Korisnik:Palapa/Mehanosinteza

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Mehanosinteza je bilo koja hemijska sinteza kod koje su ishodi reakcija utvrđeni korištenjem mehaničkih ograničenja da usmjere reaktivne molekule na određena molekularna mjesta.

Uvod[uredi | uredi izvor]

Kod uobičajene hemijske sinteze ili hemosinteze, reaktivne molekule se sudaraju sa drugima kroz nasumično termičko kretanje u tekućini ili pari. U hipotetičnom procesu mehanosinteze, reaktivne molekule će biti pridodane molekularnim mehaničkim sistemima, i njihovo susretanje će rezultirati mehaničkim kretnjama zajedno ih uvodeći u planirane sekvence, pozicije, i orijentacije. Predviđa se da će mehanosinteza izbjeći neželjene reakcije držeći potencijalne reaktante odvojenima, i ujedno će jako favorizirati željene reakcije držeći reaktante zajedno sa optimalnim orijentacijama u mnogo molekularnih vibracionih ciklusa. U biologiji, ribozom pruža primjer programabilnog mehanosintetičkog uređaja.

Primitivna, prilično ne-biološka forma mehanohemije je bila obavljena na kriogenim temperaturama koristeći skenirajući tunelski mikroskop. Za sada, takvi uređaji omogućavaju najbliži koncept fabrikacije alata za molekularni inžinjering. Šire iskorištavanje mehanosintheze čeka još napredniju tehnologiju za konstruisanje sistema molekularna mašina, sa sistemima nalik na ribozome kao atraktivnim ranim ciljevima.

Mnogo uzbuđenja u vezi napredne mehanosinteze se odnosi na njenu potencijalnu upotrebu u sklapanju uređaja na molekularnom nivou. Takve tehnike doimaju se da imaju mnoštvo primjena u medicini, avijaciji, izvlačenju resursa, proizvodnji i ratovanju.

Većina teoretskih istraživanja naprednih mašina ovog tipa se fokusiralo na korištenje ugljika, zato što of the many strong bonds it can form, the many types of chemistry these bonds permit, and utility of these bonds in medical and mechanical applications. Carbon forms diamond, for example, which if cheaply available, would be an excellent material for many machines.

Sugerisano je, posebno od strane Kim Eric Drexler-a, da će mehanosinteza biti temelj za molekularne proizvodnje bazirane na nanofabrikama sposobnim da grade makroskopske objekte sa atomskom preciznošću. Njihov potencijal je osporen, najviše od dobitnika Nobelove nagrade Richard Smalleya (koji je predložio, a zatim kritikovao nepodesan pristup baziran na malim prstima) – vidjeti nanotehnologija.

"The Nanofactory Collaboration",[1] kojeg je osnovao Robert Freitas sa Ralph Merkle-om, 2000., je fokusiran na tekuće napore koji uključuju 23 istraživača iz 10 organizacija iz 4 zemlje, koji razvijaju praktičnu istraživačku agendu[2] posebno ciljanu na poziciono kontrolisanu dijamantsku mehanosintezu i dijamantoidni nanofabrički razvoj.

U praksi, dovođenje tačno jedne molekule na poznato mjesto na mikroskopskom vrhu je moguće, ali je dokazano teška automatizacija. Pošto praktični proizvodi zahtijevaju nekoliko stotina miliona atoma, ova tehnika još nije dokazala pratičnost u formiranju realnih proizvoda.

Cilj linije istraživanja mehanosastavljanja se fokusira na prevazilaženje ovih problema kalibracijom, i odabirom odgovarajućih reakcija sinteze. Ima sugestija da se pokuša razviti specijalizovana, veoma mala (ugrubo 1,000 nanometara na jednoj strani) mašinskog alata koji može praviti kopije samog sebe koristeći mehanohemijske načine, pod kontrolom vanjskog računara. In the literature, such a tool is called an assembler or molecular assembler. Once assemblers exist, geometric growth (directing copies to make copies) could reduce the cost of assemblers rapidly. Control by an external computer should then permit large groups of assemblers to construct large, useful projects to atomic precision. One such project would combine molecular-level conveyor belts with permanently mounted assemblers to produce a factory.

In part to resolve this and related questions about the dangers of industrial accidents and popular fears of runaway events equivalent to Chernobyl and Bhopal disasters, and the more remote issue of ecophagy, grey goo and green goo (various potential disasters arising from runaway replicators, which could be built using mechanosynthesis) the UK Royal Society and UK Royal Academy of Engineering in 2003 commissioned a study to deal with these issues and larger social and ecological implications, led by mechanical engineering professor Ann Dowling. This was anticipated by some to take a strong position on these problems and potentials – and suggest any development path to a general theory of so-called mechanosynthesis. However, the Royal Society's nanotech report did not address molecular manufacturing at all, except to dismiss it along with grey goo.

Trenutni tehnički prijedlozi za nanotvornice ne uključuju samo-replicirajuće nanorobote, i nedavna etička uputstva zabranjuju razvoj neograničenih samo-replicirajućih kapaciteta u nanomašinama.[3][4]

Dijamantska mehanosinteza[uredi | uredi izvor]

There is a growing body of peer-reviewed theoretical work on synthesizing diamond by mechanically removing/adding hydrogen atoms [5] and depositing carbon atoms [6][7][8][9][10][11] (a process known as diamond mechanosynthesis or DMS[12]). For example, the 2006 paper in this continuing research effort by Freitas, Merkle and their collaborators reports that the most-studied mechanosynthesis tooltip motif (DCB6Ge) successfully places a C2 carbon dimer on a C(110) diamond surface at both 300 K (room temperature) and 80 K (liquid nitrogen temperature), and that the silicon variant (DCB6Si) also works at 80 K but not at 300 K. These tooltips are intended to be used only in carefully controlled environments (e.g., vacuum). Maximum acceptable limits for tooltip translational and rotational misplacement errors are reported in paper III—tooltips must be positioned with great accuracy to avoid bonding the dimer incorrectly. Over 100,000 CPU hours were invested in this study.

The DCB6Ge tooltip motif, initially described at a Foresight Conference in 2002, was the first complete tooltip ever proposed for diamond mechanosynthesis and remains the only tooltip motif that has been successfully simulated for its intended function on a full 200-atom diamond surface. Although an early paper gives a predicted placement speed of 1 dimer per second for this tooltip, this limit was imposed by the slow speed of recharging the tool using an inefficient recharging method[8] and is not based on any inherent limitation in the speed of use of a charged tooltip. Additionally, no sensing means was proposed for discriminating among the three possible outcomes of an attempted dimer placement—deposition at the correct location, deposition at the wrong location, and failure to place the dimer at all—because the initial proposal was to position the tooltip by dead reckoning, with the proper reaction assured by designing appropriate chemical energetics and relative bond strengths for the tooltip-surface interaction.

More recent theoretical work[13] analyzes a complete set of nine molecular tools made from hydrogen, carbon and germanium able to (a) synthesize all tools in the set (b) recharge all tools in the set from appropriate feedstock molecules and (c) synthesize a wide range of stiff hydrocarbons (diamond, graphite, fullerenes, and the like). All required reactions are analyzed using standard ab initio quantum chemistry methods.

Dodatna istraživanja [14] to consider alternate tips will require time-consuming computational chemistry and difficult laboratory work. U ranim 2000-tim, tipični eksperimentalni postupak je bio dodavanje molekule na vrh atomski force mikroskop, a zatim korištenje sposobnosti prezicnog pozicioniranja mikroskopa da gura molekulu sa vrha na drugu molekulu na supstratu. Pošto uglovi i rastojanja mogu biti precizno kontrolisani, i pošto se reakcija odvija u vakuumu, mogući su novi hemijski spojevi i aranžmani.

Historija[uredi | uredi izvor]

Tehniku pokretanja pojedinačnih atoma je predložio Eric Drexler u svojoj knjizi iz 1986. The Engines of Creation.

U 1988., istraživači na IBM's Zürich Research Institute uspješno su napisali slova "IBM" pomoću ksenonovih atoma na kriogenoj bakarnoj površini, snažno pokazavši pristup validnim. Od tada, brojni istraživački projekti su poduzeti da koriste slične tehnike da smjeste računarske podatke na kompaktan način. Nedavno je tehnika korištena da istraži nove fizičke strukture, ponekada koristeći lasere da potaknu vrhove pojedinih energetskih stanja, ili da ispitaju kvantnu hemiju pojedinih hemijskih veza.

U 1999., predložena je eksperimentalno dokazana metodologija nazvana "feature-oriented" skeniranje[15][16] (FOS). "Feature-oriented" metodologija skeniranja dozvoljava precizno kontrolisanje pozicije sonde (pipalice) mikroskopa sa skenirajućom sondom (SPM) na atomskoj površini na sobnoj temperaturi. Sugerisana metoda podržava punu automatsku kontrolu pojedinačnih i multi-sondnih instrumenata u rješavanju zadataka mehanosinteze i nanofabrikacija.

U 2003., Oyabu i ostali[17] su izvijestili prvu pojavu čistog mehanički osnovanog ostvarenja kovalentnog povezivanja i raskidanja veze, t.j., demonstracije istinske mehanosinteze - iako sa silicijem, a ne sa ugljikovim atomima.

U 2005., ispunjena je prva aplikacija za patent dijamantne mehanosinteze [18].

U 2008., je predložen grant od 3,1 miliona američkih dolara[19] kao fond za razvoj sistema mehanosinteze koji bi dokazali princip.

Također pogledati molekularna nanotehnologija, općenitiji opis mogućih proizvoda, i rasprava o tehnikama asembliranja.

Reference[uredi | uredi izvor]

  1. ^ Nanofactory Collaboration. Molecularassembler.com. Pristup 2011-07-23.
  2. ^ Nanofactory Technical Challenges. Molecularassembler.com. Pristup 2011-07-23.
  3. ^ Molecular Nanotechnology Guidelines. Foresight.org. Pristup 2011-07-23.
  4. ^ N04FR06-p.15.pmd. (PDF) . Pristup 2011-07-23.
  5. ^ Temelso, Berhane; Sherrill, C. David; Merkle, Ralph C.; Freitas, Robert A. (2006). "High-level Ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems". The Journal of Physical Chemistry A 110 (38): 11160–11173. PMID 16986851. doi:10.1021/jp061821e. 
  6. ^ Merkle, RC; Freitas Jr, RA (2003). "Theoretical Analysis of a Carbon-Carbon Dimer Placement Tool for Diamond Mechanosynthesis". Journal of Nanoscience and Nanotechnology 3 (4): 319–24. PMID 14598446. 
  7. ^ Peng, Jingping; Freitas, Robert A.; Merkle, Ralph C. (2004). "Theoretical Analysis of Diamond Mechanosynthesis. Part I. Stability of C2 Mediated Growth of Nanocrystalline Diamond C(110) Surface". Journal of Computational and Theoretical Nanoscience 1: 62–70. doi:10.1166/jctn.2004.007. 
  8. ^ a b Mann, David J.; Peng, Jingping; Freitas, Robert A.; Merkle, Ralph C. (2004). "Theoretical Analysis of Diamond Mechanosynthesis. Part II. C2 Mediated Growth of Diamond C(110) Surface via Si/Ge-Triadamantane Dimer Placement Tools". Journal of Computational and Theoretical Nanoscience 1: 71–80. doi:10.1166/jctn.2004.008. 
  9. ^ Sourina, Olga; Korolev, Nikolay (2005). "Design and Analysis of a Molecular Tool for Carbon Transfer in Mechanosynthesis". Journal of Computational and Theoretical Nanoscience 2 (4): 492–498. doi:10.1166/jctn.2005.003. 
  10. ^ De Federico, Miguel; Jaime, Carlos (2006). "Theoretical Analysis of Diamond Mechanosynthesis. Part III. Positional C2 Deposition on Diamond C(110) Surface using Si/Ge/Sn-based Dimer Placement Tools". Journal of Computational and Theoretical Nanoscience 3 (6): 874–879. doi:10.1166/jctn.2006.003. 
  11. ^ Yin, Zhi-Xiang; Cui, Jian-Zhong; Liu, Wenbin; Shi, Xiao-Hong; Xu, Jin (2007). "Horizontal Ge-Substituted Polymantane-Based C2 Dimer Placement Tooltip Motifs for Diamond Mechanosynthesis". Journal of Computational and Theoretical Nanoscience 4 (7): 1243–1248. doi:10.1166/jctn.2007.004. 
  12. ^ Diamond Mechanosynthesis. Molecularassembler.com. Pristup 2011-07-23.
  13. ^ Freitas Jr., Robert A.; Merkle, Ralph C. (2008). "A Minimal Toolset for Positional Diamond Mechanosynthesis". Journal of Computational and Theoretical Nanoscience 5 (7): 760–861. 
  14. ^ Speeding the development of molecular nanotechnology. www.foresight.org
  15. ^ R. V. Lapshin (2004). "Feature-oriented metodologija skeniranja za ispitivačku mikroskopiju i nanotehnologiju" (PDF). Nanotechnology (UK: IOP) 15 (9): 1135–1151. Bibcode:2004Nanot..15.1135L. ISSN 0957-4484. doi:10.1088/0957-4484/15/9/006.  (prjevod na ruski jezik je dostupan).
  16. ^ R. V. Lapshin (2011). "Feature-oriented scanning probe microscopy". u H. S. Nalwa. Encyclopedia of Nanoscience and Nanotechnology (PDF) 14. USA: American Scientific Publishers. str. 105–115. ISBN 1-58883-163-9. 
  17. ^ Oyabu, Noriaki; Custance, ÓScar; Yi, Insook; Sugawara, Yasuhiro; Morita, Seizo (2003). "Mechanical Vertical Manipulation of Selected Single Atoms by Soft Nanoindentation Using Near Contact Atomic Force Microscopy". Physical Review Letters 90 (17). Bibcode:2003PhRvL..90q6102O. doi:10.1103/PhysRevLett.90.176102. 
  18. ^ Robert A. Freitas Jr., “A Simple Tool for Positional Diamond Mechanosynthesis, and its Method of Manufacture,” U.S. Patent 7.687.146, issued 30 March 2010 html copy Pristup 2011-07-23.
  19. ^ Digital Matter?: Towards Mechanised Mechanosynthesis. Gow.epsrc.ac.uk. Pristup 2011-07-23.

Vanjski linkovi[uredi | uredi izvor]