Robust UHPLC Separation Method Development for Multi-API Product Containing Amlodipine and Bisoprolol: The Impact of Column Selection

This paper describes a new and fast ultra-high pressure liquid chromatographic separation of amlodipine and bisoprolol and all their closely related compounds, for impurity profiling purposes. Computer-assisted method development was applied and the impact of several state-of-the-art stationary phase column chemistries (50 × 2.1 mm, sub-2 μm, and core–shell type materials) on the achievable selectivity and resolution was investigated. The work was performed according to quality by design principles using design of experiment with three experimental factors; namely the gradient time (t _G), temperature (T), and mobile phase pH. Thanks to modeling software, it was proved that the separation of all compounds was feasible on numerous column chemistries within <10 min, by proper adjustments of variables. It was also demonstrated that the reliability of predictions was good, as the predicted retention times and resolutions were in good agreement with the experimental ones. The final, optimized method separates 16 peaks related to amlodipine and bisoprolol within 7 min, ensuring baseline resolution between all peak-pairs.     

In vitro evolution of ligands to the membrane protein caveolin

Membrane proteins comprise a third of the human genome, yet present challenging targets for reverse chemical genetics. For example, although implicated in numerous diseases including multiple myeloma, the membrane protein caveolin-1 appears to offer a poor target for the discovery of synthetic ligands due to its largely unknown structure and insolubility. To break this impasse and identify new classes of caveolae controlling lead compounds, we applied phage-based, reverse chemical genetics for the discovery of caveolin-1 ligands derived from the anti-HIV therapeutic T20. Substitution of homologous residues into the T20 sequence used a process analogous to medicinal chemistry for the affinity maturation to bind caveolin. The resultant caveolin-1 ligands bound with >1000-fold higher affinity than wild-type T20. Two types of ELISAs and isothermal titration calorimetry (ITC) measurements demonstrated high affinity binding to caveolin by the T20 variants with K(d) values in the 150 nM range. Microscopy experiments with the highest affinity caveolin ligands confirmed colocalization of the ligands with endogenous caveolin in NIH 3T3 cells. The results establish the foundation for targeting caveolin and caveolae formation in living cells.     

Anion binding by bambus[6]uril probed in the gas phase and in solution

Electrospray ionization mass spectrometry (ESI-MS) is used to probe the binding of small anions to the macrocycle of bambus[6]uril. For the halide ions, the experimental patterns suggest F(-) < Cl(-) < Br(-) < I(-), which is consistent with the order of anion binding found in the condensed phase. Parallel equilibrium studies in the condensed phase establish the association constants of halide anions and bambus[6]uril in mixed solvents. A detailed analysis of the mass spectrometric data is used to shed light on the correlations between the binding constants in the condensed phase and the ion abundances observed using ESI-MS. From the analysis it becomes apparent that ESI-MS can indeed represent the situation in solution to some extent, but the sampling in the gas-phase experiment is not 1:1 compared to that in solution.     

A unique three-dimensional coordination cluster based on a silver carbene complex

In an attempt to perform a simple anion-exchange reaction on a pincer-carbene-ligated nickel complex using AgNO(3), we instead obtained an unexpected three-dimensional (3D) Ag(7) cluster containing a [Ag(6)] core in a twisted-bowtie geometry. The reverse-transmetalation reaction by which the carbene is transferred from nickel to silver is virtually unprecedented. The CNC pincer-carbene ligands exhibit unusual bridging modes of ligand bonding for all three donor atoms. Another unique feature is that the final structure exhibits a 3D structure brought about by the connection of two-dimensional layers of the [Ag(6)] core via a seventh Ag ion.     

Equilibrium acidities of superacids

In this paper, we report the most comprehensive equilibrium superacidity scale that is available to date. Contrary to most of the past works, this scale is set up in a medium of constant composition and the obtained acidity values characterize the acidities of molecules rather than acidities of media. The current scale is thus complementary to the well-known H(0) scale in the information that it provides. The solvent used is 1,2-dichloroethane (DCE). DCE has very weak basic properties (but sufficiently high polarity) and is an appropriate solvent for measuring acidities of very strong acids of diverse chemical nature. DCE acidities of well-known superacids (CF(3)SO(2)OH, (CF(3)SO(2))(2)NH, cyanocarbon acids, etc.) as well as common mineral acids (H(2)SO(4), HI, HBr, etc.) are reported. Acidities of altogether 62 acids have been determined from 176 interlinked relative acidity measurements. The scale spans 15 orders of magnitude (from picric acid to 1,1,2,3,3-pentacyanopropene) and is expected to be a useful tool in design, use, and further acidity measurements of superacidic molecules.     

Über den transfiniten Durchmesser ebener Punktmengen

Ohne Zusammenfassung     

Light Emission Resulting from Hydroxylamine-Induced Singlet Oxygen Formation of Oxidizing LDL Particles

Abstract— Oxidation of low-density lipoprotein (LDL) by low amounts of cupric ions resulted in the formation of singlet oxygen (₁O₂, ₁DL_g) when hydroxylamine (NH2OH) was added. Direct evidence on this excited species came from partial spectral resolution of the emitted light in the red spectral region (634 nm and 703 nm), which can be attributed to the dimol decay of singlet oxygen. Additional evidence for the existence of singlet oxygen came from the enhancing effect of deuterium oxide buffer (D20) on chemiluminescence intensity and the quenching effect of sodium azide. A linear correlation between NH2OH-de-pendent chemiluminescence intensity and the amount of diene conjugates (DC) formed in this reaction was observed. Removal of adventitious transition metals by adequate chelators prevented chemiluminescence in this system; NH2OH was also found to efficiently decrease metabolites of lipid peroxidation (LPO). Our findings are consistent with a sequence of reactions in which NH2OH first converts transition metals to their reduced state, thereby stimulating the formation of alkoxy- and peroxy-radicals. Peroxyradicals decompose in a bimolecular Russel reaction to hydroxyl compounds and singlet oxygen while the majority of alkoxy radicals are eliminated by a secondary reaction with NH2OH. Identical effects were observed when reducing antioxidants such as ascorbic acid or trolox C were used instead of hydroxylamine.