Search

A two-component stapling strategy is used to covalently tether a new class of water-soluble supramolecular polymers built from bay-functionalized perylene bisimide (PBI) units.

The confinement of π-conjugated chromophores on silicon (Si) electrode surfaces is a powerful approach to engineer electroresponsive monolayers relevant to microelectronics, electrocatalysis, and information storage and processing. While common strategies to functionalize Si interfaces exploit molecularly dissolved building blocks, only a handful number of studies have leveraged the structure-function relationships of π-aggregates to tune the electronic structures of hybrid monolayers at Si interfaces. Herein, we show that the semiconducting properties of

Statement of problem Programming semiadjustable and fully adjustable articulators involves time-consuming clinical steps which can be avoided if an accurate radiographic method can accurately determine the condylar guidance angles. Purpose The purpose of this clinical study was to compare the sagittal condylar guidance in dentate individuals as determined by a clinical method, protrusive interocclusal record, and a radiographic method, cone beam computed tomography. If the methods show a correlation, then cone beam computed tomography can be used as a time-saving method of programming an articulator for patients requiring a cone beam computed tomography scan. Material and methods A total of 40 participants (20 men and 20 women) within the 20 to 40 years age group were enrolled according to the inclusion and exclusion criteria. Cone beam computed tomography scans were obtained, and by using an appropriate software program, the sagittal condylar guidance was measured for both sides. A protrusive interocclusal record was obtained by using polyvinyl siloxane material. The maxillary cast of each participant was mounted on a semiadjustable articulator with a facebow transfer, and the mandibular cast was mounted with a maximum intercuspal record. The protrusive record was then transferred to the articulator for programming. Results The right and left sagittal condylar guidance values obtained from both the protrusive interocclusal record and cone beam computed tomography method were comparable, with no significant differences (P>.05). The difference in condylar inclination values for both sexes obtained from both methods for both sides were not statistically different (P>.05). With increasing age, condylar inclination values obtained from both methods tended to decrease. The values for sagittal condylar guidance obtained from both methods (protrusive interocclusal record and cone beam computed tomography) were comparable and correlated. Conclusions Cone beam computed tomography measurement involves stable bony landmarks and can be standardized, whereas clinical methods are time consuming and can provide inaccurate results because of the instability of the materials used to register the maxillomandibular relationship. Thus, cone beam computed tomography can be used to obtain the sagittal horizontal guidance for programming semiadjustable and fully adjustable articulators for patients requiring a cone beam computed tomography scan.

The functionalization of silicon electrodes with π-conjugated chromophores opens new avenues to engineer hybrid semiconducting interfaces relevant to information storage and processing. Notably, molecularly dissolved π-conjugated units, such as ferrocene derivatives, are traditionally exploited as building blocks to construct well-defined interfaces that establish electrochemically addressable platforms with which to investigate electron transfer properties and charge storage capabilities. In contrast, planar π-conjugated building blocks such as naphthalene diimide (NDI) cores enable the formation of solvated aggregates equipped with emergent electronic structures not manifested by the parent, molecularly dissolved building blocks. To interrogate the extent to which the aggregated states of π-conjugated chromophores can be leveraged to regulate the n-type semiconducting properties of functionalized electrodes, we have devised an amphiphilic rylene core (NDI) that demonstrates a non-negligible degree of aggregation in an aqueous medium. Characterization of the electronic structures of the NDI-derived aggregates using a combination of electrochemistry, reductive titration experiments, and spectroelectrochemistry unveils the existence of π-anion stacks, the formation of which is contingent on the initial concentration of NDI building blocks. We show that grafting n-doped NDI aggregates on silicon electrode precursors equipped with a high density of anchoring groups by means of "click" reaction enables the formation of the hybrid Si-NDI electrode (Si-NDI-15@1) that facilitates electron injection by more than 400 mV when compared to Si interfaces constructed from molecularly dissolved NDI units. Furthermore, the engineering of a Si precursor surface characterized by a low density of anchoring groups provides additional proof to highlight that the potentiometric properties recorded for Si-NDI-15@1 originate from NDI units, evidencing a non-negligible degree of aggregation. The present work delivers tools to manipulate the potentiometric properties of functionalized electrodes by leveraging on the electronic structures of aggregated, π-conjugated precursors.

The molecular engineering of chromophores that enables the controlled and reliable formation of hierarchical solid-state architectures is at the forefront of developing hybrid semiconducting materi...

The surface coverage and molecular composition of redox-active molecules anchored on conductive surfaces regulate the kinetic and thermodynamic parameters of charge transfer reactions, providing a means to tune the electrochemical properties of hybrid materials. Herein, anchoring strategies and structural properties of redox-active probes, derived from ferrocene (Fc) and naphthalene diimide (NDI), are shown to regulate the electrochemical properties of functionalized p-doped Si(111) surfaces. Covalent functionalization of hydrogen-terminated Si(111) surfaces with Fc and NDI affords redox-active hybrid interfaces characterized through microscopy, spectroscopy, and voltammetry methods. Molecular design and synthetic grafting strategies modulate the electrochemical properties of the Fc-functionalized Si surfaces with a much higher (ca. 25 times) surface coverage (1.25 × 10-10 mol cm-2) for one-step photografting compared to divergent synthetic routes. Interestingly, the thermal grafting of an alkadiyne followed by "click" reaction with ferrocenyl-azide leads to one of the highest surface coverages (9.97 × 10-10 mol cm-2) of organo-iron reported and a significant anodic shift of the half-potential (>350 mV) compared to photografting methods. Similar experiments with NDI units exhibited electrochemical properties that diverge from those recorded for NDI in solution. The results presented herein offer access to novel redox-active Si interfaces that evidence tunable electrochemical properties of potential interest for microelectronic applications.

Two regioisomeric pairs of heptahelical mono- and biscoumarins that are differentiated by "inward" and "outward" disposition of the pyran-2-one moiety have been synthesized and investigated to understand the influence of helicity on excited-state and chiroptical properties. A slight variation in the helicities is found to manifest in contrasting excited-state properties of coumarin-annelated heptahelicenes; in addition to the intramolecular charge transfer, structural relaxation in the excited state is shown from theoretical calculations to cause decrease in the fluorescence quantum yield for a system with higher helicity. The optically pure enantiomers of heptahelical coumarins exhibit helicity-dependent chiroptical properties, namely, specific rotations, molar ellipticities, Cotton effects, and anisotropic dissymmetry factors. Theoretical calculations point to factors that are not readily explicable.

Investigation of photochromic and acidochromic behaviors of a set of pyridyl- and pyrimidylethynylated mono- and bis-benzopyrans reveals an intriguing influence of the N-heteroaryl ring on spectrokinetic properties of the photogenerated o-quinonoid colored reactive intermediates. While the absorption maxima of the pyridylethynylated bis-benzopyran and its photogenerated o-quinonoid colored species undergo bathochromic shifts by ca. 40 and 22 nm, respectively, in the presence of an acid (e.g., trifluoroacetic acid (TFA)), the same remain unaffected for the analogous pyrimidylethynylated bis-benzopyran and its photogenerated o-quinonoid colored species under similar conditions. Modification of the photochromic behavior of these benzopyrans and, hence, spectrokinetic properties of their photogenerated o-quinonoid species in the presence of H+ is a consequence of relative proton affinities of N-heteroaryl rings, i.e., pyridyl/pyrimidyl, and the resonance effects relayed through the ethynyl spacers in a push-pull π-delocalized-type skeleton; the mesomeric effects operate in a contrasting manner depending on the N-heteroaryl ring in the absence and in the presence of an acid. These molecular systems offer a unique opportunity to modulate both photochromic and acidochromic properties of benzopyrans and their photogenerated colored o-quinonoid intermediates by leveraging N-heteroaromatic rings.

The development of supramolecular tools to modulate the excitonic properties of non-covalent assemblies paves the way to engineer new classes of semicondcuting materials relevant to flexible electronics. While controlling the assembly pathways of organic chromophores enables the formation of J-like and H-like aggregates, strategies to tailor the excitonic properties of pre-assembled aggregates through post-modification are scarce. In the present contribution, we combine supramolecular chemistry with redox chemistry to modulate the excitonic properties and solid-state morphologies of aggregates built from stacks of water-soluble perylene diimide building blocks. The n-doping of initially formed aggregates in an aqueous medium is shown to produce π-anion stacks for which spectroscopic properties unveil a non-negligible degree of electron-electron interactions. Oxidation of the n-doped intermediates produces metastable aggregates where free exciton bandwidths (ExBW) increase as a function of time. Kinetic data analysis reveals that the dynamic increase of free exciton bandwidth is associated with the formation of superstructures constructed by means of a nucleation-growth mechanism. By designing different redox-assisted assembly pathways, we highlight that the sacrificial electron donor plays a non-innocent role in regulating the structure-function properties of the final superstructures. Furthermore, supramolecular architectures formed via a nucleation-growth mechanism evolve into ribbon-like and fiber-like materials in the solid-state, as characterized by SEM and HRTEM. Through a combination of ground-state electronic absorption spectroscopy, electrochemistry, spectroelectrochemistry, microscopy, and modeling, we show that redox-assisted assembly provides a means to reprogram the structure-function properties of pre-assembled aggregates.

Aim: The aim of the study was to compare two radiographic techniques, orthopantomograph (OPG), and cone-beam computed tomography (CBCT) in determining the sagittal condylar guidance (SCG) and to find out if CBCT can serve as an alternative aid to program semi-adjustable and fully adjustable articulators. Materials and Methods: Following the inclusion and exclusion criteria, 40 individuals (20 males and 20 females) aged between 20 and 40 years were selected. An OPG and a CBCT radiograph were obtained for each individual. Using appropriate software, the SCG was measured for both the sides, for both the radiographic methods. The values for each individual were obtained by two investigators for both the methods using the respective software and the average value was taken. After performing the Shapiro–Wilk test, paired t-test was used to compare the mean difference pairwise (for both right and left side) while t-test was used to compare the mean difference between two groups. Results: Results showed that the right and left SCG values obtained from both, OPG and CBCT methods were comparable and there were no significant differences. Statistically significant difference was not found between the left and ride side condylar inclination values for both the sex obtained from both the methods. With increasing age, condylar inclination values obtained from both the radiographic methods tend to decrease. The values for SCG obtained from both the methods (CBCT and OPG) are thus comparable and correlated. Conclusion: The values for SCG obtained from both the methods (CBCT and OPG) are comparable and correlated. Thus, CBCT being a better radiographic technique can be used for obtaining the condylar inclination for programming the semi-adjustable and fully adjustable dental articulators.

We show that n-doping supramolecular assemblies built from perylene diimide units provides a means to modulate the structure-function properties of these materials. In addition to highlighting the design principles, a combination of spectroscopic and microscopic characterization correlates an increase in the free-exciton bandwidth with the formation of mesoscale hierarchical superstructures.

A zinc metal–organic framework, i.e., Zn-MOF (Zn-DBC), with ca. 27% solvent-accessible void volume was synthesized from a rationally designed tetraacid based on sterically insulated dibenzo[g,p]chr...

Summary Exfoliation of layered porous metal-organic frameworks (MOFs) in a top-down fashion constitutes a successful approach to 2D metal-organic nanosheets (MONs), the analogs of graphene. The planned synthesis of layered MOFs is a challenging crystal-engineering exercise. Development of photochromic MONs that respond to light is a much bigger challenge; indeed, photochromic MONs are heretofore unknown. Here, we demonstrate engineering of layered MOFs and access to photochromic MONs. The strategy entails the use of programmed photochromic organic linkers characterized by a bulged core and metal-mediated self-assembly that occurs only in two dimensions, leading to layered MOFs. MONs exfoliated from such MOFs exhibit brilliant photochromism perceptible to the naked eye. We show that the MONs can be entrapped in an ormosil matrix for the development of polymer composites that display uncomplicated thermal bleaching kinetics. Thus, immobilization of photochromic 2D MONs containing void spaces in a polymer matrix for ophthalmic lens and other applications is compellingly demonstrated.

2D metal-organic framework nanosheets (MONs) lie at the heart of contemporary research on metal-organic materials. We have rationally designed and synthesized a fluorescent 6-connecting hexaacid linker H6TPA based on the 1,3,5-triphenylbenzene core to access layered MOFs by metal-assisted self-assembly. Treatment of H6TPA with In3+ salt does indeed lead to a layered porous MOF, i.e.In-TPA. It is shown that the ultrasonication-induced liquid phase of exfoliation (UILPE) of the latter in a top-down fashion affords few-layer 2D metal-organic nanosheets (MONs). The delamination of 2D MONs in ethanol occurs with 'turn-on' fluorescence, which is otherwise suppressed in the bulk material. The exfoliated MONs in ethanol exhibit blue fluorescence with a respectable quantum yield of 0.15 and serve as efficient sensory materials for 'turn-off' fluorescence detection of explosive nitroaromatic compounds (NACs). While all nitroaromatics are found to quench the fluorescence of MONs, the most electron-deficient trinitrotoluene (TNT) exhibited the highest efficiency; at 2 mM concentration of TNT, the fluorescence of 2D MONs was found to be quenched with an efficiency of 80% (permitting the detection of TNT at ca. 11 ppm level), while that of the unmetallated linker, i.e.H6TPA, was quenched with only 5% efficiency. The unique attributes of MONs, namely the rigidity of the linker upon metallation and porosity that facilitates guest confinement within the pores, for efficient sensing of nitroaromatics are thus demonstrated for the first time.

MediaChromes are molecular systems characterized by a rigid aromatic backbone bearing electron-donating (D) and accepting (A) groups conjugated in the so-called push-pull D–π–A fashion. Electronic excitation of such systems results in increase of the dipole moment in the excited state due to intramolecular charge transfer (ICT), leading to remarkable excited-state properties. We have investigated fluorosolvatochromic and halochromic (acidochromic) behavior of carbazolo-phenazine (CP), a new bipolar molecular system characterized by conjoined donor carbazole and acceptor phenazine heterocycles. CP is shown to exhibit exceptional fluoromediachromic behavior due to ICT in the excited state; the difference in the dipole moments of ground- and singlet-excited states of CP is ca. 3.6 D units. ICT occurs also in the ground state upon protonation, which manifests in brilliant naked-eye visible violet coloration, namely, acidochromism.

Access to novel bipolar carbazolo-phenazines is demonstrated by one-pot IBX-initiated multistep cascade, which involves oxidation of 2-naphthols to 1,2-naphthoquinones, Diels-Alder cycloaddition, aerial dehydroaromatization and cyclocondensation. With unprotected dienic indolylacrylates, N H⋯O hydrogen bonding in the transition state controls the product selectivity almost exclusively in favor of Diels-Alder cycloaddition over the competing Michael addition. The utility of one of the carbazolo-phenzines as applied to selective naked-eye sensing of fluoride is demonstrated.

Locking-in the conformation of supramolecular assemblies provides a new avenue to regulate the (opto)electronic properties of robust nanoscale objects. In the present contribution, we show that the covalent tethering of a perylene bisimide (PBI)-derived supramolecular polymer with a molecular locker enables the formation of a locked superstructure equipped with emergent structure-function relationships. Experiments that exploit variable-temperature ground-state electronic absorption spectroscopy unambiguously demonstrate that the excitonic coupling between nearest neighboring units in the tethered superstructure is preserved at a temperature (371 K) where the pristine, non-covalent assembly exists exclusively in a molecularly dissolved state. A close examination of the solid-state morphologies reveals that the locked superstructure engenders the formation of hierarchical 1D materials which are not achievable by unlocked assemblies. To complement these structural attributes, we further demonstrate that covalently tethering a supramolecular polymer built from PBI subunits enables the emergence of electronic properties not evidenced in non-covalent assemblies. Using cyclic voltammetry experiments, the elucidation of the potentiometric properties of the locked superstructure reveals a 100-mV stabilization of the conduction band energy when compared to that recorded for the non-covalent assembly.

This article describes an easy, economic and precise method for chairside pickup of Hader bar sleeves using condensation silicone putty and pattern resin. After torquing the titanium bar, proper block out is carried out using condensation silicone putty, followed by precisely creating space in the intaglio of the denture surface for picking up of the sleeves. Finally, pattern resin is used to pick up the attachment sleeves onto the intaglio surface of the denture.

The emergence of a novel coronavirus (SARS-CoV-2) in late 2019 has led to millions of infections and substantial morbidity and mortality across the world. COVID-19 caused by SARS-CoV-2 infection ranges from mild self-limiting disease to acute respiratory distress syndrome and death. India is presently reeling under the second wave of COVID-19 pandemic with more than 2,52,28,996 cases and 2,78,719 deaths as of 18 May, 2021 making it the country with highest reporting cases in the world. Till that date, Bangalore, the capital city of Karnataka alone reported a total of 22,42,065 COVID-19 positive cases overstretching Indian Health care system in this pandemic situation. Considering its high population densities and contact rates it poses a challenge for controlling COVID-19 which is transmitted directly from person to person. The question of herd immunity and how soon it would develop therefore appears to be highly relevant in the context of disease elimination programs.

Trigonal 3-connecting imidazole-annulated triptycene triacid (H3TPA) is a molecular module that is programmed for orthogonal self-assembly. Upon treatment with metal salts such as CoCl2, Mn(NO3)2, Zn(NO3)2 and Cd(NO3)2, highly porous isostructural MOFs are obtained in which the TPA linker undergoes metal–ligand coordination and hydrogen bonding through carboxylate groups and imidazole moieties, respectively. The MOFs are constructed by hydrogen bond-mediated offset stacking of porous (3,3) honeycomb layers formed by the self-assembly of TPA with 3-connecting triangular bimetallic SBUs. We show that the interlayer hydrogen bonds can be disrupted by solvents such as DMSO, leading to solvent-induced delamination of 2D metal–organic nanosheets. The delamination is signaled by turn-on of fluorescence, which is suppressed in the bulk state. Indeed, the extent of exfoliation with different solvents – as reflected from fluorescence quantum yields as well as solvent-induced shifts in emission maxima – can be nicely correlated with Gutmann's solvent DN numbers, which are a measure of the ability of solvents to accept hydrogens in hydrogen bonds. The results demonstrate how the bulk materials with layered structures can be (i) engineered in a ‘bottom-up’ approach by orthogonal self-assembly of an organic linker created by de novo design and (ii) in turn be exfoliated in a ‘top-down’ approach by solvent-induced ultrasonication. As bulk materials, the hydrogen-bonded MOFs lend themselves to selective as well as high adsorption of CO2 under ambient conditions as a result of the nitrogenous environment of pores conferred by the benzimidazole moieties.

Diarylbenzo- and naphthopyrans are one of the important and well-known classses of organic photochromic systems. Their photolysis leads to highly colored o -quinonoid intermediates. The mechanistic details and spectrokinectic properties of the photogenerated colored intermediates have been extensively studied. Accordingly, stereoelectronic effects have been shown to play a crucial role in controlling properties such as spectrokinetics, fatigue resistance and colorability. Much research continues unabated to develop photochromic materials with properties that surpass the existing ones for application in ophthalmic lenses as well as optical data storage devices. In the realm of materials chemistry, the diarylpyran unit is presently exploited as an essential design element to produce functional materials. Given the facile synthetic access to molecular systems that respond to light as an external stimulus leading to widely distinct physicochemical properties, we believe that more exciting research based on diarylpyran photochemistry will germinate in materials chemistry and biology in the near future. This review with a coverage of the phenomenon since its inception to the present state of application for functional materials–through synthesis and mechanistic details–should serve as an invaluable resource to an uninhibited chemist to exploit the photochromism of diarylpyrans for diverse functions/applications.

Biginelli reaction involves acid-catalyzed one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) using easily-accessible starting materials, namely, aldehyde, active methylene compound and (thio)urea. DHPMs have stimulated resurgence of interest in the past two decades due to their wide ranging pharmacological activities and presence of diverse natural products. Presently, green approaches to asymmetric Biginelli reaction are being explored for bioactive chiral DHPMs. In materials chemistry, DHPMs are increasingly finding applications in the development of materials such as polymers, adhesives, fabric dyes, etc. In view of the ease with which the Biginelli reaction is conducted, many exciting prospects await for its exploitation in various fields.

Statement of problem Occasional debonding between soft liners and denture base resin is common and limits the longevity of a relined prosthesis. Purpose The purpose of this systematic review was to compare the bond strength of commercially available soft liners with that of polymethyl methacrylate (PMMA) and urethane dimethacrylate (UDMA) denture base resins after different surface treatments and thermocycling. Material and methods Searches were performed by 2 independent reviewers in the MEDLINE/PubMed and Cochrane Library databases from January 1990 to December 2018 to identify published journal articles related to this subject. Subsequently, a hand search was also carried out for all the articles mentioned in the references of the identified full articles. Results A total of 61 articles were initially identified through database searches by the 2 reviewers. Twenty-four of the 61 articles met the inclusion criteria for qualitative analysis. Four of 6 articles showed that laser pretreatment of denture base resins increased their bonding to soft liners. Seven of 8 articles concluded that airborne-particle abrasion caused deterioration of the bonding between the liner and denture base resin. Four of 6 studies showed that acid etching, silica coating, primer or monomer application, and immersion in acetone or isobutyl methacrylate (iBMA) resulted in improved bond strengths between the liner and resin. One study reported that oxygen plasma treatment also resulted in improved bond strengths. Seven of 8 articles concluded that thermocycling resulted in decreased bond strengths. Conclusions Laser treatment, oxygen plasma pretreatment, primer or monomer application, and immersion in acetone or iBMA resulted in improved bonding of the denture base resin to soft liners. However, airborne-particle abrasion and thermocycling resulted in deterioration of the bond.

2D metal-organic nanosheets (MONs), akin to graphene, have aroused immense contemporary interest. In our quest to develop functional 2D MONs based on organic linkers designed de novo, we reasoned that benzene-tetrabenzoic acid, which has been exploited tremendously in the construction of pillared metal-organic frameworks (MOFs), could be maneuvered readily to access redox-active MONs based on the benzoquinone/hydroquinone redox couple. Herein, we show that the self-assembly of 2,3,5,6-tetrakis(p-carboxyphenyl)hydroquinone H4 BTA with Zn(NO3 )2 does lead to 2D metal-organic nanosheets that stack down the y axis, affording a layered Zn MOF. Although the crystals of the latter do not exhibit a discernible chemically induced redox switching behavior, the 2D MONs accessed by ultrasound-induced liquid-phase exfoliation (UILPE) lend themselves to a facile redox switching behavior. Treatment of a dispersion of the 2D MONs in methanol with phenyliodine(III) diacetate (PIDA) results in the oxidation of the hydroquinone core to benzoquinone. Remarkably, the latter can be reverted to the former by treatment with ascorbic acid as a reducing agent; indeed, the redox process can be made out by the naked eye. The results constitute the first example of chemically induced redox switching of 2D MONs. In view of emergent applications of 2D materials in general and MONs in particular, for example, improvement of the performance of membranes in separations by doping with MONs, the redox-switchable property may lead to the development of unique materials with heretofore unexplored potential.

Diarylbenzopyrans and their annulated derivatives are a class of photochromic compounds, which have been extensively investigated for photochromism. In fact, some naphthopyrans are employed industrially in ophthalmic lens applications. Photoirradiation of 2,2-diphenylbenzopyran leads to the formation of colored o-quinonoid intermediates. The latter revert too rapidly to allow their observation only at low temperatures (173–263 K). Annulation and other strategies are exploited to observe the colored o-quinonoid intermediates that persist for a few minutes at room temperature. We have examined photochromism of a set of silyloxy-substituted 2,2-diphenylbenzo- and naphthopyrans to explore how the mesomeric effects transmitted by the strongly e-donating silyloxy group substituted in the ring and at phenyl groups manifest in the spectrokinetic properties of their photogenerated colored o-quinonoid intermediates. We show that silyloxy substitution in the benzopyran ring leads to remarkable stabilization of the colored intermediates to enable their persistence at 283 K for a few minutes. In contrast, similar substitution in the C2-phenyl rings destabilizes the colored intermediates.

Phenyl/arylethynylation of 2,2-diphenylbenzopyrans (i.e., chromenes) permits modulation of the spectral properties of photogenerated colored o-quinonoid intermediates, and brings about remarkable stabilization of the latter, rendering the phenomenon of photochromism observable readily at room temperature. Modification of the spectrokinetic properties of the o-quinonoid intermediates are a consequence of resonance effects, with the substituent effects being relayed nicely from one end of the molecule to the other. Functionalization at the 6-position of the chromene nucleus leads to more redshifted absorptions as well as to increased lifetimes of the colored species when compared with functionalization at the 7-position. Given that photochromism is observable in the parent chromene at only low temperatures, phenyl/arylethynylation, which precludes steric inhibition of resonance, is demonstrated to render bleaching kinetics of the colored intermediates that approach those reported for industrially relevant diarylnaphthopyrans.

Fluorescence quenching by paramagnetic metal ions is attenuated in an Mn metal–organic framework (Mn-MOF) based on a pyrene linker. Based on solvent-dependent emission, the Mn-MOF is shown to serve as a solvent polarity probe. Further, sensing of nitroaromatics is demonstrated with a detection limit of ∼125 p.p.m. for TNT., An Mn metal–organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt’s solvent polarity parameter (E T N). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF.

A simple, sensitive, precise and accurate method for simultaneous estimation of metformin and sitagliptin from human plasma was developed and validated. Samples extracted from plasma using acetonitrile were separated on an SCX column and estimated using API 4000 Mass Spectrometer in the positive atmospheric pressure ionization mode (Turboionspray) by following multiple reaction monitoring transitions for both parent and daughter ions. A linear calibration plot was achieved for both the analytes in the concentration ranges of 10-2,206 ng/mL (for metformin) and 3-800.5 ng/mL (for sitagliptin) prepared in K2EDTA pooled plasma. Mean recovery for metformin was 92% and for sitagliptin was 104.5%. It is a fully validated method and successfully applied for estimation of these drug molecules during biostudies.

Anionic merocyanine colored dyes based on (4-nitro/cyanophenyl)-substituted thiazol-2-hydrazides (THAs), which are donor-π-acceptor type push-pull molecular systems and characterized with a strong intramolecular charge transfer (ICT) in the ground state, have been examined as reverse solvatochromic systems. THAs are shown to exhibit both positive and negative solvatochromism with a reversal of the latter occurring for solvents of ET(30) value of ca. 45. The observed behavior is traceable to relative contributions of benzenoid and quinonoid resonance forms of the THAs and their stabilization by solvents to different degrees. Solvatochromic studies in binary mixtures of polar aprotic and protic solvents reveal that the latter are always preferred in the solvation microsphere of THAs. Multiparametric treatment of the ET(dye) parameters by Catalan and Kamlet-Taft linear solvation energy relationships (LSERs) compellingly bears out the remarkable influence of hydrogen-bond donating (HBD) acidity, dipolarity and polarizability of the media on the spectral properties of the anionic dyes; hydrogen-bond accepting (HBA) basicity of the solvents is found to influence the least.

The photochromism of a chromene annulated on [2.2]paracyclophane, Ac-CPC, was investigated. Whereas the parent chromene 2,2-diphenylbenzopyran shows photoinduced coloration only at very low temperatures, acetyl-cyclophanochromene Ac-CPC was found to exhibit room-temperature photochromism. With no extended conjugation due to absence of any substituents in two cofacially-oriented aryl rings, the through-space delocalization of π-electrons, i.e., the phane effect, manifests nicely leading to the stabilization of the photogenerated colored o-quinonoid intermediates. The interaction between cofacial aryl rings is supported by the distance between them, as revealed by X-ray crystal structure analysis. Additionally, electrophile···nucleophile interactions are surmised to be important for intriguingly longer persistence of the photogenerated intermediates of Ac-CPC relative to the lifetime of the photogenerated intermediate generated from the parent cyclophanochromene, which is devoid of an electron-withdrawing acetyl group.

Photolysis of regioisomeric helical chromenes 1 and 2 leads to colored reactive intermediates. While the latter generally decay quite rapidly, they are found to be longer lived in 1 and highly persistent in 2. The remarkable stability of the otherwise fleeting transient in 2 allowed isolation and structural characterization by X-ray crystallography. The structural analyses revealed that steric force inherent to the helical scaffold is the origin of stability as well as differentiation in the persistence of the intermediates of 1 and 2 (1Q and 2Q). The structure further shows that diphenylvinyl moiety in the TT isomer of 2Q gets splayed over the helical scaffold such that it is fraught with a huge steric strain to undergo required bond rotations to regenerate the precursor chromene. Otherwise, reversion of 2Q was found to occur at higher temperatures. Aazahelical chromenes 3 and 4 with varying magnitudes of helicity were designed in pursuit of o-quinonoid intermediates with graded activation barriers. Their photogenerated intermediates 3Q and 4Q were also isolated and structurally characterized. The activation barriers for thermal reversion of 2Q-4Q, as determined from Arrhenius and Eyring plots, are found to correlate nicely with the helical turn, which decisively determines the steric force. The exploitation of helicity is thus demonstrated to develop a novel set of photoresponsive helicenes 2-4 that lead to colored intermediates exhibiting graded stability. It is further shown that the photochromism of 2-4 in conjunction with response of 2Q-4Q to external stimuli (acid, heat, and visible radiation) permits development of molecular logic gates with INHIBIT function.

Biginelli reaction involves acid-catalyzed one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) using easily-accessible starting materials, namely, aldehyde, active methylene compound and (thio)urea. DHPMs have stimulated resurgence of interest in the past two decades due to their wide ranging pharmacological activities and presence of diverse natural products. Presently, green approaches to asymmetric Biginelli reaction are being explored for bioactive chiral DHPMs. In materials chemistry, DHPMs are increasingly finding applications in the development of materials such as polymers, adhesives, fabric dyes, etc. In view of the ease with which the Biginelli reaction is conducted, many exciting prospects await for its exploitation in various fields.

A new LC–MS/MS method for the simultaneous determination of lamivudine, zidovudine, and nevirapine in human plasma is developed using column-coupling technique. Labeled compound of respective analyte was used as an internal standard. After extraction from 100 μL plasma by solid phase extraction method, analytes were separated on a C18 column coupled with a cation exchange column. Total run time was 4.5 min. A tandem mass spectrometric detection was conducted using multiple reaction monitoring under positive ionization mode with an electrospray ionization interface. The method was validated as per the FDA guidelines over the concentration range of 9.47–1466.67 ng/mL for lamivudine, 10.32–1600.00 ng/mL for zidovudine, and 15.05–2426.67 ng/mL for nevirapine. Precision was in the range 0.86–5.77 (intraday) and 1.92–8.19 (interday) while accuracy was 93.25–104.36 % (intraday) and 96.83–103.28 % (interday). Stabilities of stock in aqueous solutions and in plasma were also determined. The method can be applied to the pharmacokinetic study of a combination treatment.

The fluoride-mediated desilylation reaction has been exploited, for the first time, to trigger ring-opening of photochromic diarylbenzo-/naphthopyrans into highly colored anionic merocyanine dyes with high molar absorptivities to permit naked-eye sensing. The absorption spectral shifts, i.e., differences in the absorption maxima of colorless and colored forms, observed for a rationally designed set of silyloxy-substituted diarylpyrans subsequent to fluoride-induced ring opening are remarkably high (330–480 nm), and are unknown for any colorimetric probe. In particular, the disilyloxy-substituted diphenylnaphthopyran and its analog, in which the diphenyl groups are fused in the form of fluorene, allows “naked-eye” detection of fluoride in subppm levels (

A highly luminescent and water-stable homochiral Zn-MOF, i.e., Zn-PLA, developed based on pyrene-tetraacetic, selectively senses histidine amongst all other amino acids and also differentiates d and l isomers, as revealed by quenching of the fluorescence of its aqueous suspension., A highly luminescent and water-stable homochiral Zn-MOF, i.e., Zn-PLA, has been developed based on a pyrene-tetralactic acid, which inherently features concave shapes for guest inclusion, to explore sensing of amino acids by fluorescence quenching; the solid-state fluorescence quantum yield of the MOF was found to be 46%. The fluorescence of an aqueous suspension of Zn-PLA was shown to be quenched specifically by histidine amongst all the other amino acids. Selective sensing of histidine is of prime importance due to its relevance in a variety of biological functions. The lack of quenching of fluorescence of Zn-PLA by all the amino acids other than histidine has been rationalized based on the exchange of the cationic dimethylammonium species in the MOF crystals with histidine that is protonated in water; the latter is envisaged to quench the fluorescence via charge transfer in the excited state. Furthermore, the homochiral crystals of Zn-PLA were found to permit enantiodiscrimination in the quenching by the d- and l-forms such that the ratio of enantioselectivity, i.e., Kd/Kl, is 1.8, as determined by Stern–Volmer quenching plots. The highly selective as well as enantiodifferentiating sensing of amino acids by MOFs is unprecedented for any sensor type.

A comprehensive investigation of the photophysics of a broad set of fluorenones substituted with methoxy groups at different positions brings out the importance of the location of substituents on the fluorenone core in modulating fluorescence and radiationless deactivation by way of modification of the singlet-excited state energy and its character. While the substituents at para positions are found to affect neither the fluorescence quantum yield nor the lifetime, those at meta positions are found to significantly modify the latter. A cumulative effect is observed for the substituents in that the nonradiative decay (knr) becomes progressively dominant with an increasing number of meta-methoxy substituents. For example, the trimethoxy substitution in 2,4,7-trimethoxyfluorenone (8) is found to increase knr by ca. 30 fold relative to that of the parent fluorenone (1) in a polar aprotic solvent such as acetonitrile. The predominance of nonradiative decay (knr) is rationalized from stabilization of the singlet-excited state via partial charge transfer from meta-methoxy substituents to the carbonyl group. Accordingly, a nice correlation is observed for the nonradiative (knr) rate constants versus singlet-excitation energies derived from fluorescence emission maxima of all fluorenones in acetonitrile. The macrocyclic host cucurbit[7]uril (CB7) is found to not only enhance the fluorescence of the parent fluorenone (1) significantly, but also increase the singlet lifetime considerably. Based on the changes observed in the absorption spectra and the lifetimes determined, a 1:1 host–guest complex has been proposed with CB7. The fluorescence lifetime observed in the presence of CB7 suggests that the hydrophobic fluorenone (1) can be employed as a probe to report on a polar microenvironment shielded from hydrogen bonding interactions in a polar protic solvent.

Two independent cold-sensitive pet mutants in the gene (ATP5) coding for the oligomycin sensitivity conferring protein (OSCP) have been isolated in the yeast Saccharomyces cerevisiae. The mutations in both strains alter the initiating methionine codon in the ATP5 gene: ATG to ATA (Ile) and AAG (Lys). Western blot analysis of total yeast protein after the cells were grown at 18 degrees C, 30 degrees C, and 37 degrees C, indicates that the level of OSCP decreased 80% relative to the wild type strain. In addition, the level of the oligomycin-sensitive ATPase decreased 85% relative to the wild type strain, after growth at 30 degrees C. These findings indicate that for S. cerevisiae, the level of oxidative phosphorylation can decrease 85% without showing a large growth defect on media containing glycerol at 30 degrees C, but not at 18 degrees C.

Effects of arginine deficiency and hyperammonemia on the brain concentrations of amino acids and urea cycle enzyme activities in young and adult ferrets were investigated. Only young ferrets developed hyperammonemia and encephalopathy immediately after consuming the arginine-free diet. Brain ornithine and citrulline concentrations in young ferrets fed arginine containing diet were significantly lower than those in adult ferrets. Compared to rats and other animals, young and adult ferrets had lower concentrations of brain glutamic acid and glutamine. Unlike in other species, brain glutamine was not elevated in young, hyperammonemic ferrets. Brain arginase and glutamate dehydrogenase activities were significantly increased in young ferrets fed arginine-free diet. Young ferrets provide a useful animal model for investigating the neurotoxicity of acute hyperammonemia.

The problem of arsenic pollution in the ground water of West Bengal (WB), India may be a geochemical happening, but the matter is yet unsolved. To identify correlation amongst the ground water parameters (GWP), fuzzy regression analytical technique has been utilized and it is established that Na, K, Fe, pH and hardness have distinct correlations in arsenic prone areas and non-arsenic prone areas.

We investigated the systemic and pulmonary vascular effects of adenosine and determined plasma adenosine levels in pulmonary circulation in 12 newborn lambs during normoxia and during alveolar hypoxia (10% O2, 5% CO2, and 85% N2). Lambs were instrumented at 7 days of age with catheters in the descending aorta, main pulmonary artery, and right and left atria, and a flow transducer around the main pulmonary artery, and were studied following a 3-day recovery. Adenosine or an equal volume of normal saline (control) was infused into the right atrial line in doses ranging from 0.01 to 2.5 mumol/kg/min. In normoxic lambs, adenosine caused a significant decrease in pulmonary vascular resistance and increase in heart rate in doses of 0.15 to 2.5 mumol/kg/min and a decrease in systemic vascular resistance, with increase in cardiac output in doses of 0.3 to 2.5 mumol/kg/min. Baseline plasma adenosine levels in pulmonary artery and left atrium decreased significantly during alveolar hypoxia. Adenosine infusion in hypoxic lambs caused decreases in pulmonary artery pressure and pulmonary vascular resistance at all the doses tested. Aortic pressure and systemic vascular resistance decreased, and heart rate and cardiac output increased at doses greater than or equal to 0.3 mumol/kg/min in hypoxic lambs during adenosine infusion. The pulmonary vascular effects of adenosine in hypoxic lambs were attenuated by prior treatment of animals with aminophylline. Thus, adenosine appears to be an important regulator of pulmonary vascular response to hypoxia in newborn lambs. Its vasodilator effects were specific for pulmonary circulation when it was infused in doses less than or equal to 0.15 mumol/kg/min into the right atrium and appear to be mediated by P1 purinergic receptors.

We investigated the hypothesis that purine nucleotides may mediate the pulmonary vasodilation that occurs at bulb in fetal lambs. We studied nine fetal lambs 3 d after placement of intravascular catheters, a flow transducer around the left pulmonary artery, and an inflatable vascular occluder around the ductus arteriosus. The pressure-flow relationship of left lung during a brief occlusion of the ductus arteriosus was studied as an index of pulmonary vascular resistance. We investigated the pulmonary vascular effects of adenosine, ATP, or saline (control) in doses of 0.01–2.50 μmol/kg/min infused into the right atrial line, and measured blood adenosine and ATP levels in samples from the pulmonary artery and left atrium. We also investigated the mechanism of pulmonary vascular effects of adenosine and ATP. Adenosine and ATP caused significant decreases in pulmonary vascular resistance and increases in pulmonary blood flow in doses of 0.08–2.5 μmol/kg/min. The pulmonary blood flow increased to levels seen in postnatal lambs at doses of 1.2 and 2.5 μmol/kg/min of adenosine and ATP. The baseline blood adenosine and ATP levels in fetus were 8 and 70% of levels in postnatal lambs. ATP concentrations increased to postnatal levels and adenosine levels increased to 20% of postnatal levels at infusion rates of 1.2 and 23 μmol/ kg/rain. The pulmonary vasodilation caused by adenosine and ATP was attenuated by 8-phenyltheophylline and ci-bacron blue, respectively, but not by indomethacin. We conclude that adenosine and ATP are pulmonary vasodilators and increase the fetal pulmonary flow to postnatal levels in doses that increase their blood concentrations to ≤ postnatal levels. The effects of adenosine and ATP are mediated by stimulation of P1 and P2 pnrinergk receptors and are independent of prostacyclin synthesis. Purine nucleotides may be important mediators of pulmonary vasodilation that occurs in the perinatal Iamb.