Application case of differential scanning calorimeter for protein testing

　　1. Preface

When studying the structural changes of microfiber matrix complexes in keratin samples,Differential scanning calorimeterIt can be used to analyze the thermal stability changes, phase transition behavior, and possible melting or decomposition processes of keratin before and after heat treatment. For example, DSC curves can observe the possible endothermic or exothermic peaks of keratin during heating, which correspond to phenomena such as the movement of keratin molecular chains, melting of microfibers, or denaturation of proteins.

By comparing the DSC curves before and after stretching and heat treatment, researchers can understand the effects of these treatments on the thermal properties and structural stability of keratin complexes. For example, heat treatment may lead to an increase in cross-linking between keratin molecules, thereby improving the thermal stability of the material, while elongation may alter the crystallinity of keratin and affect its thermal behavior.

　　2、 Experimental steps

1. Material preparation

Untreated brown hair, untreated hair, and bleached yellow hair samples.

2. Sample preparation

Clean the hair and divide it into multiple small sections, approximately 5-7mg.

3. Moisture content　

The hair samples were equilibrated in a small chamber with a relative humidity of 50% at 23 degrees Celsius for 48 hours. After equilibration, the moisture content of bleached hair and untreated brown hair was 11.48% and 10.15%, respectively.

4. Measuring instruments

Instrument Name: DZ-DSC300C Differential Scanning Calorimeter　

Instrument brand:Nanjing DaZhan Testing Instrument

5. Experimental operation　

First, place 5-7mg of hair sample in an aluminum crucible protected by nitrogen gas (with a nitrogen flow rate of 50ml/min). Heat the sample to 70 degrees Celsius and keep it at that temperature for 30 minutes to remove moisture. Then, cool it down to 25 degrees Celsius and heat it up at a rate of 10C/min to 270 degrees Celsius. Record the absorption curve and perform three parallel experiments on each hair sample. Calculate the average absorption peak temperature and average absorption peak area.

　　3、 Results and Discussion

1. Data analysis

　　Figure 1

Figure 1 shows a typical DSC curve of an untreated hair sample, with the peak temperature defined as the denaturation temperature (Td) of the alpha helix in IFs. Denaturation includes phase transition and protein degradation. The peak area represents the denaturation △ Hd, which is the energy required for a spiral denaturation and expressed as the amount of heat absorbed per gram of dry hair (J/g) △ Hd is used to calculate RHC, RHC=100x (△ Hd/△ Hd0)%, where △ Hd0 is the average denaturation melting of untreated hair.

2. The impact of weather conditions on hair　

We investigated different parts of an 18cm untreated brown hair sample and studied the spiral absorption peaks of the scanning curve. The results are shown in Table 1.

Table 1　

It can be seen that Δ Hd decreases from the hair tip to the root, while Td continuously increases. The RHC value of the hair tips is 85.6% of that of the roots It is obvious that the weather environment has a significant impact on hair, as the closer to the ends of the hair, the longer the contact time with the environment.

3. The effects of bleaching and relaxation treatment on hair

　　Figure 2　

Figure 2 reveals the effect of bleaching time on Td and RHC of untreated hair, with RHC values decreasing as bleaching time increases. The Δ Hd of untreated hair and bleached hair were 3.85 J/g and 1.07/g, respectively. After treatment, the RHC of bleached hair decreased by 72.8% compared to untreated hair. This result indicates that bleaching treatment causes serious damage to hair. Through scanning electron microscopy (SEM) observation, it was found that the bleached hair surface had many visible small holes and damaged hair cuticles. As the bleaching time increases, Td increases because the size of Td depends on the crosslinking density of the matrix. The higher the crosslinking density, the higher the viscosity, and the greater the resistance to the helix/coil transition in IFs. We know that the content of sulfoalanine (an oxidation product of cysteine during bleaching) will increase with the prolongation of bleaching time. So the increase in Td reflects the increase in the amount of sulfoalanine and further enhanced ion interaction. We also observed that for African American hair, Td increases and △ Hd decreases with the increase of relaxation treatment time.

4. Restoration of Spiral Peak and Reconstruction of Hair　

The results of treating hair with different protein derivatives before and after bleaching are shown in Table 2.

　　Table II

After treatment with hydrolyzed wheat protein cysteine polysiloxane and a mixture of hydrolyzed wheat protein and whole propyl polysiloxane, the RHC of hair samples increased by 77.5%, 72.0%, and 88.8%, respectively. Td significantly decreased after protein treatment. Previous studies have shown that hydrolyzed wheat protein and cysteine polysiloxane can enter hair by exchanging disulfide bonds with cysteine residues on the hair. This exchange effect will cause changes in the number and structure of helices in hair, characterized by an increase in Δ Hd and a decrease in Td. We found that resident products have a better recovery effect on absorption peaks than wash away products. Generally speaking, high molecular weight protein derivatives such as hydrolyzed wheat protein and propyl polysiloxane mixtures cannot enter hair due to their large size. As mentioned earlier, bleached hair samples are severely damaged and have a porous surface, which allows polymers to enter and interact with the hair. Perhaps it is this permeation effect that can explain the significant increase in aHd of polymer treated bleached hair. After using protein derivatives on relaxed treated hair, we also found an increase in △ Hd and a decrease in Td.

4、 Experimental diagram

　　　　Figure 3: Our company's test results and analysis of human hair tissue are shown in the test chart