Structure-property relationship in functionalized azobenzene photoswitches and their supramolecular behavior

Herein, we report the design, synthesis, and supramolecular behavior of 30 structurally diverse photoresponsive azobenzene molecular systems. To establish structure-property relationships, azobenzenes appended with N-picolinyl and/or N-benzyl groups tethered directly through carboxamides or via triazolylmethyl carboxamide linkages were explored. We have evaluated the photoswitching characteristics and thermal stability of the Z isomers through systematic studies. All the targets were also screened for their aggregation behavior and supramolecular aspects. Among all the derivatives, a few carboxamide-based systems formed microcrystals upon aggregation, showing light responsiveness. In contrast, the derivatives tethered via triazolylmethyl carboxamide linkage exhibited hydrogel formation with excellent water-absorbing capacity. All supramolecular aspects of the morphology of the microcrystal and hydrogel states and their stimuli-responsiveness have been studied using spectroscopy and various microscopic techniques.

Photoswitchable Azoheteroarene-Based Chelating Ligands: Light Modulation of Properties, Aqueous Solubility and Catalysis

We report the design and synthesis of eight photoswitchable phenylazopyridine- and phenylazopyrazole-based molecular systems as chelation-type light-controllable ligands. Besides the studies on fundamental photoisomerization behaviour, the ligands were also screened for light-tuneable properties such as photochromism, phase transition, and solubility, especially in the aqueous medium. This investigation demonstrates how the modulation of aqueous solubility can be achieved through photoisomerization and can further be utilized towards controlling the amount of catalytically active Cu(I) species in the aqueous conditions. Through this approach, light control over the catalytic activity was achieved for Cu-catalyzed azide-alkyne cycloaddition (CuAAC) reactions, along with a partial recovery of the catalytically active species.

Photochemistry of 2-Iodobenzothiazole and Iodine-Triggered 2-Isocyanophenylthiyl Radical Cyclization in Argon Matrices

The photochemistry of 2-iodobenzothiazole (IBT) was investigated in an argon matrix at 4 K. Irradiating matrix-isolated IBT at λ = 254 nm led to the formation of 2-isocyanophenylthiyl radical 3 and benzothiirene 4; surprisingly, the 2-dehydrobenzothiazole radical 1 was not detected. A subsequent 365 nm irradiation or annealing of matrix containing 3 and iodine atom (at 30 K) reverted the precursor IBT, indicating an iodine-triggered thiyl radical-based cyclization, which was confirmed by computations using density functional theory. For gaining mechanistic insights, similar investigations were performed using benzothiazole BT as a precursor. Once again, the 254 nm light-induced C-S scission accompanied by H-shift led to 2-isocyanothiophenol 7. A conformational analysis of 2-isocyanothiophenol 7 and its photochemistry was also carried out with the help of IR spectroscopy under cryogenic conditions and computations. Considering the importance of thiyl radicals in biomolecular pathways, the investigations on its photochemical generation and a rare, reversible phenomenon of iodine-mediated cyclization under cryogenic conditions are insightful for fundamental photochemistry and sulfur chemistry.

Bistable Aryl Azopyrazolium Ionic Photoswitches in Water

We report a new class of arylazopyrazolium-based ionic photoswitches (AAPIPs). These AAPIPs with different counter ions have been accessed through a modular synthetic approach in high yields. More importantly, the AAPIPs exhibit excellent reversible photoswitching and exceptional thermal stability in water. The effects of solvents, counter ions, substitutions, concentration, pH, and glutathione (GSH) have been evaluated using spectroscopic investigations. The results revealed that the bistability of studied AAPIPs is robust and near quantitative. The thermal half-life of Z isomers is extremely high in water (up to years), and it can be lowered electronically by the electron-withdrawing groups or highly basic pH.

Pd(II)-catalyzed coupling of C-H bonds of carboxamides with iodoazobenzenes toward modified azobenzenes

In this paper, we report a synthetic protocol for the construction of biaryl motif-based or π-extended azobenzene and alkylated azobenzene derivatives via the Pd(II)-catalyzed bidentate directing group (DG)-aided C-H activation and functionalization strategy. In the past, the synthesis of biaryl motif-based azobenzenes was accomplished through the traditional cross-coupling reaction involving organometallic reagents and aryl halides or equivalent coupling partners. We have shown the direct coupling of C-H bonds of aromatic/aliphatic carboxamides (possessing a DG) with iodoazobenzenes as the coupling partners through the Pd(II)-catalyzed bidentate DG-aided, site-selective C-H functionalization method. Azobenzene-containing compounds are a versatile class of photo-responsive molecules that have found applications across branches of chemical, biological and materials sciences and are prevalent in medicinally relevant molecules. Accordingly, the synthesis of new and functionalized azobenzene-based scaffolds has been an attractive topic of research. Although the classical methods are efficient, they need pre-functionalized starting materials. This protocol involving the Pd(II)-catalyzed, directing group-aided site-selective C-H arylation of aromatic and aliphatic carboxamides using iodoazobenzene as the coupling partner affording azobenzene-based carboxamides is an additional route and also a contribution towards enriching the library of modified azobenzenes. We have also shown the photoswitching properties of representative compounds synthesized via the Pd(II)-catalyzed directing group-aided site-selective C-H functionalization method.

Light Modulated Reversible "On-Off" Transformation of Arylazoheteroarene Based Discotics in Nematic Organization

Three benzene-1,3,5-tricarboxamide (BTA) core-based molecular systems appended with phenylazo-3,5-dimethylisoxazole photoswitches at the peripheral position through variable-length alkoxy chains have been designed and synthesized. The supramolecular interactions of the mesogens provided discotic nematic liquid crystalline assembly as confirmed by polarized optical microscopy (POM) and X-ray diffraction (XRD) studies. Spectroscopic studies confirmed the reversible photoswitching and excellent thermal stability of the photoswitched states in solution phase and thin film. Also, atomic force microscopic (AFM) and POM investigations demonstrated the morphological changes in the self-assembly induced by the photoirradiation as monitored by the changes in the height profiles and optical appearance of the textures, respectively. Remarkably, the liquid crystalline discotic molecules showed reversible "on and off states" controlled by light at ambient temperature.

Multiple Azoarenes Based Systems - Photoswitching, Supramolecular Chemistry and Application Prospects

In the recent decades, the investigations on photoresponsive molecular systems with multiple azoarenes are quite popular in diverse perspectives ranging from fundamental understanding of multiple photoswitches, supramolecular chemistry, and various application prospects. In fact, several insightful and conceptual designs of such systems were investigated with architectural distinctions. In particular, the demonstration of applications such as data storage with the help of multistate or orthogonal photoswitches, light modulation of catalysis via cooperative switching, sensors using supramolecular host-guest interactions, and materials such as liquid crystals, grating, actuators, etc. are some of the milestones in this area. Herein, we cover the recent advancements in the research areas of multiazoarenes containing systems that have been classified into Type-1 {linear, non-linear, and core-based (A)}, Type-2 {tripodal C₃ -symmetric (C3)} and Type-3 {macrocyclic (M)} structural motifs.

Light-controlled shape-changing azomacrocycles exhibiting reversible modulation of pyrene fluorescence emission

We report the design, synthesis, and study of light-induced shape-changing azomacrocycles. These systems have been incorporated with azobenzene photoswitches using alkoxy tethers and triazole units to afford flexibility and binding. We envision that such azomacrocycles are capable of reversibly binding with the guest molecule. Remarkably, we have demonstrated fully light-controlled fluorescence quenching and enhancement in the monomeric emission of pyrene (guest). Such modulations have been achieved by the photoisomerization of the azomacrocycle and, in turn, host-guest interactions. Also, the azomacrocycles tend to aggregate and can also be controlled by light or heat. We uncovered such phenomena using spectroscopic, microscopic, and isothermal titration calorimetry (ITC) studies and computations.

Structure-Property Relationship for Visible Light Bidirectional Photoswitchable Azoheteroarenes and Thermal Stability of Z-Isomers

A modular approach has been adopted to synthesize a wide range of visible light-driven photoswitchable azoheteroarenes. In this regard, we considered ortho substitution of cyclic amines in the aryl ring and varied substitution patterns. Using detailed spectroscopic studies, we established a relationship between structure and photoswitching ability and also half-lives of the Z-isomers. Through this, we envision tunable and bidirectional longer wavelength photoswitches.

Deciphering Internal and External π-Conjugation in C3 -Symmetric Multiple Azobenzene Connected Systems in Self-Assembly

Two tripodal C₃ -symmetric photoswitchable molecular systems T1 and T2 are reported that have extended conjugation at external and internal positions using an acryl group. The influence of the extended π-bonds in their absorption properties, thermal relaxation of the photoisomers and their propensities in forming supramolecular self-assemblies have been explored through spectroscopy, and microscopic studies. In particular, the investigations on the self-assembly have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), polarized optical microscopy (POM), X-ray diffraction studies (XRD) and atomic force microscopy (AFM). Remarkably, the position of the acryl group influences the behaviour of the two target molecules in supramolecular assembly, and also in the formation of photoresponsive organic hydrogels or microcrystals.

Photochemistry of 3,6-Didehydropyridazine Biradical─An Untraceable Para Benzyne Analogue

We report matrix isolation infrared spectroscopic studies to characterize 3,6-didehydropyridazine 6, a heterocyclic analogue of para benzyne, combined with computations. In this regard, we have utilized 3,6-diiodopyridazine 11 as a photolytic precursor. The experiments toward the generation of the biradical are carried out in argon and nitrogen matrices at 4 K. Instead of the elusive biradical, we have observed a ring-opening product maleonitrile (Z)-7 upon irradiation at 254 nm. In contrast, prolonged irradiation at 254 nm leads only to Z-E isomerization, forming fumaronitrile (E)-7. The mechanistic aspects of ring-opening, product selectivity, and Z-E photoisomerization steps have been investigated in detail using high-level ab initio computations. These studies have found that 3,6-didehydropyridazine 6 is an untraceable intermediate, and the ring-opening step leading to maleonitrile is barrierless. In addition, we have proposed the involvement of the S₁ (π-π*) state via conical intersection in the Z-E photoisomerization of maleonitrile.

The curious case of the photochemistry of 2-hydroxyphenylazo-3,5-dimethylisoxazole: Unravelling the process among tautomer-ization, photoisomerization, and conformational changes

Photoswitching in azo compounds is well established. Typically, the planar trans molecule (native) can undergo isomerization to cis isomer and vice versa in solution by light. However, observing such photochemistry...

Solid-state photochromic arylazopyrazole based transition metal complexes

A new class of photoactive and chelating ligands L1-3 have been designed and synthesized by incorporating arylazo-3,5-dimethylpyrazole units in the ligand frameworks. Significantly they are designed in such a way...

Azobenzene-based unnatural amino acid scaffolds via a Pd(ii)-catalyzed C(sp3)–H arylation strategy

Azobenzene-based unnatural amino acid motifs were constructed via the Pd(ii)-catalyzed diastereoselective β-C(sp3)–H arylation and Mills azo coupling tactics.

Intermolecular CDC amination of remote and proximal unactivated Csp3 -H bonds through intrinsic substrate reactivity - expanding towards a traceless directing group

An intermolecular radical based distal selectivity in appended alkyl chains has been developed. The selectivity is maximum when the distal carbon is γ to the appended group and decreases by moving from γ → δ → ε positions. In –COO– linked alkyl chains, the same distal γ-selectivity is observed irrespective of its origin, either from the alkyl carboxy acid or alkyl alcohol. The appended groups include esters, N–H protected amines, phthaloyl, sulfone, sulfinimide, nitrile, phosphite, phosphate and borate esters. In borate esters, boron serves as a traceless directing group, which is hitherto unprecedented for any remote C_sp³–H functionalization. The selectivity order follows the trend: 3° benzylic > 2° benzylic > 3° tertiary > α to keto > distal methylene (γ > δ > ε). Computations predicted the radical stability (thermodynamic factors) and the kinetic barriers as the factors responsible for such trends. Remarkably, this strategy eludes any designer catalysts, and the selectivity is due to the intrinsic substrate reactivity.

An intermolecular amination at the distal methylene carbon has been realized in an appended alkyl chain with electron withdrawing groups. Traceless remote C_sp³–H functionalization has been accomplished using borate esters.

Response of rice (Oryza sativa L.) cultivars to elevated ozone stress

The plant response to elevated ozone stress reveals inter-species and intra-species disparity. Ozone-induced crop yield loss is predicted to increase in the future, posing a threat to the world economy. This study aims to evaluate the cultivar specific variation in rice exposed to elevated ozone. Fifteen short-duration rice cultivars were exposed to 50 ppb ozone for 30 days at reproductive stage. The physiological, biochemical, growth and yield traits of all test cultivars were significantly affected in response to elevated ozone. On an average, ozone stress decreased the tiller number by 22.52%, number of effective tillers by 30.43%, 1000 grain weight by 0.62% and straw weight by 23.83% over control. Spikelet sterility increased by 19.26% and linear multiregression 3D model significantly fits the spikelet sterility and photosynthetic traits with the R² of 0.74 under elevated ozone. Principal Component Analysis with total variance of 57.5% categorized 15 rice cultivars into four major groups, i.e., ozone sensitive (MDU6, TRY(R)2 and ASD16), moderately ozone sensitive (ASD18, ADT43, and MDU5), moderately ozone tolerant (ADT37, ADT(R)45, TPS5, Anna(R)4, PMK(R)3, and ADT(R)48), and ozone tolerant (CO51, CO47, and ADT36). This study indicates that the different responses of rice cultivars to elevated ozone stress through a change in plant physiology, biochemical, growth, and yield traits and the results directed to provide scientific information on plant adaptations to ozone stress and helps in efforts to search ozone tolerant gene for plant breeding.

Tuning of Bistability, Thermal Stability of the Metastable States, and Application Prospects in the C3 -Symmetric Designs of Multiple Azo(hetero)arenes Systems

Light-responsive molecular systems with multiple photoswitches in C₃ -symmetric designs have enormous application potential. The design part of such molecular systems is critical due to its influence in several properties associated with the photoswitches. In order to tune, and in the evaluation of the design-property relationship, we synthesized 18 tripodal systems with variations in the core, linkers, connectivity, and azo(hetero)arene photoswitches. Through extensive spectroscopic and computational studies, we envisaged the factors controlling near-quantitative photoisomerization in both the directions (bistability) and the thermal stability of the metastable states. Furthermore, we also evaluated the impact of designs in obtaining reversible photo-responsive sol-gel phase transitions, solvatochromism, photo- and thermochromism.

Temporal control in tritylation reactions through light-driven variation in chloride ion binding catalysis – a proof of concept

A proof-of-concept on temporal control in the tritylation reactions has been demonstrated using a designed tripodal triazole-linked azo(hetero)arene-based photoswitchable catalyst.

Reversibly photoswitchable alkoxy azobenzenes connected benzenetricarboxamide discotic liquid crystals with perpetual long range columnar assembly

Reversibly photoswitchable discotic liquid crystals (DLCs) with no change in columnar assembly.

Deciphering Stability of Five-Membered Heterocyclic Radicals: Balancing Act Between Delocalization and Ring Strain

Computational studies on five-membered heterocycles with single heteroatom and their isomeric dehydro-borole 1a-1c, cyclopentadiene 2a-2c, pyrrole 3a-3c, furan 4b-4c, phosphole 5a-5c, and thiophene 6b-6c radicals have been carried out. Geometrical aspects through ground state electronic structures and stability aspects using bond dissociation energies (BDE) and radical stabilization energies (RSE) have been envisaged in this regard. Spin densities, electrostatic potentials (ESP), and natural bond orbital (NBO) analysis unveiled the extent of spin delocalization. The estimated nucleus-independent chemical shifts (NICS) values revealed the difference in aromaticity characteristics of radicals. Particularly the heteroatom centered radicals exhibit odd electron π-delocalized systems with a quasi-antiaromatic character. Various factors such as, the relative position of the radical center with respect to heteroatoms, resonance, ring strain and orbital interactions influence the stability that follows the order: heteroatom centered > β-centered > α-centered radicals. Among the influences of various factors, we confirmed the existence of a competition between delocalization and the ring strain, and the interplay of both decides the overall stability order.

Through bond and through space interactions in dehydro-diazine radicals: a case study of 3c-5e interactions

Owing to the 3c-5e (3-centred-5-electrons) interactions between two nitrogen lone pairs and a radical electron, the dehydrodiazine radical isomers are very interesting from the fundamental point of view. Among them, pyrimidine has three (1a-1c), pyridazine has two (2a and 2b) and pyrazine has only one (3a) radical isomer. Based on quantum chemical calculations at the (U)B3LYP, (U)M06-2X, (U)BLYP, CBS-QB3 and (U)CCSD(T) levels with cc-pVTZ as the basis set, we found the 4-dehydropyrimidine (1b) radical to be the most stable isomer among the three pyrimidine radicals, followed by the 2-dehydropyrimidine (1a) and 5-dehydropyrimidine (1c) radical isomers. In the case of pyridazine, 3-dehydro radical isomer (2a) is more stable than 4-dehydropyridazine (2b). Bond dissociation energy (BDE) calculations and estimation of radical stabilization energies (RSE) using isodesmic reactions revealed the stability order among the six isomeric diazine radicals as 1c < 2b < 2a < 1a < 3a < 1b. Spin densities at each radical centre and non-zero values at nitrogen centres provided information about the extent of delocalization of radical electrons, which was consistent with the relative stability order of all the isomers. The multiconfigurational CASSCF and natural bond orbital (NBO) calculations suggested the presence of direct through space interactions (between lone pairs and a radical, TS) that play a dominant role over the through bond (through intervening bonds, TB) interactions in deciding the stability order. To confirm these results, we have also estimated the proton affinities (PAs) for each nitrogen atom and compared them with their respective parent diazines, where lowering of the PA values convincingly envisaged the extent and strength of interactions between the nitrogen and radical centre. Atoms-in-molecules (AIM) analysis and estimation of hyperfine coupling constants have also been performed to verify these results. All these results showed that the through space interaction between the lone pair and the radical electron is very important for the electronic structural and stability aspects in dehydrodiazine radicals.

Does a Nitrogen Lone Pair Lead to Two Centered-Three Electron (2c-3e) Interactions in Pyridyl Radical Isomers?

Each of the three isomeric pyridyl radicals (2-, 3-, and 4-dehydropyridines) contains a lone pair and an unpaired electron. As a result, a potential two centered-three electron interaction between the radical electron and the lone pair through-space (TS) and/or through-bond (TB) can exist that may influence the stability of the radicals. Due to the change in geometrical positions relative to each other, the strength of interaction can be varied. In this study, we investigated the structural and stability aspects of pyridyl radical isomers with a major emphasis on the interaction of a nitrogen lone pair with the radical center. In order to obtain evidence for such interactions, protonated and N-oxide analogues of the corresponding isomeric pyridyl radicals have been considered in such a way to understand the consequences due to unavailability of the lone pair. Similarly, electron attachment and detachment energies at the radical center (vertical detachment energy, VDE, of corresponding anions and vertical ionization energy, VIE, of radical isomers) have been calculated to find out the interaction trend upon modification at the radical center. Different levels of theory including (U)B3LYP/cc-pVTZ, (U)M06/cc-pVTZ, CBS-QB3, single-point energy calculations at (U)CCSD(T)/cc-pVTZ, and multireference CASSCF/cc-pVTZ methods have been employed in this regard. A closer inspection of geometries, relative stability order, spin density, electrostatic potential, molecular orbitals, NBO analysis, and vibrational analysis have showed a strong and stabilizing TS interaction between the radical center and the lone pair in the case of the 2-pyridyl radical. On the other hand, the 4-pyridyl radical showed stabilizing interactions only via TB coupling, whereas the TS interaction is nonexistent. Despite the presence of both interactions in the case of the 3-pyridyl radical, their overall influence is less effective toward stability.

Dehydro-oxazole, thiazole and imidazole radicals: insights into the electronic structure, stability and reactivity aspects

Computations on the effect of heteroatoms in the structural, stability and reactivity aspects of the oxazole, thiazole and imidazole radicals.

Variability of atmospheric carbonyl sulfide at a semi-arid urban site in western India

Atmospheric carbonyl sulfide (COS) is a major precursor for sulfate aerosols that play a critical role in climate regulation. Recent studies have highlighted the importance of COS measurements as a reliable means to constrain biospheric carbon assimilation. In a scenario of limited availability of COS data around the globe, we present gas-chromatographic measurements of atmospheric COS mixing ratios over Ahmedabad, a semi-arid, urban region in western India. These measurements, being reported for the first time over an Indian site, enable us to understand the diurnal and seasonal variation in atmospheric COS with respect to its natural, anthropogenic and photochemical sources and sinks. The annual mean COS mixing ratio over Ahmedabad is found to be 0.83±0.43ppbv, which is substantially higher than free tropospheric values for the northern hemisphere. Inverse correlation of COS with soil and skin temperature, suggests that the dry soil of the semi-arid study region is a potential sink for atmospheric COS. Positive correlations of COS with NO2 and CO during post-monsoon and the COS/CO slope of 0.78pptv/ppbv reveals influence of diesel combustion and tire wear. The highest concentrations of COS are observed during pre-monsoon; COS/CO2 slope of 44.75pptv/ppmv combined with information from air mass back-trajectories reveal marshy wetlands spanning over 7500km(2) as an important source of COS in Ahmedabad. COS/CO2 slopes decrease drastically (8.28pptv/ppmv) during post-monsoon due to combined impact of biospheric uptake and anthropogenic emissions.

Rational design of a room temperature molecular spin switch. The light-driven coordination induced spin state switch (LD-CISSS) approach

A record player type molecule changes spin state reversibly upon irradiation with green and blue light in solution at room temperature without measureable fatigue.

Variability of SO₂, CO, and light hydrocarbons over a megacity in Eastern India: effects of emissions and transport

The Indo-Gangetic plain (IGP) has received extensive attention of the global scientific community due to higher levels of trace gases and aerosols over this region. Satellite retrievals and model simulations show that, in particular, the eastern part IGP is highly polluted. Despite this attention, in situ measurements of trace gases are very limited over this region. This paper presents measurements of SO₂, CO, CH₄, and C₂-C₅ NMHCs during March 2012-February 2013 over Kolkata, a megacity in the eastern IGP, with a focus on processes impacting their levels. The mean SO₂ and C2H6 concentrations during winter and post-monsoon periods were eight and three times higher compared to pre-monsoon and monsoon. Early morning enhancements in SO₂ and several NMHCs during winter connote boundary layer effects. Daytime elevations in SO₂ during pre-monsoon and monsoon suggest impacts of photo-oxidation. Inter-species correlations and trajectory analysis evince transport of SO₂ from regional combustion sources (e.g., coal burning in power plants, industries) along the east of the Indo-Gangetic plain impacting SO₂ levels at the site. However, C₂H₂ to CO ratio over Kolkata, which are comparable to other urban regions in India, show impacts of local biofuel combustions. Further, high levels of C₃H₈ and C₄H₁₀ evince the dominance of LPG/petrochemicals over the study location. The suite of trace gases measured during this study helps to decipher between impacts of local emissions and influence of transport on their levels.

Magnetic bistability of molecules in homogeneous solution at room temperature

Magnetic bistability, as manifested in the magnetization of ferromagnetic materials or spin crossover in transition metal complexes, has essentially been restricted to either bulk materials or to very low temperatures. We now present a molecular spin switch that is bistable at room temperature in homogeneous solution. Irradiation of a carefully designed nickel complex with blue-green light (500 nanometers) induces coordination of a tethered pyridine ligand and concomitant electronic rearrangement from a diamagnetic to a paramagnetic state in up to 75% of the ensemble. The process is fully reversible on irradiation with violet-blue light (435 nanometers). No fatigue or degradation is observed after several thousand cycles at room temperature under air. Preliminary data show promise for applications in magnetic resonance imaging.

The 1,2,3-Tridehydrobenzene Triradical: 2B or Not 2B? The Answer is 2A!

The molecular and electronic structure of 1,2,3-tridehydrobenzene was investigated by a variety of computational methods. The two lowest electronic states of the triradical are the (2)B(2) and (2)A(1) doublet states characterized by different interactions of the unpaired electrons. Vertically, the two states are well separated in energy-by 4.9 and 1.4 eV, respectively. However, due to different bonding patterns, their equilibrium structures are very different and, adiabatically, the two states are nearly degenerate. The adiabatic energy gap between the (2)B(2) and (2)A(1) states is estimated to be 0.7-2.1 kcal/mol, in favor of the (2)A(1) state. Harmonic vibrational frequencies and anharmonic corrections were calculated for both states. Comparison with the three experimentally observed IR transitions supports the assignment of the (2)A(1) ground state for the triradical with a weakly bonding distance of 1.67-1.69 A between the meta radical centers.

Strong coupling of nonlinear electronic and biological oscillators: reaching the "amplitude death" regime

Interaction between an electronic and a biological circuit has been investigated for a pair of electrically connected nonlinear oscillators, with a spontaneously oscillating olivary neuron as the single-cell biological element. By varying the coupling strength between the oscillators, we observe a range of behaviors predicted by model calculations, including a reversible low-energy dissipation "amplitude death" where the oscillations in the coupled system cease entirely.

Hematological effects of atypical and Cameroon beta-globin gene haplotypes in adult sickle cell anemia

To examine the effects of unusual or atypical beta-globin gene cluster haplotypes on the hematological features and Hb F levels of sickle cell anemia, we studied African Americans who had an atypical or Cameroon haplotype chromosome in association with a typical haplotype. We identified over 20 atypical haplotypes. The distribution of 5' sub-haplotypes of the atypical chromosomes mirrored the distribution of common haplotypes in African Americans with sickle cell anemia. Neither 5' nor 3' subhaplotypes of the atypical chromosomes affected Hb F levels, packed cell volume, or mean corpuscular volume in individuals with a Benin chromosome. That the 5' subhaplotype is unaffected might be a consequence of the small numbers of Senegal 5' subhaplotypes in our sample, the need for linkage of both 5' and 3' subhaplotypes of any haplotype for an effect on Hb F to be present, or the likelihood that a normal beta-globin gene contributed the 5' subhaplotypes of some atypical haplotypes.