Ruthenium nanoparticles inside porous [Zn4O(bdc)3] by hydrogenolysis of adsorbed [Ru(cod)(cot)]: a solid-state reference system for surfactant-stabilized ruthenium colloids

The gas-phase loading of [Zn4O(bdc)3] (MOF-5; bdc = 1,4-benzenedicarboxylate) with the volatile compound [Ru(cod)(cot)] (cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) was followed by solid-state (13)C magic angle spinning (MAS) NMR spectroscopy. Subsequent hydrogenolysis of the adsorbed complex inside the porous structure of MOF-5 at 3 bar and 150 degrees C was performed, yielding ruthenium nanoparticles in a typical size range of 1.5-1.7 nm, embedded in the intact MOF-5 matrix, as confirmed by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (PXRD), and X-ray absorption spectroscopy (XAS). The adsorption of CO molecules on the obtained Ru@MOF-5 nanocomposite was followed by IR spectroscopy. Solid-state (2)H NMR measurements indicated that MOF-5 was a stabilizing support with only weak interactions with the embedded particles, as deduced from the surprisingly high mobility of the surface Ru-D species in comparison to surfactant-stabilized colloidal Ru nanoparticles of similar sizes. Surprisingly, hydrogenolysis of the [Ru(cod)(cot)]3.5@MOF-5 inclusion compound at the milder condition of 25 degrees C does not lead to the quantitative formation of Ru nanoparticles. Instead, formation of a ruthenium-cyclooctadiene complex with the arene moiety of the bdc linkers of the framework takes place, as revealed by (13)C MAS NMR, PXRD, and TEM.     

Nickel complexes of a pincer NN2 ligand: multiple carbon-chloride activation of CH2Cl2 and CHCl3 leads to selective carbon-carbon bond formation

A new pincer-type bis(amino)amine (NN2) ligand and its lithium and nickel complexes, including Ni(II) methyl, ethyl, and phenyl complexes, were synthesized. The Ni(II) alkyl complexes react cleanly with alkyl halides including chlorides to form C-C coupled products and Ni(II) halides. More interestingly, the Ni(II) alkyls undergo unprecedented reactions with CH2Cl2 and CHCl3 to cleave all the C-Cl bonds and replace them with C-C bonds. The reactions are highly selective and lead to the first efficient catalytic coupling of CH2Cl2 with alkyl Grignards. A conversion of 82% and a turnover number of 47 are achieved within minutes. Coupling of CD2Cl2 and 1,1-dichloro-3,3-dimethylbutane with nBuMgCl is also realized. Preliminary mechanistic study suggests a radical initiated process for these reactions.     

Complexity of "A-a" knob-hole fibrin interaction revealed by atomic force spectroscopy

During blood vessel injury, fibrinogen is converted to fibrin, a polymer that serves as the structural scaffold of a blood clot. The primary function of fibrin is to withstand the large shear forces in blood and provide mechanical stability to the clot, protecting the wound. Understanding the biophysical forces involved in maintaining fibrin structure is of great interest to the biomedical community. Previous reports have identified the "A-a" knob-hole interaction as the dominant force responsible for fibrin's structural integrity. Herein, biochemical force spectroscopy is used to study knob-hole interactions between fibrin fragments and variant fibrinogen molecules to identify the forces occurring between individual fibrin molecules. The rupture of the "A-a" knob-hole interaction results in a characteristic profile previously unreported in fibrin force spectroscopy with two distinct populations of specific forces: 110 +/- 34 and 224 +/- 31 pN. In the absence of a functional "A" knob or hole "a", these forces cease to exist. We propose that the characteristic pattern represents the deformation of the D region of fibrinogen prior to the rupture of the "A-a" knob-hole bond.     

Synthesis of compounds presenting three and four anthracene units as potential connectors to mediate infinite lateral growth at the air/water interface

We report the synthesis of molecular sheets based on the photochemically initiated dimerization of monomers with lateral anthracene units. The film thickness and composition were investigated by ellipsometry and X-ray photoelectron spectroscopy (XPS). The mechanical stability of the film was sufficient to span it over 45x45 microm-sized holes. Several model reactions were performed to illustrate the underlying chemistry and to assist in analysis. The reported experiments are considered first steps towards the ultimate goal of the rational synthesis of laterally "infinite", one-monomer-unit-thick molecular sheets with a long-range positional order and a periodic covalent-bonding pattern. Such sheets are referred to as 2D polymers and are considered a prime goal of chemical synthesis with intriguing applications.     

Conjugation and hyperconjugation in conformational analysis of cyclohexene derivatives containing an exocyclic double bond

The equilibrium geometry, ring-inversion pathway barriers for analogues of cyclohexene with an exocyclic double bond have been studied using the MP2/6-311 G(d,p) level of theory. The equilibrium conformation of the ring depends on conjugation between the endocyclic and exocyclic double bonds. Interactions between conjugated double bonds include the pi-pi conjugation and interactions between the lone pair of the heteroatom of the exocyclic double bond and the sigma-antibonding orbital of the endocyclic single bond. In the case of the tetrahydrocycles with double bonds separated by a methylene group the balance between the pi --> sigma* hyperconjugation interactions between the exocyclic double bond and the neighboring methylene group and the n --> sigma* interaction between the lone pair of the heteroatom and the sigma-antibonding orbitals of the C(sp(2))-C(sp(3)) bond determine the geometrical parameters of the ring. The character of the potential-energy surface around the saddle point depends on the position of the exocyclic double bond and the orientation of the hydrogen atom attached to the heteroatom of the V group of the periodic table in the tetrahydrocycles with double bonds separated by a methylene group.     

Quadruple systems with independent neighborhoods

A 4-graph is odd if its vertex set can be partitioned into two sets so that every edge intersects both parts in an odd number of points. Let

     

Temperature-pressure phase diagram of a D2O-D2 system at pressures to 1.8 kbar

Using a volumetric technique, the deuterium solubility, X, in heavy water (L), low-pressure hexagonal ice (I h), and high-pressure cubic clathrate ice (sII) is studied at deuterium pressures up to 1.8 kbar and temperatures from -40 to +5 degrees C. The triple point of the L + I(h) + sII equilibrium is located at P = 1.07(3) kbar and T = -4.5(8) degrees C. The molar ratios D2/D2O of phases at the triple point are X(L) = 0.020(5), X(Ih) = 0.012(5), and X(sII) = 0.207(5).     

Direct synthesis, crystal structures, high-field EPR, and magnetic studies of heterometallic polymers containing manganese(II) carboxylates interconnected by [Cu(en)2]2+

Two heterometallic polymers containing cations [Cu(en)2]2+ and either the [Mn(mal)2(H2O)2]2- (1) or [Mn2(succ)2Cl2]n2n- (2) anions (mal=malonate and succ=succinate) were investigated by X-ray crystallography, high-field electron paramagnetic resonance (EPR) spectroscopy, and magnetic susceptibility measurements. Magnetic susceptibility and EPR spectra characteristic of antiferromagnetically coupled Mn2+-Mn2+ pairs were observed in 2, and the exchange integral J=31 cm(-1) (H=JS1S2) as well as the zero-field-splitting parameter D=-3.046 cm(-1) in the triplet state of the dimanganese entity was determined.