Azobenzene is a prototypical photochromic molecule existing in two isomeric forms, which has numerous photochemical applications that rely on a precise knowledge of the molar absorption coefficients (ε). Careful analysis revealed that the previously reported absorption spectra of the "pure" isomers were in fact mutually contaminated by small amounts of the other isomer. Therefore, the absorption spectra of both trans- and cis-azobenzene in methanol were re-determined at temperatures of 5-45 °C. The thermodynamically more stable trans-azobenzene was prepared by warming the solution in the dark. To obtain the spectrum of cis-azobenzene three methods were used, which gave consistent results within the limits of error. The method based on the subtraction of derivative spectra coupled with a global analysis of the spectra recorded during thermal cis-trans isomerization is shown to give slightly more reliable results than the method using isomeric ratios determined by H-NMR. The described methods are readily generalizable to other azobenzene derivatives and to other photochromic systems. The practical implication of the re-determined ε values is demonstrated by a very high precision of spectrophotometric species analysis in azobenzene isomeric mixtures. The new ε values imply that the previously reported quantum yields must be revised.

A new photoremovable protecting group, (6-hydroxy-3-oxo-3H-xanthen-9-yl)methyl (1), with a molar absorption coefficient ε of ∼4 × 10(4) m(-1) cm(-1) at ∼520 nm for the release of carboxylates or phosphates is reported. Three derivatives of 1 (diethyl phosphate, acetate, and bromide) were isolated as complexes with DDQ and shown to release the ligands with quantum yields ≤2.4% in aqueous solution.

The quantum yields of azobenzene photoisomerization in methanol solution were redetermined using newly obtained molar absorption coefficients of its cis- and trans-isomers. The results differ substantially from those published previously, especially in the range of the nπ* absorption band. Besides actinometry, these findings are relevant for applications of azobenzene derivatives in optical switching.

Abstrak: Antioksidan merupakan senyawa yang menghambat atau menunda reaksi oksidasi molekul dengan cara menghambat proses inisiasi atau propagasi reaksi oksidasi berantai . Struktur kimiawi antioksidan, sumber radikal bebas, dan sifat fisiko-kimia sediaan sampel yang berbeda dapat memberikan hasil uji aktivitas antioksidan yang beragam. Oleh karena itu, diperlukan suatu metode analisa aktivitas antioksidan yang selektif untuk suatu jenis sampel tertentu. Studi perbandingan metode uji aktivitas antioksidan DPPH, FRAP, dan FIC telah dilakukan terhadap asam askorbat (AA), asam galat (AG), dan kuersetin. Ketiga metode uji antioksidan dibedakan berdasarkan pada jenis mekanisme reaksinya, sedangkan sampel standar antioksidan dipilih berdasarkan struktur polihidroksi atau polifenol yang umumnya mewakili dasar struktur antioksidan bahan alam. Metode uji aktivitas antioksidan terhadap radikal DPPH ditemukan paling efektif dan efisien diantara ketiga metode uji yang digunakan dengan nilai IC 50 berturut-turut 1,27; 2,44; dan 2,77 mg/L untuk AG, kuersetin dan AA. Adapun metode FIC terbukti paling tidak efektif dan efisien karena sensitivitasnya yang sangat rendah dan daya kelatnya lebih kecil dari 20%. Korelasi antara metode uji untuk semua standar antioksidan terbukti sangat tinggi (R>0,98), khususnya antara FRAP dan DPPH. Hal ini mengindikasikan adanya keterkaitan sangat kuat antara daya hambat radikal bebas dengan potensial reduksi senyawa polihidroksi (polifenol) terhadap ion besi. Secara umum kedua metode ini sangat dimungkinkan bisa saling menggantikan satu sama lain.Abstract: Antioxidants are compounds that prevent or postpone oxidation reaction of a molecule by inhibiting initiation or propagation process of the chain oxidation reaction. The chemical structure of antioxidants, free radical sources, and physico-chemical properties of different sample preparations can provide various antioxidant activity test results. Therefore, selectivity of an antioxidant activity analysis method for a particular sample type is compulsary. The comparative study of antioxidant activity assays (DPPH, FRAP, and FIC) against ascorbic acid (AA), gallic acid (GA), and quercetin was accomplished. The three antioxidant activity assays were distinguished based on their typical reaction mechanism, while the samples of antioxidant standard were selected on the polyhydroxy or polyphenol based-structure, which are commonly available as the basic skeleton of the natural antioxidants compounds. The antioxidant assay against a radical of DPPH was found to be the most effective and efficient among the three assays with IC 50 1. 27, 2.44, and 2.77 mg/L for GA, quercetin and AA, respectively. In contrast, FIC method was proven to be the least one due to its poor sensitivity and low chelating capability (<20%). The correlation between the antioxidant assay methods was found to be really high (R>0,98), particularly between the FRAP and DPPH assay. This result indicated that the radical inhibition has strong correlation with the reduction power of t...

Three monosubstituted 3-phenylselanyl and 3-phenyltellanyl BODIPY derivatives were synthesized and their spectroscopic properties were characterized and compared to those of iodine and chlorine-atoms containing analogues as well as an unsubstituted BODIPY derivative. The fluorescence quantum yields were found to decrease, whereas the intersystem crossing quantum yields (ΦISC), determined by transient spectroscopy, increased in the order of the H → Cl → Se/I → Te substitution. The maximum ΦISC, found for the 3-phenyltellanyl derivative, was 59%. The results are interpreted in terms of the internal heavy-atom effect of the substituents.

Functional cotton fabric incorporated with antibacterial microcapsules of lime (C. aurantifolia) essential oil (LO) was prepared.

Nocardiotide A has been successfully synthesized using a combination of solid‐ and solution‐phase synthesis. Peptides 1 and 2 of nocardiotide A, with different C and N termini, were synthesized on 2‐chlorotrityl chloride resin. A combination of N,N,N′,N′‐tetramethyl‐O‐(1H‐benzotriazol‐1‐yl)uronium hexafluorophosphate and hydroxybenzotriazole (HBTU/HOBt) was employed as coupling reagent and the release of the linear peptides from the resin was undertaken using AcOH and trifluoroethanol (TFE) reagents resulting in linear hexapeptides with protected side chains in good yields (83.4 % and 76 %, respectively). Peptide 1, which has Ala as C terminus and Trp as N terminus, was the only peptide that was successfully cyclized without epimerization under a dilute condition (1.25×10−3 M) using HBTU (3 equiv.) and 1 % N,N‐diisopropylethylamine (DIPEA) in dichloromethane. A combination of a small residue at the C terminus and a larger residue at the N terminus was found to be effective for the cyclization. The protecting group of the crude cyclic product was then deprotected by 95 % TFA in water and the crude was then purified to give white solid product with 16 % overall yield. The peptide was then characterized by HR‐ToFMS, 1H‐ and 13C‐NMR spectroscopy. In order to ensure the absence of epimerization during cyclization, the D‐analogue of nocardiotide A was synthesized using similar synthetic protocol. The NMR data of D‐analogue was found to have a larger difference compared to the synthetic and natural product, showing there is no epimerization at C‐terminus during cyclization.

Citrus aurantifolia is part of the Rutaceae family and belongs to the genus Citrus. It is widely used in food, the chemical industry, and pharmaceuticals because it has a unique flavor and odor. It is nutrient-rich and is beneficial as an antibacterial, anticancer, antioxidant, anti-inflammatory, and insecticide. Secondary metabolites present in C. aurantifolia are what give rise to biological action. Flavonoids, terpenoids, phenolics, limonoids, alkaloids, and essential oils are among the secondary metabolites/phytochemicals discovered in C. aurantifolia. Every portion of the plant’s C. aurantifolia has a different composition of secondary metabolites. Environmental conditions such as light and temperature affect the oxidative stability of the secondary metabolites from C. aurantifolia. The oxidative stability has been increased by using microencapsulation. The advantages of microencapsulation are control of the release, solubilization, and protection of the bioactive component. Therefore, the chemical makeup and biological functions of the various plant components of C. aurantifolia must be investigated. The aim of this review is to discuss the bioactive components of C. aurantifolia such as essential oils, flavonoids, terpenoids, phenolic, limonoids, and alkaloids obtained from different parts of the plants and their biological activities such as being antibacterial, antioxidant, anticancer, an insecticide, and anti-inflammatory. In addition, various extraction techniques of the compounds out of different parts of the plant matrix as well as the microencapsulation of the bioactive components in food are also provided.