Ce(IV) ion initiated graft polymerization of glycidylmethacrylate onto a demineralized bone matrix: effect of reaction parameters

Studies on chemical modification of demineralized bone matrix (DBM) have opened new arenas in the field of clinical orthopedics owing to its potential osteoinductivity with desired chemical functionality. To widen its usage to biomolecular delivery, graft polymerization of glycidylmethacrylate onto DBM was carried out by a free-radical initiating process using ceric ammonium nitrate as an initiator. The evidence of the grafting reaction was examined by chemical analysis using Fourier transform IR spectroscopy. The grafting condition was standardized by regulating the reaction parameters such as the concentrations of the backbone, the monomer and the initiator, the polymerization temperature and time. The optimum polymerization temperature and time to have the maximum grafting yield were 40 °C and 3 h, respectively. The percentage of grafting and the percentage of grafting efficiency were determined as a function of the reaction parameters, and both were found to increasing initially and thereafter decrease in most of the cases. The grafting results are discussed in a detailed fashion and a reaction mechanism is proposed.     

Chemoselective synthesis of multiple epoxy-bridged tetrahydropyranone ring systems

Bis- as well as tris-tetrahydropyranone ring systems were obtained via multiple tandem cyclization-1,3-dipolar cycloaddition reactions of α-diazo ketones with ketone as well as aldehyde functional groups in a chemoselective manner.     

Effect of pressure on pedal motion in stilbene molecular crystals and its dependence on the crystallographic site

We report computer simulation of a stilbene molecular crystal as a function of pressure up to 4 GPa. Molecular structure and the crystal structure of stilbene have been characterized by calculating the radial distribution function and dihedral angle distribution, features associated with pedal motion and cell parameters. Results suggest that the population of minor conformer at site 2 disappears altogether above 1.25 GPa. In contrast, the population of minor conformer at site 1 remains at around 12%. Pedal motion is not observed beyond a pressure of 0.8 and 1.4 GPa at site 1 and site 2, respectively. Specific heat and compressibility exhibit an anomaly around 1.25 GPa. The anomaly seems to be associated with the disappearance of pedal motion at site 2. Initially, increase in pressure leads to an increase in the magnitude of lattice energy, but beyond 0.5 GPa it decreases.     

Regioselective nucleophilic addition to carbonyl ylide intermediates: a novel diastereoselective synthesis of cycloalkyl fused furan-3-ones

[structures: see text] A range of cis-fused hexahydro-1-benzofuran-3(2H)-one or tetrahydro-2H-cyclopenta[b]furan-3(3aH)-one ring systems was synthesized by the rhodium(II) acetate catalyzed reaction of alpha-diazo carbonyl compounds in the presence of various oxygen, nitrogen, and sulfur nucleophiles. A double-nucleophilic addition was possible by using an excess of alpha-diazo ketone. These reactions proceeded with complete diastereoselectivity, and the stereochemistry was confirmed by the single-crystal X-ray analysis. This process discloses the first example of tandem cyclization-nucleophilic addition reaction.     

Orientational melting and reorientational motion in a cubane molecular crystal: a molecular simulation study

Detailed molecular simulations are carried out to investigate the effect of temperature on orientational order in cubane molecular crystal. We report a transition from an orientationally ordered to an orientationally disordered plastic crystalline phase in the temperature range 425-450 K. This is similar to the experimentally reported transition at 395 K. The nature of this transition is first order and is associated with a 4.8% increase in unit cell volume that is comparable to the experimentally reported unit cell volume change of 5.4% (Phys. Rev. Lett. 1997, 78, 4938). An orientational order parameter, eta(T), has been defined in terms of average angle of libration of a molecular 3-fold axis and the orientational melting has been characterized by using eta(T). The orientational melting is associated with an anomaly in specific heat at constant pressure (C(P)) and compressibility (kappa). The enthalpy of transition and entropy of transition associated with this orientational melting are 20.8 J mol(-1) and 0.046 J mol(-1) K(-1), respectively. The structure of crystalline as well as plastic crystalline phases is characterized by using various radial distribution functions and orientational distribution functions. The coefficient of thermal expansion of the plastic crystalline phase is more than twice that of the crystalline phase.     

Stopped-flow Fourier transform infrared spectroscopy of nitromethane oxidation by the diiron(IV) intermediate of methane monooxygenase

The hydroxylase component (MMOH) of soluble methane monooxygenase from Methylococcus capsulatus (Bath) was reduced to the diiron(II) form and then allowed to react with dioxygen to generate the diiron(IV) intermediate Q in the first phase of a double-mixing stopped-flow experiment. CD3NO2 was then introduced in the second phase of the experiment, which was carried out in D2O at 25 degrees C. The kinetics of the reaction of the substrate with Q were monitored by stopped-flow Fourier transform infrared spectroscopy, observing the disappearance of the asymmetric NO2 bending vibration at 1548 cm-1. The data were fit to a single-exponential function, which yielded a kobs of 0.45 +/- 0.07 s-1. This result is in quantitative agreement with a kobs of 0.39 +/- 0.01 s-1 obtained by observing the disappearance of Q by double-mixing stopped-flow optical spectroscopy at its absorption maximum of 420 nm. These results provide for the first time direct monitoring of the hydroxylation of a methane-derived substrate in the MMOH reaction pathway and demonstrate that Q decay occurs concomitantly with substrate consumption.     

Synthesis of conformationally restricted C2 symmetric macrodiolides via head to tail dimerization of carbonyl ylides

Tandem reaction of α-diazocarbonyl compounds in the presence of rhodium(II) acetate catalyst is described to furnish a range of conformationally restricted C₂ symmetric macrodiolides via head to tail dimerization of intramolecular carbonyl ylides.     

“On water” cascade synthesis of benzopyranopyrazoles and their macrocycles

Reported herein is an intramolecular 1,3-dipolar cycloaddition strategy for rapid entry into benzopyranopyrazoles (BPP) on water medium as “open flask chemistry” approach. The in situ generation of diazo functionality in two-step sequence from the appropriate alkylated salicylaldehydes undergoes smooth [3?+?2]-cycloaddition with unactivated alkynes/alkenes furnishing benzopyranopyrazoles in good yield. This methodology was also extended for the synthesis of pyrazole incorporated macrocycles. This cascade protocol involving water medium provides an atom-economical and environment friendly approach.