ABSTRACT
We use a prototypical alkane film (n-C(32)H(66) or C32) adsorbed on a SiO(2) surface to compare step heights measured by amplitude modulation atomic force microscopy (AM-AFM) with those measured in the contact mode. The C32 film exhibits layers in which the molecules are oriented with their long axis parallel to the SiO(2) surface followed by partial layers of perpendicular molecules. We show that step heights measured in the AM and contact modes agree in all cases except where the step is between a surface formed by a layer of parallel molecules and one of perpendicular molecules. In this case, the AM mode gives a false step height that is as much as 20% lower than that measured in the contact mode and inferred from synchrotron X-ray specular reflectivity measurements. We propose that the weaker van der Waals forces between the AFM tip and a perpendicular layer compared to a parallel layer causes this discrepancy. We show how to correct the false step height by using the approximately linear relationship observed between phase angle (cantilever oscillation relative to the drive signal) and cantilever height measured in an approach curve.
ABSTRACT
The synthesis of 2-[3,4-bis(n-alkan-1-yloxy)phenyl]-2-oxazolines with alkan = octan, decan, dodecan, and tridecan is presented. Their living cationic ring opening polymerization produces cylindrical macromolecules that self-organize in a hexagonal columnar two-dimensional phase. The structural analysis of these polymers was carried out by a combination of techniques including differential scanning calorimetry, thermal optical polarized microscopy, X-ray diffraction, transmission electron microscopy, electron diffraction, scanning force microscopy, and atomic force microscopy (AFM). The diameter of these cylindrical macromolecules ranges from 33 to 44 A, and therefore they represent the simplest cylindrical macromolecules that can be directly visualized by AFM on a surface. Preliminary experiments have demonstrated the use of these cylindrical macromolecules as models to investigate the creation of two-dimensional and three-dimensional order via direct visualization and thus they represent the simplest nonbiological systems that mimic the role played by the complexes of nucleic acids with proteins in structural analysis by direct visualization.
Subject(s)
Oxazoles/chemistry , Polymers/chemistry , Calorimetry, Differential Scanning , Macromolecular Substances , Magnetic Resonance Spectroscopy , Microscopy, Atomic Force , Molecular Structure , Oxazoles/chemical synthesis , Polymers/chemical synthesis , Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization , Thermodynamics , X-Ray DiffractionABSTRACT
The complex formed by myoglobin and nicotinic acid exhibits unusual spectral properties. Instead of the usual two bands in the visible region the complex shows four bands assigned to the so called twin hemochromogen. Some attempts were previously made to clarify the nature of the twin hemochromogen, but the interpretation given was somewhat doubtful. We have shown that the combination of two spectral methods, namely magnetic circular dichroism and absorption spectra, give evidence that unusual absorption spectrum of the myoglobin complex with nicotinic acid is not attributed neither to the presence of the other hemochromogen nor to the soft vibrations but is due to the strong splitting of the pure electronic Q00 band into two Qox and Q0y bands. The splitting is caused by the distortion of heme structure by its asymmetrical environment.
Subject(s)
Myoglobin , Nicotinic Acids , Animals , Chemical Phenomena , Chemistry , Circular Dichroism , Magnetics , WhalesABSTRACT
Absorption and magnetic circular dichroism spectra (77 degrees K) of nonequilibrium cytochrome c and its derivatives reduced by thermolysed electrons was studied. The low temperature spectral characteristics of reduced cytochrome c (pH 7.0, 1.6 and 10.0), dimer, carboxymetylated and formylated derivatives at netral and acid pH, also fluoride complexes differ from the characteristics of equilibrium reduced forms. The temperature increase (up to 177 degrees K) induces relaxation of nonequilibrium states. These effects are due to structural differences in the heme vicinity of the reduced and oxidized forms.
Subject(s)
Cytochrome c Group , Circular Dichroism , Hemeproteins , Magnetics , Protein Conformation , SpectrophotometryABSTRACT
Absorption and magnetic circular dichroism spectra of non-equilibrium states of myoglobin and its complexes formed by reduction oxidased forms of proteins by thermalysed electrons at 77 degrees K were studied. Mixtures of high spin and low spin ferroforms were observed for nonequilibrium states of myoglobin and its complex with fluorine, the content of the high spin form is larger in the complex. Two intense peaks were found in the alpha-band region of absorption spectra of myoglobin and its spectra with F-, OH- and imidazole. This effect is due to lowering of the active centre's symmetry. Similarity of spectral characteristics of low spin ferroforms of these complexes was explained by the strong influence of distal histidine. The low temperature reduction of azide and cyanide complexes of myoglobin led to formation of nonequilibrium low spin ferroforms whose spectra demonstrate the presence of N3- and CN- in heme iron's coordination sphere. The temperature relaxation of all nonequilibrium systems were investigated.
Subject(s)
Hemeproteins , Myoglobin , Azides , Circular Dichroism , Cyanides , Fluorides , Oxidation-Reduction , Protein Binding , Protein Conformation , SpectrophotometryABSTRACT
Absorption and magnetic curcular dichroism spectra of nonequilibrium states of peroxidase and its complexes with F-, N3-, CN- produced by reduction of oxidased forms of proteins by thermalysed electrons at 77 degrees K were studied. Mixtures of high spin and low spin ferroforms were found in nonequilibrium states of peroxidase and complexes with F- and N3-, the content of the high spin ferroform increasing as follows: N3- complex less than peroxidase less than fluorine complex. Only low spin ferroforms was found after low temperature reduction of the cyanide complex. The existence of the low spin ferroform in equilibrium states of peroxidase and its complex with F- was explained by location of iron near the porphyrine plane. In the case of azide and cyanide complexes the existence of the low spin form is due to the presence of these ligands in heme iron's coordination sphere. The temperature relaxation of all nonequilibrium forms was investigated and a possible mechanism of the process is proposed.
Subject(s)
Hemeproteins , Peroxidases , Azides , Circular Dichroism , Cyanides , Fluorides , Oxidation-Reduction , Protein Binding , Protein Conformation , SpectrophotometryABSTRACT
Absorption and magnetic circular dichroism spectra of nonequilibrium states of hemoglobin and its derivatives formed by reduction oxidased forms of hemoproteins by thermalysed electrons at 77 degrees K were studied. Mixtures of low spin and high spin ferroforms were observed for nonequilibrium hemoglobin and its complexes with inosithexaphosphate and fluorine. The content of the high spin form increasing as follows: hemoglobin, complex with inosithexaphosphate, complex with fluorine. Only low spin forms were found for cyanide and azide complexes of hemoglobin reduced at low temperature. The spectral differences of nonequilibrium low spin ferroforms were supposed to be due to the presence of different ligands in the coordination sphere of the heme iron. The alpha-band splitting was observed for the nonequilibrium imidazole complex of hemoglobin. This effect was explained by a lowe-ring of the active centre's symmetry. The temperature relaxation of all nonequilibrium systems was investigated.
Subject(s)
Hemoglobins , Circular Dichroism , Cyanides , Fetal Hemoglobin , Fluorides , Humans , Hydroxides , Imidazoles , Ligands , Methemoglobin , Oxyhemoglobins , Phytic Acid , Protein Conformation , Spectrum AnalysisABSTRACT
The absorption spectra of ferricytochrome c complexes with azide, imidazole and cyanide reduced by trapped electrons at the liquid nitrogen temperature were investigated. Differences have been found between the absorption spectra at T=77 degrees K of cytochrome c complexes reduced by radiation and the absorption spectrum of ferrocytochrome c. These differences are supposed to be due to the axial ligation of the Fe(II) by exogenous ligand. The temperature increase led to the removal of exogenous ligand from Fe(II).
