Study of Norway spruce cell wall structure with microscopy tools

The distribution and orientation of wood cell wall polymers play an important role in its physical, chemical and mechanical properties, and thus in the transformation into final products. Specifically, the orientation of cellulose elementary fibrils (EF) controls the performance of wood in almost every end use. Moreover, lignin is covalently linked to many of the cell wall polysaccharides, which imposes a serious technical challenge during the degradation of cellulose into value added products. Therefore, the deep understanding of the organization of the cell wall materials is imperative. In this study, normal Norway spruce wood was studied with a high-resolution cryo-transmission electron microscope (cryo-TEM). Both, two- (2D) and three-dimensional (3D) imaging techniques within TEM were applied on ultrathin wood sections to understand the wood structure. The defibration mechanisms in high-temperature thermomechanical pulping (HT-TMP) was also studied with a conventional TEM. Furthermore, the accessibility of cell wall lignin was studied with TEM and Raman microspectroscopy by analysing fresh and solvent extracted ultrathin sections of Norway spruce branch wood. The results showed that the organization of EFs varies from layer to layer and also within a single layer. In addition to the well-adopted concept of longitudinal EF angle in tangential plane, this study showed the presence of an out-of-plane EF angle relative to the cell wall plane. The S1 layer had a transverse EF orientation with a predominant radial lamellar structure of EF bundles. Both crossed and parallel EF orientations were detected in the S1-2 transition layer, which was supported by the defibration mechanisms in HT-TMP. EFs in the outer-S2 layer had a relatively high longitudinal EF angle and a large out-of-plane angle with respect to the tangential plane, which continued to decline inward and became almost axial in the inner-S2 layer. A transverse, out-of-plane EF orientation in the S3 transverse sections was observed. The models of the wood cell wall summarize most of the findings regarding the wood ultrastructure. Study of the lignin extracted ultrathin sections showed the change of lignin concentration in all cell wall layers during the extraction process. However, lignin obtained after extraction consists mainly of secondary wall lignin as this area contains most of the total cell wall lignin in conifer tracheids. The new observations on the wood cell wall structure may lead to a better understanding of the reactivity of cellulosic fibers in biochemical, chemical and mechanical treatments

Ugi multicomponent reaction to prepare peptide–peptoid hybrid structures with diverse chemical functionalities

Monodisperse sequenced peptides and peptoids present unique nano-structures based on their self-assembled secondary and tertiary structures. However, the generation of peptide and peptoid hybrid oligomers in a sequence-defined manner via Ugi multicomponent reaction has not yet been studied. Herein, we report a synthetic strategy that enables both the modification of peptides as well as the generation of sequence-defined peptide–peptoid hybrid structures. Our synthetic methodology rests on the fusion of solid phase peptide synthesis with Ugi multicomponent reactions. We evidence that a diversity of chemical functionalities can be inserted into peptides or used in the design of peptide–peptoid hybrids exploiting a wide functional array including amines, carboxylic acids, hydrocarbons, carbohydrates as well as polymers, introducing a sequence-defined synthetic platform technology for precision peptoid hybrids

Sequence length dependence in arginine/phenylalanine oligopeptides: Implications for self-assembly and cytotoxicity

We present a detailed study on the self-assembly and cytotoxicity of arginine-rich fragments with general form [RF]n (n = 1–5). These highly simplified sequences, containing only two l-amino acids, provide suitable models for exploring both structure and cytotoxicity features of arginine-based oligopeptides. The organization of the sequences is revealed over a range of length scales, from the nanometer range down to the level of molecular packing, and their cytotoxicity toward C6 rat glioma and RAW264.7 macrophage cell lines is investigated. We found that the polymorphism is dependent on peptide length, with a progressive increase in crystalline ordering upon increasing the number of [RF] pairs along the backbone. A dependence on length was also found for other observables, including critical aggregation concentrations, formation of chiral assemblies and half maximum inhibitory concentrations (IC50). Whereas shorter peptides self-assemble into fractal-like aggregates, clear fibrillogenic capabilities are identified for longer sequences with octameric and decameric chains exhibiting crystalline phases organized into cross-β structures. Cell viability assays revealed dose-dependent cytotoxicity profiles with very similar behavior for both glioma and macrophage cell lines, which has been interpreted as evidence for a nonspecific mechanism involved in toxicity. We propose that structural organization of [RF]n peptides plays a paramount role regarding toxicity due to strong increase of local charge density induced by self-assemblies rich in cationic groups when interacting with cell membranes

Structural behaviour and gene delivery in complexes formed between DNA and arginine-containing peptide amphiphiles

We describe in depth the structure of complexes formed between DNA and two classes of arginine-containing peptide amphiphiles, namely, the lipopeptide PRW–C16 (P = proline, R = arginine, W = tryptophan, C16 = C16 : 0 alkyl chain) and the bolaamphiphile RFL4FR (R = arginine, F = phenylalanine, L = leucine). A combination of X-ray and neutron scattering provided unprecedented insights into the local structure of these complexes. Lipopeptide-based complexes self-assembled into layered structures with large-scale fractal features, hosting DNA in the interstices. Bola-amphiphile scaffolds were characterized by planar structures with DNA strands presumably sandwiched in-between peptide nanotapes. Importantly, complexation did not affect the structural integrity of DNA in either of the two complexes. The bolaamphiphile conjugates displayed high levels of molecular ordering in contrast to the liquid-crystalline features observed in lipopeptide assemblies. Peptide–DNA complexes were assessed for their potential as a means to deliver the reporter vector pEGFP-N1 into SW480 human colon carcinoma cells. Successfully transfected cells expressed green fluorescent protein. The potentiating effect of PRW–C16 on the cellular uptake of ectopic DNA was found to be much greater than that observed with RFL4FR. In contrast to the bolaamphiphile-based conjugate, the liquid-crystalline nature of the lipopeptide complex is likely to play a key role in DNA release and transfection efficiency since these weakly bound structures require lower energy expenditure during disassembly and load release

Self-assembled arginine-capped peptide bolaamphiphile nanosheets for cell culture and controlled wettability surfaces

The spontaneous assembly of a peptide bolaamphiphile in water, namely, RFL4FR (R, arginine; F, phenylalanine; L, leucine) is investigated, along with its novel properties in surface modification and usage as substrates for cell culture. RFL4FR self-assembles into nanosheets through lateral association of the peptide backbone. The L4 sequence is located within the core of the nanosheets, whereas the R moieties are exposed to the water at the surface of the nanosheets. Kinetic assays indicate that the self-assembly is driven by a remarkable two-step process, where a nucleation phase is followed by fast growth of nanosheets with an autocatalysis process. The internal structure of the nanosheets is formed from ultrathin bolaamphiphile monolayers with a crystalline orthorhombic symmetry with cross-β organization. We show that human corneal stromal fibroblast (hCSF) cells can grow on polystyrene films coated with films dried from RFL4FR solutions. For the first time, this type of amphiphilic peptide is used as a substrate to modulate the wettability of solid surfaces for cell culture applications

The effect of lipidation on the self-assembly of the gut-derived peptide hormone PYY3–36

Lipidation is a powerful strategy to improve the stability in vivo of peptide drugs. Attachment of a lipid chain to a hydrophilic peptide leads to amphiphilicity and the potential for surfactant-like self-assembly. Here, the self-assembly and conformation of three lipidated derivatives of the gastrointestinal peptide hormone PYY3–36 is examined using a comprehensive range of spectroscopic, scattering, and electron microscopy methods and compared to those of the parent PYY3–36 peptide. The peptides are lipidated at Ser(11), Arg(17), or Arg(23) in the peptide; the former is within the β-turn domain (based on the published solution NMR structure), and the latter two are both within the α-helical domain. We show that it is possible to access a remarkable diversity of nanostructures ranging from micelles to nanotapes and fibrillar hydrogels by control of assembly conditions (concentration, pH, and temperature). All of the lipopeptides self-assemble above a critical aggregation concentration (cac), determined through pyrene fluorescence probe measurements, and they all have predominantly α-helical secondary structure at their native pH. The pH and temperature dependence of the α-helical conformation were probed via circular dichroism spectroscopy experiments. Lipidation was found to provide enhanced stability against changes in temperature and pH. The self-assembled structures were investigated using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). Distinct differences in nanostructure were observed for lipidated and unlipidated peptides, also depending on the position of lipidation. Remarkably, micelles containing lipopeptides with α-helical peptide conformation were observed. Gelation was observed at higher concentrations in certain pH intervals for the lipidated peptides, but not for unlipidated PYY3–36. Thus, lipidation, in addition to enhancing stability against pH and temperature variation, also provides a route to prepare PYY peptide hydrogels. These findings provide important insights into the control of PYY3–36 conformation and aggregation by lipidation, relevant to the development of future therapeutics based on this peptide hormone, for example, in treatments for obesity

Identifying Long-Term Deposit Customers : A Machine Learning Approach

Majority of the revenue from the banking sector is usually generated from long term deposits by customers. It is for banks to understand customer characteristics to increase product sales. To aid this, marketing strategies are employed to target potential customers and let them interact with the banks directly, generating a large amount of data on customer characteristics and demographics. In recent years, it has been discovered that various data analysis, feature selection and machine learning techniques can be employed to analyze customer characteristics as well as variables that can impact customer decision significantly. These methods can be used to identify consumers in different categories to predict whether a customer would subscribe to a long-term deposit, allowing the marketing strategy to be more successful. In this study, we have taken a R programming approach to analyze financial transaction data to gain insight into how business processes can be improved using data mining techniques to find interesting trends and make more data-driven decisions. We have used statistical analysis like Exploratory Data Analysis (EDA), Principal Component Analysis (PCA), Factor Analysis and Correlations in the given data set. Besides, the study's goal is to use at least three typical classification algorithms among Logistic Regression, Random Forest, Support Vector Machine and K-nearest neighbors, and then make predictive models around customers signing up for long term deposits. Where we have gotten best accuracy from Logistic Regression which is 90.64 % as well the sensitivity is 99.05 %. Results were analyzed using the accuracy, sensitivity, and specificity score of these algorithms.acceptedVersionPeer reviewe

Nanosheet formation by an anionic surfactant-like peptide and modulation of self-assembly through ionic complexation

The surfactant-like peptide (Ala)6-(Asp) (A6D) is shown to self-assemble into ultrathin (3 nm thick) nanosheets in aqueous solution above a critical aggregation concentration. A combination of circular dichroism and FTIR spectroscopy and X-ray diffraction shows that the nanosheets comprise interdigitated bilayers of the peptide with β-sheet conformation. The self-assembly can be modulated by addition of hexamethylenediamine which is expected to interact with the anionic C terminus (and C-terminal D residue) of the peptide. Multiple ordered nanostructures can be accessed depending on the amount of added diamine. Nanosheet and bicontinuous network structures were observed using cryogenic-TEM and small-angle X-ray scattering. Addition of hexamethylenediamine at a sufficiently large molar ratio leads to disruption of the ordered nanostructure and the formation of a solution of A6D–diamine molecular complexes with highly charged end groups. The multiple acid-functionalized nanostructures that are accessible in this system are expected to have many applications in the fabrication of new nanomaterials

Self-assembly of the toll-like receptor agonist macrophage-activating lipopeptide MALP-2 and of its constituent peptide

The self-assembly of the macrophage-activating lipopeptide MALP-2 in aqueous solution has been investigated and is compared to that of the constituent peptide GNNDESNISFKEK. MALP-2 is a toll-like receptor agonist lipopeptide with diverse potential biomedical applications and its self-assembly has not previously been examined. It is found to self-assemble, above a critical aggregation concentration (cac), into remarkable “fibre raft” structures, based on lateral aggregation of β-sheet based bilayer tapes. Peptide GNNDESNISFKEK also forms β-sheet structures above a cac, although the morphology is distinct, comprising highly extended and twisted tape structures. A detailed insight into the molecular packing within the MALP-2 raft and GNNDESNISFKEK nanotape structures is obtained through X-ray diffraction and small-angle X-ray scattering. These results point to the significant influence of the attached lipid chains on the self-assembly motif, which lead to the raft structure for the lipopeptide assemblies

Self-assembly of telechelic tyrosine end-capped PEO and poly(alanine) polymers in aqueous solution

The self-assembly in aqueous solution of three novel telechelic conjugates comprising a central hydrophilic polymer and short (trimeric or pentameric) tyrosine end-caps has been investigated. Two of the conjugates have a central poly(oxyethylene) (polyethylene oxide, PEO) central block with different molar masses. The other conjugate has a central poly(l-alanine) (PAla) sequence in a purely amino-acid based conjugate. All three conjugates self-assemble into β-sheet based fibrillar structures, although the fibrillar morphology revealed by cryogenic-TEM is distinct for the three polymers—in particular the Tyr5-PEO6k-Tyr5 forms a population of short straight fibrils in contrast to the more diffuse fibril aggregates observed for Tyr5-PEO2k-Tyr5 and Tyr3-PAla-Tyr3. Hydrogel formation was not observed for these samples (in contrast to prior work on related systems) up to quite high concentrations, showing that it is possible to prepare solutions of peptide–polymer-peptide conjugates with hydrophobic end-caps without conformational constraints associated with hydrogelation. The Tyr5-PEO6k-Tyr5 shows significant PEO crystallization upon drying in contrast to the Tyr5-PEO2k-Tyr5 conjugate. Our findings point to the remarkable ability of short hydrophobic peptide end groups to modulate the self-assembly properties of polymers in solution in model peptide-capped “associative polymers”. Retention of fluidity at high conjugate concentration may be valuable in potential future applications of these conjugates as bioresponsive or biocompatible materials, for example exploiting the enzyme-responsiveness of the tyrosine end-group