PHOTOSENSITIVE BILAYER MEMBRANES AS MODEL SYSTEMS FOR PHOTOBIOLOGICAL PROCESSES

Abstract— Photobiological processes such as photosynthesis, photomorphogenesis, photomovement, and photoreception are all associated with the membranous portions of cells. The unique properties of membrane surfaces are apparently required to achieve biologically relevant energy transduction and photocontrol phenomena and consequently the use of model membrane systems is suggested as an advantageous approach to elucidation of the important physical and chemical processes involved. Black lipid membrane (BLM) and liposome techniques are critically reviewed as preferred techniques for constructing and manipulating lipid bilayers. The lipid bilayer is considered to be the basic foundation for biological membrane models, and specific physical phenomena observed with the bilayers and their biological ramifications are analyzed. Light-stimulated polarization of the membrane and electron transfer across the bilayer are viewed as appropriate analogs of vision and photosynthesis, respectively. Bilayer-adsorbed dye experiments are the simplest systems explored that exhibit polarization and charge transfer across the membrane. Chloroplast extract BLM experiments are cited as an example of the light-stimulated transfer of electrons across the membrane under the influence of a preexisting redox gradient. Biliprotein (phycocyanin or phycoerythrin) on one side of the chloroplast extract membrane permits the direction of electron flow across the membrane so that a redox gradient is created in a manner truly analogous to photosynthesis. The potential for solar energy conversion from such membranes is explicitly considered utilizing a schematic photoelectrochemical cell. Model membranes containing bacterial rhodopsin and phytochrome represent examples of ionic gradients that result in biological energy transduction. Studies of membranes that exhibit transient photoeffects are considered potentially relevant for the elucidation of phototaxis. The analysis of many properties of photosensitive membranes is greatly aided by the use of appropriate theoretical models. It is apparent that there is a great potential for the application of photosensitive model membranes in many research areas involving complex photobiological phenomena and novel methods for solar energy conversion.     

ELECTRONIC PROCESSES AND PHOTOELECTRIC ASPECTS OF BILAYER LIPID MEMBRANES

Abstract— Owing to the complexity of biological membranes, many model systems have been studied in order to gain insight into the molecular mechanism of specific functions. One such model membrane extensively investigated in the past decade is the so-called bilayer lipid membrane (BLM). With suitable modifications, a BLM less than 100 A thick separating two aqueous solutions has been used as a model for a variety of biological membranes. This paper is devoted to a review of the properties and electronic processes of modified BLM.
Recent experiments using these membranes which contain photosynthetic pigments or dyes have demonstrated that, upon illumination, an EMF and a current can be generated. The connection between the photoelectric BLM and light-sensitive biological membranes and the rationale for this work are described.
Additionally, the effects of physical chemical parameters such as electric field, temperature, light intensity, duration of illumination and chemical agents (electron acceptors, donors, uncouplers, etc.) on the photoresponses of BLM are discussed. Other results indicate that BLM containing photoactive compounds behave similar to that of a silicon solar cell with one side of the membrane reducing and the other side oxidizing. The transverse pathway for the electron across the BLM could be provided by carotenoids such as β-carotene. Photoelectric BLM of this type represents a unique kind of energy transducing system and may well be useful in the conversion of solar energy into electricity and/or other forms of energy.     

Polymerizable phospholipids: a novel class of biomaterials

Polymerizable phospholipids are organic monomers that are able to self-assemble into membranes. This is quite similar to the self assembly of naturally occurring lipid membranes found in biological systems. The polymerizable lipids can then be polymerized to stabilize these membranes. These stabilized structures have a number of different morphologies which offer a variety of technically attractive features. This article reviews the chemical and physical properties of these materials in terms of their technological applications.     

Self‐Assembled Polymeric Membranes and Nanoassemblies on Surfaces: Preparation,Characterization, and Current Applications

Biomembranes play a crucial role in a multitude of biological processes, where high selectivity and efficiency are key points in the reaction course. The outstanding performance of biological membranes is based on the coupling between the membrane and biomolecules, such as membrane proteins. Polymer‐based membranes and assemblies represent a great alternative to lipid ones, as their presence not only dramatically increases the mechanical stability of such systems, but also opens the scope to a broad range of chemical functionalities, which can be fine‐tuned to selectively combine with a specific biomolecule. Tethering the membranes or nanoassemblies on a solid support opens the way to a class of functional surfaces finding application as sensors, biocomputing systems, molecular recognition, and filtration membranes. Herein, the design, physical assembly, and biomolecule attachment/insertion on/within solid‐supported polymeric membranes and nanoassemblies are presented in detail with relevant examples. Furthermore, the models and applications for these materials are highlighted with the recent advances in each field.     

Synthetic Membranes—Preparation,Structure, and Application

After a long period of dormancy, membrane separation processes have begun to emerge as technically significant and commercially relevant unit operations. Prior to the mid-sixties, synthetic membranes were employed for those few specialized laboratory applications which could tolerate low permeability and poor selectivity or in electrochemical applications excluding, e. g., batteries, fuel cells, chloride-alkali electrolysis, where marginal chemical stability remained a severe limitation. Within the framework of a broad R & D program started in the US in the mid-fifties and devoted to the production of fresh water from brackish and seawater, developments of more suitable membranes arose out of the application of the principles of physical chemistry, modern polymer chemistry (especially surface or interfacial polymerization and polycondensation technology), and electron microscopy. In particular, it was learned that asymmetric membrane structures comprise a very thin consolidated barrier layer (5000 Å or less for membranes with economically practical filtration rates) supported by an integral but less dense substrate which does not participate in the transport process. Later and after much effort, composite membranes were developed in which the salt-rejecting skin (still only 5000 Å thick) was placed atop a supporting matrix formed from a more chemically and mechanically stable polymer.—The main desalination research effort led to several spin-off developments in related membrane fields, e.g. the successful preparation and commercialization of ultrafiltration technology in the automobile, food, and chemical industries. Also, ion-exchange membranes prepared from perfluorinated polymers offered the electrochemical industry much better chemical stability than the earlier phenolic-resin-based ion-exchange membranes.—Current efforts are aimed at the improved selectivity and stability required for very specific separation processes (e.g. separation of heavy metal salts from waste water or selective enrichment of gases). In the future, the mechanisms of biological processes will have to be exploited for successful development of synthetic membranes suitable for more sophisticated separations.     

Functional regulation of hepatic cytochrome p450 enzymes by physicochemical properties of phospholipids in biological membranes

Knowledge regarding the regulation of hepatic cytochrome P450 (P450) is crucial to the fields of drug therapy and drug development, as well as to our understanding of the mechanisms underlying the metabolic activation of toxic and carcinogenic compounds. P450 is a membrane-anchored protein that shows a variety of interaction with membrane phospholipids, which affect the membrane topology and catalytic activities of the protein. In particular, anionic phospholipids, nonbilayer forming lipids, and the degree of saturation of the lipid fatty acyl chain play important roles in the functional regulation of P450, as well as in the bilayer structure of the membrane. However, despite the importance of phospholipids in the regulation of P450s, the interaction of the protein with membrane phospholipids, and the membrane properties induced by phospholipids which regulate P450, are unclear. In this review, we describe the effect of the physicochemical properties of the phospholipid constituents of biological membranes on hepatic P450 catalytic activity, membrane insertion (and/or penetration), and structural changes.     

In Situ Vesicle Formation by Native Chemical Ligation

Phospholipid vesicles are of intense fundamental and practical interest, yet methods for their de novo generation from reactive precursors are limited. A non‐enzymatic and chemoselective method to spontaneously generate phospholipid membranes from water‐soluble starting materials would be a powerful tool for generating vesicles and studying lipid membranes. Here we describe the use of native chemical ligation (NCL) to rapidly prepare phospholipids spontaneously from thioesters. While NCL is one of the most popular tools for synthesizing proteins and nucleic acids, to our knowledge this is the first example of using NCL to generate phospholipids de novo. The lipids are capable of in situ synthesis and self‐assembly into vesicles that can grow to several microns in diameter. The selectivity of the NCL reaction makes in situ membrane formation compatible with biological materials such as proteins. This work expands the application of NCL to the formation of phospholipid membranes.     

Probing the Interactions of Porphyrins with Macromolecules Using NMR Spectroscopy Techniques

Porphyrinic compounds are widespread in nature and play key roles in biological processes such as oxygen transport in blood, enzymatic redox reactions or photosynthesis. In addition, both naturally derived as well as synthetic porphyrinic compounds are extensively explored for biomedical and technical applications such as photodynamic therapy (PDT) or photovoltaic systems, respectively. Their unique electronic structures and photophysical properties make this class of compounds so interesting for the multiple functions encountered. It is therefore not surprising that optical methods are typically the prevalent analytical tool applied in characterization and processes involving porphyrinic compounds. However, a wealth of complementary information can be obtained from NMR spectroscopic techniques. Based on the advantage of providing structural and dynamic information with atomic resolution simultaneously, NMR spectroscopy is a powerful method for studying molecular interactions between porphyrinic compounds and macromolecules. Such interactions are of special interest in medical applications of porphyrinic photosensitizers that are mostly combined with macromolecular carrier systems. The macromolecular surrounding typically stabilizes the encapsulated drug and may also modify its physical properties. Moreover, the interaction with macromolecular physiological components needs to be explored to understand and control mechanisms of action and therapeutic efficacy. This review focuses on such non-covalent interactions of porphyrinic drugs with synthetic polymers as well as with biomolecules such as phospholipids or proteins. A brief introduction into various NMR spectroscopic techniques is given including chemical shift perturbation methods, NOE enhancement spectroscopy, relaxation time measurements and diffusion-ordered spectroscopy. How these NMR tools are used to address porphyrin–macromolecule interactions with respect to their function in biomedical applications is the central point of the current review.     

Fluorescent lipids: functional parts of fusogenic liposomes and tools for cell membrane labeling and visualization

In this paper a rapid and highly efficient method for controlled incorporation of fluorescent lipids into living mammalian cells is introduced. Here, the fluorescent molecules have two consecutive functions: First, they trigger rapid membrane fusion between cellular plasma membranes and the lipid bilayers of their carrier particles, so called fusogenic liposomes, and second, after insertion into cellular membranes these molecules enable fluorescence imaging of cell membranes and membrane traffic processes. We tested the fluorescent derivatives of the following essential membrane lipids for membrane fusion: Ceramide, sphingomyelin, phosphocholine, phosphatidylinositol-bisphosphate, ganglioside, cholesterol, and cholesteryl ester. Our results show that all probed lipids could more efficiently be incorporated into the plasma membrane of living cells than by using other methods. Moreover, labeling occurred in a gentle manner under classical cell culture conditions reducing cellular stress responses. Staining procedures were monitored by fluorescence microscopy and it was observed that sphingolipids and cholesterol containing free hydroxyl groups exhibit a decreased distribution velocity as well as a longer persistence in the plasma membrane compared to lipids without hydroxyl groups like phospholipids or other artificial lipid analogs. After membrane staining, the fluorescent molecules were sorted into membranes of cell organelles according to their chemical properties and biological functions without any influence of the delivery system.     

Engineering de novo membrane-mediated protein-protein communication networks

Mechanical properties of biological membranes are known to regulate membrane protein function. Despite this, current models of protein communication typically feature only direct protein-protein or protein-small molecule interactions. Here we show for the first time that, by harnessing nanoscale mechanical energy within biological membranes, it is possible to promote controlled communication between proteins. By coupling lipid-protein modules and matching their response to the mechanical properties of the membrane, we have shown that the action of phospholipase A(2) on acyl-based phospholipids triggers the opening of the mechanosensitive channel, MscL, by generating membrane asymmetry. Our findings confirm that the global physical properties of biological membranes can act as information pathways between proteins, a novel mechanism of membrane-mediated protein-protein communication that has important implications for (i) the underlying structure of signaling pathways, (ii) our understanding of in vivo communication networks, and (iii) the generation of building blocks for artificial protein networks.     

Synthetic and biological membranes: Common phenomena

Many of the processes occurring in nature involve membrane transport. Some of the functions performed by such membranes appear to be unique, as well as efficient, and it would be possible to make synthetic membranes having similar properties. This paper discusses some of these phenomena. Further, it may be quite possible that knowledge of synthetic membranes can be extended to better understand the changes which occur in biological ones, and this is also mentioned here.     

Membrane electrochemistry

Electrochemistry and biomembranes are interface science in that both are concerned with the phenomena at, as well as across, the interfaces. Membrane electrochemistry may be defined as the application of electrochemistry to biomembrane studies. Additionally, transport processes within the membrane are involved in biomembranes. Since biomembranes are diverse and are usually not amenable to probing by electrochemicophysical techniques, model membrane systems have been developed for their investigation.

The introduction of experimental bilayer lipid membranes (BLM) technique and its modifications have been instrumental in the development and testing of membrane transport concepts (carriers vs channels) and electronic processes in membranes. Instead merely viewing a biomembrane as a physical barrier containing carriers or channels to carry out ionic processes, an ultrathin lipid or biological membrane can also be considered as a complete ‘electrochemical cell’ with one membrane/solution interface reducing (as a cathode) and the other membrane/solution interface oxidizing (as an anode). It is now possible to understand energy transduction (charge generation, separation, and redox reactions) in terms of ultrathin lipid membranes separating two aqueous solutions.

In this paper, we shall discuss the basic principles of electrochemistry as they are applied to membrane studies. Emphasis will be on experimental bilayer lipid membranes (BLM) which have been extensively investigated as models of biomembranes.     

均相催化氧化中的活性中间体多样性

过渡金属离子在各种化学及生物氧化中扮演着极为重要的作用,现有的研究表明参与催化氧化的关键活性物种已不再局限于金属氧物种(Mn+O),金属氢氧物种(Mn+—OH)与金属过氧物种(Mn+—OOH)均被发现能够参与各种氧化反应。有些有机化合物也能直接催化有机物的氧化反应,同时,相似的有机物如NADH和辅酶Q一直在生物代谢中发挥着重要作用。但是,现有的研究结果还难以清楚解释生物体系中各种氧化酶在不同的氧化反应中选择特定活性物种的内在原因。因此,了解这些活性物种之间的氧化性能异同性将非常有助于了解酶对它们的选择,进而理解酶的催化氧化机理,为药物设计提供理论基础,同时也有助于设计新的氧化催化剂。本文对在各种均相催化氧化及生物氧化反应中出现的主要活性中间体种类、各中间体的反应性能、反应机理进行了总结,并就现有的实验数据对过渡金属氧物种与氢氧物种的氧化性能相似性及相异性进行了初步评述。     

Electronic processes and photosensitization in bilayer lipid membranes

Abstract— In part one of this paper, evidence for electronic processes in experimental and biological membranes are reviewed. The membrane under consideration, be it experimental or biological, is understood to mean an ultrathin bamer separating two aqueous phases. The question ‘can electronic processes occur in/across such a structure immersed in an aqueous environment?’ is answered affirmatively. In the second part of this paper, photosensitization by dyes and photoelectric effects in experimental bilayer lipid membranes observed recently are described.     

Constructing optimum blood brain barrier QSAR models using a combination of 4D-molecular similarity measures and cluster analysis

A new method, using a combination of 4D-molecular similarity measures and cluster analysis to construct optimum QSAR models, is applied to a data set of 150 chemically diverse compounds to build optimum blood-brain barrier (BBB) penetration models. The complete data set is divided into subsets based on 4D-molecular similarity measures using cluster analysis. The compounds in each cluster subset are further divided into a training set and a test set. Predictive QASAR models are constructed for each cluster subset using the corresponding training sets. These QSAR models best predict test set compounds which are assigned to the same cluster subset, based on the 4D-molecular similarity measures, from which the models are derived. The results suggest that the specific properties governing blood-brain barrier permeability may vary across chemically diverse compounds. Partitioning compounds into chemically similar classes is essential to constructing predictive blood-brain barrier penetration models embedding the corresponding key physiochemical properties of a given chemical class.     

细胞无机化学中值得研究的问题

在探索生命奥秘的过程中,生物无机化学研究由分子层次上升到细胞层次是一个必然的趋势,也是解决实际问题的需要.细胞无机化学研究在细胞生命体系中的无机化学反应和探索无机物对生命过程调节或干预的作用和机理,是探索生命体系复杂性研究的重要部分.细胞是保留完整生命活动特征的最小单位,存在周期、分化和受激等状态的不同.从化学的观点,细胞是一个严密设计的分子有序组装体,为一个多靶分子系统,细胞应答表现为由相关反应组合成的复杂过程.细胞无机化学研究包括无机物种在细胞膜上的结合和随后发生的膜结构和功能改变、跨细胞膜和跨生物组织屏障的转运和细胞代谢、细胞中无机化学反应同细胞信号系统的偶联、无机离子与自由基的相互代谢关系以及细胞-无机物固相的相互作用等方面.本文对当前细胞无机化学研究的重点问题进行了讨论.     

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。     

Characterization of ion-exchange membrane materials: properties vs structure

This review focuses on the preparation, structure and applications of ion-exchange membranes formed from various materials and exhibiting various functions (electrodialytic, perfluorinated sulphocation-exchange and novel laboratory-tested membranes). A number of experimental techniques for measuring electrotransport properties as well as the general procedure for membrane testing are also described. The review emphasizes the relationships between membrane structures, physical and chemical properties and mechanisms of electrochemical processes that occur in charged membrane materials. The water content in membranes is considered to be a key factor in the ion and water transfer and in polarization processes in electromembrane systems. We suggest the theoretical approach, which makes it possible to model and characterize the electrochemical properties of heterogeneous membranes using several transport-structural parameters. These parameters are extracted from the experimental dependences of specific electroconductivity and diffusion permeability on concentration. The review covers the most significant experimental and theoretical research on ion-exchange membranes that have been carried out in the Membrane Materials Laboratory of the Kuban State University. These results have been discussed at the conferences "Membrane Electrochemistry", Krasnodar, Russia for many years and were published mainly in Russian scientific sources.     

The effect of phenyltin chlorides on osmotically induced erythrocyte haemolysis

The toxicity of many amphiphilic compounds may result from their effect on the lipid phase of biological membranes. Upon incorporation such compounds may change the properties of membranes in general and in particular alter the organization of membrane lipids. These changes should affect, among other things, the mechanical properties of membranes. We selected two amphiphilic compounds, diphenyltin dichloride (Ph₂SnCl₂) and triphenyltin chloride (Ph₃SnCl), which are known to be located at different regions of the lipid bilayer and to be toxic. As a model biological membrane the erythrocyte plasma membrane was used. Analysis of the haemolysis kinetics showed differences between the effect of the compound studied on mechanical properties at so‐called non‐lytic concentrations. Diphenyltin dichloride showed a limited effect on erythrocyte haemolysis, whereas triphenyltin chloride affected all the parameters measured (extent of initial haemolysis, extent of final haemolysis and membrane mechanical strength). We correlated these effects with the location of the investigated compounds in liposomes. The presented data show that triphenyltin chloride reduces the erythrocyte plasma membrane mechanical strength and increases the extent of haemolysis under osmotic stress conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Polyunsaturation in lipid membranes: dynamic properties and lateral pressure profiles

We elucidate the influence of unsaturation on single-component membrane properties, focusing on their dynamical aspects and lateral pressure profiles across the membrane. To this end, we employ atomistic molecular dynamics simulations to study five different membrane systems with varying degrees of unsaturation, starting from saturated membranes and systematically increasing the level of unsaturation, ending up with a bilayer of phospholipids containing the docosahexaenoic acid. For an increasing level of unsaturation, we find considerable effects on dynamical properties, such as accelerated dynamics of the phosphocholine head groups and glycerol backbones and speeded up rotational dynamics of the lipid molecules. The lateral pressure profile is found to be altered by the degree of unsaturation. For an increasing number of double bonds, the peak in the middle of the bilayer decreases. This is compensated for by changes in the membrane-water interface region in terms of increasing peak heights of the lateral pressure profile. Implications of the findings are briefly discussed.