Properties and structure

The active principle of opium is morphine (Fig. 12.2) and this compound is still one of the most effective painkillers available to medicine. It is especially good for treating dull, constant pain rather than sharp, periodic pain. It acts in the brain and appears to work by elevating the pain threshold, thus decreasing the brain s awareness of pain. Unfortunately, it has a large number of side-effects which include the following  

Some side-effects are not particularly serious. Some, in fact, can be advantageous. Euphoria, for example, is a useful side-effect when treating pain in terminally ill patients. Other side-effects, such as constipation, are uncomfortable but can give clues as to other possible uses for opiate-like structures. For example, opiate structures are widely used in cough medicines and the treatment of diarrhoea. 

The dangerous side-effects of morphine are those of tolerance and dependence, allied with the effects morphine can have on breathing. In fact, the most common cause of death from a morphine overdose is by suffocation. Tolerance and dependence in the one drug are particularly dangerous and lead to severe withdrawal symptoms when the drug is no longer taken. 

Withdrawal symptoms associated with morphine include anorexia, weight loss, pupil dilation, chills, excessive sweating, abdominal cramps, muscle spasms, hyperirritability, lacrimation, tremor, increased heart rate, and increased blood pressure. No wonder addicts find it hard to kick the habit  

The first and easiest morphine analogues which can be made are those involving peripheral modifications of the molecule (that is, changes which do not affect the basic skeleton of the molecule). In this approach, we are looking at the different functional groups and discovering whether they are needed or not. 

Where additional information, such as the exact position and configuration of double bonds, is known then this knowledge can be incorporated into both the shorthand nomenclature as well as the systematic names. For example, linoleic acid could be written as cis(A-)9, cis(A-) 12-18 2 or (cw,cw)9,12-octadecadienoic acid to indicate that it is an 18-carbon fatty acid with cis double bonds 9 and 12 carbons from the carboxyl end (see Chapter 1 for conventions for geometrical isomerism). Occasionally, because of their metabolic connections, it is useful to number the double bonds from the methyl end. In that case linoleic acid would become (cw,cw)n-6,9-octadecadienoic acid with the n (o) in older literature) showing that numbering has been from the methyl end. 

of carbon Systematic atoms name Common name M.pt rc) Occurrence 

4 n-Butanoic Butyric -7.9 At high levels in the rumen, also in milk fat of ruminants 

8 n-Octanoic Caprylic 12.7 Very minor component of animal and plant fats. Major component of many milk triacylglycerols 

There is not the scope within an article such as this to give a thorough review of the experimental properties of clathrate hydrates. Instead, this Section is intended to give an idea of the sort of measurements that have been made, so that these can provide a context for the rest of the chapter. Emphasis will be given to those properties that have 

Up until the last decade there were very few direct experimental measurements of properties other than the hydrate pressure and crystal structure. There had been some attempts to determine the composition of the clathrate [10], but because of experimental difficulties in measuring the fraction of water in the hydrate phase these tended to be fairly imprecise. A small number of IR studies had also been performed [11]. However, estimates of thermodynamic properties such as heats of formation and heat capacities had tended to be through theoretical models of the hydrate pressures rather than direct measurement [12,13]. 

During the last decade there has been a rapid expansion in the scope of experimental studies on clathrate hydrates. In particular, differential scanning calorimetry studies have been used to obtain direct measurements of thermodynamic properties and accurate measurements of composition [14], and Xe NMR has been used as a direct probe of the environment of the guest molecules [15]. Measurements of the thermal conductivity have also attracted considerable interest [16]. Other related experiments include supersonic beam [6] and thin-film IR [17] studies, which have been used to study some of the processes that might contribute to nucleation of clathrate hydrates. These experiments are beginning to provide the sort of data base that is needed for a fundamental understanding of the behaviour of clathrate hydrates. 

Although ibogaine was first isolated and identified in 1901 (19-21,46), the structure of this and related alkaloids (Fig. 1) were first established by 

Taylor in 1957 (47) [see also Taylor (12,13)]. Total synthesis from nicotinamide was reported using a 13- (48) or 14-step (49) sequence. The 13C NMR spectra of several iboga alkaloids were published in 1976 (50). The synthesis of tritiated ibogaine was recently reported (51,52). 

The fibers can be further characterized by their physical and chemical properties, which are governed primarily by the composition of the glass. There are several glass fiber types, with different chemical compositions for different applications. They 

A-glass The most common type of glass for use in windows, bottles, and so on, but not often used in composites due to its poor moisture resistance. 

C-glass High chemical resistance glass used for applications requiring corrosion 

D-glass The glass with improved dielectric strength and lower density. 

E-glass A multipurpose borosilicate type and the most commonly used glass for fiber 

The same was observed for the following two polymers (3.44) and (3.45) with the mesogenic units of a schiff base structure (Frosini et al, 1981). The polyacrylate is a smectic liquid crystal from 93 °C to 258 °C. The polymethacrylate does not form any liquid crystalline phase. 

We have discussed the influence of the flexibility of the polymer backbone on the mesophase formation by examples of polyacrylates and polymethacrylates. More flexible polymers should have a stronger tendency to form more stable mesophases. Nevertheless, smectic liquid crystalline phases are the most common mesophases formed, if they do indeed form, by polymers in which no flexible spacers are used to connect main chain and 

As shown by the examples in Table 3.11, regardless of the type of polymer backbones, introduction of flexible spacers does help the formation 

Using such techniques as 2H-NMR and 2D-13C-MAS-NMR, Spiess and coworkers (Boeffel and Spiess, 1989) have been able to determine the molecular order of the different parts of the molecule. The decrease of order from the mesogenic group to the polymer chain was found. For example, in the glassy state with a frozen-in molecular order of the liquid crystalline phase, the order parameters for the polymer (3.52) (Table 3.12) were found to be 0.88, 0.52 and 0.25 respectively for the mesogenic unit, the spacer, and 

Flexible spacer and mesogenic unit Polymethacrylate ( 3.51 ) Polyacrylate ((3.52)) Polysiloxane ((3.53)) 

The structure of a polymer is taken to include both its physical and chemical attributes and is therefore very complex. As the properties of polymers depend on their structures, understanding the structure-property relationship is important for the judicious investigation of their various applications. The analysis and recording of the properties of individual polymers is a difficult task, although it is comparatively easy to predict the average properties of a class of polymer with a known structure and molecular weight. The different features of structures must be considered if the details are to be known, as discussed in Section 1.2.4 on the classification of structure. In fact, control of the structure and molecular weight of a polymer permits alteration of the properties of a polymer and hence of its applications. 

The physical properties of polymers include solubility, viscosity, density and crystallinity. 

The solubility of a polymer depends on the solvent-solute (polymer) interactions, which must be greater than the solute-solute and solvent-solvent interactions. A polymer can be solubilised by a solvent with similar solubility parameters if certain polymer-solvent interactions are present between them. Polymers with flexible chemical linkages such as -0-/-S- or linear structures, have a better solubility than polymers with rigid linkages such as -N=N-, -C=C-, -C=N-, aromatic, heterocyclic, ladder or cross-linked structures. Similarly, amorphous and flexible polymers have better solubility than crystalline or rigid polymers. 

Viscosity is the resistance to flow of material under an applied external force at a specified temperature and pressure. It depends on the nature of polymers, that is their physical and chemical structures, molecular weight, concentration of solution (for solution viscosity), temperature and pressure of the test medium and the applied external shear force. 

Polymers with a regular structure and adequate flexibility may have a long range order in their chain segments and may acquire a certain degree of 

Asbestos is a general term used to describe a variety of naturally occurring hydrated silicates that produce mineral fibers upon mechanical processing. Such fibrous silicate minerals were known from early times and were used in various products through the years. There are two varieties of asbestos  

The serpentine group of minerals, which include chrysotile asbestos, are almost identical in composition. The chemical composition of unit cell is Mg6(OH)8Si40io. Chrysotiles have layered or sheeted crystal structure containing a silica sheet of (Si20s) in which silica tetrahedra point one way (Streib 1978). A layer of brucite, Mg(OH)2, joins the silica tetrahedra on one side of the sheet structure. Two out of every three —OH are replaced by oxygen atoms. X-ray and electron microscope studies indicate 

Compositions of amphibole asbestos are more complex than the serpentine group. The structure consists of two chains based on Si40ii units separated by a group of cations. The central cation in each unit cell is attached to two hydroxyls. The metal ions that are present predominantly in amphiboles are Mg +, Fe +, Fe +, Ca +, andNa+. Minor cation substituents are Al +, Tf +, and K+. The ultimate diameters of amphiboles are about 0.1 pm. 

Both chrysotile and amphibole fibers lose hydroxyls at elevated temperatures. Dehydroxylation and decomposition occurs at 600-1050°C (1112-1922°F), depending on the species. Amphibole fibers show great resistance to acids, while chrysotiles may break down under acids. Under normal conditions, chrysotile is not readily attacked by caustic alkalies because of its alkaline surface. Dispersion of chrysotile fibers in reagent water produces alkaline solution, reaching a pH of around 10.3, attributed to Mg(OH)2. 

A Comprehensive Guide to the Hazardous Properties of Chemical Substances, by Pradyot Patnaik Copyright 2007 John Wiley Sons, Inc. 

The most important intermediates in the preparation of polyurethanes elastomers are the polyols and the diisocyanates. Also influencing properties are chain extenders such as glycols and amines. The effect of varying these components on the properties of the elastomers has been widely studied and reported (e.g. Saunders and Frisch, 1%2) and only a brief summary will be given here. 

The polyols may conveniently be grouped into three types  

Of these types the polyesters were the first type to become established, the early German Vulkollan materials using poly(ethylene adipate) with a molecular weight of about 2000. This is probably still 

Pendent methyl groups have a detrimental effect on many properties probably arising from the fact that such groups tend to stiffen the chain and reduce its rubberiness. Variation in the molecular weight of the polyester has only a moderate effect on the initial properties of the polyurethane subsequently produced. It has however been noted that in experiments with polyesters of molecular weights in the range 

1000-5000 the resultant rubbers obtained from the higher molecular weight polyesters tended to crystallize whilst when polyesters of M.W. c. 1000 were used the rubber had low strength and elasticity. For this reason molecular weights of about 2000 are used. 

The commercial poly-(4-methypent-1-ene) (P4MP1) is an essentially isotactic material which shows 65% crystallinity when annealed but under more normal conditions about 40%. For reasons given later the material is believed to be a copolymer. In the crystalline state P4MP1 molecules take up a helical disposition and in order to accommodate the side chains require seven monomer units per two turns of the helix (c.f. three monomers per turn with polypropylene and polybut-I-ene). Because of the space required for this arrangement the density of the crystalline zone is slightly less than that of the amorphous zone at room temperature. 

Perhaps the most astounding property of this material is the high degree of transparency. This arises first because both molecules and crystals show little optical anisotropy and secondly because crystalline and amorphous zones have similar densities. They also have similar refractive indices and there is little scatter of light at the interfaces between amorphous and crystalline zones. 

Experiments were earned out to investigate the transparency of various materials produced by copolymerising 4MP1 with other olefins such as but-1-ene, hex-l-ene and oct-l-ene. 

The rather knobbly side groups have a stiffening effect on the chain and result in high values for T (245°C) and Tg(50-60°C). Copolymerisation with hex-l-ene, oct-l-ene, dec-l-ene and octadec-1-ene which may be practised to reduce voidage causes some reduction in melting point and crystallinity as indicated in Table 11.9. 

Polymers below the glass transition temperature are usually rather brittle unless modified by fibre reinforcement or by addition of rubbery additives. In some polymers where there is a small degree of crystallisation it appears that the crystallines act as knots and toughen up the mass of material, as in the case of the polycarbonates. Where, however, there are large spherulite structures this effect is more or less offset by high strains set up at the spherulite boundaries and as in the case of P4MP1 the product is rather brittle. 

The cross-linked unsaturated polyester resin (UPR) is a rigid product, but its detailed microstructure is less well defined. If maleic acid is used in the condensation reaction, most of it isomerizes to the more favoured trans-isomer (fumarate), which reacts differently with styrene, as shown by the different copolymerization reactivity ratios in model reactions (Table 10.2). The data show that in the styrene/maleate system, the styrene is more likely to homopolymerize this is clearly undesirable when employed for cross-linking. The styrene/fumarate reaction is more favoured for copolymerization and hence for cross-linking. 

Continuous reinforcement of cementitious matrices is particularly attractive for fabrication of thin eiements, where cement paste or mortar is impregnated into a fabric. Eariier interest in this kind of reinforcement was driven by the need to develop new thin sheet components, that could serve as replacements for asbestos cement, or provide thin sheets with improved performance, especially with regard to toughness [1-20], New types of reinforcements were studied and developed for these purposes, and the mechanical properties of the composites as well as production technologies were explored. 

An analysis of the behaviour of cracked and uncracked corrugated sheets made with both asbestos and polypropylene reinforcement was presented by Baroonian etal. [12]. They demonstrated that the effects of cracks on any corrugation under 

Additional developments in fibrillated polypropylene composites were reported by Xu, Hannant and co-workers [8,21], who applied a fibrillated polypropylene network in the form of layered opened nets (12 net layers in [21 ]), with the majority in the longitudinal direction and the rest in transverse orientation, and impregnated them by hand, or by a special mechanized system developed for that purpose [8]. These systems could be fabricated from polypropylene only, or from a hybrid of polypropylene nets combined with glass fabrics and chopped glass fibres. Flat thin sheets, as well as corrugated ones could be produced [8j. 

This section further deals with the mechanics of continuous reinforcement based on the use of modern textile yarns, made of an assembly of yarns consisting of numerous filaments with a diameter of 10-50 pm. In these systems several hundreds or thousands of filaments are assembled into a strand, and several strands are assembled into a roving. The filaments are usual ly made of glass or a polymeric material, and are characterized by high strength or ductility, or both. The treatment in this section will refer only to reinforcements of this kind, and will not include discussion of ferrocement, which one may include in the category of continuous reinforcement. The reinforcement in ferrocement is of a different nature, steel wire mesh, which is incorporated in a mortar matrix. This material is used for a variety of applications and its properties and application are documented quite well in several recent publications [26,27], 

The parameters controlling the performance of continuously reinforced composites are more numerous and complex than those of fibre reinforced cement. 

Concerning the weight loss, it should be considered that the PEEK polymer is temperature resistant therefore, the weight loss starts at temperatures not lower than 

4 Proton Conductivity One of the most important indicators of the sPEEK s electrochemieal performances is the proton conductivity, which strictly depends on DS and humidity status as well as on other important parameters such as 

TABLE 3.7 Open-Circuit Voltage and Ohmic Resistance for a Few Literature Data About Pristine sPEEK and Its Derivative Polymers, Compared with Nafion  

High proton conductivity and low methanol permeability (PCH3OH) are two of the essential characteristics that a polymer electrolyte membrane should possess to constitute a viable alternative to Nafion in DMFC applications. These parameters may be combined to constitute the p selectivity (or, shortly, selectivity p = log[ff/P]), which is useful for clearly comparing various sPEEK membranes. Indeed, p selectivity is a common metric for evaluating membrane performances and, as reported in Table 3.6, the few data about p selectivity show that the selectivity decreases with increasing DS. Indeed, as stated earlier, for DS 70%, sPEEK becomes more soluble in methanol and, as a consequence, methanol permeability increases determining a depletion of p selectivity. 

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P. P. Ewald and H. Juretschke, Structure and Properties of Solid Surfaces, University of Chicago Press, Chicago, 1953. 

Dykstra C E 1988 Ab initio Calculation of the Structures and Properties of Molecules (Amsterdam Elsevier)... 

Although the structure of the surface that produces the diffraction pattern must be periodic in two dimensions, it need not be the same substance as the bulk material. Thus LEED is a particularly sensitive tool for studying the structures and properties of thin layers adsorbed epitaxially on the surfaces of crystals. 

Gentile F T and Suter U W 1993 Amorphous polymer miorostruoture Materials Science and Technology, Structure and Properties of Polymers vol 12, ed E L Thomas (Weinheim VCFI) pp 33- 77... 

Hasegawa M, Sugimura T, Shindo Y and Kitahara A 1996 Structure and properties of AOT reversed micelles as studied by the fluorescence probe technique Colloids Surf. A 109 305-18... 

Dubois L FI and Nuzzo R G 1992 Synthesis, structure, and properties of model organic surfaces Annu. Rev. Phys. Chem. 43 437-63... 

C Binning Jr and B Bigot 1931. Structures and Properties of Organic Liquids n-Butane and 1,2-... 

C. Lemarechal, Modelling of Molecular Structures and Properties J.-L. Rivail, Ed., 63, Elsevier, Amsterdam (1990). 

There are now extensive databases of molecular structures and properties. There are some research efforts, such as drug design, in which it is desirable to hnd all molecules that are very similai to a molecule which has the desired property. Thus, there are now techniques for searching large databases of structures to hnd compounds with the highest molecular similarity. This results in hnding a collection of known structures that are most similar to a specihc compound. 

I. B. Bersuker, Electronic Structure and Propertie. of Tramition Meta Compound. John Wiley Sons, New York (1996). 

Accompanying this text is a CD entitled Learning By Modeling As its name implies it is a learning tool designed to help you better understand molecular structure and properties and contains two major components... 

The opening paragraph of this chapter emphasized that the connection between structure and properties is what chemistry is all about We have just seen one such con nection From the Lewis structure of a molecule we can use electronegativity to tell us about the polarity of bonds and combine that with VSEPR to predict whether the mol ecule has a dipole moment In the next several sections we 11 see a connection between structure and chemical reactivity as we review acids and bases... 

Organic chemistry involves a good bit of reasoning by analogy and looking for trends The kind of reasoning we carried out in this section will become increasingly familiar as we learn more about the connection between structure and properties... 

This chapter sets the stage for all of the others by reminding us that the relationship between structure and properties is what chemistry is all about It begins with a review of Lewis structures moves to a discussion of the Arrhenius Brpnsted-Lowry and Lewis pictures of acids and bases and the effects of structure on acidity and basicity... 

Bioactive amines are also widespread in animals Avariety of structures and properties have been found in substances isolated from frogs for example One called epibatidine is a naturally occurring painkiller... 

The central message of chemistry is that the prop erties of a substance come from its structure What is less obvious but very powerful is the corollary Someone with training m chemistry can look at the structure of a substance and tell you a lot about its properties Organic chemistry has always been and continues to be the branch of chemistry that best connects structure with properties Our objective has been to emphasize the con nection between structure and properties using the tools best suited to make that connection... 

K.. Unger and H. Fischer, in Proceedings of RILEM/IUPAC International Symposium on Pore Structure and Properties of Materiails (eds. S. Modry and... 

It is apparent from items (l)-(3) above that linear copolymers-even those with the same proportions of different kinds of repeat units-can be very different in structure and properties. In classifying a copolymer as random, alternating, or block, it should be realized that we are describing the average character of the molecule accidental variations from the basic patterns may be present. In Chap. 7 we shall see how an experimental investigation of the sequence of repeat units in a copolymer is a valuable tool for understanding copolymerization reactions. This type of information along with other details of structure are collectively known as the microstructure of a polymer. 

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