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Background: In 2009, China CDC found the distribution of Culex tritaeniorhynchus and Aedes albopictus in Motuo county, Linzhi, Xizang and isolated the epidemic encephalitis V virus from Culex tritaeniorhynchus. However, with the road opend in Motuo County, the trade between people and mosquitoes transmission were more frequent. To illustrate patterns of mosquito population in Linzhi, Xizang, a mosquitoes surveillance was carried.Methods: Adult mosquitoes were collected by light traps and human landing catches, larva by container survey in six counties of Linzhi during August and September 2019. The trapped adult mosquitoes were initially counted and identified according to morphological criteria, and a part of mosquitoes were further identified by PCR. The monitoring data were recorded by Excel 2007, analyzed by SPSS 20.0 software and R.Results: Eight species of mosquitoes belonging to four genera were identified. Culex pipiens pallens (86.80%), Armigeres subalbalus (5.29%) and Aedes vexans (2.99%) were the top three species coolected by 164 light traps on 12 nights with the average mosquito density was 21.20 (mosquitoes per trap per night); Aedes albopictus were only collected in Chayu County Xiachayu Town by human landing catches with high average mosquito density (26.33 mosquitoes per hour per person). The larva were collected from waste tires, cement tanks and drums in Bomi, Milin and Lang Counties. The results of molecular identification are consistent with morphological identification. Aedes albopictus and Culex orientalis were newly recorded species for the first time. It is preliminarily speculated that there is a high potential risk of dengue fever in Xiachayu Town and a certain epidemic risk of Japanese encephalitis, while the risk of malaria is low in Linzhi.Conclusion: Mosquitoes had heterogeneous distribution throughout Linzhi, Xizang. The dominant mosquito species are Culex pipiens pallens. It is emphasized to carry out mosquito surveillance again during the peak period of mosquito activities so as to better understand the distribution and composition of local mosquitoes and assess the mosquito-borne disease risk in this area.

Animal genomes in the Qinghai-Tibetan Plateau provide valuable resources for scientists to understand the molecular mechanism of environmental adaptation. Tibetan fish species play essential roles in the local ecology; however, the genomic information for native fishes was still insufficient. Oxygymnocypris stewartii, belonging to Oxygymnocypris genus, Schizothoracinae subfamily, is a native fish in the Tibetan plateau living within the elevation from roughly 3,000 m to 4,200 m. In this report, PacBio and Illumina sequencing platform were used to generate ~385.3 Gb genomic sequencing data. A genome of about 1,849.2 Mb was obtained with a contig N50 length of 257.1 kb. More than 44.5% of the genome were identified as repetitive elements, and 46,400 protein-coding genes were annotated in the genome. The assembled genome can be used as a reference for future population genetic studies of O. stewartii and will improve our understanding of high altitude adaptation of fishes in the Qinghai-Tibetan Plateau.

Background Mechanisms for high-altitude adaption have attracted widespread interest among evolutionary biologists. Several genome-wide studies have been carried out for endemic vertebrates in Tibet, including mammals, birds, and amphibians. However, little information is available about the adaptive evolution of highland fishes. Glyptosternon maculatum (Regan 1905), also known as Regan or barkley and endemic to the Tibetan Plateau, belongs to the Sisoridae family, order Siluriformes (catfishes). This species lives at an elevation ranging from roughly 2,800 m to 4,200 m. Hence, a high-quality reference genome of G. maculatum provides an opportunity to investigate high-altitude adaption mechanisms of fishes. Findings To obtain a high-quality reference genome sequence of G. maculatum, we combined Pacific Bioscience single-molecule real-time sequencing, Illumina paired-end sequencing, 10X Genomics linked-reads, and BioNano optical map techniques. In total, 603.99 Gb sequencing data were generated. The assembled genome was about 662.34 Mb with scaffold and contig N50 sizes of 20.90 Mb and 993.67 kb, respectively, which captured 83% complete and 3.9% partial vertebrate Benchmarking Universal Single-Copy Orthologs. Repetitive elements account for 35.88% of the genome, and 22,066 protein-coding genes were predicted from the genome, of which 91.7% have been functionally annotated. Conclusions We present the first comprehensive de novo genome of G. maculatum. This genetic resource is fundamental for investigating the origin of G. maculatum and will improve our understanding of high-altitude adaption of fishes. The assembled genome can also be used as reference for future population genetic studies of G. maculatum.

In this paper, we proposed a method based on the minimum entropy principle to compensate the motion error. Since the impact of air disturbance and the flight attitude, there is a motion error of the platform motion. The motion error will cause the imaging defocusing, which will influence the quality of the imaging. Firstly, we established the imaging model of down-looking sparse linear array 3-D SAR imaging with motion error. Then, the impact of motion error is analyzed. A method based on minimum entropy principle is proposed to compensate the motion error. Finally, the cross-track signal reconstruction is finished by the compressed sensing. Experimental results demonstrated the effectiveness of the proposed method.

The de-coupling of range and velocity can be easily solved in symmetry triangular linear frequency modulation continuous wave (STLFMCW) radar. However, the peaks pairing may bring out ghost targets or miss some targets in multi-target situation. To solve this problem, a parameter estimation algorithm is proposed based on velocity compensation. Firstly, a velocity matrix containing targets velocities is obtained by peaks pairing of one-dimensional range profile. Secondly, envelope migration of one-dimensional range profile can be compensated with the velocity. And the vague parameters can be obtained by repairing the compensated peaks with the first sweep peaks. Finally, accurate parameters are obtained by rejecting the ghost targets. The effectiveness of the proposed method is demonstrated by simulations.

This paper concerns the problems of huge data and off-grid effect of cross-track direction in downward-looking linear array (DLLA) 3D SAR imaging. Since the 3D imaging needs a great deal of memory space, we consider the methods of downsampling to reduce the data quantity. In the azimuth direction, we proposed a method based on the multiple measurement vectors (MMV) model, which can enhance computational efficiency and elevate the performance of antinoise, to recover the signal. Further, in cross-track direction, since the resolution is restricted by the length of array, as well as platform size, the influence of off-grid effect is more serious than azimuth direction. Continuous compressive sensing (CCS), which can solve the off-grid effect of the classical compressive sensing (CS), is presented to obtain the precise imaging result under the noise scenarios. Finally, we validate our method by extension numerical experiments.

A metastable, polymorphic hexameric crystal structure of lithium pinacolone enolate (LiOPin) is reported along with three preparation methods. NMR-based structural characterization implies that the lithium pinacolate hexamer deaggregates to a tetramer in toluene but retains mainly the hexameric structure in nonaromatic hydrocarbon solvents such as cyclohexane. Moreover, the presence of a small amount of lithium aldolate (LiOA) dramatically influences the aggregation state of LiOPin by forming a mixed aggregate with a 3:1 ratio (LiOPin3·LiOA).

To reduce health-related threats of heat waves, interventions have been implemented in many parts of the world. However, there is a lack of higher-level evidence concerning the intervention efficacy. This study aimed to determine the efficacy of an intervention to reduce the number of heat-related illnesses.A quasi-experimental design was employed by two cross-sectional surveys in the year 2014 and 2015, including 2,240 participants and 2,356 participants, respectively. Each survey was designed to include one control group and one intervention group, which conducted in Licheng, China. A representative sample was selected using a multistage sampling method. Data, collected from questionnaires about heat waves in 2014 and 2015, were analyzed using a difference-in-difference analysis and cost effectiveness analysis. Outcomes included changes in the prevalence of heat-related illnesses and cost-effectiveness variables.Relative to the control participants, the prevalence of heat-related illness in the intervention participants decreased to a greater extent in rural areas than in urban areas (OR=0.495 vs. OR=1.281). Moreover, the cost-effectiveness ratio in the intervention group was less than that in the control group (US$15.06 vs. US$15.69 per participant). Furthermore, to avoid one additional patient, the incremental cost-effectiveness ratio showed that an additional US$14.47 would be needed for the intervention compared to when no intervention was applied.The intervention program may be considered a worthwhile investment for rural areas that are more likely to experience heat waves. Meanwhile, corresponding improving measures should be presented towards urban areas. Future research should examine whether the intervention strategies could be spread out in other domestic or international regions where heat waves are usually experienced.

Bartonella species can infect a variety of mammalian hosts and cause a broad spectrum of diseases in humans, but there have been no reports of Bartonella infection in Ochotonidae. This is the first study to detect Bartonella in plateau pikas in the Qinghai plateau, providing baseline data for the risk assessment of human Bartonella infection in this area. We obtained 15 Bartonella strains from 79 pikas in Binggou and Maixiu areas of Qinghai with a positive rate of 18.99%. Based on the phylogenetic analysis of the Bartonella citrate synthase (gltA) gene sequences, most strains were closely related to B. taylorii (3/15) and B. grahamii (12/15). The latter is a pathogenic strain in humans. Our results suggest that a corresponding prevention and control strategy should be taken into consideration in the Qinghai province.

Background The temporal variation of malaria incidence has been linked to meteorological factors in many studies, but key factors observed and corresponding effect estimates were not consistent. Furthermore, the potential effect modification by individual characteristics is not well documented. This study intends to examine the delayed effects of meteorological factors and the sub-population’s susceptibility in Guangdong, China. Methods The Granger causality Wald test and Spearman correlation analysis were employed to select climatic variables influencing malaria. The distributed lag non-linear model (DLNM) was used to estimate the non-linear and delayed effects of weekly temperature, duration of sunshine, and precipitation on the weekly number of malaria cases after controlling for other confounders. Stratified analyses were conducted to identify the sub-population’s susceptibility to meteorological effects by malaria type, gender, and age group. Results An incidence rate of 1.1 cases per 1,000,000 people was detected in Guangdong from 2005–2013. High temperature was associated with an observed increase in malaria incidence, with the effect lasting for four weeks and a maximum relative risk (RR) of 1.57 (95% confidence interval (CI): 1.06-2.33) by comparing 30°C to the median temperature. The effect of sunshine duration peaked at lag five and the maximum RR was 1.36 (95% CI: 1.08-1.72) by comparing 24 hours/week to 0 hours/week. A J-shaped relationship was found between malaria incidence and precipitation with a threshold of 150 mm/week. Over the threshold, precipitation increased malaria incidence after four weeks with the effect lasting for 15 weeks, and the maximum RR of 1.55 (95% CI: 1.18-2.03) occurring at lag eight by comparing 225 mm/week to 0 mm/week. Plasmodium falciparum was more sensitive to temperature and precipitation than Plasmodium vivax. Females had a higher susceptibility to the effects of sunshine and precipitation, and children and the elderly were more sensitive to the change of temperature, sunshine duration, and precipitation. Conclusion Temperature, duration of sunshine and precipitation played important roles in malaria incidence with effects delayed and varied across lags. Climatic effects were distinct among sub-groups. This study provided helpful information for predicting malaria incidence and developing the future warning system. Electronic supplementary material The online version of this article (doi:10.1186/s12936-015-0630-6) contains supplementary material, which is available to authorized users.

Addition of 1 equiv of polydentate amine or ether donor solvent to hydrocarbon solutions of lithium hexamethydisilazide (LHMDS) yields a variety of complexes with different aggregation states. X-ray crystallographic analyses have been carried out on six new compounds revealing three- and four-coordinate monomers, η1-coordinated mono- and disolvated dimers, and polymers of dimers. PM3 calculations were able to locate minima for a variety of possible structures for the ligands N,N,N‘,N‘-tetramethylethylenediamine and 1,2-dimethoxyethane. However, the heats of formation from these calculations are found to be unreliable in predicting the relative stabilities of the isomers. Single point ab initio calculations at the 6-31G* level on the PM3 optimized structures give energies which correspond well to the known aggregation states of LHMDS species. Deaggregation from dimers to monomers appears to be driven by a combination of steric, electronic, and chelate effects.

Since plague is an important natural focus zoonosis, the typing of natural plague foci becomes one of the elements in understanding the nature and developing related prevention program of the disease. Natural foci of plague are composed by four fundamental parts which include Eco-geographical landscape (natural plague foci), hosts, vectors and pathogens (Yersinia pestis) that comprehensively interact through the large temporal scale of evolution. Human activities have had great impact on the foci of natural plague. Based on the published serial research papers, we tried to integrate the knowledge of each factor in natural plague foci and focusing on theoretical aspects, so as to strengthen the prevention and surveillance programs of plague to be extrapolated to other zoonosis.

Aggregates consisting of lithium halides with either lithium amides or lithium enolates have been characterized by X-ray crystallography. Two structural types, solvated heterodimers and heterotrimers, have been found for halide/amide combinations. Two compounds containing both lithium halide and lithium enolate have also been identified as heterodimers. Using this information, we propose a reaction sequence for enolization and subsequent aldol addition reaction involving halide-containing aggregates. An ab initio and PM3 theoretical study of model systems shows that solvated heterodimers between LiBr and either LiNH2 or LiOC(H)=CH2 are favored over the respective homodimers. Calculations reveal a stable eight-membered ring transition state for the enolization step between LiCl·LiNH2 and acetaldehyde. Two independent transition states, a 4,8 and a 4,4,6 ring system, were calculated for the model reaction between the heterotrimer [(LiNH2)2·LiCl] and acetaldehyde. Dissociation of donor solvent was computed t...

To study the comprehensive monitoring mechanism of mouse and the effect of hemorrhagic fever with renal syndrome (HFRS) vaccine in the high prevalence areas of natural focus infectious disease of Zhejiang province in 1994 - 2010.The night trapping method was used to monitor the population proportion, density and the rate of hantavirus (HV) carriers in mice in Xikou township Longyou county in August and September from 1994 to 2010. The healthy residents in Xikou township aged 16 to 60 years were recruited. The subjects were randomly selected as vaccination group and control group according to age, sex, occupational distribution (10 178 in intervention group and 16 159 in control group). Intervention group was given purified and inactivated vaccine from suckling mouse brain, while the control group received no intervention. The prevention effect was evaluated by protective rate of vaccine.The mouse population was stable in the sixteen years and the apodemus agrarius was the main type (76.5% (564/737)). The average density of mouse was 4.73% (1170/24 727). The average rate of virus carrier of mouse was 3.87% (41/1033). In 1994 - 1995, the density of mouse was 22.82% (186/815) and the rate of virus carrier was 7.0% (10/143). In 2009 - 2010, the density of mouse decreased to 2.75% (119/4330) and the rate of virus carrier was 5.5% (13/237). The average antibody positive rate of mouse from 2005 to 2010 was 4.8% (35/728) and the rate was 4.4% (6/138), 0.0% (0/113), 11.8% (16/136), 1.0% (1/104), 3.7% (4/109) and 6.3% (8/128) in each year (P0.01). The protective rate of HFRS vaccine was 96.2% (1 case in intervention group and 41 cases in control group).The density of mouse decreased significantly in Zhejiang province. The rate of virus carrier of mouse is stable. The vaccine is effective.

To study the time between the onset and diagnosis of Dengue fever and its influencing factors in China.Data were obtained from the Infectious Disease Surveillance System (IDSS). Descriptive analysis was performed for the time interval while nonparametric tests and logistic regression analysis were used to study the related influencing factors.Time interval appeared positively skewed with distribution at median of 6 days, quartile range as 4 days, while 57.8% of them were longer than five days. Data showed that patients with longer intervals among the imported cases, being elderly, cases in non-endemic season and provinces as Fujian, Yunnan and Zhejiang appeared to have had greater influences on the disease. Median of those imported cases was six days, one day longer than locally generated cases, while median of the non-epidemic month was one day more than that of the epidemic month. In Fujian and Yunnan provinces, the medians were 7 days, one day more than that from Guangdong province. The median among young people was 5 days, one day less than that of the patients older than 20 years of age.Most Dengue patients did not get diagnosed early enough so it was of urgent need to enhance the sensitivity of the monitoring system, especially in epidemic regions and during non-epidemic season.

Purpose: To determine the larvicidal activity of the essential oil derived from Zanthoxylum avicennae (Lam.) DC. (Rutaceae) leaves and stems against the larvae of Aedes albopictus Skuse． Methods: Essential oil of Z. avicenna e leaves and stems were obtained by hydrodistillation and analyzed by gas chromatography (GC) and gas chromaotography-mas spectrometry (GC-MS). The activity of the essential oil was evaluated, using World Health Organization (WHO) procedures, against the fourth larvae of A. albopictus for 24 h and larval mortality recorded at various essential oil concentrations ranging from 12.5 - 200 μg/mL. Results: A total of 31 components of the essential oil of Z. avicennae were identified. The essential oil had higher content of monoterpenoids (65.70 %) than sesquiterpenoids (33.45 %). The principal compounds of the essential oil were 1,8-cineol (53.05 %), β-elemene (6.13 %), α-caryophyllene (5.96%), β-caryophyllene (5.09 %) and caryophyllene oxide (4.59 %). The essential oil exhibited larvicidal activity against A. albopictus with a median lethal concentration (LC50) value of 48.79 μg/mL. Conclusion: The findings obtained indicate that the essential oil of Z. avicennae has potentials for use in the control of A. albopictus larvae and could be useful in the search for newer, safer and more effective natural compounds as larvicides. Keywords: Aedes albopictus , Essential oil, Larvicidal activity, Mosquito, Zanthoxylum avicennae

To study the biological characteristics of natural reservoirs of Yesinia (Y.) pestis in China.Species and genera of natural reservoirs of Y. pestis in China and their faunal distribution were characterized with modern taxonomic techniques. The ecological roles of natural reservoirs of Y. pestis in the natural plague foci were determined according to the animal ecological experiments.There were 86 species of natural reservoirs of Y. pestis including 14 major reservoirs and 72 kinds of the secondary or occasional reservoirs.The biological characteristics of major reservoirs of Y. pestis and their roles in natural plague foci were defined.

To characterize the biological characteristics of natural vectors of Yersinia (Y.) pestis in China.Species and genera of natural vectors of Y. pestis in China and their faunal distribution were characterized with modern insect taxonomic techniques. The ecological roles of natural vectors of Y. pestis in natural plague foci were determined according to insect ecological experiments.There were 63 species of natural vectors of Y. pestis including 28 major reservoirs and 35 secondary ones.The biology characteristics of major vectors on Y. pestis and their roles in natural plague foci were defined.

Multi-locus sequence typing (MLST) is widely used to explore the population structure of numerous bacterial pathogens. However, for genotypically-restricted pathogens, the sensitivity of MLST is limited by a paucity of variation within selected loci. For Bartonella henselae (B. henselae), although the MLST scheme currently used has been proven useful in defining the overall population structure of the species, its reliability for the accurate delineation of closely-related sequence types, between which allelic variation is usually limited to, at most, one or two nucleotide polymorphisms. Exploitation of high-throughput sequencing data allows a more informed selection of MLST loci and thus, potentially, a means of enhancing the sensitivity of the schemes they comprise.We carried out SOLiD resequencing on 12 representative B. henselae isolates and explored these data using single nucleotide polymorphism (SNP) analysis. We determined the number and distribution of SNPs in the genes targeted by the established MLST scheme and modified the position of loci within these genes to capture as much genetic variation as possible.Using genome-wide SNP data, we found the distribution of SNPs within each open reading frame (ORF) of MLST loci, which were not represented by the established B. henselae MLST scheme. We then modified the position of loci in the MLST scheme to better reflect the polymorphism in the ORF as a whole. The use of amended loci in this scheme allowed previously indistinguishable ST1 strains to be differentiated. However, the diversity of B. henselae was still rare in China.Our study demonstrates the use of SNP analysis to facilitate the selection of MLST loci to augment the currently-described scheme for B. henselae. And the diversity among B. henselae strains in China is markedly less than that observed in B. henselae populations elsewhere in the world.

Background In 2003, Plasmodium vivax malaria has re-emerged in central eastern China including Yongcheng prefecture, Henan Province, where no case has been reported for eleven years. Our goals were to detect the space-time distribution pattern of malaria and to determine significant environmental variables contributing to malaria incidence in Yongcheng from 2006 to 2010, thus providing scientific basis for further optimizing current malaria surveillance and control programs. Methods This study examined the spatial and temporal heterogeneities in the risk of malaria and the influencing factors on malaria incidence using geographical information system (GIS) and time series analysis. Univariate analysis was conducted to estimate the crude correlations between malaria incidence and environmental variables, such as mosquito abundance and climatic factors. Multivariate analysis was implemented to construct predictive models to explore the principal environmental determinants on malaria epidemic using a Generalized Estimating Equation (GEE) approach. Results Annual malaria incidence at town-level decreased from the north to south, and monthly incidence at prefecture-level demonstrated a strong seasonal pattern with a peak from July to November. Yearly malaria incidence had a visual spatial association with yearly average temperature. Moreover, the best-fit temporal model (model 2) (QIC = 16.934, P2 = 0.818) indicated that significant factors contributing to malaria incidence were maximum temperature at one month lag, average humidity at one month lag, and malaria incidence of the previous month. Conclusions Findings supported the effects of environment factors on malaria incidence and indicated that malaria control targets should vary with intensity of malaria incidence, with more public resource allocated to control the source of infections instead of large scale An. sinensis control when malaria incidence was at a low level, which would benefit for optimizing the malaria surveillance project in China and some other countries with unstable or low malaria transmission.

To study the integrated monitoring program regarding mouse and plague, hemorrhagic fever of renal syndrome (HFRS) and leptospirosis.Integrated monitoring plan was used. A designated office coordinated 5 departments' actions within the Zhejiang Provincial Center for Disease Control and Prevention (CDC). Cage-trapping method was conducted to monitor the density of mice from June to October, respectively.Lishui municipal CDC had finished the integrated monitoring program on mouse and mouse-borne disease while the Longyou CDC had finished the field investigation, using the integrated monitoring program. Specimens were sent to provincial CDC. The integrated monitoring program needed more number of personnel and better coordination.Lishui reported 3 leptospirosis cases and 58 HFRS cases in 2009, with the incidence rates as 0.13 and 2.44 per 100 000, respectively. Longyou reported 2 leptospirosis case and 1 HFRS cases in 2009, with the incidence rates as 0.49 and 0.25 per 100 000, respectively. Lishui and Longyou had no plague case. Lishui caught 91 mice in 2009 and the density was 4.17%. Longyou caught 37 mice in 2009, with the density as 1.18 percent. Most mice caught from Lishui were Apodemus agrarius and the next was Mus musculus. In Longyou the Rattus tanezumi ranked the first, followed by Apodemus agrarius. The positive rate of HFRS antigen in Lishui and Longyou were 10.42% and 4.59% respectively. The positive rate of HFRS antibody in Longyou was 3.70%. The culture positive rate of leptospirosis in mouse renal of Lishui and Longyou were 0 and 0.98% respectively. The culture positive rate of leptospirosis in pig renal, duck renal, frog renal and cattle urine of Longyou was 0. The culture positive rate of leptospirosis in duck blood of Longyou was 80%.The integrated monitoring program on mouse and mouse-borne disease seemed to be feasible and could promote the integrated surveillance and control program on mouse and mouse-borne diseases in China.

To assess the efficacy of HIV/AIDS prevention and control among long-distance drivers in China.Based on the principles and methods of Cochrane systematic reviews, we searched literature from CBM (from 1978 to 2009), VIP (1989 to 2009) CNKI (1980 to 2009), and MEDLINE (1950 to 2009) and also assessed the risk of bias of the included before-after studies according to Newcastle-Ottawa scale and their characteristics. Cochrane Collaboration's software RevMan 5.0 was used for Meta-analysis.13 studies were included, with most of them were of low quality as having high risk of bias. (1) Knowledge index 1: We included 7 'pre-post' studies. Meta-analysis showed that AIDS/HIV prevention and control was effective in promoting the knowledge index 1 among long-distance drivers (RD = 0.15, 95%CI: 0.04 - 0.26). (2) Knowledge index 2: We included 10 pre-post studies, in which the results from Meta-analysis showed that AIDS/HIV prevention and control was effective in promoting the knowledge index 2 among long-distance drivers (RD = 0.24, 95%CI: 0.17 - 0.30). (3) Behavior index: We included 6 pre-post studies in which the results from Meta-analysis showed that AIDS/HIV prevention and control was effective in promoting the behavior index among long-distance drivers (RD = 0.15, 95%CI: 0.10 - 0.19).Current evidence demonstrated that HIV/AIDS prevention and control programs were effective.

Lithium diisopropylamide (LDA) crystallizes from N,N,N',"-tetramethylethylenediamine (TMEDA)/hexane mixtures as an infinite array of dimers linked by bridging (nonchelating) TMEDA ligands. 6Li and I5N NMR spectroscopic studies reveal that LDA in neat TMEDA exists as a cyclic dimer bearing a single $-coordinated TMEDA ligand on each lithium. The equilibrium of solvent-free LDA and the TMEDA-solvated dimer shows a very strong temperature dependence. TMEDA coordinates readily only at low temperature. High TMEDA concentrations are required to saturate the lithium coordination spheres at ambient temperatures. One equivalent of THF readily displaces TMEDA from the coordination sphere to produce the dimeric LDA/THF solvate characterized previously. Kinetics of metalation of 2-methylcyclohexanone N,N-dimethylhydrazone monitored by Fourier-transform infrared (FT-IR) spectroscopy are consistent with a rapid, spectroscopically undetectable dimer-monomer preequilibrium followed by rate-limiting proton transfer. The reaction rate is independent of the TMEDA concentration. Related spectroscopic and rate studies using dimethylethylamine lacking the capacity to chelate show strong parallels with the TMEDA data. We conclude that TMEDA chelates of LDA are of no measurable consequence throughout the reaction coordinate. MNDO calculations of THF and TMEDA solvates of Me,NLi and LDA monomers and dimers qualitatively support the conclusions derived from the experimental data.

Lithium diisopropylamide (LDA) crystallizes from N,N,N',"-tetramethylethylenediamine (TMEDA)/hexane mixtures as an infinite array of dimers linked by bridging (nonchelating) TMEDA ligands. 6Li and I5N NMR spectroscopic studies reveal that LDA in neat TMEDA exists as a cyclic dimer bearing a single $-coordinated TMEDA ligand on each lithium. The equilibrium of solvent-free LDA and the TMEDA-solvated dimer shows a very strong temperature dependence. TMEDA coordinates readily only at low temperature. High TMEDA concentrations are required to saturate the lithium coordination spheres at ambient temperatures. One equivalent of THF readily displaces TMEDA from the coordination sphere to produce the dimeric LDA/THF solvate characterized previously. Kinetics of metalation of 2-methylcyclohexanone N,N-dimethylhydrazone monitored by Fourier-transform infrared (FT-IR) spectroscopy are consistent with a rapid, spectroscopically undetectable dimer-monomer preequilibrium followed by rate-limiting proton transfer. The reaction rate is independent of the TMEDA concentration. Related spectroscopic and rate studies using dimethylethylamine lacking the capacity to chelate show strong parallels with the TMEDA data. We conclude that TMEDA chelates of LDA are of no measurable consequence throughout the reaction coordinate. MNDO calculations of THF and TMEDA solvates of Me,NLi and LDA monomers and dimers qualitatively support the conclusions derived from the experimental data.