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Linear dichroism

Linear dicrosim (LD) is also a very closely related technique to CD in which the difference between absorbance of perpendicularly and parallelly polarized light is measured. In this technique the plane of polaliration of light does not rotate. LD is used to determine the orientation of absorbing parts in space.

Advantages and limitations of cd

Just like any other instrument CD has its strengths and limits. The comparison between CD and NMR shown in [link] gives a good sense of capabilities of CD.

A comparison of CD spectroscopy to NMR spectroscopy.
CD NMR
Molecules of any size can be studied There is size limitation
The experiments are quick to perform; single wavelength measurements require milliseconds. This is not the case all of the time.
Unique sensitivity to asymmetry in sample’s structure. Special conditions are required to differentiate between enantiomers.
Can work with very small concentrations, by lengthening the cuvette width until discernable absorption is achieved. There is a limit to sensitivity of instrument.
Timescale is much shorter (UV) thus allowing to study dynamic systems and kinetics. Timescale is long, use of radio waves gives average of all dynamic systems.
Only qualitative analysis of data is possible. Quantitative data analysis can be performed to estimate chemical composition.
Does not provide atomic level structure analysis Very powerful for atomic level analysis, providing essential information about chemical bonds in system.
The observed spectrum is not enough for claiming one and only possible structure The NMR spectrum is key information for assigning a unique structure.

What kind of data is obtained from cd?

One effective way to demonstrate capabilities of CD spectroscopy is to cover the protein secondary structure study case, since CD spectroscopy is well-established technique for elucidation of secondary structure of proteins as well as any other macromolecules. By using CD one can estimate the degree of conformational order (what percent of the sample proteins is in α-helix and/or β-sheet conformation), see [link] .

CD spectra of samples with representative conformaitons. Adapted by permission from N. Greenfield, Nat. Proto. , 2006, 1 , 6.

Key points for visual estimation of secondary structure by looking at a CD spectrum:

  • α-helical proteins have negative bands at 222 nm and 208 nm and a positive band at 193 nm.
  • β-helices have negative bands at 218 nm and positive bands at 195 nm.
  • Proteins lacking any ordered secondary structure will not have any peaks above 210 nm.

Since the CD spectra of proteins uniquely represent their conformation, CD can be used to monitor structural changes (due to complex formation, folding/unfolding, denaturation because of rise in temperature, denaturants, change in amino acid sequence/mutation, etc. ) in dynamic systems and to study kinetics of protein. In other words CD can be used to perform stability investigations and interaction modeling.

Cd instrument

[link] shows a typical CD instrument.

A CD instrument.

Protocol for collecting a cd spectrum

Described is a general procedure for data collection, options (time constant of instrument, wavelength interval, half-bandwidth) can be varied according to needs through the instrument controlling program.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
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advantages of NAA
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how I can reaction of mercury?
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Source:  OpenStax, Physical methods in chemistry and nano science. OpenStax CNX. May 05, 2015 Download for free at http://legacy.cnx.org/content/col10699/1.21
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