Diversity of bacteria according to nutritional requirments, temperature, Oxygen conditions and water activity

Nutritional type	Energy source	Carbon source	Examples
Photoautotroph	Light	Inorganic carbon, i.e. CO2	Some purple and green bacteria (Chromatium)
Photoheterotroph	Light	Organic compounds	Some purple and green bacteria (Rhodospirillum)
Chemoautotroph (Lithotroph, Lithoautotroph)	Inorganic compounds; H2, H2S, NH3	CO2	Many Archaea and few bacteria (Nitrosomanas)
Chemoheterotroph (Heterotroph)	Organic compounds	Organic compounds	Few Arcaea and many bacteria (Pseudomonas)

Type	Minimum (0C)	Optimum (0C)	Maximum (0C)
Psychrophile	Below 0	10-15	Below 20	Contain unsaturated fatty acids in plasma membrane to tolerate.
psychrotroph	0	15-30	Above 25	Able to grow at low T but prefer moderate T
Mesophile	10-15	30-40	Below 45	Most bacteria especially the ones associated with warm-blooded animals.
Thermophile	45	45-70	Above 100	Contain Saturated fatty acids in plasma membrane. High glucose and carbon content as well as high melting point for DNA.
Hyperthermophile	80	80-115	Above 115	Contain phytane and modified proteins in plasma membrane. High glucose and carbon content as well as high melting point for DNA.

Type	Aerobic condition	Anaerobic condition
Obligate aerobe	Growth	No growth
Microaerophiles	Growth; when the O2 is at very low level	No growth
Obligate anaerobe	No growth; O2 is toxic	Growth
Facultative anaerobe/ facultative aerobe	Growth; Not essential to grow but utilized when available	Growth
Aerotolerant anaerobe	Growth; neither essential nor utilized	Growth

Type	Speciality
Halophile	Require NaCl for growth
Halo tolerant	Able to grow at moderate salt concentrations but grow best in the absence of NaCl
Osmophile	Able to grow in high levels of suger
Xerophile	Able to grow in dry conditions

Bonding in transition metal complexes:- Valence bond theory, Crystal field theory, Molecular orbital theory

There are three theories of metal to ligand bonding in complexes.

Valence bond theory

 Coordination compounds contain complex ions, in which ligands form coordinate bonds to the metal. Thus the ligand must have a lone pair of electrons, and the metal must have an empty orbital of suitable energy available for bonding. The theory considers which atomic orbitals on the metal are used for bonding. From this the shape and the stability of the complexes are predicted. The theory has two main limitations. Most transition metal complexes are coloured, but the theory provides no explanation for their electronic spectra. Further, the theory does not explain why the magnetic properties vary with temperature. For these reasons it has largely been superseded by the crystal field theory. However it is of interest for study as it shows the continuity of the development of modern ideas from Werner’s theory.

Crystal field theory

The attraction between the central metal and ligands in the complex is considered to be purely electrostatic. Thus bonding in the complex may be ion-ion attraction (between positive and negative ions such as Co³⁺ and Cl^-).  Alternatively, ion-dipole attractions may give rise to bonding (if the ligand is a neutral molecule such as NH₃ or CO).  This theory has been remarkably successful in explaining the electronic spectra and magnetism of transition metal complexes. Particularly when allowance is made for the possibility of some covalent interaction between the orbitals on the metal and ligand. When some allowance is made for covelencey, the theory is often renamed as the ligand field theory. Three types of interaction are possible. The σ overlap of orbitals, π overlap of orbitals, or dπ – pπ bonding (back bonding) due to π overlap of full d orbitals on the metal with empty p orbitals on the ligands.

Molecular orbital theory

Both covalent and ionic contributions are fully allowed for in this theory. Though this theory is the probably the most important approach to chemical bonding, it has not displaced on the other theories. This is because the quantitative calculations involved are difficult and lengthy, involving the use of extensive computer time. Much of the qualitative description can be obtained by other approaches using symmetry and group theory.

Reference: Inorganic chemistry, J.D Lee 

Preparation of solid derivatives of Carbonyl compounds (aldehydes & ketones) :- 2, 4- Dintrophenylhydrazones, Semicarbazones

The systematic procedure that involves several steps and preparations is carried out to identify unknown compounds to some extent. The preparation of derivatives usually establishes the identification of the unknown with certainty. Here the term derivative is simply referred to a compound prepared from an unknown, in order to identify the unknown compound. An ideal derivative should be a crystalline, easily purified solid with a sharp melting point, which can be prepared readily from the unknown in one direct and unambiguous step.

Many carbonyl compounds can be synthesized from the esterification reaction. There are excellent and conveniently prepared derivatives which use to identify carbonyl compounds. Oximes, Phenyl hydrazones, 2, 4-dinitrophenylhydrazones and semicarbazones are some of the best derivatives of aldehydes and ketones. In the preparation of each of these types of derivatives, the elimination of a water molecule between a molecule of the carbonyl compound and a molecule of the reagent is involved.

Dinitrophenylhydrazine is relatively sensitive to shock and friction. It is a red to orange solid usually supplied wet to reduce its explosive hazard. This is often used as a qualitative test for carbonyl groups, associated with aldehydes and ketones. The hydrazone derivatives can be used as evidence toward the identity of the original compound. These are usually yellow-red colour crystals. Crystals of different hydrazones have characteristic melting and boiling points allowing the identification of the unknown substance.

Semicarbazone is one of the most commonly used derivatives to identify aldehydes and ketones. It is a derivative of an aldehyde or ketone formed by a condensation reaction between a ketone or aldehyde and the reagent; semicarbazide. As semicarbazides are not very stable in the free form, they are usually stored in the laboratory in the form of their hydrochloride salts. Many semicarbazones are off white, crystalline solids, useful for the identification of the parent carbonyl group by melting point analysis.

conductometric titrations

In conductometric titrations, the electrical conductivity of an electrical solution is continuously monitored as one reactant is added. The accurate endpoint of can be determined by detecting a sudden change in the conductivity of the solution. It is particularly useful in titrating weak acids against weak bases. According to Ohm’s law;

I = E/R                                        

Also,

R ∝ l

R ∝ 1/A                                                   

Therefore;

R = ρ l/A

ρ = RA/l

I = Current, E= electromotive force, R= Resistance, l = Length, A= cross section area, ρ= Resistivity

The reciprocal of resistivity is conductivity. It can be expressed as K.

K = 1/ ρ

    = 1l / RA

    = G l/A

G is the conductance.

In the titration, the conducting material is the solution. So the conductance depends on the type of ions in the solution and their concentration. If the solution is located between two electrodes at constant distance and cross section area, conductance will increase when the concentration of the solution decreases.

Also when l and A are constant it is clear that,

K ∝ G

These conditions can be obtained by using a conductivity cell that consisting a pair of platinum electrodes connected to the conductivity bridge which provides current to the cell. The meter will give out the calculated conductivity of the solution.

Nitration of acetanilide (Lab report)

Introduction

Nitration is a type of chemical reaction which a nitro group is added to/substituted in a molecule. Basically it can be carried out by a mixture of concentrated nitric acid and sulphuric acid. Mixture is useful to obtain the active nitronium ion. Electrophilic aromatic substitution is a method used when a functional group is needed to be substituted on to an aromatic compound. In the nitration, nitronium ion acts as the electrophile that involves the attack of the electron-rich Benzene ring. In this experiment nitration is carried out using acetanilide.

Theory

Acetanilide displays moderately reactivity in electrophilic aromatic substitution. Also another advantage is, it’s not oxidized by nitric acid. Principally, acetanilide gives Ortho and Para mono nitroacetanilides. This position of nitronium ion is directed by the –NHCOCH₃ group attached to the benzene ring. This is due to the resonance delocalizing the benzene ring by nitrogen lone pair. Therefore Ortho and Para positions are more resonance stabilized than the Meta. Acetanilide undergoes ready nitration giving mainly the colourless P-nitroacetanilide, mixed with much smaller proportion of the yellow colour O-nitroacetanilide.

Procedure

·         About 2g of powdered acetanilide and 2mL of Glacial acetic acid were mixed well in a 100mL beaker.  4mL of con.H₂SO₄ was added to the mixture.

·         The beaker was placed in crushed ice until the temperature of the mixture was dropped down to 0-5⁰C.

·         4mL of con.H₂SO₄ was added drop wisely while stirring the viscous mixture continuously keeping the temperature below 10⁰C.

·         Afterwards the beaker was removed from the freezing conditions and allowed to stand 30 minutes at room temperature.

·         The mixture was poured onto about 20g of crushed ice and stirred to obtain crystals. The beaker was rinsed with 10mL of water containing few fragments of ice and the solution was added to the main bulk of the product.

·         It was allowed to stand for about 20minutes.

·         Later it was filtered at the pump and washed thoroughly with cold water.

·         Afterwards the crude product was recrystalized with water.

·         Finally the melting point of the product was determined.

Observations

·         Acetanilide powder was white in colour.

·         Glacial acitic acid, H₂SO₄ and acetanilide mixture was initially in pale yellow colour.

·         In cold condition, white colour crystals were formed.

·         Final purified crystals were also white.

·         The determined melting point range was 150-152⁰C.

Conclusion

The initial compounds used were known. Therefore according to those the final product should be nitroacetanilide. As the colour of the product was white, it should be Para nitroacetanilide.  

Discussion

Through the use of electrophilic aromatic substitution, acetanilide is nitrated to nitroacetanilide. There are several key steps involved in the nitration. The first step of the reaction involved in the donation of an electron pair by the acetanilide to the eletrophile, the nitronium ion. This nitronium ion was formed by the reaction of sulfuric and nitric acids. Basically the whole mechanism undergoes as below; (Benzene is shown here instead of acetanilide )

Image via en.wikipedia.org

To prevent dinitration of the acetanilide, the nitrating mixture of concentratred nitric acid and sulfuric acids were added in small portions to the acetanilide solution, so that the concentration of the nitrating agent is kept at minimum.

Also the addition of nitric acid is exothermic. Therefore the mixture would get too hot exceeding the temperature range suitable for the nitration. To avoid this, the addition of HNO₃ acid should be done very slowly, dropwisely.

Cold temperatures were used to slowdown the reaction rate and help to avoid over nitration.

Glacial acetic acid is used because it is a polar solvent capable of dissolving acetanilide and the acetate ion is a poor nucleophile, so no substitution is possible.

At the end, traces of acid should be removed because hydrogen ions catalyze the hydrolysis of the amide to p-nitroaniline. Acid is removed by pouring the mixture onto ice and water and filtering.

The melting point is determined to characterize the product. Theoretical melting point of the Para nitroacetanilide is found to be 214-216⁰C. The observed value was 150-152⁰C and it is much lower than the theoretical values and can be accounted for impurities in the product. Some impurities might be Ortho and Meta directing substances. Also there can be some experimental errors occurred during the experiment such as not controlling the exact temperatures mentioned for the reactions.