document_title: The Polar Express (film)

question_text: who plays the little boy in polar express

root

text: The Polar Express (film)

text: Plot[edit]

text: On the night of Christmas Eve, a Grand Rapids, Michigan boy is growing bitterly skeptical of the existence of Santa Claus. As he struggles to sleep, he is roused by the arrival of a steam locomotive on the street outside his home, and dons his robe to investigate, tearing the robe's pocket as he retrieves it. Outside, the train's conductor (Tom Hanks) introduces the train as the Polar Express, bound for the North Pole. The boy initially declines to board, but jumps aboard the train as it pulls away.

tag: p

text: In a passenger car, he befriends a spirited and amicable girl, and a condescending know-it-all. The train stops to pick up an impoverished child, Billy, who also declines to board; Billy changes his mind, and the boy applies the emergency brake to allow him to catch up to the train, much to the conductor's chagrin. As Billy sits alone in the train's rear dining car, hot chocolate is served in the passenger car, and the girl saves her hot chocolate for Billy. As she and the conductor cross to the dining car, the boy notices she left her ticket behind unpunched, but loses hold of the ticket between the cars when he attempts to return it. The ticket reenters the passenger car, but not before the conductor notices its absence and escorts the girl back to the rear car.

text: The know-it-all claims that the conductor will jettison the girl from the back of the train; the boy recovers the ticket and dashes to the dining car in search of the conductor, climbing onto the roof from the rear platform. He meets a hobo camping on the roof, who offers him coffee and discusses the existence of Santa Claus and belief in ghosts. The hobo skis with the boy along the tops of the cars towards the train's coal tender, where the hobo disappears. Here, the boy discovers that the girl has been made to supervise the locomotive while engineers Steamer and Smokey replace the train's headlight. The train is forced to stop while the conductor disperses a herd of caribou, whereupon the engineers return to the cabin and the boy, girl and conductor remain on the catwalk on the front of the locomotive. The throttle's split pin sheers off, causing the train to accelerate uncontrollably down a 179-degree grade and onto a frozen lake, where the engineers repair the throttle with a hairpin and drift the train to realign it with the tracks. The boy returns the girl's ticket, and as the three return to the passenger car, the boy is accosted by an Ebenezer Scrooge marionette (controlled by the hobo), taunting him and calling him a doubter.

text: The train finally arrives at the North Pole, where the conductor announces that one of the passengers will be chosen to receive the first gift of Christmas, from Santa himself. The girl discovers Billy still alone in the rear car, and she and the boy persuade him to come along; however, the boy accidentally unhitches the car, sending it back along the line to a railway turntable in Santa's workshop. The children sneak through an elf command center and a gift sorting office before accidentally being dumped into Santa's sack, where they discover that the know-it-all stowed away along with them, hoping to open his Christmas presents early. The elves rescue them as Santa arrives, and the boy grows frustrated, unable to see Santa through the crowd. A jingle bell flies loose from the galloping reindeers' reins; the boy initially cannot hear it ring, until he finds it within himself to believe. He returns the bell to Santa as he passes, and Santa selects the boy to receive the first gift of Christmas. The boy asks to keep the jingle bell, and places it in his robe pocket.

text: Four of the elves use a handcar to trundle the wayward passenger car back to the train as the children all board the Polar Express to return home, but the then boy discovers that the pocket was torn and that the bell had fallen out. He returns home and awakens Christmas morning to find a present containing the bell. He holds it to his ear and shakes it; his parents, not believing in Santa, lament how the bell is "broken".

text: Cast[edit]

text:
Tom Hanks as the Hero Boy (motion-capture only), the Hero Boy's father, the Conductor, the Hobo, Santa Claus, and the Narrator

Daryl Sabara as the Hero Boy (voice)
Josh Hutcherson as the Hero Boy (additional motion-capture)

Leslie Zemeckis as Sister Sarah (motion-capture only) and the Hero Boy's mother

Isabella Peregrina as Sister Sarah (voice)
Ashly Holloway as Sister Sarah (additional motion-capture)

Eddie Deezen as Know-It-All

Jimmy 'Jax' Pinchak as Know-It-All (additional motion-capture)

Nona Gaye as the Hero Girl

Chantel Valdivieso as the Hero Girl (additional motion-capture)
Meagan Moore as the Hero Girl (singing voice)
Tinashe as the Hero Girl (motion-capture modeling)

Peter Scolari as Billy the Lonely Boy (motion-capture only)

Hayden McFarland as Billy the Lonely Boy (additional motion-capture)
Jimmy Bennett as Billy the Lonely Boy (voice)
Matthew Hall as Billy the Lonely Boy (singing voice)

Dylan Cash as Boy on Train (voice)
Brendan King and Andy Pellick as the Pastry Chefs
Josh Eli, Rolandas Hendricks, Jon Scott, Sean Scott, Mark Mendonca, Mark Goodman, Gregory Gast, and Gordon Hart as the Waiters
Andre Sogliuzzo as Smokey and Steamer (voice)

Michael Jeter as Smokey and Steamer (motion-capture only)

Chris Coppola as Gus the Toothless Boy and an Elf

Connor Matheus as the Toothless Boy (additional motion-capture)

Julene Renee as the Red Head Girl and an Elf
Phil Fondacaro, Debbie Lee Carrington, Mark Povinelli, and Ed Gale as Elves
Charles Fleischer as the Elf General
Steven Tyler as the Elf Lieutenant and the Elf Singer
Dante Pastula as the Little Boy
Eric Newton, Aidan O'Shea, Aaron Hendry, Kevin C. Carr, Bee Jay Joyer, Jena Carpenter, Karine Mauffrey, Beth Carpenter, Bill Forchion, Devin Henderson, and Sagiv Ben-Binyamin as Acrobatic Elves
Evan Sabara as a Young Boy (additional motion-capture)

tag: ul

text: Production[edit]

text: Architecture[edit]

text: The buildings at the North Pole refer to a number of buildings related to American railroading history. The buildings in the square at the city's center are loosely based on the Pullman Factory in Chicago's Pullman neighborhood.[5]

text: Polar Express Locomotive[edit]

text: The locomotive featured in the film is an American 2-8-4 Berkshire type steam locomotive, with a cowcatcher, modeled after the Pere Marquette 1225, which had spent many years on static display near Spartan Stadium in East Lansing, Michigan on the campus of Michigan State University, where Chris Van Allsburg recalled playing on the engine when attending football games as a child.[6]

text: In July 2002, Warner Bros. approached the engine's owner, the Steam Railroading Institute, to study the engine.[7] The engine in the film is modeled from the PM #1225's drawings and the sounds from recordings made of the 1225 operating under steam.[8] The whistle, however, was taken from Sierra Railway #3.

text: IMAX 3D version[edit]

text: In addition to standard theatrical 35mm format, a 3-D version for IMAX was also released, generated from the same 3-D digital models used for the standard version.[9]

text: Home media release[edit]

text: The film was released on DVD as separated widescreen and full-screen versions in single and two-disc special editions (with bonus features) and on VHS on November 22, 2005, one year after the film came out.[10] It was released on Blu-ray with bonus features and presented in the original widescreen aspect ratio on October 30, 2007.

text: Soundtrack[edit]

text:
Performer(s)
Title
Length

Tom Hanks
"The Polar Express"
3:25

Matthew Hall & Meagan Moore
"When Christmas Comes to Town"
4:07

Steven Tyler
"Rockin' on the Top of the World"
2:35

Josh Groban
"Believe"
4:18

Tom Hanks
"Hot Chocolate"
2:33

Alan Silvestri
"Spirit of the Season"
2:34

Frank Sinatra
"Santa Claus Is Comin' to Town"
2:35

Alan Silvestri
"Seeing Is Believing"
3:47

Bing Crosby
"White Christmas"
3:05

The Andrews Sisters
"Winter Wonderland"
2:43

Perry Como &The Fontane Sisters
"It's Beginning to Look a Lot Like Christmas"
2:40

Kate Smith
"Silver Bells"
2:39

Bing Crosby & The Andrews Sisters
"Here Comes Santa Claus (Right Down Santa Claus Lane)"
3:04

Alan Silvestri
"Suite from the Polar Express"
6:02

text: Reception[edit]

text: Critical response[edit]

text: On Metacritic, which assigns a normalized rating to reviews, the film has a weighted average score of 61 out of 100 based on 36 critics, indicating "generally favorable reviews".[11] On review aggregator website Rotten Tomatoes, the film has an approval rating of 55% based on 202 reviews, with an average rating of 6.4/10. The site's critical consensus reads, "Though the movie is visually stunning overall, the animation for the human characters isn't lifelike enough, and the story is padded."[12] Despite the polarized reception from critics, The Polar Express has been popular among audiences. The Independent reported in 2011 that the film "is now seen by many as a classic".[13] CinemaScore reported that audiences gave the film a rare "A+" grade.[14]

text: Roger Ebert gave the film his highest rating of four stars, saying, "There's a deeper, shivery tone, instead of the mindless jolliness of the usual Christmas movie." And "It has a haunting, magical quality ..." Acknowledging comments by other reviewers, Ebert said, "It's a little creepy. Not creepy in an unpleasant way, but in that sneaky, teasing way that lets you know eerie things could happen."[15] Richard Roeper gave a glowing review to the film as well, saying that it "remains true to the book, right down to the bittersweet final image."[quote without source] James Berardinelli gave it a 3.5/4, stating that it is "a delightful tale guaranteed to enthrall viewers of all ages", and ranked it as the 10th best film of 2004.[16]

text: The character design and animation were criticized for dipping into the uncanny valley.[17] Peter Travers of Rolling Stone gave the film a 1 out of 4 stars, and called it "a failed and lifeless experiment in which everything goes wrong".[18] Stephanie Zacharek of Salon gave the film 1.5 stars out of 5 and said, "I could probably have tolerated the incessant jitteriness of The Polar Express if the look of it didn't give me the creeps."[19] Geoff Pevere of the Toronto Star stated, "If I were a child, I'd have nightmares. Come to think of it, I did anyway."[20] Paul Clinton from CNN called it "at best disconcerting, and at worst, a wee bit horrifying".[21]

text: Box office[edit]

text: The film opened at #2 and earned $23,323,463 from approximately 7,000 screens at 3,650 theaters, for a per-theater average of $6,390 and a per-screen average of $3,332 in its opening weekend. It also brought in a total of $30,629,146 since its Wednesday launch. The weekend total also included $2,100,000 from 59 IMAX theaters, for an IMAX theater average of $35,593, and had a $3,000,000 take since Wednesday. In its second weekend, it grossed another $15,668,101, averaging $4,293 from 3,650 venues and boosting the 12-day cumulative to $51,463,282 and over Thanksgiving weekend made another $19,389,927, averaging $5,312 from 3,650 venues and raising the 19-day cumulative to $81,479,861.[citation needed] The film has made $185,618,322 domestically (including IMAX re-releases), and $124,140,582 overseas for a total worldwide gross of $309,758,904.[2]

text: The film had its network TV premiere on ABC, December 1, 2006. The airing brought in 13.2 million viewers, winning its timeslot and ranking 20th in the Nielsen ratings that week, according to TVTango.com.

text: Awards and honors[edit]

text: The film was nominated for three Academy Awards:

text:
Best Sound Editing (Randy Thom and Dennis Leonard)
Best Sound Mixing (Randy Thom, Tom Johnson, Dennis S. Sands and William B. Kaplan)
Best Original Song for "Believe."[22]

text: The film was nominated at the 3rd Visual Effects Society Awards in the category of "Outstanding Performance by an Animated Character in an Animated Motion Picture."[23]

text: In 2008, the American Film Institute nominated The Polar Express for its Top 10 Animated Films list.[24]

text: The "Polar Express Experience"[edit]

text: In November 2007, SeaWorld Orlando debuted the Polar Express Experience, a Motion Simulator ride based on the film. The attraction is a temporary replacement for the Wild Arctic attraction. The building housing the attraction was also temporarily re-themed to a railroad station and ride vehicles painted to resemble Polar Express passenger cars. The plot for the ride revolves around a trip to the North Pole on Christmas Eve. Guests feel the motion of the locomotive as well as the swinging of the train on ice and feeling of ice crumbling beneath them. The attraction was available until January 1, 2008,[25] and is now open annually during the Christmas season.

text: The 4D film, distributed by SimEx-Iwerks, has been shown at other amusement parks around the world including Cincinnati Zoo and Botanical Garden, Dollywood (during the annual Smoky Mountain Christmas event), Vancouver Aquarium (2009 — 2010),[26] and Warner Bros. Movie World (during the White Christmas events in 2010 and 2011).

text: Video game[edit]

text: A video game based on the film was released on November 26, 2004 for GameCube, Game Boy Advance, PlayStation 2 and Windows, developed by Blue Tongue Entertainment and published by THQ.[27][28] The plot of the game is more different than the film version. Within this time, the Ebenezer Scrooge puppet who is set as the main antagonist of the game, attempts to prevent the children from believing in Santa Claus by stealing their tickets and trying to stop the children for reaching the North Pole.[29][30]


document_title: Disulfide

question_text: disulphide bond in a protein is generated between

text: Disulfide

text: Organic disulfides[edit]

text:
A selection of disulfides

FeS2,
"fool's gold"

S2Cl2,
a common industrial chemical

cystine,
crosslinker in many proteins

lipoic acid,
a vitamin

Ph2S2,
a common organic disulfide

tag: table

text: Properties[edit]

text: The disulfide bonds are strong, with a typical bond dissociation energy of 60 kcal/mol (251 kJ mol−1). However, being about 40% weaker than C−C and C−H bonds, the disulfide bond is often the "weak link" in many molecules. Furthermore, reflecting the polarizability of divalent sulfur, the S−S bond is susceptible to scission by polar reagents, both electrophiles and especially nucleophiles (Nu):[1]

text: The disulfide bond is about 2.05 Å in length, about 0.5 Å longer than a C−C bond. Rotation about the S−S axis is subject to a low barrier. Disulfides show a distinct preference for dihedral angles approaching 90°. When the angle approaches 0° or 180°, then the disulfide is a significantly better oxidant.

text: Disulfides where the two R groups are the same are called symmetric, examples being diphenyl disulfide and dimethyl disulfide. When the two R groups are not identical, the compound is said to be an asymmetric or mixed disulfide.[2]

text: Although the hydrogenation of disulfides is usually not practical, the equilibrium constant for the reaction provides a measure of the standard redox potential for disulfides:

text: This value is about −250 mV versus the standard hydrogen electrode (pH = 7). By comparison, the standard reduction potential for ferrodoxins is about −430 mV.

text: Synthesis[edit]

text: Disulfide bonds are usually formed from the oxidation of sulfhydryl (−SH) groups, especially in biological contexts.[3] The transformation is depicted as follows:

text: A variety of oxidants participate in this reaction including oxygen and hydrogen peroxide. Such reactions are thought to proceed via sulfenic acid intermediates. In the laboratory, iodine in the presence of base is commonly employed to oxidize thiols to disulfides. Several metals, such as copper(II) and iron(III) complexes affect this reaction.[citation needed] Alternatively, disulfide bonds in proteins often formed by thiol-disulfide exchange:

text: Such reactions are mediated by enzymes in some cases and in other cases are under equilibrium control, especially in the presence of a catalytic amount of base.

text: The alkylation of alkali metal di- and polysulfides gives disulfides. "Thiokol" polymers arise when sodium polysulfide is treated with an alkyl dihalide. In the converse reaction, carbanionic reagents react with elemental sulfur to afford mixtures of the thioether, disulfide, and higher polysulfides. These reactions are often unselective but can be optimized for specific applications.

text: Many specialized methods have been developed for forming disulfides, usually for applications in organic synthesis. Reagents that deliver the equivalent of "RS+" react with thiols to give asymmetrical disulfides:[3]

text: where R″2N is the phthalimido group.

text: Reactions[edit]

text: The most important aspect of disulfide bonds is their cleavage, which occurs via reduction. A variety of reductants can be used. In biochemistry, thiols such as β-mercaptoethanol (β-ME) or dithiothreitol (DTT) serve as reductants; the thiol reagents are used in excess to drive the equilibrium to the right:

text: The reductant tris(2-carboxyethyl)phosphine (TCEP) is useful, beside being odorless compared to β-ME and DTT, because it is selective, working at both alkaline and acidic conditions (unlike DTT), is more hydrophilic and more resistant to oxidation in air. Furthermore, it is often not needed to remove TCEP before modification of protein thiols.[4]

text: In organic synthesis, hydride agents are typically employed for scission of disulfides, such as sodium borohydride. More aggressive, alkali metals will effect this reaction:

text: These reactions are often followed by protonation of the resulting metal thiolate:

text: Thiol–disulfide exchange is a chemical reaction in which a thiolate group −S− attacks a sulfur atom of a disulfide bond −S−S−. The original disulfide bond is broken, and its other sulfur atom (green atom in Figure 1) is released as a new thiolate, carrying away the negative charge. Meanwhile, a new disulfide bond forms between the attacking thiolate (red atom in Figure 1) and the original sulfur atom (blue atom in Figure 1).[5][6]

text: Thiolates, not thiols, attack disulfide bonds. Hence, thiol–disulfide exchange is inhibited at low pH (typically, below 8) where the protonated thiol form is favored relative to the deprotonated thiolate form. (The pKa of a typical thiol group is roughly 8.3, but can vary due to its environment.)

text: Thiol–disulfide exchange is the principal reaction by which disulfide bonds are formed and rearranged in a protein. The rearrangement of disulfide bonds within a protein generally occurs via intra-protein thiol–disulfide exchange reactions; a thiolate group of a cysteine residue attacks one of the protein's own disulfide bonds. This process of disulfide rearrangement (known as disulfide shuffling) does not change the number of disulfide bonds within a protein, merely their location (i.e., which cysteines are bonded). Disulfide reshuffling is generally much faster than oxidation/reduction reactions, which change the number of disulfide bonds within a protein. The oxidation and reduction of protein disulfide bonds in vitro also generally occurs via thiol–disulfide exchange reactions. Typically, the thiolate of a redox reagent such as glutathione or dithiothreitol attacks the disulfide bond on a protein forming a mixed disulfide bond between the protein and the reagent. This mixed disulfide bond when attacked by another thiolate from the reagent, leaves the cysteine oxidized. In effect, the disulfide bond is transferred from the protein to the reagent in two steps, both thiol–disulfide exchange reactions.

text: The in vivo oxidation and reduction of protein disulfide bonds by thiol–disulfide exchange is facilitated by a protein called thioredoxin. This small protein, essential in all known organisms, contains two cysteine amino acid residues in a vicinal arrangement (i.e., next to each other), which allows it to form an internal disulfide bond, or disulfide bonds with other proteins. As such, it can be used as a repository of reduced or oxidized disulfide bond moieties.

text: Many specialized organic reactions have been developed for disulfides, again mainly associated with the scission of the S−S bond, which is usually the weakest bond in a molecule. In the Zincke disulfide cleavage reactions, disulfides are cleaved to give a sulfenyl halide by reaction with bromine or chlorine.[clarification needed][7][8]

text: Occurrence in proteins[edit]

text: Disulfide bonds play an important role in the folding and stability of some proteins, usually proteins secreted to the extracellular medium.[2] Since most cellular compartments are reducing environments, in general, disulfide bonds are unstable in the cytosol, with some exceptions as noted below, unless a sulfhydryl oxidase is present.[9]

text: Disulfide bonds in proteins are formed between the thiol groups of cysteine residues by the process of oxidative folding. The other sulfur-containing amino acid, methionine, cannot form disulfide bonds. A disulfide bond is typically denoted by hyphenating the abbreviations for cysteine, e.g., when referring to ribonuclease A the "Cys26–Cys84 disulfide bond", or the "26–84 disulfide bond", or most simply as "C26–C84"[10] where the disulfide bond is understood and does not need to be mentioned. The prototype of a protein disulfide bond is the two-amino-acid peptide cystine, which is composed of two cysteine amino acids joined by a disulfide bond (shown in Figure 3 in its unionized form). The structure of a disulfide bond can be described by its χss dihedral angle between the Cβ−Sγ−Sγ−Cβ atoms, which is usually close to ±90°.

text: The disulfide bond stabilizes the folded form of a protein in several ways:

text:
It holds two portions of the protein together, biasing the protein towards the folded topology. That is, the disulfide bond destabilizes the unfolded form of the protein by lowering its entropy.
The disulfide bond may form the nucleus of a hydrophobic core of the folded protein, i.e., local hydrophobic residues may condense around the disulfide bond and onto each other through hydrophobic interactions.
Related to 1 and 2, the disulfide bond link two segments of the protein chain, the disulfide bond increases the effective local concentration of protein residues and lowers the effective local concentration of water molecules. Since water molecules attack amide-amide hydrogen bonds and break up secondary structure, a disulfide bond stabilizes secondary structure in its vicinity. For example, researchers have identified several pairs of peptides that are unstructured in isolation, but adopt stable secondary and tertiary structure upon forming a disulfide bond between them.

tag: ol

text: A disulfide species is a particular pairing of cysteines in a disulfide-bonded protein and is usually depicted by listing the disulfide bonds in parentheses, e.g., the "(26–84, 58–110) disulfide species". A disulfide ensemble is a grouping of all disulfide species with the same number of disulfide bonds, and is usually denoted as the 1S ensemble, the 2S ensemble, etc. for disulfide species having one, two, etc. disulfide bonds. Thus, the (26–84) disulfide species belongs to the 1S ensemble, whereas the (26–84, 58–110) species belongs to the 2S ensemble. The single species with no disulfide bonds is usually denoted as R for "fully reduced". Under typical conditions, disulfide reshuffling is much faster than the formation of new disulfide bonds or their reduction; hence, the disulfide species within an ensemble equilibrate more quickly than between ensembles.

text: The native form of a protein is usually a single disulfide species, although some proteins may cycle between a few disulfide states as part of their function, e.g., thioredoxin. In proteins with more than two cysteines, non-native disulfide species may be formed, which are almost always misfolded. As the number of cysteines increases, the number of nonnative species increases factorially.

text: Predicting disulfide abundance[edit]

text: The number of ways i in which p disulfide bonds can be formed from n cysteine residues present in a protein is given by the formula

text: Here,

text: The above formula is the most general relation which can be used to calculate the number of possible disulfide bond isomers (or connectivities) when n is either even or odd, and when all or only some of the cysteines are involved in the formation of disulfide bonds.

text: However, many of the naturally occurring proteins that have disulfide bonds possess an even number of cysteines with all of the cysteines participating in the formation of disulfide bonds. For this specific case, n is an even number and p is equal to n/2. Substituting the value of p, the above formula for the possible number of disulfide bond connectivities simplifies to:

text: For this particular case (n is even and all cysteines form disulfide bonds), a formula which is more easier to remember is given by:

text: Both of the above relations hold good for the proteins which have an even number of cysteines and all the cysteines are involved in the formation of disulfide bonds. Both of the above formulae are derived using the same logic and essentially represent a simplification of the same starting formula.

text: As a specific example for the above case, an eight-cysteine protein such as ribonuclease A can form 105 different four-disulfide species when all the cysteines are involved in the formation of disulfide bonds. Here n = 8 and p = 4.

text: So, here

text: Only one of the 105 possible isomers is the native disulfide species. Isomerases have been identified that catalyze the interconversion of disulfide species, accelerating the formation of the native disulfide species.

text: Disulfide species that have only native disulfide bonds (but not all of them) are denoted by "des" followed by the lacking native disulfide bond(s) in square brackets. For example, the des[40–95] disulfide species has all the native disulfide bonds except that between cysteines 40 and 95. Disulfide species that lack one native disulfide bond are frequently folded, in particular, if the missing disulfide bond is exposed to solvent in the folded, native protein.

text: In order to analyze the structure of proteins, it is often necessary to break disulfide bonds. This reduction of disulfide bonds can be accomplished by treatment with 2-mercaptoethanol, dithiothreitol, or tris(2-carboxyethyl)phosphine.

text: In bacteria and archaea[edit]

text: Disulfide bonds play an important protective role for bacteria as a reversible switch that turns a protein on or off when bacterial cells are exposed to oxidation reactions. Hydrogen peroxide (H2O2) in particular could severely damage DNA and kill the bacterium at low concentrations if not for the protective action of the SS-bond. Archaea typically have fewer disulfides than higher organisms.[11]

text: In eukaryotes[edit]

text: In eukaryotic cells, in general, stable disulfide bonds are formed in the lumen of the RER (rough endoplasmic reticulum) and the mitochondrial intermembrane space but not in the cytosol. This is due to the more oxidizing environment of the aforementioned compartments and more reducing environment of the cytosol (see glutathione). Thus disulfide bonds are mostly found in secretory proteins, lysosomal proteins, and the exoplasmic domains of membrane proteins.

text: There are notable exceptions to this rule. For example, many nuclear and cytosolic proteins can become disulfide-crosslinked during necrotic cell death.[12] Similarly, a number of cytosolic proteins which have cysteine residues in proximity to each other that function as oxidation sensors or redox catalysts; when the reductive potential of the cell fails, they oxidize and trigger cellular response mechanisms. The virus Vaccinia also produces cytosolic proteins and peptides that have many disulfide bonds; although the reason for this is unknown presumably they have protective effects against intracellular proteolysis machinery.

text: Disulfide bonds are also formed within and between protamines in the sperm chromatin of many mammalian species.

text: Disulfides in regulatory proteins[edit]

text: As disulfide bonds can be reversibly reduced and re-oxidized, the redox state of these bonds has evolved into a signaling element. In chloroplasts, for example, the enzymatic reduction of disulfide bonds has been linked to the control of numerous metabolic pathways as well as gene expression. The reductive signaling activity has been shown, thus far, to be carried by the ferredoxin thioredoxin system, channeling electrons from the light reactions of photosystem I to catalytically reduce disulfides in regulated proteins in a light dependent manner. In this way chloroplasts adjust the activity of key processes such as the Calvin–Benson cycle, starch degradation, ATP production and gene expression according to light intensity.

text: In hair and feathers[edit]

text: Over 90% of the dry weight of hair comprises proteins called keratins, which have a high disulfide content, from the amino acid cysteine. The robustness conferred in part by disulfide linkages is illustrated by the recovery of virtually intact hair from ancient Egyptian tombs. Feathers have similar keratins and are extremely resistant to protein digestive enzymes. Different parts of the hair and feather have different cysteine levels, leading to harder or softer material. Manipulating disulfide bonds in hair is the basis for the permanent wave in hairstyling. Reagents that affect the making and breaking of S−S bonds are key, e.g., ammonium thioglycolate. The high disulfide content of feathers dictates the high sulfur content of bird eggs. The high sulfur content of hair and feathers contributes to the disagreeable odor that results when they are burned.

text: Inorganic disulfides[edit]

text:
The disulfide anion is S2−
2, or −S−S−. Sulfur is usually assigned to the reduced oxidation number −2, described as S2− and called sulfide. It has the electron configuration of a noble gas (argon). In disulfide, sulfur is only reduced to a state with oxidation number −1. Its configuration then resembles that of a chlorine atom. It thus tends to form a covalent bond with another S− center to form S2−
2 group. Oxygen also behaves similarly, e.g. in peroxides such as H2O2. Examples:

text:
Iron disulfide (FeS2), e.g. the mineral pyrite (V(S2)2 — patronite).
Disulfur dichloride (S2Cl2), a distillable liquid.

text: In industry[edit]

text: Disulfide and (polysulfide) bonds are the crosslinking groups that result from the vulcanization of rubber. In analogy to the role of disulfides in proteins, the S−S linkages in rubber are crosslinkers, and strongly affect the rheology of the material.

text: Related compounds[edit]

text: Thiosulfoxides are orthogonally isomeric with disulfides, having the second sulfur branching from the first and not partaking in a continuous chain, i.e. >S=S rather than −S−S−.

text: Disulfide bonds are analogous but more common than related peroxides and diselenide bonds. Intermediate compounds of these also exist, for example, thioperoxides, also known as oxaulfide bonds, have formula R1OSR2 (equivalently R2SOR1). These are isomeric to sulfoxides in a similar manner to the above; i.e. >S=O rather than −S−O−.

text: Thiuram disulfides, with the formula (R2NCSS)2, are disulfides but they behave distinctly because of the thiocarbonyl group.

text: Compounds with three sulfur atoms, such as CH3S−S−SCH3, are called trisulfides, or trisulfide bonds.

text: Misnomers[edit]

text: Disulfide is also used to refer to compounds that contain two sulfide (S2−) centers. The compound carbon disulfide, CS2 is described with the structural formula i.e. S=C=S. This molecule is not a disulfide in the sense that it lacks a S-S bond. Similarly, molybdenum disulfide, MoS2, is not a disulfide in the sense again that its sulfur atoms are not linked.

text:
CS2

MoS2