应《网络安全法》要求，自2017年10月1日起，未进行实名认证将不得使用互联网跟帖服务。为保障您的帐号能够正常使用，请尽快对帐号进行手机号验证，感谢您的理解与支持！

24小时热门版块排行榜    

小木虫论坛-学术科研互动平台» 网络生活区» 有奖问答 » 有奖问答中转子版 » 金币求助如何培养晶体
161/2返回列表12下一页
查看: 776  |  回复: 15
只看楼主 @他人 存档 新回复提醒 (忽略) 收藏    在APP中查看
当前主题已经存档。

qqlu

木虫 (正式写手)

超级木虫

[交流] 金币求助如何培养晶体

本人产物含有两个苯环，一个羟基，一个环己基，曾试过很多方法培养晶体皆未成功，特求助高人该如何培养晶体？！
回复此楼

» 猜你喜欢
1楼 2009-04-02 15:18:56
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

张忆鹏

木虫 (著名写手)

第三军团之侦察员
★
qqlu(金币+1,VIP+0):谢谢！ 4-2 15:24
可以在木虫上找一下培养单晶的书籍，
多试几次
我以前也是开始好久没做出来，在无意间就培养成功了
赞一下(2人) 回复此楼
我就是我，不要再向以前那样活着
2楼2009-04-02 15:21:48
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

279841836

木虫 (著名写手)
★
qqlu(金币+1,VIP+0):谢谢！ 4-2 15:56
看看这个！应当有用~~
http://read.freeduan.com/data/2007/0330/article_35534.htm
赞一下(2人) 回复此楼
3楼2009-04-02 15:40:47
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

279841836

木虫 (著名写手)
★
qqlu(金币+1,VIP+0):谢了！ 4-2 15:56
Crystallization belongs to the oldest techniques used in chemical laboratories. Nevertheless crystallization is referred to as more of an art than a science. In many cases crystallization is more difficult and less successful than other techniques like distillation or chromatography. Additionally there is often a lack in education about crystallization techniques. Many textbooks don't treat this topic.
As stated in many introductory chemistry textbooks, crystallization should start, if the concentation of a solution is higher than the corresponding solubility product. In fact, crystallization is kinetically hindered. This leads to the metastable condition of supersaturation: The concentration is higher than the solubility product, but crystallization has not yet started. This condition of supersaturation is the optimal condition for crystal growing. In fact it is the only condition for crystal growing: If the concentration is higher, uncontrolled spontanous crystallization sets in; if the concentration is lower, already formed crystals will dissolve.
An often used process in the laboratory is therefore the cooling of the reaction mixture until the state of supersaturation is achieved. But as stated before, crystallization is kinetically hindered and will not start, even if you wait for month. What you need are crystal seeds. The generation of these crystal seeds (nucleation) is the most difficult part of the whole crystallization process.
You can try out one of the following techniques for nucleation:
1. Nucleation is in most cases an endothermic process. Evaporation of the solvent at increased temperatures is therefore a better choice for getting crystal seeds than just cooling down. If the first crystals are visible, the growing of the crystals is thereafter controlled by lowering the temperature (crystal growing is exothermic in most cases).


N.B. Crystallization at higher temperatures can lead to other crystal forms compared to lower tempertures. Sodium sulfate crystallizes as decahydrate when crystallized below 305.53 K and without hydrate water when crystallized above 305.53 K. Calcium carbonate prefers the aragonite and vaterite modifications at higher temperatures and the calcite modification at lower temperatures.
2. The solution is cooled down until (uncontrolled) spontanous crystallization sets in. The solution is then warmed up until nearly all of the crystals are dissolved again. The remaining crystals are allowed to grow by controlled cooling.
N.B.: Unfortunally many chemist are proud of having crystals at all. They don't have the courage to re-dissolve the crystals. They just bring the results of the uncontrolled spontanous crystallization to the crystallographer. The quality of these crystals is very poor and in many cases also the results of the structure determination.
3. Ultrasound often helps to get crystal seeds. Ultrasound is used in cleaning baths, but can also be generated by scratching at the glass of the crystallization vessel.
4. Hetreogeneous nucleation. Nucleation can be affected considerably by the presence of mere traces of impurities in the system. Impurities may act as inhibitors or accelerators.
________________________________________
Golden rules
1. "Don't crystallize in the dark."
Many chemist put their crystallization vessels to a dark place, leave it there for hours, days or month, and wait somewhere else. That's the wrong way. You have to watch the process!!! If the first crystal seeds are visible, you must control the growing process (temperature, cooling rate). If no crystal seeds are visible you have to change something.
2. "Don't crystallize too concentrated."
Crystallization from too concentrated solutions often leads to glass, syrup or other unpleasant results. A good example are sugars which are very soluble in water. They therefore form high concentrations and nearly never crystallize from water. Better choose a solvent (or mixture of solvents), in which the solute is less soluble.
3. "Don't hurry."
If you need month or years for the synthesis of a compound, why should the crystallization be finished in a few hours? You don't stop the synthesis after the first dissapointing attempts, why do you stop crystallization so early.
4. "Don't forget about details."
You write an excellent, detailed laboratory notebook about your synthesis. You mention boiling and melting points, concentrations, colours, reaction times and so on. But you don't mention your crystallization conditions at all or only with one sentence. The remark "Suitable crystals were obtained by slow evaporation of the solvent" is to no help to the reader.
5. "Don't use glass vessels."
With evaporation the solvent creeps up the walls of a glass vessel, because the hydroxyl-groups of the silicate glass make it hydrophilic. Nucleation occurs therefore outside the solution. Much better are vessels made of polypropylen or teflon. The solvent doesn't creep up these vessels. You can also make glass vessels hydrophobic by silanation.
6. "Use acceptors."
Many substances are difficult to crystallize because the system don't contain acceptors for hydrogen bonds. The Cambridge Structural Database contains more than 350 substances crystallized as picrates. In other cases triphenylphosphine oxide can be used alternatively (M.C. Etter, P.W. Baures, J. Am. Chem. Soc. (1988) 110, 639-640).

Recommended books
People who want to get a deeper understandig of the matter are referred to the following three books:
A. Holden, P. Morrison: Crystals and Crystal Growing,
MIT Press, Cambridge, Massachusetts (1982)
ISBN 0-262-58050-0 (pbk.), 13.95 US$
(Very basic introduction to the subject. Because of the nice price also suitable as a gift for children of 14 years onwards.)
J.W. Mullin: Crystallization,
Butterworth-Heinemann, Oxford, Great Britain (1993)
ISBN 0-7506-1129-4, 85.00 ?
(Good overview. Thermodynamics of the nucleation and crystal growth processes. Industrial applications of crystallization.)
K.-Th. Wilke, J. Bohm: Kristallz點htung,
Verlag Harri Deutsch, Thun; Frankfurt/Main (1988)
ISBN 3-87144-971-7, 220.00 DM
(Comprehensive standard work. Only available in German. Nearly all techniques mentioned. List of compounds contains approximately 2000 substances.)
Further reading
Further Reading about Crystal Growing
C. Orvig: A Simple Method to Perform a Liquid Diffusion Crystallization,
J. Chem. Educ. (1985) 62, 84.
P. van der Sluis, A.M.F. Hezemans, J. Kroon: Crystallization of Low-Molecular-Weight Organic Compounds for X-ray Crystallography,
J. Appl. Cryst. (1989) 22, 340-344.
P. van der Sluis, J. Kroon: Solvents and X-ray Crystallography,
J. Cryst. Growth (1989) 97, 645-656.
M.C. Etter, D.A. Jahn, B.S. Donahue, R.B. Johnson, C. Ojala: Growth and Characterization of Small Molecule Organic Crystals,
J. Cryst. Growth (1986) 76, 645-655.
赞一下(1人) 回复此楼
4楼2009-04-02 15:42:18
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

chemjp

金虫 (小有名气)
★
qqlu(金币+1,VIP+0):谢了！ 4-2 15:56
培养单晶呢 要用较少的溶剂溶解 如果你的产物对空气不敏感就可以在空气中挥发长晶体。 如果敏感就在手套箱中。

关键是配制饱和溶液的饱和程度  

希望有所帮助
赞一下(2人) 回复此楼
5楼2009-04-02 15:50:23
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

hobbyzhang

荣誉版主 (文坛精英)

小木虫首席大法官
★
qqlu(金币+1,VIP+0):谢谢！ 4-2 16:07
楼主这个板块看看吧

http://muchong.com/bbs/forumdisplay.php?fid=262


培养晶体要说难也难
要说简单也简单

培养单晶其实真的是一门技术和艺术
赞一下(1人) 回复此楼
如果我儿子长大当军人，我会告诉他，做为军人，不仅要服从命令，还要服从真理和正义，生你的是父母，养你的是百姓，所以你所做的，必须对人民有利，永远记住，.
6楼2009-04-02 15:58:14
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

yuegh

铁杆木虫 (职业作家)
培养单晶呢 要用较少的溶剂溶解,关键是配制饱和溶液的饱和程度
赞一下 回复此楼
7楼2009-04-02 16:08:55
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

mayong11

铁杆木虫 (职业作家)
HEHE.....学习一下！！
赞一下 回复此楼
学海无涯，重在交流
8楼2009-04-02 18:39:25
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

hxsteven

金虫 (正式写手)
★
qqlu(金币+1,VIP+0):谢了！ 4-2 23:11
首先需要强调的是长单晶是一种艺术，而不完全归结于科学，或者说它是一门介于科学和艺术之间的技术。
对于水溶性好的分子，结晶是很困难，一般都是通过干燥缓慢去除溶剂的办法，也有的通过极缓慢的降温来获得单晶，或者在水上加入一层难溶性的有机溶剂。
对于在有机溶剂中溶解比较好的分子，他们的结晶一般都是通过扩散的办法来实现，如将乙醚或是苯扩散进入乙氰中。
对于生物大分子单晶，一般都采用悬滴法，即在一个小而密闭的容器中，下边放溶剂，上边加一滴分子饱和的溶剂，然后封闭之。
要结晶的分子一般来讲一定要纯，达到95%以上的纯度，当然也不绝对，也有的体系在较低纯度就拿到了单晶，比如饶子和院士发在CELL上的蛋白晶体结构就是从一个混合体系中拿到的。
赞一下(1人) 回复此楼
9楼2009-04-02 19:13:59
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

刘俊霞

银虫 (著名写手)
可以看看
结晶化学导论
赞一下 回复此楼
10楼2009-04-02 19:50:05
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖
相关版块跳转 我要订阅楼主 qqlu 的主题更新
161/2返回列表12下一页
普通表情 龙 兔 虎 猫 高级回复 (可上传附件)
信息提示
关闭
请填处理意见
关闭