Hinokitiol

Key takeaways

Hinokitiol belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hinokitiol to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hinokitiol from memory before moving on to harder problems.

Reference excerpt

Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive used in Japan.

History Hinokitiol was discovered by a Japanese chemist Tetsuo Nozoe in 1936. It was isolated from the essential oil component of the heartwood Taiwanese hinoki, from which the compound ultimately adopted its name. Hinokitiol is the first non-benzenoid aromatic compound identified. The compound has a heptagonal molecular structure and was first synthesized by Ralph Raphael in 1951. Due to its iron-chelating activity, hinokitiol has been called an "Iron Man molecule" in the scientific media, which is ironic because Tetsuo is translated into English as "Iron Man". Taiwanese hinoki is native to East Asian countries, particularly to Japan and Taiwan. Hinokitiol has also been found in other trees of the Cupressaceae family, including Thuja plicata Donn ex D. Don which is common in the Pacific Northwest. Woods that are rich in hinokitiol were used by people of ancient Japan for creating long-standing buildings, such as the Konjiki-dō, a japanese national treasure, one of the buildings of Chūson-ji complex, a temple in Iwate Prefecture. It kept it from harm against insects, wood-rotting fungi, and molds for a long time of about 840 years. Additionally, there are some old famous Buddhist temples and Shinto shrines using trees, later known to contain hinokitiol. Beginning in the 2000s, the biological properties of hinokitiol have become of research interest, focusing on its biological properties. And the resistance of cypress trees to wood decay was the leading reason prompting to study their chemical content and to find the substances responsible for those properties.

Natural occurrence Hinokitiol has been found in the heartwood of the conifer trees of the Cupressaceae family, including Chamaecyparis obtusa (Hinoki cypress), Thuja plicata (Western red cedar), Thujopsis dolabrata var. hondai (Hinoki asunaro), Juniperus cedrus (Canary Islands juniper), Cedrus atlantica (Atlas cedar), Cupressus lusitanica (Mexican white cedar), Chamaecyparis lawsoniana (Port Orford cedar), Chamaecyparis taiwanensis (Taiwan cypress), Chamaecyparis thyoides (Atlantic white cedar), Cupressus arizonica (Arizona cypress), Cupressus macnabiana (MacNab cypress), Cupressus macrocarpa (Monterey cypress), Juniperus chinensis (Chinese juniper), Juniperus communis (Common juniper), Juniperus californica (California juniper), Juniperus occidentalis (Western juniper), Juniperus oxycedrus (Cade), Juniperus sabina (Savin juniper), Calocedrus decurrens (California incense-cedar), Calocedrus formosana (Taiwan incense-cedar), Platycladus orientalis (Chinese thuja), Thuja occidentalis (Northern white-cedar), Thuja standishii (Japanese thuja), Tetraclinis articulata (Sandarac). Its concentration in the trees are 0.1-0.2% in Chamaecyparis taiwanensis (2 mg of hinokitiol per 1 g of dry sawdust), 0.04% in Juniperus cedrus and Thujopsis dolabrata var. hondai (0.4 mg of hinokitiol per 1 g of dry sawdust), and 0.02% in Chamaecyparis obtusa (0.2 mg of hinokitiol per 1 g of dry sawdust). There are three naturally found thujaplicins: α-thujaplicin, β-thujaplicin (hinokitiol) and γ-thujaplicin. Hinokitiol is the most common isomer and it appears to be the only isomer that exerts all biological activities attributed to thujaplicins.

Chemical synthesis There are different pathways to synthesize thujaplicins. Hinokitiol, as other thujaplicins, can be synthesized by cycloaddition of isopropylcyclopentadiene and dichloro ketene, 1,3-dipolar cycloaddition of 5-isopropyl-1-methyl-3-oxidopyridinium, ring expansion of 2-isopropylcyclohexanone, regiocontrolled hydroxylation of oxyallyl (4+3) cycloadducts, regioselectively from (R)-(+)-limonene, and from troponeirontricarbonyl complex. Hinokitiol can also be isolated through plant cell suspension cultures, or readily extracted from the wood with chemical solvents and ultrasonication. (1) Synthesis of hinokitiol from troponeirontricarbonyl complex:

(2) Synthesis of hinokitiol by electro-reductive alkylation of substituted cycloheptatrienes:

(3) Synthesis of hinokitiol through ring expansion of 2-isopropylcyclohexanone:

(4) Synthesis of hinokitiol through oxyallyl cation [4+3] cyclization (Noyori's synthesis):

Chemistry Hinokitiol is a tropolone derivative containing an unsaturated seven-membered carbon ring. It is a monoterpenoid – cyclohepta-2,4,6-trien-1-one substituted by a hydroxy group at position 2 and an isopropyl group at position 4. It is a enol and a cyclic ketone. It derives from a hydride of a cyclohepta-1,3,5-triene. Thujaplicins are soluble in organic solvents and aqueous buffers. Hinokitiol provides acetone on vigorous oxidation and gives the saturated monocyclic diol upon catalytic hydrogenation. It is stable to alkali and acids, forming salts or remaining unchanged, but does not convert to catechol derivatives. Hinokitiol, as other thujaplicins and tropolones, reversibly binds metal ions. It forms complex salts with metal ions.

Ionophore

Hinokitiol, as other tropolones, reversibly binds metal ions (i.e. Zn2+, Fe2+, Cu2+, Co2+, Mn2+, Ag2+) and form complex salts. It is considered as a broad-spectrum metallophore, and an efficient iron-chelating agent. The iron complex with hinokitiol with the formula (C10H11O2)3Fe is called hinokitin. Hinoki oil is rich in hinokitin which has an appearance of dark red crystals. The complexes made of iron and tropolones display high thermodynamic stability and has shown to have a stronger binding constant than the transferrin-iron complex. It is believed that metal-binding activity may be the principal mechanism of action underlying the most part of its biological activities, especially binding iron, zinc, and copper ions. By binding different metal ions and serving as an ionophore, it accelerates the intracellular uptake of those ions and increases their intracellular levels, thus influencing on different biological activities. It is shown that a synergistic effect in some biological activities and settings may occur when ionophores are combined with the ions they bind. As an ionophore, its molecule has an hydrophilic center and a hydrophobic part. The hydrophobic part interacts with biological membranes. The hydrophilic center binds metal ions and form ionophore-ion complexes.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Hinokitiol

Start with the simplest possible case. Write down what Hinokitiol claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hinokitiol before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hinokitiol ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hinokitiol

In research: Hinokitiol appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hinokitiol in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hinokitiol is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chelating agents, Food additives, Ionophores, so understanding it makes those chapters shorter.
In everyday life: Look for Hinokitiol outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Hinokitiol in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hinokitiol means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hinokitiol out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hinokitiol in simple terms?

Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins.

Why does Hinokitiol matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hinokitiol?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hinokitiol.