An HPLC method for the determination of the free cortisol/cortisone ratio in human urine

The measurement of the urinary free cortisol-cortisone ratio has been reported to be a sensitive indicator of renal 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD 2) activity. This converts biologically active cortisol to inactive cortisone. A decrease in its activity (e.g. through disease or inhibition caused by a therapeutic agent or a foodstuff) may increase cortisol levels and susceptibility towards hypertension. The method presented here uses a simple isocratic tandem column HPLC system. The method has been validated and found to be robust and reproducible. The lower limit of quantification (LLOQ) was found to be 10 ng/mL for both cortisol and cortisone. Samples of urine (n = 99) from patients, most of whom were on complex combinations of drugs, were analyzed and 92% of samples were found to give successful results with this method (cortisol and cortisone above LLOQ). The ratio ranged from 0.07 to 5.61. No interferences were noted from the drugs that the patients were taking. It was also found that a morning spot urine sample gave comparable results to 24 h collection samples, thus making sample collection much easier.     

An automated method for ‘clumped‐isotope’ measurements on small carbonate samples

Clumped‐isotope geochemistry deals with the state of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes rather than with the most abundant ones. Among its possible applications, carbonate clumped‐isotope thermometry is the one that has gained most attention because of the wide potential of applications in many disciplines of earth sciences. Clumped‐isotope thermometry allows reconstructing the temperature of formation of carbonate minerals without knowing the isotopic composition of the water from which they were formed. This feature enables new approaches in paleothermometry. The currently published method is, however, limited by sample weight requirements of 10–15 mg and because measurements are performed manually. In this paper we present a new method using an automated sample preparation device coupled to an isotope ratio mass spectrometer. The method is based on the repeated analysis (n = 6–8) of 200 µg aliquots of sample material and completely automated measurements. In addition, we propose to use precisely calibrated carbonates spanning a wide range in Δ₄₇ instead of heated gases to correct for isotope effects caused by the source of the mass spectrometer, following the principle of equal treatment of the samples and standards. We present data for international standards (NBS 19 and LSVEC) and different carbonates formed at temperatures exceeding 600°C to show that precisions in the range of 10 to 15 ppm (1 SE) can be reached for repeated analyses of a single sample. Finally, we discuss and validate the correction procedure based on high‐temperature carbonates instead of heated gases. Copyright © 2010 John Wiley & Sons, Ltd.     

Reply to ‘comment on “extending Hirshfeld‐I to bulk and periodic materials”’

The issues raised in the comment by Manz are addressed through the presentation of calculated atomic charges for NaF, NaCl, MgO, SrTiO $$_3$$ , and La $$_2$$ Ce $$_2$$ O $$_7$$ , using our previously presented method for calculating Hirshfeld‐I charges in solids (Vanpoucke et al., J. Comput. Chem. doi: 10.1002/jcc.23088). It is shown that the use of pseudovalence charges is sufficient to retrieve the full all‐electron Hirshfeld‐I charges to good accuracy. Furthermore, we present timing results of different systems, containing up to over 200 atoms, underlining the relatively low cost for large systems. A number of theoretical issues are formulated, pointing out mainly that care must be taken when deriving new atoms in molecules methods based on “expectations” for atomic charges. © 2012 Wiley Periodicals, Inc.     

‘Fast atom bombardment’—A rediscovered method for mass spectrometry

In 1966, Devienne and co-workers studied extensively the sputtering of various target materials by a high energy molecular beam obtained by charge exchange. They obtained secondary ions that characterized for instance, organic and biological materials. These ions were analysed by mass spectrometry. This method was developed to be patented and many devices were studied. The principle of the apparatus constructed is very simple. An ion source produces an ion current of some microamperes. The ions are accelerated at some keV, and injected into a collision chamber in order to obtain a neutral beam by resonant charge exchange. The residual ions are deflected and this beam bombards the target. The target itself is surrounded by a small metal cylinder which is held at an appropriate potential to extract the positive or negative secondary ions formed. The ion beam is accelerated and focused into the entrance slit of a mass spectrometer. After the first devices, two types of apparatus were built in 1973 and 1975. With the first one, the analysis of the masses was obtained only by an electromagnet. The energy range of the secondary ions varied from 1 to 10 keV. The second apparatus was formed by an electromagnet, a dissociation chamber, and an electrostatic analyser. With this apparatus, it was possible to measure directly masses as large as 6000 daltons. With the first apparatus it was possible to study the adsorption of oxygen on silicon, and to obtain spectra, of many organics such as camphor, nitrodiphenylamine and, as in the earlier device, the spectrum of a non-volatile organic liquid diethylhexyl azelate, was obtained. After studies on different uranium compounds and their dissociations, the second apparatus was devoted to the formation and study of the chemical properties of clusters.     

Reply on “comment on ‘statistical physics of a mesoscopic fermion system inside a rectangular box’”

This is the reply on the comment written by M. Toutounji, concerning the paper R. P. Lungu Statistical physics of a mesoscopic fermion system inside a rectangular box, Int. J. Quant. Chem., doi: 10.1002/qua.24128 (2013). © Wiley Periodicals, Inc.     

An ‘Umpolung’ Route to Peptide Mimetics of Thyrotropin-Releasing Hormone based on a cyclohexane framework

Peptide mimetics of thyrotropin-releasing hormone (TRH) in which the peptide backbone is replaced by cyclohexane were synthesized from the cyclohexenone precursor 7 . The aromatic side chains of the mimetics were derived from the corresponding aldehydes which were attached to the cyclohexenone via the Wittig reagent 8 . The TRH mimetics are active in a mouse model of cognitive performance.     

The ‘Azirine/Oxazolone Approach’ to the Synthesis of Aib‐Pro Endothiopeptides

The reaction of methyl N‐(2,2‐dimethyl‐2H‐azirin‐3‐yl)‐L ‐prolinate ( 2a ) with thiobenzoic acid at room temperature gave the endothiopeptide Bz‐AibΨ[CS]‐Pro‐OMe ( 7 ) in high yield. In an analogous manner, (benzyloxy)carbonyl (Z)‐protected proline was transformed into the thioacid, which was reacted with 2a to give the endothiotripeptide Z‐Pro‐AibΨ[CS]‐Pro‐OMe ( 12 ). The corresponding thioacid of 7 was prepared in situ via saponification, formation of a mixed anhydride, and treatment with H₂S. A second reaction with 2a led to the endodithiotetrapeptide 9 , but extensive epimerization at Pro² was observed. Similarly, saponification of 12 and coupling with either 2a or H‐Phe‐OMe and 2‐(1H‐benzotriazol‐1‐yl)‐1,1,3,3‐tetramethyluronium tetrafluoroborate/1‐hydroxy‐1H‐benzotriazole (TBTU/HOBt) gave the corresponding endothiopeptides as mixtures of two epimers. The synthesis of the pure diastereoisomer BzΨ[CS]‐Aib‐Pro‐AibΨ[CS]‐N(Me)Ph ( 21 ) was achieved via isomerization of 7 to BzΨ[CS]‐Aib‐Pro‐OMe ( 16 ), transformation into the corresponding thioacid, and reaction with N,2,2‐trimethyl‐N‐phenyl‐2H‐azirin‐3‐amine ( 1a ). The structures of 12 and 21 were established by X‐ray crystallography.     

An Answer to the Article ‘On the Misleading Interpretation of the Properties of the f-Electron Elements’

The position of the ‘Inclined W theory’, i.e., the linear correlation of the properties (P_i) of the lanthanide and the actinide ions with their ground state total orbital angular quantum numbers (L), P_i = w_iL + k_i, where w_i and k_i are the slopes and intercepts of the least squares lines, is made clear. The position of gadolinium is ambivalent, and it can be a common point for the symmetric ‘Inclined W plots’ or it may either belong to the second or the third tetrad depending on the system investigated. The propionate and the isobutyrate systems are used to elucidate the ‘Inclined W concept’. The ‘Inclined W parameters’ for the solvent extraction of the lanthanides with PMBP ligand have been calculated.     

Rebuttal to “comments on ‘some evidence against the existence of the liquid–liquid transition. IV. The temperature dependence of shear viscosity’”

Data on the temperature dependence of viscosity obtained on three different polystyrenes with narrow molecular weight distributions are fitted to the Vogel, Fulcher, Tamman, and Hesse (VTFH) equation as well as to two intersecting Arrhenius lines. Both fits are optimized by means of computer programs. The data were chosen to fit the requirements stated by Boyer. The results of the analyses support the earlier conclusions that temperature-dependent viscosity data do not indicate the presence of any liquid-liquid transition T_LL above the glass temperature T_g. In addition, evidence is presented which indicates that the viscosity at T_g of high-molecular-weight polystyrenes is proportional to the 3.4 power of the molecular weight. Hence T_g is not an isoviscous temperature.     

A fast,reproducible and low‐cost method for sequence deconvolution of ‘on‐bead’ peptides via ‘on‐target’ maldi‐TOF/TOF mass spectrometry

A novel approach to high‐throughput sequence deconvolution of on‐bead small peptides (MW < 2000 Da) using on‐target MALDI‐TOF/TOF instrumentation is presented. Short peptides of pentamer and octamer length, covalently attached to TentaGel polystyrene beads through a photolabile linker, were placed onto the MALDI target, apportioned with suitable matrix (2,5‐dihydroxybenzoic acid) and then hit with the instrument laser (Nd : YAG, 355 nm). This induced easy and highly reproducible photochemical cleavage, desorption (MS mode) and fragmentation (MS/MS mode). Peptide fragments were identified with a mass accuracy of 0.1 Da of the expected values. This technique significantly accelerates the sequence determination of positive peptide hits obtained from random combinatorial libraries when screening against biological targets, paving the way for a rapid and efficient method to identify molecular imaging ligands specific to pathological targets in cancer and other diseases. Copyright © 2009 John Wiley & Sons, Ltd.     

Reply to ‘On the non-existence of strictly diabatic molecular electronic bases'

In the preceding Letter (Chem. Phys. Lett. 330 (2000) 629–632) Kendrick, Mead and Truhlar publish a Comment in which they object to our formulation of the ‘necessary conditions for having diabatic states'. It is shown that relating themselves to what was not written in the article, these authors jumped to the wrong conclusions. The example they provided is here used to show the simplicity with which the above-mentioned necessary conditions lead to a set of ‘quantized' values for the non-adiabatic coupling terms.