L-(+)-Cysteine

121.15800

121.16

200-158-2

K848JZ4886

DTXSID8022876

C29609

Colorless crystals|White crystals

2930901000

102.12000

-2.5

DryPowder

1.6666 g/cm³ @ Temp: 45.00 °C

240 °C (decomp)

293.9ºC at 760 mmHg

131.5ºC

8.8 ° (C=8, 1mol/L HCl)

H2O: 280 g/L (25 ºC)

Store at RT.

6.73X10-7 mm Hg at 25 deg C (est)

LD50 orally in Rabbit: 1890 mg/kg

Specific optical rotation: +6.5 deg at 25 °C/D (5 N HCl); +13.0 deg at 25 °C/D (glacial acetic acid)

1.71None

Henry's Law constant = 5.30X10-11 atm-cu m/mol at 25 °C (est)

1.71|pK1 1.71 /carboxylic/; pK2 8.33 /amine/; pK3 10.78 /sulfide/

149.57 Ų [M+H]+ [CCS Type: DT, Method: stepped-field]|151.34 Ų [M+Na]+ [CCS Type: DT, Method: stepped-field]|144.47 Ų [M-H]- [CCS Type: DT, Method: stepped-field]|113 Ų [M+H]+ [CCS Type: TW, Method: calibrated with polyalanine]|144 Ų [M-H]-

Readily oxidizes to form a dimeric amino acid, cystine, in which the two cysteines are linked via a disulfide bridge, a common structural feature in proteins. Amino Acids and Proteins, D.M. Greenberg, Ed. (Charles C. Thomas, Springfield, IL, 1951) 950 pp.|In neutral or slightly alkaline aqueous solution it is oxidized to cystine by air. More stable in acidic solutions.|MP (anhydrous): 178 °C (decomposes). Specific optical rotation: +6.53 deg at 25 °C/D (calculated as cysteine) (c = 2 in 5M HCl); solubility >100 (20 °C) g/100 g H2O /L-Cysteine hydrochloride monohydrate/|Hydroxyl radical reaction rate constant = 7.96X10-11cu cm/molecule-sec at 25 °C (est)

NONH for all modes of transport

3

R22; R36/37/38

S26-S37/39

HA1600000

Xn

Stability Stable, but may be air sensitive. Incompatible with oxidizing agents, bases.

P264, P270, P301+P312, P330, P501

H302

SRP: Recycle any unused portion of the material for its approved use or return it to the manufacturer or supplier. Ultimate disposal of the chemical must consider: the material's impact on air quality; potential migration in air, soil or water; effects on animal, aquatic and plant life; and conformance with environmental and public health regulations. If it is possible or reasonable use an alternative chemical product with less inherent propensity for occupational harm/injury/toxicity or environmental contamination.|Product: Offer surplus and non-recyclable solutions to a licensed disposal company; Contaminated packaging: Dispose of as unused product.

Incompatible materials: Strong oxidizing agents.

Cysteine used as a nutrient and/or dietary supplement in animal drugs, feeds, and related products is generally recognized as safe when used in accordance with good manufacturing or feeding practice.|Substance added directly to human food affirmed as generally recognized as safe (GRAS).|The food additive amino acids may be safely used as nutrients added to foods in accordance with the following conditions: (a) The food additive consists of one or more of the following individual amino acids in the free, hydrated, or anhydrous form, or as the hydrochloride, sodium, or potassium salts. L-Cysteine is included on this list.

|Warning|H302 (82.7%): Harmful if swallowed [Warning Acute toxicity, oral]|P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, and P501|Aggregated GHS information provided by 413 companies from 13 notifications to the ECHA C&L Inventory. Each notification may be associated with multiple companies.|H302: Harmful if swallowed [Warning Acute toxicity, oral]|P264, P270, P301+P312, P330, and P501

Eye/face protection: Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).|Skin protection: Handle with gloves.|Body Protection: Choose body protection in relation to its type, to the concentration and amount of dangerous substances, and to the specific work-place. The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.|Respiratory protection: Respiratory protection is not required. Where protection from nuisance levels of dusts are desired, use type N95 (US) or type P1 (EN 143) dust masks. Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).

Suitable extinguishing media: Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.|Advice for firefighters: Wear self-contained breathing apparatus for firefighting if necessary.

ACCIDENTAL RELEASE MEASURES: Personal precautions, protective equipment and emergency procedures: Use personal protective equipment. Avoid dust formation. Avoid breathing vapors, mist or gas. Avoid breathing dust. Environmental precautions: Do not let product enter drains. Methods and materials for containment and cleaning up: Pick up and arrange disposal without creating dust. Sweep up and shovel. Keep in suitable, closed containers for disposal.

ACCIDENTAL RELEASE MEASURES: Personal precautions, protective equipment and emergency procedures: Use personal protective equipment. Avoid dust formation. Avoid breathing vapors, mist or gas. Avoid breathing dust. Environmental precautions: Do not let product enter drains.|Precautions for safe handling: Further processing of solid materials may result in the formation of combustible dusts. The potential for combustible dust formation should be taken into consideration before additional processing occurs. Provide appropriate exhaust ventilation at places where dust is formed.|Appropriate engineering controls: Handle in accordance with good industrial hygiene and safety practice. Wash hands before breaks and at the end of workday.|Gloves must be inspected prior to use. Use proper glove removal technique (without touching glove's outer surface) to avoid skin contact with this product. Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. Wash and dry hands.|SRP: Local exhaust ventilation should be applied wherever there is an incidence of point source emissions or dispersion of regulated contaminants in the work area. Ventilation control of the contaminant as close to its point of generation is both the most economical and safest method to minimize personnel exposure to airborne contaminants. Ensure that the local ventilation moves the contaminant away from the worker.

... A single ocular application of the test item L-Cysteine to rabbits at a dose of 0.1 g produced slight irritant effects, which were fully reversible within 48 hours. ...|... The single dermal application of the test item L-Cysteine to three rabbits at a dose of 0.5 g showed neither irritant nor corrosive effects. ...|... Single dermal application of the test item L-Cysteine to rats at a dose of 2000 mg/kg body weight was associated with neither mortality nor signs of toxicity but signs of irritation. ...

Cysteine was present at 5.0, 1.5 and 0.8 nmol/g in three consecutive horizon samples from an active landfill in a low permeability clay soil, located in Conica-Montemarta, Sevilla, Spain; sampling was conducted following 3 years of use(1).

IDENTIFICATION AND USE: Cysteine forms white or colorless crystals. It is used in biochemical and nutrition research, as a reducing agent in bread doughs (up to 90 ppm). It is also used as flavor enhancer and medication, including veterinary medication. HUMAN EXPOSURE AND TOXICITY: Cysteine solution (3%) was not irritating for human eyes. ANIMAL STUDIES: A single ocular application of L-cysteine to rabbits at a dose of 0.1 g produced slight irritant effects, which were fully reversible within 48 hours. The single dermal application of L-cysteine to three rabbits at a dose of 0.5 g showed neither irritant nor corrosive effects. Decreased litter size observed in rats receiving high-dose cysteine, which was related to the degeneration and/or death of ovulated unfertilized oocytes and embryos with changes in the zona pellucida, which was already affected in the ovary. Pregnant mice and rats were treated s.c. with 1.2 mg per g on the last day of pregnancy and brain degeneration was observed one day later in the fetus. L-Cysteine is considered to be non-mutagenic in the HPRT locus using V79 cells of the Chinese Hamster. L-Cysteine did not induce structural chromosomal aberrations in the V79 Chinese hamster cell line. ECOTOXICITY STUDIES: The objective of the study was to determine the effects of cysteine on postthaw sperm motility, duration of sperm motility, DNA damage, and fertility in the common carp (Cyprinus carpio). Supplementation with cysteine increased the fertilization and hatching rate and decreased DNA damage.

Acetylcysteine is a simple modified amino acid and appears to be hepatoprotective. In the many studies of acetylcysteine use with acetaminophen overdose as well as with other conditions such as contrast media nephropathy, pulmonary fibrosis, cystic fibrosis and ulcerative colitis, it has not been associated with serum enzyme elevations during therapy or with episodes of clinically apparent liver injury. Since approval of the oral and intravenous forms of acetylcysteine, there have been no published reports of hepatotoxicity and the product label does not mention liver injury as an adverse event. Indeed, acetylcysteine may be beneficial in treating liver diseases in general, although its current indications are limited to acetaminophen overdose or acetaminophen related acute liver injury.

LD50 Rat dermal >2000 mg/kg body weight|LD50 Rat oral 1890 mg/kg|LD50 Rat ip 1620 mg/kg|LD50 Rat sc 1550 mg/kg|For more Non-Human Toxicity Values (Complete) data for CYSTEINE (7 total), please visit the HSDB record page.

Cysteine is a non-essential amino acid for human development(1). Cysteine also occurs in many plants(2).

Cysteine's production and use as a dough enhancer(1) and in biochemical and nutritional research(2) may result in its release to the environment through various waste streams(SRC).

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 3(SRC), determined from a structure estimation method(2), indicates that cysteine is expected to have very high mobility in soil(SRC). The pKa values of cysteine are 1.71, 8.33 and 10.78(3), indicating that this compound will exist as a zwitterion in the environment and zwitterions generally adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(4). Volatilization from moist soil is not expected because the compound exists as an ion and ions do not volatilize. Cysteine is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 6.7X10-7 mm Hg at 25 °C(SRC), determined from a fragment constant method(2). Utilizing the Warburg test, 4.7% of the Theoretical BOD was reached in 24 hours(5) indicating that biodegradation is not an important environmental fate process in soil(SRC).|AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 3(SRC), determined from a structure estimation method(2), indicates that cysteine is not expected to adsorb to suspended solids and sediment(SRC). The pKa values of 1.71, 8.33 and 10.78(3) indicates cysteine will exist as a zwitterion at pH values of 5 to 9 and, therefore, volatilization from water surfaces is not expected to be an important fate process(SRC). According to a classification scheme(4), an estimated BCF of 3(SRC), from its log Kow of -2.49(5) and a regression-derived equation(2), suggests the potential for bioconcentration in aquatic organisms is low(SRC). Utilizing the Warburg test, 4.7% of the Theoretical BOD was reached in 24 hours(6) indicating that biodegradation is not an important environmental fate process in water(SRC).|ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), cysteine, which has an estimated vapor pressure of 6.7X10-7 mm Hg at 25 °C(SRC), determined from a fragment constant method(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase cysteine is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 1.6 hours(SRC), calculated from its rate constant of 8.0X10-11 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(3). Particulate-phase cysteine may be removed from the air by wet and dry deposition(SRC). Cysteine does not contain chromophores that absorb at wavelengths >290 nm(4) and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC).

The rate constant for the vapor-phase reaction of cysteine with photochemically-produced hydroxyl radicals has been estimated as 8.0X10-22 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 1.6 hours at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). The rate constant for the estimated OH radical reaction of cysteine with hydroxyl radicals in aqueous solutions at pH 7 is 3.5X10-10 L/mol-sec(2); this corresponds to an aquatic half-life of 1 hour at an aquatic concentration of 1X10-17 hydroxyl radicals per liter(3). Cysteine is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(4). Cysteine does not contain chromophores that absorb at wavelengths >290 nm(4) and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC).

An estimated BCF of 3 was calculated in fish for cysteine(SRC), using a log Kow of -2.49(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is low(SRC).

Using a structure estimation method based on molecular connectivity indices(1), the Koc of cysteine can be estimated to be 3(SRC). According to a classification scheme(2), this estimated Koc value suggests that cysteine is expected to have very high mobility in soil. The pKa values of cysteine are 1.71, 8.33 and 10.78(3) indicating that this compound will exist as a zwitterion in the environment and zwitterions generally adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(4).

The pKa values of cysteine are 1.71, 8.33 and 10.78(1), indicating that this compound will exist as a zwitterion at pH values of 5 to 9; therefore, volatilization from water surfaces is not expected to be an important fate process. Cysteine is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 6.7X10-7 mm Hg(SRC), determined from a fragment constant method(2).

SURFACE WATER: Cysteine was tested for but not detected in grab samples from the Huron River at the Ann Arbor, Michigan Water Treatment Plant intake, sampled in June 2004(1).

Cysteine in fruit juices purchased in supermarkets in Davis, CA(1).[Table#3867]

According to the 2012 TSCA Inventory Update Reporting data, 1 reporting facility estimated the number of persons reasonably likely to be exposed in the manufacturing, processing, or use of cysteine in the United States may be in the range of 25-49 workers per plant; the data may be greatly underestimated due to confidential business information (CBI) or unknown values(1).|Occupational exposure to cysteine may occur through inhalation and dermal contact with this compound at workplaces where cysteine is produced or used. Monitoring data indicate that the general population may be exposed to cysteine via ingestion of food. (SRC)

For the prevention of liver damage and kidney damage associated with overdoses of acetaminophen|Treatment of high-grade glioma|Parenteral nutrition

Acetylcysteine, also known as N-acetylcysteine (NAC), is a modified amino acid that is used as an antidote for acetaminophen overdose to prevent hepatic injury. Acetylcysteine is a hepatoprotective agent and has not been linked to significant serum enzyme elevations during therapy or to instances of clinically apparent acute liver injury.

Antidotes, Toxicological Emergency

/EXPL THER/ Acetaminophen-cysteine adducts (APAP-CYS) are a serum biomarker of acetaminophen exposure, formed when the oxidative metabolite of acetaminophen binds to cysteine residues of hepatic proteins. APAP-CYS adducts become elevated in cases of acute liver failure following acetaminophen overdose and have been proposed as a diagnostic tool to identify acetaminophen-induced acute liver failure when standard testing is inconclusive.|/EXPL THER/ Lead is a toxic heavy metal that adversely affects nervous tissues; it often occurs as an environmental pollutant. We investigated histological changes in the cerebral cortex, hippocampus and cerebellum of adult albino mice following exposure to lead acetate. We also studied the possible ameliorative effect of the chelating agent, L-cysteine, on lead-induced neurotoxicity. We divided albino mice into six groups: 1) vehicle-only control, 2) L-cysteine control, 3 and 4) treated for 7 days with 20 and 40 mg/kg lead acetate, respectively, and 5 and 6) treated for 7 days with 20 and 40 mg/kg lead acetate, respectively, followed by 50 mg/kg L-cysteine for 7 days. Lead acetate administration caused disorganization of cell layers, neuronal loss and degeneration, and neuropil vacuolization. Brain sections from lead-intoxicated mice treated with L-cysteine showed fewer pathological changes; the neuropil showed less vacuolization and the neurons appeared less damaged. L-cysteine at the dose we used only marginally alleviated lead-induced toxicity.|/EXPL THER/ In hamster lung cell cultures addn of l-Cysteine or vit C to media protects against or reverses abnormal growth & malignant transformation in aged controls (1-2 yr old) or young (3-6 mo) after repeated exposure to smoke of tobacco or marijuana cigarettes.|/EXPL THER/ L-Cysteine admin orally or ip to rats protected against acute toxicity of methylmercury chloride, reducing mercury content in kidney & brain but not in liver.|For more Therapeutic Uses (Complete) data for CYSTEINE (7 total), please visit the HSDB record page.

Due to this ability to undergo redox reactions, cysteine has antioxidant properties. Cysteine is an important source of sulfur in human metabolism, and although it is classified as a non-essential amino acid, cysteine may be essential for infants, the elderly, and individuals with certain metabolic disease or who suffer from malabsorption syndromes. Cysteine may at some point be recognized as an essential or conditionally essential amino acid.

L-Cysteine is the central compound in sulfur metabolism in the human body. In proteins the formation of disulfide bonds between the thiol groups of cysteine plays an important role for tertiary structure and enzymatic activity; cysteine is however always incorporated in the polypeptide chain as cysteine. L-Cysteine is degraded to pyruvate in two steps: one is removal of sulfur and the other is a transamination. Cysteine can be metabolized to form taurine and carbon dioxide through the cysteinsulfinate pathway, where the initial step is oxidation of cysteine to cysteine sulfinate. This step is catalyzed by cysteine dioxygenase. Cysteine sulfinate may then be decarboxylated to form taurine or it may be metabolized via the putative intermediate beta-sulfinylpyruvate to pyruvate and sulfite and then to carbon dioxide and sulfate.|Amino acid catabolism is essential for adjusting pool sizes of free amino acids and takes part in energy production as well as nutrient remobilization. The carbon skeletons are generally converted to precursors or intermediates of the tricarboxylic acid cycle. In the case of cysteine, the reduced sulfur derived from the thiol group also has to be oxidized in order to prevent accumulation to toxic concentrations. Here we present a mitochondrial sulfur catabolic pathway catalyzing the complete oxidation of L-cysteine to pyruvate and thiosulfate. After transamination to 3-mercaptopyruvate the sulfhydryl group from L-cysteine is transferred to glutathione by sulfurtransferase 1 and oxidized to sulfite by the sulfur dioxygenase ETHE1. Sulfite is then converted to thiosulfate by addition of a second persulfide group by sulfurtransferase 1. This pathway is most relevant during early embryo development and for vegetative growth under light limiting conditions. Characterization of a double mutant produced from Arabidopsis thaliana T-DNA insertion lines for ETHE1 and sulfurtransferase 1 revealed that an intermediate of the ETHE1 dependent pathway, most likely a persulfide, interferes with amino acid catabolism and induces early senescence.

Cysteine can usually be synthesized by the human body under normal physiological conditions if a sufficient quantity of methionine is available. Cysteine is typically synthesized in the human body when there is sufficient methionine available. Cysteine exhibits antioxidant properties and participates in redox reactions. Cysteine's antioxidant properties are typically expressed in the tripeptide glutathione, which occurs in humans as well as other organisms. Glutathione (GSH) typically requires biosynthesis from its constituent amino acids, cysteine, glycine, and glutamic acid, due to its limited systemic availability. Glutamic acid and glycine are readily available in the diets of most industrialized countries, but the availability of cysteine can be the limiting substrate. In human metabolism, cysteine is also involved in the generation of sulfide present in iron-sulfur clusters and nitrogenase by acting as a precursor. In a 1994 report released by five top cigarette companies, cysteine is one of the 599 additives to cigarettes. Its use or purpose, however, is unknown, like most cigarette additives. Its inclusion in cigarettes could offer two benefits: Acting as an expectorant, since smoking increases mucus production in the lungs; and increasing the beneficial antioxidant glutathione (which is diminished in smokers).

/SRP:/ Immediate first aid: Ensure that adequate decontamination has been carried out. If patient is not breathing, start artificial respiration, preferably with a demand valve resuscitator, bag-valve-mask device, or pocket mask, as trained. Perform CPR if necessary. Immediately flush contaminated eyes with gently flowing water. Do not induce vomiting. If vomiting occurs, lean patient forward or place on the left side (head-down position, if possible) to maintain an open airway and prevent aspiration. Keep patient quiet and maintain normal body temperature. Obtain medical attention. /Poisons A and B/|/SRP:/ Basic treatment: Establish a patent airway (oropharyngeal or nasopharyngeal airway, if needed). Suction if necessary. Watch for signs of respiratory insufficiency and assist ventilations if needed. Administer oxygen by nonrebreather mask at 10 to 15 L/min. Monitor for pulmonary edema and treat if necessary ... . Monitor for shock and treat if necessary ... . Anticipate seizures and treat if necessary ... . For eye contamination, flush eyes immediately with water. Irrigate each eye continuously with 0.9% saline (NS) during transport ... . Do not use emetics. For ingestion, rinse mouth and administer 5 mL/kg up to 200 mL of water for dilution if the patient can swallow, has a strong gag reflex, and does not drool ... . Cover skin burns with dry sterile dressings after decontamination ... . /Poisons A and B/|/SRP:/ Advanced treatment: Consider orotracheal or nasotracheal intubation for airway control in the patient who is unconscious, has severe pulmonary edema, or is in severe respiratory distress. Positive-pressure ventilation techniques with a bag valve mask device may be beneficial. Consider drug therapy for pulmonary edema ... . Consider administering a beta agonist such as albuterol for severe bronchospasm ... . Monitor cardiac rhythm and treat arrhythmias as necessary ... . Start IV administration of D5W TKO /SRP: "To keep open", minimal flow rate/. Use 0.9% saline (NS) or lactated Ringer's (LR) if signs of hypovolemia are present. For hypotension with signs of hypovolemia, administer fluid cautiously. Watch for signs of fluid overload ... . Treat seizures with diazepam or lorazepam ... . Use proparacaine hydrochloride to assist eye irrigation ... . /Poisons A and B/

/HUMAN EXPOSURE STUDIES/ ... Applied as a 3% near-neutral soln to ... human eyes ... no adverse effect is reported.|/CASE REPORTS/ A 26-year-old female with history of unexplained, severe hepatitis presented with a second episode of severe hepatitis including coagulopathy and transaminase levels >10,000 U/L. The patient reported ingesting "only a couple" of acetaminophen tablets several days prior to her presentation. An acetaminophen concentration of 14 ug/mL at presentation aroused suspicion that acetaminophen might have caused the patient's liver failure, despite her adamant denial of overdose. ...

Cysteine

Available commercially as L(+)-cysteine hydrochloride.

Food, beverage, and tobacco product manufacturing|L-Cysteine: ACTIVE|A non-essential amino acid in human development.|An amino acid derived from cystine, occurring naturally in the L-form ...

The near-infrared (NIR) fluorescence sensor for rapid, selective, and sensitive detection of cysteine (Cys) is of great importance in both biological and environmental sciences. Herein, we report a specific probe with turn-on fluorescence property, visible color change with naked-eye, and large wavelength shift on UV spectra for highly selective detection of Cys over homocysteine (Hcy) and glutathione (GSH) in both HEPES buffer (10 mM, pH 7.4) and diluted human serum. The probe based on the conjugate addition-cyclization reaction has a low limit of detection to Cys (0.16 uM as NIR fluorescence sensor and 0.13 uM as UV sensor). Kinetic study indicated that the probe has a very rapid response to Cys, owing to the much higher pseudo-first-order reaction constant with Cys (299/M/s) than with Hcy (1.29/M/s) or GSH (0.53/M/s). Upon addition of Cys to a solution of the probe, the color changed from purple to cyan, with the maximum wavelength shifting from 582 to 674 nm in the UV spectrum and a fluorescence emission at 697 nm appearing. It has been successfully applied for determination of Cys in diluted serum and bioimaging of Cys in living cells with low cell toxicity.|Gold nanoparticles (AuNPs) were synthesized at room temperature following a simple, rapid, and green route using fresh-squeezed apple juice as a reducing reagent. The optimal AuNPs, based on the particle color, stability, and color change suitable for colorimetric detection of cysteine (Cys), are synthesized using 5 mL of 10% apple juice, 1 mL of 10 mM gold precursor solution, and 1 mL of 0.1 M NaOH. Under this set of parameters, the AuNPs are synthesized within 30 min at room temperature. The average size (11.1 +/- 3.2 nm) and zeta potential (-36.5 mV) of the AuNPs synthesized were similar to those of AuNPs prepared via the conventional citrate-reduction method. In the presence of Cys, unlike with any other amino acid, the AuNPs aggregated, possibly due to the gold-sulfur covalent interaction, yielding red-to-purple color change of the sample solution. The red-shift of the localized surface plasmon resonance peak of the AuNPs responsible for the color change was recorded by UV-vis spectrometer. The effect of other potential interferents such as glucose, ascorbic acid, K(+) , Na(+) , Ca(2+) , Zn(2+) , Ag(+) , Ni(2+) , Cu(2+) , Co(2+) , and Hg(2+) were also examined. The results show that AuNPs can be used to selectively detect and measure Cys with a linear dependency in the range of 2 to 100 uM and a limit of detection (signal-to-noise ratio > 3) of 50 nM. The results suggest that the green-synthesized AuNPs are useful for simple, rapid, and sensitive colorimetric detection of Cys, which is an essential amino acid in food and biological systems.

A new fluorescent probe based on an ensemble of gold nanoclusters (AuNCs) and polymer protected gold nanoparticles (AuNPs) for turn-on sensing of L-cysteine was designed and prepared. The AuNCs were protected by bovine serum albumin and had strong fluorescence. The polymer protected AuNPs were synthesized by a facile in situ strategy at room temperature and could quench the fluorescence of AuNCs due to the Forster resonance energy transfer. Interestingly, it has been observed that the quenched fluorescence of AuNCs was recovered by L-cysteine, which could induce the aggregation of polymer protected AuNPs by sulfur group. Then the prepared fluorescent probe was successfully used for determination of L-Cys in human urines ... .|A chlorinated coumarin-aldehyde was developed as a colorimetric and ratiometric fluorescent probe for distinguishing glutathione (GSH), cysteine (Cys) and homocysteine (Hcy). The GSH-induced substitution-cyclization and Cys/Hcy-induced substitution-rearrangement cascades lead to the corresponding thiol-coumarin-iminium cation and amino-coumarin-aldehyde with distinct photophysical properties. The probe can be used to simultaneously detect GSH and Cys/Hcy by visual determination based on distinct different colors - red and pale-yellow in PBS buffer solution by two reaction sites. From the linear relationship of fluorescence intensity and biothiols concentrations, it was determined that the limits of detection for GSH, Hcy and Cys are 0.08, 0.09 and 0.18 uM, respectively. Furthermore, the probe was successfully used in living cell imaging with low cell toxicity.|A highly sensitive and selective turn on fluorescent probe P-acid-aldehyde (P-CHO) is developed for the determination of cysteine (Cys) and homocysteine (Hcy). The probe is designed and synthesized by incorporating the specific functional group aldehyde group for thiols into a stable ?-conjugated material 4,4'-(2,5-dimethoxy-1,4-phenylene) bis(ethyne-2,1-diyl) dibenzoic acid (P-acid). The probe fluorescence is quenched through donor photoinduced electron transfer (d-PET) between the fluorophore (P-acid) and the recognition group (aldehyde group). In the presence of thiols, Cys and Hcy can selectively react with aldehyde group of the probe because the inhibition of d-PET between fluorophore and recognition group. Therefore, a turn-on fluorescent sensor was established for the fluorescence recovery. Under the optimized conditions, the fluorescence response of probe is directly proportional to the concentration of Cys in the range of 4-95 nM/L, with a detection limit 3.0 nM. In addition, the sensing system exhibits good selectively toward Cys and Hcy in the presence of other amino acids. It has been successfully applied for bioimaging of Cys and Hcy in living cells with low cell toxicity.

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