ionized to give the ion H 2 PO 2
– . The
acid and its salts are readily oxidized
to the orthophosphate and consequently are good reducing agents.
phosphite See phosphonic acid.
phosphodiester bond The covalent bond that links a phosphate
group and a sugar group, by means
of an oxygen bridge, in the sugar–
phosphate backbone of a nucleic acid
molecule. See dna.
phosphoglyceric acid (PGA;
3-phosphoglycerate) See glycerate
3-phosphate.
phospholipids (phosphatides) A
group of lipids having both a phosphate group and one or more fatty
acids. Glycerophospholipids (or phosphoglycerides) are based on *glycerol; the three hydroxyl groups are
esteriÜed with two fatty acids and a
phosphate group, which may itself
be bound to one of a variety of simple organic groups (see illustration).
Sphingolipids are based on the alcohol sphingosine and contain only one
fatty acid linked to an amino group.
With their hydrophilic polar phosphate groups and long hydrophobic
hydrocarbon ‘tails’, phospholipids
readily form membrane-like structures in water. They are a major component of cell membranes.
phosphonate See phosphonic
acid.
phosphonic acid (phosphorous
acid; orthophosphorous acid) A
colourless to pale-yellow deliquescent crystalline solid, H 3 PO 3 ; r.d.
1.65; m.p. 73.6°C; decomposes at
200°C; very soluble in water and soluble in alcohol. Phosphonic acid may
be crystallized from the solution obtained by adding ice-cold water to
phosphorus(III) oxide or phosphorus
trichloride. The structure of this material is unusual in that it contains
one direct P–H bond and is more correctly written (HO) 2 HPO. The acid is
dibasic, giving rise to the ions H 2 PO 3
–
and HPO 3
2– (phosphonates; formerly
phosphites), and has moderate reducing properties. On heating it gives
phosphine and phosphoric(V) acid.
phosphonium ion The ion PH 4
+ ,
or the corresponding organic derivatives of the type R 3 PH
+ , RPH 3
+
. The
phosphonium ion PH 4
+ is formally
analogous to the ammonium ion
NH 4
+ but PH 3 has a much lower proton afÜnity than NH 3 and reaction of
PH 3 with acids is necessary for the
production of phosphonium salts.
phosphonium salts See phosphonium ion.
phosphor A substance that is ca411
phosphor
p
O
H 3 C
H 3 C
C
H
C
H
O
fatty acid
fatty acid
glycerol
phosphate group
choline
H 2 C
O
O
–
CH 3
CH 3
CH 3
(CH 2 ) 14
(CH 2 ) 14
(CH 2 ) 14 C C C
O O O CH 2
CH 2
CH 2
(CH 2 ) 7
(CH 2 ) 7
(CH 2 ) 7
(CH 2 ) 7
(CH 2 ) 7
(CH 2 ) 7
C C C
O O O C C C H H H
O O O
O O O
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2 N N N
P P P
Structure of phosphatidylcholine (lecithin), a glycerophospholipid
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– . The
acid and its salts are readily oxidized
to the orthophosphate and consequently are good reducing agents.
phosphite See phosphonic acid.
phosphodiester bond The covalent bond that links a phosphate
group and a sugar group, by means
of an oxygen bridge, in the sugar–
phosphate backbone of a nucleic acid
molecule. See dna.
phosphoglyceric acid (PGA;
3-phosphoglycerate) See glycerate
3-phosphate.
phospholipids (phosphatides) A
group of lipids having both a phosphate group and one or more fatty
acids. Glycerophospholipids (or phosphoglycerides) are based on *glycerol; the three hydroxyl groups are
esteriÜed with two fatty acids and a
phosphate group, which may itself
be bound to one of a variety of simple organic groups (see illustration).
Sphingolipids are based on the alcohol sphingosine and contain only one
fatty acid linked to an amino group.
With their hydrophilic polar phosphate groups and long hydrophobic
hydrocarbon ‘tails’, phospholipids
readily form membrane-like structures in water. They are a major component of cell membranes.
phosphonate See phosphonic
acid.
phosphonic acid (phosphorous
acid; orthophosphorous acid) A
colourless to pale-yellow deliquescent crystalline solid, H 3 PO 3 ; r.d.
1.65; m.p. 73.6°C; decomposes at
200°C; very soluble in water and soluble in alcohol. Phosphonic acid may
be crystallized from the solution obtained by adding ice-cold water to
phosphorus(III) oxide or phosphorus
trichloride. The structure of this material is unusual in that it contains
one direct P–H bond and is more correctly written (HO) 2 HPO. The acid is
dibasic, giving rise to the ions H 2 PO 3
–
and HPO 3
2– (phosphonates; formerly
phosphites), and has moderate reducing properties. On heating it gives
phosphine and phosphoric(V) acid.
phosphonium ion The ion PH 4
+ ,
or the corresponding organic derivatives of the type R 3 PH
+ , RPH 3
+
. The
phosphonium ion PH 4
+ is formally
analogous to the ammonium ion
NH 4
+ but PH 3 has a much lower proton afÜnity than NH 3 and reaction of
PH 3 with acids is necessary for the
production of phosphonium salts.
phosphonium salts See phosphonium ion.
phosphor A substance that is ca411
phosphor
p
O
H 3 C
H 3 C
C
H
C
H
O
fatty acid
fatty acid
glycerol
phosphate group
choline
H 2 C
O
O
–
CH 3
CH 3
CH 3
(CH 2 ) 14
(CH 2 ) 14
(CH 2 ) 14 C C C
O O O CH 2
CH 2
CH 2
(CH 2 ) 7
(CH 2 ) 7
(CH 2 ) 7
(CH 2 ) 7
(CH 2 ) 7
(CH 2 ) 7
C C C
O O O C C C H H H
O O O
O O O
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2 N N N
P P P
Structure of phosphatidylcholine (lecithin), a glycerophospholipid
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