Automatic Dantzig–Wolfe reformulation of mixed integer programs

Mathematical Programming - Dantzig–Wolfe decomposition (or reformulation) is well-known to provide strong dual bounds for specially structured mixed integer programs (MIPs). However, the...     

Thermodynamic study of heptane + secondary, tertiary and cyclic amines mixtures. Part IV. Excess and solvation enthalpies at 298.15 K

Partial molar enthalpies and excess enthalpies H^E of binary mixtures of heptane + secondary and tertiary n-alkyl, primary cycloalkyl, and secondary (hetero)cyclic amines have been determined at 298.15 K by isothermal titration calorimetry in the whole composition range. All mixtures showed positive H^E values which decrease with increasing amine size in each category, and decrease in the order cyclic primary > cyclic secondary > linear primary [1] > secondary > tertiary when comparing amines of similar size in different categories. From partial molar enthalpies at infinite dilution and known enthalpies of vaporization, the solvation enthalpies have been calculated either for heptane in amines and for amines in heptane. These quantities, together with their cavitational and interactional terms obtained applying the scaled particle theory, are discussed to get insight into the types and relative strength of solute-solvent interactions and into their effects on molecular structure features such as branching and cyclization.     

Looped structure of flowerlike micelles revealed by 1H NMR relaxometry and light scattering

We present experimental proof that so-called "flowerlike micelles" exist and that they have some distinctly different properties compared to their "starlike" counterparts. Amphiphilic AB diblock and BAB triblock copolymers consisting of poly(ethylene glycol) (PEG) as hydrophilic A block and thermosensitive poly(N-isopropylacrylamide) (pNIPAm) B block(s) were synthesized via atom transfer radical polymerization (ATRP). In aqueous solutions, both block copolymer types form micelles above the cloud point of pNIPAm. Static and dynamic light scattering measurements in combination with NMR relaxation experiments proved the existence of flowerlike micelles based on pNIPAm(16kDa)-PEG(4kDa)-pNIPAm(16kDa) which had a smaller radius and lower mass and aggregation number than starlike micelles based on mPEG(2kDa)-pNIPAm(16kDa). Furthermore, the PEG surface density was much lower for the flowerlike micelles, which we attribute to the looped configuration of the hydrophilic PEG block. (1)H NMR relaxation measurements showed biphasic T(2) relaxation for PEG, indicating rigid PEG segments close to the micelle core and more flexible distal segments. Even the flexible distal segments were shown to have a lower mobility in the flowerlike micelles compared to the starlike micelles, indicating strain due to loop formation. Taken together, it is demonstrated that self-assemblies of BAB triblock copolymers have their hydrophilic block in a looped conformation and thus indeed adopt a flowerlike conformation.     

Conformation of the tridimensional structure of 1,2,3,4,6-pentagalloyl-β-D-glucopyranose (PGG) by (1)H NMR, NOESY and theoretical study and membrane interaction in a simulated phospholipid bilayer: a first insight

1,2,3,4,6-Penta-O-galloyl-β-D-glucopyranose (PGG) is a polyphenolic compound found in substantial amounts in a number of medicinal herbs. We report (i) its conformational analysis by solution NMR and molecular dynamics calculation and (ii) theoretical study of its interaction with a model membrane bilayer. The galloyl groups B and E appear to play important roles in the interaction with the phospholipid bilayer.     

Synthesis of stable ruthenium carbonyl complexes containing alkynols ligands and 2(diphenylphosphino)ethyl-triethoxysilane: novel complexes to anchor on mesoporous silica SBA-15 and Al2O3 surface

Abstract  

The triruthenium complexes containing alkynols ligands have been reacted with 2(diphenylphosphino)ethyl-triethoxysilane (dpts), obtaining novel chemically stable disubstituted complexes. The same disubstituted Ru complexes above described were also synthesized following another approach based on the reaction from the phosphine substituted complex Ru₃(CO)₁₀(dpts)₂ and the same alkynols ligands used to obtain the above triruthenium complexes. One of these stable complexes, the HRu₃(CO)₇[C≡C(Me)₂(OH)](dpts)₂ compound was grafted on the mesoporous silica SBA-15 and on γ-Al₂O₃ surface in order to obtain novel hybrid materials to employ in heterogeneous catalysis. The resulting materials have been characterized by multidisciplinary approach based on inductively coupled plasma-mass spectrometry (ICP-MS), FT-IR, XRD, physisorption measurements and DR-UV–Visible spectroscopy.     

Highly strained 2,3-bridged 2H-azirines at the borderline of closed-shell molecules

Substituted 1-azidocyclopentenes and 1-azidocyclohexenes were photolyzed to generate 2,3-bridged 2H-azirines. In the case of bridgehead azirines with a six-membered carbocycle, detection by NMR spectroscopic analysis was possible, whereas even kinetically stabilized bridgehead azirines with a five-membered ring could not be characterized by low-temperature NMR spectroscopic analysis. Thus, a recent report on the latter heterocycles was corrected. Depending on the substitution pattern, irradiation of 1-azidocyclopentenes either led to products that can be explained on the basis of short-lived 2,3-bridged 2H-azirines, or gave secondary products generated from triplet nitrenes. The diverse photoreactivity of 2,3-bridged 2H-azirines was also studied by quantum chemical methods (DFT, CCSD(T), CASSCF(6,6)) with respect to the singlet and triplet energy surfaces. The ring-opening processes leading to the corresponding vinyl nitrenes were identified as key steps for the observed reactivity.     

The inorganic perspective of nerve growth factor: interactions of Cu2+ and Zn2+ with the N-terminus fragment of nerve growth factor encompassing the recognition domain of the TrkA receptor

There is a significant overlap between brain areas with Zn(2+) and Cu(2+) pathological dys-homeostasis and those in which the nerve growth factor (NGF) performs its biological role. The protein NGF is necessary for the development and maintenance of the sympathetic and sensory nervous systems. Its flexible N-terminal region has been shown to be a critical domain for TrkA receptor binding and activation. Computational analyses show that Zn(2+) and Cu(2+) form pentacoordinate complexes involving both the His4 and His8 residues of the N-terminal domain of one monomeric unit and the His84 and Asp105 residues of the other monomeric unit of the NGF active dimer. To date, neither experimental data on the coordination features have been reported, nor has one of the hypotheses according to which Zn(2+) and Cu(2+) may have different binding environments or the Ser1 α-amino group could be involved in coordination been supported. The peptide fragment, encompassing the 1-14 sequence of the human NGF amino-terminal domain (NGF(1-14)), blocked at the C terminus, was synthesised and its Cu(2+) and Zn(2+) complexes characterized by means of potentiometric and spectroscopic (UV/Vis, CD, NMR, and EPR) techniques. The N-terminus-acetylated form of NGF(1-14) was also investigated to evaluate the involvement of the Ser1 α-amino group in metal-ion coordination. Our results demonstrate that the amino group is the first anchoring site for Cu(2+) and is involved in Zn(2+) coordination at physiological pH. Finally, a synergic proliferative activity of both NGF(1-14) and the whole protein on SHSY5Y neuroblastoma cell line was found after treatment in the presence of Cu(2+). This effect was not observed after treatment with the N-acetylated peptide fragment, demonstrating a functional involvement of the N-terminal amino group in metal binding and peptide activity.     

Thermodynamic study of (heptane + amine) mixtures. III: Excess and partial molar volumes in mixtures with secondary,tertiary, and cyclic amines at 298.15 K

Excess molar volumes V^E at 298.15 K were determined by means of a vibrating tube densimeter for binary mixtures of {heptane + open chain secondary (diethyl to dibutyl) and tertiary (triethyl to tripentyl) amines} as well as for cyclic imines (C₂, C₃, C₄, C₆, and C₇) and primary cycloalkylamines (C₅, C₆, C₇, and C₁₂). The V^E values were found positive for mixtures involving small size amines, with V^E decreasing as the size increases. Negative V^E’s were found for tributyl- and tripentylamine, heptamethylenimine, and cyclododecylamine. Mixtures of heptane with cycloheptylamine showed an s-shaped curve.Partial molar volumes $V^{°}$ of amines at infinite dilution in heptane were obtained from V^E and compared with $V^{°}$ of hydrocarbons and other classes of organic compounds taken from literature. An additivity scheme, based on the intrinsic volume approach, was applied to estimate group (CH₃, CH₂, CH, C, NH₂, NH, N, OH, O, CO, and COO) contributions to $V^{°}$. These contributions, the effect of cyclization on $V^{°}$, and the limiting slope of the apparent excess molar volumes were discussed in terms of solute–solvent and solute–solute interactions.     

从原子到大分子体系的计算机模拟——计算化学50年

本文综述并修订了从20世纪50年代末至今,我们在计算化学领域所做的一些有意义的工作。序言部分把我们的工作置于当代科学的背景之下。然后我们以一种经典的基准测试体系——一种新的单粒子表象（即替代传统的原子和分子自旋轨道的化学自旋轨道）所构建的氢分子（H2）波函数——作为开始。用Hartree-Fock-Heitler-Lo...