chemistry

Molecular logic gate

Molecular logic gate is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Molecular logic gate rather than just read about it. In short: A molecular logic gate is a molecule that performs a logical operation based on at least one physical or chemical inputs and a single output. The field has advanced from simple logic systems based on a single chemical or physical input to molecules capable of combinatorial and sequential operations such as arithmetic operations (i.e. moleculators and memory storage algorithms).

Key takeaways

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

Reference excerpt

A molecular logic gate is a molecule that performs a logical operation based on at least one physical or chemical inputs and a single output. The field has advanced from simple logic systems based on a single chemical or physical input to molecules capable of combinatorial and sequential operations such as arithmetic operations (i.e. moleculators and memory storage algorithms). Molecular logic gates work with input signals based on chemical processes and with output signals based on spectroscopic phenomena. Logic gates are the fundamental building blocks of computers, microcontrollers and other electrical circuits that require one or more logical operations. They can be used to construct digital architectures with varying degrees of complexity by a cascade of a few to several million logic gates, and are essentially physical devices that produce a singular binary output after performing logical operations based on Boolean functions on one or more binary inputs. The concept of molecular logic gates, extending the applicability of logic gates to molecules, aims to convert chemical systems into computational units. The field has evolved to realize several practical applications in fields such as molecular electronics, biosensing, DNA computing, nanorobotics, and cell imaging.

Working principle

For logic gates with a single input, there are four possible output patterns. When the input is 0, the output can be either a 0 or 1. When the input is 1, the output can again be 0 or 1. The four output bit patterns correspond to a specific logic type: PASS 0, YES, NOT, and PASS 1. PASS 0 and PASS 1 always outputs 0 and 1, respectively, regardless of input. YES outputs a 1 when the input is 1, and NOT is the inverse of YES – it outputs a 0 when the input is 1. AND, OR, XOR, NAND, NOR, XNOR, and INH are two-input logic gates. The AND, OR, and XOR gates are fundamental logic gates, and the NAND, NOR, and XNOR gates are complementary to AND, OR, and XOR gates, respectively. An INHIBIT (INH) gate is a special conditional logic gate that includes a prohibitory input. When the prohibitory input is absent, the output produced depends solely on the other input.

History and development One of the earliest ideas for the use of π-conjugated molecules in molecular computation was proposed by Ari Aviram from IBM in 1988.

The first practical realization of molecular logic was by de Silva et al. in their seminal work, in which they constructed a molecular photoionic AND gate with a fluorescent output. While a YES molecular logic gate can convert signals from their ionic to photonic forms, they are singular-input-singular-output systems. To build more complex molecular logic architectures, two-input gates, namely AND and OR gates, are needed. Some early works made some progress in this direction, but they could not realize a complete truth table as their protonated ionic forms could not bind to the substrate in every case. De Silva et al. constructed an anthracene-based AND gate made up of tertiary amine and benzo-18-crown-6 units, both of which were known to show photoinduced electron transfer (PET) processes. The two molecules acted as receptors that were connected to the anthracene-based fluorophore by alkyl spacers. The PET is quenched upon coordination with protons and sodium ions, respectively, for the two receptors, and would cause the anthracene unit to fluoresce.

Examples of molecular logic gates

YES molecular logic gate An example of a YES logic gate comprises a benzo-crown-ether connected to a cyano-substituted anthracene unit. An output of 1 (fluorescence) is obtained only when sodium ions are present in the solution (indicating an input of 1). Sodium ions are encapsulated by the crown ether, resulting in a quenching of the PET process and causing the anthracene unit to fluoresce.

AND molecular logic gate This molecular logic gate illustrates the advancement from redox-fluorescent switches to multi-input logic gates with an electrochemical switch, detecting the presence of acids. This two-input AND logic gate incorporates a tertiary amine proton receptor and a tetrathiafulvalene redox donor. These groups, when attached to anthracene, can simultaneously process information concerning the concentration of the acid and oxidizing ability of the solution.

OR molecular logic gate De Silva et al. constructed an OR molecular logic gate using an aza-crown ether receptor and sodium and potassium ions as the inputs. Either of the two ions could bind to the crown ether, causing the PET to be quenched and the fluorescence to be turned on. Since either of the two ions (input "1") could cause fluorescence (output "1"), the system resembled an OR logic gate.

INH molecular logic gate The INH logic gate incorporates a Tb3+ ion in a chelate complex. This two-input logic gate displays non-commutative behavior with chemical inputs and a phosphorescence output. Whenever dioxygen (input "1") is present, the system is quenched and no phosphorescence is observed (output "0"). The second input, H+, must also be present for an output "1" to be observed.

NAND molecular logic gate Parker and Williams constructed a NAND logic gate based on strong emission from a terbium complex of phenanthridine. When acid and oxygen (the two inputs) are absent (input "0"), the terbium center fluoresces (output "1").

NOR molecular logic gate Akkaya and coworkers demonstrated a molecular NOR gate using a boradiazaindacene system. Fluorescence of the highly-emissive boradiazaindacene (input "1") was found to be quenched in the presence of either a zinc salt [Zn(II)] or trifluoroacetic acid (TFA).

XOR and XNOR molecular logic gates

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Molecular logic gate

Start with the simplest possible case. Write down what Molecular logic gate 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 Molecular logic gate 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 Molecular logic gate 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 Molecular logic gate

In research: Molecular logic gate 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 Molecular logic gate 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: Molecular logic gate is common in secondary-school and first-year university syllabi. It links to neighbouring topics Logic gates, Molecular electronics, Molecular machines, so understanding it makes those chapters shorter.
In everyday life: Look for Molecular logic gate 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.

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How to study Molecular logic gate in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Molecular logic gate 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 Molecular logic gate out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Molecular logic gate in simple terms?

Why does Molecular logic gate 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 Molecular logic gate?

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 Molecular logic gate.