Membrane Media Create Small Nanospaces for Molecular Computation

A Tool, an App and a Field: Fluorescent PET Sensors, Blood Electrolyte Analysis and Molecular Logic as Products of Supramolecular Photoscience from Northern Ireland and Sri Lanka

The general tool of fluorescent PET (photoinduced electron transfer) sensors/switches - a molecular design principle with engineering features - is outlined, with the aid of frontier orbital energy diagrams. Fluorophores such as anthracene, 1,3-diaryl-Δ² -pyrazolines and 4-amino-1,8-naphthalimides are employed within this system, alongside receptors such as amines, carboxylates, crown ethers and amino acids. This tool appealed to a multinational corporation for building a medical analyzer for electrolytes such as Na⁺ , K⁺ , Ca²⁺ and gases like CO₂ , which became a commercially successful application. Finally, the tool was a springboard for chemistry to cross into computer science. The field of molecular logic can elucidate how molecules inside us handle information. Molecular examples of the simplest logic gates such as YES, NOT, OR, AND are described. A case of a human-level computation - visual edge detection - is also included.

Enhanced ion binding by the benzocrown receptor and a carbonyl of the aminonaphthalimide fluorophore in water-soluble logic gates

Fluorescent logic gates with benzocrown ethers attached at the imide naphthalimide exhibit synergistic binding of Na⁺ and K⁺ in aqueous methanol and water.

A Personal Journey across Fluorescent Sensing and Logic Associated with Polymers of Various Kinds

Our experiences concerning fluorescent molecular sensing and logic devices and their intersections with polymer science are the foci of this brief review. Proton-, metal ion- and polarity-responsive cases of these devices are placed in polymeric micro- or nano-environments, some of which involve phase separation. This leads to mapping of chemical species on the nanoscale. These devices also take advantage of thermal properties of some polymers in water in order to reincarnate themselves as thermometers. When the phase separation leads to particles, the latter can be labelled with identification tags based on molecular logic. Such particles also give rise to reusable sensors, although molecular-scale resolution is sacrificed in the process. Polymeric nano-environments also help to organize rather complex molecular logic systems from their simple components. Overall, our little experiences suggest that researchers in sensing and logic would benefit if they assimilate polymer concepts.

Population analysis to increase the robustness of molecular computational identification and its extension into the near-infrared for substantial numbers of small objects

The first population analysis is presented for submillimetric polymer beads which are tagged with five multi-valued logic gates, YES, 2YES + PASS 1, YES + PASS 1, YES + 2PASS 1 and PASS 1 with H+ input, 700 nm near-infrared fluorescence output and 615 nm red excitation light as the power supply. The gates carry an azaBODIPY fluorophore and an aliphatic tertiary amine as the H+ receptor where necessary. Each logic tag has essentially identical emission characteristics except for the H+-induced fluorescence enhancement factors which consistently map onto the theoretical predictions, after allowing for bead-to-bead statistical variability for the first time. These enhancement factors are signatures which identify a given bead type within a mixed population when examined with a 'wash and watch' protocol under a fluorescence microscope. This delineates the scope of molecular computational identification (MCID) for encoding objects which are too small for radiofrequency identification (RFID) tagging.

Novel π-extended hybrid xanthene dyes with two spirolactone rings for optoelectronic and biological applications

Two hybrid xanthene dyes that can operate as half-subtractors in methanol and can target mitochondria have been developed.

Lighting-up protein–ligand interactions with fluorescent PET (photoinduced electron transfer) sensor designs

Extending the versatile fluorescent PET sensing/switching system causes ‘off–on’ signalling when a ligand binds to its appropriate protein.

A fluorescent combinatorial logic gate with Na+, H+-enabled OR and H+-driven low-medium-high ternary logic functions

A fluorescent combinatorial Na⁺, H⁺ logic gate is demonstrated that could represent a class of probes for investigating antiporters in biological systems.

A dithienosilole-based fluorescent chemosensor for multiple logic operations at the molecular level

A chemosensor consisting of two terpyridines covalently linked to a dithienosilole unit (1) has been synthesized, and its optical and metal sensing properties have been investigated. Due to the metal-organic coordination function, 1 can bind with many transition metal ions and display different fluorescence responses that cause it to function as a "turn-off" fluorescent chemosensor. A significant bathochromic shift in the fluorescence spectra is observed in the presence of Zn(2+). Meanwhile, the emission of 1 is weakened upon exposure to Ag(+) and Fe(2+) and completely quenched by Ni(2+), Co(2+), and Cu(2+). Based on the observed results, several logic gates, such as XNOR, INHIBIT, and IMPLICATION, have been achieved by controlling the chemical inputs.

Three novel input logic gates supported by fluorescence studies: organic nanoparticles (ONPs) as chemo-sensor for detection of Zn²⁺ and Al³⁺ in aqueous medium

Organic nanoparticles (ONPs) of N,N'-ethylenebis(salicylimine) (salen) were synthesized and applied for specific recognition of Zn(2+) and Al(3+) ions in an aqueous medium. The results show that fluorescence intensity rises with the increasing concentration of Zn(2+) in salen solution, proving that salen-ONPs detect Zn(2+) efficiently in the aqueous medium as chemo-sensor. Furthermore, the salen-ONPs/Zn(2+) system performs as an ON-OFF switch between pH 6.0 and 4.0. Amusingly, although salen-ONPs/Al(3+) does not show any significant effect in the fluorescence spectra, highest fluorescence intensity was observed when Al(3+) ion was added to salen-ONPs/Zn(2+) in a sequential order (addition of Zn(2+) to salen-ONPs, followed by Al(3+)). This system can be applied as a novel three inputs logic gate supported by the fluorescence for the detection of Zn(2+) and Al(3+) in biological and environmental samples. It appears that photo induced electron transfer (PET) occurs in the salen-ONPs when the fluorophore is excited. For salen/Zn(2+) system, the PET is being inhibited considerably by lowering the receptor HOMO energy due to the formation of a bond between the metal ion and ligand, enhancing the fluorescence emission. This is consistent with the theoretical study that the energy of HOMO of the ligand is lower than that of Zn(salen)(2+) complex.

Two and three input molecular logic operations mediated by a novel azo-azomethine based chromogenic probe through intramolecular charge transfer processes

A novel azo-azomethine based chromogenic receptor has been successfully designed and synthesized for the construction of multifunctional molecular logic circuits.

Switching of the triplet excited state of rhodamine/naphthaleneimide dyads: an experimental and theoretical study

Rhodamine-bromonaphthaleneimide (RB-NI) and rhodamine-bromonaphthalenediimide (RB-NDI) dyads were prepared for switching of the triplet excited states. Bromo-NI or bromo-NDI parts in the dyads are the spin converters, i.e., the triplet state producing modules, whereas the RB unit is the acid-activatable electron donor/energy acceptor. NI and NDI absorb at 359 and 541 nm, and the T1 state energy levels are 2.25 and 1.64 eV, respectively. RB undertakes the reversible spirolactam (RB-c) ↔ opened amide (RB-o) transformation. RB-c shows no visible light absorption, and the triplet-state energy level is ET1 = 3.36 eV. Conversely RB-o shows strong absorption at 557 nm, and ET1 is 1.73 eV. Thus, the acid-activated fluorescence-resonance-energy-transfer (FRET) competes with the ISC of NI or NDI. No triplet state was observed for the dyads with nanosecond time-resolved transient absorption spectroscopy. Upon addition of acid, strong fluorescence and long-living triplet excited states were observed. Thus, the producing of triplet state is acid-activatable. The triplet state of RB-NI is localized on RB-o part, whereas in RB-NDI the triplet state is delocalized on both the NDI and RB-o units. The ISC of spin converter was not outcompeted by RET. These studies are useful for switching of triplet excited state.

A continuous and multi valued system as molecular answer for data processing and data storage

Two molecular logic systems are presented with two independent input factors resulting in a continuous system and a system with a quaternary basis.

Fluorescent probe mimicking multiple logic gates and a molecular keypad lock upon interaction with Hg2+ and bovine serum albumin

The output fluorescence exhibited by an intramolecular charge transfer fluorescent probe 1 providing different chemical inputs mimicked multiple logic gates. A molecular keypad lock security device authorizing password entries (logic memory) and capable of solving crossword puzzles has been constructed by computing the output emission of 1 upon chemical inputs of BSA and Hg(2+). Based on logic operations the devised fluorescent keypad lock could be unlocked upon entering a correct sequence of password, 'BHU'.

Ion Translocation in Artificial Molecule-based Systems Induced by Light, Electrons, or Chemicals

Synthetic molecules and nanodevices, like their more elaborate biological counterparts, have been shown to perform several sophisticated functions, using even fairly simple molecular architectures. One limitation to developing artificial molecular arrays and networks from these miniscule building blocks is the lack of a unifying strategy whereby they can communicate or interact together, which has been successfully developed in natural systems. Understanding and harnessing these efficient biological processes could prove key in the development of future integrated molecule-based nanodevices and networks. Herein, we give a short overview of some manifestations of intra- and intermolecular communication based on chemical messengers in artificial systems, in some ways analogous to natural systems, which are in turn controlled by light, a redox process or a chemical reaction or interaction. Some advantages, limitations, and challenges are highlighted.

Towards 'Computer-on-a-Particle' Devices: Optoelectronic 1:2 Demultiplexer Based on Nanostructured Cadmium Sulfide

Nanocrystalline sulfur-doped cadmium sulfide (CdS) prepared by microwave synthesis was investigated. Photoelectrochemical and optical characteristics of sulfur-doped CdS exhibit the photoelectrochemical photocurrent switching effect. Depending on the wavelength and applied bias, the anodic and/or cathodic photocurrent was observed. The unusual behaviour of nanocrystalline CdS allowed the construction of a combinatorial logic system from this material.

Digital Operations with Molecules - Advances, Challenges, and Perspectives

This Review gives a short introduction into molecular logic and focusses then on the latest advances in the field. With regard to complex logic circuits and functions, molecular devices for arithmetic processing (adders and subtractors), multiplexers/demultiplexers, and encoders/decoders are discussed. Further on, the concept of memory for data storage and sequential logic is considered together with the latest results on molecular keypad locks. Molecular logic has been often connected to the future aim of molecular computing. However, albeit the herein described approaches constitute a starting point, major challenges like concatenation of gates, solid state devices and compartmentalization, and alternative concepts (reversible logic, multivalued logic) are waiting ahead. These points are included, as well as a view on alternative applications of molecular logic in bio-inspired approaches, combinatorial chemistry, and materials science.

A multifunctional tripodal fluorescent probe: "off-on" detection of sodium as well as two-input AND molecular logic behavior

A simple tripodal sensor (3) with multifunctional capability has been synthesized in three steps. The sensor, a naphthalene-functionalized Schiff base, displays selectivity for sodium over other important physiological and environmentally important cations through changes in the emission spectra at lambda(max) 355 nm when excited at 270 nm. Interestingly, the combined addition of both sodium and potassium produced a new band at lambda(max) 445 nm, while the addition of sodium or potassium alone produced negligible changes at this wavelength. Therefore, the conditions of a two-input AND logic operator were also satisfied.

All-optical integrated logic operations based on chemical communication between molecular switches

Molecular logic gates process physical or chemical "inputs" to generate "outputs" based on a set of logical operators. We report the design and operation of a chemical ensemble in solution that behaves as integrated AND, OR, and XNOR gates with optical input and output signals. The ensemble is composed of a reversible merocyanine-type photoacid and a ruthenium polypyridine complex that functions as a pH-controlled three-state luminescent switch. The light-triggered release of protons from the photoacid is used to control the state of the transition-metal complex. Therefore, the two molecular switching devices communicate with one another through the exchange of ionic signals. By means of such a double (optical-chemical-optical) signal-transduction mechanism, inputs of violet light modulate a luminescence output in the red/far-red region of the visible spectrum. Nondestructive reading is guaranteed because the green light used for excitation in the photoluminescence experiments does not affect the state of the gate. The reset is thermally driven and, thus, does not involve the addition of chemicals and accumulation of byproducts. Owing to its reversibility and stability, this molecular device can afford many cycles of digital operation.