Showing papers on "Side chain published in 1988"

Comparing the polarities of the amino acids: side-chain distribution coefficients between the vapor phase, cyclohexane, 1-octanol, and neutral aqueous solution

Abstract: To obtain an indication of the tendencies of amino acids to leave water and enter a truly nonpolar condensed phase, distribution coefficients between dilute solution in water and dilute solution in wet cy- clohexane have been determined for each of the common amino acid side chains at pH 7; they are found to be closely related to the inside-outside distributions of the side chains observed in globular proteins. There was no evidence that excess water enters cyclohexane in association with these solutes. Cyclohexane-to-water distribution coefficients can be combined with vapor-to-water distribution coefficients reported earlier to yield vapor-to-cyclohexane distribution coefficients. Vapor-to-cyclohexane distribution coefficients provide an experimental index of susceptibility to attraction by dispersion forces, and the corresponding free energies are found to be linearly related to side-chain surface areas. Observations using different solvents and variously substituted side chains suggest that alcohols such as 1-octanol exert a specific attraction on the side chain of tryptophan. When less polar phases are used as a reference, leucine, isoleucine, valine, phenylalanine, and methionine are found to be more hydrophobic than tryptophan.

Contribution of hydrophobic interactions to protein stability.

Abstract: A major factor in the folding of proteins is the burying of hydrophobic side chains. A specific example is the packing of alpha-helices on beta-sheets by interdigitation of nonpolar side chains. The contributions of these interactions to the energetics of protein stability may be measured by simple protein engineering experiments. We have used site-directed mutagenesis to truncate hydrophobic side chains at an alpha-helix/beta-sheet interface in the small ribonuclease from Bacillus amyloliquefaciens (barnase). The decreases in stability of the mutant proteins were measured by their susceptibility to urea denaturation. Creation of a cavity the size of a -CH2-group destabilizes the enzyme by 1.1 kcal mol-1, and a cavity the size of three such groups by 4.0 kcal mol-1.

Structure of the lambda complex at 2.5 A resolution: details of the repressor-operator interactions.

Abstract: The crystal structure of a complex containing the DNA-binding domain of lambda repressor and a lambda operator site was determined at 2.5 A resolution and refined to a crystallographic R factor of 24.2 percent. The complex is stabilized by an extensive network of hydrogen bonds between the protein and the sugar-phosphate backbone. Several side chains form hydrogen bonds with sites in the major groove, and hydrophobic contacts also contribute to the specificity of binding. The overall arrangement of the complex is quite similar to that predicted from earlier modeling studies, which fit the protein dimer against linear B-form DNA. However, the cocrystal structure reveals important side chain-side chain interactions that were not predicted from the modeling or from previous genetic and biochemical studies.

Characterization of individual tryptophan side chains in proteins using Raman spectroscopy and hydrogen-deuterium exchange kinetics

Abstract: Two Raman bands at 880 and 1350 cm/sup -1/ of tryptophan (Trp) side chains have been found useful in structural studies of the side chains in proteins. The frequency of the 880-cm/sup -1/ band reflects the strength of H bonding at the N/sub 1/H site of the indole ring: the lower the frequency is, the stronger the H bonding is. The intensity of the 1360-cm/sup -1/ band, on the other hand, is a marker of the hydrophobicity of the environment of the indole ring: particularly strong in hydrophobic environments. It is also demonstrated that a combination of stepwise deuteriation of the tryptophan side chains and difference spectrum techniques is useful to observe these marker bands due to each side chain separately. The states of six tryptophans in lysozyme revealed by the Raman spectroscopic method in solution are compared with those by X-ray diffraction in crystal. The Raman data on the outer four Trp's are consistent with the X-ray structure, whereas significant differences between solution and crystal are suggested for the strength of H bonding of the most and second most buried Trp's. Characterization of four Trp's in ..cap alpha..-lactalbumin shows that the two outer Trp's are moderately H bonded tomore » solvent water and closely surrounded by aliphatic side chains while the inner two are not H bonded nor closely surrounded by aliphatic side chains.« less

Asymmetric synthesis catalyzed by chiral ferrocenylphosphine-metal complexes

Abstract: Optically active ferrocenylphosphines containing, on the side chain, hydroxy group appropriately distant from the ferrocene nucleus have been found to be effective ligands for the palladium-catalyzed asymmetric allylic alkylation of 1,3-disubstituted 2-propenyl acetates with sodium acetylacetonate and related soft carbon nucleophiles to give the alkylation products of up to 96% ee. chiral ferrocenylphosphines which have tertiary amines on the side chain have been found to catalyze the reaction of methyl isocyanoacetate with aldehydes in dichloromethane to give optically active trans-4-methoxy- carbonyl-5-alkyl-2-oxazolines with high enantioselectivity (up to 98% ee) in a quantitative yield.

Crystal structure of the cytokine interleukin-1 beta.

Abstract: The crystal structure of human recombinant interleukin-1 beta has been determined at 3.0 A resolution by the isomorphous replacement method in conjunction with solvent flattening techniques. The model prior to refinement has a crystallographic R-factor of 42.3%. The structure is composed of 12 beta-strands forming a complex network of hydrogen bonds. The core of the structure can best be described as a tetrahedron whose edges are each formed by two antiparallel beta-strands. The interior of this structure is filled with hydrophobic side chains. There is a 3-fold repeat in the folding of the polypeptide chain. Although this folding pattern suggests gene triplication, no strong internal sequence homology between topologically corresponding residues exists. The folding topology of interleukin-1 beta is very similar to that described by McLachlan (1979) J. Mol. Biol., 133, 557-563, for soybean trypsin inhibitor.

Polymer electrolyte complexes of LiCIO4 and comb polymers of siloxane with oligo‐oxyethylene side chains

Abstract: Polysiloxanes with oligo-oxyethylene side chains of the type —O(CH2CH2O)7CH3 and —(CH2)3O(CH2CH2O)nCH3 (average n ≈ 7 and 11) were synthesized from poly(hydrogenmethylsiloxane) and characterized by 1H n.m.r., 29Si n.m.r., i.r. and g.p.c. Cyclic analogues were used as model compounds and synthesized from tetramethylcyclotetrasiloxane. Polymer electrolyte complexes were made from the comb polymers and LiClO4 by solvent-casting from THF, and their conductivities measured as a function of temperature and studied by differential scanning calorimetry and correlated with their conductivity behaviour. Maximum conductivities close to 10−4S cm−1 were achieved at room temperature and at ethylene oxide units to Li+ ratios of about 25. Cross-linking or blending with high molecular weight poly(oxyethylene) lowers the conductance somewhat but vastly improves the mechanical properties of the complexes, and the blends with PEO can be cast into thin, flexible and tough films with good conducting properties.

Role of the Hydrophobia Amino Acid Residue in the Bitterness of Pep tides

Abstract: In order to investigate the role of the side chain of amino acids in the bitterness in peptide, someioligopeptides containing glycine, alanine, aminobutyric acid, valine, isoleucine, norvaline (n-Val) and norleucine (n-Leu) were synthesized and their tastes were evaluated. For the bitter taste to be exhibited, the side chain skeleton of the amino acid should consist of at least three carbons. The peptides consisting of amino acids having a side chain of less than three carbons did not exhibit bitterness, while the peptides consisting of amino acids having a side chain of more than three carbons did exhibit bitterness. Valine exhibited an intermediate feature, the taste of valine peptides varying dependent upon the structure. The difference of the branching structure in side chains was less concerned with peptide bitterness.

Benzothiopyranoindazoles, a new class of chromophore modified anthracenedione anticancer agents. Synthesis and activity against murine leukemias.

Abstract: The synthesis of the benzothiopyranoindazoles, a new class of chromophore modified anthracenediones related to mitoxantrone, is described In this structural class the quinone moiety, which is believed to be responsible for the cardiotoxicity of the anthracyclines, has been designed out The synthesis of the benzothiopyranoindazoles was carried out by a multistep sequence from requisite 1-chloro-4-nitro-9H-thioxanthen-9-one precursors Reaction with a monoalkylhydrazine gave a 5-nitrobenzothiopyranoindazole adduct, which was catalytically reduced to a corresponding C-5 anilino intermediate Alkylation of 7 with a requisite X(CH2)nNR1R2 (X = Cl, Br; R1, R2 = H, alkyl, acyl; n = 2,3) provided target "two-armed" benzothiopyranoindazoles or A-ring methoxy and/or side chain acyl intermediates, which could be converted to 3 by appropriate deprotection methodologies Alternatively, certain target compounds 3 were synthesized by reaction of 7 with appropriately functionalized glycine precursors under Schotten-Bauman or BOP chloride condensation conditions to provide C-5 acylamino intermediates, followed by Red-Al reduction and deprotection steps Described also is the synthesis of selected benzothiopyranoindazole congeners with proximal acylamino side chains at C-5 and B-ring sulfone functionality at S-6 Potent activity was demonstrated against murine L1210 leukemia in vitro (IC50 = 10(-7)-10(-9) M) as well as against P388 leukemia in vivo over a wide range of structural variants In general, activity against the P388 line was maximized by (a) a basic side chain at N-2 and a dibasic side chain at C-5 with primary or secondary distal amine substitution, (b) certain patterns of A-ring hydroxylation with 8-OH and 9-OH most favorable, and (c) sulfide oxidation state at S-6 Besides having curative activity against the P388 line, the more active compounds were curative against murine B-16 melanoma in vivo On the basis of their exceptional broad-spectrum in vivo anticancer activity, selected compounds in this series have been chosen for development toward clinical trials

Unusual Property in a Novel L-C Side Chain Polysiloxane Series

Abstract: A new series of polymethylsiloxanes with laterally grafted mesogens has been synthesized. For compounds with short spacers, the diamagnetic anisotropy variations in the nematic state present an anomaly which suggests a nematic-nematic transition.

Group contribution analysis of the damping behavior of homopolymers, statistical copolymers, and interpenetrating polymer networks based on acrylic, vinyl, and styrenic mers

Abstract: : The integral of the loss modulus versus temperature plots in the vicinity of the glass transition temperature (loss area, LA) was characterized for various homopolymers, statistical copolymers and interpenetrating polymer networks, (IPN's), based on acrylics, vinyls, and styrenic mers. The quantity LA was found to be a molecular characteristic, governed by the structure of the individual mers. The Loss area of both IPN's and statistical copolymers obeys an additive relation of the component polymers. A group contribution analysis for LA was developed, in which each moiety contributes a specific value to LA. A table derived via this group contribution analysis permits the prediction of LA values. The results show that backbone motions and the moieties attached directly to the backbone contribute the most to the damping peak, and that long side chains act as diluents. Keywords: Methacrylic, Molecular weight, Infrared spectroscopy, Crosslinking(Chemistry), Polystyrene, Mechanical spectroscopy.

Control of the Discotic to Isotropic Transition in Alkoxy-Substituted Silicondihydroxo-Phthalocyanines by Axial Substituents

Abstract: The synthesis of a homologous series of octaalkoxy-substituted silicondihydroxo-phthalocyanines is described. The mesomorphic properties of these new materials were studied by DSC, optical microscopy and X-ray investigations. Compounds with n ≤ 4 (n is the number of carbon atoms in a single alkoxy side chain) show a discotic mesophase transition. A transition to the isotropic state is only observed when n ≤ 8. X-ray diffraction patterns of the mesophases confirm that all compounds form a hexagonal columnar mesophase of the type Dhd.

Dynamic properties of gramicidin A in phospholipid membranes.

Abstract: The flexibility of the tryptophan side chains of gramicidin A and the rotational diffusion of the peptide in methanolic solution and in three membrane systems were studied with deuterium nuclear magnetic resonance (NMR). Gramicidin A was selectively deuterated at the aromatic ring systems of its four tryptophan side chains. In methanolic solution, the tryptophan residues remained immobile and served as a probe for the overall rotation of the peptide. The experimentally determined rotational correlation time of tau c = 0.6 X 10(-9) s was consistent with the formation of gramicidin A dimers. For gramicidin A incorporated into bilayer membranes, quite different results were obtained depending on the chemical and physical nature of the lipids employed. When mixed with 1-palmitoyl-sn-glycero-3-phosphocholine (LPPC) at a stoichiometric lipid:peptide ratio of 4:1, gramicidin A induced the formation of stable bilayer membranes in which the lipids were highly fluid. In contrast, the gramicidin A molecules of this membrane remained completely static over a large temperature interval, suggesting strong protein-protein interactions. The peptide molecules appeared to form a rigid two-dimensional lattice in which the interstitial spaces were filled with fluidlike lipids. When gramicidin A was incorporated into bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) above the lipid phase transition, the deuterium NMR spectra were motionally narrowed, indicating large-amplitude rotational fluctuations. From the measurement of the quadrupole echo relaxation time, a rotational correlation time of 2 X 10(-7) s was estimated, leading to a membrane viscosity of 1-2 P if the rotational unit was assumed to be a gramicidin A dimer. (ABSTRACT TRUNCATED AT 250 WORDS)

Influence of the chemical constitution of the polymer backbone on the phase behaviour of liquid‐crystalline side‐chain polymers with side‐on fixed mesogenic groups

Abstract: The synthesis and phase behaviour of liquid-crystalline acrylates and chloroacrylates with side-on fixed mesogenic groups are described. Polymers which have similar mesogenic groups but whose polymer backbones differ in chemical constitution exhibit identical liquid-crystalline to isotropic phase transformation temperatures (Tc). The glass transition temperature (Tg) decreases with increasing flexibility of the main chain and with increasing length of the terminal groups of the mesogenic side groups. All polymers with side-on fixed mesogenic groups exhibit a nematic phase. The domain texture indicates biaxial nematic phase behaviour. In copolymers consisting of mesogenic and non-mesogenic monomers, nematic phase behaviour is still observed, Tc is strongly depressed, and Tg is similar to that of the non-mesogenic homopolymer.

Binding of unfused aromatic cations to DNA. The influence of molecular twist on intercalation

Abstract: A new type of intercalator, 1, and its nonintercalating analogue, 2, are both twisted about the torsional bonds joining the aromatic rings. Spectroscopic methods and MM2 calculations indicate that the twist for 2 is significantly greater than for 1 (48° versus 25° from MM2) in solution. X-ray crystallographic analysis indicates that the torsional angles are 10° and 19° for the two phenyl-pyrimidine plane intersections in 1. The DNA binding constant for 1 is similar to those for other strong intercalators, and viscometric, flow dichroism, and NMR experiments (nonexchangeable protons of 1, imino proton, and 31P spectra of DNA in the complex) indicate that 1 binds to DNA by intercalation. The binding constant for 2 is less than that for 1, and viscosity, dichroism, and NMR experiments demonstrate that 2 does not intercalate. The structure of 1, with a twisted aromatic system and terminal basic functions, is analogous to many groove-binding compounds, and it is, thus, unexpected that 1 forms a strong intercalation complex with DNA. The twist of 1 may complement or enhance the intrinsic propeller twist of DNA base pairs to allow intercalation. Molecular mechanics methods located two potential low-energy intercalation conformations of 1 at the CG intercalation site of the hexamer d(TACGTA). A straddling model with one side chain of 1 in each groove of DNA was rejected on kinetic grounds. The other low-energy conformation, and the one that agrees best with the experimental results, has both cationic substituents of 1 in the major groove with partial stacking of the three unfused rings with the base pairs at the intercalation site. A similar binding geometry of 1 in the minor groove was not feasible due to numerous unfavorable close contacts between the cationic groups and the DNA atoms in the minor groove. With 2 the intrinsic molecular twist is larger, and it does not form an intercalation complex. The bleomycin amplification activity of 1 is significantly greater than that for 2. © 1988 American Chemical Society.

Synthesis of a novel amphiphilic porphyrin carrying water-soluble polyether side chains of controlled chain length. Formation of a cofacial molecular assembly in aqueous media

Abstract: A novel amphiphilic porphyrin carrying poly(oxyethylene) side chains of controlled chain length was obtained by polymerization of epoxyethane initiated by an aluminium porphyrin [(5,10,15,20-tetraphenylporphyrinato)-aluminium chloride] in the presence of a porphyrin with phenolic substituents [5,10,15,20-tetrakis(4′-hydroxyphenyl)porphyrin], and was found to form cofacial aggregates spontaneously in aqueous media.

Studies on the effect of stigmatellin derivative on cytochrome band the Rieske iron‐sulfur cluster of cytochrome c reductase from bovine heart mitochondria.

Abstract: Stimatellin and its derivatives represent a third class of Q0 site inhibitor beside the hydroxyquinone derivatives and the E-β-methoxyacrylate (MOA) inhibitor [von Jagow and Link (1986) Method Enzymol 126., 253-271]. The stigmatellins consist of a chromone ring system connected to an substituted alkenyl side chain. Alteration in the side chain, i.e. saturation of the C=C double bonds, shift of methoxy group or loss of the methyl group, specifically affect the binding characterstics. Besides changing the red shift spectrum of reduced cytochrome b566 and the ERR spectrum of the Rieske iron- sulfur clusterm, the side chain alteration diminish the binding affnity and the extent of the midpoint potential shift of the iron-sulfur protein. Thus, the side chin of the molecule makes an essentils contribution to the binding energy and is hot necessary solely for partitioning the molecule into the hydrophobic phase, as assumed so far.

Effects of molecular weight distribution on the thermal properties of side-chain liquid crystalline poly(vinyl ether)s.

Abstract: Effects of Molecular Weight Distribution on the Thermal Properties of Side-Chain Liquid Crystalline Poly(vinyl ether)s

Main-chain flexibility and side-chain crystallization of widely spaced comb-like polymers

Abstract: Widely spaced comb-like polymers in which teeth (alkyl side-chains) appear on every four main-chain carbon atoms were synthesized as copolymers of styrene, or α-methylstyrene with alkyl acrylates, alkyl methacrylates, or dialkyl itaconates. Alkyl groups were dodecyl, tetradecyl, hexadecyl, and octadecyl. The long alkyl side-chains of these comb-like polymers crystallized as in conventional comb-like polymers but the extent of crystallization varied with cumulative substitution of phenyl and methyl groups on the copolymer main-chains. This is due to the influence of these substituents on the flexibility of the main-chain.

Molecular dynamics and macroscopic alignment properties of thermotropic liquid-crystalline side chain polymers as studied by dielectric relaxation spectroscopy

Abstract: It is shown that dielectric relaxation spectroscopy provides a convenient means of studying the anisotropic reorientational dynamics of the mesogenic head groups in thermotropic liquid-crystalline side chain polymers. Their alignment behaviour in directing a.c. electric fields of different amplitudes and frequencies is examined, and samples having a macroscopic alignment which is fully homeotropic, fully planar or any desired intermediate alignment have been prepared. The nature and extent of alignment in such samples has been determined by dielectric spectroscopy. In addition both the temperature and pressure variations of the average dielectric relaxation times for certain relaxation processes have been determined and a bulk alignment phenomenon in the absence of a directing electric field is reported.

The synthesis and characterization of side-chain liquid crystal polymers based on polystyrene and poly-α-methystyrene

Abstract: The polymer analogous synthesis of new liquid-crystalline side-chain polymers having polystyrene and poly-α-methylstyrene backbones bearing pendant azo-benzene mesogenic groups is described. The effects of various spacer lengths on the mesophase types were examined. Several liquid-crystalline copolymers were also prepared and their mesophase types determined.

Structure and Dilution of Mesogenic Side Chains in Liquid Crystalline Polysiloxanes

Abstract: The structure of the smectic phases in four series of homo- and copolymers based on dimethylsiloxane chains with a definite variation of the concentration of the paired mesogenic side chains has been investigated by means of X-ray methods. The dilution of the mesogenic moiety was achieved by insertion of additional dimethylsiloxane segments. A nearly linear dependence of the layer spacings on the dilution has been found. A model of the structure is proposed which consists of two sublayers one of which contains the irregularly arranged main chain whereas the other one is formed by the side chains.

Condensation polymers with pendant side chains exhibiting nonlinear optical response

Abstract: This invention provides novel condensation polymers with pendant side chains which exhibit nonlinear optical response. The polymers have utility as a transparent optical component of optical switch or light modulator devices. An invention polymer is illustrated by a condensation polymer of the following structure: ##STR1##