Dipyrido[3,2-a:2′,3′-c]phenazine-Tethered Oligo-DNA: Synthesis and Thermal Stability of Their DNA⋅DNA and DNA⋅RNA Duplexes and DNA⋅DNA⋅DNA Triplexes

Dipyrido[3,2-a:2′,3′-c]phenazine (dppz) derivatives were conjugated to 9-mer and 18-mer DNA (ODN) at a site without nucleobase, either at the 5′- or 3′-end or at a internucleotide position, via linkers of 7, 12, or 18 atoms lengths. These dppz-linked ODNs were synthesized using novel backbone glycerol phosphoramidites: Glycerol, serving as artificial nucleoside without nucleobase, was modified to amines 10 , 23 , and 24 , which were suitable for the subsequent key reaction with dppz-carboxylic acid 3 (Schemes 2 and 3). The products of these reactions (see 5 – 7 ) were then transformed to the standard phosphoramidite derivatives (see 27 , 29 , and 30 ) or used for loading on a CPG support (see 28 , 31 , and 32 ). The dppz-modified ODNs were subsequently assembled in the usual manner using automated solid-phase DNA synthesis. The 9-mer ODN-dppz conjugates 35 – 43 were tested for their ability to form stable duplexes with target DNA or RNA strands (D11 ( 60 ) or R11 ( 61 )), while the 18-mer ODN-dppz conjugates 48 – 56 were tested for their ability to form stable triplexes with a DNA target duplex D24⋅D24 ( 62 ) (see Tables 1 and 2). The presence of the conjugated dppz derivative increases the stability of DNA⋅DNA and DNA⋅RNA duplexes, typically by a ΔT_m of 7.3 – 10.9° and 4.5 – 7.4°, respectively, when the dppz is tethered at the 5′- or 3′-terminal (Table 2). The dppz derivatives also stabilize triplexes when attached to the 5′- or 3′-end, with a ΔT_m varying from 3.8 – 11.1° (Table 3). The insertion of a dppz building block at the center of a 9-mer results in a considerably poorer stability of the corresponding DNA⋅DNA duplexes (ΔT_m=0.5 to 4.2°) and DNA⋅RNA duplexes (ΔT_m=−1.5 to 0.9°), while the replacement of one interior nucleotide by a dppz building unit in the corresponding 8-mer ODN does not reveal the formation of any duplex at all. Different types of modifications in the middle of the 18-mer ODN, in general, do not lead to any triplex formation, except when the dppz derivative is tethered to the ODN through a 12-atom-long linker (Entry 9 in Table 3).     

Mechanisms of single-electron capture by the dichlorocarbene dication

The single-electron capture (SEC) by dichlorocarbene dications with eight different atomic and molecular target gases, CCl ₂ ²⁺ + G → CCl ₂ ⁺ + G⁺, has been studied by product ion spectroscopy and ion kinetic energy spectroscopy. The experimental data have been interpreted in the framework of a theoretical model mat describes the charge exchange process. Exothermic charge exchange is handled within the Landau-Zener model, whereas endothermic charge exchange is described by the Demkov model. The calculated data reproduce qualitatively the essential features of the experimental results: (1) the appearance of a reaction window centered at an exothermicity in the 4–4.5-eV range, (2) the lower SEC cross sections for endothermic charge exchange, (3) the wider internal energy distributions obtained for CCl ₂ ⁺ in the endothermic regime than in the exothermic one, which results in larger dissociation yields, (4) the excitation of molecular targets that accompany their ionization in the SEC process, and (5) the kinetic energy released on the CCl⁺ + Cl fragments in dissociative SEC.     

A practical way of grafting maleic anhydride onto polypropylene providing high anhydride contents without sacrificing excessive molar mass

This study reports a reactive extrusion process leading to very high levels of anhydride grafting (2.5–3 wt %) along polypropylene backbone without recovering grafted PP waxes at the die exit. Such high graftings are attainable without excessive degradation of the PP chain by using a brominated reagent. Simultaneously, this brominated reagent allows the tuning of the grafted PP crystallinity via epimerization of the PP backbone. Indeed, the synthesis of a mainly isotactic/atactic stereoblock polymer containing high levels of grafted succinic anhydride moieties is demonstrated by NMR and melting enthalpies recorded by DSC are definitely observed depressed and broadened. Grafting levels of around 3 wt % have been achieved and ascertained by both chemical titration and NMR spectroscopy. In addition, FTIR spectroscopy reveals an unusual observation: for the first time, only one single pair of symmetric and asymmetric carbonyl stretching bands are observed on those grafted PP, while, in other processes of anhydride grafting, those symmetric and asymmetric bands were both split in at least two bands. This suggests, for the here reported process, the absence of interacting grafted anhydride rings, i.e., absence of closely grafted anhydride moieties and absence of poly(maleic anhydride). All those observations support that this “bromine route” brings a really new grafting process for PP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2936–2947, 2008     

Polynomial auction algorithms for shortest paths

In this paper we consider strongly polynomial variations of the auction algorithm for the single origin/many destinations shortest path problem. These variations are based on the idea of graph reduction, that is, deleting unnecessary arcs of the graph by using certain bounds naturally obtained in the course of the algorithm. We study the structure of the reduced graph and we exploit this structure to obtain algorithms withO (n min{m, n logn}) andO(n ²) running time. Our computational experiments show that these algorithms outperform their closest competitors on randomly generated dense all destinations problems, and on a broad variety of few destination problems.Research supported by NSF under Grant No. DDM-8903385, by the ARO under Grant DAAL03-86-K-0171, by a CNR-GNIM grant, and by a Fullbright grant     

Microcavity polariton splitting of intersubband transitions

The optical response of the intersubband excitation of multiple two-dimensional electron gases within a semiconductor microcavity has been studied through angle-dependent reflectance measurements. Using a resonator based on total internal reflection, a clear splitting of about 14 meV of the coupled intersubband cavity modes is observed from 10 K to room temperature, with resulting polaritonlike dispersion. The experimental findings are in good agreement with theoretical calculations performed in a transfer-matrix formalism.     

Distributed asynchronous computation of fixed points

We present an algorithmic model for distributed computation of fixed points whereby several processors participate simultaneously in the calculations while exchanging information via communication links. We place essentially no assumptions on the ordering of computation and communication between processors thereby allowing for completely uncoordinated execution. We provide a general convergence theorem for algorithms of this type, and demonstrate its applicability to several classes of problems including the calculation of fixed points of contraction and monotone mappings arising in linear and nonlinear systems of equations, optimization problems, shortest path problems, and dynamic programming. This research was contacted at the M.I.T. Laboratory for Information and Decision Systems with partial support provided by the Defense Advanced Research Projects Agency under Grant No. ONR-N00014-75-C-1183.     

Existence of optimal stationary policies in deterministic optimal control

This paper considers deterministic discrete-time optimal control problems over an infinite horizon involving a stationary system and a nonpositive cost per stage. Various results are provided relating to existence of an ?-optimal stationary policy, and existence of an optimal stationary policy assuming an optimal policy exists.     

Necessary and sufficient conditions for a penalty method to be exact

This paper identifies necessary and sufficient conditions for a penalty method to yield an optimal solution or a Lagrange multiplier of a convex programming problem by means of a single unconstrained minimization. The conditions are given in terms of properties of the objective and constraint functions of the problem as well as the penalty function adopted. It is shown among other things that all linear programs with finite optimal value satisfy such conditions when the penalty function is quadratic.