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1.
Absorption changes induced in chlorophyll protein (CP 1) particles by short laser flashes have been analyzed in order to decide whether a state lasting for a few microseconds at 21°C or 800 μs at 10 K corresponds to the biradical P-700 + ... A −1 (A 1 being a chlorophyll a) or to a triplet state produced in a submicrosecond recombination of the preceding state. At 21°C the spectrum of the flash-induced Δ A (720–870 nm) presents a flat-topped band from 740 to 820 nm, clearly different from that of P-700 +. A saturation curve (Δ A vs. laser energy), obtained with a 2 or 10 ns laser pulse, indicates that Δ A saturates at a value 2- or 3-times smaller than that expected on the basis of the chemical oxidation of P-700. At 21°C the size of flash-induced Δ A is slightly decreased (5–15%) when the sample is subjected to a 400 G magnetic field. The kinetics of decay are not affected; they are not affected either by the oxygen concentration. At 10 K the spectrum of the flash-induced Δ A has been measured between 650 and 1700 nm. Between 650 and 720 nm, the spectrum presents only one major negative peak at 702 nm; it is quite different from that due to the chemical oxidation of P-700 (which has additional peaks at 688 and 677 nm). Between 720 and 870 nm, the spectrum is identical to that obtained at 21°C. Above 870 nm, the spectrum includes a broad band around 1250 nm, which is absent in P-700 +. A saturation curve leads to a maximum Δ A greater than that at 21°C and which is also greater with a 1 μs dye laser flash than with a 10 ns ruby laser flash. An analysis of the spectral data indicates that these do not fit correctly with the hypothesis of a contribution of P-700 + and of a chlorophyll a anion radical. They fit more closely with the hypothesis of a triplet state of P-700, a hypothesis which is discussed in relation to other experimental data. 相似文献
2.
The quartz crystal microbalance (QCM) was used to create a piezoelectric biosensor utilizing living endothelial cells (ECs) as the biological signal transduction element. ECs adhere to the hydrophilically treated gold QCM surface under growth media containing serum. At 24 h following cell addition, calibration curves were constructed relating the steady state Δ f and Δ R shift values observed to the numbers of electronically counted cells requiring trypsinization to be removed from the surface. We then utilized this EC QCM biosensor for the detection of the effect of [nocodazole] on the steady state Δ f and Δ R shift values. Nocodazole, a known microtubule binding drug, alters the cytoskeletal properties of living cells. At the doses used in these studies (0.11–15 μM), nocodazole, in a dose dependent fashion, causes the depolymerization of microtubules in living cells. This leads a monolayer of well spread ECs to gradually occupy a smaller area, lose cell to cell contact, exhibit actin stress fibers at the cell periphery and acquire a rounded cell shape. We observed the negative Δ f shift values and the positive Δ R shift values to increase significantly in magnitude over a 4-h incubation period following nocodazole addition, in a dose dependent fashion, with a transition midpoint of 900 nM. Fluorescence microscopy of the ECs, fixed on the gold QCM surface and stained for actin, demonstrated that the shape and cytoskeleton of ECs were affected by as little as 330 nM nocodazole. These results indicate that the EC QCM biosensor can be used for the study of EC attachment and to detect EC cytoskeletal alterations. We suggest the potential of this cellular biosensor for the real time identification or screening of all classes of biologically active drugs or biological macromolecules that affect cellular attachment, regardless of their molecular mechanism of action. 相似文献
3.
New mixed metal complexes SrCu 2(O 2CR) 3(bdmap) 3 (R = CF 3 (1a), CH 3 (1b)) and a new dinuclear bismuth complex Bi 2(O 2CCH 3) 4(bdmap) 2(H 2O) (2) have been synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction analyses. Thermal decomposition behaviors of these complexes have been examined by TGA and X-ray powder diffraction analyses. While compound 1a decomposes to SrF 2 and CuO at about 380°C, compound 1b decomposes to the corresponding oxides above 800°C. Compound 2 decomposes cleanly to Bi 2O 3 at 330°C. The magnetism of 1a was examined by the measurement of susceptibility from 5–300 K. Theoretical fitting for the susceptibility data revealed that 1a is an antiferromagnetically coupled system with g = 2.012(7), −2 J = 34.0(8) cm −1. Crystal data for 1a: C 27H 51N 6O 9F 9Cu 2Sr/THF, monoclinic space group P2 1/ m, A = 10.708(6), B = 15.20(1), C = 15.404(7) Å, β = 107.94(4)°, V = 2386(2) Å 3, Z = 2; for 1b: C 27H 60N 6O 9Cu 2Sr/THF, orthorhombic space group Pbcn, A = 19.164(9), B = 26.829(8), C = 17.240(9) Å, V = 8864(5) Å 3, Z = 8; for 2: C 22H 48O 11N 4Bi 2, monoclinic space group P2 1/ c, A = 17.614(9), B = 10.741(3), C = 18.910(7) Å, β = 109.99(3)°, V = 3362(2) Å 3, Z = 4. 相似文献
4.
1. 1. The aim of the present study is to assess the relationship between rapidity of oxygen uptake (VO2 and cardiac output (Q) kinetics at the transient phase of the onset and offset of exercise. 2. 2. Five healthy male subjects performed multiple rest-exercise-recovery transitions on an electrically braked ergometer, work rate was 50, 75, or 100 W for 6 min, respectively. 3. 3. VO2 was obtained by a breath-by-breath method, and Q was measured by an impedance method during normal breath, using an ensemble averaged method. 4. 4. On transition from rest to exercise, VO2 rapidly increased as phase I with a time constant of 7.0–7.8 s. Q also showed a similar rapid increment with a time constant of 6.3–6.8 s in phase I. 5. 5. In this phase I, VO2 increased approx. 42–68% of steady state value and Q increased 71–84%. Thereafter, VO2 and Q increased monoexponentially up to steady state with a time constant of 26.7–32.3 and 23.7–34.4 s, respectively. 6. 6. During recovery, VO2 (with a time constant of 35.7–38.1 s and time delay (TD) of −1 to −2 s), while Q remained to sustain the value of steady state exercise with a couple of time delay (TD = 2–7 s), and thereafter decreased monoexponentially (with a time constant of 18.9–31.6 s). 7. 7. The stroke volume showed the similar behavior to the Q kinetics after exercise, while heart rate rapidly decreased (time constant = 10.6–21.2 s). 8. 8. It is suggested that the delayed Q kinetics after exercise might be attributable to the sustained level of venous return and that Q kinetics is not linked with VO2 kinetics after exercise.
Author Keywords: VO2 kinetics; Q kinetics; exercise 相似文献
5.
The existence of non-axisymmetric shapes with minimal bending energy is proved by means of a mathematical model. A parametric model is used; the shapes considered have an elliptical top view whilst their front view contour is described using Cassim ovals. Taking into account the bilayer couple model, the minimization of the membrane bending energy is performed at a constant membrane area A, a constant enclosed volume V and a constant difference between the two membrane leaflet areas A. It is shown that for certain sets of A, V and A the non-axisymmetric shapes calculated with the use of the parametric model have lower energy than the corresponding axisymmetric shapes obtained by the exact solution of the general variational problem. As an exact solution of the general variational problem for non-axisymmetric shapes would yield even lower energy, this indicates the existence of non-axisymmetric shapes with minimal bending energy in a region of the V/4A phase diagram. 相似文献
6.
Warming responses of photosynthesis and its temperature dependence in two C 3 grass ( Agropyron cristatum, Stipa krylovii), one C 4 grass ( Pennisetum centrasiaticum), and two C 3 forb ( Artemisia capillaris, Potentilla acaulis) species in a temperate steppe of northern China were investigated in a field experiment. Experimental warming with infrared heater significantly increased daily mean assimilation rate ( A) in P. centrasiaticum and A. capillaris by 30 and 43%, respectively, but had no effects on other three species. Seasonal mean A was 13, 15, and 19% higher in the warmed than control plants for P. centrasiaticum, A. capillaries, and S. krylovii, respectively. The mean assimilation rate in A. cristatum and P. acaulis was not impacted by experimental warming. All the five species showed photosynthetic acclimation to temperature. The optimum temperature for photosynthesis ( Topt) and the assimilation rate at Topt in the five species increased by 0.33–0.78 °C and 4–27%, respectively, under experimental warming. Elevated temperature tended to increase the maximum rate of ribulose-1,5-bisphosphate (RuBP) carboxylation ( Vcmax) and the RuBP regeneration capacity ( Jmax) in the C 3 plants and carboxylation efficiency and the CO 2-saturated photosynthetic rate in the C 4 plant at higher leaf temperature, as well as the optimum temperatures for the four parameters. Our results indicated that photosynthetic responses to warming were species-specific and that most of the species in the temperate steppe of northern China could acclimate to a warmer environment. The changes in the temperature dependence of Vcmax and Jmax, as well as the balance of these two processes altered the temperature dependence of photosynthesis under climatic warming. 相似文献
7.
Mammary metabolism in multiparous lactating ewes fed either lucerne chaff:barley grain (L:B; 70:30) or lucerne chaff:lupin grain (L:Lu; 70:30) diets was measured while at rest, during exercise on a treadmill at 0.7 m s −1 on a 10 ° slope for 60 min, and during 30 min recovery from exercise. The effects of these treatments on plasma glucose, lactate, alpha-amino nitrogen (-amino N), non-esterified fatty acids (NEFA) and acetate were measured. Net mammary uptake of oxygen and metabolites was calculated from mammary blood flow and arteriovenous concentration ( A − V) differences. Mammary blood flow was reduced by 25% during exercise. Arterial concentrations of oxygen, glucose, lactate, -amino N and NEFA increased during exercise, whereas acetate concentration either remained unchanged or declined. Mammary A − V differences were significantly higher for oxygen, glucose, lactate and NEFA, and tended to be higher for -amino N and lower for acetate during exercise. The mammary uptakes of oxygen, glucose, lactate and -amino N were unaffected by exercise, whereas the uptake of NEFA was significantly increased and that of acetate was significantly reduced. The changes in arterial concentrations and mammary uptakes in response to exercise were not significantly affected by the diet. The responses in acetate and NEFA fluxes across the mammary gland might bring a change in the utilization of other metabolites as well as in the fatty acid composition of milk fat. 相似文献
8.
The protein encoded by the Drosophila pair-rule gene fushi tarazu (ftz) is required for the formation of the even-numbered parasegments. Here we analyze the phenotypes of ectopic expression of FTZ and FTZ protein deletions from the Tubulin 1 ( Tub1) promoter. Fusion of ftz to the Tub1 promoter resulted in low-level ectopic expression of FTZ relative to FTZ expressed from the endogenous ftz gene. The effects of ectopic expression of four FTZ proteins, FTZ 1–413 (full length wild-type FTZ), FTZ Δ257–316 (a complete deletion of the HD), FTZ Δ101–150 (a deletion that includes the major FTZ-F1 binding site) and FTZ Δ151–209 were determined. Ectopic expression of FTZ 1–413, FTZ Δ257–316 and FTZ Δ101–151 did not result in an anti-ftz phenotype; however, ectopic expression of FTZ 1–413, and FTZ Δ257–316 did result in a ftz Ual/Rpl-like phenotype. In addition, low-level ectopic expression of FTZ 1–413 and FTZ Δ257–316 rescued ftz phenotypes. This was an important observation because the even-numbered parasegment pattern of FTZ expression is considered important for normal segmentation. Therefore, the rescue of ftz phenotypes by low-level FTZ expression in all cells of the embryo suggests that the even-numbered parasegment expression pattern of FTZ is not the sole factor restricting FTZ action. Low-level ectopic expression of FTZ Δ151–209 resulted in the anti-ftz phenotype and rescued hypomorphic ftz-f1 phenotypes indicating that FTZ Δ151–209 is a hyperactive FTZ molecule. Therefore, the region encompassing amino acids 151–209 of FTZ is required in some manner for repression of FTZ activity. These results are discussed in relation to the current understanding of the mechanism of FTZ action. 相似文献
9.
Knowledge of the mechanical behaviour of immature tracheae is crucial in order to understand the effects exerted on central airways by ventilatory treatments, particularly of Total Liquid Ventilation. In this study, a combined experimental and computational approach was adopted to investigate the compliance and particularly collapsibility of preterm lamb tracheae in the range of pressure likely applied during Total Liquid Ventilation (−30 to 30 cmH 2O). Tracheal samples of preterm lambs ( n=5; gestational age 120–130 days) were tested by altering transmural pressure from −30 to 30 cmH 2O. Inflation ( Si) and collapsing ( Sc) compliance values were calculated in the ranges 0 to 10 cmH 2O and –10 to 0 cmH 2O, respectively. During the tests, an asymmetric behaviour of the Δ V/ V0 vs. P curves at positive and negative pressure was observed, with mean Si=0.013 cmH 2O −1 and Sc=0.053 cmH 2O −1. A different deformed configuration of the sample regions was observed, depending on the posterior shape of cartilaginous ring. A three-dimensional finite-element structural model of a single tracheal ring, based on histology measurements of the tested samples was developed. The model was parameterised in order to represent rings belonging to three different tracheal regions (craniad, median, caudal) and numerical analyses replicating the collapse test conditions were performed to evaluate the ring collapsibility at pressures between 0 and −30 cmH 2O. Simulation results were compared to experimental data to verify the model's reliability. The best model predictions occurred at pressures −30 to −10 cmH 2O. In this range, a model composed of median rings best interpreted the experimental data, with a maximum error of 2.7%; a model composed of an equal combination of all rings yielded an error of 12.6%. 相似文献
10.
A number of N, N′-bis(4-substituted phenyl)-1,7-diaza-12-crown-4 and N, N′-bis(4-substituted phenyl)-1, 10-diaza-18-crown-6 (where the substituents are OCH 3, CH 3, H, Cl, respectively) have been prepared by cyclization reaction of a ditosylate with the appropriately substituted diol. These new macrocyclic ligands have been characterized by means of elemental analysis, IR, 1H NMR and MS spectra. The crystal structures of N, N′-bis(4-chlorophenyl)-1,10-diaza-18-crown-6 (21) and its complex with barium thiocyanate Ba(SCN) 2 (22) have been determined by single crystal X-ray diffraction. The crystallographic data are as follows: 21: C 24H 32Cl 2N 2O 4, orthorhombic, P2 12 12 1, A=4.852(1), B=11.989(2), C=41.231(8) Å, V=2398.7(8) Å 3, Z=4; 22: C 26H 32Cl 2N 4O 4S 2Ba, monoclinic, P2 1/ c, A=8.801(2), B=11.653(9), C=15.756(6) Å, ß=105.96(3)°, V=1553.7(14) Å 3, Z=2. In the complex, the Ba atom is eight-coordinate (O(1), O(2), O(1)′, O(2)′, N(1), N(1)′, N(21), N(21)′) to form a distorted D6h geometry with the Ba atom at the center of crystallographic symmetry. 相似文献
11.
The synthesis of the 3-heptyl, and the eleven isomeric 3-methylheptyl-Δ 8-tetrahydrocannabinols (3–7, R and S methyl epimers, and 8) has been carried out. The synthetic approach entailed the synthesis of substituted resorcinols, which were subjected to acid catalyzed condensation with trans- para-menthadienol to provide the Δ 8-THC analogue. The 1′-, 2′- and 3′-methylheptyl analogues (3–5) are considerably more potent than Δ 8-THC. The 4′-, 5′- and 6′-methylheptyl isomers (6–8) are approximately equal in potency to Δ 8-THC. 相似文献
12.
Pieces of tissue, with the largest dimension not exceeding 7 mm, are fixed and dehydrated by the procedures of choice. Two stock solutions: A, for infiltration; and B, the accelerator, are used in embedding. Formulas: A, 80 ml of glycol methacrylate (2-hydroxyethyl methacrylate—Rohm and Haas Co., Philadelphia, Pa.) is mixed well with 12 ml of polyethylene glycol (Carbowax) 400 and 8 ml of water; then 0.27 gm of benzoyl peroxide added, heated to dissolve the peroxide, and allowed to cool to room temperature. B, polyethylene 200 or 400, 15 parts, and N,N-dimethylaniline, 1 part, mixed thoroughly. Tissues are first infiltrated completely with solution A, then cast in a mixture consisting of 42 parts of A mixed with 1 part of B. Polymerization occurs in 45 min to 3 hr, depending on the temperature. In a water bath at 20 C, the time required was found to be about 3 hr; at 25 C, 1.5 hr; and at 30 C, 45 min. The plastic block can be trimmed easily, and sections 1-2 μ thick readily cut. Sections can be attached to slides by water flotation, without adhesive, and should be dried at room temperature. Staining with aqueous solutions of basic and acid dyes, without removing the embedding matrix, is sharp and brilliant. When staining of the matrix by basic dyes occurs, this background stain can be completely removed by differentiating in either 2-butoxyethanol, pure ethanol, or a mixture of the two. A number of histochemical reagents have been found compatible with this embedding procedure. 相似文献
13.
Three new crystalline tin selenide salts have been prepared from the reactions of [PPh 4] 2[Sn(Se 43] in supercritical solvents. The starting material pyrolyzes in supercritical acetonitrile to form [PPh 4] 4[Sn 6Se 21] (I), and it also reacts with SnSe in supercritical ammonia leading to a mixture of [PPh 4] 4[Sn 3Se 11] 2 (II). and [PPh 4] 2[Sn(Se 4)(Se 6) 2] (III). All three compounds have been characterized by single crystal X-ray diffraction. Crystallographic data: for I, C 96H 90P 4Se 21Sn 6, space group triclinic, P-1, A = 18.763(3), B = 24.600(4), C = 13.137(1) Å, = 102.63(1), β = 93.66(1), γ = 108.72(1)°, V = 5544(1) Å 3, Z = 2, R = 0.0350, RW = 0.0317: for II, C 96H 80P 4Se 22Sn 6, space group monoclinic P2 1/ c, A = 31.500(4), B = 16.572(3), C = 22.352(3) Å, β = 103.53(1)°, V = 11344(3) Å 3, Z = 4, R = 0.0771, RW = 0.0664: for III, C 48H 40P 2Se 16Sn, space group monoclinic, C2/ c, A = 25.381(2), B = 13.934(4), C = 19.465(3) Å, β = 121.587(8)°, V = 5867(2) Å 3, Z = 4, R = 0.0807, RW = 0.0650. One of the compounds, [PPh 4] 2[Sn(Se 4(Se 62], is a molecular cluster while the other two complexes [PPh 4] 4[Sn 3Se 11] 2 and [PPh 4] 4[Sn 6Se 21], are one dimensional tin selenide chains. The structures of the two chains are related and consits of tetrahedral and distorted trigonal bipyramidal tin(IV) centers bridged by Se 2−, Se 22− and Se 32− chains. 相似文献
14.
Magnetic field-dependent recombination measurements together with magnetic field-dependent triplet lifetimes (Chidsey, E.D., Takiff, L., Goldstein, R.A. and Boxer, S.G. (1985) Proc. Natl. Acad. Sci USA 82, 6850–6854) yield a free energy change Δ G(P +H − − 3P*) = 0.165 eV ±0.008 at 290 K. This does not depend on whether nuclear spin relaxation in the state 3P* is assumed to be fast or slow compared to the lifetime of this state. This value, being (almost) temperature independent, indicates Δ G(P +H − − 3P*) Δ H(P +H − − 3P*) and is consistent with Δ G( 1P* − P +H −) and Δ H( 1P* − 3P*) from previous delayed fluorescence and phosphorescence data, implying Δ G Δ H for all combinations of these states. 相似文献
15.
Steady-state current-voltage relationships (SSCVRs) of the plasma membrane of human T-lymphocytes were studied at the physiological temperature of 37°C by using the whole-cell patch-clamp technique. SSCVRs displayed a characteristic N-like shape with a negative resistance region (NRR) in a voltage range of −45 to −35 mV. The majority of cells assayed revealed SSCVR patterns crossing the V-axis at three points (in mV): V1 = −55 to −45, V2 = −40 to −35, V3 = −30 to −10. SSCVRs of T-cells activated by phytohaemagglutinin (48–96 h) also displayed NRR, but crossed the V-axis at one point only ( V1 = −55 to −60 mV). It implies the possibility of two stable levels of membrane potential ( V1 and V3) for the resting T-cells, but only one ( V1) for activated T-cells. These data thus account for the triggering property of T-cell membrane potential previously reported. The NRR can be explained on the basis of the Hodgkin-Huxley type n4j model of K + channel kinetics. According to the model the possibility for a membrane to have on or two stable levels of membrane potential depends on the ratio of selective K + conductance to non-selective leaky conductance ( Gk/ Gleak). The steady-state level of K + conductance in resting T-lymphocytes proved to be sensitive to Ca 2+. Buffering Ca 2+ ions from either external or internal solution resulted in an appreciable increase in K + conductance. The possibility for membrane potential have two stable levels of membrane potential in connection with the Ca 2+ dependence of K + conductance was supposed to be important for Ca 2+-signalling during T-cell activation. 相似文献
16.
1. 1. By varying the redox potential of a chloroplast suspension, we obtained new evidence for an equilibrium between states S0 and S1 in the model of Kok, B., Forbush, B. and McGloin, N. (1970, Photochem. Photobiol. 11, 457–475). The mid-point potential of the S0 to S1 couple is close to that for the pool of the electron acceptor of System II, A to A−. 2. 2. The limiting steps between two consecutive photoreactions of System II in Chlorella and spinach chloroplasts, have been studied. 2.1. (a) The limiting step from S1 to S2 (noted γ1 (Δt)) is not exponential. Its temperature coefficient becomes greater as the reaction proceeds. The shape of the kinetics is an intrinsic property of each center. Chloroplasts fixed with 2% glutaraldehyde, show simple first order kinetics. 2.2. (b) The limiting step from S0 to S1 (γ0 (Δt)) exhibits the same characteristics as γ1 (Δt)). 2.3. (c) The limiting step from S2 to S3 (γ2 (Δt)) shows sigmoidal kinetics; two reactions are involved. One of the reactions exhibits the same properties as γ0 (Δt) and γ1 (Δt). 2.4. (d) The limiting step from S3 to S0 (γ3 (Δt)) is a first order reaction, two times slower than the other transitions. This reaction is interpretated in terms of oxygen release.
3. 3. We also studied the limiting steps in the presence of low concentrations (50 μM) of hydroxylamine. The results favor the binding of two molecules of hydroxylamine to every photochemical center.
Abbreviations: DCIP, dichlorophenolindophenol 相似文献
17.
The interaction between cromolyn sodium (CS) and human serum albumin (HSA) was investigated using tryptophan fluorescence quenching. In the discussion of the mechanism, it was proved that the fluorescence quenching of HSA by CS is a result of the formation of a CS–HSA complex. Quenching constants were determined using the Sterns–Volmer equation to provide a measure of the binding affinity between CS and HSA. The thermodynamic parameters Δ G, Δ H, and Δ S at different temperatures were calculated. The distance r between donor (Trp 214) and acceptor (CS) was obtained according to fluorescence resonance energy transfer (FRET). Furthermore, synchronous fluorescence spectroscopy data and UV–vis absorbance spectra have suggested that the association between CS and HSA changed the molecular conformation of HSA and the electrostatic interactions play a major role in CS–HSA association. 相似文献
18.
Kinetic results are reported for intramolecular PPh 3 substitution reactions of Mo(CO) 2(η 1-L)(PPh 3) 2(SO 2) to form Mo(CO) 2(η 2-L)(PPh 3)(SO 2) (L = DMPE = (Me) 2PC 2H 4P(Me) 2 and dppe=Ph 2PC 2H 4PPh 2) in THF solvent, and for intermolecular SO 2 substitutions in Mo(CO) 3(η 2-L)(η 2-SO 2) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH 2Cl 2 solvent. Activation parameters for intramolecular PPh 3 substitution reactions: Δ H≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; Δ S≠ values are −30.3 cal/mol K for dmpe and −16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO 2 in MO(CO) 3(η 2-L)(η 2-SO 2) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO 2 to accept a pair of electrons from the metal, with its bonding transformations of η 2-SO 2 to η 1-pyramidal SO 2, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO) 2(dmpe)(PPh 3)(SO 2) was determined crystallographically: P2 1/ c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) Å 3, Z=4, R( F)=3.49%. 相似文献
19.
In this paper are discussed a few theoretical aspects of the transfer, trapping, loss and annihilation of excitations as they occur in a photosynthetic system after a picosecond light pulse. A random-walk model is introduced to describe the dynamical behavior of the excitations in a domain and is used to calculate the parameter that determines the shape of the total fluorescence yield vs. pulse intensity curve in the case in which the reaction centers are all in the closed state (Paillotin, G., Swenberg, C.E., Breton, J. and Geacintov, N.E. (1979) Biophys. J. 25, 513–533). It is shown that this parameter depends critically on the number, λ, of connected photosynthetic units in a domain. A master equation is postulated to describe the decay of the excitations in the case where the transition of the reaction center from the open to the closed state, induced by the capture of an excitation, is included. The trapping and loss of excitation in a mixture of open and closed reaction centers, generated in the course of the transfer process, is assumed to be described by an equation that is the equivalent for a single domain of the Vredenberg-Duysens relation (Vredenberg, W.J. and Duysens, L.N.M. (1963) Nature 197, 355–357). The master equation is used to find the total probability of loss per excitation, Uλ( z), and the total fraction of reaction centers closed, Vλ( z), as a function of the average number of excitations z created in a domain when the reaction centers are all in the open state before the pulse. It is shown that, for most photosynthetic systems, an increase of Uλ( z) with z can occur only if λ 3. It is further concluded that the combined measurement of Uλ( z) and Vλ( z) can give detailed information about λ and the parameters involved in the transfer process. 相似文献
20.
The Barclay–Butler (B-B) rule, which states that a linear relationship exists between the standard Δ Hvap and Δ Svap for simple, non-associated liquids and their solutions, has been used to distinguish associated (‘abnormal’) liquids from simple (‘normal’) liquids. The exact character of the B-B plots depends on the standard states chosen for the liquid/solution and vapor. We examine the effects of using number density for both vapor and liquid states for pure liquids, non-aqueous solutions, aqueous solutions and solutions in which water is the solute. The utility of B-B plots to detect solute-induced order is strengthened, and we also find remarkable changes in the modified B-B relationship: (1) the points for small, H-bonded liquids, including water, are pulled below the general B-B line; (2) many solutions containing small, simple solutes have negative entropies of vaporization; and (3) solutions of water in several organic solvents, relevant to studies of proteins and micelles, appear ‘abnormal’. 相似文献
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