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The topology of the G-quadruplex structure can be determined by monitoring the positive or negative circular dichroism (CD) signals at specific wavelengths. [88] Parallel G-quadruplexes have negative and positive CD signals at 240 and 262 nm, respectively, whereas antiparallel G-quadruplexes place these signals at 262 and 295 nm, respectively.
The melting temperature of TBA's G-quadruplex (measuring the intensity change of the peak at 295 nm by CD) in the presence of sodium ion and potassium are 24 °C and 53 °C, respectively. [7] Compared with sodium, potassium ion fits perfectly to the cavity between two G-tetrad plane and is coordinately bound to four O6 atoms in each plane.
Circular dichroism (CD) is dichroism involving circularly polarized light, i.e., the differential absorption of left- and right-handed light. [1] [2] Left-hand circular (LHC) and right-hand circular (RHC) polarized light represent two possible spin angular momentum states for a photon, and so circular dichroism is also referred to as dichroism for spin angular momentum. [3]
Negative super helicity assists in the formation of i-motifs under physiological conditions. [32] The formation of both G-quadruplex and i-motifs occurred at neutral pH when G-quadruplex and i-motif forming sequences of the c-MYC oncogene promoter were placed into a supercoiled plasmid, inducing super helicity of both structures.
G-quadruplexes, also known as G4 DNA are secondary structures found in nucleic acids that are rich in guanine. [1] These structures are normally located at the telomeres (the ends of the chromosomes). The G-quadruplex can either be parallel or antiparallel depending on the loop configuration, which is a component of the structure.
In molecular biology, a guanine tetrad (also known as a G-tetrad or G-quartet) is a structure composed of four guanine bases in a square planar array. [ 1 ] [ 2 ] They most prominently contribute to the structure of G-quadruplexes , where their hydrogen bonding stabilizes the structure.
The CD nomenclature was proposed and established in the 1st International Workshop and Conference on Human Leukocyte Differentiation Antigens (HLDA), held in Paris in 1982. [4] [5] This system was intended for the classification of the many monoclonal antibodies (mAbs) generated by different laboratories around the world against epitopes on the surface molecules of leukocytes (white blood cells).
The canonical Watson-Crick base pairs, G:C and A:T/U as well as most of the non-canonical ones are stabilized by two or more (e.g. 3 in the case of G:C cWW) hydrogen bonds. Justifiably, a significant amount of research on non-canonical base pairs has been carried out towards bench-marking their strengths (interaction energies) and (geometric ...