Structure of N-tert-butyloxycarbonyl-[alpha]-aminoisobutyryl-DL-pipecolyl-[alpha]-aminoisobutyric acid methyl ester

C20H35N3O6 (Boc-Aib-DL-Pip-Aib-OMe, Boc = tert-butyloxycarbonyl, Aib = alpha-aminoisobutyric acid, Pip = pipecolic acid, OMe = methoxy), M(r) = 413.5, monoclinic, P2(1)/c, a = 18.055 (3), b = 15.048 (3), c = 17.173 (3) angstrom, beta = 91.7 (1)-degrees, V = 4663.8 (9) angstrom3, Z = 8, D(m) = 1.16, D(x) = 1.178 Mg m-3, lambda(Mo Kalpha) = 0.71069 angstrom, mu = 0.081 mm-1, F(000) = 1792, T = 297 K. The final R value for 4925 [I greater-than-or-equal-to 3sigma(I)] reflections is 0.065 (wR = 0.067). The peptide backbone of the two independent molecules in the asymmetric unit is folded at the -Aib-Pip- sequence to form a type-I (I') beta-bend stabilized by a 1 <-- 4 intramolecular N-H...O=C hydrogen bond between the Aib(3) peptide N-H and Boc urethane C=O groups.

Solid-state photobehaviour and crystal packing of o-chlorobenzylidene-DL-piperitone: influence of molecular topology on photobehaviour

C17H19ClO, M(r) = 274.7, triclinic, P1BAR, a = 11.154 (3), b = 12.685 (2), c = 12.713 (2) angstrom, alpha = 100.68 (1), beta = 113.58 (1), gamma = 104.50 (2)-degrees, V = 1511.1 (6) angstrom3, Z = 4, D(m) = 1.22, D(x) = 1.215 Mg m-3, Cu K-alpha, lambda = 1.5418 angstrom, mu = 2.16 mm-1, F(000) = 584, T = 293 K, R = 0.057 for 3481 observed reflections. The title compound is photostable in the crystalline state and lattice-energy calculations have been employed to rationalize the photobehaviour. The well-known beta-steering ability of the chloro group is not operative in this system as there are no Cl...Cl interactions in the crystal lattice. All five benzylidene-DL-piperitone structures so far studied are alpha-packed and the molecular topology appears to be a deciding factor even in the presence of steering groups.

Register Allocation and Optimal Spill code Scheduling in Software Pipelined Loops using 0-1 Integer Linear Programming Formulation

In achieving higher instruction level parallelism, software pipelining increases the register pressure in the loop. The usefulness of the generated schedule may be restricted to cases where the register pressure is less than the available number of registers. Spill instructions need to be introduced otherwise. But scheduling these spill instructions in the compact schedule is a difficult task. Several heuristics have been proposed to schedule spill code. These heuristics may generate more spill code than necessary, and scheduling them may necessitate increasing the initiation interval. We model the problem of register allocation with spill code generation and scheduling in software pipelined loops as a 0-1 integer linear program. The formulation minimizes the increase in initiation interval (II) by optimally placing spill code and simultaneously minimizes the amount of spill code produced. To the best of our knowledge, this is the first integrated formulation for register allocation, optimal spill code generation and scheduling for software pipelined loops. The proposed formulation performs better than the existing heuristics by preventing an increase in II in 11.11% of the loops and generating 18.48% less spill code on average among the loops extracted from Perfect Club and SPEC benchmarks with a moderate increase in compilation time.

Adlayer Structures of DL-Homocysteine and L-Homocysteine Thiolactone on Au(111) Surface: an in situ STM Study

The adsorption Of DL-homocysteine (Hcy) and L-homocysteine thiolactone (HTL) on Au(1 1 1) electrode was investigated in 0.1 M HClO4 by cyclic voltammetry and in situ scanning tunneling microscopy (STM). Hcy and HTL molecules formed highly ordered adlayers on Au(1 1 1) surface. High-resolution STM images revealed the orientation and packing arrangement in the ordered adlayers. Hcy molecules formed (2root3 x 3root3)R30degrees adlayer structure and H-bonds between carboxyl groups were assumed to be responsible for the origin of tail-to-tail or head-to-head molecular arrangement, while HTL molecules formed (4 x 6) adlayer structure, and two different orientations and appearances in the ordered adlayer were found. Structural models were proposed for the two adlayers.

Aperfeiçoamentos no DL nº 167/67 : emolumentos extrajudiciais e garantias reais em Cédulas de Crédito Rural-CCR e em Cédulas de Crédito Bancário-CCB

Consultoria de Orçamento e Fiscalização Financeira.

Arte e industria. Influencia de las formas industriales en el arte del siglo XX (1.900-1.945)

533 p. : il.

Copolimerização de 1,3-butadieno e alfa-olefinas com catalisadores à base de versatato de neodímio

Nesta Dissertação, foram realizadas reações de copolimerização de 1,3-butadieno com diferentes alfa-olefinas (1-hexeno, 1-octeno e 1-dodeceno) utilizando-se um sistema catalítico do tipo Ziegler-Natta ternário constituído por versatato de neodímio, hidreto de diisobutilalumínio e cloreto de t-butila. O sistema catalítico também foi avaliado em reações de homopolimerização com cada alfa-olefina. As condições reacionais, tanto da síntese do catalisador como das reações de polimerização, foram mantidas constantes. Foi estudada a influência de diferentes teores de cada alfa-olefina (1, 3, 5, 10, 20 e 30 % em relação ao 1,3-butadieno) sobre a conversão da polimerização, a microestrutura, a massa molar, as propriedades viscosimétricas e a estabilidade térmica dos polímeros obtidos. Foi avaliada, ainda, a influência do tamanho da cadeia da alfa-olefina sobre as características da polimerização. Os polímeros foram caracterizados por espectroscopia na região do infravermelho (FTIR), cromatografia por exclusão de tamanho (SEC), viscosimetria capilar e termogravimetria (TG). A microestrutura dos polímeros, praticamente, não variou com a adição das alfa-olefinas. A massa molar numérica média (Mn) não sofreu alterações significativas, enquanto que a massa molar ponderal média (Mw) apresentou tendência ao aumento, quanto maior foi a incorporação de comonômero. A viscosidade intrínseca não apresentou uma tendência com a adição da alfa-olefina na reação, permanecendo na faixa de 2,015 a 3,557 dL/g. A estabilidade térmica do copolímero mostrou uma tendência a aumentar com a incorporação das alfa-olefinas

The structure elucidation of a proposed intermediate in the stereoselective synthesis of dl-desoxypodocarpic acid

The hydroxyketone C-3, an intermediate in the stereo-selective total synthesis of dl-Desoxypodocarpic acid (ii), has been shown by both degradative and synthetic pathways to rearrange in the presence of base to diosphenol E-1 (5-isoabietic acid series). The exact spatial arrangements of the systems represented by formulas C-3 and E-1 have been investigated (as the p-bromobenzoates) by single-crystal X-ray diffraction analyses. The hydroxyketone F-1, the proposed intermediate in the rearrangement, has been synthesized. Its conversion to diosphenol E-1 has been studied, and a single-crystal analysis of the p-bromobenzoate derivative has been performed. The initially desired diosphenol C-6 has been prepared, and has been shown to be stable to the potassium t-butoxide rearrangement conditions. Oxidative cleavage of diosphenol E-1 and subsequent cyclization with the aid of polyphosphoric acid has been shown to lead to keto acid I-2 (benzobicyclo [3.3.1] nonane series) rather than keto acid H-2 (5-isoabietic acid series).

Polyimides Derived from 1,4-Bis [3-oxy-(N-aminophthalimide)] Benzene

A novel diamine, 1,4-bis [3-oxy-(N-aminophthalimide)] benzene (BOAPIB), was synthesized from 1,4-bis [3-oxy-(N-phenylphthalimide)] benzene and hydrazine. Its structure was determined via IR, H-1 NMR, and elemental analysis. A series of five-member ring, hydrazine-based polyimides were prepared from this diamine and various aromatic dianhydrides via one-step polycondensation in p-chlorophenol. The inherent viscosities of these polyimides were in the range of 0.17-0.61 dL/g. These polymers were soluble in polar aprotic solvents and phenols at room temperature. Thermogravimetric analysis (TGA) showed that the 5% weight-loss temperatures of the polyimides were near 450 degrees C in air and 500 degrees C in nitrogen. Dynamic mechanical thermal analysis (DMTA) indicated that the glass-transition temperatures (T(g)s) of these polymers were in the range of 265-360 degrees C. The wide-angle X-ray diffraction showed that all the polyimides were amorphous.

Synthesis and chirooptical properties of optically active poly(ester imide)s based on axially asymmetric 1,1 '-binaphthyls

A series of optically active poly(ester imide)s (PEsI's) has been synthesized by the polycondensation reactions of new axially asymmetric dianhydrides, that is, (R)-2,2'-bis(3,4-dicarboxybenzoyloxy)-1,1'-binaphthyl dianhydride and (S)-2,2'-bis(3,4-dicarboxybenzoyloxy)-1,1'-binaphthyl dianhydride, and various diamines with aromatic, semiaromatic, and aliphatic structures. The polymers have inherent viscosities of 0.45-0.70 dL/g, very good solubility in common organic solvents, glass-transition temperatures of 124-290 degreesC, and good thermal stability. Wide-angle X-ray crystallography of these polymers shows no crystal diffraction. In comparison with model compounds, an enhanced optical rotatory power has been observed for the repeat unit of optically active PEsI's based on aromatic diamines, and it has been attributed to a collaborative asymmetric perturbation of chiral 1,1'-binaphthyls along the rigid backbones.

Synthesis and characterization of hyperbranched poly(ester-amide)s based on gallic acid and DL-2-aminobutyric acid

A novel AB(3)-type monomer was prepared from gallic acid and DL-2-aminobutyric acid, and used for the synthesis of the biocompatible hyperbranched poly(ester-amide)s by self-polycondensation. The polymers were characterized via FTIR and NMR spectroscopy and thermal analysis, and the average degree of branching of the polymers was estimated to be 0.75. The polymers with abundant acetyl end groups were found to be amorphous with lower intrinsic viscosity, better thermal stability and excellent solubility.

Aromatic poly(ester imide)s and poly(amide imide)s having 1,1 '-binaphthyl-2,2 '-diyls in the main chain

Full Paper: Two new 1,1'-binaphthyl-2,2'-diyl-based dianhydrides, i.e., 2,2'-bis(3,4-dicarboxybenzamido)-1,1'-binaphthyl dianhydride (BNDADA) and 2,2'-bis(3,4-dicarboxybenzoyloxy)-1,1'-binaphthyl dianhydride (BNDEDA), were synthesized and polymerized with various aromatic diamines to afford polyimides through the traditional two-step method. The polyimides with inherent viscosities ranging from 0.27 to 0.70 dl . g(-1) showed excellent solubilities in polar solvents such as DMAc, DMSO and NMP etc., except of the poly(ester imide) prepared from BNDEDA and benzidine. Poly(ester imide)s based on BNDEDA can also be readily dissolved in weakly polar solvents such as THF, CH2Cl2 and CHCl3. The glass transition temperatures of these polyimides are in the range of 210-310 degrees C; the 5% weight loss temperatures are in the range of 390-465 degrees C in nitrogen and 384-447 degrees c in air. These polymers from light yellow, tough films that were transparent above 365 nm. The effects of different flexible units attached in the 2- and 2'-positions, i.e., amide, ester and ether, on the properties of the polyimides obtained are discussed.

Polyimides from 3,3 '-dioxo-[1,1 ']-spirodiphthalan-5,5 ',6,6 '-tetracarboxylic dianhydride

A novel dianhydride, 3,3'-dioxo-[1,1']-spirodiphthalan-5,5',6,6'-tetracarboxlic dianhydride, was synthesized and used as a monomer to prepare polyimides with several diamines via a conventional two-stage procedure. The intermediate poly(amic-acid)s had inherent viscosities of 0.84-1.71 dL/g and could be thermally converted into lightly yellow, transparent, flexible and tough films. Films cast from chemically imidized polyimides were transparent and colorless. The glass transition temperatures (Tg) were > 400 degrees C, and the 5% weight-loss temperatures were > 420 degrees C in N-2 and in air. The solubilities of these polyimides in various solvents were evaluated. The mechanical properties of some polyimides were also tested. (C) 1999 Elsevier Science Ltd. All rights reserved.