Spectral properties and inclusion of a hetero-chalcone analogue in organized media of micellar solutions and beta-cyclodextrin

The absorption and fluorescence emission spectral properties of 3-(4'-dimethylaminophenyl)-1-(2-thienyl)prop-2-en-1-one, abbreviated as DMATP, have been investigated in organized media of aqueous micellar and beta-cyclodextrin (CD) solutions. While the absorption spectra are less sensitive to the nature of the added surfactant or CD, the characteristics of the intramolecular charge transfer (ICT) fluorescence are highly sensitive to the properties of the medium. The ICT maximum is strongly blue-shifted with a great enhancement in the fluorescence quantum yield on adding micellar or CD solutions. This indicates the solubilization of DMATP in the micellar core and formation of an inclusion complex with beta-CD. The critical micelle concentration (CMC) as well as the polarity of the micellar core of SDS, CTAB and TX-100 have been determined. The CMC values are in good agreement with the reported values while the polarity is lower indicating that DMATP molecules are incorporated in the micellar core not at the micellar interface. The inclusion constants of binding of DMATP in micellar or CD have been also determined. The thermodynamic parameters of formation of DMATP:CD inclusion complex have been calculated from the temperature dependence of the fluorescence spectra of the formed complex. The negative enthalpy and free energy of formation indicate that the inclusion process is energetically favorable. The highly negative value of formation entropy (DeltaS = -162.3 J mol(-1) K(-1)) reflects the high restrictions imposed on the movement of both the host and included guest molecules which is consistent with the increase of the fluorescence yield and blue shift of the fluorescence maximum.     

Dimeric structure of transmembrane domain of amyloid precursor protein in micellar environment

Some pathogenic mutations associated with Alzheimer's disease are thought to affect structural-dynamic properties and the lateral dimerization of amyloid precursor protein (APP) in neuron membrane. Dimeric structure of APP transmembrane fragment Gln(686)-Lys(726) was determined in membrane-mimicking dodecylphosphocholine micelles using high-resolution NMR spectroscopy. The APP membrane-spanning α-helix Lys(699)-Lys(724) self-associates in a left-handed parallel dimer through extended heptad repeat motif I(702)X(3)M(706)X(2)G(709)X(3)A(713)X(2)I(716)X(3)I(720)X(2)I(723), whereas the juxtamembrane region Gln(686)-Val(695) constitutes the nascent helix, also sensing the dimerization. The dimerization mechanism of APP transmembrane domain has been described at atomic resolution for the first time and is important for understanding molecular events of APP sequential proteolytical cleavage resulting in amyloid-β peptide.     

Spectral properties of perselenosulfide

The riductive scission of a diselenide (selenocystamine) produced by disulfide gives the perselenosulfide, a new compound. Its formation kinetics, carried out a several pH values, were recorded spectrophotometrically at 375 nm. The lability of perselenosulfide bond by cianolysis has been demonstrated.     

Synthesis,characterization and kinetics of formation of silver nanoparticles by reduction with adrenaline in the micellar media

The present paper describes about the easy, simple and convenient procedure for the synthesis of silver nanoparticles (Ag-NPs) in aqueous solutions by the reduction of silver nitrate with adrenaline. The surfactant molecules of cetyltrimethylammonium bromide (CTABr) and sodium dodecyl ate (SDS) behaved differently during the reduction of Ag⁺ ions by adrenaline. The obtained data suggest that the variation of [CTABr] gave a maxima-like curve for rate constant versus [CTABr], while, the values of rate constant decreased with the increase in [SDS]. The addition of surfactant molecules stabilized the Ag-NPs. The UV–Visible spectra were analyzed to deduce the particle size. The calculated sizes of the nanoparticles were further compared by the TEM images. The XRD spectrum confirmed the crystalline nature of silver nanoparticles having the face-centered cubic crystal structure. The edge length of unit cell was found 4.076 Å. The kinetics of formation of Ag-NPs was performed at different concentrations of adrenaline, AgNO₃, NaOH and [surfactant]. The values of rate constant were independent on [adrenaline] and [AgNO₃]. The increase in [NaOH] increased the rate of agglomeration of silver particles to form Ag-NPs. A linear relationship was obtained for the plot of rate constant versus [NaOH].     

Spectral properties of conformational motion in proteins

The conformational dynamics of large fragments of protein structure within the framework of a generalized model of bounded diffusion (GMBD) have been considered. This model is a development of the known ordinary model of bounded diffusion (MBD). The latter model assumes that the driving force of motion, which is at the same time a source of friction, has negligibly small correlation time (white noise). In contrast to the MBD, the GMBD takes into account the finite character of friction correlation time, i.e. memory friction effects. Two different mechanisms of friction for the fragment are considered: (1) friction by rapid density fluctuations due to the harmonic vibrational motion of atoms and (2) friction by slow encounters with surrounding fragments of protein structure. The present theory shows that at high frequencies the power decay of the spectrum which takes place in the MBD is replaced by an exponential one. In the narrow intermediate frequency range the results of the GMBD coincide with those of the MBD. At low frequencies the results of the two models differ quantitatively, though their qualitative behaviour is similar.     

Laser-light scattering investigation of the micellar properties of gangliosides

The micellar properties of gangliosides in water solutions were investigated by quasielastic light scattering measurements. G_M1 and G_D1a gangliosides were isolated from calf brain, purified to more than 99% and dissolved in 0.025 M Tris—HCI buffer (pH 6.8) at 37°C. The average intensity of scattered light and the intensity correlation function were measured by an apparatus including a 5145 Å argon laser and a real-time digital correlator. The scattered intensity data allowed the derivation of an upper limit to the critical micelle concentration (c₀) and the evaluation of the molecular weight (M) of the micelle. The intensity correlation function gave the diffusion coefficient D, and hence the hydrodynamic radius R_H, and also contained information on the polydispersity of the sample. We find c_o < 1 × 10^?6 M for both G_M1 and G_D1a, M = 532 000 ± 50 000 and $\text{R}{}_{\mathrm{<mtext>H</mtext>}}\text{= 63.9 ± 2}\text{A}\text{?}$ for G_M1, and M = 417 000 ± 40 000 and $\text{R}{}_{\mathrm{<mtext>H</mtext>}}\text{= 59.5 ± 2}\text{A}\text{?}$ for G_D1a. The mixture 3:1 of the two gangliosides gave intermediate values for all examined parameters. The presence of cations, within the physiological concentration range. and, in particular of Ca²⁺, did not influence significantly the values of c_o and the main features of the micelle.     

Spectroscopic properties of horse liver alcohol dehydrogenase in reversed micellar solutions

Catalytic and spectroscopic properties of alcohol dehydrogenase from horse liver, incorporated in reversed micellar media, have been studied. Two different reversed micellar systems have been used, one containing an anionic [sodium bis(2-ethylhexyl)sulfosuccinate, AOT], the other containing a cationic (cetyltrimethylammonium bromide, CTAB) surfactant. With 1-hexanol as substrate the turnover number of the enzyme in AOT-reversed micelles is strongly dependent on the water content of the system. At low wo ([H2O]/[surfactant]) (wo less than 20) no enzymatic activity can be detected whereas at high wo (wo = 40) the turnover is only slightly lower than in aqueous solution. In CTAB-reversed micelles the dependence of the turnover number on wo is much less. The enzymatic activity is in this case significantly lower than in aqueous solution and increases only slightly with an increasing water content of the reversed micelles. Possible interactions of the protein with the surfactant interfaces in the reversed micellar media were studied via circular dichroism and fluorescence measurements. From the circular dichroism of the protein backbone it is observed that the protein secondary structure is not significantly affected upon incorporation in the reversed micelles since the far-ultraviolet spectrum is not altered. Results from time-resolved fluorescence anisotropy experiments indicate that, especially in AOT-reversed micelles, interactions between the protein and the surfactant interface are largely electrostatic in nature, as evident from the dependence on the pH of the buffer used. In CTAB-reversed micellar solutions such interactions appear to be much less pronounced than in AOT.     

1H NMR structural characterization of the cytochrome c modifications in a micellar environment

The interaction of cytochrome c with micelles of sodium dodecyl sulfate was studied by proton NMR spectroscopy. The protein/micelles ratio was found to be crucial in controlling the extent of the conformational changes in the heme crevice. Over a range of ratios between 1:30 and 1:60, the NMR spectra of the ferric form display no paramagnetic signals due to a moderately fast exchange between intermediate species on the NMR time scale. This is consistent with an interconversion of bis-histidine derivatives (His18-Fe-His26 and His18-Fe-His33). Further addition of micelles induces a high-spin species that is proposed to involve pentacoordinated iron. The resulting free binding site, also encountered in the ferrous form, is used to complex exogenous ligands such as cyanide or carbon monoxide. Attribution of the heme methyls was performed by means of exchange spectroscopy through ligand exchange or electron transfer. The heme methyl shift pattern of the micellar cyanocytochrome in the ferric low spin form is different from the pattern of both the native and the cyanide cytochrome c adduct, in the absence of micelles, reflecting a complete change of the heme electronic structure. Analysis of the electron self-exchange reaction between the two redox states of the micellar cyanocytochrome c yields a rate constant of 2.4 x 10(4) M(-1) s(-1) at 298 K, which is surprisingly close to the value observed in the native protein.     

Synthesis and micellar mimic properties of bile acid trimers

Two fan-shaped bile acid trimers have been synthesized via Cu^I-catalyzed azide–alkyne cycloaddition (CuAAC) ‘click chemistry’, and their extraction experiments of cresol red sodium (CR) and pyrene were investigated in the polar and non-polar solvents, respectively. The transmission electron microscopy (TEM) results showed that the homogenous hollow capsules formed with the diameter size range of 40–70 nm in a solution of water and acetone. Thus the amphiphilicity of fan-shaped bile acid trimers might be used as the promising candidate in biological and drug delivery applications.     

Spectral properties of Eigen evolution matrices

Eigen [7] has employed deterministic kinetic-like equations to describe macromolecular replication and mutation leading to selection. The solutions to these equations and their physically interesting properties depend upon the spectrum of a type of matrix appearing in those equations. Below we explicitly solve for the spectrum of a fairly general class of such matrices. These solutions are obtained recursively for equations describing macromolecules of any length v.     

Spectral properties of chlorophyll a in liquid crystal

Solution of chlorophyll a in liquid crystals mixture (MBBA + EBBA) was investigated. Chl molecules are in LC in low electric field oriented. They can be divided into two groups: one strongly interacting with LC and subjected to reorientation by the electric field, and another weakly interacting with the solvent and insensitive to the voltage applied. The emission spectrum of the first type of chlorophyll is strongly perturbed. At higher voltages, the pigment molecules orientation in the plane of the electrode is another. Pigment absorption and emission anisotropy provides information about the reorientation of LC molecules. Even at high (10^?3M) Chl concentration and regular pigment array, the interaction between the pigment and solvent exceeds pigment-pigment interaction because the solvent appears to have a stronger influence on the Chl spectrum.     

Impact of a micellar environment on the conformations of two cyclic pentapeptides.

In an effort to explore the influence of interfacial environments on reverse turns, we have performed a detailed analysis by nmr of the solution conformations of two cyclic pentapeptides in sodium dodecyl sulfate (SDS) micelles. The first peptide, cyclo (D-Phe1-Pro2-Gly3-D-Ala4-Pro5), adopts a single rigid conformation in solution (either chloroform or dimethylsulfoxide) and in crystals, whereas the second, cyclo (Gly1-Pro2-D-Phe3-Gly4-Val5), is much more flexible and adopts different conformations in the crystal and in solution. Both of these peptides are solubilized by SDS micelles, and nmr relaxation rates indicate that they are both partially immobilized by interaction with the micelles. Furthermore, some amide protons in both peptides participate in hydrogen bonds with water. In the presence of micelles, the former peptide retains a conformation essentially the same as that found in crystals and in solution, which consists of a beta turn and an inverse gamma turn. However, the micellar environment has a significant effect on the latter peptide. In particular, the population of a conformer containing a cis Gly-Pro peptide bond is increased significantly. The most likely conformation of the cis isomer, determined by a combination of nmr and restrained molecular dynamics, contains a Gly1-Pro2 delta turn and a gamma turn about D-Phe3. The nmr data on the trans isomer indicate that this isomer is averaging between two conformations that differ mainly in the orientation of the D-Phe3-Gly4 peptide bond.     

Detergent properties of apolipoprotein A1 in micellar complexes with dimyristoyl phosphatidylcholine

Bilayer micellar complexes of the human plasma apolipoprotein A1 with dimyristoyl phosphatidylcholine were prepared under kinetically controlled conditions. Detergent-like properties of Apo A1 in the complexes were expressed in terms of delta SA1 parameter (surface area of mixed micelle per an Apo A1 molecule). Analysis of our and earlier published data showed the correlation of the delta SA1 parameter with the stoichiometry of complexes. Changes of detergent-like properties were caused by cross-linking or proteolysis of Apo A1.     

Spectral properties of cytochromes from Staphylococcus aureus

Two cytochrome b with peaks at 554 and 558 nm and cytochrome a with alpha-peak at 603 nm were found in intact cells and membranes of Staphylococcus aureus using low-temperature spectrophotometry and registration of second- and fourth-order finite difference spectra of cytochromes. Analysis of the cytochrome functioning in membranes isolated from the cells at the exponential and stationary growth phases revealed no difference in the set of these carriers. Analysis of cytochrome reduction with different substrates demonstrated identity of the cytochrome composition in the respiratory chain, reduced with NADH, lactate, alpha-glycerophosphate, malate and succinate. Cytochrome omicron with gamma-peak at 416 nm in the CO-spectra was found to be involved in oxidation of all the substrates tested both in intact cells and membranes of Staphylococcus aureus.     

Spectral and electrochemical properties of vanadyl hexadecafluorophthalocyanine

A vanadyl complex with perfluorinate phthalocyanine, VOPcF₁₆, was prepared. The monomer-dimer solvent dependence was confirmed based on the solvent effect for the Q-band position-that is, VOPcF₁₆ exists as a monomer in a nonpolar solvent such as benzene, but dimerizes in a polar solvent such as acetone. Electron spin resonance data also supported the solvent dependence found. In addition, the substituent effect of fluorine atoms on the redox properties was investigated by measuring the cyclic voltammograms in dichloromethane. On the reduction side, three redox couples were observed, the first two of which were assigned as being due to the reduction of the phthalocyanine ring (to LUMO), whose potentials are 0.4–0.5 V higher than those of the tetra-t-butyl and octabutoxy derivatives, VOPc(t-Bu)₄ and VOPc(O-n-Bu)₈.     

Spectral properties of myoglobins from aquatic mammals

Spectral characteristics of ferri- and ferroderivatives of myoglobins have been studied in semiwater mammals. Extinction coefficients in the visible range of the spectrum have been determined for different derivatives of the studied heme proteins. It is established that variations in the maxima and minima of different absorption bands are inconsiderable. Close positions of isobestic points have been revealed for a system of oxyglobin and reduced myoglobin obtained from the muscles of the studied animals. Changes in spectral characteristics of methmyoglobins, induced by the effect of different pH, are identical, which evidences for similarity of the surroundings of active site of the studied heme proteins.     

Spectral properties of mosquito Aedes flavescens iridovirus

The UV absorption of the virions of mosquito Aedes flavescens iridovirus (AfIV) is shown to be due to the absorption of all viral components (capsid proteins, lipids and DNA). The AfIV virion fluorescence at room temperature is caused by the fluorescence of capsid proteins, while at low temperatures (5 K, 77 K) it is related to the fluorescence of both capsid proteins and viral DNA. The analysis of low-temperature virion phosphorescence makes it possible to identify the type of nucleic acid inside the virus. The results of the AfIV DNA analysis as well as determination of the lipid composition of virion shell are reported. The amino acid composition of the major capsid protein of the iridovirus is determined by means of sequencing the DNA fragment that is a part of the protein gene.