Trans Form Research Articles

Covalent functionalisation of graphene: novel approach to change electronic structure of graphene

Graphene (GR) attracts increasing attention due to its unique physical and chemical properties, thus potential applications in optics and electronics. However the gapless band structure greatly limits its wide applications in optoelectronic devices. Surface functionalisation proves to be an effective method to tune the properties of graphene. In this study, hybrid GR materials with enhanced properties were achieved through GR surface functionalisation by using aryl diazonium salts of photosensitive azobenzene. Conformational transition from trans to cis states of azobenzenes induces hole doping in graphene through charge transfer. Significantly different from the pristine graphene, the graphene–azobenzene hybrids exhibited strong photoisomerisation of azobenzene between cis and trans forms under UV and visible light illumination. The large photoresponse obtained from the functionalised GR could be ascribed to the rigid chemical environment with azobenzene moieties chemically bonded onto the GR surface. Such surface functionalised GR hybrids with unique optical properties position them as promising materials for optoelectronic devices.

A DFT study of the ionization and electron attachment of 2-azido pyridine

A DFT study using B3LYP/6-31G(d,p) level of theory is pursued to investigate the energy and geometry changes of 2-azido pyridine isomers in the S0, D0+, and D0−. In S0, cis-2 azidopyridine is the most stable, followed by cyclic tetrazole and trans isomer is the least stable. In D0+, the cis isomer is the most stable, followed by trans isomer, and tetrazole isomer is the least stable. In the D0− state, the trans form is the most stable, followed by the cis and the tetrazolo form is the least stable. Single point vertical excitation energy calculations of the cis form gave four excited states at 266.4, 239.4, 199.4, and 196.1nm, all having π–π∗ character. For trans isomer, five excited states at, 256.7, 250.3, 229.7, 199.0, 197.0nm all resulting from π–π∗ transitions. For the tetrazole isomer, seven excited states at 269.3, 242.7, 198.0, 187.2, 183.9, 182.1, 178.7nm all resulting from π–π∗ transitions. The geometries of the 3 isomers show noticeable changes in bond lengths, bond angles and dihedral angles, upon ionization and electron attachment. The ionization results in a remarkable variation of the NBO atomic charges as a result of ionization and electron attachment. where electron density of HOMO of the D0+ state is found to be much lower than that of the HOMO of the S0 in the case of ionization. The dipole moment calculations show that tetrazole isomer has the largest polarization in the S0 state, followed by cis isomer and trans isomer is the least polarized. The same pattern is found in the D0+ state. In the D0− state, trans isomer is the highest polarized, followed by the cis, and tetrazole isomer is the least polarized. The rotational constants calculations of cis- isomer show that the cation is elongated along the long in-plane axis and compressed along the two short out-of-plane axes while the anion is compressed along the long in-plane axis, and elongated along the two short out-of plane axes. The cation and anion of trans isomer show similar behavior to the cis isomer. The cation of cyclic tetrazole, is compressed along the long in-plane axis and elongated along the two short out-of-plane axes, while the anion elongates along the 3 mutually perpendicular axes.

Astaxanthin profiles and corresponding colour properties in Australian farmed black tiger prawn (Penaeus monodon) during frozen storage

The colour of commercial cooked black tiger prawns (Penaeus monodon) is a key quality requirement to ensure product is not rejected in wholesale markets. The colour, due to the carotenoid astaxanthin, can be impacted by frozen storage, but changes in colour or astaxanthin profile, during frozen storage, have not been studied in detail. Subsequently in this study, the aims were to define the astaxanthin (as cis, trans, mono-ester and di-ester forms) content, together with the colour properties, in both pleopods (legs) and abdominal segments. Changes in astaxanthin content and colour properties were further determined during frozen storage (−20°C). Total astaxanthin content was seen to decrease in all samples over time, with the rate of degradation being significantly greater (P < 0.05) in pleopods than abdomen. In both pleopods and abdomen, rate of degradation of esterified forms was significantly greater (P < 0.05) than non-esterified forms. Hue angle (increase), a* value (decrease) and L value (increase) were all seen to significantly change (P < 0.05) during storage, with changes being more prevalent in the pleopods. The pleopods are the key indicator of astaxanthin and colour loss in cooked black tiger prawns and preservation strategies are required to preserve astaxanthin and colour during frozen storage.

Control of cellular function by reversible photoregulation of translation.

The use of light as an external stimulus offers the potential for spatiotemporal control and is thus ideal for controlling gene expression in living cells. In commonly used caging systems, once the caging compound is removed, protein expression cannot be stopped, due to the irreversibility of the uncaging reaction. We have developed a reversible method for regulating protein expression with the aid of a photoresponsive cap that can control the translation of mRNA in a reversible manner through triggering of cis-trans photoisomerization of the cap. In its trans form, the photoresponsive cap completely inhibited translation, whereas the cis form yielded protein (12.7 times more translated protein than in the trans form). Moreover, we succeeded in controlling the levels, timing and duration of protein expression in living mammalian cells. Additionally, neuronal differentiation of PC12 cells was photoinduced by controlling constitutively active H-Ras 61L protein expression.

Photoisomerization mechanism of 1,1′-dimethyl-2,2′-pyridocyanine in the gas phase and in solution

The trans→cis and cis→trans photoisomerization mechanisms of 1,1′-dimethyl-2,2′-pyridocyanine have been investigated theoretically in the gas phase and in methanol. Two-dimensional potential energy surfaces were computed for the ground and first excited singlet states of the isolated molecule using complete active space self-consistent field method. Our computations suggest that the torsion around the central CC bonds with carbon-out-of-plane motion is the preferred photoisomerization mechanism. In the gas phase, conical intersections were found near the minima of excited state. The excited-state decay follows a barrierless minimum-energy pathway before the molecule moves to the excited-state global minimum (minS1) and the system relaxes to the ground state through a conical intersection. In methanol, the system would first reach a stationary structure of C2 symmetry after the trans form is electronically excited. Solvent polarity effects were investigated in chloroform, dichloromethane, 1-propanol, ethanol, methanol, and water. There is a significant barrier between the stationary structure of C2 symmetry and minS1 in the excited state in high polarity solvents. Thus, Me-1122P has a much longer lifetime of the excited state in solvents of high polarity.

Structural Conformational Study of Eugenol Derivatives Using Semiempirical Methods

We investigated the conformational structure of eugenol and eugenyl acetate under torsional angle effect by performing semiempirical calculations using AM1 and PM3 methods. From these calculations, we have evaluated the strain energy of conformational interconversion. To provide a better estimate of stable conformations, we have plotted the strain energy versus dihedral angle. So, we have determined five geometries of eugenol (three energy minima and two transition states) and three geometries of eugenyl acetate (two energy minima and one transition state). From the molecular orbital calculations, we deduce that the optimized trans form by AM1 method is more reactive than under PM3 method. We can conclude that both methods are efficient. The AM1 method allows us to determine the reactivity and PM3 method to verify the stability.

Transfer of nitrate ions using a polymeric-surfactant membrane

The polymer surfactant membranes used for the selective transport and separation of different species has emerged in recent years. In this work, a development of a novel class of surfactant membrane for performing nitrates ions elimination is reported. The influence of the composition of stripping solution on the separation of nitrate ions by Donnan dialysis using a polymeric membrane was studied. The membrane was prepared by dissolving a calculated amount of cellulose triacetate and poly-vinylpyrrolidone in chloroform after additive of polysorbate as surfactant. The obtained film after evaporation of the solvent is characterized by Fourier trans form infrared spectroscopy and thermo-gravimetric analysis. The degradation of the membranes occurs via two steps process whose main loss starts at 200°C is due to the thermal degradation of the polymeric chains. As application, cross ionic dialysis process was used, thus hydrogen ion from HCl medium give to the nitrate transference rather than Na+ ion from saline medium. Transference percentage is approximately two times greater in HCl medium, and it reaches 41.5% when a synthetic membrane (SM) is used. The presence of chlorhydric acid in the strip compartment gives a rise to the nitrate transference from the feed compartment through synthesized or commercial membrane at ΔpH ~3.4 during 8 h. Some other parameters were studied, particularly time transference and composition of solution (water and saline medium). Furthermore it has been shown that SM has the same performance properties as commercial one.

Phototunable Liquid‐Crystalline Phases Made of Nanoparticles

AbstractThe properties of liquid‐crystalline (LC) hybrid systems made of inorganic nanoparticles grafted with photosensitive azo compounds are presented. For materials with a large density of azo ligands at the surface, the LC structure can be reversibly melted by UV light, and the return to the LC state does not require the absorption of visible light. For systems with a lower density of azo ligands, UV light causes shortening of the distance between metal sublayers in the lamellar phase. Interestingly, the azo derivatives attached to the nanoparticle surface show very different kinetics of cis/trans conformational change as compared to the free molecules. The cis form of free ligands in solution is stable for days, whereas the isomerization of molecules attached to the nanoparticle surface to the trans form takes only a few minutes. Apparently, owing to the crowded environment, azo ligands immobilized at a metal surface behave as they would in the condensed state.

Phototunable liquid-crystalline phases made of nanoparticles.

The properties of liquid-crystalline (LC) hybrid systems made of inorganic nanoparticles grafted with photosensitive azo compounds are presented. For materials with a large density of azo ligands at the surface, the LC structure can be reversibly melted by UV light, and the return to the LC state does not require the absorption of visible light. For systems with a lower density of azo ligands, UV light causes shortening of the distance between metal sublayers in the lamellar phase. Interestingly, the azo derivatives attached to the nanoparticle surface show very different kinetics of cis/trans conformational change as compared to the free molecules. The cis form of free ligands in solution is stable for days, whereas the isomerization of molecules attached to the nanoparticle surface to the trans form takes only a few minutes. Apparently, owing to the crowded environment, azo ligands immobilized at a metal surface behave as they would in the condensed state.

Theoretical spectroscopic characterization at low temperatures of S-methyl thioformate and O-methyl thioformate.

Highly correlated ab initio methods are employed to determine spectroscopic properties at low temperatures of two S-analogs of methyl formate: S-methyl thioformate CH3-S-CHO (MSCHO) and O-methyl thioformate CH3-O-CHS (MOCHS). Both species are detectable and they are expected to play an important role in Astrochemistry. Molecular properties are compared with those of the O-analog, methyl formate. Both isomers present two conformers cis and trans. cis-CH3-S-CHO represents the most stable structure lying 4372.2 cm(-1) below cis-CH3-O-CHS. The energy difference between the cis and trans forms is drastically lower for MSCHO (1134 cm(-1)) than for MOCHS (1963.6 cm(-1)). Harmonic and anharmonic fundamentals and the corresponding intensities, as well as the rotational constants for the ground vibrational and first excited torsional states and the centrifugal distortions constants, are provided. Low torsional energy levels have been obtained by solving variationally a two dimensional Hamiltonian expressed in terms of the two torsional degrees of freedom. The corresponding 2D potential energy surfaces have been computed at the CCSD(T)/aug-cc-pVTZ level of theory. The methyl torsional barriers V3(cis) are determined to be 139.7 cm(-1) (CH3-S-CHO) and 670.4 cm(-1) (CH3-O-CHS). The A/E splitting of ground torsional state has been estimated to be 0.438 cm(-1) for CH3-S-CHO and negligible for CH3-O-CHS.

Understanding time-resolved processes in atomic-layer etching of ultra-thin Al2O3 film using BCl3 and Ar neutral beam

We scrutinize time-resolved processes occurring in atomic-layer etching (ALET) of ultra-thin Al2O3 film using BCl3 gas and Ar neutral beam by employing density functional theory calculations and experimental measurements. BCl3 gas is found to be preferentially chemisorbed on Al2O3(100) in trans form with the surface atoms creating O-B and Al-Cl contacts. We disclose that the most likely sequence of etching events involves dominant detachment of Al-associated moieties at early etching stages in good agreement with our concurrent experiments on tracking Al2O3 surface compositional variations during Ar bombardment. In this etching regime, we find that ALET requires half the maximum reaction energy of conventional plasma etching, which greatly increases if the etching sequence changes.

On Finding Exact and Approximate Solutions to Some PDEs Using the Reduced Differential Transform Method

In this research article, we give analytic approximate solution to the Sharma Tasso Olver (STO) equation and exact solutions to both the Schrodinger equation and the Telegraph equation. Also, the approximate analytical and exact solutions we present in this paper are calculated in the form of power series with easily computable components. The obtained results are in a good agreement with the exact solutions. We present an algorithm called the Reduced Differential Transform Method (RDTM) to find approximate solution and we compare the results with the exact solutions. This method reduces significantly the numerical computations compare with the existing methods such as the perturbation technique, differential transfo rm method (DTM) and the Adomian decomposition method (ADM).

Nonphospholipid fluid liposomes with switchable photocontrolled release.

We created novel nonphospholipid photosensitive liposomes from a mixture of a monoacylated azobenzene amphiphile (AzoC10N(+)) and cholesterol sulfate (Schol). This system belongs to the family of sterol-enriched nonphospholipid liposomes that were shown to form stable large unilamellar vesicles (LUVs) with enhanced impermeability. Fluid bilayers were successfully prepared from AzoC10N(+)/Schol (25/75 molar ratio) mixtures, and LUVs could be derived at room temperature using standard extrusion methods. The isomerization process of the bilayer-inserted AzoC10N(+) was characterized. Leakage from these liposomes could be induced by the photoconversion of AzoC10N(+) from its trans form to its cis form. This photocontrolled release from fluid liposomes contrasts with the case of phospholipid-based azo-containing liposomes, which are generally required to be in the gel phase to be photosensitive. It is proposed that the very high degree of conformational order of the monoalkylated amphiphile and the tight packing of the hydrophobic core of the AzoC10N(+)/Schol liposomes make them responsive to the presence of the bulky cis azo isomer. Interestingly, the liposome impermeability could be fully restored by the photoisomerization of the cis form back to the trans form, providing a sharp on-and-off control of payload release. In addition, these nonphospholipid liposomes display a very limited passive release. Therefore, it is shown that AzoC10N(+)/Schol LUVs can be used as nanocontainers, whose content can be released by light in a controlled and switchable manner.

Cis- &trans-isomerism in [Cl2Ru(dppb)N-N] complexes: Synthesis, structural characterization and X-ray crystal structure of dichloromethane solvated cis-diaminebis(diphenylphosphinobutane)ruthenium(II) complex

Three diamine-bis(diphenylphosphinobutane)ruthenium(II) complexes, isolated from the reaction of [Cl2Ru(dppb)] with diamines viz., 2,2-dimethyl-1,3-diamnopropane, 1,2-diaminocyclohexane and 1,8-diaminonaphthalene are reported. The synthesized complexes have been characterized on the basis of various physico-chemical studies viz., EDX, IR, FAB-MS, UV/Vis, NMR, TG-DTG and EXAFS studies. 31P NMR investigations confirm that the complex 3 is in cis form while the complexes 1–2 appear in trans form. The structure of complex 3 has been additionally determined by single crystal X-ray diffraction showing solvated dichloromethane. Furthermore, complex 3 crystallizes as monoclinic unit cell with P2(1)/n space group.

Nickel(II) Complexes Containing Bidentate Diarylamido Phosphine Chelates: Kumada Couplings Kinetically Preferred to β-Hydrogen Elimination

A series of divalent nickel complexes containing diarylamido phosphine ligands of the type (o-ArNC6H4PR2)− (1a, Ar = 2,6-C6H3Me2, R = Ph; 1b, Ar = 2,6-C6H3iPr2, R = Ph; 1c, Ar = 2,6-C6H3Me2, R = iPr; 1d, Ar = 2,6-C6H3iPr2, R = iPr) have been prepared and structurally characterized. The dimeric nickel chloride derivatives {[1b–d]Ni(μ-Cl)}2 (2b–d) were isolated as brick red microcrystals in high yields from the reactions of NiCl2(DME) with either Li[1b–d](solv)x or H[1b–d] in the presence of NEt3. Similar reactions employing [1a]−, however, generated homoleptic Ni[1a]2 (3a) as paramagnetic, dark red prisms in high yield. Addition of trimethylphosphine to red solutions of 2b,c in THF at room temperature afforded emerald crystals of [1b,c]NiCl(PMe3) (4b,c). Interestingly, solution NMR spectroscopic and X-ray crystallographic data of these PMe3 adducts reveal the exclusive formation of cis-4b and trans-4c, as defined by the mutual orientation of the two phosphorus donors incorporated. Metathetical reactions of 4b,c with RMgCl (R = Me, CH2SiMe3, Ph) in THF at −35 °C produced high yields of red or brownish red crystalline [1b,c]NiR(PMe3) (R = Me (5b,c), CH2SiMe3 (6b,c), Ph (7b,c)). Analogous reactions of 4c with EtMgCl or nBuMgCl, however, led instead to the isolation of the hydrido species [1c]NiH(PMe3) (8c) in quantitative yield. Solution NMR data of the methyl complexes 5b,c indicate the presence of both cis and trans isomers; the major component of 5b is cis whereas that of 5c is trans. In contrast, complexes 6b,c, 7b,c, and 8c all exist exclusively in the trans form. The chloro complexes 2b–d are all active catalyst precursors for Kumada couplings under mild conditions. In particular, this catalysis is compatible with alkyl nucleophiles that contain β-hydrogen atoms, even in reactions with chlorobenzene. The X-ray structures of 2d, 3a, 4c, 5c, 6b,c, 7c, and 8c are presented.

Electronic transduction of proton translocations in nanoassembled lamellae of bacteriorhodopsin.

An organic field-effect transistor (OFET) integrating bacteriorhodopsin (bR) nanoassembled lamellae is proposed for an in-depth study of the proton translocation processes occurring as the bioelectronic device is exposed either to light or to low concentrations of general anesthetic vapors. The study involves the morphological, structural, electrical, and spectroscopic characterizations necessary to assess the functional properties of the device as well as the bR biological activity once integrated into the functional biointerlayer (FBI)-OFET structure. The electronic transduction of the protons phototranslocation is shown as a current increase in the p-type channel only when the device is irradiated with photons known to trigger the bR photocycle, while Raman spectroscopy reveals an associated C═C isomer switch. Notably, higher energy photons bring the cis isomer back to its trans form, switching the proton pumping process off. The investigation is extended also to the study of a PM FBI-OFET exposed to volatile general anesthetics such as halothane. In this case an electronic current increase is seen upon exposure to low, clinically relevant, concentrations of anesthetics, while no evidence of isomer-switching is observed. The study of the direct electronic detection of the two different externally triggered proton translocation effects allows gathering insights into the underpinning of different bR molecular switching processes.

Azobenzene photoisomerization-induced destabilization of B-DNA.

Molecular photoswitches provide a promising way for selective regulation of nanoscaled biological systems. It has been shown that conformational changes of azobenzene, one of the widely used photoswitches, can be used to reversibly control DNA duplex formation. Here, we investigate the conformational response of DNA upon azobenzene binding and isomerization, using a threoninol linker that has been experimentally investigated recently. To this end, nonequilibrium molecular dynamics simulations are carried out using a switching potential describing the photoinduced isomerization. Attachment of azobenzene leads to a distortion of the DNA helical conformation that is similar for the trans and cis forms. However, the trans form is stabilized by favorable stacking interactions whereas the cis form is found to remain flipped out of the basepair-stacked position. Multiple azobenzene attachment augments the distortion in DNA helical conformation. The distorted DNA retains nativelike pairing of bases at ambient temperatures, but shows weaker basepairing compared to native DNA at an elevated temperature.

Effect of lycopene isolated from Chlorella marina on proliferation and apoptosis in human prostate cancer cell line PC-3.

Even though the role of lycopene from tomato (trans form) in controlling prostate cancer was reported, lycopene (cis and trans 60:40) isolated from green algae Chlorella marina was not reported so far. The present study aimed to assess the anti-proliferative and apoptotic effect of lycopene from a new source and to compare the activity with available trans lycopene by using androgen-independent human prostate cancer cell lines. Exposure of PC-3 and DU-145 cell lines to algal lycopene (AL) at a dose of 20 and 50 μM significantly inhibited the growth and colony formation, and the percentage of inhibition was higher than tomatal lycopene (TL)-treated groups. The stability of AL in cell culture medium was high, when compared to TL under standard cell culture conditions. The level of lycopene was not detected in PC-3 cell lines cultured in medium lacking lycopene. Staining cells with acridine orange and ethidium bromide, the PC-3 control cells showed largely non-fragmented intact nucleoid. Stronger apoptosis signal was induced with higher concentrations (50 μM) of algal lycopene. Increased DNA damage was observed in AL- and TL-treated cells which appear as comet during single-cell gel electrophoresis. Flow cytometry results revealed that AL caused PC-3 cells to accumulate in the G0/G1 phase and to undergo apoptosis. The effect was higher in AL groups than TL-treated groups. Algal lycopene showed very significant anti-proliferative and apoptotic effect in human prostate cancer cell lines. Therefore, algal lycopene from C.marina would be recommended for the treatment of prostate cancer.

Theoretical and spectroscopic analysis of N,N'-diphenylurea and N,N'-dimethyl-N,N'-diphenylurea conformations.

Structural organization of macromolecules is highly dependent on the conformational propensity of the monomer units. Our goal is to systematically quantify differences in the conformational propensities of aromatic oligourea foldamer units. Specifically, we investigate the conformational propensities of N,N'-diphenylurea and N,N'-dimethyl-N,N'-diphenylurea in different media using a combination of theoretical methods, and infrared and nuclear magnetic resonance spectroscopies. Our results show variation in the conformational behavior upon adding methyl substituents on N,N'-diphenylurea, and varying the environments surrounding the compounds. Our energetic analyses and conformational distributions in the gas phase show predominance of the cis-trans and trans-trans conformations for N,N'-diphenylurea, while cis-cis conformation is favored for N,N'-dimethyl-N,N'-diphenylurea. In solution, our results support the trans-trans conformer as the predominant conformer for N,N'-diphenylurea, whereas the cis-cis and cis-trans forms are favored in N,N'-dimethyl-N,N'-diphenylurea. N,N'-Dimethyl-N,N'-diphenylurea also exhibits a more dynamic conformational behavior in solution, with constant fluctuations between cis-cis and cis-trans conformations. Our detailed quantitative analyses are an important aspect in fine-tuning desired conformations and dynamic properties of this class of oligomers by providing a molecular basis for the behavior at the monomeric level.

Synthesis, characterization, electrochemical studies and DFT calculations of amino acids ternary complexes of copper (II) with isonitrosoacetophenone. Biological activities

Three mixed complexes having formula [Cu(INAP)L(H2O)2] where INAP=deprotonated isonitrosoacetophenone and L=deprotonated amino acid such as histidine, phenylalanine and tryptophan have been synthesized. They have also been characterized using elemental analyses, molar conductance, UV–Vis, IR and ESR spectra. The value of molar conductance indicates them to be non-electrolytes. The spectral studies support the binding of the ligands with two N and two O donor sites to the copper (II) ion, giving an arrangement of N2O2 donor groups. Density Functional Theory (DFT) calculations were applied to evaluate the cis and trans coordination modes of the two water molecules. The trans form was shown to be energetically more stable than the cis one.The ESR data indicate that the covalent character of the metal–ligand bonding in the copper (II) complexes increases on going from histidine to phenylalanine to tryptophan.The electrochemical behavior of the copper (II) complexes was determined by cyclic voltammetry which shows that the chelate structure and electron donating effects of the ligands substituent are among the factors influencing the redox potentials of the complexes.The antimicrobial activities of the complexes were evaluated against several pathogenic microorganisms to assess their antimicrobial potentials. The copper complexes were found to be more active against Gram-positive than Gram-negative bacteria.Furthermore, the antioxidant efficiencies of the metal complexes were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. The antioxidant activity of the complexes indicates their moderate scavenging activity against the radical DPPH.