Name: a generalized method for determining free soluble phenolic acid composition and antioxidant capacity of cereals and legumes
Uploaded: 2022-06-10T13:00:00
Description: Watch this Scientific Journal Video about A Generalized Method for Determining Free Soluble Phenolic Acid Composition and Antioxidant Capacity of Cereals and Legumes at JoVE.com

The authors gratefully acknowledge the technical support of Ms. Alison Ser and Ms. Hannah Oduro-Obeng, as well as the video editing support by Ms. Janice Fajardo and Mr. Miguel del Rosario.

1. Type of samples
<ol>
	<li>Use five whole grain samples, comprising two cereals (e.g., durum wheat and yellow corn) and three legumes (e.g., Blackeye cowpea bean, soybean, and red kidney bean) for this study.</li>
	<li>Mill 50 g of each grain in triplicates into flour, using a coffee grinder, and pass them through a 500 &#181;m sieve.</li>
	<li>Store them at -20 &#176;C.</li>
</ol>
2. Sample preparation
<ol>
	<li>Determination of dry matter content a...

<ol>
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L., Motarjemi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Encyclopedia of Food Safety. 3, 309-314 (2014).</li><li>FAO. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Food+Outlook+-+Biannual+report+on+global+food+markets.">Food Outlook - Biannual report on global food markets.</a> Food and Agriculture Organization. , (2020).</li><li>Erbersdobler, H. F., Barth, C. A., Jahreis, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Legumes+in+human+nutrition.+Nutrient+content+and+protein+quality+of+pulses.">Legumes in human nutrition. Nutrient content and protein quality of pulses.</a> Ernahrungs Umschau. 64 (9), 134-139 (2017).</li><li>Due&#241;as, M., Hern&#225;ndez, T., Estrella, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+in+vitro+antioxidant+capacity+of+the+seed+coat+and+the+cotyledon+of+legumes+in+relation+to+their+phenolic+contents.">Assessment of in vitro antioxidant capacity of the seed coat and the cotyledon of legumes in relation to their phenolic contents.</a> Food Chemistry. 98 (1), 95-103 (2006).</li><li>Khang, D. T., Dung, T. N., Elzaawely, A. A., Xuan, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phenolic+profiles+and+antioxidant+activity+of+germinated+legumes.">Phenolic profiles and antioxidant activity of germinated legumes.</a> Foods. 5 (2), 27 (2016).</li><li>Hefni, M. E., Amann, L. S., Witth&#246;ft, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+HPLC-UV+method+for+the+quantification+of+phenolic+acids+in+cereals.">A HPLC-UV method for the quantification of phenolic acids in cereals.</a> Food Analytical Methods. 12 (12), 2802-2812 (2019).</li><li>AOAC. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Official Methods of Analysis. 17th edn. , (2000).</li><li>Apea-Bah, F. 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G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sorghum-cowpea+composite+porridge+as+a+functional+food,+Part+II:+Antioxidant+properties+as+affected+by+simulated+in+vitro+gastrointestinal+digestion.">Sorghum-cowpea composite porridge as a functional food, Part II: Antioxidant properties as affected by simulated in vitro gastrointestinal digestion.</a> Food Chemistry. 197, 307-315 (2016).</li><li>Robbins, R. J., Bean, S. 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L., Wu, X., Schaich, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Standardized+methods+for+the+determination+of+antioxidant+capacity+and+phenolics+in+foods+and+dietary+supplements.">Standardized methods for the determination of antioxidant capacity and phenolics in foods and dietary supplements.</a> Journal of Agricultural and Food Chemistry. 53 (10), 4290-4302 (2005).</li><li>Ainsworth, E. A., Gillespie, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimation+of+total+phenolic+content+and+other+oxidation+substrates+in+plant+tissues+using+Folin-Ciocalteu+reagent.">Estimation of total phenolic content and other oxidation substrates in plant tissues using Folin-Ciocalteu reagent.</a> Nature Protocols. 2 (4), 875-877 (2007).</li><li>Waterhouse, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+total+phenolics.">Determination of total phenolics.</a> Current Protocols in Food Analytical Chemistry. 1, 1-8 (2002).</li><li>Huang, D., Ou, B., Prior, R. 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The whole grains were selected as representative cereal grains and legumes that find wide food applications worldwide. While variations may exist among cultivars of each grain, the focus of this study was to demonstrate a generalized method for free phenolic acid extraction and analysis for whole grains. The extraction method was modified by substantially reducing the amounts of samples and solvents, in order to reduce the amount of chemicals that would be released into the environment when such experiments are conducted...

Phenolic acids are among the most important phytochemicals studied in plants due to the vital role they play in plant defense against herbivory and fungal infection, as well as maintaining structural support and integrity in plant tissues1,2. They are abundant in the bran of cereals and seed coat of legumes3. Structurally, they are divided into two groups: the hydroxybenzoic acids (Figure 1) and hydroxycinnamic acids (Figure 2). The common hydroxybenzoic acids in cereals and legumes include gallic, p-hydroxybenzoic, 2,4-dihydroxybenzoic, protocatechuic, vanillic, and syringic acids, while the common hydroxycinnamic acids include caffeic, p-coumaric, ferulic, and sinapic acids3. Phenolic acids also possess antioxidant properties since they are able to scavenge free radicals, which cause oxidative rancidity in fats, and initiate and propagate radical-induced oxidative stress in physiological systems4,5. Due to this vital physiological role as antioxidants, they are the subject of recent research. This is because when consumed as components of plant foods, they can exert antioxidant protection.
Cereals and cereal products are major carbohydrate food sources for humans and animals worldwide6. Cereals include wheat, rice, corn (maize), barley, triticale, millets, and sorghum. Among them, corn is the most utilized, with an estimated global utilization of 1,135.7 million tonnes in 2019/2020, followed by wheat with an estimated global utilization of 757.5 million tonnes during the same period7. Cereal foods are great sources of energy to consumers since they are rich sources of carbohydrates. They also provide some protein, fat, fiber, vitamins and minerals6. In addition to their nutritional value, cereals are good sources of phytochemical antioxidants, particularly phenolic acids, which have the potential to protect the physiological system from radical-induced oxidative damage3. Legumes are also good sources of nutrients and are generally higher in protein than cereals. They also contain vitamins and minerals and are used in the preparation of various foods8. Additionally, legumes are good sources of a variety of phytochemical antioxidants, including phenolic acids, flavonoids, anthocyanins, and proanthocyanidins9,10. Different varieties of cereals and legumes may have a different phenolic acid composition. There is therefore the need to study the phenolic acid composition of cereals and legumes and their varieties, in order to know their potential health benefits with respect to phenolic antioxidants.
A number of assays have been reported for measuring the quantity of phenolic acids in cereal and legume grains, and determining their antioxidant activities. The most common methods of analysis for whole grain phenolic acids are spectrophotometry and liquid chromatography11. The aim of this work was to demonstrate a generalized high pressure liquid chromatographic method for determining free soluble phenolic acid composition, and spectrophotometric methods for determining total phenolic content and antioxidant capacity of some whole grain cereals and legumes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>15 mL Falcon conical centrifuge tubes</td>
			<td>Fisher Scientific</td>
			<td>05-527-90</td>
			<td></td>
		</tr>
		<tr>
			<td>2 mL Amber glass ID Surestop vial</td>
			<td>Thermo Scientific</td>
			<td>C5000-2W</td>
			<td></td>
		</tr>
		<tr>
			<td>2 mL Amber microcentrifuge tubes</td>
			<td>VWR</td>
			<td>20170-084</td>
			<td></td>
		</tr>
		<tr>
			<td>2,2&#8242;-Azobis(2-amidinopropane) dihydrochloride (AAPH)</td>
			<td>Sigma-Aldrich</td>
			<td>440914-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>2,2&#39;-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) (C18H18N4O6S4) &#8805;98%,</td>
			<td>Sigma Aldrich</td>
			<td>A1888-2G</td>
			<td></td>
		</tr>
		<tr>
			<td>2,2-Diphenyl-1pikrylhydrazyl (DPPH) (C18H12N5O6)</td>
			<td>Sigma Aldrich</td>
			<td>D913-2</td>
			<td></td>
		</tr>
		<tr>
			<td>6-Hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) (C14H18O4), &#8805;98%</td>
			<td>Fluka Chemika</td>
			<td>56510</td>
			<td></td>
		</tr>
		<tr>
			<td>9 mm Autosampler Vial Screw Thread Caps</td>
			<td>Thermo Scientific</td>
			<td>60180-670</td>
			<td></td>
		</tr>
		<tr>
			<td>96 well flat bottom plates</td>
			<td>Fisher Scientific</td>
			<td>12565501</td>
			<td></td>
		</tr>
		<tr>
			<td>Agilent BioTek ELx800 microplate reader</td>
			<td>Fisher Scientific</td>
			<td>BT-ELX800NB</td>
			<td></td>
		</tr>
		<tr>
			<td>Agilent BioTek Precision 2000 96/384 Automated Microplate Pipetting System</td>
			<td>Fisher Scientific</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Agilent BioTek FLx800 Microplate Fluorescence Reader</td>
			<td>Fisher Scientific</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Analytical balance SI-114</td>
			<td>Denver Instrument</td>
			<td>SI-114.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Autosampler, Waters 717 Plus</td>
			<td>Waters</td>
			<td>WAT078900</td>
			<td></td>
		</tr>
		<tr>
			<td>BD 3 mL syringe Luer-Lok Tip</td>
			<td>BD</td>
			<td>309657</td>
			<td></td>
		</tr>
		<tr>
			<td>Bransonic ultrasonic cleaner, Branson 5510</td>
			<td>Millipore Sigma</td>
			<td>Z245143</td>
			<td></td>
		</tr>
		<tr>
			<td>Corning LSE Vortex Mixer</td>
			<td>Corning</td>
			<td>6775</td>
			<td></td>
		</tr>
		<tr>
			<td>Durapore Filter (0.45 &#181;m PVDF Membrane)</td>
			<td>Merck Millipore Ltd</td>
			<td>HVLP04700&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Durapore Membrane Filters (0.45 &#181;m HV)</td>
			<td>Merck Millipore Ltd</td>
			<td>HVHP04700</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf Research&#160;plus, 0.5-10 &#181;L</td>
			<td>Eppendorf</td>
			<td>3123000020</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf Research&#160;plus, 0.5-5 mL</td>
			<td>Eppendorf</td>
			<td>3123000071</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf Research&#160;plus, 100-1000 &#181;L</td>
			<td>Eppendorf</td>
			<td>3123000063</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf Research&#160;plus, 10-100 &#181;L</td>
			<td>Eppendorf</td>
			<td>3123000047</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl acetate, HPLC grade</td>
			<td>Fisher Chemical</td>
			<td>E195-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Ferulic acid standard</td>
			<td>Sigma Aldrich</td>
			<td>128708-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescein</td>
			<td>Fisher Scientific</td>
			<td>AC119245000</td>
			<td></td>
		</tr>
		<tr>
			<td>Folin &#38; Ciocalteu phenol reagent</td>
			<td>Sigma Aldrich</td>
			<td>F9252</td>
			<td></td>
		</tr>
		<tr>
			<td>Formic acid, 99%</td>
			<td>Acros Organics, Janssen Pharmaceuticalaan 3a</td>
			<td>27048-0010</td>
			<td></td>
		</tr>
		<tr>
			<td>Gallic acid standard</td>
			<td>Sigma</td>
			<td>G7384</td>
			<td></td>
		</tr>
		<tr>
			<td>High performance liquid chromatograph (HPLC), Waters 2695</td>
			<td>Waters</td>
			<td>960402</td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol, HPLC grade</td>
			<td>Fisher Chemical</td>
			<td>A452-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro pipet tips, 0.5-10 &#181;L</td>
			<td>Fisherbrand</td>
			<td>21-197-2F</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge Sorvall Legend Micro 21 centrifuge</td>
			<td>Thermo Scientific</td>
			<td>75002435</td>
			<td></td>
		</tr>
		<tr>
			<td>Multichannel micropipette, Proline Plus, 30-300 &#181;L</td>
			<td>Sartorius</td>
			<td>728240</td>
			<td></td>
		</tr>
		<tr>
			<td>Photodiode array detector, Waters 2996</td>
			<td>Waters</td>
			<td>720000350EN</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipet tips, 1000 &#181;L</td>
			<td>VWR</td>
			<td>83007-382</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipet tips, 1-5 mL</td>
			<td>VWR</td>
			<td>82018-840</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium persulfate (K2S2O8), &#8805;99.0%</td>
			<td>Sigma Aldrich</td>
			<td>216224-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate dibasic anhydrous (K2HPO4)</td>
			<td>Fisher Scientific</td>
			<td>P288-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic (KH2PO4)</td>
			<td>Fisher Scientific</td>
			<td>P285-500</td>
			<td></td>
		</tr>
		<tr>
			<td>PYREX 250 mL Short Neck Boiling Flask, Round Bottom</td>
			<td>Corning</td>
			<td>4321-250</td>
			<td></td>
		</tr>
		<tr>
			<td>Reversed phase C18 Analytical Column (100 x 3 mm) Accucore aQ</td>
			<td>Thermo Scientific</td>
			<td>17326-103030</td>
			<td></td>
		</tr>
		<tr>
			<td>Roto evaporator, IKA RV 10</td>
			<td>IKA</td>
			<td>&#160;0010005185</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium carbonate (NaCO3) anhydrous</td>
			<td>Fisher Chemical</td>
			<td>S263-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride (NaCl)</td>
			<td>Mallinckrodt AR&#174;</td>
			<td>7581</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate dibasic anhydrous (Na2HPO4)</td>
			<td>Fisher Scientific</td>
			<td>BP332-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate monobasic anhydrous (NaH2PO4)</td>
			<td>Fisher bioreagents</td>
			<td>BP329-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Standardization pipet tips 0-200&#181;L</td>
			<td>Fisherbrand</td>
			<td>02-681-134</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringe Driven Filter unit (0.22 &#181;m)</td>
			<td>&#160;Millex&#174;-GV</td>
			<td>SLGVR04NL</td>
			<td></td>
		</tr>
		<tr>
			<td>Target micro-serts vial insert (400 &#181;L)</td>
			<td>Thermo Scientific</td>
			<td>C4011-631</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrapure water (Direct Q-3 UV system with pump)</td>
			<td>Millipore</td>
			<td>ZRQSVP030</td>
			<td></td>
		</tr>
	</tbody>
</table>

a generalized method for determining free soluble phenolic acid composition and antioxidant capacity of cereals and legumes

Phenolic acids are a class of organic compounds that bear both a phenolic group, and a carboxylic group. They are found in grains and concentrate in the bran of cereals or seed coat of legumes. They possess antioxidant properties that have generated much research interest in recent years, about their potential antioxidant protective health functions. This work presents a generalized method for the extraction of free soluble phenolic acids from whole grains and analysis of their antioxidant capacity. Five whole grain samples comprising two cereals (wheat and yellow corn) and three legumes (cowpea bean, kidney bean, and soybean), were used. The grains were milled into flour and their free soluble phenolic acids extracted using aqueous methanol. The compounds were then identified using a high-pressure liquid chromatograph (HPLC). The Folin-Ciocalteu method was used to determine their total phenolic content while their antioxidant capacities were determined using the DPPH radical scavenging capacity, Trolox equivalent antioxidant capacity (TEAC) and oxygen radical absorbance capacity (ORAC) assays. The phenolic acids identified included vanillic, caffeic, p-coumaric and ferulic acids. Vanillic acid was identified only in cowpea while caffeic acid was identified only in kidney bean. p-Coumaric acid was identified in yellow corn, cowpea, and soybean, while ferulic acid was identified in all the samples. Ferulic acid was the predominant phenolic acid identified. The total concentration of phenolic acids in the samples decreased in the following order: soybean &gt; cowpea bean &gt; yellow corn = kidney bean &gt; wheat. The total antioxidant capacity (sum of values of DPPH, TEAC and ORAC assays) decreased as follows: soybean &gt; kidney bean &gt; yellow corn = cowpea bean &gt; wheat. This study concluded that HPLC analysis as well as DPPH, TEAC, and ORAC assays provide useful information about the phenolic acid composition and antioxidant properties of whole grains.

Table 2 shows the phenolic acids that were identified in the cereal and legume grains. Based on available authentic standards, four phenolic acids were identified in the samples and they are: vanillic, caffeic, p-coumaric, and ferulic acids. Vanillic acid is a hydroxybenzoic acid while the other three are hydroxycinnamic acids. Vanillic acid was identified only in Blackeye cowpea bean while caffeic acid was identified only in kidney bean. p-Coumaric acid was identified in yellow corn, c...

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A Generalized Method for Determining Free Soluble Phenolic Acid Composition and Antioxidant Capacity of Cereals and Legumes

Phenolic acids are important phytochemicals that are present in whole grains. They possess bioactive properties such as antioxidant protective functions. This work aimed at reporting on a generalized method for the HPLC identification, total phenolic content estimation, and determination of the antioxidant capacity of phenolic acids in cereals and legumes.

Phenolic acids are a class of organic compounds that bear both a phenolic group, and a carboxylic group. They are found in grains and concentrate in the ...

A generalized method for determining free soluble phenolic acid composition and antioxidant capacity of cereals and legumes. Whole grains, including cereals and legumes, form a substantial part of human diets. Their nutritional relevance to humans has long been recognized.However, more recently, their antioxidant protective health benefits have been reported. Phenolic acids found in the outer grain layers of cereals and the seed coat of legumes contribute to the antioxidant properties of whole grains. They scavenge free radicals that cause oxidative damage to biomolecules.The two classes of phenolic acids found in whole grains are hydroxybenzoic acids and hydroxycinnamic acids. This study provides a simple method for extracting whole grain phenolic acids and determining their in vitro antioxidant capacity. Use five whole grain samples for this study, durum wheat, yellow corn, black-eye cowpea bean, soybean, and red kidney bean.Accurately weigh 100 milligrams of the whole grain flour sample directly into an amber-colored, two milliliter capacity micro centrifuge tube. The dark color of the tube helps to prevent exposure of the mixture to light. Add one milliliter of 80%aqueous methanol to each of the tubes containing examples.Vortex briefly to mix the methanol solution and sample. Sonicate the samples for 60 minutes to extract the free soluble phenolic compounds. Put a cover over the samples for the duration of sonication for added protection from light.After sonication, centrifuge the mixtures at 20, 000 times G for five minutes to sediment the solid residues, leaving the supernatant on top. Free phenolic compounds will be present in the supernatant after centrifugation. The supernatant needs to be filtered prior to injecting into the HPLC instrument.To filter the supernatant, remove the plunger of a 3 mL syringe and attach a syringe filter. The filter should have a pore size no larger than 0.22 micrometers. Pipette approximately 0.4 milliliters of the supernatant into the top of the syringe.Reinsert the plunger and push the liquid through the filter into an HPLC vial containing a vial insert. Once the instrument has been set up to run the method outlined in the manuscript for HPLC analysis, load the vials into the carousel to correspond with the sample list. Obtain HPLC chromatograms at 320 nanometers and 280 nanometers, showing distinct peaks representing different phenolic compounds.Using appropriate standard curves, quantify hydroxycinnamic acids at 320 nanometers since they have a maximum absorbance at this wavelength. By the same principle, quantify hydroxybenzoic acids at 280 nanometers. Use Trolox, a water soluble analog of vitamin E, as a standard to estimate the in vitro antioxidant capacity of the whole grain extracts.Accurately weigh one milligram of Trolox into a Falcon tube. Dissolve with four milliliters of 50%aqueous methanol to prepare a stock solution of one millimole per liter, which is the same as 1000 micromole per liter. Prepare six concentrations of Trolox that is 50, 100, 200, 400, 600, and 800 micromole per liter to plot standard curves for the estimation of DPPH radical scavenging capacity and Trolox'equivalent antioxidant capacity, TEAC.Similarly, prepare 6.25, 12.5, 25, and 50 micromole per liter Trolox concentrations for estimating oxygen radical absorbance capacity, ORAC. Make up the total volume of each concentration to 500 microliters, as shown in table one. Dilute the sample extracts with methanol prior to analysis.Here, yellow corn and cowpea extracts were diluted two times. The wheat and kidney bean extracts were diluted five times, while the soybean extract was diluted 10 times with methanol. Weigh 8.23 milligrams of ABTS into a clean, two milliliter capacity, amber micro centrifuge tube.Next, weigh 1.62 milligrams of potassium persulfate into a clean, two milliliter capacity, amber micro centrifuge tube. Dissolve each of the weighed chemicals in one milliliter distilled water by vortexing. This results in a 16 millimolar ABTS solution and a six millimolar potassium persulfate solution.Prepare the ABTS stock solution by mixing the ABTS and potassium persulfate solutions in equal volumes. The solution will immediately change to a dark color. Allow this mixture to incubate in darkness for 12 to 16 hours.Dilute the ABTS stock solution 30 times with 200 millimolar phosphate-buffered saline to form the ABTS working solution. To do this, add 58 milliliters of 200 millimolar PBS to two milliliters of the ABTS working solution. The working solution will contain 0.27 millimolar ABTS and 0.1 millimolar potassium persulfate.For the analysis, place 10 microliters of each diluted extract in a 96 well microplate. Add 190 microliters of ABTS working solution to each well and incubate for 60 minutes. Measure the absorbance of the reaction mixtures at 750 nanometers in a microplate reader.Use the Trolox standards in concentrations ranging from 100 to 800 micromole per liter to plot a calibration curve. The DPPH antioxidant assay requires a radical-generating compound, DPPH. Weigh out 1.2 milligrams of DPPH into an empty 15 milliliter capacity centrifuge tube.Dissolve the DPPH in methanol to prepare a 60 micromolar solution. The DPPH assay tests the ability of the sample extracts to scavenge free radicals produced by DPPH. Add five microliters of sample extract into the microplate wells.Next, add 195 microliters of 60 micromolar DPPH methanolic solution and incubate for 60 minutes. Measure the absorbance at 515 nanometers. Use the Trolox standards to plot a calibration curve.Figure one shows the structure of hydroxybenzoic acids found in the whole grains. In this current study, vanillic acid was the only hydroxybenzoic acid identified. Figure two shows the structure of hydroxycinnamic acids found in whole grains.In the current study, p-coumaric, caffeic, and ferulic acids were identified in the samples. Table two shows the phenolic acids identified in the samples. As mentioned earlier, vanillic acid was the only hydroxybenzoic acid identified in the samples.It was identified in the cowpea extract only. The hydroxycinnamic acid caffeic acid was identified only in kidney bean, while p-coumeric acid was identified in yellow corn, cowpea, and soybean. Ferulic acid was identified in all of the samples and was the predominant phenolic acid in the samples.The total concentration of the phenolic acids in order from greatest to least was in the order soybean, cowpea, yellow corn, and kidney bean or equivalent, followed by wheat. Table three showed the total phenolic content and antioxidant capacity of the samples. The antioxidant capacity comprised DPPH radical scavenging capacity, TEAC, ORAC, and total antioxidant capacity of the samples.The total antioxidant capacity is the sum of the DPPH, TEAC, and ORAC values. Similar to table two, soybean had the highest total antioxidant capacity. However, instead of cowpea, it was rather kidney bean that had the second highest total antioxidant capacity, although cowpea had the second highest total phenolic acid content.This anomaly is related to the structures of the individual phenolic acids and the possible antagonistic effect of the hydroxybenzoic acid vanillic acid on the antioxidant effects of the hydroxycinnamic acids in cowpea. This study concluded that whole grains differ in their phenolic acid compositions. Among the whole grains studied, soybean has the highest total amount of phenolic acids and, correspondingly, the highest antioxidant capacity.

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Chemistry

Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development

The involvement of free radicals in life sciences has constantly increased with time and has been connected to several physiological and pathological processes. This subject embraces diverse scientific areas, spanning from physical, biological and bioorganic chemistry to biology and medicine, with applications to the amelioration of quality of life, health and aging. Multidisciplinary skills are required for the full investigation of the many facets of radical processes in the biological environment and chemical knowledge plays a crucial role in unveiling basic processes and mechanisms. We developed a chemical biology approach able to connect free radical chemical reactivity with biological processes, providing information on the mechanistic pathways and products. The core of this approach is the design of biomimetic models to study biomolecule behavior (lipids, nucleic acids and proteins) in aqueous systems, obtaining insights of the reaction pathways as well as building up molecular libraries of the free radical reaction products. This context can be successfully used for biomarker discovery and examples are provided with two classes of compounds: mono-trans isomers of cholesteryl esters, which are synthesized and used as references for detection in human plasma, and purine 5',8-cyclo-2'-deoxyribonucleosides, prepared and used as reference in the protocol for detection of such lesions in DNA samples, after ionizing radiations or obtained from different health conditions.

Radical-based biomimetic chemistry has been applied to building-up libraries necessary for biomarker development.

The involvement of free radicals in life sciences has constantly increased with time and has been connected to several physiological and pathological ...

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Towards Biomimicking Wood: Fabricated Free-standing Films of Nanocellulose, Lignin, and a Synthetic Polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

The objective of this research was to form synthetic plant cell wall tissue using layer-by-layer assembly of nanocellulose fibrils and isolated lignin assembled from dilute aqueous suspensions.&#160; Surface measurement techniques of quartz crystal microbalance and atomic force microscopy were used to monitor the formation of the polymer-polymer nanocomposite material.

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and ...

Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, quantum dots should be highly fluorescent and small/monodisperse in size. While commonly used cadmium-based quantum dots possess these qualities, they are potentially toxic due to the possible release of Cd2+ ions through nanoparticle degradation. Indium-based quantum dots, specifically InP/ZnS, have recently been explored as a viable alternative to cadmium-based quantum dots due to their relatively similar fluorescence characteristics and size. The synthesis presented here uses standard hot-injection techniques for effective nanoparticle growth; however, nanoparticle properties such as size, emission wavelength, and emission intensity can drastically change due to small changes in the reaction conditions. Therefore, reaction conditions such temperature, reaction duration, and precursor concentration should be maintained precisely to yield reproducible products. Because quantum dots are not inherently soluble in aqueous solutions, they must also undergo surface modification to impart solubility in water. In this protocol, an amphiphilic polymer is used to interact with both hydrophobic ligands on the quantum dot surface and bulk solvent water molecules. Here, a detailed protocol is provided for the synthesis of highly fluorescent InP/ZnS quantum dots that are suitable for use in biomedical applications.

In this protocol, the synthesis of Cd-free InP/ZnS quantum dots (QDs) is detailed. InP-based QDs are gaining popularity due to the toxicity of Cd2+ ions that may be released through nanoparticle degradation. After synthesis, QDs are solubilized in water using an amphiphilic polymer for use in biomedical applications.

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

Synthesis of a Water-soluble Metal&amp;#8211;Organic Complex Array

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

Determining the Chemical Composition of Corrosion Inhibitor/Metal Interfaces with XPS: Minimizing Post Immersion Oxidation

An approach for acquiring more reliable X-ray photoelectron spectroscopy data from corrosion inhibitor/metal interfaces is described. More specifically, the focus is on metallic substrates immersed in acidic solutions containing organic corrosion inhibitors, as these systems can be particularly sensitive to oxidation following removal from solution. To minimize the likelihood of such degradation, samples are removed from solution within a glove box purged with inert gas, either N2 or Ar. The glove box is directly attached to the load-lock of the ultra-high vacuum X-ray photoelectron spectroscopy instrument, avoiding any exposure to the ambient laboratory atmosphere, and thus reducing the possibility of post immersion substrate oxidation. On this basis, one can be more certain that the X-ray photoelectron spectroscopy features observed are likely to be representative of the in situ submerged scenario, e.g. the oxidation state of the metal is not modified.

A protocol to avoid the oxidation of metallic substrates during sample transfer from an inhibited acidic solution to an X-ray photoelectron spectrometer is presented.

An approach for acquiring more reliable X-ray photoelectron spectroscopy data from corrosion inhibitor/metal interfaces is described. More specifically, ...

Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often result in fragile aerogels with poor shape control. The use of carboxymethylated cellulose nanofibers (CNFs) to form a covalently bonded hydrogel allows for the reduction of metal ions such as palladium on the CNFs with control over both nanostructure and macroscopic aerogel monolith shape after supercritical drying. Crosslinking the carboxymethylated cellulose nanofibers is achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine. The CNF hydrogels maintain their shape throughout synthesis steps including covalent crosslinking, equilibration with precursor ions, metal reduction with high concentration reducing agent, rinsing in water, ethanol solvent exchange, and CO2 supercritical drying. Varying the precursor palladium ion concentration allows for control over the metal content in the final aerogel composite through a direct ion chemical reduction rather than relying on the relatively slow coalescence of pre-formed nanoparticles used in other sol-gel techniques. With diffusion as the basis to introduce and remove chemical species into and out of the hydrogel, this method is suitable for smaller bulk geometries and thin films. Characterization of the cellulose nanofiber-palladium composite aerogels with scanning electron microscopy, X-ray diffractometry, thermal gravimetric analysis, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry indicates a high surface area, metallized palladium porous structure.

A synthesis method for cellulose nanofiber biotemplated palladium composite aerogels is presented.The resulting composite aerogel materials offer potential for catalysis, sensing, and hydrogen gas storage applications.

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often ...

NMR-Based Activity Assays for Determining Compound Inhibition, IC50 Values, Artifactual Activity, and Whole-Cell Activity of Nucleoside Ribohydrolases

NMR spectroscopy is often used for the identification and characterization of enzyme inhibitors in drug discovery, particularly in the context of fragment screening. NMR-based activity assays are ideally suited to work at the higher concentrations of test compounds required to detect these weaker inhibitors. The dynamic range and chemical shift dispersion in an NMR experiment can easily resolve resonances from substrate, product, and test compounds. This contrasts with spectrophotometric assays, in which read-out interference problems often arise from compounds with overlapping UV-vis absorption profiles. In addition, since they lack reporter enzymes, the single-enzyme NMR assays are not prone to coupled-assay false positives. This attribute makes them useful as orthogonal assays, complementing traditional high throughput screening assays and benchtop triage assays. Detailed protocols are provided for initial compound assays at 500 &#956;M and 250 &#956;M, dose-response assays for determining IC50 values, detergent counter screen assays, jump-dilution counter screen assays, and assays in E. coli whole cells. The methods are demonstrated using two nucleoside ribohydrolase enzymes. The use of 1H NMR is shown for the purine-specific enzyme, while 19F NMR is shown for the pyrimidine-specific enzyme. The protocols are generally applicable to any enzyme where substrate and product resonances can be observed and distinguished by NMR spectroscopy. To be the most useful in the context of drug discovery, the final concentration of substrate should be no more than 2-3x its Km value. The choice of NMR experiment depends on the enzyme reaction and substrates available as well as available NMR instrumentation.

NMR-Based Activity Assays for Determining Compound Inhibition, IC50 Values, Artifactual Activity, and Whole-Cell Activity of Nucleoside Ribohydrolases

NMR-based activity assays have been developed to identify and characterize inhibitors of two nucleoside ribohydrolase enzymes. Protocols are provided for initial compound assays at 500 &#956;M and 250 &#956;M, dose-response assays for determining IC50 values, detergent counter screen assays, jump-dilution counter screen assays, and assays in E. coli whole cells.

NMR spectroscopy is often used for the identification and characterization of enzyme inhibitors in drug discovery, particularly in the context of fragment ...

Ion Mobility-Mass Spectrometry Techniques for Determining the Structure and Mechanisms of Metal Ion Recognition and Redox Activity of Metal Binding Oligopeptides

Electrospray ionization (ESI) can transfer an aqueous-phase peptide or peptide complex to the gas-phase while conserving its mass, overall charge, metal-binding interactions, and conformational shape. Coupling ESI with ion mobility-mass spectrometry (IM-MS) provides an instrumental technique that allows for simultaneous measurement of a peptide&#8217;s mass-to-charge (m/z) and collision cross section (CCS) that relate to its stoichiometry, protonation state, and conformational shape. The overall charge of a peptide complex is controlled by the protonation of 1) the peptide&#8217;s acidic and basic sites and 2) the oxidation state of the metal ion(s). Therefore, the overall charge state of a complex is a function of the pH of the solution that affects the peptides metal ion binding affinity. For ESI-IM-MS analyses, peptide and metal ions solutions are prepared from aqueous-only solutions, with the pH adjusted with dilute aqueous acetic acid or ammonium hydroxide. This allows for pH dependence and metal ion selectivity to be determined for a specific peptide. Furthermore, the m/z and CCS of a peptide complex can be used with B3LYP/LanL2DZ molecular modeling to discern binding sites of the metal ion coordination and tertiary structure of the complex. The results show how ESI-IM-MS can characterize the selective chelating performance of a set of alternative methanobactin peptides and compare them to the copper-binding peptide methanobactin.

Ion mobility-mass spectrometry and molecular modeling techniques can characterize the selective metal chelating performance of designed metal-binding peptides and the copper-binding peptide methanobactin. Developing new classes of metal chelating peptides will help lead to therapeutics for diseases associated with metal ion misbalance.

Electrospray ionization (ESI) can transfer an aqueous-phase peptide or peptide complex to the gas-phase while conserving its mass, overall charge, ...

Electrochemical Preparation of Poly(3,4-Ethylenedioxythiophene) Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer in an aqueous and an organic solution. Cyclic voltammetry (CV) was used in the synthesis of PEDOT thin layers. Lithium perchlorate (LiClO4) was used as a dopant in both aqueous (aqueous/acetonitrile (ACN)) and organic (propylene carbonate (PC)) solvent systems. After the PEDOT layer was created in the organic system, the electrode surface was acclimatized by successive cycling in an aqueous solution for use as a sensor for aqueous samples. 
The use of an aqueous-based electropolymerization method has the potential benefit of removing the acclimatization step to have a shorter sensor preparation time. Although the aqueous method is more economical and environmentally friendly than the organic solvent method, superior PEDOT formation is obtained in the organic solution. The resulting PEDOT electrode surfaces were characterized by scanning electron microscopy (SEM), which showed the constant growth of PEDOT during electropolymerization from the organic PC solution, with rapid fractal-type growth on gold (Au) microelectrodes.

Electrochemical Preparation of Poly3,4-Ethylenedioxythiophene Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

We describe aqueous and organic solvent systems for the electropolymerization of poly(3,4-ethylenedioxythiophene) to create thin layers on the surface of gold microelectrodes, which are used for sensing low molecular weight analytes.

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of ...