Why is glycine a buffer?

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Physiological Buffer

pH Buffering

Sample Preparation

BioAssays

Misc

Cell/Culture/Growth Media

Gel Electrophoresis

Citrate Buffer (pH 3.0 to 6.2)

Acetate Buffer (pH 3.6 to 5.6)

Tris Buffer (1 M, pH 7.2)

Citrate Buffer (0.1 M, pH 6.0)

Acetate Buffer (0.1 M, pH 5.0)

Phosphate Buffer (pH 5.8 to 7.4)

Hydrochloric Acid-Potassium Chloride Buffer (0.1 M, pH 2.0)

Glycine-HCl Buffer (0.1 M, pH 3.0)

Citrate-Phosphate Buffer (0.15 M, pH 5.0)

Glycine-Sodium Hydroxide Buffer (0.08 M, pH 10)

EBSS (magnesium, calcium, phenol red) (pH 7.0)

Imidazole-HCl Buffer (0.05 M, pH 7.0)

Trizma® Buffer (pH 7.0 to 9.2)

MES (0.5 M, pH 6)

Bis-Tris Buffer (1 M, 6.5 pH)

ADA Buffer (0.5 M, 6.6 pH)

ACES Buffer (0.1 M, 6.7 pH)

PIPES Buffer (1 M, 6.8 pH)

MOPSO Buffer (0.5 M, 6.9 pH)

BES-Buffered Saline (2X) (0.05 M, pH 6.95)

TES Buffer (1 M, 7.5 pH)

MOPS Buffer (10X) (0.2 M, pH 7)

SSC buffer (20X) (3 M, pH 7)

TBS (1 M, pH 7.4)

Bicine (1 M, pH 8.26)

Tricine (1 M, pH 8.05)

TAE (1 M, pH 8.6)

CAPS (0.5 M, pH 10.4)

HEPPSO (1 M, pH 7.85)

CHES (0.5 M, pH 9.5)

Potassium Phosphate (pH 5.8 to 8.0)

Diethanolamine (1 M, pH 9.8)

Sodium Borate Buffer (1 M, pH 8.5)

Maleic Acid (1 M, pH 7.5)

Tris-Buffered Saline (TBS, 0.1 M)

Ammonium Sulfate, Saturated

Potassium Phosphate Buffer (1 M, pH 6.5)

Citrate-Phosphate Buffer (110 mM, pH 5.6)

Citrate-Phosphate Buffer (40 mM, pH 5.6)

Sodium Phosphate Solution

Sodium Acetate (3 M, pH 5.2)

TB Buffer

Tris-citrate Buffer (pH 8.0)

Borate Buffer

Glycine (0.1 M, pH 2.2)

Ammonium Bicarbonate (50 mM, pH 7.8)

Ammonium Acetate

Carbonate-Bicarbonate Buffer (pH 9.2 to 10.6)

Sodium Iodide/Sodium Sulfite Solution

Dithiothreitol (DTT) (1 M)

An amino acid can act as a buffer because it can react with added acids and bases to keep the pH nearly constant.

The general formula of an amino acid is #"H"_2"NCHRCOOH"#, where #"R"# is a side chain characteristic of each amino acid.

Because an amino acid has both an acidic group (#"COOH"#) and a basic group
(#"NH"_2#), it can act as both an acid and a base.

In very acidic media, the #"NH"_2# group is in the protonated form, and in very basic media, the #"COOH"# group is in the deprotonated form.

At an intermediate pH (the isoelectric point, pI), both ends are in their ionic form.

In glycine, the #"COOH"# group has #"p"K_text(a1) = 2.34#, and the #"H"_3"N"^"+"# group has #""K_text(a2) = 9.60#.

At the isoelectric point, #"p"I = ("p"K_text(a1) + "p"K_text(a2))/2 = 5.97#

#underbrace("H"_3 stackrelcolor(blue)(+)("N")"CHRCOOH")_color(red)("At low pH") ⇌ underbrace("H"_3 stackrelcolor(blue)(+)("N")"CHRCOO"^"-")_color(red)("At pI") ⇌ underbrace("H"_2"NCHRCOO"^"-")_color(red)("At high pH")#

Amino acids have characteristic titration curves.

For example, the titration curve for glycine looks like this:

At #"pH 2.34"#, we have equal amounts of the weak base #"RNH"_2# and its conjugate acid #"RNH"_3^"+"#.

A #"pH 9.60"#, we have equal amounts of the weak acid #"RCOOH"# and its conjugate base #"RCOO"^"-"#.

A mixture of a weak acid and its conjugate base is a buffer

In both regions, we can add small amounts of acid or base, and the pH will not change much.

Thus, an amino acid has two regions in which it can act as a buffer.

The buffer regions for glycine are pH 1.3 to pH 3.3 and from pH 8.6 to pH 10.6

Previous studies have established that the selective precipitation of a less soluble buffer component during freezing can induce a significant pH shift in the freeze concentrate. During freezing of sodium phosphate solutions, crystallization of the disodium salt can produce a pH decrease as great as 3 pH units which can dramatically affect protein stability. The objective of our study was to determine how the presence of glycine (0-500 mM), a commonly used bulking agent in pharmaceutical protein formulations, affects the pH changes normally observed during freezing in sodium phosphate buffer solutions and to determine whether these pH changes contribute to instability of model proteins in glycine/phosphate formulations. During freezing in sodium phosphate buffers, the presence of glycine significantly influenced the pH. Glycine at the lower concentrations (< or = 50 mM) suppressed the pH decrease normally observed during freezing in 10 and 100 mM sodium phosphate buffer, possibly by reducing the nucleation rate of salt and thereby decreasing the extent of buffer salt crystallization. The presence of glycine at higher concentration (> 100 mM) in the sodium phosphate buffer resulted in a more complete crystallization of the disodium salt as indicated by the frozen pH values closer to the equilibrium value (pH 3.6). Although high concentrations of glycine can facilitate more buffer salt crystallization and these pH shifts may prove to be potentially damaging to the protein, glycine, in its amorphous state, can also act to stabilize a protein via the preferential exclusion mechanism.

How can glycine act as a buffer at pH 6.00 and why? Please use chemical equations to show how it can act as a buffer at this pH specifically?

My work:

At pH 6.00 glycine acts as a buffer, because at pH 6.00 the condition is acidic and glycine is an amino acid, so its zwitterion forms an equilibrium, which means there is a positive charge on the N of the amino group and a negative charge on the carboxylate. So there are no sudden pH changes and we know buffer solutions resist sudden pH changes, so at pH 6.00 glycine acts as a buffer solution.

Equation:

What I need explained:

HOW does glycine act as a buffer at pH 6.00 with chemical equations, meaning to show an example of how it specifically buffers another species at pH 6.00 with the proper chemical equations.

Q&A Why

Why is glycine a buffer?

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