Recent development of trilayer graphene nanoribbon Schottky-barrier field-effect transistors (FETs) will be governed by transistor electrostatics and quantum effects that impose scaling limits like those of Si metal-oxide-semiconductor field-effect transistors. The current-voltage characteristic of a Schottky-barrier FET has been studied as a function of physical parameters such as effective mass, graphene nanoribbon length, gate insulator thickness, and electrical parameters such as Schottky barrier height and applied bias voltage. In this paper, the scaling behaviors of a Schottky-barrier FET using trilayer graphene nanoribbon are studied and analytically modeled. A novel analytical method is also presented for describing a switch in a Schottky-contact double-gate trilayer graphene nanoribbon FET. In the proposed model, different stacking arrangements of trilayer graphene nanoribbon are assumed as metal and semiconductor contacts to form a Schottky transistor. Based on this assumption, an analytical model and numerical solution of the junction current-voltage are presented in which the applied bias voltage and channel length dependence characteristics are highlighted. The model is then compared with other types of transistors. The developed model can assist in comprehending experiments involving graphene nanoribbon Schottky-barrier FETs. It is demonstrated that the proposed structure exhibits negligible short-channel effects, an improved on-current, realistic threshold voltage, and opposite subthreshold slope and meets the International Technology Roadmap for Semiconductors near-term guidelines. Finally, the results showed that there is a fast transient between on-off states. In other words, the suggested model can be used as a high-speed switch where the value of subthreshold slope is small and thus leads to less power consumption.
Pellitorine (1), which was isolated from the roots of Piper nigrum, showed strong cytotoxic activities against HL60 and MCT-7 cell lines. Microbial transformation of piperine (2) gave a new compound 5-[3,4-(methylenedioxy)phenyl]-pent-2-ene piperidine (3). Two other alkaloids were also found from Piper nigrum. They are (E)-1-[3',4'-(methylenedioxy)cinnamoyl]piperidine (4) and 2,4-tetradecadienoic acid isobutyl amide (5). These compounds were isolated using chromatographic methods and their structures were elucidated using MS, IR and NMR techniques.
Two new xanthones, pyranocycloartobiloxanthone A (1) and dihydroartoindonesianin C (2), were isolated from the stem bark of Artocarpus obtusus Jarrett by chromatographic separation. Their structures were determined by using spectroscopic methods and comparison with known related compounds. Pyranocycloartobiloxanthone A (1) showed strong free radical scavenging activity by using DPPH assay as well as cytotoxicity towards K562, HL-60, and MCF7 cell lines.
Detailed chemical studies on the roots of Piper sarmentosum and Piper nigrum have resulted in several alkaloids. The roots of P. sarmentosum gave a new aromatic compound, 1-nitrosoimino-2,4,5-trimethoxybenzene (1). Piper nigrum roots gave pellitorine (2), (E)-1-[3',4'-(methylenedioxy)cinnamoyl]piperidine (3), 2,4-tetradecadienoic acid isobutyl amide (4), piperine (5), sylvamide (6), cepharadione A (7), piperolactam D (8) and paprazine (9). Structural elucidation of these compounds was achieved through NMR and MS techniques. Cytotoxic activity screening of the plant extracts indicated some activity.
Investigation on the leaves of Melicope bonwickii (F.Muell.) T.Hartley (Rutaceae) afforded a new 7-(2'-hydroxy-3'-chloroprenyloxy)-4-methoxyfuroquinoline (1) together with the known 7-(2',3'-epoxyprenyloxy)-4-methoxyfuroquinoline (2), evellerine (3) kokusaginine (4) and an amide aurantiamide acetate (5). Compounds 1 and 2 showed significant activity against cervical cell lines (Hela).
During our phytochemical investigation of Haplophyllum villosum (Rutaceae), a perennial herb from Iran, a new 4,8-diaryl-3,7-dioxobicyclo-(3,3,0)-octane type lignan, eudesmin A (1), together with four known compounds--eudesmin (2), haplamine (3), umbelliferone (4) and scopoletin (5)--were isolated from aerial parts of the plant. The structures of the compounds were elucidated using NMR spectral analysis (¹H-NMR, ¹³C-NMR, HSQC, COSY and HMBC) as well as UV, IR and MS spectra and comparison with previously reported data.
A new furanodihydrobenzoxanthone, artomandin (1), together with three other flavonoid derivatives, artoindonesianin C, artonol B, and artochamin A, as well as β-sitosterol were isolated from the stem bark of Artocarpus kemando. The structures of these compounds were determined on the basis of spectral evidence. All of these compounds displayed inhibition effects to a very susceptible degree in cancer cell line tests. Compound 1 also exhibited significant antioxidant capacity in the free radical 1,1-diphenyl-2-picrylhydrazyl tests.
Extraction and chromatographic separation of the extracts of dried stem barks of Glycosmis macrantha lead to isolation of two new acridone alkaloids, macranthanine and 7-hydroxynoracronycine, and a known acridone, atalaphyllidine. The structures of these alkaloids were determined by detailed spectral analysis and also by comparison with reported data.
Our ongoing investigations on the stem bark of Mesua beccariana afforded a novel cyclodione coumarin, beccamarin, together with two known xanthones, mesuarianone, mesuasinone, two anthraquinones, 4-methoxy-1,3,5-trihydroxy-anthraquinone and 2,5-dihydroxy-1,3,4-trimethoxyanthraquinone and one coumarin, mammea A/AB. The structures were elucidated by 1D and 2D NMR and MS techniques.
A new abietene diterpene, kaempfolienol (5S,6S,7S,9S,10S,11R,13S-abiet-8(14)-enepenta-6,7,9,11,13-ol, 1), was isolated from a rhizome extract of Kaempferia angustifolia Rosc. along with the known compounds crotepoxide, boesenboxide, zeylenol, 2'-hydroxy-4,4',6'-trimethoxychalcone, (24S)-24-methyl-5α-lanosta-9(11),25-dien-3β-ol, β-sitosterol and β-sitosterol-3-O-β-D-glucopyranoside. The structures of all compounds were elucidated on the basis of mass spectroscopic and NMR data. Zeylenol (2), the major constituent of the plant, was derivatized into diacetate, triacetate and epoxide derivatives through standard organic reactions. The cytotoxic activity of compounds 1, 2 and the zeylenol derivatives was evaluated against the HL-60, MCF-7, HT-29 and HeLa cell lines.
Curcuma ochrorhiza ('temu putih') and C. heyneana ('temu giring') are two Zingiberaceous species which are commonly used in traditional medicine in Malaysia and Indonesia. Phytochemical investigations on these Curcuma species have resulted in the isolation of six sesquiterpenes, namely zerumbone (1), furanodienone (2), zederone (3), oxycurcumenol epoxide (4), curcumenol (5) and isocurcumenol (6), along with phytosterols stigmasterol and alpha-sitosterol. Compounds 1 and 2 were obtained for the first time for C. ochrorhiza while 4 was new to C. heyneana. The hexane extract of C. ochrorhiza and sesquiterpenes 1 and 3 showed very strong cytotoxicity activity against T-acute lymphoblastic leukaemia cells (CEM-SS), with IC(50) values of 6.0, 0.6 and 1.6 microg mL(-1), respectively. Meanwhile, constituents from C. heyneana (4-6) demonstrated moderate inhibition against CEM-SS in cytotoxic assay, with IC(50) values of 11.9, 12.6 and 13.3 microg mL(-1), respectively. The crude extracts and sesquiterpenes isolated were moderately active against certain bacteria tested in antimicrobial screening.
Six prenylated flavones, including one new compound, were isolated and identified from the stem bark extracts of Artocarpus altilis. The new prenylated flavone hydroxyartocarpin (1) was characterized as 3-(gamma,gamma-dimethylallyl)-6-isopentenyl-5,8,2',4'-tetrahydroxy-7-methoxyflavone and the known compounds were artocarpin (2), morusin (3), cycloartobiloxanthone (4), cycloartocarpin A (5) and artoindonesianin V (6). The structures of the compounds were determined by spectroscopic methods (IR, MS, (1)H-NMR and (13)C-NMR) and comparison with published data for the known compounds.
A new carbazole alkaloid, 3-carbomethoxy-2-hydroxy-7-methoxycarbazole, Clausine-TY (1), together with two known carbazole alkaloid, Clausine-H (2) and Clausine-B (3), were isolated from the ethyl acetate extract of the stem bark of the Malaysian Clausena excavata. The structures of these compounds were elucidated by spectroscopic analyses. The new carbazole alkaloid shows significant cytotoxicity against CEM-SS cell line.
In recent years, carbon nanotubes have received widespread attention as promising carbon-based nanoelectronic devices. Due to their exceptional physical, chemical, and electrical properties, namely a high surface-to-volume ratio, their enhanced electron transfer properties, and their high thermal conductivity, carbon nanotubes can be used effectively as electrochemical sensors. The integration of carbon nanotubes with a functional group provides a good and solid support for the immobilization of enzymes. The determination of glucose levels using biosensors, particularly in the medical diagnostics and food industries, is gaining mass appeal. Glucose biosensors detect the glucose molecule by catalyzing glucose to gluconic acid and hydrogen peroxide in the presence of oxygen. This action provides high accuracy and a quick detection rate. In this paper, a single-wall carbon nanotube field-effect transistor biosensor for glucose detection is analytically modeled. In the proposed model, the glucose concentration is presented as a function of gate voltage. Subsequently, the proposed model is compared with existing experimental data. A good consensus between the model and the experimental data is reported. The simulated data demonstrate that the analytical model can be employed with an electrochemical glucose sensor to predict the behavior of the sensing mechanism in biosensors.
The in vitro cytotoxicity tests on the extracts of Mesua beccariana, M. ferrea, and M. congestiflora against Raji, SNU-1, HeLa, LS-174T, NCI-H23, SK-MEL-28, Hep-G2, IMR-32, and K562 were achieved using MTT assay. The methanol extracts of Mesua beccariana showed its potency towards the proliferation of B-lymphoma cell (Raji). In addition, only the nonpolar to semipolar extracts (hexane to ethyl acetate) of the three Mesua species indicated cytotoxic effects on the tested panel of human cancer cell lines. Antioxidant assays were evaluated using DPPH scavenging radical assay and Folin-Ciocalteu method. The methanol extracts of M. beccariana and M. ferrea showed high antioxidant activities with low EC₅₀ values of 12.70 and 9.77 μg/mL, respectively, which are comparable to that of ascorbic acid (EC₅₀ = 5.62 μg/mL). Antibacterial tests were carried out using four Gram positive and four Gram negative bacteria on Mesua beccariana extracts. All the extracts showed negative results in the inhibition of Gram negative bacteria. Nevertheless, methanol extracts showed some activities against Gram positive bacteria which are Bacillus cereus, methicillin-sensitive Staphylococcus aureus (MSSA), and methicillin-resistant Staphylococcus aureus (MRSA), while the hexane extract also contributed some activities towards Bacillus cereus.
In a continuation of our study of the Rutaceae, detailed chemical investigation on Micromelum minutum (Rutaceae) collected from Sepilok, Sabah, Malaysia gave four new coumarins. The structures of the coumarins have been fully characterised by spectroscopic methods as 3",4"-dihydrocapnolactone 1, 2',3'-epoxyisocapnolactone 2, 8-hydroxyisocapnolactone-2',3'-diol 3 and 8-hydroxy-3",4"-dihydrocapnolactone-2',3'-diol 4.
The air-dried powdered stem bark of Calophyllum nodusum (Guttiferea) collected from Sandakan (Sabah, Malaysia), was extracted sequentially with hexane, chloroform and methanol. The solvents were removed by rotary evaporator to give dark viscous extracts. Detailed and repeated chromatographic separation of the extracts lead to isolation of two new xanthones, identified as nodusuxanthone and trapezifolixanthone A. Other common terpenoids such as betulinic acid, lupeol, stigmasterol and friedelin were also isolated from the extracts and identified. The structures of the compounds were established by detailed spectral analysis and comparison with previously reported data.
One of the most promising plants in biological screening test results of thirteen Artocarpus species was Artocarpus obtusus FM Jarrett and detailed phytochemical investigation of powdered dried bark of the plant has led to the isolation and identification of three xanthones; pyranocycloartobiloxanthone A (1), dihydroartoindonesianin C (2) and pyranocycloartobiloxanthone B (3). These compounds were screened for antioxidant, antimicrobial and tyrosinase inhibitory activities. Pyranocycloartobiloxanthone A (1) exhibited a strong free radical scavenger towards DPPH free radicals with IC50 value of 2 µg/mL with prominent discoloration observed in comparison with standard ascorbic acid, α-tocopherol and quercetin, The compound also exhibited antibacterial activity against methicillin resistant Staphylococcus aureus (ATCC3359) and Bacillus subtilis (clinically isolated) with inhibition zone of 20 and 12 mm, respectively. However the other two xanthones were found to be inactive. For the tyrosinase inhibitory activity, again compound (1) displayed strong activity comparable with the standard kojic acid.
An investigation of the chemical constituents in Artocarpus obtusus species led to the isolation of three new xanthones, pyranocycloartobiloxanthone A (1), dihydroartoindonesianin C (2), and pyranocycloartobiloxanthone B (3). The compounds were subjected to antiproliferative assay against human promyelocytic leukemia (HL60), human chronic myeloid leukemia (K562), and human estrogen receptor (ER+) positive breast cancer (MCF7) cell lines. Pyranocycloartobiloxanthone A (1) consistently showed strong cytotoxic activity against the three cell lines compared to the other two with IC(50) values of 0.5, 2.0 and 5.0 μg/mL, respectively. Compound (1) was also observed to exert antiproliferative activity and apoptotic promoter towards HL60 and MCF7 cell lines at respective IC(50) values. The compound (1) was not toxic towards normal cell lines human nontumorigenic breast cell line (MCF10A) and human peripheral blood mononuclear cells (PBMCs) with IC(50) values of more than 30 μg/mL.
The plant Artocarpus obtusus is a tropical plant that belongs to the family Moraceae. In the present study a xanthone compound Pyranocycloartobiloxanthone A (PA) was isolated from this plant and the apoptosis mechanism was investigated. PA induced cytotoxicity was observed using MTT assay. High content screening (HCS) was used to observe the nuclear condensation, cell permeability, mitochondrial membrane potential (MMP) and cytochrome c release. Reactive oxygen species formation was investigated on treated cells by using fluorescent analysis. Human apoptosis proteome profiler assays were performed to investigate the mechanism of cell death. In addition mRNA levels of Bax and Bcl2 were also checked using RT-PCR. Caspase 3/7, 8 and 9 were measured for their induction while treatment. The involvement of NF-κB was analyzed using HCS assay. The results showed that PA possesses the characteristics of selectively inducing cell death of tumor cells as no inhibition was observed in non-tumorigenic cells even at 30 μg/ml. Treatment of MCF7 cells with PA induced apoptosis with cell death-transducing signals, that regulate the MMP by down-regulation of Bcl2 and up-regulation of Bax, triggering the cytochrome c release from mitochondria to cytosol. The release of cytochrome c triggered the activation of caspases-9, then activates downstream executioner caspase-3/7 and consequently cleaved specific substrates leading to apoptotic changes. This form of apoptosis was found closely associated with the extrinsic pathway caspase (caspase-8) and inhibition of translocation of NF-κB from cytoplasm to nucleus. The results demonstrated that PA induced apoptosis of MCF7 cells through NF-κB and Bcl2/Bax signaling pathways with the involvement of caspases.