Biopolymers: origin, chemistry, and biology

A brief statement concerning the way in which biopolymers may have originated in the nonbiological world is made, including experimental evidence. This also includes a discussion of such matters as the way in which the code might have originated, that is, the relationship between polypeptides and polynucleotides as well as the secondary and tertiary structure resulting from the primary structure determination. The importance of the interaction of biopolymers with lipids for the formation of limiting membranes, leading to the formation of cells and other self-organizing cellular type organelles, is discussed. Thus, the second critical physical-chemical problem for cellular organization, namely, the biopolymer-lipid interaction, is now coming under scrutiny, both in terms of synthetic systems as well as natural ones.     

生物高分子静电纺丝研究进展

静电纺丝(电纺)技术是一种制备直径为数十纳米到数微米的纳米纤维的有效方法。由于生物高分子具有良好的生物相容性,近年来国内外对生物高分子的电纺制备进行了大量研究。这种生物高分子纳米纤维在组织工程支架、组织修复等方面有独特的优势。本文对生物高分子——多糖、蛋白质、核酸(DNA)的静电纺丝研究进行了总结。     

磷脂的合成进展

磷脂是细胞膜双层脂膜的基本结构单元，在许多生理活动中起着重要作用。磷脂的合成关键在于：(1)手性合成子甘油衍生物的合成；(2)C1和C2上不同的饱和或不饱和酰基的引入；(3)磷脂头基的偶联。本文从这三个方面出发，介绍了近年来光学活性磷脂的合成研究进展。     

Phospholipids as Functional Constituents of Biomembranes

This article describes new methods for the synthesis of biologically active phospholipids. The physical properties of such compounds are directly related to their chemical structure, the position of the substituents esterified with glycerol not only influencing the physical properties but also the biological function of the phospholipids. Phase transitions can be induced by temperature changes and—in biological systems—by changes in the surface charge or the degree of protonation. In model studies, the properties of lipid phases differ sufficiently to influence and control biological membrane processes. Alkyl glycerides can modify the properties of biological membranes quickly and reversibly to increase the permeation of active compounds. An important example is the improved transport of cytostatic drugs across the blood-brain barrier. Knowledge about the substrate specificity of enzymes that metabolize phospholipids allows the synthesis of tailored cytotoxic phospholipids which selectively accumulate in malignant tissues. Thus, the interplay of chemical synthesis and investigations of physical structure lays a foundation for the understanding of simple membrane processes on a molecular level, and the experience gained with such model systems can, in turn, be used to influence natural membranes, such as those of the blood-brain barrier or of tumors, in a directed way.     

Chemical Modifications of Biopolymers by Quinones and Quinone Methides

Many quinones and their precursors, which are transformed oxidatively into quinones and/or quinone methides, are important natural products. As secondary metabolites, they frequently possess antibiotic and cytotoxic activities, in addition to acting sometimes as pathogens. Several plants and animals, especially insects, use quinonoid substances for defense, often with spectacular results. On the macromolecular level, quinone methides have a key role in the plant kingdom in lignin biosynthesis; the biosynthesis of melanoproteins exemplifies the reactions of o-quinones in the animal kingdom. In insects, cross-linking of structural proteins through quinones and quinone methides results in the construction of the sclerotized exoskeleton. For mankind, the reactivity of quinones in biological systems has far-reaching consequences of pharmaceutical, toxicological, and technical relevance. The examples in this review show that a common principle underlies these reactions, namely, the chemical modification of biopolymers. As demonstrated particularly well in a more detailed discussion of the chemical principles of insect cuticle sclerotization, several major and important new results have emerged from the development and applications of modern methods of sample separation and from solid-state NMR spectroscopy.     

Calorimetric experiments on social insects

Direct calorimetric experiments on the social insects: honeybees, bumblebees and hornets are described as function of castes, age, number of animals in a group, temperature, sound generation, hibernation and influence of pheromones. Two honeybee subspecies, the European bee Apis mellifera carnica and the Egyptian bee Apis mellifera lamarckii, were compared calorimetrically in their energy metabolism which differed considerably in favour of the more alert Egyptian form.

Moreover, thermoelectric cooling boxes for camping were applied as simple heat conduction calorimeters and as artificial nesting facilities for bumblebees and hornets. Their colonies could be monitored calorimetrically and thermometrically throughout the season. In spring, initial nests with only a few workers and one queen were collected in the field and transferred to these boxes where they continued their normal development up to full size of several hundred individuals. By this means, energy turnover of insect colonies could be evaluated under varying conditions.     

Phospholipids in marine environments: a review

This paper provides a brief summary of environmental and ecological concepts, and analytical techniques for marine phospholipids (PL). These compounds have been recognized to be a major component of lipids which play a vital role as structural and functional components of biological membranes in all marine organisms from viruses to large animals. Major areas discussed are developed methods of PL analysis and their limitations and implications. Another important aspect of PL in marine ecosystems is also discussed here, that is, the role and dynamics of PL as a significant component of the nutrient phosphorus (P). However, information on PL as a P component in marine environments, such as their spatial and temporal distribution, their contribution to the total P pool, and their biological availability as the nutrient P source, is still limited. It is argued that this is due to the separation of marine PL studies into either “lipid studies” or “nutrient P studies”. New techniques are reviewed that can be developed as a powerful tool to unite the two aspects of PL studies.     

生物高分子聚苹果酸及其衍生物的合成与应用前景

生物高分子对生命过程十分重要,它们表现出了卓越的特性和潜在的应用前景,因而一直是国内外学者的一个新的研究热点。聚苹果酸及其衍生物作为一类新型的生物高分子同样具有一些独特的性质。本文介绍了聚苹果酸及其衍生物的结构和性能特点,全面综述了它们的合成与制备方法研究的进展,展示了它们作为生物医用材料在药物释放体系、组织工程等领域中的应用前景。     

The Differential Calorimetric Study of the Reactivity of Unstable Compounds

The detection of unstable intermediates in chemical, photochemical, and radiation-chemical reactions can be greatly facilitated by the use of thermoanalytical methods. Special advantages are offered by differential thermal analysis (DTA), since it permits fast, easy investigation, from about ?150°C upward in some cases, over a wide temperature range. In this way processes that under normal conditions follow one another with immeasurable rapidity can be separated on the basis of their different temperature dependences. The great sensitivity of the method also allows the use of very dilute solutions, so that the studies can be confined to unimolecular processes. The value of the method for the determination of energetic and kinetic data is illustrated by its application to the photochemically obtanable, unstable, ozonide-like epidioxydihydrofurans.     

Calorimetric analysis of the ethanolysis of 1,2-epoxybutane

Polyethers, which are produced by alcoholysis of oxiranes, are often used as solvents in chemical plants. The spectra of the products can be influenced by the choice of the catalyst (acid or base). The results of the base-catalyzed ethanolysis of 1,2-epoxybutane are displayed. The reaction was investigated calorimetrically by varying the molar ratio between ethanol and 1,2-epoxybutane, the starting temperature and the concentration of the catalyst sodium hydroxide. Additionally, the influence of the used alcohol will be shown in one example. To determine the activation parameters, the experiments were evaluated by the nonlinear software package TA-kin v3.3.     

Trimethylarsonium-Based Cationic Phospholipids for Gene Delivery

Abstract

Lipophosphoramide-based cationic lipids are a class of synthetic vectors used for gene delivery that can be produced in multigram scale. The use of trimethylarsonium moiety as a cationic polar head was beneficial to produce efficient gene delivery vectors for in vivo applications. Moreover, this type of cationic lipid can also exhibit some bactericidal effects.     

Actional Mechanism of Trifluoroacetic Acid for the Separation of Biopolymers by Reversed-phase Liquid Chromatography

The present paper covers the actional mechanism of trifluoroacetic acid for the separation of biopolymers investigated by using the parameters of stoichiometric displacement model for retention(SDM-R) in reversed-phase liquid chromatography. It was found that the trifluoroacetic acid(TFA) may participate in, or stimulate the association among displacing agent molecules in mobile phase, and decrease the affinity of both the associate molecules of the displacing agent and the TFA-protein ion-pairing. The former dominates over the separation selectivity of biopolymers as the concentration of TFA is lower than a given value, and the two contrary functions partly offset to each other and the latter dominates as its concentration is greater than the given value.     

Calorimetric investigation of complex reaction courses in organic chemistry

Acetylation of different hexanediols as a complex reaction has been investigated by calorimetry. The calorimetric curves demonstrate that the reaction rate depends on the molecular structure. In case of 1,6- and 2,5-hexanediols, the activation parameters have been obtained by nonlinear evaluation procedures with the program TA-kin v3.3. The kinetic results show, that the formation of the diester is characterized by higher activation energies than that of the monoester.     

Relationships between miscibility behavior and chemical structure of phospholipids in pseudobinary systems

The influence of chain length differences of cephalines and the influence of the head group methylation on the miscibility behavior of N-methylated phosphatidylethanolamine (PE) mixtures in aqueous dispersions were tested. Nine different phase diagrams were studied by means of differential scanning calorimetry. The phase diagrams of the five pseudobinary cephaline/cephaline/water systems (fatty acid chain length: C _n , n = 12–18) showed that in the high temperature L_α phase all the homologous cephalines were completely miscible. In the low-temperature phase a distinct succession of the phase diagram types was observed according to increasing chain length differences of the PEs: complete miscibilty (C₁₂/C₁₄; C₁₄/C₁₆), peritectic mixing behavior (C₁₂/C₁₆; C₁₄/C₁₈), eutectic mixing behavior (C₁₂/C₁₈). Furthermore four phase diagrams of pseudobinary phospholipid systems consisting of N-methylated PEs with different numbers of methyl groups and a constant length of fatty acid chains were investigated and compared. These four phase diagrams showed phase separations in the low-temperatures phase (gel phase). The width and the concentration range of the miscibility gaps changed systematically with increasing degree of methylation of the head group of the mixing components and are connected with different possibilities of PEs to form hydrogen bridges between the mixture components. Received: 26 August 1999/Accepted: 30 August 1999     

Calorimetric and nuclear byproduct measurements in electrochemical confinement of deuterium in palladium

We present the results of a new experiment with our multicell set-up implemented with mass spectrometric measurements of⁴He and a highly improved neutron detector. The excess heat measured is comparable with the results of other laboratories, but no neutrons were found and the tritium excess was lower than expected from the power excess. ⁴He has been measured in the electrolysis gases and a tentative correlation of ⁴He with excess power is presented and discussed.     

Calorimetric investigations of urease inhibition by heavy metal ions

The subject of this publication is calorimetric investigations on the inhibitor effect of heavy metal ions on the enzyme urease. The obtained results allow quantification of the inhibitors (Cd²⁺-, As³⁺-, Zn²⁺-, Pb²⁺-ions) via the initial reaction rate of enzymatically catalysed urea hydrolysis. The interpretation potential of the calorimetric measurements is underlined by the determination of the inhibiting mechanisms for the example of Cd²⁺- and As³⁺-ions, the findings on the time regime of the inhibition process, and the detection of heavy metal ions in the ppm range. The use of several different buffer substance revealed the influence of the latter on the intensity of heavy metal inhibition. This opens the path to both the selective analysis of heavy metals via pattern recognition and to the improvement of detection sensitivity.     

Calorimetric study of sodium-rich zirconium phosphate

The heat capacity investigation of crystalline pentasodium zirconium tris(phosphate) was carried out in a vacuum adiabatic calorimeter between 7 and 340 K and in a differential scanning calorimeter of the heat bridge type between 330 and 620 K. Between 389 and 424 K, an isostructural solid-to-solid phase transition of Na₅Zr(PO₄)₃, has been found, the nature of which is connected with a centering of off-centered zirconium atoms in octahedral sites and an occupation transfer between sodium sites in the structure. The results were used to calculate the characteristics of the phase transition and the thermodynamic functions of Na₅Zr(PO₄)₃: the transition temperature T°_trs, enthalpy of transition Δ_trsH°, entropy of transition Δ_trsS°; enthalpy H°(T)−H°(0), entropy S°(T) and Gibbs function G°(T)−H°(0) over the range from 0 to 620 K. From hydrofluoric acid solution microcalorimetry, the enthalpy of solution of Na₅Zr(PO₄)₃ at 298.15 K has been determined and the standard enthalpy of formation has been derived. By combining the data obtained by the two techniques, the Gibbs function of formation of Na₅Zr(PO₄)₃ at 298.15 K has been calculated.     

An Effective Fluorescent Sensor for Choline-Containing Phospholipids

A set of weak CH⋅⋅⋅O interactions is responsible for the recognition of tetraalkylammonium ions (ball-and-stick structure) by the tripodal receptors depicted in the diagram, in which the binding pocket is lined with squaramide units. The association constants of the fluorescent receptors are remarkably high at about 10⁵ M ⁻¹ and can be used for signaling the presence of selected choline phospholipids. Z=RNH, where R=alkyl, arylamino; X⁻=BH₄⁻, Cl⁻, Br⁻, I⁻.     

Direct Electrochemistry of Horseradish Peroxidase Immobilized in Calcium Carbonate Microsphere Doped with Phospholipids

Protein electrochemistry affords a direct method to study the biological electron transfer processes. However, supplying a biocompatible environment to maintain the native state of protein is all‐important and challengeable. Here, we chose vaterite, one of the crystalline polymorphs of calcium carbonate, with highly porous nature and large specific surface area, which was doped with phospholipids, as the matrix to immobilize horseradish peroxidase (HRP). The integrity of HRP was kept during the simple immobilization procedure. By virtue of this organic/inorganic complex matrix, the direct electrochemistry of HRP was realized, and the activity of HRP for catalyzing reduction of O₂ and H₂O₂ was preserved.     

Calorimetric measurements and first principles to study the (Ag-Li) liquid system

Integral molar enthalpies of mixing were determined by drop calorimetry for (Ag-Li) liquid alloys at two temperatures (1253 and 873) K. The integral molar enthalpies of mixing are negative in the entire range of concentrations. For the mole fraction of lithium X_Li = 0.5664, minimum value of the integral enthalpy of mixing of at ΔH_m = −11.679 kJ/mol was observed. For (Ag-Li) liquid alloys, between T = (873 and 1253) K no temperature dependence was observed. Ab initio molecular dynamics was used to simulate liquid phase structures at T = 873 K (Li-rich side) and at T = 1250 K (Ag-rich phase) for subsequent calculation of the vibrational energy, respectively. Our measured and calculated data were compared with literature data.