Impacts of diffuse radiation on light use efficiency across terrestrial ecosystems based on Eddy covariance observation in China.

Ecosystem light use efficiency (LUE) is a key factor of production models for gross primary production (GPP) predictions. Previous studies revealed that ecosystem LUE could be significantly enhanced by an increase on diffuse radiation. Under large spatial heterogeneity and increasing annual diffuse radiation in China, eddy covariance flux data at 6 sites across different ecosystems from 2003 to 2007 were used to investigate the impacts of diffuse radiation indicated by the cloudiness index (CI) on ecosystem LUE in grassland and forest ecosystems. Our results showed that the ecosystem LUE at the six sites was significantly correlated with the cloudiness variation (0.24 ≤ R(2) ≤ 0.85), especially at the Changbaishan temperate forest ecosystem (R(2) = 0.85). Meanwhile, the CI values appeared more frequently between 0.8 and 1.0 in two subtropical forest ecosystems (Qianyanzhou and Dinghushan) and were much larger than those in temperate ecosystems. Besides, cloudiness thresholds which were favorable for enhancing ecosystem carbon sequestration existed at the three forest sites, respectively. Our research confirmed that the ecosystem LUE at the six sites in China was positively responsive to the diffuse radiation, and the cloudiness index could be used as an environmental regulator for LUE modeling in regional GPP prediction.

[Radiometers performance attenuation and data correction in long-term observation of total radiation and photosynthetically active radiation in typical forest ecosystems in China].

Based on the total radiation and photosynthetically active radiation (PAR) observations with net radiometer (CNR1) and quantum sensor (Li-190SB) in 4 ChinaFLUX forest sites (Changbaishan, Qianyanzhou, Dinghushan, and Xishuangbanna) in 2003-2008, this paper analyzed the uncertainties and the radiometers performance changes in long-term and continuous field observation. The results showed that the 98% accuracy of the total radiation measured with CNR1 (Q(cNR1)) could satisfy the technical criterion for the sites except Xishuangbanna where the Q(CNR1) was averagely about 7% lower than Q(CM11), the radiation measured with high accuracy pyranometer CM11. For most sites, though the temperature had definite effects on the performance of CNR1, the effects were still within the allowable range of the accuracy of the instrument. Besides temperature, the seasonal fog often occurred in tropical rain forests in Xishuangbanna also had effects on the performance of CNR1. Based on the long-term variations of PAR, especially its ratio to total radiation in the 4 sites, it was found that quantum sensor (Li-190SB) had obvious performance attenuation, with the mean annual attenuation rate being about 4%. To correct the observation error caused by Li-190SB, an attempt was made to give a post-correction of the PAR observations, which could basically eliminate the quantum sensor's performance attenuation due to long-term field measurement.

Boronated thymidine analogues for boron neutron capture therapy.

Concise synthetic methods for synthesizing 3-carboranyl thymidine analogues (3CTAs) modified with cyclic and acyclic alcohols have been developed. The synthesis of these potential boron neutron capture therapy (BNCT) agents and their preliminary biological evaluation is described.

Hydrophilically enhanced 3-carboranyl thymidine analogues (3CTAs) for boron neutron capture therapy (BNCT) of cancer.

Five novel 3-carboranyl thymidine analogues (3CTAs) were designed and synthesized for boron neutron capture therapy (BNCT) of cancer. Phosphorylation of all five 3CTAs was catalyzed by recombinant human thymidine kinase (hTK1) using adenosine triphosphate (ATP) as the phosphate donor. The obtained phosphorylation rates ranged from 4% to 64.5% relative to that of thymidine. The compound with the most favorable hTK1 binding properties had a k(cat)/K(M) value of 57.4% relative to that of thymidine and an IC(50) of inhibition of thymidine phosphorylation by hTK1 of 92 microM. Among the five synthesized 3CTAs, this agent had also the overall most favorable physicochemical properties. Therefore, it may have the potential to replace N5-2OH, the current lead 3CTA, in preclinical studies. An in silico model for the binding of this compound to hTK1 was developed.

Synthesis and biological evaluation of neutral and zwitterionic 3-carboranyl thymidine analogues for boron neutron capture therapy.

Novel 3-carboranyl thymidine analogues (3CTAs) were synthesized as potential boron delivery agents for boron neutron capture therapy (BNCT). This library includes six zwitterionic NH(3)(+)-nido-m-carborane-substituted thymidine analogues (Thds) and the corresponding neutral NH(2)-closo-m-carborane-substituted counterparts. All compounds of this library were good substrates for recombinant human thymidine kinase 1 (TK1) with phosphorylation rates up to 89% relative to that of Thd. One compound out of this library, 3-[3-(7-NH(3)(+)-nido-m-carboran-1-yl)propan-1-yl]thymidine (19b), showed selective retention in TK1-expressing murine L929 wild-type tumors versus L929 TK1 (-) tumors in biodistribution studies. The biological evaluation of the zwitterionic NH(3)(+)-nido-m-carborane-substituted Thds indicated improved aqueous solubility and similar or even superior potential as BNCT agents compared with different classes of 3CTAs (Cancer Res. 2004, 64, 6280-6286 and 6287-6295). To complete previous structure-activity relationship (SAR) studies, 3-[(closo-o-carboranyl)methyl]thymidine (4) was also synthesized and evaluated.

The synthesis and biochemical evaluation of thymidine analogues substituted with nido carborane at the N-3 position.

Several thymidine analogues substituted with closo- and nido-carborane at the N-3 position were synthesized. The nido-carboranyl thymidine analogues were designed to be effective substrates for human thymidine kinase 1 in combination with an increased water solubility sufficient for clinical application in boron neutron capture therapy. This was done because N-3 substituted closo-carboranyl thymidine analogues previously synthesized in our laboratories were good TK1 substrates but were poorly water-soluble. Newly synthesized zwitterionic amino nido- and the corresponding neutral closo-m-carboranyl thymidine analogues exhibited excellent TK1 phosphorylation rates up to 75% relative to thymidine, indicating that these compounds were good substrates for thymidine kinase 1. Thin layer chromatographic studies were indicative of increased hydrophilicity of the synthesized nido-carboranyl thymidine analogues compared with their closo-carboranyl counterparts and previously reported closo-carboranyl thymidine analogues.

Folate receptor-mediated liposomal delivery of a lipophilic boron agent to tumor cells in vitro for neutron capture therapy.

PURPOSE: This study was aimed at the in vitro evaluations of folate receptor (FR)-targeted liposomes as carriers for a lipophilic boron agent, K[nido-7-CH3(CH2)15-7,8-C2B9H11, in FR-overexpressing tumor cells for neutron capture therapy. METHODS: Large unilamellar vesicles (-200 nm in diameter) were prepared with the composition of egg PC/chol/K[nido-7-CH3(CH2)15-7,8-C2B9H11] (2:2:1, mol/mol), with an additional 0.5 mol % of folate-PEG-DSPE or PEG-DSPE added for the FR-targeted or nontargeted liposomal formulations, respectively. RESULTS: Boron-containing, FR-targeted liposomes readily bound to KB cells, an FR-overexpressing cell line, and were internalized via FR-mediated endocytosis. The boron uptake in cells treated with these liposomes was approximately 10 times greater compared with those treated with control liposomes. In contrast, FR-targeted and nontargeted liposomes showed no difference in boron delivery efficiency in F98 cells, which do not express the FR. The subcellular distribution of the boron compound in KB cells treated with the FR-targeted liposomes was investigated by cellular fractionation experiments, which showed that most of the boron compound was found in either the cytosol/endosomal or cell membrane fractions, indicating efficient internalization of the liposomal boron. CONCLUSION: FR-targeted liposomes incorporating the lipophilic boron agent, K[nido-7-CH3(CH2)15-7,8-C2B9H11], into its bilayer were capable of specific receptor binding and receptor-mediated endocytosis in cultured KB cells. Such liposomes warrant further investigations for use in neutron capture therapy.

Synthesis and biological evaluation of 3'-carboranyl thymidine analogues.

Boron neutron capture therapy (BNCT) is a chemoradio-therapeutic method for the treatment of cancer. It depends on the selective targeting of tumor cells by boron-containing compounds. One category of BNCT agents with potential to selectively target tumor cells may be thymidine derivatives substituted at the 3'-position with appropriate boron moieties. Thus, several thymidine analogues were synthesized with a carborane cluster bound to the 3'-position either through an ether or a carbon linkage. The latter are the first reported carborane-containing nucleosides in which the carboranyl entity is directly linked to the carbohydrate portion of the nucleoside by a carbon-carbon bond. Low but significant phosphorylation rates in the range of 0.18% that of thymidine were observed for the carbon-linked 3'-carboranyl thymidine analogues in phosphoryl transfer assays using recombinant preparations of thymidine kinases 1 (TK1) and thymidine kinases 2 (TK2). Some of the ether-linked 3'-carboranyl thymidine analogues appeared to be slightly unstable under acidic as well as phosphoryl transfer assay conditions and were, if at all, poor substrates for TK1.