Leenawaty Limantara

Effects of Nonpolar and Polar Solvents on the Qx and QY Energies of Bacteriochlorophyll a and Bacteriopheophytin a

The effects of nonpolar and polar solvents on the Qx and Qy energies of bacteriochlorophyll (BChl) a and bacteriopheophytin (BPhe) a were examined by electronic absorption spectroscopy. All of the four different energies exhibited a linear dependence on R(n) = (n2 ‐ l)/(n2+ 2), where n is the refractive index of the solvent, in both nonpolar and polar solvents. The energy of each state of both pigments could be expressed as v = ‐dR(n) + e (in cm‐1) where coefficient d was related to the dispersive interaction between the solute and the solvent molecules. A theory developed by Nagae showed that coefficient d originates from the quantum‐mechanical fluctuation of the multipole moments of the solute, in terms of which the following characteristics of the observed d values were explained: (1) In all of the four cases of the Qx, and Qy energies of both BChl a and BPhe a, the d values for the polar solvents were smaller than those for the non‐polar solvents. (2) In both nonpolar and polar solvents, the d value of BChl a was larger than that of BPhe a in the Qy energy, whereas the d value of BPhe a was larger than that of BChl a in the Qx energy. (3) The d value of the Qx energy was larger than that of the Qy, energy for either case of BChl a or BPhe a.

Aggregation forms of 8-ethyl-12-ethyl farnesyl bacteriochlorophyll c in methanol-chloroform mixtures as revealed by 1H NMR spectroscopy

Abstract 8-Ethyl-12-ethyl farnesyl bacteriochlorophyll c was dissolved in chloroform and changes in the 1 H NMR spectrum due to the titration of methanol were traced. Based on the changes in chemical shift and in peak intensity, the structures of two aggregate forms have been proposed. Form I showing the Q y electron absorption at 675 nm was ascribed to a dimer which has a “piggy-back” stacking of the macrocycles and a pair of MgŻOH coordination bonds. This structure was confirmed by an intermolecular 1 H 1 H nuclear Overhauser effect correlation. However, Form II showing the Q y absorption at 705 nm was ascribed to an oligomer in which the dimer units are stacked to form an inclined column.

SOLVENT EFFECTS ON TRIPLET-STATE BACTERIOCHLOROPHYLL A AS DETECTED BY TRANSIENT RAMAN SPECTROSCOPY AND THE ENVIRONMENT OF BACTERIOCHLOROPHYLL A IN THE LIGHT-HARVESTING COMPLEX OF RHODOBACTER SPHAEROIDES R26

The frequency of BChl that was bound to the light‐harvesting complex (LHC) of Rhodobacter sphaeroides R26 was found to be 1598 cm‐1, a result which suggests that a pair of BChl molecules form a dimer in the LHC in the T1 state.

Transient Raman spectroscopy of 15N-substituted bacteriochlorophyll a. An empirical assignment of T1 Raman lines

15N-substituted bacteriochlorophyll a (BChl a) was extracted from the cells of Rhodobacter sphaeroides 2.4.1 grown in a medium containing 15N-ammonium sulfate and yeast concentrate. The T1 Raman spectra of 14N-and 15N-BChl a were obtained as the difference spectra of high-power minus low-power of one-color, pump-and-probe measurements using 420 nm, 5 ns pulses. A set of empirical assignments of the T1 Raman lines was made, based on shifts upon 14N→15N substitution. The S0 Raman spectra of the two BChls were also obtained by using the 457.9 nm cw beam, and a set of assignments of the S0 Raman lines was given for comparison.

Rapid nitrogen determination of soybean leaves using mobile application

Nitrogen is one of the important nutrients elements for the growth of soybean plants. In this paper we propose mobile application that can be used nondestructively to estimate the nitrogen content of soybean leaves. We named this software “Mata Daun”. The primary concept of this software is to relate the RGB (Red, Green, Blue) value of the captured soybean image with its nitrogen content. Furthermore, the captured image is processed into Enhanced Color Visibility (ECV) index using digital image processing method for the ease of software algorithm process. Calibration process and field trial were conducted to found the relation between ECV index and soybean leaves nitrogen content. The calibration result showed that the nitrogen readings by this application had a fairly strong relationship (R2 =0.70) with the soybean leaves nitrogen content (Agriexpert CCN-6000 readings). The field test result also gave the same strong positive relationship between predicted and real soybean leaves nitrogen content (R2 =0.93).

EFFECTS OF SINGLET AND TRIPLET EXCITATION, OXIDATION AND AXIAL COORDINATION ON THE BOND ORDERS IN THE MACROCYCLE OF BACTERIOCHLOROPHYLL A AS REVEALED BY RESONANCE RAMAN SPECTROSCOPY

Abstract Application of resonance-Raman spectroscopy to bacteriochlorophyll a (BChl a) to detect the effects of excitation to the lowest triplet (T1) and singlet (S1) excited states, of one-electron oxidation to the cation radical (D0) state, and of the state of axial co-ordination on the bond orders in the macrocycle is reviewed; reference is made also to the case of bacteriopheophytin a (BPhe a) to show the effect of the central magnesium. The Raman lines of BChl a and BPhe a in the S0, T1 and S1 states have been assigned empirically based on the isotope shifts upon full 15N substitution. Shifts of the characterized Raman lines upon excitation to the T1 and S1 states are correlated to changes in the bond orders: In BChl a, systematic changes in the bond orders, i.e. decrease in the bond orders of the Ca′–Cm and Ca–Cb bonds and increase in the bond order of the Ca–N bonds, are found in the order, the S0, T1 and then S1 state. In BPhe a, the bond order of the Ca′–Cm bonds decreases almost equally upon triplet and singlet excitation. The penta- and hexa-coordinated states (with one and two axial ligands, respectively) have been identified in T1 BChl a and D0 BChl a+ by two different regions of the ring-breathing (Ca′–Cm stretching) frequencies. The classification of solvents into the penta- and hexa-coordinating ones agree among three different electronic states, i.e. S0 BChl a, T1 BChl a and D0 BChl a+ (except for the case of 2-propanol in which transformation from the penta- to the hexa-coordinated state takes place upon oxidation). The ring-breathing frequency is always lower in the hexa-coordinated state than in the penta-coordinated state, suggesting a decrease in the bond order of the Ca′–Cm bonds in the former. The key feature of the hexa-coordinated state is the expansion of the macrocycle core to accommodate in its plane the magnesium atom to enable the equivalent axial ligation of two solvent molecules, whereas the key feature of the penta-coordinated state is axial polarization between the magnesium atom sitting out of the macrocycle plane and the oxygen or nitrogen atom of a single solvent molecule as ligand. Therefore, the hexa-coordinated state tends to be formed in solvents having higher electron donating power (the donor number, DN>17.5 and Taft’s parameter, β>0.5), and the penta-coordinated state in solvents having stronger dielectric stabilization (Taft’s parameter, π*>0.65). The two coordination states were not found in S1 BChl a.

Solvent effects on the resonance Raman spectra of bacteriochlorophyll a cation radical

Abstract Resonance Raman (RR) spectra were measured for the cation radical of bacteriochlorophyll a in acetone, methanol, dichloromethane and mixed solvents of acetone and methanol. The ring-breathing (C a -C m stretching) frequency of the radical (abbreviated as v r + ) was observed at 1601 cm −1 in acetone (forming a penta-coordinated monomer), at 1587 cm −1 in a methanol (forming a hexa-coordinated monomer) and at 1600 cm −1 in dichloromethane (forming a penta-coordinated aggregate). The RR spectrum of the radical in dichloromethane is almost identical to the transient RR spectrum ascribed to ‘the aggregated T 1 species of Bchl a ’ formed in the particular solvent by Nishizawa, Limantara, Nanjou, Nagae, Kakuno and Koyama, indicating that their interpretation needs to be revised.

The T1 and S1 raman spectra of 15N- and 2H-enriched bacteriochlorophyll a: changes in bond order upon triplet and singlet excitation

The Raman spectra of bacteriochlorophyll a with natural abundance and 15N- and 2H-enriched isotope compositions were recorded in the S0, T1 and S1 states. On the basis of isotope shifts, Raman lines were characterized in each state. Comparison of the characterized Raman lines showed the following. (1) Upon triplet excitation of the macrocycle, a decrease in bond order takes place in the Ca′Cm bond having the highest bond order, whereas an increase in bond order takes place in the CaN bond having the lowest bond order. (2) The trend is enhanced further in the S1 state.

THE ENVIRONMENT OF THE FOUR NITROGEN ATOMS OF BACTERIOCHLOROPHYLL A IN SOLUTIONS AS REVEALED BY 15N NMR SPECTROSCOPY

Abstract The 50 MHz 15 N NMR spectra of 15 N-enriched bacteriochlorophyll a were recorded in twelve different solvents. The 15 N signals of the four nitrogens in the tetrapyrrole rings I, II, III and IV (signals I, II, III and IV) were assigned by the use of correlations with those of the α, β and δ methine 1 H. Signals I and III appeared in the higher field, while signals II and IV appeared in the lower field; the difference in the chemical shifts within each pair of signals was small. The results indicate an approximate D 2h symmetry of the nitrogen environment, with higher electronic density on the ring I and ring III nitrogens.

Stability of Palm Carotenes in an Organic Solvent and in a Food Emulsion System

Palm carotene has potential as an application for a natural food colorant with bioactivity as pro-vitamin A and an antioxidant. However, during processing and storage, the palm carotene encounters excessive treatments. In this study, the stability of palm carotenes was observed in organic solvent and a food emulsion system in order to learn its molecular behavior, as well as to evaluate the color stability due to exposure to light and temperature. Spectroscopy and chromatography measurements proved the formation of cis isomers and even colorless compounds after the treatment of its acetonic solution at 90°C (11 h) or under excessive illumination (11,470 lux). An application of 0.050–0.500% concentrate of palm carotene into emulsion system gave diverse shades of yellowness, which remained without any obvious color difference (ΔE ≤ 2) after 28 days at 4°C (dark) or 8 days at 30°C under average illumination of most display racks at stores (2500 lux).