SUNADARI ƊAYA, AN KAMA SHI YANA TASHI DA WALƘIYAR X-RAY

Don ganin yadda sunadari ke aiki, masana ilimin halitta za su so su kalli yadda yake canza siffa. Yin hakan yana nufin ganin ƙwayar halitta ɗaya daga kusurwoyi da yawa, da hasken da ke da gajeren tsawon raƙuma (wavelength) sosai. Matsalar ita ce electron da X-ray, su kaɗai ne masu bincike masu isasshen ƙarfi, suna kuma lalata ƙwayar halittar da suke ɗaukar hotonta. Cryo-electron microscopy yana kauce wa wannan ta hanyar daskarar da dubban ƙwayoyin halitta a cikin ƙanƙara da kuma haɗa matsakaicin hotuna masu hayaniya da yawa.

X-ray suna zubar da ƙarfi kusan ninki dubu a kowane abin watsawa fiye da electron. Amma akwai wata kofar tsira, da aka sani da “diffraction kafin lalacewa” (diffraction before destruction): da bugun daga X-ray free-electron laser da ke ɗaukar femtosecond kaɗan kawai, ana rubuta zanen hasken da aka watsa kafin ƙwayar halittar ta sami lokacin tarwatsewa. Ƙwayar halittar ba ta buƙatar daskarewa ko wani mai riƙe ta — ana iya kama ta tana tashi. Har zuwa yanzu, wannan ya yi aiki a kan manyan ƙwayoyin cuta (viruses). Sunadari ɗaya, da aka ɗauki hotonsa mai fuska uku da X-ray masu ƙarfi, ya ci gaba da kasancewa ba a iya kaiwa gare shi ba.

Jinin tsutsar ƙasa a cikin wuri maras iska

Wata babbar tawagar ƙasashen duniya ƙarƙashin jagorancin Paul Lourdu Xavier da Henry Chapman a DESY a Hamburg, tare da European XFEL da cibiyoyi da dama a duniya, ta zaɓi erythrocruorin: wani babban haemoglobin, da aka tsarkake daga jinin kusan tsutsotsin ƙasa ɗari. Nauyinsa megadalton 3.6 ne kuma yana da siffa mai daidaito sosai, zobba biyu da aka jera kan juna da rami a tsakiya.

An fesa sunadaran zuwa ƙananan ɗigogi, an kawar da cajin su kuma an mai da su zuwa wani siririn layi da ke tafiya kusan mita 100 a daƙiƙa ɗaya ta cikin wani ɗaki maras iska. An ƙara helium don rage hasken bango daga iskar gas da ta rage. A kan wannan layin, an harba bugun daga European XFEL a Schenefeld, Jamus: photon na X-ray masu kiloelectronvolt 6, an matsa su a kan wani wuri mai nanometre 180 da 220, kowane bugu yana ɗaukar kusan femtosecond 25.

Kowace walƙiya tana mayar da kusan kashi uku bisa huɗu na atom ɗin da ke cikin ƙwayar halittar zuwa ion — amma tana ƙarewa kafin fashewar da ta biyo baya ta sami lokacin ɓata hoton.

Hotuna miliyan 270 don siffa ɗaya

• A cikin sa’o’i 21, na’urar ganowa ta rubuta hotuna miliyan 270.
• 188,557 ne kawai daga cikinsu — kashi 0.07% — suka ƙunshi zanen diffraction, galibi daga sunadari ɗaya.
• An rarraba mafi kyau 50,000 zuwa ƙungiyoyi 144 na kusurwoyin kallo masu kama da juna, waɗanda suka ba da hotunan projection masu shimfiɗa a ƙudurin kusan ångström 15.
• Daga zanen 26,908 da aka zaɓa, tawagar ta sake gina diffraction a fuska uku, sannan ta riƙe 1,248 mafi tsabta don lissafa taswirar electron na sunadarin mai fuska uku a kusan ångström 20. Tana nuna ramin tsakiya da daidaito na ninki shida da ake tsammani daga tsarin da aka sani.

Sunadarin da ke ƙanƙancewa yana tashi

Dukkan sake ginin fuska uku sun fito a matse fiye da tsarin crystal da aka sani, musamman a kan gajeren gefe. Tawagar ta danganta wannan ga wurin maras iskar kansa: idan aka fitar da shi daga ruwa, sunadarin yana ƙanƙancewa. Kwaikwayon kwamfuta na dukkan ƙwayar halittar sun yarda — tana ƙanƙancewa da kashi 2.5% a cikin nanosecond ɗinta na farko, sannan a hankali. Wannan bambanci tsakanin ƙwayoyin halitta wataƙila shi ne dalilin da ya sa hoton fuska uku ya fi na fuska biyu dushewa.

Marubutan sun lissafa matakai na gaba: kare sunadarai daga wannan rugujewa, ta ƙananan ɗigogi, gajeriyar tafiya ko daskarewa nan take, ko ta kawo su a cikin wani siririn takardar ruwa sosai; da bugun X-ray masu tsayayye, gajeru da ƙarfi. Kwaikwayo suna nuna cewa lalacewar haske (radiation damage) za ta ƙara muhimmanci yayin da hotuna ke ƙara bayyana.

Zuwa fina-finan ƙwayoyin halitta ɗaya-ɗaya

Ångström ashirin yana nesa da ganin atom. Amma marubutan suna bayyana wannan a matsayin burin da aka bi na kusan shekaru talatin: sunadari ɗaya, keɓantacce, da aka ɗauki hotonsa mai fuska uku da X-ray masu ƙarfi, ba tare da crystal ko daskarewa ba. Alƙawarin da ke bayan sa shi ne lokaci — tayar da sunadari da kama shi yana tsakiyar motsi, walƙiya ɗaya bayan ɗaya.