Interplay of thermochemistry and Structural Chemistry,the journal (volume 28, 2017, issues 3–4) and the discipline

Structural Chemistry - The contents of issues 3 and 4 of Structural Chemistry from the calendar year 2017 are summarized in the present review. A brief thermochemical commentary and recommendations...     

Interplay of thermochemistry and Structural Chemistry: the journal (volume 29, 2018, issues 5–6) and the discipline

The contents of issues 5 and 6 of Structural Chemistry from the calendar year 2018 are summarized in the present review. A brief thermochemical commentary and recommendations for future research have been added to the summary of each paper.

     

Degradation studies of quetiapine fumarate by liquid chromatography–diode array detection and tandem mass spectrometry methods

Quetiapine fumarate (QUE) is an antipsychotic agent with a chemical structure that is susceptible to degradation; therefore, it is important to study its stability using appropriate analytical tools. Knowledge of the stability profile of a drug is important because chemical degradation of its active component often results in a loss of potency, affecting its efficacy and safety. This current work reports degradation studies of QUE as drug substance, under different stress conditions such as oxidation, hydrolysis, heat, humidity and photolysis, by a stability‐indicating LC method. The chemical stability was evaluated using a simple HPLC/diode array detection method, with a core‐shell C₁₈ column under isocratic conditions, which allows the separation of all primary degradation products (DPs) in a short run time. QUE was mainly degraded under oxidative and hydrolytic conditions, with the formation of three and two DPs, respectively, which were identified by electrospray ionization–tandem mass spectrometry. The method was properly validated in terms of linearity, accuracy, precision, selectivity, robustness and quantitation limit. Commercial tablets containing 25 mg of QUE were quantified, with results obtained within the United States Pharmacopeia limits. The proposed method is suitable to assess the stability and perform routine analysis of QUE in pharmaceutical samples.     

Some new group divisible designs with block size 4 and two or three group sizes

Group divisible designs (GDDs) with block size 4 and at most 30 points are known for all feasible group types except three, namely $2^3{5}^4,3^5{6}^2$, and $2^2{5}^5$. In this paper we provide solutions for the first two of these three 4‐GDDs without assuming any automorphisms. We also construct several other 4‐GDDs. These include classes of 4‐GDDs of types ${\left(3m\right)}^4{\left(6m\right)}^q{\left(3n\right)}^1$ for $0\le n\le \left(q+1\right)m$ where $q\in \left\{2,3\right\}$ and solutions for 4‐GDDs of types $3^t{6}^s$ for a wide range of values of $s\ge 2,t\ge 4$ satisfying $t\equiv 0$ or $1\left(\mathrm{mod}4\right)$, including all cases with $4\le t\le s?1$. Most of the remaining unknown 4‐GDDs of type $3^t{6}^s$ have $\left(s?1\right)<t<2\left(s?1\right)$.     

Development and validation of a rapid and sensitive UPLC–MS/MS assay for simultaneous quantification of paclitaxel and cyclopamine in mouse whole blood and tissue samples

The prominent stromal compartment surrounds pancreatic ductal adenocarcinoma and protects the tumor cells from chemo‐ or radiotherapy. We hypothesized that our nano formulation carrying cyclopamine (CPA, stroma modulator) and paclitaxel (PTX, antitumor agent) could increase the permeation of PTX through the stromal compartment and improve the intratumoral delivery of PTX. In the present study a sensitive, reliable UPLC–MS/MS method was developed and validated to quantify PTX and CPA simultaneously in mouse whole blood, pancreas, liver and spleen samples. Docetaxel was used as the internal standard. The method demonstrated a linear range of 0.5–2000 ng/mL for whole blood and tissue homogenates for both PTX and CPA. The accuracy and precision of the assay were all within ±15%. Matrix effects for both analytes were within 15%. Recoveries from whole blood, liver, spleen and pancreas homogenates were 92.7–105.2% for PTX and 72.8–99.7% for CPA. The stability was within ±15% in all test biomatrices. The validated method met the acceptance criteria according to US Food and Drug Administration regulatory guidelines. The method was successfully applied to support a pharmacokinetic and biodistribution study for PTX and CPA in mice biomatrices.     

Interplay of thermochemistry and Structural Chemistry, the journal (Volume 26, 2015, Issues 1–2) and the discipline

Structural Chemistry - The contents of issues 1 and 2 of Structural Chemistry from the calendar year 2015 are summarized in the present review. A brief thermochemical commentary and possible...     

Studies of C<Subscript>8</Subscript> aromatics adsorption in BaY and mordenite molecular sieves using the headspace technique

A headspace technique, that consists in analyzing the composition of the vapor phase in equilibrium with the condensed phase of a mixture in a sealed vial containing the adsorbent sample, has been recently applied to acquire equilibrium data for adsorption of xylenes in liquid phase. In this study, we used this technique to measure experimental binary equilibrium data for C₈ aromatics in Y and mordenite zeolitic molecular sieves. For the Y zeolite, we also measured C₈ aromatics quaternary equilibrium data. Measurements were made at temperatures between C 40–80 °C. A more tedious, but traditional, chromatographic pulses method was also used to validate some of the results.     

Influence of 1,4‐dioxane solvent inclusion on the crystal structure of 5,5′‐diphenyl‐2,2′‐(p‐phenylene)di‐1,3‐oxazole (POPOP)

Crystallization of 5,5′‐diphenyl‐2,2′‐(p‐phenylene)di‐1,3‐oxazole (POPOP), C₂₄H₁₆N₂O₂, from chloroform or 1,4‐dioxane yielded crystals in pure and solvated forms, respectively. The solvated crystals of POPOP were found to contain 1,4‐dioxane in a strict 1:2 compound–solvent stoichiometry, C₂₄H₁₆N₂O₂·C₄H₈O₂, thus being a defined solvent‐inclusion compound. The crystal system is monoclinic in both cases and the asymmetric unit of the cell contains only half of the molecule (plus one dioxane molecule in the case of the solvated structure), owing to the centrosymmetry of the di‐1,3‐oxazole molecule.     

Enzymatic determination of cholesterol and triglycerides in serum lipoprotein profiles by asymmetrical flow field-flow fractionation with on-line, dual detection

Alterations of lipoproteins (LPs) and related lipid levels in blood serum are correlated to the risk of coronary artery disease (CAD). Fast, possibly automated methods to obtain complete, multi-parametric LP profiles are therefore welcome to be developed for routine, clinical analysis practice. In this work, asymmetrical flow field-flow fractionation (AF4) with on-line, dual post-fractionation reaction detection (PFRD) is applied to develop a method for single-run, simultaneous quantification of cholesterol (CHOL) and triglycerides (TGs) in each fractionated LP class. The enzymatic reagents used for the post-fractionation reaction are available as commercial kits for certified, standard clinical protocols for the analysis of CHOL and TGs in serum. Using CHOL and glycerol as reference standards, a new procedure is applied to optimize the experimental conditions for PFRD-based, quantitative analysis. Upon optimized PFRD and AF4 conditions, results obtained for the determination of total CHOL (TC), TGs, HDL-cholesterol (HDL-C), and LDL-cholesterol (LDL-C) in a set of serum samples from healthy donors are found in agreement with the values provided by a clinical laboratory. The intra-day and inter-day precisions of the method were found always lower than 10% (CV). When the method was applied to serum samples from patients affected by sepsis, differences in CHOL and TG profiles between patients and healthy donors were observed.