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Question: Describe about the experiment of Glucose Molecule?     Answer: 1.0 Aim of Experiment: To carry out initial structural analysis of α-D-(+) -Glucose using NMR techniques (1-dimensional) such as 13C-DEPT 135, 1H-NMR and 13C-NMR. In addition to perform, further structural analysis by 2-dimensional NMR such as HSQC, COSY, HMBC and TOCSY. Also, observe the influence of its structural characteristics on coupling constant and chemical shift on the NMR spectrum. 2.0 Introduction Glucose molecule Glucose is a simple monosaccharide sugar, which is considered as one of the most important carbohydrates. Glucose is used as a resource of energy in plants and animals. It is found that glucose is one of the main products used in respiration and photosynthesis. Glucose is found in nature as D-glucose, which is commonly known as dextrose. Food industries manufactured glucose always in dextrose form. A glucose molecule is consisted of carbon, hydrogen and oxygen molecules. The chemical formula of glucose is C6H12O6. Glucose is composed of 6 carbon atoms and contains an aldehyde group as the functional group, therefore glucose can be classified as an aldohexose. Glucose molecule can further be classified into either L or D series depending on the maximum number of its chiral center, C-5. At this C-5 position, if OH functional group is situated at the left of the plane, it can be classified as L-glucose. On the other hand, D-glucose is the mirror image of L-glucose. it is observed that glucose is more stable in its ring structure compared to open-chain structure. The reason behind the stability of ring structure is, the hydroxyl group on C-5 is prone to react with the carbonyl group on C-1, which results in the production of a closed pyranose ring (Figure 1). Therefore, glucose is further found in two isomeric forms such as α-D-glucose and β-D-glucose. In α-D-glucose, the OH functional group on C-1 is formally trans to the CH2OH (on C-5). On the other hand, these two groups are found in cis position in β-D-glucose (Figure 1). In this experiment, the structural properties of α-D-glucose are focused, as glucose is the most abundance aldohexose found in living organisms. To find out the structural properties of this monosaccharide, the researchers have used many NMR spectroscopy techniques. Figure 1: Anomeric forms of D-glucose NMR spectroscopy NMR (Nuclear magnetic resonance) induces transitions between different nuclear spin states of samples by using radiofrequency radiation in a magnetic field (Stothers, 2012). It is found that NMR spectroscopy is generally used in quantitative measurements; however, it is most useful to determine the structure of molecules (along with mass spectrometry and IR spectroscopy) (Günther, 2013). The utilization of NMR spectroscopy to determine the structural characterization arises because different atoms in a molecule face different magnetic fields. This phenomenon is responsible for the transitions of different resonance frequencies in an NMR spectrum (Graaf, 2013). It is found that the interactions between different nuclei are responsible for the deviation of the spectra lines. Therefore, the splitting lines of spectra can be used to gain information about the closeness of different atoms in a molecule. NMR spectroscopy is therefore can be applied in a number of areas of science (Keeler, 2011). It is observed that the chemists used NMR spectroscopy (simple one-dimensional techniques) regularly to observe the chemical structure (Jiang et al. 2011). On the other hand, the chemists used two-dimensional techniques to study the structures of complicated molecules (Morales et al. 2012).   3.0 Experimental Procedure Preparation of sample At first pure α-D-glucose (89mg) was weighed and dissolved in of deuterated dimethyl sulfoxide (d6-DMSO). Then the sample was pipette into a dry and clean NMR tube. After that, the the NMR tube was sealed with parafilm and labeled. At last the sample was subjected to the NMR spectrometer. NMR spectrometer There are three steps involved in acquiring a spectrum from NMR spectrometer and these are: Sample loading: At first, the NMR tube was placed in a sample holder, known as “spinner”. Depth gauge was used to maintain the correct height of the NMR tube. After that, the sample was positioned in the NMR sample tray waiting to be analyzed. Instrument Locking and Shimming. Data acquisition and processing It was found that NMR spectrum was modified using “Spinworks” software. SpinWorks is a software package for the dealing out of 1D and 2D data. Spinworks also included modules for the simulation, dynamic NMR spectra and analysis of second order spectra. It can perform spectral simulations to determine chemical shifts and coupling constant. All the information obtained below was obtained through Dr. Ramesh. Dr. Ramesh separated the class into many groups and each group visited the NMR device. The NMR devise is located in the basement of the chemistry department where the guide explained details about the NMR device working procedure. It is observed that many precautions steps need to be taken before running the NMR sequence. These steps are do not bring mobile phones, any metallic objects, coins, etc. near to the NMR sequence, since it may cause damage to the magnet. The guide also advised not to touch the NMR magnet as it can hamper the NMR’s homogeneity properties. In addition, personnel with metallic im[plants and heart pace makers should not come near to the NMR spectrometer.   4.0 Results In figure2, hydrogen and carbons nuclei are numbered for α-D-glucose molecule to interpret NMR result. In the following structure of glucose, 6 carbon atoms are shown, which are referring to 6 different environments. There are also 11 hydrogen atoms, which are referred to 10 different environments.  Figure 2: Carbon and hydrogen nuclei numbering for α-D-glucose molecule Table 1: 1H-NMR showing the chemical shift of assigned proton nuclei (Figure 2), its multiplicity patterns and the coupling constant J (Hz) Chemical shift, δ (ppm) Assigned nuclei multiplicity Coupling constant, J (Hz) 6.22 95-6.2395 O-H2 d, doublet 4.28 4.9046-4.884 C-H1 t, triplet 4.02,4.22 4.8232-4.8088 O-H8 d, doublet 5.76 4.7077-4.6959 O-H6 d, doublet 4.72 4.527-4.51 O-H4 d, doublet 68 4.4288-4.3389 O-H11 t, triplet 5.92, 5.7 3.6109-3.3645 C-H5,C-H9, C-H10,10’ m, multiplet - 3.1288-2.9868 C-H3, C-H7 m, multiplet - Chemical shift, δ (ppm) Assigned nuclei multiplicity Coupling constant, J (Hz) 6.22 95-6.2395 O-H2 d, doublet 4.28 4.9046-4.884 C-H1 t, triplet 4.02,4.22 4.8232-4.8088 O-H8 d, doublet 5.76 4.7077-4.6959 O-H6 d, doublet 4.72 4.527-4.51 O-H4 d, doublet 68 4.4288-4.3389 O-H11 t, triplet 5.92, 5.7 3.6109-3.3645 C-H5,C-H9, C-H10,10’ m, multiplet - 3.1288-2.9868 C-H3, C-H7 m, multiplet -  Table 2: 13CNMR analysis showing the chemical shift of assigned carbon nucleiand its phasing behavior in 13C DEPT-135 NMR spectrum in (Figure 2) Assigned nuclei Chemical shift, δ (ppm) 13C-DEPT 135 PHASING C-1 92.13 CH- Positive C-3 72.97 CH- Positive C-2 72.24 CH- Positive C-5 71.92 CH- Positive C-4 70.54 CH-Positive C-6 61.06 CH2-Negative Table 3: shows the observed correlation of 1H nuclei (Figure 2) in 2D Correlation Spectroscopy (COSY) NMR spectrum and 2D Total Correlation Spectroscopy (TOCSY) NMR spectrum *C indicate 1H-1H nuclei in COSY spectrum, D indicate 1H-1H nuclei in TOCSY spectrum   H1 H2 H3 H4 H5 H6 H7 H8 H9 H10.10' H11 H1                       H2 C,D                     H3 C,D D                   H4 D D C,D       D         H5 D D C,D D               H6 D     D C,D             H7       D C             H8       D D   C,D         H9           D C,D D       H10,10'             D D C     H11             D D D C,D   Table 4: shows the observed correlation of 1H-13C nuclei (Figure 2) in 2D Heteronuclear Single Quantum Correlation (HSQC) NMR spectrum and 2D Heteronuclear Multiple Bond Correlation (HMBC) spectrum *X symbol indicates1H-13C nuclei in HSQC, Y symbol indicate 1H-13C nuclei in HMBC   C1 C2 C3 C4 C5  C6 H1 X Y Y       H2 Y X,Y         H3     X,Y       H4 Y Y Y X     H5   Y   Y X,Y   H6     Y Y     H7     Y   Y Y H8       Y Y   H9             H10,10’       Y Y X H11         Y Y     Discussions Many NMR techniques are used to analyze glucose molecule. In the H-NMR spectrum, it is found that C-H peaks are clustered and overlapped comparing to the O-H peaks, which are well separated among each other. The hydroxyl protons (O-H) are mostly located in the middle of the spectrum ranging from 4.34ppm to 4.82 ppm (except O-H2 that appeared more deshielded at approximately 6.2ppm). On the other hand, the C-H protons are mostly located at around 2.99ppm to 3.61ppm (except C-H1, which appeared at 4.9ppm). The proof of this pattern can be found in the 2D-HSQC spectrum in which the O-H region stated above was blank (showing no interaction) while the C-H regions showed correlation signal between the positioned carbon with its bonded hydrogen ( for example: C5-H5). HSQC helped to determine the correlation of hydrogen and carbon in a single bonded position. Hydroxyl protons are more deshielded compared to C-H protons due to the presence of electronegative atom, oxygen; which is the reason behind the shifting of hydroxyl-protons more to the left compared to C-H protons. The presence of electronegative atom pulls the electron density away from proton nucleus, which in turn makes it more vulnerable towards the applied magnetic field, thus appeared downfield of NMR spectrum. However, an exception of for this pattern is also observed. Further analysis of C-H nuclei at C-1 showed that it is highly deshielded compared to the other C-H nuclei. This is because of the same reasons as hydroxyl groups (the presence of an electron withdrawing atom, oxygen). In fact it is observed that the O-H proton at this carbon is the most deshielded one among its species located in the other carbon skeletons. Therefore, positioning the C-H protons and O-H protons on the skeleton of glucose is hard while only depending on the 1H-NMR spectrum. The reason is, the O-H groups of protons are rather quite the same chemical environment between one each other except O-H2, which are difficult to determine the sequence and it is also found that the C-H are even worse as it exist as multiples except for C-H1. Therefore, to locate the proton peak, 2D-COSY NMR analysis of this molecule is very helpful. 2D-COSY NMR is a technique, which is helpful to track the correlation of 1H-1H up to 3 bond lengths. By studying the correlation peaks of this spectrum one can resolve the complex multiplets of C-H protons in which for the first multiplet (δ=3.37ppm - 3.61ppm), there are four C-H protons resonate at this frequency: C-H5,C-H9 and C-H10,10’and for the second multiplet (δ=3.37ppm - 3.61ppm) there are only two protons resonate: C-H3 and C-H7. It is found that the integral values in 1H-NMR is equivalent to the number of protons in each of this multiplet (which is 4.4 and 2.1 respectively). However, it is observed that the multiplicities of C-H protons are rather difficult to study except for C1-H1. On the other hand, The O-H proton splitting patterns are easy and simple to interpret. All of the C1-H1 and O-H protons followed the multiplicity rules, (2nI+1). Such as, the reason behind the triplet appearance of C1-H1 peaks is that it is split by two hydrogen protons O-H2 and C-H3 and for the O-H11. In addition, it is also appeared as triplet because it is split by two hydrogens at C-6. In 1H NMR spectrum, the coupling constant can be observed. It is observed that J value for the splitting of O-H protons are larger compared to C-H protons. the analysis 13C NMR revealed there are 6 different environments of carbon atoms which one of it is highly deshielded and this is certainly C-1 due to the presence of oxygen atom bonded to it. C-6 is surrounded by more electrons due to the presence of two hydrogen atoms attached to it, therefore it is The most shielded carbon in this molecule. Evidence of this peak is C-6 can be observed, firstly in 13C-DEPT 135, but in the chemical shift the peak is negative phasing (indicate CH2), however, the other CH carbons are in the positive phasing. In HSQC spectrum, it is found that there are two spots plotted a
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