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At least 991 records · Page 55Linked to original sources

PubMed1994

A meta-analysis of the therapeutic role of oil soluble contrast media at hysterosalpingography: a surprising result?

OBJECTIVE: To evaluate the therapeutic effect of oil-soluble contrast media compared with water-soluble contrast media after hysterosalpingography (HSG) in infertile couples. DESIGN: Meta-analysis of four randomized clinical trials (RCTs) and six nonrandomized controlled studies evaluating pregnancy rates after the use of oil- or water-soluble contrast media during HSG. SETTING: Institute of Epidemiology and Health Services Research, Leeds, United Kingdom. PATIENTS: Four identified RCTs studied 800 patients and six nonrandomized studies comprised an additional 1,806 patients, all experiencing primary or secondary infertility. INTERVENTION: Hysterosalpingography as part of infertility investigation. MAIN OUTCOME MEASURE: Pregnancy rates after HSG. RESULTS: Pregnancy rates were significantly higher in the oil-soluble contrast media group compared with the water-soluble contrast media group in the RCTs. Inclusion of the six nonrandomized studies did not alter this conclusion. This apparent benefit was greatest for patients with unexplained infertility. CONCLUSIONS: Oil-soluble contrast media have a therapeutic effect compared with water-soluble media and this effect is greatest for patients who have been diagnosed as having unexplained infertility. New techniques for the evaluation of tubal patency support the hypothesis that tubal "plugs" may be involved in proximal tubal blockage.

Clinical Trials as Topic↗

PubMed1996

Evaluation of a soluble E-selectin enzyme-linked immunosorbent assay under posttraumatic conditions.

The up-regulation of E-selectin, one of the adhesion molecules on the endothelium, is an important event in the mediation of the inflammatory response. Because the presence of E-selectin cannot be determined directly in vivo except by invasive biopsy techniques, the only available information concerning its activity is the serum level of the soluble form. Therefore we tried to measure soluble E-selectin levels in trauma and sepsis situations, where endothelial activation is supposed to occur. We have investigated the soluble E-selectin levels in a group of patients undergoing the trauma associated with cardiac surgery and the use of extracorporeal circulation, some of whom developed a systemic inflammatory response syndrome (SIRS). We have also confirmed that our enzyme-linked immunosorbent assay (ELISA) will detect the levels of soluble E-selectin that are produced as a result of the exposure of cultured human umbilical endothelial cells to even low levels of endotoxin. The data presented in this paper indicate that in patients with SIRS after extracorporeal circulation, the levels of circulating soluble E-selectin are numerically higher but---at least in this group of patients---not statistically significantly different from the levels in patients who have undergone the surgery. These results suggest that the measurement of serum levels of soluble E-selectin is not a reliable method for monitoring the onset of SIRS in patients having undergone surgical trauma, although we have confirmed that our ELISA will detect the levels of soluble E-selectin that are produced as a result of the exposure of cultured human endothelial cells to even low levels of endotoxin.

Adult↗

PubMed2002

Evaluation of a rapid physical-chemical method for the determination of extant soluble COD.

Characterization of total chemical oxygen demand (COD) in wastewater is critical for accurate modeling of constituent biotransformation steps. We evaluated the accuracy and precision of a commonly used soluble COD determination technique (coagulation using ZnSO4 at pH 10.5) in relation to three other physical-chemical separation techniques: destabilization with a non-hydrolyzing trivalent cation (LaCl3), sequential filtration, and ultracentrifugation. Samples of deionized water and domestic wastewater were spiked with aliquots of synthetic soluble COD and recoveries using the different separation methods were compared. Although mechanisms of coagulation using LaCl3 and ZnSO4 are different, the mean COD recoveries using these methods were in close agreement. Further, sorption of soluble COD onto zinc hydroxide precipitate flocs appeared to be negligible. The two coagulation methods yielded statistically different (p = 0.05) soluble COD values when applied to nine independent wastewater samples (obtained on nine different days). but the difference was less than 10%. The COD quantified by the coagulation techniques corresponded most closely with the < 1,000 Da molecular weight fraction defined as "truly soluble COD". Centrifugation of wastewater samples amended with mercuric chloride (HgCl2) at 10 mg/L overestimated the soluble COD concentration. Our results confirm that coagulation using either ZnSO4 or LaCI3 is appropriate for the rapid determination of soluble COD fraction in wastewater matrices.

Biotransformation↗

PubMed2002

Aqueous solubilities of non-ortho and mono-ortho PCBs at four temperatures.

The temperature-dependent aqueous solubilities of 12 non-ortho and mono-ortho coplanar PCBs (IUPAC Nos. 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, and 189) were determined at 5 degrees C, 15 degrees C, 25 degrees C, and 35 degrees C. A generator-column/extractor-column technique was used, followed by off-line GC/ECD analysis. The relative standard deviations for the measurements were < or = 7.4%. The determined solubilities increase exponentially with temperature from 5 degrees C to 35 degrees C for all 12 tested PCBs, and their enthalpies of solution were determined to range from 22.3 to 45.0 kJ/mol. The determined solubilities of PCB 77 at 25 degrees C were further compared with the results reported previously and with the calculated data. Within homolog groups, congeners with more ortho-substitution generally have greater aqueous solubilities. The measured aqueous solubilities of 58 congeners compiled from the literature and from this study were used for evaluation of quantitative structure-property relationships relating chlorine substitution pattern to the aqueous solubilities. A useful equation by which to estimate aqueous solubilities was derived on the basis of multi-regression analysis, which employs easily calculable molecular descriptors. The validity of this equation is demonstrated by comparison of the estimated values with experimental values. This newly developed model agrees well with log K(ow)-based model predictions.

Environmental Pollutants↗

PubMed1998

Increased levels of soluble forms of adhesion molecules in Takayasu arteritis.

The present series of experiments were designed to determine if soluble forms of vascular cell adhesion molecule-1 and inter cellular adhesion molecule-1 are elevated in the setting of Takayasu arteritis. Plasma levels of these soluble adhesion molecules were measured by enzyme-linked immunosorbent assay in 73 Takayasu arteritis and 36 age-matched normal controls and examined with respect to the age of patients. Soluble vascular cell adhesion molecule-1 levels were significantly higher in Takayasu arteritis (mean 871.4 ng/ml, P<0.01) compared with controls (mean 607.9 ng/ml). No difference was found in soluble inter cellular adhesion molecule-1 levels between these two groups. Comparison of soluble vascular cell adhesion molecule-1 and inter cellular adhesion molecule-1 in these patients subdivided by age into three groups indicated significantly higher levels of these molecules in individuals over 50 years old compared to those under 39 years old (P<0.05). These data suggest that the measurement of soluble vascular cell adhesion molecule-1 may be clinically important in Takayasu arteritis. The correlation of soluble vascular cell adhesion molecule-1 and inter cellular adhesion molecule-1 levels with age may indicate some relationship with progression of this disease.

Adolescent↗

PubMed2001

Comparison of soluble and immobilized acetate for removing Pb from contaminated soil.

Five lead (Pb) contaminated soils were used in a laboratory and modeling study to examine the effects of soluble and immobilized acetate on Pb removal from a contaminated soil as a function of pH. Soluble acetate was added as sodium acetate; immobilized acetate was added in the form of a cation exchange resin. For comparative purposes, Pb adsorption with no acetate also was measured as a function of pH. A surface complexation modeling framework was used to interpret experimental data. Experimental results showed the cation exchange resin was much more effective than soluble acetate in removing Pb from soils due to a strong affinity of the resin for Pb. In addition, concentrations of soluble Pb in resin/soil slurry were very low, minimizing the pollution threat if discharged. As deduced from modeling studies, soluble acetate performed poorly compared to the resin, in part, due to adsorption of the soluble PbAc(+) complex. The effectiveness of both soluble and immobilized acetate was diminished below pH 4 as a result of competition by H(+) for acetate. Modeling results based on resin affinity for Pb compare well with experimental data for resin/soil mixtures, suggesting that Pb partitioning in resin/soil mixtures may be predicted reasonably well if soil/Pb and resin/Pb partitioning are known. Thus, the modeling approach may be used as a screening tool to determine the performance of alternative resins.

Acetates↗

PubMed2002

Activation and up-regulation of spinal cord nitric oxide receptor, soluble guanylate cyclase, after formalin injection into the rat hind paw.

Nitric oxide synthase is expressed abundantly in the spinal cord, and nitric oxide (NO) has been shown to play important roles in the central mechanism of inflammatory hyperalgesia. However, the expression and function of the NO receptor, soluble guanylate cyclase, is not fully understood in this processing at the spinal cord level. In the present study, we report that the soluble guanylate cyclase alpha(1) subunit but not the beta(1) subunit was expressed in rat spinal cord, particularly in the dorsal horn. We showed that intrathecal administration of a selective inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, produced a significant anti-nociception demonstrated by the decrease in the number of flinches and shakes in the formalin-induced inflammatory pain model. This was accompanied by a marked reduction in formalin-induced c-fos expression in the spinal cord. During formalin-induced long-lasting inflammation, we found that the expression of the alpha(1) subunit of soluble guanylate cyclase was dramatically increased in the lumbar spinal cord on the second and fourth days after formalin injection into the dorsal side of a hind paw. Intraperitoneal pretreatment with an N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine maleate (MK-801), and a neuronal NO synthase inhibitor, 7-nitroindazole, not only significantly blocked formalin-induced secondary thermal hyperalgesia but also suppressed formalin-produced increase in the alpha(1) subunit of soluble guanylate cyclase in the spinal cord. The present results indicate that peripheral inflammation not only initially activates but also later up-regulates soluble guanylate cyclase expression via the NMDA receptor-NO signaling pathway, suggesting that soluble guanylate cyclase might be involved in the central mechanism of formalin-induced inflammatory hyperalgesia in the spinal cord.

Animals↗

PubMed2001

Solubility prediction of salmeterol xinafoate in water--dioxane mixtures.

The mole fraction solubility of salmeterol xinafoate was determined in various concentrations of dioxane in aqueous binary mixture. Maximum solubility was observed in 90% v/v dioxane and solubility parameter of the solute was estimated from solubility peak equal to 24.99 MPa(0.5). The predicting capability of four different cosolvency models was also evaluated employing a five data point training set. The solubility data at other cosolvent concentrations were predicted using the trained models, with percentage average errors for 28 drug solubility data sets in water-cosolvent mixtures lying between 12.5 and 15.0%. Further predictive model is proposed for accurate solubility predictions based on a minimum number of experiments. The percentage average error where tested was 10.6%.

Albuterol↗

PubMed1997

An adaptation of hydrophobic interaction chromatography for estimation of protein solubility optima.

This study describes an adaptation of hydrophobic interaction chromatography (HIC) that can be used to estimate protein solubility optima. The method does not support determination of absolute, e.g. quantitative solubility, however it does provide a basis for identifying the salt concentration, pH, or additive concentrations that support the highest relative solubility. The magnitude of a given salt's effects are consistent with its ranking in the Hofmeister series. IgG in solutions of strong 'precipitating' salts exhibits a classical salting-in/salting-out curve, described by a solubility minimum at low ionic strength, increasing to a well-defined maximum, and then losing solubility with further elevation of salt concentration. The direct effect of pH on protein solubility, as well as its indirect effect via modification of the ionic equilibria of dissolved salts, can also be tracked. Cooperative effects of solubility modifiers such as amino acids can likewise be assessed. The technique can be a useful tool in the development of liquid formulations for protein pharmaceuticals.

Chemistry, Pharmaceutical↗

PubMed2000

Proposition of group molar constants for sodium to calculate the partial solubility parameters of sodium salts using the van Krevelen group contribution method.

The aim of this study is to propose, for the first time, a set of group molar constants for sodium to calculate the partial solubility parameters of sodium salts. The values were estimated using the few experimental partial solubility parameters of acid/sodium salt series available either from the literature (benzoic acid/Na, ibuprofen acid/Na, diclofenac Na) or determined in this work (salicylic acid/Na, p-aminobenzoic acid/Na, diclofenac), the group contribution method of van Krevelen to calculate the partial parameters of the acids, and three reasonable hypothesis. The experimental method used is a modification of the extended Hansen approach based on a regression analysis of the solubility mole fraction of the drug lnX(2) against models including three- or four-partial solubility parameters of a series of pure solvents ranging from non-polar (heptane) to highly polar (water). The modified method combined with the four-parameter model provided the best results for both acids and sodium derivatives. The replacement of the acidic proton by sodium increased the dipolar and basic partial solubility parameters, whereas the dispersion parameter remained unaltered, thus increasing the overall total solubility parameter of the salt. The proposed group molar constants of sodium are consistent with the experimental results as sodium has a relatively low London dispersion molar constant (identical to that of -OH), a very high Keesom dipolar molar constant (identical to that of -NO(2), two times larger than that of -OH), and a very high hydrogen bonding molar constant (identical to that of -OH). The proposed values are: F((Na)d)=270 (J cm(3))(1/2) mol(-1); F((Na)p)=1030 (J cm(3))(1/2) mol(-1); U((Na)h)=17000 J mol(-1). Like the constants for the other groups, the group molar constants proposed for sodium are certainly not the exact values. However, they are believed to be a fair approximation of the impact of sodium on the partial solubility parameters and, therefore, can be used as such in the group contribution method of van Krevelen.

Algorithms↗

PubMed2003

Physicochemical investigation of the effects of water-soluble polymers on vinpocetine complexation with beta-cyclodextrin and its sulfobutyl ether derivative in solution and solid state.

The studies reported in this work aimed to elucidate the inclusion complex formation of vinpocetine (VP), a poorly water-soluble base type drug, with beta-cyclodextrin (betaCD) and its sulfobutyl ether derivative (sulfobutyl ether beta-cyclodextrin (SBEbetaCD)), with or without water-soluble polymers (PVP and HPMC), by thoroughly investigating their interactions in solution and solid state. Phase solubility studies were carried out to evaluate the solubilizing power of both cyclodextrins (CDs), in association with water-soluble polymers, towards VP and to determine the apparent stability constants (Kc) of the complexes. SBEbetaCD showed higher solubilizing efficacy toward VP than the parent betaCD due to its greater solubility and complexing abilities, what was reflected in higher Kc values. Improvement in Kc values for ternary complexes clearly proves the benefit on the addition of water-soluble polymers to promote higher complexation efficiency. VP-CDs (1:1) binary and ternary systems were prepared by physical mixing, kneading, co-evaporation, and lyophilization methods. In the solid state, drug-carrier interactions were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and Fourier-transform infrared spectroscopy. The results of these analysis suggested the formation of new solid phases, some of them in amorphous state, allowing to the conclusion of strong evidences of binary and ternary inclusion complex formation between VP, CD and water-soluble polymers, particularly for co-evaporated and lyophilized binary and ternary products.

Chemical Phenomena↗

PubMed2002

Overexpression of DsbC and DsbG markedly improves soluble and functional expression of single-chain Fv antibodies in Escherichia coli.

Single-chain Fv antibodies (scFv), a group of reconstructed molecules with several disulfide bonds, are prone to aggregate as inclusion bodies, the insoluble species of natural proteins, when expressed in Escherichia coli, especially at high level. Recovery of functionally active products from inclusion bodies is onerous and ineffective. We have increased the soluble and functional scFv yields by fusing either DsbC or DsbG, two E. coli disulfide isomerases with general chaperone function, to scFvs. Compared to the totally insoluble inclusion bodies of scFvs expressed separately, more than half of each fusion protein DsbC-scFv or DsbG-scFv was soluble, according to SDS-PAGE analysis. The more effective solubility was obtained when the fused protein DsbG-scFv was co-expressed simultaneously with DsbC under the same promoter. Under this condition, the soluble portion of DsbG-scFv increased from about 50% to 90% measured by scanning SDS-PAGE gel. Co-expression of DsbC can change fusion protein CBD-scFv from totally insoluble when expressed in E. coli separately to a considerable portion of soluble CBD-scFv. Antigen-binding activity assay showed that scFvs retained full affinity to specific antigens. We also determined that general molecular chaperones GroEL and GroES had no effects on the solubility of scFvs when co-expressed with scFv in E. coli. We propose that the correct formation of disulfide bonds in scFvs is the crucial factor responsible for solubility of scFvs.

Base Sequence↗

PubMedDate not supplied

Functional localization of soluble guanylate cyclase in turtle retina: modulation of cGMP by nitric oxide donors.

The second messenger cyclic guanosine monophosphate (cGMP) plays a role in many aspects of retinal processing. cGMP-gated channels function in photoreceptors, Müller, bipolar, and ganglion cells; and cGMP can modulate gap-junction conductivity. In the inner retina, both particulate and soluble guanylate cyclases can elevate levels of cGMP. The soluble isoform of guanylate cyclase is activated by nitric oxide (NO). In turtle retina, nitric oxide synthase, the enzyme that synthesizes NO, has been previously localized in discrete amacrine cells, somata in the ganglion cell layer, and in many processes in the inner plexiform layer. However, there have been no studies localizing soluble guanylate cyclase in the turtle retina. To functionally localize soluble guanylate cyclase, we stimulated retinas with the NO donors (+/-)-S-nitroso-N-acetylpenicillamine or spermine (nitric oxide) adduct, and then used immunocytochemistry to localize increases in cGMP-like immunoreactivity (cGMP-LI). The cells containing soluble guanylate cyclase should show cell autonomous increases in cGMP-LI in response to stimulation with NO. NO-stimulated increases in cGMP-LI occurred in many distinct amacrine cell types, select bipolar cells, some somata in the ganglion cell layer, and in discrete bands of processes in the inner plexiform layer. The pattern of cGMP-LI demonstrated qualitative dose response differences to the NO donors. This is the first localization of soluble guanylate cyclase in specific retinal neurons in the turtle; and the first functional activation of soluble guanylate cyclase in the amacrine cells of any species. The broad neuronal distribution of NO-stimulated cGMP-LI suggests that the NO/soluble guanylate cyclase/cGMP cascade is involved at several levels of visual processing in the inner retina.

Animals↗

PubMed1986

Thermoinactivation and aggregation of alpha beta units in soluble and membrane-bound (Na,K)-ATPase.

Stability and conformational transitions of soluble and fully active alpha beta units of (Na,K)-ATPase in n-dodecyl octaethylene glycol monoether (C12E8) are examined. Sedimentation equilibrium centrifugation gave a molecular weight of 143 000 for the alpha beta unit eluting from TSK 3000 SW gel chromatography columns. Fluorescence analysis and phosphorylation experiments show that E1-E2 transitions between both dephospho and phospho forms of soluble (Na,K)-ATPase are similar to those previously observed in the membrane-bound state. The two conformations can also be identified by their different susceptibilities to irreversible temperature-dependent inactivation. E1 forms of both soluble and membrane-bound (Na,K)-ATPase are more thermolabile than E2 forms. Gel chromatography on TSK 3000 SW and 4000 SW columns shows that thermal inactivation of soluble (Na,K)-ATPase at 40 degrees C is accompanied by aggregation of alpha beta units to (alpha beta)2 units and higher oligomers. The aggregates are stable in C12E8 but dissolve in sodium dodecyl sulfate. Similar aggregation accompanies inactivation of membrane-bound (Na,K)-ATPase at 55-60 degrees C. These data suggest that inactivation both in the soluble and in the membrane-bound state involves exposure of hydrophobic residues to solvent. The instability of the soluble E1 form may be related to inadequate length of the dodecyl alkyl chain of C12E8 for stabilization of hydrophobic protein domains that normally associate with alkyl chains of phospholipids in the membrane. Interaction between alpha beta units-does not seem to be required for the E1-E2 conformational change, but irreversible aggregation appears to be a consequence of denaturation of (Na,K)-ATPase in both soluble and membranous states.

Adenosine Diphosphate↗

PubMed1996

Structural properties of UMP-kinase from Escherichia coli: modulation of protein solubility by pH and UTP.

UMP-kinase from Escherichia coli, unlike the analogous enzyme from eukaryotic organisms, is an oligomeric protein subjected to complex regulatory mechanisms in which UTP and GTP act as allosteric effectors. While the enzyme has an unusually low solubility at neutral pH (< or = 0.1 mg of protein/ mL), its solubility increases markedly above pH 8 and below pH 4. Furthermore, the solubility of the bacterial UMP-kinase at neutral pH is greatly enhanced in the presence of Mg-free UTP. Thermal denaturation experiments have demonstrated that UTP also increases the stability of the protein. Fourier-transform infrared spectroscopy and circular dichroism show that the secondary structure of the protein is the same at neutral and at alkaline pH. These data indicate that variations in enzyme solubility must be related to subtle changes in the tertiary and/or quaternary structure which modulate the exposure of hydrophobic surfaces in the protein molecule. A variant of UMP-kinase, obtained by site-directed mutagenesis (Asp159Asn), which is similar to the wild-type enzyme in its stability and kinetic properties, has a much increased water solubility (> 5 mg protein/mL) even at neutral pH. This suggests that salt bridges may be involved in the equilibrium between the soluble and aggregated forms of the wild-type enzyme, and that conformational changes induced upon binding of UTP increase the protein solubility by disrupting these salt bridges.

Allosteric Regulation↗

PubMed2000

Relation between solubility and surface hydrophobicity as an indicator of modifications during preparation processes of commercial and laboratory-prepared soy protein isolates.

Because water solubility is the main hydration property of proteins, solubility values of commercial and laboratory soy protein isolates, prepared under different conditions, were comparatively analyzed. In contrast, the surface hydrophobicity manifested by proteins is a physicochemical property that determines, to a great extent, the tendency of protein molecules to aggregate and so to lose solubility. On these grounds, the solubility of isolates was analyzed as a function of the surface hydrophobicity of their proteins, and, as a result, three well-defined groups of laboratory isolates were identified: (A) native, (B) partially or totally denatured with high solubility and surface hydrophobicity, and (C) totally denatured with low solubility and surface hydrophobicity. Commercial isolates could not be included in any of these groups; they were grouped as (A') partially native and (C') totally denatured. Solubility values in these two groups were similar to those of group C, but the surface hydrophobicity levels were much lower. The different processes leading to the groups mentioned above are discussed, along with the way the soy proteins are influenced by the specific preparation conditions, namely, protein concentration, chemical or thermal treatments, presence of salts, drying, and phospholipid addition, among others.

Food Handling↗

PubMed1993

Nucleoside conjugates. 13. Synthesis and antitumor activity of 1-beta-D-arabinofuranosylcytosine conjugates of thioether lipids with improved water solubility.

A series of ara-CDP-rac-1-S-alkyl-2-O-acyl-1-thioglycerols (3-12), analogues of highly active Cytoros2 (1), was prepared, and solubility, lipophilicity, and structure-activity relationships of these conjugates were investigated. The conjugates with sn-1 alkyl (< C18) and sn-2 fatty acyl (< C14) substituents of the thioglycerol were water-soluble, while those with the sn-1 alkyl (> C14) and the sn-2 fatty acyl (> C16) were sparingly soluble. The latter formed micelles upon sonication. Conjugate 7 containing the sn-1 tetradecyl and the sn-2 palmitoyl (C16) groups formed micelles by both sonication and shaking. The partition coefficients (1-octanol/PBS) of the water-soluble conjugates were about 20 times greater than that of ara-C. The water-insoluble showed a more than 40 times increase. A single dose of the micelle-forming conjugates 7 and 10 produced a significant increase in life span (ILS > 421%) with 50% long-term survivors (> 45 days) in mice bearing ip-implanted L1210 lymphoid leukemia. These results were comparable to those of previous micelle-forming conjugate 1 (Cytoros). In contrast, the water-soluble conjugates at single doses were less effective (ILS 81-386% with 0-33% long-term survivors). However, three divided doses of the water-soluble conjugates were found to be as effective as a single dose of micellar solution of the water-insoluble. The results indicate that conjugate 7 and most of the water-soluble derivatives warrant further investigation.

Animals↗

PubMed1999

Physical properties of parabens and their mixtures: solubility in water, thermal behavior, and crystal structures.

The peculiar solubility behavior of propylparaben (propyl ester of 4-hydroxybenzoic acid) in aqueous solution, when tested separately and together with methyl-, ethyl-, and butyl-parabens, has been investigated in detail. The results clearly indicate that the decrease in solubility (approximately 50% compared to the solubility value of propylparaben alone) is typical of those mixtures containing also ethylparaben, as demonstrated by solubility experiments on binary, ternary, and quaternary mixtures of the parabens. Phase diagrams of all the six binaries show that propylparaben and ethylparaben are the only pair that form almost ideal solid solutions near the melting temperatures. Moreover, phase-solubility analysis shows that propylparaben and ethylparaben, at room temperature, can also form solid solutions whose solubility is related to the composition of the solid phase at equilibrium. To achieve an independent confirmation of the possible solid solution formation that supports the above interpretation of the solubility behavior, the crystal structures of the four parabens have been examined and isostructurality has been found to exist only between ethylparaben and propylparaben. Powder X-ray diffraction has also been performed on ethylparaben, propylparaben, and their solid solutions obtained by recrystallization from water. The progressive shift of distinctive diffraction peaks with phase composition clearly indicates that propylparaben and ethylparaben form substitutional solid solutions. The small value (<1) of the disruption index provides thermodynamic support for substitutional solid solutions based on isostructural crystals.

Calorimetry, Differential Scanning↗