The length of esterifying alcohol affects the aggregation properties of chlorosomal bacteriochlorophylls

Abstract Chlorosomes, the main light-harvesting complexes of green photosynthetic bacteria, contain bacteriochlorophyll (BChl) molecules in the form of self-assembling aggregates. To study the role of esterifying alcohols in BChl aggregation we have prepared a series of bacteriochlorophyllide c (BChlide c) derivatives differing in the length of the esterifying alcohol (C(1), C(4), C(8) and C(12)). Their aggregation behavior was studied both in polar (aqueous buffer) and nonpolar (hexane) environments and the esterifying alcohols were found to play an essential role. In aqueous buffer, hydrophobic interactions among esterifying alcohols drive BChlide c derivatives with longer chains into the formation of dimers, while this interaction is weak for BChlides with shorter esterifying alcohols and they remain mainly as monomers. All studied BChlide c derivatives form aggregates in hexane, but the process slows down with longer esterifying alcohols due to competing hydrophobic interactions with hexane molecules. In addition, the effect of the length of the solvent molecules (n-alkanes) was explored for BChl c aggregation. With an increasing length of n-alkane molecules, the hydrophobic interaction with the farnesyl chain becomes stronger, leading to a slower aggregation rate. The results show that the hydrophobic interaction is the driving force for the aggregation in an aqueous environment, while in nonpolar solvents it is the hydrophilic interaction.     

Performance of the DFT-D method, paired with the PCM implicit solvation model, for the computation of interaction energies of solvated complexes of biological interest

In this work we investigate the performance of the DFT method, augmented with an empirical dispersion function (DFT-D), paired with the PCM implicit solvation model, for the computation of noncovalent interaction energies of biologically-relevant, solvated model complexes. It is found that this method describes intermolecular interactions within water and ether (protein-like) environments with roughly the same accuracy as in the gas phase. Another important finding is that, when environmental effects are taken into account, the empirical dispersion term associated with the DFT-D method need be modified very little (or not at all), in order to obtain the optimum, most well balanced, performance.     

Thermoelectric properties of perovskites: Sign change of the Seebeck coefficient and high temperature properties

The possibility to change the Seebeck coefficient sign has been evidenced in the LaCoO₃ perovskites. A small hole doping (Co³⁺/Co⁴⁺) will result in a large positive Seebeck coefficient, while a small electron doping (Co²⁺/Co³⁺) will give a large negative Seebeck coefficient at room temperature. This mechanism is shown to be efficient as well in 1D Ca₃Co₂O₆ deriving from hexagonal perovskites. By doping Ca₃Co₂O₆ with Ti⁴⁺, a mixed valency Co²⁺/Co³⁺ is introduced and the thermopower turns negative.

At high temperature, the Seebeck coefficients of LaCoO₃ and related compounds decrease to small values due to the spin state transition. The values converge towards a positive value, close to +20 μV/K at 800 K. This suggests that at high T, the Seebeck coefficients in the case of localized charges do not depend on the doping, but only on the spin and orbital degeneracies. On the other hand, in the case of metallic-like samples as electron-doped manganites, the properties can be described up to high T in terms of a single-band metal. Due to the linear variation of S as a function of T and the almost constant value of ρ, the ratio S²/ρ which is crucial for high temperature applications increases.     

Alumazene adducts with pyridines: synthesis, structure, and stability studies

Lewis acid-base adducts of the alumazene [2,6-(i-Pr)2C6H3NAlMe]3 (1) with pyridine (py) and 4-dimethylaminopyridine (dmap) were synthesized and structurally characterized: 1(py)2 (2), 1(py)3 (3), 1(dmap)2 (4), and 1(py)(dmap) (5). The bisadducts 2, 4, and 5 form the trans isomers. The trisadduct 3 exhibits an unexpected cis-cis isomer and can be prepared only in the presence of excess py. The planarity of the alumazene ring is lost upon coordination of the Lewis base molecules. A comparison of the Al-N(base) bond distances and pyramidality at Al suggests the higher basicity of dmap. NMR spectroscopy confirms stability to dissociation of the bisadducts in solution while the trisadduct 3 is labile and converts to 2. The thermodynamics of the adduct formation has been investigated experimentally and theoretically. Thermodynamic characteristics of the 1(py)n (n=2, 3) dissociation reactions in the temperature range 25-200 degrees C have been derived from the vapor pressure-temperature dependence measurements by the static tensimetric method. In all experiments, excess py was employed. Quantum chemical computations at the B3LYP/6-31G* level of theory have been performed for the 1(py)n and model complexes [HAlNH]3(py)n (n=1-3). Obtained results indicate that for the gas phase adducts upon increasing the number of py ligands the donor-acceptor Al-N(py) distance increases in accord with decreasing donor-acceptor bond dissociation energies.     

Electrocatalytic Nanostructured Ferric Tannates: Characterization and Application of a Polyphenol Nanosensor

A novel core–shell hybrid nanomaterial composed of peculiar maghemite nanoparticles (surface‐active maghemite nanoparticles (SAMNs)) as the core and tannic acid (TA) as the shell was developed by self‐assembly of ferric tannates onto the surface of SAMNs by simple incubation in water. The hybrid nanomaterial (SAMN@TA) was characterized by using UV/Vis, FTIR, and Mössbauer spectroscopies, magnetization measurements, and X‐ray powder diffraction, which provide evidence of a drastic reorganization of the iron oxide surface upon reaction with TA and the formation of an outer shell that consists of a cross‐linked network of ferric tannates. According to a Langmuir isotherm analysis, SAMN@TA offers one of most stable iron complexes of TA reported in the literature to date. Moreover, SAMN@TA was characterized by using electrical impedance spectroscopy, voltammetry, and chronoamperometry. The nanostructured ferric tannate interface showed improved conductivity and selective electrocatalytic activity toward the oxidation of polyphenols. Finally, a carbon‐paste electrode modified with SAMN@TA was used for the determination of polyphenols in blueberry extracts by square‐wave voltammetry.     

Selective measurement of heteronuclear 1H-13C dipolar couplings in motionally heterogeneous semicrystalline polymer systems

A pulse sequence for the selective recoupling of heteronuclear dipolar interactions in mobile amorphous phase of powdered semicrystalline polymers is described. 1H-13C dipolar interactions are selectively measured by PISEMA-type sequence. Selection of 13C magnetization originating from amorphous phase is achieved by a train of saturation pulses followed by a short delay and a direct excitation pulse on 13C spins. The development of undesired net 13C magnetization during the recoupling sequence is prevented by the efficient "reverse" 13C --> 1H cross-polarization. The efficacy of the 2D method to measure 1H-13C dipolar couplings selectively for mobile components is demonstrated on powdered crystalline L-alanine, semicrystalline polyethylene, and nanocomposite polyamide-6/montmorillonite.     

The applications of infrared thermography in surgical removal of retained teeth effects assessment

Journal of Thermal Analysis and Calorimetry - Coal has played a significant role in daily life. However, the highly effective combustion and reducing combustion-caused hazards of the coal still...     

Synthesis and structure of lanthanide complexes with large-bite diphosphine dioxide ligands

Three large-bite diphosphine dioxide ligands were reacted with lanthanide salts to yield either molecular or polymeric complexes. The two flexible ligands gave bischelate complexes of general formulae [Ln(dppfO₂)₂Cl_x(NO₃)_2−x][FeCl₄] and [Ln(dppdO₂)₂(NO₃)₂]NO₃, where dppfO₂ and dppdO₂ are bis(diphenylphosphoryl)ferrocene and bis(diphenylphosphoryl)diphenyl ether, respectively. Reactions of the rigid bis(diphenylphosphoryl)benzene (dppbO₂) with lanthanide salts yielded linear coordination polymers of a 1:1.5 metal-to-ligand stoichiometry. The compounds were studied by single crystal X-ray diffraction, IR spectroscopy, mass spectrometry, and TG/DSC techniques.     

DNA-directed protein immobilization on mixed self-assembled monolayers via a streptavidin bridge

The simultaneous detection of multiple analytes is an important consideration for the advancement of biosensor technology. Currently, few sensor systems possess the capability to accurately and precisely detect multiple antigens. This work presents a simple approach for the functionalization of sensor surfaces suitable for multichannel detection. This approach utilizes self-assembled monolayer (SAM) chemistry to create a nonfouling, functional sensor platform based on biotinylated single-stranded DNA immobilized via a streptavidin bridge to a mixed SAM of biotinylated alkanethiol and oligo(ethylene glycol). Nonspecific binding is minimized with the nonfouling background of the sensor surface. A usable protein chip is generated by applying protein-DNA conjugates which are directed to specific sites on the sensor chip surface by utilizing the specificity of DNA hybridization. The described platform is demonstrated in a custom-built surface plasmon resonance biosensor. The detection capabilities of a sensor using this protein array have been characterized using human chorionic gonadotropin (hCG). The platform shows a higher sensitivity in detection of hCG than that observed using biotinylated antibodies. Results also show excellent specificity in protein immobilization to the proper locations in the array. The vast number of possible DNA sequences combine with the selectivity of base-pairing makes this platform an excellent candidate for a sensor capable of multichannel protein detection.