BEST IELTS Academic Reading Test 35
ACADEMIC READING TEST 35 – PASSAGE – 2
ACADEMIC READING TEST 35
READING PASSAGE – 2
A buzz in the world of chemistry
A. For the past few years, one of the buzz terms in the pharmaceutical, agrochemical and biotechnology industries has been ‘combinatorial chemistry’. Surf the net and find thousand s of references to it. Read any of the general science weeklies, such as nature or new scientist, and every few issues, another worthy author is going to save the 21st century from everything nasty with this miraculous technology. Some of the more specialist journals have even devoted whole issues to reviewing combinatorial chemistry.
B. These reviews all have the same format. First, there is the section from research and development director of a major chemical company, a person who was not worked at the bench for years, if not decades. This is filled with business speak; the jargon keeps the shareholder happy and makes them proud to own a bit of something at the forefront of science. Section two is from a director of a venture capital funded synthetic chemistry company located on a green field side, probably in a protacabin, or, perhaps, in a new business park, rent free for the first five years from the local authority of a small town no one has heard of. He discusses the molecular modeling packages that they are using to build ‘virtual’ libraries containing millions of compounds. The third section is by someone who, in fact, practices combinatorial chemistry and who developed automated system to do the syntheses and to assay the products. They can probably synthesise a few thousands compound per week.
C. We know that organic chemistry is the chemistry of carbon, biochemistry the chemistry of life and physical chemistry the application of physics to chemical behaviour. What then is combinatorial chemistry?
D. combinatorial chemistry is the branch of synthetic organic chemistry. We all remember mathematics classes at school just before end of the term when we were given silly sums to do: How many waves can five differently coloured beads are arranged on a string? (120). Maths teachers call these permutation and combination problems; hence, combinatorial chemistry.
E. After the development of solid phase peptide synthesis in the 1960s by Merrifield, soon synthetic peptide chemists were also doing permutation and combination sums. There are 20 naturally occurring amino acids, the building blocks of peptides and proteins, the workhouse molecules of life. How many ways can these be arranged, or chemical bonded, to synthesise novel peptides which might be put to any number of uses in the pharmacy? If we take just one molecule of each of the 20 amino acids and join the together to form a peptide, we find that we can arrange these in 20! Or 2.432902008177*1018 ways. Nature knows no such restraint; it can use multiple copies of each amino acid, and so can synthesise 2020 or 1.048576*1026 twenty amino acid peptides. Proteins contains hundreds of amino acids. The number of possible sequences are truly innumerable!
F. They become even more so when one considers the other polymeric molecules of life: the lipids, carbohydrates and nucleic acids.
G. classically trained synthetic chemists strive for purity. One remembers twelve years ago chemist synthesizing a 20 residue peptide. He went of the lab, was ever so busy, producing a different high performance liquid chromatography (HPLC) trace every few days to show his biologist customers how the reactions were progressing. A few months after the request was placed, the biologists were given a few milligrams of their desired peptide and half a rain forest worth of HPLC printout!
H. That was fine when only one product was sought. Now the demand is for thousands of products to satisfy the automated high- through-put screening system employed by the major pharmaceutical companies. How can this be achieved?
I. let us consider solid phase synthesis strategies. In these, the compound of interest is synthesised on a solid support, a resin bead. These beads are typically 100 microns in diameter made from cross-linked polyvinyl; benzene or polyethylene glycol polymers.
J. Using the Tea-bag method, developed by Houghten in the 1980s, typically about 100 mg of the 100 micron beads are put into polypropylene mesh sacs which have a 75 micron mesh size. These are thermally sealed closed and the synthesis takes place on the resin beads with the sac. During the synthesis reaction cycles, the sacs are transferred from reagent pot to pot in sequence, and at the end of the synthesis, the product is cleaved off the bead, characterized and purified as need be. Using this strategy, one need to use a separate sac for each compound to be synthesized and automated systems have now been developed for multiple sac manipulation.
K. The sensitivity of compound analytical techniques has developed apace with the technology, and whereas, in the 1980s, one required several millimoles of product to characterize, now this can be done with femtomoles or in some cases attomoles (10-18moles)! Therefore, one need only recover product from 1 bead, about 2-3 picmoles. Automated systems are now being developed to synthesise on single magnetic beads using only2-3nanoliters of reagent per cycle. When the ‘classical’ Tea-bag strategy was developed, 100 milliliters per cycle were considered to be a phenomenal solvent cost-cutting exercise.
I The development of high- the-put automated screening has demanded from synthetic chemistry large arrays or libraries of compound to satisfy the investment made in installing these systems. Will combinatorial chemistry be able to meet this demand? Are the synthesizes well enough developed to meet this? Peptide and oligonucleotide solid phase strategies have been well enough developed over the past 30 years. Will solution methods and other novel chemistries be able to keep apace? Can ‘virtual’ chemical be used to remedy ‘real’ problems? After all, we are living a real world.
Complete the text below, which is a summary of paragraphs A-E. Choose your answers from the word list and write them in boxes
Example: There is a wealth of ………….(Example)….to combinatorial chemistry on the internet.
There are more words than spaces, so you will not be able to use them all. You may use each word only once.
How combinatorial chemistry began
Combinatorial chemistry as an…… (15)……..of synthetic organic chemistry has been very much….. (16)…… in recent years, ……(17)……in a plethora of articles written by experts in the field. Moreover, all the reviews in specialist publications….. (18)……..the same formula. But what about the origin of combinatorial chemistry? It comes from permutation and combination problems in mathematics…… (19)……solid phase peptide synthesis was developed, synthetic peptide chemists started doing similar calculations as well. The 20 naturally occurring amino acids provided them with… (20)…possibilities.
in the air
Look at paragraphs I and J which describe the Tea-bag method. Using the information in the passage, complete the flow chart below.
Write your answers in boxes on your answer sheet.
Use NO MORE THAN THREE WORDS for each answer.
Below is a list if the regular types of contributor to chemistry reviews.
Which three contributors are described by the writer? Write your answer A-F in the order they occur in the text in boxes 12-14 on the answer sheet.
A. A direct of s technology Business Park.
B. Someone who is from a major company and involved directly in research.
C. Someone who is involved in the new technology of combinatorial chemistry.
D. An amateur chemist who synthesizes thousands of compounds per week.
E. The director of a small obscurely located and investment funded operation.
F. An out-of-practice director of some major chemical enterprise.
Choose the appropriate letter (A-D) and write it in boxes on your answer sheet
29. Physical chemistry……
A. deals with the way physics is applied to chemical behaviour.
B. is closely connected with organic chemistry.
C. deals with the way chemistry is applied to physical behaviour.
D. led to the development of combinatorial chemistry.
16. in vogue
18. follow religiously
21. (polypropylene) mesh sacs
22. thermal sealing /being thermally sealed
23. resin beads
24. pot to pot
25. characterized and purified.