Potassium Acetate Buffer Research Articles

Comparison of potassium catalysts on zeolite sodium A and X in transesterification of palm oil and active species specification

Heterogeneous catalysts consisting of potassium supported on zeolites are active for transesterification, but the effect of zeolite properties is not clearly understood. This work compares catalysts containing 12 wt.% potassium on zeolite sodium A and X (12K/NaA and 12K/NaX) in terms of performance and physicochemical properties. Both catalysts were prepared by ultrasound-assisted impregnation with potassium acetate buffer. 12K/NaA is a better catalyst in transesterification of palm oil, giving a higher biodiesel yield than 12K/NaX in the first run (99.1 ± 0.3 % and 77.9 ± 2.2 %, respectively). From characterization by CO2-TPD, XRD, FTIR, XPS, and SEM-EDS, both catalysts have similar basicity but different dispersion of carbonates and interaction on the zeolites. The 12K/NaA has those species on external surfaces and more monodentate carbonate than 12K/NaX. Ion exchange occurs between potassium ions from the precursor and sodium ions from the zeolite. Moreover, 12K/NaA is more stable, providing higher biodiesel yields in the second and third catalytic cycles.

Comparative Properties of K/NaX and K/NaY from Ultrasound-Assisted Impregnation and Performance in Transesterification of Palm Oil.

This work aims to compare physicochemical properties and catalytic performance of potassium supported on zeolite NaX and NaY (K/NaX and K/NaY, respectively) prepared by ultrasound-assisted impregnation from potassium acetate buffer precursor. Calcination converts the potassium precursor to carbonate, which occupies the zeolite cavities and disperses on the external surface. Both calcined samples show a decrease in zeolite phases, BET surface areas, and pore volumes. With the smaller changes, K/NaX is more stable than K/NaY. Moreover, K/NaX has higher basicity than K/NaY and is more active in the decomposition of 2-methylbut-3-yn-2-ol (MBOH), producing dominant products from basic sites. Both K/NaX and K/NaY are active in the transesterification of palm oil, producing more than 94% of the biodiesel yields in the first run. However, the yields drop in the second run because of the leaching of potassium species into glycerol and biodiesel products. The spent K/NaX has a similar phase to the fresh one, whereas the spent K/NaY shows more structure collapse. With better structural stability, less potassium leaching, and less decline in biodiesel yields in the second run, K/NaX is a better catalyst than K/NaY.

Poly[dipotassium [(μ6-2,2',2'',2'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-acetato)-disilver(I)] 5.2-hydrate

The reaction of AgNO3 with the ligand 2,2',2'',2'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-acetic acid in the presence of a potassium acetate buffer lead to the formation of a silver(I)-potassium-organic framework, poly[dipotassium [(μ6-2,2',2'',2'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-acetato)-disilver(I)] 5.2-hydrate], {K2[Ag2(C16H16N2O8S4)]·5.2H2O} n , (I). The asymmetric unit is composed of half a binuclear silver complex located about a center of symmetry, a potassium cation and 2.6 disordered water mol-ecules. The whole binuclear silver complex is generated by inversion symmetry with the pyrazine ring being located about an inversion centre. The ligand coordinates in a bis-tetra-dentate manner. The binuclear silver complex anions are linked via bridging Ag⋯S⋯Ag zigzag bonds, forming a network lying parallel to the bc plane. The networks are linked by Ocarboxyl-ate⋯K +⋯Ocarboxyl-ate bridging bonds to form a framework. The disordered water mol-ecules are present near to the K+ cations.

A new tetra-kis-substituted pyrazine carb-oxy-lic acid, 3,3',3'',3'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-propionic acid: crystal structures of two triclinic polymorphs and of two potassium-organic frameworks.

Two polymorphs of the title tetra-kis-substituted pyrazine carb-oxy-lic acid, 3,3',3'',3'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene))tetra-kis-(sulfanedi-yl]}tetra-propionic acid, C20H28N2O8S4, (H4L1), have been obtained, H4L1_A and H4L1_B. Each structure crystallized with half a mol-ecule in the asymmetric unit of a triclinic P unit cell. The whole mol-ecules are generated by inversion symmetry, with the pyrazine rings being located about inversion centers. The crystals of H4L1_B were of poor quality, but the X-ray diffraction analysis does show the change in conformation of the -CH2-S-CH2-CH2- side chains compared to those in polymorph H4L1_A. In the crystal of H4L1_A, mol-ecules are linked by two pairs of O-H⋯O hydrogen bonds, enclosing R 2 2(8) ring motifs forming layers parallel to plane (100), which are linked by C-H⋯O hydrogen bonds to form a supra-molecular framework. In the crystal of H4L1_B, mol-ecules are also linked by two pairs of O-H⋯O hydrogen bonds enclosing R 2 2(8) ring motifs, however here, chains are formed propagating in the [001] direction and stacking up the a-axis. Reaction of H4L1 with Hg(NO3)2 in the presence of a potassium acetate buffer did not produce the expected binuclear complex, instead crystals of a potassium-organic framework were obtained, poly[(μ-3-{[(3,5,6-tris-{[(2-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazin-2-yl)meth-yl]sulfan-yl}propano-ato)potassium], [K(C20H27N2O8S4)] n (KH3L1). The organic mono-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. A carb-oxy H atom is disordered by symmetry and the charge is compensated for by a potassium ion. A similar reaction with Zn(NO3)2 resulted in the formation of crystals of a dipotassium-organic framework, poly[(μ-3,3'-{[(3,6-bis-{[(2-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazine-2,5-di-yl)bis(methyl-ene)]bis-(sulfanedi-yl)}dipropionato)dipotassium], [K2(C20H26N2O8S4)] n (K2H2L1). Here, the organic di-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. Two symmetry-related acid groups are deprotonated and the charges are compensated for by two potassium ions.

Determination of iodine level in consumer table salt from production to consumption: a cross-sectional study in occupied Palestinian territory

BackgroundIodination of table salt (salt for table use) is one of the best methods to eliminate iodine deficiency disorders (IDDs) and associated thyroid diseases. Iodate and iodide levels in table salt may vary for many reasons. There are no studies of the concentration of iodine in salt packs on the shelf and in use (open packs). This study aimed to quantify iodine in salt from twelve brands on the Palestinian market, either produced locally or imported, and both on the shelf and in use (opened). MethodsSamples of table salt (99) were collected from randomly selected market places and households in eleven governorates of the occupied Palestinian territory. From each household, three samples were collected; the first when the consumer started to use the salt package, the second when the package was half consumed, and the third when the package was almost empty. In addition, 12 salt packages were purchased from a local market, one package for each studied brand. The samples were treated and the absorbance of iodate in the sample was measured using a spectrophotometer at 665·6 nm, based on a previous method. In brief, a specific mass of salt was dissolved, then potassium iodide, hydrochloric acid, methylene blue, and acetate buffer (pH 4) were added. The solution was mixed and diluted. A reference solution using 99% sodium chloride was also created with this method. Finally, the absorbance of iodate was measured, and the iodate concentration obtained by subtracting the absorbance of the sample solution from that of the reference solution. The iodate content was then compared to the content printed on the salt package. Iodine content was also quantified for a number of samples after exposure to oven heat or being boiled or heated in water, as well as after exposure to light or dark. FindingsOf the 99 samples, 23 had lost 61% of their iodine content, 28 had lost 80%, and nine had lost all of their iodine. A little less than half (43 of 93) of the samples followed the Palestinian Standard regarding iodine content (3·5–5·5 mg per 100 g), and 70% (69 of 99) complied with the UNICEF recommendation (1·5 mg per 100 g). Iodine content in a newly opened pack (measured immediately after opening) was different from samples taken when the pack was half full, and when the pack was almost empty (0·023 mg/g, 0·0206 mg/g, and 0·0195 mg/g, respectively). The study also showed that up to 68% of iodine was lost during heating in a water solution, whereas dry heat led to a loss of 26%. Iodine loss was higher in light than in dark storage conditions (its concentration dropped from 48·2 mg/kg to 23·6 mg/kg in the dark, and decreased to 22·2 mg/kg in light). InterpretationA significant proportion of iodine is lost from salt after production and during consumption. There should be more awareness regarding the importance of using iodised salt, and education for consumers about salt storage. The iodine content in salt packages should be monitored by regulatory authorities. FundingNone.

Palladium(II) Incorporation in the All‐Inorganic Cryptand [As4W40O140]28–: Synthesis and Structural Characterization of [Pd2Na2KAs4W40O140(H2O)]21–

The palladium(II)‐containing 40‐tungsto‐4‐arsenate(III) [Pd2Na2KAs4W40O140(H2O)]21– (1a) was synthesized by reaction of PdSO4 with the cryptate heteropolyanion [As4W40O140]28– in potassium acetate buffer. The title compound was characterized by single‐crystal XRD, IR, TGA, and elemental analysis.

Sandwich type organic-inorganic hybrid of 3d–4f heterometallic containing germanotungstates [{Cu2(1,10-phen)2(μ-CH3COO)2}Ln(α-GeW11O39)2]11 −: Syntheses, crystal structures, magnetic and photoluminescence properties

Alkali salts of organic-inorganic hybrid 3d-4f heterometallic containing derivatives of sandwich type germanotungstates: [{Cu2(1,10-phen)2(μ-CH3COO)2}Ln(α-GeW11O39)2]11− [Ln=PrIII (1a), NdIII (2a), SmIII (3a), EuIII (4a), GdIII (5a); 1,10-phen=1.10-phenanthroline] have been prepared in the aqueous potassium acetate buffer (pH4.7) solution. All these compounds were synthesized following by one pot reaction procedure under mild reaction conditions. All compounds were isolated as mixed alkali sodium/potassium salts from the solution and used for further structural characterization by single crystal XRD, powder-XRD, FT-IR, liquid UV/vis, solid state photoluminescence spectroscopy and thermo-gravimetric analysis. FT-IR spectra and powder-XRD pattern suggest that all compounds (1a–5a) are isomorphous. Further single crystal XRD analysis shows that all these compounds exhibit sandwich-type [Ln(α-GeW11O39)2]13− structural feature in the polyoxoanions as the fundamental building block units, and the copper complexes coordinated with 1,10-phen and acetate ligands are coordinated to the terminal oxygen of the polyanion. The compounds 1a, 3a and 4a show good photoluminescence properties at room temperature. The compound 5a shows weak ferromagnetic behavior.

Identification of potassium phase in catalysts supported on zeolite NaX and performance in transesterification of Jatropha seed oil

Zeolite NaX was synthesized by using rice husk silica and used as a catalyst support. It was impregnated with potassium acetate buffer solution to produce xK/NaX where x was potassium loading of 4, 8, 12 and 16wt.%. After calcination the zeolite characteristic in all catalysts were still observed. The surface area and micropore volume decreased with potassium loading indicating that the cavities were occupied. The potassium precursor was mainly converted to carbonate which had strong basicity. As the basicity increased with the potassium loading, the bettter catalytic performance in transesterification of Jatropha seed oil to biodiesel was observed. The best catalyst was 16K/NaX which gave 95.2±0.96% biodiesel yield.

Study of redox behavior of Cu(II) and interaction of Cu(II) with lysine in the aqueous medium using cyclic voltammetry

Potassium chloride (0.1 M) and acetate buffer of different pH are used to study the redox behavior of Cu(II) ions in absence and presence of lysine amino acid. The potential window +1500 mV and -1000 mV was used to study the redox properties at solid glassy carbon electrode. Silver/silver chloride is used as a reference electrode and the counter electrode used is Pt. One pair of cathodic and anodic peaks for the Cu(II)/Cu(0) system is showed in cyclic voltammograms indicating the presence of two-electron transfer. The interaction between metal and ligand is supported by the shift of peak potential and charge transfer rate constant (k s ) values. Concentration effect of Cu(II) ions and solution pH effect on the interaction was also studied. The quasi-reversible process is indicated by a higher value of peak current ratio and peak potential separation (ΔE).

ChemInform Abstract: Syntheses, Crystal Structure, Electrochemistry and Luminescence Properties of Lanthano‐Germanotungstates.

AbstractNa3K10 [La(α‐GeW11O39)2] ·27H2O(I), Na3K10 [Ce(α‐GeW11O39)2] ·28H2O (II) and the acetate‐bridged hybrid dimeric complexes Na6K6 [{Pr(μ‐OAc)GeW11O39(H2O)}2] ·25H2O (III), Na4K8 [{Nd(μ‐OAc)GeW11O39(H2O)}2] ·22H2O (IV), and Na3K9 [{Sm(μ‐OAc)GeW11O39(H2O)}2] ·19H2O (V) are prepared by reacting a trilacunary Na10[GeW9O34] precursor with Ln(NO3)3 (Ln: La, Ce, Pr, Nd, Sm) in a KOAc buffer at pH 4.7 followed by slow solvent evaporation (60 °C, 1 h; yields of 53—59% after 4—5 weeks).

Preparation of resorbable carbonate-substituted hollow hydroxyapatite microspheres and their evaluation in osseous defects in vivo

Hollow hydroxyapatite (HA) microspheres, with a high-surface-area mesoporous shell, can provide a unique bioactive and osteoconductive carrier for proteins to stimulate bone regeneration. However, synthetic HA has a slow resorption rate and a limited ability to remodel into bone. In the present study, hollow HA microspheres with controllable amounts of carbonate substitution (0–12wt.%) were created using a novel glass conversion route and evaluated in vitro and in vivo. Hollow HA microspheres with ~12wt.% of carbonate (designated CHA12) showed a higher surface area (236m2g−1) than conventional hollow HA microspheres (179m2g−1) and a faster degradation rate in a potassium acetate buffer solution. When implanted for 12weeks in rat calvarial defects, the CHA12 and HA microspheres showed a limited capacity to regenerate bone but the CHA12 microspheres resorbed faster than the HA microspheres. Loading the microspheres with bone morphogenetic protein-2 (BMP2) (1μg per defect) stimulated bone regeneration and accelerated resorption of the CHA12 microspheres. At 12weeks, the amount of new bone in the defects implanted with the CHA12 microspheres (73±8%) was significantly higher than the HA microspheres (59±2%) while the amount of residual CHA12 microspheres (7±2% of the total defect area) was significantly lower than the HA microspheres (21±3%). The combination of these carbonate-substituted HA microspheres with clinically safe doses of BMP2 could provide promising implants for healing non-loaded bone defects.

Effect of fluoride-releasing restorative materials on bacteria-induced pH fall at the bacteria–material interface: An in vitro model study

ObjectivesInhibition of bacterial acid production by dental restorative materials is one of the strategies for secondary caries prevention. This study aimed to evaluate the effect of fluoride-releasing restorative materials on bacteria-induced pH fall at the bacteria–material interface. MethodsFour fluoride-releasing restorative materials, glass-ionomer cement (GIC), resin-modified glass-ionomer cement (RMGIC), resin composite (RC) and flowable resin composite (FRC) were used. Each specimen was immersed in potassium phosphate buffer at pH 7.0 for 10min and 4 weeks, and in potassium acetate buffer at pH 5.5 for 4 weeks. An experimental apparatus was made of polymethyl methacrylate and had a well with restorative materials or polymethyl methacrylate (control) at the bottom. The well was packed with cells of Streptococcus mutans, and the pH at the interface between cells and materials was monitored using a miniature pH electrode after the addition of 1% glucose for 90min, and the fluoride released into the well was quantified using a fluoride ion electrode. ResultsThe pH of GIC (4.98–5.18), RMGIC (4.77–4.99), RC (4.62–4.75) and FRC (4.54–4.84) at 90min were higher than that of control (4.31–4.49). The fluoride amounts released from GIC were the highest, followed by RMGIC, RC and FRC, irrespective of immersion conditions. Saliva coating on materials had no significant effect. ConclusionsThe fluoride-releasing restorative materials inhibited pH fall at the bacteria–material interface. The degree of inhibition of pH fall seemed to correspond to the amount of fluoride detected, suggesting that the inhibition was due to the fluoride released from these materials. Clinical significanceA little amount of fluoride actually released from the fluoride-releasing materials may have caries preventive potential for oral bacteria.

The application of differential pulse cathodic stripping voltammetry in the determination of trace copper in whole blood

Electrochemical stripping analysis is a very important and widely used tool for the trace determination of various elements and compounds. The method is based on accumulation of Cu (II) ions onto platinum electrode, followed by the reduction of the species by differential pulse cathodic stripping voltammetry. The effect of various parameters such as pH of supporting electrolyte, accumulation of potential and time, scan rate and speed of rotating electrode on the selectivity and sensitivity were studied. The best conditions were found to be pH = 6.5 potassium acetate buffer, the accumulation potential of 0 mV (vs. Ag/AgCl), the accumulation time of 50 s, rotational speed of the working electrode 1500 rpm and the scan rate of 25 mV s-1. The peak current is proportional to the concentration of copper over the range 0.53-107 ng/mL with a detection limit of 0.159 ng/mL and an accumulation time of 50 s. The developed method was validated by the analysis of reference materials certified by total blood.

Di- and Tri-Cobalt Silicotungstates: Synthesis, Characterization, and Stability Studies

Di- and tricobalt silicotungstate complexes, K(5)Na(4)H(4)[{Na(3)(μ-OH(2))(2)Co(2)(μ-OH)(4)} (Si(2)W(18)O(66))]·37H(2)O (1) and K(6)Na(3)[Na(H(2)O){Co(H(2)O)(3)}(2){Co(H(2)O)(2)}(Si(2)W(18)O(66))]·22H(2)O (2), have been synthesized through reaction of cobalt chloride and [A-α-SiW(9)O(34)](10-) in acidic buffer solution. They have been characterized by X-ray crystallography, elemental analysis, cyclic voltammetry, infrared, and UV-vis spectroscopy. In 1, two cobalt atoms as well as three sodium atoms are incorporated in the central pocket of the [Si(2)W(18)O(66)](16-) polyanion. In 2, one cobalt atom and one sodium atom are incorporated in the pocket of [Si(2)W(18)O(66)](16-); two other cobalt atoms in this complex protrude outside the pocket and connect with WO(6) units of other [Si(2)W(18)O(66)](16-) polyanions to form a one-dimensional polymeric structure. The crucial parameters in the synthesis of these two compounds are discussed, and their stability in different buffer solutions is studied. The decomposition of 1 or 2 in heated potassium acetate buffer (pH 4.8, 1 M) yields K(11)[{Co(2)(H(2)O)(8)}K(Si(2)W(18)O(66))]·17H(2)O (3) based on spectroscopic studies and an X-ray crystal structure.

Enhancing concentration and mass sensitivities for liquid chromatography trace analysis of clopyralid in drinking water

A theoretical treatment was developed and validated that relates analyte concentration and mass sensitivities to injection volume, retention factor, particle diameter, column length, column inner diameter and detection wavelength in liquid chromatography, and sample volume and extracted volume in solid-phase extraction (SPE). The principles were applied to improve sensitivity for trace analysis of clopyralid in drinking water. It was demonstrated that a concentration limit of detection of 0.02 ppb (μg/L) for clopyralid could be achieved with the use of simple UV detection and 100 mL of a spiked drinking water sample. This enabled reliable quantitation of clopyralid at the targeted 0.1 ppb level. Using a buffered solution as the elution solvent (potassium acetate buffer, pH 4.5, containing 10% of methanol) in the SPE procedures was found superior to using 100% methanol, as it provided better extraction recovery (70-90%) and precision (5% for a concentration at 0.1 ppb level). In addition, the eluted sample was in a weaker solvent than the mobile phase, permitting the direct injection of the extracted sample, which enabled a faster cycle time of the overall analysis. Excluding the preparation of calibration standards, the analysis of a single sample, including acidification, extraction, elution and LC run, could be completed in 1 h. The method was used successfully for the determination of clopyralid in over 200 clopyralid monoethanolamine-fortified drinking water samples, which were treated with various water treatment resins.

Inorganic-organic hybrids constructed of bis(undecatungstogermanate)lanthanates polyoxoanions and oxalate-bridged dinuclear copper complexes and their magnetic properties

A series of inorganic-organic hybrids K2Na m H9−m [{Ln(GeW11O39)2}{Cu2(bpy)2(μ-ox)}]·nH2O (bpy = 2,2-bipyridine and ox = oxalate; Ln = La, Nd, Sm, Eu, Gd; n = 19, 17, 22, 20, 19; m = 4, 4, 4, 9, 2) were isolated after reacting in a potassium acetate buffer. X-ray structural analyses show that compounds 1–5 are isomorphic and consist of [Ln(GeW11O39)2]13− polyoxoanion building blocks and oxalate-bridged dinuclear copper metalorganic complex with a 1D chain structure. The 1D chain further connects into the 3D framework by π-π interactions with neighboring bpy groups. The magnetic susceptibility data indicate that antiferromagnetic coupling between the neighboring Cu2+ ions in the structure and the rare earth ions affects magnetic property of the structure.

PH buffer assessment and Pitzer’s equations

Traceable measurement of the quantity pH in media outside the limits of the recent IUPAC recommendation requires an alternative to the Bates–Guggenheim convention. The Pitzer’s approach to ion interactions is widely appraised and offers a suitable approach to the estimation of single-ion activity coefficients. For this purpose, the underlying electrolyte data need to be consistent and the uncertainty in existing Pitzer’s data needs to be assessed. Such an assessment is attempted in this study for pH in potassium acetate buffer medium. The re-evaluation of Pitzer’s data from potassium nitrate data revealed inconsistencies and wide uncertainty margins. The uncertainty contribution from binary Pitzer’s parameters to an assessment of pH in seawater resulted in an uncertainty in pH of about 0.03 (95% confidence interval). This contribution has to be taken into account in the overall uncertainty budget. Lack of appropriate data for other pH buffer systems (e.g., phosphate buffers) is noted.

An Acetate‐Functionalized Tetranuclear Zirconium Sandwiching Polyoxometalate Complex

AbstractThe dimeric, zirconium‐sandwiching compound K4H6[Zr4(OH)6(CH3COO)2(α‐PW10O37)2]·23H2O (1) was obtained by the reaction of lacunary [PW11O39]7– and ZrCl4 in a 1 M potassium acetate buffer. It was characterized by elemental and thermogravimetric analysis, X‐ray crystallography, solution 183W NMR, FTIR, and UV spectroscopy, and cyclic voltammetry (CV). All the studies indicate that compound 1 is stable both in the solid state and in solution. The cyclic voltammograms indicate good electrocatalytic activity in the reduction of nitrite.

Mechanistic aspects of the Fenton reaction under conditions approximated to the extracellular fluid

The Fenton reaction was investigated, in a medium approximating to that of the extracellular fluid (ECF), by rapid-mixing stopped flow experiments and HPLC analysis using sodium terephthalate (TA 2−). The reactive intermediate of the Fenton reaction hydroxylates the essentially nonfluorescent, TA 2− to the brilliant fluorophor 2-hydroxy-terephthalate (OH-TA), which allows the Fenton reaction to be monitored in stopped-flow experiments. There was no artefactual quenching of the fluorescence by substances present in the Fenton-reaction mixture or in the artificial cerebrospinal fluid (aCSF) that might have influenced OH-TA quantification. A mathematical model based on kinetic considerations was developed. This explains the observed independence of the OH-TA concentration on the amount of TA 2− present in aCSF as well as its dependence on TA 2− concentration in potassium acetate buffer. A mechanism based on this model, involving complex formation between Fe(II), TA 2− and H 2O 2, followed by an intra-molecular hydroxylation accompanied by an intra-molecular electron transfer was developed. The results are consistent with a reactive intermediate, which causes oxidative stress in vivo, not being a free hydroxyl radical, but a ferryl species or a “crypto” radical. The biological implications of these results are discussed.

Synthesis and Structure of Asymmetric Zirconium‐Substituted Silicotungstates, [Zr6O2(OH)4(H2O)3 (β‐SiW10O37)3]14‐ and [Zr4O2(OH)2(H2O)4 (β‐SiW10O37)2]10‐.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.