On the biodegradation of beta-peptides

A consortium of microorganisms was established that was able to grow with the beta-tripeptide H-beta-HVal-beta-HAla-beta-HLeu-OH, with the beta-dipeptide H-beta-HAla-beta-HLeu-OH, and with the beta-amino acids H-beta-HAla-OH, H-beta-HVal-OH, and H-beta-HLeu-OH as the sole carbon and energy sources. This growth was achieved after several incubation-transfer cycles with the beta-tripeptide as the substrate. During degradation of the beta-tripeptide H-beta-HVal-beta-HAla-beta-HLeu-OH, the temporary formation of a metabolite was observed. The metabolite was identified as the beta-dipeptide H-beta-HAla-beta-HLeu-OH by nuclear magnetic resonance spectroscopy and mass spectrometry. This result indicates that in the course of the degradation of the beta-tripeptide, the N-terminal beta-HVal residue was cleaved off by a not yet known mechanism. During the subsequent degradation of the beta-dipeptide, formation of additional metabolites could not be detected. The growth-yield coefficients Y(x/s) for growth on the beta-di- and beta-tripeptide both had a value of 0.45. When a 1:1 mixture of the beta-tripeptide and the corresponding alpha-tripeptide H-Val-Ala-Leu-OH was added to the enrichment culture, the alpha-peptide was completely utilized in six days and thereafter growth of the culture stopped. This result indicates that even in beta-peptide enrichment cultures, alpha-peptides are the preferred substrates. Our experiments clearly show for the first time that beta-peptides and beta-amino acids are amenable to biodegradation and that a microbial consortium was able to utilize these compounds as sole carbon and energy sources. Furthermore, the preparation of beta-amino acids, of derivatives thereof, and of beta-di- and beta-tripeptides is described.     

Theoretical analysis of secondary structures of beta-peptides

Unlike alpha-amino acids, peptides formed from beta-amino acids (beta-peptides) display stability toward enzymatic degradation and may form turns and helices with as few as four residues. Because both the C alpha and C beta of the beta-amino acid may bear substituents, a large number of beta-amino acids can be synthesized. Beta-peptides form various well-defined secondary structures, including 14-helix, 12-helix, 10/12-helix, 10-helix, 8-helix, turn structures, sheets, and hairpins. For all of these reasons, beta-amino acids have been increasingly used as building blocks for molecular design and pharmaceutical applications. To explain the conformational features of beta-peptides, several quantum mechanics and molecular dynamics studies that rationalize the observed conformational features have been reported. However, a systematic account that unifies various factors critical to the conformational features is still lacking. In this Account, we present a detailed analysis of the conformational features of various beta-peptides. We start by studying the basic local conformational features of beta-peptides using di- and tripeptide models. Then, various secondary structures of unsubstituted beta-peptides with differing numbers of residues are investigated using a repeating unit approach to derive the intrinsic backbone conformational features. We find that the 10/12-helix is intrinsically most stable for the beta-peptide backbone. The 14-helix, 12-helix, and 10-helix structures have similar stabilities for beta-peptide backbones of four to six residues. The substituent effects on the stabilities of beta-peptide secondary structures are then analyzed. Combined with the substituent effect and the intrinsic backbone preferences, all experimental observations of secondary structure formation can be understood. For example, the 10/12-helix is favored for like-beta(2)/beta(3)-peptides, unlike-beta(3)/beta(3)-peptides, and beta(3)/beta-hGly-peptides because these substitution patterns do not cause steric problems for the 10/12-helix. Beta(3)-peptides, beta(2)-peptides, and beta (2,3)-peptides favor the 14-helix because the substituents in these peptides benefit the 14-helix the most but significantly destabilize the 10/12-helix. Because the 10/12-helix is intrinsically favored and has two favorable positions in each residue for substituents, many more hybrid beta-peptides are predicted to exist in this secondary structure, which suggests the need for further experiments. These results are valuable for determining the best use of these building blocks in the design of well-structured molecules with desirable chemical functions.     

Variability of water uptake studies of biomedical polymers

Water uptake influences many properties of polymers and has been widely studied. In the context of polymeric biomaterials, several publications reported an unusual high variability of analytical results, without further investigating the cause for this phenomenon. Using selected polymers from the library of L ‐tyrosine‐derived polyarylates and poly(D ,L lactic acid), we showed that nonaged and nonannealed compression molded film samples exhibit the typical large variation in water uptake observed in previous reports. The introduction of an annealing step allows accurate and reproducible water uptake measurements for these polymers. We evaluated the use of ³H‐radiolabeled water for the determination of water uptake, finding that the use of radiolabeled water yields statistically indistinguishable measurements, compared to gravimetric methods, while providing significant advantages in throughput and sensitivity. Using the recommended methods of annealing and ³H‐radiolabled water, the water uptake profiles of 24 polymers of the library of L ‐tyrosine‐derived polyarylates are reported. This article addresses experimental concerns related to water uptake studies and may assist other researchers in improving the accuracy of their water uptake results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Cellular uptake, evolution, and excretion of silica nanoparticles in human cells

A systematic study on the interaction of silica nanoparticles (NPs) with human cells has been carried out in the present work. Endocytosis and exocytosis are identified as major pathways for NPs entering, and exiting the cells, respectively. Most of the NPs are found to be enclosed in membrane bounded organelles, which are fairly stable (against rupture) as very few NPs are released into the cytoplasm. The nanoparticle-cell interaction is a dynamic process, and the amount of NPs inside the cells is affected by both the amount and morphology (degree of aggregation) of NPs in the medium. These interaction characteristics determine the low cytotoxicity of SiO(2) NPs at low feeding concentration.     

Probing the proteolytic stability of beta-peptides containing alpha-fluoro- and alpha-hydroxy-beta-amino acids

One of the benefits of beta-peptides as potential candidates for biological applications is their stability against common peptidases. Attempts have been made to rationalize this stability by altering the electron availability of a given amide carbonyl bond through the introduction of polar substituents at the alpha-position of a single beta-amino acid. Such beta-amino acids (beta-homoglycine, beta-homoalanine), containing one or two fluorine atoms or a hydroxy group in the alpha-position, were prepared in enantiopure form. A versatile method for preparing these alpha-fluoro-beta-amino acids by the homologation of appropriate alpha-amino acids and C-OH->C-F or C=O-->CF(2) substitution with DAST, is described. Consequently, a series of beta-peptides possessing an electronically modified residue at the N terminus or embedded within the chain was synthesized, and their proteolytic stability was investigated against a selection of enzymes. All ten beta-peptides tested were resilient to proteolysis. Introducing a polar, sterically undemanding group, into the alpha-position of beta-amino acids in a beta-peptide chain does not appear to facilitate localized or general enzymatic degradation.     

Kinetic studies on radio-selenium uptake by ion exchange resin

Kinetic studies on the sorption of radioactive Se (IV) ion on Amberlite MB9L have been carried out under a wide range of temperature, pH, initial concentration, and resin weight. Analyses of the experimental data by two theoretical models commonly used to explain the ion exchange kinetics and shrinking core model (SCM), and homogeneous diffusion model (HDM) against exponential diffusion decay model (EDM) show a greater preference of EDM over HDM and SCM at all reaction conditions. The obtained regression coefficient values in case of HDM and SCM are in general not high enough to give a satisfactory fit for the experimental data. The estimated values for EDM parameters provides a good satisfactory fit for the yielded adsorption results as the corresponding linear regression values are high. The sorption process is found to be accompanied with fast film diffusion and slow diffusion between the reacted layer and the shrinking un-reacted core within the ion exchange resin. It also shows that ion exchange as the controlling step offers the lowest probability due to the highest obtained diffusion parameters over the normal tested reaction conditions.     

Cellular uptake mechanisms of functionalised multi-walled carbon nanotubes by 3D electron tomography imaging

Carbon nanotubes (CNTs) are being investigated for a variety of biomedical applications. Despite numerous studies, the pathways by which carbon nanotubes enter cells and their subsequent intracellular trafficking and distribution remain poorly determined. Here, we use 3-D electron tomography techniques that offer optimum enhancement of contrast between carbon nanotubes and the plasma membrane to investigate the mechanisms involved in the cellular uptake of shortened, functionalised multi-walled carbon nanotubes (MWNT-NH(3)(+)). Both human lung epithelial (A549) cells, that are almost incapable of phagocytosis and primary macrophages, capable of extremely efficient phagocytosis, were used. We observed that MWNT-NH(3)(+) were internalised in both phagocytic and non-phagocytic cells by any one of three mechanisms: (a) individually via membrane wrapping; (b) individually by direct membrane translocation; and (c) in clusters within vesicular compartments. At early time points following intracellular translocation, we noticed accumulation of nanotube material within various intracellular compartments, while a long-term (14-day) study using primary human macrophages revealed that MWNT-NH(3)(+) were able to escape vesicular (phagosome) entrapment by translocating directly into the cytoplasm.     

Cellular uptake of tailored copolymer synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization

The tailored copolymer poly(methoxy-PEG acrylate-co-N-hydroxysuccinimide-co-fluorescein diacetate 5-maleimide) (P1) and block copolymer poly(N-isopropylacrylamide)-b-poly(methoxy-PEG acrylate-co-N-hydroxysuccinimide-co-fluorescein diacetate 5-maleimide) (P2) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, which were both water-soluble, fluorescent and containing active group N-hydroxysuccinimide (NHS). Due to the temperature-sensitive poly(N-isopropylacrylamide) unit, the latter copolymer P2 formed nanoparticles at 37 °C in aqueous medium. Both P1 and P2 were taken up by cultured human umbilical vein endothelial cells (HUVECs) and localized mainly in the cytoplasm, which could subsequently be detected by confocal laser scanning microscopy (CLSM).     

HeLa cell entry by guanidinium-rich beta-peptides: importance of specific cation-cell surface interactions

Short cationic oligomers, including arginine-rich peptides and analogous beta-amino acid oligomers ("beta-peptides"), can enter the cytoplasm and nucleus of a living cell from the extracellular medium. It seems increasingly clear that multiple entry pathways are possible, depending upon the structure of the guanidinium-rich molecule, the type of cell, and other factors. We have previously shown that conformational stability and spatial clustering of guanidinium groups increase the HeLa cell entry efficiency of short helical beta-peptides bearing six guanidinium groups, results that suggest that these beta-peptides could be useful tools for studying the entry process. Here we describe studies intended to identify the point in the entry process at which helix stability and spatial arrangement of guanidinium groups exert their effect. Our results suggest that key distinctions involve the mode of interaction between different guanidinium-rich beta-peptides and the HeLa cell surface. A specific guanidinium display appears to be required for proper engagement of cell-surface heparan sulfate proteoglycans and concomitant induction of endocytic uptake.     

Microcomputer-based system for data acquisition and analysis of oxygen uptake studies

The use of a Warburg Respirometer to study oxidation reactions is tedious and time-consuming. A microcomputer-based oxygen uptake device that is more sensitive than a Warburg Respirometer is described. The device consists of stainless steel or Teflon reaction vessels coupled to ultrasensitive pressure transducers. A high speed analog to digital convertor is used to poll the transducers. The direct memory access (DMA) controller of an IBM XT is used to poll the convertor and store the data in memory. Software used to program the DMA controller and IBM XT is described. The reproducibility and utility of the device is demonstrated with a brief study of lipid oxidation.     

Biosorptive uranium uptake by a Pseudomonas strain: characterization and equilibrium studies

The biosorptive uranium(VI) uptake capacity of live and lyophilized Pseudomonas cells was characterized in terms of equilibrium metal loading, effect of solution pH and possible interference by selected co‐ions. Uranium binding by the test biomass was rapid, achieving >90% sorption efficiency within 10 min of contact and the equilibrium was attained after 1 h. pH‐dependent uranium sorption was observed for both biomass types with the maximum being at pH 5.0. Metal uptake by live cells was not affected by culture age and the presence of an energy source or metabolic inhibitor. Sorption isotherm studies at a solution pH of either 3.5 or 5.0 indicated efficient and exceptionally high uranium loading by the test biomass, particularly at the higher pH level. At equilibrium, the lyophilized Pseudomonas exhibited a metal loading of 541 ± 34.21 mg g^?1 compared with a lower value by the live organisms (410 ± 25.93 mg g^?1). Experimental sorption data showing conformity to both Freundlich and Langmuir isotherm models indicate monolayered uranium binding by the test biomass. In bimetallic combinations a significant interference in uranium loading was offered by cations such as thorium(IV), iron(II and III), aluminium(III) and copper(II), while the anions tested, except carbonate, were ineffective. Uranium sorption studies in the presence of a range of Fe³⁺ and SO₄^2? concentrations indicate a strong inhibition (80%) by the former at an equimolar ratio while more than 70% adsorption efficiency was retained even at a high sulfate level (30 000 mg dm^?3). Overall data indicate the suitability of the Pseudomonas sp biomass in developing a biosorbent for uranium removal from aqueous waste streams. © 2001 Society of Chemical Industry     

天然纤维复合泡沫材料的制备

研究了以天然纤维作为骨架材料，聚乙烯醇及其衍生物为泡沫体，并且利用Lyocell纤维的增强作用，采用适当的交联加速剂，制备成的一种新型的可降解亲水泡沫材料。通过正交实验法探讨其最佳制备条件，并对其性能进行了表征。     

The isotherm,kinetic and thermodynamic studies of the cadmium uptake by colpomenia sinuosa

ABSTRACT

A number of isotherm models were studied and modeled for colpomenia sinuosa. The experimental data were fitted among the 12 biosorption kinetic models. Thermodynamic studies indicated a spontaneous and endothermic process. The morphology of the biosorption process was revealed by Fourier transfer infrared (FT-IR) analysis and scanning electron microscope (SEM). The isotherm and kinetic parameters were compared with other microorganisms.     

利用粉煤灰生产混凝土多孔砖

介绍粉煤灰混凝土多孔砖生产的原材料选择、粉煤灰性能、混合料处理、坯体成型与养护等工艺技术及其利废节能的优越性.     

用物理发泡剂制备韧性泡沫硅橡胶

用物理发泡剂制备了具有特殊性能要求的韧性泡沫硅橡胶,重点介绍了原材料预处理、成型技术及加工工艺参数等。应用本工艺可对复杂曲面、平面薄片（厚度≤０．３ｍｍ）、不同密度、不同厚度、不同孔隙率及不同力学性能要求的泡沫硅橡胶实现一次性成型,材料综合物理性指标优于化学发泡,具有一定的实用价值。