Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

ESI‐MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamic huffman coding

This note shows how to maintain a prefix code that remains optimum as the weights change. A Huffman tree with nonnegative integer weights can be represented in such a way that any weight w at level l can be increased or decreased by unity in O(l) steps, preserving minimality of the weighted path length. One-pass algorithms for file compression can be based on such a representation.     

Aztec Diamonds, Checkerboard Graphs, and Spanning Trees

This note derives the characteristic polynomial of a graph that represents nonjump moves in a generalized game of checkers. The number of spanning trees is also determined.     

Determination of clindamycin in plasma or serum by high-performance liquid chromatography with ultraviolet detection

A simple, sensitive high-performance liquid chromatographic assay for the determination of clindamycin in human plasma or serum has long been hampered by inability to separate it from endogenous compounds. We describe here such an assay. Proteins from a 200-microliters sample were precipitated by addition of acetonitrile containing the internal standard, triazolam. The sample was then vortex-mixed and centrifuged at approximately 3000 g for 10 min. The supernatant was evaporated to about 250 microliters under nitrogen, and 10-30 microliters were analyzed using an autoinjector. An octadecylsilane column with acetonitrile-water-phosphoric acid-tetramethylammonium chloride as mobile phase and ultraviolet detection at 198 nm provided a reproducibly quantifiable peak corresponding to 0.17 micrograms/ml. Retention times for clindamycin and triazolam averaged 8 and 11.8 min, respectively. Replicate standard curves run over a 36-h period showed no loss of integrity; r2 values generally exceeded 0.999. The method has successfully been applied to the analysis of samples taken up to 12 h after administration of intravenous infusions of 600-1200 mg in healthy volunteers.     

Fibonacci multiplication

A curious binary operation on the nonnegative integers is shown to be associative.     

Fabrication process parameters significantly affect the perovskite oxygen carriers materials (OCM) performance in chemical looping with oxygen uncoupling (CLOU)

Journal of Thermal Analysis and Calorimetry - The CLOU performance of the CaTixMn0.9?xMg0.1O3 (CMTM) perovskite-type system was investigated, comparing materials produced at laboratory scale...     

Lattices and Their Consistent Quantification

The order‐theoretic concept of lattices is introduced along with the concept of consistent quantification where lattice elements are mapped to real numbers in such a way that preserves some aspect of the order‐theoretic structure. Symmetries, such as associativity, constrain consistent quantification, and lead to a constraint equation known as the sum rule. Distributivity in distributive lattices also constrains consistent quantification and leads to a product rule. The sum and product rules, which are familiar from, but not unique to, probability theory, arise from the fact that logical statements form a distributive (Boolean) lattice, which exhibits the requisite symmetries.