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TWIK-related acid-sensitive potassium (TASK) channels--members of the two pore domain potassium (K.sub.2P) channel family--are found in neurons.sup.1, cardiomyocytes.sup.2-4 and vascular smooth muscle cells.sup.5, where they are involved in the regulation of heart rate.sup.6, pulmonary artery tone.sup.5,7, sleep/wake cycles.sup.8 and responses to volatile anaesthetics.sup.8-11. K.sub.2P channels regulate the resting membrane potential, providing background K.sup.+ currents controlled by numerous physiological stimuli.sup.12-15. Unlike other K.sub.2P channels, TASK channels are able to bind inhibitors with high affinity, exceptional selectivity and very slow compound washout rates. As such, these channels are attractive drug targets, and TASK-1 inhibitors are currently in clinical trials for obstructive sleep apnoea and atrial fibrillation.sup.16. In general, potassium channels have an intramembrane vestibule with a selectivity filter situated above and a gate with four parallel helices located below; however, the K.sub.2P channels studied so far all lack a lower gate. Here we present the X-ray crystal structure of TASK-1, and show that it contains a lower gate--which we designate as an 'X-gate'--created by interaction of the two crossed C-terminal M4 transmembrane helices at the vestibule entrance. This structure is formed by six residues (.sup.243VLRFMT.sup.248) that are essential for responses to volatile anaesthetics.sup.10, neurotransmitters.sup.13 and G-protein-coupled receptors.sup.13. Mutations within the X-gate and the surrounding regions markedly affect both the channel-open probability and the activation of the channel by anaesthetics. Structures of TASK-1 bound to two high-affinity inhibitors show that both compounds bind below the selectivity filter and are trapped in the vestibule by the X-gate, which explains their exceptionally low washout rates. The presence of the X-gate in TASK channels explains many aspects of their physiological and pharmacological behaviour, which will be beneficial for the future development and optimization of TASK modulators for the treatment of heart, lung and sleep disorders. The X-ray crystal structure of the potassium channel TASK-1 reveals the presence of an X-gate, which traps small-molecule inhibitors in the intramembrane vestibule and explains their low washout rates from the channel., Author(s): Karin E. J. Rödström [sup.1] , Aytug K. Kiper [sup.2] , Wei Zhang [sup.1] [sup.5] , Susanne Rinné [sup.2] , Ashley C. W. Pike [sup.1] , Matthias Goldstein [sup.2] [...]

Move over X-ray crystallography. Cryo-electron microscopy is kicking up a storm by revealing the hidden machinery of the cell., Author(s): Ewen Callaway Author Affiliations: Illustration by Viktor Koen In a basement room, deep in the bowels of a steel-clad building in Cambridge, a major insurgency is under way. A [...]

The article presents a detailed analysis of the history of the arginine biosynthetic enzyme. The results reveal that the added, as well as the internally produced arginine highly represses the enzyme formation, as the potential required for this enzyme synthesis is found to be in excess of what is required.

A study was conducted to investigate in detail the [super 1]H NMR spectra of the ferriheme center and nearby protein residues in the high- and low-spin forms of the nitrophorins (NPs) from Rhodnius prolixus. The structures of the ferriheme complexes in terms of the orientation of the histidine imidazole ligand orientations depends on the heme cavity shape and could be altered by mutation of amino acids with side chains (phenyl vs tyrosyl) near the potential position where a heme vinyl group would be in one of the isomers.

Expansins are small extracellular proteins that promote turgor-driven extension of plant cell walls. EXPB1 (also called Zea m 1) is a member of the [beta]-expansin subfamily known in the allergen literature as group-1 grass pollen allergens. EXPB1 induces extension and stress relaxation of grass cell walls. To help elucidate expansin's mechanism of wall loosening, we determined the structure of EXPB1 by x-ray crystallography to 2.75-[Angstrom] resolution. EXPB1 consists of two domains closely packed and aligned so as to form a long, shallow groove with potential to bind a glycan backbone of [approximately equal to] 10 sugar residues. The structure of EXPB1 domain 1 resembles that of family-45 glycoside hydrolase (GH45), with conservation of most of the residues in the catalytic site. However, EXPB1 lacks a second aspartate that serves as the catalytic base required for hydrolytic activity in GH45 enzymes. Domain 2 of EXPB1 is an Ig-like [beta]-sandwich, with aromatic and polar residues that form a potential surface for polysaccharide binding in line with the glycan binding cleft of domain 1. EXPB1 binds to maize cell walls, most strongly to xylans, causing swelling of the cell wall. Tests for hydrolytic activity by EXPB1 with various wall polysaccharides proved negative. Moreover, GH45 enzymes and a GH45-related protein called 'swollenin' lacked wall extension activity comparable to that of expansins. We propose a model of expansin action in which EXPB1 facilitates the local movement and stress relaxation of arabinoxylancellulose networks within the wall by noncovalent rearrangement of its target. plant cell wall

Molecular imprinting techniques have proved to be a highly accessible method for producing molecule-specific recognition materials for a variety of applications, ranging from sensing to catalysis and separations. In noncovalent imprinting, it is anticipated that polymerizable complexes are created in the prepolymerization solution via self-assembly of functional monomers and template molecules resulting from inherent chemical complementarity, which will ideally form binding sites within the cross-linked matrix after polymerization. On the basis of [sup.1]H NMR data and X-ray crystallographic evidence, we now infer a more important role for template self-association for the recognition properties of quercetin-imprinted polymers. While directly applicable to fundamental understanding of the molecular imprinting mechanism of this polyphenol, on a more generic scale, this work also demonstrates the utility of this strategy toward analyzing complex noncovalent interaction mechanisms between small molecules. These interactions are of particular interest for quercetin and other members of the flavone/flavonoid class of compounds, which are radical-scavenging polyphenols of substantial interest to biomedicine.

Abstract: A novel two-step procedure involving the formation of 1-arylidene-2-tetralones from 2-tetralone and subsequent Michael addition of a cyclic secondary amine on the alkenone followed by in situ aerial oxidation [...]

The preparation and characterization of a wide selection of transition metal dependent polymetallic dithiocarbamate nanosized host structures, including a new X-ray crystal structure of one of them are reported. The results have shown that these novel polymetallic assemblies strongly bind nanosized fullerene guest species.

The ubiquitin C-terminal hydrolase UCH-L1 (PGP9.5) comprises > 1% of total brain protein but is almost absent from other tissues [Wilkinson, K. D., et al. (1989) Science 246, 670-673]. Mutations in the UCH-L1 gene have been reported to be linked to susceptibility to and protection from Parkinson's disease [Leroy, E., et al. (1998) Nature 395, 451-452; Maraganore, D. M., et al. (1999) Neurology 53, 1858-1860]. Abnormal overexpression of UCH-L1 has been shown to correlate with several forms of cancer [Hibi, K., et al. (1998) Cancer Res. 58, 5690-5694]. Because the amino acid sequence of UCH-L1 is similar to that of other ubiquitin C-terminal hydrolases, including the ubiquitously expressed UCH-L3, which appear to be unconnected to neurodegenerative disease, the structure of UCH-L1 and the effects of disease associated mutations on the structure and function are of considerable importance. We have determined the three-dimensional structure of human UCH-L1 at 2.4-[Angstrom] resolution by x-ray crystallography. The overall fold resembles that of other ubiquitin hydrolases, including UCH-L3, but there are a number of significant differences. In particular, the geometry of the catalytic residues in the active site of UCH-L1 is distorted in such a way that the hydrolytic activity would appear to be impossible without substrate induced conformational rearrangements. neurodegeneration | ubiquitination | ubiquitin ligase | x-ray crystallography

Human indoleamine 2,3-dioxygenase (IDO) catalyzes the cleavage of the pyrrol ring of L-Trp and incorporates both atoms of a molecule of oxygen ([O.sub.2]). Here we report on the x-ray crystal structure of human IDO, complexed with the ligand inhibitor 4-phenylimidazole and cyanide. The overall structure of IDO shows two [alpha]-helical domains with the heme between them. A264 of the flexible loop in the heme distal side is in close proximity to the iron. A mutant analysis shows that none of the polar amino acid residues in the distal heme pocket are essential for activity, suggesting that, unlike the heme-containing monooxygenases (i.e., peroxidase and cytochrome P450), no protein group of IDO is essential in dioxygen activation or proton abstraction. These characteristics of the IDO structure provide support for a reaction mechanism involving the abstraction of a proton from the substrate by iron-bound dioxygen. inactive mutants (F226A, F227A, and R231A) retain substrate-binding affinity, and an electron density map reveals that 2-(N-cyclohexylamino)ethane sulfonic acid is bound to these residues, mimicking the substrate. These findings suggest that strict shape complementarities between the indole ring of the substrate and the protein side chains are required, not for binding, but, rather, to permit the interaction between the substrate and iron-bound dioxygen in the first step of the reaction. This study provides the structural basis for a heme-containing dioxygenase mechanism, a missing piece in our understanding of heme chemistry. iron | kynurenine | tryptophan | x-ray crystallography

The biological function of metalloproteins is closely tied to the geometric and electronic structures of the metal sites. Here, we show that the geometric structure of the metal site of a metal-Ioprotein in solution can be determined from experimentally measured electron-nuclear spin-spin interactions obtained by NMR. Thus, the geometric metal site structure of plastocyanin from Anabaena variabilis was determined by including the paramagnetic relaxation enhancement of protons close to the copper site as restraints in a conventional NMR structure determination, together with the distribution of the unpaired electron onto the ligand atoms. Also, the interproton distances (nuclear Overhauser enhancements) and dihedral angles (scalar nuclear spin-spin couplings) normally used in NMR structure determinations were included as restraints. The structure calculations were carried out with the program X-PLOR and a module that takes into account the specific characteristics of the paramagnetic restraints. A well defined metal site structure was obtained with the structural characteristics of the blue copper site, including a distorted tetrahedral geometry, a short Cu-Cys [S.sup[gamma]] bond, and a long Cu-Met [S.sup.[delta]] bond. Overall, the agreement of the obtained metal site structure of Anabaena variabilis plastocyanin with those of other plastocyanins obtained by x-ray crystallography confirms the reliability of the approach. metal site structure | metalioproteins | paramagnetic nuclear relaxation

The prolyl aminopeptidase complexes of Ala-TBODA [2-alanyl-5-tert-butyl-(1, 3, 4)-oxadiazole] and Sar-TBODA [2-sarcosyl-5-tert-butyl-(l, 3, 4)-oxadiazole] were analyzed by X-ray crystallography at 2.4 resolution. Frames of alanine and sarcosine residues were well superimposed on each other in the pyrrolidine ring of proline residue, suggesting that Ala and Sar are recognized as parts of this ring of proline residue by the presence of a hydrophobic proline pocket at the active site. Interestingly, there was an unusual extra space at the bottom of the hydrophobic pocket where proline residue is fixed in the prolyl aminopeptidase. Moreover, 4-acetyloxyproline-[beta]NA (4-acetyloxyproline [beta]-naphthylamide) was a better substrate than Pro-[beta]NA. Computer docking simulation well supports the idea that the 4-acetyloxyl group of the substrate fitted into that space. Alanine scanning mutagenesis of Phe139, Tyr149, Tyrl50, Phe236, and Cys271, consisting of the hydrophobic pocket, revealed that all of these five residues are involved significantly in the formation of the hydrophobic proline pocket for the substrate. Tyr149 and Cys271 may be important for the extra space and may orient the acetyl derivative of hydroxyproline to a preferable position for hydrolysis. These findings imply that the efficient degradation of collagen fragment may be achieved through an acetylation process by the bacteria.

The synthesis, structure, and properties of an example of a stable diaryldigermyne, BbtGe=GeBbt was reported. It was found that the vibrational spectroscopy was a good method to discuss the bonding property of an unprecedented multiple bond of heavier main group elements.

The metabotropic glutamate receptor 1[alpha] (mGluR1[alpha]) is crucial for some forms of synaptic plasticity, by inducing various cell responses via coupling to various types of G proteins. Upon glutamate binding, an actie conformation, closed-open/active, of the extracellular domain is stabilized, which induces dimeric rearrangement in the intracellular domains, resulting in the initiation of downstream signals. We have confirmed that mGluR1[alpha] functionally interacts with both Gq and Gs pathways; a combination of fluorescent indicators showed that glutamate increased intracellular [Ca.sup.2+] and cAMP concentration ([[[Ca.sup.2+]].sub.i] and [[cAMP].sub.i]). By contrast, [Gd.sup.3+], a different type of ligand whose recognition site on mGluR1[alpha] is distinct from the glutamate site, increased only [[[Ca.sup.2+]].sub.i] and the concentration-activation curve was bell-shaped. FRET analysis revealed that a low concentration of [Gd.sup.3+] induced dimeric rearrangement of the intracellular domains of mGluR1[alpha] as does glutamate, whereas a high concentration of [Gd.sup.3+] reversed the FRET efficiency, which was consistent with a bell-shaped relationship between concentration and Gq activation. These results suggest that [Gd.sup.3+] induces an active and a sort of 'inactivated' conformation in mGluR1[alpha]. The [Gd.sup.3+]-induced active state is considered to correspond to the closed-closed/active conformation, revealed by previous x-ray crystallographic studies. In conclusion, the glutamate-induced closed-open/active state coupled both to Gs and Gq proteins whereas the [Gd.sup.3+]-induced closed-closed/active conformation state preferred Gq to Gs, suggesting that mGluR1[alpha] serves not only as a simple on/off switch but also as a multiple signaling path regulator. FRET | G protein-coupling receptor

We have used NMR spectroscopy and x-ray crystallography to determine the three-dimensional structure of PF1378 (Pfu Pop5), one of four protein subunits of archaeal RNase P that shares a homolog in the eukaryotic enzyme. RNase P is an essential and ubiquitous ribonucleoprotein enzyme required for maturation of tRNA. In bacteria, the enzyme's RNA subunit is responsible for cleaving the single-stranded 5' leader sequence of precursor tRNA molecules (pre-tRNA), whereas the protein subunit assists in substrate binding. Although in bacteria the RNase P holoenzyme consists of one large catalytic RNA and one small protein subunit, in archaea and eukarya the enzyme contains several ([greater than or equal to] 4) protein subunits, each of which lacks sequence similarity to the bacterial protein. The functional role of the proteins is poorly understood, as is the increased complexity in comparison to the bacterial enzyme. Pfu Pop5 has been directly implicated in catalysis by the observation that it pairs with PF1914 (Pfu Rpp30) to functionally reconstitute the catalytic domain of the RNA subunit. The protein adopts an [alpha]-[beta] sandwich fold highly homologous to the single-stranded RNA binding RRM domain. Furthermore, the three-dimensional arrangement of Pfu Pop 5's structural elements is remarkably similar to that of the bacterial protein subunit. NMR spectra have been used to map the interaction of Pop5 with Pfu Rpp30. The data presented permit tantalizing hypotheses regarding the role of this protein subunit shared by archaeal and eukaryotic RNase P. crystallography | NMR | ribonuclease P | ribonucleoprotein

The function of LuxR homologues as quorum sensors is mediated by the binding of N-acyl-L-homoserine lactone (AHL) signal molecules to the N-terminal receptor site of the proteins. In this study, site-directed mutagenesis was carried out of the amino acid residues comprising the receptor site of LuxR from Vibrio fischeri, and the ability of the L42A, L42S, Y62F, W66F, D79N, W94D, V109D, V109T and M135A LuxR mutant proteins to activate green fluorescent protein expression from a [P.sub.luxl] promoter was measured. X-ray crystallographic studies of the LuxR homologue TraR indicated that residues Y53 and W57 form hydrogen bonds to the 1-carbonyl group and the ring carbonyl group, respectively, of the cognate AHL signal. Based on the activity and signal specificity of the LuxR mutant proteins, and on molecular modelling, a model is suggested in which Y62 (corresponding to Y53 in TraR) forms a hydrogen bond with the ring carbonyl group rather than the 1-carbonyl group, while W66 (corresponding to W57 in TraR) forms a hydrogen bond to the 1-carbonyl group. This flips the position of the acyl side chain in the LuxR/signal molecule complex compared to the TraR/signal molecule complex. Halogenated furanones from the marine alga Delisea pulchra and the synthetic signal analogue N-(sulfanylacetyl)-L-homoserine lactone can block quorum sensing. The LuxR mutant proteins were insensitive to inhibition by N-(propylsulfanylacetyl)-L-homoserine lactone. In contrast, the mutations had only a minor effect on the sensitivity of the proteins to halogenated furanones, and the data strongly suggest that these compounds do not compete in a 'classic' way with N-3-oxohexanoyl-L-homoserine lactone for the binding site. Based on modelling and experimental data it is suggested that these compounds bind in a non-agonist fashion.

The effect of ancillary phosphine ligands on the structure and hydroformylation activity of Rh-N-heterocyclic carbene complexes of type [Rh(IMes)(P[R.sub.3])(CO)Cl] and [Rh(SIMes)(P[R.sub.3])(CO)Cl] is described. Very high selectivities for the branched isomer (>95:5) were obtained in the hydroformylation of vinylarenes in all cases except for R = OPh. The new complexes were characterized spectroscopically and by X-ray crystallography. Key words: hydroformylation, rhodium, N-heterocyclic carbene, IMes. On decrit l'effet des ligands phosphines d'appoint sur la structure et l'activite d'hydroformylation de carbenes complexes Rh-H-heterocyclique, du type [Rh(IMes)(P[R.sub.3])(CO)Cl] et [Rh(SIMes)(P[R.sub.3])(CO)Cl]. Dans tous les cas excepte celui ou R = OPh, des selectivites tres elevees de l'isomere ramifie (>95 : 5) ont ete obtenues lors de l'hydroformylation de vinylarenes. Les nouveaux complexes ont ete caracterises par spectroscopie et par diffraction des rayons X. Mots cles : hydroformylation, rhodium, carbene N-heterocyclique, IMes. [Traduit par la Redaction]

Steroidogenic factor-1 (SF-1) and liver receptor homologue-1 (LRH-1) belong to the fushi tarazu factor 1 subfamily of nuclear receptors. SF-1 is an essential factor for sex determination during development and regulates adrenal and gonadal steroidogenesis in the adult, whereas LRH-1 is a critical factor for development of endodermal tissues and regulates cholesterol and bile acid homeostasis. Regulatory ligands are unknown for SF-1 and LRH-1. A reported mouse LRH-1 structure revealed an empty pocket in a region commonly occupied by ligands in the structures of other nuclear receptors, and pocket-filling mutations did not alter the constitutive activity observed. Here we report the crystal structures of the putative ligand-binding domains of human SF-1 at 2.1-[Angstrom] resolution and human LRH-1 at 2.5-[Angstrom] resolution. Both structures bind a coactivator-derived peptide at the canonical activation-function surface, thus adopting the transcriptionally activating conformation. In human LRH-1, coactivator peptide binding also occurs to a second site. We discovered in both structures a phospholipid molecule bound in a pocket of the putative ligand-binding domain. MS analysis of the protein samples used for crystallization indicated that the two proteins associate with a range of phospholipids. Mutations of the pocket-lining residues reduced the transcriptional activities of SF-1 and LRH-1 in mammalian cell transfection assays without affecting their expression levels. These results suggest that human SF-1 and LRH-1 may be ligand-binding receptors, although it remains to be seen if phospholipids or possibly other molecules regulate SF-1 or LRH-1 under physiological conditions. x-ray crystallography | phospholipid | nuclear receptor | steroid | bile

Research has been conducted on the 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene. The single-crystalline photochromism of this compound has been investigated via the X-ray crystallographic analysis and the results indicate that the photocyclization reaction of the molecule with the shorter distance between the the reactive carbons prevails over the other molecule reaction.

Research has been conducted on the X-ray crystallography. The time-resolved crystallographic examination of the mechanism in biochemical systems has been carried out and discussed.

Research has been conducted on the transcription factor interactions. The x-ray crystal structure of the lambda repressor C-terminal domain determined via multiwavelength anomalous diffraction is described.

Research has been conducted on the phospholamban (PLB) transmembrane domain. Results indicate that the high-resolution structure of the PLB pentamer can be determined by X-ray crystallography.

Research has been conducted on the cesium 5-cyano-1,2,3,4-tetrazolate. The preparation of cesium by 3+2 cycloaddition reaction of CsN (sub)3 and (CN ) (sub)2 in SO (sub)2 is described.

Research has been conducted on the copper-zinc superoxide dismutase. The characterization of the truncated and full-length forms of the yeast copper chaperone for SOD has been carried out.

Research has been conducted on the cytochrome subunit of the Rhodopseudomonas viridis photosynthetic reaction center (RC). The mutant RC structure has been determined via X-ray crystallography.

Research has been conducted on the new type ruthenium complex. The preparation and characterization of the complex have been reported.

Research has been conducted on the eight-membered ring systems that contain germanium and selenium. Crystallographic evidence for selenium-germanium transannular bonding is presented.

Research has been conducted on the Cu (super)II and Cu (super)I chlorides. Reactions of these chlorides with R (sub)2 P(S)-NHP(S)R' (sub)2 (R, R' = (super)i Pr; R = (super)i Pr; R' = Ph; and R = EtO, R' = OPh) are analyzed.

A study was conducted to determine the syntheses and properties of a series of dinuclear ruthenium complexes with tetra-2-pyridylpyrazine. X-ray crystallography analysis showed that the coordination geometry around each ruthenium atom is experiencing significant distortion. It was also observed that the complexes' ligands carry two bipyridine groups that are linked through eight- and nine-atom bridges.

1H NMR studies were utilized to analyze the restricted rotation around the P-C bond in metalated phosphonium salts. Results indicated that the restricted rotation around the P-C bond in a series of complexes was shown to be restricted at room temperature or lower. The estimated values of deltaG* for the process lie in the range 67.3-42.2 kiloJoule*1/mol. Steric effects as well as electronic effects were strong determinants.

Chirality, or where something rotates either right or left, was first discovered in organic compounds in 1815. German chemist Emil Fischer designed a system to classify the absolute configuration of chiral molecules in the early 1900s. The concept of chirality is essential for X-ray crystallography and so chemists need to understand the impact of the chirality of a molecule within a crystal lattice.

Computer programs have been developed to overcome the limitations of extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray crystallography techniques in determining the iron-ligand bond lengths in myoglobin. The programs analyze structural information and compute the expected spectra over a wide range of Cartesian coordinate sets. Simulated spectra, generated using the ab initio EXAFS code FEFF 6.01, are compared with experimental spectra. Simulated data for photolyzed solution of the myoglobin-carbon monoxide complex at 10 K agreed with crystallographic data.

X-ray crystallographic studies of the cadmium substituted phosphotriesterase reveal the presence of ions, one ligated by two nitrogen and four oxygens forming a distorted octahedron and the other a trigonal bipyramid with two nitrogen- and three oxygen- containing ligands. Crystallization of the natural protein which has two zinc ions has not been possible. The enzyme has the rare capacity to hydrolyze common pesticides as well as the phosphofluoridates, though the exact mechanism is unknown, and it is an important weapon against chemical warfare.

A highly reactive oxo compound of rhenium (Re) is produced in 60 percent yield by the reduction of the rhenium(VII) compound by triphenylphosphine in tetrahydrofuran. This compound is insoluble in water and tetrahydrofuran and slightly soluble in chloroform and dichloromethane and is a versatile material for the synthesis of monomeric compounds of Re(V). The characteristics of the compound as analyzed by elemental analyses, IR, 1H NMR spectroscopies and X-ray crystallography is also discussed.

Synthesis of a wide array of lanthanide complexes involve crystallization of lanthanide trichlorides from epsilon-caprolactone and caprolactone/THF mixtures. X-ray crystallography of the complexes which include, LnCl3(THF)2, LnCl3L3, (LnCl4(THF)2)-, (LnCl2(THF)5)+, (LnL8)3+ and (Cl3-Ln(mu-Cl3)LnCl3)3- indicate no correlation between radical size and structure. The coordination chemistry and geometry of LnCl3 varies extensively depending on experimental conditions such as the presence of an oxygen donor ligand in solution.

X-ray diffraction methods enable analysis of the structure and geometry of surface corrugations in semiconductors. Braggs diffraction of the corrugated semiconductor surfaces yields space maps around the reciprocal lattice points, which provide details on damage layers, sublattice strain effects and geometry of the layers. (001) Cd(1-x)Zn(x)Te surface corrugations are analyzed by this method.

X-ray analysis of dirithromycin in the 1-propanol solvate form and cyclohexane trisolvate form reveals a greater degree of variability in the polyether side chain of dirithromycin. Solid-state hydrogen bonding and noncrystalline structures are examined using FTIR. Different solvates of similar crystallographic structure are differentiated with 13C solid state NMR. Dynamic processes in dirithromycin crystals are analyzed using variable- temperature 13C NMR and X-ray studies.

X-ray structural analysis revealed the structure of specific large-ring thiacyclophanes, which comprised six sulfur atoms and two ortho- or meta-xylyl groups. Hydroxy and chloro intermediates were employed in a stepwise procedure to synthesize these thiacyclophane compounds. The CH3CN ligands were aligned on different sides of the macrocycle ring.

X-ray crystallography analyzed the crystal structure and the hydride ligand migration barrier of specific tricobalt mono(ethylidyne) clusters. The different facets of the cluster, which comprised symmetrically aligned cobalt atoms, were capped with different ligands such as the mu3-CCH3 ligand. The migration barrier was located between pairs of cobalt atoms, close to each other.

Diethyl cyanophosphonate was used to promote amide bond formation in a specific dolastatin 10 Boc-dolaproinyl-dolaphenine compound, which was synthesized together with four chiral isomers. X-ray crystal structure analyses were used to study the stereochemical assignments in these compounds. Dolastatin 10, which demonstrated antineoplastic activity, was used in anticancer drugs.

Three different cyclic thiacrown ethers are synthesized by a technique involving cesium-based ring closure of an alpha, omega-dihalide with dithiol as a key reaction step. X-ray crystallography proves the crown-like conformation in the solid state. One ether gives discrete stoichiometries with MeCN and THF ligand while for others this is not always the case.

Isomers of Na3Co(PMG)2 are obtained by the reaction between glyphosate (PMG) and Na3Co(CO3)3.3H(2)O in water at room temperature. The crystal structure of this molecule has two identical crystallographically-independent molecules in the asymmetric unit. Glyphosate forms a monomeric 2:1 complex with Co(super 3+) acting as a tridentate ligand. NMR studies show that the rate of isomerization of the fac-RS-all-trans isomer to other isomers is high for the Co(III) complex.

The structural differences in the red- and yellow forms of (Pt(2, 2'-bpy)(Cl)2) are not due to differences in hydration stoichiometry. IR studies show that the yellow to red transformation has no significant intramolecular change. X-ray studies show that the Pt-Pt distances and arrangement of molecules in adjacent layers are different for two forms. EXAFS is employed to confirm the structural differences and similarities between two forms.