Di-hydroxy malonic acid as a building block of hydrogen-bonded 3-dimensional architectures

An examination of the crystal structures of di-hydroxy malonic acid 1 (P2₁/na = 5.384(2), b = 6.268(2), c = 14.354(8) Å, = 103.57(3)°) and N-ethylbenzylammonium di-hydroxy hydrogenmalonate 2 (P2₁2₁2₁ a = 13.373(2), b = 15.342(4), c = 18.741(4) Å,) has highlighted the influence of directional O–H···O interactions in the assembly of hydroxy-substituted dicarboxylic acids. The complementarity of carboxylic and hydroxy groups in 1 creates a very dense 3-D structure (D _c = 1.919 g cm^–3) through four O–H···O hydrogen bonds. In 2, the anions form infinite, spiraling chains created by head-to-tail O–H···O hydrogen bonds. Neighbouring chains are crosslinked into a complex 3-D anionic network with channels parallel to a and b. The cations are positioned within these channels and held in place via two N–H···O interactions.     

Probing Metal Ion Complexation of Ligands with Multiple Metal Binding Sites: The Case of Spiropyrans

Among known molecular switches, spiropyrans attract considerable interest because of their reversible responsiveness to external stimuli and the deep conformational and electronic changes that characterize the switching process between the two isomeric forms [spiropyran (SP) and merocyanine (MC)]. Metal coordination is one of the most interesting aspects of spiropyrans for its potential in sensing, catalysis, and medicinal chemistry, but little is known about the details surrounding spiropyran–metal ion binding. We investigated the interplay between an N‐modified 8‐methoxy‐6‐nitrospiropyran (SP‐E), designed to provide appropriate molecular flexibility and a range of competing/collaborative metal binding sites, with Mg²⁺, Cu²⁺ and Zn²⁺, which were chosen for their similar coordination geometry preferences while differing in their hard/soft character. The formed molecular complexes were studied by means of UV/Vis, fluorescence, and NMR spectroscopies and mass spectrometry, and the crystal structure of the SP‐E–Cu complex was also obtained. The results indicate that the Mg²⁺, Zn²⁺ and Cu²⁺ complexes have identical coordination stoichiometry. Furthermore, the Mg²⁺ and Zn²⁺ complexes display fluorescence properties in solution and visible‐light responsiveness. These results provide important spectroscopic and structural information that can serve as a foundation for rational design of spiropyran‐based smart materials for metal sensing and scavenging applications.     

Excited‐State Dynamics of Isolated DNA Bases: A Case Study of Adenine

We present a summary of recent advances in the understanding of the UV photophysics of the isolated DNA base adenine, emphasizing a discussion of the mechanisms behind the ultrafast relaxation following excitation to the ππ* band. Drawing on our femtosecond time‐resolved photoelectron spectroscopy experiments, we discuss differences in the ultrafast relaxation of adenine and 9‐methyladenine and consider the relative merits of the various proposed mechanisms.     

A method for rational Chebyshev approximation of rational functions on the unit disk and on the unit interval

A method for construction of CF approximants in some cases of rational approximation of a rational function f on the unit disk and on the unit interval is presented. The inverted square root of the greatest positive eigenvalue and a corresponding eigenvector of an eigenvalue problem defined by the coefficients of f gives the solution.     

The robustness of the semi-Markov and delay time single-component inspection models to the Markov assumption

The context of planned preventive maintenance lends itself readilyto probabilistic modelling. Indeed, many of the published theoreticalmodels to be found in the literature adopt a Markov approach,where states are usually ‘operating’, ‘operatingat one of several levels of deterioration’, and ‘failed’.However, most of these models assume the required Markovianproperty and do not address the issue of testing the assumption,or the related task of estimating parameters. It is possiblethat data are inadequate to test the assumption, or that theMarkov property is believed to be not strictly valid, but acceptableas an approximation. In this paper we consider within a specificinspection–maintenance context the robustness of a Markov-basedmodel when the Markov assumption is not valid. This is achievedby comparing the output of an exact delay time model of an inspection–maintenanceproblem with that of a semi-Markov approximation. The importanceof establishing the vadility of the Markov property in the modellingapplication is highlighted. If the plant behaviour is seen tobe nearly Markov, in the case considered the semi-Markov modelgives a good approximation to the exact model. Conversley ifthe Markov assumption is not a good approximation, the semi-Markovmodel can lead to inappropriate advice.     

Novel cationic carotenoid lipids as delivery vectors of antisense oligonucleotides for exon skipping in Duchenne muscular dystrophy

Duchenne Muscular Dystrophy (DMD) is a common, inherited, incurable, fatal muscle wasting disease caused by deletions that disrupt the reading frame of the DMD gene such that no functional dystrophin protein is produced. Antisense oligonucleotide (AO)-directed exon skipping restores the reading frame of the DMD gene, and truncated, yet functional dystrophin protein is expressed. The aim of this study was to assess the efficiency of two novel rigid, cationic carotenoid lipids, C30-20 and C20-20, in the delivery of a phosphorodiamidate morpholino (PMO) AO, specifically designed for the targeted skipping of exon 45 of DMD mRNA in normal human skeletal muscle primary cells (hSkMCs). The cationic carotenoid lipid/PMO-AO lipoplexes yielded significant exon 45 skipping relative to a known commercial lipid, 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine (EPC).     

Balancing supramolecular reagents for reliable formation of co-crystals

The rational design and synthesis of a supramolecular reagent (SR) composed of two distinct hydrogen bonding sites (pyrazole-benzamide), and four co-crystals resulting from reactions between this SR and a variety of carboxylic acids are described; the observed primary intermolecular interaction is consistent and predictable in each case.     

Collision-induced dissociation pathways of yeast sphingolipids and their molecular profiling in total lipid extracts: a study by quadrupole TOF and linear ion trap-orbitrap mass spectrometry

The yeast Saccharomyces cerevisiae synthesizes three classes of sphingolipids: inositolphosphoceramides (IPCs), mannosyl-inositolphosphoceramides (MIPCs), and mannosyl-diinositolphosphoceramides (M(IP)2C). Tandem mass spectrometry of their molecular anions on a hybrid quadrupole time-of-flight (QqTOF) instrument produced fragments of inositol-containing head groups, which were specific for each lipid class. MS(n) analysis performed on a hybrid linear ion trap-orbitrap (LTQ Orbitrap) mass spectrometer with better than 3 ppm mass accuracy identified fragment ions specific for the amide-linked fatty acid and the long chain base moieties in individual molecular species. By selecting m/z of class-specific fragment ions for multiple precursor ion scanning, we profiled yeast sphingolipids in total lipid extracts on a QqTOF mass spectrometer. Thus, a combination of QqTOF and LTQ Orbitrap mass spectrometry lends itself to rapid, comprehensive and structure-specific profiling of the molecular composition of sphingolipids and glycerophospholipids in important model organisms, such as fungi and plants.     

Towards a general condition based maintenance model for a stochastic dynamic system

This paper considers a stochastic dynamic system subject to random deterioration, with regular condition monitoring and preventive maintenance. A model is presented to advise at a monitoring check what maintenance action to take based upon the condition monitoring and preventive maintenance information obtained to date. A general assumption adopted in the paper is that the performance of the system concerned can not be described directly by the monitored information, but is correlated with it stochastically. The model is relevant to a large class of condition monitoring techniques currently employed in industry including vibration and oil analysis. The model is constructed under fairly general conditions and includes two novel developments. Firstly, the concept of the conditional residual time is used to measure the condition of the monitored system at the time of a monitoring check, and secondly, contrary to previous practice, the monitored observation is now assumed to be a function of the system condition. Relationships between the observed history of condition monitoring, preventive maintenance actions, and the condition of the system are established. Methods for estimating model parameters are discussed. Since the model presented is generally beyond the scope for an analytical solution, a numerical approximation method is also proposed. Finally, a case example is presented to illustrate the modelling concepts in the case of non-maintained plant.