Platinum stilbazoles: ring-walking coupled with aryl-halide bond activation

The reaction between tetrakis(triethylphosphine)platinum(0) and 4-[trans-2-(4-bromophenyl)vinyl]pyridine (1) is examined. Initially, the metal center coordinates to the bridging double bond of 1. Complexes 2 and 3 were fully characterized, and their X-ray crystallography structures are presented. Upon heating, either in solution or in the solid state, complex 2 undergoes C-Br oxidative addition to give complex 3. Kinetic studies revealed that this conversion is unimolecular and does not involve dissociation of the metal center from the double bond. Density functional studies show that a plausible mechanism involves the metal center "walking" around the pi-system from the bridging C=C double bond to the C-Br bond.     

Influence of linker molecules on charge transport through self-assembled single-nanoparticle devices

We investigate electrical characteristics of single-electron electrode/nanoisland/electrode devices formed by alkanedithiol assisted self-assembly. Contrary to predictions of the orthodox model for double tunnel junction devices, we find a significant ( approximately fivefold) discrepancy in single-electron charging energies determined by Coulomb blockade (CB) voltage thresholds in current-voltage measurements versus those determined by an Arrhenius analysis of conductance in the CB region. The energies do, however, scale with particle sizes, consistent with single-electron charging phenomena. We propose that the discrepancy is caused by a multibarrier junction potential that leads to a voltage divider effect. Temperature and voltage dependent conductance measurements performed outside the blockade region are consistent with this picture. We simulated our data using a suitably modified orthodox model.     

Parkintin: a new flavanone with epoxy-isopentyl moiety from Parkinsonia aculeata Linn. (Caesalpiniaceae)

A new flavanone with epoxy-isopentyl moiety named parkintin has been isolated from the methanol soluble part of Parkinsonia aculeata Linn. belonging to the family Caesalpiniaceae. The structure of parkintin has been established with the aid of spectroscopic techniques including COSY and HMBC experiments.     

Color versus bioactivity in the flowers of Bougainvillea spectabilis (Nyctaginaceae)

The methanolic extracts of Bougainvillea spectabilis (Nyctaginaceae) flowers (five different colors) were screened biologically by performing four bioassays: antibacterial, antifungal, brine shrimp lethality and phytotoxicity. It was observed that the methanolic extract of white flowers was the most biologically active among all tested extracts. The extracts of white, orange and shocking pink flowers inhibit, while the extracts of red and violet flowers promote, the growth of Lemna plants. The extract of white flowers also exhibits toxicity against shrimp larvae with a LD50 value of 33.5627 microg/mL. However, none of the tested samples gave positive responses against any tested fungi.     

On the topology of foliations with a first integral

The main objective of this article is to study the topology of the fibers of a generic rational function of the type in the projective space of dimension two. We will prove that the action of the monodromy group on a single Lefschetz vanishing cycle generates the first homology group of a generic fiber of . In particular, we will prove that for any two Lefschetz vanishing cycles ₀ and ₁ in a regular compact fiber of , there exists a mondromyh such thath( ₀)=± ₁.Partially supported by CNPq-Brazil.     

Pattern Matching with Swaps

Let a text string T of n symbols and a pattern string P of m symbols from alphabet Σ be given. A swapped version T′ of T is a length n string derived from T by a series of local swaps (i.e., t′_ℓ ← t_ℓ + 1 and t′_ℓ + 1 ← t_ℓ), where each element can participate in no more than one swap. The pattern matching with swaps problem is that of finding all locations i for which there exists a swapped version T′ of T with an exact matching of P in location i of T′. It has been an open problem whether swapped matching can be done in less than O(nm) time. In this paper we show the first algorithm that solves the pattern matching with swaps problem in time o(nm). We present an algorithm whose time complexity is O(nm^1/3 log m log σ) for a general alphabet Σ, where σ = min(m,Σ).     

Optimal adjustment of manpower-requirement forecasts: A case study of Iran

The manpower forecasting models are frequently used in development planning. The usual approach in these models is to correlate the manpower requirement with the level of economic activities and to declare the forecasted figures as the educational targets of the development plan. In this paper we show that because of uncertainties involved in these forecasts, and due to the lack of a cost consideration mechanism in the above models, the implementation of such an educational plan causes an inefficiency in the society's allocation of resources. We then derive an adjustment rule which modifies the manpower-requirement forecasts based on balancing the trade-offs between the cost of educational and the degree of target realization.For demonstration purposes, we apply the above rule to the case of Iran and, through this application, we introduce a methodology for analyzing the sensitivity of results to different types of errors contained in the manpower-requirement forecasts.     

Examples of asymmetric differentiable manifolds

Mathematische Annalen -