Mechanisms of interaction of tetrahydrocortisol and its complex with apolipoprotein A-I and DNA regulatory cis-elements of CC(GCC)5/GG(CGG)5 type

An IR-spectroscopy study of the mechanism of interaction between duplex CC(GCC)5/GG (CGG)5Li2 and tetrahydrocortisol or tetrahydrocortisol-apolipoprotein A-I complex revealed the formation of hydrogen bonds between the OH group of the tetrahydrocortisol A-ring and the C=0 group of cytosine or guanine. Tetrahydrocortisol forms hydrogen bonds with the PO2-group of the duplex and with the OH-group of monosaccharide. The interaction of tetrahydrocortisol and apolipoprotein A-I with the duplex occurs at the same active site, namely, with the C=O-group of bases. The order --> order structural transition takes place in the duplex under the action of tetrahydrocortisol. The order --> disorder structural transition takes place in the duplex under the action of tetrahydrocortisol-apolipoprotein A-I complex.     

Isolation of bacteriophage MX4, a generalized transducing phage for Myxococcus xanthus.

The structure of α-chitin has been determined by X-ray diffraction, based on the intensity data from deproteinized lobster tendon. Least-squares refinement shows that adjacent chains have alternating sense (i.e. are antiparallel). In addition, there is a statistical distribution of side-chain orientations, such that all the hydroxyl groups form hydrogen bonds. The unit cell is orthorhombic with dimensions a = 0.474 ± 0.001 nm, b = 1.886 ± 0.002 nm and c = 1.032 ± 0.002 nm (fiber axis); the space group is P2₁2₁2₁ and the cell contains disaccharide sections of the two chains passing through the center and corner of the ab projection. The chains form hydrogen-bonded sheets linked by CO…HN bonds approximately parallel to the a axis, and each chain has an O-3′H…O.5 intramolecular hydrogen bond, similar to that in cellulose. Adjacent chains along the ab diagonal have different conformations for the CH₂OH groups: on one chain these groups form O.6H…O.6′ intermolecular hydrogen bonds to the CH₂OH group on the adjacent chain along the ab diagonal. The latter group is oriented to form an intramolecular O.6′H…O.7 bond to the carboxyl oxygen on the next residue. The results indicate that a statistical mixture of CH₂OH orientations is present, equivalent to half oxygens on each residue, each forming inter- and intramolecular hydrogen bonds. As a result the structure contains two types of amide groups, which differ in their hydrogen bonding, and account for the splitting of the amide I band in the infrared spectrum. The Inability of this chitin polymorph to swell on soaking in water is explained by the extensive intermolecular hydrogen bonding.     

Interaction of metal ions with humic-like models. Part 5. The crystal and molecular structure of diaquabis(2,6-dihydroxybenzoato)-dioxouranium(VI) octahydrate

The crystal and molecular structure of the complex [UO₂(DHB)₂(H₂O)₂]·8H₂O (DHB = 2,6-di- hydroxybenzoato) has been determined from single- crystal X-ray analysis and refined to a final R value of 0.033 for 3620 observed reflections. The complex crystallizes in the monoclinic system, space group C2/m, with a = 6.704(3), b = 20.171(6), c = 9.454(4) Å and Z = 2. The coordination about the uranyl group, which is linear, involves two bidentate carboxylate groups and two water molecules in trans positions giving rise to an irregular hexagonal bipyramid. Intra- molecular hydrogen bonds between phenolic and carboxylate groups forming six-membered rings allow the molecule to be nearly planar. Spectroscopic (IR, NMR and electronic absorption) data and thermal properties of the compound are also reported.     

Monensin A methyl ester complexes with Li+, Na+, and K+ cations studied by ESI-MS, 1H- and 13C-NMR, FTIR, as well as PM5 semiempirical method

Monensin A methyl ester (MON1) was synthesized by a new method and its ability to form complexes with Li+, Na+, and K+ cations was studied by electrospray ionization-mass spectroscopy (ESI-MS), 1H and 13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), and PM5 semiempirical methods. It is shown that MON1 with monovalent metal cations forms stable complexes of 1:1 stoichiometry. The structures of the complexes are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. In the structure of MON1, the oxygen atom of the C=O ester group is involved in very weak bifurcated intramolecular hydrogen bonds with two hydroxyl groups, whereas in the complexes of MON1 with monovalent metal cations the C=O ester group is not engaged in any intramolecular hydrogen bonds. Furthermore, it is demonstrated that the strongest intramolecular hydrogen bonds are formed within the MON1-Li+ complex structure. The structures of the MON1 and its complexes with Li+, Na+, and K+ cations are visualized and discussed in detail.     

The structures of bis(1H,5H-S-methylisothiocarbonohydrazidium) di-μ-chloro-octachlorodibismuthate(III) tetrahydrate and tris(1H-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III)

The structures of bis(1H⁺,5H⁺-S-methylisothiocarbonohydrazidium) di-μ-chlorooctachlorodibismuthate(III) tetrahydrate: (C₂H₁₀N₄S)₂(Bi₂Cl₁₀)· 4H₂O (compound [I]) and of tris(1H⁺-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III): (C₂H₉N₄S)₃(BiCl_5.67I_0.33) (compound [II]) were determined from single crystal X-ray diffractometer data. Both compounds crystallize as triclinic (P ); crystals [I] with Z = 1 formula unit in a cell of constants: A = 10.621(3), B = 9.989(5), C = 7.439(3) Å, α = 88.31(2), β = 84.51(2), γ = 68.88(2)°, final R = 0.0427 for 2229 unique reflections with I 2σ(I); crystals [II] with Z = 2 and cell dimensions: A = 14.109(4), B = 12.209(9), C = 8.206(7) Å, α = 103.54(3), β = 104.95(2), γ = 81.96(2)°, final R = 0.0411 for 3637 unique reflections (1 2σ(I)). The structure of [I] is built up of diprotonated organic cations, water molecules and dinuclear centrosymmetric [Bi₂Cl₁₀]⁴⁻ anions held together by N-HCl, N-HO, O-HCl hydrogen bonds and Van der Waals interactions. The [Bi₂Cl₁₀]⁴⁻ complex consists of two edge-sharing octahedra in which three pairs of bonds of similar length are observed (Bi-Cl_av = 2.602(5), 2.712(4), 2.855(5) Å). The structure of [II] consists of monoprotonated cations and [BiCl_5.67I_0.33]³⁻ anions held together by a tridimensional network of hydrogen bonds. Each bismuth atom is octahedrally surrounded by six chlorine atoms, one of which is statistically substituted by a iodine atom.     

A density functional theory study on the hydrogen bonding interactions between luteolin and ethanol

Ethanol is one of the most commonly used solvents to extract flavonoids from propolis. Hydrogen bonding interactions play an important role in the properties of liquid system. The main objective of the work is to study the hydrogen bonding interactions between flavonoid and ethanol. Luteolin is a very common flavonoid that has been found in different geographical and botanical propolis. In this work, it was selected as the representative flavonoid to do detailed research. The study was performed from a theoretical perspective using density functional theory (DFT) method. After careful optimization, there exist nine optimized geometries for the luteolin ? CH₃CH₂OH complex. The binding distance of X ? H···O, and the bond length, vibrational frequency, and electron density changes of X ? H all indicate the formation of the hydrogen bond in the optimized geometries. In the optimized geometries, it is found that: (1) except for the H2’, H5’, and H6’, CH₃CH₂OH has formed hydrogen bonds with all the hydrogen and oxygen atoms in luteolin. The hydrogen atoms in the hydroxyl groups of luteolin form the strongest hydrogen bonds with CH₃CH₂OH; (2) all of the hydrogen bonds are closed-shell interactions; (3) the strongest hydrogen bond is the O3’ ? H3’···O in structure A, while the weakest one is the C3 ? H3···O in structure E; (4) the hydrogen bonds of O3’ ? H3’···O, O ? H···O4, O ? H···O3’ and O ? H···O7 are medium strength and covalent dominant in nature. While the other hydrogen bonds are weak strength and possess a dominant character of the electrostatic interactions in nature.     

f-Element/crown ether complexes. 16. Synthesis,crystallization and crystal structure of [Dy(OH2)8]Cl3·18-crown-6·4H2O

When crystals of [Dy(OH₂)₇(OHMe)] [DyCl(OH₂)₂(18- crown-6)]₂Cl₇·2H₂O [1] are allowed to warm from 5 °C to ambient temperature (22 °C) under the original solvent mixture (1:3 CH₃OH: CH₃CN), they redissolve and the title complex can be isolated by slow evaporation of the resulting solution. The crystal structure of this complex, [Dy(OH₂)₈]Cl₃·18-crown-₆·4H₂O, has been determined. It crystallizes in the monoclinic space group, P2₁/c, with a = 10.395(1), b = 18.684(1), c = 16.259- (3) Å, β= 102.56(1)°, and D_calc = 1.61 g cm⁻³ for Z = 4. A final conventional R value of 0.041 was obtained by least-squares refinement using 3453 independent observed [F_o⩾5σ(F_o)] reflections. The [Dy(OH₂)₈]³⁺ cations and crown ether molecules are hydrogen bonded in a polymeric chain with the crown molecules separating the cations and a total of seven DyOH₂···O(crown ether) hydrogen bonds. The chains are connected by a hydrogen bonding network consisting of the cations, chloride ions, and uncoordinated water molecules. The geometry of the cation is best described as a bicapped trigonal prism with distortions on the reaction pathway toward dodecahedral symmetry. The two capping atoms average 2.41(1) Å from Dy, the remaining DyO distances average 2.38(2) Å. The 18-crown-6 molecule has the D_3d conformation normally observed except for a distortion of one OCCO unit containing the oxygen atom accepting two hydrogen bonds.     

Crystal structure of 9-amino-N-[2-(4-morpholinyl)ethyl]-4-acridinecarboxamide bound to d(CGTACG)2: implications for structure–activity relationships of acridinecarboxamide topoisomerase poisons

The structure of the complex formed between d(CGTACG)₂ and 9-amino-N-[2-(4-morpholinyl)ethyl]-4-acridinecarboxamide, an inactive derivative of the antitumour agents N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and 9-amino-DACA, has been solved to a resolution of 1.8 Å using X-ray crystallography. The complex crystallises in the space group P6₄ and the final structure has an overall R factor of 21.9%. A drug molecule intercalates between each of the CpG dinucleotide steps with its side chain lying in the major groove, and its protonated morpholino nitrogen partially occupying positions close to the N7 and O6 atoms of guanine G2. The morpholino group is disordered, the major conformer adopting a twisted boat conformation that makes van der Waals contact with the O4 oxygen of thymine T3. A water molecule forms bridging hydrogen bonds between the 4-carboxamide NH and the phosphate group of guanine G2. Sugar rings are found in alternating C3′-exo/C2′-endo conformations except for cytosine C1 which is C3′-endo. Intercalation perturbs helix winding throughout the hexanucleotide compared with B-DNA, steps 1 and 2 being unwound by 10 and 8°, respectively, while the central TpA step is overwound by 11°. An additional drug molecule lies at the end of each DNA helix linking it to the next duplex to form a continuously stacked structure. The protonated morpholino nitrogen of this ‘end-stacked’ drug hydrogen bonds to the N7 atom of guanine G6, and its conformationally disordered morpholino ring forms a C–H···O hydrogen bond with the guanine O6 oxygen. In both drug molecules the 4-carboxamide group is internally hydrogen bonded to the protonated N10 atom of the acridine ring. We discuss our findings with respect to the potential role played by the interaction of the drug side chain and the topoisomerase II protein in the poisoning of topoisomerase activity by the acridinecarboxamides.     

Preparation and crystal structure of manganese(II) isothiocyanate tetrahydrate

Crystals of Mn(NCS)₂·4H₂O were isolated from an aqueous solution obtained by mixing solutions of barium thiocyanate and manganese(II) sulphate tetrahydrate. The crystals are monoclinic with a = 7.827(7), b = 9.208(1), c = 7.456(5) Å, β = 112.57(5)°, space group P2₁/c. The structure consists of discrete centrosymmetric trans-[Mn(NCS)₂(H₂O)₄] octahedra linked by hydrogen bonds.     

Preparation and crystal structure of bis(acetato)(trans-1,2-diaminocyclohexane)platinum(II)

The structure of the complex [Pt(trans-1,2-di- aminocyclohexane) (acetate)₂]·H₂O has been determined by X-ray diffraction. This racemic compound is orthorhombic, space group Aba2, a = 20.813(9), b = 7.926(5), c = 17.296(8) Å, Z = 8. The structure was refined on 1214 nonzero Cu Kα reflections to R = 0.028. The square planar environment of Pt includes the amino groups of the diamine in cis positions and oxygens from two monodentate acetates. The PtN and PtO distances average 2.00(3) and 2.02(3) Å, respectively. The bite of the diamine ligand imposes a NPtN angle of 85(1)°, whereas the small OPtO angle of 85(1)° probably results from packing effects. The average plane through the puckered cyclohexyl ring makes an angle of 19° with the PtN₂O₂ plane. The molecules are stacked by pairs along the b axis. The two molecules of each pair are 180° apart about the stacking axis, and form altogether four NH···O hydrogen bonds.     

On the possible influence of different pathways of binding of amides with water on “Pyramidalization” of valence bonds of peptide group nitrogen

With the aim to study solvation effects in peptide structure organization, the behavior of the energy of different types of hydration in simple amines and amides has been analyzed. On the example of quantum-chemical DFT and PM3 calculations of amino derivatives of composition CH₃-(CH₂)₃)-NH₂, (CH3)₂-NH, CH₃-NH₂, NH₃, CH₂=CH-NH₂, H-CC-NH₂, O=C(CH)₃-N(CH₃)₂, O=C(CH₃)-NH(CH₃), O=C(CH₃)-NH₂, O=CH-N(CH₃)H, and O=CH-NH₂ it has been shown that: (1) in the given set of molecules, the proton acceptor N…H-O variant of hydrogen bonding of NH₂ group with a water molecule is dominating only for the simplest amines. Being primordially weaker, the proton donor N-H…OH variant of water H-bonding gradually increases in energy in the given set as the basicity of the compound decreases, and for the case of amides of carboxylic acids it becomes already a significant channel of the hydration; (2) the intermolecular N-H…O=C bonding of trans-N-methylacetamides, which models the peptide hydrogen bonds in proteins, induces “planarization” of its initially nonplanar O=C-NH fragments. However, the addition of water molecules to the complex through the proton acceptor N…H-O variant of binding of N atom not only restores but even strengthens the “pyramidalization” of valence bonds of peptide groups.     

Comparative structural studies of the first row early transition metal(III) chloride tetrahydrofuran solvates

Two compounds of empirical formula MCl₃- (THF)₃, M = V and Cr, have been characterized by single crystal X-ray studies. The VCl₃(THF)₃ molecule, which has a mer octahedral stereochemistry, crystallizes in the monoclinic space group P2₁/c with a= 8.847(2),b= 12.861(5),c= 15.134(3) Å, β = 91.94(2)°, V = 1721(1) ų and Z = 4. The V-Ci(1) and V-CI(2) distances have a mean value of 2.330 [3] Å while V-CI(3) = 2.297(2) Å, The VO(1) and VO(2) distances have a mean value of 2.061[8] Å while V-O(3) = 2.102(3) Å cis ClVCl angles average 92.0[5]° and cis OVO angles average 86.2[2]° . The isostmctural complex, CrCl₃(THF)₃, has a crystal structure made up of discrete octahedral mer-CrCl₃(THF)₃ molecules with the following unit cell dimensions (space group P2₁/c): a = 8.715(1), b= 12.786(3), c = 15.122(3) Å, β = 92.15(1)°, V = 1684(1) ų and Z = 4. The CrCl(1) and CrCl(2) distances have a mean value of 2.310131 Å while CrCl(3) = 2.283(2) Å. The CrO(1) and CrO(2) distances have a mean value of 2.0101171 Å while CrO(3) = 2.077(4) Å. cis ClCrCl angles average 90.9[4]° and cis OCrO angles average 86.1 [2]°. The structures of these two octahedral complexes and those previously reported for ScCl₃(THF)₃ and TiCl₃(THF)₃ are compared and certain general trends are discussed.     

Preparation and crystal structure of the hydroxo-bridged complex biscyclo-tri-μ-hydroxo-tris[(trans-1,2-diaminocyclohexane)platinum(II)] tris

The title compound, [C₁₈H₄₅N₆O₃Pt₃]2(SO₄)₃·14H₂O, belongs to space group C2/c, with a = 25.90(2) Å, b = 14.33(2) Å, c = 23.74(3) Å, β = 122.88(7)°, and Z = 4. The structure was refined on 2899 independent nonzero reflections to an R factor of 0.042. The crystal contains hydroxobridged cyclic [Pt₃(OH)₃(C₆H₁₄N₂)₃]³⁺ ions, in which the Pt₃O₃, ring has a chair conformation. The coordination around each Pt atom is square planar and the cyclohexyl ring lies roughly in the same plane. A large cavity between two trimeric ions related by a twofold axis is filled with one SO₄^2- ion and five water molecules, which participate in an intricate network of hydrogen bonds among themselves and with the hydroxo and amino groups of the complex cation. These units are held together in the crystal by stacking interactions between Pt(OH)₂(C₆H₁₄N₂) “planes” belonging to adjacent molecules, as well as by hydrogen bonds involving the remaining SO₄^2- ions and water molecules. The presence of the cyclohexane ring precludes λ-δ interconversion in the chelate ring and imparts rigidity to the Pt(trans-dach)²⁺ unit.     

Intramolecular hydrogen bonding: synthesis and crystal structure of nickel(II) and copper(II) complexes of a tetradentate amine oxime

In the reaction of the tetradentate ligand 3,3′-(1,4- butanediyldiamino) bis (3-methyl-2-butanone)-dioxime (BnAO) with nickel(II) and copper(II), the monomeric [Ni(BnAO-H)]I·H₂O and a mixed monomer/dimer salt [Cu(BnAO-H)H₂O]₂[(Cu(BnAO-H))₂](ClO₄)₄, respectively, are formed, and all complexes have an intramolecular hydrogen bond between cis oxime groups. The OHO bonds give the characteristic infrared absorptions as well as the downfield proton-NMR signal (Ni complex). [Ni(BnAO-H)]I·H₂O crystallizes in space group P2₁/a with a=13.511(2), b=10.599(2), c=14.096(2) Å, β=97.52°, Z=4 and D_c=1.623 g/cm³. The structure was solved by Patterson and Fourier methods and refined by full-matrix least-squares techniques to a final R of 0.021 for 2124 reflections with I 2σ(I). The nickel(II) atom in the complex has slightly distorted square planar geometry with an intramolecular O···O contact of 2.417(7) Å. The copper(II) complex crystallizes in space group P2₁/c with a =13.425(2), b=21.446(3), c=14.349(4) Å, β= 104.4(5)°, Z=8 (monomers) and D_c=1.485 g/cm³. The final R value for this complex was 0.053 for 3033 reflections with I 2σ(I). This structure contains a monomeric [Cu(BnAO-H)H₂O]⁺ ion and a dimeric [(Cu(BnAO-H))₂]²⁺ ion, having intramolecular O···O hydrogen bonds of 2.421(5) and 2.531(5) Å, respectively. The copper(II) ions have square-pyramidal coordination with the axial positions occupied by an oxygen of the water of hydration in the monomer and by an oxime oxygen atom in the dimer. A center of symmetry relates the two halves of the dimer. The copper atom in each case is out of the plane of the four nitrogen atoms toward the axial site. The copper(II) complex is unusual in that the crystal contains both a monomer and a dimer.     

Some new derivatives of Ni(II) with uracil,uridine and nucleotides

This paper describes the synthesis of compounds of Ni(II) with uracil, uridine and the nucleotides 5′UMP, 5′CMP, 5′GMP and 5′IMP, and their characterization, carried out by elemental analysis, by studying the infrared spectra, diffuse reflectance and conductivity measurement.In the complexes of NiURA (and NiURD) with acetate, direct coordination of the metal ion to the C₄O group of the pyrimidine ring is inferred from the changes observed on the infrared spectrum of the corresponding bands at vCO. The variations in frequency of the vCOO symmetric and asymmetric bands of the acetate group together with the conductivity and reflectance results seem to indicate the dimer structure of the compounds.In the compounds of NiURA (and NiURD) with ethylenediamine indirect bonding of Ni(II)to the pyrimidine ring is inferred, probably established through hydrogen bonds involving the C₄O groups in the base or nucleoside and the −NH₂ groups in the ethylenediamine.In the complexes of Ni-nucleotide, bonding seems to occur through the heterocyclic ring (C₄O for 5′UMP, N(3) for 5′CMP, N(7) for 5′GMP and 5′IMP) together with additional interactions through the phosphate group.     

A ferromagnetically coupled tetranuclear pseudo-cubane copper(II) cluster: magnetic and ESR studies

A tetranuclear copper(II) complex [Cu₄(NSI)₄] · 2C₂H₅OH · 2H₂O (NSI=hydroxethylsalicydeneimine) has been synthesized and characterized by X-ray diffraction analysis. The compound crystallizes in the monoclinic system, space group P2(1), a=9.494(3) Å, b=18.687(5) Å, c=13.149(4) Å, β=110.162(5)°, Z=2, R₁=0.0482 and wR₂=0.0978. The crystal structure contains a tetranuclear pseudo-cubane core based on an approximately cubane array of alternating copper and oxygen atoms. Each copper atom resides in a distorted square planar coordination environment with one nitrogen and three oxygen atoms from two NSI ligands. The tetranuclear units are linked in the crystal by O-H?O hydrogen bonds and weak Cu?O co-ordination bonds into one-dimensional structure. Variable temperature (5-300 K) magnetic measurements indicate the existence of ferromagnetic interactions among copper atoms. The IR and ESR spectra have also been investigated.     

Proton polarizability of poly(L-tyrosine)–hydrogen phosphate hydrogen bonds as a function of alkali cations

We studied films of poly(L -tyrosine) with hydrogen phosphate (residue/phosphate, 1:1) by ir spectroscopy. The influences of the alkali cations (Li⁺, Na⁺, K⁺) and of the degree of hydration were clarified. If Li⁺ ions are present, the OH ?^?OP hydrogen bonds formed in the dried films between the tyrosine OH groups and hydrogen phosphate are asymmetrical. The formation of hydrogen phosphate–hydrogen phosphate hydrogen bonds is prevented by the presence of the Li⁺ ions. With an increase in the degree of hydration, the tyrosine–phosphate bonds are not broken but become slightly stronger. Completely different behaviour is found if K⁺ ions are present. In dry films, the OH ?^?OP ? O^? ?HOP hydrogen bonds formed between tyrosine and hydrogen phosphate show large proton polarizability. The tyrosine proton has a noticeable residence time at the acceptor O atom of the phosphate. The difference in the behaviour of the system with K⁺ ions when compared to the system with Li⁺ ions can be explained, since the hydrogen acceptor O atom of phosphate ions is more negatively charged due to the weaker influence of the K⁺ ions. Furthermore, POH ?^?OP hydrogen bonds between hydrogen phosphate molecules are formed. With an increase in the degree of hydration, the tyrosine–hydrogen phosphate hydrogen bonds are broken, all tyrosine protons are found at the tyrosine residues, and the -PO₃^? groupings are in a symmetrical environment, indicating that the K⁺ ions are removed from these groupings. If the degree of hydration increases further, hydrogen-bonded systems such as hydrogen phosphate–water–hydrogen phosphate are formed that show large proton polarizability due to collective proton motion. When Na⁺ ions are present, the OH ?^?OP ? O^? ?HOP hydrogen bonds formed in dry films still show proton polarizability, but the residence time of the tyrosine proton at the phosphate is very short.     

Calixarene building block bis(2-hydroxyphenyl)methane (2HDPM) and hydrogen-bonded 2HDPM-H2O complex in electronic excited state

Intramolecular and intermolecular hydrogen bonding in electronic excited states of calixarene building blocks bis(2-hydroxyphenyl)methane (2HDPM) monomer and hydrogen-bonded 2HDPM-H₂O complex were studied theoretically using the time-dependent density functional theory (TDDFT). Twenty-four stable conformations (12 pairs of enantiomers) of 2HDPM monomer have been found in the ground state. From the calculation results, the conformations 1a and 1b which both have an intramolecular hydrogen bond are the most stable ones. The infrared spectra of 2HDPM monomer and 2HDPM-H₂O complex in ground state and S₁ state were calculated. The stretching vibrational absorption band of O₂???H₃ group in the monomer and complex disappeared in the S₁ state. At the same time, a new strong absorption band appeared at the C=O stretching region. From the calculation of bond lengths, it indicates that the O₂???H₃ bond is significantly lengthened in the S₁ state. However, the C₁???O₂ bond is drastically shortened upon electronic excitation to the S₁ state and has the characteristics of C=O band. Furthermore, the intramolecular hydrogen bond O₂???H₃?·?·?·?O₄ of the 2HDPM monomer and the intermolecular hydrogen bonds O₂???H₃?·?·?·?O₇ and O₇???H₉?·?·?·?O₄ of 2HDPM-H₂O complex are all shortened and strengthened in the S₁ state.

Experimental concurrent infection of Afar breed goats with Oestrus ovis (L1) and Haemonchus contortus (L3): interaction between parasite populations, changes in parasitological and basic haematological parameters

The study was conducted to examine the occurrence and interaction between Oestrus ovis and Haemonchus contortus in experimentally infected Ethiopian Afar breed of goats. Twenty goats were divided into four groups (O, OH, H, and C) of five animals each. Each animal of groups O and OH received weekly infections for 5 weeks with 66 first instar larvae (L₁) of O. ovis. Then animals of groups OH and H were infected with a single dose of 5000 third stage larvae (L₃) of H. contortus. Goats of group C were kept free of any infection as non-infected control. Faecal egg count (FEC), blood cell count, total serum protein level and body weight were recorded weekly throughout the study period. At necropsy worm burden, female worm length, fecundity and larval burden of O. ovis in the nasal-sinus cavities of infected animals were assessed. The results showed that the presence of H. contortus in the abomasum of goats of group OH had no influence on the development of O. ovis. On the contrary, a significant reduction (P < 0.05) in FEC, worm burden, fecundity and female worm length was revealed in group OH animals compared to the mono-infected animals (group H). This was associated with eosinophilia and reduced packed cell volume.     

Synthesis and structure of an organosamarium aryloxide complex, (C5 Me5)2 Sm(OC6HMe4-2,3,5,6)

Bis(pentamethylcyclopentadienyl)samarium bis- (tetrahydrofuranate), (C₅Me₅)₂Sm(THF)₂, reacts with 2,3,5,6-tetramethylphenol in toluene to yield (C₅Me₅)₂Sm(OC₆HMe₄-2,3,5,6). The compound crystallizes in the space group P2₁/c with a = 8.725(3) Å, b=18.821(6) Å, c=18.461(6) Å, β= 111.17(2)°, V = 2827(2) ų and D_c=1.340 g cm⁻³ for Z = 4. Molecules of the aryloxide complex are monomeric and exhibit a bent metallocene structure with a nearly linear Sm---O---C(aryloxide) linkage: Sm---O = 2.13(1) Å, O---C = 1.29(2) Å, and Sm---O---C = 172.3(13)°. Reaction of the samarium complex with phenyllithium produces the previously- characterized species (C₅Me₅)₂Sm(C₆H₅)(THF).