CT scans to detect lung cancer Essay Example | Topics and Well Written Essays - 500 words

CT scans to detect lung cancer - Essay Example In this research, the researchers have concluded that 80 percent of lung cancers can be detected in early stages through CT screening and what they are trying to tell is lung cancer is not all that bad, which is actually beneficial for a tobacco company because, the worst health problem projected against smoking is lung cancer. Funding by any other company other than a tobacco company could have avoided this conflict of interest. 2. CT screening is fraught with risk of radiation. It is also an expensive procedure and can contribute to unnecessary biopsies and surgeries in those with cancers that actually do not progress. Because of this, critics have raised ethical issues about routine screening of individuals at risk of cancer, i.e., those with history of smoking. The better way to prevent lung cancer is to educate people about the risks associated with smoking a nd various measures to prevent smoking. 3. The researchers, Dr. Henschke and Dr. Yankelevitz did not disclose one patent and 10 pending patents concerned to screening of lung cancer with CT scan. The patent was issued to general Electric, one of the prominent makers of CT scanners.

Critically assess the Prime Minister's powers.Review the role of the Essay

Critically assess the Prime Minister's powers.Review the role of the media in British politics.Is the higher civil service a - Essay Example Nevertheless, the individual who is appointed to this position must enjoy the support of the majority in the parliament, especially the lower house of the British legislature, also referred to as the House of Commons. This is because, the House of Commons is charged with the responsibility of enacting the necessary legislations that runs the government and the whole country. Therefore, the prime minister must enjoy the support of the majority in the House of Commons, so that he can be supported in enacting the necessary legislations and policies, which runs the government (Hennessy, 2001 p17). The most important aspect of the position of the British Prime Minister is the fact that; this position is not established by the British constitutional laws, but is just guided by the conventions, which have been in place for a long-term. The British Prime Minister plays various roles. First, he is the head of the political party or the coalition of parties that have the majority members of pa rliament in the House of Commons, and thus plays a legislative role (Kavanagh & Seldon, 2008 p87). He is responsible for guiding the legislation of the policies that favors the running of the government, as well as those necessary to execute the objectives and manifestos of the party or coalition enjoying the majority in the parliament. This position evolved as a result of the long term historical struggle to shift power from the sovereign to the parliament. However, constitutionally and legally, the monarch still remains the head of government, who enjoys the prerogative powers and is thus responsible for the whole running of the country. Therefore, the position of the British Prime Minister is political, which occurs as a result of the monarch sharing his/her powers to head the government with an individual of his/her choice, who enjoys the confidence of many members of parliament (Blick & Jones, 2010 p62). Despite the immense political authority that the position of the British P rime Minister holds, it is merely an extension of the powers of the Sovereign, who is the legal and constitutional leader of the government (King, 1985 p257). As the head of the party of the majority in parliament, the British Prime Minister is responsible to oversee the formulation and passing of the necessary legislations, which are essential to see the government operate effectively. In this sense therefore, the British Prime Minister heads the policy and law formulation process, to ensure that the laws and the policies that are formulated are in line with the government intentions and objectives, thus serves to facilitate the performance of the government (Hennessy, 2001 p21). This remains the reason as to why the British Prime Minister must be the leader of the party or coalition that enjoys majority support. The other role of the British Prime Minister is the executive role. The British Prime Minister is the head of the cabinet, which is the executive arm of the government (Ka vanagh & Seldon, 2008 p84). The power of the British Prime Minister as the head of the executive arm of the government includes the powers to constitute the cabinet. Therefore, he is responsible for appointing the cabinet ministers, who in turn heads different departments of the government

How does your understanding of Postcolonial Theory inform your Essay

How does your understanding of Postcolonial Theory inform your interpretaion of Salman Rushdie's Midnight's Children and Tsitsi Dangarembga's Nervous Condition - Essay Example Post colonial theory was based on the two theoretical concepts of the time, related to identity, i.e. ‘otherness’ and ‘hybridity’. The colonized people were diverse in their nature and tradition .They are ‘other ‘to the colonizers but are different from one another also. Such a drastic situation was meticulous to India and Africa. Both the countries had shared the common pain of identity and tradition. A comprehensible understanding of the political and cultural aspects of the countries is needed to unravel the stories in its full meaning. ‘Midnights Children’ and ‘Nervous Condition’ are such great novels of the time dealt successfully with the postcolonial theory and there by the self search of the natives Salman Rushdie’s ‘Midnight’s children’ is a novel about Indian independence, the partition and their aftermath. The novel is Rushdie’s interpretation of a period of about seventy years in India’s modern history dealing with the events leading to the partition of India and beyond .The novel encapsulates the experiences of three generation of Sinai family living in Srinagar, Amritsar and Agra and then in Bombay and finally migrating to Karachi. Tsitsi Dambengara’s Nervous condition’ is set in the post colonial Rhodesia of 1960s. The narrator and the main character, Thambu, expresses her experience with colonization, as a child growing up from a poor African community, with tremendous correctness and detail. She is anything but typical. A great deal of the novel reveals the development of Thambu as she becomes a young lady and the relationship with her cousin Nyasha .As they mature we can identify the difference in their characters . Tsitsi also adopt the method of narration as Saleem in ‘Midnights children’ .Saleem works in a pickle factory by day and records his experiences in the night hoping that one day the world would taste the pickle of history. Alongside of

Global Climate Models Essay Example | Topics and Well Written Essays - 500 words

Global Climate Models - Essay Example Furthermore, recent studies have shown that the model is very efficient in estimating global climate change. It has been adopted by many nations globally because of its effective understanding of climate sensitivity. Moreover, the ECHAM5 reproduces the global metrics of the tropical cyclones. The other submodels before the ECHAM5 include the ECHAM4 which reproduces the extremes and variability of rainfall (Randall and Wood). The model was developed in 2005 by the Beijing Climate Centre. It was designed as a global ocean, atmospheric global model to reflect or study the mean climatological state (Bader, 2008). Therefore, it was not designed climate change in China, but to be used all over the globe. Additionally, it is very important to note that this model is used to predict global and East Asian seasonal climate. It presents a very high resolution of climate forecasts in China and more so it produces monthly scale forecasts of the climate in this region (Palmer, 2014). As a result, the monthly extended dynamic range system is thus based on the BCC-CM1 model. The BCC-CM1, 2005 has proved to be very accurate in predicting seasonal climate change as compared to the atmospheric and ocean models. After the analysis of the two climate models, it is crystal clear that the models were created in the same year and that both of them are coupled employing a combination of two models in one. However, the two models greatly differ from each other. The BCC-CM1, 2005 was designed in China while the ECHAM5/MPI-ON was designed in Germany. The most important difference is that the BCC-CMI model is very effective in predicting seasonal climate change. On the other hand, the ECHAM5/MPI-OM forecast climate change in the long run (Semenov & Stratonovitch, 2010). The computation of the ECHAM5 is meant to predict the climate change globally, but for a long duration of time.  Ã‚  

Gender Roles in American Households Essay Example for Free

Gender Roles in American Households Essay The social phenomenon of changing gender roles in American households is explored in this paper. Are men and women sharing more equally in assuming household responsibilities? Do women still bear the majority of the responsibility? How do race, age, and cultural influence play a role in the division of labor in the household? I have done research on the change in gender roles among people of different ages, genders, and race. Data was collected to see if there is a difference in change between races, if there is a significant change in roles between generations, and if men and women view the change the same or differently. To gain the data I used surveying and interviewing as my research methodologies. These methods were used as they were the most practical ways to obtain enough information needed to form conclusions. Caucasian, Asian, and African Americans of both genders and diverse ages were surveyed and interviewed. I feel my research will show that with each generation, as more women entered the work force, the households of all races have undergone significant change in which women and men are sharing both work and domestic duties more equitably. That being said, the distribution of domestic chores does contribute to household stratification of gender roles. Both currently and historically race plays a role in that stratification. Gender role research is socially relevant because each individual in a household is impacted by it. Gender roles in the household can be a factor in whether a marriage is happy and successful. They also influence decision making in the family and parent and child relationships. Researchers could use my data to delve deeper into the impact of gender roles in different types of households. Since everyone grows up in some type of household setting, the research could have far reaching implications for most of the population. The first research method I choose to collect data is the survey. Using a survey to collect data allowed me to reach a large number of people. Family and friends helped in distributing and collecting the surveys. My parents work at a hospital, my Aunt is a teacher, and my friend attends a large university. That allowed me to reach the age groups, genders, and races I needed in order to collect enough data. Included in my survey were both questions about today and about the past. In addition, using a survey allowed me to ask questions that were not opened ended and could easily be converted to statistical data. In the end, I had responses from a minimum of fifteen respondents in each of eighteen categories. The categories are Caucasian females ages 19-30, Caucasian males ages 19-30, Caucasian females ages 31-49, Caucasian males ages 31-49, Caucasian females ages 50 and above, Caucasian males age 50 and above, and the same for both African Americans and Asian Americans. Because of the large number of groups I needed to collect data on, I felt 15 individuals per category would be a large enough number to get a representative sample. I looked at the responses and felt I had a good sample. Had that not been the case, I would have handed out more surveys. Included in the survey were questions on the household the person grew up in and questions about their household today. For example, respondents were asked if they were raised in a two parent home. This is a question I checked the responses to when I determined if I had collected enough surveys. It was necessary to have enough positive answers to this question since gender roles is the issue I am looking at. Also on the survey were questions asking your race and age, who you were raised by, if your mother worked outside the home, percentage of division of household chores, and whether the perceived change in gender roles is positive. I did not have any problems with the survey itself. The only difficulty was finding fifteen respondents for a few of the categories. The second research methodology I used was the interview. In interviewing I was hoping to be able to ask follow up questions and steer the interview in a direction that would supply me with the information I needed. The survey did not lend itself to follow up questions. In addition, participant observation and experimentation methodologies were not at all suited to investigate the question of changing household gender roles. I interviewed one person from each of the three races I was researching. In addition, each was from a different age category. All of the interviews were conducted separately as I would not have wanted to inconvenience the people who were nice enough to participate. All were interviewed once in an informal manner since I believe that discussing your childhood and present home life is best accomplished in a comfortable setting. I interviewed Dr. Espejo, a 49 year old of Asian decent by telephone as she was unavailable in person. Helen Bonokallie, a 24 year old of African decent was my second interview. I spoke with Helen at her workplace as she works third shift and that was most convenient for her. My last interview was with Sylvia Johnson, a 66 year old Caucasian. I interviewed her in her living room. I have known Sylvia my entire life and have a close personal bond with her. Aside from choosing my subjects for interviewing and directing the questions to get the answers I needed I did not shape the outcome of the interview. The survey results revealed several trends related to gender roles in American families. The following charts and statistical analysis help to clarify the collected data from the surveys. The three tables that follow represent each of the three races I surveyed. Each chart shows the three age groups surveyed and their responses to two questions. The first, as a child what percentage of household work was done by each of your parents? The second, in your home today, what percentage of household work is done by the male and what percentage is done by the female? Looking at the charts a few trends are seen. First, regardless of race, the percentage of work done by the male is greater in the adult household as compared to the father in the childhood home. That indicates that with each generation gender roles in the home have changed. Ratio of CaucasianCaucasianCaucasianCaucasianCaucasianCaucasian work doneAge 19-30Age 19-30Age 31-49Age 31-49Age 50+Age 50+ female:malechildhoodadultchildhoodadultchildhood adult In %householdhouseholdhouseholdhouseholdhouseholdhousehold 50-504%40%0%38%0%0% 60-400%40%4%31%0%40% 70-3012%20%15%23%0%40% 75-250%0%11%8%0%13% 80-2014%0%0%0%20%7% 85-1512%0%11%0%3%0% 90-1058%0%30%0%30%0% 95-50%0%11%0%27%0% 100-00%0%18%0%20%0%. Ratio of AsianAsianAsianAsianAsianAsian work doneAge 19-30Age 19-30Age 31-49Age 31-49Age 50+Age 50+ female:malechildhoodadultchildhoodadultchildhood adult householdhouseholdhouseholdhouseholdhouseholdhousehold 50-500%26%0%0%0%0% 60-400%39%0%16%0%0% 70-307%30%0%36%0%28% 75-2510%0%0%12%0%0% 80-2023%5%17%24%3%22% 85-157%0%10%12%13%0% 90-1050%0%30%0%23%36% 95-50%0%30%0%25%0% 100-03%0%13%0%36%14% Ratio of African AfricanAfricanAfricanAfricanAfrican work doneAge 19-30Age 19-30Age 31-49Age 31-49Age 50+Age 50+ female:malechildhoodadultchildhoodadultchildhood adult householdhouseholdhouseholdhouseholdhouseholdhousehold 50-500%0%0%0%0%6%. 60-400%63%0%18%0%18% 70-3031%31%7%28%0%38% 75-2531%0%8%12%5%7% 80-2015%6%8%36%25%12% 85-150%0%23%0%0%0% 90-1023%0%46%6%30%19% 95-50%0%8%0%25%0% 100-00%0%0%0%15%0% In addition, under no circumstance did the males of any race or age perform more household work than the females. The data also shows that there is no difference in gender roles today among Caucasians, African Americans, and Asian Americans in the 19-30 age group. In the Asian American group of individuals fifty and older, 72% of women still do 80-100% of the household work today. In contrast, in the same age group, only 7% of Caucasian women and 31% of African American women perform 80-100% of household work. According to the 2004 United States Census, 69% of Asians were born in another country (Lee and Pituc 2007). This is significant in that many older Asian-Americans adhere to traditional cultural values. Traditional Asian gender roles prescribe for women to place the role of wife and mother above all others: men are expected to be the breadwinner and spokesperson. Asian cultural values consequently encourage distinct spheres for men and women and a gendered household division of labor in which the burden of household duties such as housekeeping tasks and childcare rest heavily on women (Lee and Pituc 2007: 1). The following graph was compiled based on the survey question; did your mother work outside the home? The y-axis is percentage of working mothers and the x-axis is the age of those surveyed. The graph shows that over time more mothers have become workers outside the home. It also indicates that for all age categories 70% of African American women were in the workforce. Kane stated â€Å"White women have a history of lower levels of labor force participation and higher levels of economic dependence on men than do African-American women† (2000 p. 421). This graph when looked at in conjunction with the 3 charts above shows a correlation between women working outside the home and men giving more help around the house. The last survey question was do you think the change in gender roles in the household is positive or negative. The results were 99% positive and 1% negative. The information obtained from my interviews mirrored the information I got from the surveys. Talking to Sylvia, the 66 year old Caucasian, the idea that generation and women in the workplace play a part in changing gender roles was reinforced. Sylvia related what her home was like as a child, indicating that household work was entirely done by her non-working mom. Her home on the other hand is different in that her husband does help out to some extent. She also said her children’s homes are even more equitable when it comes to dividing household chores. Dr. Espejo’s parents worked together and shared responsibilities in the home. It is the same in her home today, where she and her husband, both physicians, share household duties. Dr. Espejo stated that she feels sharing of household responsibilities strengthens the relationship between a husband and wife and between parents and children. This may be explained by a 2003 study conducted by Y. Espiritu. Trask (2006) states: Based on an analyses of various studies of Asian-American families, Espiritu found that more educated couples tended to share and practice greater egalitarian relationships within households. While women still performed more of the housework, their husbands did participate in all aspects of family work. This increased participation by men may be explained due to an equal monetary contribution from men and women which led to wives successfully forcing their husbands to participate in domestic chores. (P. 4) In my interview with Helen, she pointed out that sharing responsibility around the house helps to equalize the stress between both male and female. In the African- American household she grew up in her father did the cooking and laundry while her mother cleaned and helped the children with homework. A recent study has a possible explanation for the sharing of household work in Helen’s childhood home. The study concluded, â€Å"When referencing the family and work, black men may be less traditional because they are more sensitive to oppression in general, may share resistance with black women to racial inequality, and often gain acceptance of women in the workforce during early years while being raised by a single working mother† (Carter 2006: 209). In addition, Blee and Tickamyer state, â€Å"African American men do not equate masculinity with success, wealth, ambition, and power, but rather with self-determinism and accountability† (1995 p. 21). All three interview subjects expressed that change in gender roles where there is a more equal distribution of household responsibilities is very positive. The research I have done shows that over time gender roles have changed among the three races I studied. Every group I looked at had fathers who helped out less around the house than the males in their homes today. One important reason for this could be the fact that over time more women have entered the workforce outside the home. It simply has become a necessity for men to help out more around the house. In addition to more women in the work force, culture and race play a role in gender and the household stratification of gender roles. Culture remains important to many Asians Americans, especially the older generation. In those cultures Asian men are seen as the breadwinner and women as household caretakers. That dictates women being almost entirely responsible for the household. In contrast, African American men do not define their masculinity by success, but instead by accountability. That leads to many African American men being more equitable in sharing household chores. Since everyone in a household is affected by gender roles, this subject is very important socially. It is a subject worth investigating further as the findings could impact many people. References Blee, Kathleen and Ann Tickamyer. 1995. â€Å"Racial Differences in Men’s Attitudes about Women’s Gender Roles. † In Journal of Marriage and Family. Vol. 57, pps 21-30. Carter, J. Scott and Mamadi Corra. 2009. â€Å"The Interaction of Race and Gender: Changing Gender Role Attitudes, 1974-2006. † In Social Science Quarterly. Vol. 90, pps 196-211 Kane, Emily. 2000. â€Å"Racial and Ethnic Variations in Gender-Related Attitudes. † In Annual Review of Sociology. Vol. 26, pps 419-436 Lee, Sandra and Stephanie Pituc. 2007. â€Å"Asian Women and Work-Family Issues. † In Sloan Work and Family Research Encyclopedia. pps 1-6 Trask, Bahira. 2006. â€Å"Traditional Gender Roles. † In Sloan Work and Family Research Encyclopedia. pps 1-5.

X-ray Crystallography Technique Analysis

X-ray Crystallography Technique Analysis 1 Limitations of x-ray crystallography From the first crystalline structure determination of table salt in 1914; whose structure elucidation proved the existence of ionic compounds (6), single crystal x-ray diffraction (SC-XRD) has been widening our view of the hidden world of molecular structures. Today, SC-XRD continues to be the only structural analysis method that offers direct structural information at the atomic level. As such, this technique has been vital for reliably solving many structures of small molecules such as neurotransmitters, antibiotics and industrial catalysts. SC-XRD utilises the ability of crystalline atoms to scatter or diffract a beam of incident x-ray into a series of amplified and spatially constrained beams (3). The angles and intensities of these beams can be measured and computationally processed by a crystallographer to produce a 3-dimensional image of the density of electrons in the crystal. Aside from the expertise required to process the reflection data produced, the fundamental requirement of crystals for this technique acts as major limitation, since single molecules scatter the incident x-ray to produce a weak, continuous beam that provides little useful information for analysis. While technological advances in recent decades including highly intense x-ray beams produced by synchrotrons and the development of more powerful algorithms for molecular structure imaging have allowed the size of the crystal required to be increasingly smaller, the need for a crystal has still not been eliminated. This poses a great issue as many t arget compounds are very difficult to crystallise, thus requiring experienced specialists; while others will simply not crystallise at all. In 2013, a new protocol, later coined the crystalline sponge method (CSM), was reported that attempted to bypasses this intrinsic limitation of the target molecule needing to be crystalline (1). 2 The journey of the crystalline sponge method Expectations Fujita and his team described the new method that promised to speed up SC-XRD drastically by eliminating the crystallization step of the target molecule. This was done using porous metal organic frameworks (MOFs) that act as crystalline sponges. Due to the high molecular recognition capability of their pores, these sponges can absorb target molecules from the sample solution into their pores.   In their study, Fujita and his team used two MOFs synthesised from tris(4-pyridyl)-1,3,5-triazine (TTP, 1) and the appropriate metal salt as their crystalline sponges: {[(Co(NCS)2)3(TTP)4]à ¢Ã¢â€š ¬Ã‚ ¢x(solvent)}n (2) and {[(ZnI2)3(TTP)2]à ¢Ã¢â€š ¬Ã‚ ¢x(solvent)}n (3). In both complexes, the void spaces showed strong binding properties for incoming guest molecules making them ideal crystalline sponges. The as-synthesized complexesà ¢Ã¢â€š ¬Ã¢â‚¬ °2 and 3 contained solvents in the void. By soaking the crystals of 2 and 3 in a guest solution, guest molecules slowly penetrate these wet cavities by guest exchange, and are concentrated at the molecular-recognition pockets surrounded by TTP. A characteristic of the strong host-guest interaction in the crystals of 2 and 3 lies in panel ligandà ¢Ã¢â€š ¬Ã¢â‚¬ °1, which attracts various guests onto its electron-deficient à Ã¢â€š ¬-plane. The slow guest exchange allows for the process to remain under thermodynamic control, rendering the geometry of the included guests to be regularly ordered and well equilibrated, thus making it possible to analyse the accommodated guests by crystallography since the molecular structure of the absorbed guest will be displayed, along with the host framework. Since theoretically, only one crystal is needed to perform the experiment, Fujitas team found that even trace sample amounts of the microgram-nanogram scale can be analysed in this protocol. When the team used only 80à ¢Ã¢â€š ¬Ã¢â‚¬ °ng of guaiazulene guest sample with a crystal of 3 (80à ¢Ã¢â€š ¬Ã¢â‚¬ °ÃƒÆ'-à ¢Ã¢â€š ¬Ã¢â‚¬ °80à ¢Ã¢â€š ¬Ã¢â‚¬ °ÃƒÆ'-à ¢Ã¢â€š ¬Ã¢â‚¬ °80à ¢Ã¢â€š ¬Ã¢â‚¬ °ÃƒÅ½Ã‚ ¼m3), they were surprised to see the guestà ¢Ã¢â€š ¬Ã¢â‚¬ °was still clearly observed. Considering that the experiment was carried out using a laboratory X-ray machine, it seemed promising to accomplish crystallography with synchrotron X-ray experiments even on a mass of In order to assess the scope of the method, the team carried out blind crystallographic analysis of six appropriate samples (Fig) with only ~5à ¢Ã¢â€š ¬Ã¢â‚¬ °ÃƒÅ½Ã‚ ¼g of each sample. In conjunction with mass spectroscopic data, all six structures were correctly assigned, with three of the structures solved solely from the crystallographic data. Additionally, the protocol was successfully used to determine the absolute stereochemistry of santonin 4, an anthelminthic drug bearing four chiral centres. Unlike common absolute structure determinations, this was achieved without the chemical introduction of heavy atoms on the guest skeleton since the host framework contains heavy atoms (Zn and I) that show enhanced anomalous scattering effects. (Expand The most impressive result of the teams protocol however was determining the absolute structure of miyakosyneà ¢Ã¢â€š ¬Ã¢â‚¬ °A 5, a scarce natural marine product recently isolated from a marine sponge Petrosia sp. The structure contains three chiral centres on its main alkyl chain, two of which, C3 and C26, had been previously determined to be 3R and 26R respectively. However, since the difference between the two long alkyl groups on C14 is only one methylene unit, determining the absolute configuration at C14 was ineffective by conventional spectroscopic and chemical methods. As the amount of miyakosyneà ¢Ã¢â€š ¬Ã¢â‚¬ °A was very limited, preparation a single crystal for X-ray crystallography would propose a huge challenge. The team were able apply their method to the full characterization of miyakosyneà ¢Ã¢â€š ¬Ã¢â‚¬ °A to determine the absolute configuration at C14 and reported success. For its appraisers, it was this result that made this new protocol transformational (4) and understandably it led to a lot of excitement in the field. 1.3 The Fall The initial lustre of the protocol was dulled as Fujita and his team published a correction on the initial report later that year (1b). Previously unnoticed ambiguities in the crystallographic data, alongside further investigation of by the team found the initial assignment of stereochemistry at C14 of 5 to have been incorrect. Synthetic studies by the team determined the methyls stereochemistry was opposite to the original assignment reported. Poor data quality was concluded to be the cause of this errors. Additionally, more problems were met as other research groups tried to use the technique in their own labs. Although success with the technique was achieved for simple molecules, in the first few months, other groups found little success with any interesting structures, particularly large molecules or molecules containing alkaline chemical groups (8b). Fujitas team were able to aid other industrial and academic groups to master the technique in one to two weeks. Additionally, more of the issues in reproducibility were improved by the release of a more detailed report of the method (1c) that described the sponge synthesis, pore-solvent exchange and selection requirements for high quality single crystals for crystallography. However, this did not address the issue of poor data quality that led to the misassignment of 5. Since poor data quality can be attributed to all steps of the CSM, including cystal synthesis, solvent exchange, guest-soaking, data collection and crystallographic ref inement of the host-guest complex molecules; in order to move the CSM from the fascinating idea phase into becoming the transformational and reliable new technology it was envisioned to be, much work was required to optimise all these steps. 3. {[(ZnI2)3(TTP)2]à ¢Ã¢â€š ¬Ã‚ ¢x(solvent)}n: The most successful sponge to date 3.1 Andvantages of {[(ZnI2)3(1)2]à ¢Ã¢â€š ¬Ã‚ ¢x(solvent)}n In their initial paper, Fujita and his team reported using sponges 2 and 3. With further investigation, in the case of complex 2, it was observed that guest molecules absorbed in the sponge were prone to static disorder as they tend to lay on the symmetry elements of the cubic lattice (Fm3m). Additionally, complex 2 was shown to undergo unfavourable transformations when removed from solution (8c). This destabilising transformation, accompanied by a colour change from orange to green, resulted in a semiamorphous solid with a significantly altered coordination environment at the metal centre. As such, the less symmetric (C2/c) complex 3 has been employed as the primary host complex for the crystalline sponge. The versatility of 3 as a crystal sponge stems from several advantages in host-guest complexation in the pores. Firstly, the size of the pores is ideal for accommodating organic molecules of common sizes, while the hydrophobic nature of the pore cavities provides favourable bindin g of common organic molecules. Also, ligand 1 in the complex offers flat and electron-deficient binding site, appropriate for stacking with aromatic compounds and for CH-à Ã¢â€š ¬ interactions even with aliphatic compounds (9). Since the I atoms in the ZnI2 are good hydrogen-bond acceptors and the pyridyl protons of the ligand 1 are good hydrogen-bond donors, they provide efficient binding sites through hydrogen-bonding. Finally, the framework of sponge 3 is reatively flexible with the size of the guest not strictly limited to the pore size of the complex. Molecules larger than the portal are often accommodated by expanding the pore size. (1.3) 3.2.1 Synthesis of {[(ZnI2)3(1)2]à ¢Ã¢â€š ¬Ã‚ ¢x(solvent)}n and solvent exchange by Fujita method and updated Clardy method In their investigations, Fujita and co-workers prepared 3 by layering a solution of zinc iodide in methanol onto a denser solution of TTP (1) in nitrobenzene. The solution is allowed to stand for 7 days, over which crystals form at the boundary of the two solvents as they diffuse before dropping to the bottom of the test tube and being isolated by filtration. The as-synthesised crystals contain nitrobenzene molecules in the void spaces. However, since nitrobenzene has a high affinity to the pores, target guests are poorly absorbed into the as-synthesised crystal. As such, a solvent exchange step that replaces nitrobenzene with an inert, noninteractive solvent is required prior to soaking the crystal in the target guest solution. Cyclohexane can be adopted as the inert solvent, while pentane also proves useful for guest soaking at temperatures below 0oC. The solvent exchange step is carried out by soaking the crystal in the inert solvent for 7 days at 50oC. The success of the process can be monitered throughout by observing the disappearance of the signal at 1346 cm-1 in an Infrared (IR) spectrum, which can be assigned to nitrobenzene. Completion of the process is confirmed by SC-XRD by the presence of ordered cyclohexane molecules in the pores. The sponge may now be used for guest absorption. This solvent exchange process may complicate the refinement of the structure, since some nitrobenzene may reamin within the sponge structure after exchange (Vinogradova et al., 2014). This becomes an issue if the target guest molecule contains cyclohexyl or aromatic rings, as it may be difficult to distinguish the guest from residual solvent, especially if   the site occupancy is low or the data quality is poor. Accompanied with heavy use of crystallographic restraints, this increases the risk of misassignment of the desired guest molecule by using residual solvent electron density. Additionally, if the residual solvent and the guest interact similarly with the host, the likelihood of occupational disorder increases and making structure refinement much more challenging. Clardy and co-workers later reported a simpler and less timely preparation method for the synthesis of sponge 3 using similar conditions to those reported by Fujita and his team. (5sync) Instead of conducting the layer diffusion step with TTP in nitrobenzene, TTP is dissolved in chloroform. As such, the as-synthesised crystals of sponge 3 contain chloroform in the pores. Since chloroform has a much lower affinity for the solvent pores than nitrobenzene, the solvent exchange step can be omitted and the as-synthesised crystals used immediately. As well as saving 7 days of preparation by omitting the solvent exchange step, this method is also milder as it does not require the crystal to be heated for long periods of time. This reduces the chances of introducing imperfections in the crystal. This omission also minimises the number of solvents that the crystal is exposed to, reducing issues in structure refinement. Although some CHCl3 might remain within the sponge after guest inclusion, due to its longer C-Cl bond length (à ¢Ã‹â€ Ã‚ ¼1.7à ¢Ã¢â€š ¬Ã¢â‚¬ ¦Ãƒâ€¦) and larger Cl electron density, CHCl3 can still be observed. This greater electron density for CHCl3 exerts a larger influence on the structure factors relative to incorporated guest compared to nitrobenzene, however the benefits of CHCl3 usage override this issue. In addition to the desired crystals, this preparation method has been found to simultaneously form other crystalline structures. Firstly, a crystalline compound with the formula [{(ZnI2)3(TPT)2 ·CHCl3}n] (2), having a much smaller pore size has been viewed. Fortunately, this crystalline structure can be easily distinguished from the desired structure from its morphology (Fig). A second undesired crystal has more recently been observed with consistently distinct unit parameter, but having indistinguishable morphology to the desired structure from its morphology (Fig). Both these crystals are believed to form due to slight changes in humidity and temperature as well as variations in mixing in the initial stages of the layering process.   desired crystal. Both these crystals are believed to form due to slight changes in humidity and temperature as well as variations in mixing in the initial stages of the layering process.

De Vaca and Smith :: Social Issues, Indian Life

Both Alvar Nunez Cabeza de Vaca and John Smith hold different attitudes regarding their accounts of Indian life. The difference in attitudes may have resulted from the difference in treatments that each man received while in captivity. De Vaca’s experience is a humbling one. His account of Indian life is written in a thoughtful manner, and he describes the Indians kindly. While he describes his captivity as â€Å"melancholy and wretched† (De Vaca 34), it’s clear that he harbors no ill feelings towards the Indians. He states that he and his men were treated well, that they lived as â€Å"free agents† (De Vaca 32) and tried to accustom themselves to Indian life. He’s highly observant of the Indian life. He records the Indian lifestyles in detail; his account reads more like a cultural anthropology study. His account of Indian life ends on a sympathetic note towards the Indians especially after he realizes his misjudgment of the Christians. â€Å"We often misjudge the motives of men,† de Vaca writes, â€Å"We thought we had effected the Indians’ liberty, when the Christians were but poising to pounce (De Vaca 36).† Smith, on the other hand, describes his account in a boastful manner. His account of Indian life reads like a fantastic adventure novel in which he is the glorified hero. He continuously refers to the Indians as â€Å"savages† (Smith 46) or â€Å"barbarians† (Smith 48) throughout his account. He even describes them as â€Å"devils† (Smith 51). At one point, he thinks that the Indians are trying to â€Å"fat him to eat him† (Smith 50). Smith’s account is so incredibly dramatic that he expects â€Å"every hour to be put to one death or other† (Smith 52). Also, the incident with Pocahontas saving Smith appears to be highly romanticized. Smith’s manner of writing, in which he writes of himself in the third person, only adds to the boastful tone of this account. It makes the entire account seem impersonal. It also makes Smith appear self-important and frivolous. One can only speculate on why there is such a huge difference in these two writers’ attitudes. Their backgrounds may be factors that have influenced their attitudes. For de Vaca, it may be his religious background that has influenced him and shaped his attitude. In his account, he acknowledges his religion several times. â€Å"My only solace in these labors was to think of the sufferings of our Redeemer, Jesus Christ, and the blood He shed for me,† de Vaca writes.