How solvent controls electronic energy transfer and light harvesting

The way that solvent (or host medium) modifies the rate of electronic energy transfer (EET) has eluded researchers for decades. By applying quantum chemical methods that account for the way solvent (in general any host medium including liquid, solid, or protein, etc.) responds to the interaction between transition densities, we quantify the solvent screening. We find that it attains a striking exponential attenuation at separations less than about 20 A, thus interpolating between the limits of no apparent screening and a significant attenuation of the EET rate. That observation reveals a previously unidentified contribution to the distance dependence of the EET rate.     

High-dimensional variable screening and bias in subsequent inference,with an empirical comparison

We review variable selection and variable screening in high-dimensional linear models. Thereby, a major focus is an empirical comparison of various estimation methods with respect to true and false positive selection rates based on 128 different sparse scenarios from semi-real data (real data covariables but synthetic regression coefficients and noise). Furthermore, we present some theoretical bounds for the bias in subsequent least squares estimation, using the selected variables from the first stage, which have direct implications for construction of p-values for regression coefficients.     

Cellulose microfiber functionalized with N,N'-bis (2-aminoethyl)-1,2-ethanediamine as a solid sorbent for the fast preconcentration of Cd(II) in flow system analysis

The present paper describes the synthesis of a new chemically modified cellulose microfiber through oxidation with sodium periodate and functionalization with N,N′-bis (2-aminoethyl)-1,2-ethanediamine for the fast and selective preconcentration of Cd(II) ions in flow system analysis. The new sorbentsorbent was characterized by FTIR, SEM, and surface area values. The uptake behavior of Cd(II) ions onto this sorbent was evaluated from kinetic data, pseudo-first-order and pseudo-second-order models, as well as from Langmuir, Freundlich and Langmuir-Freundlich adsorption isotherms. The maximum sorption capacity of 4.59 mg g⁻¹ was estimated by the Langmuir-Freundlich model with fast kinetics for the sorption of Cd(II) described by the pseudo-second-order kinetic model. After characterization, the sorbent was packed in a mini-column, and a fast flow injection preconcentration system for Cd(II) determination by FAAS was developed. The best Cd(II) preconcentration condition, obtained by means of factorial design and response surface methodology, was achieved at pH 9.36 and a flow rate of 10 mL min⁻¹ followed by elution with 1.0 mol L⁻¹ nitric acid. By using 78 s preconcentration time, fast and highly sensitive determination of Cd(II) ions could be achieved with a limit of quantification of 0.20 μg L⁻¹, preconcentration factor of 26, consumption index of 0.5 mL, concentration efficiency of 20 min⁻¹, and sample throughput of 39 h⁻¹. The repeatability for 10 replicate determinations was found to be 7.8 and 2.5% for Cd(II) ion concentrations of 5.0 and 100.0 μg L⁻¹, respectively. The new sorbent efficiency for the interference-free preconcentration of Cd(II) ions was assessed by analysis of tap, mineral and lake waters, as well as synthetic seawater and normal saline waters. Furthermore, complex samples, such as biological samples, could be analysed by the proposed method in accordance with the accuracy attested by analysis of certified reference materials, TORT-2 (lobster hepatopancreas), and DOLT-4 (dogfish liver).     

Essential oil composition of leaves of Stachys yemenensis obtained by supercritical CO₂

This article reports the composition of the essential oil from the leaves of Stachys yemenensis. The essential oil was extracted by supercritical CO? (90 bar; 40 °C) and its chemical composition was determined by gas chromatography and gas chromatography-mass spectrometry. The major components of the sample were α-phellandrene (13.9%), β-phellandrene (11.7%), elemol (12.0%), spathulenol (6.7%), β-eudesmol (5.0%), α-eudesmol (4.75%) and squalene (4.8%). On the exhausted matrix, deprived of the volatiles, we carried out a high-pressure (250 bar) treatment for the extraction of squalene (49.7%). The antimicrobial activity of the essential oils has been assayed by using the broth dilution method on two American Type Culture Collection (ATCC) strains, Escherichia coli ATCC 35218 and Staphylococcus aureus ATCC 43300, and two clinical strains, Candida albicans and Candida glabrata.     

Mechanochemical Synthesis of Catalytic Materials

The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field due to its simplicity, scalability, and eco-friendliness. Besides, it provides materials with distinct features, such as nanocrystallinity, high defect concentration, and close interaction of the components in a system, which are, in most cases, unattainable by conventional routes. Consequently, this research field has recently become highly popular, particularly for the preparation of catalytic materials for various applications, ranging from chemical production over energy conversion catalysis to environmental protection. In this Review, recent studies on mechanochemistry for the synthesis of catalytic materials are discussed. Emphasis is placed on the straightforwardness of the mechanochemical route—in contrast to more conventional synthesis—in fabricating the materials, which otherwise often require harsh conditions. Distinct material properties achieved by mechanochemistry are related to their improved catalytic performance.     

Sulfur K-edge X-ray absorption spectroscopy of 2Fe-2S ferredoxin: covalency of the oxidized and reduced 2Fe forms and comparison to model complexes

Ligand K-edge X-ray absorption spectroscopy (XAS) provides a direct experimental probe of ligand-metal bonding. In previous studies, this method has been applied to mononuclear Fe-S and binuclear 2Fe-2S model compounds as well as to rubredoxins and the Rieske protein. These studies are now extended to the oxidized and reduced forms of ferredoxin I from spinach. Because of its high instability, the mixed-valence state was generated electrochemically in the protein matrix, and ligand K-edge absorption spectra were recorded using an XAS spectroelectrochemical cell. The experimental setup is described. The XAS edge data are analyzed to independently determine the covalencies of the iron-sulfide and -thiolate bonds. The results are compared with those obtained previously for the Rieske protein and for 2Fe-2S model compounds. It is found that the sulfide covalency is significantly lower in oxidized FdI compared to that of the oxidized model complex. This decrease is interpreted in terms of H bonding present in the protein, and its contribution to the reduction potential E degrees is estimated. Further, a significant increase in covalency for the Fe(III)-sulfide bond and a decrease of the Fe(II)-sulfide bond are observed in the reduced Fe(III)Fe(II) mixed-valence species compared to those of the Fe(III)Fe(III) homovalent site. This demonstrates that, upon reduction, the sulfide interactions with the ferrous site decrease, allowing greater charge donation to the remaining ferric center. That is the dominant change in electronic structure of the Fe(2)S(2)RS(4) center upon reduction and can contribute to the redox properties of this active site.     

Formation and relaxation of excited states in solution: a new time dependent polarizable continuum model based on time dependent density functional theory

In this paper a novel approach to study the formation and relaxation of excited states in solution is presented within the integral equation formalism version of the polarizable continuum model. Such an approach uses the excited state relaxed density matrix to correct the time dependent density functional theory excitation energies and it introduces a state-specific solvent response, which can be further generalized within a time dependent formalism. This generalization is based on the use of a complex dielectric permittivity as a function of the frequency, epsilonomega. The approach is here presented in its theoretical formulation and applied to the various steps involved in the formation and relaxation of electronic excited states in solvated molecules. In particular, vertical excitations (and emissions), as well as time dependent Stokes shift and complete relaxation from vertical excited states back to ground state, can be obtained as different applications of the same theory. Numerical results on two molecular systems are reported to better illustrate the features of the model.     

Adhesion of human osteoblasts to titanium: A morpho-functional analysis with confocal microscopy

Properties of surface affect the interactions between the implant and osteoblasts and direct the clinical osteointegrative outcome. The aim of this in vitro study was to describe the adhesion of living human osteoblasts to titanium disks with differently prepared surfaces: sand blasted with ZrO₂ particles and acid-etched (Soft-SLA, S-SLA) or with Al₂O₃ particles and acid-etched (Hard-SLA, H-SLA), smooth surface (SS).Confocal microscopy was exploited to follow cell morpho-functional features either on living cells (cell shape with calcein-acethoxymethylester and mitochondria with tetramethylrhodamine methyl ester) or on fixed cells (immunocytochemistry of β1-integrin and of actin) 6 h or 24 h after seeding. The underlying surface was visualized simultaneously on the same field.No cytotoxic effect was detected at any time and on any surface.At 6 h after seeding, osteoblasts showed either a rounded or polygonal shape on both rough surfaces. Several features suggested that adhesion was faster with a higher level of organization on S-SLA than on H-SLA. Indeed osteoblasts grown on S-SLA were wider and with more extended protrusions than those on H-SLA. Active mitochondria on S-SLA occupied perinuclear areas and cellular prolongations, whereas on H-SLA they were mainly focused around nucleus. Organization of integrin β1-subunit and actin, confirmed different kinetics of cell adhesion. At 6 h integrin β1-subunit was distributed along the periphery on the cell-biomaterial focal complexes in cells grown on S-SLA, whereas it was unevenly dispersed in membrane of cells cultured on H-SLA. Stress actin fibers were well defined in cells cultured on S-SLA, whereas they were scarcely evident on H-SLA. Osteoblasts seeded on smooth surface for 6 h had morpho-functional features typical of adhesion, with some elements characterized by an elongated shape with an evident main longitudinal axis. At 24 h osteoblasts were spread-out onto all surfaces. Nonethless, different morphologies were shown in response to the different surfaces tested: polygonal cells prevailed on SLA surfaces, whereas almost all the cells on SS were long with two principal prolongations.At 24 h number of cells adhered to the three kind of surfaces was similar, but during the following three days, cells seeded on S-SLA and on SS proliferated to a greater extent than those cultured on H-SLA.Analysis of morpho-functional parameters performed in living cells, and in particular the study of mitochondria organization, proved to be a valuable tool to follow cell-biomaterial adhesion. A higher level of spreading occurring in osteoblasts grown on S-SLA and SS at early times accounted for a faster subsequent cell proliferation. Nonethless, these comparable activities were exerted by cells showing polygonal or elongated shapes when grown respectively on S-SLA or on SS. The former is typical of osteogenic cells, whereas the latter resumes a fibroblast-like morphology, that would result in an ineffective in vivo osteointegrative process.