Properties of Amino Acids:
Amino acids have number of physical and chemical properties which are closely connected to the overall structural features.
Physical Properties:
Physical properties of amino acids comprise:
i) At ordinary temperature amino acids are white crystalline solids.
ii) All amino acids contain high melting points (more than 200oC).
iii) They decompose when heated at high temperature, rather than melting.
iv) They are stable in aqueous solution, and with some exceptions, they can be heated as high as 120oC for the short periods with no decomposition, even in acid or alkaline solution.
v) All amino acids are soluble in water and alcohol but insoluble in non-polar solvents.
Optical Activity of Amino Acids:
Apart from glycine, other amino acids have centre of asymmetry at α-carbon (chiral centre). Such molecules are optically active, that is they are able to rotate plane of plane- polarized light when they are put in the polarimeter, an instrument that estimates specific rotation of optically active substance. Amino acid is said to be dextrorotatory if it rotates plane to right (clockwise from point of view of observer). In contrast, if direction of rotation is to left (anticlockwise), amino acid is supposed to be laevorotatory. Dextrorotatory molecules are designated by prefix '+ or d' whereas laevorotatory enantiomers are designated with prefix '- or l'.
Absorption of Light by Amino Acids:
Phenylalanine, tryptophan and tyrosine absorb light strongly in ultraviolet region (λ=100 to400 nm). This property is attributable to presence of aromatic nucleus in their side chains. Presence of the amino acids in polypeptides, is being utilized to quantify polypeptides. Amino acids are not known to absorb visible light (λ=400 to 800 nm) and are thus colorless.
Acid-Base Property of Amino Acids:
In solution, amino acid shows ionic property. Both amino and carboxyl groups joined to its alpha carbon exist in their ionic states (COO-, +NH3), thus making it dipolar ion, or zwitterion (a German term for 'hybrid ion'). This zwitterion can perform as the acid or as base.
As an acid (a proton donor):
As a base (a proton acceptor):
Titration Curve of Simple Amino Acids:
The simple amino acid, such as glycine or alanine, is monoamino monocarboxylic α-amino acid. Such amino acid is diprotic. That is, it's completely protonated form (+H3N-CH2-COOH) can yield 2 protons- one from -COOH group and other from -NH3+ group.
Most important features of the curve are:
i) Two distinct stages on curve correspond with deprotonation of proton-donor groups.
ii) At the begin of titration (at low pH) amino acid is mainly a cation (a positive ion) and at the end, it is anion (a negative ion).
iii) Midpoint of any titration is point of inflection where pH is equal pKa of protonated group being titrated. For the diprotic amino acid, carboxyl group is first to release proton with a pKa value of about 2.34. Approx 9.69 you find another point of inflection corresponding to pKa of amino group.
iv) Another significant point of inflection exists at pH 6.01 of titration curve. This pH is referred to as pI (isoelectric point) of amino acid. At its pI, the amino acid is dipolar (zwitterion) and is electrically neutral (net charge = 0).
Because of variation in structures of the side chains, few amino acids may carry extra protonated groups in their R-groups with resultant variation in nature of their titration curves. Additionally, pI values of amino acids have been used in analytical separation of mixture of amino acids.
Tutorsglobe: A way to secure high grade in your curriculum (Online Tutoring)
Expand your confidence, grow study skills and improve your grades.
Since 2009, Tutorsglobe has proactively helped millions of students to get better grades in school, college or university and score well in competitive tests with live, one-on-one online tutoring.
Using an advanced developed tutoring system providing little or no wait time, the students are connected on-demand with a tutor at www.tutorsglobe.com. Students work one-on-one, in real-time with a tutor, communicating and studying using a virtual whiteboard technology. Scientific and mathematical notation, symbols, geometric figures, graphing and freehand drawing can be rendered quickly and easily in the advanced whiteboard.
Free to know our price and packages for online biology tutoring. Chat with us or submit request at [email protected]
tutorsglobe.com flower is a modified stem evidence assignment help-homework help by online flower-a metamorphosed shoot tutors
tutorsglobe.com leverage assignment help-homework help by online financial management tutors
www.tutorsglobe.com offers reaction classification by reaction type homework help, assignment help, online tutoring assistance, organic chemistry solutions by online qualified tutor's help.
tutorsglobe.com mechanism of respiration assignment help-homework help by online respiration tutors
tutorsglobe.com environmental impacts assignment help-homework help by online energy crisis and its environmental impact tutors
Aves tutorial all along with the key concepts of Features of Class Aves, Features of Subclass Archaeonithes, Class Subclass Neornithes, Superorder Odontognathae, Palaeognathae, Struthioniformes and Tinamiformes
alkaline earth metals tutorial all along with the key concepts of extraction of alkaline earth metals, uses of alkaline earth metals, physical properties, solubility, lattice energy and hydration energy
The loss and profit statement and balance sheet and another financial report can then be generated using the ledger accounts listed in the trial balance.
www.tutorsglobe.com offers variance analysis homework help, variance analysis assignment help, answering questions to variance analysis accounting solutions, online tutoring by tutors.
tutorsglobe.com chromosomal aberrations assignment help-homework help by online modern concept of natural selection tutors
tutorsglobe.com structure of fungi assignment help-homework help by online fungi tutors
tutorsglobe.com marginal utility and mrs assignment help-homework help by online choices and preferences of consumer tutors
www.tutorsglobe.com offers answering questions to theories of international trade, the principle of absolute advantage, economics assignment help - homework help by online tutors.
molecular theory of matter tutorial all along with the key concepts of structure of matter, description of brownian motion, atomic structure, molecules, states of matter, kinetic molecular theory of matter, assumptions of kinetic theory of gases, properties of fluids at rest
Six-membered Ring–Pyridine tutorial all along with the key concepts of Occurrences of six-membered ring, Nomenclature and Isomerism, Preparations of six-membered ring, Properties of Pyridine, Uses of Pyridine, Structure of Pyridine and Derivatives of Pyridine
1955161
Questions Asked
3689
Tutors
1453401
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!