Trans Form Research Articles

Vibrational Spectroscopic Identification of the [AlCl2]+ Cation in Ether-Containing Liquid Electrolytes

A Raman and IR study of AlCl3-based ethereal solutions is here presented and aims at identifying the [AlCl2]+ cation, which has been so far unambiguously characterized by 27Al NMR spectrometry. To do that, experimental–theoretical vibrational spectroscopy was so employed, and the data are interpreted successfully. As a known amount of water is added to the tetrahydrofuran (THF)-containing electrolyte, a Raman band at 271 cm−1 has its intensity increased along with the most intense band of [AlCl4]−, and such behavior is also seen for a band at 405 cm−1 in the IR spectra. New bands at around 420 and 400 cm−1 are observed in both Raman and IR spectra for the tetraglyme (G4)-based systems. The [AlCl2(THF)4]+ complex, in the cis and trans forms, is present in the cyclic ether, while the cis-[AlCl2(G4)]+ isomer is identified in the acyclic one.

Isomer-Specific, Cryogenic Ion Vibrational Spectroscopy Investigation of D2- and N2-Tagged, Protonated Formic Acid Complexes Using Two-Color, IR-IR Photobleaching.

Here we analyze cryogenic ion vibrational spectra of tagged protonated formic acid (PFA) with electronic structure and anharmonic vibrational calculations to establish the isomers generated by electrospray ionization (ESI) followed by buffer gas cooling to ∼25 K. Two isomers are identified (the trans form (E,Z) and the cis form (E,E)) and generated in comparable abundance despite the fact that the calculated E,E structure lies 6.40 kJ mol-1 above the E,Z form. A large (∼60 kJ mol-1) barrier separates them such that the E,E form can be kinetically trapped upon cooling in the ion trap. The anticooperativity between the H-bonds of the OH groups is explored by measuring the shift in the D2-bound OH fundamental when a second D2 is attached. Both isomers are observed in the N2-tagged counterparts, displaying the expected red-shifted OH bands. These results indicate that ESI generates both isomers and both must be considered when analyzing cluster spectra based on the PFA core ion.

Hematologic Parameters Cut-off Assessment of Adult Alpha-Thalassemia Patients in Iran

Background: Thalassemia is one of the most common blood disorders in Iran. Alpha-thalassemia is caused by the deletion of the alpha-globin gene. The frequency of deletions in the alpha-globin gene is associated with microcytosis and hypochromia, making hematological parameters valuable predictive tools in the initial identification of alpha-thalassemia patients. This study aimed to compare hematologic parameters such as Mean Corpuscular Volume (MCV), Mean Corpuscular Hemoglobin (MCH), red blood cell (RBC) count, and hemoglobin (HGB) levels in silent and minor patients, whose genotypes were genetically characterized, with normal patients to establish cut-off points for these groups. Materials and Methods: The study involved a total of 860 patients with alpha-thalassemia, including 267 cases of silent, 261 cases of minor, and 332 cases of normal alpha-thalassemia. Results: Analysis of blood indices based on sex revealed that the male group had higher values than the female group. Assessment of alpha-thalassemia in minor patients showed that the Cis form (—/αα) had higher microcytosis than the Trans form (–α/–α) in this group. This difference was also observed between α-3.7α/ α-3.7α and (αα)-MED/αα as two different genetic forms in minor patients, with (αα)-MED/αα being in the Cis form. Data indicated that the cut-off value was insignificant in silent patients compared to the normal group. However, minor patients with MCH≤23.7 and MCV≤74.9 had an AUC greater than 0.9 (p-value< 0.01), distinguishing them from the normal group. Conclusion: Comparing hematological parameters in these groups illustrated that MCV and MCH are the best predictor parameters for distinguishing between groups.

Thermally Stable Heteroleptic Trans‐Bis(Chelate) Ruthenium(II) Complex Bearing 2,2’‐Bipyridine and Acetylacetonato: Synthesis, Isomerization, and Crystal Structure

AbstractThermally stable trans‐bis(chelate)‐type Ru(II) complexes are challenging to prepare owing to steric hindrance between the two chelate ligands. Herein, we investigated the isomerization of a heteroleptic cis‐bis(chelate) complex to obtain its trans form. cis‐[Ru(acac)(bpy)(dmso‐S)2](OTf)⋅0.5H2O (1⋅(OTf)⋅0.5H2O; acac−=acetylacetonato; bpy=2,2’‐bipyridine; dmso=dimethyl sulfoxide; OTf−=CF3SO3−) was prepared by reacting trans(O,S)‐[Ru(bpy)(dmso‐S)2(dmso‐O)2](OTf)2 (P0) with Li(acac) in acetone at 298 K. In 1⋅(OTf)⋅0.5H2O, the two labile dmso‐O ligands of P0 were replaced by an acac− ligand. The dihedral angle between the chelate rings of bpy and acac− in 1+ was 76.7°, suggesting steric hindrance between ligands owing to the two bulky dmso‐S ligands at the cis position. 1⋅(OTf)⋅0.5H2O was thermally stable in DMSO and acetone; however, in methanol and water, a dmso‐S ligand was dissociated from 1+, and the complex isomerized to trans‐[Ru(acac)(bpy)(dmso‐S)(solvent)]+. Refluxing of 1⋅(OTf)⋅0.5H2O in methanol for 18 h, evaporation to dryness under vacuum, and treatment with water yielded trans‐[Ru(acac)(bpy)(dmso‐S)(OH2)](OTf) (2⋅(OTf)) with excellent purity. 2⋅(OTf) was characterized by X‐ray crystallography, elemental analysis, and 1H NMR spectroscopy. As expected, steric hindrance was not observed between the trans‐arranged bpy and acac−, and the two chelates laid flat on the equatorial plane in 2+.

Photoinduced Birefringence and Liquid Crystal Orientation on Polymers with Different Azobenzene Content in the Main Chain.

In this paper, we give an overview of novel main-chain azobenzene-based fluorinated poly(arylene ether)s with different content of azo groups, aiming at providing a better understanding of the link between a number of N═N bonds and the macroscopic response of the material. We discuss chemical synthesis and molecular structure and report on a comprehensive analysis of the polymer properties, thermal behavior, and mechanical strength. We show that a higher content of azobenzene moieties reduces the mechanical strength of the polymer materials. On the other hand, polymers with a higher content of azobenzene demonstrate higher values of induced birefringence due to a larger number of azobenzene in the trans form. The photoisomerization constants of all polymers fall within a very close range. The minor variations are attributed to the number of azobenzene groups in the polymer composition and the conformational arrangements of the polymer chain packing. The developed light-sensitive polymers were employed for dynamic control and manipulation of the liquid crystal orientation by polarization of the incident light. After the double irradiation of the substrates using appropriate photomasks, we made patterned cells that consist of domains with different high-resolution liquid crystal director orientations.

Oxacalix[4]arene functionalized macrocycle with columnar liquid crystal phase and self-assembly tuned by reversible photoisomerization process

Oxacalix[4]arene is a unique type of macrocyclic compound closely related to calixarenes. It consists of four aromatic rings connected by oxygen bridges. This molecule exhibits a remarkable blend of rigidity and flexibility, making it adaptable to various molecular interactions. In present study, we present our findings on the synthesis and characterization of four new supramolecular bowl-shaped materials (FOC1-FOC4) originating from the robust core structure of tetranitro oxacalix[4]arene. The thermal decomposition was analyzed through the thermogravimetric analysis. All four oxacalix[4]arene-based macrocycles adopted a 1,3-alternate (saddle-like) conformation and exhibited a columnar hexagonal phase with a behavior to self-assemble at room temperature. All four macrocycles (FOC1-FOC4) displayed enantiotropic mesophases within a temperature range of 56.0 °C to 63.0 °C. Further, the relationship between the molecular structure, particularly the varying alkyl chains, and the mesomorphic properties of these compounds was also examined. It was found that the mesomorphic behavior of FOC3 and FOC4 was significantly influenced by cis and trans isomerization. These two compounds exhibited photoswitching behavior, transitioning between their cis and trans forms when exposed to 365 nm light. Notably, they displayed a prolonged stability in the cis form after UV exposure, which is valuable for applications requiring precise control over the switching process.

In Situ Photoreversible Tuning of Chemical Interface Damping in Single Gold Nanorods Through Cucurbit[8]uril-Based Host-Guest Interactions.

Chemical interface damping (CID) is a recently proposed plasmon-damping pathway based on the interfacial hot-electron transfer from metal to adsorbate molecules. However, the in situ reversible tuning of CID in single gold nanorods (AuNRs) has remained a considerable challenge. In this study, we used total internal reflection scattering microscopy and spectroscopy to investigate the CID induced by p-aminoazobenzene (p-AAB), which has fast photoisomerization characteristics, attached to single AuNRs. We demonstrated the in situ reversible tuning of CID in single AuNRs by switching between ultraviolet (UV, 365 nm) and visible (vis, 465 nm) irradiation to induce photoresponsive structural conversions between the cis and trans forms of p-AAB in ethanol, leading to different lowest unoccupied molecular orbital (LUMO) energies for both forms. The localized surface plasmon resonance (LSPR) line width was wide under vis irradiation but narrow under UV irradiation, indicating that hot electrons are more efficiently transferred to trans-p-AAB with a low LUMO energy level. We further investigated the in situ photoreversible tuning of CID by manipulating supramolecular host-guest interactions between cucurbit[8]uril (CB[8]) and p-AAB in the single AuNRs. Additionally, real-time in situ reversible tuning of CID in single AuNRs was achieved through photonic switching of the cis-trans forms of p-AAB inside CB[8]. The LSPR line width was narrow under vis irradiation but gradually widened under UV irradiation before narrowing again upon returning to vis irradiation, unlike the case with p-AAB only. These results can be ascribed to the fact that cis-p-AAB completely encapsulated within CB[8] in water is thermodynamically more favorable than trans-p-AAB. Therefore, we have discovered a new strategy for tuning the CID by performing p-AAB photoisomerization and adjusting the wavelength of incident light in single AuNRs. In addition, this study demonstrates that CID can be effectively applied to the development of biosensors to detect guest molecules and their structural changes inside the cavity of CB[8] in single AuNRs.

Effect of Bipyridines on Catalytic Oxygen Reduction by Oxamidato‐Bridged Dicopper(II) Complexes

ABSTRACTThe oxygen reduction reaction (ORR) has a crucial impact on the energy conversion efficiency and the performance of fuel cells, it is urgent to deliver low‐cost efficient ORR catalysts for the aim to scale up the utilization of fuel cells. In this study, three oxamidate copper(II) complexes [Cu2(trans‐L)(H2O)2(ClO4)2]·2H2O (Cuox), [Cu2(cis‐L)(bpy)(ClO4)2]·CH3OH (Cuoxbpy), and [Cu2(cis‐L)(mebpy)(ClO4)](ClO4) (Cuoxmebpy) (L = N,N–bis(2–pyridylmethyl)oxamide, bpy = 2,2′–bipyridine, and mebpy = 4,4′–dimethyl–2,2′–bipyridine) were prepared and characterized. The configuration of L varied from the trans form to the cis form as the bipyridines were introduced to the dicopper complex. The redox properties of three oxamidate copper(II) complexes and their catalytic activities for the ORR were studied in neutral aqueous solutions. The ORR onset potentials by Cuox, Cuoxbpy, and Cuoxmebpy were 0.417, 0.502, and 0.481 versus RHE, respectively. Three complexes homogeneously catalyzed the ORR to predominantly generate H2O2. A bimolecular catalytic pathway was proposed for the ORR mediated by Cuox, whereas a single‐molecular pathway was by Cuoxbpy and Cuoxmebpy. This work demonstrated that oxamidate metal complexes are promising ORR catalyst candidates provided that their electronic structures are appropriately tuned by altering the substituent on the organic ligands.

A novel cinnamic and caffeic acid-conjugated peptide analogs with anticonvulsant and analgesic potency: Comparative analyses of trans/cis isomers.

The novel cinnamic acid (CA) (H4-CA, H5-CA, and H7-CA) and caffeic acid (KA) (H4-KA, H5-KA, and H7-KA) hemorphin analogs have recently been synthesized and their trans isomers have been tested for antiseizure and antinociceptive activity. In the present study, the cis forms of these compounds were tested and compared with their trans isomers in seizure and nociception tests in mice. The cis-H5-CA and H7-CA compounds showed efficacy against psychomotor seizures, whereas the trans isomers were ineffective. Both the cis and trans KA isomers were ineffective in the 6-Hz test. In the maximal electroshock (MES) test, the cis isomers showed superior antiseizure activity to the trans forms of CA and KA conjugates, respectively. The suppression of seizure propagation by cis-H5-CA and the cis-H5-KA was reversed by a kappa opioid receptor (KOR) antagonist. Naloxone and naltrindole were not effective. The cis-isomers of CA conjugates and cis-H7-KA produced significantly stronger antinociceptive effects than their trans-isomers. The cis-H5-CA antinociception was blocked by naloxone in the acute phase and by naloxone and KOR antagonists in the inflammatory phase of the formalin test. The antinociception of the KA conjugates was not abolished by opioid receptor blockade. None of the tested conjugates affected the thermal nociceptive threshold. The results of the docking analysis also suggest a model-specific mechanism related to the activity of the cis-isomers of CA and KA conjugates in relation to opioid receptors. Our findings pave the way for the further development of novel opioid-related antiseizure and antinociceptive therapeutics.

Unraveling biological disparities in configurational isomers of pyrazolyl-dihydrofurans using in vitro, DFT and in silico approach

The biological disparities in the high activity of one isomeric form over another have attracted significant interest from medicinal chemists and opened new avenues for synthesizing pure diastereoisomeric drugs.A series of diastereoisomeric pure pyrazolyl-dihydrofurans (6a-6ae) were synthesized in good to excellent yields, and their structures were determined using NMR, LCMS and X-ray crystallography. The difference in the stability of cis and trans isomers has been established using DFT-based studies. Using the serial dilution method, the developed synthetics were evaluated for their bio-efficacy against bacterial and fungal strains. The cytotoxicity was evaluated against mouse fibroblast cells as well as using the seed germination method.All the reactions proceeded smoothly and resulted into cis as the significant isomer; the stability over trans isomer has been established using DFT-based computational studies. Considering 6a and 7a as prototype, the difference in their biological response has been evaluated through in vitro anti-microbial assay. A significant difference in the biological activity has been observed, as the cis isomer (6a) has been found to be more potent over its respective trans isomer (7a) in bacterial assay. As far as the fungal response is concerned, no difference in their biological activity has been observed. The investigated compounds are non-cytotoxic against mouse fibroblast cells and Brassica nigra seeds. The experimentally determined in vitro results have been established using in silico studies.The cis isomer (6a) with an MIC of 3.25 µg/mL has been found to be more potent than the respective trans (7a) form (MIC = 6.25–12.5 µg/mL) when evaluated against different gram positive and negative strains utilized in the present study. However, no disparity in their biological response has been observed in fungal studies.

Wavelength-dependent photoisomerization of trans-4,4′-azopyridine: Nonadiabatic dynamics simulation

The trans–cis photoisomerization processes of 4,4′-azopyridine upon S1 and S2 excitations have been investigated by nonadiabatic dynamics simulations based on multi-reference CASSCF calculations. 119 sampling trajectories were simulated starting from the trans form excited to the S1 (S2) state and the cis-isomer quantum yield is evaluated to be (3 ± 2)% ((18 ± 4)%), which is qualitatively in agreement with the recent experimental results in ethanol. We found that rotation around the central N-N bond accompanied by the N-N-C symmetrical bending vibrations is the main mechanism in photoisomerization of the target molecule excited to the S1 and S2 states. Upon S1 excitation, S1-S0 transition occurs earlier along the C-N-N-C torsional coordinate, leading to a low cis-isomer quantum yield. Upon S2 excitation, half of the simulated trajectories are trapped in a potential well on the S2 state, from which the twisted conical intersections are more easily reached in the internal conversion, resulting in a higher cis-isomer quantum yield.

The photochemical trans → cis and thermal cis → trans isomerization pathways of azobenzo-13-crown ether: A computational study on a strained cyclic azobenzene system.

The isomerization of azobenzo-13-crown ether can be expected to be hindered due to the polyoxyethylene linkage connecting the 2,2'-positions of azobenzene. The mixed reference spin-flip time-dependent density functional theory results reveal that the planar and rotational minima of the first photo-excited singlet state (S1) of the trans-isomer pass through a barrier (2.5-5.0 kcal/mol) as it goes toward the torsional conical intersection (S0/S1) geometry (<CNNC ≈ 98°), which is responsible for the cis isomer formation. The second excited singlet state (S2) of the trans form has a nearly planar minimum along the N-N stretching mode, which approaches a sloped S2/S1 intersection geometry. This excited state has a rotational minimum (<CNNC ≈ 99°) as well. Both these minima have a characteristic S2-S1 energy gap of 9 kcal/mol and may undergo internal conversion. A comparison of this system with an analogous 2,2'-dimethoxy-substituted azobenzene system reveals less strain in the rotational path of the latter on the S1 surface, indicating the possibility of its better trans → cis yield than the azocrown. The completely planar S2 geometry of the dimethoxy system has easy access to the linear concerted inversion path, which seems to be the reason behind its reported slightly lower π-π*(S2) yield than n-π*(S1). The thermal cis → trans isomerization path of the azobenzo-13-crown passes through a transition state (frequency 453i cm-1), which corresponds to Gibbs free energy of activation value of 26 kcal/mol in the gas-phase and isooctane. Our study also confirms that its trans isomer strongly binds Li+ among the alkali metal ions, and this observation may open up possibilities for practical applications of this azobenzo-crown.

Theoretical study on the structure, spectroscopic, and current–voltage behavior of 11-Cis and Trans retinal isomers in rhodopsin

In this study, the electronic transport properties of 11-Cis and Trans retinal, components of rhodopsin, were investigated as optical molecular switches using the nonequilibrium Green’s function (NEGF) formalism combined with first-principles density functional theory (DFT). These isomers, which can be reversibly converted into each other, were examined in detail. The structural and spectroscopic properties, including infrared (IR), Raman, nuclear magnetic resonance (NMR), and ultraviolet (UV) spectra, were analyzed using the hybrid B3LYP/6–311 + + G** level of theory. Complete vibrational assignments were performed for both forms utilizing the scaled quantum mechanical force field (SQMFF) methodology. To evaluate the conductivity of these molecules, we utilized current–voltage (I-V) characteristics, transmission spectra, molecular projected self-consistent Hamiltonian (MPSH), HOMO–LUMO gap, and second-order interaction energies (E2). The trendline extrapolation of the current–voltage plots confirmed our findings. We investigated the effect of different electrodes (Ag, Au, Pt) and various connection sites (hollow, top, bridge) on conductivity. The Ag electrode with the hollow site exhibited the highest efficiency. Our results indicate that the Cis form has higher conductivity than the Trans form.

Very stable open form of 2H-naphthopyran: A theoretical study

Using DFT calculations, it was shown that the intermediate stacked form of the ground state of 2H-naphthopyran can be formed not only during the relaxation of the intramolecular S1 excimer but also during the thermal recovery of the closed form from the trans–trans and cis–trans isomers of the open form. The potential well corresponding to the intermediate form is an additional factor in the stability of the open form, since from this well the molecule can return to the open cis–trans form using thermal motion. The cis–trans and trans–trans isomers of the open form are separated from each other by potential barriers with a height of 1.25 eV. Their overcoming by thermal motion is less likely than the transition of the cis–trans form to the intermediate stacked form. The absorption of conformers in the visible region, which determines the color of the open form, was calculated using TD-DFT; the resulting vibronic absorption band of the trans–trans form coincided well with the experimental one.

Photo-transformations of 2-aminothiazole-4-carboxylic acid in low-temperature matrices

The structure, spectroscopic properties and photo-induced conformational changes of 2-aminothiazole-4-carboxylic acid (ACA) isolated in argon and nitrogen matrices were studied using matrix-isolation FTIR spectroscopy and DFT calculations undertaken at the B3LYPD3/6–311++G(3df,3pd) level of theory. Out of 18 stable isomers, the three most stable structures with the five-membered ring stabilized by two C=C and C=N double bonds and with different arrangement of the carboxyl group were identified in both matrices after deposition. Conformer ACA1 has trans and conformers ACA2 and ACA3 have cis conformation of the COOH group and the calculated abundance of 69.5%, 18.2% and 12.2%, respectively. Following irradiation at 285 nm, a rotation of the OH group around the C–O bond in ACA1 was detected leading to increase of ACA2. The corresponding reverse photo-rotamerization was detected at 296 nm, resulting in the recovery of the initial isomer ACA1. Upon NIR irradiation a dominant process was rotamerization within the carboxylic group leading to changes in the population of the ACA1 trans and ACA2 cis forms.

Cationic Azobenzenes as Light-Responsive Crosslinkers for Alginate-Based Supramolecular Hydrogels.

Azobenzene photoswitches are fundamental components in contemporary approaches aimed at light-driven control of intelligent materials. Significant endeavors are directed towards enhancing the light-triggered reactivity of azobenzenes for such applications and obtaining water-soluble molecules able to act as crosslinkers in a hydrogel. Here, we report the rational design and the synthesis of azobenzene/alginate photoresponsive hydrogels endowed with fast reversible sol-gel transition. We started with the synthesis of three cationic azobenzenes (AZOs A, B, and C) and then incorporated them in sodium alginate (SA) to obtain photoresponsive supramolecular hydrogels (SMHGs). The photoresponsive properties of the azobenzenes were investigated by UV-Vis and 1H NMR spectroscopy. Upon irradiation with 365 nm UV light, the azobenzenes demonstrated efficient trans-to-cis isomerization, with complete isomerization occurring within seconds. The return to the trans form took several hours, with AZO C exhibiting the fastest return, possibly due to higher trans isomer stability. In the photoresponsive SMHGs, the minimum gelation concentration (MGC) of azobenzenes was determined for different compositions, indicating that small amounts of azobenzenes could induce gel formation, particularly in 5 wt% SA. Upon exposure to 365 nm UV light, the SMHGs exhibited reversible gel-sol transitions, underscoring their photoresponsive nature. This research offers valuable insights into the synthesis and photoresponsive properties of cationic, water-soluble azobenzenes, as well as their potential application in the development of photoresponsive hydrogels.

Photoresponse of new azo pyridine functionalized poly(2-hydroxyethyl methacrylate-co-methyl methacrylate)

A new azo polymer containing photoisomerizable azo pyridine functionalities was synthesized via Mitsunobu reaction of 4-(4-hydroxyphenylazo)pyridine with poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (p(HEMA-co-MMA)) for creating new photochromic materials. The resulting polymer with azo pyridine side groups was characterized for structural, thermal, and optical properties. UV–vis, 1H NMR and IR spectroscopies confirmed that all hydroxyl groups in p(HEMA-co-MMA) were substituted with azo dye. The obtained azo copolymer exhibited high thermal stability (around 240 °C) and a glass transition temperature (113 °C), promising for applications. The trans-to-cis isomerization upon UV irradiation and the thermal back reaction of the azo chromophore in the copolymer in the solid state was studied. A photostationary state with 50% content of cis-isomers upon 6 min of UV irradiation was reached, and during 48 h dark relaxation at ambient temperature, all cis-isomers converted to the trans form. Additionally, the possibility of efficient photogeneration of surface relief gratings with high amplitude of azo copolymer surface modulation was demonstrated.

Geometry-induced Oligomerization of Fluorine-substituted Phenylazothiazole Photoswitches.

Photoswitches are molecules that can absorb light of specific wavelengths and undergo a reversible transformation between their trans and cis isomeric forms. In phenylazo photoswitches, it is common for the less stable cis (Z) isomer to convert back to the more stable trans (E) isomer either through photochemical or thermal means. In this research, we designed new derivatives of phenylazothiazole (PAT) photoswitches, PAT-Fn, which feature fluorine substituents on their phenyl component. These derivatives can reversibly isomerize under visible light exposure with the enrichment of E and Z isomers at photostationary state (PSS). Surprisingly, we observed an unconventional phenomenon when these PAT-Fn (n ≧2) photoswitches were in their cis isomeric state in the absence of light. Instead of the anticipated transformation from cis to trans isomer, these compounds converted to an oligomeric compound. Our detailed experimental investigation and theoretical calculations, indicated the crucial role of fluorine substituents and the distinctive geometric arrangement of the cis isomer in driving the unexpected oligomerization process originating from the cis isomeric state.

Evaluation of Plant Essential Oils as Natural Alternatives for Alcohol-based Mouthwashes: Spotlight—Lemongrass and Citronella Java

Abstract Objective The purpose of our study was to evaluate plant-derived essential oils (EOs) as natural alternatives to commercial alcohol-based mouthwashes in the prevention of dental caries since several recent studies have linked high incidence of oral cancer among users with a history of prolonged use of alcohol-based mouthwashes. Materials and Methods Lemongrass, Citronella Java, Gingergrass, and Caraway seed EOs were tested against commonly occurring multidrug-resistant (MDR) oral bacteria namely Micrococcus luteus, Enterococcus faecalis, Streptococcus oralis, and Streptococcus salivarius. Agar well diffusion method was used to determine the antibacterial effectiveness of these EOs. Samples of Citronella Java and Lemongrass EO were also analyzed by gas chromatography (GC). Results Lemongrass and Citronella Java exhibited the highest antibacterial activity against all four bacterial strains. Inhibition zones of Lemongrass were 12, 21.3, 28.3, and 32 mm in diameter against E. faecalis, M. luteus, S. oralis, and S. salivarius, respectively. In comparison, inhibition zones of Citronella Java were 11.5, 17, 20.7, and 20.2 mm in diameter against E. faecalis, M. luteus, S. oralis, and S. salivarius, respectively. A significant finding in our study was that antibacterial activity of Lemongrass was much higher than that of tetracycline, a broad-spectrum antibiotic, against S. oralis and S. salivarius, while the inhibitory effects of Citronella Java against these two oral streptococci were comparable to tetracycline. The major components of Citronella Java identified by GC were citronellal, citronellol, and geraniol, whereas Lemongrass was primarily composed of cis and trans forms of citral. Conclusion Our results suggest that Lemongrass and Citronella Java could be promising natural alternatives to alcohol-based mouthwashes against MDR oral bacteria in the prevention of dental caries.

Sequence effects on the thermal cis–trans isomerization of side‐chain stearate‐containing azobenzene polymers

AbstractPhotochromic azobenzenes undergo light‐mediated trans–cis isomerization. The cis isomer reverts to the trans isomer thermally. To investigate the effect of different monomer sequences on the thermal stability of cis‐azobenzene, a series of copolymers, namely, block, and random structures containing stearic acid and azobenzene moieties as their side chains have been synthesized through reversible addition–fragmentation chain transfer (RAFT) polymerization. In this study, we investigate the photoisomerization of the trans and cis forms of the polymers and also the thermal reversal of the cis‐azobenzene photochromic systems. The isomerization data revealed significant differences in the isomerization timescales between the polymers and the corresponding monomer. It was observed that the local polarity around the azobenzene units within a polymer was significantly influenced by the chain segment depending on whether it was in the vicinity of the hydrophobic alkyl chains or other azobenzene units. This local environment of the azobenzene units regulates the stabilization of the transition states during the cis–trans thermal isomerization, consequently affecting the half‐life of the cis isomer.