Density functional theory study of triphenyl phosphite: molecular flexibility and weak intermolecular hydrogen bonding

The high conformational flexibility of triphenyl phosphite (TPP) is investigated by density functional theory (DFT) calculations. First, through a scan of the molecular potential energy surface, we bring to light a new stable conformation of an isolated molecule, not yet encountered in the crystal states of TPP. Different relevant conformations of the TPP monomer in the gas state are further presented and discussed in terms of molecular structure, relative energy, and dipole moments. Second, we considered dimer and trimer of TPP starting from their structural topology within the hexagonal crystal, which is characterized by the existence of molecular rods. It is shown that weak C-H...O intermolecular hydrogen bonds in TPP cannot definitely be excluded, and finally this point is discussed in the scope of the glacial state problem.     

Combined theoretical and experimental analysis of the bonding in the heterobimetallic cubane-type Mo(3)NiS(4) and Mo(3)CuS(4) core clusters

X-ray structural data for the cubane-type clusters [Mo3CuS4(dmpe)3Cl4](+) and Mo3NiS4(dmpe)3Cl4 (dmpe = 1,2-bis(dimethylphosphino)ethane) with 16 metal electrons have been compared with optimized structural parameters calculated using "ab initio" methodologies. Compound Mo3NiS4(dmpe)3Cl4 crystallizes in the cubic noncentrosymmetric space group P213 with a Mo-Ni distance of 2.647 Angstrom, that is 0.2 Angstrom shorter than the Mo-Cu bond length in the isoelectronic copper cluster. The best agreement between theory and experiments has been obtained using the B3P86 method. In order to validate the B3P86 results, accurate infrared and Raman spectra have been acquired and the vibrational modes associated to the cubane-type Mo3M'S4 (M' = Cu or Ni) unit have been assigned theoretically. The electronic changes taking place when incorporating the M' into the Mo3S4 unit have been analyzed from a theoretical and experimental perspective. The bond dissociation energies between M'-Cl and Mo3S4 fragments show that formation of [Mo3CuS4(dmpe)3Cl4](+) is 135 kcal/mol energetically less favorable than the Ni incorporation. The more robust nature of the Mo3NiS4 fragment has been confirmed by mass spectrometry. The X-ray photoelectron spectroscopy (XPS) spectra of the trimetallic and tetrametallic complexes have been measured and the obtained binding energies compared with the computed electronic populations based on topological approaches of the electron localization function (ELF). The energies and shapes of the Cu 2p and Ni 2p lines indicate formal oxidation states of Cu(I) and Ni(II). However, the reductive addition of nickel into [Mo3S4(dmpe)3Cl3](+) causes a small decrease in the Mo 3d binding energies. This fact prevents an unambiguous assignment of an oxidation state in a conventional way, a circumstance that has been analyzed through the covariance of the electronic populations associated to the C(M') core and V(Mo3Ni) and V(S(2)') valence basins where Mo3NiS4 is a particularly electronically delocalized chemical entity.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.     

Use of a partial-filling technique in affinity capillary electrophoresis for determining binding constants of ligands to receptors

This work evaluates the concept of a partial-filling technique in affinity capillary electrophoresis (ACE) using two model systems: vancomycin from Streptomyces orientalis and carbonic anhydrase B (CAB, EC 4.2.1.1). In this technique the capillary is first partially-filled with ligand followed by a sample of receptor and non-interacting standard and electrophoresed. Analysis of the change in the mobility ratio, M, of the receptor, relative to the non-interacting standard, as a function of the concentration of the ligand, yields a value for the binding constant. These values agree well with those estimated using other binding and ACE techniques. Data demonstrating the quantitative potential of this method is presented.     

Biocompatibility Study of Electrospun Nanocomposite Membranes Based on Chitosan/Polyvinyl Alcohol/Oxidized Carbon Nano-Onions

In recent decades, the number of patients requiring biocompatible and resistant implants that differ from conventional alternatives dramatically increased. Among the most promising are the nanocomposites of biopolymers and nanomaterials, which pretend to combine the biocompatibility of biopolymers with the resistance of nanomaterials. However, few studies have focused on the in vivo study of the biocompatibility of these materials. The electrospinning process is a technique that produces continuous fibers through the action of an electric field imposed on a polymer solution. However, to date, there are no reports of chitosan (CS) and polyvinyl alcohol (PVA) electrospinning with carbon nano-onions (CNO) for in vivo implantations, which could generate a resistant and biocompatible material. In this work, we describe the synthesis by the electrospinning method of four different nanofibrous membranes of chitosan (CS)/(PVA)/oxidized carbon nano-onions (ox-CNO) and the subdermal implantations after 90 days in Wistar rats. The results of the morphology studies demonstrated that the electrospun nanofibers were continuous with narrow diameters (between 102.1 nm ± 12.9 nm and 147.8 nm ± 29.4 nm). The CS amount added was critical for the diameters used and the successful electrospinning procedure, while the ox-CNO amount did not affect the process. The crystallinity index was increased with the ox-CNO introduction (from 0.85% to 12.5%), demonstrating the reinforcing effect of the nanomaterial. Thermal degradation analysis also exhibited reinforcement effects according to the DSC and TGA analysis, with the higher ox-CNO content. The biocompatibility of the nanofibers was comparable with the porcine collagen, as evidenced by the subdermal implantations in biological models. In summary, all the nanofibers were reabsorbed without a severe immune response, indicating the usefulness of the electrospun nanocomposites in biomedical applications.     

Superelectrophilic Activation of N‐Substituted Isatins: Implications for Polymer Synthesis,a Theoretical Study

The stability and reactivity of mono‐ and multi‐protonatred N‐substituted isatin derivatives were studied at PBE0/aug‐cc‐pvtz//PBE0/6‐31+G** level of theory in triflic acid (TFSA) solution. Calculations showed that the monocationic intermediates are the principal reactive species in the reaction of hydroxyalkylation of isatin derivatives in TFSA media. Electron‐withdrawing substituents on the nitrogen atom increase the reactivity of isatin‐containing electrophiles towards aromatic hydrocarbons, in accordance with their expected electronic influence. Steric factors also play an important role in the reactivity of isatin‐containing electrophiles, especially in the second reaction step, due to their more sterically hindered reactive center.

     

The seesaw path to leptonic CP violation

Future experiments such as SHiP and high-intensity \(e^+ e^-\) colliders will have a superb sensitivity to heavy Majorana neutrinos with masses below \(M_Z\). We show that the measurement of the mixing to electrons and muons of one such state could establish the existence of CP violating phases in the neutrino mixing matrix, in the context of low-scale seesaw models. We quantify in the minimal model the CP reach of these future experiments, and demonstrate that CP violating phases in the mixing matrix could be established at 5\(\sigma \) CL in a very significant fraction of parameter space.     

Solvent‐Free Fabrication of polyHIPE Microspheres for Controlled Release of Growth Factors

The growth factor bone morphogenetic protein 2 (BMP‐2) is utilized in surgical procedures to improve bone regeneration; however, current treatments deliver BMP‐2 at amounts greater than 100 000 fold of physiological levels, which increases treatment costs and risk of side effects. Drug‐eluting microcarriers developed to improve these therapies have faced significant commercialization challenges including particle size distributions, solvent removal, low encapsulation efficiency, and bioactivity loss. In this study, a solvent‐free method is presented for fabrication of uniform polyHIPE microspheres for controlled growth factor release. Emulsion templating principles and fluid dynamics were used to fabricate uniform particles with tunable particle size (200–800 μm) and pore size (10–30 μm). The ability to independently tune particle and pore size is expected to provide excellent control of release kinetics. Overall, this solvent‐free method for making porous microspheres displays strong promise for the controlled release of BMP‐2 and other growth factors.

     

Structural, calorimetric and magnetic properties study of the Cu0,91Fe0,09O system

In this work the Cu_0.91Fe_0.09O nanocrystalline system was prepared via the co-precipitation method. Using Mössbauer Spectrometry, X-Ray Diffraction, Vibrating Sample Magnetometry, Thermogravimetry and Differential Scanning Calorimetry, we study the magnetic behavior, and the structural and calorimetric properties of this system. X-ray diffraction shows only the presence of the CuO structural monoclinic phase, suggesting that Cu atoms are substituted by Fe ones. This hypothesis was confirmed by Mössbauer spectrometry at room temperature, because it shows that the spectrum is formed by two doublets, which correspond to Fe^?+?2 and Fe^?+?3 sites. Hysteresis cycles obtained by vibrating sample magnetometry detect a soft ferromagnetic behavior at room temperature with coercive fields between 8 and 20 Oe. At T = 20 K the sample shows a hard-magnetic behavior. The thermogravimetry results show a Néel temperature (T _N > 440 °C). The differential scanning calorimetry curve show two endothermic peaks in the 90–120 °C range.     

Syntheses, structural and spectroscopic characterization of novel zinc(II)-bis(trithiocarbimato) complexes and bis(N-methylsulfonyldithiocarbimate)-sulfide

Four zinc(II)-bis(trithiocarbimato) complexes with the general formula A₂[Zn(RSO₂NCS₃)₂] [A = Ph₄P⁺: R = CH₃ (1), 4-CH₃C₆H₄ (2); A = Bu₄N⁺: R = CH₃ (3), 4-CH₃C₆H₄ (4)] were obtained by the reaction of sulfur with the correspondent zinc(II)-bis(dithiocarbimato) complexes. Additionally, the compound (Ph₄P)₂[(CH₃SO₂NCS₂)₂S)] (5) was prepared from the potassium methylsulfonildithiocarbimate by oxidation with iodine. The compounds were characterized by elemental analyses and IR, ¹H NMR and ¹³C NMR spectroscopies. The compounds 4 and 5 were also characterized by X-ray diffraction techniques. The compound 4 crystallizes in the centrosymmetric space group C2/c of the monoclinic system. The Zn(II) is in a distorted tetrahedral environment (ZnS₄) in compound 4, and differ from the coordination mode observed in compound 1, which involves one sulfur and one nitrogen atom of each trithiocarbimate ligand. Compound 5 is the first example of a compound containing a bis(N-alkylsulfonyldithiocarbimate)-sulfide dianion and crystallises in the non-centrosymmetric space group P4₁2₁2 of the tetragonal system.