Challenges in tissue engineering: are hydrogels the answer?

Carmen Piras

Gels are materials with several applications in everyday life. They can be defined as coherent systems composed of a liquid as the majority component, and a solid as the minority component. In these systems, the liquid is the dispersion medium, with the solid acting as the dispersed constituent. These materials can be classified in different ways depending upon their origin, composition, constitution and the kind of interactions that are responsible for the formation of the gel. One of the main classifications is based on the medium they encompass and, in this case, further subdivisions can be made, into organogels, hydrogels, xerogels and aerogels.

  • In organogels, organic solvents represent the disphydrogel-wound-care-fillerersion medium.
  • In hydrogels, water is the dispersion medium, making them highly absorbent and flexible materials. Due to these amongst many other properties, they can be used for several applications, such as drug delivery, tissue engineering, regenerative medicine, diagnostics and clinical practice.
  • Xerogels are formed after evaporation by drying with unhindered shrinkage of the solvent in a hydrogel or an organogel. The main properties of these gels are high porosity and enormous surface area. These characteristics make them suitable for various optical, acoustic and thermal applications.
  • Aerogels are highly porous, low-density materials with excellent insulation properties, formed by evaporation of the solvent in supercritical conditions. They are utilised for several applications in the field of cosmetics and insulation.


id35162Despite being around for only a few decades, hydrogels are now a class of versatile materials that have become a sine qua non in everyday life e.g. hair gel, nappies, contact lenses, wound healing products and medicines. They can be defined as three-dimensional, cross-linked networks of water-soluble molecules. These aggregates can assume different morphologies (micelles, vesicles, fibres, ribbons or sheets), depending on their molecular structure. Due to their composition, but also due to the conditions under which the hydrogels are formed, they present lots of interesting properties. One of these is the ability to absorb water, which is caused by the presence of hydrophilic groups within the molecules that constitute the gel. The presence of water inside the hydrogels, together with their swelling and elasticity properties, permits some solute molecules entrapped in the structure to diffuse, which is very important for the applications of these materials in drug delivery. Another important characteristic related to this application is their porosity that can be modified by controlling the density of cross-links in the gel matrix. The porosity of these materials is responsible for the release of drugs loaded into the matrix. Hydrogels can also show massive changes of their volume in response to the variation of external conditions, such as pH, temperature, solvent quality, etc. Furthermore, these materials show physicochemical similarity with the native extracellular matrix. This characteristic, accompanied by the high water content, makes them considerably biocompatible and permits their utilization in tissue engineering and in biomedical and pharmaceutical fields. Hydrogels derived by natural molecules, such as polypeptides and carbohydrates, also show natural biodegradability, high biocompatibility and low toxicity that make these materials especially suitable for this kind of application.


Tissue engineering has been of great interest to scientists for many years, as it holds great promise for tissue and organ regeneration. The high amount of water that hydrogels can incorporate, the presence of pores large enough to host living cells, and the similarity of these materials to the extracellular matrix, make them suitable candidates as matrices for tissue engineering. Many publications over the decades showed how they can be used for cartilage regeneration, bone and skin repair, and recently also for cardiac tissue repair (especially as injectable materials).

cuoreHydrogels used for such purposes are predominately based on natural polymers or derivatives, such as collagen, hyaluronic acid, chitosan and alginate, which allow high viability and proliferation rates for cells, due to the abundance of chemical signals. This also helps the formation of neo-tissues, which is fundamental for organ regeneration and repair.

Although hydrogels based on natural polymers show interesting properties and a wide range of biomedical applications, synthetic chemistry can also be used to produce similar materials from synthetic polymers such as poly(ethylene glycol) and pluronics. Hydrogels obtained from these polymers, however, behave as inert scaffolds for cells, due to the absence of active binding sites. To overcome this problem, peptides, growth factors and other bioactive compounds can be added to the network.

The use of hydrogels in tissue engineering has been facilitated by bio-fabrication techniques, which enable the industrial production of biomaterials. Different methods can be used for this purpose:

  1. Laser-induced forward transfer technology, which allows the precise deposition of materials and cells in small 3D structures.
  2. Inkjet printing, which permits the deposition of bioink (i.e. a hydrogel) on a substrate from a very small orifice.
  3. Robotic systems, which are dispensing systems that use disposable plastic syringes to release hydrogels with suspended cells onto a building platform.

Although hydrogels have now been studied for a number of years and their characteristics and applicability have been massively improved and tuned to many different purposes, the development of effective, low-price, non-toxic materials with high rates of water absorption, biocompatibility and biodegradability for tissue engineering still remains a challenge. However, research on hydrogels is one of the most rapidly developing fields of material science, showing their enormous potential in tissue engineering and organ regeneration.



Chocolate, why it is so irresistible? The chemistry behind pleasure and addiction

Carmen Piras

Chocolate is one of the most cheap and popular antidepressants available in the market. What is in chocolate and why is it so good and irresistible? After you will read this articleyou will realise it is all about chemistry! All the properties of chocolate, in fact, depend on different molecules that are predominantly present in cocoa, one of the main components of chocolate.


Cocoa comes from the seeds of a plant with very ancient origins. The ancient civilisations of Olmecs, Mayas and Aztecs used to 1cultivate it as a food and as currency trading. The last led to the first name of the plant “Amygdalae Pecuniariae” (“Money Almond”), later replaced by the Swedish botanist Carl Von Linne with “Theobroma Cacao” (“Food of Gods”), which referred to the religious cults of these populations.

The consumption of cocoa was reserved mainly to upper classes (nobles, warriors and priests) that used to drink it for its energising and aphrodisiac properties with the addition of chilli, hot spices, anise, cinnamon and vanilla to mitigate the bitter taste. In 1528 it was imported to Europe, when the Spanish Conquistador Cortez offered it as a gift to the Spanish Royal Family. From Spain, the recipe of chocolate spread throughout Europe: Italy first, then France, England, Austria, Switzerland, Germany and then Scandinavia.


Cocoa plant (Theobroma Cacao L.) is an evergreen tree that can reach up to 20 meters height. It can be cultivated only in certain areas, as it requires hot humid climates and mild temp2eratures ideally between 20 and 30°C. The main producing countries are, for this reason, situated in Africa (Ghana, Cameroon, Nigeria, Ivory Coast, Madagascar), Asia (Indonesia, Malaysia, Sri Lanka), Oceania (New Guinea, Papua) and Central and South America (Mexico, Brazil, Colombia, Ecuador, Venezuela).

3The fruits are collected a couple of times a year and the beans are extracted after natural fermentation. The fermentation takes place outdoors, in a 2 to 12 days period of time depending on weather conditions and quality of the beans. This process regards the sugars contained in the mucilage (glucose and fructose) and it is vital for the chemical composition and the biochemical characteristics. Once extracted, the seeds are then dried in order to stop the fermentation and decrease the moisture content to avoid the formation of mould. The drying process takes from 7 to 15 days when the seeds are exposed to the sun. The dry beans can be then processed to produce a variety of derivatives (e.g. chocolate, cocoa powder, pralines, snacks).


The chemical composition of cocoa, thus the percentages of main components, varies depending on the geographical origin. The main components are:

  • water (5-7%)
  • lipids (45-53% – especially fatty acids such as palmitic acid, arachidic acid, linoleic acid, linolenic acid, stearic acid and sterols)
  • proteins (10-15% – g. albumin, prolamin, glutelin, globulin and enzymes)
  • starch and carbohydrates (2-4% – i.e. fructose, sucrose, lactose, cellulose, lignin)
  • tannin (6%)
  • gums (2-3%)
  • polyphenols (g. catechins, anthocyanins, proantocyanins)
  • organic acids
  • vitamins (vitamin A, B1, B2, B6, biotin, folic acid, nicotinamide)
  • minerals (e. sodium, potassium, magnesium, iron, chlorine, fluorine, iodine, chromium, nickel, zinc)
  • natural bioactive molecules.

The last are responsible not only for the aroma of cocoa, but also for the effects it induces. The characteristic aroma of cocoa can be attributed to different fermentation products (firstly vicilin, but also pyrazines, esters, aldehydes, ketones, alcohols, hydrocarbons, furans and phenols), whereas other natural components cause the effects that are normally associated with cocoa consumption. These include:

  • Theobromine and caffeine (methylxantines)

4These two molecules are present in different percentage (2-2.7% theobromine and 0.6-0.8% caffeine) and they induce:

  • increased concentration and attention
  • improved waking state
  • improved skeletal muscle contractility
  • vasodilatation
  • diuresis.

Theobromine has a lower stimulant effect compared to caffeine, which however is present at a lower concentration. Both molecules act as antagonists of adenosine purinergic P1 receptors. Adenosine has normally an inhibitory effect on central nervous system; consequently the antagonist action is responsible for the psychostimulant effects of these substances, but also for the side effects related to abuse, such as insomnia, tachycardia and agitation.

  • Biogenic amines (tyramine, tryptamine, histamine, 2-phenylethylamine)

5These are vasoactive molecules that, at a high concentration or in combination with MAO inhibitors (drugs with an antidepressant effect), may cause the so-called “cheese reaction”, which is characterised by redness, headache, pressure changes and even circulatory shock.

Among these molecules, 2-phenylethylamine is considered responsible for chocolate desire. Its structure is very similar to amphetamine, therefore it interacts with the same receptors, inducing various stimulant effects such as:

  • improved waking state
  • psychostimulation
  • reduction of fatigue
  • reduced sense of hunger.
  • Anandamide


This molecule interacts with the cannabinoid CB1 receptors inducing:

  • behavioural effects
  • effects on cognitive functions
  • improved mood
  • improved sensory perceptions
  • euphoria
  • sense of accomplishment and satisfaction.
  • Salsolin and salsolinol


These are alkaloids dopamine-derivatives, which are also present in the brain as endogenous molecules. They are responsible for the antidepressant effect of chocolate and the psychological dependence due to two actions on central nervous system:

  • inhibition of MAO enzymes and tyrosine hydroxylase, which results in increased serotonin levels with consequent improvement of mood
  • inhibition of catecholamines re-uptake (e. norepinephrine and dopamine), with consequent antidepressant effect and psychological dependence.
  • Clavamide, which has a considerable antioxidant activity.9
  • Tetratetrahydro-b-carboline, which act as neuromodulators on MAO enzymes, thus contributing to the antidepressant action.10


 All these molecules together with others are responsible for the different effects of chocolate.

  1. Antidepressant effect12

Serotonin, associated with methylxanthines and 2-phenylethylamine, is responsible for the induction of endorphins production, opioids that are naturally synthesized by the brain and that have an exhilarating effect.

  1. Feeling of pleasure and addiction

13The feeling of pleasure induced by chocolate can be correlated to various substances, including theobromine, caffeine and anandamide, which act on the brain reward circuit. This is modulated by the neurotransmitter dopamine, whose release is induced by natural rewarding stimuli (e.g. food, and water), or drugs. It acts by facilitating the establishment of a positive memory related to cocoa assumption, with consequent sensation of pleasure after chocolate consumption and desire of more chocolate.

  1. Antioxidant effect

This is related to the presence of flavonoids, a class of polyphenols present at a higher concentration than in other commonly consumed foods. The antioxidant activity is important to fight free radicals, which are formed as a result of oxidative stress and are responsible for damage to cells and cellular components.

  1. Protective action on cardiovascular system

Due to the fact that dark chocolate promotes increased levels of HDL cholesterol, the “good cholesterol”. This improves the functioning of blood vessels (by increasing the ability of the endothelium to dilate) and prevents heart diseases.

Although chocolate has many positive effects, it is not for everyone! Are indeed excluded diabetics, people with allergies, gastroesophageal reflux (as chocolate consumption causes an increased gastric acidity), hyperuricemia, headache (due the presence of tyramine, that could trigger crises), obesity or liver diseases (due to the high lipid content).

Anyway, after reading this article, next time you will be in a bad mood, try to have some chocolate and it might act as a magic medicine!


Chemistry on the crime scene

Carmen Piras

1One of my favourite TV series is Criminal Minds, an American police series set primarily at the FBI’s Behavioural Analysis Unit, Quantico (Virginia). It focuses on a skilled team of FBI profilers who catch serial killers through behavioural profiling. Besides Criminal Minds, other series recently captured the interest of the audience, such as CSI, Law and Order and Cold Case. In all these TV programs the police solve the cases quickly and efficiently, thanks to the talent of the agents but also thanks to the evidence that is collected on the crime scene and analysed by the chemists in a crime laboratory, who provide essential information to reconstruct the story. Although the role of forensic chemistry is fundamental in case solving, this is not often recognised. However, chemistry plays a key role to put together the pieces of the puzzle in all investigations.


In few words, a forensic chemist analyses physical evidence collected from the crime scene and provides the obtained information to the detective who is working on the case to solve the crime. The analysis of physical and chemical properties of substances is a crucial part of the process. The physical properties (e.g. appearance, texture, colour, solubility, polarity and odour) can be observed and measured without altering the 2composition of the matter. By contrast, the chemical properties may only be observed by performing a chemical reaction or change, characteristic of a particular substance. For example, cocaine is a drug that can be described as a fine white powder (physical property); it also reacts with cobalt thiocyanate to give a blue-coloured product (chemical property). These different properties of cocaine help the investigators to identify it.

Chemical and physical properties, however, can only be used for presumptive analyses, as sometimes these characteristics are not enough by themselves to identify a substance. Methamphetamine, for example, gives a deep blue-coloured product when it reacts with sodium nitroprusside in the presence of sodium bicarbonate. Nevertheless, other substances with a similar molecular structure will react in the same way, giving the same product. For this reason, confirmatory analyses, which are based upon unique properties of substances, are required to identify a sample with certainty.


 Different techniques can be applied for this purpose and most of them are spectroscopic techniques. The ultraviolet-visible-near infrared spectroscopy, for instance, is ued to test certain drugs of abuse to confirm their property to absorb UV light at a certain wavelength. This property depends on the presence of chromophores in the structure of the compound, which are functional groups that can absorb UV light and are responsible for its colour. Another technique is represented by Fourier Transform infrared spectroscopy (FTIR), which gives a characteristic spectrum for each compound depending on which functional groups are present in the molecule structure. The analysis of the obtained spectrum depends on the recognition of these functional groups in the molecule, thus allowing its identification. These techniques are often used in combination with others, especially if the analysed sample is in fact a mixture of two or more compounds. In this case, the compounds in the mixture can be separated and individually analysed using a gas chromatograph-mass spectrometer (GC-MS). This instrument allows the separation of the different components in the mixture and their recognition by breaking them into fragments whose mass can be measured. The generated fragments are exclusive foreach compound, enabling specific identification.

Another technique used to separate different compounds in a mixture is thin layer chromatography (TLC), which can be applied to separate drugs, fibre dyes, poisons and inks. This method exploits the different polarity of the compounds in th3e mixture, permitting their separation by the different interaction with a solvent system (mobile phase) and a flat glass plate (stationary phase). Polar compounds tend to interact more with the stationary phase, therefore they “run less” on the TLC plate; whereas less polar compounds interact more with the mobile phase, therefore they “run more” on the plate and can be separated from compounds that have a different polarity.


All the above techniques are applied to recognize and identify specific substances. However, the work of a forensic chemist also involves other types of analysis. The colour tests, for example, are utilized to probe drug samples for their chemical properties. These reactions are carried out on ceramic or plastic dishes c4alled spot plates, which contain several wells. Each well is filled with a small amount of the questioned drug and a chemical known to produce a coloured product in the presence of the drug. This allows for presumptive identification of many drugs. Some drugs can also be recognized through microcrystalline tests, which analyse representative crystalline structures under the microscope with transmitted illumination. These tests, though, are more complicated than the colour tests as few forensic chemists are sufficiently trained to recognize the characteristic crystalline structures.

Different analyses can be performed to verify the properties of soil relating to a specific location where a crime was committed. This can help to confirm, for example, if the soil 5found under the shoes or on the car of a suspect is the same as that of the crime scene. Soil is a mixture of organic and inorganic materials whose properties can be analysed (pH, density, composition, colour, texture) through microscopic techniques, as well as sieves to determine the size distribution of a sample, and density gradients to evaluate the distribution of densities comprised in the soil mixture.

Other common items of evidence collected on a crime scene are fingerprints. All fingerprints are unique for each individual (even twins have different fingerprints!) and they can be very useful to identify a suspect, especially if their fingerprints had been previously recorded in databases collected by law enforcement agencies. Latent fingerprints cannot be visualized by eye but development techniques can be used to observe them. One of these is called powder dusting, which involves the use of powders (dark, light or fluorescent) to see contrast a7nd to highlight the fingerprints, which can then be lifted and preserved using a fingerprint tape. Another substance that can be used to colour fingerprints is called ninhydrin, which is used in biochemistry for qualitative and quantitative determination of a-amino acids. This substance gives a purple-coloured product upon reaction with the amino acids contained in fingerprint residues. Further techniques that can be used for fingerprint development include the silver nitrate reaction (reaction between silver nitrate and soluble sodium/potassium salts to give a white solid product called silver chloride, which produces silver and chlorine purple-black gas when exposed to ultraviolet light) an6d the iodine sublimation (based on the absorption of iodine vapours by the fingerprint’s components to give an amber-coloured product). Finally, if the fingerprints contain traces of blood, these can be observed by employing luminol, a derivative of phthalic acid, which allows the detection of blood traces through reaction with metal cations (e.g. the iron-shaped cation present in the heme group of haemoglobin) to give a blue luminescencent product called 3-aminophthalate.


 Many different techniques are used to analyse evidence, which are essential to solve a case. Therefore, although it is not well known, forensic chemistry gives a vital contribution to all investigations. Think about it next time you watch a police TV series…




Soap:properties and production….So much chemistry in just a bubble

Carmen Piras 

Soap is a sine qua non in everyday life that has a very ancient tradition.


Itmount sapos use dates back to the Babylonians and the Egyptians, who used to combine animal and vegetable oils with alkaline salts to produce it. According to the roman legend, the word “soap” comes from Mount Sapo, where the animals were sacrificed. The fat from sacrificed animals together with wooden ashes were washed by the rain to the Tiber River, where people used to wash their clothes and found out that this mixture could help to clean the clothes. A similar word was also present in German language for a mixture of ash and fats that was utilized to dye the hair red. Gallic women have been the first to realize that this mixture could easily remove stains. This recipe didn’t change for centuries and had a great diffusion all over the world, however it evolved during the years, finally allowing the industrial production of soap from the mid-nineteenth century. Since then soap, which was initially considered a luxury, became widely available to everyone.


From a chemical point of view, soaps are water-soluble sodium or potassium salts of fatty acids. They are obtained by mixing a strong base with fats and oils from animal or plant sources. When these are heated up together, they react in the so-called “saponification reaction”. In the past, this reaction was performed using fat and lye, which was obtained from leaching ashes through a purification process by filtration and heating. Nowadays, the principle is the same, but some variations have been introduced to make the process easier and quicker.reaction

In the saponification reaction fats and oils comes usually from animal or plant sources. These are used in the form of triglycerides, whose structure is composed of a glycerol molecule to which are linked three molecules of fatty acids. When these react with a base, the alkaline conditions hydrolyse the triglyceride allowing the formation of the corresponding salt (which constitutes the soap) and glycerin, which is reused for other purposes in industrial processes.

Each soap molecule is constituted by two moities:

fatty-acid-structure1An hydrophobic moiety or “tail”, which is a long hydrocarbon chain

An hydrophilic “head”, which is represented by the carboxylate group that forms the sodium or potassium salts and is negatively charged.

This hydrophilic part of the molecules interacts with water molecules through hydrogen bonding and ion-dipole interactions, whereas the hydrophobic parts attract dirt and do not interact with water molecules. However, this long hydrocarbon chains interact with each other by dispersion forces and form structures called micelles. In each micelle, the molecules are oriented in a way that allows the hydrophobic moieties of the molecules to hide from water, giving rise to a spherical structure. The hydrophilic heads of the molecules, instead, interact with water, but since they are negatively charged, they repel other micelles, which remain dispersed in water.



The industrial manufacture of soap has a long tradition and it can be performed through discontinuous or continuous processes.

The discontinuous processes include different phases:

  1. Saponification, which is carried out in boilers heated with direct fire or steam, by stirring the fat mixture and the base that is gradually added. This operation takes about 3-4 hours keeping the temperature around 100°C. However, the same process can be carried out in few minutes under pressure and at higher temperatures (250°C).
  2. Salting: from the saponification a colloidal solution is obtained and it contains soap, glycerin and base residues. These two components can be separated from the lye simply by adding sodium chloride (kitchen salt). During this stage, also soap and glycerin are separated and the glycerin can be recovered and reused for other industrial purposes (cosmetic and pharmaceutical industries).
  3. Strong change: This process allows removing the fat that has not saponified by adding a strong caustic solution. In this way, all the fat is converted into soap. This step can be followed by a second salting treatment.
  4. Pitching: During this process, the soap is boiled again with water, to form two different layers

– “Neat soap”, which is formed by 70% soap and 30% water

– “Nigre”, which contains most of the impurities (salts and dirt) and most of the water

The neat soap is collected and cooled and finally treated with other substances such as emollients, colorants and perfumes.

The continuous processes are the most common applied production systems and also the most convenient, as the prices are consistently reduced and the obtained products have consistent characteristics.



Soap can be easily made at home with some nice experiments that will help you to understand the chemistry and to create your own unique soap.

Some nice recipes are described in this website:

Or you can simply follow this youtube video:



What is paper made of…. A short journey through the chemistry of paper

Carmen Piras

During the weekend I often go to a nice café for a slice of carrot cake and a cup of coffee. On a lazy Saturday morning there is nothing better than reading a book while tasting goimagesod coffee. Whilst I was enjoying my coffee, last weekend I realised how paper was everywhere….My book, the coffee cup, the plate where my cake was sitting, the napkins and a newspaper on the table! All these things not only are made of paper, but different types of paper with different properties depending on their purpose. I then thought I wanted to know more about the chemistry of this material and hopefully this article will make you think about it next time you will be reading a magazine or a book with a nice hot coffee in your hands.


Paper has always been used in numerous applications. Its history begins from 3000 BC, when the Egyptians discovered how to exploit the fibers of a plant (Cyperus Papyrus) that grew on the banks of Nile River to obtain a paper-like material. This material was called pappapyrus from the Latin word papyrus and the Greek πάπυρος, and from this word the modern word paper. However, the merit of the invention of paper as we know it today has to be attributed to the Chinese Ts’ai Lun, an officer of the court of the emperor in 105 BC. From China, the paper, reached Middle East and Europe, where, in the XIII Century the first “paper mills” were built. With the introduction of industrial labor in the XIX Century, the production of paper could finally be carried out on a large scale and at a relatively low price.


The main component is undoubtedly cellulose, the most common structural polymer in the plant world. Its chemical structcelluloseure consists of multiple units of glucose linked together by b-glycosidic bonds that form long linear chains connected through hydrogen bonds.

Several other substances are also present, including:

– adhesives, which reduce the absorption of water making the paper less hygroscopic and more compact

– filler materials, which make the paper more opaque and consistent

– dyes.

Depending on the type of paper and the type of processing other components may be present, such as hemicellulose. This polymer has a chemical structure that is similar to cellulose, but presents lateral branches formed by glycosidic units. Because of its structure, hemicellulose has a greater tendency to form hydrogen bonds and this makes the paper less stable and more easily degradable when exposed to chemical and physical factors.

Another polymer that can be found in paper is represented by lignin. There are different types of lignin, which are composed of three different monomers:

– Cumaryl alcohollignin

– Coniferyl alcohol

– Sinapyl alcohol

Other substances may also be used as additives to improve the degree of whiteness, opacity and smoothing. These include:

– Titanium dioxide

– Kaolin

– Calcium carbonate

– Talc.

Binder materials play also an important role; they are added in order to facilitate the adhesion of pigments and are used for coating. Among these we can highlight:

– Polysaccharide compounds, such as starch, arabic gum, tragacanth gum

newspapers– Fat compounds, such as waxes and drying oils, including linseed oil, sunflower oil, poppy seed oil

– Resins, such as turpentine, rosin or mastic, which are used as protective coatings.

All these components confer different characteristics to the paper (e.g. consistency, opacity, thickness), which can be exploited for the production of different types.

The paper making process is nicely described in this video: https://

Have a look at this video, if you want to make your own home made paper, it’s easy and funny:

Fifty shades of chemistry and their application in art

Carmen Piras

There pigmenti x introhas always been a very strong link between chemistry and art. The grinding of the pigments, the use of dispersants and the appropriate choice of the surfaces on which the color lays, are a clear example of this tight relationship. Chemistry, in fact, has always been very important not only to promote the evolution of art, but also for the maintenance of cultural heritage, allowing to protect it from the action of chemical and physical agents and to restore it when damaged.


This close link between chemistry and art has evolved over the years. Thpittura rupestree first traces of use of mineral pigments date back to the Paleolithic (300.000-10.000 B.C.). Archaeological excavations in Zambia revealed some pigments preserved in a niche, probably used as a warehouse, in the caves of Twin River. These mainly included iron oxide (red), iron oxide hydrate (yellow) and coal (black) and were  probably destined to body painting. Only later, thanks to a wider dissemination of communication and commerce, more rare minerals began to be used. The Neolithic was not very innovative from this point of view, but in this period was introduced the use of white colour, which was obtained from domestic animals bones that were dried and heated at high temperatures.

Egypegizi pigmentitian civilization, by contrast, was more revolutionary. The Egyptians, in fact, discovered copper minerals such as malachite and azurite, lead ores, tin ores, chalk, many rare coloured minerals, stibite, native iron, cinnabar, natron and lime. Furthermore, the considerable knowledge of alchemy they had, led to the use of pigments such as Egyptian blue (a mixture of copper silicate and calcium, which was obtained by fusing white sand, gypsum and malachite), Egyptian yellow (produced by reacting an antimony derivative with a lead salt or a corresponding oxide in high-temperature ovens) and white lead. This last pigment was used for thousands of years until the second half of ‘800. More scientifically, it can be defined as lead hydroxycarbonate and its use was prohibited since 1921, due to its high toxicity.


Alchemy had a great development also in Greek and Roman civilizations, which played a very important role in promoting and transmitting the empirical knowmurex commonledge accumulated over time. To the Phoenicians, instead, can be attributed fabric dyeing. Shades of red, such as madder or kermes, were the most utilized colours in dyeing techniques and they were obtained from vegetable or animal extracts. Alizarin, for example, was extracted from the roots of Rubia Tinctorum; Kermes was obtained by an insect (Kermes Vermilio) that lived on oaks; whereas purple was extracted from a mollusk (Murex Common).

Some of these dyes were also used during the Middle Ages, when the oil technique started to become popular. To fix the colour to the fabrics, the dyes were anchored on alum particles (sulfate hydrates of aluminum and potassium), which adhered firmly to the textile fibers; this technique is also known as “etching”. Alum also allowed lighting up the colour, making it brighter and stronger.

alchemistsWith the decline of the Roman Empire and the beginning of the middle Ages, the known alchemical techniques did not go lost, but were collected and developed by the Arabs, which integrated them with the knowledge from China and India. The most famous alchemist of the time was known as the Geber and was born in 722 A.D. To Geber and its school, was attributed the discovery of important substances such as concentrated acetic acid, hydrochloric acid, sulfuric acid, nitric acid, caustic soda and aqua regia. Aqua regia was one of the rare mixtures able to dissolve gold and for years it fueled the desire of alchemists to transform the substances into gold and vice versa.

The Middle Ages brought to the discovery of new pigments (especially shades of blue) and lacquers, which were obtained by adsorbing the dye on white solid particles (for example alumina).


Subsequently, during the XV Century, oil painting was introduced. This technique adopted for the first time as a dispersing medium for the color, poppy oil, walnut oil or flax oil, instead of yolk and albumen, which were used for tempera paint, technique that was gradually applied less and less. Compared to tempera paint, the mixed with oil colours showed several advantages, since the oil protected the pigments from the attack of external agents and slowed degradation.

New pigments were then introduced in ‘600, century in which, thanks to the colonial empires, some prominent pigments reached Europe. These included:

Lacquer Kermes (cochineal carminic acid, a plant pest), imported from Mexico

Indian yellow (magnesium salt of euxantico); probably the first fluorescent yellow

Gamboge (intense golden yellow), extracted from South-East Asia plants

Kassel, a black-brown pigment extracted from peat.


tubetti colori a olioWith the progress of chemistry between the ‘700 and ‘900, many new compounds were synthesized and enriched the palette of many painters due to a significant reduction of costs compared to the past. Another important novelty was the introduction, in 1840, of tin tubes with ready for use colours (i.e. pigments already mixed with linseed oil), whereas in the past each artist had to prepare the colours at time of use.

Numerous new organic pigments were introduced, especially between 1930 and 1940, with an estimate of up to about 600 pigments in the late ‘900.

It is interesting to note that the painters were not aware of the toxicity of some of the chemicals they used as colours. For example, it was hypothesized that Cezanne, who loved emerald obtained from acetoarsenite copper, contracted diabetes because of the arsenic contained in the colour he used. The same pigment together with lead chromate yellow pigments were thought to be responsible for the aggravation of Van Gogh’s neurological problems and that a similar poisoning was responsible for Monets blindness. The use of pigments containing toxic heavy metals, such as mercury, arsenic, lead, cadmium and chromium may also have caused Renoir’s rheumatoid arthritis and Klee’s skin disease. However, the toxicity of these pigments was recognized only from the ‘900.

New synthetic pigments enriched the Nineteenth Century: pigments synthetic

  • Phthalocyanines, which became indispensable for brilliant colors
  • Quinacridones, red and magenta
  • Azopigments, yellow, orange and red
  • Diketopirrols, orange, red and scarlet, as an alternative to cadmium-based pigments
  • Anthraquinones, several shades of red.

These pigments, compared to natural pigments such as carotene, were much more stable and lasting in time. Moreover, their chemical structure could be modified, changing in this way their properties.

In conclusion, there has always been a strong link between chemistry and art, which over the centuries has evolved, giving a great contribution to art. Artists may therefore be considered a bit chemists and, vice versa, chemists a bit artists.


  • “Alchimie nell’arte”, Adriano Zecchina


From the coffee plant to the cup: a journey through the chemistry of coffee

Carmen Piras

Coffee is definitely one of the most popular and addictive drinks in the world. However, to obtain the coffee we drink from the plant, there are numerous steps in which the beans are extracted and treated to finally achieve the powder. Before we start our journey through the magic world of coffee, we will go back to the past to explore its history and find out how it arrived in Europe and became so popular.



The word “coffee” comes from the Arabic word “qahwa”, originally used to describe a dark red beverage that was extracted from some seeds and caused exciting and stimulating effects. The turkish “kahve” came from this word, later the Italian word “caffè” and then “coffee”. According to the legend, the history of coffee began in the Ethiopian province of Kaffa, where a shepherd used to take his goats to graze. One day, he noticed that the goats, after eating the berries of the coffee plant, became more active and energetic. For this reason, he decided to roast the seeds of the plant and grind them to obtain an infusion. Coffee was probably subsequently exported by some slaves in Yemen and Saudi Arabia, where, in the fifteenth century, it started to be cultivated. Initially, Arabs banned coffee exportation; however in 1616 some Dutch merchants managed to bring some plants to the Netherlands, which could be cultivated in greenhouses. The Dutch began then to cultivate coffee plants in their colonies in India and Indonesia, from where coffee was exported to Europe by some merchants of Venice. From 1650, coffee was also exported to England, France, Germany and Austria. Nevertheless, it was from the ‘700 that coffee started to be grown on a large scale in the British and Dutch colonies, reaching in this way Central and South America, which currently holds the primate of world production (Colombia and Brasil). As coffee consumption was growing, the first coffee houses arose and diffused as meeting places for discussion and dissemination of political, literary and philosophical ideas. Important coffee houses were opened in Oxford, London, Paris, Vienna, Venice and Florence.


coffee plant

The coffee plant, Coffea, belongs to the family of Rubiaceae, which includes over 6,000 species of small trees and shrubs. The mainly produced species are represented by: – Coffea Arabica (Arabica Coffee – about 60% of world production): cultivated in Latin America, India, Indonesia, Africa and Middle East – Coffea Canephora (Robusta Coffee): cultivated in West and Central Africa, Southeast Asia and Brazil – Coffea Liberica (Liberica Coffee): cultivated in Malaysia and West Africa – Coffea Dewevrei (Excelsa Coffee): cultivated in Africa.


 Due to its botanical characteristics, the coffee plant grows easily in mountain areas. Depending on the variety it takes up to 3 or 4 years for the plant to start to produce fruits, which are then collected by hand or by machine. Each fruit looks like a red berry similar to cherries and contains two seeds (coffee beans), which are removed from the fruit and dried before being roasted. This process can be performed in two ways:

1. Dry method: the whole fruit is dried under the sun on large concrete patios. This is the most important stage of the process, as it can affect the quality of the obtained green coffee. The dried cherries are stored in silos and subsequently sent to the mill where they are processed to remove the outer layers of the cherry and obtain the beans.

2. Wet method: in this case the pulp is removed from the cherry by a machine and it is placed in large fermentation tanks to remove coffee mucilage through enzymatic reactions. When the fermentation is completed, the coffee is then dried under the sun or with a mechanical dryer and finally stored. In both cases, before the coffee is ready to be exported and sold it passes through the final stages of “curing”, which involves a number of cleaning, sorting and grading operations.


 coffee beans

The roasting process is then fundamental to obtain all the aroma and flavors and it is crucial to produce a high quality coffee. This is done by heating the coffee beans to 180-240oC for 8-15 minutes in order to obtain the caffeol or coffee oil, which is the essence of coffee. The roasting process has to be carefully controlled to obtain a uniform resulting flavor. Coffee is then assessed for taste to create a flavor profile and evaluate its quality. This process is called “cup tasting” or “cupping“.


The decaffeination process is performed on green coffee beans to extract the caffeine from the beans. Four different methods can be applied for this purpose:

– Water method

– Ethyl acetate method

– Liquid CO2 method

– Methylene chloride method

All these methods involve some common steps:

  1. The caffeine is made available for extraction by swelling the green coffee beans or steaming
  2. The caffeine is extracted
  3. Solvent residues are removed from the beans by steam stripping
  4. The decaffeinated coffee beans are finally dried.



Depending on personal preferences, coffee can be prepared in different ways.

Espresso is one of the most common ways of making coffee. It was invented in Italy and it is made with specific machines which force hot water through ground, compacted coffee into the cups below. On top of the black coffee, lies a golden brown liquid called “crema” that can be used by an expert taster to judge the quality of the coffee. The Moka-Napoletana is another common way to make coffee in Italy and it combines the characteristic of espresso and the percolator made coffee. It works by boiling the water into a lower chamber and forcing it through the coffee which seats on a filter. A similar process is used by the Percolator, which works by heating the coarsely ground coffee and cold water until the water starts boiling and bubbles up in the top of the unit. A different way of making coffee is the Plunger/Cafetiere method, which works by placing the coffee and warm water into the pot. After few minutes the plunger is then pushed down to separate the infusion from the coffee grounds.


 coffee cup

The most important active component of coffee is definitely caffeine. However, a huge number of chemical compounds and over 1000 aroma compounds are also contained in coffee.


  • Caffeine is an alkaloid that belongs to the family of xanthine (from the greek “xanthos”, yellow), which also includes theobromine and theophylline. The mechanism of action of caffeine can be re-conducted to its action as an antagonist of the adenosine A2A receptor, which is part of the class of purinergic receptors. This has a stimulating action on the central nervous system, on catecholamines release, on gastric acid production and on metabolism. The psychotropic effects include increased state of alert and ability to concentrate, improved physical and mental efficiency. By contrast, higher doses induce agitation, tremors, nausea, restlessness and diuresis.

Phenolic compounds in coffee

  • Coffee also contains numerous Phenolic Compounds, which represent 12% of the dry weight of green unroasted beans. These include: quinic acid, trans-cinnamic acid, p-coumaric acid, caffeic acid, ferulic acid, 4-O-caffeoylquinic acid, 3,5-O-caffeolquinic acid, 5-O-feruloylquinic acid, 3-O-caffeoylquinic acid. These compounds are responsible for the bitter taste of coffee, its brown colours and also its antioxidants properties.

 For more information: