**Abstract**

Polyesteramides PNOBDME (C34H38N2O6)n, Poly[oxy(1,2-dodecane)-oxycarbonyl-1,4-phenylene-amine-carbonyl-1,4-phenylene-carbonyl-amine-1,4 phenylene-carbonyl], and PNOBEE (C26H22N2O6)n, Poly[oxy(1,2-butylene) oxy-carbonyl-1,4-phenylene-amine-carbonyl-1,4-phenylene-carbonyl-amine-1,4-phenylene-carbonyl], have been designed and synthesized as cholesteric liquid crystals (LCs)—through a condensation reaction between 4- 4′-(terephthaloyldiaminedibenzoic chloride) (NOBC) and racemic glycol, DL-1,2-dodecanediol or DL-1,2-butanediol, respectively—as chemical modifications of multifunctional cholesteric LC polyesters, involving new properties but holding the precursor helical macromolecular structures. The new compounds have been characterized by <sup>1</sup> H and 13C-NMR, COSY and HSQC, exhibiting two 1 H-independent sets of signals observed for each enantiomer, attributed to two diastereomeric conformers, *gg* and *gt*, of the torsion containing the asymmetric carbon atom in the spacer. They have also been characterized by x-ray diffraction with synchrotron radiation source. Thermal behaviour of the new compounds is studied by thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis. The substitution of the ester groups in the mesogen by amide groups causes an increase of thermal stability with respect to the precursors. Optical rotatory dispersion (ORD) is evaluated. Morphology of powdered PNOBDME exhibits spherical clusters of about 5 μm in diameter homogeneously dispersed. Molecular models show helical polymeric chains with stereoregular head-tail, isotactic structure, explained as due to the higher reactivity of the primary hydroxyl with respect to the secondary one in the glycol through the polycondensation reaction. Besides being biocompatible, these synthetic polyesteramides have proved to act as non-viral vectors in gene therapy and be able to transfect DNA to the nucleus cell. Similar new cationic cholesteric liquid crystal polyesters have also been synthesized in our laboratory.

**Keywords:** cholesteric LC polymer, biocompatible polyesteramides, synthesis, characterization, SAXS/WAXS, molecular simulation

## **1. Introduction**

In 1944, Erwin Schrödinger, one of the founders of quantum mechanics, completed in Dublin a small book entitled *What Is Life? The Physical Aspect of the Living Cell* [1]. He predicted there the concept of "aperiodic crystal", to define a gene or perhaps the whole fibre of the chromosome, "that in my opinion, is the material

carrier of life…," "able to grow in aggregates bigger and bigger without the clumsy resource of repetition in three directions" as crystals do [2].

The concept of "aperiodic crystal" was surprisingly premonitory 9 years before the structure of DNA fibres was determined by x-ray diffraction as a helical structure by Franklin [3] ("Photograph 51" in **Figure 1(a)**), Wilkins [5] and Watson and Crick who reported the double helix with periodic order along the sugar-phosphate helical backbone, every 34 Å, and with the *aleatory* distribution of the complementary base pairs [4] (**Figure 1(b)**). The sequence of base pairs along the structure, without lateral periodic order, being convenient to endow DNA of their capacity to store genetic information.

In 1988 Ringsdorf evidenced the parallelism between thermotropic and lyotropic liquid crystals (LCs) in materials science and lipids in life science, with common amphiphilic nature [6]. Both self-organize their molecules in supramolecular systems, leading to functional units in highly oriented systems, exhibiting new properties. The importance of lyotropic LCs for the life sciences has been known for a long time as a prerequisite for the development of life and the ability of cells to function. In materials sciences, the concept of function through organization led to the development of new liquid crystalline materials for advanced applications.

Since 1992 the International Union of Crystallography redefined the concept of crystal as: "Any solid which has a diffraction pattern essentially discrete" (Fourier space) [7]. Since then, the *crystal family* was accepted to be composed of *periodic* and *aperiodic crystals*, and liquid crystals belong to the last group.

With increasing temperature, they do not directly go from the crystalline state into the melt, but, in the middle, they undergo a *mesophase* state which combines the order of perfect crystals and mobility of liquids.

All mesophases exhibit long-range orientational order, by keeping the parallel orientation of their longitudinal molecular axes. Two major classes can be

#### **Figure 1.**

*(a) Photograph 51 by [3]; (b) DNA crystal structure according to [4]. Details of double-stranded PolyA-PolyT and PolyC-PolyG are shown at the right-hand side.*

**81**

**Figure 3.**

**Figure 2.**

*Cholesteric Liquid Crystal Polyesteramides: Non-Viral Vectors*

**1.1 Synthetic cholesteric liquid crystal polymers**

DL-1,2-dodecanediol or DL-1,2-butanediol, respectively.

differentiated: *nematic* (with molecular centres distributed isotropically) and *smectic* (with their molecular centres organized in layers). The special array of nematic planes stacked in a helical superstructure with a prevalent screw direction is called

DNA behaves as liquid crystal with the special array of the nematic planes, containing complementary base pairs, stacked in a superstructure with chiral helical symmetry of the charge distribution [8–10]. **Figure 3** shows micrographs of the

Two multifunctional cholesteric liquid crystal polyesters (ChLCP), named PTOBDME [C34H36O8]n and PTOBEE [C26H20O8]n, with chemical formulations in **Figure 4**, were synthesized in our laboratory—through a condensation reaction between 4-4′-(terephthaloyl-dioxybenzoylchloride) (TOBC) and racemic glycol,

Although only racemic materials were used in their synthesis, a cholesteric, chiral morphology, theoretically unexpected, was found for PTOBDME, m = 9 in **Figure 4**. Evidence of this was obtained when a white solid, recrystallized as the second fraction from toluene mother liquor after the filtration of the polymer, was

result had been previously attained for liquid crystal PTOBEE, m = 1 in **Figure 4**.

(0.0056 mol/l, toluene). The synthetic method [11, 12], based on the previously reported by Bilibin [13, 14], leads to the obtaining of two or more fractions with progressively enriched diastereomeric excess. Its structure and diastereomeric

The structure of these optically active cholesteric LC polymers was characterized by NMR, Raman spectroscopy, steady-state fluorescence and SAXS/WAXS [16, 17], as rigid or semirigid helical LC polymers chains with flexible branches (chiral groups are located in the backbone), **Figure 5**, one of the major types of

Both polymers behave as thermotropic and lyotropic. They self-assemble in nanocavities in solution, with different conformations depending on the solvent

*Types of liquid crystal mesophases: (a) nematic, (b) smectic a and (c) cholesteric, helical pitch.*

*Cholesteric mesophase of liquid crystal DNA exhibiting columnar hexagonal phase.*

589 = −1.43 (1.538 g/100 ml, toluene). A similar

25

589 = −2.33

25

Its second fraction was isolated as –PTOBEE, with a value of [α]

macromolecules forming the cholesteric mesophase [18].

cholesteric mesophase of DNA as the columnar hexagonal phase.

*DOI: http://dx.doi.org/10.5772/intechopen.91317*

the cholesteric mesophase (**Figure 2**).

identified as –PTOBDME, with [α]

excess could be characterized by NMR [15].

*Cholesteric Liquid Crystal Polyesteramides: Non-Viral Vectors DOI: http://dx.doi.org/10.5772/intechopen.91317*

*Liquid Crystals and Display Technology*

store genetic information.

carrier of life…," "able to grow in aggregates bigger and bigger without the clumsy

In 1988 Ringsdorf evidenced the parallelism between thermotropic and lyotropic liquid crystals (LCs) in materials science and lipids in life science, with common amphiphilic nature [6]. Both self-organize their molecules in supramolecular systems, leading to functional units in highly oriented systems, exhibiting new properties. The importance of lyotropic LCs for the life sciences has been known for a long time as a prerequisite for the development of life and the ability of cells to function. In materials sciences, the concept of function through organization led to the development of new liquid crystalline materials for advanced applications.

Since 1992 the International Union of Crystallography redefined the concept of crystal as: "Any solid which has a diffraction pattern essentially discrete" (Fourier space) [7]. Since then, the *crystal family* was accepted to be composed of *periodic*

With increasing temperature, they do not directly go from the crystalline state into the melt, but, in the middle, they undergo a *mesophase* state which combines

All mesophases exhibit long-range orientational order, by keeping the parallel orientation of their longitudinal molecular axes. Two major classes can be

*(a) Photograph 51 by [3]; (b) DNA crystal structure according to [4]. Details of double-stranded PolyA-PolyT* 

and *aperiodic crystals*, and liquid crystals belong to the last group.

the order of perfect crystals and mobility of liquids.

The concept of "aperiodic crystal" was surprisingly premonitory 9 years before the structure of DNA fibres was determined by x-ray diffraction as a helical structure by Franklin [3] ("Photograph 51" in **Figure 1(a)**), Wilkins [5] and Watson and Crick who reported the double helix with periodic order along the sugar-phosphate helical backbone, every 34 Å, and with the *aleatory* distribution of the complementary base pairs [4] (**Figure 1(b)**). The sequence of base pairs along the structure, without lateral periodic order, being convenient to endow DNA of their capacity to

resource of repetition in three directions" as crystals do [2].

**80**

**Figure 1.**

*and PolyC-PolyG are shown at the right-hand side.*

differentiated: *nematic* (with molecular centres distributed isotropically) and *smectic* (with their molecular centres organized in layers). The special array of nematic planes stacked in a helical superstructure with a prevalent screw direction is called the cholesteric mesophase (**Figure 2**).

DNA behaves as liquid crystal with the special array of the nematic planes, containing complementary base pairs, stacked in a superstructure with chiral helical symmetry of the charge distribution [8–10]. **Figure 3** shows micrographs of the cholesteric mesophase of DNA as the columnar hexagonal phase.
