Name : Choirunnisa Mayara
UJIAN AKHIR SEMESTER
MATA KULIAH
: KIMIA BAHAN ALAM
SKS
: 2
DOSEN
: Dr. Syamsurizal, M.Si
WAKTU
: 22-29
Desember 2012
PETUNJUK : Ujian ini open
book. Tapi tidak diizinkan mencontek, bilamana ditemukan, maka anda dinyatakan
GAGAL. Jawaban anda diposting di bolg masing-masing.
1. Explain the triterpenoid biosynthetic pathway, identify important factors that determine the quantities produced many triterpenoids.
Answer:
Terpenoids are built up from C5 units, isopentenyl diphosphate (IPP). IPP is supplied from the cytosolic mevalonic acid (MVA) pathway and the plastidal methylerythritol phosphate (MEP) pathway. Triterpenoids and sesquiterpenoids are biosynthesized via the MVA pathway, whereas monoterpenoids, diterpenoid, and tetraterpenoids are biosynthesized via the MEP pathway. The first diversifying step in triterpenoid biosynthesis is the cyclization of 2,3-oxidosqualene catalyzed by oxidosqualene cyclase. Triterpenoid biosynthesis starts from mevalonic pathway, reacts with IPP generating DMPP. DMPP react with IPP, GPP formed reacted again with IPP, FPP formed. Reaksikan with FPP FPP at a later formed skualena. Skualena undergo cyclization that would eventually form triterpenoid compounds.
the factors that most influence is cyclic in skualena.
2. Describe the structure determination of flavonoids, specificity and intensity of absorption signal by using IR and NMR spectra. Give the example of at least two different structures!
answer :
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained. It relies on the phenomenon of nuclear magnetic resonance and can provide detailed information about the structure, dynamics, reaction state, and chemical environment of molecules.
Most frequently, NMR spectroscopy is used by chemists and biochemists to investigate the properties of organic molecules, though it is applicable to any kind of sample that contains nuclei possessing spin. Suitable samples range from small compounds analyzed with 1-dimensional proton or carbon-13 NMR spectroscopy to large proteins or nucleic acids using 3 or 4-dimensional techniques. The impact of NMR spectroscopy on the sciences has been substantial because of the range of information and the diversity of samples, including solutions and solids.
Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy. As with all spectroscopic techniques, it can be used to identify and study chemicals. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectrometer.
The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher-energy near-IR, approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength) can excite overtone or harmonic vibrations. The mid-infrared, approximately 4000–400 cm−1 (2.5–25 μm) may be used to study the fundamental vibrations and associated rotational-vibrational structure. The far-infrared, approximately 400–10 cm−1 (25–1000 μm), lying adjacent to the microwave region, has low energy and may be used for rotational spectroscopy. The names and classifications of these subregions are conventions, and are only loosely based on the relative molecular or electromagnetic properties.
3. In the isolation of alkaloids, in the early stages of acid or base required conditions. Explain the basis of the use of reagents, and give examples of at least three kinds of alkaloids.
answer:
Alkaloid needs acid condition to produces salts. Alkaloid salts already in base form would then be withdrawn by organic solvents. For example, in the isolation of caffeine, caffeine in the aqueous phase was extracted with chloroform as in acid solubility of caffeine in chloroform greater solubility in water. Similarly, in the isolation of nicotine, the addition of 10% sulfuric acid in the solution aims to be a solution in acid, because the caffeine extraction using ethanol a more optimal under acidic conditions. Nicotine and morphine to the same treatment results are the same.
4. Describe the relationship between biosynthesis, methods of isolation and structural determination of compounds of natural ingredients. Give an example.
answer:
Biosynthesis, isolation and structure determination are closely related to each other. Synthesis and purification of the material is not the final goal for chemists. That must be defined is the structure of the material has been synthesized and purified. before the determination of the structure, we must first know its biosynthesis process. of the biosynthesis of these compounds, we'll get step-by-step formation of the compound, the compound reacts with what, and what are the factors that influence it. of biosynthesis we will also know the properties of natural materials such compounds, so we can design an isolation method based on the nature and possible reactions to extract them how to manufacture the compound. manufacture in the lab will be successful if we use the appropriate tools and materials, solvents, indicators, temperature also affects the success of the experiment. after isolation, then we can identify the compound. This stage is the stage that Palin difficult. It must be recognized that until the latter half of the 20th century, chemists are not equipped with enough tools to overcome this difficulty. Some chemists proposed structure is not appropriate even for a few years. However, the situation changed drastically since developed various spectroscopic techniques such as NMR, IR, UV, and others. NMR (Nuclear Magnetic Resonance) method in particular is highly superior to other methods. For crystalline solids, X-ray crystallographic analysis proved to be very useful.When the physical and chemical properties of the investigated compounds are not appropriate with any compound that are well known in the literature, the possibility of this compound is a new compound, has never been synthesized or has not been reported.
