Spring 2009 EE 710: Nanoscience and Engineering

Transcription

1 Sping 009 EE 70: Nanoscience and Engineeing Pat 5: Chemical Inteactions at the Nanoscale Images and figues supplied fom Honyak, Dutta, Tibbals, and Rao, Intoduction to Nanoscience, CRC Pess, Boca Raton, Chapte 0 (008). Instucto: John D. Williams, Ph.D. Assistant Pofesso of Electical and Compute Engineeing Associate Diecto of the Nano and Mico Devices Cente Univesity of Alabama in Huntsville 406 Optics Building Huntsville, AL Phone: (56) Fax: (56) williams@eng.uah.edu

2 Bonding Attactive foces between atoms fom stong intamolecula bonds as a esult of chemical inteactions Covalent: cabon cabon Ionic: sodium chloide Metallic: nickel clustes Intemolecula bonding: Binding inteactions between molecules Hydogen bonding JDW, UAHuntsville ECE, Sping 009

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4 Bonding Definitions: Physical Pocess: No change in the chemical stuctue of the molecule ChemicalPocess: Change in the chemicalstuctue of the molecule Intemolecula bonds ae physical in natue because they do not significantly change molecula stuctue Howeve is the esult of folding a potein a chemical pocess? The shape of the chemicalstuctue isalteed as well as its chemical eactivity but the atom to atom bonding within the molecule emains mostly unchanged JDW, UAHuntsville ECE, Sping 009 4

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7 Intemolecula bonding Unlike covalent bonds which equie enegies of appoximately 400 kt and ae theefoe stable tbl at STP envionments, Intemolecula bonds (0.00 KT) depend significantly on the immediate envionment. Molecules held togethe by intemolecula binding ae chaacteized using: Pimay stuctue is not alteed Stength of the bonds is elatively weak compaed to Covalent, Ionic, o metallic bonding Solvent is impotant duing synthesis of lage molecules and thei maintenance Both enthalpicand entopic conditions ae impotant tto oveall fee enegy Although individually weak, the summed enegy ove all the bonds in a system can be significant. JDW, UAHuntsville ECE, Sping 009 7

8 Types of Intamolecula bonding Ion Ion and Ion Dipole Inteactions Puely electostatic Van de Waals Dipole Dipole inteactions Coulombic alignment of two o moe pemanent dipoles Hydogen Bonding Extemely stong dipole dipole inteactions Occus between two highly electonegative and small atmos like O and N and a shaed H. Highly diectional and quite specific Hydophobic Inteactions Bonding between nonpola molecules in aqueous solvents Alignment of nonpola egions changes the shape of the molecule and povides moe attachment fo pola sections though hydogen o othe intamolecula bonding mechanisms. Repulsive Foces Steic epulsion occus when electon clouds ovelap Hydophylic epulsion occus in pola liquids with nonpola elements in attempt to maximize hydogen bonding Repulsive entopic elasticity: epulsive foces due to compession of long chain macomolecules Repulsive osmotic: fom electical double layes between two chaged sufaces and steic alignment in macomolecules JDW, UAHuntsville ECE, Sping 009 8

9 Ion Dipole Inteactions Enegy of an Ion Dipole attaction zeμ cosθ Eion dipole = 4πε ε o Z is the atomic numbe (no of electons in obital) μ is the dipole moment Cosθ is the angle of appoach of the ion to the cente of the dipole Stongestt inteaction ti occus at θ=0 Metal cations coodinated in the cente of oganic ings called dative bonding Dipola gp eceptos in potein folding Ionophoes: lipid soluble stuctue that est within a cellula membane. These stuctue pass ions to egulate chage and salt concentation ti within the cell JDW, UAHuntsville ECE, Sping 009 9

10 Dipole Dipole Inteactions Enegy of a Dipole Dipole attaction E E ion dipole dipole dipole μ AμB = 4πε ε o 3 μ AμB = 3 4πε ε o (cosθ cosθ A θ = 0 B sinθ sinθ cosφ) A B φ is the out of plane otation Basis fo the Hydogen bond On a lage scale, collective bonding impats stuctue to DNA JDW, UAHuntsville ECE, Sping 009 0

11 Dative Bonds Stabilization of metal ions by binding sites (ligands) that donate electon pais to vacant metal oute obitals Like a covalent bond in which electons ae shaed, but in dative bonding, both electons ae donated by only one atom Stengthand type of bond aeactuallyactually ion dipole (coodination) bonding One of the significant achievements of nanocluste science: stabilization of Au55 clustes with oganic ligands. Clustes can be died, packaged, shipped, solvenated and utilized to attach gold diectly to biological poteins using the ligand binde. Chelates: specialized fom of metal coodination binding that involves a molecule with at least two ligands Pocess of binding metals to fom macocyclic ings is called chelation JDW, UAHuntsville ECE, Sping 009

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13 π Inteactions Inteplane π bond inteactions between oganic ings ae esponsible fo the thee dimensional stuctue of gaphite. π bond inteactions between oganic ings ae esponsible fo the binding between nucleotides in DNA Allow fo chelation of metal ions Povide numeous confomational shapes in supamolecula chemisty JDW, UAHuntsville ECE, Sping 009 3

14 Hydogen Bonding Twice as stong as dipole dipole bonding 535Ang in length (covalent H is < Ang) Summation of H bonding ove a suface esults in mateial phase changes that ae quite stable w..t. thei local envionment In liquid wate H bonds ae fomed and boken evey 0 s Stuctue of confined wate at the nanoscale is diectly dependent on hydogen bonding Solubility of NaClfo example deceases by a facto of when confined to 8 Angstom poes whee hydogen bonds ae not available 5% of the lattice enegy of solid dihydogen phoshate salts is due to hydogen bonding Also plays a significant ole in the geomety of potein cystals Macoscopic hydophobicity is due to a lack of hd hydogen bonding at the suface JDW, UAHuntsville ECE, Sping 009 4

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16 Van de Waals Attactions Lack diectionality and theefoe not as impotant in supamolecula chemisty Impotant in molecula cavities in which small molecules can be tapped by lage clustes Vey impotant tin polyme chemisty howeve whee self assembly depends on local binding enegies Also impotant in fulleene clustes whee binding is distance dependent and not diectionally dependent due to symmety Unchaged state of fulleenes and nanotubes make them extemely stable with attactive and epulsive foces dependent on inteatomic sepaation moe than dipole bonding JDW, UAHuntsville ECE, Sping 009 6

17 Van de Waals Attactions Van de Waals Attactions Boken down into thee contibutions Keesom vdw attaction ( ) ) ( C T k V p p = = μ μ Debye vdw inteaction ( ) k B T o p πε ) ( C + α μ α μ London vdw foce (dispesive) ( ) ) ( C V o = + = πε α μ α μ ( ) ) ( C I I I I V d o = + = πε α α is the distance between nuclei μ Is the dipole moment, α is the polaizability, I is the ionization potential 7 JDW, UAHuntsville ECE, Sping 009

18 Hamake Equation fo VdW Used fo colloids o and dothe solubilized mateials a Vdw attaction and epulsion fo spheical paticles can be estimated using: V w ( ) A 6 d R + 4Rd + d R + 4Rd + 4d + ln d d + 4Rd + 4Rd + 4d = A is the Hamake constant which anges fom 0=9 to 0 0 J Wate: *0 0 J Metals: 5 40*0 0 J Quatz: 8.7*0 0 J JDW, UAHuntsville ECE, Sping 009 8

19 Hydophobic Effect Least undestood yet vey impotant in biological mateials the attaction ti between wate and itself is the eason fo the unfavoable intefacial enegy between wate and a hydocabon Tanfod, 973 Thus the lack of fee enegy associated with c H bonding ove H OH bonding yields stuctual minimization of non oxygenated cabon mateials in the pesence of hydophilic solvents JDW, UAHuntsville ECE, Sping 009 9

20 Amino Acids and Poteins Numeous methods used to detemine hydophobicity of biological compounds Used to detemine shape and functionality of such stuctues The amount of hydophobicity and hydophilicity ae caclulated togethe to detemine shape and binding constants of these molecules Advanced calculations of vdw volumes ae used outinely in developing dug compounds. JDW, UAHuntsville ECE, Sping 009 0