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Nowadays there is a worldwide growing interest in the Inkjet Printing technology owing to its potentially high levels of geometrical complexity, personalization and resolution. There is also social concern about usage, disposal and accumulation of plastic materials. In this work, it is shown that sugar-based biodegradable polyurethane polymers exhibit outstanding properties as polymer-matrix for gold nanoparticles composites. These materials could reach exceptional stabilization levels, and demonstrated potential as novel robust inks for Inkjet based Printing. Furthermore, a physical comparison among different polymers is discussed based on stability and printability experiments to search for the best ink candidate. The University of Seville logo was printed by employing those inks, and the presence of gold was confirmed by ToF-SIMS. This approach has the potential to open new routes and applications for fabrication of enhanced biomedical nanometallic-sensors using stabilized AuNP. Spanish Ministerio de Economía y Competitividad MINECO, (Grants Nos. CTQ2016- 78703-P and MAT2016-78703-P) Junta de Andalucía (Consolidation Grant for Research Group FQM135 and 2017/FQM-386, P-2018/809) University of Seville (V y VI Plan Propio PP2016-5937)

A theoretical method based on Dissipative Particle Dynamics (DPD) was applied for the study of the interaction between coarse-grained models of chitosan and gold nanoparticles. These models were used to understand the role of chitosan in the stabilization of gold nanoparticles (5 and 7 nm). In addition, this stabilization was also supported by synthesized and characterized chitosan-gold nanoparticles comparing their stabilities with typical citrate-gold nanoparticles. Finally, the role of chitosan as a capping agent through the steric and electrosteric mechanisms in aqueous media with different pH values was also evaluated.

The stabilizing effect of lysozymes to salt addition over a gold colloid are exploited in order to detect lysozymes in human urine samples. The present research is aimed at the development of a fast, naked-eye detection test for urinary lysozymuria, in which direct comparison with a colorimetric reference, allows for the immediate determination of positive/negative cases. CIEL*a*b* parameters were obtained from sample absorbance measurements, and their color difference with respect to a fixed reference point was measured by calculating the ∆E76 parameter, which is a measure of how well the colors can be distinguished by an untrained observer. Results show that a simple and quick test can reliably, in less than 15 min, give a positive colorimetric response in the naked eye for concentrations of a urinary lysozyme over 57.2 µg/mL. This concentration is well within the limits of that observed for leukemia-associated lysozymurias, among other disorders. Universidad de Sevilla 2010/00000762, PP2016-5937, 2019/00000570, 2020/00001068, 2020/00001073 Junta de Andalucía 2019/FQM-386

The design and preparation of novel nanocarriers to transport cancer drugs for chemotherapy purposes is an important line of research in the medical field. A new 5-fluorouracil (5-Fu) transporter was designed based on the use of two new biocompatible gold nanosystems: (i) a gold nanoparticle precursor, Au@16-Ph-16, stabilized with the positively charged gemini surfactant 16- Ph-16, and (ii) the compacted nanocomplexes formed by the precursor and DNA/5-Fu complexes, Au@16-Ph-16/DNA-5-Fu. The physicochemical properties of the obtained nanosystems were studied by using UV-visible spectroscopy, TEM, dynamic light scattering, and zeta potential techniques. Method tuning also requires the use of circular dichroism, atomic force microscopy, and fluorescence spectroscopy techniques for the prior selection of the optimal relative Au@16-Ph-16 and DNA concentrations (R = CAu@16-Ph-16/CDNA), biopolymer compaction/decompaction, and 5-Fu release from the DNA/5-Fu complex. TEM experiments revealed the effective internalization of the both precursor and Au@16-Ph-16/DNA-5-Fu-compacted nanosystems into the cells. Moreover, cytotoxicity assays and internalization experiments using TEM and confocal microscopy showed that the new strategy for 5-Fu administration enhanced efficacy, biocompatibility and selectivity against lung cancer cells. The differential uptake among different formulations is discussed in terms of the physicochemical properties of the nanosystems. Universidad de Sevilla 2019/00000570, 2020/00001068, 2010/00000762, PP2016-5937, 2020/00001073 Junta de Andalucía 1804032996/2017, 2018/00000810, 2019/FQM-386

Stable oleuropein-coated gold nanoparticles in aqueous media were synthesized for the first time. Oleuropein (OLE) concentration in the reaction medium was found to greatly influence the outcome and stability of the resulting nanocolloid, with a marked decrease in particle size being found for the more concentrated oleuropein solutions. The protection mechanisms involved in the stabilized nanosystems were analyzed. Oleuropein self-assembled structures were found to be formed at a concentration threshold of [OLE] &gt, 5 &times, 10&minus, 5 M, and observed through the use of CryoSEM imaging. Those structures were responsible for both the increased stability and the decrease in size observed at the more concentrated solutions.

The use of silver nanoparticles stabilized with citrate and polyvinylpyrrolidone as a sensor for aluminum ions determination is proposed in this paper. These non-functionalized and specific nanoparticles provide a highly selective and sensitive detection system for aluminum in acidic solutions. The synthesized nanoparticles were characterized by transmission electron microscopy. Surface plasmon band deconvolution analysis was applied to study the interaction between silver nanoparticles and aluminum ions in solution. The interaction band in the UV-visible region was used as an analytical signal for quantitation purposes. The proposed detection system offers an effective AND wide linearity range (0.1&ndash, 103 nM), specificity for Al(III) in THE presence of other metallic ions in solution, as well as high sensitivity (limit of detection = 40.5 nM). The proposed silver-nanoparticles-based sensor WAS successfully used for detecting Al(III) in real water samples.

The interactions of citrate-capped 10-nm gold nanoparticles with a cationic model surfactant, CTACl, and an anionic one, SDS, are explored. Results show that for CTACl, values of the c.m.c. close to those reported in the absence of nanoparticles can be obtained by simple colorimetric measurements. For SDS, its interaction with the same-charge nanoparticles is explored through the use of an indirect colorimetric method involving NaCl addition, and a surfactant-nanoparticle interaction model is postulated in this basis. C.m.c. measurements for SDS in the presence of AuNPs show that, despite both substrates being anionic, SDS micelle formation is actually promoted in the presence of gold nanoparticles.

Nowadays there is a worldwide growing interest in the Inkjet Printing technology owing to its potentially high levels of geometrical complexity, personalization and resolution. There is also social concern about usage, disposal and accumulation of plastic materials. In this work, it is shown that sugar-based biodegradable polyurethane polymers exhibit outstanding properties as polymer-matrix for gold nanoparticles composites. These materials could reach exceptional stabilization levels, and demonstrated potential as novel robust inks for Inkjet based Printing. Furthermore, a physical comparison among different polymers is discussed based on stability and printability experiments to search for the best ink candidate. The University of Seville logo was printed by employing those inks, and the presence of gold was confirmed by ToF-SIMS. This approach has the potential to open new routes and applications for fabrication of enhanced biomedical nanometallic-sensors using stabilized AuNP.

The effect of the addition of low concentrations of an inner electrolyte on ds-DNA CT-DNA (calf thymus DNA) and ss-DNA conformational changes induced by small N-(2-mercaptopropionyl)glycine gold nanoparticles (AuNPs) is here studied in detail by using different spectroscopic and structural techniques. The high affinity of ss-DNA to AuNPs compared with ds-DNA is easily demonstrated by the results of competitive binding with SYBR Green I (SG). Additionally, it is proven that at 25.0 °C, AuNPs/ds-DNA and AuNPs/ss-DNA complexes undergo a transition from extended-coil to more compact structures when the AuNPs concentration (CAuNPs) is increased, which for the ds-DNA system is accompanied by partial denaturation. Particularly, for the AuNPs/ss-DNA system all of these techniques confirm that at a high CAuNPs, the compaction process is followed by a discrete transition to aggregation and an increase in structure size. A thorough analysis of the conformational changes described indicates that these processes are larger in low salt concentration and at high temperature. However, the most striking feature of this work is the abnormal melting temperature profiles (Tm) registered at high R = CAuNPs/CDNA ratios, which are remarkable and of interest for chemical sensing. At a suitable R ratio, which varies depending on CNaCl, a complex melting profile for the AuNPs/ds-DNA system was registered with two characteristic transitions: Tm,1 = 65.0 °C and Tm,2 = 95.0 °C. The highly sensitive atomic force microscopy technique performed at 25.0 °C and 65.0 °C also showed a different behaviour in both ss- and AuNPs/ds-DNA systems, which explains the characteristic melting curves. Specifically for the AuNPs/ss-DNA system, AFM at 25.0 °C revealed the formation of large-sized aggregates formed by AuNPs/ss-DNA compact structures linked by AuNPs. However, when both AuNPs/ds-DNA and AuNPs/ss-DNA complexes were incubated at 65.0 °C, the formation of highly stable ordered structures was always visualized at high R. Therefore, this shows that some key parameters for effective control of the formation of DNA/RNA-linked particles are: the selection of an optimal temperature below the ds-DNA melting point, an appropriate CAuNPs, and the addition of low CNaCl. The optimization of these parameters for each AuNPs/DNA system could improve biological sensing and DNA/RNA delivery.

We report a practical, economical and sensitive method for DNA and lysozyme biomolecule detection based on previous aggregation of an anionic citrate gold nanoparticle, Au@citrate, induced by N,N’-bis(dimethyldodecyl)-α,ω-alkanediammonium dibromide series (m-s-m, m = 12, s = 3 and 6) gemini surfactants. Starting from Au@citrate/12−s−12 aggregated complexes, disaggregation processes were induced, effectively and immediately, by increasing biopolymer concentrations. This phenomenon that changes the optical properties of the systems was originated by the strong, kinetically rapid interactions of Au@citrate with the biopolymer, favoring the formation of different highly stabilized Au@citrate/biopolymer/12−s−12 complexes, which particular structures were visualized via the AFM technique. In all cases, the order of addition of the reagents was demonstrated to be crucial for the success of the reaction, and therefore effective biomolecule detection. The new approach highlights a way to avoid problems derived from the time lapse observed in previously reported sensors based on gold nanoparticle’ aggregation phenomena, with a limit of detection in the nanomolar range. The results showed a better linear response in sensors prepared from 12−6−12 surfactant, in line with both the greater difference observed between the equilibrium binding constants for 12−6−12/biopolymer and Au@citrate/biopolymer interactions, and the significant interparticle distance among Au@citrate nanoparticles through the aggregates.

The interactions of DNA, whether long, hundred base pair chains or short-chained oligonucleotides, with ligands play a key role in the field of structural biology. Its biological activity not only depends on the thermodynamic properties of DNA-ligand complexes, but can and often is conditioned by the formation kinetics of those complexes. On the other hand, gold nanoparticles have long been known to present excellent biocompatibility with biomolecules and are themselves remarkable for their structural, electronic, magnetic, optical and catalytic properties, radically different from those of their counterpart bulk materials, and which make them an important asset in multiple applications. Therefore, thermodynamic and kinetic studies of the interactions of DNA with nanoparticles acting as small ligands are key for a better understanding of those interactions to allow for their control and modulation and for the opening of new venues of research in nanomedicine, analytic and biologic fields. The interactions of gold nanoparticles with both DNA polymers and their smaller subunits; special focus is placed on those interactions taking place with nonfunctionalized gold nanoparticles are reviewed in the present work.

A variety of methylenemalononitriles and ethyl cyanoacrylates derived from both aromatic and heteroaromatic aldehydes were synthesized by Knoevenagel condensation catalysed with native and modified chitosan-based heterogeneous catalysts. The efficiency of our hydrogel organocatalysts, chitosan hydrogel beads and ureidyl-chitosan derivative hydrogel disks, was evaluated as function of pH, temperature and catalyst concentration by considering reaction rates, conversions, E/Z stereoselectivities, and kinetic studies of a model reaction between 4-nitrobenzaldehyde and ethyl cyanoacetate. An unprecedented study by solid state 13 C CP MAS NMR of the employed catalyst when reaction was quenched after a 50% of conversion, has demonstrated that an imine-chitosan intermediate is formed during this process. Analysis of E / Z ethyl cyanoacrylate isomer mixtures for determining the corresponding stereoselectivity was carried out by NMR measuring carbon-proton coupling constants ( 3 J C,H ) using a novel CLIP-HSQMCB experiment. Additionally, DFT calculations let us rationalise the observed E / Z stereoselectivities as well as to evaluate the role of ureidyl moiety on interaction with aldehydes and imine intermediate formation with chitosan derivative.

A theoretical study of the interaction of ibrutinib with both cysteine/methyl-cysteine and gold surface is presented. The interest of ibrutinib is that binds through its acrylamide group with the S atom from Cys481 residue of Bruton-tyrosine-kinase (BTK) protein and inhibits the maturation of B-lymphocytes. In a first part, the interaction of ibrutinib through its acrylamide group with cysteine/methyl-cysteine is studied in the range of 298 to 315 K to analyse the effect of increasing the temperature in the binding of the drug with the amine-acid. The interaction is favoured at physiologic temperature but its stability decreases at higher temperatures. Thus, in patients with fever the drug may present a lower effectivity and certain amount of free drug in the blood may appear increasing the risk of toxicity for them. In the second part, the interaction of ibrutinib with a gold surface was studied to explore the possibility of using gold nanoparticles as ibrutinib deliverer. The most stable interaction corresponds to the structure with the nitrogen atoms from pyrimidine moiety and from NH2 directly focused over gold atoms keeping acrylamide group of ibrutinib free for joining to BTK. Therefore, according to the theoretical results gold nanoparticles may be used as ibrutinib deliverer.

The adsorption of adenine molecules and its derivatives on citrate capped gold nanoparticles (AuNPs) is quantified by a colorimetric method. The strength of the interaction is reflected in the aggregation grade of the colloids, that is detected though the changes in the absorption spectra of the samples, which allow for the determination of apparent binding constants. The positive charge of adenine molecules facilitates the approach to the colloid surface, a fact that is reflected in the measured binding free energies being more negative than those of neutral molecules. In the case of nucleosides and nucleotides, the aggregated structures are smaller or simply do not appear. Theoretical calculations based on density functional theory (DFT) were performed in order to compare the interaction of adenine, adenosine and AMP with gold nanoparticles. Our results indicate the relevance of the N atom of the amino group of adenine, adenosine and AMP in the stabilization with the nanoparticle surface. Thus, in this stabilization the amino group adopts a pyramidal disposition typical of a sp3 hybridization, being found the gold-adenine interaction more stable than that of adenosine and AMP.

The development of a new method for covalent immobilization of biomolecules on the surface of bare gold nanoparticles (AuNPs) by using crosslinking agents in one step is presented. A very compatible biopolymer such as chitosan has been used as a target molecule to probe the viability of the proposed methodology. Click chemistry, based on biocompatible reactions and coupling with 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide allow to analyze the covalent interactions between the metal nanoparticles and the biopolymer. Spectra deconvolution technique and Zeta potential measurements confirm the covalent interaction. The present study allows to quantify the proportion of AuNPs covalently adhered to the chitosan, which depends on the solution pH. The obtained results indicates that covalent interactions can be increased up to 25% in relation to total system interactions, which are mostly electrostatic. The proposed strategy opens up a new pathway for biomedical applications because the control of the chemical linkage can be directly performed on the nanoparticle surface without using any molecular intermediate, which may improve the encapsulation efficiency on drug delivery therapies.

To achieve optimal results when employing nanoparticles in biomedical fields, choosing the right type of nanoparticle and determining the correct procedure for drug loading are key factors. Each type of nanoparticle presents a determined set of characteristics that are, in some cases, unique. In general, their surface charge, geometry or hydrophilic character may be limiting factors, depending on what their intended application is. Once synthesized, additional factors, such as their interaction with biological systems and liberation mechanisms into the target cells, also need to be taken into account. Multiple advantages arise from the use of nanoparticles, such as the capability to solubilize hydrophobic compounds and an increased bioavailability. Those advantages justify the extensive and delicate study that should be undertaken in order to use them as drug delivery agents. One of the most important factors for the design of a drug delivery system with nanoparticles is achieving a high drug-to-nanoparticle ratio. In this Minireview, all of these key factors, both physicochemical and biological, are described, and special emphasis is placed on loading methods employed to introduce drugs into nanoparticles.

The equilibria and kinetics aspects of the binding of small gold nanoparticles, AuNPs, stabilized with tiopronin to DNA in B and C conformation (B-DNA and C-DNA), has been investigated in ethanol/water mixtures using different techniques. Two modes of binding are displayed: groove binding and partial intercalation, depending on the ethanol content, [EtOH], and the molar ratio, R = CAuNPs/CDNA. Two reaction mechanisms are proposed for AuNPs/DNA interaction in each polymer conformation, and the reaction parameters are evaluated. For lower ethanol levels, ([EtOH] up to 30%), when DNA is in the B form, the simplest mechanism according to the kinetic and thermodynamic results proved to be a three-step series mechanism reaction scheme which evolves in the formation of the groove complex. In this context, solvent hydration as well as the solvent effective viscosity are the main factors that influence kinetics. In contrast, for high ethanol levels, when DNA is in a C-like conformation, the mechanism is more complex involving three parallel reactions, in which AuNPs self-aggregation plays a key role in the switch from partial intercalation to groove binding. On the whole, it is evident that AuNPs aggregation and the DNA conformation are two key factors that must be taken into account in order to control the mechanism of AuNPs/DNA interaction.

We decorated a single giant DNA (1.66 × 105 base pairs) with gold nanoparticles through the simple procedure of mild warming, without denaturation of the DNA molecule. Single-molecule observation with fluorescence microscopy revealed that individual decorated DNA molecules stay in the bulk solution by avoiding aggregation and precipitation, and exhibit translational and conformational fluctuation, i.e., Brownian motion. An analysis of the intra-chain fluctuation of single DNA molecules revealed that the apparent spring constant and damping coefficient of a DNA chain increased by ca. 13- and 5-fold, respectively, upon decoration with gold nanoparticles. Observation by transmission electron microscopy revealed that gold nanoparticles were stably attached to the DNA skeleton. UV-visible measurements revealed the absence of any detectable change in surface plasmon resonance, suggesting that the gold nanoparticles assemble without the formation of a densely packed aggregate. CD measurements showed that the secondary structure of decorated DNA is still essentially the B-form. Spanish Ministerio de Economía y Competitividad CTQ2016-78703-P Universidad de Sevilla 2010/00000762 OTRI 2010/00000762 JSPS KAKENHI 15H02121 25103012

We report herein results regarding reactivity and assembly of citrate-capped gold nanoparticles (AuNPs) mediated by captopril (cap) and S-nitrosocaptopril (NOcap), two angiotensin converting enzyme inhibitors and antihypertensive agents. The results were compared with that of cysteine (Cys), a thiol-containing amino acid found in plasma. The interparticle interactions were characterized by monitoring the evolution of the surface plasmon resonance band using the spectrophotometric method. The original gold nanoparticles were efficiently modified by small amounts of Mn(+2) ions, which are adsorbed onto the surface of 15.4 nm citrate-capped gold nanoparticles, giving rise to manganese-gold nanoparticles (Mn-AuNPs) that, in mild acid medium, have proved to be highly sensitive and a rapid colorimetric detection method for thiols. Depending on the concentration of the Mn(+2) ions the aggregation of AuNPs can be rapidly induced. The kinetics of the assembly process has been studied. Good first-order kinetics has been observed, with the exception of captopril-mediated nanoparticle aggregation at low concentration of either cap or acid. The rate of Cys-mediated assembly of gold nanoparticles in aqueous 10 mM acetic acid is more than 20-times faster than pure AuNPs and concentrations of Cys as low as 34 nM can be detected in less than 40 min under conditions of stable Mn-AuNPs. Similar effects were observed with cap or NOcap. The assembly-disassembly reversibility is shown with cap and NOcap and depends highly on pH.

We explore the possibilities of quantifying the interaction of both adenine and thymine with non-functionalized, anionic citrate gold nanoparticles (AuNPs). Following the plasmon absorbance band's red shifts, dependent of the AuNPs aggregation state, apparent binding free energies of the system are obtained for the sum of the two processes (nucleobase interaction plus nanoparticle aggregation). A deconvolution procedure confirms those results. Those apparent binding free energies are, in both cases, in good agreement with previous studies indicating an increased reactivity for adenine. Moreover, density functional theory (DFT) calculations were carried out both to model the structures and to theoretically support and help understand the observed experimental stability of adenine as compared to thymine over gold nanoparticles. Theoretical results indicate the N atom in the amino group of adenine adopts a pyramidal sp3 hybridization character, stabilizing the interaction with Au as compared to thymine.

It is well known that single-stranded DNA (ssDNA) is easily able to adsorb on citrate-capped, non-functionalized gold nanoparticles (AuNPs). However, the affinity of double-stranded DNA (dsDNA) for them is much more limited. The present work demonstrates that long dsDNA suffers from a bending conformational change when anionic nanoparticles are present in solution. A striking decrease in the persistence length of the double helix in the absence of salt is observed through dynamic light scattering (DLS), viscometric, and atomic force microscopy (AFM) methods. Long dsDNA is therefore shown to be able to interact with anionic gold nanoparticles. To date, only ssDNA detection has been described by making use of interparticle cross-linking aggregation mechanisms; however, the data shown in this work allow for the development of new methods for detecting dsDNA in solution by using aggregated AuNPs as a starting point. The aggregation state is induced by the controlled addition of an inert electrolyte. A deconvolution procedure of the experimental plasmon shows how individual bands corresponding to aggregated nanoclusters diminish as the DNA concentration increases in the presence of 0.075 M NaCl.

Low-generation polyamidoamine (PAMAM) dendrimers are known to adsorb on the surface of gold nanoparticles (AuNPs) causing aggregation and color changes. In this paper, a thorough study of this affinity using absorption spectroscopy, colorimetric, and emission methods has been carried out. Results show that, for citrate-capped gold nanoparticles, interaction with the dendrimer is not only of an electrostatic character but instead occurs, at least in part, through the dendrimer’s uncharged internal amino groups. The possibilities of the CIELab chromaticity system parameters’ evolution have also been explored in order to quantify dendrimer interaction with the red-colored nanoparticles. By measuring and quantifying 17 nm citrate-capped AuNP color changes, which are strongly dependant on their aggregation state, binding free energies are obtained for the first time for these systems. Results are confirmed via an alternate fitting method which makes use of deconvolution parameters from absorbance spectra. Binding free energies obtained through the use of both means are in good agreement with each other.

AuNP effects on the oxidation reaction of [Ru(NH3)5pz](2+) with S2O8(2-) were studied. Experimental results show the effects produced by gold nanoparticles of different sizes, which are then discussed by using an approach based on the two-state model. Changes in the observed reactivity are explained by a change in the degree of association of the reactants to the nanoclusters, which depends on the negative surface potential of the gold nanoparticles. TEM and zeta potential measurements show that this potential determines the binding strength of one of the reactants ([Ru(NH3)5pz](2+)) to the citrate gold surface. The number of binding sites on a citrate nanoparticle receptor has also been determined. The experimental results confirm that an electron transfer reaction can be used as a probe for the determination of the free energy of binding of cationic metal complexes to gold nanoparticles.

The electron transfer reaction between [Ru(NH3)5pz]2+ and [Co(C2O4)3]3− was studied in the presence of monomers and aggregates of bile salts (sodium deoxycholate, sodium taurodeoxycholate, and sodium glycocholate) at 298.2 ± 0.1 K. The results show a decreasing rate constant with the successive addition of bile salts. To rationalize the trends of the reaction rate on the [bile salts], two models were used. One of them takes into account the aggregation feature by considering a stepwise self-association between monomers, whereas the other assumes the formation of a critical micellar concentration. Binding constants between [Ru(NH3)5pz]2+ species and deoxycholate or taurodeoxycholate aggregates were higher than that for glycocholate aggregates. These results are consistent with the way in which the monomers are added to form the bile anion aggregates.

The binding of pyrene-1-carboxaldehyde (1-PyCHO) with ctDNA was investigated through absorption, intrinsic and induced circular dichroism, viscosity measurements and steady-state fluorescence. The binding and the number of monomer units of the polymer involved in the binding of one dye molecule (site size) have been quantified. The results indicated that the 1-PyCHO molecule binds to the ctDNA in an intercalative mode. The spectroscopic evidence of this intercalation process is also corroborated by the effect of urea, iodide-induced fluorescence quenching of pyrene-1-carboxaldehyde and competitive binding using a fluorescent intercalator, SYBR Green I (SG). The induced circular dichroism (ICD) spectra of pyrene-1-carboxaldehyde complexed with ctDNA show that pyrene-1-carboxaldehyde intercalates into ctDNA and that the intercalation orientation of pyrene to the DNA base-pairs long axis is heterogeneous. On the other hand, the intrinsic circular dichroism (CD) spectra show a stabilization of the right-handed B form of ctDNA, due to the intercalation process.

Using pyren-1-carboxyaldehyde as a fluorescent probe, alcohol and salt–DNA interactions have been studied and quantified in terms of free energies of binding. This quantification implies the determination of the “true” free energy of binding of the probe, after correction through solubility measurements of the equilibrium binding constant of the probe to DNA. According to results, the interaction of alcohols is indirect and is based on the changes that they cause in the structure of water, changes which in turn alter the degree of hydration of DNA. On the other hand, salts interact with DNA through coulombic forces. A linear correlation between the free energy of binding for the different salts and the valency of the cations has been found.

AlOOH nanoparticles have been used to study the strength and character of the binding of the persulphate ion (S2O82−), at pH = 5.4, to them. The strength of the binding has been studied using a kinetic approach which consists of the study of the oxidation kinetics of a metal cation complex ([Ru(NH3)5pz]2+ (pz = pyrazine)) by S2O82− at different NaCl concentrations. When the ionic strength increases, the strength of the binding decreases, as a consequence of the partial neutralization of the charge on the AlOOH surface which, at pH = 5.4, is positively charged. The increase of the ionic strength also produces a change in the character of the binding, which changes from anticooperative to noncooperative when the ionic strength increases. The nonelectrostatic and electrostatic components of the free energy of binding are determined. The nonelectrostatic component of the free energy of binding is almost zero. On the other hand, the values of the differences of electrostatic potential at the AlOOH/solutions in...

Gold nanoparticles (AuNPs) capped with N-(2-mercaptopropionyl)glycine have been used to study the strength and character of the binding of a cationic metal complex, [Ru(NH3)5pz]2+ (pz = pyrazine), at pH = 8, to these nanoparticles. The strength of the binding has been studied using a kinetic approach consisting of the study of the kinetics of the oxidation of this ruthenium complex by S2O82- at different NaCl concentrations. When the ionic strength increases, the strength of the binding decreases, as a consequence of the partial neutralization of the charge on the AuNPs which, at pH = 8, has the tiopronin residue negatively charged. The increase of the ionic strength also produces a change in the character of the binding, which changes from anticooperative to noncooperative when the ionic strength increases. The nonelectrostatic and electrostatic components of the free energy of binding are determined. From the latter, we have obtained the values of the electrostatic potential differences at the AuNPs/solutions interface.

The interaction between the [Co(en)2Cl2]+trans-dichlorobis cobalt(III)bis(ethylenediammine) and an anionic micelle of sodium dodecyl sulphate (SDS) is considered in the framework of the exponential mean spherical approximation (EMSA) in order to obtain the equilibrium binding constant between the metal complex ion and the micelle. This calculation has been carried out at different [SDS] concentrations as well as at different [NaCl] concentrations. The objective was to compare with previous experimental data in order to check if only considerations of electrostatic interactions are able to explain the behaviour of charged metal ions in the presence of micelles of SDS.

Review: some of the most relevant synthetic procedures reported up to date, with a special focus on synthetic routes to nonfunctionalized gold nanoparticle in aqueous media, influence of synthesis conditions on the shape, stability, and reactivity of the nanoparticles; 92 refs.

Aqueous gold colloids with a mean diameter of 15.4 ± 1.5 nm have been transferred into a range of water–alcohol mixtures. The influence of these mixtures (methanol, ethanol, 2-propanol, and tert-butanol), which present different hydrophobic properties, on the surface plasmon band of gold nanoparticles has been studied. Shifts of gold nanoparticles’ surface plasmon band (SPB) depend on the number of methyl groups and hydrophobic character of the alcohol molecule. Results from deconvolution analysis are explained considering variations on the grade of alcohol adsorption on the nanoparticle surface. TEM images indicate aggregation of the nanoclusters in mixtures of 2-propanol and tert-butanol. ζ potential measurements support the exchange of citrate ions by alcohol molecules, which in turn reflects the existence of an additional electrostatic component.

Since Faraday first described gold sol synthesis, synthetic routes to nanoparticles, as well as their applications, have experienced a huge growth. Variations in synthesis conditions such as pH, temperature, reduction, and the stabilizing agent used will determine the morphology, size, monodispersity, and stability of nanoparticles obtained, allowing for modulation of their physical and chemical properties. Although many studies have been made about the synthesis and characterization of individual nanosystems of interest, to our knowledge the common, general traits that all those synthesis share have not been previously compiled. In this review, we aim to offer a global vision of some of the most relevant synthetic procedures reported up to date, with a special focus on nonfunctionalized gold nanoparticle synthetic routes in aqueous media, and to display a broad overview of the influence that synthesis conditions have on the shape, stability, and reactivity of nanoparticle systems.

Potential NLO-phore materials based on chitosan are described for the first time in this study. A series of fluorescent and quaternized pyridinium– chitosan derivatives have been synthesized by reaction of this polymer with easily available tunable pyrylium tetra fluoroborate salts. Among other spectroscopic techniques, 19 F NMR, 13 C CPMAS NMR and 2D diffusion experiments, were used to con firm the structures of the new pyridinium– chitosan complexes that show high fluorescence intensity. Degrees of N -substitution were achieved lower than 4.3%, allowing the original physicochemical properties of the biopolymer to be preserved. DFT calculations have been performed to investigate the molecular features related to the NLO properties in these compounds. NLO behavior was found to be clearly dependent on the nature and location of the substituent into the pyridinium core. Theoretical data reveal a large permanent dipolar moment, polarizabilities and hyperpolarizabilities making these molecules promising candidates as supramolecular devices exhibiting NLO properties with potentially enhanced solvatochromic properties. Agencia Española de Cooperación Internacional para el Desarrollo A/023577/09, A/030422/10 Junta de Andalucía FQM 142, P09-AGR-4597

The DNA conformational changes induced by different members of the N,N0-bis(dimethyldodecyl)-a-ualkanediammonium dibromide series (m-s-m, m ¼ 12, s ¼ 3 and 6) and the analogous series of hexadecyl gemini surfactants (m ¼ 16, s ¼ 3 and 6) were investigated in aqueous media by means of circular dichroism (CD), zeta potential, dynamic light scattering (DLS), viscometry, and atomic force microscopy (AFM) methods. The measurements were carried out by varying the gemini surfactant–DNA molar ratio, R ¼ Cm-s-m/CDNA. For the conditions investigated two significantly different conformational changes were observed, the second of them being worth noting. At low molar ratios, all methods concurred by showing that gemini surfactants were able to form ordered aggregates which precedes DNA compaction. The second effect observed, at high molar ratios, corresponds to the transition from the compact state to a new more extended conformation. The degree of decompaction and the morphologies of the visualized structures are different not only depending on the surfactant tail's length, but also on the spacer's length. The results obtained for the 16-3-16/DNA and 16-6-16/DNA systems point out that the compaction/decompaction processes are somewhat different to those previously visualized for the analogous monoquaternary chain surfactant CTAB. Consejería de Educación y Ciencia of the Junta de Andalucía FQM-03623

The title reaction was studied in different reaction media: aqueous salt solutions (NaNO3) and water-cosolvent (methanol) mixtures. The observed rate constants, k(obs), show normal behavior in the solutions containing the electrolyte, that is, a negative salt effect. However, the solvent effect is abnormal, because a decrease of the rate constant is observed when the dielectric constant of the reaction medium decreases. These effects (the normal and the abnormal) can be explained using the Marcus-Hush treatment for electron transfer reactions. To apply this treatment, the true, unimolecular, electron-transfer rate constants, k(et), have been obtained from k(obs) after calculation of the rate constants corresponding to the formation of the encounter complex from the separate reactants, k(D), and the dissociation of this complex, k(-D). This calculation has been carried out using an exponential mean spherical approach (EMSA).

A kinetic study of the reaction between [Fe(CN) 6 ] 4− (hexacyanoferrate (II)) and [Co(en) 2 Cl 2 ] + ( trans -dichlorobis cobalt(III) bis(ethylenediammine)) has been carried out in sodium dodecyl sulphate (SDS) micellar solutions containing NaCl. The results are discussed by using an approach based on the pseudophase model. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants ([Co(en) 2 Cl] + in the present Letter) to the micelles, which depends on the surface potential of the micelles. The electrostatic and non-electrostatic components of the free energy of binding are determined by two different methods and the results of these determinations are compared.

The substitution reaction of 4,4′-bpy (4,4′-bipyridine) for the aquo ligand in aquopentacyanoferrate (II) was studied in solutions containing α-, β- and γ-cyclodextrins. We conclude that the well-known pseudophase model is equivalent to the Bronsted equation in regard to the interpretation of the cyclodextrins effects on reactivity. The equivalence follows from the fact that both pseudophase and Bronsted approaches can be used to rationalize kinetic data and permit to quantify the inclusion of the aromatic ligand in the cyclodextrins.