Thermal Characteristics of SrO-2B(2)O(3) Glasses

Transparent SrO-2B(2)O(3) (SBO) glasses were fabricated via the conventional melt-quenching technique. X-ray diffraction (XRD) and differential thermal analysis (DTA) studies carried out on the as-quenched glasses confirmed their amorphous and glassy nature, respectively. The thermal parameters were evaluated for the as-quenched glass-plates using non-isothermal DTA experiments. The average values of the activation energies for the glass transition and crystallization of these glasses were 800 +/- 10 kJ/mol and 298 +/- 10 kJ/mol respectively. The values of the kinetic parameters that were obtained by different non-isothermal techniques were in close agreement.

Magnetic trapping of Yb in the metastable P-3(2) state

We report magnetic trapping of Yb in the excited P-3(2) state. This state, with a lifetime of 15 s, could play an important role in studies ranging from optical clocks and quantum computation to the search for a permanent electric dipole moment. Yb atoms are first cooled and trapped in the ground state in a 399-nm magneto-optic trap. The cold atoms are then pumped into the excited state by driving the S-1(0) -> P-3(1) -> S-3(1) transition. Atoms in the P-3(2) state are magnetically trapped in a spherical quadrupole field with an axial gradient of 110 G/cm. We trap up to 10(6) atoms with a lifetime of 1.5 s.

(2-Chlorobenzo[h]quinolin-3-yl)methanol

In the title molecule, C14H10ClNO, all non-H atoms are coplanar (r.m.s deviation = 0.0266 angstrom). In the crystal, symmetry-related molecules are hydrogen bonded via intermolecular O-H center dot center dot center dot O interactions, forming chains along the b axis.

1-[(2-Chloro-7-methyl-3-quinolyl)methyl]pyridin-2(1H)-one

In the title compound, C16H13ClN2O, the quinoline ring system is essentially planar, with a maximum deviation of 0.021 (2) angstrom. The pyridone ring is oriented at a dihedral angle of 85.93 (6)degrees with respect to the quinoline ring system. In the crystal structure, intermolecular C-H center dot center dot center dot O hydrogen bonds link the molecules along the b axis. Weak pi-pi stacking interactions [centroid-centroid distances = 3.7218 (9) and 3.6083 (9) angstrom] are also observed.

Ethyl 6-chloro-2-[(2-chloro-7,8-dimethylquinolin-3-yl)methoxy]-4-phenylquino line-3-carboxylate

In the title compound, C30H24Cl2N2O3, the two quinoline ring systems are almost planar [maximum deviations = 0.029 (2) and 0.018 (3) angstrom] and the dihedral angle between them is 4.17 (8)degrees. The dihedral angle between the phenyl ring and its attached quinoline ring is 69.06 (13)degrees. The packing is stabilized by C-H center dot center dot center dot O, C-H center dot center dot center dot N, weak pi-pi stacking [centroid-centroid distances = 3.7985 (16) and 3.7662(17) angstrom] and C-H center dot center dot center dot pi interactions.

1-[(2-Chloro-7,8-dimethylquinolin-3-yl)methyl]pyridin-2(1H)-one

In the title compound, C17H15ClN2O, the quinoline ring system is nearly planar, with a maximum deviation from the mean plane of 0.074 (2) angstrom, and makes a dihedral angle of 81.03 (7)degrees with the pyridone ring. The crystal packing is stabilized by pi-pi stacking interactions between the pyridone and benzene rings of the quinoline ring system [centroid-centroid distance = 3.6754 (10) angstrom]. Furthermore, weak intermolecular C-H center dot center dot center dot O hydrogen bonding links molecules into supramolecular chains along [001].

Approaches to sesquiterpenes containing three contiguous quaternary carbon atoms. Synthesis of 3-methoxythapsene

Synthetic approach to 3-alkoxythapsane, comprising of the carbon framework of a small group of sesquiterpenes containing three contiguous quaternary carbon atoms has been described. A combination of alkylation, orthoester Claisen rearrangement and intramolecular diazoketone cyclopropanation has been employed for the creation of the three requisite contiguous quaternary carbon atoms.

Monoclinic polymorph of Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe(anhydrous). Parallel packing of 3(10)-/alpha-helices and a transition of helix type

The structures of two crystal forms of Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe have been determined. The triclinic form (P1, Z = 1) from DMSO/H2O crystallizes as a dihydrate (Karle, Sukumar & Balaram (1986) Proc, Natl, Acad. Sci. USA 83, 9284-9288). The monoclinic form (P2(1), Z = 2) crystallized from dioxane is anhydrous. The conformation of the peptide is essentially the same in both crystal system, but small changes in conformational angles are associated with a shift of the helix from a predominantly alpha-type to a predominantly 3(10)-type. The r.m.s. deviation of 33 atoms in the backbone and C beta positions of residues 2-8 is only 0.29 A between molecules in the two polymorphs. In both space groups, the helical molecules pack in a parallel fashion, rather than antiparallel. The only intermolecular hydrogen bonding is head-to-tail between helices. There are no lateral hydrogen bonds. In the P2(1) cell, a = 9.422(2) A, b = 36.392(11) A, c = 10.548(2) A, beta = 111.31(2) degrees and V = 3369.3 A for 2 molecules of C60H97N11O13 per cell.

Chain structures in alkali metal borophosphates: synthesis and characterization of K3[BP3O9(OH)3] and Rb3[B2P3O11(OH)2]

Two new alkali metal borophosphates, K-3[BP(3)o(9)(OH)(3)] and Rb-3[B2P3O11(OH)(2)], were synthesized by applying solvothermal techniques using ethanol as solvent. The crystal structures were solved by means of single-crystal X-ray diffraction (K-3[BP3O9(OH)(3)], monoclinic, C2/c (No. 15), a = 2454.6(8) pm, b = 736.3(2) pm, c = 1406.2(4) pm, beta = 118.35(2)degrees, Z = 8; Rb-3[B2P3O11(OH)(2)], monoclinic, P2(1)/c (No. 14), a = 781.6(2) pm, b:= 667.3(2) pm, c = 2424.8(5) pm, beta = 92.88(1)degrees, Z = 4). Both crystal structures comprise borophosphate chain anions. While for the rubidium compound a loop-branched chain motif is found as common for most of the chain anions in alkali metal borophosphates, the crystal structure of the potassium phase comprises the first open-branched chain with the highest phosphate content found so far in this group of compounds. Both chain anions are Closely related to known anhydrous or hydrated phases, and the structural relations are discussed in terms of how the presence of OH groups and hydrogen bonds as well as number, charge, and size of charge balancing cations influence the 3D structural arrangement. The anionic entities are classified in terms of general principles of structural systematics for borophosphates.

Hybrid peptide hairpins containing alpha- and omega-amino acids: Conformational analysis of decapeptides with unsubstituted beta-, gamma-, and delta-residues at positions 3 and 8

The effects of inserting unsubstituted omega-amino acids into the strand segments of model beta-hairpin peptides was investigated by using four synthetic decapeptides, Boc-Lcu-Val-Xxx-Val-D-Pro-Gly-Leu-Xxx-Val-Val- OMe: pepticle 1 (Xxx=Gly), pepticle 2 (Xxx=beta Gly=beta hGly=homoglycine, beta-glycine), pepticle 3 (Xxx=gamma Abu=gamma-aminobutyric acid), pepticle 4 (Xxx= delta Ava=delta-aminovaleric acid). H-1 NMR studies (500 MHz, methanol) reveal several critical cross-strand NOEs, providing evidence for P-hairpin conformations in peptides 2-4. In peptide 3, the NMR results support the formation of the nucleating turn, however, evidence for cross-strand registry is not detected. Single-crystal X-ray diffraction studies of peptide 3 reveal a beta-hairpin conformation for both molecules in the crystallographic asymmetric unit, stabilized by four cross-strand hydrogen bonds, with the gamma Abu residues accommodated within the strands. The D-Pro-Gly segment in both molecules (A,B) adopts a type II' beta-turn conformation. The circular dichroism spectrum for peptide 3 is characterized by a negative CD band at 229 rim, whereas for peptides 2 and 4, the negative band is centered at 225 nm, suggesting a correlation between the orientation of the amide units in the strand segments and the observed CD pattern.

N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yI)colcemid, a probe for different classes of colchincine-binding site on tubulin

The nature of binding of 7-nitrobenz-2-oxa-1,3-diazol-4-yl-colcemid (NBD-colcemid), an environment-sensitive fluorescent analogue of colchicine, to tubulin was tested. This article reports the first fluorometric study where two types of binding site of colchincine analogue on tubulin were detected. Binding of NBD-colcemid to one of these sites equilibrates slsowly. NBD-colcemid competes with colchicine for this site. Binding of NBD-colcemid to this site also causes inhibition of tubulin self-assembly. In contrast, NBD-colcemid binding to the other site is characterised by rapid equilibration and lack of competition with colchicine. Nevertheless, binding to this site is highly specific for the cholchicine nucleus, as alkyl-NBD analogues have no significant binding activity. Fast-reaction-kinetic studies gave 1.76 × 105 M–1 s–1 for the association and 0.79 s–1 for the dissociation rate constants for the binding of NBD-colcemid to the fast site of tubulin. The association rate constants for the two phases of the slow site are 0.016 × 10–4 M–1 s–1 and 3.5 × 10–4 M–1 respectively. These two sites may be related to the two sites of colchicine reported earlier, with binding characteristics altered by the increased hydrophobic nature of NBD-colcemid.

Theory of laminar flame propagation with non-normal diffusion.

A study has been made of the problem of steady, one-dimensional, laminar flame propagation in premixed gases, with the Lewis number differing from (and equal to) unity. Analytical solutions, using the method of matched asymptotic expansions, have been obtained for large activation energies. Numerical solutions have been obtained for a wide range of the reduced activation temperature parameter (n {geometrically equal to} E/RTb), and the Lewis number δ. The studies reveal that the flame speed eigenvalue is linear in Lewis number for first order and quadratic in Lewis number for second order reactions. For a quick determination of flame speeds, with reasonable accuracy, a simple rule, expressing the flame speed eigenvalue as a function of the Lewis number and the centroid of the reaction rate function, is proposed. Comparisons have been made with some of the earlier works, for both first and second order reactions.

Transformation reactions of α-pinene—I : Reactions of ethyl (−)-2,2-dimethyl-3-ketocyclobutyl acetate

Some transformation reactions of α-pinene to give 4- and 3-membered ring compounds, not hitherto obtained from this source, are described. The study furnished a convenient method of preparation of the optically active cyclobutanone IVa, the title compound which served as the key substrate for all the transformations reported.