On Weyl's identity

Summary The Weyl Identity (as orignally stated by H. Weyl and used by A. Winter) is not totally correct. Presented here is the correct version of the Identity, a concise proof of it and some applications. Entrata in Redazione il 28 febbraio 1970.     

The syntheses and electrochemical studies of a ferrocene substituted diiminopyridine ligand and its p, s, se, and te complexes

A new reversible, redox active diiminopyridine ligand (1Fc) containing pendant ferrocene functionalities was isolated and fully characterized. The reaction of 1Fc with chalcogen pseudohalides of sulfur, selenium, and tellurium yielded the respective N,N',N″-chelated chalcogen dications. Phosphorus chemistry proceeded in a related manner but, in this case, by the direct addition of 1Fc with PI(3) to yield the N,N',N″-chelated P(I) cation. These species represent the first synthesized main group complexes involving a redox active diiminopyridine ligand containing pendant ferrocenes. Electrochemical studies of the free ligand shows a reversible two-electron process. The chelated phosphorus cation, however, displayed three events, the first being a quasi-reversible two-electron process, involving the oxidation at the P(I) center, resulting in a P(III) cation. The subsequent reversible one- and two-electron processes arise from the ligand framework and pendant ferrocenes, respectively.     

Spectrophotometric determination of molybdenum and tungsten in niobium with dithiol

A new procedure for the determination of molybdenum and tungsten in niobium has been developed. The method involves the formation of the intensely colored complex of molybdenum with toluene-3,4-dithiol in an aqueous medium and its extraction into carbon tetrachloride followed by the reduction of tungsten and the formation and extraction of its complex. The recommended reagent is stable for at least 90 days. Both the molybdenum and the tungsten dithiol complexes are formed quantitatively within 5 min. Interlaboratory evaluation of the method reveals within-laboratory and between-laboratory relative standard deviations of about 1.5% and 2.9% respectively.     

Managed bioremediation of soil contaminated with crude oil soil chemistry and microbial ecology three years later

Analysis of samples taken from three experimental soil lysimeters demonstrated marked long-term effects of managed bioremediation on soil chemistry and on bacterial and fungal communities 3 yr after the application of crude oil or crude oil and fertilizer. The lysimeters were originally used to evaluate the short-term effectiveness of managed (application of fertilizer and water, one lysimeter) vs unmanaged bioremediation (one lysimeter) of Michigan Silurian crude oil compared to one uncontaminated control lysimeter. Three years following the original experiment, five 2-ft-long soil cores were extracted from each lysimeter, each divided into three sections, and the like sections mixed together to form composited soil samples. All subsequent chemical and microbiological analyses were performed on these nine composited samples. Substantial variation was found among the lysimeters for certain soil chemical characteristics (% moisture, pH, total Kjeldahl nitrogen [TKN], ammonia nitrogen [NH₄-N], phosphate phosphorous [PO₄-P], and sulfate [SO₄ ⁻²]). The managed lysimeter had 10% the level of total petroleum hydrocarbons (TPH-IR) found in the unmanaged lysimeter. Assessment of the microbial community was performed for heterotropic bacteria, fungi, and aromatic hydrocarbon-degrading bacteria (toluene, naphthalene, and phenanthrene) by dilution onto solid media. There was little difference in the number of heterotrophic bacteria, in contrast to counts of fungi, which were markedly higher in the contaminated lysimeters. Hydrocarbon-degrading bacteria were elevated in both oil-contaminated lysimeters. In terms of particular hydrocarbons as substrates, phenanthrene degraders were greater in number than naphthalene degraders, which outnumbered toluene degraders. Levels of sulfate-reducing bacteria seem to have been stimulated by hydrocarbon degradation.     

Simple perturbation and perturbation-variation treatments of the 1sσg and 2pσu states of H

First-order wave functions and binding energies of the 1sσ_g and 2pσ_u states of H are calculated by simple methods for internuclear separations between 0.2 and 10_a0. An exact perturbation treatment of the lsσ_g state with a zeroth-order function of the form N exp (-sRλ/2) exp (sR μ2) yields only fair results. An alternative method starts with zeroth-order functions of the form N exp (-sRλ/2)[exp (-sRμ/2) ± exp (sRμ/2)] for the 1 and 2 states, respectively. An approximate first-order trial function is set up and the energies are determined variationally. For both states the results are comparable to those obtained by exact perturbation treatments of the same order.     

Further development of reduced graphs for identifying bioactive compounds

Reduced graphs provide summary representations of chemical structures. Here, a variety of different types of reduced graphs are compared in similarity searches. The reduced graphs are found to give comparable performance to Daylight fingerprints in terms of the number of active compounds retrieved. However, no one type of reduced graph is found to be consistently superior across a variety of different data sets. Consequently, a representative set of reduced graphs was chosen and used together with Daylight fingerprints in data fusion experiments. The results show improved performance in 10 out of 11 data sets compared to using Daylight fingerprints alone. Finally, the potential of using reduced graphs to build SAR models is demonstrated using recursive partitioning. An SAR model consistent with a published model is found following just two splits in the decision tree.     

Sequence and structural duality: designing peptides to adopt two stable conformations

To improve our understanding of conformational transitions in proteins, we are attempting the de novo design of peptides that switch structural state. Here, we describe coiled-coil peptides with sequence and structural duality; that is, features compatible with two different coiled-coil motifs superimposed within the same sequence. Specifically, we promoted a parallel leucine-zipper dimer under reducing conditions, and a monomeric helical hairpin in an intramolecularly disulfide bridged state. Using an iterative process, we engineered peptides that formed stable structures consistent with both targets under the different conditions. Finally, for one of the designs, we demonstrated a one-way switch from the helical hairpin to the coiled-coil dimer upon addition of disulfide-reducing agents.     

Isolation and determination of toxic congeners of polychlorinated biphenyls in environmental samples

A Method has been developed for the separation and enrichemen of there non-ortho, eight mono-ortho, and di-ortho substituted polychlorinated biphenyls (PCBs) from Aroclor formulations and environmental samples. The fractionation is accomplished using high performance liquid chromatography (HPLC) with a 2-(1-pyrenyl)ethyldimethylsilysily silca column. GC-MSD with an optimized temperature program was used for quantitation, Hexane, pentane, cyclohexane, iso-octane, and 2-propanol were tested as a mobile phase for the isolation of the thirteen target PCBs in a Aroclor 1242, 1254, and 1260 (1:1:1) misture, Pentane at room temperature with a slow rate of 0.7 ml/min is the condition of choice. The average recovery of thirteen target PCBs spiked in the Aroclor mixture is 99.5% with an average relative standard deviation of 4.5%. The average method detection limit is 8pg/μl. Targer PCBs in the reference solis, incinarator ash, and sediment samples were measured.     

Ultrasound-Triggered Delivery of Iproplatin from Microbubble-Conjugated Liposomes

The Pt^IV prodrug iproplatin has been actively loaded into liposomes using a calcium acetate gradient, achieving a 3-fold enhancement in drug concentration compared to passive loading strategies. A strain-promoted cycloaddition reaction (azide- dibenzocyclooctyne) was used to attach iproplatin-loaded liposomes L(Pt) to gas-filled microbubbles (M), forming an ultrasound-responsive drug delivery vehicle [M−L(Pt)]. Ultrasound-triggered release of iproplatin from the microbubble-liposome construct was evaluated in cellulo. Breast cancer (MCF-7) cells treated with both free iproplatin and iproplatin-loaded liposome−microbubbles [M−L(Pt)] demonstrated an increase in platinum concentration when exposed to ultrasound. No appreciable platinum uptake was observed in MCF-7 cells following treatment with L(Pt) only or L(Pt)+ultrasound, suggesting that microbubble-mediated ultrasonic release of platinum-based drugs from liposomal carriers enables greater control over drug delivery.     

Dynamics of bubble formation in highly viscous liquids

There has recently been considerable interest in the development of devices for the preparation of monodisperse microbubble suspensions for use as ultrasound contrast agents and drug delivery vehicles. These applications require not only a high degree of bubble uniformity but also a maximum bubble size of 8 mum, and this provides a strong motivation for developing an improved understanding of the process of bubble formation in a given device. The aim of this work was to investigate bubble formation in a T-junction device and determine the influence of the different processing parameters upon bubble size, in particular, liquid viscosity. Images of air bubble formation in a specially designed T-junction were recorded using a high-speed camera for different ratios of liquid to gas flow rate (Ql/Qg) and different liquid viscosities (microl). It was found that theoretical predictions of the flow profile in the focal region based on analysis of axisymmetric Stokes flow were accurate to within 6% when compared with the experimental data, indicating that this provided a suitable means of describing the bubble formation process. Both the theoretical and experimental results showed that Ql/Qg and mul had a significant influence upon bubble formation and eventual size, with higher flow rates and higher viscosities producing smaller bubbles. There were, however, found to be limiting values of Ql/Qg and mul beyond which no further reduction in bubble size was achieved.