Main Chain Length Research Articles

INFLUENCE OF MAIN CHAIN LENGTH OF POLYCARBOXYLATE-BASED SUPERPLASTICIZER ON ULTRA-HIGH-STRENGTH CONCRETE

Recently, design concrete strength of 150MPa has been used, and polycarboxylate-based superplasticizer has become an essential ingredient to produce ultra-high-strength concrete. In this study, the main chain length of polycarboxylate-based superplasticizer was focused on to optimize performance of dispersing ability at low water cement ratio on ultra-high-strength concrete. Short main chain length exhibited high dispersing ability and low concrete viscosity at low water cement ratio. It was estimated that the thickness of water film on cement particle demanded three times of the main chain length. The main chain length was found to have influence on dispersing ability.

First homo‐peptides undergoing a reversible 310‐helix/α‐helix transition: Critical main‐chain length

The difference in length between the more elongated peptide 3(10)-helix and the more compact alpha-helix is about 0.4 A/residue. This property makes the 3(10)-/alpha-helix reversible conversion very promising as a molecular switching tool between the N- and C-terminal functions of a peptide backbone. In this work, using homo-peptides of various main-chain length, all based on the strongly helicogenic, Calpha-tetrasubstituted alpha-amino acid Calpha-methyl-L-valine, we show that a well defined, solvent controlled, reversible 3(10)-/alpha-helix transition takes place even in a homo-oligomer as short as a terminally blocked hexapeptide. Homo-peptide sequences blocked as a urethane or an acetamide at the N-terminus and as a methyl ester or an N-alkyl amide at the C-terminus are all appropriate. The nature of the occurring helical species in the various solvents tested was assessed by electronic or vibrational circular dichroism.

Peptaibiomics: Microheterogeneity, Dynamics, and Sequences of Trichobrachins, Peptaibiotics from Trichoderma parceramosumBissett (T. longibrachiatumRifai)

From the culture broth of the filamentous fungus Trichoderma parceramosum, strain CBS 936.69, a mixture of polypeptide antibiotics (pepaibiotics), named trichobrachin (TB), was isolated. Three major groups designated TB I, TB II, and TB III could be separated and isolated by preparative TLC on silica gel. Individual peptides of these three groups were sequenced by on-line LC/ESI-MS(n). The mixture of N-acetylated peptides comprises ten 19-residue peptides with a free C-terminal Gln residue (TB I peptides), two 18-residue peptides with a free C-terminal Gln residue (TB II 1 and 2), seven 20-residue peptides with a C-terminal amide-bound phenylalaninol (TB II 3-10), and 34 eleven-residue peptides with either a C-terminal leucinol or isoleucinol or valinol (TB III 1-34). Monitoring production and degradation of peptaibiotics in a pilot experiment revealed that the biosynthesis of TB II and TB III peptides starts two days after the beginning of fermentation. After five days of fermentation, the concentration of TB II decreased, whereas the amount of TB I increased. This observation unequivocally demonstrates that those two 18-residue TB I and TB II peptides with the free carboxy terminus result from enzymatic C-terminal degradation of the 20-residue TB II peptides. In analogy to the technical terms proteome and proteomics, the terms peptaibiome and peptaibiomics have recently been proposed for the entirety and dynamics of the Aib-containing peptides (comprehensively named peptaibiotics). Consequently, the entire peptaibiome of T. parceramosum grown under submerse conditions in shake-flasks for five days comprises at least 54 peptides differing in main-chain length and microheterogeneity, i.e., exchange of amino acids and the C-terminal 1,2-amino alcohol.

Synthesis and Characterization of the Bismaleimides Containing Aliphatic-ether Chain for Microelectronics Application

AbstractThis project aims to develop and characterize a series of bismaleimide (BMI) polymers based on maleic anhydride and aliphatic-ether diamines. The effects of varying the chain length of aliphatic-ether diamines on the resultant bismaleimide systems were evaluated so that their suitability for microelectronics applications could be evaluated. The synthetic reaction and properties of the bismaleimide materials were investigated using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermo- Gravimetric Analysis (TGA), Dielectric Thermal Analysis (DEA) and rheometry. Results showed that thermal, dielectric and rheological properties were all affected by the main chain length of BMI. The magnitude of the dielectric constant at 100 kHz increases with the increasing chain length. The curing peak temperature, curing heat and degradation temperature of BMI, all decrease with the increasing chain length.

Evolution of ordinary Portland cement hydration with admixtures by spectroscopic techniques

The various waterproofing admixtures may prevent water from penetrating concrete in different ways, but primarily by rendering it hydrophobic. Spectroscopic techniques have proved to be the appropriate tools for studying cement hydration in the presence of different admixtures. A combination of Fourier Transform-Raman and 29 Si nuclear magnetic resonance (NMR) spectroscopy were used here to monitor OPC hydration and C-S-H gel formation with two different waterproofing admixtures. The Q1/Q0 ratio was determined with the former technique to evaluate the influence of the waterproofing substances on C-S-H gel formation rate and intensity, whereas 29Si NMR was employed to establish the relative amount of C-S-H gel formed at different hydration times as well as to calculate the main chain length.

Turn and helical peptide spacers: Combined distance and angular dependencies in the exciton‐coupled circular dichroism of intramolecularly interacting bis‐porphyrins

In a previous study we examined by the exciton-coupled circular dichroic method the distance effect generated by three-rigid-turn and helical-peptide spacers. In this connection porphyrins were confirmed to be excellent reporter chromophores. In the present investigation we have completed this research by expanding the original analysis to the assessment of the combined role of the chromophore distance and orientation with use of the same porphyrin derivatives and additional four analogous spacers of different main-chain lengths. We find that not only the intramolecular separation of the chromophores, but the angular dependence between the directions of their effective transition moments as well, are responsible for the onset and modulation of the intensity of the exciton-coupling phenomenon of the porphyrin Soret band.

Switching in molecular shapes: main chain length driven rod–circle transition of isolated helical polysilanes

Unique conformations such as rod, semicircle, and circle structures of isolated semi-flexible helical polysilanes were observed by atomic force microscopy (AFM); the chain topology was significantly related to the chain length (molecular weight) on the surfaces.

Identification and composition of cuticular hydrocarbons of the major Afrotropical malaria vector Anopheles gambiae s.s. (Diptera: Culicidae): analysis of sexual dimorphism and age‐related changes

Forty-eight cuticular hydrocarbons (CHCs) were characterized by gas chromatography-mass spectrometry from the epicuticular surface of the major Afrotropical malaria vector Anopheles gambiae. The hydrocarbons identified were 14 n-alkanes, 16 monomethyl alkanes, 13 dimethyl alkanes, 5 alkenes, with main-chain lengths ranging from C(17) to C(47), and the results are consistent with those from other Culicidae species. Qualitative differences were not observed between laboratory pools of three females and males, between different age-groups (0-16 days) and between single field specimens, whereas quantitative differences in CHC profiles were observed. Differences between sexes were more marked in individuals aged 0-2 days than in older ones. Both sexes undergo strong CHC profile changes with age, and individuals aged 0-2 days differ remarkably from the older ones. The possibility of exploiting these changes for estimating the age of mosquito was explored through multivariate analyses of the relative abundance of the compounds, using either the whole CHC profile or a subset of CHCs. Such a method allows us to assign more than 85% of females and 75% of males to the correct age-group. Although preliminary, these results show that the method is promising, as it has already been shown in Aedes aegypti and An. stephensi. The correct determination of the vector age (particularly in the case of the An. gambiae complex of sibling species) provides valuable information in malaria epidemiology and in evaluation of the effectiveness of vector control strategies. Further efforts will be made to validate this method on single specimens reared in seminatural conditions before being proposed to medical entomologists working in the Afrotropical region.

Order to disorder transition of comb copolymer A m+1 B m: a self-consistent field study

The order to disorder transition of comb copolymers A m+1 B m is investigated by the self-consistent field theory. Although there are only two components in a molecule, the side chain number m affects the phase diagram largely due to the fact that the architecture of a comb copolymer is not invariant under the interchange of A- with B-monomers. With the increase of the side chain number, the interaction (Flory–Huggins) parameter of the order-to-disorder transition (ODT) increases at the same composition and the lowest ODT occurs at the smaller volume fraction of the main chain f A. The influences of the side chain density and the side chain length on the phase behavior were discussed in detail. The relation χ N ODT ∝ f A α exists with the fixed main chain length. The comb copolymer with the large side chain number m and the long main chain sections (or short side chain) is more stable. The results are helpful to design nano- or bio-materials with complex architecture or tailor the phase behavior of comb copolymers.

NMR Investigation of the Main‐Chain Orientation in Liquid‐Crystalline Side‐Chain Polymers

AbstractThe main‐chain orientation in different groups of liquid‐crystalline side‐chain polymers was investigated using several NMR techniques. For two polyesters the average orientation of the main chain in dependence on the main‐chain spacer length could be found from 2D PASS experiments. In polysiloxanes with different mesogenic side groups and different spacer lengths this information could be received from chemical shift anisotropy measurements. Additionally, application of a modified β‐echo allowed the separation of the dipolar 29Si‐29Si interaction and to characterize the transversal anisotropy of the main‐chain segments. Comparison with small angle neutron scattering results gave good agreement, where the different length scale of both methods has to be taken into account.

Diffusion of Rod‐Like Polypeptides in the Liquid Crystalline and Isotropic Phases as Studied by High Field‐Gradient NMR Spectroscopy

AbstractIn this lecture the measurements and analyses of the isotropic and anisotropic diffusion coefficients(D) of rod‐like polypeptide such as poly(γ‐L‐glutamate)(PLG) with n‐alkyl side chains, of which the main chain takes the α‐helical conformation, as a function of the main chain length in the thermotropic and lyotropic liquid crystalline phases over a wide range of temperatures from 30 to 80°C by means of pulse high field‐gradient spin echo 1H NMR method have been introduced. In the anisotropic diffusion, the D∥ value in direction parallel to the α‐helical chain axis is found to be much larger than the D⊥ value in direction perpendicular to the α‐helical chain axis. The diffusion process is followed by the Kirkwood theory. Further, it is described that the diffusion in the nematic liquid crystalline phase is much slower than that in the isotropic phase.

Efficient Divergent Synthesis of Dendronized Polymers with Extremely High Molecular Weight: Structural Characterization by SEC-MALLS and SFM and Novel Organic Gelation Behavior

High molecular weight poly(p-hydroxystyrene) (PHS) was dendronized in high yield by the divergent grafting of aliphatic polyester dendrons using acetal and ketal protected anhydride derivatives of bis(hydroxymethyl)propionic acid. Relatively low polydispersities (PDI = 1.1-1.3) were maintained throughout the dendronization process. Detailed characterization of a series of these polymers by size exclusion chromatography (SEC) and SEC with multi-angle laser light scattering (SEC-MALLS) clearly shows the effect of dendron steric bulk on the persistence length (ξ) of the polymer main chain in solution. As a result of the fixed degree of polymerization (DP), the main chain rigidification that accompanies lateral dendron growth causes an unusual relationship between R g,z and molecular weight across a series of generations. The rodlike structure and contour length of the alkylated dendronized polymers was also characterized by scanning force microscopy (SFM) on mica, highly oriented pyrolytic graphite (HOPG), and molybdenum disulfide (MoS 2 ) surfaces. One of the G3 dendronized polymers with an alkylated periphery showed significant physical gelation behavior at concentrations below 1 wt % in several organic solvents, which constitutes additional evidence that the solution phase rigidity of a polymer chain can be enhanced by dendronization.

The influence of side-chain and main-chain spacer lengths on the thermal and structural properties of diethanolamine based side-chain polyesters

A series of linear side-chain aliphatic polyesters have been synthesized from α-(bis(2-hydroxyethyl)amino)-ω-(4’-methoxybiphenyl-4-oxy) alkanes and aliphatic acid chlorides. The side-chain and main-chain spacer lengths were varied and their influences on thermal and structural properties of polyesters, as determined by DSC and X-ray diffraction, are discussed.

Dendronized Rigid−Flexible Macromolecular Architectures: Syntheses, Structure, and Properties in Bulk

Side-chain dendronized polymers consisting of regularly segmented alternating rigid−flexible main-chain units and side dendritic wedges are synthesized and analyzed in their bulk state using various experimental methods. High molecular weight polymers were obtained in most cases enabling the formation of self-supporting films. The thermal and mechanical characterization of these polymers, by means of DSC and dynamic mechanical analyses, has revealed a highly ordered nature, which was further supported from SALS and POM experiments. Additionally, their transition temperatures seem to strongly depend on the main-chain flexible spacer's length, in a manner resembling the odd−even effect. The existence of organizational features in both isotropic and macroscopically oriented samples was concluded for these polymeric materials due to the intense and well-resolved diffractions in their WAXS patterns. From qualitative analyses of the WAXS patterns corresponding to oriented filaments, the development of layered structures is postulated, comprised of main-chain polymeric backbones while the side dendrons occupy the space between the layers. Actually, two types of LC ordering for the extended backbones within the main-chain layers could be distinguished. In general, the exact polymeric structure, side-dendrons' generation and main-chain flexible spacers' length, greatly influence the final polymeric properties, such as phase transitions and structural parameters.

Conformational and structural analysis of the equilibrium between single- and double-strand beta-helix of a D,L-alternating oligonorleucine.

Alternating sequences of D and L residues in peptides are directly related to the formation of several kinds of regular helical conformations usually called beta-helices. The major feature of these structures is that they can be associated with the transmembrane ion-conducting channel activity in some natural antibacterial peptides. The study of alternating D,L synthetic peptides is critical to understand how factors such as surrounding media, main chain length, type of side chain and terminal groups, among others, can determine the adoption of a specific kind of beta-helix. Early studies pointed out that the peptides Boc-(D-NLeu-L-NLeu)(6)-D-MeNLe-L-Nl-D-Nl-L-Nl-OMe (Boc: tert-butyloxycarbonyl) and Boc-L-Nle-(D-Nle-L-Nle)(5)-D-MeNle-L-Nle-D-Nle-L-Nle-OMe adopt in chloroform a unique detectable conformation single beta(4.4)- and double beta(5.6) upward arrow downward arrow -helix, respectively. The influence of terminal groups on the final stable conformation of N-formylated peptides has been studied in this work. The initial basic NMR data analysis of a synthetic alternating D,L-oligopeptide with ten norleucines, N-methylated on the residue 7 and having HCO- and -OMe as terminal groups clearly indicates the coexistence of two different conformations in equilibrium. NMR data and molecular dynamics calculations point to a dimeric antiparallel beta-helix structure beta(5.6) upward arrow downward arrow for the main conformation. On the other hand, NMR data suggest a single beta-helix structure beta(4.4) for the second conformation. Finally, a thermodynamic analysis of the equilibrium between both conformations has been carried out by one-dimensional NMR measurements at ten different temperatures. The temperature at which 50% of dimer conformation is dissociated is 319 K. In addition, the dimer-monomer equilibrium curve obtained shows a DeltaG>0 for the whole range of studied temperatures, and its behavior can be considered similar to the thermodynamic denaturation protein processes.

Trichogin: a paradigm for lipopeptaibols.

Lipopeptaibols are members of a novel family of naturally occurring, short peptides with antimicrobial activity, characterized by a lipophilic acyl chain at the N-terminus, a high content of turn/helix inducing alpha-aminoisobutyric acid and a 1,2-amino alcohol at the C-terminus. Using solution methods, the prototypical lipopeptaibol trichogin GA IV and a large series of appropriately designed analogues were synthesized, which allow: (i) determination of the minimal lipid chain and peptide main-chain lengths for the onset of membrane activity, and (ii) exploitation of a number of physico-chemical techniques aimed at assessing the trichogin preferred conformation under a variety of conditions and at investigating its mechanism of interaction with the phospholipid membranes.

Structure of Calcium Silicate Hydrates Formed in Alkaline‐Activated Slag: Influence of the Type of Alkaline Activator

The influence of the alkaline activator (NaOH, waterglass, or Na2CO3) on the structure of the hydrated calcium silicate formed in alkali‐activated slag (AAS) cement pastes has been investigated by FTIR, 29Si and 27Al magic‐angle scattering nuclear magnetic resonance, and TEM/EDX techniques. In all cases, the main product formed after 7 d of activation, with activators giving an Na2O concentration of 4%, is a semicrystalline calcium silicate hydrate with a dreierkette‐type anion. In these structures, linear finite chains of silicate tetrahedra (Q2 units) are linked to central Ca‐O layers, and tetrahedral aluminum occupies bridging positions in the chains. The main chain length and the amount of aluminum incorporated in the tetrahedral chains depend on the activator used. The detection of Q3 silicon entities in alkaline‐activated slags is discussed in relation to the possible formation of cross‐linked structures that may be responsible for increased flexural and compressive strengths in AAS mortars.

Ab Initio MO Studies on Polysilane Oligomer Radical Anions as Model Molecules of Polysilane Radical Anions

Polysilane oligomer radical anions with up to six Si atoms have been theoretically investigated as model molecules of high polymer polysilane radical anions by ab initio MO theory. According to the calculated results, the polysilane oligomer radical anions can exist as bound anions having a σ-type ground state with an unpaired electron occupying a Si−Si antibonding σ* orbital. They are stabilized with an increase in the Si−Si main chain length both in terms of the boundness of an unpaired electron and bonding strength. The π-type states, on the other hand, exist as excited states for these oligomer radical anions. The calculated results strongly suggest that polysilane radical anions with a π-type ground state are hardly generated regardless of their molecular size and geometry. The Si 3d orbital contributions in the ground and excited states of the polysilane radical anions, such as dπ−dπ conjugations, have also been investigated.

Orientation of the Main Chain in Liquid-Crystalline Side-Chain Polyesters with Variation of Main-Chain Spacer Length

Previous X-ray investigations on liquid-crystalline side chain polyesters with variable spacer length in the side chain as well as in the main chain led to the assumption that the structure will change qualitatively if the main chain spacer length exceeds a certain value. We obtained indications supporting this assumption by applying two-dimensional 13 C NMR. It was shown that for a sample with main chain spacer shorter than the critical length, the main chain segments align perpenducular to the side chains ( = - 0.46), and for spacer length larger than critical length, the main chain segments preferentially orient themselves parallel to the side chain ( = - 0.28)

The effect of main chain length of 2-methylalkane on adsorption onto OH in the micropores of zeolite

The adsorption of 2-methylalkanes (propane, butane and pentane) onto ferrierite zeolite was studied by infrared (IR) spectroscopy at temperatures below room temperature. It was found that 2-methylpropane molecules penetrate into micropores only partially, and that only a small fraction of the acidic OH groups available in the micropores interact with the alkyl groups of 2-methylpropane. The interaction is therefore considered to represent interaction between the methyl groups and OH groups located close to the entrance of the micropores. Increasing the carbon number of the main alkyl chain of 2-methylalkanes resulted in a proportional increase in the fraction of acidic OH groups interacting with alkyl groups. Infiltration of n-alkane molecules into the micropores of ferrierite therefore appears to be hindered by methylation of the carbon at the second position. In general, stability was achieved when the longest alkyl chain had entered the micropores of ferrierite, allowing the pore length of ferrierite to be estimated from the extrapolated length of the main alkyl chains. The estimated length of up to 30 nm is consistent with SEM observation.