Absence Of Salt Research Articles

Micellar effects on aromatic nucleophilic substitution by the ANRORC mechanism. Hydrolysis of 2‐chloro‐3,5‐dinitropyridine

The hydrolysis of 2‐chloro‐3,5‐dinitropyridine by sodium hydroxide in the presence of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl) and sodium dodecyl sulfate (SDS) has been studied. The reaction follows a consecutive reaction path involving the formation of a long‐lived intermediate 3 and finally giving the product, 3,5‐dinitro 2‐pyridone 2. The mechanism follows an addition of the nucleophile, ring opening and ring closure (ANRORC) reaction path. The rate constant was observed to be first‐order dependent on [OH−]. The rate of reaction increased on increasing [CTABr] and, after reaching to the maxima, it started decreasing. The anionic SDS micelles inhibited the rate of hydrolysis. The results of the kinetic experiments were treated with the help of the pseudophase ion exchange model and the Menger–Portnoy model. The added salts, viz. NaBr, Na‐toluene‐4‐sulphonate, and (CH3)4NBr on varying [CTACl] and [SDS] inhibited the rate of reaction. The various kinetic parameters in the presence and absence of salts were determined and are reported herewith. Copyright © 2011 John Wiley & Sons, Ltd.

Method Validation for the Trace Analysis of Geosmin and 2-Methylisoborneol in Water by ?Salt-Free? Purge-and-Trap Sampling/GC-MS, Using the Eclipse 4660 Sample Concentrator

The Eclipse 4660 purge-and trap sample concentrator, coupled to a gas chromatograph-mass spectrometer, was fully validated for trace analysis of the taste-odorants geosmin (GSM) and 2-methylisoborneol (2-MIB) in the absence of salt or methanol. The procedure involved purging a 25 mL sample volume, at 80°C, for 11 min. Quantitation was done by separation on an HP 5-MS capillary column (30 m × 0.25 mm × 0.25 μm), followed by mass spectrometric detection in the selected ion monitoring (SIM) mode. The method was found to be linear (r2 ≥ 0.995) over the calibration range 0-100 ng/L for both target analytes. The overall accuracy, determined by recovery, was 104.21% ± 19.46 (mean ± SD, range = 65.29-143.13%) for 2-MIB, and 85.24% ± 8.28 (mean ± SD, range = 68.66-101.82%) for GSM. The within-day precision averaged 7.97% for 2-MIB, and 8.77% for GSM. The day-to-day precision was 20.96% for 2-MIB, and 7.52% for GSM. The limit of quantitation (LOQ) was 6 ng/L and 5 ng/L for 2-MIB and GSM; the limit of detection (LOD) was 5 ng/L and 4 ng/L for 2-MIB and GSM respectively. Earlier findings regarding the dehydration of 2-MIB to 2-methyl-2-bornene (2-M-2-B) were confirmed. The average amount of 2-M-2-B formed was 27% (range: 15-50%), with RSD = 33.26%. There is evidence of dehydration of 2-MIB to 2-M-2-B at sample purge temperature of 40°C and higher. The poor day-to-day precision for 2-MIB has been proposed to be due to the inconsistent amount of 2-M-2-B formed. A minimum sample purge temperature of 40°C is required to purge 2-MIB and GSM from water, which can be detected by GC/MS under the purge-and-trap conditions at a concentration of 100 ng/L. The developed method was found to be sensitive, accurate, precise and reproducible for trace analysis of geosmin in water matrices.

Novel pH-Sensitive Physical Hydrogels of Carboxymethyl Scleroglucan

A carboxymethyl derivative of scleroglucan (Scl-CM) with derivatization degree 300 ± 10 was synthesized and characterized by Fourier transform infrared spectroscopy, potentiometer titration, mucus adhesion studies, and rheological measurements. Rheological measurements showed the ability of the polymer to undergo sol-gel transitions even in the absence of salts. Swelling experiments, performed on freeze-dried samples in different media, showed good affinity of these hydrogels toward the aqueous media and a pH-sensitive behavior. Four nonsteroidal anti-inflammatory drugs (NSAIDs) were loaded into the physical hydrogels obtained from 2.0% (w/v) solutions of the polymer. The results of the release studies carried out in conditions simulating the gastrointestinal tract showed that the new hydrogels could be suggested for the modified oral delivery of NSAIDs, particularly damaging for the gastric mucosa. In vivo studies proved the biocompatibility of the matrix and the absence of any gastric damage for administration of ulcerogenic doses of diclofenac loaded into the hydrogel (DIC/Scl-CM-300). Moreover, DIC/Scl-CM-300 was found to be effective in peripheral analgesia.

Extraordinary transgressive phenotypes of hybrid tomato are influenced by epigenetics and small silencing RNAs

Hybrid organisms may fail to develop, be sterile or they may be more vigorous than either of the parents. Examples of hybrid vigour or hybrid necrosis in the F1 are often not inherited stably in subsequent generations if they are associated with overdominance. There can also be transgressive phenotypes that are inherited stably in these later generations, but the underlying mechanisms are not well understood. Here we have investigated the possibility that stable transgressive phenotypes in the progeny of crosses between cultivated tomato (Solanum lycopersicum cv. M82) and a wild relative (Solanum pennellii, accession LA716) are associated with micro or small interfering(si) RNAs. We identified loci from which these small(s)RNAs were more abundant in hybrids than in either parent and we show that accumulation of such transgressive sRNAs correlated with suppression of the corresponding target genes. In one instance this effect was associated with hypermethylation of the corresponding genomic DNA. Our results illustrate a potential role of transgressive sRNAs in plant breeding and in natural evolution with wild plants.

Anionic Polyelectrolyte-Stabilized Nanoparticles via RAFT Aqueous Dispersion Polymerization

We report the synthesis of anionic sterically stabilized diblock copolymer nanoparticles via polymerization-induced self-assembly using a RAFT aqueous dispersion polymerization formulation. The anionic steric stabilizer is a macromolecular chain-transfer agent (macro-CTA) based on poly(potassium 3-sulfopropyl methacrylate) (PKSPMA), and the hydrophobic core-forming block is based on poly(2-hydroxypropyl methacrylate) (PHPMA). The effect of varying synthesis parameters such as the salt concentration, solids content, relative block composition, and anionic charge density has been studied. In the absence of salt, self-assembly is problematic when using a PKSPMA stabilizer because of lateral repulsion between highly charged anionic chains. However, in the presence of added salt this problem can be overcome by reducing the charge density within the coronal stabilizer layer by either (i) statistically copolymerizing the KSPMA monomer with a nonionic comonomer (2-hydroxyethyl methacrylate, HEMA) or (ii) using a binary mixture of a PKSPMA macro-CTA and a poly(glycerol monomethacrylate) (PGMA) macro-CTA. These diblock copolymer nanoparticles were analyzed by (1)H NMR spectroscopy, gel permeation chromatography (GPC), dynamic light scattering (DLS), transmission electron microscopy (TEM), and aqueous electrophoresis. NMR studies suggest that the HPMA polymerization is complete within 2 h at 70 °C, and DMF GPC analysis confirms that the resulting diblock copolymers have relatively low polydispersities (M(w)/M(n) < 1.30). NMR also suggests a significant degree of hydration for the core-forming PHPMA chains. Depending on the specific reaction conditions, a series of spherical nanoparticles with mean diameters ranging from 50 to 200 nm with tunable anionic surface charge can be prepared. If a binary mixture of anionic and nonionic macro-CTAs is utilized, then it is also possible to access a vesicular morphology.

Correlation between catalysis and tertiary structure arrangement in an archaeal halophilic subtilase

Nep (Natrialba magadii extracellular protease) is a halolysin-like peptidase secreted by the haloalkaliphilic archaeon N. magadii that exhibits optimal activity and stability in salt-saturated solutions. In this work, the effect of salt on the function and structure of Nep was investigated. In absence of salt, Nep became unfolded and aggregated, leading to the loss of activity. The enzyme did not recover its structural and functional properties even after restoring the ideal conditions for catalysis. At salt concentrations higher than 1 M (NaCl), Nep behaved as monomers in solution and its enzymatic activity displayed a nonlinear concave-up dependence with salt concentration resulting in a 20-fold activation at 4 M NaCl. Although transition from a high to a low-saline environment (3–1 M NaCl) did not affect its secondary structure contents, it diminished the enzyme stability and provoked large structural rearrangements, changing from an elongated shape at 3 M NaCl to a compact conformational state at 1 M NaCl. The thermodynamic analysis of peptide hydrolysis by Nep suggests a significant enzyme reorganization depending on the environmental salinity, which supports in solution SAXS and DLS studies. Moreover, solvent kinetic isotopic effect (SKIE) data indicates the general acid-base mechanism as the rate-limiting step for Nep catalysis, like classical serine-peptidases. All these data correlate the Nep conformational states with the enzymatic behavior providing a further understanding on the stability and structural determinants for the functioning of halolysins under different salinities.

Whitening regenerated cellulose fibers using fluorescent agent, surfactants, and salt—color indices measurements

AbstractThe whitening efficiency of regenerated cellulose fibers using sodium 4,4′‐distyrylbiphenyl sulfonate in the presence of an anionic surfactant (sodium dodecylsulfate) and a cationic surfactant (dodecyl trimethyl ammonium chloride) and salt (NaCl) was determined by fluorescence spectroscopy and color index values (brightness, whiteness, and yellowness). Epifluorescence images gave an intense blue color with an apparent uniform emission distribution. In absence of salt, the whitening efficiency was higher for aqueous solutions containing cationic surfactant below critical micellar concentration (cmc). In presence of salt, whitening efficiency was higher for anionic surfactant and more important. The concentration of surfactant required for greater brightness, whiteness, and yellowness was lower than that required in absence of salt. These data were discussed by the decrease of the cmc and by the screening of the modified cellulose fibers by counter ions coming from the salt. The role of surfactants was explained by the admicelization during the sorption process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effects of chain stiffness and salt concentration on responses of polyelectrolyte brushes under external electric field.

We report a molecular dynamics study on non-equilibrium dynamics of polyelectrolyte brushes under external electric fields. In this work, the effects of chain stiffness and salt concentration on static and dynamic responses of the brushes are addressed in detail. Our simulations indicate that varying these parameters induce rich electro-responsive behavior of the brushes. The increase of salt concentration results in the enhancement of an opposite electric field formed by non-equilibrium distribution of cations and anions, which resists stretching or shrinkage of grafted chains. At strong positive electric fields, the flexible brushes are more sensitive to the change of salt concentration. When reversing the electric field, the stiff brushes undergo a conformational transition from collapse to complete stretching. At high salt concentrations, dynamic responsive magnitude of the brush thickness to added electric field is strongly reduced. It was found that the fall time for the stiff brush becomes much shorter than that for the flexible brush. Additionally, increasing ion concentration leads to an excess extension or shrinkage of flexible brushes. For strongly stiff brushes, such phenomenon occurs in the presence or absence of salt.

Comparison of salt stress resistance genes in transgenic Arabidopsis thaliana indicates that extent of transcriptomic change may not predict secondary phenotypic or fitness effects

Engineered abiotic stress resistance is an important target for increasing agricultural productivity. There are concerns, however, regarding possible ecological impacts of transgenic crops. In contrast to the first wave of transgenic crops, many abiotic stress resistance genes can initiate complex downstream changes. Transcriptome profiling has been suggested as a comprehensive non-targeted approach to examine the secondary effects. We compared phenotypic and transcriptomic effects of constitutive expression of genes intended to confer salt stress tolerance by three different mechanisms: a transcription factor, CBF3/DREB1a; a metabolic gene, M6PR, for mannitol biosynthesis; and the Na⁺/H⁺ antiporter, SOS1. Transgenic CBF3, M6PR and SOS1 Arabidopsis thaliana were grown together in the growth chamber, greenhouse and field. In the absence of salt, M6PR and SOS1 lines performed comparably with wild type; CBF3 lines exhibited dwarfing as reported previously. All three transgenes conferred fitness advantage when subjected to 100 mm NaCl in the growth chamber. CBF3 and M6PR affected transcription of numerous abiotic stress-related genes as measured by Affymetrix microarray analysis. M6PR additionally modified expression of biotic stress and oxidative stress genes. Transcriptional effects of SOS1 in the absence of salt were smaller and primarily limited to redox-related genes. The extent of transcriptome change, however, did not correlate with the effects on growth and reproduction. Thus, the magnitude of global transcriptome differences may not predict phenotypic differences upon which environment and selection act to influence fitness. These observations have implications for interpretation of transcriptome analyses in the context of risk assessment and emphasize the importance of evaluation within a phenotypic context.

Analysis of the Extracellular Polysaccharide-based Structures Produced by a Halophylic Archaeon

This paper investigates the components distribution and structure of an extracellular polysaccharide (EPS) produced by the halophilic archaeon Haloferax mediterranei in the presence or absence of the archaeon by using optical microscopy. The results show that EPS at the end of cultivation is arranged as a discontinuous biofilm and the cells are embedded in this biofilm. EPS and cells cannot be separated through centrifugation, cells remaining attached to the polysaccharide; the biofilm in the supernatant has a similar aspect as in the cultivation broth. The biofilm formed from the supernatant by drying at room temperature is very rich in salts from the cultivation broth (around 200 g/l from which 125 g/l NaCl) and consists on salt crystals which incorporate or are embedded by a film of EPS, distributed discontinuously and having some globular components. In the absence of salts (removed through dialysis), the biofilm formed in the aqueous environment is discontinuous and consists on globular polysaccharides connected by linear EPS which entraps cells remained after centrifugation.

Responses to salt stress in Juncus acutus and J. maritimus during seed germination and vegetative plant growth

Responses to increasing salinity, during seed germination and vegetative plant growth, were studied in two related species of Juncus, J. maritimus and J. acutus. In both species, germination was optimal in the absence of salt, reduced by about 50% in the presence of 200 mM NaCl, and completely inhibited by NaCl concentrations above 300 mM. Previous exposure of the seeds to salt, up to 500 mM NaCl, did not affect the germination capacity in J. acutus, and clearly enhanced it in J. maritimus. A concentration-dependent inhibition of plant growth was observed in the presence of NaCl for both species, together with the parallel accumulation of sodium ions in the leaves, as determined by cation exchange HPLC. Regarding the levels of divalent cations, in J. acutus Ca2+ and Mg2+ increased up to about two-fold in plants treated with 500 mM NaCl, as compared to control plants, whereas in J. maritimus they were three- to four-fold higher than in J. acutus in the absence of salt, and did not change significantly with increasing NaCl concentrations. These results suggest that Ca2+ and Mg2+ participate in defence mechanisms against salt stress, which would be constitutive in J. maritimus and salt-inducible in J.acutus.

Estimated pKa values for specific amino acid residues in daptomycin

Daptomycin is a cyclic lipopeptide antibiotic. The ionization constants of daptomycin have not been individually elucidated. The objective of this research is to determine the sequence‐specific ionization constants of daptomycin in the monomeric state. The pH titrations of daptomycin were performed by nuclear magnetic resonance (NMR) spectroscopy. The sequence‐specific pKa values for the four acidic residues and one aromatic amine (Kyn‐13) in daptomycin were determined by two‐dimensional total correlation spectroscopy 1H NMR. From the NMR pH titration, the estimated pKa values for Asp‐3, Asp‐9, and methylglutamic acid (mGlu‐12) were determined to be 4.2, 3.8, and 4.6 in the absence of salt, and 4.1, 3.8, and 4.4 in the presence of 150 mM NaCl, respectively. The pKa value for Asp‐7 is estimated to be approximately 1.0 in the absence of salt and 1.3 in the presence of salt. The estimated Hill coefficients for Asp‐7 were 0.72 and 1.31 in the absence and presence of salt, respectively. The increase in Hill coefficients from 0.72 to 1.31 with increasing salt concentration is consistent with the estimated lower pKa in the absence of salt, and suggests that a salt bridge is formed in solution possibly between Asp‐7 acidic group and the neighboring Orn‐6 basic group. © 2011 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:4225–4233, 2011

Fabrication of functional micro-clusters by heteroaggregation of oppositely charged protein-coated lipid droplets

This manuscript describes the formation and characterization of colloidal dispersions formed by heteroaggregation of oppositely charged protein-coated lipid droplets. Micro-clusters were formed by mixing a dilute dispersion of β-lactoglobulin-coated lipid droplets ( d 32 ∼ 0.18 μm, 0.1 wt%) with a dilute dispersion of lactoferrin-coated lipid droplets ( d 32 ∼ 0.14 μm, 0.1 wt%) under conditions where the two proteins had opposite charges (pH 7). The mean particle diameter, electrical charge, and microstructure of the mixed dispersions were measured as a function of particle ratio (0–100%) and ionic strength (0–400 mM NaCl). The characteristics of the micro-clusters formed depended on the ratio of positive-to-negative droplets and ionic strength. In the absence of salt, the largest clusters were formed at intermediate particle ratios (40–60%). In a mixed system (40% LF; 60% BLG), large clusters were formed at low ionic strength due to strong electrostatic attraction between oppositely charged droplets. These clusters partly dissociated at intermediate ionic strengths due to reduction in electrostatic attraction. However, further aggregation occurred at high ionic strengths due to reduction in electrostatic repulsion. Micro-clusters may be useful functional ingredients to modulate the physicochemical properties of products in the food, agrochemical, personal care, and pharmaceutical industries, such as release characteristics, rheology, and stability.

Diffusion of Lysozyme in Buffered Salt Solutions

The diaphragm cell technique was used to measure the diffusion coefficient of lysozyme in buffered solutions with and without NaCl. In the absence of salt, the pseudobinary diffusion coefficient decreases with increasing lysozyme concentration. In the presence of NaCl, the main term D11 decreased slowly with increasing NaCl concentrations and exceeded the pseudobinary values by 4–10%. The main term D22 did not vary significantly with NaCl concentration and was slightly less than the binary diffusion coefficient for NaCl. The cross-term D21 increased sharply with salt concentration. The cross-term D12 is small and decreased slowly with salt concentration. These results are consistent with the expected electrostatic interactions between lysozyme and salt in the diffusion process.

Application of a hydrolyzable cationic agent, poly(acryloxyethyl trimethylammonium chloride), in salt‐free reactive dyeing for good dyeing properties

AbstractPoly(acryloxyethyl trimethylammonium chloride) (PAOTAC), in which cationic groups were connected with the polymer skeleton through ester bonds, was applied in the salt‐free reactive dyeing of cotton with the aim of achieving good dyeing properties. Exhaust and exhaust–pad–steam dyeing procedures were used with the cotton cationized with PAOTAC in the absence of salt; for comparison, both dyeing procedures were also applied with the untreated cotton in the presence of salt. The dyeing results show that only the exhaust–pad–steam dyeing procedure was suitable for dyeing cationic cotton to achieve a high dye fixation. Color yields, colorimetric properties, fastness properties, dyeing levelness, and penetration behaviors with different dyeing methods were evaluated. Compared with the dyeings with untreated cotton in conventional exhaust dyeing, dyeings with cationic cotton in the exhaust–pad–steam procedure showed equivalent or even better fastness with generally higher color yields and good dye penetration. Possible reasons for the improved salt‐free dyeing properties were proposed, and the hydrolysis of ester bonds within PAOTAC under the dyeing conditions was proven by IR spectroscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Influence of Glucose Concentration on the Membrane Stability of Human Erythrocytes

The action of glucose as an osmolyte in relation to blood cells is not well-characterized in the literature. This study aimed to study the influence of glucose concentration on the stability of red blood cells. The stability of erythrocytes was evaluated by the half-transition point obtained from the curves of lysis induced by glucose in the absence of salt or by increase in medium hypotonicity in the absence and the presence of different concentrations of glucose. In the presence of 0.9 g/dl NaCl, there was no hemolysis with increasing concentration of glucose from 0 to 10 g/dl. In the absence of NaCl, the dependence of hemolysis with the 0-10 g/dl glucose was described by a decreasing sigmoid, with fully lysed and fully protected cells being encountered in the presence of 0-2 and 4-10 g/dl glucose, respectively. The possible origin of such stabilization effect is discussed with base of what is known about osmostabilization of biological complexes and about the influence of glucose on the rheological properties of erythrocytes.

Structural Rearrangement of β-Lactoglobulin at Different Oil–Water Interfaces and Its Effect on Emulsion Stability

Understanding the factors that control protein structure and stability at the oil-water interface continues to be a major focus to optimize the formulation of protein-stabilized emulsions. In this study, a combination of synchrotron radiation circular dichroism spectroscopy, front-face fluorescence spectroscopy, and dual polarization interferometry (DPI) was used to characterize the conformation and geometric structure of β-lactoglobulin (β-Lg) upon adsorption to two oil-water interfaces: a hexadecane-water interface and a tricaprylin-water interface. The results show that, upon adsorption to both oil-water interfaces, β-Lg went through a β-sheet to α-helix transition with a corresponding loss of its globular tertiary structure. The degree of conformational change was also a function of the oil phase polarity. The hexadecane oil induced a much higher degree of non-native α-helix compared to the tricaprylin oil. In contrast to the β-Lg conformation in solution, the non-native α-helical-rich conformation of β-Lg at the interface was resistant to further conformational change upon heating. DPI measurements suggest that β-Lg formed a thin dense layer at emulsion droplet surfaces. The effects of high temperature and the presence of salt on these β-Lg emulsions were then investigated by monitoring changes in the ζ-potential and particle size. In the absence of salt, high electrostatic repulsion meant β-Lg-stabilized emulsions were resistant to heating to 90 °C. Adding salt (120 mM NaCl) before or after heating led to emulsion flocculation due to the screening of the electrostatic repulsion between colloidal particles. This study has provided insight into the structural properties of proteins adsorbed at the oil-water interface and has implications in the formulation and production of emulsions stabilized by globular proteins.

Dual Roles of the Cardin-Weintraub Motif in Multimeric Sonic Hedgehog

The fly morphogen Hedgehog (Hh) and its mammalian orthologs, Sonic, Indian, and Desert hedgehog, are secreted signaling molecules that mediate tissue patterning during embryogenesis and function in tissue homeostasis and regeneration in the adult. The function of all Hh family members is regulated at the levels of morphogen multimerization on the surface of producing cells, multimer release, multimer diffusion to target cells, and signal reception. These mechanisms are all known to depend on interactions of positively charged Hh amino acids (the Cardin-Weintraub (CW) motif) with negatively charged heparan sulfate (HS) glycosaminoglycan chains. However, a precise mechanistic understanding of these interactions is still lacking. In this work, we characterized ionic HS interactions of multimeric Sonic hedgehog (called ShhNp) as well as mutant forms lacking one or more CW residues. We found that deletion of all five CW residues as well as site-directed mutagenesis of CW residues Lys(33), Arg(35), and Lys(39) (mouse nomenclature) abolished HS binding. In contrast, CW residues Arg(34) and Lys(38) did not contribute to HS binding. Analysis and validation of Shh crystal lattice contacts provided an explanation for this finding. We demonstrate that CW residues Arg(34) and Lys(38) make contact with an acidic groove on the adjacent molecule in the multimer, suggesting a new function of these residues in ShhNp multimerization rather than HS binding. Therefore, the recombinant monomeric morphogen (called ShhN) differs in CW-dependent HS binding and biological activity from physiologically relevant ShhNp multimers, providing new explanations for functional differences observed between ShhN and ShhNp.

Influence of NaOH, HCl, NaCl, and CaCl2 electrolytes on aggregation stability of aqueous craft lignin dispersion according to data of filtration through track membranes

The method of filtration through track membranes with different capillary diameters (50–2500 nm) is used to study the aggregation stability of dilute (10 mg/l) aqueous dispersions of craft lignin in NaCl and CaCl2 solutions (0–10−1 mol/l) at pH 9.5–2.0. It is shown that, in the absence of salts, the isolation of craft lignin on filters increases at decreasing pH, i.e., upon approaching the isoelectric point of craft lignin (pH 2.0). The addition of the salts enhances the efficiency of craft lignin rejection, which is higher in the case of CaCl2. The sizes of craft lignin aggregates in solutions of different compositions are determined from the obtained data.

Salt-mediated self-assembly of thioctic acid on gold nanoparticles.

Self-assembled monolayer (SAM) modification is a widely used method to improve the functionality and stability of bulk and nanoscale materials. For instance, the chemical compatibility and utility of solution-phase nanoparticles are often improved using covalently bound SAMs. Herein, solution-phase gold nanoparticles are modified with thioctic acid SAMs in the presence and absence of salt. Molecular packing density on the nanoparticle surfaces is estimated using X-ray photoelectron spectroscopy and increases by ∼20% when molecular self-assembly occurs in the presence versus the absence of salt. We hypothesize that as the ionic strength of the solution increases, pinhole and collapsed-site defects in the SAM are more easily accessible as the electrostatic interaction energy between adjacent molecules decreases, thereby facilitating the subsequent assembly of additional thioctic acid molecules. Significantly, increased SAM packing densities increase the stability of functionalized gold nanoparticles by a factor of 2 relative to nanoparticles functionalized in the absence of salt. These results are expected to improve the reproducible functionalization of solution-phase nanomaterials for various applications.