Metabonomics: the use of electrospray mass spectrometry coupled to reversed-phase liquid chromatography shows potential for the screening of rat urine in drug development

The application of liquid chromatography/mass spectrometry (LC/MS) followed by principal components analysis (PCA) has been successfully applied to the screening of rat urine following the administration of three candidate pharmaceuticals. With this methodology it was possible to differentiate the control samples from the dosed samples and to identify the components of the mass spectrum responsible for the separation. These data clearly show that LC/MS is a viable alternative, or complementary, technique to proton NMR for metabonomics applications in drug discovery and development.     

The structure of dehydrated zeolite 3A (Si/Al = 1.01) by neutron profile refinement

A neutron powder diffraction study of a dehydrated commercially available potassium exchanged zeolite A (Linde 3A) has shown that the diffraction pattern can be indexed in cubic space group $\text{Fm}\text{3}\text{c}$. For this sample there is 63% exchange of potassium for sodium (K⁺/Na⁺ = 1.69). Data collected at a neutron wavelength of 2.98 Å shows no evidence of rhombohedral distortion and suggests that the assignment of space group $\text{Fm}\text{3}\text{c}$ is correct. The final structural model is closely analogous to that found for dehydrated sodium zeolite A (J. M. Adams, D. A. Haselden, and A. W. Hewat, J. Solid State Chem.44, 245 (1982); J. J. Pluth and J. V. Smith, J. Amer. Chem. Soc.102, 4074 (1980). Unusual features of previous refinements of potassium containing zeolite A samples, i.e., “zero coordinate” cations (P. C. W. Leung, M. B. Kunz, K. Seff, and I. E. Maxwell, J. Phys. Chem.83, 741 (1979)) or potassium inside the β-cage (J. J. Pluth and J. V. Smith, J. Phys. Chem.83, 741 (1979)) have not been found. Refinements using the same 1.9 Å neutron powder diffraction data were also obtained with the models of Leung et al. and Pluth and Smith (1979) as starting points (denoted LKSM and PS, respectively) and comparison is made with these. The final R factors for the three refinements were R_pw (A. K. Cheetham and J. C. Taylor, J. Solid State Chem.21, 253 (1977)) = 10.24% for the model presented here, R_pw = 10.38% (PS model), and R_pw = 10.61% (LKSM model).     

Peak alignment of urine NMR spectra using fuzzy warping

Proton nuclear magnetic resonance (1H NMR) spectroscopic analysis of mixtures has been used extensively for a variety of applications ranging from the analysis of plant extracts, wine, and food to the evaluation of toxicity in animals. For example, NMR analysis of urine samples has been used extensively for biomarker discovery and, more simply, for the construction of classification models of toxicity, disease, and biochemical phenotype. However, NMR spectra of complex mixtures typically show unwanted local peak shifts caused by matrix and instrument variability, which must be compensated for prior to statistical analysis and interpretation of the data. One approach is to align the spectral peaks across the data set. An efficient and fast warping algorithm is required as the signals typically contain ca. 32,000-64,000 data points and there can be several thousand spectra in a data set. As demonstrated in our study, the iterative fuzzy warping algorithm fulfills these requirements and can be used on-line for an alignment of the NMR spectra. Correlation coefficients between the aligned and target spectra are used as the evaluation function for the algorithm, and its performance is compared with those of other published warping methods.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

The structure of dehydrated Na zeolite A (SiAl = 1.09) by neutron profile refinement

Contrary to the recent work of J. M. Thomas et al. (J. Chem. Soc. Chem. Commun., 678, 1981), it was found that a high-resolution neutron powder diffraction pattern of a sample of dehydrated Na zeolite A (with $\text{Si}\text{Al}$ ratio 1.09) can be indexed and refined in the cubic groups $\text{Pm}\text{3}\text{m (R}{}_{\mathrm{<mtext>pw</mtext>}}\text{= 11.0\%)}$ (A. K. Cheetham and J. C. Taylor, J. Solid State Chem.21, 253, 1977) and $\text{Fm}\text{3}\text{c (R}{}_{\mathrm{<mtext>pw</mtext>}}\text{= 10.3\%)}$, whereas in the rhombohedral space group $\text{R}\text{3}$ refinement was unsuccessful. For two other samples having $\text{Si}\text{Al}$ ratios of 1.03 and 1.12 the diffraction patterns again showed no evidence of rhombohedral distortion and can be indexed using a cubic unit cell. It appears that the Si, Al ordering of zeolite A, and hence the crystal symmetry, must depend upon the conditions of preparation of the zeolite.     

The structure of a carbon monoxide adduct of cobalt-exchanged zeolite A (Co5.25Na1.5A · 1.5CO) by neutron profile refinement

The structure of a carbon monoxide adduct of cobalt-exchanged zeolite A, CO_5.25Na_1.5A · 1.5CO, has been determined by Rietveld neutron profile refinement. The space group used was $\text{Fm}\text{3}\text{c}$ with a = 24.1557(14) Å; the final R_pw was 13.8%. All exchangeable cations are located in sites adjacent to the 6-rings; 3.75 of the cobalt cations sit 0.4 Å inside the β-cage (Co(2)) and are arranged tetrahedrally about the eight 6-ring sites in the β-cage. The sodium cations (Na(1)) reside just inside the α-cage in sites similar to those found previously for zeolites 3A, 4A, and 5A. The remaining 1.5 cobalt cations (Co(1)) are located in sites similar to those for sodium, but they are also coordinated to the carbon monoxide molecules, which lie on, or close-to, the threefold axis which passes through the 6-ring. Inside the β-cage there is a tetrahedral aluminum complex of AlO₄ type, the oxygen atoms (O1) of which point toward six rings not occupied by cobalt cations, Co(2). Each of the oxygen atoms of this complex is involved in a hydrogen bond (2.83 Å) to the 6-ring oxygen O(3). Approximately $\text{2}\text{3}$ of these bonds are of type O1H···O(3) and $\text{1}\text{3}$ of type O1···HO(3).     

Use of liquid chromatography/time-of-flight mass spectrometry and multivariate statistical analysis shows promise for the detection of drug metabolites in biological fluids

The process of metabolite identification is essential to the drug discovery and development process; this is usually achieved by liquid chromatography/tandem mass spectrometry (LC/MS/MS) or a combination of liquid chromatography/mass spectrometry (LC/MS) and nuclear magnetic resonance (NMR) spectroscopy. Metabolite identification is, however, a time-consuming process requiring an experienced skilled scientist. Multivariate statistical analysis has been used in the field of metabonomics to elucidate differences in endogenous biological profiling due to a toxic effect or a disease state. In this paper we show how a combination of liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) and multivariate statistical analysis can be used to detect drug metabolites in a biological fluid with no prior knowledge of the compound administered.