Intramolecular Bridges Research Articles

1,8-Bis(hexamethyltriaminophosphazenyl)naphthalene, HMPN: A Superbasic Bisphosphazene “Proton Sponge”

It is shown that a combination of Schwesinger's phosphazene base concept and the idea of the disubstituted 1,8-naphthalene spacer, first introduced by Alder in paradigmatic 1,8-bis(dimethylamino)naphthalene (DMAN), yields a new superbase, HMPN, which represents the up to date most basic representative of this class of "proton sponges", as evidenced by the theoretically estimated proton affinity PA = 274 kcal/mol and the measured pK(BH+) (MeCN) 29.9 +/- 0.2. HMPN is by nearly 12 orders of magnitude more basic than Alder's classical 1,8-bis(dimethylamino)naphthalene (DMAN). The title compound, HMPN, is prepared and fully characterized. The spatial structure of HMPN and its conjugate acid is determined by X-ray technique and theoretical DFT calculations. It is found that monoprotonated HMPN has an unsymmetrical intramolecular hydrogen bridge (IHB). This cooperative proton chelating effect renders the bisphosphazene more basic than Schwesinger's set of "monodentate" P1 phosphazene bases. The density functional calculations are in good accordance with the experimental results, providing some complementary information. They conclusively show that the high basicity of HMPN is a consequence of the high energy content of the base in its initial neutral state and the intramolecular hydrogen bonding in the resulting conjugate acid with contributions to proton affinity of 14.1 and 9.5 kcal/mol, respectively.

Structural optimization of pep7, a small peptide extracted from epimorphin, for effective induction of hair follicle anagen

Epimorphin is representative of a unique class of stromal membrane-anchored proteins that plays distinct functions depending on its membrane topology. When exposed extracellularly, this molecule acts as a morphoregulator for various tissues including hair follicle epithelia. Previous study identified its functional domain (the pep7 domain: SIEQSCDQDE) for hair follicular morphogenesis followed by the successful generation of a chemically modified active peptide. Here, we report optimization of this peptide by the introduction of sequential mutations and subsequent structural determination. We found that three residues from the C-terminus are dispensable, and alternation of the seventh amino acid to an Alanine residue enhanced activity. To favour the biologically active conformation, epsilon-Acp (NH(CH(2))(5)CO) linked to a Cysteine residue was connected at the N-terminus followed by the introduction of an intramolecular disulphide bridge, the modification process of which could be included in the peptide synthesis. The obtained modified peptide, termed 'EPM (epimorphin-derived) peptide', has a Mw of 950 Da and exerts an inductive effect on hair follicle regeneration at a concentration of approximately 0.00001% or even lower. The action of this EPM peptide was more apparent in mice treated with 1% minoxidil, suggesting its potential clinical benefit as a new type of hair-regenerating agent.

Structural Genomics of Thermotoga maritima Proteins Shows that Contact Order Is a Major Determinant of Protein Thermostability

Despite numerous studies, understanding the structural basis of protein stability in thermophilic organisms has remained elusive. One of the main reasons is the limited number of thermostable protein structures available for analysis, but also the difficulty in identifying relevant features to compare. Notably, an intuitive feeling of "compactness" of thermostable proteins has eluded quantification. With the unprecedented opportunity to assemble a data set for comparative analyses due to the recent advances in structural genomics, we can now revisit this issue and focus on experimentally determined structures of proteins from the hyperthermophilic bacterium Thermotoga maritima. We find that 73% of T. maritima proteins have higher contact order than their mesophilic homologs. Thus, contact order, a structural feature that was originally introduced to explain differences in folding rates of different protein families, is a significant parameter that can now be correlated with thermostability.

Human xylosyltransferase I: functional and biochemical characterization of cysteine residues required for enzymic activity.

XT-I (xylosyltransferase I) is the initial enzyme in the post-translational biosynthesis of glycosaminoglycan chains in proteoglycans. To gain insight into the structure-function relationship of the enzyme, a soluble active form of human XT-I was expressed in High Five insect cells with an apparent molecular mass of 90 kDa. Analysis of the electrophoretic mobility of the protein under non-reducing and reducing conditions indicated that soluble XT-I does not form homodimers through disulphide bridges. In addition, the role of the cysteine residues was investigated by site-directed mutagenesis combined with chemical modifications of XT-I by N-phenylmaleimide. Replacement of Cys471 or Cys574 with alanine led to a complete loss of catalytic activity, indicating the necessity of these residues for maintaining an active conformation of soluble recombinant XT-I by forming disulphide bonds. On the other hand, N-phenylmaleimide treatment showed no effect on wild-type XT-I but strongly inactivated the cysteine mutants in a dose-dependant manner, indicating that seven intramolecular disulphide bridges are formed in wild-type XT-I. The inhibitory effect of UDP on the XT-I activity of C561A (Cys561-->Ala) mutant enzyme was significantly reduced compared with all other tested cysteine mutants. In addition, we tested for binding to UDP-agarose beads. The inactive mutants revealed no significantly different nucleotide-binding properties. Our study demonstrates that recombinant XT-I is organized as a monomer with no free thiol groups and strongly suggests that the catalytic activity does not depend on the presence of free thiol groups, furthermore, we identified five cysteine residues which are critical for enzyme activity.

Identification of a Disulfide Switch in BsSco, a Member of the Sco Family of CytochromecOxidase Assembly Proteins,

BsSco is a membrane-associated protein from Bacillus subtilis characterized by the sequence CXXXCP, which is conserved in yeast and human mitochondrial Sco proteins, and their bacterial homologues. BsSco is involved in the assembly of the Cu(A) center in cytochrome c oxidase and may play a role in the transfer of copper to this site. We have characterized the soluble domain of BsSco by biochemical, spectroscopic, and structural approaches. Soluble BsSco is monomeric in solution, and the two conserved cysteines are involved in an intramolecular cystine bridge. The cystine bridge is easily reduced, and circular dichroism spectroscopy shows no large-scale changes in BsSco's secondary structure upon reduction. The crystal structure of soluble BsSco, determined at 1.7 A resolution, reveals typical elements of a thioredoxin fold. The CXXXCP motif, in which Cys45 and Cys49 are conserved, is located in a turn structure on the surface of the protein. In various native and His135Ala mutant structures, both disulfide-bonded and non-disulfide-bonded forms of CXXXCP are observed. However, despite extensive attempts, copper has not been found near or beyond the CXXXCP motif, a presumptive copper-binding site. Another potential copper binding residue, His135, is located in a highly flexible loop parallel to the CXXXCP loop but is more than 10 A from Cys45 and Cys49. If these three residues are to coordinate copper, a conformational change is necessary. The structural identification of a disulfide switch demonstrates that BsSco has the capability to fill a redox role in Cu(A) assembly.

Microporous dinuclear copper(II) trans-1,4-cyclohexanedicarboxylate: heterogeneous oxidation catalysis with hydrogen peroxide and X-ray powder structure of peroxo copper(II) intermediate

A two-dimensional microporous dinuclear copper(II) trans-1,4-cyclohexanedicarboxylate, [Cu II,II 2(OOCC 6H 10COO) 2] ⋅ H 2O ( 1), can act as a heterogeneous catalyst for selective oxidations of various alcohols with hydrogen peroxide. Complex 1 catalyzed the selective oxidations of 2-propanol, cyclohexanol, benzyl alcohol, 2-octanol, and 1-octanol with >99% selectivities in a heterogeneous system. A green-colored active intermediate, H 2[Cu II,II 2(OOCC 6H 10COO) 2(O 2)] ⋅ H 2O ( 2), observed in the reaction of 1 with a 20-fold excess H 2O 2 in acetonitrile was characterized by elemental analysis, TG/DTA, magnetic susceptibility, FT-IR, diffuse reflectance UV–vis, EPR, X-ray powder diffraction (XRPD), resonance Raman spectra, BET surface area, pore size distribution, and nitrogen occlusion measurements. The molecular structure of 2 was determined from XRPD data and refined by the Rietveld method. The microporous structure of 2 was constructed by intramolecular bridging of μ-1,2- trans Cu OO Cu species between two-dimensional [Cu 2(O 2CC 6H 10CO 2)] layers. The complex 2 was the first example of the microporous copper(II) peroxo complex for heterogeneous oxidation catalysis.

Synthesis and behavior of novel phthalocyanines possessing intramolecular crown ether bridges between their different aromatic rings for effective extraction multi metal inclusion

Novel Cu- and Co-phthalocyanines (7a–e, 8a, b) possessing intramolecular crown ether bridges between their different aromatic rings were successfully synthesized from the reaction of the corresponding bisphthalonitriles (6a–e) bearing polyethyleneoxy chains in the presence of CuCl and CoCl2, respectively. As 1,8-diazabicyclo [5.4.0]-7-undecene (DBU) was used as a base in n-pentanol at reflux temperature for 30 h under N2 atmosphere, these new phthalocyanines were found to be characteristic of satisfactory solubility in some of organic solvents, and showed strong absorption bands in ultraviolet and visible wave length region (λmaxZ719–739 nm). Extraction experiment of metal chlorides (NaCl, KCl, MgCl2, CaCl2, CeCl3, ZnCl2, FeCl3) in chloroform was carried out by using Cu-phthalocyanine (7b) bearing two intramolecular bridges with tri(ethyleneoxy) chains. Among these metal salts, 7b formed a complex (9b) with only FeCl3, which showed a dark-red amorphous solid. Spectroscopic analysis of the complex (9b) indicated that original strong absorption bands near 738 nm characteristic for phthalocyanines completely disappeared, and new two strong bands appeared near 799–853 nm. FAB-MASS spectrum of the complex (9b) showed that new strong peaks came out in the region centered at m/z Z1879 and 1881 besides original peaks in the region centered at 1488, which corresponded to molecular peak of the starting phthalocyanine (7b). These facts indicated that the complex (9b) included two molecules of FeCl3 into the protonated crown ether bridges of the phthalocyanine skeleton. Furthermore, it was found that the complex (9b) was transformed to the original phthalocyanine (7b) quantitatively by treatment with triethylamine.

A Structural Basis of Equisetum arvense Ferredoxin Isoform II Producing an Alternative Electron Transfer with Ferredoxin-NADP+ Reductase

We have determined the crystal structure, at 1.2-A resolution, of Equisetum arvense ferredoxin isoform II (FdII), which lacks residues equivalent to Arg(39) and Glu(28) highly conserved among other ferredoxins (Fds). In other Fds these residues form an intramolecular salt bridge crucial for stabilization of the [2Fe-2S] cluster, which is disrupted upon complex formation with Fd-NADP(+) oxidoreductase (FNR) to form two intermolecular salt bridges. The overall structure of FdII resembles the known backbone structures of E. arvense isoform I (FdI) and other plant-type Fds. Dramatically, in the FdII structure a unique, alternative salt bridge is formed between Arg(22) and Glu(58). This results in a different relative orientation of the alpha-helix formed by Leu(23)-Glu(29) and eliminates the possibility of forming three of the five intermolecular salt bridges identified on formation of a complex between maize FdI and maize FNR. Mutation of FdII, informed by structural differences with FdI, showed that the alternative salt bridge and the absence of an otherwise conserved Tyr residue are important for the alternative stabilization of the FdII [2Fe-2S] cluster. We also investigated FdI and FdII electron transfer to FNR on chloroplast thylakoid membranes. The K(m) and V(max) values of FdII are similar to those of FdI, contrary to previous measurements of the reverse reaction, from FNR to Fd. The affinity between reduced FdI and oxidized FNR is much greater than that between oxidized FdI and reduced FNR, whereas this is not the case with FdII. The pH dependence of electron transfer by FdI, FdII, and an FdII mutant with FdI features was measured and further indicated that the binding mode to FNR differs between FdI and FdII. Based on this evidence, we hypothesize that binding modes with other Fd-dependent reductases may also vary between FdI and FdII. The structural differences between FdI and FdII therefore result in functional differences that may influence partitioning of electrons into different redox metabolic pathways.

Conformational and dynamical properties of the niruriside in aqueous solution: a molecular dynamics approach

The conformational and dynamical hydration features of the niruriside, a compound extracted from the medicinal plant Phyllantus niruri, were investigated in 10 ns molecular dynamics (MD) simulation. Inhibitory activity against hepatitis B has been reported for aqueous extract of P. niruri and, in particular, for the niruriside compound, against HIV replication; making it a natural antiviral candidate. In order to elucidate the niruriside conformational characteristics in water, dihedral angle transitions, intramolecular hydrogen bonds and water bridge formation were monitored. Direct interaction of niruriside with solvent and hydrogen bond formation were analyzed through the radial atomic pair distribution functions. Despite the large number of hydrogen bond acceptor atoms of this molecule, the hydration number was relatively low, indicating poor capacity of water binding. However, simulations showed a great structural stability of this compound in aqueous solution with no evidence of internal hydrogen bonds or water-bridge interactions responsible for preserving its structure. We presume that the intrinsic molecular rigidity results from a combined effect of hydrophilic and hydrophobic interactions. The existence of two hemispherical regions of opposite characteristics provides an amphiphilic nature to the niruriside molecule and brings attention to a possible relationship with its potential antiviral agent function.

Structural and functional analysis of the gpsA gene product of Archaeoglobus fulgidus: A glycerol‐3‐phosphate dehydrogenase with an unusual NADP+ preference

NAD(+)-dependent glycerol-3-phosphate dehydrogenase (G3PDH) is generally absent in archaea, because archaea, unlike eukaryotes and eubacteria, utilize glycerol-1-phosphate instead of glycerol-3-phosphate for the biosynthesis of membrane lipids. Surprisingly, the genome of the hyperthermophilic archaeon Archaeoglobus fulgidus comprises a G3PDH ortholog, gpsA, most likely due to horizontal gene transfer from a eubacterial organism. Biochemical characterization proved G3PDH-like activity of the recombinant gpsA gene product. However, unlike other G3PDHs, the up to 85 degrees C thermostable A. fulgidus G3PDH exerted a 15-fold preference for NADPH over NADH. The A. fulgidus G3PDH bears the hallmarks of adaptation to halotolerance and thermophilicity, because its 1.7-A crystal structure showed a high surface density for negative charges and 10 additional intramolecular salt bridges compared to a mesophilic G3PDH structure. Whereas all amino acid residues required for dihydroxyacetone phosphate binding and reductive catalysis are highly conserved, the binding site for the adenine moiety of the NAD(P) cosubstrate shows a structural variation that reflects the observed NADPH preference, for example, by a putative salt bridge between R49 and the 2'-phosphate.

High-Resolution X-ray Structure of the Unexpectedly Stable Dimer of the [Lys(-2)-Arg(-1)-des(17−21)]Endothelin-1 Peptide

Previous structural studies on the [Lys((-2))-Arg((-1))]endothelin-1 peptide (KR-ET-1), 540-fold less potent than ET-1, strongly suggested the presence of an intramolecular Arg(-1)-Asp(8) (R(-1)-D(8)) salt bridge that was also observed in the shorter [Lys((-2))-Arg((-1))-des(17-21)]endothelin-1 derivative (KR-CSH-ET). In addition, for these two analogues, we have shown that the Lys-Arg dipeptide, which belongs to the prosequence, significantly improves the formation of the native disulfide bonds (>or=96% instead of approximately 70% for ET-1). In contrast to what was inferred from NMR data, molecular dynamics simulations suggested that such an intramolecular salt bridge would be unstable. The KR-CSH-ET peptide has now been crystallized at pH 5.0 and its high-resolution structure determined ab initio at 1.13 A using direct methods. Unexpectedly, KR-CSH-ET was shown to be a head-to-tail symmetric dimer, and the overall interface involves two intermolecular R(-1)-D(8) salt bridges, a two-stranded antiparallel beta-sheet, and hydrophobic contacts. Molecular dynamics simulations carried out on this dimer clearly showed that the two intermolecular salt bridges were in this case very stable. Sedimentation equilibrium experiments unambiguously confirmed that KR-ET-1 and KR-CSH-ET also exist as dimers in solution at pH 5.0. On the basis of the new dimeric structure, previous NMR data were reinterpreted. Structure calculations were performed using 484 intramolecular and 38 intermolecular NMR-derived constraints. The solution and the X-ray structures of the dimer are very similar (mean rmsd of 0.85 A). Since the KR dipeptide at the N-terminus of KR-CSH-ET is present in the prosequence, it can be hypothesized that similar intermolecular salt bridges could be involved in the in vivo formation of the native disulfide bonds of ET-1. Therefore, it appears to be likely that the prosequence does assist the ET-1 folding in a chaperone-like manner before successive cleavages that yield the bioactive ET-1 hormone.

Reversible Photocontrol of Peptide Helix Content: Adjusting Thermal Stability of the Cis State

Cross-linking reagents based on an azobenzene core can be used to reversibly photoregulate secondary structure when introduced as intramolecular bridges in peptides and proteins. Photoisomerization of the azobenzene core in the trans to cis direction is triggered by photon absorption but isomerization from cis to trans occurs thermally as well as photochemically. The rate of the thermal process effectively determines the half-life of the cis form as well as the extent to which the trans form can be recovered. We designed and characterized a series of methanethiosulfonate (MTS)-bearing thiol-reactive azo-benzene-based cross-linkers. These cross-linkers are shown to permit photoregulation of helix content in a test peptide with half-lives for the cis conformation ranging from 11 s to 43 h at 25 degrees C. The cross-linkers described here thus broaden the range of reagents available for reversible photocontrol of peptide and protein conformation.

Mutation analysis of congenital cataracts in Indian families: identification of SNPS and a new causative allele in CRYBB2 gene.

To study some functional candidate genes in cataract families of Indian descent. Nine Indian families, clinically documented to have congenital/childhood cataracts, were screened for mutations in candidate genes such as CRYG (A-->D), CRYBB2, and GJA8 by PCR analyses and sequencing. Genomic DNA samples of either probands or any representative affected member of each family were PCR amplified and sequenced commercially. Documentation of single nucleotide polymorphisms (SNPs) and candidate mutations was done through BLAST SEARCH (http://www.ncbi.nlm.nih.gov/blast/Blast.cgi?). Several single nucleotide polymorphisms in CRYG, CRYBB2, and GJA8 genes were observed. Because they do not co-segregate with the phenotype, they were excluded as candidates for the cataract formation in these patients. However, a substitution (W151C in exon 6 of CRYBB2) was identified as the most likely causative mutation underlying the phenotype of central nuclear cataract in all affected members of family C176. Protein structural interpretations demonstrated that no major structural alterations could be predicted and that even the hydrogen bonds to the neighboring Leu166 were unchanged. Surprisingly, hydropathy analysis of the mutant betaB2-crystallin featuring the amino acids at position 147 to 155, further increased the hydrophobicity, which might impair the solubility of the mutant protein. Finally, the Cys residue at position 151 might possibly be involved in intramolecular disulphide bridges with other cysteines during translation, possibly leading to dramatic structural changes. Exon 6 of CRYBB2 appears to be a critical region susceptible for mutations leading to lens opacity.

Growth-regulatory Human Galectin-1: Crystallographic Characterisation of the Structural Changes Induced by Single-site Mutations and their Impact on the Thermodynamics of Ligand Binding

Human galectin-1 is a potent multifunctional effector that participates in specific protein-carbohydrate and protein-protein (lipid) interactions. By determining its X-ray structure, we provide the basis to define the structure of its ligand-binding pocket and to perform rational drug design. We have also analysed whether single-site mutations introduced at some distance from the carbohydrate recognition domain can affect the lectin fold and influence sugar binding. Both the substitutions introduced in the C2S and R111H mutants altered the presentation of the loop, harbouring Asp123 in the common "jelly-roll" fold. The orientation of the side-chain was inverted 180 degrees and the positions of two key residues in the sugar-binding site of the R111H mutant were notably shifted, i.e. His52 and Trp68. Titration calorimetry was used to define the decrease in ligand affinity in both mutants and a significant increase in the entropic penalty was found to outweigh a slight enhancement of the enthalpic contribution. The position of the SH-groups in the galectin appeared to considerably restrict the potential to form intramolecular disulphide bridges and was assumed to be the reason for the unstable lectin activity in the absence of reducing agent. However, this offers no obvious explanation for the improved stability of the C2S mutant under oxidative conditions. The noted long-range effects in single-site mutants are relevant for the functional divergence of closely related galectins and in more general terms, the functionality definition of distinct amino acids.

Structural evidence for guanidine–protein side chain interactions: crystal structure of CutA from Pyrococcus horikoshii in 3 M guanidine hydrochloride

This study was carried out to investigate the structural perturbation of the protein’s local structure by the denaturants under non-denaturing conditions. Crystal structure of CutA from an archaeon Pyrococcus horikosii ( PhoCutA), a heavy-metal binding protein, was determined at 1.6-Å resolution in the presence of 3 M guanidine HCl (GdnHCl). Native PhoCutA has a large number of short intramolecular hydrogen bonds and salt bridges on the protein surface, of which greater than 90% of hydrogen bonds and all salt bridges were retained in 3 M GdnHCl. Hydrogen bonds that disappeared in the GdnHCl crystal structure were mainly located on the protein surface, especially around the structurally perturbed loop, suggesting interactions between peptide groups and GdnHCl. Only a few GdnH + ions were observed in the crystal structure, although none at the surface, of the protein. Two GdnH + ions were observed in the center of the trimeric structure, replacing water molecules, and were hydrogen bonded with Asp84 and Asp86 of each chain. The exterior loop from Tyr39 to Lys44, including Trp40–Trp41, was perturbed structurally. Decreases in temperature factors were observed in β strand 5 and the N terminus of helix 3. These results suggest the specific bindings of GdnH + with some acidic residues and the non-specific bindings around Trp residues and peptide groups on the protein surface and that binding of GdnHCl to the native protein is limited, resulting in local structural perturbation.

Organic chlorine as a hydrogen-bridge acceptor: evidence for the existence of intramolecular O--H...Cl--C interactions in some gem-alkynols.

The acceptor capabilities of "organic" halogen, CX (X=F, Cl, Br, I), with respect to hydrogen bonding are controversial, and unactivated organic chlorine is generally deemed to be a poor acceptor. Hydrogen bridges of the type O--H...Cl--C are uncommon and occur mainly in an intramolecular situation when the donor group is sterically hindered, so that the formation of intermolecular interactions is difficult. In this paper, intramolecular O--H...Cl--C interactions in a series of chloro-substituted gem-alkynols are studied. We describe various features of this interaction using crystallographic, spectroscopic and computational methods. The O--H...Cl--C interaction occurs in five of the six compounds under consideration here (CDDA, 14DDDA, 15DDDA, 18DDDA, 15MKA). Solution (1)H NMR spectroscopy shows that the interaction is intramolecular and that it is a true hydrogen bond. DFT calculations give a stabilisation energy around 4.0 kcal mol(-1). In the crystal structures of the compounds studied, the intramolecular O--H...Cl--C interactions fit into the overall scheme of cooperative interactions. These structures may be derived from that of the unsubstituted compound DDA by means of synthon exchange and the O--H...Cl--C interaction fares surprisingly well in the presence of competing stronger acceptors. The crystal structures show an unusual degree of modularity for compounds that generally form interactions that are weak and variable. It is noteworthy that the so-called "weak" acceptor, organic chlorine, is able to sustain a good intramolecular hydrogen bridge that is of an attractive and stabilizing nature and which is of potential importance in crystal engineering and supramolecular chemistry.

Synthesis and electrophysiological characterization of cyclic morphiceptin analogues

A challenge in opioid peptide chemistry and pharmacology is the possibility to develop novel peptides with peripheral selectivity. An enzymatically stable opioid peptide could involve an antidiarrheal effect. For this reason, we constrained the highly selective and potent tetrapeptide morphiceptin with a 6-atom bridge, resulting in a cyclic amide and an ester analogue, 2 and 3, respectively. Taking advantage of the functional coupling of the opioid receptor with the heteromultimeric G-protein-coupled inwardly rectifying K + (GIRK1/GIRK2) channel, either the wild-type μ-, κ-, δ- or a mutated μ-opioid receptor (hMORS329A) was functionally co-expressed with GIRK1/GIRK2 channels and a regulator of G-protein signaling (RGS4) in Xenopus laevis oocytes. The two-microelectrode voltage clamp technique was used to measure the opioid receptor activated GIRK1/GIRK2 channel responses. Both cyclic analogues were equally potent via the wild-type μ-opioid receptor hMORwt (EC 50 value 976.5±41.7 for 2 and 1017.7±60.7 for 3), while the EC 50 value for Tyr-Pro-Phe-D-Pro-NH 2 measured 59.3±4.8 nM. These three agonists displayed a four to five times decreased potency via hMORS329A as compared to the wild type. Interestingly, no effect on κ- and δ-opioid receptors was observed. The intramolecular bridge created by cyclization of morphiceptin prevents dipeptidyl peptidase IV from interacting with these analogues. We conclude that constraining morphiceptin with a 6-atom bridge resulted in enzymatically stable peptidomimetics that are exclusively active on μ-opioid receptors. These analogues provide an interesting template in the promising approach for the design of potential antidiarrheal agents.

New approach to the suppression of phthalocyanine aggregation: synthesis of cobalt phthalocyanine complexes containing intramolecular bridges based on 2,7-disubstituted 9,9-bis(2,3-dicyanophenoxymethyl)fluorenes and study of their physical and catalytic properties

A series of new cobalt monophthalocyanine complexes containing intramolecular bridges between the C(1(11)) and C(25(15)) carbon atoms of phthalocyanine with perpendicular rigid fluorenyl substituents was synthesized from 2,7-di(H,But)-9,9-bis(2,3-dicyanophenoxymethyl)fluorenes. The spectral and catalytic properties of the synthesized complexes and cobalt 1,8(11),15(18),22(25)-tetraethoxyphthalocyaninate were studied.

Simulation of Molecular Dynamics of the Tetrapeptide Ala-Gly-Asp-Pro

A quantum-chemical calculation procedure intended for studying geometries and electronic structures of various peptides was tested using the tetrapeptide Ala-Gly-Asp-Pro as example. The trajectory of the molecular dynamics of the Ala-Gly-Asp-Pro molecule in the surrounding of water molecules was followed for a period of 1500 ps. The conformation of the peptide molecule does not change within this period. The water surrounding of the Ala-Gly-Asp-Pro molecule prevents formation of an intramolecular salt bridge between the nitrogen atom of the terminal amino group and oxygen atoms of the side carboxy group of Asp. It is suggested that the mechanism of the physiological action of Ala-Gly-Asp-Pro may involve hydrogen bonding with one or several functional groups of this molecule.

Synthesis and crystal structures of a new series of intramolecular bridged alkylcobaloxime complexes.

A new series of intramolecular bridged alkylcobaloxime complexes were prepared by heating a solution of aqua-(3-bromopropyl)cobaloxime (1) through an intramolecular nucleophilic substitution. They are characterized by EA, ESI-MS, and (1)H NMR. Crystal structures of Br(O-C(3)H(6)-(dmgH))(dmgH)Co(III) (2), [H(2)O(O-C(3)H(6)-(dmg))(dmgH(2))Co(III)]ClO(4) (3), [Py(O-C(3)H(6)-(dmg))(dmgH(2))Co(III)]ClO(4) (4), [Bzm(O-C(3)H(6)-(dmg))(dmgH(2))Co(III)]ClO(4) (5), and Im(O-C(3)H(6)-(dmg))(dmgH)Co(III) (6') were determined by X-ray diffraction. It is revealed that an intramolecular tri-methylene bridge exists between cobalt and one of the equatorial oxime oxygens forming a six-membered ring in the complexes. Additionally, the axial bases have some influences in their structure parameters, for example, Co-L bond lengths; folding angles in equatorial ligands; hydrogen atom positions in O-H-O bridge; and the orientations of those L planes with respect to the equatorial planes.