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Sheet Structure (sheet + structure)
Selected AbstractsInclusion Compounds of L,D-Dipeptide with Small Sulfoxides: Flexible Sheet Structure of (S)-Phenylglycyl-(R)-phenylglycine.CHEMINFORM, Issue 51 2007Motohiro Akazome Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Electrospun Silk Fibroin Mats for Tissue EngineeringENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 3 2008A. Alessandrino Abstract Processing Silk Fibroin (SF) with electrospinning (ES) offers a very attractive opportunity for producing a variety of 2D and 3D matrices with great potential for tissue regeneration and repair due to the superior biocompatibility and mechanical properties of SF. Different combinations of ES parameters were explored to investigate the best experimental set-up related to the dimension and uniformity of the fibers in the electrospun silk fibroin (ES-SF) mats. Using SEM it was found that the ES-SF mats contain uniform fibers with a diameter in the nanometric range obtained by electrospinning a 7.5,% w/v SF solution in formic acid, with an electric field of 2.4,kV/cm and a spinneret-collector distance of 10,cm. FT-IR and DSC analyses were performed to investigate the structure of the ES-SF mats before and after immersion in methanol for different times (5, 10, and 15,min). The methanol treatment was able to promote the crystallization of SF by conformational transition of random coil and other poorly ordered conformations (turns and bends) to the ,-sheet structure. The degree of crystallinity was enhanced as shown by the trend of both the FT-IR crystallinity index and the melting/decomposition peak temperature (from DSC). To study the cytocompatibility of ES-SF mats, tests with L929 murine fibroblasts were carried out. Samples were seeded with the cells and incubated for 1, 3, and 7,days at 37,°C. At each time point, SEM investigations and Alamar blue tests were performed. The SEM images showed cell adhesion and proliferation just after 1,day and cell confluence at 7,days. Alamar blue test demonstrated that there were very low differences between cell viability on ES-SF mats and the tissue culture plastic control. [source] Lipid-induced conformational transition of the amyloid core fragment A,(28,35) and its A30G and A30I mutantsFEBS JOURNAL, Issue 10 2008Sureshbabu Nagarajan The interaction of the ,-amyloid peptide (A,) with neuronal membranes could play a key role in the pathogenesis of Alzheimer's disease. Recent studies have focused on the interactions of A, oligomers to explain the neuronal toxicity accompanying Alzheimer's disease. In our study, we have investigated the role of lipid interactions with soluble A,(28,35) (wild-type) and its mutants A30G and A30I in their aggregation and conformational preferences. CD and Trp fluorescence spectroscopic studies indicated that, immediately on dissolution, these peptides adopted a random coil structure. Upon addition of negatively charged 1,2-dipalmitoyl- syn -glycero-3-phospho- rac -(glycerol) sodium salt (PG) lipid, the wild-type and A30I mutant underwent reorganization into a predominant ,-sheet structure. However, no conformational changes were observed in the A30G mutant on interaction with PG. In contrast, the presence of zwitterionic 1,2-dipalmitoyl- syn -glycero-3-phosphatidylcholine (PC) lipid had no effect on the conformation of these three peptides. These observations were also confirmed with atomic force microscopy and the thioflavin-T assay. In the presence of PG vesicles, both the wild-type and A30I mutant formed fibrillar structures within 2 days of incubation in NaCl/Pi, but not in their absence. Again, no oligomerization was observed with PC vesicles. The Trp studies also revealed that both ends of the three peptides are not buried deep in the vesicle membrane. Furthermore, fluorescence spectroscopy using the environment-sensitive probe 1,6-diphenyl-1,3,5-hexatriene showed an increase in the membrane fluidity upon exposure of the vesicles to the peptides. The latter effect may result from the lipid head group interactions with the peptides. Fluorescence resonance energy transfer experiments revealed that these peptides undergo a random coil-to-sheet conversion in solution on aging and that this process is accelerated by negatively charged lipid vesicles. These results indicate that aggregation depends on hydrophobicity and propensity to form ,-sheets of the amyloid peptide, and thus offer new insights into the mechanism of amyloid neurodegenerative disease. [source] Biophysical characterization of the interaction of high-density lipoprotein (HDL) with endotoxinsFEBS JOURNAL, Issue 23 2002Klaus Brandenburg The interaction of bacterial endotoxins [lipopolysaccharide (LPS) and the ,endotoxic principle' lipid A], with high-density lipoprotein (HDL) from serum was investigated with a variety of physical techniques and biological assays. HDL exhibited an increase in the gel to liquid crystalline phase transition temperature Tc and a rigidification of the acyl chains of the endotoxins as measured by Fourier-transform infrared spectroscopy and differential scanning calorimetry. The functional groups of the endotoxins interacting with HDL are the phosphates and the diglucosamine backbone. The finding of phosphates as target groups is in accordance to measurements of the electrophoretic mobility showing that the zeta potential decreases from ,50 to ,60 mV to ,20 mV at binding saturation. The importance of the sugar backbone as further target structure is in accordance with the remaining negative potential and competition experiments with polymyxin B (PMB) and phase transition data of the system PMB/dephosphorylated LPS. Furthermore, endotoxin binding to HDL influences the secondary structure of the latter manifesting in a change from a mixed ,-helical/,-sheet structure to a predominantly ,-helical structure. The aggregate structure of the lipid A moiety of the endotoxins as determined by small-angle X-ray scattering shows a change of a unilamellar/inverted cubic into a multilamellar structure in the presence of HDL. Fluorescence resonance energy transfer data indicate an intercalation of pure HDL, and of [LPS],[HDL] complexes into phospholipid liposomes. Furthermore, HDL may enhance the lipopolysaccharide-binding protein-induced intercalation of LPS into phospholipid liposomes. Parallel to these observations, the LPS-induced cytokine production of human mononuclear cells and the reactivity in the Limulus test are strongly reduced by the addition of HDL. These data allow to develop a model of the [endotoxin]/[HDL] interaction. [source] The Interest Rate Risk Exposure of Financial Intermediaries: A Review of the Theory and Empirical EvidenceFINANCIAL MARKETS, INSTITUTIONS & INSTRUMENTS, Issue 4 2003By Sotiris K. Staikouras The paper surveys current and previous research on financial institutions' interest rate risk exposure. The implications of such exposure are discussed and motivating insights are emphasized. Various theoretical frameworks and models are presented. For each one an overview of the studies and any relationship to each other is provided. In a cross-industry analysis, other idiosyncratic risk factors are considered and their importance is delineated. A number of empirical relations are established. More specifically, there is an inverse relationship between interest rate changes and common stock returns of financial institutions. The intermediaries' apparent yield sensitivity is mainly attributed to the duration gap inherent in their balance sheet structure. Furthermore, the aforesaid equity sensitivity due to other possible dynamics such as dividend yield, unanticipated inflation and regulatory lags is also considered. Changes in economic regimes have altered volatility in market yields with a subsequent effect, positive or negative, on financial intermediaries' equity returns. The issue of the risk-return compensation is further analyzed, and findings suggest that the interest rate risk is priced by capital markets. Finally, a few other issues are identified as avenues for future research. [source] Interaction of a ,-sheet breaker peptide with lipid membranesJOURNAL OF PEPTIDE SCIENCE, Issue 2 2010Giuseppe Vitiello Abstract Aggregation of ,-amyloid peptides into senile plaques has been identified as one of the hallmarks of Alzheimer's disease. An attractive therapeutic strategy for Alzheimer's disease is the inhibition of the soluble ,-amyloid aggregation using synthetic ,-sheet breaker peptides that are capable of binding A, but are unable to become part of a ,-sheet structure. As the early stages of the A, aggregation process are supposed to occur close to the neuronal membrane, it is strategic to define the ,-sheet breaker peptide positioning with respect to lipid bilayers. In this work, we have focused on the interaction between the ,-sheet breaker peptide acetyl-LPFFD-amide, iA,5p, and lipid membranes, studied by ESR spectroscopy, using either peptides alternatively labeled at the C- and at the N-terminus or phospholipids spin-labeled in different positions of the acyl chain. Our results show that iA,5p interacts directly with membranes formed by the zwitterionic phospholipid dioleoyl phosphatidylcholine and this interaction is modulated by inclusion of cholesterol in the lipid bilayer formulation, in terms of both peptide partition coefficient and the solubilization site. In particular, cholesterol decreases the peptide partition coefficient between the membrane and the aqueous medium. Moreover, in the absence of cholesterol, iA,5p is located between the outer part of the hydrophobic core and the external hydrophilic layer of the membrane, while in the presence of cholesterol it penetrates more deeply into the lipid bilayer. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd. [source] Oligopeptide-mediated helix stabilization of model peptides in aqueous solutionJOURNAL OF PEPTIDE SCIENCE, Issue 2 2003Yoshitaka Maeda Abstract Oligopeptide-mediated helix stabilization of peptides in hydrophobic solutions was previously found by NMR and CD spectroscopic studies. The oligopeptide included the hydrophobic amino acids found in its parent peptide and were interposed by relevant basic or acidic amino acids. The strength of the interactions depended on the amino acid sequences. However, no helix-stabilizing effect was seen for the peptides in phosphate buffer solution, because the peptides assumed a random-coil structure. In order to ascertain whether the helix-stabilizing effect of an oligopeptide on its parent peptide could operate in aqueous solution, model peptides EK17 (Ac-AEAAAAEAAAKAAAAKA-NH2) and IFM17 (Ac-AEAAAAEIFMKAAAAKA-NH2) that may assume an ,-helix in aqueous solutions were synthesized. Interactions were examined between various oligopeptides (EAAAK, KAAAE, EIFMK, KIFME, KIFMK and EYYEE) and EK17 or IFM17 in phosphate buffer and in 80% trifluoroethanol (TFE),20% H2O solutions by CD spectra. EAAAK had little effect on the secondary structures of EK17 in both buffer and TFE solutions, while KAAAE, which has the reverse amino acid sequence of EAAAK, had a marked helix-destabilizing effect on EK17 in TFE. EIFMK and KIFME were found to stabilize the ,-helical structure of EK17 in phosphate buffer solutions, whereas KIFMK and EYYEE destabilized the ,-helical structure of EK17. EIFMK and KIFME had no effect on IFM17, because unexpectedly, IFM17 had appreciable amounts of ,-sheet structure in buffer solution. It was concluded that in order for the helix-stabilizing effects to operate effectively, the following factors should be satisfied: (1) the model peptide, the ,-helical conformation of which is to be stabilized, should essentially assume an ,-helical structure by nature, and (2) the hydrophobicity of the side-chains of the oligopeptide should be high enough for the oligopeptide to perform stable specific side chain,side chain intermolecular hydrophobic interactions with the model peptide. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd. [source] Vibrational Spectroscopic Studies on the Disulfide Formation and Secondary Conformational Changes of Captopril,HSA Mixture after UV-B IrradiationPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2005Mei-Jane Li ABSTRACT The effects of pH and ultraviolet-B (UV-B) irradiation on the secondary structure of human serum albumin (HSA) in the absence or presence of captopril were investigated by an attenuated total reflection (ATR)/Fourier transform infrared (FTIR) spectroscopy. The UV-B exposure affecting the stability of captopril before and after captopril,HSA interaction was also examined by using confocal Raman microspectroscopy. The results indicate that the transparent pale-yellow solution for captopril,HSA mixture in all pH buffer solutions, except pH 5.0,7.0, changed into a viscous form then a gel form with UV-B exposure time. The secondary structural transformation of HSA in the captopril,HSA mixture with or without UV-B irradiation was found to shift the maxima amide I peak in IR spectra from 1652 cm,1 assigned to ,-helix structure to 1622 cm,1 because of a ,-sheet structure, which was more evident in pH 3.0, 8.0 or 9.0 buffer solutions. The Raman shift from 1653 cm,1 (,-helix) to 1670 cm,1 (,-sheet) also confirmed this result. Captopril dissolved in distilled water with or without UV-B irradiation was determined to form a captopril disulfide observed from the Raman spectra of 512 cm,1, which was exacerbated by UV-B irradiation. There was little disulfide formation in the captopril,HSA mixture even with long-term UV-B exposure, but captopril might interact with HSA to change the protein secondary structure of HSA whether there was UV-B irradiation or not. The pH of the buffer solution and captopril,HSA interaction may play more important roles in transforming the secondary structure of HSA from ,-helix to ,-sheet in the corresponding captopril,HSA mixture than UV-B exposure. The present study also implies that HSA has the capability to protect the instability of captopril in the course of UV-B irradiation. In addition, a partial unfolding of HSA induced by pH or captopril-HSA interaction under UV-B exposure is proposed. [source] Structural stability and heat-induced conformational change of two complement inhibitors: C4b-binding protein and factor HPROTEIN SCIENCE, Issue 5 2004Lena Kask C4BP, C4b-binding protein; FH, factor H; CCP, complement control protein; CD, circular dichroism; FTIR, Fourier transform-infrared spectroscopy; PT, prothrombin; VCP, vaccinia virus complement control protein Abstract The complement inhibitors C4b-binding protein (C4BP) and factor H (FH) both consist of complement control protein (CCP) domains. Here we examined the secondary structure of both proteins by circular dichroism and Fourier-transform infrared technique at temperatures ranging from 30°C,90°C. We found that predominantly ,-sheet structure of both proteins was stable up to 70°C, and that a reversible conformational change toward ,-helix was apparent at temperatures ranging from 70°C to 90°C. The ability of both proteins to inhibit complement was not impaired after incubation at 95°C, exposure to extreme pH conditions, and storage at room temperature for several months. Similar remarkable stability was previously observed for vaccinia virus control protein (VCP), which is also composed of CCP domains; it therefore seems to be a general property of CCP-containing proteins. A typical CCP domain has a hydrophobic core, which is wrapped in ,-sheets and stabilized by two disulphide bridges. How the CCP domains tolerate harsh conditions is unclear, but it could be due to a combination of high content of prolines, hydrophobic residues, and the presence of two disulphide bridges within each domain. These findings are of interest because CCP-containing complement inhibitors have been proposed as clinical agents to be used to control unwanted complement activation that contributes to many diseases. [source] The role of irregular unit, GAAS, on the secondary structure of Bombyx mori silk fibroin studied with 13C CP/MAS NMR and wide-angle X-ray scatteringPROTEIN SCIENCE, Issue 8 2002Tetsuo Asakura Abstract Bombyx mori silk fibroin is a fibrous protein whose fiber is extremely strong and tough, although it is produced by the silkworm at room temperature and from an aqueous solution. The primary structure is mainly Ala-Gly alternative copolypeptide, but Gly-Ala-Ala-Ser units appear frequently and periodically. Thus, this study aims at elucidating the role of such Gly-Ala-Ala-Ser units on the secondary structure. The sequential model peptides containing Gly-Ala-Ala-Ser units selected from the primary structure of B. mori silk fibroin were synthesized, and their secondary structure was studied with 13C CP/MAS NMR and wide-angle X-ray scattering. The 13C isotope labeling of the peptides and the 13C conformation-dependent chemical shifts were used for the purpose. The Ala-Ala units take antiparallel ,-sheet structure locally, and the introduction of one Ala-Ala unit in (Ala-Gly)15 chain promotes dramatical structural changes from silk I (repeated ,-turn type II structure) to silk II (antiparallel ,-sheet structure). Thus, the presence of Ala-Ala units in B. mori silk fibroin chain will be one of the inducing factors of the structural transition for silk fiber formation. The role of Tyr residue in the peptide chain was also studied and clarified to induce "locally nonordered structure." [source] The effects of disulfide bonds on the denatured state of barnasePROTEIN SCIENCE, Issue 12 2000Jane Clarke Abstract The effects of engineered disulfide bonds on protein stability are poorly understood because they can influence the structure, dynamics, and energetics of both the native and denatured states. To explore the effects of two engineered disulfide bonds on the stability of barnase, we have conducted a combined molecular dynamics and NMR study of the denatured state of the two mutants. As expected, the disulfide bonds constrain the denatured state. However, specific extended ,-sheet structure can also be detected in one of the mutant proteins. This mutant is also more stable than would be predicted. Our study suggests a possible cause of the very high stability conferred by this disulfide bond: the wild-type denatured ensemble is stabilized by a nonnative hydrophobic cluster, which is constrained from occurring in the mutant due to the formation of secondary structure. [source] Neuro-fuzzy structural classification of proteins for improved protein secondary structure predictionPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 8 2003Joachim A. Hering Abstract Fourier transform infrared (FTIR) spectroscopy is a very flexible technique for characterization of protein secondary structure. Measurements can be carried out rapidly in a number of different environments based on only small quantities of proteins. For this technique to become more widely used for protein secondary structure characterization, however, further developments in methods to accurately quantify protein secondary structure are necessary. Here we propose a structural classification of proteins (SCOP) class specialized neural networks architecture combining an adaptive neuro-fuzzy inference system (ANFIS) with SCOP class specialized backpropagation neural networks for improved protein secondary structure prediction. Our study shows that proteins can be accurately classified into two main classes "all alpha proteins" and "all beta proteins" merely based on the amide I band maximum position of their FTIR spectra. ANFIS is employed to perform the classification task to demonstrate the potential of this architecture with moderately complex problems. Based on studies using a reference set of 17 proteins and an evaluation set of 4 proteins, improved predictions were achieved compared to a conventional neural network approach, where structure specialized neural networks are trained based on protein spectra of both "all alpha" and "all beta" proteins. The standard errors of prediction (SEPs) in % structure were improved by 4.05% for helix structure, by 5.91% for sheet structure, by 2.68% for turn structure, and by 2.15% for bend structure. For other structure, an increase of SEP by 2.43% was observed. Those results were confirmed by a "leave-one-out" run with the combined set of 21 FTIR spectra of proteins. [source] 10-Benzyl-4-oxo-2,3,4,10-tetrahydropyrimido[4,5- b]quinolin-2-iminium chloride sesquihydrate: a polarized electronic structure within a complex hydrogen-bonded sheet structureACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Jorge Trilleras In the title compound, C18H15N4O+·Cl,·1.5H2O, one water site is fully ordered with unit occupancy while the other, which lies close to an inversion centre in the space group C2/c, has only 0.5 occupancy. The cation exhibits bond fixation in the fused carbocyclic ring and electronic polarization in the terminal heterocyclic ring. The components are linked into complex sheets by a combination of N,H...O, N,H...Cl, O,H...O, O,H...Cl and C,H...O hydrogen bonds. [source] Phenyl-ring rotational disorder in the two-dimensional hydrogen-bonded structure of the 1:1 proton-transfer salt of the diazo-dye precursor 4-(phenyldiazenyl)aniline (aniline yellow) with l -tartaric acidACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Graham Smith In the structure of the 1:1 proton-transfer compound from the reaction of l -tartaric acid with the azo-dye precursor aniline yellow [4-(phenyldiazenyl)aniline], namely 4-(phenyldiazenyl)anilinium (2R,3R)-3-carboxy-2,3-dihydroxypropanoate, C12H12N3+·C4H5O6,, the asymmetric unit contains two independent 4-(phenyldiazenyl)anilinium cations and two hydrogen l -tartrate anions. The structure is unusual in that all four phenyl rings of the two cations have identical rotational disorder with equal occupancy of the conformations. The two hydrogen l -tartrate anions form independent but similar chains through head-to-tail carboxyl,carboxylate O,H...O hydrogen bonds [graph set C(7)], which are then extended into a two-dimensional hydrogen-bonded sheet structure through hydroxy O,H...O hydrogen-bonded links. The anilinium groups of the 4-(phenyldiazenyl)anilinium cations are incorporated into the sheets and also provide internal hydrogen-bonded extensions, while their aromatic tails are layered in the structure without significant association except for weak ,,, interactions [minimum ring centroid separation = 3.844,(3),Å]. The hydrogen l -tartrate residues of both anions exhibit the common short intramolecular hydroxy,carboxylate O,H...O hydogen bonds. This work provides a solution to the unusual disorder problem inherent in the structure of this salt, as well as giving another example of the utility of the hydrogen tartrate anion in the generation of sheet substructures in molecular assembly processes. [source] Low-dimensional hydrogen-bonded structures in the 1:1 and 1:2 proton-transfer compounds of 4,5-dichlorophthalic acid with the aliphatic Lewis bases triethylamine, diethylamine, n -butylamine and piperidineACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Graham Smith The structures of the proton-transfer compounds of 4,5-dichlorophthalic acid (DCPA) with the aliphatic Lewis bases triethylamine, diethylamine, n -butylamine and piperidine, namely triethylaminium 2-carboxy-4,5-dichlorobenzoate, C6H16N+·C8H3Cl2O4,, (I), diethylaminium 2-carboxy-4,5-dichlorobenzoate, C4H12N+·C8H3Cl2O4,, (II), bis(butanaminium) 4,5-dichlorobenzene-1,2-dicarboxylate monohydrate, 2C4H12N+·C8H2Cl2O42,·H2O, (III), and bis(piperidinium) 4,5-dichlorobenzene-1,2-dicarboxylate monohydrate, 2C5H12N+·C8H2Cl2O42,·H2O, (IV), have been determined at 200,K. All compounds have hydrogen-bonding associations, giving discrete cation,anion units in (I) and linear chains in (II), while (III) and (IV) both have two-dimensional structures. In (I), a discrete cation,anion unit is formed through an asymmetric R12(4),N+,H...O2 hydrogen-bonding association, whereas in (II), chains are formed through linear N,H...O associations involving both aminium H-atom donors. In compounds (III) and (IV), the primary N,H...O-linked cation,anion units are extended into a two-dimensional sheet structure via amide,carboxyl N,H...O and amide,carbonyl N,H...O interactions. In the 1:1 salts (I) and (II), the hydrogen 4,5-dichlorophthalate anions are essentially planar with short intramolecular carboxyl,carboxyl O,H...O hydrogen bonds [O...O = 2.4223,(14) and 2.388,(2),Å, respectively]. This work provides a further example of the uncommon zero-dimensional hydrogen-bonded DCPA,Lewis base salt and the one-dimensional chain structure type, while even with the hydrate structures of the 1:2 salts with the primary and secondary amines, the low dimensionality generally associated with 1:1 DCPA salts is also found. [source] Crystallographic characterization of the first reported crystalline form of the potent hallucinogen (R)-2-amino-1-(8-bromobenzo[1,2- b;5,4- b,]difuran-4-yl)propane or `bromodragonfly': the 1:1 anhydrous proton-transfer compound with 3,5-dinitrosalicylic acidACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2010Graham Smith The 1:1 proton-transfer compound of the potent substituted amphetamine hallucinogen (R)-2-amino-1-(8-bromobenzo[1,2- b;5,4- b,]difuran-4-yl)propane (common trivial name `bromodragonfly') with 3,5-dinitrosalicylic acid, namely 1-(8-bromobenzo[1,2- b;5,4- b,]difuran-4-yl)propan-2-aminium 2-carboxy-4,6-dinitrophenolate, C13H13BrNO2+·C7H3N2O7,, forms hydrogen-bonded cation,anion chain substructures comprising undulating head-to-tail anion chains formed through C(8) carboxyl,nitro O,H...O associations and incorporating the aminium groups of the cations. The intrachain cation,anion hydrogen-bonding associations feature proximal cyclic R33(8) interactions involving both an N+,H...Ophenolate and the carboxyl,nitro O,H...O associations and aromatic ,,, ring interactions [minimum ring centroid separation = 3.566,(2),Å]. A lateral hydrogen-bonding interaction between the third aminium H atom and a carboxyl O-atom acceptor links the chain substructures, giving a two-dimensional sheet structure. This determination represents the first of any form of this compound and is in the (R) absolute configuration. The atypical crystal stability is attributed both to the hydrogen-bonded chain substructures provided by the anions, which accommodate the aminium proton-donor groups of the cations and give crosslinking, and to the presence of the cation,anion aromatic ring ,,, interactions. [source] Intermolecular dihydrogen- and hydrogen-bonding interactions in diammonium closo -decahydrodecaborate sesquihydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2010Teshome B. Yisgedu The asymmetric unit of the title salt, 2NH4+·B10H102,·1.5H2O or (NH4)2B10H10·1.5H2O, (I), contains two B10H102, anions, four NH4+ cations and three water molecules. (I) was converted to the anhydrous compound (NH4)2B10H10, (II), by heating to 343,K and its X-ray powder pattern was obtained. The extended structure of (I) shows two types of hydrogen-bonding interactions (N,H...O and O,H...O) and two types of dihydrogen-bonding interactions (N,H...H,B and O,H...H,B). The N,H...H,B dihydrogen bonding forms a two-dimensional sheet structure, and hydrogen bonding (N,H...O and O,H...O) and O,H...H,B dihydrogen bonding link the respective sheets to form a three-dimensional polymeric network structure. Compound (II) has been shown to form a polymer with the accompanying loss of H2 at a faster rate than (NH4)2B12H12 and we believe that this is due to the stronger dihydrogen-bonding interactions shown in the hydrate (I). [source] Nonsyndromic mental retardation and cryptogenic epilepsy in women with Doublecortin gene mutationsANNALS OF NEUROLOGY, Issue 1 2003Renzo Guerrini MD DCX mutations cause mental retardation in male subjects with lissencephalypachygyria and in female subjects with subcortical band heterotopia (SBH). We observed four families in which carrier women had normal brain magnetic resonance imaging (MRI) and mild mental retardation, with or without epilepsy. Affected male subjects had SBH or pachygyria-SBH. In two families, the phenotype was mild in both genders. In the first family, we found a tyr138his mutation that is predicted to result in abnormal folding in the small hinge region. In the second family, we found an arg178cys mutation at the initial portion of R2, in the putative ,-sheet structure. Carrier female subjects with normal MRI showed no somatic mosaicism or altered X-inactivation in lymphocytes, suggesting a correlation between mild mutations and phenotypes. In the two other families, with severely affected boys, we found arg76ser and arg56gly mutations within the R1 region that are predicted to affect DCX folding, severely modifying its activity. Both carrier mothers showed skewed X-inactivation, possibly explaining their mild phenotypes. Missense DCX mutations may manifest as non-syndromic mental retardation with cryptogenic epilepsy in female subjects and SBH in boys. Mutation analysis in mothers of affected children is mandatory, even when brain MRI is normal. Ann Neurol 2003 [source] Zero-, one- and two-dimensional hydrogen-bonded structures in the 1:1 proton-transfer compounds of 4,5-dichlorophthalic acid with the monocyclic heteroaromatic Lewis bases 2-aminopyrimidine, nicotinamide and isonicotinamideACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Graham Smith The structures of the anhydrous 1:1 proton-transfer compounds of 4,5-dichlorophthalic acid (DCPA) with the monocyclic heteroaromatic Lewis bases 2-aminopyrimidine, 3-(aminocarbonyl)pyridine (nicotinamide) and 4-(aminocarbonyl)pyridine (isonicotinamide), namely 2-aminopyrimidinium 2-carboxy-4,5-dichlorobenzoate, C4H6N3+·C8H3Cl2O4,, (I), 3-(aminocarbonyl)pyridinium 2-carboxy-4,5-dichlorobenzoate, C6H7N2O+·C8H3Cl2O4,, (II), and the unusual salt adduct 4-(aminocarbonyl)pyridinium 2-carboxy-4,5-dichlorobenzoate,methyl 2-carboxy-4,5-dichlorobenzoate (1/1), C6H7N2O+·C8H3Cl2O4,·C9H6Cl2O4, (III), have been determined at 130,K. Compound (I) forms discrete centrosymmetric hydrogen-bonded cyclic bis(cation,anion) units having both R22(8) and R12(4) N,H...O interactions. In (II), the primary N,H...O-linked cation,anion units are extended into a two-dimensional sheet structure via amide,carboxyl and amide,carbonyl N,H...O interactions. The structure of (III) reveals the presence of an unusual and unexpected self-synthesized methyl monoester of the acid as an adduct molecule, giving one-dimensional hydrogen-bonded chains. In all three structures, the hydrogen phthalate anions are essentially planar with short intramolecular carboxyl,carboxylate O,H...O hydrogen bonds [O...O = 2.393,(8),2.410,(2),Å]. This work provides examples of low-dimensional 1:1 hydrogen-bonded DCPA structure types, and includes the first example of a discrete cyclic `heterotetramer.' This low dimensionality in the structures of the 1:1 aromatic Lewis base salts of the parent acid is generally associated with the planar DCPA anion species. [source] N,N,-Bis[tris(hydroxymethyl)methyl]ethanediamide: six O,H,O hydrogen bonds generate only a two-dimensional structureACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2001Jennifer N. Ross Molecules of the title compound, C10H20N2O8, adopt a conformation which is almost centrosymmetric. The molecules are disordered over two sets of sites with an occupancy ratio of 0.94:0.06. In the major form, there are two intramolecular O,H,O hydrogen bonds [O,O 2.756,(4) and 2.765,(4),Å; O,H,O 144 and 146°], in which the two amidic O atoms act as acceptors. In addition, there are four intermolecular O,H,O hydrogen bonds [O,O 2.650,(3),2.666,(3),Å; O,H,O 158,171°]; these link each molecule to six others in a continuous sheet structure which contains five distinct ring motifs, two of the S(7) type, two of the R(10) type and one of the R(22) type. [source] Conformations of Betanova in aqueous trifluoroethanol,BIOPOLYMERS, Issue 10 2010Danny P. Chagolla Abstract Conformations of the designed peptide Betanova in 42% trifluoroethanol/water (v/v) were explored. Circular dichroism (CD) observations provided no evidence for the presence of significant amounts of ,-structures in water, in TFE/water, or in ethanol/water. Nuclear magnetic resonance (NMR) diffusion experiments showed no significant difference in the hydrodynamic radius of the peptide in water and in 42% TFE/water. However, calculations indicated that the hydrodynamic radii of the triple-stranded ,-sheet, originally proposed for Betanova by Kortemme et al. (Science 1998, 281, 253-256), and a variety of partially folded forms of Betanova would be similar and likely could not be convincingly distinguished by diffusion experiments. Temperature coefficients (,,/,T) of the peptide NH chemical shifts are similar in water and 42% TFE/water, implying that most of these protons are highly solvent exposed in both solvents and likely do not participate in intramolecular hydrogen bonding interactions. Possible exceptions to this conclusion are the Lys9 and Lys15 residues, where a more positive coefficient may indicate that these residues are involved to some extent in local turn structures. Peptide proton,solvent fluorine intermolecular nuclear Overhauser effect (NOE)s at 25°C were consistent with the presence of a mixture of conformations, which could include the triple-stranded ,-sheet structure as a minor component. At 0°C, peptide-TFE NOEs indicated that TFE interacts strongly enough with many protons of Betanova that alcohol-peptide interactions persist for times of the order of nanoseconds, appreciably longer than the encounter time characteristic of mutual diffusion of TFE and the solute. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 893,903, 2010. [source] Terahertz time-domain spectroscopy of poly- L -lysineBIOPOLYMERS, Issue 8 2010Ohki Kambara Abstract Poly- L -lysine is known to have three different secondary structures depending on solvent conditions because of its flexible nature. In previous work (Kambara et al., Phys Chem Chem Phys 2008, 10, 5042-5044), we observed two different types of structural changes in poly- L -lysine. In the present study, we investigated the low-frequency spectrum of poly- L -lysine with a ,-sheet structure in the solid state by terahertz time-domain spectroscopy. On the basis of this spectroscopic analysis, we found that the low-frequency dynamics differed from those of other polypeptides. Furthermore, we performed powder X-ray diffraction measurement on poly- L -lysine, which was found to be highly amorphous compared with other polypeptides. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 735,739, 2010. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Conformational transition and liquid crystalline state of regenerated silk fibroin in waterBIOPOLYMERS, Issue 6 2008Xin-Gui Li Abstract The conformational transition of molecular chains of regenerated silk fibroin (SF) aqueous solution is systematically investigated by circular dichroism, Raman, IR, and UV,vis spectroscopies. It is found that an initial random coil conformation of the SF can be readily changed into an ordered ,-sheet structure by optimizing the solution conditions, such as the SF concentration, pH, temperature, or metal-ion content. Circular dichroic spectra quantitatively confirm a steadily decreased content of the random coil conformation but a significantly increased ,-sheet content after an ultrasonic or extruding treatment. Furthermore, the extrusion is more powerful to achieve high ,-sheet content than the ultrasonic. It is interesting that the polarized optical micrographs of the SF aqueous solution extruded by injection illustrate the formation and existence of liquid crystalline state. A study of extrusion in vitro could be used as a model system to understand the natural silk spinning process in silkworm. © 2007 Wiley Periodicals, Inc. Biopolymers 89: 497,505, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Determination of intermolecular distance for a model peptide of Bombyx mori silk fibroin, GAGAG, with rotational echo double resonanceBIOPOLYMERS, Issue 2 2002Tsunenori Kameda Abstract Rotational echo double resonance NMR spectroscopy is applied for the determination of the distance of intermolecular chains of pentapeptide, GAGAG (G: Gly, A: Ala), a model typical of the crystalline domain in Bombyx mori silk fibroin. 1:4 mixture of G[1- 13C]AGAG and GAG[15N]AG with antiparallel ,-sheet structure was used to determine the distance of intermolecular hydrogen bonding between adjacent molecules within pleated sheet and the 13C,15N interatomic distance was determined to be 4.3 Å. On the other hand, 1:4 mixture of GAG[1- 13C]AG and GAG[15N]AG gave information on the interpleated sheet arrangement. When we assumed the same distances between two interpleated sheets, the distance was calculated to be 5.3 Å and the angle 15N,13C,15N was 180°. © 2002 Wiley Periodicals, Inc. Biopolymers 64: 80,85, 2002 [source] Insight Into the Kinetic of Amyloid , (1,42) Peptide Self-Aggregation: Elucidation of Inhibitors' Mechanism of ActionCHEMBIOCHEM, Issue 17 2007Manuela Bartolini Dr. Abstract The initial transition of amyloid , (1,42) (A,42) soluble monomers/small oligomers from unordered/,-helix to a ,-sheet-rich conformation represents a suitable target to design new potent inhibitors and to obtain effective therapeutics for Alzheimer's disease. Under optimized conditions, this reliable and reproducible CD kinetic study showed a three-step sigmoid profile that was characterized by a lag phase (prevailing unordered/,-helix conformation), an exponential growth phase (increasing ,-sheet secondary structure) and a plateau phase (prevailing ,-sheet secondary structure). This kinetic analysis brought insight into the inhibitors' mechanism of action. In fact, an increase in the duration of the lag phase can be related to the formation of an inhibitor,A, complex, in which the non-amyloidogenic conformation is stabilized. When the exponential rate is affected exclusively, such as in the case of Congo red and tetracycline, then the inhibitor affinity might be higher for the pleated ,-sheet structure. Finally, by adding the inhibitor at the end of the exponential phase, the soluble protofibrils can be disrupted and the A, amyloidogenic structure can revert into monomers/small oligomers. Congo red and tetracycline preferentially bind to amyloid in the ,-sheet conformation because both decreased the slope of the exponential growth, even if to a different extent, whereas no effect was observed for tacrine and galantamine. Some very preliminary indications can be derived about the structural requirements for binding to nonamyloidogenic or ,-sheet amyloid secondary structure for the development of potent antiaggregating agents. On these premises, memoquin, a multifunctional molecule that was designed to become a drug candidate for the treatment of Alzheimer's disease, was investigated under the reported circular dichroism assay and its anti-amyloidogenic mechanism of action was elucidated. [source] Studies on the conformational properties of CP-1042,55, the hinge region of CP-10, using circular dichroism and RP-HPLCCHEMICAL BIOLOGY & DRUG DESIGN, Issue 6 2000E. Lazoura Abstract: The conformational properties of CP-1042,55, a peptide corresponding to the hinge region of CP-10, were investigated using circular dichroism spectroscopy and reverse-phase high-performance liquid chromatography (RP-HPLC). The circular dichroism studies indicated that CP-1042,55 formed considerable secondary structure in the presence of hydrophobic solution environments including 50% acetonitrile, 50% trifluoroethanol and 200 mm sodium dodecyl sulfate, which comprised a mixture of ,-helix and ,-sheet. The effect of temperature on the conformation of CP-1042,55 was investigated between 5 and 40°C, with very small changes in the spectra being observed.RP-HPLC was then used to investigate the effect of temperature on the conformation of CP-1042,55 in the presence of a hydrophobic surface. Using a C18 -adsorbent, CP-1042,55 exhibited a conformational transition at 25°C, which was associated with an increase in the chromatographic contact area and the binding affinity of the peptide for the stationary phase. In addition, near-planar bandbroadening behaviour indicated that conformational species interconverted with rapid rate constants compared with the chromatographic time scale. These results indicated that the conformational change at 25°C in theRP-HPLC system most likely corresponds to the unfolding of an ,-helical and/or ,-sheet structure to an extended coil structure. Therefore, the strong chemotactic properties of this peptide may be attributed to its ability to form considerable secondary structure in the presence of a hydrophobic environment. [source] Biomimetic Self-Assembly of Tetrapeptides into Fibrillar Networks and OrganogelsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2008Sajid Iqbal Abstract The self-assembly features of a family of tetrapeptides with a silk-inspired structure are presented. An exhaustive study of the influence of the terminal alkyl chain length in this process is undertaken. Scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), FTIR spectroscopy, and circular dichroism were used for structural analysis. These compounds, as in the natural model, self-assemble into antiparallel ,-sheet structures that further organize to form fibrillar aggregates. Furthermore, some of them arecapable of forming a crowded network that entraps thesolvent leading to physical gels with different microscopic morphologies. A model for the assembly process is proposed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Protein-Enabled Synthesis of Monodisperse Titania Nanoparticles On and Within Polyelectrolyte MatricesADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Eugenia Kharlampieva Abstract Here, the results of a study of the mechanism of bio-enabled surface-mediated titania nanoparticle synthesis with assistance of polyelectrolyte surfaces are reported. By applying atomic force microscopy, surface force spectroscopy, circular dichroism, and in situ attenuated total reflection Fourier-transform infrared spectroscopy, structural changes of rSilC-silaffin upon its adsorption to polyelectrolyte surfaces prior to and during titania nanoparticle growth are revealed. It is demonstrated that the adhesion of rSilC-silaffin onto polyelectrolyte surfaces results in its reorganization from a random-coil conformation in solution into a mixed secondary structure with both random coil and , -sheet structures presented. Moreover, the protein forms a continuous molecularly thin layer with well-defined monodisperse nanodomains of lateral dimensions below 20,nm. It is also shown that rSilC embedded inside the polylelectrolyte matrix preserves its titania formation activity. It is suggested that the surface-mediated, bio-enabled synthesis of nanostructured materials might be useful to develop general procedures for controlled growth of inorganic nanomaterials on reactive organic surfaces, which opens new perspectives in the design of tailored, in situ grown, hybrid inorganic,organic nanomaterials. [source] The Role of Prion Peptide Structure and Aggregation in Toxicity and Membrane BindingJOURNAL OF NEUROCHEMISTRY, Issue 6 2000Dawn L. Rymer Abstract: Prion diseases are neurodegenerative disorders associatedwith a conformational change in the normal cellular isoform of the prionprotein, PrPC, to an abnormal scrapie isoform, PrPSC.Unlike the ,-helical PrPC, the protease-resistant core ofPrPSC is predominantly ,-sheet and possesses a tendency topolymerize into amyloid fibrils. We performed experiments with two synthetichuman prion peptides, PrP(106-126) and PrP(127-147), to determine how peptidestructure affects neurotoxicity and protein-membrane interactions. Peptidesolutions possessing ,-sheet and amyloid structures were neurotoxic toPC12 cells in vitro and bound with measurable affinities to cholesterol-richphospholipid membranes at ambient conditions, but peptide solutions lackingstable ,-sheet structures and amyloid content were nontoxic and possessedless than one tenth of the binding affinities of the amyloid-containingpeptides. Regardless of structure, the peptide binding affinities tocholesterol-depleted membranes were greatly reduced. These results suggestthat the ,-sheet and amyloid structures of the prion peptides give riseto their toxicity and membrane binding affinities and that membrane bindingaffinity, especially in cholesterol-rich environments, may be related totoxicity. Our results may have significance in understanding the role of thefibrillogenic cerebral deposits associated with some of the prion diseases inneurodegeneration and may have implications for other amyloidoses. [source] Interaction between amyloid ,-protein aggregates and membranesJOURNAL OF PEPTIDE SCIENCE, Issue 10 2004Atsuko Kakio Abstract The conversion of soluble, nontoxic amyloid ,-protein (A,) to aggregated, toxic A, rich in ,-sheet structures is considered to be the key step in the development of Alzheimer's disease. Therefore, extensive studies have been carried out on the mechanisms involved in A, aggregation and the characterization of A, aggregates formed in aqueous solutions mimicking biological fluids. On the other hand, several investigators pointed out that membranes play an important role in A, aggregation. However, it remains unclear whether A, aggregates formed in solution and membranes are identical and whether the former can bind to membranes. In this study, using a dye-labeled A,-(1,40) as well as native A,-(1,40), the properties of A, aggregates formed in buffer and raft-like membranes composed of monosialoganglioside GM1/cholesterol/sphingomyelin were compared. Fourier transform infrared spectroscopic measurements suggested that A, aggregates formed in buffer and in membranes have different ,-sheet structures. Fluorescence experiments revealed that A, aggregated in buffer did not show any affinity for membranes. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||