Separation of dansylated 17β-estradiol, 17α-estradiol, and estrone on a single HPLC column for simultaneous quantitation by LC–MS/MS

We show here that baseline separation of dansylated estrone, 17β-estradiol, and 17α-estradiol can be done, contrary to previous reports, within a short run time on a single RP-LC analytical column packed with particles bonded with phenyl-hexyl stationary phase. The chromatographic method coupled with isotope dilution tandem MS offers a simple assay enabling the simultaneous analysis of these analytes. The method employs ¹³C-labeled estrogens as internal standards to eliminate potential matrix effects arising from the use of deuterated estrogens. The assay also offers adequate accuracy and sensitivity to be useful for biological samples. The practical applicability of the validated method is demonstrated by the quantitative analyses of in vivo samples obtained from rats treated with Premarin®.

Laccase-mediated oxidation of the steroid hormone 17β-estradiol in organic solvents

Laccase-mediated oxidation of the steroid hormone 17β-estradiol 1 in organic solvents or in a biphasic system allowed the isolation of the C–C and C–O dimers 1a–d. Concerning the C–C dimers, the relative ratio of the symmetric 4-4′ 1c and asymmetric 4-2′ 1d products was influenced by the catalyst used. Both 1c and 1d were formed as an equimolar mixture of diastereomeric atropisomers.     

β-diketone interactions: Part 5. Solvent effects on the keto ⇋ enol equilibrium

The keto ⇋ enol equilibrium of pentane-2,4-dione (PD) has been measured in 21 solvents at infinite dilution and a linear free energy relationship (LFER) tested against four solvent polarity vectors: ϵ, E_T, π* and A + B. The best correlation coefficient is found for A + B. Similarly 3-methyl-pentane-2,4-dione (MePD) has been studied in 14 solvents and 3-ethylpentane-2,4-dione (EtPD) in six. The results suggest that the cyclic hydrogen bonding of the enol remains intact in all the solvents studied.     

SPE and HPLC monitoring of 17-β-estradiol in Egyptian aquatic ecosysetms

Solid-phase extraction and HPLC methods are described for monitoring of 17-β-estradiol residues in Egyptian aquatic ecosystems (water, fish, mollusks, sediment, and drinking water) at the Nile River, Suez Canal region, and northeast of Egypt. Molecular imprinted polymer was prepared and used in extraction. High performance liquid chromatography (HPLC) columns used were Supelcosil C₁₈ and Nucleosil C₁₈. The mobile phases used were different combinations of water and acetonitrile. The concentration of 17-β-estradiol in water, aquatic animals, and sediment samples were of 265.13–7988.12 µg/L, 0.503–96.167, and 0.775–11.884 µg/kg, respectively. Marine lake was contained with high levels of 17-β-estradiol (P < 0.05). Similarly, the Nile River downstream showed high levels of 17-β-estradiol. The detected concentrations in mollusks were significantly higher than those detected in fish. Tilapia fish did not show 17-β-estradiol. Contrarily, low concentrations were detected in the rivulet streams supplied by the Nile River. Besides, 17-β-estradiol was also detected in the sediments at low levels. Detection of 17-β-estradiol in the Egyptian ecosystems attracted attention toward heavy reliance on some esterogenic medicinal products in Egypt. The monitoring of 17-β-estradiol in other water bodies was recommended. Besides, the development of methodologies of bioremediation to eliminate 17-β-estradiol from the Egyptian and other water resources of the world was also suggested.     

Solvent effects on the electronic spectra of vanadyl(IV) ß-diketonate derivatives

The visible spectra of VO(acac-Cl)₂ and VO(acac-Br)₂ have been measured in several solvents with a wide range of donor properties. Spectra in the non-coordinating solvent benzene show little difference from those of other vanadyl ß-diketonates. Results for other solvents show a linear relationship between the energy differences of the first two visible bands, D_1,2 and the solvent Donor Numbers. The smaller sensitivity of D_1,2 for these species to Donor Number (relative to that for VO(acac)₂) has been interpreted in terms of a decreased tendency of the substituted species to undergo reaction with donor molecules.     

Electrochemical characterization of 17β-estradiol with fast-scan cyclic voltammetry

We have developed a sensitive and stable electrochemical method for 17β-estradiol (E2) detection using fast-scan cyclic voltammetry (FSCV). Recently, E2 was proposed to function as a rapid synaptocrine signaling molecule in the brain; however, methods to directly monitor subsecond fluctuations in E2 are currently unavailable, limiting our understanding of the dynamics and mechanism of rapid E2 release. FSCV at carbon-fiber microelectrodes enables subsecond detection of electroactive neurochemicals directly in tissues like the brain. Here, we have electrochemically characterized E2 using FSCV for use in a tissue matrix. The limit of detection of E2 is 31.2±2.5 nM with FSCV, which will enable low nanomolar fluctuations in extracellular E2 to be monitored with hundred millisecond temporal resolution. We also identify specific parameters for waveform modification to improve future detection. This method will significantly improve E2 sensing capabilities and will have far-reaching impacts on improving our understanding of dynamic E2 signaling in the brain.     

Surface plasmon resonance-based immunoassay for 17β-estradiol and its application to the measurement of estrogen receptor-binding activity

A rapid and simple surface plasmon resonance (SPR)-based immunoassay for detection of 17-estradiol was developed. The assay was designed as an inhibitive format, in which 17-estradiol–BSA conjugates are immobilized on an SPR sensor chip and the binding of antibody to the chip is measured. The binding was inhibited by 17-estradiol in the concentration range 0.468 to 21.4 nmol L^–1 with an IC₅₀ value of 2.29±0.10 nmol L^–1. Although not as sensitive as traditional radioimmunoassay (RIA) and enzyme-linked immunoassay (ELISA), this method requires no separation and washing after addition of the antibody, steps which are relatively time-consuming. Estrogen receptor (ER)-binding was then investigated using this SPR immunoassay for the determination of the amount of unbound 17-estradiol after competition with test compounds for the ER-binding. Inhibition of the binding of 17-estradiol to ER by diethylstilbestrol (DES) was successfully measured by injecting the reaction mixture into the SPR sensor after addition of the antibody. This binding assay requires no separation of unbound 17-estradiol from the mixture and no radioisotope- or fluorescence-labeling of 17-estradiol. These results show the potential usefulness of the SPR sensor both detecting 17-estradiol and evaluating the ER-binding activity of xenoestrogens such as DES in a single assay system.     

Solvent effects upon the NH vibrational frequencies of phosphoramides

The effect of various, solvents upon the NH vibrational frequencies of the phosphoryl trisanilide (PTA) thiophosphoryl trisanilide (TTA), phosphoryl triscyclohexylamide (PTC) and thiophosphoryl triscyclohexylamide (TTC) was measured. The solvent shifts for the different amides are correlated and there is also some correlation between solvent shifts and Gutmann's solvent donicities. For the calculation of the solvent shifts a better linear relation was obtained through an equation of three terms which takes into account the donicity, the acceptor number, the dipole moment and the relative permittivity of the solvent. The last term considers the interaction of the solvent dipole moment with the induced dipole on the NH bond. These correlations are discussed.     

Dependence of the Kβ/Kα intensity ratio on the oxidation state

The K/K X-ray intensity ratios were measured for pure Cr, Mn, Co and Cu belonging to the 3 d shell as well as in their compounds, to look for the influence of the chemical environment on the fluorescence yield ratios. The vacancies in the K shell created by 59.5 keV -rays from an²⁴¹Am source and the X-rays were measured using a Ge(Li) detector. A steady increase of the K/K intensity ratio was observed with increasing oxidation. The present results agree with previously published experimental data.     

Development of Magnetic Particle-based Chemiluminescence Enzyme Immunoassay for the Detection of 17β-estradiol in Environmental Water

In the present work, a simple, fast, and highly sensitive chemiluminescence enzyme immunoassay for 17β-estradiol (E2) in environmental water samples was developed, using magnetic particles (MPs) labeled with secondary antibody as both the immobilization matrix and the separation tools. The specific anti-E2 polyclonal antibody (PcAb) was produced against a conjugate of estradiol–bovine serum albumin. The specificity of the anti-E2 antibody was studied. The results showed that the antibody did not cross-react with the structurally related endocrine-disrupting compounds, including estrone, ethinyl E2, estriol, E2-17-glucuronide, E2-3-sulfate-17-glucuronide, androstenedione, and dihydrotestosterone. The water samples were pretreated with solid-phase extraction using C₁₈ cartridges for the removal of matrix effects. Several physicochemical parameters including the dilution ratios of E2-6–horseradish peroxidase conjugate and anti-E2 PcAb, immunoreaction time, volume of chemiluminescent substrate and MPs, chemiluminescence reaction time, and pH of assay solution were studied and optimized. At optimal experimental conditions, it was found that the proposed method exhibited high performance with detection limit of 2.0 pg/mL, linear range of 20–1,200 pg/mL, and total assay time of 45 min. Both inter- and intra-assay coefficient of variation were less than 10%. The average recoveries of three different spiked concentration samples ranged from 86.3% to 108%. The method was successfully applied to the determination of E2 in river, waste, and tap water, and showed a good correlation with the commercially available radioimmunoassay kit.     

Solvent interactions in the excited state of non-planar donor—acceptor molecules

In order to probe solute—solvent interactions in the intramolecular charge transfer (TICT) state of 2,6,N,N-tetramethylcyanoaniline (TMCA) fluorescence spectra, quantum yields and lifetimes of this compound were measured in binary mixtures of n-hexane with chlorinated hydrocarbons. An isoemissive point in the fluorescence spectra was observed as the composition of the solvent was varied. Evidence for both clustering of polar solvent molecules around the excited solute and for non-specific long-range interactions with the polar bulk of the solution was found. The properties of the solvent affect primarily the efficiency of non-radiative deactivation. Fluorescence quenching by saturated amines gives good evidence that TMCA emission arises from a highly polar state in both polar and non-polar solutions.     

Solvent effects on the complexation of 1-alkanols by parent and modified cyclodextrins. Calorimetric studies at 298 K

The formation of complexes of parent and alkylated cyclodextrins (CDs) with 1-heptanol and 1-octanol has been studied calorimetrically at 298 K in water and in concentrated aqueous solutions of urea. The forces involved in the association process are discussed in the light of the signs and values of the thermodynamic parameters obtained: association enthalpy, binding constant, Gibbs free energy, and entropy. It was inferred that: (i) in water, the formation of complexes for parent and substituted α-cyclodextrins (αCDs) is determined by enthalpy. For parent and substituted β-cyclodextrins (βCDs), instead, hydrophobic interactions are the prevailing forces determining complexation, as indicated by the small and negative or positive enthalpies and by the high and positive entropies. (ii) In urea, hydrophilic interactions are attenuated. The formation of complexes with alkylated CDs does not occur. (iii) The analysis of the thermodynamic properties confirms that inclusion is a process dominated by hydration phenomena. Modifications experienced by the solvent water in the hydration shells of the interacting substances upon association determine the formation of the complexes.     

Reactions of the OH adducts of cytosine and its derivatives with TEMPO and TEMPOL: A steady state γ-radiolysis and pulse radiolysis study

The reactions of the OH adducts of cytosine and its derivatives with nitroxides namely TEMPO and TEMPOL have been followed by steady state -radiolysis and pulse radiolysis. Pulse radiolysis studies show that the transient OH adducts of cytosine and its derivatives react with TEMPO and TEMPOL by electron transfer reaction and not by adduct formation as was observed in the case of thymine. The second order rate constants for these electron transfer reactions are of the order of 10⁷ - 10⁸ dm³ mol^-1 s^-1.     

Solvent and substituent effects on aggregation constants of perylene bisimide π-stacks--a linear free energy relationship analysis

A series of six perylene bisimides (PBIs) with hydrophilic and hydrophobic side chains at the imide nitrogens were applied for a comparative study of the solvent and structural effects on the aggregation behaviour of this class of dyes. A comparison of the binding constants in tetrachloromethane at room temperature revealed the highest binding constant of about 10(5) M(-1) for a PBI bearing 3,4,5-tridodecyloxyphenyl substituents at the imide nitrogens, followed by 3,4,5-tridodecylphenyl and alkyl-substituted PBIs, whereas no aggregation could be observed in the accessible concentration range for PBIs equipped with bulky 2,6-diisopropylphenyl substituents at the imide nitrogens. The aggregation behaviour of three properly soluble compounds was investigated in 17 different solvents covering a broad polarity range from nonpolar n-hexane to highly polar DMSO and water. Linear free energy relationships (LFER) revealed a biphasic behaviour between Gibbs free energies of aggregation and common empirical solvent polarity scales indicating particularly strong π-π stacking interactions in nonpolar aliphatic and polar alcoholic solvents whilst the weakest binding is observed in dichloromethane and chloroform. Accordingly, PBI aggregation is dominated by electrostatic interactions in nonpolar solvents and by solvophobic interactions in protic solvents. In water, the aggregation constant is increased far beyond LFER expectations pointing at a pronounced hydrophobic effect.     

Hydrophobic Silica Sol Coatings on Textiles—the Influence of Solvent and Sol Concentration

Hydrophobic silica sol coatings on textiles were investigated with respect to the influence of the solvents and the concentration of the sol. For this purpose, two silica sols, prepared with the hydrophobic additives octyltriethoxysilane and perfluoroctyltriethoxysilane were diluted by different solvents: water, ethanol and aceton.In case of using pure water for dilution, the hydrophobicity of coated textiles decreases drastically with increasing dilution of the applied sol. For coatings on polyester fabrics or mixed fabrics made from polyester and cotton, the use of the organic solvents ethanol or aceton leads to significant hydrophobicity even in case of strong dilution down to a sol concentration < 1%. The hydrophobic effect of coated polyamide textile is less. The reason for different hydrophobicity of coated textiles resulting from the use of water instead of organic solvents is explained by different surface morphologies of the coatings deposited on the textile fibres, as observed by REM. In case of using organic solvents the coatings contain a more flat morphology which covers the fibres completely. In contrast, sols with higher water content lead to less adhesive coatings with crack formation.The use of a combination of water with less inflammable organic solvents such as di(propylene glycol) n-propyl ether (Dowanol^TM DPnP) in hydrophobic silica sols yields textile coatings with good hydrophobicity, even in case of low sol concentration. For practical application of textile coatings, especially silica sols with high water content are of interest, due to less risk of inflammation and lower ecological impact. Therefore, the use of water diluted hydrophobic silica sols with small amounts of DPnP offers a chance for textile refinement by the sol–gel technique.     

Effect of Solvent Characteristics on the Photophysics of Hydroxyl Aromatic Compounds

The effect of solvent characteristics on the absorption and emission properties of 1- and 2-naphthols have been studied and the results interpreted in terms of the general and specific solute-solvent interactions. Measurements were performed in several solvents and analysis of the absorption and emission wavelengths were made using Lippert’s model for general solvent effects. A near linear relationship between the Stokes shift (D[`(n)]\Delta\bar{\nu}) and the orientation polarizability (Δf) were observed for both 1- and 2-naphthols in most of the alkanols, thus showing evidence of a general solvent effect. However, in 1,4-dioxane–water mixtures the plots deviate from linearity indicating the dominance of specific solvent effects that are not included in Lippert’s equation. In the case of interactions between the fluorophores and dioxane–water mixtures, excess Stokes’ shifts are observed in the order of dioxane composition 10%>20%>30%>50%>60%>80%. This may be due to excited state proton transfer (ESPT) and the involvement of hydrogen bonding between the protic group of the fluorophore and the solvents.     

Non-adiabatic effects on oxygen atom fine structure populations in the predissociation of the A2Σ+ state of OH

Multichannel scattering calculations are used to evaluate the role of non-adiabatic interactions and interference effect on the predissociation linewidths of several vibrational levels of the A²Σ⁺ state of OH due to coupling to three different repulsive electronic states. Oxygen atom fine structure branching ratios are calculated as a possible probe of the predissociation pathway. Non-adiabatic effects are found to be very strong for the lower vibrational predissociative A²Σ⁺ levels and to remain non-negligible even for the higher vibrational states of A ²Σ⁺.     

Buffering effects on the solution behavior and hydrolytic degradation of poly(β-amino ester)s

With a vast, synthetically accessible compositional space and highly tunable hydrolysis rates, poly(β-amino ester)s (PBAEs) are an attractive degradable polymer platform. Leveraging PBAEs in a wide range of applications hinges on the ability to program degradation, which, thus far, has been frustrated by multiple confounding phenomena contributing to the degradation of these charged polyesters. Basic conditions accelerate hydrolysis, yet reduce solubility, limiting water access to amines and esters. Further, the high buffering capacity of PBAEs can render buffers ineffective at controlling solution pH. To unify understanding of PBAE degradation and solution properties, this study examines PBAE hydrolysis as a function of pH and buffer concentration as well as polymer hydrophobicity. At low buffer concentrations, the PBAE amines and the acid produced during hydrolysis control solution pH. Meanwhile, at high buffer concentrations that afford relatively constant pH, hydrolysis rate increases with pH, despite the reduced PBAE solubility. Increasing the hydrophobic content of PBAEs eventually hinders the capacity of the polymer to accept protons from solution, limiting the pH increase and slowing hydrolysis. These studies showcase the role of buffering on the pH-dependent degradation and solution properties of PBAEs, providing guidance for programming degradation in applications ranging from drug delivery to thermosets.