Littérature scientifique sur le sujet « N-dimer (ND) or C-dimer (CD) »

The new [(teeda)CdFe(CO)4]2 complex has been isolated from the reaction of [(NH3)2CdFe(CO)4]n with tetraethylethylenediamine. Unlike previous structural reports of ligand adducts of [L2CdFe(CO)4]x complexes, which have all been trimeric species composed of six-membered Cd3Fe3 rings, the teeda complex crystallized as a dimer, analogous to [(2,2-bpy)ZnFe(CO)4]2. As in the zinc dimer, significant distortion arises from steric interactions between the axial carbonyl ligands on opposing iron centers. The complex sits on an inversion center, leading to two independent Cd–Fe distances, 2.7244(6) and 2.7433(6) Å, and crystallizes in the monoclinic space group P21/a with a = 14.8546(2) Å, b = 15.1647(3) Å, c = 15.5252(3) Å, β = 90.9517(12)°, and Dcalc = 1.719 g/cm3 at 150(1) K.

The title compound, [Cd2(C7H10NS2)4], is a neutral dinuclear cadmium(II) complex bearing four bisN,N-diallyldithiocarbamate ligands coordinating to two CdIIcations. In each of the monomeric subunits, there are four S atoms of two dithiocarbamate ligands [Cd—S = 2.5558 (3), 2.8016 (3), 2.6050 (3) and 2.5709 (3) Å] that coordinate to one CdIIatom in a bidentate mode. The dimers are located over an inversion centre bridged by two additional bridging Cd—S bonds [2.6021 (3) Å], leading to a substantial distortion of the geometry of the monomeric subunit from the expected square-planar geometry. The five-coordinate environment around each of the CdIIions in the dimer is best described as substantially tetragonally distorted square pyramidal. The dithiocarbamate groups are themselves planar and are also coplanar with the CdIIions. The negative charge on these groups is delocalized by resonance across the S atoms bound to the CdIIcation. This delocalization of the π electrons in the dithiocarbamate groups also extends to the C—N bonds as they reveal significant double bond character [C—N = 1.3213 (16) and 1.3333 (15) Å].

Unfolding of the soluble colicin E1 channel peptide was examined with the use of urea as a denaturant; it was shown that it unfolds to an intermediate state in 8.5 M urea, equivalent to a dimeric species previously observed in 4 M guanidinium chloride. Single tryptophan residues, substituted into the peptide at various positions by site-directed mutagenesis, were employed as fluorescent probes of local unfolding. Unfolding profiles for specific sites within the peptide were obtained by quantifying the shifts in the fluorescence emission maxima of single tryptophan residues on unfolding and plotting them against urea concentration. Unfolding reported by tryptophan residues in the C-terminal region was not characteristic of complete peptide denaturation, as evidenced by the relatively blue-shifted values of the fluorescence emission maxima. Unfolding was also monitored by using CD spectroscopy and the fluorescent probe 2-(p-toluidinyl)-naphthalene 6-sulphonic acid; the results indicated that unfolding of helices is concomitant with the exposure of protein non-polar surface. Unfolding profiles were evaluated by non-linear least-squares curve fitting and calculation of the unfolding transition midpoint. The unfolding profiles of residues located in the N-terminal region of the peptide had lower transition midpoints than residues in the C-terminal portion. The results of unfolding analysis demonstrated that urea unfolds the peptide only partly to an intermediate state, because the C-terminal portion of the channel peptide retained significant structure in 8.5 M urea. Characterization of the peptide's global unfolding by size-exclusion HPLC revealed that the partly denatured structure that persists in 8.5 M urea is a dimer of two channel peptides, tightly associated by hydrophobic interactions. The presence of the dimerized species was confirmed by SDS/PAGE and intermolecular fluorescence resonance energy transfer.

δ-Crystallin is a soluble structural protein in avian eye lenses that confers special refractive properties. In the presence of GdmCl (guanidinium chloride), tetrameric δ-crystallin undergoes dissociation via a dimeric state to a monomeric molten globule intermediate state. The latter are denatured at higher GdmCl concentrations in a multi-state manner. In the present study, the X-ray structure of goose δ-crystallin was determined to 2.8 Å (1 Å=0.1 nm). In this structure the first 25 N-terminal residues interact with a hydrophobic cavity in a neighbouring molecule, stabilizing the quaternary structure of this protein. When these 25 residues were deleted this did not produce any gross structural changes, as judged by CD analysis, but slightly altered tryptophan fluorescence and ANS (8-anilino-1-naphthalenesulphonic acid) spectra. The dimeric form was significantly identified as judged by sedimentation velocity and nondenaturing gradient gel electrophoresis. This mutant had increased sensitivity to temperature denaturation and GdmCl concentrations of 0.3–1.0 M. This protein was destabilized about 3.3 kcal/mol (1 kcal=4.184 kJ) due to N-terminal truncation. After incubation at 37 °C N-terminal truncated proteins were prone to aggregation, suggesting the presence of the unstable dimeric conformation. An important role for the N-terminus in dimer assembly of goose δ-crystallin is proposed.

The synthesis of [Ln{N(SiMe3)2}2(THF)(µ-Cl)]2 (Ln = Ce, 1; Nd, 2) by reaction of sodium bis(trimethylsilyl)amide (2 equiv.) with LnCl3 is reported. The same complexes were also isolated from the ligand redistribution reactions of Ln[N(SiMe3)2]3 and LnCl3 (2:1 ratio) in THF at 80°C. The crystal structure of 2, determined by X-ray diffraction, revealed a centrosymmetric dimer with bridging chlorides and pentacoordinate metal centres. 1H NMR studies show that the solid state structure is not maintained in solution. NMR evidence for the presence of Ln[N(SiMe3)2]3 and two other bis(trimethylsilyl)amide containing species, presumably Ln[N(SiMe3)2]Cl2(THF)x and Ln[N(SiMe3)2]2Cl(THF)y, is presented.Key words: lanthanide, amide, neodymium, cerium, crystal structure, X-ray, nuclear magnetic resonance, redistribution.

Background: Limited information is provided on the quantitative cytomorphometric study of the cervical Pap test. The cervical Pap test is an important screening program for cervical cancer. A quantitative cytomorphometric examination of cervical Pap is used to accurately identify precancerous and cancerous lesions early and to reduce the occurrence and avoidance of invasive cancer. This study was aimed to assess the cytomorphological parameters (nuclear diameter [ND], cytoplasm diameter [CD], and nuclear-to-cytoplasmic ratio [N/C ratio]) of squamous epithelial cells from a cervical Pap smear. Methods and Results: A prospective study was performed on 142 consecutive cervical Pap smears from women with gynecological clinical complaints. The ND and CD were determined by the Optika optical microscope camera using a digitizer cursor in both axes. The final images were taken with an X40 magnification. The ND, CD, and the N/C ratio were then measured and expressed in micrometers. The women were classified into 5 age groups: 5(3.5%) in the age group of <19 years, 46(32%) in the 20-29 group, 67(47.2%) in the 30-39 group, 23(16.2%) in the 40-49 group, and 1(0.7%) woman was over age 50. There were no significant differences in the N/C ratio of superficial cells between age groups. The ND, CD, and the N/C ratio were significantly higher in women with clinical complaints than in women without clinical complaints Conclusion: Cytomorphometic analysis might assist in the identification of cellular alterations due to gynecological diseases and increase the sensitivity and accuracy of the Pap smear technique.

Weakly diffracting crystals of benz[cd]indol-2(1H)-one (naphtholactam), C11H7NO, were unsuitable for data collection by early photographic methods. However, a diffractometer data set collected at room temperature in 1989 was solved and refined. The peak scans were broad, and the results indicated disorder or a satellite crystal. Recent data collection (on another crystal from the same sample) with an area detector at 100 K revealed the same disorder, and made it possible to refine two different, more complete, disorder models. Both models assume an occasional 180° rotation of the nearly planar centrosymmetriccis-lactam dimer. The refinements differ, especially in the anisotropic displacement parameters for the –C(=O)—NH– portion of the molecule. Both models at 100 K give a C—N (`amide') bond distance of 1.38 Å, about 0.04 Å longer than the average distance in saturated γ-lactams in the Cambridge Structural Database. Cohesive packing interactions between molecules include opposing-dipole dimers; the packing may explain the 10:1 ratio favoring the major-occupancy molecule.

The Schiff base (I) upon reacting with mercaptoacetic acid in dry benzene undergoes cyclization and forms N-(2-carbamoylthienyl)-C-(3′-carboxy-2′-hydroxyphenyl)thiazolidin-4-one, LH3(II). A MeOH solution ofIIreacts with Mn(II), Cu(II), Cd(II), Zr(OH)2(IV), and UO2(VI) ions and forms the coordination compounds, [Mn(LH)(MeOH)2], [Cu(LH)]2, [Cd(LH)], [Zr(OH)2(OAc)2(LH3)], and [UO2(NO3)(LH2)(MeOH)]. The compounds have been characterized on the basis of elemental analyses, molar conductance, molecular weight, spectral (IR, reflectance, and EPR) studies and magnetic susceptibility measurements. LH3behaves as a neutral tridentate ONS donor ligand in [Zr(OH)2(OAc)2(LH3)], monobasic tridentate ONS donor ligand in [UO2(NO3)(LH2)(MeOH)], dibasic tridentate OOS donor ligand in [Cu(LH)]2and dibasic tetradentate OONO donor ligand in [Mn(LH)(MeOH)2] and [Cd(LH)]. [Cu(LH)]2is dimer, while all other compounds are monomers in diphenyl. A square-planar structure for [Cu(LH)]2, a tetrahedral structure for [Cd(LH)], an octahedral structure for [Mn(LH)(MeOH)2], a pentagonal-bipyramidal structure for [Zr(OH)2(OAc)2(LH3)], and an eight-coordinate structure for [UO2(NO3)(LH2)(MeOH)] are proposed. The ligand (II) and its compounds show antibacterial activities towardsE. coli. (Gram negative) andS. aureus(Gram positive).

Room-temperature single-crystal X-ray structure determinations carried out on rare earth bromides crystallized from water at room temperature define three series of hydrates LnBr3.nH2O. For Ln = La, Ce, a heptahydrate phase (n = 7) is defined, triclinic P 1, a ≈ 8·6, b ≈ 9·4, c ≈ 8·3 Å, α ≈ 108, β ≈ 99, γ ≈ 72°, isomorphous with the array described for the ‘early’ (Ln = La-Pr) rare earth chlorides, being binuclear [(H2O)7Ln(-Br)2Ln(OH2)7] Br4, Z = 1 dimer; conventional R on |F| were 0·051, 0·042 for 2323, 3451 independent ‘observed’ (I > 3σ(I)) diffractometer reflections respectively. For Ln = Pr(-)Dy, a hexahydrate phase is defined, monoclinic P 2/n, a ≈ 10·0, b ≈ 6·8, c ≈ 8·2 Å, β ≈ 93·5°, Z = 2 f.u., isomorphous with the array defined for the heavier (Ln = Nd, Lu, Y) rare earth chlorides, being [(H2O)6LnBr2] Br, with R 0·029, 0·034 for No 1590, 1388 respectively. For Ln = Ho(-)Lu, Y, an octahydrate is defined for the first time, monoclinic P 21/n, a ≈ 8·1, b ≈ 16·0, c ≈ 10·1 Å, b ≈ 94·0°, Z = 4 f.u., a new array of the form [Ln(OH2)8] Br3 emerging, with R 0·061, 0·048, 0·042 for No 1191, 2402, 1674 respectively, the metal environment being square antiprismatic.

AbstractHückel molecular orbital (HMO) quantities, viz., electron densities, charge densities, bond orders, free valences, total π-electron energies and highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO–LUMO) or band gaps of {X,Y}-cyclacene graphs under next-nearest-neighbour (nnn) approximations are expressed in analytical forms within a certain range of nnn approximation parameter (m). The critical values of m for {X,Y}-cyclacenes with varying X (=C, N, B) and Y (=C, N, B) are calculated. For {X,X}-cyclacenes with a π-electron on each atom, all HMO quantities except total π-electron energies for a given value of m are found to be independent of X. The cyclic dimer (CD) is constructed in obtaining the eigenvalues corresponding to the singular points of the density of states (DOS) of such {X,Y}-cyclacene. Although the HOMO–LUMO gap of the CD differs from that of the cyclacene with a large number of repeating units (i.e. n ⟶ ∞) but becomes the same for m = 0. The analytical expressions can be used for facile computer programming in obtaining the HMO quantities. Such nnn interaction approximations actually release, to some extent, the strain that results in due to the geometrical structures of such cyclacenes, which is evident from the plots of strain energy per segment vs. contribution of such interactions on the total π-electron energy, where the slopes decrease with an increase in m. The vertical absorption energy difference for singlet-triplet states bears excellent linear correlation with the HOMO–LUMO gaps for a certain m value (m = 0.3) in the case of an even n, but for an odd n, such energy difference remains invariant.

"Zero-length" dimers of ribonuclease A, a novel type of dimers formed by two RNase A molecules bound to each other through a zero-length amide bond [Simons, B.L. et al. (2007) Proteins 66, 183-195], were analyzed, and tested for their possible in vitro cytotoxic activity. Results: (i) Besides dimers, also trimers and higher oligomers can be identified among the products of the covalently linking reaction. (ii) The "zero-length" dimers prepared by us appear not to be a unique species, as was instead reported by Simons et al. The product is heterogeneous, as shown by the involvement in the amide bond of amino and carboxyl groups others than only those belonging to Lys66 and Glu9. This is demonstrated by results obtained with two RNase A mutants, E9A and K66A. (iii) The "zero-length" dimers degrade poly(A).poly(U) (dsRNA) and yeast RNA (ssRNA): while the activity against poly(A).poly(U) increases with the increase of the oligomer's basicity, the activity towards yeast RNA decreases with the increase of oligomers' basicity, in agreement with many previous data, but in contrast with the results reported by Simons et al. (iv) No cytotoxicity against various tumor cells lines could be evidenced in RNase A "zero-length" dimers. (v) They instead become cytotoxic if cationized by conjugation with polyethylenimine [Futami, J. et al. (2005) J. Biosci. Bioengin. 99, 95-103]. However, polyethylenimine derivatives of RNase A "zero-length" dimers and native, monomeric RNase A are equally cytotoxic. In other words, protein "dimericity" does not play any role in this case. Moreover, (vi) cytotoxicity seems not to be specific for tumor cells: polyethylenimine-cationized native RNase A is also cytotoxic towards human monocytes.
"Zero-length" dimers of ribonuclease A, a novel type of dimers formed by two RNase A molecules bound to each other through a zero-length amide bond [Simons, B.L. et al. (2007) Proteins 66, 183-195], were analyzed, and tested for their possible in vitro cytotoxic activity. Results: (i) Besides dimers, also trimers and higher oligomers can be identified among the products of the covalently linking reaction. (ii) The "zero-length" dimers prepared by us appear not to be a unique species, as was instead reported by Simons et al. The product is heterogeneous, as shown by the involvement in the amide bond of amino and carboxyl groups others than only those belonging to Lys66 and Glu9. This is demonstrated by results obtained with two RNase A mutants, E9A and K66A. (iii) The "zero-length" dimers degrade poly(A).poly(U) (dsRNA) and yeast RNA (ssRNA): while the activity against poly(A).poly(U) increases with the increase of the oligomer's basicity, the activity towards yeast RNA decreases with the increase of oligomers' basicity, in agreement with many previous data, but in contrast with the results reported by Simons et al. (iv) No cytotoxicity against various tumor cells lines could be evidenced in RNase A "zero-length" dimers. (v) They instead become cytotoxic if cationized by conjugation with polyethylenimine [Futami, J. et al. (2005) J. Biosci. Bioengin. 99, 95-103]. However, polyethylenimine derivatives of RNase A "zero-length" dimers and native, monomeric RNase A are equally cytotoxic. In other words, protein "dimericity" does not play any role in this case. Moreover, (vi) cytotoxicity seems not to be specific for tumor cells: polyethylenimine-cationized native RNase A is also cytotoxic towards human monocytes.