How to use the vibrational data for a better understanding of bonding structure and reactivity of organometallic complexes

The infrared frequency and intensity values of the main vibrational modes of selected examples of hydrocarbon ligands bonded to metals are reported. Despite the approximations on the vibrational analysis, the data offer fundamental information on structure, bonding, and reactivity of the metal-ligand unit, successfully comparable with those obtained by other sources (structural analysis, nmr spectroscopy, MO calculation). A future extension of this topic to the study of the adsorbate surface interaction is proposed, in light of the well-known cluster-surface analogy.     

Synthesis of amino derivatives of 5-aralkylidene-3-pyrrolin-2-ones

Preparation of some derivatives of 5-aralkylidene-3-pyrrolin-2-ones is reported. Compounds with an amino group on the phenyl ring at the 3-position of the pyrrolinone ring showed suitable properties as potential UV-A filters. Some of the compounds were quaternarized to enhance their solubility in aqueous solvents.     

Different binding thermodynamics of Ni2+, Cu2+, and Zn2+ to bacitracin A1 determined by capillary electrophoresis

Thermodynamics of the binding of Ni(2+), Cu(2+) and Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis measuring the peptide effective mobility at different pH in the presence of increasing concentration of the three ligands. The affinity follows the order Ni(2+) > Cu(2+) > Zn(2+), with association constant values of (2.3 +/- 0.1)x10(4), (4.9 +/- 0.2)x10(3), and (1.5 +/- 0.1)x10(3) M(-1), respectively. The only model able to rationalize mobility data implies that metal ion binds to the P(0) peptide form. Moreover, mobility values indicated a change of bacitracin A(1) acidic properties on Ni(2+) and Cu(2+) binding, with a shift of the pK(a) of N-terminal Ile-1 from 7.6 to about 5 and of the pK(a) of the delta-amino group of D-Orn-7 from 9.7 to about 7. Even though on Zn(2+) binding a shift of the N-terminal Ile-1 pK(a) was observed, restrictions in the pH range suitable for investigation, due to precipitation phenomena, did not allow establish if the shift of D-Orn-7 lateral chain pK(a) also occurred. Nonetheless, if present, the shift should be limited to the 7.8-9.7 range. Mobility data indicated that the Stokes radius of the complexes is ca. 3 A lower than that of the free peptide. The present results indicate that metal-ion binding to bacitracin A(1) is more complex than previously assumed.     

A multi-objective integrated facility location-hardening model: Analyzing the pre- and post-disruption tradeoff

Two methods of reducing the risk of disruptions to distribution systems are (1) strategically locating facilities to mitigate against disruptions and (2) hardening facilities. These two activities have been treated separately in most of the academic literature. This article integrates facility location and facility hardening decisions by studying the minimax facility location and hardening problem (MFLHP), which seeks to minimize the maximum distance from a demand point to its closest located facility after facility disruptions. The formulation assumes that the decision maker is risk averse and thus interested in mitigating against the facility disruption scenario with the largest consequence, an objective that is appropriate for modeling facility interdiction. By taking advantage of the MFLHP’s structure, a natural three-stage formulation is reformulated as a single-stage mixed-integer program (MIP). Rather than solving the MIP directly, the MFLHP can be decomposed into sub-problems and solved using a binary search algorithm. This binary search algorithm is the basis for a multi-objective algorithm, which computes the Pareto-efficient set for the pre- and post-disruption maximum distance. The multi-objective algorithm is illustrated in a numerical example, and experimental results are presented that analyze the tradeoff between objectives.     

The vibrational spectra of the cyanide ligand revisited: terminal cyanides

A comparison is made between the vibrational characteristics of the carbonyl and cyanide ligands. There are significant differences; the latter has a smaller dipole moment and a larger quadrupole moment associated with the bond stretch. This quadrupole moment may be linked to the observation that the totally symmetric nu(CN) mode does not lie at the highest frequency for some cyanide complexes. There are problems with the pi-bonding model commonly used to interpret the nu(CN) data. For instance, for the first transition row hexacyanoanions, the spectra are almost independent of t2g occupancy but are very sensitive to the formal charge. It is suggested that the observed nu(CN) frequency shifts on complex formation are in large measure determined by the effective charge on the cation to which the cyanide group is attached, and a new model, the Internal Vibrational Stark Effect, is suggested to account for this. The model is supported by DFT calculations. Raman spectra of some cubic cyano species are reported, along with polarization and intensity data.     

Radical polymeric photoinitiators bearing side‐chain camphorquinone moieties linked to the main chain through a flexible spacer

New polymeric photoinitiators bearing the side‐chain camphorquinone moiety spaced from the backbone by a long and flexible connection have been prepared and tested in the photocuring of acrylic monomers upon irradation with visible light in the presence of tertiary amine coinitiator. The results indicate that the photoinitiating activity of the polymeric initiators may be comparable to the related combination of low molecular weight derivatives when the camphorquinone component has a polymeric structure, and depends on the chemical structure of both the components of the initiator/coinitiator pair. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5879–5888, 2005     

Predicting the Performance of Granulation Binders Through Micro‐Mechanistic Observations

The selection of an appropriate polymeric binder to be used to agglomerate drug with excipients is a critical issue for the development of high shear wet granulation processes for pharmaceutical tablet systems. The aim of the study reported here is to determine the potential for successful granulation through measurement of the interactions of two polymer binder solutions, hydroxypropyl methylcellulose (HPMC) and polyvinyl‐pyrrolidone (PVP), with individual paracetamol drug crystals. A novel micro‐force balance (MFB) has been used to measure different parameters of the crystal‐to‐binder interaction, including the forces exerted by axially strained liquid bridges formed between either two paracetamol crystals or between a reservoir of binder solution and a single paracetamol crystal, the paracetamol‐to‐binder wettability, the post rupture volume distribution and the residue deposited on each crystal. Video images of the separation sequences were obtained simultaneously for analysis of bridge geometry, contact angles, volume distribution and binder residues. It was found that the formation of liquid bridges and their ability to bond particles together depends on the amount of binder left on a crystal after contacting a reservoir of binder (for example, large binder drop). Crystals in contact with HPMC were able to retain more liquid from a binder reservoir than those contacted with PVP solutions. This behaviour is seen to be more important to the final granule strength than the liquid binding force holding particles together in the wet agglomerate.     

Pulse behaviour of a compact RF discharged CO2 slab laser

We present the measurements made on a medium power, 35 cm long, radio-frequency discharge CO₂ slab laser operated in a pulsed regime obtained by switching the RF discharge. In this way, pulses with peak power up to 480 W at pulse repetition frequencies in the range 1 to 10 kHz have been obtained. Pulse energy and average extracted power have been experimentally characterized with respect to the pulse repetition frequency and to the pulse duration, and the pulse shape and characteristic times have been measured. We also investigated the propagation properties of the beam emerging from our laser.     

EXAFS-XANES evidence of in situ cesium reduction in Cs-Ru/C catalysts for ammonia synthesis

We present here a X-ray absorption spectroscopy (XAS) investigation on the local chemical order and electronic structure of Cs and Ba, promoters of the Ru/C catalysts for ammonia synthesis that attracted interest because of highly increased productivity. The role of the promoters is still largely unclear, although indirect evidence for Cs partial reduction has been obtained by this and other groups. Our XAS analysis with in situ H(2) reduction directly supports the partial Cs reduction in the promoted Ru/C catalysts, depending on the presence of Ru and on the graphitization degree of the support. Higher coordination of Ba was observed with respect to Cs in the reduced samples, without evidence of heavy atoms (Ru, Cs, and Ba) in the surroundings. Because of the strong electropositive nature of Cs, direct experimental evidence of its partial reduction is of outstanding significance also for other applications.     

Aerodynamic assessment of a rotary entry vehicle for Mars landing: an experimental analysis

Meccanica - A theoretical and experimental study has been undertaken, under ESA contract, by a team including GMV, the University of Bologna and EADS-Astrium, to assess the feasibility of an entry...