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Dimerization Constants (dimerization + constant)
Selected AbstractsBackbone dynamics of SDF-1, determined by NMR: Interpretation in the presence of monomer,dimer equilibriumPROTEIN SCIENCE, Issue 11 2006Olga K. Baryshnikova Abstract SDF-1, is a member of the chemokine family implicated in various reactions in the immune system. The interaction of SDF-1, with its receptor, CXCR4, is responsible for metastasis of a variety of cancers. SDF-1, is also known to play a role in HIV-1 pathogenesis. The structures of SDF-1, determined by NMR spectroscopy have been shown to be monomeric while X-ray structures are dimeric. Biochemical data and in vivo studies suggest that dimerization is likely to be important for the function of chemokines. We report here the dynamics of SDF-1, determined through measurement of main chain 15N NMR relaxation data. The data were obtained at several concentrations of SDF-1, and used to determine a dimerization constant of ,5 mM for a monomer,dimer equilibrium. The dimerization constant was subsequently used to extrapolate values for the relaxation data corresponding to monomeric SDF-1,. The experimental relaxation data and the extrapolated data for monomeric SDF-1, were analyzed using the model free approach. The model free analysis indicated that SDF-1, is rigid on the nano- to picosecond timescale with flexible termini. Several residues involved in the dimer interface display slow micro- to millisecond timescale motions attributable to chemical exchange such as monomer,dimer equilibrium. NMR relaxation measurements are shown to be applicable for studying oligomerization processes such as the dimerization of SDF-1,. [source] Recognition of protonated aliphatic ,,,-diamines by coproporphyrin I tetraanion in waterJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2002Alejandro Flores-Villalobos Abstract Interactions of aliphatic ,,,-diamines [H2N(CH2)nNH2, 2,,,n,,,8] with coproporphyrin I tetraanion (CP) were studied by spectrophotometry, fluorimetry and 1H NMR spectroscopy in the pH range 7,10 and ionic strengths 0.01,0.1,M. Diprotonated diammonium cations induce dimerization of CP by forming 1:1 complexes with CP which undergo much stronger self-aggregation than free CP tetraanions. On increasing the number of methylene units n connecting the ammonium groups, the binding constants for the complex formation with monomeric CP (KL) increase but the dimerization constants of the resulting complexes decrease. A hydrophobic contribution to the binding free energy of ,1.6,±,0.2,kJ,mol,1 per methylene unit was obtained from the linear correlation of logKL values extrapolated to zero ionic strength vs the number of methylene units (n,=,2,6). A model for diammonium-induced porphyrin dimerization is proposed, which involves complexation of diammonium cations with CP monomer via a combination of electrostatic and hydrophobic interactions and subsequent formation of porphyrin face-to-face dimers in which diammonium cations serve as the stabilizing bridges via ion pairing to carboxylate groups of two CP monomeric units. Copyright © 2001 John Wiley & Sons, Ltd. [source] Self-Assembly of Bis(merocyanine) Tweezers into Discrete Bimolecular ,-StacksCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009Andreas Lohr Dr. Abstract Dipolar aggregation: Examples of a novel class of tweezer molecules have been constructed through the tethering of two dipolar merocyanine chromophores. The electrostatic-interaction-directed self-assembly of these tweezers affords centrosymmetric bimolecular complexes with a unique aggregate geometry of four ,-stacked chromophores (see picture) with an alternating arrangement of their dipole moments and very high dimerization constants, even in the good solvating solvent chloroform. Examples of a novel class of tweezer molecules have been constructed through the tethering of two dipolar merocyanine chromophores by a naphthalenedimethylene or dimethylenediphenylmethane spacer. The electrostatic-interaction-directed self-assembly of these bis(merocyanine) tweezers affords centrosymmetric bimolecular complexes with very high dimerization constants of up to >109,M,1, even in the good solvating solvent chloroform. This pronounced self-association of the bis(merocyanine) tweezers is attributed to the strongly dipolar nature of the merocyanine chromophores and a unique aggregate geometry of four ,-stacked chromophores with an alternating arrangement of their dipole moments. The structural assignment of the tetrachromophoric ,-stack has been accomplished by MALDI-TOF mass spectrometry and ROESY NMR spectroscopy. Furthermore, molecular modeling studies have accounted for the relationships between the dimerization constants and optical properties of the bimolecular complexes of the present bis(merocyanine) dyes and the structure of the spacer and the positions at which the merocyanine chromophores are attached. [source] Effect of Core Twisting on Self-Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline PhasesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Zhijian Chen Abstract A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3,a,f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by 1H,NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The ,,, aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. Concentration-dependent UV/Vis measurements and VPO analysis revealed that these core-twisted ,-conjugated systems show distinct self-dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3×104 and 30,M,1. The photoluminescence spectra of the dimers of PBIs 3,a,f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective ,,, stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the , systems on their ,,, stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case (3,a) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non-fluorescent H -type into strongly fluorescent J -type packing of the dyes. [source] | ||||||||||