Sodium dodecyl sulfate : A very useful surfactant for Scientific Invetigations

Sodium dodecyl sulfate  is most researched and best understood widely used anionic  surfactant. It is  obtained in  a state of  powder as  well as  in pellet  and used  in Polymer  Biotechnology and Biochemistry. This review article is related to present and future uses of sodium dodecylsulphate in different applied fields. The critical micelle concentration (cmc) of Sodium dodecylsulphate changes with change in temperature and addition of electrolyte. It causes skin and eye irritation in higher concentration but such effect decreases with decrease in concentration and widely used as cleaning agent and house hold products.

Introduction 

The most common sulphate surfactant is sodium dodecylsulphate  (SDS)      probably  most  extensively studied  anionic  surfactant  known  to  science  [Warra: 2013].  It  is  sometimes  referred  to  as  sodium laurylsulphate  (SLS).  It  is  an  organic  compound commercially found in the form of Powder or Pellet. It is found that pellet form  is more  soluble in water  and less toxic than the powder form. Like all detergents it removes oils from the skin and can cause skin and eye irritation in higher concentration. If the concentration is less than 1%, it's such carcinogenic character decreases. It's cmc in pure water at 250C is 0.0082M  [Mukerjee  and Mysels:1971] and  the  aggregation  number  at  this  concentration  is usually  considered  to  be  about  62  [Turro  and Yekta:1978]. If  any electrolyte is  added to  a solution of SDS or temperature or pressure changes, the aggregation behavior  of  SDS affected.  For example,  when chloride, acetate and propionate co-ions are added to  the aqueous solution of SDS, then the value of cmc affected.  Acetate, propionate and  butyrate do  not have any effect on  the  cmc  of  SDS.  Butyrate  ion,  however,  shows influence  on  the  adsorption  behaviour  and  aggregation number  of  SDS.  Thus,  co-ion  with  up  to  four  carbon atoms  does  not  affect  the  cmc  of  SDS.  Further investigation  is  required  to  ascertain  the  minimum number  of  carbon  atoms  required  in  the  co-ion  for showing    the  influence  on  cmc  of  SDS  [Umlong  and Ismail : 2006]. 

As other surfactants sodium dodecylsulphate has an amphiphilic molecule that is contained hydrophilic and hydrophobic  moiety.  Research showed  that SDS  is not carcinogenic  when  either  applied  directly  to  skin  or consumed [CIR: 1983].The micelle ionization fraction (α) of  SDS  is  around  30%[Barney  et.al:  1998].  Molecular weight is 288.5 and micelle molecular weight is 18000g. SDS can be prepared by reacting dodecanol with sulfuric acid  and  reacting  the  products  with  sodium  hydroxide [Warra: 2013]. The reactions are given below:

It  can  also  prepared  by  neutralization  of  Dodecane (Dodecyl) Sulfuric acid  ester with  Caustic alkali[Warra: 2013]. 

Molecular formula of SDS is C12H 22SO4Na.  Structure of SDS can be represented as follows:

SDS  is  an organosulfate  compound consisting  of  a  12-carbon  chain  as tail  attached  to  a sulfate group,  having head  and  tail  the  amphiphilic properties  required  for a detergent[ Singh:2012]. 

It  has  been  found  that  SDS  acts as irritate   to skin of the face with for constant exposure  to long  time (more  than  an  hour)  in  young  adults  [Marrakchi  and Maibach: 2006]. SDS may cause chronic skin problems in individuals with chronic skin hypersensitivity, such affect is more in some people than others [Agner: 1991; Nassif et.al: 1994; Löffler and Effendy: 1999]. In animal studies SDS  appears  to cause  skin and  eye  irritation. SDS can contact  the  face  from  aerosolized  dust  during  SDS preparation  for laboratory  purposes. To  prevent contact with  face  and  eyes,  a dust  free  “pellet”  form of  SDS is available  which  essentially  eliminates  SDS  dust inhalation  and  contact  with  the  face.  Sodium dodecylsulphate is extensively used both for fundamental studies as well as in many industrial applications [Tadros: 2005].  SDS  is  mainly  used  in  detergents  for  laundry with  many  cleaning  applications[Smulders  et.al:  2002]. SDS  is  a highly  effective surfactant and  is  used in  any task  requiring  the  removal  of  oily  stains  and residues[Devesa-Rey et.al: 2011].  Surfactants such as SLS are also found in ointments and creams  as  well  as  in  cleansers  [Chhetri  et.al:  Healthy Health  Products].  Sodium  dodecylsulfate  is  used  in household and car cleaning products because of its ability to  produce  foam, cut  through  grease,  and suspend  soil particles  in such a way so that they can easily be washed away[Warra: 2013]. 

Walker  et.al:2005  studied  the acute  and  short-term  toxicity  in  rats  that  have  been  made  on  the surfactants sodium lauryl sulphate,  sodium lauryl (3EO) ethoxysulphate and their matches C12–C15 alcohol sodium sulphate  and  C12–C15  alcohol  sodium  (3EO) ethoxysulphate.  The  acute  oral  LD50s  of  the  four materials  were  found  to  range  from  1 to  2  g/kg.  This clearly indicates the toxicity level of sodium lauryl sulfate (SLS). SLS is reported to be a strong oxidizing agent and is a highly toxic compound. This causes respiratory, eye and skin irritation. Carcinogenic nitrates can form in the manufacturing of SLS or by its inter reaction  with other nitrogen bearing ingredients  which show permanent eye damage in young  animals from  skin contact  in non  eye areas. The studies indicated that SLS enters and maintains the residual levels in the heart, the liver, the lungs and the brain from skin contact. This poses a serious health threat by its use in shampoos, cleansers, and tooth pastes. SLS is used  in  almost  all  health  products  including  soaps, shampoos, bubble baths,  tooth paste, washing up  liquid, Laundry  detergent,  children  soaps  and  shampoos  stain remover, carpet cleaner, fabric glue, body wash, shaving cream, mascara, mouth wash, skin cleanser, moisturizing lotion and sun screen. 

A clinical study found SLS toothpaste caused a higher  frequency  of  aphthous  ulcers  than  both cocoamidopropyl betaine or a detergent-free paste, on 30 patients  with  frequent  occurrences  of  such ulcers[Herlofson  and  Barkvoll:1996].  A  clinical  study comparing toothpastes with and without SLS found that it had  no  significant  effect  on  ulcer  patterns[  Healy et.al:1999].SDS is  commonly  used  in preparing proteins for  electrophoresis in  the  SDS-PAGE technique[Olędzka et.al:2012]. SDS is a powerful anionic detergent that binds tightly to proteins, denaturing  them fully at elevated temperature (100°C) in the presence of a reducing  agent  like  mercaptoethanol.  Multi-subunit proteins (whose subunits are noncovalently associated or covalently  attached  by  disulfide  bonds)  are  dissociated into monomeric units by the combined action of SDS and a reducing agent at elevated temperature. So  much SDS binds  to  a  protein  that  the  protein’s  intrinsic  charge  is overwhelmed  by  the  bound  SDS[Ward  and  Swiatek: 2009].

Sodium  dodecylsulfate  is  also  used  in  the  analysis of hemoglobin  [Oshiro  et.al:1982].  Sodium dodecylsulfate (SDS) appears more effective than Triton X-100 for removing nuclei from dense tissues and organs such  as  the  kidney and  temporomandibular  joint  while preserving  tissue  mechanics  [Nakayama et.al: 2010; Lumpkins et.al: 2008]. 

The  addition  of a  detergent  such  as  SDS to  a decellularization  protocol  can  make  the  difference between  complete  and  incomplete  cell  nuclei  removal [Yang  et.al: 2010].  Sodium  laurylsulfate  temporarily diminishes perception  of sweetness  [Michael: 1985],  an effect commonly  observed after recent  use of toothpaste containing this ingredient [Josh: Discovery Health]. SDS represent  an  effective    microbicide,  it  can  inhibit  and prevent  infection  by  various enveloped and  non-enveloped viruses such  as  the Herpes  simplex  viruses, HIV, and the Semliki Forest Virus[Piret et.al: 2001]. SDS is  used  in  Biotechnology  for  numerous  applications [Angerhofer and Pezzuto: 1993].