Second sphere coordination behavior of aquo and amine ligands bound to a η-benzeneruthenium(II) cation

The bis(oxazoline) ligand, 2,2-bis[4(R)-phenyl-1,3-oxazolon-2-yl]propane (bpop), was introduced to the η⁶-benzenemthenium(II) moiety on treatment with [Ru(η⁶-C₆H₆)Cl₂]₂ to give [Ru(η⁶-C₆H₆)(bpop)Cl]⁺. Aquo and amine complexes [Ru(η⁶-C₆H₆)(bpop)(L)]²⁺ (L = H₂O (1), NH₂R; R = H (2) , Me (3) , and n-Bu (4) ) were prepared by treating the chloride complex with AgBF₄ in the presence of L. X-ray structure determinations of 1 and 3 were carried out. Both complexes possessed a three-leg piano stool structure with the N or O donors located at the three comers of a pseudo octahedron. The aquo complex 1 exhibited a dynamic NMR feature in which two magnetically nonequivalent oxazoline parts observed at lower temperatures were interchanged with each other at higher temperatures. This observation was ascribed to the formation of a C₂-symmetric 16-electron intermediate via Ru-OH₂ cleavage, which is slower in acetone than in dichloromethane owing to more effective solvation by acetone around hydrogens of the coordinated water molecule. The two diastereotopic N-hydrogens of 4 underwent deuterium exchange with CD₃OD with greatly different rates from each other owing to different energy of NHO (D) (CD₃) interaction. Carboxylate and sulfonate ions (A⁻) formed second sphere complexes with 4 by means of NHA⁻ hydrogen bonding, as evidenced by continuous shift of NH₂ resonances with increasing amounts of the anions added.     

Analysis of zinc binding sites in protein crystal structures

The geometrical properties of zinc binding sites in a dataset of high quality protein crystal structures deposited in the Protein Data Bank have been examined to identify important differences between zinc sites that are directly involved in catalysis and those that play a structural role. Coordination angles in the zinc primary coordination sphere are compared with ideal values for each coordination geometry, and zinc coordination distances are compared with those in small zinc complexes from the Cambridge Structural Database as a guide of expected trends. We find that distances and angles in the primary coordination sphere are in general close to the expected (or ideal) values. Deviations occur primarily for oxygen coordinating atoms and are found to be mainly due to H-bonding of the oxygen coordinating ligand to protein residues, bidentate binding arrangements, and multi-zinc sites. We find that H-bonding of oxygen containing residues (or water) to zinc bound histidines is almost universal in our dataset and defines the elec-His-Zn motif. Analysis of the stereochemistry shows that carboxyl elec-His-Zn motifs are geometrically rigid, while water elec-His-Zn motifs show the most geometrical variation. As catalytic motifs have a higher proportion of carboxyl elec atoms than structural motifs, they provide a more rigid framework for zinc binding. This is understood biologically, as a small distortion in the zinc position in an enzyme can have serious consequences on the enzymatic reaction. We also analyze the sequence pattern of the zinc ligands and residues that provide elecs, and identify conserved hydrophobic residues in the endopeptidases that also appear to contribute to stabilizing the catalytic zinc site. A zinc binding template in protein crystal structures is derived from these observations.     

Targeting Brucella melitensis with polymeric nanoparticles containing streptomycin and doxycycline

Treatment and eradication of intracellular pathogens such as Brucella is difficult because infections are localized within phagocytic cells and most antibiotics, although highly active in vitro , do not actively pass through cellular membranes. Thus, an optimum strategy to treat these infections should address targeting of active drugs to the intracellular compartment where the bacteria replicate, and should prolong the release of the antibiotics so that the number of doses and associated toxicity can be reduced. We incorporated streptomycin and doxycycline into macromolecular nanoplexes with anionic homo- and block copolymers via cooperative electrostatic interactions among the cationic drugs and anionic polymers. The approach enabled simultaneous binding of both antibiotics into the nanoplexes, and their use resulted in an improvement in performance as compared with the free drugs. Administration of two doses of the nanoplexes significantly reduced the Brucella melitensis load in the spleens and livers of infected BALB/c mice. The nanoplexes were more effective than free drugs in the spleens (0.72-log and 0.51-log reductions, respectively) and in the livers (0.79-log and 0.42-log reductions, respectively) of the infected mice. Further research regarding the design of optimum nanoplex structures will be directed towards alterations in both the core and the shell properties to investigate the effects of the rates and pathways of entry into immune cells where the brucellae replicate.     

Mechanically Recoverable and Highly Efficient Perovskite Solar Cells: Investigation of Intrinsic Flexibility of Organic–Inorganic Perovskite

Highly efficient solar cells with sustainable performance under severe mechanical deformations are in great demand for future wearable power supply devices. In this regard, numerous studies have progressed to implement flexible architecture to high‐performance devices such as perovskite solar cells. However, the absence of suitable flexible and stretchable materials has been a great obstacle in the replacement of largely utilized transparent conducting oxides that are limited in flexibility. Here, a shape recoverable polymer, Noland Optical Adhesive 63, is utilized as a substrate of perovskite solar cell to enable complete shape recovery of the device upon sub‐millimeter bending radii. The employment of stretchable electrodes prevents mechanical damage of the perovskite layer. Before and after bending at a radius of 1 mm, power conversion efficiency (PCE) is measured to be 10.75% and 10.4%, respectively. Additionally, the shape recoverable device demonstrates a PCE of 6.07% after crumpling. The mechanical properties of all the layers are characterized by nanoindentation. Finite element analysis reveals that the outstanding flexibility of the perovskite layer enables small plastic strain distribution on the deformed device. These results clearly demonstrated that this device has great potential to be utilized in stretchable power supply applications.     

A growth‐rate composition formula for the growth of E. coli on co‐utilized carbon substrates

When bacteria are cultured in medium with multiple carbon substrates, they frequently consume these substrates simultaneously. Building on recent advances in the understanding of metabolic coordination exhibited by Escherichia coli cells through cAMP‐Crp signaling, we show that this signaling system responds to the total carbon‐uptake flux when substrates are co‐utilized and derive a mathematical formula that accurately predicts the resulting growth rate, based only on the growth rates on individual substrates.     

Reduction potential variations in azurin through secondary coordination sphere phenylalanine incorporations

Recent evidence has shown that the properties of metal binding sites can be tuned by more than the ligands in the primary coordination sphere. We investigated the incorporation of four phenylalanine residues into the secondary coordination sphere of the small soluble blue copper protein azurin. The locations for placement of these residues in azurin were based on the structure of the highly hydrophobic blue copper protein rusticyanin, which is known to have a significantly higher reduction potential than azurin. Using site-directed mutagenesis, these residues in close proximity to the copper binding site were mutated to large hydrophobic phenylalanine residues individually and in combination. We also added the Met121Leu mutation on top of the Phe mutations to construct a total of 13 variants. We found little change in the UV-visible absorption and EPR data for these proteins, however modest increases in reduction potential were observed with increases by as much as 30 mV per Phe residue. Furthermore, we observed the increases in potential to be additive.     

Effects of physical connection and genetic identity of neighbouring ramets on root-placement patterns in two clonal species

Root-placement patterns were examined in the clonal species Glechoma hederacea and Fragaria vesca when grown with different types of neighbours. Three different patterns were predicted as consequences of different types of interactions between roots: the avoidance pattern if root growth decreases in the presence of neighbouring roots; the intrusive pattern if root growth increases towards neighbouring roots; and the unresponsive pattern if root growth is unaffected by neighbouring roots. Experiments were conducted in which physical connection between ramets, and the genetic identity of neighbouring ramets, were manipulated. The patterns of distribution of entire root systems and elongation rates of individual roots were measured. Root systems and individual roots of G. hederacea avoided contact with roots of neighbouring ramets, irrespective of connection to the neighbour and its genetic or specific identity. In contrast, F. vesca roots grew equally towards and away from intraspecific ramet neighbours and their elongation was stimulated by contact with roots of G. hederacea ramets. These results demonstrate that root-placement patterns of plants grown with different types of neighbours vary between species, and suggest that factors additional to resource depletion could be involved in their development.     

Giant extracellular Glossoscolex paulistus Hemoglobin (HbGp) upon interaction with cethyltrimethylammonium chloride (CTAC) and sodium dodecyl sulphate (SDS) surfactants: Dissociation of oligomeric structure and autoxidation

The effects of two ionic surfactants on the oligomeric structure of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) in the oxy - form have been studied through the use of several spectroscopic techniques such as electronic optical absorption, fluorescence emission, light scattering, and circular dichroism. The use of anionic sodium dodecyl sulphate (SDS) and cationic cethyltrimethyl ammonium chloride (CTAC) has allowed to differentiate the effects of opposite headgroup charges on the oligomeric structure dissociation and hemoglobin autoxidation. At pH 7.0, both surfactants induce the protein dissociation and a significant oxidation. Spectral changes occur at very low CTAC concentrations suggesting a significant electrostatic contribution to the protein–surfactant interaction. At low protein concentration, 0.08 mg/ml, some light scattering within a narrow CTAC concentration range occurs due to protein–surfactant precipitation. Light scattering experiments showed the dissociation of the oligomeric structure by SDS and CTAC, and the effect of precipitation induced by CTAC. At higher protein concentrations, 3.0 mg/ml, a precipitation was observed due to the intense charge neutralization upon formation of ion pair in the protein–surfactant precipitate. The spectral changes are spread over a much wider SDS concentration range, implying a smaller electrostatic contribution to the protein–surfactant interactions. The observed effects are consistent with the acid isoelectric point (pI) of this class of hemoglobins, which favors the intense interaction of HbGp with the cationic surfactant due to the existence of excess acid anionic residues at the protein surface. Protein secondary structure changes are significant for CTAC at low concentrations while they occur at significantly higher concentrations for SDS. In summary, the cationic surfactant seems to interact more strongly with the protein producing more dramatic spectral changes as compared to the anionic one. This is opposite as observed for several other hemoproteins. The surfactants at low concentrations produce the oligomeric dissociation, which facilitates the iron oxidation, an important factor modulating further oligomeric protein dissociation.