Surface Mobility of Amorphous <i>o</i>‑Terphenyl: A Strong Inhibitory Effect of Low-Concentration Polystyrene

Previous work has shown that a surface wave on amorphous <i>o</i>-terphenyl (OTP) decays by viscous flow at high temperatures and by surface diffusion at low temperatures. We report that the surface mass transport can be efficiently suppressed by low-concentration polymers. Surface-grating decay has been measured for OTP containing 1 wt % polystyrene (PS, <i>M</i>_w = 1–8 kg/mol), which is miscible with OTP. The additive has no significant effect on the decay kinetics in the viscous-flow regime, but a significant effect in the surface-diffusion regime. In the latter case, surface evolution slows down and becomes nonexponential (decelerating over time). The effect increases with falling temperature and the molecular weight of PS. These results are attributed to the very different mobility of PS (slow) and OTP (fast) and their segregation during surface evolution, and relevant for understanding the surface mobility of multicomponent amorphous materials

Enhanced Crystal Nucleation in Glass-Forming Liquids by Tensile Fracture in the Glassy State

Crystal nucleation in a supercooled liquid typically attains its maximal rate near the glass transition temperature Tg and slows down with further cooling, becoming exceedingly slow in the glassy state. We report that cooling a liquid well below its Tg can actually increase the rate of nucleation because of tensile fracture. Cooling liquid griseofulvin (an antifungal drug) approximately 80 K below its Tg induces extensive network fracture due to tensile stress from a thermally less expansive container, and reheating the sample above Tg leads to crystallization that otherwise would not occur. An extensive statistical study revealed a direct connection between fracture and crystal nucleation. This phenomenon explains puzzling results in the literature concerning anomalous nucleation in deeply supercooled liquids and is relevant for selecting storage conditions to ensure the physical stability of amorphous drugs

Regioselective Synthesis of Highly Substituted Imidazoles via the Sequential Reaction of Allenyl Sulfonamides and Amines

A novel synthesis of imidazoles from electron-withdrawing group-substituted allenyl sulfonamides with amines was developed. The 4- and 5-functionalized imidazoles were constructed regioselectively, which depended on the substituents on the nitrogen atoms

New Polymorphs of ROY and New Record for Coexisting Polymorphs of Solved Structures

With six polymorphs coexisting at room temperature, 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) is the top system in the current Cambridge Structural Database (Feb. 2005) for the number of polymorphs of solved crystal structures. Here we report two new ROY polymorphs, Y04 and YT04, and the crystal structure of YT04. Y04 is a metastable polymorph that tends to crystallize first from a melt at room temperature, and YT04 is a product of solid-state transformation of Y04. Despite its late discovery, YT04 is the densest among the polymorphs at 25 °C and likely the second most stable at 0 K. The conformation of ROY in YT04 is similar to those in the other two yellow polymorphs (Y and YN) but significantly different from those in the orange and red colored polymorphs (ON, OP, ORP, and R). Having escaped years of solution crystallization in several laboratories, Y04 and YT04 exemplify polymorphs that are likely missed by solvent-based screening and discovered through alternative routes

Regioselective Synthesis of Highly Substituted Imidazoles via the Sequential Reaction of Allenyl Sulfonamides and Amines

A novel synthesis of imidazoles from electron-withdrawing group-substituted allenyl sulfonamides with amines was developed. The 4- and 5-functionalized imidazoles were constructed regioselectively, which depended on the substituents on the nitrogen atoms

Selective Nucleation and Discovery of Organic Polymorphs through Epitaxy with Single Crystal Substrates

Crystallization of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (1), previously found to produce six conformational polymorphs from solution, on single-crystal pimelic acid (PA) substrates results in selective and oriented growth of the metastable “YN” (yellow needle) polymorph on the (101)PA faces of the substrate. Though the freshly cleaved substrate crystals expose (101)PA and (111)PA faces, which are both decorated with [101̄]PA ledges that could serve as nucleation sites, crystal growth of YN occurs on only (101)PA. Goniometry measurements performed with an atomic force microscope reveal that the (001)YN plane contacts (101)PA with a crystal orientation [100]YN||[010]PA and [010]YN||[101̄]PA. A geometric lattice analysis using a newly developed program dubbed GRACE (geometric real-space analysis of crystal epitaxy) indicates that this interfacial configuration arises from optimal two-dimensional epitaxy and that among the six polymorphs of 1, only the YN polymorph, in the observed orientation, achieves reasonable epitaxial match to (101)PA. The geometric analysis also reveals that none of the polymorphs, including YN, can achieve comparable epitaxial match with (111)PA, consistent with the absence of nucleation on this crystal face. In contrast, sublimation of 1 on cleaved succinic acid (SA) substrates, which expose large (010)SA faces decorated with steps along [101̄]SA, affords growth of several polymorphs, each with multiple orientations, as well as oriented crystals of a new metastable polymorph on the (010)SA surfaces. The lack of polymorphic selectivity on (010)SA can be explained by the geometric lattice analysis, which reveals low-grade epitaxial matches between (010)SA and several polymorphs of 1 but no inherent selectivity toward a single polymorph. These observations demonstrate the sensitivity of crystal nucleation to substrate surface structure, the potential of crystalline substrates for selective nucleation and discovery of polymorphs, and the utility of geometric lattice modeling for screening of substrate libraries for controlling polymorphism

New Polymorphs of ROY and New Record for Coexisting Polymorphs of Solved Structures

With six polymorphs coexisting at room temperature, 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) is the top system in the current Cambridge Structural Database (Feb. 2005) for the number of polymorphs of solved crystal structures. Here we report two new ROY polymorphs, Y04 and YT04, and the crystal structure of YT04. Y04 is a metastable polymorph that tends to crystallize first from a melt at room temperature, and YT04 is a product of solid-state transformation of Y04. Despite its late discovery, YT04 is the densest among the polymorphs at 25 °C and likely the second most stable at 0 K. The conformation of ROY in YT04 is similar to those in the other two yellow polymorphs (Y and YN) but significantly different from those in the orange and red colored polymorphs (ON, OP, ORP, and R). Having escaped years of solution crystallization in several laboratories, Y04 and YT04 exemplify polymorphs that are likely missed by solvent-based screening and discovered through alternative routes

ROY: Using the Method of Molecular Voronoi–Dirichlet Polyhedra to Examine the Fine Features of Conformational Polymorphism

Crystal chemical analysis of 12 polymorphs of 5-methyl-2-[(2-nitrophenyl)­amino]-3-thiophenecarbonitrile (ROY) (C12H9N3O2S)the current record-holder of the number of structurally characterized polymorphic modificationswas carried out using the method of molecular Voronoi–Dirichlet (VD) polyhedra. Based on the k-Φ criterion, it was found that each of the 14 reported to-date independent ROY molecules has a unique conformation. A method for quantifying the significance of noncovalent interactions of various natures together with a new type of graph showing average partial contributions of single contacts of a given type to the values of integral parameters was proposed. The capabilities of the method of molecular VD polyhedra were successfully tested on the example of several forms of ROY with multiple structural solutions. The analysis showed that noncovalent interactions vary more between different forms of ROY than between different structural solutions of the same form. It was calculated that different structural solutions of the same form of ROY may feature up to five varying noncovalent contacts. The k-Φ criterion approved itself as a very sensitive parameter which can easily detect even the subtlest differences in atomic interactions strictly and quantitatively

Two DSC Glass Transitions in Miscible Blends of Polyisoprene/Poly(4-<i>tert</i>-butylstyrene)

Conventional and temperature-modulated differential scanning calorimetry (DSC) experiments have been carried out on miscible blends of polyisoprene (PI) and poly(4-tert-butylstyrene) (P4tBS) over a broad composition range. This system is characterized by an extraordinarily large Tg difference (∼215 K) between the two homopolymers. Two distinct calorimetric glass transitions were observed in blends of intermediate compositions (25%−50% PI) by both conventional and temperature-modulated DSC. Good agreement was found between the component Tg values measured by the two methods. Fitting of the component Tg values to the Lodge−McLeish model gives a ϕself of around 0.63 for PI in this blend and 0.03 for P4tBS. The extracted ϕself for PI is comparable to reported values for PEO in blends with PMMA and is significantly larger than values reported for PI in other blends with smaller homopolymer Tg differences. This observation is consistent with the presence of a nonequilibrium or confinement effect in PI/P4tBS blends, which results in enhanced dynamics of the fast component below the Tg of the slow component

Interaction of Bacteriophage λ Protein Phosphatase with Mn(II): Evidence for the Formation of a [Mn(II)]₂ Cluster^†

The interaction of bacteriophage λ protein phosphatase with Mn2+ was studied using biochemical techniques and electron paramagnetic resonance spectrometry. Reconstitution of bacteriophage λ protein phosphatase in the presence of excess MnCl2 followed by rapid desalting over a gel filtration column resulted in the retention of approximately 1 equiv of Mn2+ ion bound to the protein. This was determined by metal analyses and low-temperature EPR spectrometry, the latter of which provided evidence of a mononuclear high-spin Mn2+ ion in a ligand environment of oxygen and nitrogen atoms. The Mn2+-reconstituted enzyme exhibited negligible phosphatase activity in the absence of added MnCl2. The EPR spectrum of the mononuclear species disappeared upon the addition of a second equivalent of Mn2+ and was replaced by a spectrum attributed to an exchange-coupled (Mn2+)2 cluster. EPR spectra of the dinuclear (Mn2+)2 cluster were characterized by the presence of multiline features with a hyperfine splitting of 39 G. Temperature-dependent studies indicated that these features arose from an excited state. Titrations of the apoprotein with MnCl2 provided evidence of one Mn2+ binding site with a micromolar affinity and at least one additional Mn2+ site with a 100-fold lower affinity. The dependence of the phosphatase activity on Mn2+ concentration indicates that full enzyme activity probably requires occupation of both Mn2+ sites. These results are discussed in the context of divalent metal ion activation of this enzyme and possible roles for Mn2+ activation of other serine/threonine protein phosphatases