Competitive C-I versus C-CN reductive elimination from a Rh(III) complex. Selectivity is controlled by the solvent

The RhIII complex [(PNP)Rh(CN)(CH3)][I] 5, obtained by oxidative addition of methyl iodide to [(PNP)Rh(CN)] 2, reacts selectively in two pathways: In aprotic solvents C-I reductive elimination of methyl iodide followed by its electrophilic attack on the cyano ligand takes place, giving the methyl isonitrile RhI complex [(PNP)Rh(CNCH3)][I] 3, while in protic solvents C-C reductive elimination of acetonitrile takes place forming an iodo RhI complex [(PNP)RhI] 9. Reaction of 2 with ethyl iodide in aprotic solvents gave the corresponding isonitrile complex, while in protic solvents no reactivity was observed. The selectivity of this reaction is likely due to a hydrogen bond between the cyano ligand and the protic solvent, as observed by X-ray diffraction, which retards electrophilic attack on this ligand.     

Charge regulation with fixed and mobile charged macromolecules

Uncompensated charges do not usually occur in Nature and any local charge should be a result of charge separation. Dissociable chemical groups at interfaces in contact with ions in solution, whose chemical equilibrium depends both on short-range non-electrostatic and long-range electrostatic interactions, are the physical basis of this charge separation, known as charge regulation phenomena. The charged groups can be either fixed and immobile, as in the case of solvent-exposed solid substrate and soft bounding surfaces (e.g., atomically smooth mica surfaces and soft phospholipid membranes), or free and mobile, as in the case of charged macro-ions (e.g., protein or other biomolecules). Here, we review the mean-field formalism used to describe both cases, with a focus on recent advances in the modeling of mobile charge-regulated macro-ions in an ionic solution. The general form of the screening length is derived, and is shown to combine the concept of intrinsic capacitance (introduced by Lund and Jönsson) with bulk capacitance, resulting from the mobility of small ions and macro-ions. The advantages and disadvantages of different formulations, such as the cell model vs. the collective approach, are discussed, along with several suggestions for future experiments and modeling.     

Pricing decisions in a dual supply chain of organic and conventional agricultural products

Annals of Operations Research - We analyze a dual-channel supply chain comprising two suppliers that offer vertically-differentiated agricultural products; specifically, one offers an organic...     

Minimal average degree aberration and the state polytope for experimental designs

For a particular experimental design, there is interest in finding which polynomial models can be identified in the usual regression set up. The algebraic methods based on Gröbner bases provide a systematic way of doing this. The algebraic method does not, in general, produce all estimable models but it can be shown that it yields models which have minimal average degree in a well-defined sense and in both a weighted and unweighted version. This provides an alternative measure to that based on “aberration” and moreover is applicable to any experimental design. A simple algorithm is given and bounds are derived for the criteria, which may be used to give asymptotic Nyquist-like estimability rates as model and sample sizes increase.     

Porphine and pyrrole-substituted porphyrin from cyclocondensation of tripyrrane with mono-substituted pyrroles

The condensation of non-substituted tripyrrane with mono-substituted pyrroles did not lead to corrole, but to porphine and 5-pyrrolyl-porphyrin. Both compounds were fully characterized by a combination of spectroscopic methods and X-ray crystallography.     

Anion-binding properties of the tripyrrolemethane group: a combined experimental and theoretical study

Tripyrrolemethane- and bistripyrrolemethane-containing systems were recently reported to be efficient and selective hosts for anions. Nevertheless, the basic intrinsic properties of tripyrrolemethane as a ligand for anions have not yet been explored. Here we report the study of the anion-binding properties of the tripyrrolemethane group. We applied a combined experimental and theoretical approach to determine the affinity of the tripyrrolemethane system for different anions in the gas phase, in solution and in the crystalline state. In the crystal, the tripyrrolemethane group forms a number of different complexes with the bromide ion, some involving the participation of more than one ligand species. Despite the very similar basicity of fluoride and dihydrogen phosphate, the tripyrrolemethane ligand exhibits a clear preference for the fluoride anion in solution, which indicates an anion-binding system and not merely deprotonation. Although the affinity of the tripyrrolemethane ligand for other ions was negligible in solution, gas-phase studies show that complexation with larger halide ions is favoured over complexation with fluoride.     

Triggered release of aqueous content from liposome-derived sol-gel nanocapsules

Liposomes prepared from a mixture of L-alpha-dipalmitoylphosphatidylcholine and the PEGilated phospholipid N-(carbonylmethoxypoly(ethylene glycol 2000))-1,2-distearoyl-sn-glycero-3-phosphoethanolamine were used as templates for the production of silica and alkylated silica approximately 100 nm capsules, "liposils", entrapping aqueous solutions of anionic dyes. Triggered release of this content was successfully affected by either low-frequency ultrasound or by microwave treatments. Cryo-TEM was used to follow the formation process of these particles, which are aggregated in a chain-like manner. A mechanism explaining this phenomenon is suggested.     

Mono-, and dibenzacridine imines. Synthesis of 1a,11b- dihydrobenz[c]azirino[α]acridine, 4b,5a-dihydrodibenz[c,h]- azirino[α]acridine and 1a,13b-dihydrodibenz[c,j]azirino[α]acridine

The syntheses of the K-imine derivatives of benz[c]acridine, dibenz[c,h]acridine and dibenz[a,h]acridine are described. The parent hydrocarbons 1, 6 and 11 were oxidized with sodium hypochlorite under phase transfer conditions to the corresponding K-oxides 4,9 and 14 , which in turn were reacted with sodium azide. The resulting azido alcohols were then cyclized with tributylphosphine to the title compounds 5,10 and 15.     

Covering a laminar family by leaf to leaf links

The Tree Augmentation Problem (TAP) is: given a tree T=(V,E) and a set E of edges (called links) on V disjoint to E, find a minimum-size edge-subset F⊆E such that T+F is 2-edge-connected. TAP is equivalent to the problem of finding a minimum-size edge-cover F⊆E of a laminar set-family. We consider the restriction, denoted LL-TAP, of TAP to instances when every link in E connects two leaves of T. The best approximation ratio for TAP is 3/2, obtained by Even et al. (2001, 2009, 2008) [3], [4] and [5], and no better ratio was known for LL-TAP. All the previous approximation algorithms that achieve a ratio better than 2 for TAP, or even for LL-TAP, have been quite involved.For LL-TAP we obtain the following approximation ratios: 17/12 for general trees, 11/8 for trees of height 3, and 4/3 for trees of height 2. We also give a very simple3/2-approximation algorithm (for general trees) and prove that it computes a solution of size at most , where t is the minimum size of an edge-cover of the leaves, and t^∗ is the optimal value of the natural LP-relaxation for the problem of covering the leaf edges only. This provides the first evidence that the integrality gap of a natural LP-relaxation for LL-TAP is less than 2.