Molecular cable

Figure 27. Tetrakisl4, 5 -bis(decoxy)ben20-18-crown-61phthalocyanine 22. Proposed structure of the crystalline phase (a) view along the normal on the Pc xy-plane and (b) view along the molecular x-axis. (c) Multiwired molecular cable self-assembled in chloroform solution.

Since caroviologens are rather fragile compounds, they can be protected from the environment by inclusion into polyanionic derivatives of (J-cyclodextrin in a rotaxane fashion 102 [8.156]. Also, in the design of molecular devices, it may be desirable to introduce some extent of redundancy in order to reduce the risk of device failure. This is the case in the tris-carotenoid macrobicycle 103 that represents a sort of triple-threated molecular cable whose crystal structure 104 has been determined. It forms a dinuclear Cu(i) complex 105 in which the bound ions introduce a positive charge at each of the species, a feature of potential interest for transmembrane inclusion [8.157]. 

Compound 114b can be regarded as multifunctional molecular cable with the central electron conducting phthalocyanine surrounded by the ion channels formed by the crown ethers and isolated by the alkyl chains. 

Fig. 12 Electron transfer pathways in self-assembled monolayers (a) communication of immobilized dehydrogenases via the oxidation of NADH at PQQ-modified SAMs and (b) possible designs for molecular cables through a SAM.

Future challenging aspects involve the design of molecular cables in order to directly connect the active site of an enzyme with the electrode surface. For this purpose, either the overall electron-transfer distance can be subdivided by integration of redox relays into the monolayer (Fig. 12b) or parts of the nonconducting alkyl spacer may be replaced by conducting oligomers (Fig. 12c). 

Electrical Properties. Erom a chemical standpoint, HDPE is a saturated aUphatic hydrocarbon and hence a good insulator. Its electrical characteristics are given in Table 1. Because polymer density and molecular weight affect electrical properties only slightly, HDPE is widely used for wire and cable insulation. 

DTDP > DIDP > DINP > DOP > DIHP > DBP. Higher molecular weight esters such as trimeUitates are even more thermally stable and trimeUitate esters find extensive use in the demanding cable specifications which have strict mass loss requirements. 

Butyl ruhher vulcanizates have tensile strengths up to 2,000 psi, and are characterized hy low permeahility to air and a high resistance to many chemicals and to oxidation. These properties make it a suitable rubber for the production of tire inner tubes and inner liners of tubeless tires. The major use of butyl rubber is for inner tubes. Other uses include wire and cable insulation, steam hoses, mechanical goods, and adhesives. Chlorinated butyl is a low molecular weight polymer used as an adhesive and a sealant. 

Many polymer items are designed specifically to make contact with other materials. Where surface contact is concerned, two key properties are coefficient of friction and abrasion resistance. Polymers used in such applications include ultra high molecular weight polyethylene, polyacctal, fluorinated polymers, and natural and synthetic rubbers. Examples that we routinely come across include furniture upholstery, bushings and gears in office equipment, and bicycle tires. Industrial uses include the outer cover of electrical cables, and pipes that convey abrasive liquids such as slurries and powders. 

Low melting point Low boiling point Physically soft Malleable, not brittle Low electrical conductivity Dissolve in non-polar solvents Insoluble in polar solvents Ice melts in the mouth Molecular nitrogen is a gas at room temperature We use petroleum jelly as a lubricant Butter is easily spread on a piece of bread We insulate electrical cables with plastic3 We remove grease with methylated spiritb Polyurethane paint protects the window frame from rain... 

Even though for each peptide or protein the MPL value for the protofibril may be different, all the available data can be summarized in a fairly simple scheme. The basic subunit of all amyloid fibrils is a 4- to 5-nm-wide protofibril whose detailed molecular architecture is species dependent. All the other structures observed can be either described as ribbons, sheets, or multistranded cables of protofibrils (Fig. 3). 

Figure 1. Stylised chemical sensor comprising a conducting cable or track to convey the electronic signal to the outside world, a transducer to sense the chemical signal and convert it into an electronic form, and a chemically sensitive film or membrane at which the molecular binding event occurs.

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