What is true about inorganic compounds?

IV.A Overview

Inorganic compounds have been used for centuries for their pharmacological properties. Recently, however, the understanding of how inorganic compounds interact with biological molecules has enabled chemists, biologists, and physicians to synthesize and test the medicinal qualities of these compounds in a more systematic way. The unique properties of inorganic compounds enable new mechanisms to be exploited in the treatment of many diseases.

Some of the unique properties being explored include the following: (1) physiologically relevant redox potentials for cancer drugs that cleave DNA and drugs that remove harmful oxygen radicals; (2) ligand exchange for many anticancer drugs, including cisplatin, one of the leading drugs for cancer treatment; (3) photophysical properties, for maladies ranging from psoriasis to cancer; (4) properties of new drugs to treat diabetes without using insulin; (5) radioactivity for use in imaging agents; and (6) paramagnetism for magnetic resonance imaging (MRI) agents. Examples of each of these properties is given below and in Fig. 11. Some of the complexes are already in clinical use, while others are in clinical trials.

In addition to the use of inorganic compounds to treat illnesses, treatments for genetic defects in inorganic ion metabolism and environmental exposure to toxic ions are also discussed. The majority of these disfunctions are treated with some sort of chelation therapy (for overexposure) or metal substitutes (for underexposure). These therapies are briefly discussed below.

6.3.2 Role of trace elements on bioactivity of bioceramics

Inorganic compounds can effectively influence bone development or regeneration to influence the biological properties of these materials [15]. Among various dopants, strontium (Sr2+) and silver (Ag1+) gained significant interest as it shifts the bone remodeling equilibrium toward osteogenesis and infection control [16,17]. Five percent Sr-substituted biphasic CaP was shown to increase the expression of Type I collagen and mRNA with a reduction in matrix metalloproteinases (MMP-1 and MMP-2) production [16]. Sr–Hardystonite has been shown to enhance expression of alkaline phosphatase, Runx-2, osteopontin, osteocalcin (OC), and bone sialoprotein [18]. Nano Sr–HA has been shown to increase ALP activity and mineralization compared to nano-HA [19]. Overall it is predicted that the increased expression of these specific proteins not only increases the osteoconductive properties of Sr-doped CaPs, but also signifies osteoinductivity (Table 6.7).

Addition of zinc (Zn2+) in CaP ceramics has been shown to significantly increase new bone formation in vivo when compared to the pure composition [20]. New bone formation in rabbit at 4 weeks was significantly promoted with 0.03 wt% Zn-doped α-TCP cement [20]. Recently, it has been shown that zinc suppresses significant repression of basal NF-κB activity in preosteoclast cells in vitro and also showed significant reduction in tumor necrosis factor alpha and stimulation of osteoblast mineralization [21]. Presence of Zn2+ in the culture media was also found to increase angiogenic growth factor, vascular endothelial growth factor (VEGF), secretion in osteoblast-like MC3T3-E1 cells [22].

Recently it has been shown that 0.6 at% Mg-doped octacalcium phosphate significantly promoted the synthesis of procollagen-Type I, transforming growth factor beta 1 (TGF-β1), ALP, and OC compared to pure octacalcium phosphate [23]. It has been shown that magnesium hydroxide temporarily (up to 4 weeks) reduced osteoclast formation in the surrounding area of a magnesium hydroxide implant [24]. The presence of Mg2+ can also locally restrict osteoclast proliferation and chemotaxis, which increases bone growth.

Silicon (Si) was also shown to have a significant effect on increased osteoblast proliferation, differentiation, and bone mineral density. α-TCP cement doped with 1% Si has been shown to have a 20% increase in bone contact area compared to undoped cement 3 weeks after surgery [25]. A composite scaffold of siloxane-doped poly(lactic acid) and vaterite composite coated with HA results in a 3–4-fold increase in osteoblast cells and a 1.5 times increase in ALP activity [26]. It has also been reported that the presence of Si also led to differentiation of human mesenchymal stem cells (MSCs) and a moderate increase in ALP activity after 14 and 21 days.

Recently it has been shown that silicon (Si) can be an effective element in inducing angiogenesis as well as improving the osteoinductivity of HA [27]. It has been shown that silicate substituted CaP results in a higher amount of bone formation (26±7.8%) compared to stoichiometric CaP (2.2 ± 2.0%) in female sheep at 12 weeks [28]. Using micro-computed tomography (μCT) and nano-CT, Alt et al. have shown that a xerogel composed of 70 wt% sol-gel silica and 30 wt% collagen can induce 3.1±1.2% volume vessel formation within the fracture zone of a rat femur in 6 weeks [29]. A higher endothelial specific cytokine release was noticed in biphasic CaP (60% HA and 40% β-TCP)–silica composite [30].

14.2.3 Organic inhibitors

Inorganic compounds such as nitrite, nitrate, chromate, and dichromate have been extensively investigated as inhibitors. Toxicity of these compounds limits their use in corrosion protection. Alternatives are organic corrosion inhibitors containing sulfur, nitrogen, or oxygen atoms and organic heterocyclic compounds containing polar groups [9–13]. These compounds adsorb and form a covalent bond on the metal surface [14]. Organic inhibitors cover the entire surface area of the corroding metal with a thick film consisting of several monolayers and change the structure of the double layer at the metal interface, decreasing depolarization rate. They may also act as a barrier film by blocking anodic and cathodic active sites or decreasing electroactive species transport rate to or from the metal surface. Lower inhibitor concentration is effective only for strong adsorption. The film is formed by the adsorption of positively or negatively charged soluble organic compounds. Film-forming organic compounds may exhibit anodic, cathodic, or mixed properties. Film-forming inhibitors by adsorption include amines, imidazolines, quaternaries, and acetylenic alcohols. Positively charged anodic inhibitors are primary amines, RNH2, secondary amines, R2NH, tertiary amines, R-N(CH3)2, diamines, R-NHCH2CH2CH2NH2, amides, R-CONH2, and polyethoxylated compounds. Negatively charged compounds are sulfonates. Effective polar groups include hydroxyl, nitrogen, sulfur, phosphorous, or selenium. The charged ionic species initially form a physisorbed film through van Der Waals forces. The film is then stabilized through chemisorption [15].

The position of the corrosion potential with respect to its potential at zero charge (PZC) determines the surface charge of the metal. The overpotential is defined as the difference between the corrosion potential and the potential at zero charge. At negative overpotentials, cations, while at positive overpotential, anions are adsorbed. Electrostatic adsorption is due to attractive forces between inhibiting organic ions or dipoles and the charged surface of the metal. In electrostatic adsorption, the ions are not in contact with the metal. They are separated by a layer of water molecules. The electrostatic adsorption process is almost independent of temperature and has very low activation energy.

In chemisorption, unshared electron pairs or “p” electrons from organic compounds interact with the metal orbitals to form a coordinate-type bond. The interaction proceeds in the presence of heteroatoms (P, Se, S, N, and O) that possess lone-pair of electrons and/or aromatic rings in the adsorbed molecules [16,17]. Chelate forms through a coordinate covalent bond by electron transfer from organic compounds to metal. The chemisorption has higher activation energy than electrostatic adsorption. It is a temperature-dependent phenomena, it occurs slowly, and is not reversible.

Organic molecules are chemisorbed on the surface of the metal due to unsaturated bonds on the heteroatoms. They favor electronic binding with the metal substrate [15,18,19]. Adsorption of surface active organic compounds increases with the charge of the metal surface, their molecular mass, and with the dipole moment [20]. The amount of inhibitor adsorbed on the surface increases by increasing the concentration of the inhibitor in the solution. Inhibitor effectiveness is improved by the strength of the adsorption bond and with greater molecular weight, asymmetry, and electron density [21]. Drazic et al. [22–27] studied the adsorption of ions and organic molecules on iron electrodes and defined corrosion-inhibiting properties of anodic reactions [22,23], cathodic reactions [24,25], or both [26,27]. The adsorption mechanism for cathodically protected surfaces is similar to the mechanism of anodically polarized surfaces.

Inhibitors such as imidazolines, amines, diamines, pyrimidines and their fatty acid, naphthenic acid and sulfonate compounds are used in refinery processes. The electron-rich polar group of these molecules adsorbs on the metal surface, while the nonpolar hydrocarbon part of the molecule forms a hydrophobic film that repels water.

A synergistic effect is observed between cathodic protection of pipeline and inhibitors. An efficiency increase is observed when the pipeline is cathodically polarized in the presence of an organic inhibitor. Organic inhibitors that contain nitrogen such as aryl and alkyl amines, aniline [28–31], imidiazoline derivatives [32,33], and ketones [33] are used in industrial acid cleaning, acid-descaling, and acid-pickling. Figure 14.8 shows the inhibitor effect on steel polarization behavior corroding in pickling acid [31]. The corrosion current drastically decreased with inhibitors added to the pickling acid solution. A mixture of nitrite and glycerophosphate are synergistic for steel protection [34].

8.3.2 Inorganic Compounds Elimination

Inorganic compounds potentially present in the syngas derived from biomass gasification are nitrogen-, sulfur-, and chlorine-containing compounds (such as NH3, HCN, H2S, and HCl), along with alkali metals. Inorganic gas compounds are of concern due to their corrosive nature and because they are both poisons for metal-based catalysts, such as nickel or iron-based catalysts, and they are precursors of regulated emission products such as NOx and SOx. Alkali metals in the ash material are also of concern for both gasifiers and end-use systems as they can lead to an agglomeration phenomenon in fluidized bed reactors [22], hot corrosion of metal surfaces, and catalyst deactivation [31]. In their solid form, alkali metals are eliminated with particle matter removal systems that have been described elsewhere [36]. Inorganic gas containing nitrogen, sulfur, and chlorine, such as NH3, HCN, H2S, and HCl, are highly undesirable for further syngas processing (Fisher-Tropsch reaction, production of methanol, dimethylether, or large-scale production of hydrogen). It is therefore necessary to ensure an efficient elimination of such contaminants, whose removal is essential for preserving high-process efficiency and avoiding the formation of undesirable by-products [36]. Compared to coal, biomass often contains 100 times less sulfur (typically in a form of hydrogen sulfide (H2S) or carbonyl sulfide (COS)) [45], which usually does not exceed 0.5 g kg− 1. Nitrogen contaminants occur as cyanide (HCN) and ammonia (NH3) which can decompose to molecular nitrogen (N2) during biomass gasification [36].

The technologies for the removal of sulfur and nitrogen compounds are typically based on adsorption or absorption techniques. According to the temperature of the gas released from the cleaning-up device, they could be classified as hot (wet) techniques when T > 300 °C or cold (dry) techniques when T < 100 °C. Hot gas cleaning technologies are highly effective from the energetic point of view because they avoid cooling and reheating of the gas stream issued from gasification reactor. Cold cleaning techniques may suffer from energetic inefficiencies and production of waste gas streams, however, they are highly efficient for the removal of sulfur and nitrogen impurities [36]. Applying hot techniques, removal of sulfur compounds (typically SO2 and H2S) is based on their adsorption on porous solids such as metal oxides (e.g., ZnO and Fe2O3, Cu2O), thus, creating metal sulfur compounds [36]. Nitrogen removal consists, in the selective catalytic oxidation or thermal catalytic decomposition of NH3 forming N2, hydrogen and eventually NOx when applying nickel- or iron-based catalysts [38].

Cold adsorption or absorption methods are based on either physical or chemical adsorption processes typically carried out in wet scrubbers [46]. The well-known Selexol and Rectisol [47,48] acid gas purification technologies are both based on physical adsorption processes (with dimethyl ethers of polyethylene glycol and methanol, respectively) [49]. They are operated at relatively high pressures (several MPa) followed by removal of impurities using pressure swing or stream striping. These processes are typically applied for the removal of acid gases such as COS and H2S, which could be advantageously further treated for sulfur recovery by using the Claus process (reaction of H2S and SO2) [50]. The Selexol process can operate selectively to recover H2S and CO2 as separate streams, while Rectisol provides a better removal of greater percentages of acid gas components, ensuring a higher purity of the cleaned gas. Both processes are often more economical than the amine processes based on chemical absorption and could be used in a selective manner. Adsorption of nitrogen contaminants in the cold cleaning process is carried out by the adsorption in water.

Chemical adsorption processes are based on the interaction between amines (monoethanol and diethanol amines) and acid gases (H2S, CO2) [48]. The process known also as “amine gas treating” (eventually “gas sweetening”) consists of the acid gas reaction with aqueous solutions of various alkylamines. As in physical adsorption processes, in the case of H2S-rich stripped gas, the stream is usually routed into a Claus process for the recovery of elemental sulfur [50].

Recently, particular attention has been dedicated to novel membrane systems for the removal of gas impurities from syngas. As an example, we could mention supported ionic liquids for the separation of O2, H2S, SOx, and CO2 from syngas [51], or molten salts membranes for selective separation of CO2 with the possibility of simultaneous desulfurization and dechlorination of the syngas stream [52,53].

1.4.1 Inorganic compounds

The inorganic compounds used for wood fibre composites are cement, clay and lime. In ancient Egypt and China, clay had first been used to make walls. In the early to mid-1940s, natural fibre–cement composite was first investigated in Australia.278

Wood fibre–inorganic compound composites are one of the most successful applications of wood fibres in the composite industry. They have been widely used as corrugated or flat roofing materials, cladding panels and water containers, in a large number of building and agriculture applications. One of the drawbacks associated with wood fibres in inorganic application is their dimensional instability when the composites are subjected to changing relative humidity (RH) atmosphere. This instability is promoted by: (i) the water sensitivity of cellulose fibres, (ii) the effects of carbonation, high alkali content of the cement matrix and the generation of incompatible stresses. However, the addition of wood fibre can bring three benefits: (i) improving the toughness, tensile strength and the cracking deformation of the composite; (ii) increasing the solids retention and (iii) capturing CO2 and locking it up in buildings.

Inorganic species

Many inorganic compounds are naturally present in the feed solutions and process waters used in industry and can cause significant fouling of membranes. They include calcium sulphate, calcium carbonate, calcium phosphate, silica, metal oxides and hydroxides (particularly of iron and aluminium), colloidal sulphur and other inorganic particulates. Calcium salts are major inorganic foulants in brackish water, wastewater and agricultural drainage water processing [59,60]. Inorganic (salt) fouling can be also a problem in MF systems used for biotechnological applications. For example, Nagata et al. [61] have used a fermentation media containing both K2HPO4 and urea. These species reacted during steam sterilization (autoclaving) to form a K2NH4PO4 precipitate, which was then deposited on the membrane surface during MF of the broth to harvest the cells. This problem could be eliminated by reformulating the fermentation medium, by separately sterilizing the different medium components to avoid this chemical reaction, or by using a different method of sterilization.

23.1.5 Zinc Oxide

Another inorganic compound that humans encounter frequently is zinc oxide. Although it is a metal oxide and most metal oxides are the anhydrides of bases, ZnO is an amphoteric oxide. As the hydroxide in aqueous solutions, it reacts as a base toward acids such as HCl,

(23.2)Zn(OH)2 + 2 HCl → ZnCl2 + 2 H2O

and as an acid toward NaOH,

(23.3)Zn(OH)2 + 2 NaOH → Na2[Zn(OH)4] + 2 H2O

Zinc oxide is a white solid that has been used as a pigment. As with the sulfide, the two forms are wurtzite and zinc blende (see Section 4.1.3).

Because zinc oxide is effective at blocking ultraviolet radiation, it is widely used in sunscreens, suntan lotions, and many forms of cosmetics. It has been used in various ointments and salves since antiquity. A popular ointment known as calamine contains both ZnO and Fe2O3, the latter to the extent of approximately 0.5%. When used in a finely divided state, ZnO has antibacterial properties, which leads to its use in a wide variety of both pharmaceuticals and cosmetics. Zinc is the metal ion located in the reactive center of the enzyme carbonic anhydrase which results in it being classified as an essential trace metal. Because of this, zinc compounds are added to several foods. Zinc oxide is essentially nontoxic, but as with many other substances, vapors emitted from the materials heated to high temperature or as finely divided powders constitute a hazard.

Introduction

Major inorganic compounds, such as trace elements, are of concern as contaminants of terrestrial and aquatic systems because of their persistence and toxicity at low concentrations. There is considerable evidence that the bioavailability and toxicity of such trace elements are markedly influenced by the physicochemical forms in which they are present in waters, in sediments, and in soils. Specifically, concerns about trace elements relate to utilization, disposal, and discharge of sewage and wastes. With regard to aquatic systems, complexation reduces the toxicity of dissolved trace elements to a range of aquatic organisms and trace element uptake and toxicity often relate best to the free metal ion activity. In general, systematic differences in the geochemistry of groundwater evaluation in aquifers are traceable to local solid variability. For instance, variations in Sr isotopes and Mg/Ca and Sr/Ca ratios offer insight into the influence of soils on groundwater geochemistry, sources of dissolved constituents in groundwater, water–rock interaction pathways, and groundwater residence time.

The chemical composition of water in relation to the Earth's crust constitutes the focus of the science called geohydrochemistry or simply geochemistry. Water quality is one of the primordial environmental factors determining which flora and fauna will thrive and which material will dissolve or precipitate. Environmental research helps gain insight into aspects such as economics, sensitivity, and relevance in pollution studies: economics for the possibility of cost-effective direct measurement without complicated extractions prior to analysis, sensitivity because of an analytically more agreeable result when compared to the solid phases in soil, and relevant on account of a direct selection of the mobile phases.

2.06.2.4 Structure and Bonding

In inorganic compounds, where zinc is almost invariably present in its divalent form, the common coordination numbers for zinc are 4 through 6. Systematic crystal structure analyses and computational studies on zinc complexes have shown that zinc’s preference for octahedral over tetrahedral coordination is not nearly as pronounced as that of magnesium. The energy penalty for changes in coordination from 6 to 5 or from 6 to 4 is also much lower for zinc than for magnesium, and this may explain zinc’s role in catalytic enzymes where coordinative flexibility is crucial.10 Because of zinc’s filled 3d shell, there are no ligand field effects and four-coordinate zinc is always tetrahedral, unless a rigid multidentate ligand imposes a planar coordination geometry.

In organozinc compounds, whether neutral or charged, zinc never exceeds coordination number 4, and in cases where this rule appears to be violated the additional bonds are invariably not fully developed. With its closed-shell 1s22s22p63s23p64s23d10 electron configuration, zinc must be promoted to a 4s14p1 configuration to form two covalent bonds. This sp hybridization scheme limits neutral, two-coordinate organozinc compounds to linear molecules of the type ZnR2 or RZnX, in which zinc uses two 4sp hybrid orbitals to bind both ligands. Numerous high-quality computational studies have shown (see Section 2.06.4.7), however, that at least in diorganozinc compounds only the 4s orbitals are appreciably involved in bonding, with little or no participation from the 3d and 4p orbitals.

Additional bonds are thus donor bonds, and to accept electron pairs from neutral and anionic ligands, zinc uses the two remaining 4p orbitals to form sp2 and sp3 hybrids. In the absence of steric effects, discrete, homoleptic, anionic tri- and tetraorganozinc compounds (zincates) have almost always ideal trigonal-planar and tetrahedral geometries, respectively.

Which is the following is true about inorganic compounds?

Which of the following best describes inorganic compounds?

How do you define inorganic compounds?

What does the inorganic compounds contain?