Carboxylic Acid Sodium Research Articles

Synthesis of 1,4‐Dicarbonyl Compounds via Visible‐Light‐Induced Decarboxylative Radical Cascade Reactions

AbstractWe herein report a method for the synthesis of 1,4‐dicarbonyl compounds using light‐activated electron donor‐acceptor (EDA) complexes. This multi‐component reaction involves the photoactivation of EDA complexes formed by carboxylic acid derivatives, triphenylphosphine, and sodium iodide, resulting in single‐electron reduction. The subsequent decarboxylation fragmentation leads to the formation of nucleophilic alkyl free radicals, which can undergo sequential radical coupling reactions with electron‐deficient and electron‐rich olefins. This method has been successfully applied to various aliphatic carboxylic acid derivatives, including tertiary, secondary, and primary ones, as well as multiple types of electron‐deficient olefins and enol silyl ethers. The entire process is conducted under mild conditions, indicating its potential for the synthesis of valuable synthetic compounds.

Development of water-soluble phenazine-2,3-diol-based photosensitizers for singlet oxygen generation.

Phenazine-2,3-diol-based dyes, KY-1Na and KY-2Na bearing one and two carboxylic acid sodium salts, respectively, have been newly developed as water-soluble photosensitizers (PSs) possessing the ability to generate singlet oxygen (1O2). In order to evaluate the solubility of KY-1Na and KY-2Na in water, the hydrophobicity/hydrophilicity of the two PSs was investigated by experimental measurement of the logarithms (log Po/w) of the 1-octanol/water partition coefficient (Po/w) for the PS. The log Po/w values of both KY-1Na and KY-2Na were determined to be -0.9, indicating that both the PSs are more hydrophilic than Rose Bengal (-0.6) and have hydrophilicity equivalent to methylene blue (-0.9). Both the PSs in water show a broad photoabsorption band in the range of 500 to 600 nm. Thus, we estimated the 1O2 quantum yields (ΦΔ) of KY-1Na and KY-2Na in water by using 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) as a water-soluble 1O2 scavenger. It was found that in water the ΦΔ value (0.19) of KY-2Na is higher than that of KY-1Na (0.06). Density functional theory (DFT) calculations suggested that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions for the molecular structure of KY-2Na are adequately separated, leading to a decrease in the energy gap (ΔEST) between the singlet state (S1) and the triplet state (T1) that causes efficient intersystem crossing (ISC), compared to that for the molecular structure of KY-1Na. Indeed, time-dependent DFT (TD-DFT) calculations demonstrated that the ΔEST(S1-T1) value (0.82 eV) of KY-2Na is smaller than that (0.98 eV) of KY-1Na, resulting in a relatively high ΦΔ value of KY-2Na. Consequently, we demonstrate that phenazine-2,3-diol-based PSs bearing carboxylic acid salts possess high solubility and moderate 1O2 generation ability in water.

COFs-based electrolyte accelerates the Na+ diffusion and restrains dendrite growth in quasi-solid-state organic batteries

Solid-state sodium-ion batteries exhibit a great promising opportunity for the future energy storage, and thus exploring a high-efficiency sodium-ion conductor is the urgent challenge. Covalent organic frameworks (COFs) have accurately directional and well-defined ion channels and are a promising and optimal platform for solid-state Na-ion conductor. In this work, we study the first example of carboxylic acid sodium functionalized polyarylether linked COF (denoted as NaOOC-COF) as an advanced Na-ion quasi-solid-state conductor film. Benefiting from the well-defined ion channels, the functionalized NaOOC-COF exhibits an outstanding Na+ conductivity of 2.68 × 10−4 S cm−1 at room temperature, low activation energy (Ea) with 0.24 eV and high transference number of 0.9. Particularly, the NaOOC-COF shows long-time cycling performance in the assembled quasi-solid-state battery, and can restrain dendrite growth through interface regulation. Furthermore, the Na+ diffusion mechanism in whole-cell system is investigated thoroughly. Such extraordinary Na-ion transport result based on COFs is achieved for the first time. This novel strategy may exploit the new area of Na-ion quasi-solid-state electrolytic devices, and simultaneously accelerate the progress of functionalized COFs.

Optimizing nanoscale morphology and improving carrier transport of PCDTBT-PCBM bulk heterojunction by cyclic carboxylate nucleating agents

Abstract In this work, four cyclic carboxylate commercial nucleating agents, bicyclo [2.2.1] heptane-2,3-dicarboxylic acid disodium salt (HPN-68L), sodium salt of hexahydrophthalic acid (HHPA-Na), sodium benzoate (Be-Na) and calcium salt of hexahydrophthalic acid (HPN-20E) were respectively added into poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′ benzothiadi-azole)] (PCDTBT)-[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend. Atomic force microscopy (AFM) and UV–vis measurements indicate that the addition of carboxylic acid sodium salts can effectively optimize the morphology of active layer, decrease the phase domain size and increase the optical absorption intensity of PCDTBT-PCBM blends. The PCDTBT-PCBM-additive ternary devices were fabricated and found that adding carboxylic acid sodium salts can improve the hole mobility, balance the hole and electron mobility and finally increase the power conversion efficiency (PCE). Fixed the additive content as 5%, the modulation ability of the bicyclic dicarboxylic acid sodium salt HPN-68L is best, monocyclic dicarboxylic acid sodium salt HHPA-Na comes second, monocyclic carboxylic acid sodium salt Be-Na is worst. The addition of carboxylic acid calcium salt HPN-20E has no effects on the morphology and optical absorption intensity of the PCDTBT-PCBM blend, and the photoelectric properties of PCDTBT-PCBM-HPN-20E ternary device decreases in comparison with those of pristine PCDTBT-PCBM binary device. The modulation ability of cyclic carboxylate is related to its surface free energy and its location in the PCDTBT-PCBM blend. HPN-68L locates in the interfacial region between PCDTBT and PCBM, other cyclic carboxylates locates in the PCBM. Our finding suggests the addition of cyclic carboxylic acid sodium salts can be a facile approach to optimize the morphology and increase the electrical properties of organic materials for future development of organic photovoltaic devices.

Rheological and thermo-responsive characteristics of the mixed aqueous solution of gemini cationic surfactant and hydroxyl naphthalene carboxylic acid sodium

ABSTRACTThe new thermo-switchable wormlike micellar systems were developed by mixing the gemini cationic surfactant, 2-hydroxypropyl-1,3-bis (dimethylmyristylammonium chloride) (14-3(OH)-14(2Cl) and sodium 1-hydroxynaphthalene-2-carboxylate (1SHNC) and sodium 2-hydroxynaphthalene- 3-carboxylate (2SHNC) in a certain concentration range. Their viscoelastic and thermos-responsive behaviors as a function of the salts concentration or temperature were investigated via rheological and cryo-TEM investigations. The results demonstrated that the zero-shear viscosity (η0) significantly increased while raising salt concentrations above a threshold concentration (CS*) until reaching maximum and then decreased. For the mixed solutions before the maximum, the zero-shear viscosity linearly decreased with increasing temperature and conformed to the Arrhenius law. However, for those mixed systems displaying thermo-responsive characteristic after the summit, the curve of η0 as a function of temperature exhibited a maximum over the whole temperature range, namely, the systems showed thermo-thickening and thermo-thinning behaviors at low and high temperatures. The abovementioned phenomena were explained by the formation of hydrogen bond in 14-3(OH)-14(2Cl) molecules and the different solubility of SHNC under different temperatures, and the transition mechanisms of the aggregates were analyzed accordingly.

Temperature-dependent hygroscopic behaviors of atmospherically relevant water-soluble carboxylic acid salts studied by ATR-FTIR spectroscopy

Model of aerosols and cloud formation processes requires extensive data on hygroscopic properties of water soluble organic species at lower troposphere relevant temperatures, which are ubiquitously found in atmospheric aerosols. Recent field studies (Kerminen et al., 1998) have revealed that sea salt aerosols can be efficiently chemically processed by water soluble carboxylic acids and lead to chloride depletion and formation of carboxylic acid salts. In this study, we report hygroscopic properties of four carboxylic acid salts, namely, sodium formate, sodium acetate, sodium oxalate and sodium succinate at temperatures commonly encountered in the lower troposphere ranging from 295.8 K to 270.0 K for the first time via attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of these carboxylic salts as a function of temperature were derived using both changes in water-to-solute (WSR) data and changes in band positions and shapes of carboxylate asymmetric and symmetric stretch modes. Hygroscopic data were also fitted by polynomial and corresponding coefficients were obtained. Our results have shown that these carboxylic acid salts exhibit strong temperature dependence and they would deliquesce at a lower humidity and are more likely to remain deliquesced when they are elevated in the troposphere. Since all these carboxylic acid salts present very different hygroscopic behaviors at lower temperatures from that of NaCl, chemically processed sea salt aerosols by carboxylic acids are expected to have fairly different phase state, size, and water content, consequently affecting their reactivity, lifetime, and ability to serve as cloud condensation nuclei.

Aggregation of Oligomeric Surfactant Constructed by Four-Armed Carboxylic Acid Sodium and Cationic Surfactant.

A star-shaped oligomeric-like surfactant with variable oligomeric degrees has been formed with a four-arm carboxylate salt (4EOCOONa) and cationic single chain surfactant dodecyl trimethylammonium bromide (DTAB). The aggregation of the 4EOCOONa/(DTAB)n complexes has been investigated by surface tension, electrical conductivity, isothermal titration microcalorimetry, ζ potential, dynamic light scattering, 1H NMR spectroscopy, and steady-state fluorescence measurements. The calorimetric result shows that 4EOCOONa interacts strongly with DTAB and each 4EOCOONa molecule binds with six DTAB molecules, wherein four DTAB molecules electrostatically bind to one 4EOCOONa molecule and additional two DTAB molecules further bind to the 4EOCOONa/(DTAB)n complex by hydrophobic interaction. The critical micelle concentration (CMC) of the 4EOCOONa/(DTAB)n complexes is remarkably lower than the CMC of DTAB, similar to synthesized star-shaped oligomeric surfactants. The micelle properties of the DTAB/4EOCOONa mixtures depend on the component changes of the 4EOCOONa/(DTAB)n complexes. By increasing the DTAB/4EOCOONa molar ratio and/or concentration, the DTAB/4EOCOONa mixtures gradually form the complexes of 4EOCOO(DTA)13-, 4EOCOO(DTA)22-, 4EOCOO(DTA)3-, 4EOCOO(DTA)4, and 4EOCOO(DTA)62+, and the corresponding aggregates are small anionic micelles with loose molecular packing, and nearly nonionic or positively charged small micelles with more compact packing. Moreover, the positive charge of the small micelles increases with the increase of the concentration and the DTAB/4EOCOONa molar ratio. Therefore, constructing oligomeric-like surfactants by adding appropriate organic salts into conventional surfactants is a convenient method to achieve desired properties of surfactant aggregates.

Simply incorporating an efficient redox additive into KOH electrolyte for largely improving electrochemical performances

In this work, a novel redox additive of calcon carboxylic acid sodium salt (abbr. CS) has been implemented for the first time in KOH electrolyte for largely improving the electrochemical performance of a supercapacitor. By directly carbonizing potassium citrate monohydrate at 800°C, giving rise to the Carbon-800 sample, and the resulting specific capacitance can reach up to 128.4Fg−1 at 3Ag−1 when measured in a three-electrode system with the conventional 6molL−1 KOH electrolyte. To further elevate these capacitances, certain amount of CS as a redox additive is introduced into KOH electrolyte. Remarkably, the Carbon-800-15 sample by adding CS 15mmolL−1 into 6molL−1 KOH electrolyte displays a highly improved specific capacitance of 237.0Fg−1 at 3Ag−1 in a three-electrode system, which is almost the 2.1 times than that of the pristine one. In addition, the Carbon-800-15 sample also possesses an elevated energy density of 11.4Whkg−1 at the power density of 1.5kWkg−1 when measured in a two-electrode system, much larger than the 7.3Whkg−1 of the Carbon-800 sample. The improved performance incurred by CS additive is attributed to the fast redox reactions at the electrolyte/electrode interface. Apparently, the present efficient and low-cost redox additive of CS is expected to be implemented for largely improving the performances of a supercapacitor.

Donor-acceptor star-shaped conjugated macroelectrolytes: synthesis, light-harvesting properties, and self-assembly-induced Förster resonance energy transfer.

A novel series of donor-acceptor star-shaped conjugated macroelectrolytes (CMEs), denoted as 4FTs, including anionic carboxylic acid sodium groups (4FNaT), neutral diethanolamine groups (4FNOHT), and cationic ammonium groups (4FNBrT), were designed, synthesized, and explored as an excellent platform to investigate the impact of various polar pendent groups on self-assembly behaviors. The resulting CMEs with donor-acceptor star-shaped architectures exhibited distinct light-harvesting properties. The interactions between 4FTs and TrNBr, a star-shaped monodisperse CME grafted with cationic quaternary ammonium side chains, were investigated in H2O and CH3OH using steady-state, time-resolved fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Highly favored energy transfer has been proven by the excellent spectral overlap between TrNBr fluorescence and 4FTs absorptions which can be tuned by adjusting the pendent polar groups and solvents. It is suggested that self-assembled structures are formed between TrNBr and 4FNaT, while there is no obvious change for TrNBr/4FNOHT and TrNBr/4FNBrT in both H2O and CH3OH at low concentrations (<10(-6) M). This result is confirmed by the change of the TrNBr and 4FTs fluorescence properties and the time-resolved fluorescence data. The overall results manifest that at low concentrations the self-assembly between TrNBr and 4FTs is dominated by the electrostatic interactions. This study suggests that the functionalization of pendent polar groups of star-shaped CMEs has proven to be effective to modulate the self-assembly behaviors in dilute solutions and thus provide a strategy to further manage the optoelectronic properties.

Data in support of dual-functionalized cellulose nanofibrils prepared through TEMPO-mediated oxidation and surface-initiated ATRP

We previously studied a suitably 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) that can be further functionalized with initiating sites and overcame the obstacle of performing atom transfer radical polymerization (ATRP) in the presence of neutral carboxylic acid sodium salt groups [1]. Herein, characterization of the modified TOCNs and of the products from surface-initiated (SI) ATRP of the (nano)celluloses with styrene (St) was performed using nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and contact angle (CA) measurements. From the analysis of 1H NMR, a high purity of sacrificial initiator (i.e., 2-hydroxyethyl 2-bromoisobutyrate (HEBiB)) was confirmed. HEBiB was utilized to trace the SI ATRP with the generated free PSt. Gradually molecular weight evaluations were revealed from GPC analysis (ca. Mn=21,000 and Đ=1.10) using different TOCNs, implying the insignificant contribution to the kinetics from the grafted initiating sites. The TOCN-g-PSts were further characterized by contact angles and displayed an obvious reversibility between hydrophilicity and hydrophobicity in tens of minutes. These results illustrated a simple and facile approach for controlling the graft length and composition of TOCNs through SI ATRP.

Dual-functionalized cellulose nanofibrils prepared through TEMPO-mediated oxidation and surface-initiated ATRP

Although several analogues of cellulose nanofibres displaying unprecedented physical properties have been developed recently (e.g., fibrillated cellulose nanofibrils; cellulose nanocrystals; bacterial nanocellulose; 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)–oxidized cellulose nanofibrils (TOCNs)), only a few reports have described using these cellulose nanofibrils for advances in macromolecular engineering with the powerful tool of surface-initiated atom transfer radical polymerization (SI ATRP). In this paper, we describe the first example of a suitably oxidized TOCN that can be further functionalized with initiating sites at the residual primary OH groups and overcome the obstacle of performing ATRP in the presence of neutral carboxylic acid sodium salt groups. Characterization of the modified TOCNs and of the products from SI ATRP of the (nano)celluloses was performed using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, viscometry, scanning electron microscopy, electron spectroscopy for chemical analysis, X-ray diffraction, contact angle measurements, and thermogravimetric analysis. We demonstrate, through SI ATRP from the TOCN using a vinyl monomer (i.e., styrene), a simple and facile approach for controlling the graft length and composition. We then investigated the efficacy of using the dual-functionalized TOCN nanomaterials to remove a commonly persistent organic pollutant and heavy metal ions from water.

Structure–activity relationship and mechanisms of reagents used in scheelite flotation

Effects of carboxylic acid collector, benzohydroxamic acid (BHA), sodium hexametaphosphate (SHAP), sodium silicate, and oxalic acid on scheelite flotation were studied through flotation tests, quantum chemical calculation, and flotation solution computational chemistry. In terms of the calculation results, the relationship between chemical reactions occurring on the scheelite surface and molecular structures of the reagents were analyzed. The results show that BHA and carboxylic acid collectors interact with scheelite in different forms and the recovery of scheelite using sodium oleate as collector declines successively from SHAP, sodium silicate, to oxalic acid. Moreover, it is found that the performance of depressant in scheelite flotation is directly related to the group electronegativity, indicating that the latter is a dominant factor that determines the former. These findings will be helpful to the academic research communities of scheelite flotation.

High-temperature alkaline stability of cement set retarders and their performance at 70–90°C

Hydroxycarboxylic acid salt (sodium gluconate), sodium lignosulfonate and a combination of carboxylic acid and sulfonate-type retarder (poly(4-styrenesulfonic acid-co-maleic acid) sodium salt) are typical set retarders for oil-well cement. The potential high-temperature alkali degradation of these retarders is assessed, and its role in altering the kinetics of cement hydration at temperatures between 70 and 90°C. The high-temperature alkaline stability of cement set retarders is poorly studied. However, it may represent one way to understand the delay in hydration induced by such additives, and the discontinuity of cement hydration, with the longer setting times at higher temperatures in that range. Degradation products are identified and their thermal stability is evaluated. Retarders containing carboxylic acid become partially fragmented at high pH and 90°C. The effect on cement setting kinetics is similar for hydrolysed retarders containing carboxylic acid groups: the setting times are longer at 80°C than at 70 and 90°C. The sulfonate groups of lignosulfonate-type retarder, treated at pH 13·4, 90°C, are partially converted to sulfate and the ether groups to alkoxides. The setting time changes linearly with temperature for the high-pH-treated lignosulfonate retarder in the studied temperature range.

Development of Concrete Construction Technology in Winter

Nearly twenty years, freezing damage prevention of concrete construction in winter, construction methods of generalized integrated heat storage, the third generation of water-reducing agent (Poly carboxylic acid sodium), the theory of critical maturation degree, composite antifreeze, the key and matching technology of concrete construction under negative temperature and so on are all emerging constantly. Development progress of winter construction technology is promoted. All kinds of technology and economic about construction methods in winter are compared in this paper. The selection basis of concrete construction methods in winter is provided for different conditions.

Initiation efficiency and cytotoxicity of novel water-soluble two-photon photoinitiators for direct 3D microfabrication of hydrogels

The lack of efficient water-soluble two-photon absorption (TPA) photoinitiators has been a critical obstruction for three dimensional hydrogel microfabrications with high water load by two-photon induced polymerization (TPIP). In this paper, a series of cyclic benzylidene ketone-based two-photon initiators, containing carboxylic acid sodium salts to improve water solubility, were synthesized via classical aldol condensation reactions. The cytotoxicity of cyclopentanone-based photoinitiators is as low as that of the well-known biocompatible photoinitiator Irgacure 2959 as assessed in the dark with MG63 cell line. In z-scan measurement, the TPA cross sections of the investigated initiators are only moderate in water, while the TPA values for hydrophobic analogues measured in chloroform were much higher. All novel initiators exhibited broad processing windows in TPIP tests using hydrophilic photopolymers with up to 50 wt% of water. Impressively, microfabrication of hydrogels with excellent precision was possible at a writing speed as high as 100 mm s−1.

Relationship between Exothermic Effect and Crystal Growth in the Hydration Process of Waterproof Gypsum

The new type of gypsum compound waterproof agent was composed of organic emulsion that emulsified by polyvinyl alcohol and stearic acid and saline waterproof agent made of carboxylic acid sodium, aluminium sulfate etc. The influences on the hydration exothermic effect and crystal growth of gypsum were studied when different amount of the organic emulsion, the saline waterproof agent were added. According to the hydration exothermic effect and microstructure of crystal growth of gypsum after mixing the different amount of waterproof agent, the relationship between gypsum hydration exothermic effect and gypsum crystal growth were discussed theoretically.

Research on Hydration of Waterproof-Typed Semi-Hydrated Gypsum

The influences of saline waterproof agent composed of carboxylic acid sodium (RCOONa), Al2(SO4)3,K2SO4 on the hydration of semi-hydrated gypsum were investigated. The results showed: (1) with the concentration of K2SO4 increasing, the ζ potential rose due to the increasing K+ entering the electric double layer of gypsum; (2) with the concentration of Al2(SO4)3 heightening, the ζ potential gradually decreased as a result of the formed AFt phase during the hydration process and the increasing Al3+ entering the electric double layer of gypsum. The ζ potential rose because the RCOO-base groups adhered to the surface of gypsum crystal, which slowed down the growth rate of the gypsum crystal in direction c, and short hexahedron poles were produced.

A novel cell support membrane for skin tissue engineering: Gelatin film cross-linked with 2-chloro-1-methylpyridinium iodide

A novel method for preparing cell support membrane which employs heterogeneously cross-linking (CR) process to prepare water-insoluble gelatin (GEL) films was suggested, and compared with 1-ethyl-(3,3-dimethylaminopropyl)carbodiimide. In this study, we found that 2-chloro-1-methylpyridinium iodide (CMPI) is an effective zero-length cross-linker of gelatin, and showed a superior activation ability of carboxylic acid sodium salt under heterogeneous reaction. The CMPI-CR-GEL films showed high water uptake ability, reasonable biodegradability, and excellent cytocompatibility. In vitro studies with 3T3 fibroblasts demonstrated an increased cell viability for those cells grown on CMPI-CR-GEL membranes, and significantly increased cell numbers from Day 1–12. Furthermore, under heterogeneous process, the gelatin film can fabricate in advance, and maintained the original dimension, thickness, and shape after cross-link. Meanwhile, the reaction residues can be easy removed by rinsing and washing processes. These characteristics make the process easily transfer to industrial manufacturing in the future.

金属ストロンチウムを用いる新しい合成手法の開発

We found the interesting results that alkylation of carboxylic acids with methyl iodide using strontium metal proceeded smoothly to afford the corresponding monomethylated ketones, rather than the dimethylated alcohols, preferentially in moderate to good yields. Using the carboxylic acid sodium salt, the yield decreases slightly, but the reaction controls the over–addition of methyla-ting agent to give the dramatically improvement with high selectivities. Next, when benzoic acid reacted with metallic strontium and alkyl iodides, the unexpected reactions occurred to give p–alkylated products of the aromatic ring of benzoic acid in a trace amount. We were interested in the p–allylated product because this allylation reaction is unusual in these conditions and there are only a few reports of the p–alkylation of aromatic carbonyl compounds. As the results of various investigations, the p–alkylated products were obtained predominantly in good yields. Furthermore, it was found that the convenient bulky tert–benzylic alcohol benzoates were prepared by the dialkylation of methyl benzoate with methyl or i–butyl iodide in the presence of metallic strontium, followed by the addition of benzoyl chloride, benzoic anhydride or acetic anhydride as two portions.

Effects of carboxylic acids on nC 60 aggregate formation

The discovery that negatively charged aggregates of C 60 fullerene ( nC 60) are stable in water has raised concerns regarding the potential environmental and health effects of these aggregates. In this work, we show that nC 60 aggregates produced by extended mixing in the presence of environmentally relevant carboxylic acids (acetic acid, tartaric acid, citric acid) have surface charge and morphologic properties that differ from those produced by extended mixing in water alone. In general, aggregates formed in the presence of these acids have a more negative surface charge and are more homogeneous than those produced in water alone. Carboxylic acid identity, solution pH, and sodium ion concentration, which are all intricately coupled, play an important role in setting the measured surface charge. Comparisons between particle sizes determined by analysis of TEM images and those obtained by dynamic light scattering (DLS) indicate that DLS results require careful evaluation when used to describe nC 60 aggregates.