparticles show maximum absorbance with a red shift of 30 ± 5 nm (390–400 nm) from their initial absorbance (425–430 nm). FT-Raman and ¹H-NMR spectroscopic measurement confirmed the surface functionalization of glucosamine on the silver surface through the carbonyl group of a secondary amide linkage (–NH–CO–), elucidated by the conjugation of N-hydroxysuccinimide (NHS)-terminated silver nanoparticles and the amino group of glucosamine. Antimicrobial experiments with well-characterized silver nanoparticles (AgNPs) and glucosamine-functionalized silver nanoparticles (GlcN-AgNPs) demonstrate that GlcN-AgNPs have similar and enhanced minimum inhibitory concentration (MIC) against eight gram-negative and eight gram-positive bacteria compared with AgNPs. MIC data shows that Klebsiella pneumoniae (ATCC 700603) and Bacillus cereus isolate express high levels of inhibition, with the quantity and magnitude of inhibition being higher in the presence of GlcN-AgNPs.     

Photolysis of 6-ethoxy-2,2,4-trimethyl-8-nitro-1,2-dihydroquinoline. Unusual dependence on the irradiation wavelength

The spectral and kinetic parameters of transient species generated in the irradiation of 6-ethoxy-2,2,4-trimethyl-8-nitro-1,2-dihydroquinoline were examined by stationary and pulse photolysis in the solvents: heptane, acetonitrile, methanol, and ethanol. Upon excitation of the long-wavelength absorption band (λ_ex > 450 nm), a reversible photochemical reaction was revealed, and the spectral and kinetic parameters of three transient species observed in the photolysis were characterized (λ_max = 390, 400, and 420 nm (acetonitrile), k = 97, 500, and 2000 s⁻¹, respectively). The absorption spectra and the rate constants of the decay of transient species are almost independent of the medium polarity and the presence of oxygen in the system. The excited state generated during irradiation to the short-wavelength absorption band (290 < λ_ex < 350 nm) is inactive in the photochemical reaction and deactivates without the formation of transient species. The mechanism of the reversible photochemical reaction is suggested, which involves the opening of the heterocycle N-C bond upon photoexcitation of the long-wavelength absorption band and the thermal back reaction.     

The reactive state in the photo-rearrangement of o-nitrobenzaldehyde

The primayy step of the o-nitrobenzaldehyde-o-nitrosobenzoic acid photorearrangement in solution has been studied by flash absorption with 35 ps 355 nm light pulses. Flash photolysis of o-nitrobenzaldehyde in acetonitrile or THF solutions produces a transient absorption with a maximum at ca. 440 nm. Formation of the transient was < 35 ps, the laser pulse width, and within experimental error, no furthrr buildup was observed. The transient which decayed at nanosccond times is attributed to a remarkably reactive ketene intermediate formed by H abstraction of the aldehydic hydrogen by the excited state of the nitro group. Decay of the ketene was more rapid in water-acetonitrile, methanol-acetonitrile, tert-butyl alcohol and in THF than in acetonitrile solution. It is suggested that the intramolecular reaction of the ketene intermediate is enhanced in THF relative to acetonitrile because of the ability of THF to faciliaate proton transfer associated with the reaction. The addition of the triplet quencher cis-piperylene to a solution of o-nitrobenzaldehyde in THF did not accelerate decay of the transient nor reduce its yield. The n,π* triplet excited state band observed in the 625–650 nm region for a number of the nitroaromatic compounds was not observed in the case of o-nitrobenzaldehyde. The results provide evidence that in the direct irradiation on o-nitrobenzaldehyde in THF or acetonitrile solutions, the intramolecular reaction occurs from the singlet rather than the triplet excited state.     

Characterization of the Triplet State of Tanshinone IIA and its Reactivity by Laser Flash Photolysis

Tanshinone IIA (Tan IIA) has the properties of cardiovascular protection, anti‐inflammation, antioxidation and anticancer. Its light‐induced instability has drawn our interests in its photochemistry. Therefore, laser flash photolysis herein was used to investigate the transient photochemistry of Tan IIA. Our results show that direct photoexcitation by 355 nm laser pulses or photosensitization by energy transfer can lead to the formation of the triplet state of Tan IIA (³Tan IIA*). The triplet absorption spectrum and molar absorption coefficient, and ISC quantum yield were determined. Self‐quenching of ³Tan IIA* by its ground state was identified as an autooxidation reaction. ³Tan IIA* was proved to react quickly with N, N‐dimethylaniline, tert‐butylhydroquinone and propyl gallate via electron transfer with the diffusion‐controlled rate constants. One of the products with maximum absorption around 390 nm was assigned to the radical anion of Tan IIA. Our results indicate that ³Tan IIA* is a reactive transient species and can be generated by photosensitization or direct photoexcitation. According to our results, the possible role of Tan IIA as a photosensitizer to induce potential phototoxicity via Type‐II pathway in the presence of O₂ can be predicted.     

The effect of fructose derived carbon shells on the plasmon resonance and stability of silver nanoparticles

Carbon nanoparticles between 10 and 50 nm in diameter and carbon shells of various thickness around silver nanoparticles were synthesized by the hydrothermal reaction of fructose. The effect of the carbon shells on the plasmon resonance of the silver nanoparticles and their stability in sodium chloride solutions was investigated. The shell thickness can be adjusted to have insignificant damping of the plasmon resonance and provide stabilization of the particles in solutions with high ionic strength. Hydrazine–carbonyl cross-linking reactions were performed to link fluorescent dye molecules to carbonyl groups on the carbon shell surface.     

Preparation of silver nanoparticles with controlled particle size

Silver colloids show different colors due to light absorption and scattering in the visible region based on plasmon resonance. The resonance wavelength depends on particle size and shape. Here we report chemical reduction methods for preparation of silver nanoparticles exhibiting multicolor in aqueous solutions. Depending on chemical conditions the obtained nanoparticles are different regarding size and morphology.In order to investigate the relationship between size, stability and color of silver colloids we obtained silver nanoparticles in aqueous solutions using different reducing agents. The effect of polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) on stabilization of obtained silver colloids was investigated. We have also studied the effect of silver precursor and its concentration on the formation of stable silver colloids.UV-VIS spectrum for silver colloids contains a strong plasmon band near 410 nm, which confirms silver ions reduction to Ag° in the aqueous phase. The formation of metal silver was also confirmed by powder X-ray diffraction (XRD) analysis. The diameter size of silver nanoparticles was in the range from 5 nm to 100 nm     

Effect of strong coupling on interfacial electron transfer dynamics in dye-sensitized TiO2 semiconductor nanoparticles

Dynamics of interfacial electron transfer (ET) in ruthenium polypyridyl complex [{bis-(2,2′-bpy)-(4-[2-(4′-methyl-[2,2′]bipyridinyl-4-yl)-vinyl]-benzene-1,2-diol)}ruthenium(II) hexafluorophosphate] (Ru-cat) and 5,10,15-tris phenyl-20-(3,4-dihydroxy benzene) porphyrin (TPP-cat)-sensitized TiO₂ nanoparticles have been investigated using femtosecond transient absorption spectroscopic detection in the visible and near-infrared region. We have observed that both Ru-cat and TPP-cat are coupled strongly with the TiO₂ nanoparticles through their pendant catechol moieties. We have observed a single exponential and pulse-width limited (<100 fs) electron injection from nonthermalized-excited states of Ru-complex. Here electron injection competes with the singlet-triplet manifold relaxation due to strong coupling of catecholate binding, which is a unique observation. Optical absorption spectra indicate that the catechol moiety interacts with TiO₂ nanoparticles showing the characteristic pure catechol-TiO₂ charge-transfer (CT) band in the visible region. Transient absorption studies on TPP-cat/TiO₂ system exciting both the Soret band at 400 nm and the Q-band at 800 nm have been carried out to determine excitation wavelength-dependence on ET dynamics. The reaction channel for the electron-injection process has been found to be different for both the excitation wavelengths. Excitation at 800 nm, is found directly populate directly the excited CT state from where diffusion of electrons into the conduction band takes place. On the other hand, excitation at 400 nm light excites both the CT band of cat-TiO₂ and also Soret band of TPP-cat.     

Ag nanoparticles deposited onto silica,titania, and zirconia mesoporous films synthesized by sol–gel template method

A variety of Ag nanoparticles/oxide mesoporous films with templated silica, titania, and zirconia was synthesized by sol–gel method at glass, aluminum, and silicon substrates using metal alkoxides (tetraethoxysilane, titanium tetraisopropoxide, and zirconium tetrapropoxide) and AgNO₃ as precursors of oxide films and Ag nanoparticles, respectively, and Pluronic P123 as a template agent. Oxide films alone and Ag/oxide composites were characterized using hexane adsorption, X-ray diffraction (XRD), Raman and ultraviolet (UV)/vis spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. The distribution of Ag nanoparticles within the films, their sizes, intensity, and position of surface plasmon resonance (SPR) absorbance band at λ = 400 nm, as well as the textural and structural characteristics of whole films depend on treatment temperature, types of substrates and oxide matrices, oxide crystallization, and Ag content. Ag nanoparticles form preferably on the outer surface of the films under lower sintering temperatures if the amount of loaded silver is low. Oxide crystallization (e.g., TiO₂) promotes silver embedding into the outer film layer. At higher silver content (≥10 at.%) and higher calcination temperature (873 K), silver nanoparticles could be entrapped more uniformly along the film profile because of more intensive evaporation of silver droplets from the outer surface of the films on heating.     

Synthesis of anisotropic silver nanoparticles and investigation of their sensory properties

A simple procedure has been proposed for synthesis of planar triangular silver nanoparticles. Optimal conditions have been determined for particles to form, and the particles have been characterized by physicochemical methods. The halide-ion-sensory properties of sols of anisotropic silver nanoparticles prepared in different ways have been studied; sensitivity to halide ions is based on the changes in positions and intensities of longitudinal surface plasmon resonance (SPR) peaks in the range 500–800 nm in the optical absorption spectra of solutions.     

Laser photolysis of 2-phenylheptamethyltrisilane

Two transient absorptions have been detected in the 266 nm laser photolysis of 2-phenylheptamethyltrisilane in cyclohexane solution at room temperature, and their time evolution was recorded in the presence and absence of air and added trapping agents. The shorter-lived 440 nm transient (t1/2 < 20μs) is tentatively assigned to the silylene :SiMePh and the more persistent 380 nm transient to the disilene MePhSiSiMePh. The reactivity of this silylene is much lower than had been expected.     

Preparation and characterization of silver nanoparticles by chemical reduction method

Silver nanoparticles were prepared by the reduction of AgNO(3) with aniline in dilute aqueous solutions containing cetyltrimethlyammonium bromide, CTAB. Nanoparticles growth was assessed by UV-vis spectroscopy and the average particle size and the size distribution were determined from transmission electron microscopy, TEM. As the reaction proceeds, a typical plasmon absorption band at 390-450nm appears for the silver nanoparticles and the intensities increase with the time. Effects of [aniline], [CTAB] and [Ag(+)] on the particle formation rate were analyzed. The apparent rate constants for the formation of silver nanoparticles first increased until it reached a maximum then decreased with [aniline]. TEM photographs indicate that the silver sol consist of well dispersed agglomerates of spherical shape nanoparticles with particle size range from 10 to 30nm. Aniline concentrations have no significant effect on the shape, size and the size distribution of Ag-nanoparticles. Aniline acts as a reducing as well as adsorbing agent in the preparation of roughly spherical, agglomerated and face-centered-cubic silver nanoparticles.     

抗氧化剂没食子酸丙酯合成纳米银及其应用

在十六烷基三甲基溴化铵(CTAB)存在下, 硝酸银与没食子酸丙酯在碱性介质中发生还原反应, 制得纳米银; 考察了反应时间、 氢氧化钠浓度、 反应温度以及PG/Ag⁺浓度比等条件对合成纳米银粒子的影响. 利用扫描电子显微镜对纳米银颗粒形貌和尺寸进行了表征, 结果表明获得了分散性良好的球形粒子. 实验中还发现在还原银离子制备纳米银过程中会产生强烈的表面等离子共振峰, 用紫外-可见光谱监测制备过程得到的纳米银紫外吸收带范围为400~450 nm, 最大吸收波长为420 nm, 光谱强度与抗氧化剂的浓度成正比. 将纳米银的这一特性用于定量测定没食子酸丙酯(PG)、 二丁基羟基甲苯(BHT)、 叔丁基对羟基茴香醚(BHA)和叔丁基对苯二酚(TBHQ)等抗氧化剂, 所得检出限分别为0.0752, 0.1242, 0.0693和0.0701 mg/L, 线性范围分别为0.2~1.8, 0.2~3.4, 0.2~3.4和0.2~3.0 mg/L.     

Preparation of colloidal stable fluoroalkyl end‐capped oligomer/silver nanocomposites––application to the surface modification of traditional organic polymers with these nanocomposites

A variety of fluoroalkyl end‐capped oligomers/silver nanocomposites were prepared by the reactions of silver ions with poly(methylhydrosiloxane) in the presence of fluoroalkyl end‐capped N,N‐dimethylacrylamide oligomer, N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide oligomer, N,N‐dimethylacrylamide cooligomer containing poly(dimethylsiloxane) segments in organic media such as toluene and 1,2‐ dichloroethane. These fluorinated oligomers/silver nanocomposites thus obtained were found to exhibit clear plasmon absorption bands around 420 nm related to the formation of silver nanoparticles. In particular, these composites could display narrow plasmon absorptions around 420 nm in toluene by the addition of trioctylamine (TOA). On the other hand, the corresponding non‐fluorinated N‐(1,1‐ dimethyl‐3‐oxobutyl)acrylamide oligomer was not able to afford such a plasmon absorption under similar conditions. These fluorinated oligomers/silver nanocomposites in organic media have been found to be stable for more than 10 days. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements showed that silver nanoparticles could be effectively encapsulated into fluorinated oligomeric aggregate cores to afford colloidal stable fluorinated oligomers/silver nanocomposites. Fluorinated oligomers/silver nanocomposites were also applied to the surface modification of traditional organic polymers such as polystyrene (PSt) and poly(methyl methacrylate) (PMMA) to exhibit not only a good oleophobicity imparted by fluorine but also a higher surface antibacterial activity related to the silver nanoparticles on their surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Absorption spectra of large colloidal silver particles in aqueous solution

Calculations of the optical absorption spectra of spherical particles of silver with a radius (r) of 10 to 80 nm in water were performed. The single intense absorption band for small particles (r=10 nm) with a maximum at about 395 nm is gradually broadened and shifted to the long-wave region with an increase in the particle size (to 435 nm atr=40 nm). In the case of large particles, the band splits into several components absorbing light in the visible spectral region. The results are in good agreement with the optical characteristics of colloidal solutions of silver obtained upon radiochemical reduction of Ag⁺ ions in aqueous solution. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 201–203, January, 1997.     

Investigations of photochromism of 4-(2',4'-dinitrobenzyl)-pyridine by nanosecond laser absorption spectroscopy

The photochromism of 4-(2',4'-dinitrobenzyl)-pyridine was investigated by means of laser flash photolysis. Two coloured transients were observed in the spectral ranges of 390–430 nm and 510–590 nm in ethanol and acetonitrile. The first band (390–430 nm, lifetime ≈ 100–500 ns) is the absorption band of the aci-nitro form and the second band (510–590 nm, lifetime ? 0.5 s) is the absorption band of the polymethine form of 4-(2',4'-dinitrobenzyl)-pyridine. The measurements showed that the lifetime of the aci-nitro form depends on the energy of the laser flash in the case of the acetonitrile solution. Such dependence was not observed in ethanol solution. No short-lived transients were detected in n-heptane solution.     

Green synthesis of colloidal silver nanoparticles using natural rubber latex extracted from Hevea brasiliensis

Colloidal silver nanoparticles were synthesized by an easy green method using thermal treatment of aqueous solutions of silver nitrate and natural rubber latex (NRL) extracted from Hevea brasiliensis. The UV–Vis spectra detected the characteristic surface plasmonic absorption band around 435 nm. Both NRL and AgNO₃ contents in the reaction medium have influence in the Ag nanoparticles formation. Lower AgNO₃ concentration led to decreased particle size. The silver nanoparticles presented diameters ranging from 2 nm to 100 nm and had spherical shape. The selected area electron diffraction (SAED) patterns indicated that the silver nanoparticles have face centered cubic (fcc) crystalline structure. FTIR spectra suggest that reduction of the silver ions are facilitated by their interaction with the amine groups from ammonia, which is used for conservation of the NRL, whereas the stability of the particles results from cis-isoprene binding onto the surface of nanoparticles. Therefore natural rubber latex extracted from H. brasiliensis can be employed in the preparation of stable aqueous dispersions of silver nanoparticles acting as a dispersing and/or capping agent. Moreover, this work provides a new method for the synthesis of silver nanoparticles that is simple, easy to perform, pollutant free and inexpensive.     

Slow salt-induced aggregation of citrate-covered silver particles in aqueous solutions of cellulose derivatives

In this work, the salt-induced aggregation of bare and polymer-covered silver particles has been studied with the aid of light scattering and UV-visible spectroscopy. Light scattering on a suspension of bare silver particles at a low salt concentration shows that the cluster fractal dimension d _f changes from 1.6 to 2 in the course of the aggregation process, whereas no restructuring of the clusters is observed at a higher salinity where d _f ≈ 1.6. The growth of the clusters over time can be described by a power law R _h ∝ t ^α , where R _h is the apparent hydrodynamic radius. The UV-visible experiments revealed that increasing the size of the bare silver particles lead to a significant broadening and red-shift of the absorbance band, whereas for salt-induced growth of Ag clusters, a blue-shift and broadening was observed. Addition of salt to a suspension of silver particles and hydroxyethylcellulose divulged a slower broadening of the surface plasmon peak than without polymer.     

Triplet states of humic acids studied by laser flash photolysis using different excitation wavelengths

The spectra and kinetics of short-lived intermediates formed from aqueous (0.1 N NaOH) solutions of the natural mixture of humic and fulvic acids (HFA) were studied by laser flash photolysis using excitation wavelengths of 337, 390, 470, and 520 nm. Laser photolysis of HFA with light of 520 and 470 nm results in the formation of triplet excited states (T_HFA) characterized by the broad absorption spectrum with a maximum near 630 nm and lifetimes of 0.15 ms in deoxygenated solutions. The formation of two types of T_HFA with lifetimes of 0.1 and 2 ms and absorption spectra with maxima at 570 nm is observed under photolysis with light of 337 and 390 nm. The estimation of quantum yields of T_HFA gives 1 and 0.3% under photolysis with excitation wavelengths of 337 and 520 nm, respectively. The rate constants of T_HFA quenching by molecular oxygen are equal to (7—8)·10⁸ L mol^–1 s^–1.     

Laser-induced changes in silver metal nanoparticles incorporated in viscous media

The effect of laser pulse irradiation on silver metal nanoparticles in ethylene glycol and glycerol is studied and compared with the parallel processes in aqueous solutions. The influence of 355 nm laser pulse irradiation at the surface plasmon frequency and on the size of the silver nanoparticles is examined by UV-Vis absorption spectroscopy and by transmission electron microscopy. It appears that viscosity of the medium plays a crucial role for the stabilization of the melted particles in the absence of the stabilizer. In ethylene glycol containing PVP, fragmentation of particles was observed. In neat glycerol, similar excitation led to morphological changes as the nanoparticles fused to produce particles of larger size. The changes in reduction of shape and size are considered to occur through melting and vaporization of the silver nanoparticles.