Flexible linking groups

Cobalt(II) nitrate induces a columnar nematic phase in the 1 2 complex with 98 (Table 7) as deduced from X-ray scattering which is stable for 30 K. Also, nickel(II) nitrate turned 98 into a liquid crystal with an unknown phase. The complex between 99 and copper(II) nitrate showed the same unknown mesophase. The phase range was 140 K but the samples decompose before clearing. A possible reason for the induction of a mesophase by complexation is the stiffening of the crown and the adjacent flexibly linked groups [112]. 

TABLE 54.6. Thermal and thermal-oxidative stability of some simpie flexible linking groups. ... 

Figure 15.5. Repeat compression cycles of A. a styrene-reinforced aerogel monolith without flexible linking groups and (density = 0.122g/cm, surface area = 366 mVg) B. a st5rrcne-rcinforced monolith with 49 mol% Si derived fnrni hexyl-linked BTMSH (density = 0.232 g/cm, surface area =158 mVg tmd C. the monolith from B. before and after two compressirms. Reprinted from [18], Copyright 2009 American Chemical Society.

Scheme 15.6. Synthesis of MTMS-based aerogels with BTMSPA used as both a flexible linking group and site for tri-isocyanate crosslinking. Reprinted from [38], Cop3uight 2010 American Chemical Society.

While there is a trade-off between modulus and elastic recovery in polymer-reinforced aerogels using flexible linking groups, the combination of MTMS and BTMSPA used in the... 

Figure 5.1 The structure of a glycerophospholipid. A simple diagram showing the charges on the head group. In this struction, palmitic and oleic acids, provide the hydrophobic component of the phospholipids and choline (and four bases) and the phosphate group provide the hydrophilic head. The unsaturated fatty acid, oleic acid, provides a kink in the structure and therefore some flexibility in the membrane structure which allows for fluidity. The more unsaturated the fatty acid, the larger is the kink and hence more fluidity in the membrane. Cholesterol molecules can fill the gaps left by the kink and hence reduce flexibility. Hydroxyl groups on the bases marked are those that form phosphoester links. Choline and inositol may sometimes be deficient in the diet so that they are, possibly, essential micronutrients (Chapter 15).

Fig. 8 General structure of semi-flexible oligobenzoate Hekates 34—36. (a) These stars may consist of three identical arms (34), two (35) or three (36) different arms. Thereby the length (n,m,l), the peripheral chains (R, R", R "), the linking groups X (OOC, COO, CONH) to the core and the substituents Y (H, I) can he adjusted, (b) Borderline conformers - star-shaped, f.-shaped and cone-shaped conformers - for a non-symmetric oligobenzoate scaffold (X = OOC). They can be created by rotation about the C-O single bond within the carboxy linking group to the core...

Direct attachment of biomolecules to the surface can introduce a steric constraint to reactivity of the molecule which is not encountered when considering molecules free in a solution. This effect can be minimized if, for example, a spacer is introduced between the biomolecule and the linking group. The spacer can be of nearly any desired length and possess a variety of chemical characteristics, that is, it can be rigid or flexible, hydrophilic or hydrophobic, charged or neutral.1,9... 

The activated carboxyl group is then transferred from carboxybiotin to pyruvate to form oxaloacetate. The long, flexible link between biotin and the enzyme enables this prosthetic group to rotate from one active site of the enzyme (the ATP-bicarbonate site) to the other (the pyruvate site). 

Chromophores With a Flexible Link. Bichromophores containing at one side a naphtyl group and at the other side a series of chromophores, linked by a polymethylene chain [10] have been studied by means of emission spectroscopy. 

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