In group frequency region, the peaks corresponding to different functional groups can be observed. According to corresponding peaks, functional group can be determined. Each atom of the molecule is connected by bond and each bond requires different IR region so characteristic peaks are observed.
This region of IR spectrum is called as finger print region of the molecule. It can be determined by characteristic peaks. Identification of substances. IR spectroscopy is used to establish whether a given sample of an organic substance is identical with another or not.
This is because large number of absorption bands is observed in the IR spectra of organic molecules and the probability that any two compounds will produce identical spectra is almost zero. So if two compounds have identical IR spectra then both of them must be samples of the same substances. IR spectra of two enatiomeric compound are identical. So IR spectroscopy fails to distinguish between enantiomers. By the way, HCA builds the hierarchical tree of dissimilarity between data points that is called dendrogram.
Well-known parameters of clinical studies such as sensitivity and specificity can be used to describe the performance of the methods in disease diagnosis. Explanation of sensitivity, specificity, positive true and false , and negative true and false values can be found in Severcan et al. Stability of body fat is key point to maintain metabolic homeostasis. Excess amount of energy is stored in the form of triglycerides in the lipid droplets of adipocytes and result in the increase in the number of adipocyte hyperplasia or enlargement in the size of adipocytes hypertrophy.
Adipose tissue depots are classified into white adipose tissue WAT and brown adipose tissue BAT , each of them has unique structure and function. They differ in their degree of vascularization and innervation.
Brown adipose tissue BAT is highly specialized in thermogenesis and maintaining body temperature [ 46 ]. Both tissues are capable to store triglycerides [ 47 ]. White adipose tissue has been organized in different anatomical location as visceral white adipose tissue VAT and subcutaneous white adipose tissue SCAT. VAT has higher amount of plasminogen activator inhibitor-1 PAI-1 , IL6 and higher expression of glucocorticoid, androgen, AT 1 and beta-3 adrenergic receptor than in the subcutaneous tissue.
The products of VAT are driven to the liver via portal vein system, affecting its function. SCAT possesses higher concentrations of leptin and adiponectin. The secretions of SCAT are released into the general circulation [ 48 ]. Therefore, WAT paves the way for different metabolic diseases and presents great detrimental effect to human health [ 49 , 50 ].
Adipose tissue responds to excess triglycerides accumulation by inducing an immune response. Excessive fat accumulation results in changes in cellular and structural remodeling processes and causes alterations in the endocrine and metabolic systems. This inflammatory state is associated with increased accumulation of macrophages in adipose tissues along with the production of inflammatory cytokines and their secretion into the circulation e.
These cytokines mediate inflammation or play an active role in immune and inflammatory responses to obesity. Increased circulating levels of inflammatory markers are associated with obesity-related pathologies.
Plasminogen activator inhibitor 1 PAI1 causes impaired fibrinolysis and promotes atherosclerosis [ 56 , 57 ]. These associations are affected by adipose tissue distributions. In the literature, visceral adipose tissue has been implicated as a major risk factor for insulin resistance, type 2 diabetes [ 48 , 58 ], cardiovascular disease [ 59 ], stroke [ 60 ], and metabolic syndrome [ 61 ].
Therefore, visceral fat is thought to be the more dangerous adipose tissue. The liver is the major organ of lipid metabolism and can store lipids, which could lead to fatty liver syndrome. Obesity-induced inflammation is emerged as a result of change in the cytokine profile, in particular, decrease in adiponectin and increase in leptin levels, mitochondrial dysfunction, accelerated adipocyte death and endoplasmic reticulum ER stress. Endoplasmic reticulum is a major site for protein and for lipid synthesis.
In the ER, proteins are folded into their native confirmation and undergo posttranslational modifications, which are important for their structure and activity. In the case of nutrition overload, function of ER is impaired, protein folding is disturbed, ER stress develops and activates a signaling network called the unfolded protein response UPR to restore ER homeostasis [ 64 , 65 ].
It is known that ER stress is linked with obesity-related pathologies including insulin resistance, type 2 diabetes, hypertension, and nonalcoholic fatty liver disease [ 5 , 65 , 66 ]. Consequently, adipose tissue serves as a main site for activation of the inflammatory response in obesity. Biological samples contain biochemical substances such as lipids, proteins, carbohydrates, proteins, and nucleic acids, and these biomolecules have their unique vibrational fingerprints. Therefore, disease-induced changes in the position, bandwidth, signal intensity, and area of the spectral bands of the system of interest, can be monitored by IR spectroscopy.
In current chapter, the applications of IR mid and near , spectroscopic and microspectroscopic techniques in obesity research will be discussed in detail. Recent studies pointed out the importance of adipose tissue in diagnosis and treatment of obesity and obesity related diseases.
Therefore, adipose tissues draw attraction in obesity research. Figure 2 shows a representative IR spectrum of a human adipose tissue. This spectrum is quite complex and contains several bands, which arise from different functional groups belonging to biomolecules of the system. The relevant band assignments of the bands are given in Table 1 [ 67 , 68 ]. It is known that obesity constitutively results in storage of triglycerides in different adipose tissues [ 2 ]. As seen from Figure 3 , successful discrimination of the obese, obesity-related insulin resistant and control groups was achieved with high sensitivity and specificity.
Based on the spectral differences, the results revealed the power of FTIR spectroscopy coupled with chemometric in internal diagnosis of abdominal obesity. In conclusion, the VAT and especially, the SCAT samples can be easily examined by ATR-FTIR spectroscopy coupled with chemometrics in human studies and this combined technique will shed light on the internal diagnosis of obesity in medical research [ 43 ].
In the other study of the same group, lipid profiles in terms of the content and structure of skeletal muscle and adipose tissues were determined to understand better the characteristics of juvenile-onset spontaneous obesity without high fat diet induction. Spectral differences indicated differences in lipid structure and content of BFMI lines, which may originate from different insulin sensitivity levels of the lines.
This makes them promising animal models for spontaneous obesity. The referred study will shed light to the understanding of the generation of insulin resistance in obesity without high fat diet induction [ 69 ]. A recent FTIR microspectroscopic study of the same group aimed to characterize and compare VAT and SCAT in terms of macromolecular content and investigate transdifferentiation between white and brown adipocytes [ 34 ]. In order to achieve this, the gonadal visceral and inguinal subcutaneous adipose tissues of male BFMI lines, which are spontaneously obese were studied.
This could originate from it possessing a lower amount of brown adipose tissue. The current study clearly revealed the power of FTIR microspectroscopy in the precise determination of obesity-induced structural and functional changes in inguinal and gonadal adipose tissue of mice lines [ 34 ]. The absorbance in the spectral maps was represented in color-coded images, where low absorption was represented in blue and high absorption was represented in red color.
Adapted from [ 34 ], with permission from Royal Society of Chemistry. The epididymal adipose tissue, liver, and muscle of 29 BXD recombinant inbred mouse strains fed with high fat diet were used to analyze the role of white adipose tissue as a mediator of inflammation.
The content of total fat, unsaturated fat, lipid to protein ratio, and collagen and collagen integrity were measured in tissue of interest and the results of IR analysis were revealed differences in the biomolecular composition of adipose and liver tissues among high fat diet-fed BXD RI strains that reflect genetic variation. Rsad2, which may modulate lipid droplet contents and lipid biosynthesis, and Colec11, which may play a role in apoptotic cell clearance and maintenance of adipose tissue were suggested as potential quantitative trait candidate genes.
This study showed the efficiency and suitability of ATR-FTIR spectroscopy to identify quantitative trait loci QTLs that influence various traits and heightened the power of gene mapping studies. Bortolotto et al. TFA content in all adipose tissues analyzed was higher than reported in other countries. The TFA depot in visceral fat was higher than other fatty tissues for morbidly obese and nonobese patients.
Gazi et al. Stimulating increased thermogenic activity in adipose tissue is an important biological target for obesity treatment. Aboualizadeh et al. PCA analysis successfully operated to groups. Nonalcoholic fatty liver disease NAFLD is a frequent lesion associated with obesity, diabetes, and the metabolic syndrome. The potential of mid-IR fiber evanescent wave spectroscopy was used as a minimum-invasive method for evaluating the liver status during NAFLD.
In the study, 75 mice were subjected to a control, high-fat or high-fat-high carbohydrate diets. The mid-IR spectra were acquired from serum, and then analyzed to develop a predictive model of the steatosis level.
Animals subjected to enriched diets were obese. The relationship between the spectroscopy-predicted and observed levels of steatosis, expressed as percentages of the liver biopsy area, was not linear. The data suggest that mid-IR spectroscopy combined with statistical analysis allows identifying serum mid-IR signatures that reflect the liver status during NAFLD [ 73 ].
In another work [ 74 ], the potential of FTIR microspectroscopy for grading steatosis on frozen tissue sections was evaluated. The use of the bright IR source emitted by synchrotron radiation SR allowed the investigation of the biochemical composition at cellular level.
PCA method was applied to spectral data. Infrared IR spectroscopy 1 Introduction. Currently reading Uses of IR spectroscopy. Energy levels. More complicated molecules. Category Analytical chemistry Analysis Spectroscopy. Organic chemistry 7. Infrared radiation causes parts of a molecule to vibrate.
The wavelengths which are absorbed to cause the vibrations stretches and bends will depend on the type of chemical bond and the groups or atoms at the ends of these bonds. In infrared spectroscopy, infrared radiation is passed through a sample of the organic compound and then into a detector which measures the intensity of the transmitted radiation at different wavelengths. Related articles.
Ideas Back to basics with spectrophotometry TZ How to demonstrate the Beer—Lambert law using your smartphone as a light meter. Ideas Teach justice and cooperation through chemistry TZ Link forensic science and the Covid pandemic to your lessons on instrumental analysis, separation techniques, data interpretation and health with UN sustainable development goals 16 and Load more articles.
No comments yet. You're not signed in. O 2 is more electronegative than H 2 and carries a negative charge, while H has a partial positive charge. The vibrational modes are illustrated below:.
CO 2 is a linear molecule and thus has the formula 3N It has 4 modes of vibration 3 3 CO 2 has 2 stretching modes, symmetric and asymmetric. The CO 2 symmetric stretch is not IR active because there is no change in dipole moment because the net dipole moments are in opposite directions and as a result, they cancel each other.
In the asymmetric stretch, O atom moves away from the C atom and generates a net change in dipole moments and hence absorbs IR radiation at cm The other IR absorption occurs at cm Two of its bands are degenerate and one of the vibration modes is symmetric hence it does not cause a dipole moment change because the polar directions cancel each other.
Thus "a" can be written as. On differentiating a second time the equation becomes. Using the harmonic oscillator and wave equations of quantum mechanics, the energy can be written as. Transitions in vibrational energy levels can be brought about by absorption of radiation, provided the energy of the radiation exactly matches the difference in energy levels between the vibrational quantum states and provided the vibration causes a change in dipole moment.
This can be expressed as. The frequency of radiation v that will bring about this change is identical to the classical vibrational frequency of the bond v m and it can be expressed as.
Molecular vibrational frequencies lie in the IR region of the electromagnetic spectrum, and they can be measured using the IR technique. In IR, polychromatic light light having different frequencies is passed through a sample and the intensity of the transmitted light is measured at each frequency.
When molecules absorb IR radiation, transitions occur from a ground vibrational state to an excited vibrational state Figure 1. For a molecule to be IR active there must be a change in dipole moment as a result of the vibration that occurs when IR radiation is absorbed. Dipole moment is a vector quantity and depends on the orientation of the molecule and the photon electric vector.
The dipole moment changes as the bond expands and contracts. When all molecules are aligned as in a crystal and the photon vector points along a molecular axis such as z. Absorption occurs for the vibrations that displace the dipole along z.
Vibrations that are totally x or y polarized would be absent. Dipole moment in a heteronuclear diatomic molecule can be described as uneven distribution of electron density between the atoms. One atom is more electronegative than the other and has a net negative charge. The transition moment integral, that gives information about the probability of a transition occurring, for IR can also be written as.
Relating this to IR intensity we have. In order for a transition to occur by dipole selection rules , at least one of the integrals must be non zero.
Most of the IR used originates from the mid IR region. The table below indicates the IR spectral regions. IR deals with the interaction between a molecule and radiation from the electromagnetic region ranging 40 cm A linear wavenumber is often used due to its direct relationship with both frequency and energy.
The frequency of the absorbed radiation causes the molecular vibrational frequency for the absorption process. The relationship is given below. IR spectroscopy is a great method for identification of compounds, especially for identification of functional groups. Therefore, we can use group frequencies for structural analysis. Group frequencies are vibrations that are associated with certain functional groups.
It is possible to identify a functional group of a molecule by comparing its vibrational frequency on an IR spectrum to an IR stored data bank.
Here, we take the IR spectrum of Formaldehyde for an example. The value obtained from the following graph can be compared to those in reference data banks stored for Formaldehyde. It's important to note that this value is dependent on other functional groups present on the molecule. The higher cm -1 indicates a large dipole moment change. It is easier to bend a molecule than stretch it, hence stretching vibrations have higher frequencies and require higher energies than bending modes.
The finger print region is a region from cm Each molecule has it's own characteristic print and is often cumbersome to attach any values to this region. Infrared spectroscopy can also be applied in the field of quantitative analysis, although sometimes it's not as accurate as other analytical methods, like gas chromatography and liquid chromatography.
0コメント