精细化学品生产工艺学 (9).pdf

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1、Supramolecular Nanotube Architectures Based on Amphiphilic MoleculesToshimi Shimizu,*Mitsutoshi Masuda,and Hiroyuki MinamikawaNanoarchitectonics Research Center(NARC),National Institute of Advanced Industrial Science and Technology(AIST),Tsukuba Central 5,1-1-1 Higashi,Tsukuba,Ibaraki 305-8565,Japan

2、Received June 22,2004Contents1.Introduction14012.Theoretical Background of Chiral Self-Assembly14043.Methods for Nanotube Formation14073.1.Chiral Self-Assembly14073.2.Packing-Directed Self-Assembly14083.3.Amphiphilic Polymer Assembly14083.4.Molecular Sculpting14083.5.Template Processes14093.6.Other

3、Methods14094.Molecular Structure and Nanotube Morphology14094.1.Low-Molecular-Weight Amphiphiles14094.2.Amphiphilic Polymers14204.3.Polymerization and Cross-Linking14215.Control of Dimensions14235.1.Outer Diameter14235.2.Inner Diameter14245.3.Length14255.4.Wall Thickness14266.Synthesis of Hybrid Tub

4、ular Structures14276.1.Classification of Template-Directed Syntheses 14276.2.exo-Templating14276.3.endo-Templating14327.Applications and Properties14347.1.Technological Applications14347.2.Mechanical Properties14357.3.NanotubeVesicle Networks14367.4.Properties of Water Confined in a HollowCylinder14

5、388.Concluding Remarks14389.Acknowledgment143910.References14391.IntroductionAmphiphilic molecules,of which soap is a typicalexample,possess antagonistic hydrophilic and hy-drophobic moieties in the same molecule.Carbohy-drate amphiphiles,commonly referred as glycolipids,greatly contribute to the st

6、ructural stability and thefunction of biomembranes in living systems.1,2Inaqueous media,lipid molecules self-assemble intodiverse aggregate morphologies,depending on themolecular shape and solution conditions such as lipidconcentration,electrolyte concentration,pH,andtemperature.3On the basis of man

7、y systematicexperiments,Kunitake et al.detailed the relation-ships between the structures of synthetic bilayer-forming compounds and the resulting self-assembledmorphologies:4-6the molecular conformation,a va-riety of functionalities necessary for aggregation,andthe location and orientation of those

8、 functionalitiesToshimi Shimizu(center)was born in Osaka,Japan,in 1952.He receivedhis B.S.(1975)and M.S.(1977)degrees in polymer chemistry from KyotoUniversity,Japan,and in 1983 he received his Ph.D.degree,also fromKyoto University.In 1977,he joined the Research Institute of Polymersand Textiles,par

9、t of what was then the Agency of Industrial Science andTechnology(now the National Institute of Advanced Industrial Scienceand Technology,AIST),Japan.After postdoctoral research at the FreeUniversity Berlin with Professor J.-H.Fuhrhop,he joined the NationalInstitute of Materials and Chemical Researc

10、h(NIMC),AIST,in 1993.Since2001,he has been the director of the Nanoarchitectonics Research Center(NARC),AIST.He is also now directing a Core Research for EvolutionalScience and Technology(CREST)project entitled“Functional High-Axial-Ratio Nanostructure Assembly for Nano-Space Engineering”funded byth

11、e Japan Science and Technology Agency(JST).His research focuseson noncovalent synthesis and structural analysis of high-axial-rationanostructures generated by the self-assembly of amphiphilic molecules.Mitsutoshi Masuda(left)was born in Kagawa,Japan,in 1966.He receivedhis Ph.D.in organic chemistry f

12、rom Tokyo University of Agriculture andTechnology,Japan,in 2000.He joined the Research Institute of Polymersand Textiles in 1992.He joined NIMC in 1993 and started working withDr.Toshimi Shimizu in 1994.After a period of postdoctoral work withProf.E.W.Meijer at the Eindhoven University of Technology

13、 in 2001 onthe polymerization of columnar assemblies,he began working at NARC.His key research interests are the self-assembly of glycolipids and covalentfixation of the assemblies for the construction of well-defined nano-objects.Hiroyuki Minamikawa(right)received his B.Sc.(1986)and M.Sc.(1988)degr

14、ees in chemistry from the University of Tokyo.He worked at theResearch Institute of Polymers and Textiles from 1988 to 1992 and atNIMC from 1993 to 2001.He has studied the physicochemical propertiesof synthetic glycolipid assemblies and their applications for membraneproteins.Since 2001,he has been

15、working with Dr.Toshimi Shimizu atNARC.His research interests include the molecular design of syntheticglycolipids,and structural and thermodynamic aspects of glycolipidassemblies.1401Chem.Rev.2005,105,1401144310.1021/cr030072j CCC:$53.50 2005 American Chemical SocietyPublished on Web 03/24/2005play

16、 a crucial role in determining the self-assemblingbehavior.7,8Thus,rational design of molecular struc-tures and self-assembly conditions permits the regu-lation of the self-assembled morphologies with 1-100nm dimensions with single-nanometer precision.Carbon nanotubes,which were first discovered byI

17、ijima in the early 1990s,9,10have recently demon-strated the reality of the world of nanotechnology.In a chemical field,there are hollow cylindricalsupramolecular objects consisting of many identicallipid molecules as building blocks.The dimensionsof the smallest lipid nanotubes(LNTs)are similarto t

18、hose of both multiwall carbon nanotubes(CNTs)and microtubules consisting of tubulin proteins(Fig-ure 1).These three tubular objects share a commonfeature:the hollow cylindrical structures are stabi-lized by helical arrangements of constituent units(carbon atoms,lipid molecules,or tubulin dimers).Alt

19、hough studies of carbon nanotubes in a physicalfield and biologically generated microtubules arenumerous,there have been only a few systematicstudies of lipid or polymer nanotubes.11,12No definiteguidelines for the design of molecular structures ofnanotube-forming amphiphiles have been laid out.The

20、relationship between the combination of hydro-philic and hydrophobic moieties in the amphiphilesand the size of the resulting nanotube structures hasnot been determined.Hollow cylindrical structures of lipid moleculesappeared in a series of aggregate morphologies withhigh axial ratios.The first repo

21、rts of the formationof LNTs from bilayer-forming amphiphiles 1(8,9),13-162,17and 318,19came independently and almost simul-taneously from three research groups in the UnitedStates and Japan.It should be noted that thesenanotubes were reported about seven years beforeIijima discovered the existence o

22、f multiwall carbonnanotubes.9Many amphiphilic polymers can self-assemble togenerate various morphologies,including micelles,rods,and vesicular aggregates.20,21Nanotube forma-tion is,however,limited to several block copolymersystems.22-27The reason for this limitation is thatnanotube formation genera

23、lly requires highly orderedmolecular packing and anisotropic intermolecularinteractions,and most coil-coil block copolymersshow higher chain flexibility and fewer anisotropicintermolecular interactions than low-molecular-weight lipids.Furthermore,many of the polymernanotubes are generated under kine

24、tic conditionsand then become trapped,for example,by the glassynature of the insoluble core of the nanotube.Thus,among the several types of diblock copolymers,rod-coil block copolymers have a tendency to form poly-mer nanotubes.The diameters of lipid-and copolymer-based nano-tubes characteristically

25、 span the region between 10and 1000 nm.Neither top-down-type microfabrica-tion procedures nor any fabrication methods for car-bon nanotubes can generate tubular structures withthese dimensions.Therefore,lipid-and copolymer-based nanotubes with well-defined hollow cylinders,whose diameters are 10-100

26、 times those of thesmallest molecular nanotubes,28-30are expected to actas novel host substances in mesoscale host-guestchemistry.These cylinders should be able to accom-modate guest substances 10-100 times as large asFigure 1.Representative nanotube structures with a hollow cylinder ca.10 nm wide,t

27、he profiles of which are classifiedon the basis of physical,chemical,and biological viewpoints.The bottom column indicates the building block that makesup the tubular assemblies.The images of the carbon nanotube and the microtubule are provided by NEC Corporation andNational Partnership for Advanced

28、 Computational Infrastructure(NPACI),respectively.1402Chemical Reviews,2005,Vol.105,No.4Shimizu et al.conventional guest molecules such as metal cations,aromatic compounds,or a single polymer chain.Thediameter distribution of a variety of known tubularobjects is summarized in Figure 2.Molecular nano

29、-tubes such as cyclodextrin and cyclic peptide nano-tubes have inner diameters less than 1 nm.28-35Thecyclodextrin nanotubes can encapsulate a variety ofsingle polymer chains in the inner cavity,whereascyclic peptide nanotubes can translate alkali or alkalimetal cations through to the inner volume.C

30、arbonnanotubes,metal sulfides such as molybdenum disul-fide,36,37and clay layer structures such as imogolite38span generally the diameter region from 1 to 10 nm,which is larger than the diameters of molecularnanotubes.On the other end of the size spectrum arehollow polymer fibers with diameters of c

31、a.100 m.The smallest tubular materials commercially avail-able may be finely pulled glass capillaries for micro-injection use,which have a 500 nm inner diam-eter at the tip(Femtotip,Eppendorf Co.Ltd.).Lipid-and copolymer-based nanotubes are the main nano-tubes in the 10-1000 nm size region(see Figur

32、e 2).The need to improve miniaturization and deviceperformance in the microchip and microelectronicsindustry has recently inspired many investigationsinto supramolecular chemistry.In particular,theability to precisely control the inner and outerdiameters of self-assembled LNTs directly deter-mines t

33、heir suitability for technological applications.Understanding how structural variation affects nano-tube dimensions at the molecular level would facili-tate a more efficient and systematic approach togenerating rationalized tubular libraries.The pur-pose of this review is to summarize recent advance

34、sand to address several approaches to controlling thedimensions of lipid and polymer nanotubes,focusingon the outer and inner diameters,lengths,andmembrane wall thickness.Synthetic inorganic nanomaterials,although di-verse in composition,generally lack the structuralvariety characteristic of supramo

35、lecular structuresand other organic structures.39In addition,thestructural hierarchy and macroscopic shape of inor-ganic nanostructures,such as spheres,40-42tubes,43,44fibers,45,46and hollow shells,44,47-49depend on thesubtle interplay of extrinsic factors associated withthe growth mechanism.Recentl

36、y,self-assembled tubular structures madeof glycolipids or phospholipids have been used astemplates to yield metal oxide nanotubes,as well asorganic-metallic and organic-inorganic nanohybridswith high axial ratios.11,50-52Figure 3 illustrates thevariety of nanotubes derived from the self-assemblyof l

37、ipids and amphiphilic copolymers.Lipid head-groups can function as templates for the nucleation,growth,and deposition of inorganic substances on theexternal surface of preformed organic templates(Figure 3c,d,and h).The well-known 1(8,9)nano-tubes have been successfully mineralized with nickel,11copp

38、er,11alumina,51and silica.52Metal nanowires lessthan 50 nm wide can also be produced by templatinga hollow cylinder of tobacco mosaic virus(TMV)53orLNTs(Figure 3e and g).54Furthermore,silica nano-tubes obtained using a self-assembled rod as atemplate for the sol-gel reaction of silica precursorscan

39、provide a novel confined nanospace for the self-assembly of lipids,leading to the fabrication of avariety of hybrid nanotubes with concentric organicand inorganic layers(Figure 3j,k,and m).55Suchhollow cylindrical nano-and microstructures madeof organic,inorganic,or organic-inorganic hybridmaterials

40、 have potential technological applicationsas sensor/actuator arrays,56,57nanowires,58and op-toelectronic devices.59,60The variety of self-assembled tubular morphologieswith well-defined diameters,lengths,and wall thick-Figure 2.Diameter distribution of tubular structures that exist in the real world

41、.Lipid nanotubes with less than 10 nmdiameters are generally unavailable.Abbreviations:LNT,lipid nanotube;NT,nanotube;SWCNT,single-wall carbonnanotube;MWCNT,multiwall carbon nanotube;M.W,molecular weight;Agg.,aggregation.Nanotube Architectures Based on Amphiphilic MoleculesChemical Reviews,2005,Vol.

42、105,No.41403nesses possess fascinating characteristics for creatingnovel hybrid tubular nanostructures.Note thatthe generation of a variety of tubular structures con-sisting of inorganic,organic-inorganic,and organic-metal hybrids starts with molecular self-assembly.Therefore,in this review,the term

43、 supramolec-ular nanotube architectures is defined broadly toinclude hybrid nanotubes as well.We begin thisreview with a description of the theoretical back-ground for the chiral self-assembly of LNTs(sec-tion 2)and then present an overview of methods fornanotube formation(section 3).Next,we focus o

44、nprogress in research on molecular structure andsupramolecular nanotube architectures made inthe past decade(sections 4 and 5,respectively).Wenext describe the template-directed production ofinorganic tubular structures(section 6),which arepromising applications of LNTs.Finally,we alsotouch on the n

45、ovel properties of single LNTs(sec-tion 7).First,however,we must define the terminology oftubular structures.The tubes that have emerged re-cently can be grouped into two principal classifica-tions,depending on tube diameter:(1)nanoscaletubes(nanotubes)and(2)microscale tubes(micro-tubes or tubules)(

46、Figure 4).Depending on the tubeconstituents,a species name is added as a prefix:forexample,carbon nanotube,lipid nanotube,or goldnanotube.The term tubule generally refers to a smalltube or canal:uriniferous tubule and seminiferoustubule are examples that can be found in medicaldictionaries.Microtubu

47、le is a well-known term for acytoskeletal element of eukaryotic cells that is a long,generally straight,hollow tube.Although the termlipid tubule is also commonly used,it seems to besynonymous with the term lipid nanotube.To confergenerality on the terminology of nanotubes and toavoid confusion,we u

48、se the terms lipid nanotube andpolymer nanotube in place of lipid tubule,togetherwith silica nanotube,gold nanotube,and hybridnanotubes.2.Theoretical Background of ChiralSelf-AssemblyTheories based on molecular chirality have beenused to explain the molecular packing of LNTs.Figure 3.Variety of nano

49、tube structures whose syntheses start with molecular self-assembly of low-molecular-weight orpolymer amphiphiles.(a and b)Molecular self-assembly into a nanotube or rod.(c)Coating of metals.(d and f)Depositionof metal alkoxides on the surfaces of the nanotubes and the subsequent calcination into a d

50、ouble-layered metal oxidenanotube.(e and g)Filling of metals and the subsequent removal of the organic shell that will result in the formation ofa metal nanowire.(h and i)Deposition of metal alkoxides on the surface of the rod and the subsequent calcination into asingle-layered metal oxide nanotube.