Influence of the sample toxic profile on the suitability of a high performance liquid chromatography method for official paralytic shellfish toxins control

An HPLC-FLD method, involving pre-chromatographic oxidation of the PSP toxins with hydrogen peroxide and periodate, has been AOAC validated through a collaborative trial and adopted as AOAC Official Method. This method could be a candidate for replacing the mouse bioassay (MBA) for the Official Control of PSP toxins at European level, once accepted by the legislation. An interlaboratory exercise has been organized by the CRLMB to evaluate its "fitness for purpose" for the Official Control of PSP toxins in the EU laboratories. Eighteen EU laboratories took part in the study and had to analyze six bivalve mollusc samples with several PSP toxic profiles. The performance of the participant laboratories in the application of this method was compared with that obtained at the collaborative trial. Information on problems/drawbacks encountered by participants in the application of this method was also sought. The HPLC validated method is only applicable for Official PSP Control for certain samples. This depends on sample PSP toxic profile. Results obtained for samples where only GTX2,3 and STX were present were satisfactory and in agreement with MBA results. Results obtained for a sample with a toxic profile dominated by GTX6 and suspected to contain also C1,2 and C3,4 were not satisfactory. GTX5 and dc-STX could be quantified, although the results achieved (total toxicity) were lower than those obtained by MBA. It can be also useful as a screening method, complementary to MBA, helping in the reduction of the animals used. However, the lack of several PSP standards, the fact that the method is not validated for all the PSP toxins, and several drawbacks found in its application are a handicap to fully implement it for Official PSP Control as a viable replacement for bioassay.     

A combined molecular modeling study on gelatinases and their potent inhibitors

Zinc‐dependent matrix metalloproteinase (MMP) family is considered to be an attractive target because of its important role in many physiological and pathological processes. In the present work, a molecular modeling study combining protein‐, ligand‐ and complex‐based computational methods was performed to analyze a new series of β‐N‐biaryl ether sulfonamide hydroxamates as potent inhibitors of gelatinase A (MMP‐2) and gelatinase B (MMP‐9). Firstly, the similarities and differences between the binding sites of MMP‐2 and MMP‐9 were analyzed through sequence alignment and structural superimposition. Secondly, in order to extract structural features influencing the activities of these inhibitors, quantitative structure‐activity relationship (QSAR) models using genetic algorithm‐multiple linear regression (GA‐MLR), comparative molecular field (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were developed. The proposed QSAR models could give good predictive ability for the studied inhibitors. Thirdly, docking study was employed to further explore the binding mode between the ligand and protein. The results from all the above analyses could provide the information about the similarities and differences of the binding mode between the MMP‐2, MMP‐9 and their potent inhibitors. The obtained results can provide very useful information for the design of new potential inhibitors. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Structure and Properties of Poly(vinyl alcohol) Hydrogels Obtained by Freeze/Thaw Techniques

The relationships between the structure and the viscoelastic properties of freeze/thaw PVA hydrogels obtained by repeatedly freezing and thawing dilute solutions of PVA in D₂O(11% w/w PVA) in as-prepared and rehydrated states are investigated. Our results indicate that the PVA chains and solvent molecules are organized at different hierarchical length scales, which include the presence of micro- and macro-pores, into a network scaffolding. The porous network is ensured by the presence of crystallites, which act as knots interconnected by portions of PVA chains swollen by the solvent. X-ray diffraction and SANS techniques are used to obtain structural information at short (angstroms) and medium (nanometers) ranges of length scales, concerning the crystallinity, the size of small crystalline aggregates and the average distance between crystallites in PVA hydrogels. Indirect information concerning the structural organization on the large length scales (microns) are provided by viscoelastic measurements. The dynamic shear elastic moduli at low frequency and low strain amplitude, G′, are determined and related to the degree of crystallinity. These data indicate that a minimum crystallinity of 1% is required for these PVA samples to exhibit gel behaviour and have allowed obtaining the order of magnitude of the average mesh size in these gels. Finally, it is shown that the negative effect of aging, inducing worse physical and mechanical properties in these systems, may be prevented using a drying/re-hydration protocol able to keep the physical properties of the as-prepared PVA hydrogels.     

Comparison of different fluorimetric HPLC methods for analysis of acidic polyether toxins in marine phytoplankton

The human toxic syndrome, diarrhetic shellfish poisoning (DSP), is caused by polyether toxins that are present in bivalve molluscs but originate from some species of marine phytoplankton. During the last few years different HPLC methods with fluorescence detection (FLD) have been proposed for analysis of marine toxins, including polyether toxins, in shellfish and phytoplankton. Several derivatization reagents have been proposed in the literature, with the aim of converting the acidic DSP toxins into their corresponding fluorescent derivatives. In this work we report results obtained from HPLC–FLD analysis of extracts from phytoplankton, including Dinophysis spp., harvested off the south-west coast of Ireland. Three different reagents were used for fluorescent derivatization: 3-bromomethyl-6,7-dimethoxy-1-methyl-2(1H)-quinoxalinone (BrDMEQ), 9-chloromethylanthracene (CA), and in situ 9-anthracenyldiazomethane (ADAM). Derivatization was performed under conditions previously optimised. The DSP derivatives were cleaned using different SPE procedures then analysed by HPLC–FLD. In this study, the use of BrDMEQ, CA, and in situ ADAM was compared in terms of sensitivity and selectivity. Evaluation of HPLC methods for analysis of DSP toxin derivatives was also conducted; the presence of okadaic acid (OA), dinophysistoxin-2 (DTX-2), and pectenotoxin-2 seco acids (PTX1SAs) was detected in the sample extracts studied.     

A gadolinium(III) complex: synthesis,structure, photophysical profile and its role in the degradation of nitroaromatics

The synthesis and structural characterization of a gadolinium(III) complex with phenanthroline and thiocyanate ligands have been accomplished. The X-ray crystal structure reveals that Gd(III) in a slightly distorted square anti-prism coordinated with four thiocyanate ions and two phenanthroline molecules; one phenanthroline is protonated which compensates the charge of Gd(III) center. The crystal structure shows chemically significant non-covalent interactions like hydrogen bonding involving the thiocyanate ligand and π–π interactions between uncoordinated phenanthrolinium and coordinated phen. Investigation on the intermolecular interactions and crystal packing via Hirshfeld surface analysis reveals that close contacts are mainly associated with weak interactions. The fingerprint plots demonstrate that these weak interactions are important for crystal packing. The Gd(III) complex shows photophysical activity. The compound is capable of degrading toxic pollutants like nitroaromatics and may have far reaching consequences for cleaning these toxic pollutants from industrial effluents.     

Rapid and sensitive identification of ricin in environmental samples based on lactamyl agarose beads using LC‐MS/MS (MRM)

Ricin, a plant‐derived toxin extracted from the seeds of Ricinus communis (castor bean plant), is one of the most toxic proteins known. Ricin's high toxicity, widespread availability, and ease of its extraction make it a potential agent for bioterrorist attacks. Most ricin detection methods are based on immunoassays. These methods may suffer from low efficiency in matrices containing interfering substances, or from false positive results due to antibody cross reactivity, with highly homologous proteins. In this study, we have developed a simple, rapid, sensitive, and selective mass spectrometry assay, for the identification of ricin in complex environmental samples. This assay involves three main stages: (a) Ricin affinity capture by commercial lactamyl‐agarose (LA) beads. (b) Tryptic digestion. (c) LC‐MS/MS (MRM) analysis of tryptic fragments. The assay was validated using 60 diverse environmental samples such as soil, asphalt, and vegetation, taken from various geographic regions. The assay's selectivity was established in the presence of high concentrations of competing lectin interferences. Based on our findings, we have defined strict criteria for unambiguous identification of ricin. Our novel method, which combines affinity capture beads followed by MRM‐based analysis, enabled the identification of 1 ppb ricin spiked into complex environmental matrices. This methodology has the potential to be extended for the identification of ricin in body fluids from individuals exposed (deliberately or accidentally) to the toxin, contaminated food or for the detection of the entire family of RIP‐II toxins, by applying multiplex format.     

Stripping Chronopotentiometry with Dry‐Preservable Supporting Electrolyte

The determination of some toxic metals by stripping chronopotentiometry with a supporting solution having an unconventional composition has been investigated with the aim of using such components in disposable measuring cells preservable in dry state and quite ready for use, only needing addition of a small volume of sample. The new supporting solution is prepared with a solid strong acid, p‐toluenesulfonic acid, in the place of the inorganic acids commonly used to improve the cation availability. The other components are, as usual, sodium chloride, which fixes the potential of the screen‐printed silver – silver chloride reference electrode, and mercury(II) chloride as the plating agent. This supporting solution has been tested in batch measurements with the mercury film glassy carbon electrode as well as with screen‐printed carbon‐ink electrodes, either with mercury film or bare. The physical shape of the mercury layer electrolytically deposited on screen‐printed carbon‐ink electrodes from a supporting solution containing 0.1 M p‐toluenesulfonic acid and 0.1 M sodium chloride has been investigated by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) microanalysis. In chronopotentiometric stripping p‐toluenesulfonic acid performs as well as the usual inorganic strong acids, particularly in terms of sensitivity. At 0.1 mol dm^?3 it proved very suitable for the determination of toxic metals, in particular lead(II), at levels down to a few μg dm^?3. The overall results appear promising and can open new avenues for preparing disposable cells for on‐field stripping chronopotentiometric determination of toxic metals.     

Bioassay Guided Isolation and Identification of a Cytotoxic Compound from Azadirachta indica Leaves

This study aimed to investigate the structural features of the isolated flavonol glycoside, which might behave as a cytotoxic compound. The hexane, chloroform, ethyl acetate, and aqueous fractions of an 80% methanol solution of Neem (Azadirachta indica) (Family: Meliaceae) leaves were subjected to a cytotoxicity bioassay against brine shrimp, Artemia salina. The ethyl acetate fraction exhibited the highest cytotoxic effect, supported by the lowest lethal concentration, a LC₅₀ value of 1.35±0.40 ppm. A compound, Quercetin 3‐O‐β‐D‐glucopyranoside, was isolated from the most toxic fraction of the ethyl acetate via preparative liquid chromatography and then identified via ultraviolet‐visible (UV‐Vis), infrared (IR), mass spectrum (MS) and nuclear magnetic resonance (NMR) analyses. The compound was further confirmed by physical state, color, solubility, and melting point determination. The cytotoxic results suggest that the leaf ethyl acetate fraction consists of toxic compounds, which point towards the isolation of Quercetin 3‐O‐β‐D‐glucopyranoside.     

Theoretical studies of the g factors and local structures of the Ni3+ centers in Na2Zn(SO4)2·4H2O and K2Zn(SO4)2·6H2O crystals

The local structures and the g factors g_i (i = x, y, z) for Ni³⁺ centers in Na₂Zn(SO₄)₂·4H₂O (DPPH) and K₂Zn(SO₄)₂·6H₂O (PHZS) crystals are theoretically studied by using the perturbation formulas of the g factors for a 3d⁷ ion with low spin (S = 1/2) in orthorhombically compressed octahedra. In these formulas, the contributions to g factors from both the spin-orbit coupling interactions of the central ion and ligands are taken into account, and the required crystal-field parameters are estimated from the superposition model and the local geometry of the systems. Based on the calculations, the Ni-O bonds are found to suffer the axial compression δz (or Δz) of about 0.111 Å (or 0.036 Å) along the z-axis for Ni³⁺ centers in DPPH (or PHZS) crystals. Meanwhile, the Ni-O bonds may experience additional planar bond length variation δx (≈0.015 Å) along x- and y-axes for the orthorhombic Ni³⁺ center in DPPH. The theoretical g factors agree well with the experimental data. The obtained local structural parameters for both Ni³⁺ centers are discussed.     

Insight into the structural requirements of pyrimidine-based phosphodiesterase 10A (PDE10A) inhibitors by multiple validated 3D QSAR approaches

Schizophrenia is a complex disorder of thinking and behaviour (0.3?0.7% of the population is affected). The over-expression of phosphodiesterase 10A (PDE10A) enzyme may be a potential target for schizophrenia and Huntington’s disease. Because 3D QSAR analysis is one of the most frequently used modelling techniques, in the present study, five different 3D QSAR tools, namely CoMFA, CoMSIA, kNN-MFA, Open3DQSAR and topomer CoMFA methods, were used on a dataset of pyrimidine-based PDE10A inhibitors. All developed models were validated internally and externally. The non-commercial Open3DQSAR produced the best statistical results amongst 3D QSAR tools. The structural interpretations obtained from different methods were thoroughly analysed and were justified on the basis of information obtained from the crystal structure. Information from one method was mostly validated by the results of other methods and vice versa. In the current work, the use of multiple tools in the same analysis revealed more complete information about the structural requirements of these compounds. On the basis of the observations of the 3D QSAR studies, 12 new compounds were designed for better PDE10A inhibitory activity. The current investigation may help in further designing new PDE10A inhibitors with promising activity.     

Efficacy and Limitations of Chemically Diverse Small-Molecule Enzyme-Inhibitors against the Synergistic Coagulotoxic Activities of Bitis Viper Venoms

Snakebite remains a significant public health burden globally, disproportionately affecting low-income and impoverished regions of the world. Recently, researchers have begun to focus on the use of small-molecule inhibitors as potential candidates for the neutralisation of key snake venom toxins and as potential field therapies. Bitis vipers represent some of the most medically important as well as frequently encountered snake species in Africa, with a number of species possessing anticoagulant phospholipase A₂ (PLA₂) toxins that prevent the prothrombinase complex from inducing clot formation. Additionally, species within the genus are known to exert pseudo-procoagulant activity, whereby kallikrein enzymatic toxins cleave fibrinogen to form a weak fibrin clot that rapidly degrades, thereby depleting fibrinogen levels and contributing to the net anticoagulant state. Utilising well-validated coagulation assays measuring time until clot formation, this study addresses the in vitro efficacy of three small molecule enzyme inhibitors (marimastat, prinomastat and varespladib) in neutralising these aforementioned activities. The PLA₂ inhibitor varespladib showed the greatest efficacy for the neutralisation of PLA₂-driven anticoagulant venom activity, with the metalloproteinase inhibitors prinomastat and marimastat both showing low and highly variable degrees of cross-neutralisation with PLA₂ anticoagulant toxicity. However, none of the inhibitors showed efficacy in neutralising the pseudo-procoagulant venom activity exerted by the venom of B. caudalis. Our results highlight the complex nature of snake venoms, for which single-compound treatments will not be universally effective, but combinations might prove highly effective. Despite the limitations of these inhibitors with regards to in vitro kallikrein enzyme pseudo-procoagulant venom activity, our results further support the growing body of literature indicating the potential use of small molecule inhibitors to enhance first-aid treatment of snakebite envenoming, particularly in cases where hospital and thus antivenom treatment is either unavailable or far away.     

Cobalt(III), zinc(II), cadmium(II) and palladium(II) complexes with the hydrolysed and non-hydrolysed condensation products of 2-acetylpyridine with ethyl hydrazinoacetate: X-ray structure analysis of mer-bis{(E )-2-[N′-(1-pyridin-2-yl-ethylidene)hydrazino] acetato}cobalt(III) tetrafluoroborate

Four Co(III), Zn(II), Pd(II) and Cd(II) complexes with ligands derived in situ from acetylpyridine and ethyl hydrazinoacetate or hydrolysed ethyl hydrazinoacetate were prepared. An X-ray structural analysis showed that the Co(III) complex is octahedral with two tridentate (E)-2-[N′-(1-pyridin-2-yl-ethylidene)hydrazino]acetate (apha) ligands, each forming two five-membered rings with the metal ion. In the tetrahedral Zn(II) complex, only a single apha ligand was coordinated, in the same way as that in the Co(III) complex. In the case of the tetrahedral Cd(II) complex the non-hydrolysed form of (E)-2-[N′-(1-pyridin-2-yl-ethylidene)hydrazino]acetic acid ethyl ester (aphaoet) coordinated as a bidentate and the two remaining coordination sites were occupied by Cl^? and CH₃COO^? ions. In addition, the square-planar neutral Pd(II) complex was synthesized, having the same bidentate as in the Cd(II) complex and two Cl^? ions in the remaining coordination sites. Due to their being diamagnetic, all four complexes were characterized by ¹H-NMR and ¹³C-NMR spectroscopy.     

Detection of total microcystin in fish tissues based on lemieux oxidation and recovery of 2-methyl-3-methoxy-4-phenylbutanoic acid (MMPB) by solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC/MS)

Microcystins (MCs) are widespread cyanobacterial toxins in freshwater systems, and have been linked to both acute and chronic health effects. A growing number of studies suggest that MC can bioaccumulate in food webs. Although, several methods (i.e. ELISA, LC-MS) have been developed for analysis of MC in water, extraction (for subsequent analysis) of the toxin from biological matrices (i.e. animal tissues) is impeded owing to covalent binding of toxins and active sites of their cellular targets, i.e. protein phosphatases. As an alternative approach, chromatographic methods for analysis of a unique marker, 2-methyl-3-methoxy-4-phenylbutanoic acid (MMPB), the product of the Lemieux oxidation of MCs, have been previously developed, and shown to measure total (bound and unbound) MC. Application, however, has been limited by poor recovery of the analyte. An improved recovery method is proposed – specifically the use of solid-phase microextraction (SPME). The MMPB analogue, 4-phenylbutanoic acid (4PB), and oxidized MC, were used to develop methods, and we specifically investigated several SPME fibres, and post-oxidation steps. Specifically, a method employing post-oxidation methyl esterification, followed by headspace SPME recovery of MMPB, was developed, and subsequently applied to analysis of environmental samples (i.e. fish tissues) previously shown to contain MCs. The method shows high linearity for both water and tissues spiked with MC, and an improved limit of quantitation of approximately 140?ng?g^?1. Evaluation of field samples by SPME-GC/MS detected considerably higher levels of MC, than detected by conventional methods (i.e. ELISA), and it is proposed that this technique reveals MC (particularly in the bound form) that is not detected by these methods. These results indicate that the developed method provides improved detection capability for MC in biological matrices, and will enhance our ability to understand bioaccumulation in freshwater food webs, as well as monitor exposure.     

Complex palytoxin‐like profile of Ostreopsis ovata. Identification of four new ovatoxins by high‐resolution liquid chromatography/mass spectrometry

Over the past decades, Italian coastlines have been plagued by recurring presence of the benthic dinoflagellate Ostreopsis ovata. Such an alga has caused severe sanitary emergencies and economic losses due to its production of palytoxin‐like compounds. Previous studies have confirmed the presence of ovatoxin‐a (OVTX‐a) as the major toxin of the algal toxin profile together with small amounts of putative palytoxin (PLTX). In our ongoing research on O. ovata toxins we report herein on in‐depth investigation of an O. ovata culture carried out by high‐resolution (HR) liquid chromatography/mass spectrometry (LC/MS) and tandem mass spectrometry (MS²). Particularly, the presence of putative PLTX and OVTX‐a was confirmed and the occurrence in the extract of four new palytoxin‐like compounds, OVTX‐b, ‐c, ‐d, and ‐e, was highlighted. Elemental formulae have been assigned to the new ovatoxins and information has been gained about their structural features. A quantitative study of the O. ovata culture extract indicated that the whole of the new ovatoxins represents about 46% of the total toxin content and, thus, their presence has to be taken into account when LC/MS‐based monitoring programs of either plankton or contaminated seafood are carried out. Copyright © 2010 John Wiley & Sons, Ltd.     

Reconstitution of the Cytb5–CytP450 Complex in Nanodiscs for Structural Studies using NMR Spectroscopy

Cytochrome P450s (P450s) are a superfamily of enzymes responsible for the catalysis of a wide range of substrates. Dynamic interactions between full‐length membrane‐bound P450 and its redox partner cytochrome b₅ (cytb₅) have been found to be important for the enzymatic activity of P450. However, the stability of the circa 70 kDa membrane‐bound complex in model membranes renders high‐resolution structural NMR studies particularly difficult. To overcome these challenges, reconstitution of the P450–cytb₅ complex in peptide‐based nanodiscs, containing no detergents, has been demonstrated, which are characterized by size exclusion chromatography and NMR spectroscopy. In addition, NMR experiments are used to identify the binding interface of the P450–cytb₅ complex in the nanodisc. This is the first successful demonstration of a protein–protein complex in a nanodisc using NMR structural studies and should be useful to obtain valuable structural information on membrane‐bound protein complexes.     

An Unusual Family of Glycosylated Peptides Isolated from <Emphasis Type="BoldItalic">Dendroaspis angusticeps</Emphasis> Venom and Characterized by Combination of Collision Induced and Electron Transfer Dissociation

This study describes the structural characterization of a totally new family of peptides from the venom of the snake green mamba (Dendroaspis angusticeps). Interestingly, these peptides differ in several points from other already known mamba toxins. First of all, they exhibit very small molecular masses, ranging from 1.3 to 2.4 kDa. The molecular mass of classical mamba toxins is in the range of 7 to 25 kDa. Second, the new peptides do not contain disulfide bonds, a post-translational modification commonly encountered in animal toxins. The third difference is the very high proportion of proline residues in the sequence accounting for about one-third of the sequence. Finally, these new peptides reveal a carbohydrate moiety, indicating a glycosylation in the sequence. The last two features have made the structural characterization of the new peptides by mass spectrometry a real analytical challenge. Peptides were characterized by a combined use of MALDI- TOF/TOF and nanoESI-IT-ETD experiments to determine not only the peptide sequence but also the composition and the position of the carbohydrate moiety. Anyway, such small glycosylated and proline-rich toxins are totally different from any other known snake peptide and form, as a consequence, a new family of peptides.     

Synthesis and characterization of transition metal-vitamin B13 complexes mixed with a co-vitamin

The synthesis and structural characterization of mixed vitamin-metal complexes are reported. A complex bearing two vitamins (B3 and B13) on the same metal centre, nicotinamide(orotato)nickel(II) pentahydrate, has been prepared and characterised by single-crystal X-ray diffraction methods. A complex of Cr(III) with vitamins C and B13, bis(ascorbato)orotatochromium(III) dihydrate, has been isolated and its nature investigated by means IR, ¹³C?NMR, API-ES and thermogravimetric measurements. Theoretical calculations have been performed to propose a structure in accord with results obtained.     

Thermal Behaviour and Decomposition Kinetics for Two Palladium(II) Complexes with 1-aminopyrene and its Derivative

The thermal decomposition studies for two palladium(II) complexes Pd(apyr)₂Cl₂ and Pd(pmpa)Cl₂ (apyr=1–aminopyrene and pmpa=N–(2–pyridylmethylene)–1–pyrenylamine) were carried out in pure nitrogen using TG-DTG techniques. The non-isothermal kinetic parameters for the two complexes were evaluated employing the method suggested by Málek, esták, Koga et al. Based on the above results, thermal behaviour of the complexes were carefully discussed, which showed that not only the parameters value, but also the decomposition pattern and mechanism for complex 1 are different from complex 2.This revised version was published online in November 2005 with corrections to the Cover Date.     

Analysis of Methylcitric Acid by Enantioselective Multidimensional Gas Chromatography-Mass Spectrometry

Methylcitric acid (2-hydroxybutane-1,2,3-tricarboxylic acid–MCA) is a structural analogue of citric acid, but due to an additional methyl group it is a chiral molecule with two stereogenic centers and thus four stereoisomers are conceivable. MCA occurs naturally as prominent metabolite in body fluids of patients with inherited metabolic diseases such as propionic acidemia, methylmalonic aciduria, or holocarboxylase synthetase deficiency. Therefore methylcitric acid is considered to be an important diagnostic marker for these diseases. MCA is most likely produced from accumulated propionyl-CoA in these diseases by the enzyme si-citrate synthase from the citric acid cycle; however, there are other enzymes known which could catalyze the same reaction with different stereoselectivity, such as re-citrate synthase or the more specific enzyme methylcitrate synthase, found in microorganisms. Almost all methods dealing with MCA in the literature are non-enantioselective. For that reason there is no information about occurrence of MCA enantiomers in healthy people, patients with propionic acidemia, methylmalonic aciduria, or holocarboxylase synthetase deficiency and about value of enantiomeric distribution for diagnosis and long-term treatment. The enantioselective analysis of MCA as corresponding trimethyl ester was achieved by enantioselective multidimensional gas chromatography coupled with mass spectrometry using heptakis-(2,3-di-O-methyl-6-O-tert-butyl-dimethylsilyl)-β-cyclodextrin as chiral stationary phase. The described method allows a reliable screening of MCA in complex matrices like urine without time consuming sample preparation and with mass selective detection. During this investigation urine samples from various patients and healthy controls were analyzed. As concluded, MCA is a good diagnostic marker and can be easily measured by the method presented. Only the two stereoisomers (2S,3R) and (2S,3S) were detectable in patients and healthy controls. The varying ratios of these stereoisomers cannot presently be correlated with the health status of patients, although there are some indications that this might be possible. However, the quantitative levels of MCA, determined as the ratio of MCA absolute peak area divided by 1,000 to the creatinine contents of urine samples in this investigation, showed a dependence on the state of health and MCA would thus also be a possible marker for long-term treatment. Such a substance is of major interest nowadays since there are different studies searching for such a long-term marker in propionic acidemia or methylmalonic aciduria.     

CRYSTAL STRUCTURES OF Cd(H2O)2Cu(CN)3·2H2O,K[Cd(H2O)2Cu2(CN)5]·2H2O AND K2[Cd(H2O)Cu4(CN)8]·1.5H2O. STRUCTURES OF MULTI-DIMENSIONAL FRAMEWORKS FORMED WITH CADMIUM(II), COPPER(I) AND BRIDGING CYANO GROUPS

Abstract

In an attempt to form new multi-dimensional structures of cyano complexes including cadmium(II) and copper(I), four new complexes were obtained successively from an aqueous solution at intervals of from a few days to a few months. The complex 1 obtained first was unstable in the atmosphere. The crystal structures of the other complexes (2–4) obtained from second to fourth were determined by single crystal X-ray structure determinations. Their crystal data are as follows: 2 Cd(H₂O)₂ Cu(CN)₃·2H₂O, monoclinic, C2/m, a = 14.038(1), b = 9.944(1), c = 7.738(1) Å, β = 116.019(7)°, Z = 4; 3 K[Cd(H₂O)₂Cu₂(CN)₅]·2H₂O, triclinic, PI, a = 17.429(9), b = 16.519(7), c = 10.085(5) Å, α = 128.60(3), β = 137.44(2), γ = 45.82(2)°, Z = 4; 4 K₂[Cd(H₂O)Cu₄(CN)₈]·1.5H₂O, monoclinic, C2/c, a = 19.387(2), b = 16.056(3), c = 12.663(2)Å, β = 110.419(9)°, Z = 4. The main structural feature found in the complexes is that the whole framework consists of two networks, a Cd-Cu(I)-CN complex network that has an infinite network formed with bridging cyano groups between the metal atoms and a network formed with hydrogen bonding among water molecules. The second network is connected to Cd in the Cd-Cu(I)-CN complex network via a water ligand coordinated to Cd. In 2 a planar network of [CdCu(CN)₃] complexes are stacked along the c axis and the second network links the stacked complexes. 3 has a stacked structure of [Cd(H₂O)₂Cu(CN)₅]^2? in a bi-layered structure. The second network of 3, which includes K⁺ ions with an electrostatic interaction, spreads over the crystal, penetrating vacant spaces of the metal complex network. 4 has a double lattice structure with a pair of enantiomeric three-dimensional [Cd(H₂O)Cu₄(CN)₈]^2? complexes inter-penetrating each other. There are three structural factors for forming these framwork structures: (1) a non-planar coordination structure for Cd(II) that extends the planar structure of the Cu(I)-CN complex to a three-dimensional structure for the Cd-Cu(I)-CN complex; (2) a trigonal planar coordination structure for Cu(I) that generates vacant space in the metal complex network and makes possible hydrogen bonds to form the second network; (3) structural distortions of bridging cyano groups and a coordination structure of Cu(I) that cause variations of the metal complex network structure.